Production Processes I

Production Processes I

September 29

2012 Lecture Notes: Team Work of SE MECH/AUTO Students

For Private Circulation within PIIT, New Panvel Only.

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Q1) Write a note on classification of mfg. Processes?

Name: Tanmay Adiwarekar.

Class: SE-Auto.

Roll no.: 301.

Ans.:

Production process

Removal Process

SERIAL

Mechanical

i. Cutting

ii. Grinding

iii. Broaching

iv. Polishing

v. Water Jet

Thermal

i. Laser cutting

ii. Flame cutting

iii. plasma cutting

Chemical

Electrical

i. EDM

PARALLEL

Mechanical

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i. Die Stamping

Thermal

Chemical

i. ECM

ii. Photolithography

Electrical

i. EDM

ADDITION PROCESS

SERIAL

Mechanical

i. 3D Printing

Thermal

i. Laser

ii. Sintering

Chemical

i. Stereolithography

Electrical

3

PARALLEL

Mechanical

i. HIP

Thermal

i. Sintering

Chemical

i. LPCVD

ii. Plating

Electrical

SOLIDIFICATION PROCESS

SERIAL

Mechanical

i. Ultrasonic

ii. Welding

Thermal

i. Plasma apray

Chemical

Electrical

i. E-beam

ii. Welding

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iii. Arc welding

iv. Resistance welding

PARALLEL

Mechanical

i. Inertia

ii. Bonding

Thermal

i. Casting

ii. molding

Chemical

i. Diffusion Bonding

Electrical

DEFORMATION PROCESS

SERIAL

Mechanical

i. Bending

ii. Forging(open)

iii. Rolling

Thermal

i. Line heating

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Chemical

Electrical

PARALLEL

Mechanical

i. Drawing

ii. Forging

Thermal

Chemical

Electrical

Comparision

1. Turning process

Advantages

All types of materials can be turned.

Most versatile machine capable of producing external and internal circular

profiles and flat surfaces.

Low tooling cost.

Large components can be turned.

Limitations

Requires skilled labour.

Low production rate.

Close tolerances and fine finish cannot be achieved.

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2.Boring

Advantages

All types of materials can be bored.

Variety of internal circuler profiles can be obtained.

Low tooling cost.

Large components can be bored.

Provides better dimensional control and surface finish.

Limitations


Low production rate.

Suitable for internal profiles only.

Stiffness of boring bar is important consideration.

3. Shaping Process

Advantages

Suitable for producing flat and contour profiles on small workpieces.

Suitable for low production rate.

Low tooling and equipment cost.

Limitations


Large size workpieces cannot be used.

Only simple profiles can be obtained.

Close tolerance and fine finish cannot be obtained.

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4. Planing Process

Advantages

Suitable for producing flat and contour profile small workpieces.

Suitable for low production rate.

Low tooling and equipment cost.

Limitations


Only simple profile can be obtained.

Close tolerance and fine finish cannot be obtained.

5. Milling Process

Advantages

Variety of shapes including flats, slots and contours can be obtained.

Versatile operation with wide variety of toolings and attachments.

Suitable for low and medium production rate.

Better dimensional control and surface finish.

Limitations


Tooling relatively more expansion.

6. Drilling Process

Advantages

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Inexpensive tooling and equipment.

Most suitable for producing round holes of various sizes.

High production rate.

Machine can be used for reaming and tapping.

Limitations

Requires semi-skilled labour.

Basically a rough machining operation.

Q.2) Write a note on mfg of pig ion?

PIG IRON

All iron and steel products are derived originally from pig iron.This is the

raw material obtained from the chemical reaction of iron ore in a blast

furnace. The process of reduction of iron ore to pig iron is known as

smelting.

The main raw materials required for a pig iron are: (1) iron ore, (2)cooking

coal, and (3)flux.

The coke used in the blast furnace should be a very high class hard coke

obtained from good quality coking colas containing as low phosphorous

and sulphur as possible.

Flux is a mineral substance that is charged into a blast furnace to lower

the melting point of the ore and to promote the removal of the ash, sulphur

and the residues of the burnt fuel.

Blast furnace

The blast furnace is a vertical furnace designed for continuous operation. The

smelting room of the blast furnace comprises a throat, stack, body, bosh, and

hearth.

The raw materials known as the charge, are taken to the top of the furnace by

a specially designed bucket called “skip” running along an incline.

The charge is then introduced into the throat of the furnace by means of a

double bell and hopper arrangement to prevent the escape of blast furnace

gas which is used as fuel.

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The proportions of the raw materials are approximately one-half iron ore, one-

third fuel, and one-sixth flux.

A hot blast is forced into the furnace through a number of nozzles called

tuyeres .The tuyeres are cooled by water circulating between the pipe walls.

The air blast is heated to minimize fuel consumption by passing the cold air

blast through the heated checker-work of hot blast stoves.

The temperature of the furnace just above the level of the tuyeres being

1000°C to 1700°C all substances inside the furnace start melting in the heat.

The limestone that serves as a flux is combined with the ore to form a molten

slag which floats on the top of the molten iron. The slag is tapped off from the

furnace through the slag hole. The molten iron is tapped at intervals from six

to twelve hours through a tapping hole, the blast being turned off meanwhile.

The furnace is kept in operation until it gets worn-out.

According, to the type of plant the molten iron may be used in one or more of

the following ways.

1. Cast in pig bed.

2. Cast in pig-casting machine.

3. Transferred in hot metal ladles direct to an adjacent steel-making process.

Pig beds are sand moulds in the form of a grid prepared in the ground

alongside the furnace. The bars cast in this way are about 1m long with a D-

shaped cross-section measuring about 100mm each way.

The modern method of casting pig iron which has largely superseded the

older pig-bed method is to employ a pig casting machine. This consists of a

series of haematite iron or steel moulds, each about 660 mm × 220mm × 90

mm, fixed to an endless chain conveyor, the assembly being mounted on a

suitable construction arranged on a slight slope.

While the iron is in the furnace it picks up to 3 to 4 per cent of carbon and a

small amount of sulphur from the coke. The silicon, manganese and

phosphorus as well as most of the sulphur in the pig iron are derived from the

ore. The high amount of carbon makes the pig iron very hard and brittle and

unsuitable for making any useful article.

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Pig iron, is therefore, refined and remelted to produce other varieties of iron

and steel.

Diagram of blast furnace

Modern Development

Electric pig iron furnaces are becoming popular where suitable metallurgical coke

is not available in sufficient quantities and where electricity is cheap. The

advantage with the furnace is that coke consumption is reduced by 50 percent,

as heating is done by electricity and only reduction of the iron ore is done by

coke.

A medium sized furnace of the type can produce 110 to 110 mm tones per day.

Another process which is also being developed is the sponge iron process. This

new process for treating low grade iron ore by direct reduction, in place of the

conventional blast furnace method , is being fast developed.

Pritam Bakal

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Roll no=ae302

Q3 What are mfg process of WROUGHT IRON?

ANS

- Wrought iron is a highly refined with a small amount of slag forged out into fibres. The

chemical analysis of the metal shows as much as 99% of iron.

- The slag characteristic of wrought iron is useful in blacksmithing operations and gives

the material its peculiar fibrous structure. The non-corrosive slag constituent causes

wrought iron to be resistant to progressive corrosion.

- Moreover, the presence of slag produces a structure which diminishes the effect of

fatigue caused by shocks and vibration.

- It is tough, malleable and ductile and has an ultimate tensile strength of about 35 kgf

per mm2(350 N/mm2).

- It cannot be melted ,but at a white heat, it becomes soft enough to take any shape

under the hammer, i.e it can be forged. It admits readily of being welded.

- This iron has the property if been able too withstand sudden and excessive shock

load without permanent injury. It rust more quickly cast iron but stands salt water better.

It can neither be hardened nor tempered like steel.

- This is produce by two commercial methods—

1. PUDDLING PROCESS. 2. ASTON OR BYERS PROCESS.

1. PUDDLING PROCESS

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- Pig iron for this purpose is first subject to a preliminary process of refining, the

object is to remove silicon as completely as possible together with greter part of the

phosphorus , and to convert the graphite into combined carbon and this produce

white iron

- The next purpose is to convert the white iron into wrought iron

- To do this the slabs of white iron are broken into pieces and taken to the puddling

furnace which is a coal fire reverberatory furnace. The obtain is known as blooms

having a mass of about 50 kg.

- The hot metal is then passed through grooved rollers which convert blooms into

bars called muck bars or puddle bars, which have cross section of approx 15 to 100

mm.

- This bars are cut into short length, fastened together in piles, reheated to a

welding temperature and again rolled into bars.

2. ASTON AND BYERS PROCESS

- In aston and byers process, to produce wrought iron, the pig iron is first melted in a

cupola furnace and refining of molten metal is done in a Bessermer converter.

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- At the same time, a quantity of iron silicate slag in prepared in an open hearth

furnace. The refined so made in the Bessemer converter is poured at predetermined

rate into a ladle containing the molten slag already prepared.

- After the excess slag is poured from the ladle , the remaining mass of iron and slag is

taken to a press where some slag is removed.

- The rectangular block formed in the press is known as bloom.

- The hot bloom as before is immediately passed through rolling mills to produce

products of wrought iron of different shapes and sizes.

Rohit dalvi

Q4) Write a short note on manufacturing of cast ironAE305

Cast iron is iron or a ferrousalloy which has been heated until it liquefies, and is then poured

into a mould to solidify. It is usually made from pig iron. The alloy constituents affect its colour

when fractured: white cast iron has carbide impurities which allow cracks to pass straight

through. Grey cast iron, or grey iron, has graphitic flakes which deflect a passing crack and

initiate countless new cracks as the material breaks.Carbon (C) and silicon (Si) are the main

alloying elements, with the amount ranging from 2.1 to 4 wt% and 1 to 3 wt%, respectively. Iron

alloys with less carbon content are known as steel. Iron Production

The Manufacturing of Cast Iron:

There are four stages in manufacturing; Design, Pattern Making, Mould

Making and Casting.

Design: converting ideas into solid metal requires a planned approach that

takes into account the function of the object as well as its appearance. For machine tools the stresses and conditions a machine operates under need to

be considered. For architectural purposes it may be structural ability,

supportive strength or decorative embellishment.

Engineering companies provide detailed, often complex, manufacturing drawings. Architects supply drawings/elevations which in most cases need to

be reproduced as manufacturing drawings showing precise dimensions,

metal thickness etc so that the next stage, Pattern Making, can progress.

Occasionally no plans or drawings exist, especially for conservation and restoration projects where original samples are, however, available. In these

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cases Hargreaves can use detailed measurements and photographs taken

from the originals to make new drawings and patterns for precise

reproduction. Pattern Making: once a design has been approved and a manufacturing

drawing produced a pattern can be made, normally in wood but sometimes

using fibreglass or plastics. Patterns have to be exactly the shape of the

finished item and precise in their dimensions as they are used to make the sand moulds. Patterns can be re-used to make more moulds and, if looked

after, can last for many years making thousands of moulds. Any irregularity

or mistake will be reproduced in the casting. Not only this but patterns must

allow for shrinkage of the metal when it cools and also create channels or runners to allow the molten metal to flow into the mould and risers to allow

for the escape of gases. It is complex and extremely skilled work and our

pattern makers are all apprentice trained and highly experienced.

Mould Making: the next stage is to make a mould in sand into which the molten iron can be poured. The pattern is packed into sand that has been

mixed with clay or resin and when removed leaves the shape for the casting.

Moulds are usually made in two parts and held in ‘boxes’ for the actual

pouring. When the two halves of the mould are placed face to face, one on

top of the other, a cavity is created into which the molten iron can be poured. In the case of very large castings these are created in moulds dug

out of sand in the foundry floor.

A critical factor in mould making is the runner system, a network of channels

that allow the molten metal to run into the mould. There is great skill and expertise in this part of the process, if the molten iron does not run quickly

enough it will solidify before it reaches the casting shape, if it runs too

quickly or violently it could damage the mould and spoil the casting .Many

castings i.e. bollards and columns are not solid but have hollow centres or cavities. To create a cavity the internal shape of the casting is formed by

making a sand core, which is then placed in the mould cavity. This is another

part of the process requiring great skill to ensure precise metal thickness

and form. The molten iron runs round the core so that when the casting is

broken out of its mould the internal sand core remains. It is then removed to leave a cavity.

When breaking out the casting the sand mould is destroyed, but of course

new moulds can bemade from the pattern using the same sand after it has

been re-cycled. Casting: This is the final part of the process and the one most people

associate with foundries.

Melting and pouring iron at 1,350 degrees centigrade is a spectacular and

potentially violent process. Safety is the highest priority in any foundry. First the furnace is carefully loaded to ensure the correct chemical

characteristics for the prescribed grade of iron are achieved. The iron is then

melted in the furnace and poured off to go into the awaiting moulds. Slag or

foundry waste is put to one side for disposal.

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After the iron has cooled in the moulds it is broken out. All the excess iron

from the process, the runners etc are cleaned off in a process known as

fettling, which also includes grinding and shot blasting, to produce a finished casting. Any excess iron can then go back to be melted down again.

Foundry Process – casting a bollard.

1. A wooden pattern is made, in this case of half a bollard, and placed in a

box ready for sand moulding. The inside of the pattern box is coated with either micronised talcum powder or micronised aluminium to ease mould

release.

2. Moulds are made using a sand and resin mix packed around the pattern.

The mould in this example is made in two halves. When the sand resin mix has ‘set’ the mould can be removed from the pattern box and the second

half of the mould can be made. The inside of the mould is treated with a

refractory paint to protect what will be the finished surface when the molten

iron pours in. 3. A sand core is made that fits precisely within the mould leaving a space

between the core and the mould that will produce a constant and exact

metal thickness.

4. The top half is fitted face to face over the bottom half of the mould and

core. It is now ready for metal pouring. 5. When the molten iron has solidified and cooled down the sand mould is

broken open, revealing the finished casting. All the sand is then recycled to

make more moulds.

6. Any extraneous iron (runner systems etc) are removed at the fettling stage, as is the sand core. Once the fettling (finishing) is complete, the

casting is shot blasted ready for painting, if required, and delivery.

7. The finished casting in place, doing a job that may last for decades.

Finally, when no longer required the entire casting can be broken up andrecycled.

Ha, South

Parade, Halifax, West Yorkshire, HX3 9HG Q5) explain the types to manufacture steel ANS

1.THE BESSEMER PROCESS

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In Bessemer process air is blown through molten pig iron contained in a special furnace

known as a converter which shaped like a huge concrete mixer .The converter is made

of steel plates lined inside with refractory material. The type of refractory lining used

depends upon the character of the steel –making process, i.e. upon the acid process or

basic process.In the acid process, the converter is lined with silica brick which is known

in the refractory trade as “acid”. The acid process does not eliminate phosphorus or

sulphur from the metal. In the basic process, the converter is lined with dolomite, which

is known as “basic”. It removes phosphorus and to some extent sulphur.

There are Three distinctive stages may be noted in the conversion of normal pig iron

steel in bessember process.

(1) the slag formation or blowing period

(2) the brilliant flame blowing period

(3) the reddish smoke period.

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The first stage commences as soon as the blast is put on under pressure of about 2 to

2.5 atm (200 to 250 kN/m*2) gauge, and the vessel turned through the tuyeres in the

bottom. The oxygen of the blast oxidizes the iron to ferrous oxide. As a slag, the

ferrous oxide mixes with the metal. Having greater affinity for oxygen, the silicon and

manganese which separate as oxides (insoluble in the moten metal) go into the slag.

These reactions are accompanied by the evolution of a large amount of heat which

raises the temperature from 1,250 degree C 1,525 degree C. This stage lasts for three

or four minutes, and may also be called the silicon blow.

The second stage commences after the oxidation of iron, silicon and manganese, when

the metal has reached a sufficiently high temperature. This creates favourable

conditions for intensive burning of carbon for the molten bath. The dissolved carbon is

oxidized by the ferrous oxide of the slag. The gas evolved during this stage is rich in

carbon monoxide which burns at the nose o the converter with a dazzling white flame.

It takes about eight to twelve minutes, as a rule, to eliminate the carbon.

The third stage begins when he flame “drops” a sign that the carbon has been

practically removed from the charge. This stage lasts for one o two minutes after

which the converter is turned to the horizontal position. The additions of deoxidizes

such as ferromanganese, ferrosilicon or aluminium are made to the metal bath to

eliminate the oxygen and to bring the manganese and silicon content of the steel to the

specified value.

2.THE L-D PROCESS

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The latest development in steel making processes is the L-D process. The LD process

consist of blowing a jet of almost pure oxygen (about 99.5 %) at high pressure and

travelling at supersonic speed through a water cooled lance on to the surface of molten

iron held in a converter lined with basic refractories such as dolomite or mangesite . The

tip of the lance is with in about 1200mm from the surface of the bath. The blowing of

oxygen at super sonic speed produces intense heat (about 2500Degree C to 3000

degree C)and reduced the blowing time by 18 to 20 % of its original .The latter is

achieved by increasing the proportion of steel scrap in the charge upto 30-33%in stead

of 5-8%

3.THE OPEN HEARTH PROCESS:

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In the open hearth process for producing steel, pig iron,steel scarp, and iron oxide in the

form of iron ore or scale are melted in a Siemens-Martin open hearth furnace , so called

because the molten metal lies in a comparative shallow pool on the furnance bottom or

hearth. The hearth is surrounded by a roof and walls of refractory bricks. The charge is

fed through a charging door and heated to 1600degree C to 1650 degree C mainly by

radiation of heat from the burning of gaseous fuels above it. It is not the amount of

heat but rather the high temperature heat that is essential for the purpose.

In practice a considerable quantity of steel scrap is previously charged and heated in

the furnace and a partly purified molten iron known as blown metal from the Bessemer

converter is added to this .Thus the impurities of the pig iron are diluted and the refining

doesnot take so long as if the entire charge was pig iron . Very often more than 60% of

the charge consist of scrap . the process of making steel in this way is known as the

DUPLEX process because it takes place in two stages

1.Blowing molten pig iron in the Bessemer converter

2.Further purification of the blown metal in the open hearth furnace.

At the end of the process, when the impurities (silicon,manganese,etc) have been

brought down to the required level , the metal is trapped off through a tap hole in the

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furnace. Addition of ferromanganese &ferrosilicon are made to bring the steel to the

correct composition,later a small addition of aluminium is made to deoxidize the metal

further. In some case the carbon is reduced practically to Zero

In acid practice , a liningof silica sand is used on the hearth and an acid slag high in

silica is produced on the metal during the refining process .Acid slag cannot remove

phosphorus for which basic lining is used in basic practice , a lining of manganese is

used and limestone is charged on the raw material, A basic slag high in lime is

produced on the bath after the metal melts.

The steel made by open hearth process is considered to be of better quality due to the

fact that carefully selected materials low in sulphur and phosphorus are used in it.

4.THE CRUCIBLE PROCESS

A crucible melting shop consist of a series of melting holes arranged round one or more

sides ,the holes are lined with a fire brick and having their tops level with the floor of the

melting shop.Each hole takes two crucible. The crucibles are handmade from fire clay

and ae shaped in cast iron molds with a wooden core shaped to form a side of the

crucible. Each pot holds about 25 kg and is used for three melts before been discarded.

At the beginning of the process 2 pots with cover are put in the hole on stands or bricks

and the coke fire made up.when the pots are white hot thecharge is put in through a

charger shaped like a funnel , the lid is adjusted and the melting hole is fitted with coke

the charge consist of cut piece of Swedish iron and blister bar followed by pig iron and

any alloying element that may be required .

After charging the process consist of two stages melting and killing . To replenishment

of the fire,which last about an hour, are usually sufficient to melt the contents of the pot,

which will then have the appearance of a thick simmering liquid with a slag floating on

the top . if an attempt were made to cast this into the ingot mould the gas in it would

cause the metal to boil over the top of the mould and the ingot would be full of

blowholes. The metal , therefore must be killed to rid it of these oculed gases. The laast

or “killing fire” is made up and small amount of manganeseor alluminium added to the

content of the pot . this brings about chemical reactions in the metal and results in the

boiling off the gases . finally , the crucible is pulled out of the hole with special tongs&

after the surface of the metal has been cleared of slag it is teemed or poured into

previously prepare ingot mould.

5.THE ELECTRIC FURNACE PROCESS

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Within recent years, the melting of steel by electric furnaces has developed rapidly for

the availability of cheap electric power. Electricity is used solely for the production of

heat and does not impart any special properties to the steel.

The advantageous features of electric furnace process are as follows

1.It generates extremely high temperature about 2000 degree C, in the melting chamber

without introducing oxygen or nitrogen from the air or impurities from the fuel.This

facilitates the removal of the harmful impurities such as oxygen,sulphur & phosphorus

and also nometallic inclusions

2. the temperature at all times may be easily controlled and regulated.

3.It permits the addition of expensive alloying element such as chromium

,nickel,tungsten etc.

There are two types of electric furnace used in the manufacture of steel .

1.Direct arc furnace .

2.High frequency induction furnace.

THE DIRECT ARC FURNACE

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1.electode

2.refractory lining

3.arc

4.molten metal

The direct arc furnace consist of a steel shll lined with refractory ans a removable roof

through which the carbn or graphite electrode pass.Graphite electrode offer less

resistance on current and are considered to be more durable at high temperature but

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they are more expensive than the carbon electrode. The number of electrode

correspond to the number of places

The electrode are lowered into the furnace and the current is switched on . the heat

generated by a powerful spark between the electodes and the metallic charge on the

hearth melts the charge . the charge usually consists of steel scrap and ironoxide in the

form of iron oxide ore.Pig iron is not directly treated in the electric furnace, though

sometimes it is partly purified in an open hearth furnace & then transferred to electric

furnaces for final treatment and alloying . When the furnace is in operation , the

electrodeare consumed and they become shorter. So a definite distance must be

maintained between the electrode and the charge by raising or lowering them by

automatic control. Whenever necessary, a new electode is built up on top of the old

modern arc furnace are built in 0.5 to 80 tonnes capacity but most favoured are those

with capacity of up to 80 tonnes. A melt is produced in 6-8 hours for an arc furnace 30-

35 tonnes in capacity

HIGH FREQUENCY INDUCTION FURNACE

The high frequency induction furnace consists of a transformer . It has a primary coil

about which an alternating magnetic field is set up with magnetic lines of force of a

definite density when an alternating current is passed through the coil. The magnetic

field induces alternating eddy currents in the secondry circuit which comprises a

crucible containing the metal charge . the eddy current heat up and melt the metal.

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An induction crucible furnce comprises a refractory crucible and a coil or inductor.

The latter is made or copper tubing through which cooling water circulates and is

arranged inside the refractory crucible. An insulating lining is provided between the coil

and the crucible. The metal to be melted is charged into the crucible where it is melted

down by the heavy secondry current induced by the magnetic flux of the primary coil.

The crucible can be tilted on horizontal trunions to pour the molten metal.

Induction furnace usually operates ,on an alternating current with a frequency of 500 to

2500 hertz . the generator rating is selected so as to optain 1 to 0.4 kw per kg of the

metallic charge.

Induction furnace are most often employed in making high alloy steel and special

purpose alloys. An advantage of this furnace is that they donot require electrodes. This

prevents carburization of the metal and simplifies control of the process . A vigorous

stirring action is produced to the electromagnetic force in the crucible . the circulation of

the metal accerated chemical reaction and enables homogeneous metal to be obtaines.

Induction furnaces are available in wide range of capacity 50 to 10 tonnes

6.DUPLEX PROCESS

Combination method of steel making is known as duplex method the following

combination are usually done

1.basic and acidic open hearth furnace.

2.A basic open hearth furnace and a bsic electric furnace.

3. A Bessemer converter and a basic open hearth furnace.

Bradley_dsouza AE306

Q6) WRITE A NOTE ON : CAST IRON FAMILY & THEIR PROPERTY DIFFERENCES

NAME: SREYAS.S.ERANDE

CLASS: SE- AUTO

ROLL NO : 307

ANS : -

25

A MOLTEN FURNACE

CAST IRON :

Cast iron is pig iron remelted and there by refined together with definite amount of

limestone , steel scrap and spoiled castings in a cupola or other form of remelting

furnace,and poured into suitable moulds of required shape.

It contains about 2-4 % of carbon,a small % of silicon,sulphur,phosphorous &

manganese and certain amount of alloying elements, e.g., nickel

,chromium,molybdenum , copper and vanadium.

Carbon in cast iron exist in two forms associated together:

1) As the compound cementite i.e., in a state of chemical composition and the iron is

known as the white cast iron and

2) As free carbon i.e., in a state of mechanical mixture

Carbon in the 1st form is called “ COMBINED CARBON “ and in the latter is called “GREY

CAST IRON “.

An intermediate stage between these two varieties of iron shows patches of grey in the

white structure. This iron is called MOULED IRON .

CHEMICAL COMPOSITIONS OF IRON & STEEL PRODUCTS (APPROXIMATE)

MATERIAL CARBON (%)

SILICON (%)

MANGANESE (%)

SULPHUR (%)

PHOSPHOROUS (%)

Pig iron 3.00-4.00 0.50-3.00 0.10-1.00 0.02-0.10 0.03-2.00

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Grey cast iron

2.50-3.75 1.00-2.50 0.40-1.00 0.06-0.12 0.10-1.00

Malleable cast iron

2.20-3.60 0.40-1.10 0.10-0.40 0.03-0.30 0.10-0.20

White cast iron

1.75-2.30 0.85-1.20 0.10-0.40 0.12-0.35 0.05-0.20

Wrought iron

0.02-0.03 0.10-0.20 0.02-0.10 0.02-0.04 0.05-0.20

Carbon steel

0.05-2.00 0.05-0.30 0.30-1.00 0.02-0.20 0.02-0.15

The quality of cast iron thus depends not upon the absolute amount of carbon it

contains, but upon the conditions in which that carbon exists.

The varieties of cast iron in common are:

1) GREY CAST IRON 5) CHILLED CAST IRON

2) WHITE CAST IRON 6) ALLOY CAST IRON

3) MALLEABLE CAST IRON 7) MEEHANITE CAST IRON

4) NODULAR CAST IRON

GREY CAST IRON :

This is obtained by allowing the molten metal to cool and solidify slowly. On solidifying

, the iron contains the greater part of carbon graphite flakes.

Grey cast iron contains large quantities of carbon and relatively small quantities of the

other element e.g., silicon phosphorous, sulphur and manganese .

It presents a dull grey crystalline or granular structure and a strong light will give a

glistering effect due to reflection of the graphite flakes.

The presence of this free graphite is also seen when filing or machining cast iron as it

makes hands black.

The cast iron is brittle and may easily be broken if a heavy hammer is used .

The strength of cast iron is much greater in compression then in tension.

The ultimate tensile strength of cast iron varies between 12-13 kgf per mm² (120 – 130

N/mm²) and depends upon composition of the iron.

In compression, grey cast iron will withstand about 60-70 kgf/mm² (600-700 N/mm²)

before fracturing, whilst in shear its strength is approx. 15-20 kgf/mm² (150-225

N/mm²).

The hardness ranges from 150-240 BHN.

The main advts. In favour of its uses are:

1) Its cheapness,

27

2) Its lo meltin tem C – C and fl idit hen in the molten

condition, and

3) It is easily machined.

A further good property of cast iron is that the free graphite in its structure seems to

act as a lubricant, and when large machine slides are made of it a very free –working

action is obtained.

The fluidity analysis of the iron enables it to be used widely for making castings of parts

having intricate shapes and in almost all cast iron forms.

WHITE CAST IRON :

White cast iron contains carbon exclusively in the form of cementite(iron carbide).

This is obtained by the presence of relatively large quantities of manganese, a very small

amount of silicon, & by rapid cooling.

The ordinary rate of cooling in sand produces free graphite while rapid cooling helps to

produce cementite.

Moreover, manganese encourages the formation of carbide.

The approx. chemical composition of white cast iron is given in table.

The white cast iron is very hard (the hardness ranges from 400-600 BHN)

White cast iron is also cast as in the intermediate material for making malleable cast

iron.

White cast iron does not rust so much as they grey kind.

MALLEABLE CAST IRON :

The ordinary cast iron is hard and brittle. It is , therefore, unsuitable for articles which

are thin , light and subjected to shock and vibration or for small castings used in various

machine components.

The application of the term 'malleable' to castings is rather a misnomer because they

are not very malleable when compared with the standards of malleability.

When compared with grey iron castings, however which are fairly brittle, malleable

castings do possess a degree of toughness, and this is probably why they have been so

named.

Malleable castings are first made from an iron having all of its carbon in the combined

form i.e., from white cast iron.

Two methods are then used for malleabilizing the castings:

1) white heart, and

2) black heart.

The names refer to the colour of the fracture given by castings produced by cash

method.

28

CHEMICAL COMPOSITIONS IN % OF MALLEABLE CAST IRON :

TYPE CARBON (%)

SILICON (%)

MANGANESE (%)

SULPHUR (%)

PHOSPHOROUS (%)

White iron 3.2-3.6 0.4-1.1 0.1-0.4 0.10-0.3 0.1

Black iron 2.2-2.8 0.7-1.1 0.3-0.4 0.03-0.1 0.1

The white heart process is primarily used for thin walled components, the weight of

which ranges from a few grams to about 20 kg.

the black heart process is used for thick walled workpieces weighing upto 100kg,

especially those which have to be machined by means of cutting tools.

It is, therefore, seen that malleable cast iron, both white heart and black heart

compared with cast iron, is less brittle and therefore, stronger and tougher. it has the

advantage of being more fluid.

The maximum thickness of castings suitable for making this malleabilizing process is

about 20 mm for the white heart and 25-35mm for black heart process. The tensile

strength of malleable castings is about 18 kgf/mm² (180N/mm²).

on account of the special manner in which malleable cast iron is produced, it is

employed mainly for thin walled & small workpiece.

Such parts are for example, hinges,door keys,spanners,mountings of all sorts,

gearwheels, crancks, levers, thin walled components of sewing machines, textile

machines & others.

Malleable cast iron which has been a very suitable material for small and medium size

mass produced castings of high strength for a long time, has recently been suspended in

several fields by spheroidal graphite iron.

This is common called Ductile iron.

DUCTILE IRON :

SPHEREOIDICAL GRAPHITE IRON , is also called nodular cast iron, is of a higher grade

because graphite is precipitated not in the form of flakes but in the form of spheroids.

this can be achieved by various methods ,e.g.,by the addition of one of the following

elements: magnesium, serium, calcium, bismuth, zinc, cadmium, titanium or boron.

Ferro-silicon is use as an inoculant.

Spheroidical cast iron can be produced in thicker pieces than those produced by

malleable cast iron.

Outstanding characteristics of spheroidical cast iron are high fluidity, which permits the

castings of intricate shapes, and an excellent combination of strength and ductility.

The tensile strength of an iron is about 33kgf/mm² (330N/mm²)

29

This material is also known as Ductile iron.

Spheroidical cast iron is widely used in cast parts where density and pressure tightness

is a highly desirable quality.

They include hydraulic cylinders, valves, pipes and pipe fittings,cylinder head for

compressors & diesel engines. Rolls for rolling mills and many types of centrifugally cast

irons are also made of spheroidical cast iron.

CHILLED CAST IRON :

Quick cooling is called "chilling" and the iron so produced is "chilled iron".

All castings are chilled at their outer surface by coming in contact with the cool sand in

the mould.

Since cast iron has a higher thermal conductivity than sand, the chilled portions of the

casting undergo rapid solidification and cooling and thereby produce a herd surface.

But thishardness only penetrates about 1-2mm in depth.

Sometimes a casting is chilled intentionally & sometimes becomes chilled accidentally to

a small depth.

intentionally chilling is carried out by using cast iron instead of sand for those portions

of the mould where hard surfaces are required.

Where these are touched by the molten metal, its surface is suddenly cooled and

converted into white cast iron.

Chills are used on those castings where some parts are required to have the hardness of

white cast iron, while others are required to have relatively soft and tough core of grey

cast iron.

ALLOY CAST IRON :

Alloy cast iron have been developed in recent years to overcome certain inherent

deficiencies in ordinary cast iron and to give qualities more suitable for special purposes.

The addition of nickel, chromium, molybdenum, titanium, silicon, copper and other

alloying elements confer special properties to tjis cast iron.

The use of 1-2 % of nickel is suitable good quality iron offers a simple and effective

means of improving the properties and the service given by iron castings.

It ensures machinability & uniformity of structure of the cast iron.

By the use of nickel of the order of 25%, enhanced life can also be obtained in parts

subjected to abrasive wear.

Cylinders or cylinder liners of all sizes form the smallest to the largest afford outstanding

examples.

Nickel cast iron is also used in withstanding caustic corrosion.

30

For this reason, it is widely employed for making caustic pots, pipes and other castings

in contact with caustic liquor.

The addition of only 1% of nickel gives as all round benefit for this purpose.

The most useful reason for using nickel in cast iron is to obtain density and pressure

tightness in castings with large and varying sections.

This has led to the application of nickel cast for many parts of steam and hydraulic

machinery, compressors and internal combustion engines.

Where improvement in the wearing quality is of importance, chromium additions with

the nickel are often found useful.

Cast iron alloyed in this manner finds wide application for pumps of all types i.e.,which

fractional, as well as erosive, wear has to be considered.

Alloy cast iron containing 10-30% chromium and 1-3% total carbon, also exhibits a high

degree of heat resistance combined with strength at high temperatures.

Cast iron alloyed with 10 % nickel & 6% manganese becomes non-magnetic cast iron is

known with the name as "Nomag".

MEEHANITE CAST IRON :

Cast iron in which metal iron has been treated with calcium sillicide is known by the

name of MEEHANITE.

Calcium sillicide acts as a graphitiser and produces a fine graphite structure giving a cast

iron an excellent mechanical propertise.

The high qualities of meehanite iron are, however, not solely due to the calcium sillicide

but also due to careful control of all the factors involved in melting of the iron in the

cupola or electric furnace and in the moulding of the casting.

Very fine calcium sillicide remains in the iron after solidification.

The metal used is low in silicon, moderately low in carbon which is limited about 2.5-3 %

This normally would be white if cast, but graphitising by meehanite system of control

provides a range of materials to meet the broad requirements of engineering industries.

There are almost more than 26 types of meehanite metal available at present under five

broad classification :

a) general engineering,

b) heat resisting,

c) wear resisting,

d) corrosion resisting,

e) nodular "S" type.

All meehanite irons have high strength toughness, ductility and easy machinability.

They therefore claim to bridge the gap between ordinary cast iron and steel.

The castings weigh from 5000-6000 kg.

31

The metal is closed-grained and shows a Brinell no of 200 to 210.

Meehanite iron response to heat treatment unlike ordinary grey cast iron .

It can be hardened either wholly or on the surface.

It can also be toughened by suitable treatment.

Of the various applications, it is ideally suited for machine tool casting.

PROPERTIES, CHARACTERISTICS AND USES OF A CAST IRON :

TYPE FORM OF CARBON

COMPO- SITION & STRE- NGTH

TENSILE STRENGTH (1.102 kgf/mm²) or MPa

COMP- RESSIVE YIELD (MPa)

ELASTIC MODU- LUS

% ELON- GATION

HARD NESS

TYPICAL APPL.

YIELD

ULTIMATE

Grey Cast iron

Flakes Slow cooling of a high Si cast iron melt

-- 135 240 105 1 130 Ingot moulds, automobile cylinders, pistons, machine castings,etc.

32

White Cast iron

Carbide FeзC

Quench cooling of a low Si cast iron melt

-- 410 690 138 -- 400 Ploughshares, chilled rolls, dies, wearing plates, stamping shoes, balls,etc.

Nodu-llar Or Spheroidic-al Grap-hite iron

Spheroids

Alloying elements added to spherodise carbon during slow cooling

310 410 550 170 15 180 Machine castings subjected to bending & vibrations,& other appl where strength & ductility are important.

Ferrit-ic Malle-able iron

Temper Carbon

Annealed white cast iron casting

225 345 225 170 14 120 Valve bodies, hinges, manhole covers, machine castings etc.

Preal-itic Malle-able iron

Temper Carbon

Annealed white cast iron casting

475 650 475 170 10 200 Camshafts, crankshafts, gears, cams, rocker arms, gunmounts, spanners, wrenches.

33

Q7) CLASSIFICATION OF STEEL. [ROLL NO:09;SE AUTO]

Steel classification is important in understanding what types are used in certain applications

and which are used for others. For example, most commercial steels are classified into one of

three groups: plain carbon, low-alloy, and high-alloy. Steel classification systems are set up and

updated frequently for this type of information.

Generally, carbon is the most important commercial steel alloy. Increasing carbon content

increases hardness and strength and improves hardenability. But carbon also increases

brittleness and reduces weldability because of its tendency to form martensite. This means

carbon content can be both a blessing and a curse when it comes to commercial steel.

And while there are steels that have up to 2 percent carbon content, they are the exception.

Most steel contains less than 0.35 percent carbon. To put this in perspective, keep in mind

that's 35/100 of 1 percent.

Now, any steel in the 0.35 to 1.86 percent carbon content range can be hardened using a heat-

quench-temper cycle. Most commercial steels are classified into one of three groups:

Plain carbon steels

Low-alloy steels

High-alloy steels

Plain Carbon Steels

These steels usually are iron with less than 1 percent carbon, plus small amounts of manganese,

phosphorus, sulfur, and silicon. The weldability and other characteristics of these steels are

primarily a product of carbon content, although the alloying and residual elements do have a

minor influence.

Plain carbon steels are further subdivided into four groups:

Low

Medium

High

34

Very high

Low. Often called mild steels, low-carbon steels have less than 0.30 percent carbon and are the

most commonly used grades. They machine and weld nicely and are more ductile than higher-

carbon steels.

Medium. Medium-carbon steels have from 0.30 to 0.45 percent carbon. Increased carbon

means increased hardness and tensile strength, decreased ductility, and more difficult

machining.

High. With 0.45 to 0.75 percent carbon, these steels can be challenging to weld. Preheating,

postheating (to control cooling rate), and sometimes even heating during welding become

necessary to produce acceptable welds and to control the mechanical properties of the steel

after welding.

Very High. With up to 1.50 percent carbon content, very high-carbon steels are used for hard

steel products such as metal cutting tools and truck springs. Like high-carbon steels, they

require heat treating before, during, and after welding to maintain their mechanical properties.

Low-alloy Steels

When these steels are designed for welded applications, their carbon content is usually below

0.25 percent and often below 0.15 percent. Typical alloys include nickel, chromium,

molybdenum, manganese, and silicon, which add strength at room temperatures and increase

low-temperature notch toughness.

These alloys can, in the right combination, improve corrosion resistance and influence the

steel's response to heat treatment. But the alloys added can also negatively influence crack

susceptibility, so it's a good idea to use low-hydrogen welding processes with them. Preheating

might also prove necessary. This can be determined by using the carbon equivalent formula,

which we'll cover in a later issue.

High-alloy Steels

For the most part, we're talking about stainless steel here, the most important commercial

high-alloy steel. Stainless steels are at least 12 percent chromium and many have high nickel

contents. The three basic types of stainless are:

Austenitic

Ferritic

Martensitic

35

Martensiticstainless steels make up the cutlery grades. They have the least amount of

chromium, offer high hardenability, and require both pre- and postheating when welding to

prevent cracking in the heat-affected zone (HAZ).

Ferriticstainless steels have 12 to 27 percent chromium with small amounts of austenite-

forming alloys.

Austeniticstainless steels offer excellent weldability, but austenite isn't stable at room

temperature. Consequently, specific alloys must be added to stabilize austenite. The most

important austenite stabilizer is nickel, and others include carbon, manganese, and nitrogen.

Special properties, including corrosion resistance, oxidation resistance, and strength at high

temperatures, can be incorporated into austenitic stainless steels by adding certain alloys like

chromium, nickel, molybdenum, nitrogen, titanium, and columbium. And while carbon can add

strength at high temperatures, it can also reduce corrosion resistance by forming a compound

with chromium. It's important to note that austenitic alloys can't be hardened by heat

treatment. That means they don't harden in the welding HAZ.

* Stainless steels always have a high chromium content, often considerable amounts of nickel,

and sometimes contain molybdenum and other elements. Stainless steels are identified by a

three-digit number beginning with 2, 3, 4, or 5.

Figure 1

Be sure to check the appropriate AISI and SAE publications for the latest revisions.

Steel Classification Systems

Before we look at a couple of common steel classification systems, let's consider one more

high-carbon metal, cast iron. The carbon content of cast iron is 2.1 percent or more. There are

four basic types of cast iron:

Gray cast iron, which is relatively soft. It's easily machined and welded, and you'll find it used

for engine cylinder blocks, pipe, and machine tool structures.

White cast iron, which is hard, brittle, and not weldable. It has a compressive strength of more

than 200,000 pounds per square inch (PSI), and when it's annealed, it becomes malleable cast

iron.

36

Malleable cast iron, which is annealed white cast iron. It can be welded, machined, is ductile,

and offers good strength and shock resistance.

Ductile cast iron, which is sometimes called nodular or spheroidal graphite cast iron. It gets this

name because its carbon is in the shape of small spheres, not flakes. This makes it both ductile

and malleable. It's also weldable.

Now let's take a look at a typical steel classification system (see Figure 1). Both the Society of

Automotive Engineers (SAE) and the American Iron and Steel Institute (AISI) use virtually

identical systems. Both are based on a four-digit system with the first number usually indicating

the basic type of steel and the first two numbers together indicating the series within the basic

alloy group.

Keep in mind there may be a number of series within a basic alloy group, depending on the

amount of the principal alloying elements. The last two or three numbers refer to the

approximate permissible range of carbon content in points (hundredths of a percent).

These classification systems can become fairly complex, and Figure 1 is just a basic

representation. Be sure to reference the most recent AISI and SAE publications for the latest

revisions.

That's a look at some basics concerning the iron-carbon-steel relationship and its influences on

welding and metal alloys. Next time we'll look at hardening and ways to make metals stronger.

We'll also consider the influences of some key alloying elements and the effects of welding on

metallurgy.

CARBON STEEL:Carbon steel is steel where the main interstitial alloying constituent is carbon.

The American Iron and Steel Institute (AISI) defines carbon steel as the following: "Steel is

considered to be carbon steel when no minimum content is specified or required for chromium,

cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other

element to be added to obtain a desired alloying effect; when the specified minimum for

copper does not exceed 1.04 percent; or when the maximum content specified for any of the

following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60,

copper 0.60."[1]

37

The term "carbon steel" may also be used in reference to steel which is not stainless steel; in

this use carbon steel may include alloy steels.

As the carbon content rises, steel has the ability to become harder and stronger through heat

treating, but this also makes it less ductile. Regardless of the heat treatment, a higher carbon

content reduces weldability. In carbon steels, the higher carbon content lowers the melting

point.[2]

Contents [hide]

1 Types

1.1 Mild and low carbon steel

1.2 Higher carbon steels

2 Heat treatment

3 Case hardening

4 See also

5 References

6 Bibliography

[edit]Types

See also: SAE steel grades

Carbon steel is broken down in to four classes based on carbon content:

[edit]Mild and low carbon steel

Mild steel, also called plain-carbon steel, is the most common form of steel because its price is

relatively low while it provides material properties that are acceptable for many applications.

Low carbon steel contains approximately 0.05–0.15% carbon[1] and mild steel contains 0.16–

0.29%[1] carbon; making it malleable and ductile, but it cannot be hardened by heat treatment.

Mild steel has a relatively low tensile strength, but it is cheap and malleable; surface hardness

can be increased through carburizing.[3]

It is often used when large quantities of steel are needed, for example as structural steel. The

density of mild steel is approximately 7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3)[4] and the

Young's modulus is 210 GPa (30,000,000 psi).[5]

38

Low carbon steels suffer from yield-point runout where the material has two yield points. The

first yield point (or upper yield point) is higher than the second and the yield drops dramatically

after the upper yield point. If a low carbon steel is only stressed to some point between the

upper and lower yield point then the surface may develop Lüder bands.[6] Low carbon steels

contain less carbon than other steels and are easier to cold-form, making them easier to

handle.[7]

[edit]Higher carbon steels

Carbon steels which can successfully undergo heat-treatment have a carbon content in the

range of 0.30–1.70% by weight. Trace impurities of various other elements can have a

significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make

the steel red-short. Low alloy carbon steel, such as A36 grade, contains about 0.05% sulfur and

melts around 1426–1538 °C (2599–2800 °F).[8] Manganese is often added to improve the

hardenability of low carbon steels. These additions turn the material into a low alloy steel by

some definitions, but AISI's definition of carbon steel allows up to 1.65% manganese by weight.

Medium carbon steel

Approximately 0.30–0.59% carbon content.[1] Balances ductility and strength and has good

wear resistance; used for large parts, forging and automotive components.[9]

High carbon steel

Approximately 0.6–0.99% carbon content.[1] Very strong, used for springs and high-strength

wires.[10]

Ultra-high carbon steel

Approximately 1.0–2.0% carbon content.[1] Steels that can be tempered to great hardness.

Used for special purposes like (non-industrial-purpose) knives, axles or punches. Most steels

with more than 1.2% carbon content are made using powder metallurgy. Note that steel with a

carbon content above 2.0% is considered cast iron.

[edit]Heat treatment

Iron-carbon phase diagram, showing the temperature and carbon ranges for certain types of

heat treatments.

39

Main article: Heat treatment

The purpose of heat treating carbon steel is to change the mechanical properties of steel,

usually ductility, hardness, yield strength, or impact resistance. Note that the electrical and

thermal conductivity are slightly altered. As with most strengthening techniques for steel,

Young's modulus is unaffected. Steel has a higher solid solubility for carbon in the austenite

phase; therefore all heat treatments, except spheroidizing and process annealing, start by

heating to an austenitic phase. The rate at which the steel is cooled through the eutectoid

reaction affects the rate at which carbon diffuses out of austenite. Generally speaking, cooling

swiftly will give a finer pearlite (until the martensite critical temperature is reached) and cooling

slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.77 wt% C) steel results

in a pearlitic structure with a-ferrite at the grain boundaries. If it is hypereutectoid (more than

0.77 wt% C) steel then the structure is full pearlite with small grains of cementite scattered

throughout. The relative amounts of constituents are found using the lever rule. Here is a list of

the types of heat treatments possible:

Spheroidizing: Spheroidite forms when carbon steel is heated to approximately 700 °C for over

30 hours. Spheroidite can form at lower temperatures but the time needed drastically

increases, as this is a diffusion-controlled process. The result is a structure of rods or spheres of

cementite within primary structure (ferrite or pearlite, depending on which side of the

eutectoid you are on). The purpose is to soften higher carbon steels and allow more

formability. This is the softest and most ductile form of steel. The image to the right shows

where spheroidizing usually occurs.[11]

Full annealing: Carbon steel is heated to approximately 40 °C above Ac3 or Ac1 for 1 hour; this

assures all the ferrite transforms into austenite (although cementite might still exist if the

carbon content is greater than the eutectoid). The steel must then be cooled slowly, in the

realm of 20°C (68.4°F) per hour. Usually it is just furnace cooled, where the furnace is turned off

with the steel still inside. This results in a coarse pearlitic structure, which means the "bands" of

pearlite are thick. Fully annealed steel is soft and ductile, with no internal stresses, which is

often necessary for cost-effective forming. Only spheroidized steel is softer and more

ductile.[12]

Process annealing: A process used to relieve stress in a cold-worked carbon steel with less than

0.3 wt% C. The steel is usually heated up to 550–650 °C for 1 hour, but sometimes

temperatures as high as 700 °C. The image rightward shows the area where process annealing

occurs.

Isothermal annealing: It is a process in which hypoeutectoid steel is heated above the upper

critical temperature and this temperature is maintained for a time and then the temperature is

40

brought down below lower critical temperature and is again maintained. Then finally it is

cooled at room temperature. This method rids any temperature gradient.

Normalizing: Carbon steel is heated to approximately 55 °C above Ac3 or Acm for 1 hour; this

assures the steel completely transforms to austenite. The steel is then air-cooled, which is a

cooling rate of approximately 38 °C (100.4 °F) per minute. This results in a fine pearlitic

structure, and a more-uniform structure. Normalized steel has a higher strength than annealed

steel; it has a relatively high strength and ductility.[13]

Quenching: Carbon steel with at least 0.4 wt% C is heated to normalizing temperatures and

then rapidly cooled (quenched) in water, brine, or oil to the critical temperature. The critical

temperature is dependent on the carbon content, but as a general rule is lower as the carbon

content increases. This results in a martensitic structure; a form of steel that possesses a super-

saturated carbon content in a deformed body-centered cubic (BCC) crystalline structure,

properly termed body-centered tetragonal (BCT), with much internal stress. Thus quenched

steel is extremely hard but brittle, usually too brittle for practical purposes. These internal

stresses cause stress cracks on the surface. Quenched steel is approximately three to four (with

more carbon) fold harder than normalized steel.[14]

Martempering (Marquenching): Martempering is not actually a tempering procedure, hence

the term "marquenching". It is a form of isothermal heat treatment applied after an initial

quench of typically in a molten salt bath at a temperature right above the "martensite start

temperature". At this temperature, residual stresses within the material are relieved and some

bainite may be formed from the retained austenite which did not have time to transform into

anything else. In industry, this is a process used to control the ductility and hardness of a

material. With longer marquenching, the ductility increases with a minimal loss in strength; the

steel is held in this solution until the inner and outer temperatures equalize. Then the steel is

cooled at a moderate speed to keep the temperature gradient minimal. Not only does this

process reduce internal stresses and stress cracks, but it also increases the impact

resistance.[15]

Quench and tempering: This is the most common heat treatment encountered, because the

final properties can be precisely determined by the temperature and time of the tempering.

Tempering involves reheating quenched steel to a temperature below the eutectoid

temperature then cooling. The elevated temperature allows very small amounts of spheroidite

to form, which restores ductility, but reduces hardness. Actual temperatures and times are

carefully chosen for each composition.[16]

41

ALLOY STEEL:Every steel is truly an alloy, but not all steels are called "alloy steels". Even the

simplest steels are iron (Fe) (about 99%) alloyed with carbon (C) (about 0.1% to 1%, depending

on type). However, the term "alloy steel" is the standard term referring to steels with other

alloying elements in addition to the carbon. Common alloyants include manganese (the most

common one), nickel, chromium, molybdenum, vanadium, silicon, and boron. Less common

alloyants include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead,

and zirconium.

The following is a range of improved properties in alloy steels (as compared to carbon steels):

strength, hardness, toughness, wear resistance, hardenability, and hot hardness. To achieve

some of these improved properties the metal may require heat treating.

Some of these find uses in exotic and highly-demanding applications, such as in the turbine

blades of jet engines, in spacecraft, and in nuclear reactors. Because of the ferromagnetic

properties of iron, some steel alloys find important applications where their responses to

magnetism are very important, including in electric motors and in transformers.

Contents [hide]

1 Low-alloy Steels

2 Material science

3 See also

4 References

4.1 Notes

4.2 Bibliography

[edit]Low-alloy Steels

Low-alloy steels are usually used to achieve better hardenability, which in turn improves its

other mechanical properties. They are also used to increase corrosion resistance in certain

environmental conditions.[3]

With medium to high carbon levels, low-alloy steel is difficult to weld. Lowering the carbon

content to the range of 0.10% to 0.30%, along with some reduction in alloying elements,

increases the weldability and formability of the steel while maintaining its strength. Such a

metal is classed as a high-strength low-alloy steel.

42

Some common low alloy steels are:

D6AC

300M

256A

Principal low-alloy steels[4]

SAE designation Composition

13xx Mn 1.75%

40xx Mo 0.20% or 0.25% or 0.25% Mo & 0.042% S

41xx Cr 0.50% or 0.80% or 0.95%, Mo 0.12% or 0.20% or 0.25% or 0.30%

43xx Ni 1.82%, Cr 0.50% to 0.80%, Mo 0.25%

44xx Mo 0.40% or 0.52%

46xx Ni 0.85% or 1.82%, Mo 0.20% or 0.25%

47xx Ni 1.05%, Cr 0.45%, Mo 0.20% or 0.35%

48xx Ni 3.50%, Mo 0.25%

50xx Cr 0.27% or 0.40% or 0.50% or 0.65%

50xxx Cr 0.50%, C 1.00% min

50Bxx Cr 0.28% or 0.50%

51xx Cr 0.80% or 0.87% or 0.92% or 1.00% or 1.05%

51xxx Cr 1.02%, C 1.00% min

51Bxx Cr 0.80%

52xxx Cr 1.45%, C 1.00% min

61xx Cr 0.60% or 0.80% or 0.95%, V 0.10% or 0.15% min

86xx Ni 0.55%, Cr 0.50%, Mo 0.20%

87xx Ni 0.55%, Cr 0.50%, Mo 0.25%

43

88xx Ni 0.55%, Cr 0.50%, Mo 0.35%

92xx Si 1.40% or 2.00%, Mn 0.65% or 0.82% or 0.85%, Cr 0.00% or 0.65%

94Bxx Ni 0.45%, Cr 0.40%, Mo 0.12%

ES-1 Ni 5%, Cr 2%, Si 1.25%, W 1%, Mn 0.85%, Mo 0.55%, Cu 0.5%, Cr 0.40%, C 0.2%, V 0.1%

[edit]Material science

Alloying elements are added to achieve certain properties in the material. As a guideline,

alloying elements are added in lower percentages (less than 5%) to increase strength or

hardenability, or in larger percentages (over 5%) to achieve special properties, such as

corrosion resistance or extreme temperature stability.[2]

Manganese, silicon, or aluminium are added during the steelmaking process to remove

dissolved oxygen, sulfur and phosphorus from the melt.

Manganese, silicon, nickel, and copper are added to increase strength by forming solid

solutions in ferrite. Chromium, vanadium, molybdenum, and tungsten increase strength by

forming second-phase carbides. Nickel and copper improve corrosion resistance in small

quantities. Molybdenum helps to resist embrittlement. Zirconium, cerium, and calcium increase

toughness by controlling the shape of inclusions. Manganese sulfide, lead, bismuth, selenium,

and tellurium increase machinability.[5]

The alloying elements tend to form either compounds or carbides. Nickel is very soluble in

ferrite; therefore, it forms compounds, usually Ni3Al. Aluminium dissolves in the ferrite and

forms the compounds Al2O3 and AlN. Silicon is also very soluble and usually forms the

com o nd SiO •MxO . Man anese mostl dissolves in ferrite formin the com o nds MnS

MnO•SiO b t ill also form carbides in the form of Fe Mn 3C. Chromi m forms artitions

between the ferrite and carbide phases in steel, forming (Fe,Cr3)C, Cr7C3, and Cr23C6. The type

of carbide that chromium forms depends on the amount of carbon and other types of alloying

elements present. Tungsten and molybdenum form carbides if there is enough carbon and an

absence of stronger carbide forming elements (i.e., titanium & niobium), they form the carbides

Mo2C and W2C, respectively. Vanadium, titanium, and niobium are strong carbide forming

elements, forming vanadium carbide, titanium carbide, and niobium carbide, respectively.[6]

Alloying elements also have an effect on the eutectoid temperature of the steel. Manganese

and nickel lower the eutectoid temperature and are known as austenite stabilizing elements.

With enough of these elements the austenitic structure may be obtained at room temperature.

44

Carbide-forming elements raise the eutectoid temperature; these elements are known as

ferrite stabilizing elements.[7]

Principal effects of major alloying elements for steel[8]

Element Percentage Primary function

Aluminium 0.95–1.30 Alloying element in nitriding steels

Bismuth - Improves machinability

Boron 0.001–0.003 A powerful hardenability agent

Chromium 0.5–2 Increases hardenability

4–18 Increases corrosion resistance

Copper 0.1–0.4 Corrosion resistance

Lead - Improved machinability

Manganese 0.25–0.40 Combines with sulfur and with phosphorus to reduce the

brittleness. Also helps to remove excess oxygen from molten steel.

>1 Increases hardenability by lowering transformation points and causing transformations

to be sluggish

Molybdenum 0.2–5 Stable carbides; inhibits grain growth. Increases the toughness of steel,

thus making molybdenum a very valuable alloy metal for making the cutting parts of machine

tools and also the turbine blades of turbojet engines. Also used in rocket motors.

Nickel 2–5 Toughener

12–20 Increases corrosion resistance

Silicon 0.2–0.7 Increases strength

2.0 Spring steels

Higher percentages Improves magnetic properties

Sulfur 0.08–0.15 Free-machining properties

Titanium - Fixes carbon in inert particles; reduces martensitic hardness in chromium

steels

Tungsten - Also increases the melting point.

45

Vanadium 0.15 Stable carbides; increases strength while retaining ductility; promotes

fine grain structure. Increases the toughness at high temperatures

Q8. Explain the effect of alloying element on iron.

ANS:

Besides carbon, cast iron and wrought iron generally contains small amount of silicon,

sulphur, manganese etc. Some ideas of the effect of these elements on the iron are

given here under.

Carbon is dissolved in pure liquid iron and if the solution is solidified slowly

the carbon tends to separate out giving the structure which is the mixture of

pure iron and graphite. This gives a fairly tough iron which breaks with dark

glistering fracture. It is easily machined. If the same iron is cast and cooled

quickly, it is hard, has a higher tensile strength, it is difficult to machine and

breaks with a close white fracture. The white constituent is iron carbide

called cementite

Silicon is cast iron may be present up to 2.5%. It promotes the formation of

free graphite which makes the iron soft and easily machinable.At the same

time, this element inhibits the pickup of carbon during the melting of iron. It

also produces sound casting free from blow holes because of its high

affinity for oxygen.

A very small percentage of silicon makes wrought iron hard, brittle

and unforgeable.

Sulphur is generally regarded as harmful is cast iron. It lowers the viscosity

of the melt and tends to make the cast iron hard and brittle. So it should be

kept well below 0.1% for most foundry purpose.

In wrought iron, 0.02-0.04% OF Sulphur produces shortness

i.e the metal becomes brittle and unworkable at red heat, although

possessing the usual qualities when cold.

Manganese tends in a different way to whiten and harden cast iron by

encouraging the formation of carbide. It is therefore, often kept below

0.75%. But it helps to exert a controlling influence over the harmful effect of

sulphur, and for any particular purpose these two impurities should be

considered in conjunction.

Phosphorus in cast iron aids fusibility and fluidity but induces brittleness. It

is rarely allowed to exceed 1%. Phosphoric irons are useful, however, for

casting when cheapness is essential.

It wrought iron, the presence of only a very small amount of phosphores is

very injurious and only 0.1% is sufficient to make the iron cold-shot, i.e. the

46

metal is brittle and liable to crack when cold but may be malleable and

easily worked at red heat.

Nickel act as a graphitizer but is only half efficient as silicon. Small amount

helps to refine the size of grain and graphite flakes. Most additions are from

0.25-2%. Largest amount from 14-38% are added in grey iron to resist heat

and corrosion and have low expansitivity

Chromium acts as carbide stabilizer in cast iron. Thus it intensifies chilling

of cast iron, increases strength, hardness and wear-resistance and is

conductive to fine grain structure. Most addition of chromium range from

0.15-0.90% with or without other alloying elements. Chromium of 1% or

more makes casting hard to machine with 3% chromium, white cast iron is

formed. Special iron to resist corrosion and high temperature contains as

much as 35% chromium.

Molybdenum ranges from 0.25-1.5%. This is added along or with other

elements to improve tensile strength, hardness, and shock resistance of

casting. The presence of molybdenum in cast iron produces fine and highly

dispersed particles of graphite and good structural uniformity this improves

toughness, fatigue strength, machinability hardnability, and high

temperature strength.

Copper promotes formation of graphite. It is usually present in cast iron

from 0.02-2.5%.

Vanadium amounts from 0.1-0.5%. This is to increase strength, hardness

and machinability.

name KISHOR.S.GUNJALKAR

rollno=AE310

Q9 Explain the effects of alloying elements on steel

ANS

Effects of Alloying Elements on steel :

Many of the special alloy steels have been developed to provide material which

will pass through a heat treatment process more successfully.

Influencing speed and temperature is possible by alloying small amounts of other

elements.

It counteracts the mass effect(see table.) and distortional influences.

Some of the steels possess non distortional characteristics which is necessary

when making dies

47

Some alloy steels reach their ideal condition of hardness by relatively mild oil

quench from a temperature of about 800 C.

Table of alloying elements :

Elements Effects Remark(s)

Al Promotes De-oxidization Promotes nitriding Restricts grain growth

Typically low percentage

B Increases hardenability Percentage(0.01-0.03) used in steels with carbon content less than 0.6%

C Increases brittleness Forms hard carbides with iron, chromium and vanadium Increases strength & wear resistance

Saturation content increases upto 0.87%

Co Impairs impact strength slightly. Contributes to red hardness. Sustains hardness during tempering.

Cr Increases hardenability Increases resistance to corrosion, abrasion & wear. increases high temperature strength

Typical percentage 0.5-2 to increase hardenability. Typical percentage 4-8 to increase corrosion & wear resistance.

Cu Increases corrosion resistance Strengthens low alloy steels Increases hardenability

Typical percentage 0.1-0.4 Typical percentage 0.2-0.9 to increase strength Used in spring steels

Si Acts as deoxidizer Improves magnetic properties when present in large percentage

Typically high percentage to increase magnetic properties

S Improves machinability of very low carbon steels

Typical percentage 0.08-0.15 Normally considered an impurity

P Promotes cold-shortness Increase strength & resistance to corrossion

48

N Hardens slightly & reduces ductility forms hard nitrides with Aluminium & introduced externally in balanced Al steels promotes grain growth at high temperatures

Normally undesirable

Ni Increases hardness, strength, ductility, impact resistance. Narrows the hardening range & lowers the critical point reducing danger of warpage and cracking. Decreases machinability.

Large amounts give resistance to oxidation at high temperatures

Pb Forms minute strings and finely divided particles

Ti Increases austentic hardenability. Reduces martensitic hardness in Cr steels .

Fixes carbon in inert particles, resulting in remarkable carbide forming effect.

V Increases strength while retaining ductility. Produces fine grain size. Increases hardenability.

Typical percentage of 0.15. Forms stable carbides that persist at quite high temperature. Normally used in combination with chromiun

W Imparts hardness and wear resistance. Significantly improves red hardness. Imparts strength at high temperatures.

Typical percentage 4 to impart wear resistance Typical percentage 18 to improve red hardness. Used in high speed tool materials

Making of steel in workshops :

49

Cantilever plate racks

Surface Grinder

Carbide Tipped Plate saws:

50

Die Package ready for shipment:

Tejas kamble roll no 15

,

51

Q10) All types of irons and its properties and its applications.

Nishant.A.Karnik,Roll no: AE17 , Dept:Automobile engineering

Ans: Types of cast irons:

1. white cast iron: hard, wear resistant, brittle of practically unmachinable.

2. gray cast iron: flakes form from melt.

3. chilled cast iron: surface white cast iron and interior of gray cast iron.

4. mottle iron (mixed iron):

a) contains graphite flakes, secondary cementite and pearlite.

b) extreme brittleness.

52

5. SG iron- (nodular iron):

a) nodules of graphite.

b) obtained by treating molten alloy with Mg, Ge, Ca, Ba, Li, Zr.

6. Mehanite iron: addition of calcium siliside.

7 .malleable cast iron :

a) temper carbon-irregularly round-shaped graphite.

b) Ht-called malleablishing ht of white cast iron.

8. Vermicular graphite cast iron:

a) graphite shape is between flakes and spheres.

b).treatment is same as that for ductile iron.

c) better ductility and strength as compared to gray cast iron.

9. Alloy cast irons

Gray cast iron characterstics:

1.Poor tensile strength:

a) Cast iron have poor tensile strength due to the presence of graphite flakes

The notch effect of graphite flakes causes stress concentration at the tip of

flakes causing an early failure.

b) The graphite flakes act as discontinuity in an otherwise continous martix

and act as micro cracks hence not used in tensile applications.

2. High compressive strength:

The compressive strength is 6 to 10 times its tensile strength due to

secondary bonding of graphite and crack closure. The cracks tend to close

under compressive loading.

3. Good machinability:

a) Graphite has lubricating properties . The presence of graphite and lubricant

allows machining without cutting fluid. The chips obtained are

53

discontinuous

b) However graphite forms lot of black deposites on operator hands and

vicinity and extensive cleanliness is required.

4. Good castability:

Cast iron has low melting temp and low shrinkage making it exellent material

for casting.

5. Poor weldability:

At high temperatures the free carbon quickly combines with atmospheric

oxygen to form carbon dioxide. The composition of the material remaining in

the weld changes.

Applications:

Lathe bed, machine beds, crank case, pump cover, flywheel and manhole cover.

White cast iron characterstics:

a) Freshly fractured surface of white cast iron is shining bright due to the

presence of pearlite and cementite. No free carbon is present in this cast

iron.

b) The cast iron is extremely brittle, hard, poorly machinable, has poor

weldability and generally useless for manufacturing other than casting.

c) However it finds use after subjecting to the best treatment called as

malleabilising.

Applications:

Mill rolls, raw material for malleable cast iron, crusher plates , grinding wheel

dressers etc.

Nodular iron characteristics:

a) the harmful effect of graphite flake notches is eliminated in this type of

cast iron by inoculation. Inoculation is a process of making additions to the

liquid metal in the mould.

54

b) The inoculants is placed in the spure basin and covered with metallic grid

before pouring molten cast iron into the mould. This practice prevents

evapouration on inoculant giving better spherodisation.

c) Inoculation is alloy addition to change internal morphology of cast iron.

Inoculant could be shots of 15 % Mg-Ni cerium compound added in ladle or

in mould.

Applications:

Casings of fluid coupling, turbine housing, Crankshaft ,cams.

Malleable cast iron :

a) Raw material of this is white cast iron. Malleable cast iron is obtained by

heat treating white cast iron. The heat treatment known as malleabilising

consist heating and cooling in a cycle

b) This causes Fe3C = 3Fe+c transformation. The carbon so seperated diffuses

and gather at specific spots. This carbon is known as temper carbon

c) Due to prolonged heat treatment this cast iron is costly but can show

highest ductility amongst cast irons

Applications:

Steering rods of automobiles, connecting levers in earth movers, tractor components

etc.

55

Mottled cast irons:

Due to different cooling rates in different locations of same component , the

casting may shown microstructure of bothy- Gray cast iron and white cast iron

in different zones.

Q11.State uses of different types of steels (ALL)

ANS

Different Types Of Steel And Their Uses:

Steel is basically an alloy of iron and carbon with a small percentage of other metals

such as nickel, chromium, aluminum, cobalt, molybdenum, tungsten etc. Steel is a hard

ductile and malleable solid and is probably the most solid material after plastic and iron.

If we draw a comparison between iron and steel, we find steel in many ways even better

than iron. Steel may not be as strong as iron is but it far more resistant and does not

corrode and gets rusted like iron does.

There are many different types of steel classified on the basis of the type of metal used

and the percentage content of the metal in the particular type of steel.

Below given are some commonly used types of steel:

56

High-Carbon Steel Blade

High-Carbon Steel

Carbon steel is simply composed of iron and carbon with a more percentage of carbon

in it than the iron.

It is probably the most commonly used type of steel. The presence of excess carbon

makes this type of steel is softer than the other types of steel which contain some

percentage of other elements as well.

Carbon steel is mostly used in the making of wood cutting tools because they can be

sharpened easily. However it cannot be used in the making of tools used for the cutting

of hard substances because it is not hard enough for that purpose. It is also used in the

making of axes, swords, scissors and other cutting tools.

Mild Steel Rings

57

Stainless Steel Utensils

Mild Steel

The mild carbon steel just like the high carbon steel is simply composed of iron and

carbon but it has a very low content of carbon in it.

This steel is used in the making of vehicle frames, panels, boxes, cases and sheet

metal for roofs. It is now also used as a replacement for wrought iron in the making

railroad rails.

Medium Carbon Steel

The medium carbon steels have a normal content of carbon that means that they are

not as hard as the high carbon and neither are they as strong the Mild carbon steel.

They are used in the making of tool frames and springs.

Stainless Steel

Stain less steel is the most resistant and commonly used steel of all the types. It apart

from carbon contains 11% chromium and some amount of nickel. It is probably the most

resistant steel of all the types.

Although all the types of steel are generally resistant to rust and corrosion, the stainless

steel in particular is resistant to any sort of external attack. Even a scratch cannot stay

on the surface of stainless steel.

This steel is used in the making of crockery, wrist watches, kitchen utensils, cutlery and

surgical equipments.

Steel Cable

High Speed Steel

58

High speed steel is an alloy of steel which may consists of either of the following metals:

tungsten, cobalt, molybdenum or chromium.

High speed steel is probably the toughest of all the types. The term high speed is given

to it due to the fact that it has the ability to cut the metals.

And that is the reason it is used in the making of drills and tools and power saws.

The hardness and rigidity of high speed steel depends on the metal used in the making

of the alloy and its percentage of composition in it.

Basically this steel is used in the making of tools that cut other metals.

Cobalt Steel

Cobalt is much like the high speed steel with an excess of cobalt present in it.

It is too like the high speed steel is used for drilling purposes.

It might not be as hard as the high speed steel is but it too can drill through certain types

of metals. The drill tools made of cobalt steel have a touch of brown color.

Nickel Chromium Steel

Nickel chromium steel is has is a special type of steel which apart from being strong s

also shock resistant therefore it is commonly used as an armor plate.

Aluminum Steel

Aluminum steel is smooth steel with a high content of aluminum. Because of its strong

and smooth surface it is used in the making of furniture.

Chromium Steel

Chromium steels have a high content of chromium and are resistant to corrosion.

They are very strong, ensile and are elastic in nature. They are used in the making of

Automobile and airplane parts.

name :Ajay Kashyap Roll.No.:318.

Q 12) Advantages of Nonferrous metal & alloy?

Name: Amit Khairaokar

Roll No: 319

Branch: Automobile

59

NONFERROUS METALS

ADVANTAGES OF NONFERROUS METAL AND ALLOYS

• Nonferrous metals are those which do not contain iron as base. Their • melting points are generally from hot shortness possess low strength at high

temperature, and thair shrinkage is generally more than that of ferrous metals. Nonferrous metals are used for the following reasons: 1. Resistance to corrosion 2. Special electronical and magnetic property 3. Softness and facilities of cold corrosion 4. Fusibility and ease of casting 5. Good formability 6. Low density 7. Attractive colour

• The principal nonferrous metals used in engineering purrose are aluminium, copper, lead, tin, zinc, nickel etc and their alloy

Metal Alloy Uses

• Stainless steel is used to make a wide variety of items. • An alloy is created when a metal is mixed with more than one element. There are

two types of alloys---ferrous and nonferrous. A ferrous alloy is iron-based. Steel

60

and cast iron are examples of ferrous alloys. Nonferrous alloys are any alloy that is not iron-based. Aluminum, brass and bronze are examples of nonferrous alloys.

62

Q13. Note on aluminium and its alloys

Name : ImranKhan

Class: S.E.(AUTO)

Roll no. AE 320

Ans: Aluminium:

Aluminium has several excellent properties as below:

(1) It is ductile and malleable due to FCC structure.

(2) It is light in weight (specific gravity- 2.7 gm/cm3)

(3) It has very good thermal and electrical conductivity. On weight to weight basis , it

carries more electricity then copper.

(4) It has excellent ability of getting alloyed with other elements like Cu, Si, Mg, Mn,

Zn etc.

(5) It has excellent corrosion and electric resistance yhis is due to formation of

Al2O3 film on the metal surface corrosion

(6) The metals and its alloys can be anodized for decoration and increasing

corrosion resistance.

(7) It has low ductile-brittle transition temperature (-40 C)

(8) It is non magnetic and non sparkling in character, and has a low neutron

absorption coefficient it also has high reflectivity for heat and radiant energy,

APPLICATIONS:

(1) It is extensively used in form of alloys for aerospace and automobile

parts for structure of all types.

(2) Used for overheld cables. Sometimes thinner film of steel is

necessary.

(3) Used in heat exchange components. In manufacturing piston, the high

conductivity enables higher compression ratios to be used.

(4) It is used in chemical plants for handling strong acids and in food

industries for pan and hollow ware

(5) Aluminium foils is used in packaging and to seal bottles

(6) Its affinity for oxygen enables it to be used as deoxidant in steels. Also

used as “thermit”, for welding rails, ships, sterns and for manufacture

of ferro-titaniumn product of aluminium i.e Al2O3 which is non toxic

63

Alloys of aluminum:

(1) Aluminum finds its widest use when alloyed with small amounts of other metals.

The addition of small quantities of other alloying element converts this soft , weak

metal into hard into strong and hard metal, while still retaining its light weight.

(2) Alloys can be classified as cast or wrought, both groups containing alloys that

are age hardened. The alloys in each of this two classes are further classified

according to whether they respond to heat treatment of strengthening type.

(3) For the casting of general engineering use , aluminium is alloyed with small

amounts of copper and zinc in proportion of 12.5 to 14.5 percent zinc 2.5 to 3.0

percent of copper.

(4) An important series of casting and forging alloys having high strength have been

recently developed for use in aeroplane construction.

(5) One example of such alloy is : zinc 5 percent , magnesium 3 percent copper 2.2

percent , nickel up to 1 percent aluminium the remainder.

(6) An important and interesting wrought alloy is known as duralumin. This is

composed of 3.54 to 4.5 percent of copper 0.4 to 0.7 percent ofmanganese, 0.4

to 0.7 percent of magnesium, and aluminium the remainder. It is widely used

wrought condition for forging, stampings, bars, sheets, tubes and rivets. It is

interesting because of its age hardening property

(7) Another alloy known as Y-alloy contains 3.5 to 4.5 percent of copper, 1.8 to 2.3

percent of nickel and 1.2 to 1.7 percent magnesium.

(8) Berrylium copper are solution heat treated and precipation hardened. Aging time

is 2 to 3 hours at around 325 c.

Aluminium bronze containing more than 10 percent aluminium are quenched from 650

c and subsequently tempered at low temperature

Alloys Composition Properties Applications

Duralumin 4% Cu,Al Good hardness strength age hardenable

Aircraft industry

LM6 12 % Si,Al High corrosion resistance,good fluidity

Intricate castings for automobile and pump parts

LM13 12.5% Si, 2.5% Ni, 1% Cu, 1.2 Mg, Al

Good forgability and low coefficient of

Forged automobile pistons

64

thermal expansion

LM 5 5% SI, Al Good weldability and corrosion resistance

Cable sheathing and marine applications

LM 10 10% Mg ,Al Age hardenable but poor castability

Aircraft and automobile components

Q 14) NOTE ON COPPER AND ITS ALLOYS?

ANS:

1) Copper is known for its very high thermal and electrical conductivity.

2) It therefore finds extensive application in electrical conductors, transformer winding ,

contact

materials, heat exchangers, radiators, refrigerators, etc.

3) copper alloys are classified as BRASSES AND BRONZES.

PURE COPPER:

1) very soft, ductile

2) with poor machinability

3) good corrosion resistance

APPLICATIONS:

1) automobile radiator

2) water heaters

3) refrigerators

4) heat exchanger

5) distillery equipment

6) electrical applications

copper is known for its very high thermal and electrical conductivity.it therefore

finds extensive applications in electrical conductors, transformerswinding, contact materials,

heat exchangers, radiators, refrigerators, etc.

IMPORTANTS TYPES OF COPPER INCLUDE:

1) O.F.H.C. (Oxygen-free, high conductivity copper): this is 99.98% pure and used in

electrical industries.

2) Tough-pitch copper: partially deoxidized copper (containing 0.04 to 0.08% oxygen)

3) free-cutting copper minimum 95% copper with 0.5% tellurium or lead.

65

SOME IMPORTANT ALLOYS OF COPPER:

1) ALLOY= copper +0.5% chromium

CONDUCTIVITY= 85% of pure copper

USES= spot welding electrodes, switchgears, heat interchangers.

2) ALLOY= 32% of pure copper

CONDUCTIVITY= 32% of pure copper

USES= bourdon tubes, flexible bellows, non-sparking tools.

COPPER ALLOY:

Copper may be alloyed with a wide range of other element to produce many different alloy

group of industrial importance the most important are:

1) Copper aluminum (aluminum bronzes)

2) Copper –tin-antimony (Babbitt metal)

3) Copper-tin (the tin bronzes)

4) Copper tin phosphorus(the phosphor bronzes)

5) Copper zinc (the brasses)

6) Copper-nickel (the cupronickels)

ANIKET MAHAJAN

323(automobile)

Q 15) Write a note on zinc and its alloys.

Name-Nitin P. Mali

Branch-Automobile

Roll no.-325

66

Ans-The chief ores of zinc are zinc blende and calamine.In the extraction of the metal the ore is

first roasted in a reverberatory furnace to convert the sulphide to oxide and in the case of

calamine to drive off carbonic acid and water.The roasted ore is then reduced either in a

furnace or electrolytically.

Zinc s a fairly heavy bluish white metal used principally because of its low cost corrosion

resistance and alloying properties.The melting point of zinc is 419 celcius.

The protection of iron and steel fromcorrosion is done more oftenwith zinc than with any

other metal coating.The oldest and most important methods of applying the zinc coating are

known as galvanizing. When rolled into sheets zinc is used for roof covering and for providing a

damp proof noncorrosive lining to containers etc. Zinc casts well and forms the base of various

die-casting alloys. A typical high strength die-casting alloy would have the following

composition and properties-

COMPOSITION

Cu=1.25% Al=4% Mg=0.08%

Fe=0.10% Pb=0.007% Cd=0.0007%

Sn=0.007% Zn=remainder

PROPERTIES-

UTS=32 kgf/mm^2 or 320 MPa % elongation=7%

Charpy impact no. =65J or 6.5kgm Melting point=425 celcius

Q16) Note On Tin And Its Alloys

Ans:

Tin is a soft white metal with good corrosion resistance and bearing properties. It is extensively

used for coating steel in the manufacture of tin case. Tin coated copper tubing is used for

handling fresh water containing large percentages of carbon dioxide and oxygen. In addition, tin

is used as an alloying element in copper, aluminium lead based alloys. Tin acts as a catalyst

when oxygen is in solution and helps accelerate chemical attack.

Alloys of tin

Babbitt (copper, antimony, lead; used for bearing surfaces)

Britannium (copper, antimony)

http://en.wikipedia.org/wiki/Catalyst

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Babbitt_%28metal%29

http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Antimony

http://en.wikipedia.org/wiki/Lead

http://en.wikipedia.org/wiki/Britannium



67

Pewter (lead, copper)

Solder (lead, antimony)

Terne (lead)

1) Babbitt

There are many Babbitt alloys in addition to Babbitt's original. Some common compositions are:

90% tin, 10% copper

89% tin, 7% antimony, 4% copper

80% lead, 15% antimony, 5% tin

76% copper, 24% lead

75% lead, 10% tin

67% copper, 28% tin, 5% lead

2) Britannium

Britannia metal or britannium is a pewter-type alloy favoured for its silvery appearance and

smooth surface. Brittania metal melts at 255 degrees Celsius.[1]

The composition is

approximately 93% tin, 5% antimony, and 2% copper.

3) Pewter

Pewter is a malleablemetalalloy, traditionally 85–99% tin, with the remainder consisting of

copper, antimony, bismuth and (sometimes, and less commonly today) lead. Copper and

antimony act as hardeners while lead is common in the lower grades of pewter, which have a

bluish tint. It has a low melting point, around 170–230 °C (338–446 °F), depending on the exact

mixture of metals. The word pewter is probably a variation of the word spelter, a term for zinc

alloys.

4) Solder

Tin has long been used as a solder in the form of an alloy with lead, tin accounting for 5 to 70%.

Tin forms a eutectic mixture with lead containing 63% tin and 37% lead. Such solders are

primarily used for solders for joining pipes or electric circuits.

5) Terne

Terne is an alloy coating that was historically made of lead and tin used to cover steel, in the

ratio of 20% tin and 80% lead. Currently, lead has been replaced with the metal zinc and is used

in the ratio of 50% tin and 50% zinc. This alloy has a low melting point approximately 360

degrees FahrenheitTerne is used to coat sheet steel to inhibit corrosion. It is one of the cheapest

alloys suitable for this Terne coated stainless steel (TCS) or copper is commonly used to replace

terne metal roofs as either material will outlast terne metal.

http://en.wikipedia.org/wiki/Pewter



http://en.wikipedia.org/wiki/Solder



http://en.wikipedia.org/wiki/Terne


http://en.wikipedia.org/wiki/Tin




http://en.wikipedia.org/wiki/Pewter

http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Britannium#cite_note-0




http://en.wikipedia.org/wiki/Ductility

http://en.wikipedia.org/wiki/Ductility





http://en.wikipedia.org/wiki/Bismuth


http://en.wikipedia.org/wiki/Melting_point

http://en.wikipedia.org/wiki/Spelter

http://en.wikipedia.org/wiki/Zinc

http://en.wikipedia.org/wiki/Solder

http://en.wikipedia.org/wiki/Eutectic_system

http://en.wikipedia.org/wiki/Plumbing

http://en.wikipedia.org/wiki/Electric_circuit

http://en.wikipedia.org/wiki/Terne




http://en.wikipedia.org/wiki/Steel


http://en.wikipedia.org/wiki/Zinc

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Corrosion

68

NAME : MAYUR MHATRE

Roll No : AE-326

Q17) Write a short note on lead and its alloys,properties and its application.

Ans:

LEAD:

Lead is a bluish greay metal with a high mettalic lusture when freshly cut.It is very

durable and versatile material.The heavy metal obtained from the bottom of the

furnance is furthure oxidised in bessemer's converter to remove most of the impurities.

PROPERTIES:

Lead has properties of high density and easy wokability.It has very good resistance to

corrosion and many acids have no chemical actions on it.Its melting point is (327+273)k

and specific gravity is 11.35.It is the softest and heaviest of all the common metals.It is

very mellable and may be readly formed into foil.It can readly be scrached with

fingernail when pure.

APPLICATIONS:

The lead pipes installed by romans in the public baths in Bath,England,nearly 2000 yrs.

ago and still in use.Lead is used in saftey plugs in boilers,fire door releases and fuses.It

is also used in various alloys such as brass and bronze.It finds extensive applications

as sheaths for electric cables,both overhead and underground.Its sheets are used for

making roofs,guters etc.It is employed for chemical labs andplant drains.In the soldering

process,an alloy of lead and tin is most widely utilized as solder material for joining

metals in joining processes.

IMPORTANT LEAD ALLOYS:

The most common alloying elements with lead are antimony and tin.The Pb-Sb phase

diagram is of eutectic type with eutetic composition of 11.2% Sb and eutectic

temprature of (251.2+273)k.Antomony is generally added to lead to increase the

recrystallization temperature and to increase hardness and strength. The commercial

alloys contain antimony from 1-12% and are used for storage battery plates, cable

sheathing, collapsible tubes and for building constructions.

Here are some following alloys:-

69

1.Antimonial-lead:-Its composition varies from 6-8% of antimony with balanced

lead. Antimonial lead is highly resistant to sulphuric acid and many chemical solutions

containing sulphuric acid. The hardness and strength of antimonial lead is more than

the lead. It has a high tensile strength of about 470 kg/cm2 and elongation of 22%.

Lead containing 13% antimony, 1% tin, 0.5% arsenic and 1% copper has got good

properties. The castings obtained are quite strong too.

2.Lead-Tin alloys:-An alloy containing 10-25% tin and 90-75% lead is used for metallic

coating for sheet iron. Such a coating is applied by hot dipping process. Sheet which is

coated with such an alloy is used for the manufacture of containers. When harder more

resistant coating is required, antimony is also added. Alloys of lead, tin and antimony

are used as type metals.

3.Alloys of Lead for cable industries:-Cables require a flexible covering and sheating for

protection from moisture and oil. Bearing lead and 1% antimony lead are used for

covering electric power and communication cables due to the following reasons:-

1.These are impeded to moisture and oil.

2.These can be readily extruded.

3.These have got ample stress.

4.These are not corroded in all normal atmospheric environment.

5.These are pliable sheathing can be reeled and unreeled and can be bent around

sharp corners.

Fusible alloys are the alloys of eutectic composition of Pb, Bi, Sn, Sb and Cd, and

low melting points. They have meltings points as (60+273)k and melt at constant

temperature. Some of the compositions of these alloys are given in table.

Fusible alloys

Sr.No Alloys Bi Pb Sn Cd M.P;deg C.

70

(1) (2) (3) (4)

Newton’s metal Rose’s metal Wood’s metal Lipowitz metal

50 50 50 50

31.25 28 25 27

18.75 22 12.5 13

- - 12.5 10

94.5 93.75 70 60

name:Rahul Mishra

rollno.:327

Q18.write a note on Bronzes.

ANS:-

Bronzes

Bronzes are the alloys of copper containing elements other than zinc.in these alloys

zinc may be present in small amount. originally the name bronze was used to denote

copper-tin alloys. commercially important bronzes are aluminium-tin bronzes, beryllium

bronzes and silicon bronzes. These are discussed below.

Aluminium Bronzes

Aluminium bronzes are the alloys of copper and aluminium in which copper is the base

and aluminium is the alloying element.

The maximum solubility of aluminium is copper is 9.4%(at 565C) and eutectoid

transformation occurs at 11.8% aluminium. Commercial aluminium bronzes contain 4 to

11% aluminium. Other elements such as Fe, Ni, Mn and si may be added to these

bronzes for improvement of certain properties.in general, these bronzes are

characterized by:

1. Good strength, ductility and toughness

2. Good bearing properties

3. Good corrosion resistance

4. Good fatigue resistance

These alloys are lustrous and their colour is the finest of all the copper alloys

and hence are frequently called as imitation gold.

71

Alloys of low aluminium content (4 to 7% AI) i.e. single phase alloys can be

fabricated by cold working processes such as drawing, pressing, rolling, etc.

beacauseof their good ductility and malleability. In the annealed state, they show

tensile strength of 35 kg/mm2 with elongation of over 50%. The hardness is the

range of 80 to 90 VPN. These bronzes are available in sheet plate and tube

forms, and are used is jewellery cigarette cases, heat exchangers, chemicals

plants, etc.

Two phase aluminium bronzes can be cast, host, rolled or hot forged. Sand

cast alloys show a tensile strength of45 to55 with elongation between 20 to 30%.

The hot worked alloys show better mechanical properties not only at room

temperature but also at elevated temperature. They are used for pump casting,

valve- fittings,propellers, contacts. These alloys show a marked shrinkage during

solidification and hence careful foundry practice is necessary

Tin Bronzes

Tin bronzes are the alloys of copper and tin.

The solubility of tin in copper is 13.5% at 798 C, increases to 15.8% and remains

constant upto 520 C, decreases to 11% at 350 C, and to about 1% at room

temperature. A peritectic reaction occurs at 798 C in alloys contaibing 13.5 to25%

tin resulting in the formation of intermediate phase.The solubility limits are also

affected by the cooling rate and alloys upto 8% tin usually show single phase solid

solution at room temperature, even though the equilibrium solubility limit at room

temperature is about 1%

Tin has good affinity towards and hence during the melting of copper- tin

alloys, tin oxide is formed.This tin oxide appears in the soldified metal and

reduces ductility and malleability. Such bronzes are mechanically weak, porous

and show dirty patches on machined surfaces.Due to this, tin bronzes are

deoxidised, hey are cast as quicked as possible to avoid again the formation of

tin- oxide.Tin bronzes are divided into four groups on the basis of their content as

below:

1.Alloysupto 8% tin: They are single phase and have good ductility and

malleability alongwith good corrosion resistance.They can be easily cold worked

and hence are used in the form of sheets, wire and for coins.

2.Alloys between 8 to 12%: They are principally used for pumps,gear,heavy

load bearing and marine fittings to resist sea water corrosion

3.Alloys between 12 to 20%: They are mainly used for bearings.

72

4.Alloys between 20 to 25%: They are principally used for bells and are called

as bell metals. Alloys from this group are very hard and brittle, and give ringing

sound.

In general, all the tin bronzes have good corrosion resistance.Single phase

bronzes with about less than 8% tin are good for cold working and two phase

bronzes with more than 8% tin are suitable for casting.

The usual additions to these bronzes are lead and nickel. Lead increase

properties and increases fluidity of melt.The bronzes containing lead between 8

to 30% are called plastic bronzes.High leaded bronzes containing above 22%

lead are ued in railway as axle bearings.

Some of the important tin bronzes are given below:

1.Coinage bronze:

It contains about 5% tin and 1% zinc, The zinc is used for the deoxidtion of

melt. It is widely used for the manufacture of coins and hence is called coinage

bronze.

2.Gun metal:

It contains about 10% tin and 2% zinc. Zinc acts as a deoxidiser and also

improves fludity of melt. It is widely used for gun barrels and ordnance parts,

marine castings, gears,bearings,valve bodies and similar applications

3.Phosphor bronze:

smachinablity, improves bearing Phosphor bronzes are alloys of copper and tin

containing phosphors.Phosphorus is a powerful deoxidiser and when it is used

solely as a deoxidiser, only traces of phosphorus remains in te alloy. Higher

amounts of phosphorus than necessay for complete deoxidation serves as an

alloying elements and improves the mechanical properties and castability by

increasing the fluidity of melt.

Phosphor bronzes are of two types:

(1).Wrought phosphor bronzes:They contains 2.5 to 8% tin and 0.1 to 0.35%

phosphorus. They are widely used for springs, wire gauzes, wire brushes and

electrical contacts.

73

(2).Cast phosphor bronzes: They contain 5 to 13% tin and 0.3 to 1%

phosphorus,and are mainly used for gears,bushings, slide valves and similar

applications. Increase in phosphorus increase the fludity of melt and general soundness

of casting. Howeve,due to the formation of hard Cu3P compound, the casting becomes

more brittel. Addition of large amount of phosphorus i.e. exceeding 1% makes the

casting excessively brittle and unsuitable for the purpose.

Beryllium Bronzes:

The solubility of beryllium in copper is 2.1% at 864 C and decreases with

decreasing temperature. Due to this, the alloys containing beryllium between 1.5

to 2% exhibit precipitation hardening. Beryllium bronzes are produced both in the

cast and wrought forms

These alloys have the following properties:

1.Good corrosion resistance.

2.Good fatigue resistance.

3.High resilience and good bearing properties.

4.Low elastic hysteresis and non sparking characteristics.

They are widely used for springs, diaphragms, flexible bellows, gears,

bearings and certain tools. Like bammers requiring hardness and non sparking

properties.They are also used for electrical contacts and moulds for forming of

plastics.Because of high cost of beryllium, the alloys are costly and hence the use

of these the use of these alloys is justified only when other alloys with lower cost

do not fulfil the requirments of a particular application.

Silicon Bronzes:

The alloys of copper and silicon are called silicon bronzes. The solubility of

silicon in copper is about 5.3% at 854 C and decreases to less than 4% at room

temperature. The silicon content in these alloys usually varies between 1 and

5.5%. These bronzes have high resistance to corrosion, high tensile strength,and

high toughness. They are cheaper than tin-bronzes. However, their resistance to

salt water corrosion under impingement attack conditions is less. They can be

cold and hot worked, and also can be cast. The other elements which are added

to these bronzes for increasing strength and machinability are Mn, Fe, Zn, Sn and

Pb. They are produced in the form of strips, plates, wires, rods, tubes, pipes and

castings, and find applications as high strength bolts, riverts, springs, propeller

74

shafts and bells. They are available under the trade names suda as Everdur and

Hercualoy

Name=Akshay.D.Mohite

Roll no:- 328

Q19. Write note on Bearing Metals and their application areas.

ANS

Materials used to transmit loads to a shaft rotating relative to the bearing are called a

Bearing Material.

A film of oil separates the moving parts and hence the material of the bearing is of

no much importance except for its mechanical properties.

However, during starting, stopping and in severe running conditions the oil film

cannot be maintained and metal to metal contact may occur resulting in excessive

wear and or seizure of the bearing.

To avoid the above problems, a good bearing material should have the following

properties:-

The friction between the bearing and the rotating part should be as small as

possible to reduce the power loss in transmissions.

The affinity between the shaft and the bearing material should be minimum.

It should be hard and wear resistant for longer life. It should not be harder

than the shaft so as to avoid the damage to the shaft.

It should have sufficient load bearing ability (i.e. the material should have

good mechanical properties at ambient and elevated temperatures because

many times the temperature may rise due to improper lubrication.)

It should have sufficient plasticity and deformability to take care of large

deflections and misalignment of the shaft.

It should have high fatigue resistance.

It should have good resistance to galling and seizing.

It should have good thermal conductivity so that the heat , if any produced is

dissipated quickly.

It should not have very high or very low Melting point.

It should have high oil retaining capacity.

It should have a good corrosion resistance.

It should be cheap and readily available.

A homogenous material of a single phase type does not satisfy these

requirements because of the following reasons:

75

Soft materials have less μ (coefficient of friction) but more A (True or real

Area of contact) and for hard metal μ but less A. Therefore, neither a

soft nor a hard homogenous material reduces the frictional force to the

lowest value; and hence it is said that a homogenous material is not

suitable as a bearing material.

Heterogeneous materials consisting of two or more phases of different hardness

values are more suitable as bearing material.

(This is because, as the shaft rotates the soft phase wears out faster and a thin

film all over the surface and hence the μ becomes that of the soft phase. Due to

wearing of soft phase, depressions are produced in these micro regions which

increase the oil retaining capacity. The hard phase stands out in relief and hence

all the load comes over the hard phase and therefore, A becomes that of hard

phase. As a result, both μ and A are less and hence F is less(F = μ X A ) .

)

Bearing materials generally used:-

White metal Alloys (Babbitts):

Babbitts are either lead-based or tin based alloys. Both the type contains

antimony.

A typical alloy from lead-based Babbitt contains :

80% lead

10% Antimony

10%tin

and that from tin based Babbitt group contains

90% Tin

5% Antimony

5% Copper

Structural Description:

1. The micro structural of a Babbitt consists of hard cuboids

(cube shaped particles) of Sn-Sb in a soft matrix of eutectic.

2. Microstructures may consist of hard needles of CuSn(or

Cu6Sn5) and hard star shaped crystals of Cu3Sn, if the Babbitt

contains copper.

3. Copper is added to reduce the gravity segregation of cuboids.

During solidification, Sn-Sb cuboids are formed first and being

lighter than the melt, tend to float to the surface. Due to this,

the bearing becomes too hard at the top and too soft at the

bottom. This trouble of gravity segregation is reduced by either

rapid cooling or by the addition of copper.

76

Copper – Lead alloys:

1)Lead is insoluble in copper and hence the microstructure consists of

soft particles of lead distributed in hard matrix of copper.

2) Alloys contain 20-40% lead with small amount of tin.

3) Used widely in automotive and aeronautic industries.

Silver Bearings:

1) Plated with lead to reduce the risk of seizure. Such bearings are called

as silver bearings.

2) Coated with Indium to increase corrosion resistance of lead to acidic

oils.

3) Used for heavy load conditions such as in aircrafts.

4) Have High strength

High corrosion resistance

Excellent anti- seizure properties.

Tin – Bronzes:

1) Contains 10% phosphor bronze, gun metal and 15% tin bronze.

Sometimes lead is added (5-15%) for applications where lubricants or

alignment is likely to be unsatisfactory.

2) Used for heavy load conditions.

Aluminium Alloys:

1) Contain – Sn, Cu, Ni, Fe, Si and Mn, and the structure consists of fine

particles of Sn, NiAl3 CuAl2 phases in a matrix of aluminium solid

solution.

For better strength, the alloys are bonded to steel by pressure welding.

2) Used at High speeds and loads, connecting rods and as main bearings

in automobiles.

3) Properties: Good corrosion resistance, High fatigue strength and good

anti-seizure.

Gray Cast Iron:

1) Contains – Gray cast Iron with A-type Graphite flake distribution of

ASTM flake size number ~3

2)Used as bearing materials for refrigeration compressors and

railways(Goods Trains).

Porous Self – lubricating bearings:

1) Manufactured by powder metallurgy. Porous bearings are made from

copper or iron base powders with as much as 40-50% porosity and are

77

impregnated with oil. During the use the oil from the pores slowly comes

out and forms a lubricating film on the moving surface. When working is

stopped, the oil goes back to the pores by capillary action. They do not

require any external lubrication and hence are called as self lubricating

bearings. Wastage of oil in these bearings is almost nil.

2) Cu (90%) – Sn(10%) – graphite and Fe(96%).

3) Widely used as self-lubricating Bearings.

Dry and Anticorrosive bearings:

1) Non metallic materials such as Teflon (poly tetra fluoroethylene),

Nylon, Graphite and molybdenum disulphide can be used as bearing

materials under light loads.

With steel backing, they can be used at high loads and high or low

speeds from very low to moderately high temperatures.

2)Low coefficient of friction, Excellent Corrosion resistance.

Name : Shreenath Nair. RollNo=ae 330.

Q 20) Write a note on nickel & its alloys.

-Dhaval Patel

Roll no. 334(A.E.)

Ans:

1) Nickel was first isolated and classified as a chemical element in 1751 by Axel

Fredrik.

2) It is a silvery-white lustrous metal with a slight golden tinge.

3) Nickel belongs to the transition metals and is hard and ductile.

4) Pure nickel shows a significant chemical activity that can be observed when

nickel is powdered to maximize the exposed surface area on which reactions can

occur, but larger pieces of the metal are slow to react with air at ambient

conditions due to the formation of a protective oxide surface.

5) Nickel is rarely found on Earth's surface.

6) Although some nickel is obtained commercially from oxide ores, arsenical ores &

the ores of copper, manganese & iron, at least 85% of all nickel production is

obtained from sulphide ores.

Properties:

78

High melting point. (1455 °C)

High density. (8.9 gm/cc)

Good corrosion & oxidation resistance.

Good workability & mechanical properties.

Mechanical properties are retained at high temperature.

Can be age hardened.

Used for:

Electro plating

Evaporators

Kettle heating coils

Spark plug

Electrodes

Jewellery parts

Diaphragms

Aircraft parts

Measuring instruments etc.

Pure nickel is tough, silver-coloured metal, rather harder than copper, and of about

the same strength, but possessingsomewhat less ductility. It closely resembles iron in

several of its properties, being malleable &weld able, & perceptibly magnetic,but unlike

iron it is little affected by dilute acids, is far less readily oxidisable, and deteriorates

much rapidly under atmosphericinfluences. For this reason articles of iron & steel are

frequently nickel-plated to protect them from rusting. Nickel is much usedfor cooking

utensils & other vessels for heating & boiling. Nickel enters as a constituent into a large

number of ferrous &nonferrous alloys & frequently finds application as a catalyst in

important industrial processes.

Nickel alloys which are particularly useful for general industrial purposes are described

below:

1) MONEL METAL:

i) It is an alloy of 60 % nickel, 38 % copper & a small amount of aluminium or

manganese. It is a tough & ductile metal & can be readily machined. It welds

without difficulty. It can be heat-treated. It is also resistant to corrosion by

most agents &has high strength at elevated temperatures.

ii) Monel metal is used in the form of rod, sheet, wires & welded tubing. It is

widely employed for structural & machineparts which must have a very high

79

resistance to corrosion & high strength as steam turbine blade, impeller of

centrifugal pump,etc.

2) GERMAN SILVER:

i) An alloy of copper (25-50 %), nickel (10-35%), &zinc (25-35%) is known as

German silver. Sometimes, tin & lead are also added. It is hard & ductile. This

is usually of bright silvery colour,but may also assume various other pleasing

colours by adjusting the proportions of copper & zinc. It has in addition to

colour,good mechanical & corrosion resisting properties. It is also known as

Ni-silver.

ii) German silver is used for making utensils & resistances in electrical work.

3) ICONEL:

i) It contains 75-80% nickel, 10-15% chromium & the rest iron. It can be used

for parts that are exposed to hightemperature for extended period. It is less

reactive than nichrome to acid.

4) NICHROME:

i) This is an alloy of nickel with chromium & is used widely as resistance wire for

electrical appliances.

5) NIMONICS:

i) A new type of nickel alloy called nimonics are being developed, which by

proper heat treatment attain excellent properties for very high temperature

service as well as under intermittent heating and cooling conditions. They

contain 15-18% chromium, 15-18% cobalt, 3.5-5 % molybdenum, 1.2-4%

titanium, 1.2-5% aluminium, and the remainder nickel.

Q 21) Note on Brasses

Name: Kalpesh E. Patil

Roll No: AE 335

Branch: SE Automobile

Brasses are the alloy of copper and zinc. The mechanical properties of brasses depend

on the amount of zinc in the alloy i.e. the properties depend on the type and amount of

phases.

80

Brasses are classified either on the basis of structure i.e. alpha brasses and alpha-beta

brasses or color i.e. red and yellow brasses.

• Alpha Brasses:-

They are soft, ductile, and malleable have fairly good corrosion resistance in annealed

condition All the alpha-brasses are suitable for cold rolling, wire drawing, press work,

and such other operations.

Some of the important brasses from this group are as below:

• Cap copper:

It contains zinc between 2 to 5%. Zinc is used deoxidizer for the deoxidizer at of

copper. If zinc is not added, copper oxide present in the structure reduce

ductility and malleability. Cap copper is very ductile and is used for caps of

detonators in ammunition factories.

• Gilding metals:

They contain zinc from 5 to 15% and have

different shades of color from reddish to yellowish according to the zinc content. They

are used for bullet envelopes, drawn containers, condenser tubes, coins, needles

because of color like gold.

• Cartridge brass:

It contains about 30% zinc and has maximum ductility and malleability among all

the brasses, and is used for forming by deep drawing, stretching, trimming,

spinning and press work operations. It is also knows as 70-30 brass. It is used

for cartridge cases, radiator fins, lamp, fixtures, rivets and springs.

• Admiralty brass:

About 1% tin is added to cartridge brass to improve the corrosion resistance and

such a brass is called as brass. It is used for condenser tubes and heat

exchangers in steam power plants. A typical admiralty brass contains about

22%Zn, 2%Al and about 0.04%as and is widely used for marine application.

• Alpha-Beta Brasses

Commercial alpha-beta brasses contain zinc between 32 to 40%. They are hard

strong as compared to alpha-brasses and are fabricated by hot working

processes. These two phases alloy becomes single phase beta alloy at higher

temperatures. Disordered beta has more ductility as compare to ordered beta.

81

Alpha-beta brasses are hot worked at a temperature of about 600. Since zinc is

cheaper than copper. Alpha-beta brasses are cheap as compared to alpha-

brasses. Some of the important brasses from this group are given below:

• Mounts metal:

It contains about 40% zinc with balance copper. The alloy becomes single

phase at about 700. However, it can be readily hot worked or rolled in the

temperature range of 600 to 800.

It is used for shafts, nuts and bolts, pump parts and similar application

where corrosion is not too severe.

• Naval brass:

Addition of about 1% tin to Mounts metal increases corrosion resistance to

marine environment and the brass is called as naval brass bronze. Brass with

39% zinc and 1% tin is used for marine hardware, propeller shafts, piston rods,

nuts and welding rods.

• Leaded brass:

Lead is added in small amount (1 to 3%) to improve machine-ability of marine of

brasses and such a brass is called as leaded brass. Lead is insoluble in both

the liquid and solid states and hence appears as globules in the microstructure.

• High tensile brasses:

Alloying elements such as Al, Fe, Sn, Mn, and Ni are frequently added to 60-

40 brass to increase its tensile strength. Brasses containing one or more of the

above elements are called high tensile brasses. One of these is the manganese

bronze containing about 1% Mn, 2% Fe, 39% Zn and balance copper.

• Brazing brass:

Brass with 50-50 composition is used for brazing purpose. The 50% zinc brass

melt at lower temperature (-870) and can be used for joining of commercial

brasses. This brass is brittle due to the presence of gamma phase and can be

crushed to power manually and mechanically for its use in powder form.

Q.22) NOTE ON METALS FOR NUCLEAR ENERGY

NAME:-KUNAL B PATIL

82

ROLL NO.:-336

BRANCH:-AUTOMOBILE

Ans:

Recent nuclear power developments has created a demand for materials to withstand

stringent condition imposed, and as a result some metals, previously considered “rare”

are now coming in the use in a wide perspective. The various metals for producing

nuclear energy are used as raw materials, moderates reflectors, fuel elements, fuel

canning materials, control elements, and pressure vessel materials. Thus, uranium,

thorium, plutonium, zirconium, beryllium, niobium and their alloys are primarily used for

nuclear engineering purposes.

URANIUM

The most important metal found in nature and used for nuclear energy is uranium. This

is used as nuclear fuel and is radioactive, easily oxidized and exits in three allotropic

forms. This has a poor resistance to corrosion and needs to be protected for use as fuel

elements by roll cladding a thin aluminum or zirconium jacket. The metal in pure

condition is weak and is susceptible to severe irradiation damage and growth in the

reactors environments. Additions of some alloying elements such as chromium,

molybdenum, plutonium, zirconium etc are added make the material highly suitable for

nuclear power.

Uranium compounds, such as UO2 as dispersion in cermets or as ceramic slugs, have

been found to give better service. Uranium oxide is highly refractory, shows no phase

change in an inert atmosphere, and possesses a good strength and a high corrosion

resistance. But it has a low thermal shock resistance, poor thermal conductivity and a

high coefficient of expansion. The melting point of uranium is 1850 0C.

THORIUM

Thorium is another possible fuel and is free and is free from phase changes below 1480

0C. Thorium (90Th 234) is also a radioactive metal like uranium and this can be converted

into uranium (92U 234) by beta decay. The mechanical properties of thorium which is soft

and weak when pure, are drastically changed by small addition of impurities. Only 0.2%

of carbon raises its tensile strength from 14 to 38 kgf/mm2 (140 to 380 MPa). Small

addition of titanium, zirconium, and niobium decreases the strength of thorium.

83

Thorium like uranium is an emitter of alpha rays and releases considerable quantity of

the radioactive products during processing, but this being a cubic metal (fcc) is less

susceptible to irradiation damage. The melting point of thorium is 1845 0C.

PLUTONIUM

This is a synthetic element and does not occur in nature. It is produced through neutron

absorption by fertile U238 and subsequent beta decays. Plutonium melts at 640 0C. It is

extremely toxic and emits alpha rays. Due to its being naturally fissionable, plutonium

continues to emit high energy gamma and other radiation. The metal is chemically more

reactive than uranium and has a poor resistance to corrosion. It has six allotropic forms.

The chief application of plutonium is in the production of atomic weapons and also in

breeder reactors. Since some plutonium alloys and compounds emit neutrons,

adequate health protection is necessary while using these materials.

ZIRCONIUM

Zirconium minerals contain 0.5 to 2 % hafnium which is a Strong absorber of neutrons

and must therefore be removed. The main use of zirconium is for cladding fuel elements

and for structural components in water-cooled systems. So it must have increased

carrion resistance. Zircaloy-2 containing 1.5% Zn, 0.1% Fe, 0.05% Ni and 0.1% Cr

provides better corrosion resistance and is generally used in water-cooled reactors.

Zirconium has a relatively poor resistance to CO2 at elevated temperatures, but this is

improved by the addition of 0.5% Cu, 0.5% Mo with an increasing strength to 51

kgf/mm2 (510 Mpa) and improved creep resistance at 450 0C. This zirconium is specially

useful in gas cooled reactors. The melting point of Zirconium is 1750 0C.

BERYLLIUM

Beryllium is a light metal and melts at about 1280 0C. The metal is used as a moderator,

reflector and neutron source. This is very reactive and forms compounds with the

furnace atmospheres and refractories. Vacuum or inert gases are necessary during

melting.

The cast metal is usually coarse grained and brittle and powder metallurgy methods are

employed in the fabrication of beryllium components.

Beryllium is a toxic metal. Its compounds are also very toxic. Safety measures are to be

taken when handling this metal.

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NIOBIUM (COLUMBIUM)

This has a high melting point 1950 0C and good strength, ductility and corrosion

resistance especially to liquid sodium coolants, and excellent capability of coexistence

with uranium. Its oxidation resistance above 400 0C is indifferent, but is greatly

improved by alloying.

The metal niobium, titanium, hafnium, tantalium and zirconium alloys are all used in jet

aircraft, reactors, and missiles and for nuclear reactor.

Q 23) Write a short note on pure iron ?

Name: Vikas Singh

Class: SE(automobile)

Roll no: 347

Answer: Pure iron is a soft metal having a crystalline structure . A representation of its

microstructure is shown in fig.1. This diagram, together with others which will be seen later, has

been drawn to represent a photomicrograph, a method used extensively for the examination

and study of metals. To obtain a photomicrograph a small piece of the metal is filled to a flat

surface, and the surface is gradually brought to a high finish by successive polishing. The

polished surface is then treated with dilute acid which etches the constituents and their

boundaries, enabling them to be distinguished when seen through a microscope. By placing a

camera at the microscope eyepiece, a photograph of the microstructure may be obtained. The

microscope reveals the structure to an enlarged scale, and the magnification is usually stated

underneath the photograph (e.g. x200 as shown in Fig.1).

It will be noticed that the structure of pure iron looks like a map with fields separated

by hedges. The shapes looking like the fields are the crystals, and the lines like hedges are

where they join together. It may help us to visualize the structure of the metal if we imagine it

as similar to bricks and mortar; the crystals being the bricks and their boundaries the mortar. A

section through such a structure would appear somewhat similar to our photograph. If the

reader measures the average size of the crystals on Fig.1 and divides by the magnification

factor, he will find that the crystal size of the specimen is about 4/100mm. The size of the

crystals in iron and steel depends upon the treatment the metal has received, and in the steel

used in the workshop the crystals may vary from 1/100 to 20/100mm. these micrographs

represent a portion of metal structure about as large as a pin point.

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Q. 24 Note on the property difference of various Irons.

ANS

=> Properties of Various Irons are :-

Cast Iron

Cast iron has high content of carbon

least tensile strength

moderate resistance to compression

Not ductile nor malleable

Cannot be welded

Cannot be Forged

Low melting point (approx 1148°C )

Wrought iron

Wrought iron has low content of carbon

Tensile strength higher than cast iron

Least resistant to compression

Highly ductile and malleable

Easy to weld

Can be Forged

Higher melting point (approx 1537°C )

Malleable Cast Iron

It is an iron-carbon alloy

Can be forged

Good ductility and strength

Pig iron

Carbon content ranges from 3 - 4.5% ,with varying quantities of Si, S, P,

and Mn.

Melting point (12000C )

It is briitle , hard and fairly fusible

Steel

Moderate carbon content(less than cast iron but higher than wrought iron)

Tensile strength highest

Highest compression resistance

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Not easy to weld

Melting point (1400 0C)

Carbon Steel

Carbon is the main alloying element

Generally Carbon content is less than 1%

Good tensile strength

In carbon steels, the higher carbon content lowers the melting point

As the carbon content rises, steel has the ability to become harder

and stronger through heat treating, but this also makes it less ductile

Alloy steel

Alloy steels are hard and strong

Are ductile and malleable

Can be welded

Capable to withstand corrosion

- Kaustubh Raul

Roll no=AE339

Q25) Explain the property differences of various steels?

ANS:

Differences are:

1. PLAIN CARBON STEEL:

Steel is essentially an iron-carbon alloy containing less than 1.6% of

carbon; Apart from carbon, steel contains small amounts of manganese,

silicon, sulpher and phosphorus also.

These impurities remain from the manufacturing process. Such steels are

known as plain carbon steels.

These steels may also be heat treated to obtain the required properties.

Plain carbon steel may be approximately divided according to their carbon

contain into:

Mild steel- up to 0.25% carbon

Medium carbon steel-

up to 0.25-0.6%carbon

High carbon steel-

up to 0.6-1.5%carbon

2. MILD STEELS

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Steels which contains up to about 0.15%carbon have outstanding ductility,

and for this reason are often used for boiler plates, solid-drawn tubes, tec.

Steels of a similar carbon content are often used for case-hardening,

although alloy steels are perhaps more frequently used for this purpose.

Those steels having carbon contents in the upper part of this range have a

tremendously wide field of application. It is generally used for industrial

products such as nuts, bolts, tubes, channels, beams, machine

components.

3. MEDIUM-CARBON STEELS

This range of steels is used extensively for forging and castings. These

steels are much harder and stronger than the mild steels, though their

ductility is lower.

They can be hardened by heating to a high temperature and quenching

quickly.

This property is of very great importance since it greatly increases the

field of application of the steels. Steels in this range are very widely used

for components requiring a higher tensile strength than mild steel

possesses, e.g. all kinds of the shafts, axels, gears, rotors, engine

castings connecting rods.

4. HIGH CARBON STEELS

These are much higher steels of lower carbon content, but less ductile,

steels having carbon contents in the low part of the range are used for

springs, wire rope, and clutch plates.

Exercise compare the hardness of the above steels. This may be carried

out using the file test.

5. HIGH-SPEED STEELS

High speed steals are of great importance in modern metal-cutting

practice, since they permit the use of higher cutting speeds than those

possible with ordinary carbon steel tools.

This is due to the fact that high-speed steels continue to cut satisfactorily

even when the cutting edge is at a dull red heat.

The main constitution in most types of high-speed steel is tungsten, which

is normally present in amounts from 14-18%.

Other elements usually present are chromium(3.5%) and vanadium(1%),

together with about 0.7-0.8% carbon. Two of the most commonly used

types are those containing 14% and 18% tungsten, together in each case

with about 4% chromium and 1% vanadium.

NAME: DEEPAK REMULKAR

ROLL NO.: AE 340

88

Q 26) Explain the classification of various Production Systems

Name:- Manoj Sharma, roll no:-

342

Branch :- [SE]Automobile engineering

The objective of an enterprise is to provide goods or services, and to earn profits.

These days, many firms are focusing on continuous improvement and customer

delight.

A continuous search for areas of improvement in the production system is needed.

For this, a clear understanding of recent developments in production system,

industrial engineering and management is necessary.

To achieve these objectives, the firms need to convert some inputs like men,

material, money, energy, information, etc, into useful outputs like finished products

and services in required quantity and quality.

The transformation of the inputs into pre specified outputs is achieved through

production process.

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PROJECT PRODUCTION

Many civil engineering projects for construction or military related activities are project

production.

In this, complex and large manufacturing tasks are undertaken.

Generally, work is carried out at the site of the work rather than in a factory.

All resources such as tools, material, labor, etc, reach the site themselves.

Ship building activity is an example of project production.

A fixed position plant layout is recommended for this variety of production system.

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Production systems

Production systems can be classified as Job Shop, Batch, Mass and Continuous Production

systems.

Fig Classification of production systems

JOB PRODUCTION

Job shop production are characterised by manufacturing of one or few quantity of

products

designed and produced as per the specification of customers within prefixed time and

cost.

The distinguishing feature of this is low volume and high variety of products.

A job shop comprises of general purpose machines arranged into different departments.

Each job demands unique technological requirements, demands processing on machines

in a

certain sequence.

Characteristics

The Job-shop production system is followed when there is:

1. High variety of products and low volume.

2. Use of general purpose machines and facilities.

3. Highly skilled operators who can take up each job as a challenge because of uniqueness.

4. Large inventory of materials, tools, parts.

5. Detailed planning is essential for sequencing the requirements of each product, capacities

for each work centre and order priorities.

Advantages

Following are the advantages of job shop production:

1. Because of general purpose machines and facilities variety of products can be produced.

2. Operators will become more skilled and competent, as each job gives them learning

opportunities.

3. Full potential of operators can be utilised.

4. Opportunity exists for creative methods and innovative ideas.

Classification of production system

Job production Batch production

Flow[Mass] production

Continuous production

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Limitations

Following are the limitations of job shop production:

1. Higher cost due to frequent set up changes.

2. Higher level of inventory at all levels and hence higher inventory cost.

3. Production planning is complicated.

4. Larger space requirements.

BATCH PRODUCTION

Batch production is defined by American Production and Inventory Control Society

(APICS) “as

a form of manufacturing in which the job passes through the functional departments in

lots

or batches and each lot may have a different routing.”

It is characterised by the manufactureof limited number of products produced at regular

intervals and stocked awaiting sales.

Characteristics

Batch production system is used under the following circumstances:

1. When there is shorter production runs.

2. When plant and machinery are flexible.

3. When plant and machinery set up is used for the production of item in a batch and

change of set up is required for processing the next batch.

4. When manufacturing lead time and cost are lower as compared to job order production.

Advantages

Following are the advantages of batch production:

1. Better utilisation of plant and machinery.

2. Promotes functional specialisation.

3. Cost per unit is lower as compared to job order production.

4. Lower investment in plant and machinery.

5. Flexibility to accommodate and process number of products.

6. Job satisfaction exists for operators.

Limitations

Following are the limitations of batch production:

1. Material handling is complex because of irregular and longer flows.

2. Production planning and control is complex.

3. Work in process inventory is higher compared to continuous production.

4. Higher set up costs due to frequent changes in set up.

MASS PRODUCTION

Manufacture of discrete parts or assemblies using a continuous process are called mass

production.

This production system is justified by very large volume of production.

The machines are arrangedin a line or product layout.

Product and process standardisation exists and all outputs follow thesame path.

Characteristics

Mass production is used under the following circumstances:

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1. Standardisation of product and process sequence.

2. Dedicated special purpose machines having higher production capacities and output rates.

3. Large volume of products.

4. Shorter cycle time of production.

5. Lower in process inventory.

6. Perfectly balanced production lines.

7. Flow of materials, components and parts is continuous and without any back tracking.

8. Production planning and control is easy.

9. Material handling can be completely automatic.

Advantages

Following are the advantages of mass production:

1. Higher rate of production with reduced cycle time.

2. Higher capacity utilisation due to line balancing.

3. Less skilled operators are required.

4. Low process inventory.

5. Manufacturing cost per unit is low.

Limitations

Following are the limitations of mass production:

1. Breakdown of one machine will stop an entire production line.

2. Line layout needs major change with the changes in the product design.

3. High investment in production facilities.

4. The cycle time is determined by the slowest operation.

CONTINUOUS PRODUCTION

Production facilities are arranged as per the sequence of production operations from the

first operations to the finished product.

The items are made to flow through the sequence of operations through material handling

devices such as conveyors, transfer devices, etc.

Characteristics

Continuous production is used under the following circumstances:

1. Dedicated plant and equipment with zero flexibility.

2. Material handling is fully automated.

3. Process follows a predetermined sequence of operations.

4. Component materials cannot be readily identified with final product.

5. Planning and scheduling is a routine action.

Advantages

Following are the advantages of continuous production:

1. Standardisation of product and process sequence.

2. Higher rate of production with reduced cycle time.

3. Higher capacity utilisation due to line balancing.

4. Manpower is not required for material handling as it is completely automatic.

5. Person with limited skills can be used on the production line.

6. Unit cost is lower due to high volume of production.

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Limitations

Following are the limitations of continuous production:

1. Flexibility to accommodate and process number of products does not exist.

2. Very high investment for setting flow lines.

3. Product differentiation is limited.

Q27. The magnetic particle (magnaflux) testing.

Ans. There are several methods of magnetic particle testing. All these methods are

used to detect various kinds of flaws in ferromagnetic components such as weldings,

castings and forgings of iron and steel. The component to be inspected for flaws is

magnetized (fig. 4.1) and inspection medium is applied to the component or

magnetization of the component and application of inspection medium can be done

simultaneously. In the dry method of inspection, a special fine ferromagnetic powder Is

applied on the surface by means of a hand shaker, vibrating screen or by any other

suitable method so that the powder uniformly distributes on the surface of the

component. In the wet method of inspection, a liquid containing fine ferromagnetic

particle suspended in some carrier such as kerosene or petroleum oil is applied by

sitable method such as dipping, spraying or brushing.

Magnetization of the component is done either by using an external magnetic Yoke

coil or by passing an electric current through it. A magnetic pole is formed at the crack

or flaw, which causes the magnetic powder to concentrate on this area and the flaw

gets easily detected. When the part is magnetized lengthwise (fig. 4.2), transverse

cracks are easily detected. This is done by energizing a coil around the bar. When part

is magnetized cross-wise by a circular magnetic field (fig. 4.3) lengthwise cracks are

easily detected. This is done by passing an electric current, either alternating or direct,

through the component, the use of alternating currents limits the test for detection of

only those flaws which are open at the surface. This is due to the fact that alternating

currents try to flow from near the surface i.e. skin effect. However direct current

magnetization makes it possible to detect surface as well as subsurface discontinuities.

The detection of subsurface defects will depend upon the strength of the magnetic

field, the distance from the surface at which defect is located, the ratio of the height of

defect to the thickness of the component, and the width of the discontinuity. This is

because the leakage fields caused by discontinuities diffuse and decrease in intensity

with increase in distance from the discontinuities. Under favourable conditions of

testing, defects as much as 2" deep from the surface may be detected.

In both the methods, the ferromagnetic particles effectively concentrate and outline

the boundaries of the defects. However, dry method is more sensitive for revealing

deep- seated discontinuities to that of wet method and also is easy to carry out.

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For better contrast powders or liquids of different colours can be used. Dry powders

are available in grey, black and red colours whereas liquids are available in black and

red colours.

In a Magnaglo method of testing, special fluorescent ferromagnetic powders are

applied by wet method similar to Magnaflux method. The component is inspected in a

dark room with UV light of wave lengths between 3500 to 4000A. Such a powder emits

greenish-yellow light under influence of ultraviolet light and gives a better contrast to

detect a flaw.

The parts should be demagnetized before putting to service. This can be accomplished

as below:

(i) By subjecting the component to a continuously reversing and steadily

decreasing magnetic field or

(ii) By slowly withdrawing the component through an open solenoid while

alternating current is flow

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(Name-Amey.D.Shinde, roll no.- 344, SE-Auto)

99

Q 28) Explain dye penetrant inspection SANTOSH SINGH SE-Auto Roll no.- 46 Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components. Penetrants are classified into sensitivity levels. Visible penetrants are typically red in color, and represent the lowest sensitivity. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Since Fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to defects. When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surface finish of the specimen, and the size of defects sought. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradation. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some lint free cloths, and adequate visible light. Stationary systems with dedicated application, wash, and development stations, are more costly and complicated, but result in better sensitivity and higher samples through-put.

Inspection steps

100

Below are the main steps of Liquid Penetrant Inspection: 1. Pre-cleaning: The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment. Application of the penetrant to a part in a ventilated test area. 2. Application of Penetrant: The penetrant is then applied to the surface of the item being tested. The penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant. 3. Excess Penetrant Removal: The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering your ability to do a proper inspection. 4. Application of Developer: After excess penetrant has been removed a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water soluble. Choice of developer is governed by penetrant compatibility (one can't use water-soluble or suspendable developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.

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The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience [the indication size is not the actual size of the defect] 5. Inspection: The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after 10 to 30 minute development time, depends of product kind. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws. 6. Post Cleaning: The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled. Advantages and disadvantages The main advantages of DPI are the speed of the test and the low cost. Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed. Conducting the test on rough surfaces, such-as-welded welds, will make it difficult to remove any excessive penetrant and could result in false indications. Water-washable penetrant should be considered here if no other option is available. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the workpiece Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary. Q 29) Fluorescent-Penetrant (zyglo)Inspection (FPI)

MihirTalreja

Roll no: 348

Se(auto)

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Fluorescent-Penetrant Inspection (FPI) is a type of dye penetrant inspection in which a

fluorescent dye is applied to the surface of a non-porous material in order to detect defects

that may compromise the integrity or quality of the part in question. Noted for its low cost and

simple process, FPI is used widely in a variety of industries.

Materials

There are many types of dye used in penetrant inspections. FPI operations use a dye much

more sensitive to smaller flaws than penetrants used in other DPI procedures. This is because of

the nature of the fluorescent penetrant that is applied. With its brilliant yellow glow caused by

its reaction with ultraviolet radiation, FPI dye sharply contrasts with the dark background. A

vivid reference to even minute flaws is easily observed by a skilled inspector.

Because of its sensitivity to such small defects, FPI is ideal for most metals which tend to have

small, tight pores and smooth surfaces. Defects can vary but are typically tiny cracks caused by

processes used to shape and form the metal. It is not unusual for a part to be inspected several

times before it is finished (an inspection often follows each significant forming operation).

Selection of inspection type is, of course, largely based on the material in question. FPI is a

nondestructive inspection process which means that the part is not in any way damaged by the

test process. Thus, it is of great importance that a dye and process are selected that ensure the

part is not subjected to anything that may cause damage or staining.

Inspection Steps:

See the following main steps in a Fluorescent Penetrant Inspection Process:

1. Initial Cleaning:

http://en.wikipedia.org/wiki/Dye_penetrant_inspection

103

Before the penetrant can be applied to the surface of the material in question one must ensure

that the surface is free of any contamination such as paint, oil, dirt, or scale that may fill a

defect or falsely indicate a flaw. Chemical etching can be used to rid the surface of undesired

contaminates and ensure good penetration when the penetrant is applied. Sandblasting to

remove paint from a surface prior to the FPI process may mask (smear material over) cracks

making the penetrant not effective. Even if the part has already been through a previous FPI

operation it is imperative that it is cleaned again. Most penetrants are not compatible and

therefore will thwart any attempt to identify defects that are already penetrated by any other

penetrant. This process of cleaning is critical because if the surface of the part is not properly

prepared to receive the penetrant, defective product may be moved on for further processing.

This can cause lost time and money in reworking, overprocessing, or even scrapping a finished

part at final inspection.

2. Penetrant Application:

The fluorescent penetrant is applied to the surface and allowed time to seep into flaws or

defects in the material. The process of waiting for the penetrant to seep into flaws is called

Dwell Time. Dwell time varies by material and the size of the indications that are intended to be

identified but is generally around 30 minutes. It requires much less time to penetrate larger

flaws because the penetrant is able to soak in much faster. The opposite is true for smaller

flaws.

3.Excess Penetrant Removal:

After the identified dwell time has passed, penetrant on the outer surface of the material is

then removed. This highly controlled process is necessary in order to ensure that the penetrant

is removed only from the surface of the material and not from inside any identified flaws.

Various chemicals can be used for such a process and vary by specific penetrant types.

Typically, the cleaner is applied to a lint-free cloth that is used to carefully clean the surface.

4. Developer Application:

Having removed excess penetrant a contrasting developer may be applied to the surface. This

serves as a background against which flaws can more readily be detected. The developer also

causes penetrant that is still in any defects to surface and bleed. These two attributes allow

defects to be easily detected upon inspection. Dwell time is then allowed for the developer to

achieve desired results before inspection.

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5. Inspection:

In the case of fluorescent inspection, the inspector will use ultraviolet radiation with an

intensity appropriate to the intent of the inspection operation. This must take place in a dark

room to ensure good contrast between the glow emitted by the penetrant in the defected

areas and the unlit surface of the material. The inspector carefully examines all surfaces in

question and records any concerns. Areas in question may be marked so that location of

indications can be identified easily without the use of the UV lighting. The inspection should

occur at a given point in time after the application of the developer. Too short a time and the

flaws may not be fully blotted, too long and the blotting may make proper interpretation

difficult.

6. Final Cleaning:

Upon successful inspection of the product, it is returned for a final cleaning before it is either

shipped, moved on to another process, or deemed defective and reworked or scrapped. Note

that a flawed part may not go through the final cleaning process if it is considered not to be

cost effective.

Advantages:

Highly sensitive fluorescent penetrant is ideal for even the smallest imperfections

Little training is needed for the operator/ inspector

Low cost and potentially high volume

Potential Disadvantages:

Requires adequate cleaning (neglect of this step can have costly repercussions)

Test materials can be damaged if compatibility is not ensured

Penetrant stains clothes and skin and must be treated with care

Limited to surface defects

Penetrants stain cloth, skin and other porous surfaces brought into contact. One should verify

compatibility on the test material, especially when considering the testing of plastic

components. Further information on inspection steps may be found in industry standards (e.g.

the American Welding Society, American Society for Testing and Materials, the British

Standards Institute, and the Society forAutomotive Engineers).

105

Q.30 expain sonic and ultrasonicinspection techniques

Ans shantanu ae52

sonic testing is used to measure the thickness of metal in

areas that can’t be accessed for direct meas rement

the most common being cylinder walls and roll bar tubing.

For this article I’m oin to foc s on the en ine block’s c linder alls.

How a sonic tester works:

Just like a bat or a radar gun, the sonic tester sends out a sound wave and then calculates the

thickness of the metal by measuring the time for the reflected wave to return.

ULTRASONIC INSPECTION

In ultrasonic testing use is made of the basic physical property that

sound waves travel at known constant velocities through any sympathetic

medium. By measuring the time for a sound wave to travel through a

material it can be determined how far that wave has travelled. In this

way sound waves can be used to measure distances. Use can also be made

of the fact that sound waves are reflected at an interface between two

materials such as steel and air to detect defects.

In order to develop and make the best of these principles the basic

physical properties of sound should be understood.

The majority of ultrasonic testing equipment operates on the pulse echo

system, i.e. the time for a pulse of sound to travel through a

material, bounce off a reflector and then return to the transducer is

106

measured.

Q 31) Explain the concept of radiographic tests?

These tests are based on the absorption and dispersion of X-ra s or γ-rays passing

through material.

By means of a luminescent screen or photographic plate, points of varying radiation

intensity that occur at faults can be detected.

X-ra rod ce b Betatron devices or γ-rays produces by radio-active decay processes

are used.

In this method radiations are passed through the being examined and then allowed to

impinge upon sensitive film.

If object have some deffect more radiation is passed through that area and film will

show dark area.

By this method a very small defect can’t be detected as scattering is used to detect

defect

In general, X-rays are preferred for laboratory testing

Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137)

can be used as a source of photons. Neutron radiographic testing (NR) is a variant of

radiographic testing which uses neutrons instead of photons to penetrate materials. This

can see very different things from X-rays, because neutrons can pass with ease through

lead and steel but are stopped by plastics, water and oils.

In addition to γ-rays some X-rays which having short wavelength are more effective in

the study of thick sections.

In radiographic tests, the inclusions appear darker, while blow holes, cavities and

porosity appear lighter than surrounding metal.

107

Production of radiograph

Arrangement of radiographic a welded joint

108

Writing diagram for self rectifying filament tube

Q 32)Differentiate between X ray and γ ray radiography

Ajit Prabhakaran

X rays Y rays (gamma rays)

In X-rayradiography , only one component can be examined at a time.

In gamma ray radiography, many components can be examined at a time.

X-rays equipment is large in size.

Gamma rays equipment is small in size.

Due to more intensity in X-rays it is faster and requires time in seconds or minutes.

Due to less intensity of gamma rays it is slower and requires exposure time which is in hours.

X-rays are having larger wavelength,hence their penetration power is less.

Gamma rays are having shorter wavelength than x rays, hence having more penetration power.

109

X rays gives better results for components less than 50mm thickness.

Gamma rays give poor results for smaller thickness components.

Q 33) Eddy current testing

Akshay bhivshet roll no AE359

When a coil carrying current is brought near a metallic specimen, eddy current are

developed in the specimen due to electromagnetic induction. The magnitude of the

induced eddy current depends on the following factors.

1) The magnitude and frequency of alternating current flowing in the coil

2) The magnetic conductivity of the specimen

3) The magnetic permeability of the specimen

4) The shape of the specimen

5) The relative position of the coil and specimen

6) The microstructure and hardness of the specimen

7) The amount and type of the defect in the specimen

The changes in eddy current will change the magnetic impedence of the

specimen or component which is converted into voltage and observed on a

voltmeter or oscilloscope. These present certain difficulties because the

impedence value changes `due to change of spacing between the coil and the

specimen however by utilising the phase or time relation or the amplitude of the

eddy current ,this problem can be overcome

The test coils are of two types:

1) Absolute coils: they directly measure inductance.

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2) Differential coils: here pairs of the coils are used they are connected in series

and opposing each other. a standard specimen is surrounded by one coil and

the specimen under test is surrounded by another coil. When the output from

the two coils is zero the specimen under test is similar to the standard

specimen otherwise they are different. Detect free component can be chosen

as standard specimen and the other components can be tested for defects.

However other factor like size, shape, microstructure, hardness, etc should

remain constant. in the fig below u can see the eddy current tester

Eddy current tester

Eddy current method can be used for the following purposes:

1) To measure or identify such condition and properties as electrical conductivity,

magnetic permeability, grain size, heat treatment condition, hardness and

physical dimension.

2) To sort out dissimilar metals and detect difference in their composition

microstructure and other properties

3) To measure coating thickness

Eddy current testing has the following advantages

1) It is very fast

2) It does not require direct electrical contact with the part being inspected

3) It can be made automatic for high speed inspection and can be used to inspect

the entire production output if desired

The limitation of this method is that the defect at or near the centre of the component

will not be detected because the eddy current flow only through the surface.

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Q 34) DIFFERENTIATE BETWEEN DESTRUCTIVE AND NON DESTRUCTIVE TESTING

THE NEED FOR TESTING METALS IS TO ENSURE THAT THE DESIGN REQUREMENTS

HAVE BEEN MET AND THE COMPONENT MANUFACTURED AER FIT FOR THE

INTENDED OPERATION

DESTRUCTIVE TESTING:

* ENGINEERING COMPONENTS ARE DESIGNED AS PER CERTAIN SERVICE

CONDITIONS. PHYSICAL CONDITIONS ILVOL DIFFERENT TYPES OF LOADS COMING

ON TO THE COMPONENT DURING ACTUAL USE BUT THE EXACT WORKING

CONDITION S CANNOT BE SIMULATED IN THE LABORATORY.

* THEREFORE, CERTAIN BASIC PROPERTIES LIKE HARDNESS, STRENGTH, DUCTILITY

ARE EVALUATED BY STANDARD TESTS AND EQUIPMENT IN THE LABORATORY.

THESE AER USED AS BASIC PARAMETERS FOR DESIGN CALCULATIONS.

eg: IMPACT TESTING MACHINE , UNIVERSAL TESTING MACHINE

NONDESTRUCTIVE TESTING:

*NON-DESRTRUCTIVE TESTING IS ONE OF THE IMPORTANT METHODS USED FOR

EVALUATION AND QUALITY CONTROL OF METAL COMPONENTS

*DURING TESTING THE METAL COMPONENT DOES NOT GET DAMAGED

*THE TESTING METHODS ARE VISUALI INSPECTION, MAGNETIC PARTICLE TESTING.

eg:- ULTRASONIC TESTING, RADIOGRAPHIC TESTING

Q 35) Write a note on tool steels.

SANMESH S. WAGHMARE

SE-Auto Roll no-361

Tool Steels :

These steels are specailly used for working, shaping and cutting of metals. Large no. of

steels are available for this purpose. They are classified and designated according to

American Iron and Steel Institute (AISI) as below :-

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1) Cold work tool steel

2) Hot work tool steels

3) High speed tool steels

4) Special purpose tool steels

The names of the various classes indicate some of the special properties of these

steels.

All the tools steels should be hard, tough and wear resistant. Also the tendency for

decarburization, oxidation and grain growth during their heat treatments should be

minimum.

1) Cold work tool steels :- These steels are used for cold working of metals. They have

good hardness and wear resistant at low temperature. Some of the steels from this

group contain very little or no-alloying elements and hence are less expensive.

Depending on their hardening characteristics, they are classified into sub-groups such

as water hardening steels (W-series), oil hardening steels (O-series), air hardening

steels (A-series),and high carbon high chromium steels (D-series).

i) Water hardening steels:- They are essentially plain carbon steels with high carbon

content (0.6 to 1.4%). In general low carbon contents are used for impact and shock

loading conditions.

Even though these steels are cheap, there are no. of limitations in their use which are

as belows:-

a) Their red hardness and strength at elevated temperature is poor. These steels

temper rapidly and become soft at high temperature. Due to this, they cannot be used

for hot working of metals or cutting metals with high speeds.

b) Their distortion during hardening is more because of poor hardenability. This leads to

heavy warpage and cracking of large and complex dies during hardening.

c) Because of their poor hardenability they are of shallow hardening type and hence are

at disadvantage with respect to deep hardening steels.

d) Their tendency to oxidation, decarburisation and grain coarsening during heat

treatment is more.

ii) Oil hardening tool steels :- Their hardenablitiy is better than the water hardening tool

steels and therefore, they can be hardened by oil quenching. They are not so expensive

as other tool steels and are used for blanking and forming dies, shear blades, master

tools, cutting tools and gauges. The distortion during hardening is less and hence they

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are also called as oil hardening non-shrinkage (OHNS) steels.

iii) Air hardening steels :- These steels have high hardenability due to the addition of

various alloying elements such as Mn, Cr, Mo and W in sufficient amount. The total

content of alloying elements exceeds 5%. These steels have less distortion during

hardening, high resistance and good depth of hardening. They are used for thread

rolling and slitting dies, drawing dies, intricate die shapes, gauges and punches.

iv) High carbon high chromium steels (HCHC) :- They have high hardenability and

hence can be hardened by oil or air quenching. Their distortion during hardening is less.

They maintain sufficient hardness upto about 500 C due to the presence of alloy

carbides. They are used for drawing dies, blanking dies, forming dies, coining dies,

trimming dies, shear blades, cutting tools, gauges, etc.

Since oil hardening, air hardening and high carbon, high chromium steels show less

distortion during hardening they are also called as non-deforming or non-shrinkage tool

steels.

These steels are particularly useful for master tools, gauges and dies which must not

cahnge size after heat treatment.

2) Hot work tool steels :- These steels are mainly used for hot working of metals such as

for stamping, drawing, forming, piercing, extruding, upsetting and swagging. They have

good strenght , toughness, hardness and wear resistance at elevated temperatures.

They have excellent resistance to tempering/ softening at elevated temperatures.

Because of their high ductility, toughness and resistance to splitting, they are

used for aluminium and magnesium die, casting dies, extrusion dies, forging dies,

mandrels and hot shears.

They have excellent red hardness and resistnce to wear at elevated

temperatures and hence are used for dummy blocks, hot extrusion dies for brass, nickel

and steel, forging dies and hot punches. Hot work tool steels are designated by H-

series.

3) High speed tool steels :- These steels maintan high hardness upto a temperature of

about 550 C and hence can be used for cutting metals at high speed. They also have

high wear resistance and cutting ability.

High speed steels are divided into 2 types depending upon the principal

alloying elements. The first group is called tungsten high speed tseels which contain

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high amount of W with other elements such as Cr, V and Co. They are designated by T-

series. The second group of high speed steels is called as molybdenum steels. This

type is designated by M-series.

W, Mo, Cr and V are carbide formers and hence form respective carbides.

These alloy carbides increase red hardness, wear rsistance and cutting ability at high

temperature. In this respect vanadium is most powerful.

These steels are used for drills, taps, reamers, milling cutters, saws, lathe

tools, punches, drawing dies and wood working tools.

4) Special purpose tool steels :- Remaining tool steels are grouped together under the

heading special purpose tool steels. The steels under this group are shock resisting tool

steels (S-series), low alloy tool steels(L-series), carbon-tungsten tool steels (F-series)

and mould steels (P-series).

Shock resisting tools steels contain less carbon for better shock

resistance. Due to this, their hardness after hardening is also less. To increase

hardness one or more of the elements such as Mn, Cr, W, Mo, V and Si are addded.

These steels are used for punches, chiesels, concrete breakers, rivet sets, forming dies,

shear blades, etc.

Low alloy tool steels are similar in characteristics to the water hardening

tool steels. The principal alloying element of this group is chromium. These steels are

used where high wear resistance and toughness are required.

Carbon-tungsten tool steels containhigh carbon with tungsten as the

alloying elements. As compared to water hardening steels (W-series), they have much

higher wear and abrasion resistance, and are used for application such as broachees,

reamers, burnishing tools, taps, etc.

Mould steels are mainly used for plastic moulds. The mould should have

high surface hardness to take care of abrasive action of moulding powder and tough

core to wuthstand the shock during the compression cylce.

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In conclusion, it may be stable that alloy tool steels are justified in

application requiring –

1) Abrasive hardness, to provide the superior wear resistance of complex alloy

carbides,

2) Toughness, as required by cold forming tools and punches,

3) Red hardness, as required in hot working tools and high speed cutting tools to resist

tempering and retain hardness and

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4) non-deforming properties, to resit distortion and cracking during heat treatment of

complicated forming dies.

Q36 ) Short note on non ferrous cutting tool materials.

Arjun Parameswaran

Me 302

Ans:

Non Ferrous Cutting Tool Materials

In addition to tool steels, there are few other materials used for cutting purposes. The

following materials are popular from this class:

(1) Alumina cutting tools

They are made from Al2O3 by powder metallurgical techniques such as sintering and

pressing. Alumina is extremely hard and wear resistant. These tools are brittle like most

of the ceramics but give very satisfactory service when properly mounted and

supported. They are used for continuous shallow cuts at high speeds.

(2) Cemented carbides

They are made from carbide powders of refractory metals such as W, Ta, Ti etc.

bonded by Co and manufactured by powder metallurgy. They are widely used as cutting

tips of various tool parts and are joined by either brazing or mechanical fastening.

Cemented carbides are called cermets when refractory carbides such as WC, TiC

etc. are put in a ductile metal matrix with a higher amount of Co and Ni. Cermets have

high hardness, and high resistance to oxidation and thermal shock.

(3) Stellites

Stellites are cast alloy tools having high hardness in the range of Rc 60-65 with

excellent red hardness, wear resistance and corrosion resistance. Like cemented

carbides, they cannot be machined and hence are cast to a rough shape followed by

grinding to final shape.

These alloys contain C, W and Cr in a Co matrix, the major constituent being Cr. A

typical grade consists of 30% Cr, 19% W, 2% C, 3.5% Ni and the rest Co.

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They can be used up to a temperature of 550⁰C without much of a decrease in

performance. Their most useful field is as single point lathe turning tools wherein they

are brazed to mild steel shanks and used.

Q 37) What are the application of powder metallurgy?

NAME-NIKHIL.DEORE

ROLLNO:ME308

Ans.1. AUTOMOTIVE APPLICATION:

In motor car industry ,porous bearing are used for starter,wipers,sliding doors, dynamos,

clutches and brakes of the car, buses trucks and tractors. Sintered gears are widely used in car

and trucks. Electrical contacts, crank shaft drive, piston rings, connecting rods and brake lining

are other powder metallurgy parts for the automotive application. Sintered friction materials

are used for brakes in cars, trucks, aircrafts and similar application.

2. DEFENCE APPLICATION:

Metal powder play an important role in Military and national defense Systems. These powders

find use in rocket, missile, carriage cases, bullets and military pyrotechnics such as tracers,

incendiaries etc.

3.HIGH TEMPERATURE APPLICATION:

Refractory metals and refractory metal carbides find application in high temperature services.

Components made of W, Mo and Ta by P/M are widely used is the electric light bulbs,

fluorescent tubes radio valves, mercury are rectifiers and X-ray tubes in the form of filament,

cathode, anode, screen and control grids. Refractory metal carbides are used for dies, rolls,

cutting tools, etc at high temperatures. Production of super alloys is also possible by P/M.

4. AEEROSPACE APPLICATIONS:

Metal powders play an important role in rockets, missiles, satellites and space vehicles. Metal

powers of Be, Al, Mg and Zr are used as solid fuels in rockets and missiles.

Tungsten parts with uniform distribution of porosity are used in plasmas tensines and ion

engines which are operated at about 1800 degree Celsius Bronze oearings , filters and ferrite

cores for transformers and inductor coils and Aloico magnetic material in communication

systems are used in various space satellites and vehicles.

5. ATOMIC ENERGY APPLICATIONS:

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Composite materials are supplied in various fuel elements and control rod system. Dispersion

strengthened material are used in atomic reactors, magneto-hydrodynamic generators, high

temperature gas turbines and computers Uranium oxide dispersion strengthened stainless steel

is used as a fuel element Beryllium, zirconium and hafnium metal powders are used as control

rods and radiation reflectors, Zirconium is used as cladding material and beryllium as

moderator in nuclear reactors.

6. OTHER APPLICATION:

Parts in clocks and timing devices, typewriter, adding machines, calculator permanent magnets

and laminated bimetallic strips.

Q 38) Advantages and limitations of powder metallurgy.

Saurav Dutta (ME-309)

Powder metallurgy has several unique advantages which are as below:

1. Metal plus metal components can be manufactured by P/M. There is almost no need of referring to their equilibrium or phase diagram. Components of any desired composition can be manufactured.

2. Metal plus non-metal components can be manufactured which are quite difficult to manufacture by the usual methods.

3. Controlled porosity can be obtained in the components. This is essential for certain applications like liquid and gas filters, self-lubricating bearings and insulating bricks. The amount of porosity along with control oversize, shape and distribution of pores can be obtained to achieve the desired properties of the component.

4. It is possible to manufacture components with properties similar to the parent metals, whereas if the components are manufactured by melting, the alloy may have different properties from their parent metals.

5. Production of refractory metals like W, Ti, Th, Mo, etc. is possible without melting e.g. manufacture of ductile tungsten in wire form for incandescent lamp filaments.

6. Components from metals which are completely insoluble in the liquid state can be manufactured with uniform distribution of one metal into the other. However, if they are manufactured by melting and casting, the distribution of one phase into the other is non uniform e.g. the material of journal bearing should have soft and hard phases.

Powder metallurgy has some drawbacks as given below which limits its applications in

some of the situations.

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1. Most of the powder s used in P/M are fine and fine powders of some of the metals like Mg, Zr, Ti, Al, etc. are likely to explode and cause fire hazards when they come to contact with air and hence, they should be preserved carefully. Other metal powders also likely to get oxidized slowly in air and hence, they must be stored properly to avoid their deterioration.

2. It is not suitable to manufacture small number of components because of high initial investment on tooling and equipment.

3. Large sized components cannot be manufactured because of the limited capacity of presses available for compaction.

4. Complex shaped parts cannot be manufactured easily by P/M. 5. Components with theoretical density cannot be manufactured. 6. P/M parts have poor corrosion resistance because they are porous. Due to this

porosity, large internal surface area gets exposed to corrosive environment.

Q 39) GIVE THECHARACTERIZATION AND TESTING OF METAL POWDERS?

Sarvesh A.Gadhe

Roll no.310

(Ans.)The desired properties in the component depend on the properties of metal

powders used for its manufacture.Therefore, it is essential to test these powders for

their properties in the selection of right type of powder for a given application.

The following properties should be evaluated:

(1) Chemical composition with type and amount of impurity.

(2) Shape, size and distribution.

(3) Porosity.

(4) Microstructure.

Specific surface, density, flow rate, compacting and sintering are the other

important properties which depend on the above properties of metal powders.

(1) Chemical Composition

Chemical composition and impurities in metal powders are determined by

standard techniques of chemical analysis such as gravimetric, volumetric,

colorimetric, and spectroscopy. The choice of a method depends upon the type

of element, amount and the accuracy with which it is to be determined. Impurities

need to be determined with accuracy as the influence the compacting and

sintering characteristics.

(2) Shape, size and distribution:

Powder shape, size and distribution can be measured by using any one method:

(a) Sieve Method

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Different sieves are arranged one below the other as per their mesh

numbers, the coarsest being at the top.100 gram of metal powder is placed

on the top sieve and the entire stack of sieves is vibrated for 15 minutes by a

standard shaking machine which gives circular and translator motions to the

screens. After this, the amount of powder retained on each sieve is

measured. From these weights, size and size distribution can be found out.

Sieve method gives accurate result when the powder is in the size range of

44 to 840 microns.

(b) Microscopic Method

Optical and electron microscopes are used for measurement of size and

distribution of particle. Optical or electron microscopy can be used for

measurement of particle sizes above 0.1 micron and electron microscopy for

particle sizes of smaller than 0.1 micron.

(c) Sedimentation Method:

This involves suspending a small quantity of powder sample in a fluid

medium and allowing the particles to settle for a suitable time. Settling

velocity of a spherical particle is proportional to the square of the particle

diameter and particles of equal sizes can be separated on the basis of

settling velocities.

(d) Elutriation Method:

this method is used for determination of size distribution of fine particles. The

metal powder is allowed to settle in a moving liquid or gas of a constant

velocity. The particles with settling velocity of less than the velocity of rising

fluid will be carried upwards and those with higher settling velocities will settle

at the bottom. By altering the velocity of medium, the particles can be

separated according to their sizes. The method is suitable for powder sizes in

the range of 5 to 100 microns.

(3) Particle porosity and microstructure:

For the determination of properties, microscopy is used. The powder is mounted in

some suitable medium for observation under microscope. Depending on its

suitability, either hot mounting or cold setting method is used.

(a) Hot Mounting: The metal powder in small quantity is mixed with Bakelite powder,

mounted using a standard specimen mounting press, polished, etched in a

suitable etchant, washed with water and alcohol and dried using blast of hot air

and examined under microscope.

(b) Cold Mounting: Small quantity of metal powder is mixed with suitable polymeric

liquid and hardener. This medium is poured in a steel tube of a suitable size. This

liquid from the medium polymerises and becomes hard in a period of 10 to 15

min. Subsequently the sample is removed and polished, etched, washed and

examined under the microscope.

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(4) Other Properties :

(a) Specific Surface: It is defined as the total surface area of a powder per unit

weight(cm²/kg).

(b)Density:

(A)Apparent Density: The apparent density of a powder is defined as the mass

per unit volume of loose or unpacked powder.

(B)Tap Density: The tap density is the apparent density of the powder after it has

been mechanically shaked or tapped until the level of the powder remains

constant.

(c) Flow Rate: It is the ability of powder to flow readily and confirm to the mould

cavity.

(d) Compacting or Pressing Properties:

These are represented by the terms compressibility and compatibility.

Compressibility is defined as the powders ability to deform under applied

pressure and is measured as below:

(a) Ratio of the green density of compact to the apparent density of the powder.

(b) Ratio of the height of the uncompact powder in the die to the height of the

pressed compact.

(c) Ratio of the volume of powder poured into the die to the volume of the

pressed compact.

GREEN DENSITY: It is the density of a cold compact and largely depends on

the basic properties of powder particles. Green Density increases with

increase of(A)compaction pressure ,(B)particle size (C)apparent density and

decrease of(A)particle irregularity, (B) particle hardness, (C)compacting

speed.

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The general dependence of green density on other factors is shown

schematically as

Variation of Green Density with (a)Apparent Density and (b)Compacting

pressure

Green Strength : It is the mechanical strength of a green compact and is

expressed in kg per square mm.This property Is determined by conducting

transverse rupture test or radial crushing test on green powder compacts of

suitable size and shape using standard testing machines.

Green Spring: The compacts expand as soon as they are ejected out of the

die cavity and this effect is called Green Spring.It is necessary to determine

the amount of green spring for the manufacture of components with close

dimensional tolerances.

(e)Sintering Characteristics:

The idea of sintering characteristics is obtained by testing on following

properties:

(A)Dimentional change during sintering:

% shrinkage(or growth)=change in length X 100 ……….(used in carbide

industries)

Sintered length

% shrinkage (or growth)=change in length X 100 ……….(used in bearing

industries)

Sintered length

(B)Mechanical properties: Mechanical properties of sintered compacts such

as compressive strength, hardness,etc. are determined by using appropriate

methods of testing. These results are necessary for deciding the suitability of

the component for a particular service application.

(C) Microstructure: Metallographic examination of sintered components will

not only reveal the size, shape, distribution and amount of phases, their

distribution grain size, inclusions and homogeneity of components. Because

of the presence of porosity, due cares should be taken during polishing and

etching of samples to avoid erroneous observations and results.

Q 40Write a note on manufacturing of metal powders.

Saurabh P Gardi

SE MECHANICAL

Roll no 312

123

Ans. There are various methods for the manufacturing of metal powders and each

method gives a powder of different size, shape and distribution and has different

characteristics. The various processes are classified into 4 types:

1 MECHANICAL PROCESS:

(1) Machining: This method is used to produce fillings, turnings, chips, etc which are

then pulverized by crushing and milling. Since relatively coarse and irregularly shaped powder particles are obtained by this method, it is suitable only for few special cases such as Mg powder in pyvorectoic applications, silver solders and dental alloys.

(2) Crushing: The solid materials are crushed by hammers, jaw crushers, gyratory crushers etc. The powder particles of brittle materials are angular in shape and ductile materials are flaky in shape. This method is suitable for brittle materials.

(3) Milling: This is the most important and widely used method. In ball milling method, the material is tumbled or rotated in a container with large

no of hard balls. The speed of the container is properly controlled so that the balls

hit the material making the particles finer and finer. The grinding action is at its

optimum level at critical speed because the balls are lifted up to the top of the drum

and fall down on the material. It is widely used for carbide metal mixtures and

cements.

(4) Shotting: In this method molten metal is poured on a vibrating screen and the liquid droplets are solidified either in air or a neutral gas. The size of the particles is nearly spherical.

(5) Graining: It involves thesame procedure as the shotting the only difference being

the solidification of molten metal droplets is done in water. (6) Automization: It consists of mechanical disintegration of a molten metal by

compressed air or inert gas. The disintegrated particles may be solidified in controlled atmosphere, vacuum or water. Usually the powder shape is irregular however; spherical particles may be obtained by changing the conditions.

2 PHYSICAL PROCESS

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(1) Condensation: In this method, metal vapors are condensed to formmetal powders. It is suitable for volatile metals like Zn, Mg and Cd. The powder shape is

nearly spherical. (2) Thermal decomposition (or Gaseous pyrotocia): Fine metal powders of some

metals like Fe, Ni, W, Mo, Cu, etc are manufactured by thermal decomposition of their respective carbonyl vapors. It gives metal powders of very high purity and the CO produced can be recycled.

3 CHEMICAL PROCESS

(1) Reduction: In this method, a suitable compound of metal such as oxide, halide, oxalate or formate is reduced by a suitable reducing agent to obtain the metal in the powder form. The reducing agent may be a solid or a gas usually, carbon, hydrogen, ammonia and CO. It is extensively used for the manufacturing of Fe, Cu, Ni, W, Mo and Co powders.

(2) Intergranular Corrosion: It is a fact that grain boundary of any metal corrodes

faster than the grains. In this method, grain boundary area of metal under consideration is corroded by a suitable electrolyte so as to separate out the grains from the polycrystalline metal. The powder of stainless steel is made by this method where chromium carbide gets separated and the steel gets sensitive to corrosion.

(3) Precipitation from aqueous solution (Simple displacement): This process is

based on the principal that a less noble metal displaces a more noble metal from the aqueous solution containing the ions of the more noble metal. For e.g. silver is displaced from silver nitrate solution by Cu or Fe. The displaced metal separates in the form of powder. It is also used to prepare Cu powder where Fe is used to displace Cu from CuSO4 solution.

4 ELECTRO-CHEMICAL PROCESS (Electro deposition)

In this method, metal powders are obtained by electro depositions from aqueous

solutions or fused salts. The plant is similar to electroplating plant. In electroplating,

conditions are adjusted in such a way that the plated layer on cathode is continuous

and adherent. However, in electro deposition, every attempt is made to make the layer

coarse, loose and non adherent. i.e. electro-deposition is a reverse adaptation of

electroplating.

125

The conditions which favour the powder formation on cathode are: (a) high current

density (b) low metal ion concentration (c) high acidity (d) low temperature and (e)

circulation of electrolyte in such a way to avoid and suppress convection.

There are three different kinds of electrodeposition which are in practical use:-

(1) Deposition as a hard and brittle mass which is subsequently ground to powder. (2) Deposition as a soft and spongy substance, loosely adherent and fluffy texture

which is easily powdered by light rubbing. (3) Direct deposition as powder from the electrolyte which drops to the bottom of the

cell.

This method is suitable for commercial production of powders of Cu, Be, Zn, Sn, Ni, Cd,

Ag, Pb. The particle shape is dendritic and particle size depends on the conditions of

electrodeposition. The purity of powder is high and may exceed 99.9%.

Q 41) Write note on powder conditioning?

NAME: GEORGE VARGHESE

ROLL NO: Me313

The metal powders obtained may not be suitable for their further processing. To make

them suitable powder conditioning is done which involves mechanical, thermal or

chemical treatments or alloying and are described below:

a) Annealing:

Before mixing or blending of powders, annealing is usually done in inducing

atmosphere or in vacuum. This eleminates work hardening effects, reduces the

oxide content and purity level and alters the apparent density. High temperature

annealing increases the apparent density of powder and reduces the pressure

requirements, whereas low temperature annealing decreases the apparent

density of powder and increases the pressure requirements during compaction.

These powders form I spongy mass during annealing and hence it is pulverised

to obtain the powder. This should be done carefully to reduce work hardening in

the powder.

b) Blending or mixing

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In this process through mixing of powders of the same material or of different

materials is done for obtaining the desired properties during compaction sintering

and in the final sintered component. This gives uniform distribution of particles in

the compact and consistent performance of the powder during pressing sineering

for obtaining this at improved level small amount (<1%) of lauryl alcohol or

camphot is usually is added to the powder during mixing. This also improves

bonding of particles which improves green strength of compacts. Various types of

machines are used for mixing or blending. However a double cone or Y-cone

mixture is more comman . Certain materials like grafite, stearic acid, stearates of

Zn and Li etc… are added to this powders during mixing which may have this

following function:

1) It may act as lubricant, reducing the friction between the punch and the die

walls.

2) It may easily transform to gas or vapour which creates porosity during

sintering.

3) It may act as binder,increasing green strength which facilitates handling of the

cold compacts.

Alloying additions can also be done during mixing to improve properties of the

component.

Mixing or blending may be done in either dry or wet condition. Wet mixing gives

more uniform distribution of powder particles and is done by using such liquids as

alcohol,benzene,glecerine,acetone or distilled water. After mixing is complete, the

above liquid medium can be removed by an appropriate drying tecnique.

Q 42) Manufacturing Oil Impregnated Porous Bearings

Vinit.V.Joshi

Roll No: Me 315

These bearings are manufactured from either bronze, brass, iron or aluminium alloy

powders with or without graphite. However, bronze bearings are widely used and are

made from Cu and Sn (90:10) with addition of graphite. Graphite increases porosity and

also improves pressing characteristic. Some amount of free graphite is desirable

because it is a solid lubricant and takes care under severe loading condition. However,

large amounts of graphite will reduce the strength of bearing. The steps in the

production of a porous bronze bearing are as below :

1) Mixing

2) Cold compaction

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3) Sintering

4) Repressing (i.e. sizing) or machining

5) Impregnation

Metal powders of Cu and Sn with small amounts of fine natural graphite are blended or

mixed to obtain the desired alloy composition (90 Cu : 10 Sn). This powder is cold

compacted at pressures between 20 to50 kg/mm2 to form green compacts of desired

shape and size.

These compacts are sintered in a reducing atmosphere at a temperature of about

8000C. A typical sintering cycle consists of holding the compact at 400-4500C for the

removal of part of the graphite and diffusion of molten Sn into the Cu, followed by

further heating to 8000C for periods as short as 5 mins. At this temperature , a tin-rich

liquid phase is formed which is absorbed by the copper.

Distortion occuring during sintering can be eliminated by repressing (i.e. sizing) or

machining. If the pore size is large, sizing can be done and if it is small, machining

should be done. For small pore sizes, sizing should not be done because it may result

in closure of pores.

The repressed or mechanical components are impregnated with oil or hot oil using

pressure, vacuum or a combination of these. Such an oil impregnated bearing is called

self lubricating bearing because it does not require external lubrication. These bearing

must have the following characteristics for their efficient working:

i. Sufficient porosity (30 to 50%) to retain the maximum possible amount of oil.

ii. Inter connected porosity in the largest proportion and should be uniformly

distributed throughout the material.

iii. Sufficient strength to sustain the loads.

iv. Good dimensional accuracy.

When the porosity is more, the strength of the bearing is less. Such bearing have more

oil retaining capacity but less load sustaining ability and hence they are suitable for

high speeds and low load conditions. When the porosity is less, the strength of the

bearing is more. Such bearing have less oil retaining capacity but more load bearing

ability and high load conditions. These bearings contain more amount of free graphite

which compensates for the less quality of oil. The working of bearing is as below:

As the speed of the shaft increases, the temperature of bearing rises due to frictional

heat. This results in decrease of viscosity and increases in volume of the oil. Due to

this, the oil is pulled out from the pores and gets rapidly circulated along with the

rotating shaft. With decrease of shaft speed, pressure decreases and temperature also

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decreases; and due to this, the oil goes back to pores by capillary action. There is no

wastage of oil and working of the bearing is smooth and silent.

These bearings find applications in places which are inaccessible or difficultly

accessible. These are the places which are impossible or difficult for regular lubrication.

They are also used in certain applications where it is desirable that the oil should not

come in contact and contaminate the product (e.g. in food and textile industries)

Q43)Manufacturing of Cemented Carbides

Name: Jubin Thomas Roll no :316

Ans: Cemented Carbides are important products of Powder Metallurgy. They find wide

applications as cutting tools, wire drawing and deep drawing dies, drills and stone working tools. They are manufactured from refractory carbide metals like W, Mo, Ti, Ta or Nb. These carbides are extremely hard (hardness more than 3000 VPN) and retain hardness up to a very high temperature. However they are extremely brittle and hence sometimes fall under shock loading. To increase their shock resisting ability metals such as Co, Ni, Cr are used up to 20% and the processing is done by Powder Metallurgy. The hard carbide powders are bonded or cemented together by these metals or alloys. The steps in the manufacture of cemented carbides are as follows:

1. Manufacturing of powder: Carbide powders of the refractory metals are produced either from their respective oxides or metals. Metal oxides can be reduced to metals with the help of carbon or hydrogen and the metals are converted to carbides by direct reaction with carbon. 2. Milling: Carbide powders are mixed in the required proportion along with the powder of metallic binder by a wet mixing method. Lubricants such as paraffin wax dissolved in gasoline, camphor in ether or light hydrocarbons and glycerine in alcohol are mixed to these powders just prior to compaction which facilitates pressing and avoids defects and cracks in the compacts.

3. Cold pressing and sintering: This mixture is compacted at a pressure of 35 to 45 kg/mm2 and the compacts are heated to about 400oC for a sufficient period to remove the lubricant by volatilisation. Sintering of these compacts is carried out in two stages. The preliminary sintering is done using H2 atmosphere at a temperature of 925 to 11500C wherein strength is imparted to the compact. The second stage is done at a temperature of 1300 to 1500oC for a minimum of two hours in H2 atmosphere or vacuum. The liquid phase formed at this temperature binds the particles, and the mixture is called as cemented carbides. During this stage large amount of shrinkage occurs in the component hence, the component must have over sized dimensions before sintering.

4. Machining: Machining is done to obtain close tolerances. Machining is carried out in two stages. During the first step, it is roughly grounded using silicon carbide grinding

129

wheels and in the second step it is grounded with the help of metal bonded diamond wheels.

Flow chart of manufacturing of Cemented carbides

Q 44) Manufacturing of CERMETS?

NAME: TUSHAR KADAM

ROLL NO: Me318

BRANCH: (SE) MECH

Ans: They are manufactured from the powders of ceramics and metals by powder

metallurgy. Cermets are a short form of ceramic plus metal. Ceramics have excellent

high temperature strength and hardness whereas metals have good shock resisting

ability. The above properties are combined together by mixing the powders of ceramics

and metals and processing by P/M. Ceramics particles are bonded by metal particles

and hence the properties of ceramics depends upon the type of ceramics, types and

amount of metallic binder and other powder metallurgical parameters. Some cermets

are also made by impregnation of porous ceramics structure with a metallic binder. The

amount of binders usually varies between 20% to 70%.The most common ceramics are

oxides, carbides or borides of metals such as Ws, Cr, Ti, Be, Al and Si, and the bonding

metals are Fe, Ni, Cr, and Co

- APPLICATIONS OF CERMETS:

Machining

Cold pressing and sintering

Milling

Manufacturing of powder

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Cermets find applications in rocket and jet engines, as spinning tools for hot metals, hot

forging dies and other similar high temperature applications. They are also suitable for

cutting of metals at high speeds with medium to light chip loads

Q45) Manufacturing of Sintered Carbide Tipped Tools.. Roll no. : Me 320 Ans:

First Powder

The initial step in forming tungsten carbide is to mix carbon black with tungsten metal and metal oxides. These raw materials are heated until a powder is created. This is the initial tungsten carbide powder.

Second Powder

The tungsten carbide powder must be mixed with a special wax and with cobalt in a ball mill. The mixing at this stage is critical because the tungsten tries to form itself into large crystals, while a quality tungsten carbon compound requires that you have billions of tiny crystals of an even consistency suspended in the cobalt matrix. Failure to thoroughly mix the powder, wax and cobalt will result in uneven lumps, similar to those in gravy, in the final product. A proper mix at this stage will result in a very fine powder. The wax in the mix holds the powder together so it can be shaped.

Molding Into Chalk

The final fine powder is put into molds where it is pressed into shape and heated at temperatures ranging between 1,000 and 1,500 degrees F. During this process the wax melts out while the resulting substance sticks together like a soft chalk. This chalk-like substance can be easily machined into the shape that is wanted in the mold.

Final Firing

The shaped tungsten carbide is sintered, or heated, at temperatures ranging from 2,500 to 2,700 degrees F. It will shrink by up to 15 percent in size during this process and up to 35 percent in volume, as the chalk is heated and subjected to up to 30 tons of pressure to form it into the final hardened tip for a tool.

131

Q 46) Mfg of DIAMOND IMPREGNATED TOOLS

132

Name:samiksha kashid

Me 321

These tools are manufactured from a mixture of diamond dust and powder of a bonding

material such as mild steel. Co or cemented carbides by P/M. The size of diamond particles

varies between 60 to 400 meshes depending upon the specific application. The finer sizes are

mainly used for finishing operation such as boning, lapping and polishing where medium and

course sizes are grinding and cutting wheels. The amount of diamond dust in tool is expressed

by a concentration number and 100 concentration means 25 percent by volume. This is about

0.88 grams of diamond dust per cubic centimetre. Most of the diamond units are made with

concentration between 25 and 100. The size of diamond particles and amount of diamond

determines the cutting performance and life of the tool.

These tools are manufactured by cold compaction and sintering diamond powder is thoroughly

mixed with the bond metal powder by the method of mixing cold compacted and sintered at a

temperature below 10000 Celsius using vaccum or H2 atmosphere. Tools manufactured by this

procedure show high porosity and hence hot pressing and pressure sintering is used reduce

high porosity.

Hot pressing is done in the temperature range of 600 to 9000 c using atmospheric pressure of

12 to 20 kg/mm2 in slightly reducing atmosphere.

In pressure sintering heating is done under pressure to a temperature slightly higher than that

for hot pressing and the product obtained is very similar to that obtained in hot pressing.

In most of the cases, the working face of the diamond tool is prepared by P/M and set in a

shank material by soldering, brazing, mechanical fixing or using adhesives.

These tools give closed dimensional tolerances and good surface finish at high cutting speeds.

Use of coolants recommended to increased tool life, cutting efficiency and surface finish.

They are used in cutting, drilling, shaping, sawing and finishing of various materials such as

concrete, rocks, glass, quartz, refractories and cemented carbides. They are also used for wire

drawing dies for the production of fine wire of Ni, Monel, Cu, bronzes and steels.

133

Manufacture of diamond impregnated tools

Diamond dust+powder of bonding material

Cold compaction

Sintering

Hot pressing

Pressure sintering

134

Manufacture of diamond impregnated tools

Diamond dust plus powder of

bonding material.

It is prepared by P/M and set in shank material

Cold compaction and sintering

diamond powder is thoughourly mixed with the

bond metal powder below 10000 C using vaccum or H2 atmosphere

Hot pressing (600 to 9000 c and atm pressure of 12 to

20 Kg/mm2 in slightly reducing

atmosphere.

135

Q 47) Mfg of refractory metals

Due to high melting temperatures and reactivity with the environment at elevated

temperatures, their productivity on commercial scale with economy and purity is not possible

by smelting or other processes. Hence they are manufactured by powder metallurgy.

These include metals such as W,Mo,Nb,Ta,Pt and others from the refractory and other metal

groups.

PRODUCTION OF TUNGSTEN AND MOLYBDENUM

The oxides of ammonium salts of these metals are reduced by H2 and fine powders are

obtained. These are cold compacted at pressures from 15 to 75 kg/mm2 using paraffin wax as

lubricant and simple rectangular shapes are obtained. These green compacts are presinteredat

around 1000°C using H2 atmosphere. This operation gives sufficient strength necessary for

subsequent handling and clamping required during the main sintering operation.

136

Final sintering is done by passing an electric current through the ends of these compacts using

water cooled contacts in H2 atmosphere or in vacuum. Current densities of the order of 1000

amps/cm2 are used in low voltages such as less than 50 V. The temperature attained is very

close to the melting point of the metal.

After this treatment , the bars still have appreciable porosity which makes them brittle. The

porosity is reduced by rolling, forging or swaging at temperatures between 1300 to 1700°C for

tungsten and 1400°C for molybdenum. As the deformation continues , the working

temperature is gradually reduced.

Tungsten is used for applications such as thoriated tungsten filaments for electric bulbs,

electrical contacts, heating elements for high temperature furnaces , etc.

Molybdenum is used for applications such as heating elements for high temperature furnaces ,

electric lamp filaments support in wire form , electrodes and stirrers for glass melting

equipments , and hot working tools and dies.

ANSWER BY –

FAAIZ KAZI

(SE MECH)

FLOW CHART FOR MANUFACTURING OF TUNGSTEN ORE, MOLYBDENUM ORE, NIOBIUM &

TANTALUM ORES TO PRODUCTS IS SHOWN-

FLOW CHARTS BY-

ARUN MANDAL

328 (SE MECH)

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Q 48) Sintered metal friction materials

Abhilash

Me 323

1. Friction materials are used in devices like clutches brakes in which elements of

controlled friction are necessary

2 . For better performance the friction materilas should posess the following properties

sufficient coefficient of friction

with increase in temp minimum reduction in coefficient of friction

high thermal conductivity and corrosion resistance

high temp strength

high wear and abrasion resistance

3. None of the materilas satisfy all the above requirements hence one oer more metals

are mixed together in the powder form and processed by powder metallurgy

The manufacturing of coper based friction material is as follows

1. Blending of raw materials

in this 90% bronze materials and 10% non metals are used

The blending is carried out in double cone on Y-cone blends

To minimize gravity segregation small amount of light fraction is used

2. compacting

It is carried at a pressure of 30kg/mm square

As the compact is fragile hence it shoyld be handled carefuly prior to sintering

3. Sintering

Sinterin is carried at a temp of 800 oC under load using protective atmosphere

According to the size of the component duration of sintering is selected. generally 46

gours is considered

4. Sizing

After sintering it is machined to exact sizwe and shape if require

Q 49) PRODUCTION OF SINTERED STRUCTURAL COMPONENTS:

Anushree

Me 324

Ans:

141

It is essential to study the various steps in the manufacture of a component by powder

metallurgy to understand and realize the advantages and limitations of the process. The steps

are as below:

1) Powder Production

2) Blending or Mixing

3) Compacting

4) Sintering

5) Sizing or Impregnation

6) Testing and Inspection

1) POWDER PRODUCTION:

Powders are manufacture by various methods and the powder from each method has

typical properties. The methods for the manufacture of powder and the methods of

characterization are described in brief in this chapter subsequent to advantages and limitations.

A right type of powder should be used for obtaining the specific properties in the component.

2) BLENDING or MIXING:

Powders of metals or metals and non-metals are carefully blended to obtain uniform

and homogenous mixture. This is essential for obtaining the desired properties in the

component after sintering. During blending or mixing, lubricants are usually added to reduce

the friction between the die wall and punches to obtain better uniformity of density

distribution in cold compact. The removal of lubricants is essential during or prior to sintering of

the compacts because they may adversely affect the mechanical properties. Various types of

blenders or mixers are available to suit the particular requirements of the component to be

produced. For better mixing, tumbling action is necessary and hence blender of the double

cone or Y-cone is used.

142

3) COMPACTING:

Compaction in metal dies is of the most important method for shaping of metal

powders. The powder mix is fed into the die cavity through a hopper and feed shoe is oscillated

to assist the powder flow. The volume of the powder is controlled by adjusting the position of

the bottom punch in the cavity die. When the die has been evenly filled with powder, the upper

surface is leveled by a sweep of the feed shoe and the top punch is pushed into the die cavity.

The pressure is then applied on any one punch or simultaneously on both the punches to

compact the powder.

After maximum compression, the upper punch is removed and the compact is ejected

by raising the lower punch, leaving it free for the next similar operation.

It is at this stage, the powder mass acquires its shape and sufficient strength to

withstand ejection handling. Pressure should be properly controlled since lower pressure gives

fragile compacts and higher pressures cause tool distortion and breakage. The usual pressures

are between 1-150 kg/sq.mm . The density of compact depends on the pressure applied.

Pressure can be applied by mechanical or hydraulic presses.

143

4) SINTERING:

Sintering is carried out to increase strength and hardness of a green compact and

consists of heating the compact to some temperature under controlled conditions with or

without pressure for a definite time.

Sintering process is concerned with :

a) Diffusion : This takes place especially on the surface of the particles as the temperature rises.

b) Densification : This decreases the porosity present in the green compact and increases the particle contact area. Due to this, the compact size decreases. This decrease may not occur uniformly because of variations in the density of compact and hence this leads to the distortion of component.

c) Recrystallization and Grain Growth: this occurs between the particles at contact area, leading to a structure similar to the original one.

The main driving force for sintering is the decrease in free energy due to

decrease of surface area. The property changes are shown.

Depending on the temperature of sintering, sintering process is classified as solid

phase sintering or liquid phase sintering. The most common method is solid phase

144

sintering in which the green compacts are heated usually above the recrystallization

temperature of low melting metal.

The liquid phase sintering is carried out above the melting point of one of the

alloy constituents or above the melting point of an alloy formed during sintering.

During sintering, proper type of atmosphere must be used or sintering may be

done in vacuum. The sintering atmosphere may be reducing or oxidizing or neutral.

Reducing atmospheres are most widely used during sintering and are divided

into three classes below:

a) Dry hydrogen or dissociated ammonia. b) Exothermic atmosphere having low or medium carbon potential c) Endothermic atmosphere enriched wit hydrocarbon gas to produce a

carburizing atmosphere. The choice of an atmosphere depends on the characteristics of the

materials and also on the desired properties in the sintered product.

Instead of cold compaction, hot compaction can be employed. In hot

compaction, te powder is placed into the die and pressure is applied simultaneously

with heat. The other methods which are used for shaping of powders in hot compaction

are:

a) Powder or sinter forging b) Hot Extrusion c) Hot Rolling

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d) Hot isostatic compaction e) Hot coining

5) SIZING (COINING) or IMPREGNATION:

The sintered compact may have slightly different size from the desired one due

to distortion occurring during the sintering process. The size rectification is done by

placing the component in a master die and applying pressure. This is called sizing. Due

to this, the interconnected porosity is likely to get closed and filling of these pores with

oil or some other metals will not be possible. Therefore, if the component is to be

impregnated, sizing should be avoided. However, the close dimensional tolerances

obtained by machining prior to impregnation.

6) TESTING AND INSPECTION:

The component should be tested for various properties before it is put to

service. Te various tests which are conducted are compressive strength, tensile strength,

porosity, density, hardness, composition, microstructure, etc. It is also inspected for

146

size, shape and amount of defects. Once the component satisfies the properties, it is

ready for use.

The final properties of a sintered component depend on several parameters such

as:

a) Size, shape, distribution, porosity, density, chemical composition, surface characteristics, etc. of particles.

b) Compacting pressure,type and amount of lubricant used, etc. c) Sintering temperature and time, type of sintering etc. d) Type of atmosphere.

Q 50) State the Significance of Sintering and Presintering

Tushar Lanjekar

Me 327

Ans:

1. Sintering is a method used to create objects from powders.It is performed to achieve

all possible final strength and hardness needed in the finished product.

2. Temperature,time and sintering atmosphere are three most important variables. It is

based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it

occurs much faster at higher temperatures.

3. In most sintering processes, the powdered material is held in a mold and then heated

to a temperature below the melting point. The atoms in the powder particles diffuse

across the boundaries of the particles, fusing the particles together and creating one

solid piece. Because the sintering temperature does not have to reach the melting point

of the material, sintering is often chosen as the shaping process for materials with

extremely high melting-points such as tungsten and molybdenum.

4. It may also be carried out under protective gas normally hydrogen orin a vacuum if

the material tends to react with the protective gas.

http://en.wikipedia.org/wiki/Powder_(substance)

http://en.wikipedia.org/wiki/Diffusion

http://en.wikipedia.org/wiki/Absolute_zero

http://en.wikipedia.org/wiki/Tungsten

http://en.wikipedia.org/wiki/Molybdenum

147

5. Sintering is traditionally used for manufacturing ceramic objects, but finds

applications in almost all fields of industry. The study of sintering and of powder-related

processes is known as powder metallurgy. A simple, intuitive example of sintering can

be observed when ice cubes in a glass of water adhere to each other.

6. Very high levels of purity and uniformity in starting materials

7. Preservation of purity, due to the simpler subsequent fabrication process (fewer

steps) that it makes possible

8. Stabilization of the details of repetitive operations, by control of grain size during the

input stages

9. Absence of binding contact between segregated powder particles – or "inclusions"

(called stringering) – as often occurs in melt processes

10. No deformation needed to produce directional elongation of grains

11. Capability to produce materials of controlled, uniform porosity.

Capability to produce near net shape objects.

Capability to produce materials which cannot be produced by any other

technology.

Capability to fabricate high strength material like turbines.

http://en.wikipedia.org/wiki/Ceramic

http://en.wikipedia.org/wiki/Powder_metallurgy

http://en.wiktionary.org/wiki/Purity

http://en.wikipedia.org/wiki/Manufacturing

http://en.wikipedia.org/wiki/Crystallite

http://en.wikipedia.org/wiki/Deformation_(engineering)

148

Significance of PRESINTERING

1. Presintering is the process of heating the green compact to a temperature below

the sintering temperature.

2. This is done to remove the lubricants and binders added during blending and to

increase the strength of the compact.

3. All metals do not require presintering.

4. Some metals like tungsten carbide are easily machined after presintering.After

sintering they become so hard that they cannot be machined.

Q 51) STATE THE ADVANTAGES OF NON CONVENTIONAL MACHINING PROCESS.

NAME – ARUN MANDAL

ROLL NO-ME 328

In view of the limiting characteristics of the conventional machining processes, a

considerable effort has been made during the last few decades in developing and

perfecting a number of newer methods which do not produce chips of the conventional

type. These processes are collectively called nonconventional machining processes. the

following are the various types of machining processes along with their advantages:

Electrical Discharging Machining(EDM)

ADVANTAGES OF EDM:

Can be used on even hard materials like tungsten carbide and alloys.

Good surface finish.

There are no defects due to elastic deformation.

149

Tool material need not be harder than work material.

Can machine even complicated shapes

Electrochemical machining (ECM)

ADVANTAGES OF ECM:

The process can be used for materials of any hardness as long as they are

conductors of electricity.

The process is fast with fairly good accuracy and surface finish.

No burrs are produced

The surface produced is free from mechanical stress

The process can easily be automated.

ULTRASONIC MACHINING(USM)

ADVANTAGES OF USM:

USM can perform machining operations like drilling ,milling and grinding on

any material irrespective of the fact whether the material is insulator or

conductor

Hard, brittle materials can be easily machined

150

There is no scrap loss due to breakage of delicate components during

processing

Multiple holes can be generated in one pass by combining a number of tools

Equipment is safe to operate

LASER BEAM MACHINING (LBM)

ADVANTAGES OF LBM

It can melt and vaporize any known material. even non metalic refractory materials

can be easily worked with.

It can produce holes with high L/D ratio

The heat affected zone is small. This can help in machining close to heat sensitive

areas

The ability to focus the beam at very narrow spots makes machining of extremely

small holes possible

High production rate

ELECTRON BEAM MACHINING (EBM)

151

ADVANTAGES OF EBM:

EBM can be used for metal removal, welding or annealing depending on the heat

density.

Very high velocities can be obtained by using enough voltage

The very precise control of the electron beam results in machining tolerances of

the order of 0.005mm

EBM can be used effectively for drilling or slot making in materials having

particularly having low melting points and low thermal conductivity.

Automatic multi beam set ups are available for increasing the rate of machining

PLASMA ARC WELDING(PAM)

ADVANTAGES OF PAM:

Cuts any metal that is electrically conductive

Faster than oxy fuel torch cutting by about 10-12 times

Can cut plates up to 150mm thick

ABRASIVE JET MACHINING (AJM)

152

ADVANTAGES OF AJM:

The process can easily machine brittle materials having thin sections and intricate

shapes which are not easily accessible

Very little heat is generated during the process so there is no heat affected zone or

change of microstructure.

The process is characterized by low power consumption and capital investment

Good surface finishes of 10 to 50 microns are possible with the process using finer

abrasives.

Q 52) Note on abrasive jet machine.

NAME: GIRISH H MARGAJE

ROLL NO: ME 330

Ans : In AJM,the material removal takes place due to the impingement of the fine

abrasive particle. These particle move with a high speed air steam. The abrasive

particles are typical of 0.025mm diameter and the air discharge at a pressure of several

atmospheres.

The fundamental principle of Abrasive jet machining involves the use of high-

speed stream of abrasive particles carried by a high pressure gas or air on

the work surface through a nozzle.

The metal removal occurs due to erosion caused by the abrasive particle

impacting the work surface at high speed. With repeated impacts, small bits

of material get loosened and fresh surface is exposed to the jet. Fig show the

schematic diagram of working process.

153

The filtered gas, supplied under a pressure of 2 to 8 kgf/cm2 to the mixture

chamber containing the abrasive powder and vibrating at 50Hz entrains the

abrasive particle and is passed into a connecting hose.

Nozzle mounted on a fixture at high velocity ranging from 150 to 300 m/min.

It,s controlled by the amplitude of vibration of the mixing chamber. Also

pressure regulator controls the gas flow and pressure. To control the size

and shape of the cut either the workpiece or the nozzle is moved by cams ,

pantrographs or other suitable mechanisms. The carrier gas should be

cheap,non-toxic and easily available.

Air and nitrogen are two of the most widely used gas in AJM. The abrasive

generally employed are aluminium oxide ,silicon carbide ,glass powder or

specially prepared sodium bicarbonate. Particle size vary from 10 to 50

microns. Larger size are used for rapid removal and smaller size for good

surface

In addition to the above abrasive, dolomite of 200 grit size is found suitable

for light cleaning and etching. Glass beeds of diameter 0.30 to 0.60mm are

light polishing and deburring. Since nozzle are subject to a great degree of

abrasion wear, they are made of hard material like as tungsten carbide or

synthetic sapphire

Since it,s made of tungsten carbide they an average life of 10 to20

hours,while those made of synthetic sapphire last for about 300 hours pf

operation when used with 27microns.Gases used are nitrogen, carbon

dioxide or clean air. The metal removal rate depends upon the diameter of

nozzle, composition of abrasive –gas mixture, jet pressure, hardness of

particle and that of work material, particle size, velocity of jet and distance of

workpiece from the jet.

A typical material removal rate for abrasive jet machining is 16mm3/min in

cutting glass.

Accuracy: With close control of the various parameter a dimensional tolerance of

0.05mm can be obtained .On normal production work an accuracy of 0.1mm is

easily held.

Applications: The process finds application in cutting slots, thin sections, contouring,

drilling, for producing shallow crevices, deburring, and for producing intricate shapes in

hard and brittle materials. It is often used for cleaning and polishing of plastics, nylon

and Teflon components, frosting of the interior surface of the glass tubes, etching of

marking on glass cylinder, etc .

154

Advantages: The advantage of AJM are:

1. Ability to cut intricate hole shapes in materials of any hardness and

brittleness.

2. Ability to cut fragile and heat-sensitive materials without damage as no

heat is generated due to the passing of gas or air.

3. Low capital cost.

Disadvantages: The disadvantages of the process lie in the following:

1. Material removal rate is slow and its applications is therefore limited.

2. The machining accuracy is poor and the nozzle wear rate is high.

3. Additional cleaning of the work surface may occur as there is a

possibility of sticking

abrasive grains in softer materials.

Water jet machining is another variation where a high pressure jet of

water is directed

on a surface to remove material.

155

Mechanics Of AJM: When an abrasive particle impinges on the work surface at a

high velocity, the impact causes a tiny brittle fracture and the

following air carries away the dislodged small workpiece

particle. This is shown in figure .

Abrasive Jet Machine Summary And Characteristics

The abrasive jet machines are manufactured and marketed by a

single manufacturer (namely, S.S. White Co., New York) under the name

“Abrasive jet machine“ Figure below shows the principal

features of an abrasive jet machine.

156

1) Mechanics of material removal Brittle fracture by impinging abrasive

grains at high speed

2) Media Air,CO2

3) Abrasive Al2O3,Sic. 0.025mm diameter,2-

20g/min,nonrecirculating

4) Velocity 150-300 m/sec

5) Pressure 2-10 atm

6) Nozzle WC, sapphire

Orifice area 0.05-0.2mm2

Life 12-300hr

Nozzle tip distance 0.25-

75mm

7) Critical parameters Abrasive flow rate and velocity, nozzle

tip distance from work surface, abrasive

grain size and jet inclination

8) Material application Hard and brittle metals, alloys, and non-

metallic materials (e.g., germanium, silicon,

glass, ceramics, and mica) Specially suitable

for thin sections.

9) Shape(job) application Drilling, cutting, deburring, etching,

cleaning,

10) Limitations Low metal removal rate (40 mg/min,

15mm3/min) , embedding of abrasive in

workpiece, tapering of drilled holes,

possibility of stray abrasive action.

Q 53) Write a note on Ultrasonic Machining

Daanish MukadamME-337

Anamil Mehta

Ans:

The term Ultrasonic is used to describe a vibratory wave of frequency above that of

upper frequency limit of the human ear i.e., above 16 kHz. The device for converting

any type of energy into mechanical vibrations, and for this piezo-electric effect in natural

or synthetic crystals or magne-tostriction effect exhibited by some metals is utilized.

‘Magne-tostriction’ means a change in the dimension occurring in ferromagnetic

materials subjected to an alternating magnetic field.

157

The basic USM process involves a tool(made of ductile and tough material) vibrating

with a very high frequency and a continuous flow of an abrasive slurry in the small gap

between the tool and the work surface. The tool is gradually fed with uniform force. The

impact of the hard abrasive grains fractures the hard and brittle work surface, resulting

in the removal of the work material in the form of small wear particles which are carried

away by the abrasive slurry. The tool material, being tough and ductile, wears out at

much slower rate.

The electronic oscillator and amplifier convert the available electrical

energy of low frequency to high frequency power of the order of 20 kHz which is

supplied to the transducer. The transducer operates my magnetostriction. The high

frequency power supply activates the stack of the magntostrictive material which

produces longitudinal vibratory motion of the tool. The amplitude of this vibration is

inadequate for cutting purposes. This is, therefore, transmitted to the penetrating tool

through a mechanical focusing device which provides an intense vibration of the desired

amplitude at the tool end.

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Feed mechanism

The objective of the feed mechanism is to apply the working force during the

machining operation. An instrument showing the movement of the tool indicates the

depth of machining. Ythe basic types of feed mechanisms are the

1. Counterweight type

2. Spring type

3. Pneumatic and hydraulic type

4. Motor type

Cutting rate:-

Cutting rate by using USM varies on certain factors are:

1. Grain size of abrasive..

2. Abrasive materials.

3. Concentration of slurry.

4. Amplitude of vibration.

5. Frequency.

Accuracy:-

The maximum speed of penetration in soft and brittle materials is of order 20 mm/min

but for hard materials the penetration rate is lower. Dimensional accuracy up to ±0.005

mm is possible and surface finishes down to a Ra value of 0.1-0.125μ can be obtained.

Limitations:--

The major limitation of the process is its comparatively low cutting rates. Tool

replacement is essential in the production of accurate blind holes. The tool material

employed in USM should be tough and ductile. The mass lengths of the tool also pose

difficulty as the tool material absorbs much of the ultrasonic energy, reducing the

efficiency. Longer tool causes overstressing.

159

The commonly used abrasives are: alumina, silicon carbide and diamond dust. The

abrasive slurry is circulated to the work tool interface by pumping. A refrigerated cooling

system is used to cool the abrasive slurry to a temperature of 5 to 6˚C. The liquid to

produce abrasive slurry should have the following characteristics:

1. Good wetting characteristic

2. Low viscosity.

3. High thermal conductivity.

4. Anti-corrosive property.

5. Approximately having equal density with abrasive.

6. Low cost.

`The size of abrasive varies between 200 and 2000 grit. Coarse grades are good for

roughing, whereas finer grades are used for finishing. Fresh abrasive cut better and the

slurry therefore is replaced periodically.

Application:-

The simplicity of the process makes it economical for a wide range of applications such

as:

1. Introducing round holes and holes of any shape for which a tool can be made.

The range of obtainable shapes can be increased by moving the work piece

during cutting.

2. In performing /machining operations like drilling , grinding, prosiling and milling

operations on all materials both conducting and non-conducting.

3. In machine glass, ceramic .tungsten and other hard carbides, gem , stones such

as synthetic ruby

4. In cutting threads in components made of hard metals and alloys by

approximately rotating and translating eithers the work piece or the tool.

5. In making tungsten carbide and diamond wire drawing dies and sies for forging

and extrusion processes.

6. Enabling a dentist to drill a hole of any shape on teeth without creating any pain.

Summary:-

Mechanics of removal Brittle fracture caused by impact of

abrasive grains due

Tool vibrating at high frequency.

Medium Slurry

Abrasives B4C, SiC, Al2O3, Diamond 100-800 grit size

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Vibration

Frequency 15-30 kHz

Amplitude 25-100 µm

Tool

Material Soft Steel

Material Removal Rate 1.5 for WC work piece, 100 for glass

work piece

Tool wear rate

Gap 25-40 µm

Critical parameters Frequency, amplitude, tool material, grit size.

Abrasive material, feed force, slurry

concentration, slurry viscosity

Materials Application metals and alloys, semiconductors, non-

metals

Shape Application Round and irregular holes, impressions

Limitations Very low mrr, tool wear, depth of holes and

cavities small

Q 54) ELECTRO-CHEMICAL MACHINING

Name: Milton Menezes

Roll No: Me332

Branch: Mechanical

Ans: Electro-chemical machining is the process of metal removal by the controlled dissolution

of the anode of an electrolytic cell, for the metal and alloys which are difficult or impossible to

machine by mechanical machining process.

It is based on Michael Farada ’s La of Electrol sis.

WORKING OF ECM:

In the actual process, the cathode is tool shaped, more or less like the mirror image of

the finished work piece. The work piece is connected to the positive supply. The tool or

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cathode, connected to the negative terminal, is advanced towards the anode (work piece)

through the electrolyte that completes the electrical circuit between the anode and cathode

Electrolyte that completes the electrical circuit between the anode and cathode. Metal is then

removed from the work piece through electrical action, and the cathode (tool) shape is

reproduced on the work piece. The electrolyte bath is pumped at high pressure through gap

between the work piece and tool must be circulated at a rate sufficiently high to conduct

current between them and carry heat. The electrolysis process that takes place at the cathode

liberates hydroxyl ions (negatively charged) and free hydrogen. The hydroxyl ions combine with

the metal ions of the anode to form insoluble metal hydroxides and the material is thus

removed from the anode. The process continues and the cathode (tool) reproduces its shape in

the work piece (anode). The tool does not contact the work piece producing no direct friction

and, therefore, does not wear and no heat build-up occurs.

The electric current is of the order of 50 to 40,000 A at 5 to 30 V D.C for current density

of 20 to 300 A/cm^2, across a gap of 0.05 to 0.7 mm between the tool and the work piece. The

electrolyte flows through this gap at a velocity of 30 to 60 m/s forced by an inlet pressure of

about 20 kgf/cm^2. Suspended solids are removed from the electrolytes by setting,

centrifuging, or filtering, and the filtered electrolyte is recirculated for use.

The electrolysis process:

In the electrolytic circuit shown in fig.20.6 the electron-flow is from, the work piece, through

the power supply to the tool. Many chemical reactions occur at the cathode, the anode, and

the electrolyte.

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At the cathode the following reactions are possible:

1. M+ + e- M (M denotes any metal)

2. 2H+ +2e- H2 (hydrogen evolution)

The following reactions occur at the anode with a halogen electrolyte:

1. M M+ + e- (metal dissolution)

2. 2H2O O2 + 4H+ + 4e-

3. 2Cl- Cl2 + 2e-

It has been established that the metal dissolution reaction is main or the only reaction that

occurs. As an example, let the machining of iron in a NaCl electrolyte can be considered.

Fe Fe++ + 2e-

NaCl Na+ + Cl-

2H2O + 2e- 2(OH)- + H2

Fe++ + 2(OH)- Fe(OH)2

Fe (OH)2 + Air Fe(OH)3

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2Fe + 4H2O + O2 2Fe (OH)3 + H2

At the cathode, the reaction products are FeCl2, Fe(OH)2, FeCl(OH), Fe(OH)3 which form a

layer. Thus, it is seen how iron is removed by electrolytic action. It is interesting to note that the

salt is not being consumed and the metal is being machines at the expense of electrical energy

and a little of water. The electrolyte acts only as a carrier of current. From this it can further be

seen that current of 1000 A would dissolve iron at the rate of about 15 g/min, and the generate

hydrogen and the rate of about 300 cm3/min.

APPLICATION:

The main application of ECM process are in machining of hard-heat-resisting alloys, for

cutting cavities in forging dies, for drilling holes, machining of complex external shapes like that

of turbine blades, aerospace components, machining of tungsten carbide and that of nozzles in

alloy metal. Almost any conducting material can be machined by this method.

ADVANTAGES:

1. The metal removal rate by this process is quite high for high strength-temperature-resistance

(HSTR) materials compared to conventional machining processes.

2. Residual stress is low.

3. It can machine configurations which are beyond the capability of conventional machining

process.

4. Surface finish is in the order of 0.2 to 0.8 microns.

5. Tool wear is nearly absent.

6. Extremely thin metal stocks can be easily worked without ______.

DISADVANTAGES:

1. The specific power consumption in this process is nearly 100 times more than in turning or

milling steel.

2. Non-conducting materials cannot be machined.

3. Conversion and rust of ECM machine can be hazard. But preventing measures can help in this

regard.

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Q 55)ELECTRIC-DISCHARGE MACHINING(EDM)

BY:-SRIJITH MENON

ROLL NO:-ME333

DEPARTMENT:-MECHANICAL

PRINCIPLES OF EDM:-

●EDM is a non-traditional way of machining.

●InEDM,the spark is pulsed at frequencies ranging from a few hundred to several

hundred thousand kilohertz.

●The workpiece and electrode are separated by a dielectric.

●The dielectric is usually a low-viscosity hydrocarbon or mineral oil.

●The tool and the workpiece are brought together,the gap between them is maintained

by a servomechanism comparing actual gap voltage to preset reference voltage.

●The gap is raised until the dielectric barrier is ruptured,which usually occurs at a

distance of 0.001in.(0.03 mm) or less and at about 70V.

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●Technically,thedielecric is ionized to form a column or a path between the work piece

and the tool so that a surge of current takes place and the spark is produced.

●The spark discharge is contained in a microscopically small area,but the force and the

temperatures resulting are impressive.

●The temperatures around 10,000˚C and pressures many thousand times greater than

the atmospheric are created,all in less than 1µs for each spark.

●Thus the minute part of the workpiece is vaporized.

●The metal is expelled as the column of ionized dielectric vapor collapses.

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●The tiny particles are cooled into spheres and are swept away from the machining gap

by the flow of dielectric fluid.

ELECTRODE MATERIALS:-

●The selection of the electrode material depends on the:-

(i) material removal rate,

(ii) wear ratio,

(iii) ease of shaping the electrode,

(iv) cost.

●The most commonly-used electrode materials are

brass,copper,graphite,Alalloys,copper-tungsten alloys and silver-tungsten alloys.

●The methods used for making the electrodes are:-

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(i) conventional machining(used focopper,brass,Cu-W alloys,Ag-W alloys and graphite),

(ii)casting (used for Zn base die casting alloy, Zn-Sn alloys and Al alloys),

(iii) metal spraying,

(iv) press forming.

●Flow holes are normally provided for the circulation of the dielectric and these holes

should be as large as possible for rough cuts to allow large flow rates at a low pressure.

DIELECTRIC FLUIDS:-

●The basic requirements of an ideal dielectric fluid are:-

(i) low viscosity,

(ii) absorbence of toxic vapours,

(iii) chemical neutrality,

(iv) low cost.

●Ordinary water posseses all these properties,but since it causes rusting in the work

and machine,it is not used.

●The most commonly-used type of fluid is hydrocarbon(petroleum) oil,Kerosene,liquid

paraffin and silicon oils are also used as dielectric fluids.

TOOL ELECTRODE WEAR:-

●During the EDM operation,the electrode(i.e. the tool) gets eroded due to the sparking

action.

●The materials having good electrode wear characteristics are the same as those that

are generally difficult to machine.

●One of the principle materials used for the tool is Graphite which goes directly to the

vapor phase without melting.

●The war ratio (Rq),defined by the ratio of the material removed from the work to the

material removed from the tool,is found to be related to Ro,

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Ro=melting point of the work/melting point of the tool,

As,

Rq≈2.25 Ro-2.3

APPLICATIONS:-

●The most frequent use of EDM is for tool and die work and moulds of plastic.

SUMMARY OF EDM CHARACTERISTICS:-

●Mechanics of material removal :- Melting and evaporation

aided by cavitation.

●Medium :- Dielectric fluid.

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●Tool Materials :-Cu,brass,Cu-W alloy,

Ag-W alloy,Graphite.

●Material removed rate/tool wear rate:- 0.1-10

●Gap :- 10-125µm.

●Maximum Material Removal Rate :- 5×103 mm3/min.

●Specific Power Consumption(typical) :- 1.8W/mm3/min.

●Critical Parameters :-Voltage,Capacitance,

Spark Gap,Di-electric Circulation,

Melting temperature.

Q56.Write a note on Electron Beam Machining. (by Aniket Mhatre) Ans:-Electron Beam Machining is the metal removal process by a high velocity focused

stream of electrons which heats, melts and vaporizes the work material at the point of bambardment. Principle: A beam of electrons is emitted from the electron gun which is basically a triode consisting of

A cathode which is a hot tungsten filament (25000C) emitting high negative potential electrons.

A grid cup, negatively based with respect to the filament.

An anode which is heats at ground potential, and through which the high velocity electrons pass.

Diagram:

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Working:

The gun is supplied with electric current from a high voltage D.C. source.The flow of electrons is controlled by the negative bias applied to the grid cup.The electrons passing through the anode are accelerated to two-thirds of the velocity of lightby applying 50 to 150 kV at the anode,and this speed is maintained till strike the workpiece. Due to the pattern of the electrostatic field produced by the grid cup,the elecrons are focused and made to flow in the form of converging beam through a hole in the anode. A magnetic deflection coil is used to make the electron beam circular having a cross-sectional diameter of 0.01 to 0.02 mm and deflect it anywhere. A built-in microscope with a magnification of 40 on the workpiece enables the operator to accurately locate the beam impact and observe the actual machine operation. As the beam impacts on the workpiece surface the K.E. of high velocity electrons are immediately converted into the thermal energy and it vaporized the material at the spot of its impact.The power density being very high(about 1.5 billion W/cm3). Advantages:

1.EBM is an excellent method for microfinishing. 2.It can drill holes or cut slots which otherwise cannot be made. 3.It is possible to cut any known materials, metal or nonmetal that can exist in vacume. 4.Due to no cutting tool pressure, distortion-free machining having precise dimensions can be achieved. Disadvantages:

1.High equipment cost . 2.It requires employment of high skill operator. 3.Only small cuts are possible. 4.Requirement of vacume restricts the size of specimens that can be machined. Application of EBM: 1.To drill fine gas orifaces, less than 0.002mm, in space nuclear reactors, turbine blades for supersonic Aero-engines. 2.To produce metering holes in injector nozzles in diesel engines. 3.To scribe thin films. 4.To remove small broken taps from holes. SUMMARY OF EBM CHARACTERISTICS

Mechanics of material removal Melting, vaporizing Medium Vacume Tool Beam of electrons moving at very high velocity Maximum material removal rate 10 mm3/min. Specific power consumption 450 W/mm3-min (typical) Critical parameters Accelerating voltage, beam current, beam

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Diameter, work speed,material temperature Materials application All materials Shape application Drilling fine holes, cutting contours in sheet, Cutting narrow slots Limitations Very high specific energy consumption, necessity of vacume,expensive machine

Q 57) Note on laser beam machining?

J. mohammed muktharali (SE- MECH)

Me 335

Ans: Laser is an electromagnetic radiation. It produces monochromatic light

which is in the form of an almost collimated beam that can be focused optically on to

very small spots of less than 0.002 mm dia. The word ‘LASER’ stands for ‘Light

Amplification by Stimulated Emission of Radiation’.

Principle:

The presence of light of the appropriate frequency stimulated emission will

occur in the upper energy level when the atoms will begin to emit and chain reaction will

occur by causing more to emit and the whole avalanche would dump down together.

This is called lasing action.

172

A basic laser circuit consist of three parts:

(1)a pair of mirrors,

(2) a source of energy and

(3)an optical amplifier is popularly called the laser.

173

To these basic parts must be added a control system and a cooling system.

In the operation the work piece to be cut is placed on the Aluminium

worktable (which is resistant to being cut by laser beam). The laser head is traversed

over the work piece and an operator visually inspect the cut while manually adjusting

the control panel. The actual profile is obtained from linked mechanism, made to copy

the matter drawing or actual profile, placed on a near-by bench.

The laser is short pulses, has a power output of nearly 10kW/cm^2 of the beam

cross section .BY focusing a laser beam in a spot 1/100 of a square mm is size.the

beam can be concentrated in short flash to power density of 100,000kW/cm^2 and an

energy of several joules lasting for a minute fraction of seconds .

174

The mechanism by which a laser beam removes material from the surface

being worked involves a combination of melting and evaporation process , with some

materials, mechanism is purely of evaporation .

Machining rate:

Laser can be used for cutting as well as for drilling .The material removal rate in

LBM is comparatively low and is of the order of the 4000mm3/hr. the cutting is found

from the following relationship:

Application of LBM:

Laser machining process Is at present found to be suitable only in exceptional cases

like machining very small holes and cutting complex profile in thin, hard material like

ceramic. It is also used in partial cutting or engraving. Other

Advantages:

1. There is no direct contact between the tool and the work piece.

2. Machining of any material including nonmetal is possible.

3. Drilling and cutting of area not readily accessible or possible

4. heat affected zone is small because of the collimated beam.

5. Extremely small holes can be machined.

6. There is no tool wear.

7. Soft material like rubber and plastics can be machined.

Limitation:

1.Its overall efficiency is extremely low (10 to 15 per cent).

2. The process is limited to thin sheets.

3. It has very low material removal rate.

4. The machined holes are not round an straight.

5. The laser system is quite troublesome since the life of the flash lamp is short.

6. Cost is high.

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7. Output energy from LASER is difficult to control precisely.

SUMMARY OF LBM CHARACTERISTICS

Mechanics of material removal Melting ,vaporization

Medium Normal atmosphere

Tool High power laser beam Critical parameters

Beam power intensity,

Beam diameter ,melting temperature

Materials application All materials

Shape application Drilling fine holes

Limitations Very large power consumption, cannot

cut materials with high heat conductivity

and high reflectivity

Q 58) Write a note on plasma arc machining

Onkar Mohite

Me 336

Ans: 1. When a flowing gas is heated to a sufficiently high temperature to

become partially ionized it is known as ‘plasma’. This is virtually a mixture of free

electrons, positively charged ions and neutral atoms.

2. Plasma arc machining is a material removal process in which the

material is removed by directing a high velocity jet of high temperature (11,000 to

30,000 0C) ionized gas on the work piece.

3. In a plasma torch, known as the gun or plasmatron, a volume of gas

such as H2, N2, O2, etc, is passed through a small chamber in which a high frequency

spark (arc) is maintained between the tungsten electrode (cathode) and the copper

nozzle (anode), both of which are water cooled.

176

4. In certain torches an inert gas-flow surface rounding the main flame is provided to

shield the gas from atmosphere. The high velocity electrons generated by arc collide

with the gas molecules and produce dissociation of diatomic molecules of the gas

resulting in ionization of the atoms and causing large amounts of thermal energy to be

liberated.

5. The plasma forming gas is forced through a nozzle duct of the torch in

such a manner as to stabilize the arc. Much of the heating of the gas takes place in the

constricted region of the nozzle duct resulting into relatively high exit gas velocity and

very high core temperature up to 30,000 0C.

6. The plasma jet melts the work piece material and the high velocity gas

stream effectively blows the molten metal away. The material removal rate can be

increased by increasing gas flow rates.

7. The depth of heat affected zone depends on the work material, its

thickness and cutting speed. On a work piece of 25mm thickness the heat affected zone

is about 4mm and it is less at high cutting speeds.

8. Typical flow rate of the gas is 2 to 11 m3/hr. Direct current, rated at

about 400V and 200kW output is normally required. Arc current ranges gas flow is

delivered to the nozzle at pressure up to 1.4MPa.

Accuracy: This is a roughing operation to accuracy of about 1.5mm with corresponding

surface finish. Accuracy on the width of slots and diameter of holes is ordinarily from

±0.8mm on 6 to 30mm thick plates, and ±3.0mm on 100 to 150mm thick plates.

Applications of PAM: This is chiefly used to cut stainless steel and aluminum alloys.

Profile cutting of metals, particularly of these metals and alloys, has been used

successfully in turning and milling of materials which are hard and difficult to machine.

177

Advantages and limitations: The principal advantage of this process is that it is almost

equally effective on any metal, regardless of its hardness of refractory nature. There

being no contact between the tool and work piece, only a simply supported work piece

structure is enough.

The main disadvantages of this process are the metallurgical change of the surface and

low accuracy. Safety precautions are necessary for the operator and those in near-by

areas. This adds additional cost.

Characteristics:

Technique: Heating of workpiece by high temperature ionized plasma and

causing quick melting

Tool: Plasma jet

Critical parameters: Voltage, Current, Electrode gas flow rate, Nozzle dimensions,

melting temperature.

Material of workpiece: All materials which conduct electricity

Shape application: cutting plates

Limitation: Low accuracy

Q 59] Note on ion beam machining?

NAME: JOEL. K .REJU

BRANCH : MECHANICAL

-An ion beam is a type of particle beam consisting of ions.

-Ion beams have many uses in electronics manufacturing (principally ion implantation) and

other industries.

-Ion beam machining takes place in a vacuum chamber, with charged atoms (ions) fired from an

ion source towards a target (the workpiece) by means of an accelerating voltage.

-The process works on principles similar to electron beam machining, the mechanism of

material removal is quite different.

Ion beam machining (IBM) is closely associated with the phenomenon of sputtering.

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ION BEAM MACHINING APPARATUS:

PRINCIPLE OF ION BEAM MACHINE

-When an ion strikes the surface of a material it usually collides with an atom there.

-This collision often occurs in a direction that is normal to the surface.

179

-On the one hand, if the mass of the ion is less than that of the atom of the surface, the former,

will bounce back, away from the surface; and the atom will be driven in a direction further into

the material.

-On the other hand, if the mass of the incident ion is greater than that of the surface atom,

-after collision, the ion and atom move from the position of collision towards the interior of the

surface of material.

-Usually both particles move into the material at energies that are less than that of the incident

ion, yet much greater than the lattice energy.

IBM SYSTEM:

APPLICATIONS OF IBM

-Ion beams can be used for sputtering or ion beam etching and for ion beam analysis.

180

-Ion beam etching, or sputtering, is a technique conceptually similar to sandblasting, but using

individual atoms in an ion beam to ablate a target.

-Reactive ion etching is an important extension that uses chemical reactivity to enhance the

physical sputtering effect

1] ION BEAM ETCHING

-Removin atoms b s tterin ith an inert as is called ‘ion millin ’ or ‘ion etchin ’.

-Sputtering can also play a role in reactive ion etching (RIE), a plasma process carried out with

chemically active ions and radicals, for which the sputtering yield may be enhanced significantly

compared to pure physical sputtering.

2] ION BEAM SPUTTERING

-Ion-beam sputtering (IBS) is a method in which the target is external to the ion source.

-A source can work without any magnetic field like in a Hot filament ionization gauge . In a

Kaufman source ions are generated by collisions with electrons that are confined by a

magnetic field as in a magnetron.

- They are then accelerated by the electric field emanating from a grid toward a target.

3] SMOOTHING

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The use of IBM for smoothing of laser mirrors and for modifying the thickness of thin films and

membranes without affecting surface finish .

4]TEXTURING

-Hudson has demonstrated that an ion-beam source is a controlled method for texturing

surfaces.

-A typical result is presented which a structure resembling closely packed cones was produced.

-As well as the nickel and copper, Hudson went on to investigate 26 materials, including

stainless steel, silver and gold.

ADVANTAGES OF IBM:

-Low temperature processing reduces handling an stress problems.

-No dimensional changes

-Good adhesion of treated surface

-New alloys possible

-Can improve corrosion, oxidation, wear, hardness, friction, fatigue

DISADVANTAGES OF IBM

-Ver shallo treatment < μm

-High cost

-The surface can be weakened by radiation effects

Q 60)Write a note on chemical machining

Jay Nibandhe

S.E.MECH-339

Ans:

Chemical machining is the stock removal process for the production of desired

shapes and dimensions through selective or overall removal of material by controlled

chemical attack with acids or alkalis .The metal is gradually transformed into metallic

salt by chemical reaction and is ultimately removed in this form. Areas from where

material, known as ‘MASKANT’ and ‘RESIST’ .Nearly all the materials,from metals to

ceramics ,can be chemically machined .

182

The component to be machined is first cleaned in a solution of mild alkali at 80°C to

90°C ,followed by washing in clean water. One of the roughest methods is to coat the

component all over by spraying or dipping. This removes dust and oil . The cleaning

ensures a good adhesion of the coating or masking agent which is applied to protect the

portions of which are not to be machined. After cleaning the component is dried and

coated with the maskant material which must be cut and peel photoresist or screen-

print, type. Finally, the metal is removed by etching. The process can be suitably

applied to different types of operations such as milling, blanking, and engraving. The

different chemical machining processes can be classified as:

1) Chemical milling

2) Chemical engraving

3) Chemical blanking

1) Chemical milling

Sometimes called Chemilling or contour machining or etching is used mainly to produce

shapes is used mainly to produce shapes by selective or overall removal of metal parts

from relatively large aurface areas. The main purpose is to achieve shallow but

complex profiles, reduction in weight by removing unwanted material

from the surface as in the skin of an aircraft .

Chemical milling entails four steps:

1) Cleaning 3) Etching

2) Masking 4) De-masking

The components are thoroughly cleaned and degreased by immersion in

trichloroethylene vapour or some alternative chemical cleaner followed by

washing in clear water . The component is then coated with a cut and peel

maskant by brushing , dipping or spraying (0.2mm).This can be suitable fluid with

a neoprene base or some alternative plastics solution impervious to the action of

the etching agent .When dried , by mild heating or otherwise the desired shape to

be processed on the work material is cut on the maskant with sribe knife and the

unmachined portions of the maskant are peeled away .

MASKANT MATERIALS FOR DIFFERENT METALS

METAL ETCHANT TEMP °C MASKANTS

Aluminium Alkaline 90 Acrylonitrile rubber, butyl

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rubber

Ferrous metals Acid 54 Polyvinyl chloride, polyethelene butyl rubber

Magnesium Acid <38 Polymers

Titanium Acid 20-35 Translucent chlorinated polymers

Beryllium Acid 20-54 Vinyl, neoprene, butyl

Nickel Acid 45-50 Neoprene

2) Chemical engraving

This process is done by masking the entire mold, mold inserts to

ejector pins, etc., leaving only the area where the logo or copy is to be

placed. After this process is complete the Verbiage is then placed on

the area instructed and submerged in an acid bath . This process

allows the customer to have their logos, instruction verbiage, etc.

anywhere on their mold cavity or core where more economical ways

are prohibited. Whether you would like the engraving etched to a

specified depth or you want to create your company's logo or verbiage

with a texture surrounding the graphics, we can do it. This is created

by generating an acid resist film from your supplied electronic file or

camera-ready artwork.

184

3) Chemical blanking

Chemical Blanking is similar to the blanking of sheet metals and it is applied to

produce features, which penetrate through the thickness of the material, with the

exception that the material is removed by chemical dissolution rather than by shearing.

Typical applications for chemical blanking are the burr-free etching of printed-circuit

boards, decorative panels, and thin sheet metal stampings, as well as the production of

complex or small shapes. It is otherwise called as Chem-blanking, Photo forming, Photo

fabrication, or Photo etching. In this process, the metal is totally removed from certain

areas by chemical action. The process is used chiefly on the sheets and foils. This

process can work almost any metal, however, it is not recommended for material thinner

than 2 mm. A Schematic sketch of the chemical blanking process is shown in Figure-2.

The work piece is cleaned, degreased and pickled by acid or alkalis. The cleaned metal

is dried and photo resist material is applied to the work piece by dipping, whirl coating or

spraying. It is then dried and cured. The technique of photography has been suitably

employed to produce etchant resistant images in photo resist materials. This type of

maskant is sensitive to light of a particular frequency, usually ultraviolet light, and not to

room light. This surface is now exposed to the light through the negative, actually a

photographic plate of the required design, just as in developing pictures. After exposure,

the image is developed. The unexposed portions are dissolved out during the

developing process exposing the bare metal. The treated metal is next put into a

machine, which sprays it with a chemical etchant, or it may be dipped into the solution.

The etching solution may be hydrofluoric acid (for titanium), or one of the several other

chemicals. After 1 to 15 minute, the unwanted metal has been eaten away, and the

finished part is ready for immediate rising to remove the etchant. Chemical blanking by

using photo resist maskants can suitably make printed circuit boards and blanking of

intricate designs.

The advantages of this process are summarized below:

Very thin material (0.005 mm) can be suitably etched.

High accuracy of the order of plus or minus 0.015 mm can be maintained.

High production rate can be met by using automatic photographic technique.

185

Advantages of CHM Disadvantages of CHM

Easy weight reduction

Corrosive etchant damages the equipment

No effect of workpiece materials properties such as hardness

Metal thicker than 2 mm cannot be usually machined

The good surface quality Simultaneous material removal operation

No burr formation

Requirement of high skilled worker

No stress introduction to the workpiece

Applications of CHM

1) Removal of metal from a portion or the entire surface of formed or irregularly

shaped parts such as forgings, casting, extrusions or formed wrought stock .

2) Manufacture of burr-free, intricate stampings.

186

Q 61) Note on Electrochemical Grinding.

Name: Chetan Dattatray Niladhe.

Branch: Mechanical R No:340

Ans:

Electrolyte grinding is a modification of both the grinding and electrochemical machining . In

this process, machining is affected both by the grinding action and by the electrochemical

rocess. Hence in the tr e sense it ma be called ‘mechanically assisted electrochemical

machinin ’.

In ECG, the metal bonded grinding wheel impregnated with a non conductive abrasive is made

the cathode & the workpiece the anode as in ECM .The electrolyte ,which is usually sodium

nitrite ,with a concentration of 0.150 to 0.300 kg/lit of water ,is passed through nozzle in the

machining zone in order to complete the electrical bridge between the anode & the cathode

.The work & wheel do not make contact with each other because they are kept apart by the

insulating abrasive particles which protrude from the face of the grinding wheel .A constant gap

of 0.025mm is maintain into which a stream of electrolyte is directed the electrolyte is carried

past the work surface at high speed by the rotary action of the grinding wheel .with the rotation

of grinding wheel ,metal is removed from the workpiece by the simultaneous electrolyte &

abrasive action .Actually ,abrasive grains on the surface of the wheel serve to act as a paddle

which pick up the electrolyte & cause a pressure to a build-up at the work area .The

phenomena of metal removal is illustrated in the fig .shown below.

Electrochemical grinding.

187

The wheel & work conditions are shown below. The electrolyte is entrapped in small cavities of

semi conductive oxide between projecting nonconductive abrasives forming electrolytic cell.

When the cells come in contact with the work the current flows the wheel to the work & these

leads to the electrochemical composition of work. The short circuiting between the wheel &

work is prevented due to point contact made by abrasion in order to make the surface more

receptive.

The wheel and work condition in electro-chemical grinding.

ELECTROCHEMICAL MACHINING PLANT

The stiffness and the material of the components are the few important points that

should be kept in mind when designing an electrochemical machine. Though, at a first

glance, it appears that the machining force is negligible as there is no physical contact

between the tool and the workpiece surface, very large forces may develop between

them due to the high pressure of the electrolyte required to maintain an adequate flow

velocity through the narrow gap . So, the machine must possess enough rigidity to avoid

any significant deflection of the tool which may destroy the accuracy of the parts being

machined. A change of temperature may also cause some relative displacement

between the tool and the workpiece, and the design should take care of it.

To avoid corrosion, wherever possible, the non-metallic materials should be used.

When the strength and stiffness are required, the plastic coated metals should be used.

The material used to hold the workpiece is exposed to anodic attack, and Ti appears to

be most suitable because of its passivity. When different metals are in contact in the

188

presence of the electrolyte, especially when the machine is idle, corrosion may occur. To

minimize this, the metals are in contact should be so chosen that they do not differ

much in their electrochemical behaviour. The slideways cannot be protected

permanently, and so they are heavily coated with grease. Sometimes a corrosion

protection may be provided by applying a small electrical potential in such a direction

that the whole structure more noble electrochemically. This is commonly known as

cathodic protection.

The pump is the most important element of the ancillary plant. Generally, the positive

displacement pumps made of stainless steel. The tank for the electrolyte, the pipeline,

and the valves are normally made of PVC. The schematic diagram of ECM as shown

below:

Electrochemical machining plant

SUMMARY OF ECM CHARACTERISTICS

Mechanics of material removal Electrolysis

Medium Conducting electrolyte

Tool materials Cu, brass ,steel

Material removal rate /Tool wear rate

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Gap 50-300 mm

Maximum material removal rate 15*10^3 mm^3/min

Specific power consumption 7 W/mm^3/min

Critical parameters Voltage, current, feed rate, electrolyte& conductivity

Materials application All conducting metals and alloys.

Shape application Blind complex cavities, curved surfaces,

through cutting, large through cavities.

Limitations High specific energy consumption, not

applicable with electrically non conducting

materials and for jobs with very small

dimension, expensive machine.

Q 62)Explain the classification of un-conventional machining processes

Gaurav Pandey

Ans:

Types of energy Basic mechanism of metal removal

Transfer media Energy source Processes

Mechanical Erosion shear High velocity particles. Physical contact

Pneumatic/hydraulic pressure Cutting tool

AJM,USM Conv.machining

Chemical Chemical ablation

Reactive environment

Corrosive agent CHM

Electro-chemical

Ion displacement

Electrolyte High current ECM,ECG

Thermo-electric Fusion Hot gases Ionized material IBm

190

Vaporization Electron Radiation

High voltage Amplified light

PAM EBM EDM LBM

Mechanical

Abrasive Jet Machining (AJM)

Ultrasonic Machining (USM)

Chemical

Chemical Machining (CHM)

Electro-chemical

Electro-Chemical Matching (ECM)

Electro-Chemical Grinding (ECG)

Thermo-electric

Ion-Beam Machining (IBM)

Plasma Arc Machining (PAM)

Electrical Discharge Machining (EDM)

Electron-Beam Machining (EBM)

Laser-beam Machining (LBM)

Q 63) Note on material application of various unconventional process.

NAME- Pankaj B. Patil,

R. No.- Me 342

MATERIAL APPLICATION OF NON-TRADITIONAL MACHINING

Process Aluminium steel Super Alloy

Titanium

Refrac- tories

Ceramics Plastic Glass

USM P F P F G G F G

AJM F F G F G G F G

ECM F G G F F N N N

CHM G G F F P P P F

191

EDM F G G G G M N N

EBM F F F F G G F F

LBM F F F F P G F F

PAM G G G F P N P N G= Good, P= Poor, F= Fair, N= Not applicable.

Q64.Write A note process capability of various unconventional machining.

Name- Lovleen T. Phadtare

Roll no- ME 345

PROCESS MRR mm3/min

TOLERANCE (micron)

SURFACE FINISH (micron)

DEPTH OF SURFACE DAMAGE (micron)

POWER (watts)

USM 300 75 0.2—0.5 25 2400

AJM 0.8 50 0.5—1.2 25 250

ECM 15000 50 0.1—2.5 5 1,00,000

CHM 15 50 0.5—2.5 125 —

EDM 800 15 0.2—1.2 250 2700

EBM 1.6 25 0.5—2.5 125 15O(average) 200(peak)

LBM 0.1 25 0.5—1.2 500 2(average) 2000(peak)

PAM 75 125 ROUGH 500 50,000

CONVENTIAL MACHINING

50,000 50 0.5—5 25 3000

192

Q 65) Differentiate between welding, soldering ,brazing and riveting

Anita Gupta

SE Auto

WELDING SOLDERING BRAZING RIVETING

1. These are the

strongest joints

usedto bear the

load.Strength of a

weldedjoint may be

morethan the

strength ofbase

metal.

These are weakest

joint out of three.

Notmeant to bear

theload. Use to

makeelectrical

contactsgenerally.

These are stronger

than soldering but

weaker than

welding.These can be

used tobear the load

uptosome extent.

These are

stronger than

soldering,

brazing but

weaker than

welding. Their

metals are

chosen largely

for their

tolerance for

cold forging.

2. Temperature

requiredis upto

3800ºC ofwelding

zone.

Temperature

requirement is

upto450ºC.

It may go to 600ºC

inbrazing.

It may vary

from 225° C to

550° C in

riveting.

3.

Work piece to be

joined need to be

heated till their

melting point.

No need to heat the

work pieces.

Work pieces are

heated but below

their

melting point.

Work pieces

are heated at

the right

temperatures.

4. Mechanical

propertiesof base

metal may

change at the joint

due

to heating and

cooling.

No change in

mechanical

properties after

joining.

May change in

mechanical

properties

of joint but it is

almost

negligible.

No change in

mechanical

properties but

it decreases

the physical

properties of a

substrate.

5. Heat cost is involved

and high skill level

is

required.

Cost involved and

skill requirements

are

very low.

Cost involved and

skill

required are in

between others two

Cost is

involved and

skill

requirements

is high and

shared by 4 of

a team.

6. Heat treatment is

generally required to

eliminate

undesirable

No heat treatment is

required.

No heat treatment is

required after

brazing.

Heat

treatment is

required before

riveting.

193

effects of welding.

7. No preheating of

work piece is

required

before welding as it

is

carried out at high

temperature.

Preheating of

work pieces before

soldering is good for

making good quality

joint.

Preheating is

desirable

to make strong joint

as

brazing is carried out

at relatively low

temperature.

Metal is

heated to

make it

expand, and as

it cools the

contraction

further

tightens the

joint.

8.

9. Welding has its

applications in

Shipbuilding,

aerospace, railway

rolling stock,

automotive industry

Soldering is used in

Electronic circuits,

Wire joining,

Automobile

radiators,Joining of

aluminium

Wires, Plumbing, etc.

Brazing is used in

making of

condensers in

transportation,

making drill bits in

construction sites

and in aerospace

industry include

wing and jet engine

components.

Riveting is still

widely used in

applications

where light

weight and

high strength

are critical,

such as in an

aircraft.

Q66: Explain the classification of welding methods

ANS:

There are about 35 different welding and brazing processes and several soldering

methods in use by industry today.

There are various ways of classifying the welding and allied processes. For example,

they may be classified on the basis of:

i. Source of heat, i.e., flame, arc, etc.

194

ii. Type of interaction i.e., liquid/liquid (fusion welding) or solid/solid (solid state

welding).

In general, various welding and allied processes are classified as follows:

1. Gas Welding

Air-acetylene welding

Oxy-hydrogen Welding

Oxy-acetylene welding

Pressure gas Welding

2. Arc Welding

Carbon Arc Welding

Flux Cored Arc Welding

TIG (or GTAW) Welding

Plasma Arc welding

Electroslag Welding and Electro gas welding

Stud Arc Welding

Shielded Metal Arc Welding

Submerged Arc Welding

MIG ( or GMAW) Welding

3. Resistance Welding

Spot welding

Seam welding

Projection Welding

Resistance Butt Welding

Flash Butt Welding

Percussion Welding

High Frequency Resistance Welding

4. Solid State Welding

Cold Welding

Diffusion Welding

Explosive Welding

Forge Welding

Friction Welding

Hot pressure Welding

Roll Welding

Ultrasonic Welding

5. Thermo –Chemical Welding processes

Thermit Welding

Atomic Hydrogen Welding

6. Radiant Energy Welding processes

195

Electron Beam Welding

Laser Beam Welding

Name: Swapnamurti. B.W

Roll no=ae354

Q67) Draw and explain the set up of gas welding

Ans: The basic equipments used to carry gas welding are-

1. Oxygen gas cylinder

2. Acetylene gas cylinder

3. Oxygen pressure regulator

4. Acetylene pressure regulator

5. Oxygen gas hose

6. Acetylene gas hose

7. Welding torch with a set of nozzles and gas lighter

8. Trolleys for transporting oxygen and acetylene cylinders

9. Filler rods and fluxes

10. Protective clothing

1. Oxygen gas cylinder

Oxygen cylinders are painted black in color and the valve outlets are screwed right

handed

The usual sizes of oxygen cylinders are 3400,5200and 6800 litre

Oxygen cylinder is made up of mild steel and alloy steel

The oxygen volume in a cylinder is directly proportional to its pressure

A safety nut is provided in order to prevent the rise in temperature due to high

pressure thereby reducing the chances of bursting

196

2. Acetylene gas cylinder

An acetylene cylinder is painted maroon in color and the valves are screwed left handed

It is a solid drawn cylinder which is charged to a pressure of 1552kn/ m sq

The usual size of acetylene cylinder cylinders are 2800 and 5600 litre

It has an inside diameter of 12”( 30 cm) with wall thickness 0.175”( 0.438mm) and

length of 40.5” (101.25cm)

An acetylene cylinder is filled with a spongy material such as balsa wood which is

saturated with chemical solvent called acetone

197

3 and 4. Oxygen and Acetylene pressure regulators

The pressure of the gases obtained from cylinders is considerably higher than the gas

pressure therefore the purpose of using gas gas pressure regulator is as follows-

To reduce the high pressure of the gas inside the cylinder to a suitable working

pressure

To produce a steady flow of gas under varying cylinder pressures.

A pressure regulator is fixed with two pressure gauges. One indicating the gas

pressure and the other indicating the reduced gas pressure

It is connected between the cylinder and the hose

They are classified in two types

a) Single stage regulator b) Two stage regulator

200

Difference between Oxygen and acetylene pressure regulators

5 and 6. Oxygen and Acetylene gas hose

The hose which supplies oxygen to the welding torch is blue in color and has right

handed thread connections where as the acetylene hose is red in color and has left handed

thread connections with chamfers or grooves on the nuts

The hoses to be used should be strong, non-porous, flexible and not subject to kinking

The hose is resistant to action of gases normally used in welding

201

The outer casing is made up of tough abrasion resistant rubber

The hoses are very robust and capable of withstanding high pressures

7. Welding torch with a set of nozzles and gas lighter

a) Welding torch

Oxygen and fuel gases which have been reduced in pressure are fed through

suitable hoses to a welding torch which mixes and controls the flow of gases to

the welding nozzle wherein the gas mixture is burnt to produce flame

There are two types of welding toch

1) High pressure (or equal pressure) type

2) Low pressure(or injector) type

1) High pressure (or equal pressure) type

High pressure torches are used with (dissolved) acetylene stored in cylinders at

a pressure of 8 bar

It is lighter and simpler

It does not need an injector

It is less troublesome

2) Low pressure(or injector) type

Low pressure blow pipes are used with acetylene obtained from an acetylene generator

at a pressure of 200 mm head of water

Its advantage is that it makes proportions of the two gases constant while the torch is

in operation

202

b) Welding nozzle

The welding nozzle or tip is that portion of the torch which is located at the end of the

torch

It contains the opening through which the oxygen and acetylene gas mixture passes

prior to ignition and combustion

It enables the welder to guide the flame and to direct it with maximum ease and

efficiency

The nozzle depends upon the design of the welding torch

c) Gas lighter

It provides a convenient, safe, and inexpensive means of lightning the torch thereby

eliminating the use of match stick which can burn the welder’s hand

Gas lighters are constructed from flint and steel

203

8. Trolleys for transporting oxygen and acetylene cylinders

Trolley should accommodate one oxygen cylinder and one acetylene cylinder required

for gas welding

The cylinders can be mounted on a trolley side by side as well as one after the other

depending upon the site where the work is going on

The trolleys may have rubber tires or steel rim wheels

The cylinders are held in place with chains and supported on the bottom with a steel

platform

9. Filler rods and fluxes

a) Filler rods

Filler metal which is available in the form of rods is called filler rods

They have the same or nearly the same chemical compositions as the base metal

Filler rods are available in various compositions and sizes

b) Fluxes

In order to avoid the formation of oxides due to oxygen in the air hence flux is

employed during welding

Flux is a material which is used for removal of oxides and other undesirable

substances

204

Flux is fusible and non-metallic

They are available in the form of powders, pastes and liquids.

10. Protective clothing

Gloves protect the hands of a welder

Leather or asbestos apron is very useful while doing welding in seating position

Leather skull cap or peaked cap is essential while doing overhead welding

Leather jackets or leggings can also be used as a protective clothes while working

Safety boots are necessary to protect the feet

Name: Cherag j.Kerawalla

Roll No: 62

Q 68) EXPLAIN DIFFERENT TYPES OF FLAMES USED IN OXYACETYLENE WELDING.

VASIM KHAN

AE 321

ANS:-

Oxy-acetylene gas welding is accomplished by melting edges or surfaces to be joined by gas

flame and alloying the molten metal to flow together, thus forming solid continuous joint upon

cooling. This process particularly suitable for joining metal sheets and plates having thickness of

2 to 50mm. With material thicker than 15 mm, additional metal called filler metal is added to

the weld in the form of welding rod. The composition of the filler rod is usually the same as the

part being welded, To remove the impurities and oxides present on the surface of the metal to

be joined and to obtain a satisfactory bond a flux is always employed the welding except mild

steel which is more manganese and silicon that acts as deoxidising agent.

205

Various gas combinations can be used for producing a hot flame for welding metals.

Common mixture of gases is oxygen and acetylene, oxygen and hydrogen, oxygen and other

fuel gas, and air and acetylene mixture is used to a much greater extent than the other and has

a prominent place in the welding industry.

FLAME TEMPERATURE OF DIFFERENT GASES

FUAL GASES FLAME TEMPERATURE IN °C USED FOR STEEL SHEETS HAVING A THICKNESS IN MM

City gas 1700 3

Hydrogen 1900 7

Methane 2000 7

Water gas 2300 8

Acetylene 3200 50

GAS FLAME

The correct adjustment of the flame is important for reliable works. When oxygen and

acetylene are supplied to torch in nearly equal volumes, a neutral flame is produced.

The heat is in accordance with a pair of chemical reactions. The primary reaction occurs

at a inner cone, where the temperature reaches in between 3050 to 3450 °c. the

reaction in the inner cone is

C2H2 + O2⇒2CO + H2 + heat

The secondary combustion process is in the outer envelope in which the flame attains a

temperature around 2100 °C near the inner cone and around 1250 °C at the end point of

the flame. The secondary flame equation is:

4CO + 2H2 +3O2⇒4CO2 + 2H2O + heat

The temperature developed in the flame is a result of these reactions that will reach

3200 to 3300°c

206

Oxy- acetylene gas flame

A neutral flame has two zones:

A sharp brilliant cone extending a short distance from the tip of the torch ,

An outer cone or envelope only faintly luminous and of a bluish colour

The oxidizing flame is one which there is an excess of oxygen. This flame has two zones: The small inner cone which has two zones:

The small inner which has purplish unge. The outer cone in case of oxidizing flame the inner cone is not sharply defined is that of neutral flame. The flame is necessary For welding brass . In steel this will result in a large grain size, increased brittleness with lower strength and elongation .

Q69.WHAT ARE THE PRECAUTIONS THAT NEED TO BE TAKEN WHILE GAS WELDING? A. FUMES and GASES can harm your health.

Keep your head out of the fumes. Do not breathe fumes and gases caused by the flame. Use proper ventilation. The type and the amount of fumes and gases depend on the type of materials, equipment and supplies used. Air samples can be used to find out what respiratory protection is needed. 1. Provide enough ventilation wherever gas welding, cutting, and heating operations are performed. Proper ventilation will protect the operator from the evolving noxious fumes and gases. The degree and type of ventilation needed will depend on the specific operation. It varies with the size of work area, on the number of operators, and on the types of materials used. Potentially hazardous materials may exist in certain fluxes, coatings,

207

and filler metals. They can be released into the atmosphere during heating, such as for welding and cutting. In some cases, general natural-draft ventilation may be adequate. Other operations may require forced-draft ventilation, local exhaust hoods, booths, personal filter respirators or airsupplied masks. Operations inside tanks, boilers, or other confined spaces require special procedures, such as the use of an air supplied hood or hose mask. 2. Check the atmosphere in the work area and ventilation system if workers develop unusual symptoms or complaints. Measurements may be needed to determine whether adequate ventilation is being provided. A qualified person, such as an industrial hygienist, should survey the operations and environment. Follow their recommendations for improving the ventilation of the work area. 3. Do not weld, cut, or heat dirty plate or plate contaminated with unknown material. The fumes and gases which are formed could be hazardous to your health. Remove all paint and galvanized coatings before beginning. All fumes and gases should be considered as potentially hazardous. HEAT RAYS (INFRARED RADIATION from the flame or hot metal) and SPATTER can injure eyes and burn skin. Wear correct eye, ear, and body protection. Flames and hot metal emit infrared rays. Operators may receive eye and skin burns after over exposure to infrared rays. Long overexposures may cause a severe eye burn. Hot welding spatter can cause painful skin burns and permanent eye damage. To be sure you are fully protected from the infrared radiation and spatter, follow these precautions: 1. Wear safety goggles made for gas welding and cutting purposes. They will protect your eyes from radiation burns and from sparks or spatter. Use the correct lens shade to prevent eye injury. Choose the correct shade from the table below. Observers should also use proper protection. 2. Protect against eye injury, mechanical injury, or other mishaps. Wear safety glasses with side shields when you are in any work area. 3. Wear clean, fire-resistant, protective clothing. Some operations produce sparks and spatter. Protect all skin areas from sparks or spatter. Avoid spark and spatter traps by wearing a jacket with no pockets, and pants with no cuffs. Sleeves should be rolled down and buttoned. Collars should be buttoned. Wear high, snug fitting safety shoes and gauntlet gloves. Protect your head by wearing a leather cap or hard hat. Wear ear protection where there is a chance of sparks or spatter entering your ears. Do not wear clothing stained with grease and oil. It may burn if ignited by the flames or sparks and spatter. For high heat work, such as heavy cutting, scarfing, or oxygen lance operations, face shields, fire-resistance aprons, leggings, or high boots may be needed. Remove all flammable and readily combustible materials from your pockets, such as matches and cigarette lighters. NOISE can damage hearing.

208

Wear correct ear protection. Wear ear protective devices or earplugs when heavy cutting, scarfing, or oxygen lancing is being performed, or in noisy work areas. In addition, proper ear protection can prevent hot spatter from entering the ear. WELDING

Containers and piping can explode by heat of welding or cutting unless properly cleaned and vented. Toxic fumes can be formed when welding, cutting or heating metal which has been in contact with an unknown material. Do not weld or cut any material or container unless it has been cleaned by qualified personnel. The welding or cutting of containers or piping which previously held flammable liquid or an unknown material is extremely dangerous unless they are first properly cleaned. Enough combustible or potentially toxic material may remain to be an explosion, fire, or poison hazard when the material is vaporized by heat from the welding or cutting torch. Ventilating ducts exhausting flammable or toxic gases should be considered as a hazardous container. Make sure surrounding pipelines or containers are protected before striking a flame. OXYGEN

Oxygen causes fire to burn more rapidly. Anything that burns in air burns violently in oxygen. 1. Avoid oxygen regulator fires (ORF). USE NO OIL! Keep regulators, hoses, torches and other oxy-fuel gas equipment free of grease, oil, and other combustibles. Oil grease, coal dust, and similar combustible materials once ignited bum violently in the presence of oxygen and may cause serious bums or explosions. Never handle oxygen cylinders or equipment in the same areas with grease or oil. The results of an uncontained ORF can be a catastrophic explosion. The explosive burning of materials can cause injury, burns, or death. 2. Never use lubricants on oxy-fuel gas equipment. Connections are designed for seating leak tight without sealants or lubricants. 3. Never substitute oxygen for compressed air. “Oxygen” should never be called “air”. Oxygen should never be used in pneumatic tools, in oil preheating burners, to start internal combustion engines, to blow out pipelines, to dust clothing or work, for pressure tests of any kind, or for ventilation. Using oxygen for air may result in serious burns or explosions. 4. Never allow oxygen or oxygen-rich air to saturate your clothing. A Materialsthat can be ignited in air have lower ignition temperaturesin oxygen. FUEL GASES fuel gasses can explode in air or oxygen if ignited by a flame,spark or other ignition source.fuel gas can cause rapid suffocation without warning. Acetylene,natural gas and liquified petroleum gas such as propane, butane, propylene (FG-2, etc.) and MAPP* are commonly used gases in gas welding, cutting, and heating processes. These gases can displace the oxygen required for normal breathing. An atmosphere with less than 18%

209

oxygen can cause rapid dizziness, unconsciousness, or even death. Therefore, be aware of the following precautions: 1. make sure that a confined area is well ventilated before entering it. if there is doubt, check area with an oxygen analyzer to be sure it contains a life supporting atmosphere. Otherwise, wear an air-supplied respirator. A second person, similarly equipped, should be standing by. 2. Do not bring gas cylinders into confines areas. 3. Never release fuel gas where it might cause a fire or explosion. Fuel gases should never be released into the air near other welding or cutting work, near sparks or flame caused by other means, nor in confined spaces. Sparks from circuit breakers, thermostats, etc. can also cause ignition. If necessary to release fuel gas, release it outdoors. Choose a place where there is least likely to be a significant hazard, and where the flammable gas will soon dissipate. 4.Never use acetylene at pressures above 15 psi. Using acetylene at pressures in excess of 15 psi gauge pressure (or about 30 psi absolute pressure) is a hazardous practice. To do so is contrary to insurance regulations and is prohibited by law in many places. Free gaseous acetylene, depending upon confinement conditions, is potentially unstable at pressures above 15 psig. Some conditions can cause the acetylene to decompose with explosive violence. Experience indicates 15 psig is generally acceptable as a safe upper pressure limit. The 30 psi absolute pressure limit is intended to prevent unsafe use of acetylene in pressurized chambers such as caissons, underground excavations, and tunnel construction. (Absolute pressure is equal to gauge pressure plus atmospheric pressure, which at sea level averages 14.7 lb. per sq. in. Thus, at sea level, a gauge pressure reading of 15 lb. per sq. in. is equal to an absolute pressure of 29.7 lb. per sq. in.) Note that under no flow conditions some regulators will indicate up to 24 psig on its delivery pressure gauge, but as soon as the gas valve is turned on, the delivery pressure will return to 15 psig or less. This is an acceptable condition HANDLING, STORAGE, AND USE OF CYLINDERS Cylinders, if mishandled, can rupture and violently release gas. Handle all cylinders with care. Misuse can cause injury or death. 1. Always read the cylinder label. Cylinders should be clearly labeled with the name of the gas to identify the contents. The cylinder contents may have their own unique hazards. Know and follow the information on the cylinder label. If the cylinder does not bear a gas label, or if the label is not legible, DO NOT USE THE CYLINDER. Do not assume the identity of the gas by the cylinder paint color or other means. Return the cylinder to the gas supplier for gas identification or cylinder replacement. 2. Handle, store, and use cylinders In an upright and secured position. Prevent cylinder damage; secure cylinders by chain or strap to suitable cylinder carts, benches, wall, post, or racks. Never secure cylinders to electrical lines or conduits. If transporting cylinders in vehicles such as pick-up trucks, secure other cargo as well so it cannot roll or slide and damage the cylinders. Transport with the regulator removed, cylinder valve closed, and cap in place. Prevent explosions, never transport cylinders in the trunk of a

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car or other confined spaces. Do not place cylinders in confined unventilated spaces such as closets, drawers, cabinets, or tool boxes. Always provide plenty of ventilation. Ventilation will prevent the accumulation of hazardous quantities of gas in case of a leak. If stored outside, prevent ice or snow from collecting on cylinders with recessed tops. 3. Use suitable hand trucks or racks for moving cylinders. Properly capped, cylinders may be moved for short distances by rolling them on their base. Care must be taken to prevent the cylinder from rolling or sliding out of control. Avoid rough handling. Do not slide or drag cylinders. Do not bump cylinders. Do not allow cylinders to drop or tip over. Do not roll cylinders on a wet floor or steel dock plate. 4. Never use or transport a leaking cylinder. If leakage is noted with valve opened or closed, or around safety-relief devices, immediately move the cylinder out-doors, well away from any source of ignition. Notify the supplier immediately for instructions as to further handling of the cylinder and to its return. Before you start welding or cutting operations, leak test the cylinder valve packing gland (see pg. 20, item I I) and all hose and regulator connections. Make sure there are no leaks. Remember, flammable gases can explode. 5. Unless in use, cylinder valves should be kept closed at all times. This will prevent accidental release of gas. 6. When manually lifting cylinders, do not raise them by the valve-protection cap. The cap may accidently and suddenly come loose. The cylinder may fall and rupture. 7. Never use slings or electromagnets for lifting and transporting cylinders. Use a cradle or suitable platform when transporting them by crane or derrick. 8. Never tamper with safety-relief devices on gas cylinders. They are provided to vent the contents to relieve excessive pressure within the cylinders if the cylinders are exposed to fire or excess temperatures. When fuse plugs melt, escaping fuel gases may ignite and cause a fire or explosion. 9. Never use any gas from a cylinder except through an approved pressure-reducing regulator. A regulator is designed for reducing the high pressure of the compressed cylinder contents to a constant, controllable working pressure for the equipment in use. A single approved regulator may, however, be connected to the outlet of manifolded cylinders supplying one or more use points. Pressure-reducing regulators shall be used only for the gas and pressures for which they are intended. Use no adapters. Never interchange regulators between gases. Use the proper gas pressures recommended for the equipment as furnished by the equipment manufacturer. Do not move, transport, or store any cylinder with regulator attached, except on an approved cart. 10. On cylinders equipped without handwheels, always use the special T-wrench or key for opening and closing acetylene cylinder valves. Leave the T-wrench or key in position, ready for immediate use, so that the acetylene can be quickly turned off in case of emergency. This will reduce the chance of accidental fires and explosions. If this wrench is lost, obtain a new one without delay from the acetylene supplier.

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11. Do not open an acetylene cylinder valve more than one and one-half turns. This permits adequate flow of acetylene and allows ready closing of the valve in an emergency situation. 12. Should the valve outlet of a cylinder become clogged with ice, thaw with warm — not boiling — water. Fusible plugs in the valve or cylinder head can melt as low as 1650 F (740 C) on some cylinders. Never use a flame or other heating device for this purpose. 13. Do not use a hammer, wrench, or pliers for opening and closing cylinder valves equipped with handwheels. Using force, other than hand, may damage the valve and cause sudden release of pressure. If the valve cannot be readily opened or closed leak tight by hand, immediately notify your supplier to have it exchanged for a new cylinder. Store leaking cylinders outside in a safe place with plenty of ventilation. 14. Never let the recessed top of a cylinder become filled with water, or be used as a place for tools. Nothing should interfere with quick closing of the cylinder valve, or possibly damage the fusible plugs or other safetyrelief devices in the cylinder head. 15. Never use any cylinder, full or empty, as a roller or support. The cylinder walls may be damaged and result in rupture or explosion. 16. Never transfer any gas from one cylinder to another or attempt to mix any gases in a cylinder. Any attempt to transfer or mix gases could result in a cylinder rupture or explosion. 17. Cylinders should not be placed where they might become part of an electrical circuit. They must never be used as a grounding connection. Accidental arcing could cause a local defect (arc-burn) which could lead to eventual cylinder rupture. 18. Store all gas cylinders in a separate, dry, well-ventilated room. Do not let full or empty cylinders stand around and clutter up work areas. They may interfere with operations, and they may be subjected to damage. 19. Full and empty cylinders should be stored separately. Storage location should be arranged so that the old stock of cylinders can be removed first. Cylinders should not be exposed to continuous dampness nor to grease and oil. They should not be stored near salt water or corrosive chemicals or fumes. Corrosion can weaken the cylinder. This can eventually lead to sudden rupture or explosion. 20. Store and use cylinders away from welding and cutting work. They should not be exposed to falling objects, moving machinery, and vehicular traffic. Storage areas should be located where cylinders will not likely be knocked over. Cylinders should be secured by suitable means such as chains or straps. 21. Store cylinders at least 20 feet from any combustible materials. To prevent rupture due to gas or liquid expansion, the cylinders should not be subjected to temperatures above approximately 125° F (52° C). Flammable-gas cylinder storage areas should be heated by indirect means, and meet the design requirements of National Fire Protection Association NFPA Standard 51 or 58. Smoking, open flames, and other sources of ignition must be prohibited in areas where oxygen and flammable gases are

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stored. 22. Cylinders should be grouped by types of gas. Where gases of different types are stored at the same location, oxygen cylinders should be separated from flammable-gas cylinders a minimum distance of 20 feet or by a non-combustible barrier at least 5 feet high having a fire-resistance rating of at least 1/2 hour. (Refer to NFPA Standard 51.) 23. Cylinders used in public areas or at construction sites should be located where they cannot be tampered with by unauthorized persons. Store cylinders in accordance with state and local regulations and in accordance with appropriate standards of the Occupational Safety and Health Administration (OSHA). DASH PATEL ROLL NO. 333

Q 70) Advantages, disadvantages and applications of GAS WELDING

Varun Nair

AE 331

The most common gas welding process is oxyfuel welding, also known as oxyacetylene welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still widely used for welding pipes and tubes, as well as repair work.

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The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.

Heat of combustion of Oxygen with Acetylene or any other fuel gas to generate a flame with intense heat

Copper coated Filler Material melts & fuses together the edges of the parts to be welded .

Applications Thin section welding Heat sensitive materials’ joining Joins almost all ferrous & non-ferrous metals In automotive & aircraft industries

Q71) Draw and explain CARBON ARC WELDING? What are its types? Give

advantages, disadvantages and applications of carbon arc welding?

ANS:-

CARBON ARC WELDING

http://en.wikipedia.org/wiki/Oxygen

214

CARBON ARC WELDING (CAW) is a process which produces coalescence of

metals by heating them with an arc between a nonconsumable CARBON

(GRAPHITE) electrode and the work-piece.

It was the first arc-welding process ever developed but is not used for many

applications today, having been replaced by TWIN ARC CARBON WELDING

and other variations.

The purpose of arc welding is to form a bond between separate metals.

In carbon-arc welding a carbon electrode is used to produce an electric arc

between the electrode and the materials being bonded.

This arc produces extreme temperatures in excess of 3,000°C. At this

temperature the separate metals form a bond and become welded together.

TYPES OF CARBON ARC WELDING

1. SINGLE CARBON ARC WELDING –

Single Carbon arc welding is a welding process in which heat is produced by

an arc between a carbon electrode and a work piece. The work piece is heated

and melted by the arc and a joint is formed. Shielding is typically not employed.

Filler metal may be used. Nowadays, TEG welding is used in place of carbon-arc

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welding in many applications

2. DOUBLE CARBON ARC WELDING –

Double Carbon Arc Welding is a variation of carbon arc welding in which an arc

is established when two carbon electrodes are brought together. The arc forms in

front of the apex angle formed by the electrodes and fans out to create a soft

heat or arc flame—softer than a single carbon arc. Shielding and pressure are

not used. Pressure and filler metals are sometimes used. Twin carbon electrode

arc welding is sometimes used for brazing.

216

ADVANTAGES OF CARBON ARC WELDING

Heat input controlled with arc length adjustments,

Less distortion,

Easy to mechanize process,

Butt welding of thinner jobs,

Simple & less skill required,

Cost is relatively low.

DISADVANTAGES OF CARBON ARC WELDING

Carbon infusion,

Separate filler metal,

Poor quality, prone to welding defects,

APPLICATIONS OF CARBON ARC WELDING

Non ferrous metals and alloys,

In preheating, brazing,

In castings’ repairs.

NAME: HIMANSHU VIJAY KALE

217

ROLL NO.: AE 314

Shielded metal arc welding (SMAW), also known as manual metal arc (MMA)

welding, flux shielded arc welding or informally as stick welding, is a manual arc

welding process that uses a consumable electrode coated in flux to lay the weld.

An electric current, in the form of either alternating current or direct current from

a welding power supply, is used to form an electric arc between the electrode and

the metals to be joined. As the weld is laid, the flux coating of the electrode

disintegrates, giving off vapors that serve as a shielding gas and providing a

layer of slag, both of which protect the weld area from atmospheric

contamination.

Because of the versatility of the process and the simplicity of its equipment and

operation, shielded metal arc welding is one of the world's most popular welding

processes. It dominates other welding processes in the maintenance and repair

industry, and though flux-cored arc welding is growing in popularity, SMAW

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continues to be used extensively in the construction of steel structures and in

industrial fabrication. The process is used primarily to weld iron and steels

(including stainless steel) but aluminium , nickel and copper alloys can also be

welded with this method.

Shielded Metal Arc Welding (SMAW)

Advantages

· Versatility - readily applied to a variety of applications and a wide choice of

electrodes

· Relative simplicity and portability of equipment

· Low cost

· Adaptable to confined spaces and remote locations

· Suitable for out-of-position welding

Disadvantages

· Not as productive as continuous wire processes

· Likely to be more costly to deposit a given quantity of metal

· Frequent stop/starts to change electrode

· Relatively high metal wastage (electrode stubs)

· Current limits are lower than for continuous or automatic processes

(reduces deposition rate)

219

Q73.]Explain TIG welding. Give its advantages,disadvantages,limitations .

EXPLAINATION:-

® Gas Tungsten Arc Welding, commonly referred to as "TIG" welding, is a high

quality,commonly used welding process to produce precision welds.

® Temperatures of a TIG welder can reach up to 11,000°F.

® Because it uses a non-consumable solid tungsten electrode shielded with an inert

gas flow (inert means non-combustible and does not support combustion).

® This expensive and slow welding process uses a non-consumable tungsten electrode

and a shielding gas which protects the welding area from contamination.

® The concentrated heat and precise control of the TIG arc allows thin material (.010

in.) to be welded.

® TIG welding is a relatively slow process but it provides high quality welds.

® Another important factor to consider is that nearly all TIG machines also haveStick

welding capabilities.(they are often referred to as TIG/Stick welders).

® While costing more than MIG or Stick-only welders, a single TIG/Stick machine gives

the user greater flexibility depending upon what you want to weld with it!

® The TIG welding process is probably the most difficult of all welding processes to

learn.

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Advantages of the TIG welding process:-

1)Non-consumable electrode

Other strategies like Stick Welding also referred to as SMAW utilizes consumable

electrodes. This is also great somehow. However, the welder need to halt his function

occasionally to be able to replace the consummated rod. This could have an impact on

the all round quality of the completed product. However, TIG Welders use a distinct arc

with a non-consumable electrode which facilitates for constant and undisturbed work

leading to flawless finish.

2)Uses a number of shielding gases including helium (He) and argon (Ar).

3)Is easily applied to thin materials.

4)Produces very high-quality superior welds.

5)With filler metal or without:

There is also a good quantity of flexibility enjoyed by TIG Welders. By way of example,

they are able to do the job using a consumable filler metal to produce a weld fill. This is

appropriate for several programs. Even so, there are scenarios wherein a filler weld just

isn’t necessary as in the case of autogenous welds.

6)Provides precise control of welding variables (i.e. heat).

7)Welding yields low distortion.

8)Leaves no slag or splatter.

9)Fine for non-ferrous metals:

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For novices, it appears natural that welding really should function for all forms of metals.

But this is not the case. Until close to the 20 th century, welding non-ferrous metals or

metals which can be not iron based is often a really demanding task. TIG welders on

the flip side can function with these metals without having a issue. These contain non-

ferrous metals like aluminum, copper, and magnesium.

DISADVANTAGES:-

Some TIG problems include:

1)difficult arc starting.

2)an erratic arc, porosity, excessive electrode consumption, arc wandering, and

oxidized weld deposit.

3)A lot more complicated:

TIG Welders are typically a lot more skilled and better trained. And this is just rightly so

contemplating the higher complexity of the approach and the greater skill requirement of

the techniques used.Great control and precision is needed to keep the arc at just the

correct length from the work pieces.

4)Slower technique:

An additional difficulty using the strategy that make it maybe less productive on certain

situations. Although the finish is mostly more desirable in comparison to SMAW for

instance, the time consumed by strategy is also typically much more. This will make it

greater suited for quality-oriented finishes but not on fast repairs.

5)Safety problems:

The usage of non-consumable electrode is an advantage. Yet, it also works to a

negative aspect. Becoming non-consumable indicates the absence of flux coating which

takes care of consumable rods. This lead to the absence of smoke screen which helps

blur out the light show and make the procedure more endurable for the eyes. As a

result, TIG welders are exposed to increased concentration of light which can trigger

one thing comparable to sunburn other than prospective eye damage. These

nevertheless could be remedied by putting on of correct gears.

LIMITATIONS:-

1) Requires greater welder dexterity than MIG or stick welding.

2)Lower deposition rates.

3)More costly for welding thick sections.

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APPLICATIONS:-

1)While the aerospace industry is one of the primary users of gas tungsten arc welding,

the process is used in a number of other areas.

2)Many industries use GTAW for welding thin workpieces, especially nonferrous metals.

3)It is used extensively in the manufacture of space vehicles, and is also frequently

employed to weld small-diameter.

3)thin-wall tubing such as those used in the bicycle industry.

4)In addition, GTAW is often used to make root or first pass welds for piping of various

sizes.

5) In maintenance and repair work, the process is commonly used to repair tools and

dies, especially components made of aluminum and magnesium.

6) Because the weld metal is not transferred directly across the electric arc like most

open arc welding processes, a vast assortment of welding filler metal is available to the

welding engineer. In fact, no other welding process permits the welding of so many

alloys in so many product configurations.

7) Filler metal alloys, such as elemental aluminum and chromium, can be lost through

the electric arc from volatilization. This loss does not occur with the GTAW process.

8)Because the resulting welds have the same chemical integrity as the original base

metal or match the base metals more closely.

8.1]GTAW welds are highly resistant to corrosion and cracking over long time

periods.

8.2]GTAW is the welding procedure of choice for critical welding operations like

sealing spent nuclear fuel canisters before burial.

Ashwi n Roll.No.:-AE304

Q74.explain mig welding

ans

This process is also known as metal arc gas shielded welding and used to wield low carbon dioxide

shielding gas.

223

Gas metal arc wielding is a gas shielded metal arc welding process which uses the high heat of electric

arc between continuously fed, consumable electrode wire and the material to be welded. Metal is

transferred through protected arc column to work.

In this process, the wire is fed continuously from a reel through a gun to constant surface which imparts

a current upon the wire .A fixed relationship exist between the rate of wire burn off and threw welding

current so that the welding machine at a given wire feed rate will produce necessary current to maintain

the arc .The current ranges from 100 to 400A depending upon the diameter of the wire ,and the speed

of melting of the way be upon 5m/min. The welding machine is dc constant voltage, with both straight

and reverse polarities available.

The welding gun can be either air or water cooled depending upon the current be used. With the higher

amperages, a water cooled gun is used. The welding wire is very often bare. Very lightly coated or flux

core wire is used. The wire is usually in diameter of 0.09 to 1.6mm, however sizes upto 32 mm are

made.

Metal JoiningMetal Joining Metal Inert Gas WeldingMetal Inert Gas Welding

Arc between a Arc between a

continuously wire fed continuously wire fed

consumable metal consumable metal

electrode & the jobelectrode & the job

Separate filler not Separate filler not

requiredrequired

No flux, shielding by inert No flux, shielding by inert

gasgas

Welding rate controlled Welding rate controlled

with self adjusting arc with self adjusting arc

principleprinciple

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AISWARYA PILLAI

Roll no:-Me346

Metal JoiningMetal Joining

Metal JoiningMetal Joining AdvantagesAdvantages

Faster than TIGFaster than TIG

Deeper penetrationDeeper penetration

Both thick & thin jobs possibleBoth thick & thin jobs possible

Easy to mechanizeEasy to mechanize

No fluxNo flux

DisadvantagesDisadvantages ComplexComplex

Air drafts may disrupt the gas shieldingAir drafts may disrupt the gas shielding

Higher base metal cooling ratesHigher base metal cooling rates

Not for outdoorsNot for outdoors

ApplicationsApplications Welding tool steels & diesWelding tool steels & dies

Manufacturing refrigerator partsManufacturing refrigerator parts

Aircraft, civil, automotive industryAircraft, civil, automotive industry

Non ferrous metals & their alloysNon ferrous metals & their alloys

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Q75 explain submerged arc welding with adv/ limitation / application

Ans gaurav

Submerged arc welding (SAW)

Submerged arc welding (SAW) is a common arc welding process. It requires a non-continuously

fed consumable solid or tubular electrode. The molten weld and the arc zone are protected

from atmos heric contamination b bein “s bmer ed” nder a blanket of ran lar f sible fl x

consisting of lime, silica, manganese oxide, calcium fluoride and other compounds. When

molten, the flux becomes conductive, and provides a current path between the electrode and

the work. This thick layer of flux completely covers the molten metal thus preventing spatter

and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of

the shielded metal arc welding (SMAW) process.

Submerged Arc Welding (SAW) uses heat generated by an arc formed when an electric current

passes between a welding wire and the work piece. The tip of the welding wire, the arc, and the

weld joint are covered by a layer of granular flux. The heat generated by the arc melts the wire,

the base metal and the flux. The flux shields the molten pool from atmospheric contamination,

cleans impurities from the weld metal, and shapes the weld bead. Depending on the design of

the flux, it can also add alloying elements to the weld metal to alter the chemical and

mechanical properties of the weld.

Electrode:

SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1/16 in. to 1/4 in. (1.6 mm to 6 mm). In certain circumstances, twisted wire can be used to give the arc an oscillating movement. This helps fuse the toe of the weld to the base metal.

Key SAW process variables:

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Wire feed speed (main factor in welding current control) Arc voltage Travel speed Electrode stick-out (ESO) or contact tip to work (CTTW) Polarity and current type (AC or DC) & variable balance AC current

Material applications:

Carbon steels (structural and vessel construction) Low alloy steels Stainless steels Nickel-based alloys Surfacing applications (wear-facing, build-up, and corrosion resistant overlay of

steels)

Advantages:

High deposition rates (over 45 kg/h have been reported). High operating factors in mechanized applications. Deep weld penetration. Sound welds are readily made (with good process design and control). High speed welding of thin sheet steels up to 5 m/min is possible. Minimal welding fume or arc light is emitted. The process is suitable for both indoor and outdoor works. Distortion is much less. Welds produced are sound, uniform, ductile and corrosion resistant and have good

impact value. Single pass welds can be made in thick plates with normal equipment. The arc is always covered under a blanket of flux, thus there is no chance of spatter

of weld. 50% to 90% of the flux is recoverable. Environmentally friendly

Limitations:

Limited to ferrous (steel or stainless steels) and some nickel based alloys. Normally limited to the 1F, 1G, and 2F positions. Normally limited to long straight seams or rotated pipes or vessels. Requires relatively troublesome flux handling systems. Flux and slag residue can present a health & safety concern. Requires inter-pass and post weld slag removal.

Application of Submerged Arc Welding:

227

Submerged arc welding is especially used for large products and in the fabrication of pressure vessels, penstocks, boilers etc.

.

By- Gaurav Kulkarni

SE (AUTO)

Q76. explain electroslag welding and its advantages and limitations

228

ANS

Electroslag welding (ESW) is a highly productive, single pass welding process for thick materials in a vertical or close to vertical position. It is similar to electrogas welding, except the arc starts in a different location. An electric arc is initially struck by wire that is fed into the desired weld location and then flux is added. Additional flux is added until the molten slag, reaching the tip of the electrode, extinguishes the arc. The wire is then continually fed through a consumable guide tube into the surfaces of the metal workpieces and the filler metal are then melted using the electrical resistance of the molten slag to cause coalescence. The wire and tube then move up along the workpiece while a copper retaining shoe is used to keep the weld between the plates that are being welded.

ESW Common Uses

Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick. It can also be used on structural steel if certain precautions are observed.

Advantages of ESW

Joint preparation is much simpler than other welding processes. Thicker steels can be welded more economically. ESW gives extremely high deposition rates. Residual stresses and distortion produced are low. Flux consumption is very low. No spattering or intense arc flashing occurs.

Before welding begins, the gap between two vertically-positioned metal pieces is

filled with flux. An arc is then struck between an electrode and the work-piece.

The resulting heat melts the flux, forming molten slag. The electric current

running through the molten slag allows it to maintain its liquid state.

http://www.gawdawiki.org/wiki/Flux

http://www.gawdawiki.org/wiki/Arc

http://www.gawdawiki.org/wiki/Electrode

229

When the slag reaches a temperature of approximately 3,500°F (1,930°C), the

consumable electrode and work-piece edges melt. Metal droplets are deposited

into the weld pool, joining the pieces

Name-akshay .j. shetty

roll no-343

Q77. Explain flux core arc welding.its advantage limitation and applications.

ANS

Flux Cored Metal Arc Welding

1. Consumable tubular wire filled inside with flux & alloy additions.

2. Shielding gas is optional & flux alone will do.

3. Flux ingredients create gas atmosphere after melting & float on the top to cover

the weld pool from contamination.

4. Electrode is wire fed

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Advantages

- High quality, flexible welding tech.

- Neat appearance

- Variety of steels & wide ranges of thicknesses

- Easy to mechanize

- High travel speeds

Disadvantages

- Only for ferrous metals. Especially steels

- Slag cleaning

- Expensive

- Only for flat welding position

Applications

- Replaces MIG

- For surfacing & build-up

- Only for ferrous metals & their alloys to any thickness ranges

- Bulldozer frames & blades

- Tractors & other locomotive fabrications

Name=Mahesh waman

Roll no=355

Q.78)Explain and compare the forehand & backhand welding techniques.

NAME:KETAN JAMDHARE(S.E AUTO.)

ROLL NO:63

FOREHAND WELDING

Forehand welding is often called PUDDLE or RIPPLE WELDING. In this method of welding, the

rod is kept ahead of the flame in the direction in which the weld is being made. You point the

flame in the direction of travel and hold the tip at an angle of about 45 degrees to the working

surfaces. This flame position preheats the edges you are welding just ahead of the molten

puddle.

231

Move the rod in the same direction as the tip, and by moving the torch tip and the welding rod

back and forth in opposite, semicircular paths, you can distribute the heat evenly. As the flame

passes the welding rod, it melts a short length of the rod and adds it to the puddle. The motion

of the torch distributes the molten metal evenly to both edges of the joint and to the molten

puddle. The forehand method is used in all positions for welding sheet and light plate up to 1/8

of an inch thick. This method is ideal because it permits better control of a small puddle and

results in a smoother weld. The forehand technique is not recommended for welding heavy

plate due to its lack of base metal penetration.

Leftward/Forehand

Flame away & the filler directed towards the completed weld.

Preheating achieved

Good control, neat

More consumption of filler

Joint is not visible

For thinner sections

BACKHAND WELDING

232

In backhand welding the torch tip pre-cedes the rod in the direction of welding and the flame

points back at the molten puddle and completed weld. The welding tip should make an angle of

about 60 degrees with the plates or joint being welded. The end of the welding rod is placed

between the torch tip and the molten puddle.Less motion is used in the backhand method than

in the forehand method. If you use a straight welding rod, you should rotate it so the end rolls

from side to side and melts off evenly. You might have to bend the rod when working in

confined spaces. If you do, it becomes difficult to roll a bent rod, and to compensate, you have

to move the rod and torch back and forth at a rather rapid rate. When making a large weld, you

should move the rod so it makes complete circles in the molten puddle. The torch is moved

back and forth across the weld while it is advanced slowly and uniformly in the direction of the

welding.

The backhand method is best for welding material more than 1/8 of an inch thick. You can

use a narrower view at the joint than is possible in forehand welding. An included angle of 60

degrees is a sufficient angle of bevel to get a good joint. The backhand method requires less

welding rod or puddling as the forehand method.

By using the backhand technique on heavier

material, you can increase your welding speed, better your

control of the larger puddle, and have more complete fusion at the weld root. If you use a

slightly reducing flame with the backhand technique, a smaller amount of base metal is melted

while welding the joint. When you are welding steel with a backhand technique and as lightly

reducing flame, the absorption of carbon by a thin surface layer of metal reduces the melting

point of the steel. This speeds up the welding operation, this technique is also used in surfacing

with chromium-cobalt alloys

Rightward/Backhand

Flame towards the completed weld & filler rod in between.

Lesser consumption of filler

Joint is visible

For thick sections

Better quality with lesser defects

233

Q 79) Explain the concept of flux and name few?

Name:- Mayur.U.Vaishampayan

SE Automobile Engineering

Roll No.:- AE 351

Ans:-

Flux is basically a chemical cleaning agent, flowing agent, or purifying agent. They are used in

both extractive metallurgy and metal joining. As a cleaning agent fluxes facilitate soldering,

brazing, and welding by removing oxidation from the metals to be joined. Flux is a substance

which is nearly inert at room temperature, but which becomes strongly reducing at elevated

temperature, preventing the formation of metal oxides. Additionally, flux allow solder to flow

easily on the working piece rather than forming beads as it would otherwise. In high

temperature metal joining processes(welding, brazing and soldering), the primary purpose of

flux is to prevent oxidation of the base and filler materials. The role of in joining processes is

typically dual: dissolving of oxides on metal surface, which facilitates wetting by molten metal,

and acting as an oxygen barrier by coating the hot surface, preventing its oxidation. In some

applications molten flux also serves as a heat transfer medium, facilitating heating of the joint

by soldering tool or molten solder. Fluxes are also used in foundries for removing impurities

from molten nonferrous metals such as aluminium, or for adding desirable trace elements such

as titanium. Flux can be powder, pastes or liquid. They are fusible and non metallic. They

234

prevent oxidation. They have higher affinity to oxygen, reacts readily and forms oxides and

floats over the top of the weld bead to cover it from further contamination. They are removed

later on by chipping, filing or grinding.

Name of some fluxes:- Borax, Boric Acid, Lime,Magnesium

.

Q 80) Explain the Physics of Arc Welding.

Name: Kartik Bhatt

Roll No.: SE-303 SE-Auto

Heating with an electric ARC

Application of pressure & filler metal is optional

Uses either direct (DC) or alternating (AC) current, and consumable or non-consumable

electrodes. The welding region is sometimes protected by some type of inert or semi-inert

gas, known as a shielding gas, and/or an evaporating filler material

235

Arc is struck/drawn between an electrode & the workpiece

Electrode is consumable or non-consumable.

Electrode is flux coated or bare

Twin electrodes can put workpiece out of the electric circuit

Polarities can be reversed while welding different materials

DC gives one polarity at a time

AC reverses the polarities in cycles which aids arc cleaning action

DCSP, job positive, more HAZ

DCRP, job negative, lesser HAZ

AC, implies cyclic, better control, more electrode life & optimum HAZ

236

More the angle more the penetration

Angle implies stability to the arc

Negative waveform controls penetration

Positive waveform controls arc cleaning action

Q 81) Explain plasma arc welding with advt/limitn/applications

Abdul rahman sheikh

237

Roll no. : 341

The electric arc is formed between an electrode which is usually made of sintered tungsten and

the workpiece. In PAW positioning the electrode within the body of the torch the plasma arc

can be separated from the shielding gas envelope. The plasma is then forced through a fine-

bore copper nozzle which constricts the arc, the plasma exits the orifice at high velocities

(approaching the speed of sound) and a temperature approaching 20,000 °C.This process uses a

non-consumable tungsten electrode and an arc constricted through a fine-bore copper nozzle.

Plasma arc welding is an advancement over the gas tungsten arc welding process

(GTAW).plasma arc welding can be used to join all metals that are weldable with GTAW (i.e.,

most commercial metals and alloys).

Advantages

The main advantage of plasma welding lies in the control and quality produced in the part being

welded. The torch design allows for better control of the arc, as well as a higher tolerance for in

torch standoff distance. Welds are typically cleaner and smoother when using the PAW process.

Smaller heat-affected zones result in welds that are very strong and less noticeable, which is

important for some parts.

Limitations

Some of the limitaions related to low and high current plasma arc welding include:

1. due to narrow constricted arc, the process has little tolarence for joint mis alignment.

2. manual plasma welding torches are generally more difficult to manipulate than a comparable

GTAW torch.

3. for consistent weld quality, the constricting nozzel must be well maintained and regularly

inspected for signs of deteriorations.

A major limitation in implementing a plasma welding process is the relatively high startup

costs. Plasma welding equipment tends to be expensive. Because it is a more specialized

welding process, the training and expertise required is also more intense.

Q 82) Explain the concept of resistance welding with advantages, limitations and applications.

Ashish R. Bhagwat

ME-303

Ans. Resistance Welding

238

Heat and application of pressure

H=I2RT, Heat, Current, Resistance and time of current flow

Heat is generated with increase in current

Increasing current density can decrease the time for the weld

Resistance of the work pieces R3, R5

Resistance of electrodes R1, R7

Contact resistance between electrode and work surfaces R2, R6

Resistance between the faying surfaces R4

R4 must be optimum & relatively higher to obtain a sound weld & to avoid overheating

Refer fig. below

Squeeze, initiation, upper electrode gradually applies pressure & current starts flowing

at the end of the cycle

Weld, current flows, passes through electrodes & work-pieces

Hold, sustained pressure at the welding point when the last impulse of current seizes.

Off, time lag to the second weld

239

Advantages

Fast

No filler

Semi-automatic

Less skilled labour

Less weld defects

Both similar & dissimilar metals welded

Disadvantages

High initial cost

High maintenance

Surface preparations

Bigger job thicknesses not possible

Application

Joining sheets, rods, bars, tubes

Metal furniture

Aviation & automotive industry

Making fuel tanks of cars & tractors

240

Making wire fabric

Q83.Draw and Explain the Rocker Arm Resistance Spot Welding machine?

Akshay Patil

Ans:

1.Frame which is the main body of the machine, houses transformer and the tap switch.

2. Upper arm is movable and the lower arm is fixed.

3. There are welding electrodes on both the arms.

4. Step down transformer is used which reduces the voltage and proportionally

increases the current.

5. Different knob controls to adjust current flow, water flow, hold and squeeze etc are

available.

6. Operated with foot lever or air cylinder.

7. Other variants are press type machine and a portable gun.

8. In press type machine the job can be clamped on the knee table.

Q 84) Draw & explain various types resistance welding procedures

Uthresh Uthaman

Me 356

241

Ans] Types of Resistance welding techniques :-

1.

242

2.

3.

243

4.

244

5.

Q 85) Explain the cold welding with advantages and limitations.

Name:-Kunal Sanjay Deore

Roll No.:-ME307

Sol :

Principle: The welding of two materials under high pressure or vacuum without the use of heat.

Cold welding is a method for joining non-ferrous metals and their alloys without using heat,

fillers or fluxes. Round wire sections, dissimilar materials and materials of different sizes can all

be welded with BWE's proven cold welding technology. A cold weld is generally stronger than the

parent material and has the same electrical characteristics.

Def:Cold welding is a solid-state welding process wherein coalescence is produced by the

external application of mechanical pressure at room temperature .pressure causes substantial

deformation at the weld.

A characteristic of cold welding is the total absence of heat and flux. For the satisfactory

cold welding , at least one of the metals to be joined must be highly ductile and should not

exhibit extreme work hard.

245

Process:

For the cold welding, when two such surfaces are pressed together, the oxide film from the

high spots fragmentates and metal behind that suffers plasticdeforamation ; metal to metal

contact occurs because of the fragmentation of the oxide film.any metal can be made to weld

by shearing the two surface at sufficiently high normal pressure.in the cold welding procedure,

two metal sheets brought into the overlapping contact and a punch is pressed into them .the

interface between the sheets is thereby subjected to a transvers tensile strain while it is under

a high compressive stress .the tensile strain causes fragmentation of the oxide film, permitting

metallic contact and bonding of the two sheets. Cold welds are characterized by deep

indentation on the outer surface of the work piece.the various joints are possible by this

process such as butt welds ,lap welds.

246

Advantages:

1. Limited dismantling

2. Virtually no deformation

3. Fastest repair capabilities

4. Metal does not "deteriorate" during welding

5. The weld joint is stronger than the metal itself

6. Cold welding is the only reliable method of joining aluminum and copper

7. It makes possible to weld containers with materials not to be heated (e.g.,

explosives).

Limitations

− it can not be used for joining ferrous metals;

− limitations concerning the form and size of elements to be joined. For example, cold

welding can not be used for welding of long pipes;

− cold butt welding can not be used for joining thin multiconductor wires;

− as a rule, cold welding can not be used in places difficult of access;

− replacement of some welded element with others requires readjustments of the

equipment and replacement of the rigging. Therefore, as a rule, cold welding is not

used in small-scale production.:

Q86:Explain concept of Diffusion (Bonding) Welding with

Advantages/Limitations/Applications?

GAURAV .D.VARPE

SE (MECHANICAL)

ROLL NO: 357

Diffusion (Bonding) Welding:

1) Transmigration of atoms

2) Application of pressure at an elevated temperatures

3) Faying surfaces actually grow together with atomic diffusion with no

macroscopic deformation with no relative motion between the parts.

247

4) Heating below 1100°C fastens the diffusion process

5) Individual peaks & valleys i.e. surface roughness are deformed at the

microscopic level for surfaces to mate at the cohesive force level

6) At an elevated temperatures thermodynamic instability causes

movement/migrations at atomic level & helps diffusion.

7) Base metals with different temperature gradients diffuse easily

Gas pressure bonding

Parts to be joined are held in contact to an elevated

temperature of about 815°C & an inert gas pressure is built

up around simultaneously

Vacuum fusion bonding

In vacuum parts are pressed mechanically at an elevated

temperature. Used for ferrous metals wherein the pressure &

temperature required are more.

Eutectic fusion bonding

The filler material with low melting point is kept in between

the faying surfaces. (Ti, Ni, Ag)

Low temperature diffusion bonding process wherein the filler

metal forms the eutectic compound with the base metals to

aid diffusion.

Low strength, less stable welds

8) Cleaning is critical: Mechanical abrasion/grinding, Chemical etching etc is used

Diagram:

248

Advantages of Diffusion Welding .

1) Autogenous welds possible 2) Continuous leak-tight welding 3) Well suited for ceramics

Limitations Of Diffusion Welding .

1) Cleaning & removal of oxide layer is difficult 2) Not for mass production 3) Time consuming & control of pressure, temperature w.r.t. time is difficult for

dissimilar metals

Applications of Diffusion Welding .

1) Applied in atomic industry, aerospace. 2) The B1 Bomber & Space shuttle constructions are classic applications of

diffusion bonding. 3) Fabrication of composite materials.

Q 87)Explain concept of ultrasonic welding with advt/limitn/applications

Aditi Borhade

Ultrasonic Welding

249

Local application of high frequency vibratory energy to the mating surfaces held

together under clamping pressure

Vibration induces oscillating shear stress parallel to the weld interface of the

clamped job. The combination of pressure & vibrations causes movement of the

metal molecules & brings about a sound union between the mating surfaces

Very fast process under moderate pressures with no application of heat, filler

rod.

Ultrasonic frequency (@20Khz up to 170KHz) is capable of disintegrating the

surface oxide layer & disperses the moisture hence only degreasing is required

prior to the weld.

250

Equipment

Frequency converter

Provides high frequeacncy electrical power at the designed

frequency

Transducer-coupling system

Converts electrical power into elastic vibratory power & a

coupling system including sonotrode (Ni based super alloy, high

fatigue) tip which conducts the vibratory power to the weld zone.

Pieces to be welded are clamped between the sonotrode tip & an

Anvil

Anvila

It is analogous to the table where the job is placed & provides the

necessary reaction to the clamping force. To prevent energy loss,

the anvil assembly is structurally isolated form the welder frame.

Both sonotrode tip & the anvil are faced with the high speed steel

to impart wear resistance

Force application device

Provides static clamping force normal to the plane of weld.

251

Timer

Controls the weld intervals in different types of welds.

Welding Variables

Clamping force

Ensures the contact between the welding tip & welding surfaces

Proper clamping force permit the shortest weld interval

Too much of a clamping force damages the surface in contact with

the workpiece.

Power requirements

Higher for thicker/harder materials & less for thinner/soft

materials

Power means high frequency electrical watts delivered to the

transducer.

Time

High power short weld time produces superior welds to low

power longer weld time welds.

Heavy sections require more welding time than thinner sections

An ultrasonic weld usually takes few seconds to complete.

Types of Ultrasonic welds

Spot welding

Individually spaced or overlapping spots

Ring Welding

Circular welds in the diameter ranging from 3mm to 50mm

Also oval, square or rectangular shaped closed welds

Line Welding

252

Sonotrode tip instead of a spherical radius has elongated

geometry so as to produce a narrow line welds

Continuous Seam Welding

Work-pieces are clamped between a rotating circular sonotrode

tip & a traversing table.

Continuous seam welds may overlap & produce total bonding

over the extended surface area.

Advantages

Surface preparation is not critical

Not hazardous

Dissimilar metals with vast difference in melting points can be joined

Both thin & thick sections can be welded

Virtually no HAZ & hence no micro-structural changes

Welding of glass is possible

Disadvantages

High initial cost, not economical

Possibility of cold welding of base metal with the tip or anvil

Fatigue loading shortens the equipment life

Applications

For thinner work-pieces in lap joints

Welding of glass

Welding of electrical & electronic components

Bi-metallic junctions

In refrigeration & Air conditioning industry

253

Q 88) Introduction to Explosive Welding

Sanjay

Me 49

Introduction

Explosive welding is a solid state welding process, which uses a controlled explosive detonation

to force two metals together at high pressure. The resultant composite system is joined with a

durable, metallurgical bond.

Explosive welding under high velocity impact was probably first recognized by Garl in 1944.

Explosive welding was first recognized as a possibility in 1957 in the United States when it was

observed by Philipchuck that metal sheets being explosively formed occasionally stuck to the

metal dies. Between that and now the process has been developed fully with large applications in

the manufacturing industry.

It has been found to be possible to weld together combinations of metals, which are impossible,

by other means.

The Process

This is a solid state joining process. When an explosive is detonated on the surface of a metal, a

high pressure pulse is generated. This pulse propels the metal at a very high rate of speed. If this

piece of metal collides at an angle with another piece of metal, welding may occur. For welding

to occur, a jetting action is required at the collision interface. This jet is the product of the

surfaces of the two pieces of metals colliding. This cleans the metals and allows to pure metallic

surfaces to join under extremely high pressure. The metals do not commingle, they are

atomically bonded. Due to this fact, any metal may be welded to any metal (i.e.- copper to steel;

titanium to stainless). Typical impact pressures are millions of psi. Fig. 1 shows the explosive

welding process.

254

Explosives

The commonly used high explosives are –

Explosive Detonation velocity , m/s

RDX (Cyclotrimethylene trinitramine, C3H6N6O6 8100

PETN (Pentaerythritol tetranitrate, C5H8N12O4) 8190

TNT (Trinitrotoluene, C7H5N3O6) 6600

Tetryl (Trinitrophenylmethylinitramine, C7H5O8N5) 7800

Lead azide (N6Pb) 5010

Detasheet 7020

Ammonium nitrate (NH4NO3) 2655

255

Applications

1) Joining of pipes and tubes.

2) Major areas of the use of this method are heat exchanger tube sheets and pressure vessels.

3) Tube Plugging.

4) Remote joining in hazardous environments.

5) Joining of dissimilar metals - Aluminium to steel, Titanium alloys to Cr – Ni steel, Cu to

stainless steel, Tungsten to Steel, etc.

6) Attaching cooling fins.

7) Other applications are in chemical process vessels, ship building industry, cryogenic

industry, etc.

Advantages

1) Can bond many dissimilar, normally unweldable metals.

2) Minimum fixturing/jigs.

3) Simplicity of the process.

4) Extremely large surfaces can be bonded.

5) Wide range of thicknesses can be explosively clad together.

6) No effect on parent properties.

7) Small quantity of explosive used.

Limitations

1. The metals must have high enough impact resistance, and ductility.

2. Noise and blast can require operator protection, vacuum chambers, buried in sand/water.

3. The use of explosives in industrial areas will be restricted by the noise and ground

vibrations caused by the explosion.

4. The geometries welded must be simple – flat, cylindrical, conical.

256

Q.89 Explain concept of friction and inertia welding its advantages and

limitations and applications?

Name: Aditya Kallianpur

Roll no: Me 319

ANS:

257

Friction Welding Process

Friction welding is a solid state welding process wherein coalescence is produced by

the heat obtained from mechanically induced sliding motion between rubbing surfaces.

The work parts are held together under pressure

Friction welding, or spin welding, is an eco-friendly, metal joining process used to bond

similar or dissimilar metals together. This process is accomplished without the use of

filler metals, fluxes, or shielding gases. It also minimizes energy consumption, produces

no fumes, gases, smoke, or waste. Initially, friction welded components were, as a rule,

circular. With today's technologies, the applications, components, material types, sizes

and shapes that can be joined are endless.

A simple explanation defines the friction welding process as rotating one component

against a fixed component under pressure. This action efficiently prepares and cleans

the weld interface, and generates sufficient low temperature, frictional heat, for at least

one of the materials to become plastic at the joint interface. This "Solid State" (non-

melting), joining process produces a merging between the materials via the heat

developed by the induced rubbing motion, and the applied load between the two

surfaces. At this point, rotation stops rapidly and the components are forged together.

Operational steps in Frictional welding

1. The two components to be friction welded are held in axial alignment.

2. One component that is held in the chucking spindle of the machine , is rotated

and accelerated to the desired speed.

3. The other component that is stationary and is held in movable clamp is moved

forward to come into pressure contact with the rotating component.

4. Pressure and rotation are maintained until the resulting high temperature makes

the component’s metals plastic for welding with sufficient metal behind the

interface becoming softened to permit the components to be forged together.

258

Inertia Friction Welding

Inertia welding is similar to friction welding because both use friction to develop heat the

temperatures developed are below melting point of the metals being welded but high

enough to create plastic flow and intermolecular bonding.

Energy is provided by the machine's kinetic energy that is stored in a rotating system or

mass. The energy available in a stored energy system is finite. This requires specific

parameters of mass/weight, speed, and pressure to meet the requirements of the weld

union. When the desired rotational speed is achieved, kinetic energy is transferred into

the freely rotating part. Constant forge pressure is applied until a plastic state is

reached. Rotation stops due to controlled pressure as the desired total displacement

length of material (upset) is met. Rotational speeds are normally higher than direct drive

friction welding. The majority of the total displacement comes at the very end of the

weld cycle as compared to being spread out over the middle to end of the cycle.

Operational step in Inertia Welding

1. One component is rigidly clamped in a stationary chuck or fixture which has to

resist high axial load and torque.

2. At this moment, the drive to the flywheel is cut off and the two components are

instantly brought together under high pressure.

3. Upon application of this axial force, the weld itself serves to brake the flywheel to

rest , converting flywheel kinetic energy to frictional heat and forging action and

the weld interface.

259

Operational steps in inertia welding

Fibre flow lines in friction and inertia welds .

Advantages of Friction/Inertia Welding

Low cost manufacturing alternative and machining process.

Weld complex shapes or circular shapes at all stages of components: finished,

semi-finished, and raw stock

Optimizes material usage; near net-shapes or for cost containment

260

Solution-based manufacturing and machining process to reduce material cost,

reduce tooling cost, reduce R&D cost, reduce weight, and/or reduce machining

cost.

Solution-based manufacturing and machining process to increase quality,

increase manufacturing through-put, and/or increase speed-to-market

Readily join combinations of steels & non-ferrous metals

Dissimilar metal combinations can be joined

Powder metal components can be welded to other powder metals, forgings,

casting or wrought materials

Joint strength equal to or greater than parent metal

Self-cleaning action reduces or eliminates surface prep time and cost

Joint preparation is not critical; machined, saw cut, and even sheared surfaces

are weldable

Integrity of welded joints is very reliable

Cost reduction for complex forgings/castings

Highly precise & repeatable process

1OO% metal-to-metal joints yield parent metal properties

Low welding stress

Components can be stronger & lighter than what other welding methods yield

Environmentally friendly, no fumes produced

Simplification of component design

Substitution of costly with less costly materials

No filler metals, fluxes, or protective gases needed

Can choose manual loading or optional automated loading

Joints can withstand high temperature variations

With inertia/friction welding there is less shortening of the component as

compared to that in flash or butt welding

Reduced scrap parts rate

Reduced HAZ (heat affected zone)

High rate of production.

Limitations of Friction/Inertia welding

Cast iron in any form is not weldable because the free graphite acts as a

lubricant and limits frictional heating.

Friction welding is perhaps one the least sensitive of all welding methods for

joining materials with wide differences in physical properties since the heat is

generated directly as the weld where the bond is to be developed.

261

The use of this process is restricted to flat and angular butt welds where one part

is normal to the other part .

So far the process has been applied only to the joining of small pieces in the form

of stock.

Sometimes, quite a heavy flash is forced out in all inertia and friction welds.

If tubing is welded, flash may have to be removed from inside the joint.

Flash from medium and high carbon steels being hard , must either be removed

while it is hot or annealed before it is machined.

Thrust pressure in inertia welding will range from 700 to 2800 kg/cm2 , which

requires a heavy rigid machine.

Application of friction/inertia welding

1. Friction/Inertia welding is finding varied applications for join

steels,superalloys,non-ferrous metal and combinations of metals.

2. It frequently replaces brazing and (metallic)arc, electron beam, pressure, flash or

resistance butt welding.

3. Among its varied applications are :

a) production of steering shafts and worm gears , control shafts ,axle shafts engine

valves, transmission shafts, etc for automobile industry.

b) production of bimetallic shafts, joining of superalloy turbine wheels to steels

shafts, joining of thin walled containers to bases etc.

c) production of cutting tools like drills, taps ,reamers and some of the shanked

milling cutters where HSS cutting body is welded to carbon steel shanks

d) manufacture of aluminium steel transition joints, copper-to-aluminium transition

pieces for electrical and refrigeration industry (Dissimilar metal welding)

e) Welding together relatively simple forgings to make complex shapes.

f) Fabrication of axle cases where a forgoing or axle spindled is welded to tubular

banjo or beam (Transportation industry)

g) Production of pump shafts and control valve shafts involving joints between plain

carbon and corrosion resistance alloy steel (Oil and gas industries)

h) Joining together dissimilar steel in the manufacture of bimetal fasteners that are

used to support insulation covers that are used in nuclear plant construction .

Q 90) Explain thermit welding & it’s applications.

NAME: MANOJ B. PAWAR

R.NO: Me 344

262

Ans:

THERMIT WELDING

Thermit welding is primarily a fusion-welding process in which the weld is affected by

pouring superheated liquid thermit steel around the part to be united. In case thermit

pressure welding, only the heat of the “thermit” reaction is utilised to bring the surface of

the metal to be welded in a plastic state and mechanical pressure is then applied to

complete the weld.

The thermit process for welding metal is based on the chemical reaction between

finely divided aluminium and iron oxide.

Where, 1-Crucible, 2- Slag Basin, 3- Runner, 4- Wax Pattern, 5-Sand Plug

6- Pre-heating, 7- Work-piece, 8- Riser

The thermit is a mixture of finely divided aluminium and iron oxide, the ratio by weight

being approximately three parts of iron oxide to one part of aluminium. The mixture,

placed in a refractory-lined crucible, is ignited with the help of a highly inflammable

composed of barium peroxide. The temperature produced by the thermit reaction is

approximately 3000 degree celsius or about twice the temperature of the melting point

of the steel.

In making pressure welds by the thermit process, a pattern of wax is shaped

around the parts to be welded. A sheet iron box is placed around the wax pattern and

placed between the pattern and box is filled and rammed with sand. Pouring the heating

263

gates and risers are cut in the sand and a flame is directed into the heating opening.

The wax pattern melts and drains out but the heating is continued to raise the

temperature of the parts to be welded. This preheating is done before the liquid metal is

poured into the mould in order to prevent chilling of the steel. Then the burner or torch

removed and the heating gate is plugged with sand. The superheated metal produced

by the thermit reaction in a crucible is poured into the mould surrounding the surface to

be welded. After the welding temperature is reached mechanical pressure is applied to

complete the weld.

APPLICATIONS

The thermit pressure welding is used to a great extent in the welding of pipes, cables,

conductors, rails, shafts and broken machinery frames and rebuilding of large gears,

etc.

Q 91) What is Electron Beam Welding ? Give its advantages, limitations and

applications.

Abhay A. Gaikwad

Me 311

A) Electron beam welding utilizes energy from fast moving beam of electrons focused

on the work piece.

The electrons strike the metal which gives up kinetic energy almost completely into

heat. The beam is created in high vacuum (10-3 to10-5 mm Hg).

If the work is done is such a vacuum, no electrodes, gases or filler metals can

contaminate it, and pure weld can be made.

Moreover , high vacuum is necessary around the filament so that it will not burn up

and will also produce and focus a stable beam.

In all types of electron beam machine , a tungsten filament which serves as a cathode

emits a mass of electron that are accelerated and focused to a 0.25 – 1 mm diameter

beam of high energy density up to 0.5 to 10 kW/mm2

Heat generated is about 25000 C. This generated heat is sufficient to melt and vaporize

the work piece material and thus fills a narrow weld gap without even the use of the filler

rod.

264

The speed of beam is steeped up to one half to two thirds of the speed of light by

passing it through a high voltage electrostatic field. An electromagnetic lens is

employed to obtain correct focusing of beam

Pressure required is near zero for the formation of beam.

Characteristics of Electron Beam Welding:

Medium required Vacuum

Tool Beam of electron moving at a very high velocity

Maximum material removal rate 10 mm3/min

Specific power consumption (typical)

450 W/mm3-min

Critical parameters Accelerating voltage, beam current, beam diameter , work speed, melting temperature

Material application All materials

Shape application Drilling fine holes, cutting contours in sheets, cutting narrow slots.

Limitations:

Very high specific energy consumption

Necessity of vacuum

Expensive machine

265

Advantages:

Welds are clean.

Energy input is in a narrow and concentrated beam.

Shielding gas required.

No porosity as there is absence of air.

Distortion is eliminated.

Speed is as fast as 2500mm/min.

It can weld or cut any metal or ceramic, diamond, sometimes as thick as 150mm.

Applications:

Welding done in Automobile, Airplane, Aerospace, Farm and other type of

equipment including bal bearing over 100mm.

Q 92) What are the advantages, disadvantages and limitations of LASER BEAM

WELDING?

Name: Akshay .R. Kadam Roll No: Me317

Lasers are devices which are capable of generating a very intense beam of optical radiation. The

ord ‘laser’ is an acron m of Li ht Am lification b Stim lated Emission of Radiation.

An even more concentrated beam is produced, but at a lower overall efficiency, with the laser

beam. A CO2 laser pumped with 500 W emits far-infrared light (10.6um wavelength) and

develops a peak energy density of 80kW/sq.mm, yet the heat affected zone is only 0.05 to

0.1mm wide. Oxygen blown on the surface of the metals reduces the heat reflection and

increases material removal rates by oxidation; inert gas increases heat transfer for non-metals.

266

The laser has the advantage that vacuum is not necessary and it is finding limited but growing

application, particularly for thin gauge metals. Lasers using for work such as welding very small

wires to electronic devices and similar work is called micro welding. Welding speed of about

2500 mm/min is achieved on steel sheet 1.5mm thick.

In practice, numerical control is sed to move the ork iece; and laser’s se in heav

production work is still limited.

Mechanics of material removal Melting, vaporization

Medium Normal atmosphere

Tool High power laser beam

Maximum material removal rate 3 mm3/min

Specific power consumption (typical) 1000 W/mm3/min

Critical parameters Beam power intensity, beam

diameter,

melting temperature

Materials application All materials

Shape application Drilling fine holes

Limitations Very large power consumptions,

cannot cut materials with high heat

conductivity and high reflectivity

267

Q 93) Draw and explain Brazing and its types.

Sagar S Kurde

Me 326

Ans.

Brazing

Metallic parts are heated above 427°C & the joint is filled with a non-ferrous filler metal. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action with no penetration into the base metal. The filler wets the joining surfaces, adheres & solidifies to form a brazed joint. The melting point of filler metal is above 427°C but well below the melting point of the base metals.

Types of brazing processes

Torch Brazing

Oxy-fuel gas welding kit provides the heat for brazing. The job is cleaned & joint is spread with flux after preheating to brazing temperature, the filler metal is hand fed to the joint later. Simple & cheap. Relatively slow process. Flame application is limited. Joint must be accessible.

Furnace Brazing

For a number of like/similar joints to be brazed simultaneously. Components are pre-assembled & the filler is pre-placed over the joint. Hydrogen atmosphere is employed in the furnace to avoid contamination. The furnace is either gas fired or electrically heated.

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Precise temperature control is possible & uniform heating takes place. High initial cost. Castings & forgings up to 1.5Kg with similar joints design can be brazed.

Vacuum Brazing

Furnace atmosphere is evacuated i.e. vacuum instead of hydrogen. More precise & clean. Good for brazing reactive metals.

Induction Brazing

Very rapid heating, high production rate. Components are fluxed, filler is pre-placed & placed near an induction coil, heat transfer by induction. Eddy currents & hysteresis losses help increase the temperature. Frequency of the AC employed decides the depth of brazing joint possible. Higher the frequency, shallower the heating. Larger assemblies not possible

Dip Brazing

Components to be brazed are fluxed & dipped into the molten metal bath of filler held at brazing temperature by electrical heating in a graphite crucible. Fixtures needed to hold the assembly in the bath. Wet parts if dipped cause explosion. Oxidation is prevented.

Resistance Brazing

Brazing with standard spot welding machine. W & Mo electrodes are used. Rapid

process. Joint must be accessible.

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Infrared Brazing

Radiant heat obtained below the red rays is utilized for brazing. Ring of high powered lamps is the source heat placed in a chamber around the parts/assemblies to be brazed. The chamber is evacuated or inert gas atmosphere is employed.

Carbon Arc Brazing

Carbon arc welding setup of one or twin electrodes is used.

Flow Brazing

Molten filler metals is poured into the pre-fluxed joints to be brazed

Block Brazing

Blocks heated by a gas flame or an arc are applied to the brazing joint to attain the brazing temperature

Silver Brazing

Known as silver soldering/dry soldering. Silver alloy filler is used for brazing. Was confined to the ornaments industry, now used in joining tool bits to shank, making condensers & evaporators, making tractor fuel tanks. 45% Ag, 15% Cu, 16% Zn & 24%

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Cd with M.P. 607°C is used. Flux can be applied in powder or paste form by dipping the filler rod or spraying or brushing. The removal of flux residues post-brazing is as critical to avoid corrosion. Ag alloy being extremely fluid, penetrates into the joint readily, leak-proof & strong. Very costly though.

Q 94) Explain different types of Soldering with diagram.

Vishal J. Walawalkar

Roll No. Me-359

Ans:

Soldering

Melting point of the filler metal is less than 427°C. Diffusion is

secondary in contrast to brazing. The strength at elevated

temperatures & corrosion resistance of the joint is poorer to brazed

joint.

Filler metals distributed into the joint by capillary action. Flux is used.

Soldered joint is not meant for carrying loads, joint design should

make the load act on base metal hence. Butt, lap, scarf joints

possible.

Solder is a non ferrous alloy of Zn, Al, Sn, Pb, Cd, Ag in

combinations.

Soldering Methods

Soldering Iron

Soldering iron with a copper tip is electrically heated. Solder

can be in wire form. Used in electronics applications.

Portable.

Torch method

Gas torch. For larger part where iron won’t do.

Dipping

Assembled & pre-fluxed parts dipped into molten solder

bath. Used for electrical motor armatures, cans of all types,

radiators

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Wave method

Assembled parts are carried over a conveyor touching the

wave of molten solder, pumped out from the bath through a

narrow slot.

Induction

Assembled & pre-fluxed parts with pre-placed solder are

placed on conveyors or rotating tables & made to pass

through high frequency induction coil. Current induced by

coil into parts heats them up.

Resistance method

Parts with pre-placed flux & solder are sandwiched between

electrodes.

Furnace/Hot Plate

Prepared joints are either heated in a protective furnace

atmosphere or by placing on a flame or electrically heated

plate.

Spraying

Solder is applied to the pre-fluxed part by a spraying gun.

Used in automotive & electronics industry.

Ultrasonic

High frequency vibrations break the oxide layer & exposes

the fresh base metal surface to wetting by solder. Flux is

eliminated.

Condensation

A vessel open to atmosphere contains a boiling fluid heated

by immersion heaters, forms a cloud of saturated vapour

above the boiling liquid. The cool pre-fluxed & solder pre-

placed joint suspended into the vessel, the vapour

condenses on the joint loosing the latent heat of

vapourization provides soldering temperature

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Q. 95) Write a note on the defects in welding

Ankush Roy

Roll no: Me 363Ans:

Defects in Welding

Cracks

Residual stresses induced during welding due to application of heat

& pressure lead to cracking. Stress relieving heat treatment post

welding is an option to reduce crack formation.

Lamellar tearing

Cracks running parallel to the workpiece surface due to very high

residual stresses & poor ductility of the base metal.

Distortion

Amount of temperature difference at various points along the weld

joint leads to uneven expansion/contraction of the base metals i.e.

distortion of the joint. Using welding fixtures to clamp the base

metals can limit the distortion effect.

Incomplete penetration

It is the distance from the weld top surface to the extent/root of the

weld bead/nugget formed. Penetration decides the strength of the

weld. Poor joint design, less arc currents, faster arc travel speeds

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Inclusion

Slag or any other foreign material which does not get the chance to

reach & float over the weld top surface, gets entrapped into the weld

& lowers the strength of the weld. Too long arcs. Insufficient slag-

cleaning of previous pass weld in the multi-pass welding.

Porosity/Blow Holes/Gas Pockets

Porosity is a group of small voids while blow holes/gas pockets are

larger holes or cavities formed inside the weld. Occur mainly due to

the entrapped gases. Gases form with atmospheric contamination of

the weld & gets diffused into the molten weld pool. Gas solubility

decreases with the cooling of weld pool thus entrapped gases exit

the molten metal during cooling, if the cooling rate is too high for the

gases to escape, they get entrapped & leave a void inside.

Poor fusion

The filler metal may not fuse properly with the base metal surfaces

due to low arc current, faster arc travel speeds or due to poor

weaving technique. Also if the base metal surfaces to be welded are

not cleaned properly would not allow the filler to adhere. Incorrect

joint design may also lead to poor fusion at the weld.

Poor weld bead appearance

If the weld bead is not deposited straight & the bead thickness

varies from place to place due to poor skilled labour or due to an arc

blow (wandering of arc due to the magnetic field around)

Spatter

The metal particles being thrown out of the flux shielded metal

electrode & deposited on the base metals due to improper coating of

flux, too high arc current or due to damp electrodes

Undercutting

A groove gets formed along sides of the weld bead due to improper

welding technique & or too much of electrode weaving.

Overlapping

The weld metals flows form electrode over the parent metal surface

stays there without getting properly fused or united with the surface.

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Q96. Draw and state different joint geometry used in welding?

Moosa kazi

Me 63

Ans .

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Q 97) Write a note on Weldability

-By VIVEK SINGH

Roll No: Me353

Weldability is a capacity of a material to be welded under the fabrication conditions

imposed into a specific suitably designed structure and to perform satisfactorily in the

intended service.

Weldability encompasses the

1) Metallurgical compatibility of a metal/alloy with any specific welding process.

Metallurgical compatibility implies that the base metal and weld metal can be

combined within the degree of dilution encountered in a specific process without the

production of deleterious constituents or phases.

2) Ability of a metal/alloy to be welded with mechanical soundness.

The mechanical soundness must meet soundness requirements and

normal engineering standards.

3) Serviceability of the resultant welded joints. Serviceability factors, e.g., may concern

the ability of the welded structure to work under low and high temperature, impact

load, etc.

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A metallic material with adequate weldability should fulfill the following

requirements:

1) Have full strength and toughness after welding.

2) Contribute to good weld quality even high dilution.

3) Have unchanged corrosion resistance after welding.

4) Should not be embrittled when stress relieving.

Effect of alloying elements on Weldability

1) Increase or decrease hardenability of the HAZ. The elements that have greatest

effect on the hardenability of the steel are C, Mo, Cr, V, Ni and Si.

The effect of these alloying elements on controlling the tendency to form HAZ

martensite, and thus cold cracking may be expressed as carbon equivalent (CE)

= %C + %Mn/4 + %Ni/20 + %Cr/10 + %Cu/40 - %Mo/50 - %V/10

2) Form age-hardening precipitates.

3) Provide grain refinement (aluminium, vanadium, titanium, zirconium and nitrogen

act as grain refiners in carbon and low alloy steels).

4) Reduced segregation.

5) Control ductile-to-brittle transformation temperature.

6) Form substitutional alloys and strengthen the metal by solid solution hardening.

7) Form interstitial alloys and increase mechanical properties by lattice distortion,

(e.g., carbon and boron, form interstitial alloys with steels).

8) Form carbides.

9) Provide deoxidation of molten metal without loss of primary alloying elements (e.g.,

titanium, zirconium, aluminium, silicon, etc., have affinity for oxygen than iron and

thus act as deoxidizers in carbon and low alloy steels).

Q 98. What are the various remedies to avoid welding defects?

Name- Vishal k.r. Shanker

Roll no.-Me 306

Ans- 1) The base metal may be preheated before welding so as to cool down the

rate of cooling

of the work piece.

2) Annealing of the base metal can be donepost welding to relieve stresses.

3) Jigs and fixtures can be applied to avoid warping of the base metal.

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4) In welding of alloy steel,a filler with similar chemical properties as that of the

base metal should be used.

5) The fatigue strength of weld can be improved by peening.

6) Selection of proper joint and edge preparation of work pieces is generally

required before welding them.

7)Use of padding or chills to adjust the cooling rate of weld must be done

appropriately.

8) A skilled welder is a must to produce a good welding job.

Q 99) Short note on metallurgical effects of welding.

ROLL NO. 352

A- Welding operation gives many metallurgical effects.

1. Weld Metal is essentially a small casting, with the inherent effects characteristics of a

casting. Appreciation of these characteristics can be easily attend by a study of

mechanism of solidification of metals and alloys.

2. Absorption of gases by weld metals and reactions is important in controlling the

porosity of a weld.E.g Hydrogen and aluminium

Gas such as hydrogen is more easily dissolved in the molten metal at a high

temperature and may subsequently trapped in the solid metal if the cooling is

rapid. Gas may either be retained in the micro structure or may form bubbles

which can become trapped as porosity in the fast freezing metal period.

Gas – Metal reaction may take one of the two forms: Physical (Endothermic)

solution, or exothermic reaction to form a stable chemical compound.

Endothermic solution does not exhibit fusion, but can result in porosity, either

due to super saturation with the weld pool of a particular gas or reaction

between two gases.

Sometimes it may result in the embrittlement of HAZ also.

3. Slag inclusions are frequently trapped in fusion welds due to joint or bed contour and

there is difficulty or removing or melting the slag in subsequent runs.

4. Hot Cracking of welds under constraint welding conditions, the contractional strains,

sometimes, cause inter crystalline cracks in hot welds. The fractured surface been tilted

with oxidation film. Hot cracking of welds occurs at elevated temperatures. This maybe

attributed directly to the low ductility of the base metal at temperatures not too far

below melting. High arc welding currents cause large columnar crystals to form with

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definite flames of weakness. At the throat of the weld. Austenic steels (E.g 25Cr, 20Ni)

which normally solidifies with large columnar crystals are pron to this difficulty.

Q 100) Explain the construction & working of Lathe Machine Tool.

- By Vyshakh Sunny

S.E.-Mech(354)

Ans.]

282

*] Different Processes that can be done on Lathe Machine :-

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Q101) Write a short note on milling machine and it’s types.

Name : Paresh Garude

Roll no. Me362

A : A milling machine is a machine tool that removes metal as the work is fed against a rotating

multipoint cutter. The cutter rotates at a high speed and because of the multiple cutting edges

it removes metal at a very fat rate. The machine can also hold one or more no. Of cutter at a

time. This is why a milling machine finds wide application in production work. This is superior to

other machine as regards accuracy and better surface finish and is designed for machining a

variety of tool room work.

Types of milling machine:

The milling machine maybe classified in several forms covering a wide range of work and

capacities but the choice of any particular machine is determined primarily by the nature of the

work to be undertaken in relation to the size and operation to be performed. The usual

classification according to the general design of the milling machine are:

1. Column and knee type

a. Head milling machine

b. Plain milling machine

c. Universal milling machine

d. Omniversal milling machine

e. Vertical milling machine

2. Manufacturing of fixed bed type

a. Implex milling machine

b. Duplex milling machine

c. Triplex milling machine

3. Plainer type

4. Special type

a. Rotary table milling machine

b. Drum milling machine

c. Planetary milling machine

d. Pantograph, profiling and tracer control milling machine

1. Column and knee type : For general hop work the mpot commonly used is the column

and knee type where the table is mounted on the knee casting which in turn is mounted

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on the vertical slides of the main column. The knee is vertically adjustable on the

column o that the table can be moved up and down to accommodate work of various

height. The column and knee milling machines are classified according to the various

methods of supplying power to the table, different movement on the table and

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different axis of rotation of the main spindle.

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a. Head milling machine ; The simplest of all types of milling machine is the hand miller in

which the feeding moment of the table is supplied by hand control. The cutter is mounted

on the horizontal arbour on is rotated by a power. The machine is relatively smaller in is

than that of the other types and is particularly suitable for light and simple milling

operations much as machining slots, grooves and key ways.

b. Plain milling machine: the plain milling machines are much more rigid and sturdy than

hand millers for accommodating heavy work pieces. The milling machine table maybe

fed by hand or power against a rotating cutter mounted on a horizontal arbour. A plain

milling heavy horizontal spindle in also called horizontal spindle machine. In a plain

milling machine the table maybe fed in a longitudinal cross for vertical directions. The

feed is longitudinal when the table is moved at right angles to the spindle. It is crossed

when the table is parallel to the spindle and the feed is vertical when the table is

adjusted in a vertical plane.

c. Universal milling machine : It is so named because it maybe adapted to a very wide

range of milling operations. A milling machine can be distinguish from a plain milling

machine in that the table of the milling machine is mounted on a circular swivelling base

which has degree graduation and the tail can be swivelled to any angle up to 45 degree

on either ides of a normal position. The table can be swivelled about a vertical axis and

set an angle other than right angles to the spindle. Thus in a universal milling machine

an addition to three movement a incorporated in a milling machine, the table may have

fourth movement when it is fed at an angle to the milling cutter. The additional feature

enables in to perform helical milling operation which cannot be done on a plain milling

machine unless a spiral milling attachment is used. The capacity of a milling machine is

considerably increased by the use of special attachments such as diving head or index

head, vertical milling attachment, rotary attachment, slotting attachment etc. The

produce can produce spur, spiral, bevel gears, twist drills, remerse milling cutters etc.

Beside doing all conventional milling operations. It may also be employed with

advantage with any and every type of operation that can be performed on a shaper or a

drill press. A universal machine is therefore a tool room machine designed to produce

an accurate work.

d. Omniversal milling machine : In this machine the table beside having all the movement

of a milling machine can be tilted in a vertical plane by providing a swivel arrangement

at the knee. Also the entire knee assemble is mounted in such a way that it may fed in a

longitudinal direction horizontally. The additional swivelling arrangement of the table

enables it to the machine taper, spiral grooves in remerse, bevel gears etc.it is

essentially a tool room and experimental shop machine.

e. Vertical milling machine : it can be distinguish from a horizontal milling machine by the

position of its spindle which is vertical or perpendicular to the work table. The machine

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maybe of plain or universal type and has all the movements of the table from proper

setting and feeding the work. The spindle head which is clamped to the vertical column

maybe swivel at an angle permitting the milling cutter mounted on the spindle to work

on an angular surface. In one machines the spindle can also be adjusted up or down

relative to the work, the machine is adapted for machining grooves slots and flat

surfaces. The end mills and face milling cutters are the usual tools mounted on the

spindle.

2. Manufacturing or fixed bed type : The fixed bed type milling machines are

comparatively large, heavy and rigid differ radically from column and knee type milling

machines by the constriction of its table mounting. The table is mounted directly on the

ways to fixed bed. The table movement is restricted to reciprocation at right angles to

the spindle axe with no provision for cross or vertical adjustment. The cutter mounted

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on the spindle head maybe moved vertically on the column and spindly may be adjusted

horizontally to provide cross adjustment. The name simplex, duplex, triplex indicates

that machine is provided with single, double, and triple spindle heads respectively.

3. Planer Type : The Plano miller as it is called is a massive machine built up for heavy duty

work having spindle head adjustable in vertical in transverse direction. It resembles a

planer and like a milling machine, it has a cross rail capable of being raised or lowered

carrying cutters their heads and the saddle all supported by rigid uprights. There may be

a number of independent spindles carrying cutters on the rail as well as two heads on

the uprights. The arrangement of independently driving multiple cutter spindles enables

number of work surfaces to be machined simultaneously thereby obtaining great

reduction in production time. The essential difference between a planer and a Plano

miller lies in the table movement in a Plano miller machine is much slower than that of a

planning machine. Modem Plano thrillers are [provided with high power driven spindle

powered to the extent of 100 h.p and the rate of metal removal tremendous. The use of

the machine is limited to production work only and in considered ultimate in metal

removing capacity.

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4. Special type: Milling machines of non conventional design have been developed to unit

special purposes. The feature that they have in common are the spindle for rotating the

cutter and provision for moving to tool or the work in different directions. The following

special types of machines are described below.

a. Rotary table machine: the construction of the machine is a modification to a vertical

milling machine and is adapted for machining flat surfaces at production rate. The

face milling cutters are mounted on two or more vertical spindles and a numbers of

work pieces are clamped on the horizontal surface of a circular table which rotates

about a vertical axis. The cutters may be set at different heights relative to the work

so that when one of the cutters is roughing the pieces, the other is finishing them. A

continuo loading and unloading of work pieces may be carried out by the operator

while the milling is in progress.

b. Drum milling machine: The drum milling machine is similar to a rotary table milling

machine in that its work supporting table which is called a drum, rotates in a

horizontal axis. The face milling cutters mounted on three or four spindle heads

rotate in a horizontal axis and remove metal from work pieces supported on both

the faces on the machine.

c. Planetary milling machine: In a planetary milling machine, the work is held

stationary while the revolving cutters or cutter move in a planetary path to finish a

cylindrical surface on the work either internally or extremely or simultaneously. The

machine is particularly adapted for milling internal or external threads of different

pitches.

d. Pantograph, profiting and tracer controlled milling machine: A pantograph milling

machine can duplicate a job by using a photograph mechanism which permit the size

of a work piece reproduced to be a miller than equal to or greater than the size of

the template or model used for the purpose. A profiling machine duplicates the full

size of the template to the machine. This is practically a vertical milling machine of

bed type in which the spindle can be adjusted vertically and the cutter head

horizontally across the table. The movement of the cutter us regulated by a

hardened guide pin. The tracer controlled milling machine reproduces irregular or

complex shapes of dies, moulds etc. By synchronised movement of the cutter and

tracing element.

Q 102) Draw and explain the basics of shaping machine

Paresh

ROLL NO. 350

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A shaper is a type of machine tool that uses linear relative motion between the

workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is

analogous to that of a lathe, except that it is (archetypally) linear instead of helical.

(Adding axes of motion can yield helical toolpaths, as also done in helical planing.) A

shaper is analogous to a planer, but smaller, and with the cutter riding a ram that moves

above a stationary workpiece, rather than the entire workpiece moving beneath the

cutter. The ram is moved back and forth typically by a crank inside the column;

hydraulically actuated shapers also exist.

Shapers are mainly classified as higher, draw-cut, horizontal, universal, vertical, geared, crank, hydraulic, contour and traveling head.[1] The horizontal arrangement is the most common. Vertical shapers are generally fitted with a rotary table to enable curved surfaces to be machined (same idea as in helical planing). The vertical shaper is essentially the same thing as a slotter (slotting machine), although technically a

distinction can be made if one defines a true vertical shaper as a machine whose slide can be moved from the vertical. A slotter is fixed in the vertical plane.

Small shapers have been successfully made to operate by hand power. As size increases, the mass of the machine and its power requirements increase, and it becomes necessary to use a motor or other supply of mechanical power. This motor drives a mechanical arrangement (using a pinion gear, bull gear, and crank, or a chain over sprockets) or a hydraulic motor that supplies the necessary movement via hydraulic cylinders.

1 - machine column (frame) 2 - main gearing (gear train and oscillating slider crank mechanism) 3 - ram 4 - ram head with tool slide and tool post 5 - machine table 6 - saddle 7 - table support 8 - drive (electro-motor)

The various components have to fulfil special tasks. Their exact functioning essentially depends on the proper operation of the control elements.

We distinguish between the following components:

- Basic components

• machine column (frame) with baseplate • table support

- Main components

• drive (electromotor)

http://en.wiktionary.org/wiki/linear#Adjective

http://en.wikipedia.org/wiki/Machining

http://en.wikipedia.org/wiki/Lathe

http://en.wikipedia.org/wiki/Helix

http://en.wikipedia.org/wiki/Planer_%28metalworking%29#Helical_planing

http://en.wikipedia.org/wiki/Planer_%28metalworking%29

http://en.wikipedia.org/wiki/Crank_%28mechanism%29

http://en.wikipedia.org/wiki/Hydraulic_cylinder

http://en.wikipedia.org/wiki/Shaper#cite_note-0

http://en.wikipedia.org/wiki/Rotary_table

http://en.wikipedia.org/wiki/Planer_%28metalworking%29#Helical_planing

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• main gearing (gear train, crank arm)

• feed mechanism

• workpiece clamping fixture (compound slide with table, saddle - clamping at the saddle)

• ram with tool slide and tool clamping fixture (tool post, mechanism for forward and backward shaping)

- Additional components

• starting cams for shaping with formed tool • stops for shaping with formed tool • devices for push-type slotting • gang-type toolholder

The faultless interaction of the individual components and the workmanlike operation of the shaping machines result in the manufacture of workpieces of the required quality and accuracy,

Basic components

The basic components are the machine column and the table support.

The box-like machine column (frame) is made of grey cast iron making possible vibration-free working and even heavy cuts (big metal-removal volume per stroke).

Robust guideways for the ram have been arranged at the upper side.

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Figure 2 - Ram guides

1 - flat guide, 2 - dovetail guide

The front side has been equipped with robust guideways for the compound slide, with additional support for the table that can be adjusted in height by means of a spindle (see Fig. 1, part 7).

Why is the machine column (frame) of stable design and made of grey cast iron? _________________________________________________________________ _________________________________________________________________ _________________________________________________________________

Main components

The drive for the main and feeding motion is effected by means of a three-phase motor which is mounted in or on the machine frame.

295

The main gearing consists of a gear train. It is a toothed gearing which in most cases is switchable in 4, 6 or 8 steps, thus providing various speeds of the ram.

Figure 3 - Main gearing of a mechanical shaping machine

1 - electromotor 2 - vee-belt drive 3 - toothed gearing with toothed gears z1 - z12, z12 simultaneously being crank gear/I - III shafts 4 - ram 5 - crank gear 6 - oscillating slider crank mechanism 7 - sliding block

The toothed gearing is followed by the heart of the shaping machine, namely the transmission for transforming the rotary motion into the straight-lined primary motion of the ram. The feed gear produces the automatic transverse motion of the table with the workpiece set up on it (feed motion). It is guided from the main gearing by transmission elements to the table spindle. The transmission elements are arranged on the operating side of the machine. A clutch can be actuated by means of a control lever as a result of which engagement or disengagement of the drive is effected.

http://collections.infocollections.org/ukedu/collect/ukedu/index/assoc/gtz111be/p09a.gif

296

Figure 4 - Feed gear

1 - table spindle 2 - ratchet wheel 3 - connecting rod (push rod) 4 - retaining pawl (catcher) 5 - toothed gear z1 6 - toothed gear z2 7 - eccentric pin 8 - link

Shaping is a technique with straight-lined motion (cutting and feed motion). The feed motion takes place in steps.

Figure 5 - Conditions of motion during shaping

1 - tool 2 - workpiece

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3 - cutting motion 4 - feed motion

The workpiece clamping fixture (compound slide) consists of saddle and machine table (see Fig. 1, parts 6 and 5).

The machine table is additionally supported.

The ram carries the ram head consisting of swivel-head plate, tool slide, clapper box with tool block and toolholder (tool post).

Figure 6 - Ram head with tool slide

1 - clapper 2 - toolholder 3 - tool base 4 - clapper axis 5 - clapper box 6 - tool slide 7 - crank with actuating screw

298

8 - dividing ring 9 - swivel-head plate 10 - ram

During the working stroke the tool block rests on the clapper box (as a result of the cutting pressure), during the return stroke it is lifted. In this way the tool tip is protected. With older shaping machines the tool is dragging over the work-piece during the return stroke. The working position is reached by the dead weight and, thus, by falling back. Modern machines have an automatic tool lifter.

For shaping oblique surfaces the tool slide can be swivelled on the swivel-head plate. In order to maintain the mobility of the tool block, it is also possible to set the clapper box on the tool slide at an angle, i.e. to swivel it in the circular slot.

Figure 7 - Setting of the tool box when oblique surfaces are to be shaped

1 - tool box 2 - workpiece

Additional components

Additional components are mounted for special operations. Recessing and shaping with formed tool can be carried out with automatic infeed, if adjustable stops or starting cams are mounted. For machining circular-arc shaped parts special ram heads have been developed. The decision in favour of one or the other kind of machining depends on the shape or configuration of the workpiece to be manufactured.

Q 103) Draw and explain the basics of planning machine

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Name: Sanket Sheti Roll No: 364

PLANNING MACHINE:

A planer is a heavy and large machine tool which has been designed to produce

flat surface on the workpiece of large dimensions. In a planer, the work which is

supported on the table reciprocates past the stationary cutting and the feed is supplied

by the lateral movement of the tool.

Planning machine parts:

The principal parts of the planner are:

1. Bed 2. Table or platen 3. Housing or column 4. Crossrail 5. Tool head 6. Driving and feed mechanism

Bed:

The bed of planer is a box like casting having cross ribs. It is a very large in size and heavy in weight and supports the column and all other moving parts of the machine.

The bed is slightly longer than twice the length of the table so that full length of the table may be moved on it.

It is provided with prison ways over the entire length on its top surface and the table slides on it. In a standard machine, two V types of guideways are provided. It should be horizontal and parallel to each other.

The hollow space within the box like structure of the bed houses the driving mechanism for the table.

Table:

The table supports the work and reciprocates along the ways of the bed. The planer table is a heavy rectangular casting and is made of good quality cast iron.

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The top face of the planer table is accurately finished in order to locate work correctly. T slots are provided on the entire length of the table so that the work and work holding devices may be bolted upon it.

Accurate holes are drilled on the top surface of the planer table at regular intervals for supporting the poppets and stop pins. At each end of the table a hollow space is left which acts as a through for collecting chips.

A groove is cut on the side of the table for clamping planer reversing dogs at different positions.

Hydraulic bumpers are sometimes fitted at the end of the bed to stop the table from overrunning giving cushioning effect. In some machines, if the table overruns, a large cutting tool bolted to the underside of the table will take deep cut on a replaceable block attached to the bed, absorbing kinetic energy of the moving table.

Housing:

The hosing also called column or upright the rigid box like vertical structure placed on each side of the bed and are fastened to the slides of the bed.

They are heavily ribbed to take up severe forces due to cutting. The front face of each housing is accurately machined to provide precision ways on which the crossrail may be made to slide up and down for accommodating different heights of work

Two side tool heads also slide upon it.

The housing enclose the crossrail elevating screw, vertical and crossfeed screws for tool heads, counterbalancing weight for the crossrail, etc.these screws may be operated either by hand or power.

Cross rail:

The crossrail is a rigid box life casting connecting the two housing .this construction ensures rigidity of the machines.

The crossrail may be raised or lower on the face of the housing and can be clamped at any desired position by in manual, hydraulic or electrical clamping device.

In order that the cross rail is moved up and down uniformly on both ends, both the elevating screws are rotated simultaneously by a horizontal shaft, mounted on the top of the machine ,through a set of beveled gears.

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The front face of the crossrail is accurately machined to provide a guide surface for the toolhead saddle, usually two toolhead are mounted upon the cross rail which are called railheads.

The crossrail has screws for vertical and cross feed of the toolheads and a screw for elevating the rail these screws may be rotated either by hand or by power.

Toolhead:

The tool head consist of a saddle, swivel base, vertical slide, apron, clapper box, clapper block, tool post and downfeed screw.

The saddle is fitted on the ways of the crossrail on which the tool head may be fitted.

The tool head on the crossrail are independently operated.

Planer operations:

Operations performed in a planer are similar to that of a shaper. The only

difference is that a planer is specially designed for planning large work, whereas

a shaper can machine only small work. The common operations performed in a

planer are:

1) Planning flat horizontal surfaces

2) Planning vertical surfaces

3) Planning at an angle and machining dovetails

4) Planning curved surface

5) Planning slots and grooves

Planning horizontal surface:

While machining horizontal surfaces the work is given a reciprocating movement

along with the table and the tool is fed crosswise to complete the cut. Both the railheads

may be used for simultaneously removal of the metal from two cutting edges .the work

is supported properly on the table ,proper planning tool is selected ,the depth of cut

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,speed and feed are adjusted and the work is finished to the required dimensions by

taking roughing and finishing cuts.

Planning vertical surface:

The vertical surface of a work is planed by adjusting the saddle horizontally along

the crossrail until the tool is in a position to give the required depth of cut. The vertical

slide is adjusted perpendicular to the planer table and the apron is swiveled in a

direction so that the tool will swing clear out of given machined surface during the return

stroke .the downfeed is given by rotating the downfeed screw .

Planning angular surface:

For dovetail work, cutting V grooves, etc. the tool head is swiveled to the required

angle and apron is given then further swiveled away from the work to give relief to the

tool cutting edge during the return stroke, by rotating downfeed screw tool is fed at an

angle to the planer table.

Planning slots or grooves:

Slots or grooves are cut by using slotting tools the operation is similar that of

shaper.

Q104) Draw and explain the basics of drilling machine

Ans: A drilling machine comes in many shapes and sizes, from small hand-held power

drills to bench mounted and finally floor-mounted models. They can perform operations

other than drilling, such as countersinking, counterboring, reaming, and tapping large or

small holes. Because the drilling machines can perform all of these operations,.

USES

A drilling machine, called a drill press, is used to cut holes into or through metal, wood,

or other materials (Figure 4-1). Drilling machines use a drilling tool that has cutting

edges at its point. This cutting tool is held in the drill press by a chuck or Morse taper

and is rotated and fed into the work at variable speeds. Drilling machines may be used

to perform other operations. They can perform countersinking, boring, counterboring,

spot facing, reaming, and tapping

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FIGURE OF A DRILLING MACHINE:

CHARACTERISTICS

All drilling machines have the following construction characteristics a spindle. sleeve or

quill. column, head, worktable, and base.

1. The spindle holds the drill or cutting tools and revolves in a fixed position in a sleeve.

In most drilling machines, the spindle is vertical and the work is supported on a

horizontal table.

2. The sleeve or quill assembly does not revolve but may slide in its bearing in a

direction parallel to its axis. When the sleeve carrying the spindle with a cutting tool

is lowered, the cutting tool is fed into the work: and when it is moved upward, the

cutting tool is withdrawn from the work. Feed pressure applied to the sleeve by hand

or power causes the revolving drill to cut its way into the work a few thousandths of

an inch per revolution. work a few thousandths of an inch per revolution.

3. The column of most drill presses is circular and built rugged and solid. The column

supports the head and the sleeve or quill assembly.

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4. The head of the drill press is composed of the sleeve, spindle, electric motor, and

feed mechanism. The head is bolted to the column.

5. The worktable is supported on an arm mounted to the column. The worktable can be

adjusted vertically to accommodate different heights of work. or it may be swung

completely out of the way. It may be tilted up to90° in either direction, to allow for

long pieces to be endor angled drilled.

6. The base of the drilling machine supports the entiremachine and when bolted to the

floor, provides forvibration-free operation and best machining accuracy.The top of

the base is similar to a worktable and maybeequipped with T-slots for mounting work

too large forthe table

Written by Krishna vatwani

Q 105 ) Explain the quick return theories of shaping machine.

NAME:SHRIKALP POKHARKAR

ROLL NO: 347

The principle of quick return motion is shown in the fig1.When the link is in the position PM, the

ram will be at the extreme backward position of its stroke, and when it is at PN, the extreme

forward position of the ram will have been reached.PM and PN are shown tangent to the crank

pin circle. The forward cutting stroke, therefore, takes place when the crank pin circle rotates

through the angle C1 KC2 and the return stroke takes place when the crank rotates through the

angleC2LC1.It is evident that the angle C1KC2 made by the forward or cutting stroke is greater

than the angle C2LC1 described by the return stroke. The angular velocity of the crank pin being

constant the return stroke is therefore, completed within a shorter time for which it is known as

quick return motion. The ratio between the cutting time and return time may be determined by a

formula:

CUTTING TIME /RETURN TIME=C1KC2/ C2LC1

The only disadvantage lies with this mechanism is that the cutting speed and return speed is not

constant throughout the stroke. It is maximum when the rocker arm is at the two extremities and

the aped is maximum when the rocker arm is vertical.

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Fig 1

Withworth quick return mechanism:

The Withworth quick return mechanism is shown in the fig2 and a simple line diagram of the

mechanism is shown in the fig3.The bull gear is mounted on a large fixed pin A upon which it is

free to rotate. The crank plate 4 is pivoted eccentrically upon the fixed pin 2 on the top of which

is mounted the sliding block 3 .Sliding block 3 fits into the slots provided on the crank plate 4.At

the other end of the crank plate 4,a connecting rod 6 connects the crank plate by a pin 9 and the

ram 8 by a pin 7.When the bull gear will rotate at a constant speed the crank pin 2 with the

sliding block 3 will rotate on a crank circle of radius A2 and the sliding block 3 will cause the

crank plate to rotate about the point 5 with a variable angular velocity. Pin 9 fitted on the other

end of the crank plate 4 will rotate in circle and the rotary motion of the pin 9 will be converted

into reciprocating movement of the ram similar to the crank and connecting rod mechanism. The

axis of the reciprocating of the ram passes through the pin 5 and is normal to the line A5.

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1. Driving pinion, 2.Crank pin, 3.Sliding block, 4.Crank plate, 5.Pivot for crank plate,

6.Connecting rod, 7.Connecting pin or ram, 8.Ram, 9.Pin, A. Fixed pin.

Fig 2

1. Driving opinion, 2.Crank plate, 3.Sliding block, 4.Crank pin for connecting rod, 5.Pivot for

crank plate, 6.Ram, 7.Bull gear, A. Fixed pin.

Fig 3

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When the pin 2 is at the position C the ram will be at the extreme backward position but

when the pin is at the position B, the extreme forward position of the ram will have been

reached. When the pin 2 travels from C to B the crank pin 9 passes through the backward

position to the forward position in the cutting stroke, and the return stroke is completed when the

pin 2 travels from B to C or the pin passes from the forward position to backward position. As

the angular velocity of the crank pin is uniform the time taken by the crank pin 2 to travel

through an arc covering CEB is greater than the time to move through an arc covering BDC.Thus

a quick return motion is obtained by the mechanism.

The length of the stroke of the ram may be changed by shifting the position of pin 9

closer or away from the pivot 5.The position of stroke may be altered by shifting the position of

pin7 on the ram.

Q106. State and explain different types of milling machine tools? Also state their

applications?

Mayur D Chaudhari

Me 305

Ans:

*Milling : Milling is a process or method of giving a specific shape or a form to the metal

parts by removing the metal with slowly removing tool known as ‘milling cutter’ .

*Milling machine: Milling machine is a machine tool which removes metals the work is

fed against a multiple cutting edge cutter.

*Types of milling machines:

1. Column and Knee Type: Main shape of column knee type of milling machine is shown in Figure below. This milling machine consists of a base having different control mechanisms housed there in. The base consists of a vertical column at one of its end. There is one more base above the main base and attached to the column that serves as worktable equipped with different attachments to hold the workpiece. This base having worktable is identified as “knee” of the milling machine. At the top of the column and knee type milling machines are classified according to the various methods of supplying power to the table, different movements of the table and different axis of rotation of the main spindle. These are described in brief as below.

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a. Head Milling Machine :

In case of head milling machine feed motion is given by hand and movements of the machine are provided by motor. This is simple and light duty milling machine meant for basic operations.

b. Plain Milling Machine : Plain milling machine is similar to hand milling machine but feed movement can be

powered controlled in addition to manual control.

c. Universal Milling Machine : A universal milling machine is named so as it is used to do a large variety of operations.

The distinguishing feature of this milling machine is it table which is mounted on a

circular swiveling base which has degree graduations. The table can be swiveled to any

angle upto 45o on either side of normal position. Helical milling operation is possible on

universal milling machine as its table can be fed to cutter at an angle. Provision of large

number of auxiliaries like dividing head, vertical milling attachments, rotary table, etc.

make it suitable for wide variety of operations.

d. Omniversal Milling Machine : Omniversal milling machine is like a universal milling machine with additional feature that its table can be tilted in a vertical plane by providing a swivel arrangement at the knee. This enables it to make taper spiral grooves in reamers, bevel gears, etc.

e. Vertical Milling Machine : Position of spindle is kept vertical or perpendicular to the worktable in case of vertical

milling machine.

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2. Fixed bed type milling machine: It is also known as manufacturing type milling

machine. Its table is mounted directly on the ways of fixed bed. Table movement is

restricted to reciprocation only. Cutter is mounted on the spindle head which can move

vertically on the column. Duplex milling machine has double spindle heads, one on each

side of the table. Triplex milling machine has three spindle heads one each side of the

table and third one is mounted on the cross rail. Bed type milling machine is shown in

Figure.

3. Planer Type: The plano miller , as it is called , is a massive machine built up for

heavy duty work, having spindle heads adjustable in vertical in transverse directions. In

a planer, the table moves to give the cutting speed, but in a plano-milling machine is

much slower than that of a planning machine.

4. Special type of milling machines: Milling machines of non conventional design have

been developed to suit special purposes. The features that they have in common are

the spindle for rotating the cutter and provision for moving the tool or the work in

different directions.

Following special types of machines of interest are described below:

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a. Rotary table machine: The face milling cutters are mounted on two or more

vertical spindles and a number of workpieces are clamped on the horizontal

surface of a circular table which rotates about a vertical axis.

b. Drum milling machine: The Drum milling machine is similar to a Rotary table

milling machine. It rotates in horizontal axis and the face milling cutters mounted

on 3 or 4 spindle head rotate in horizontal axis and remove metal from

workpieces supported on both the faces of the drum. The finished machined

parts are removed after one complete turn of the drum, and then the new ones

are clamped on it.

c. Planetary milling machine: In a Planetary milling machine, the work is held

stationery while the revolving cutter or cutters move in a planetary path to finish a

cylindrical surface on the work either internally or externally or simultaneously.

d. Pantograph milling machine: A pantograph machine can duplicate a job by using

a pantograph mechanism which permits the size of the workpiece reproduced to

be smaller than , equal to or greater than the size of a template or model used for

the purpose.

e. Profiling machine: A Profiling machine duplicates the full size of the template

attached to the machine. This is practically a vertical milling machine of bed type

in which the spindle can be adjusted vertically and the cutter head horizontally

across the table. The movement of the cutter is regulated by a hardened guide

pin.

f. Tracer controlled milling machine: The tracer controlled milling machine

reproduces irregular or complex shapes of dies, moulds, etc by synchronized

movements of the cutter and tracing element.

Q.107) Draw and state applications of different types of lathe machine tools?

Danish Malim

APPLICATION OF CAPSTAN LATHES

The Ram or slides is lighter and can be moved more quickly than asaddles but lacks some

rigidly.Because of convienienceand speed and limited quickly travel of the turret,the ram type

construction is ideally suited for the production of parts relatively short in length which are

turned from the bar and where the ram everhang can be kept short forgings castings and

stampings can also be machinedby using jaw chucks

The ram type capstan lathe is made in the following size ranges. bar diameters= 12mm to 60

mm swing over bed=200mm to 300mm swing overcross slide=100mm to 200mm maximum

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turret moment= 75mm to 350mm

APPLICATION OF TURRET LATHES

The saddle type construction, i.e the turret lathes is heavier as a longer sroke and is more

rigid.it provide good support for the tools and the means to move the tools along way when

neceesary.It is more rigid.it provides good support for the tools and the means to move the

tools a long way necessary.it is more suitable for longer and heavier cuts, i.e, for the machining

of forgings and castings

the saddle type lathe(turret lathe) is made usually in the following size and ranges

Bar diameter=small lathes upto 50 mm and

=large lathes upto 1oo mm

swing over bed=350 mm to 900 mm over

swing over cross slide=250 mm to 650 mm

maximum turret movement=750 mm to 2000mm

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APPLICATION OF CENTRE LATHES

Lathe operations:

Straight turning:

This operation is performed for producing a cylindrical surface by removing the excess material from the workpiece.

The cutting tool is held in the tool post and fed into the rotating work parallel to the lathe axis.

It may be rough turning or finish turning.

Rough turning is done by taking heavy depth of cur and giving high feed rate at low cutting speed.

Finish turning is done taking by small depth of cut and giving small feed at high cutting speed.

Step turning:

Step turning is also called as shoulder turning.

When a workpiece of different diameters is turned, the surface formed one diameter to the other is called shoulder.

The machining of this part of the workpiece is known as shoulder turning.

Facing:

It is the operation of machining the ends of a workpiece to produce ea flat surface with the axis.

It involves feeding of the tool perpendicular to the axis of rotation of the workpiece.

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Drilling:

For drilling the workpiece is held in a suitable device such as face plate, chuck and the drill is held in the sleeve or barrel of the tailstock.

Dead center is removed and drill chuck or sleeve is inserted in the place.

Then, the drill is fed by hand by rotating the hand wheel or the tailstock.

First a shorter length is drilled, by using smaller and shorter drill, followed by producing the required diameter by using the correct drill size.

The already drilled hole acts as a guide for the latter drill.

Boring:

It is an operation which is employed for machining internal surface, hence also called as internal turning.

Boring is done to enlarge the already drilled the hole and boring them to the exact required size.

Reaming:

Reaming is finishing operation because a very small amount of materials removed during the operation.

It is performed when a very high grade of surface finish ad dimensional accuracy required.

Knurling:

Outer surface of some components such as dumbels, handle, measuring instruments and tools gauges etc. are generally provided with rolled impression on them.

The depressions are provided for better grip as compared to smooth surface.

The indentions are known as knurls and corresponding surface is known as knurling surface.

The operation performed on producing knurled surface called as knurling.

Parting off:

It is an operation employed for cutting away a desired length from the bar stock, hence also called as cutting off.

tools used for this is known as parting tool and have a longer point as they are required to cut from outside surface right upto the center of the job.

Chamfering:

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It is an operation of beveling the extreme ends of a workpiece.

Chamfering is done to remove the burrs, to protect the end of the workpiece from the being damaged and have better appearance.

Grooving:

It is an operation through which a groove of approximately same which is produced one the job.

For grooving, the reduction in diameters is effected by cross feed of the tool.

Forming:

Some operation having neither cylindrical nor tapered surface are said to have shape or formed surface.

For machining such shapes, special tools are used which are called form tool.

In this, shape and size of the cutting edge of a tool correspondence to the shape and size of the surface to be produced.

Q 108) Write a short note on singe point cutting tool.

Name : Thomas Vaidyan

315

R.no : 355

Ans.

Back Rake is to help control the direction of the chip, which naturally curves into the

work due to the difference in length from the outer and inner parts of the cut. It also

helps counteract the pressure against the tool from the work by pulling the tool into the

work.

Side Rake along with back rake controls the chip flow and partly counteracts the

resistance of the work to the movement of the cutter and can be optimized to suit the

particular material being cut. Brass for example requires a back and side rake of 0

degrees while aluminum uses a back rake of 35 degrees and a side rake of 15 degrees.

Nose Radius makes the finish of the cut smoother as it can overlap the previous cut and

eliminate the peaks and valleys that a pointed tool produces. Having a radius also

strengthens the tip, a sharp point being quite fragile.

All the other angles are for clearance in order that no part of the tool besides the actual

cutting edge can touch the work. The front clearance angle is usually 8 degrees while

the side clearance angle is 10-15 degrees and partly depends on the rate of feed

expected.

Minimum angles which do the job required are advisable because the tool gets weaker

as the edge gets keener due to the lessening support behind the edge and the reduced

ability to absorb heat generated by cutting.

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The Rake angles on the top of the tool need not be precise in order to cut but to cut

efficiently there will be an optimum angle for back and side rake.

Q109) Draw and explain the milling cutters.

Name: Aiswarya Pillai Roll No. 346 Batch: 3 Branch: Mechanical

Classification of Milling Cutters:

Milling cutters are usually made of high-speed steel and are

available in a great variety of shapes and sizes for various purposes. You

should know the names of the most common classifications of cutters,

their uses, and, in a general way, the sizes best suited to the work at hand.

Milling Cutter Nomenclature:

1. The pitch refers to the angular distance between like or adjacent

teeth.

2. The pitch is determined by the number of teeth. The tooth face is

the forward facing surface of the tooth that forms the cutting edge.

3. The cutting edge is the angle on each tooth that performs the

cutting.

4. The land is the narrow surface behind the cutting edge on each

tooth.

5. The rake angle is the angle formed between the face of the tooth

and the centerline of the cutter. The rake angle defines the cutting edge

and provides a path for chips that are cut from the workpiece.

6. The primary clearance angle is the angle of the land of each tooth

measured from a line tangent to the centerline of the cutter at the cutting

edge. This angle prevents each tooth from rubbing against the workpiece

after it makes its cut.

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7. This angle defines the land of each tooth and provides additional

clearance for passage of cutting oil and chips.

8. The hole diameter determines the size of the arbor necessary to

mount the milling cutter.

9. Plain milling cutters that are more than 3/4 inch in width are

usually made with spiral or helical teeth. A plain spiral-tooth milling

cutter produces a better and smoother finish and requires less power to

operate. A plain helical-tooth milling cutter is especially desirable when

milling an uneven surface or one with holes in it.

Helical Milling Cutters:

The helical milling cutter is similar, to the plain milling cutter, but the

teeth have a helix angle of 45° to 60°. The steep helix produces a shearing

action that results in smooth, vibration-free cuts. They are available for arbor

mounting, or with an integral shank with or without a pilot. This type of

helical cutter is particularly useful for milling elongated slots and for light

cuts on soft metal.

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Side Milling Cutters:

Side milling cutters are essentially plain milling cutters with the addition

of teeth on one or both sides. A plain side milling cutter has teeth on both

sides and on the periphery. When teeth are added to one side only, the cutter

is called a half-side milling cutter and is identified as being either a right-

hand or left-hand cutter. Side milling cutters are generally used for slotting

and straddle milling.

End Milling Cutters:

1. The end milling cutter, also called an end mill, has teeth on the end as

well as the periphery. The smaller end milling cutters have shanks for chuck

mounting or direct spindle mounting. End milling cutters may have straight

or spiral flutes. Spiral flute end milling cutters are classified as left-hand or

right-hand cutters depending on the direction of rotation of the flutes. If they

are small cutters, they may have either a straight or tapered shank.

2. The most common end milling cutter is the spiral flute cutter

containing four flutes. Two-flute end milling cutters, sometimes referred to as

two-lip end mill cutters, are used for milling slots and keyways where no

drilled hole is provided for starting the cut. These cutters drill their own

starting holes. Straight flute end milling cutters are generally used for milling

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both soft or tough materials, while spiral flute cutters are used mostly for

cutting steel.

3. Large end milling cutters (normally over 2 inches in diameter) are called

shell end mills and are recessed on the face to receive a screw or nut for

mounting on a separate shank or mounting on an arbor, like plain milling

cutters. The teeth are usually helical and the cutter is used particularly for

face milling operations requiring the facing of two surfaces at right angles to

each other.

T-Slot Milling Cutter:

The T-slot milling cutter is used to machine T-slot grooves in worktables,

fixtures, and other holding devices. The cutter has a plain or side milling

cutter mounted to the end of a narrow shank. The throat of the T-slot is first

milled with a side or end milling cutter and the headspace is then milled with

the T-slot milling cutter.

Concave and Convex Milling Cutters:

Concave and convex milling cutters are formed tooth cutters shaped to

produce concave and convex contours of 1/2 circle or less. The size of the

cutter is specified by the diameter of the circular form the cutter produces.

Corner Rounding Milling Cutter:

The corner-rounding milling cutter is a formed tooth cutter used for milling

rounded corners on work pieces up to and including one-quarter of a circle.

The size of the cutter is specified by the radius of the circular form the cutter

produces, such as concave and convex cutters generally used for such work

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as finishing spur gears, spiral gears, and worm wheels. They may also be

used to cut ratchets and spline shafts.

Q 110)Explain The Drill Bit

Name:- Girish Kulkarni

Roll No:-Me 325

Ans: The web thickness should be around 1/8th of the drill diameter, except for small

diameters where thicker webs improve the strength and rigidity of the drill shank. This

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can however impede chip flow.

Conversely, with a thinner the web although the drill will have less rigidity, chip flow and

removal should be easier and it is easier to get the drill to start the hole.

Normally the web thickness increases along the length of the drill (away from the point).

When the drill tip is being reground, the exposed web should also be thinned to

compensate for grinding back up the length of the drill.

The cutting angle should be around 135 degrees. Larger angles produce thinner chips

that should be easier to remove, which is important when drilling stainless steels. Lower

angles of around 120 can however be used for drilling free-machining grades (eg 303

1.4305). Wear to the drill point can indicate that a larger point angle should be used.

Both cutting edges must be at the same angle to the centre line of the drill and be the

same length. A mixture of chip sizes can indicate that that the two cutting edge angles

and lengths are not the same. Lip relief angles decrease as the drill diameter increases.

Excessive feed pressure, poor cutting with sharp drills or drill breakages can indicate

that the drill tip has an insufficient lip relief angle. Conversely, if the drill is tending to dig-

in then a reduced lip angle may be better. In any event, it is essential that drills are

sharp and properly ground.

When drilling deep holes, reduce the speed and feed as the drill moves into the metal.

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Q 111>. State & explain the different angles deployed on single point cutting tool.

ans Anamil Mehta

S.E Mech (331)

323

1.Side cutting edge angle (Cs) (lead angle ) – It is the angle between side cutting edge & side of tool flank.

The complementary angle of the side cutting edge is called “Approach angle”. With lager side cutting edge angle the chips produced will be thinner & wider which will distribute the cutting forces & heat produced more over cutting edge. On other hand greater the component for force tending to separate the work & tool. This causes chatter.

2.End cutting edge angle (Ce) –

This is the angle between end cutting edge & line normal to tool shank. It satisfactory value is 80 to 150.

This is denoted by “Ce” Function – Provide clearance or relief to trailing end of cutting edge.

It prevent rubbing or drag between machined surface & the trailing port of cutting edge.

3..Back rack/ Front rake / Top rake angle (αb) –

It is the angle between face of tool & plane parallel to base.

It is denoted by “αb”

4..Side rake angle (αs) –

It is angle between face of tool & the shank of the tool.

It is denoted by “αs”

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5..Front clearance angle / End relief angles – The angle between front surface of the tool & line normal to base of the tool is

known as a front clearance angle It avoid rubbing of workpiece against tool.

6..Side clearance /relief angle –

This formed by the side surface of the tool with a plane normal to the base of the tool. It avoid rubbing between flank & workpiece when tool is fed longitudinally.

7..Lip angle / cutting angle – It is the angle between face & flank. Longer lip angle stronger will be cutting

edge. This angle is maximum when clearance & rake angle are minimum. Lager

lip angle allows high depth of cut, high cutting speed, work on hard material. It

increase tool life & transfer heat fastly.

Q 112) DRAW AND EXPLAIN VARIOUS PROCESSES ON CENTER LATHE

Adarsh

Me 301

Turning

The lathe can be used to reduce the diameter of a part to a desired dimension. First,

clamp the part securely in a lathe chuck. The part should not extend more that three

times its diameter. Then install a roughing or finishing tool (whichever is

appropriate). If you're feeding the saddle toward the headstock use a right-hand

turning tool. Move the tool off the part by backing the carriage up with the carriage

hand-wheel, then use the cross feed to set the desired depth of cut. In the clip

below, a finish cut is made using the power feed for a smoother finish. Remember

that for each thousandth depth of cut, the work diameter is reduced by two

thousandths.

Facing

325

A lathe can be used to create a smooth, flat, face very accurately perpendicular to

the axis of a cylindrical part. First, clamp the part securely in a lathe chuck. Then,

install a facing tool. Bring the tool approximately into position, but slightly off of the

part. Always turn the spindle by hand before turning it on. This ensures that no parts

interfere with the rotation of the spindle. Move the tool outside the part and adjust

the saddle to take the desired depth of cut. Then, feed the tool across the face with

the cross slide. If a finer finish is required, take just a few thousandths on the final

cut and use the power feed. Be careful clearing the ribbon-like chips; They are very

sharp. Do not clear the chips while the spindle is turning. After facing, there is a very

sharp edge on the part. Break the edge with a file.

Parting

A parting tool is deeper and narrower than a turning tool. It is designed for

making narrow grooves and for cutting off parts. When a parting tool is installed,

ensure that it hangs over the tool holder enough that the holder will clear the

workpiece (but no more than that). Ensure that the parting tool is perpendicular

to the axis of rotation and that the tip is the same height as the center of the

part. A good way to do this is to hold the tool against the face of the part. Set the

height of the tool, lay it flat against the face of the part, then lock the tool in

place. When the cut is deep, the side of the part can rub against sides of the

groove, so it's especially important to apply cutting fluid.

Drilling

A lathe can also be used to drill holes accurately concentric with the centerline of

a cylindrical part. First, install a drill chuck into the tail stock. Make certain that

the tang on the back of the drill chuck seats properly in the tail stock. Withdraw

the jaws of the chuck and tap the chuck in place with a soft hammer. Move the

saddle forward to make room for the tailstock. Move the tailstock into position,

and lock the it in place (otherwise it will slide backward as you try to drill). Before

starting the machine, turn the spindle by hand. You've just moved the saddle

forward, so it could interfere with the rotation of the lathe chuck. Always use a

center-drill to start the hole. You should use cutting fluid with the center-drill. It

has shallow flutes (for added stiffness) and doesn't cut as easily as a drill bit.

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Always drill past the beginning of the taper to create a funnel to guide the bit in.

In this clip, a hole is drilled with a drill bit. Take at most one or two drill

diameters of material before backing off, clearing the chips, and applying cutting

fluid. If the drill bit squeaks, apply solvent more often. The drill chuck can be

removed from the tail stock by drawing back the drill chuck as far as it will easily

go, then about a quarter turn more. A pin will press the chuck out of the collet.

Boring

Boring is an operation in which a hole is enlarged with a single point cutting tool.

A boring bar is used to support the cutting tool as it extends into the hole.

Because of the extension of the boring bar, the tool is supported less rigidly and

is more likely to chatter. This can be corrected by using slower spindle speeds or

by grinding a smaller radius on the nose of the tool.

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Chamfering

Parting (Cutoff) / Grooving

Tool is fed radially into rotating work at some location to cut off end of part, or provide a

groove

Threading

Pointed form tool is fed linearly across surface of rotating workpart parallel to axis of rotation

at a large feed rate, thus creating threads

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GROOVING

• Done at end of thread to permit full travel of nut up to a shoulder or at edge of

shoulder for proper fit

• Also called recessing, undercutting, or necking

• Rounded grooves used where there is strain on part

Q.113 Draw & explain the various operations possible on milling machine.

NAME: Sandeep Yadav ROLL NO.: 361

ANS:

1.plain milling 9.end milling

2.face milling 10.saw milling

3.slide milling 11.milling key ways, grooves & slots

4.straddle milling 12.gear milling

5.angular milling 13. Helical milling

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6.gang milling 14.cam milling

7.form milling 15.thread milling

8.profile milling

Plain milling:

The plain milling is the operation of production of a plain, flat, horizontal surface parallel to

the axis of rotation of a plain milling cutter. The operation is also called slab milling. To

perform the operation, the work and the cutter are secured properly on the machine. The

depth of cut is adjusted by rotating the vertical feed screw of the table and the machine is

started after selecting proper speed and feed. See figure:

Face milling:

The face milling operation is performed by a face milling cutter rotated about an axis

perpendicular to the work surface. The operation is carried in a plain milling machine, and

the cutter is mounted on a stub arbour to produce a flat surface. The depth of cut is adjusted

by rotating the cross feed screw of the table. See figure:

Side milling:

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The side milling is the operation of production of a flat vertical surface on the side of a

workpiece by using side milling cutter. The depth of cut is adjusted by rotating the vertical

feed screw of the table. See figure:

Straddle milling:

The straddle is the operation of production of flat vertical surfaces on both sides of a

workpiece by using two side milling cutters mounted on the same arbour. The distance

between the two cutters is correctly adjusted by using suitable spacing collars. The straddle

milling is very commonly used to produce square or hexagonal surfaces. See figure:

Milling hexagonal bolt head:

One of the common examples of side milling or straddle milling is the operation of milling

hexagonal bolt heads. The procedure adapted to mill a hexagonal bolt head, (seen in fig.), is

described below:

1.the width across the flat of the bolt head is first determined.

2.two half side milling cutters are mounted on the arbor and the distance between them is

correctly adjusted equal to the width across the flat of the bolt head by using suitable spacing

collars.

3.a universal dividing head is mounted on the table with its spindle swivelled to the vertical

position.

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4.the workpiece is centred below the cutter and the first cut is taken.

5.the workpiece is mounted at the nose of the dividing head spindle by the help of a suitable

chuck.

6.the workpiece is rotated through one sixth of a revolution by using the indexing mechanism

and then the second cut is taken.

7.the workpiece is turned again by one sixth of a revolution and the third cut is taken. This

finishes the work and the hexagonal bolt head is produced.

8.if instead of using straddle milling, a single side milling cutter is used , the work will have

to be rotated through one sixth of a revolution for six number of times to finish six faces of

the work.

See figure:

Angular milling:

The angular milling is the operation of production of an angular surface on a workpiece other

than at right angles to the axis of the milling machine spindle. The angular groove may be

single or double angle and may be of varying included angle according to the type and shape

of the angular cutter used. One simple example of angular milling is the production of V-

blocks. See figure:

Gang milling:

The gang milling is the operation of machining several surfaces of a workpiece

simultaneously by feeding the table against a number of cutters having same or different

diameters mounted on the arbor of the machine. The method saves much of machining time

and is widely used in repetitive work. The cutting speed of a gang of cutters is calculated

from the cutter of the largest diameter.

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See figure:

Form milling:

The form milling is the operation of production of irregular contours by using form cutter.

The irregular contour may be convex, concave, or of any other shape. After machining, the

formed surface is checked by a template gauge. The cutting speed for form milling is 20% to

30% less than that of the plain milling. See figure:

Profile milling:

The profile milling is the operation of reproduction of an outline of a template or complex

shape of a master die on a workpiece. Different cutters may be used for profile milling. An

end mill is one of the most widely used milling cutter in profile milling work. See figure:

End milling:

The end milling is the operation of production of a flat surfacewhich may be vertical,

horizontal or at an angle in reference to the table surface. The cutter used is an end mill. The

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end milling cutters are also used for production of slots, grooves or keyways. A vertical

milling is most suitable for end milling operation. See figure:

Saw milling:

The saw milling is the operation of production of a narrow slots or grooves on a workpiece

by using a saw milling cutter. The saw milling can also be performed for complete parting-

off operation. The cutter and the workpiece are set in a manner so that the cutter is directly

placed over one of the T-slots of the table. See figure:

Milling keyways, grooves and slots:

The operation of production of keyways, grooves and slots of varying shapes and sizes can

be performed in a milling machine by using a plain milling cutter, a metal slitting saw, an

end mill or by a side milling cutter. The open slots can be cut by a plain milling cutter, a

metal slitting saw, or by a side milling cutter. The closed slots are produced by using

endmills. A dovetail slot or a T-slot is manufactured by using special type of cutters designed

to give the required shape on the workpiece. The T-slot is produced by first milling a plain

slot on the workpiece and then the shank of the T-slot milling cutter is introduced through the

first machined slot. The second slot is cut at right angles to the first slot by feeding the work

past the cutter. See figure:

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An woodruff key is produced by using a woodruff key slot cutter. Standard keyways are cut

on shafts by using side milling cutters or end mills. The cutter is exactly at the centre line of

the workpiece and then the cut is taken. See figure:

Gear cutting:

The gear cutting operation is performed in a milling machine by using a form relieved cutter.

The cutter may be cylindrical type or end mill type. The cutter profile corresponds exactly

with the tooth space of the gear. Equally spaced gear teeth are cut on a gear blank by holding

the work on a universal dividing head and then indexing it. See figure:

Helical milling:

The helical milling is the operation of production of helical flutes or grooves around the

periphery of a cylindrical or conical workpiece. The operation is performed by swivelling the

table to the required helix angle and then by rotating and feeding the work against rotary

cutting edges of a milling cutter. The usual examples of work performed by helical milling

operations are: the production of helical milling cutters, helical gears, cutting helical grooves

or flutes on a drill blank or a reamer.

Cam milling:

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The cam milling is the operation of production of cams in a milling machine by the use of a

universal dividing head and a vertical milling attachment. The cam blank is mounted at the

end of the dividing head spindle and an end mill is held in the vertical milling attachment.

The axis of the cam blank and the end mill spindle should always remain parallel to each

other when set for cam milling. The dividing head is geared to the table feed screw so that

the cam is rotated about its axis while it is fed against the end mill. The axis of the cam can

be set from zero to ninety degrees in reference to the surface of the table for obtaining

different rise of the cam.

In the first case, when the dividing head spindle or the cam axis is set perpendicular to the

table, as the table advances and the blank is turned, the centre distance between the dividing

head spindle axis and the cutter axis is gradually reduced. This causes the radius of the cam

to be shortened, and produces a spiral lobe with a lead which is same as that for which the

machine is geared. See figure:

In the second case, the setting of the dividing head spindle and the cutter axis is made

horizontal and parallel to each other. If the cam, which is mounted at the end of the dividing

head spindle, is now rotated and fed against the cutter, the centre distance between the two

spindle axis will remain unaltered. This would result in the milling of a circle and the lead of

the spiral would be zero.

It follows from the above two conditions that if the dividing head spindle or the cam axis is

set at any angle between zero to ninety degrees, the amount of lead given to the cam will

change from zero to the maximum lead for which the machine is geared. See figure:

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Thus with one set of change gears only, the production of cams having differentleads are

possible by simply setting the dividing head spindle to the required angle.

In fig.11.62, A,B,C are three sides of a right angled triangle that represents vectorially the

three movements of the cam and the table. The side C represents the distance moved by the

table per revolution of the cam. The side A represents the movement of the cam axis towards

the cutter per revolution. This distance is known as cam rise or lead of the cam. The side B

represents the distance moved by the cam along the axis of the cutter. The angle θ is the

inclination of the dividing head for a given cam rise or lead of the cam. The required angle of

inclination may be calculated from the formula given below. This is derived from the right

angled triangle ABC.

Sin θ = cam rise per rev. = lead of the cam =

A

Lead of the table lead of the table C

Thread milling:

The thread milling is the operation of production of threads by using a single or multiple

thread milling cutter. The operation is performed in special thread milling machines to

produce accurate threads in small or large quantities. The operation requires three driving

motions in the machine: one for the cutter, one for the work and the third for the longitudinal

movement of the cutter.

When the operation is performes by a single thread milling cutter, the cutter head is swivelled

to the exact helix angle of the thread. The cutter is rotated on the spindle and the work is

revolved slowly about its axis. The thread is completed in one cut by setting the cutter to the

full depth of the thread and then feeding it along the entire length of the workpiece.

When the thread is cut by a multiple thread milling cutter, the cutter axis and the work

spindle are set parallel to each other after adjusting the depth of cut equal to the full depth of

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the thread. The thread is completed by simply feeding the revolving cutter longitudinally

through a distance equal to the pitch length of the thread while the work is rotated through

one complete revolution. See figure:

Q.114 ) Draw and explain the thread cutting on centre lathe

SAJAN MHATRE

THREAD CUTTING

Thread cutting is one of the most important operations performed in a lathe.The principle of

thread cutting is to produce a helical groove on a cylindrical or conical surface by feeding the

tool longitudinally when the job is revolved between centres or by a chuck. The longitudinal feed

should be equal to the pitch of the thread to be cut per revolution of the work piece. The

leadscrew of the lathe, through which the saddle receives its traversing motion, has a definite

pitch. A definite ratio between the longitudinal feed and rotation of the headstock spindle should

therefore be Found out so that the relative speeds of rotation of the work and the leadscrew will

result in the cutting of a screw of the desired pitch. This is affected by change gears arrange

between the spindle and the leadscrew or by the change gear mechanism or feed box use in a

modern lathe where it provides a wider range of feed and the speed ratio can be easily and

quickly change illustrates the principle of thread cutting.

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Calculation for change wheels:

To calculate the wheels required for cutting a screw of certain pitch it is necessary to know

how the ratio is obtained, and exactly where the driving and driven wheels are to be placed.

Suppose the pitch of a lead screw is 12 mm and it is required to cut a screw of 3 mm pitch,

then the lathe spindle must rotate 4 times the speed of the lead screw,

That is

Spindle turn 4

Lead screw turn 1

But

Spindle turn mean = 4 means that

Lead screw turn 1

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Driver teeth = 1 since a small gear

Driven teeth 4 rotators faster than Larger one Which it is

connected.

Hence,

Driver teeth = lead screw turn

Driven teeth spindle turn

= pitch of the screw to be cut

Pitch of the lead screw

In English measurement,

Driver teeth = thread per inch on lead screw

Driven teeth thread per inch on work

Often engine lathes are equipped with the set of gears ranging from 20-120 teeth of step

of 5 teeth and 1 gear with 127 teeth.

The types of gear connection on a lathe may be simple, and compound. In a simple train, shown

in fig. the gear on the spindle drives direct through the intermediate gear to the gear on the lead

screw.

This intermediate gears has no effect on the ratio between the driver and the driven, but merely

acts as a connection between the two, and serves to keep the rotation of driver and driven in the

same direction. In a compound train, shown in fig.

The stud carries two wheels which are keyed together so that they rotates as a unit.

The gear on the stud shaft act as a driver and in all calculation it is consider as the spindle

gear, as usually it turns at the same spindle speed. In modern lathes using quick change gears the

correct gear ratio for cutting a particular thread is quickly obtained by simple shifting the levers

in different position which are given on the charts or instruction plates supplied with the

machine.

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Q 115) Draw and explain the taper turning on centre lathe

Anagha.Anil.Bhatkar

S.E. Mechanical

A taper may be turned in the lathe by bending the tool at an angle to the axis of rotation of the

workpiece. The angle tapered by the path of the tool with the axis of the workpiece should

correspond to the half taper angle.

While turning taper,it is essential that the tool cutting edge should be set accurately on the

centerline of the workpiece, otherwise correct taper will not be obtained. A taper may be turned

by one of the following methods:

1.By a broad nose form tool

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2. By offsetting the tailstock centre

3. By a taper turning attachment

4. By swiveling the compound rest

5. By combining longitudinal and cross feed in a special lathe.

Taper turning by a form tool: A broad nose tool having straight cutting edge is set to the work

at half taper angle,and is fed straight into the work to generate a tapered surface .The half angle

of taper will correspond to 90 minus side cutting edge angle of the tool. In this method,the half

angle should be checked properly before use. This method is limited to short length of taper only.

This is due to the reason that the metal is removed by the cutting edge, and may increase the

length of the taper will necessitate the use of a wider cutting edge. This will require excessive

cutting power,which may distort the work due to vibration and may spoil the work surface.

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FIGURE 1: TAPERTUNINGBY A FORM TOOL

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By combining longitudinal and cross feed in a special lathe:This is a more specialized method

of turning taper. In certain lathes both longitudinal and cross feeds may be engaged

simultaneously causing the tool to follow a diagonal path which is the resultant of the magnitude

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of the two feeds. The direction of the resultant may be changed by varying the rate of feeds by

change gram provided inside the apron.

Q 116) State and explain the various attachment and accessories use in lathe machince .

NAME : PRASAD DILIP KOKATE

DIV : S E MECH

Mandrels: 1) A mandrels is adevice for holding and roating a hollow piece of work that has

been previously drilled or bored. 2) The work revolves with the mandrel which is mounted

between two centers. 3) The ends ofmandrel are slightly smaller in diameter and flattened to

provide effective gripping surface of the lathe dog set screw.

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Plain mandrel: 1)The plain mandrel is illustrated . 2)This type of mandrel is most commonly

used in shops and finds wide application where a large number of idential pieces having standard

size holes are required to be mounted on it. For different sure size of holes in work pieces

different mandrel are used.

Collar mandrel: 1) A collar mandrel having solid collars is used for runing workpieces having

holes of large diameter,usually above 100mm. 2) This construction reduce weight and fits better

than a solid mandrel of equal size. 3) A collar mandrel is illustrated.

Screwed mandrel: 1) A screwed mandrel illustrated is in threaded at one end with a collar,

worship having internal threads are screwed on to it against the collar for machining. 2) It may

be right left handed square, ‘V’ or any other type.

Drill chuck: 1) A drill chuck is sometimes used in a lathe for holding straight shank drill ,

reaming or tapping operations. 2) The chuck may be hold either in headstock or tailstock

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spindle. 3) It has self –centering jaws which may be operated by rotating a key. 4) A drill chuck

is explained in Art.

Face plates :1) A face plate consists of a circular disc bored out and threaded to fit the nose of

the lathe spindle. 2) This has the radial. Plain and ‘T’ slots for holding work by bolts and clamps.

3) Face plats are used for holding work pieces which cannot be conveniently held between

centers or by chucks.

Angel plates :1) This is a cast iron plate having two faces machined to make them absolutely at

right angles to each other. 2) Hotels and slots are slots are provided on both faces so that a may

be clamped on a faceplate and can hold the workpicece on the other face by bolts and clamps.

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Collet chuck :1) Collet chucks are used for holding bar stock in production work. 2) Where

quick setting and accurate centering is needed. 3) Illustrates a collectchuck. The chuck attached

to the spindle by a nut consists of a thin cylindrical bushing known as collect having a slot cut

lengthwise on its periphery.

Combinational chuck :1) As the name implies, a combination chuck. 2) Self centering and

independent chuck in take advantage of both the type. 3) The jaws may be operated individually

by separated screws or simultaneously by the scroll disc. 4) The screw mounted on the frame

have teeth cut on it underwirewhich with the scroll and all the jaws together with screws move

radically when the scroll is made to rotate by a pinion.

Magnetic chuck :1) The front view of a magnetic chuck. 2) The chuck is used for holding a very

thin work piece made to magnetic material which cannot be held in an ordinary chuck. 3) It is

also used where any distortion of the work piece due to the pressure of the jaws is undesirable.

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Lathe centre : 1) Attachments are additional equipment used for specific purpose they include

stops, ball turning rests, thread chasing dials, and they timing, milling, grinding, gear cutting,

cutter, relieving and turning attachment. 2) Ordinary centers, B-Ball center, C-Frictionless

center-I. Insert type certified, roller bearing, thrust bearing, housing, D. Half center, E, center-1,

Brazed tip, F, insert type centre-l. insert, G, pipe centre. H use.

Lathe centre :1) The most common method of holding the work in lathe is between the two

centre-live centre and dead centre. 2) This two centre take up the thrust due to metal cutting and

the entire load of the working piece on small bearing surface.3) The dead centre is subjected to

wear due to friction. 4) The included angel of the centre is usually 60 for general purpose work

and 75 for heavy work.the ordinary centre is the type used for most general work. In the

tripped centre, the point consist of a hard alloy tip brazed into an ordinary steel shank the ball

centre is used to minimized wear and strain on the ordinary centre except that little less than half

of the centre has been ground away. 5) This construction facilities facing of the bar ends without

removal of the centre.

6) The insert type of centre is used for reasons of economy as only the high speed steel insert can

be replace instead of replacing the whole centre. The rotating or frictionless centre is always

used in tail stock for supporting heavy work revolving at a high speed.

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Q 117 ) Draw and explain the concept of cutting speed, feed and depth of cut . Adarsh Me 301 CUTTING SPEED

Cutting speed for lathe work may be defined as the rate in meters per minute at whichthe

surface of the job moves past the cutting tool. Machining at a correct cutting speed is

highly important for good tool life and efficient cutting. Too slow cutting speeds

reduceproductivity and increase manufacturing costs whereas too high cutting speeds

result inoverheating of the tool and premature failure of the cutting edge of the tool. The

followingfactors affect the cutting speed:

(i) Kind of material being cut,

(ii) Cutting tool material,

(iii) Shape of cutting tool,

(iv) Rigidity of machine tool and the job piece and

(v) Type of cutting fluid being used.

Calculation of cutting speed Cs, in meters per minute

Cs = ((22/7) × D × N)) /1000

Where

D is diameter of job in mm.

N is in RPM

FEED

1. Feed is defined as the distance that a tool advances into the work during one revolution of

the headstock spindle. It is usually given as a linear movement per revolution of the

spindle or job. During turning a job on the center lathe, the saddle and the tool post move

along the bed of the lathe for a particular feed for cutting along the length of the rotating

job.

In the British system it is expressed in inches per revolution

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2. Increased feed reduces cutting time but increased feed greatly reduces the tool life. The

feed depends on factors such as size, shape, strength and method of holding the

component, the tool shape and it’s setting as regards overhang, the rigidity of the

machine, depth of cut, power available, etc. Coarser feeds are used for roughing and finer

feeds for finishing cuts.

DEPTH OF CUT

1. The depth of cut (t) is the perpendicular distance measured from the machined surface to

the uncut surface of the workpiece. In a lathe the depth of cut is expressed as follows:

Depth of cut= (d1-d2)/2

where, d1=diameter of the work surface before machining.

And d2=diameter of the machined surface.

2. Other factors remaining constant, the depth of cut varies inversely as the cutting speed.

For general purposes, the ration of the depth of cut to the feed varies from 10:1.

Q118) Short note on capstan and turret lathes, with applications.

Arjun Parameswaran

Me 302

Ans:

Generally, both capstan and turret lathes are simply called as ‘turret lathes’. A turret

lathe differs from an engine lathein that, the tail stock is replaced b a hexagonal turret

which can be swiveled about a vertical axis and moved longitudinally along the bed to

bring tools into cutting positions, the regular tool post is replaced by a square cross-

slideturret and the cross slide may support a square turret on the rear. In this way

minimum 14 tools can be mounted at one time. This number can be increased by using

multiple at each position. The advantage of incorporating multiple tool holders is the

chief distinguished feature of the turret lathe. This enables setting up of all tools for a

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job. Except for sharpening, they don’t need further handling.

Block diagram of turret lathe.

Elements of turret lathe.

TYPES OF TURRET LATHES:

The two main types of turret lathe are (a) Ram type turret lathe, and (b) Saddle type

turret lathe.

(a)Ram type turret lathe: in this type of lathe, the revolving turret is mounted on a ram

or a slide carried in a base which can be clamped in any position along the bed of the

machine. This type of lathe is somewhat lighter in construction and therefore can be

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quickly and easily operated. This lathe is also called “Capstan lathe”.

Capstan lathe slide arrangement.

(b) Saddle type turret lathe: on this lathe, the revolving turret is mounted on a saddle

which moves back and forward directly on the machine. This is also simply known as

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“turret lathe”. This type is heavier, has longer stroke and is more rigid.

Turret lathe slide arrangement.

Applications of Capstan Lathes: The ram or the slide is lighter and can be moved

more quickly than a saddle but lacks some rigidity. Because of convenience and speed

and limitedtravel of the turret, the ram type construction is ideally suited for the

production of parts relatively short in length which are turned from the bar, and where

the ram everhang can be kept short. Forgings, castings and stampings can also be

machined by using jaw chucks.

The ram type turret lathe is made in following size ranges:

Bar diameters = 12mm to 60mm

Swing over bed = 200mm to 300mm

Swing over cross-slide = 100mm to 200mm

Maximum turret movement = 75mm to 350mm

Application of Turret Lathes: The saddle type construction, i.e., the turret lathe is

heavier, has a longer stroke and is more rigid. It provides good supportfor the tools and

the means to move the tools a long way when necessary. It is more suitable for longer

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and heavier chucking work which requires longer and heavier cuts, i.e., for the

machining of forgings and castings.

The saddle type lathe (turret lathe) is made usually in the following size ranges:

Bar diameter = small lathes upto 50 mm, and

Large lathes upto 100 mm

Swing over bed = 350 mm to 900 mm and over

Swing over cross-slide = 250 mm to 650 mm

Maximumturret movement = 750 mm to 2000 mm

Q 119) Draw different geometries of single point cutting tool,state application

Ashish R. Bhagwat

ME-303

Ans.

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Q 120) Write a note on automats (single and multi-spindle)?

Mayur D Chaudhari

Me 305

Ans:

AUTOMATIC LATHES

• These are machine tools in which components are machined automatically.

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• The working cycle is fully automatic that is repeated to produce duplicate parts

with out participation of operator.

• All movements of cutting tools, their sequence of operations, applications,

feeding of raw material, parting off, un loading of finished parts all are done on

machine.

• All working & idle operations are performed in definite sequence by control

system adopted in automatic which is set up to suit a given work.

• Only operation reqd to be performed manually is loading of bar stock/ individual

casting/ forged blanks.

These machines are used when production requirements are too high for turret lathes to

produce economically

Advantages

• Greater production over a given period.

• More economy in floor space.

• More consistently accurate work than turrets.

• More constant flow of production.

• Scrap loss is reduced by reducing operator error.

• During machine operation operator is free to operate another machine/ can

inspect completed parts.

Depending upon number of work spindles, automatic lathes are classified as:

1. Single Spindle Automatics.

2. Multi Spindle Automatics.

Type of Single Spindle Automatics:

a) Automatic Cutting Off Machine:

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• These machines produce short w/p’s of simple form by means of cross sliding

tools. Machines are simple in design.

• Head stock with spindle is mounted on bed.

• 2 cross slides are located on bed at front end of spindle.

• CAMS on cam shaft actuate movements of cross slide through system of levers.

Operation:

• The reqd length of work(stock) is fed out with a cam mechanism, up to stock stop

which is automatically advanced in line with spindle axis at each end of cycle.

• Stock is held in collet chuck of rotating spindle.

• Machining is done by tolls that are held in slides operating only in cross wise

direction.

• Typical simple parts (3 to 20 mm dia) machined on such a machine is shown in

fig.

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b) Single spindle Automatic Screw m/c:

• Used for producing small screws(12.7 to 60 mm dia) generally, but also in

production of all sorts of small turned parts.

• These are completely automatic bar type turret lathes, designed for machining

complex internal & external surfaces on parts made of bar stock/separate blanks.

• Up to 10 different cutting tools can be employed at one time in tooling of this kind

of screw machine.

• 2 cross slides(front & rear) are employed for cross feeding tools.

• Vertical tool slides for parting off operation may also be provided .

• Head stock is stationary & houses the spindle.

• Bar stock is held in collet chuck & advanced after each piece is finished & cut off.

• All movements of machine units are actuated by cams mounted on cam shaft.

• Bar stock is pushed through stock tube in a bracket & its leading end is clamped

in rotating spindle by means of collet chuck.

• By stock feeding mechanism bar is fed out for next part.

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• Machining of central hole is done by tools that are mounted on turret slide.

• Parting off/ Cutting off, form tools are mounted on cross slide.

At end of each cut turret slide is with drawn automatically & indexed to bring next

tool to position

c) Swiss type automatic screw/Sliding head screw:

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• As name implies in this m/c head stock is movable & tools are fixed.

• These machines are used for machining long accurate parts of small diameter.(2

to 25mm).

• Bar stock is held in rotating collet in head stock & all longitudinal feeds are

obtained by cam which moves entire head stock as unit.

• Rotating bar stock is fed through hard bushing in centre of tool head.

• Tool head consists of 5 single point tools is placed radially around bushing.

• Mostly diameter turning is done by 2 horizontal slides, other 3 slides used for

operations such as knurling, chamfering, cutoff.

• Tools are controlled & positioned by cams that bring tool in as needed to turn,

face, form, cutoff w/p from bar as it emerges from bushing. Close tolerances

0.005 to 0.00125 mm are obtained.

II) Multi Spindle Automatics:

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• These are fastest type of production machines and are made in a variety of

models with 2,4,5,6,8 spindles.

• In contrast with single spindle m/c where one turret face at a time is working on

one spindle, in multi spindle m/c all turret faces works on all spindles at same

time.

• Production capacity is higher, machining accuracy is lower compared to single

spindle.

• Because of longer set up time, increased tooling cost this machines are less

economical than other on short runs, more economical for longer runs.

a) Parallel Action Automatics/ Multiple Flow m/c:

• In this type of machine same operation is performed on each spindle, w/p is

finished in each spindle in one working cycle.

• It means that

No. of components being machined== No. of spindles in machine.

• Rate of production is high & machine can be used to machine simple parts only

since all the machining processes are done at one position.

• These machines are usually automatic cutting off bar type machines, used to

perform same work as single spindle automatic cut off machines.

365

• Machine consists of frame with head stock at right end.

• Horizontal work spindles that are arranged one above the another

are housed in this head stock.

Cross slides are located at right & left hand sides of spindles & carry cross feeding

tools. All working & auxiliary motions of machine unit are obtained from CAM mounted

on cam shaft.

b) Six Spindle Progressive Action Multi Spindle:

• In this design of machine, the w/p is machined in states & progressively in station

after station.

• Head stock is mounted on left end of base of machine.

• It carries spindle carrier which rotates about a horizontal axis through centre of

machine.

• Working spindles are mounted on this spindle carriers.

• Spindles carry collets & bars from which w/p’s are machined.

• Bar stock is fed through each spindle from rear side.

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• On face of spindle carrier support are mounted cross slides which carry tools for

operations such as cutoff, turning, facing, forming, chamfering.

• No. of slides === No. of spindles.

• Main tool slide (end tool slide) extends from middle of this support.

• Fed of each tool, both cross slide & end tool slides is controlled by its own

individual cams.

• In this diagram spindle carrier indexes on its own axis by 60° at each cutting tool

retraction.

• As spindle carrier indexes, it carries work from one station to another station

where different tolls operate on work.

• Stock moves round the circle in counter clock wise direction & returns to station

no. 6 for cutting off.

Q 121) Write a note on work and tool holding devices in center lathe.

Name:-Kunal Sanjay Deore

Roll No.:-ME307

Sol : There are several work and tool holding devices in lathe machine like lathe centres,

chucks, face plate, mandrels, toolposts, tailstock.

Lathe Centers:Lathe centres are used to hold the workpice inn lathe..The most common

method of holding the work in lathe is between the two centers- live center and dead center.

These two centers take up the thrust due to metal cutting and the entire load of the workpiece

on a small bearing surface. So they are made of very hard materials to resists deflection and

wear. There are different types of centers for different types of works.The different types of

centers are Ordinary centers, ball center, insert type of center, rotating or frictionless center etc.

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Chucks: A chuck is one of the most important device fir holding and rotating a piece of work in

a lathe. Workpieces of short length, and large diameter or of irregular shape which can not be

conveniently mounted between the centers are held quickly and rigidly in a chuck. A chuck is

attached to lathe spindle by means of bolts with the back plate screwed on the spindle nose.

Accurate alignment of the chuck with the lathe axis is effected by spigotting .

The Different types of chucks are

1. Fore jaw independent chuck:-This type of chuck is used for setting up of heavy and

irregular shaped articles.

2. Three jaw universal chuck:-This type of chuck is suitable for holding round , or

hexagonal, and other similar work piece and the job is centred automatically and

quickly.

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3. Air or hydraulic operated chuck:-This type of chuck is used in the mass production work

for its effective gripping capacity.

4. Magnetic chuck:-This type of chuck is suitable for holding a very thin job of magnetic

materials which can not be held in an ordinary chuck.

5. Collet chuck:-These are used for holding bar stock in production work where quick

setting and accurate centring is needed.

6. Combination chuck:-This can be used both as self centring and independent chuck to

take the advantage of both.

7. Drill chuck:-It is sometimes used in lathe machine for holding straight shank drill,

reamer or tapping operations.

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Face Plates: A face plate consists of circular disk board out and threaded to fit the nose of the

lathe s indle. This has a radial lane and ‘T’ slots for holdin the ork b bolt and clam s. Face

lates are sed for holdin the ork iece hich can’t be conveniently held between the

centers or by chuck(as shown in fig. belo

Mandrels: A mandrels is a device for holding and rotating a hollow piece of work that has been

previously drilled or bored. The work revolves with a mandrel whichnis mounted between the

two centers. The mandrel should be true with a accurate center holes for machining outer

surface of the workpiece concentric with its bore. To avoid the distortion ant wear, it is made

up of high carbon steel. The ends of mandrels are slightly smaller in diameter and flattened to

provide effective gripping surface of the lathe dog set screw. The mandrel is rotated by dog and

catch plate and it drives the work by friction.

There are different types of mandrel:

1.Plane Mandrel:-This type of mandre is suitable for only one size of bore. For different sizes of

holes in workpiece different mandrels are used.

2.Step Mandrel:- This type of mandrel is used for turning collars, washers, and odd sized jobs

used in reparing workshope.

3.Collar Mandrel:-A collar mandrel having solid collars is used for turning the workpiece of

larger diameter,usually above 100 mm.

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4.Screwed Mandrel:-It is threde at one end with a collar.workpiece having internal thredeing

are screwed on it.

5.Cone Mandrel:-This type mandrel is suitable for holding the workpiece having different hole

diameter.

6.Gang Mandrel:-These mandrels are used to hold a set of hollow workpiece between two

collars by tightening the nut.

Tailstock : The tailstock is located on the innerways at the right hand end of the bed.This has

two main uses:

(1) It supports the other end of work when it is bieng machined between centres.

(2) It holds a tool for performing operations such as drilling, reaming, tapping etc.

A tailstock is showned in the fig. below

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The tool post: This is located on the top of the compound rest to hold the tool and to enable it

to be adjusted to a convinient position.The rigidity of the tool holder and effective method of

securing are the main factors in designing a toolpost.There are diifferent types of the toolpostas

follows:

(1) Single screw tool post:- This consist of a round bar with a slotted hole in centre for

fixing the tool by means set screw.The toolpost is not rigid enough for heavy work as

only one clamping screw is provided.

(2) Four bolt tool post:- The tool is held in position by two straps and four bolts.This type

forms very firm support for eithere a single or double tool set up.

(3) Open side tool post:- This arrangement ensures quick replacement of tool.

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(4) Four way tool post:-This type of tool post is used in moderately heavy lathes and is

suitable for repitition work.

Q 122) Write a note on work & tool holding devices used on milling machine tool?

NAME-NIKHIL.DEORE

ROLLNO:ME308

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Milling machine (Vertical, Manual) No Text 1.Face milling cutter 2.Spindle 3.Spindle

head 4.Column 5.Table 6.Saddle 7.Knee 8.Base 9.Spindle switch 10.Spindle speed

gear lever 11.Spindle speed control lever 12.Oil tank 13.Table manual wheel 14.Table

lock bar 15.Saddle automatic moving bar 16.Saddle automatic moving control dial

17.Saddle manual wheel 18.Knee manual wheel 19.Quick button

In the vertical mill the spindle axis is vertically oriented. Milling cutters are held in the

spindle and rotate on its axis. The spindle can generally be extended (or the table can

be raised/lowered, giving the same effect), allowing plunge cuts and drilling. There are

two subcategories of vertical mills: the bedmill and the turret mill. Turret mills, like the

ubiquitous Bridgeport, are generally smaller than bedmills, and are considered by some

to be more versatile. In a turret mill the spindle remains stationary during cutting

operations and the table is moved both perpendicular to and parallel to the spindle axis

to accomplish cutting. In the bedmill, however, the table moves only perpendicular to

the spindle's axis, while the spindle itself moves parallel to its own axis. Also of note is a

lighter machine, called a mill-drill. It is quite popular with hobbyists, due to its small size

and lower price. These are frequently of lower quality than other types of machines,

however.spindle)A horizontal mill has the same sort of x–y table, but the cutters are

mounted on a horizontal arbor (see Arbor milling) across the table. A majority of

horizontal mills also feature a +15/-15 degree rotary table that allows milling at shallow

angles. While endmills and the other types of tools available to a vertical mill may be

used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side

and face mills, which have a cross section rather like a circular saw, but are generally

wider and smaller in diameter. Because the cutters have good support from the arbor,

quite heavy cuts can be taken, enabling rapid material removal rates. These are used to

mill grooves and slots. Plain mills are used to shape flat surfaces. Several cutters may

be ganged together on the arbor to mill a complex shape of slots and planes. Special

cutters can also cut grooves, bevels, radii, or indeed any section desired. These

specialty cutters tend to be expensive. Simplex mills have one spindle, and duplex mills

have two. It is also easier to cut gears on a horizontal mill.

THE TYPES OF DEVICES ON MILLIMG MACHINE:

A.CUTTER:

The pitch refers to the angular distance between like or adjacent teeth.

The pitch is determined by the number of teeth. The tooth face is the forward facing

surface of the tooth that forms the cutting edge.

The cutting edge is the angle on each tooth that performs the cutting.

The land is the narrow surface behind the cutting edge on each tooth.

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The rake angle is the angle formed between the face of the tooth and the centerline of

the cutter. The rake angle defines the cutting edge and provides a path for chips that

are cut from the workpiece.

The primary clearance angle is the angle of the land of each tooth measured from a line

tangent to the centerline of the cutter at the cutting edge. This angle prevents each

tooth from rubbing against the workpiece after it makes its cut.

This angle defines the land of each tooth and provides additional clearance for passage

of cutting oil and chips.

The hole diameter determines the size of the arbor necessary to mount the milling

cutter.

Plain milling cutters that are more than 3/4 inch in width are usually made with spiral or

helical teeth. A plain spiral-tooth milling cutter produces a better and smoother finish

and requires less power to operate. A plain helical-tooth milling cutter is especially

desirable when milling an uneven surface or one with holes in it.

TYPES OF CUTTER:

The helical milling cutter is similar, to the plain milling cutter, but the teeth have a helix

angle of 45° to 60°. The steep helix produces a shearing action that results in smooth,

vibration-free cuts. They are available for arbor mounting, or with an integral shank with

or without a pilot. This type of helical cutter is particularly useful for milling elongated

slots and for light cuts on soft metal.

1.SIDE MILLING CUTTER:

Side milling cutters are essentially plain milling cutters with the addition of teeth on one

or both sides. A plain side milling cutter has teeth on both sides and on the periphery.

When teeth are added to one side only, the cutter is called a half-side milling cutter and

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is identified as being either a right-hand or left-hand cutter. Side milling cutters are

generally used for slotting and straddle milling.

2.End Milling Cutters :

The end milling cutter, also called an end mill, has teeth on the end as well as the

periphery. The smaller end milling cutters have shanks for chuck mounting or direct

spindle mounting. End milling cutters may have straight or spiral flutes. Spiral flute end

milling cutters are classified as left-hand or right-hand cutters depending on the

direction of rotation of the flutes. If they are small cutters, they may have either a

straight or tapered shank. The most common end milling cutter is the spiral flute cutter

containing four flutes. Two-flute end milling cutters, sometimes referred to as two-lip end

mill cutters, are used for milling slots and keyways where no drilled hole is provided for

starting the cut. These cutters drill their own starting holes. Straight flute end milling

cutters are generally used for milling both soft or tough materials, while spiral flute

cutters are used mostly for cutting steel.Large end milling cutters (normally over 2

inches in diameter) are called shell end mills and are recessed on the face to receive a

screw or nut for mounting on a separate shank or mounting on an arbor, like plain

milling cutters. The teeth are usually helical and the cutter is used particularly for face

milling operations requiring the facing of two surfaces at right angles to each othER.

3.T-Slot Milling Cutter

The T-slot milling cutter is used to machine T-slot grooves in worktables, fixtures,

and other holding devices. The cutter T-Slot Milling Cutter has a plain or side

milling cutter mounted to the end of a narrow shank. The throat of the T-slot is

first milled with a side or end milling cutter and the headspace is then milled with

the T-slot milling cutter.

Concave and Convex Milling Cutters

Concave and convex milling cutters are formed tooth cutters shaped to produce

concave and convex contours of 1/2 circle or less. The size of the cutter is specified by

the diameter of the circular form the cutter produces.

4.Corner Rounding Milling Cutter

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The corner-rounding milling cutter is a formed tooth cutter used for milling rounded

corners on workpieces up to and including one-quarter of a circle. The size of the cutter

is specified by the radius of the circular form the cutter produces, such as concave and

convex cutters generally used for such work afinishing spur gears, spiral gears, and

worm wheels. They may also be used to cut ratchets and spline shafts.

B.Collets

A collet is a form of a sleeve bushing for reducing the size of the hole in the milling

machine spindle so that small shank tools can be fitted into large spindle recesses.

They are made in several forms, similar to drilling machine sockets and sleeves, except

that their tapers are not alike.

C.Spindle Adapters

A spindle adapter is a form of a collet having a standardized spindle end. They are

available in a wide variety of sizes to accept cutters that cannot be mounted on arbors.

They are made with either the Morse taper shank or the Brown and Sharpe taper with

tang having a standard spindle end.

D.Chuck Adapter

A chuck adapter is used to attach chucks to milling machines having a standard spindle

end. The collet holder is sometimes referred to as a collet chuck. Various forms of

chucks can be fitted to milling machines spindles for holding drills, reamers, and small

cutters for special operations.

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E.Quick-Change Tooling

The quick-change adapter mounted on the spindle nose is used to speed up tool

changing. Tool changing with this system allows you to set up a number of milling

operations such as drilling, end milling, and boring without changing the setup of the

part being machined. The tool holders are mounted and removed from a master holder

mounted to the machine spindle by means of a clamping ring.

Q 123) Write note on NC and CNC machine tooling?

Sarvesh A. Gadhe

Roll No. 310

Numerical control (NC) refers to the automation of machine tools that are operated by

abstractly programmed commands encoded on a storage medium, as opposed to

controlled manually via hand wheels or levers, or mechanically automated via cams

alone. The first NC machines were built in the 1940s and 1950s, based on existing tools

that were modified with motors that moved the controls to follow points fed into the

system on punched tape. These early servomechanisms were rapidly augmented with

analog and digital computers, creating the modern computer numerical control (CNC)

machine tools that have revolutionized the machining processes.

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A CNC machining center

In modern CNC systems, end-to-end component design is highly automated using

computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. The

programs produce a computer file that is interpreted to extract the commands needed to

operate a particular machine via a postprocessor (for specific controller), and then

loaded into the CNC machines for production. Since any particular component might

require the use of a number of different tools-drills, saws, etc., modern machines often

combine multiple tools into a single "cell". In other cases, a number of different

machines are used with an external controller and human or robotic operators that

move the component from machine to machine. In either case, the complex series of

steps needed to produce any part is highly automated and produces a part that Modern

CNC mills differ little in concept from the original model built at MIT in 1952. Mills

typically consist of a table that moves in the X and Y axes, and a tool spindle that

moves in the Z (depth). The position of the tool is driven by motors through a series of

step-down gears in order to provide highly accurate movements, or in modern designs,

direct-drive stepper motor or servo motors. Open-loop control works as long as the

forces are kept small enough and speeds are not too great. On commercial

metalworking machines closed loop controls are standard and required in order to

provide the accuracy, speed, and repeatability demanded.

As the controller hardware evolved, the mills themselves also evolved. One change has

been to enclose the entire mechanism in a large box as a safety measure, often with

additional safety interlocks to ensure the operator is far enough from the working piece

for safe operation. Most new CNC systems built today are completely electronically

controlled.

CNC-like systems are now used for any process that can be described as a series of

movements and operations. These include laser cutting, welding, friction stir welding,

ultrasonic welding, flame and plasma cutting, bending, spinning, pinning, gluing, fabric

cutting, sewing, tape and fiber placement, routing, picking and placing (PnP), and

sawing.closely matches the original CAD design.

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Tools with CNC variants

Drills

EDMs

Lathes

Milling machines

Wood routers

Sheet metal works (Turret Punch)

Wire bending machines

Hot-wire foam cutters

Plasma cutters

Water jet cutters

Laser cutting

Oxy-fuel

Surface grinders

Cylindrical grinders

3D Printing

Induction hardening machines

Numerical control (NC) was developed with these goals in mind:

To increase production

To reduce labor costs

To make production more economical

To do jobs that would be impossible or impractical without NC

To increase the accuracy of duplicate parts

Advantages:

Increased productivity

Reduced tool/fixture storage and cost

Faster setup time

Reduced parts inventory

Flexibility that speeds changes in design

Better accuracy of parts

Reduction in parts handling

Better uniformity of parts

380

Better quality control

Improvement in manufacturing control

Disadvantages

Increase in electrical maintenance

High initial investment

Higher per-hour operating cost than traditional machine tools

Retraining of existing personnel

Direct numerical control (DNC)

Direct numerical control (DNC), also known as distributed numerical control (also DNC),

is a common manufacturing term for networking CNC machine tools. On some CNC

machine controllers, the available memory is too small to contain the machining

program (for example machining complex surfaces), so in this case the program is

stored in a separate computer and sent directly to the machine, one block at a time. If

the computer is connected to a number of machines it can distribute programs to

different machines as required. Usually, the manufacturer of the control provides

suitable DNC software. However, if this provision is not possible, some software

companies provide DNC applications that fulfill the purpose. DNC networking or DNC

communication is always required when CAM programs are to run on some CNC

machine control.

Wireless DNC is also used in place of hard-wired versions. These types of control are

very widely used in Automobile, Engineering, Sheet Metal, Aeronautic Industry.

Q 124) Draw and explain machining center.

NAME: GEORGE VARGHESE

ROLL NO: Me313

Most CNC milling machines (also called machining centers) are computer

controlled vertical mills with the ability to move the spindle vertically along the Z-axis.

This extra degree of freedom permits their use in diesinking, engraving applications,

and 2.5D surfaces such as relief sculptures. When combined with the use of conical

381

tools or a ball nose cutter, it also significantly improves milling precision without

impacting speed, providing a cost-efficient alternative to most flat-surface hand-

engraving work.

CNC machines can exist in virtually any of the forms of manual machinery, like horizontal mills. The most advanced CNC milling-machines, the multiaxis machine, add two more axes in addition to the three normal axes (XYZ). Horizontal milling machines also have a C or Q axis, allowing the horizontally mounted workpiece to be rotated, essentially allowing asymmetric and eccentric turning. The fifth axis (B axis) controls the tilt of the tool itself. When all of these axes are used in conjunction with each other, extremely complicated geometries, even organic geometries such as a human head can be made with relative ease with these machines. But the skill to program such geometries is beyond that of most operators. Therefore, 5-axis milling machines are practically always programmed with CAM.

With the declining price of computers and open source CNC software, the entry price of CNC machines has plummeted.

382

Diagrams of machining center

383

Q 125) Draw and State application of various Milling Cutters and their

applications

Vinit.V.Joshi

Roll No :Me 315

Side Milling Cutters

Side milling cutters are essentially plain milling cutters with the addition of teeth

on one or both sides. A plain side milling cutter has teeth on both sides and on the

periphery. When teeth are added to one side only, the cutter is called a half-side

milling cutter and is identified as being either a right-hand or left-hand cutter.

Side milling cutters are generally used for slotting and straddle milling.

Half- Side Milling Cutter

• Used when only one side of cutter required

• Also make with interlocking faces so two cutter may be placed side by side for slot

milling

• Have considerable rake

• Able to take heavy cuts

Angular Cutters

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• Single-angle

• Teeth on angular surface

• May or may not have teeth on flat

• 45º or 60º

• Double-angle

• Two intersecting angular surfaces

with cutting teeth on both

• Equal angles on both side of line

at right angle to axis

Single angle Double angle

Helical Milling Cutters

The helical milling cutter is similar, to the plain milling cutter, but the teeth have

a helix angle of 45° to 60°. The steep helix produces a shearing action that results

in smooth, vibration-free cuts. They are available for arbor mounting, or with an

integral shank with or without a pilot. This type of helical cutter is particularly

useful for milling elongated slots and for light cuts on soft metal.

385

Heavy Duty Plain Cutters

Have fewer teeth than light-duty type

Provide for better chip clearance

Helix angle varies up to 45º

Produces smoother surface because of shearing action and reduced chatter

Less power required

End Milling Cutters

The end milling cutter, also called an end mill, has teeth on the end as well as the

periphery. The smaller end milling cutters have shanks for chuck mounting or

direct spindle mounting. End milling cutters may have straight or spiral flutes.

Spiral flute end milling cutters are classified as left-hand or right-hand cutters

depending on the direction of rotation of the flutes. If they are small cutters, they

may have either a straight or tapered shank.

386

The most common end milling cutter is the spiral flute cutter containing four

flutes. Two-flute end milling cutters, sometimes referred to as two-lip end mill

cutters, are used for milling slots and keyways where no drilled hole is provided

for starting the cut. These cutters drill their own starting holes. Straight flute end

milling cutters are generally used for milling both soft or tough materials, while

spiral flute cutters are used mostly for cutting steel.

Large end milling cutters (normally over 2 inches in diameter) are called shell end

mills and are recessed on the face to receive a screw or nut for mounting on a

separate shank or mounting on an arbor, like plain milling cutters. The teeth are

usually helical and the cutter is used particularly for face milling operations

requiring the facing of two surfaces at right angles to each other.

Shell End Milling Cutter

• Face milling cutters under 6 inch

• Solid, multiple-tooth cutters with teeth on face and periphery

• Held on stub arbor

• May be threaded or use key in shank to drive cutter

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Woodruff Key Slot Milling Cutter

• Similar in design to plain and side milling cutters

• Small (up to 2 in) solid shank, straight teeth

• Large mounted on arbor with staggered teeth

• Used for milling semicylindrical keyseats in shafts

• Designated by number

system

Fly Cutter

• Single-pointed cutting tool with cutting end ground to desired shape

• Mounted in special

adapter or arbor

• Fine feed must be used

388

• Used in experimental

work instead of a

specially shaped cutter

•

T-Slot Milling Cutter

The T-slot milling cutter is used to machine T-slot grooves in worktables,

fixtures, and other holding devices. The cutter has a plain or side milling cutter

mounted to the end of a narrow shank. The throat of the T-slot is first milled with

a side or end milling cutter and the headspace is then milled with the T-slot

milling cutter.

Concave and Convex Milling Cutters

Concave and convex milling cutters are formed tooth cutters shaped to produce

concave and convex contours of 1/2 circle or less. The size of the cutter is

specified by the diameter of the circular form the cutter produces.

Corner Rounding Milling Cutter

The corner-rounding milling cutter is a formed tooth cutter used for milling

rounded corners on workpieces up to and including one-quarter of a circle. The

size of the cutter is specified by the radius of the circular form the cutter produces,

such as concave and convex cutters generally used for such work as finishing spur

gears, spiral gears, and worm wheels. They may also be used to cut ratchets and

spline shafts.

389

Q126) Write a note on Screw Cutting.

Name: Jubin Thomas R No : 316

Ans : Cutting screw threads on a centre lathe is called as screw cutting. It is a very

commonly performed operation on a lathe. In thread cutting, helical grooves are

produced on a cylindrical or conical surface by feeding the tool longitudinally when the

workpiece is revolved between the centres. Both external and internal threads can be

cut on a lathe. For both of these, a proper system of gearing between the lathe spindle

and lead screw is required, so as to establish a desired speed ratio between them.

Threads of odd and reduced pitches

When a pitch is required which cannot be obtained by any arrangement of the available change wheels, alternative methods have to be employed. Often even if the exact pitch necessary is beyond the scope of available gears, a very near compromise may be arranged. One method of dealing with such cases is to reduce the ratio to a continued fraction, find the value of its successive convergents, and employ the nearest approximation for which a gear ratio can be made up. As an example of the application of this method to a problem we will work out the following. Example. A thread of 1.75mm is to be cut on a die-casting mould and the pitch is to be made 2% longer than standard to allow for contraction of the finished casting. Find suitable change wheels to cut the thread (Leadscrew =5mm pitch.) Ans:

390

Thread cutting by setting the taper attachment The above result could have been obtained in another manner-by using the normal change wheels for the thread required and employing the taper attachment. By setting the taper attachment to the required angle, setting over the tailstock to throw the work parallel with the movement of the tool, and disconnecting the cross-slide in the same way as for taper turning, the thread may be cut. The only observation is that the tool must be set with the centre line perpendicular to the work axis and not perpendicular with the lathe bed. The application of this method is limited to small over length percentages on account of the limits to which the work may be set over, and the capacity of the taper attachment. In any case it is not advisable to employ it for large angles because of the unsatisfactory conditions at the centres of a job with a large set-over. Pitch variator A third method of cutting threads having a constant small increase or decrease in pitch is to use a pitch variator which can be fitted to certain lathes. This consists of a train of

391

gears and a hardened slide which together produce the desired lateral movement of the leadscrew end abutment. This equipment is mounted on the end of the lathe bed. Module and diametral pitches

If a worm has to be threaded having a pitch suitable for meshing with a wormwheel or gear cut to a module or diametral pitch, it is convenient to be able to select a satisfactory set of change wheels. Module pitches The module pitch (m) is the length (in mm) that each tooth would occupy if the teeth in a gear were spaced along its pitch diameter. So that if D= Pitch diameter, T= Number of teeth, m= module, then D(mm)= mT

and m=

If p(mm)=circular pitch,

=D=mT and m=

The module (in mm) is the height of the tooth above the pitch line (addendum). Example. Change wheels to thread a worm suitable for matching up with a 3 module gear; leadscrew 5mm pitch

Circular pitch (p) = = 3x

=

mm

Ratio

=

= ⁄

=

=

=

Diametral pitches The diametral pitch (P) is the English (inch) method for specifying gear elements. This pitch is represented by the number of teeth per inch of diameter, so that

P=

or D=

and since, from above, D=mT.

mT=

and P=

In using the above formulae, the appropriate conversion from inches to millimetres must be made. The cutting of a diametral (inch) pitch on a metric lathe necessitates one of the following: (a) Use of a 127 T wheel as a driver in the train to give an exact ratio. (b) Use of either a 51 T or a 63 T as a driver to give a very near approximation. (c) Convert the pitch to mm and find the nearest ratio by a continued fraction.

392

Example: Change wheels to thread a worm suitable for meshing with an 8 P gear : lathe leadscrew = 6mm pitch.

Circular pitch for 8P=

=

and using each of the above methods in turn,

(a)

⁄

⁄

(b)

(from above)

Using the ratio ⁄ instead of ⁄ ,

The actual pitch obtained

x6

(c) Circular pitch of worm

= 9.978mm

and the fourth convergent of a continued fraction works out as ⁄

This gives a ratio

and results in a pitch of 6 x

10mm for the worm

Q 126) Note on the usage of dividing head and circular table in milling Jubin Thomas Me 316

Ans

393

Sections of a universal head The dividing head is an important auxiliary to the universal milling machine. Divisional accuracy

The essential requirement of a dividing head is that it shall be reliable in its division of the circle, and the accuracy demanded will depend to some extent on the work. For example, a slight discrepancy could be tolerated in such work as gashing the blank for a milling cutter to accommodate the blades, or milling the hexagon on an ordinary bolthead, but extreme accuracy should be maintained in the cutting of a gear or the millin of s line’s on a shaft to mate ith corres ondin ke a s in a hole. In any case, even when we say that certain work need not be very accurate, we are still talking within small fractions of a degree as possible errors, and in its accuracy of division a good dividing head should be akin to the pitch accuracy of a good leadscrew. Without suitable equipment it is difficult to carry out tests on the accuracy of division of a head. A limited number of checks may be taken with a sine bar clamped to the chuck or faceplate, measuring from the machine table with slip gauges, but the most convenient method is to employ a graduated reference disc in conjunction with a microscope. A suitable-sized disc for the purpose would be about 200-250mm diameter, graduated in degrees round its edge or on its face at the periphery. The graduations must be accurate, so the disc should be obtained from a reliable firm of instrument makers. To complete the equipment a microscope is necessary, with means for supporting and clamping it, and for focusing it on the disc. The eyepiece of the microscope must be provided with a scale corresponding to the graduations on the disc

394

and designed so that small divisions of a degree may be measured. When making a test, the disc should be clamped lightly to the spindle, or to one of its attachments, and set concentric. The microscope is clamped in positions and is focused on the scale. During the test, periodic, cumulative and erratic errors should be investigated, as well as the effect of reversing rotation and the ability of the spindle to come to the same position after several indexings. The optical dividing head operate son a principle which is free from the errors and deterioration associated with mechanical movements, and where sustained high accuracy is important the higher cost of such equipment is justified.

Q 127) Write short notes on helical or spiral milling?

Name: Akshay .R. Kadam Roll No: Me317

One of the most important indexing operations to be performed on milling machine is the

helical or spiral milling. Generation of flutes on twist drills, milling of helical and spiral gears,

milling of worms and cutter, etc. are some of the examples of this class. In the case of helical

milling, the job is rotated and side by side it is moved linearly due movement of table under the

rotating cutter fixed in one position. This is done by connecting the worm shaft to the milling

table feed screw with the help of a set of gears. Lead of the helix depends upon the rate at

which the job is rotated with respect to table movement.

While performing helical milling the following points must be taken under consideration:

1. The table of the milling machine must be set at an angle (equal to the helix angle) to the

normal position of the table. This is done so that when the job advances and at the

same time revolves also, the impression left by the cutter in the job will be identical to

the contour of the cutter. The direction in which the table is swivelled determines the

hand of spiral.

2. There must be a proper relation between the movement of job and table.

3. The job is to be fed to the cutter by the table movement.

Lead of the helical milling machine is the distance through which the table moves when the

spindle of dividing head moves through one revolution without any change in velocity ratio

between the dividing head spindle and the table feed screw.

395

Sometimes it is necessary to introduce change gears between the worm shaft and the table

feed screw, because when the table travels a distance equal to the lead of helix, the job

must have completed one revolution. This can be achieved by introducing change gears.

The formula given below holds good for the change gears.

[(Gear on table feed screw) Driver] / [(Gear on spindle) Driven] =

(Lead of machine) / (Lead of helix on the job).

Q 128 ) Explain various index in procedure in milling with suitable example?

NAME: TUSHAR KADAM

ROLL NO: Me318

BRANCH: (SE) MECH

Ans:

INDEXING UNUSUAL DIVISION:

The makers of most dividing heads provide a range of index plates which give wide selections of

division, and, in addition, some supply plates for dealing with uncommon requirements,

Standard index plates. For the readers information we repeat the whole circle available on

several well known dividing heads.

Brown and Sharpe: 15, 16, 17, 18, 19, 20, 21, 23, 27, 29, 31, 33, 37, 39, 41, 43, 47, 49.

Parkinson Cincinnati Herbert 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43, 46, 47, 49, 51, 53, 54, 57,

58, 59, 62, 66.

On a number of dividing heads, division outside the head, division outside the range given on the

plates must be obtained by compounding, or by a system of differential indexing. Whichever

method is used, the solution is generally available in table s supplied by the makers, but as we

396

know that many readers will prefer to understand the principle involved, and will wish to display

the mathematical ability in working it out, we give the methods below.

COMPOUND INDEXING:

Normally the index plate is locked by a plunger fitting in one of the circles of holes. The

principle in compound indexing is to obtain the required division in two stages:

By a movement of crank in usual way;

By adding or subtracting a further movement obtained by rotating the index plate and controlled

by the locking plunger.

If both movements have been made in the same direction, the total indexing will have been

5/20 +1/15 = 15/60 + 4/60 = 19/60 on turns

If the plates had been turned opposite to the crank we should had

5/20 -1/15 = 15/60 – 4/60 = 11/60

And by compounding in this way a large division of section may be obtained.

If n is the number of divisions desired on the work, then 40/n is the indexing, and the fractions

Representing the two movements must give 40/n when added or subtracted. At the same time

the denominators of the fractions must be numbers representing whole circle available on the

plate being used. The determination is really one of the trial and error, but the device given

below will assist in finding the solution.

Example: To determine compound indexing for (a) 93 and (b) 153 division (a) 93 division.

Here we require two fractions which when added or subtracted given the fraction 49/93, and

which have denominators equal to whole circle on the plates.

Put the numbers down and factorise them (place the denominator above and the 40 below a line

thus)

(93= 31 *3) / (40 = 2*2*2*5)

Now choose numbers representing two – holes circle in the same plate, write them below the 40

and factorise; write their difference above the line and factorise

10= 5*2

93= 31*3

―

397

40= 2*2*2*5

31= 31*1

21= 7*3

Hence 21 and 31 circles will be suitable and we require to find the respective number of holes to

be indexed let this be a and b, let these be a and b , then

a/2 ± b/31 = 40/93

(7*3) (31*1) (31*3)

Putting over a common denominator,

a/21 ± b/31 = 40/93

(7*3) (31*1) (31*3)

Putting over a common denominator,

(31a - 21b = 280) / (7*31*3)

From which, by the trial and error,

31a ±21b = 280

When a=b=28

Hence the indexing required is to subtract 28 holes in 31-hole circle from 28 holes in a 21

circles, i.e.

28 in 21 circle forwards

28 in 31 circle backwards

(b) 153 divisions

Working as before we know

1=1

153 = 17*3*3

―

40= 2*2*2*5

18=3*3*2

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17=17*1

In this case we have adopted 18 and 17 hole circles so that

a/17 ± b/18 = 40/153

(17*1) (3*3*2) (17*3*3)

And, putting over a common denominator

(18a ±17b = 80) / (17*3*3*2)

When a=12 and b=8

(18*12-17*8) = (216-136) = 80

Hence subtract an indexing of 8 holes in an 18 circle from 12 holes in a 17 circle.

DEFFERENTIAL INDEXING:

This is really automatic method of performing compound indexing .The mechanism of a

universal dividing head incorporating a shaft C which is parallel with the main spindle and

protrudes from the rear of the head. This shaft is connected through equal bevels and gears to a

gear fixed on the index plate. It is thus possible, when the index plate is unlocked, to drive it

through an equal ratio from shaft C. When the crank plunger is registering in a hole in the plate,

the crank and worm rotate as one with it. When the head is arranged for differential indexing, the

index plate is released from its locking plunger, leaving it free to turn, and at the same time, it is

geared back to the spindle of the head. Thus, as the spindle is rotated via the crank and worm, the

gear trains causes the index plate to turn backwards or forwards and the net result is same as if

the index plate were released and rotated by hand as in compound indexing. Differential

indexing is more straightforward and has wider application than compound indexing. A dramatic

sketch showing how the head is arranged for this form of indexing and the problem is to

calculate the indexing and gear ratio necessary for any given number of divisions. We shall best

illustrate this by working a few examples.

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EXAMPLE: To determine the differential indexing for (a) 93 and (b) 153 divisions

93 indexing

The indexing required is 40/93 turns of the crank per division, and when this has been operated

93 times the crank has turned (40/93)*93=40 times, i.e. the work has turned one complete circle,

as it should. This could be obtained by simple indexing only if a 93-holes circle were available.

Use an available whole circle which will give something near to it, e.g.

40/93=4/9.3=8/18.6

Let us take 93 moves of hole in an 18 circle,

93* 8/18 = 744/18 411/3 turns on the crank

But, as we have seen, the crank must make only 40 turns during the 93 indexing and we must

therefore subtract 11/3 turns . This is done by gearing up to the plate so that while the spindle

make 1 turn the plate make 11/3 turns in the opposite direction.

Hence with an indexing of 8 holes, in an 18-holes circle, the gear ratio from spindle to plate

Driver/driven = 4/3= 64/48

153 divisions

Indexing =40/153.

Approximate indexing=1/3083 and using a 27-holes this gives (1/3.83)* 27= 7 holes approx.

400

Taking 153 moves of 7 holes in a 27-hole circle

=153*7 /27 = 1071/27 = 3918/27

This is 40-3918/27 = 9/27 turns less than the requisite 40 turns and the deficit must be made up

by gearing the plate to rotate in the same direction as the crank

Ratio; driver/driven = 9/27 = 1/3 = 24/72

Hence for 153 divisions the indexing us 7 holes in a 27 – hole circle with a gear ratio of 24/72,

plate and crank revolving in the same direction.

The reader will notice that the choice of an approximate indexing is quite arbitrary, and for any

different example many different solutions are possible which will give the indexing desired. To

avoid fruitless trials which have to be discarded on amount of the gears ratio being impossible to

obtain, the following factors should be taken into account:

The hole circle chosen for approximate indexing should be a number whose factors

accommodate themselves to the gears available, e.g. use hole circle of 18, 20, 21, 27, etc. for the

B and S gear range.

The difference from 40 of the product should represent an amount for which a reasonable gear

ratio is possible, e.g. if the multiplication gave 401/8, a gear ratio of 1 to 8 would be necessary.

This is not convenient arrangement and a difference ranging from ½ to 11/2 is most suitable.

ANGULAR INDEXING:

Sometimes it is necessary to index an angle which cannot be obtained exactly with any of the

circle available. Under such conditions a very close result may be obtained by an approximation

derived from a continued fraction. The following example should make the method clear:

xample indexing to give the nearest approximation to a division of 51 37 using the

Cincinnati index pates

Since one turn of the crank gives an angular displacement of 9° on the work, the indexing

necessary is

51 37 = 5 whole turns + 6 37 / 9 of a turn

Treating the fraction and converting to minutes we have

6 37 / 9 = 397 / 540

Which to index exactly would necessitate a move of 397 holes in a 540- whole circle!

Converting this to a continued fraction:

401

39) 540 (1

397

―

143)397(2

286

―

111)143(1

111

―

32) 111(3

96

―

15)32(2

30

―

2)15(7

14

―

1)2(2

And the continued fraction is

1

402

―

1+1

―

2+1

―

1+1

―

3+1

2+1

―

7+1

―

2

The convergent of this fraction in order, are

1/1; 2/3; 3/4; 11/15; 25/34; 186/53; 397/540

The fifth convergent (25/340 is the most advanced one that can be used, since there is a 34-hole

circle in the Cincinnati range.

Hence the nearest indexing will be 5 whole turns and 25holes in a 34-hole circle. This will give

an angle of 5 25/34 9= 5121 /34= 51 – 37 -31/2 ,i.e. an error of 3 ½ seconds of angle which

is well within the accuracy limits of an ordinary dividing head.

Q129. Draw and explain various operations on drilling machine.

Sagar S Kurde

Me 326

Ans.

403

Various operations of drilling machine are:

1. Drilling

2.Reaming

It is Accurate way of sizing and finishing the pre-existing hole. It has Multi tooth

cutting tool.Accuracy of 0.005mm can be achieved

3.Boring

Boring precisely enlarges an already existing hole using a single point cutter.

4.Counterboring

This process creates a stepped hole in which a larger diameter follows a smaller diameter partially into a hole.

5.countersinking

This process is similar to counterboring but the step in the hole is cone-shaped.

6.Tapping

The process of cutting threads using a tap is called Tapping.

7.Friction drilling

drilling holes using plastic deformation of the subject (under heat and pressure) instead of cutting it.

404

Q 130) Draw and explain basic slotting machine.

NAME: GIRISH H MARGAJE

ROLL NO: ME 330

Ans : The different parts of a slotting machine are:

1. Base 5. Rotating table

2. Column 6. Ram and toolhead assembly

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3. Saddle

4. Cross-slide

Base or bed : The is rigidly built to take up all the cutting forces and entire load of

the machine. The top of the bed is accurately finished to provide

guideways on which the saddle is mounted. The guideways are

perpendicular to the column face.

Column : The column is the vertical member which is cast integral with the

base and houses driving mechanism of the ram and feeding

mechanism .The front vertical face of the column is accurately

finished for providing ways on which the ram reciprocates.

Saddle : The saddle is mounted upon the guideways and may be moved toward or

away from the column either by power or manual control supply longitudinal feed to the

work. The top face of the saddle is accurately finished to provide guideways for the

cross-slide. These guideways are perpendicular to the guideways on the base.

Cross-slide : The cross-slide is mounted upon the guideways of the saddle and may

be moved parallel to the face of the column. The movement of the slide may be

controlled either by hand or power to supply crossfeed.

Rotary table : The rotary table is a circular table which is mounted on the top of the

cross-slide. The table may be rotated by rotating a worm which meshes with a worm

gear connected to the underside of the table.The rotation of the table may be effected

either by hand or power. In some machine the table is graduated in degrees that

enables the table to be rotated for indexing or dividing the periphery of a job in equal

number of parts. T-slots are cut on the top face of the table for holding the work by

different clamping devices. The rotary table enables a circular or contoured surface to

be generated on the workpiece.

Ram and toolhead assembly : The ram is reciprocating member of the machine

mounted on the guideways of the column. It supports the tool at its bottom end on a

toolhead. A slot is cut on the body of the ram for changing theposition of stroke. In some

machines, special type of toolholders are provided to relieve the tool during its return

stroke.

406

Slotting Machine

1. Base, 2.Feed gear, 3.Cross-slide, 4.Table, 5.Crossfeed handle, 6.Longitudinal

feed handle,

7.Circular feed handle, 8.Tool, 9.Ram, 10.Crank disc, 11.Lever for counterbalance

weight,

12.Bull gear, 13.Cone pulley, 14.Column, 15.Feed shaft, 16.Pawl actuating crank.

Q131. Draw and explain the various grinding machines, site the differences

Onkar Mohite

Me 336 Ans:

Grinding machines are classified according to the quality of surface finish as

1. Rough grinders.

2. Precision grinders.

1. Rough grinders

407

Rough grinders are those grinders whose chief work is the removal of stock

without any reference to the accuracy of the results. Types of rough grinders are

a. Floor stand and bench grinders

A floor stand grinder has a horizontal spindle with wheels usually at both ends

and is mounted on a base or pedestal. There is provision for driving the wheel

spindle by belt from motor at the rear, at floor level. Frequently the wheels are

mounted directly on the motor shaft extensions, in which case the motor is on the

top of the stand. A small size machine mounted on a bench is called bench

grinder. These machines are used for snagging and off-hand grinding of tools

and miscellaneous parts. Polishing wheels may be run on these grinders.

b. Portable and flexible shaft grinders

A portable grinder resembles a portable or electric hand drill with a grinding

wheel mounted on the spindle. A flexible shaft grinder has grinding wheel on the

end of a long flexible shaft driven by a motor on a relatively stationary stand. It

can be easily moved about and may be used to the advantage in removing

comparatively small amount of stock from widely separated areas. Heavy tools of

these kinds are used for roughing and snagging and small ones for blurring and

die work.

c. Swing frame grinders

408

A swing frame grinder has a horizontal frame about 2 to 3m long suspended at

its center of gravity so as to move freely within the area of operation. The

operator applies the wheel on one end of the frame to work. This is used for

snagging particularly for castings that are too large for the operator to hold up to

the wheel. This machine is moved around with a jib crane suspended from

columns, or by mobile units.

d. Abrasive belt grinders

A strip of abrasive cloth of the correct length and width is formed into an endless

belt by cementing the ends together, and this is slipped over two drums, one of

which is driven at high speed. The smooth rear side of the cloth slides over a

heavy metal plate. The plat or platen may be flat, or it may be shaped to suit the

shape of the particular workpiece. Work may be applied, commonly by hand,

against the open belt, platen or shaped forms to reach various curves and flat

surfaces. Machines may be dry-belt, wet-belt, or combination type. Abrasive- belt

grinders are used for heavy stock removal or for light polishing work.

2. Precision grinders

a. Cylindrical center-type grinders

The Centre-type cylindrical grinders are intended primarily for grinding plain

cylindrical parts and can also be used for grinding contoured cylinders, fillets,

and even cams.

Working:

The workpiece is usually held between dead centers and rotated by a

dog and driver on the face plate. The work may also be rotated about its

409

own axis in a chuck. There are four movements involved in a cylindrical

centre-type grinding:

I. The work must revolve

II. The wheel must revolve

III. The work must pass the wheel

IV. The wheel must pass the work

They are equipped with a mechanism which enables the grinding wheel

to be fed in automatically towards the work for successive cuts. Hand

feed is employed only in adjusting the wheel or starting the cut. A

provision is also made for varying the longitudinal movement of the work

or the wheel, and the rotating speed of the work to suit different

conditions. Transverse of the work past the wheel or vice versa, is

controlled by dogs which cause the table or wheel to reverse at the end

of each stroke. An important feature of some types of grinders is that the

operation may be stopped automatically when the workpiece has been

finished to size

In machines of the cylindrical type, two distinct types of grinding

operations are done. In the first, called traverse grinding, the work is

reciprocated as the wheel feeds to produce cylinders longer than the

width of the wheel face. In the second, called plunge grinding, the work

rotates in affixed position as the wheel feeds to produce cylinders of a

length equal to or shorter than the width of the wheel. This has the

important advantage the cylindrical shapes can be produced as easily as

straight cylinders in a single “plunge” of the wheel simply by forming the

periphery of the wheel.

BLOCK DIAGRAM OF A PLAIN CENTRAL TYPE GRINDER 1. Head stock, 2.Grinding, 3.Wheel head, 4.Tail stock, 5.Upper table,

6.Lower table, 7.Base,

Plain centre-type grinders:

It is essentially a lathe on which a grinding wheel has been

substituted for the single point tool.

410

Universal centre-type grinders:

These are widely used in tool rooms for grinding tools and have additional features. The

headstock spindle of a universal centre-type grinder may be used alive or dead, so that

the work can be held and revolved by chuck as well as ground between centres.

411

The headstock can be swiveled at an angle in a horizontal plane.

The wheel head and slide can be swiveled and traversed at any angle. The wheelhead

can also be arranged for internal grinding by addition of an auxiliary wheelhead to

revolve small wheels at high speeds.

b. Centreless Grinders

Centreless grinding is a method of grinding exterior cylindrical, tapered, and

formed surfaces on workpieces that are not held and rotated on centres. Both

the wheels are rotated in the same direction. The work rest is located

between the wheels. The work is placed upon the work rest, and the latter,

together with the regulating wheel, is fed forward, forcing the work against the

grinding wheel. The axial movement of the work past the grinding machine is

obtained by tilting the regulating wheel at a slight angle from horizontal.

Centreless grinding may be done in 3 ways

I. Throughfeed: The work is passes completely through the space

between the grinding wheel and regulating wheel.

412

II. Infeed: The regulating wheel is drawn back so that workpiece may be

placed and then it is moved in to feed the work against the grinding

wheel.

III. Endfeed grinding: The work is fed lengthwise between the wheels and

is ground as it advances until it reaches the end stop.

c. Internal grinders

Internal grinders are used to finish straight, tapered, or formed holes to the

correct size, shape, and finish. There are 3 general types of internal grinders:

I. Chucking grinders: In chucking grinders the workpiece is chucked and

rotated about its own axis to bring all parts or other surfaces to be

ground in contact with grinding wheel.

413

II. Planetory grinders: In this the workpiece is mounted on reciprocating

table and is not revealed.

III. Internal centreless grinders: In this work is supported by three rolls,

regulating roll, pressure roll and support roll.

d. Surface grinders:

Surface grinders are used for grinding flat surfaces at work piece. According to the spindle position and the type of table. The surface grinders are classified as follows: 1. Horizontal spindle – Reciprocating table surface grinder. 2. Horizontal spindle – Rotary table surface grinder. 3. Vertical spindle – Reciprocating table surface grinder. 4. Vertical spindle – Rotary table surface grinder.

414

BLOCK DIAGRAM OF A HORIZONTAL SPINDLE SURFACE GRINDER 1. Column, 2.Wheel head, 3.Table, 4.Wheel, 5.Saddle, 6.Base

417

Horizontal spindle reciprocating table surface grinder: Base: It is a rectangular box type costing. The driving mechanism is placed inside the base. Vertical column is mounted at its back. The top of the base has horizontal guide ways perpendicular to the column. Column: The column is mounted on the base. It has vertical guide ways. The wheel head slides vertically along these guide ways. Saddle: The saddle is mounted on the base. It slides along the guide ways of the base perpendicular to the column cross feed can be given by moving the saddle. The saddle has horizontal guide ways on its top. Table:

Longitudinal feed is given by moving the table along these guide ways parallel to the column. Magnetic chuck can be used for holding ferrous materials. 36 37 Wheel head: Wheel head is mounted on the vertical guide ways of the column. It has a horizontal motor for driving the grinding wheel. Principle of operation:

The grinding is done by reciprocating the work piece on the table under the grinding wheel which rotates at high speed. Cross feed is given by moving the saddle after the end of every stroke. After grinding the full width of work piece, depth of cut is given by moving the wheel head vertically downwards.

418

e. Tool and cutter grinders

They are mainly used mainly to sharpen and recondition multiple tooth cutters

like reamers, milling cutters, drills, taps, hobs and other types of tools used in

the shop.

They are classified according to the purpose of grinding into 2 groups:

1. Universal tool and cutter grinders.

2. Single-purpose tool and cutter grinders.

Tool grinding may be divided into two subgroups: tool manufacturing and tool

resharpening. There are many types of tool and cutter grinding machine to

meet these requirements. Simple single point tools are occasionally

sharpened by hand on bench or pedestal grinder. However, tools and cutters

with complex geometry like milling cutter, drills, reamers and hobs require

sophisticated grinding machine commonly known as universal tool and cutter

grinder.

3. Some special Grinding macines

a) Crankshaft grinders

b) Piston grinders

c) Roll grinders

d) Cam grinders

e) Thread grinders

f) Way grinders

g) Tool post grinders

132) State the operation possible and hence application of grinding machine

419

Jay Nibandhe

S.E.MECH-339

Ans:

The grinding machine consists of a power driven grinding wheel spinning at the required

speed (which is determined by the wheel’s diameter and manufacturer’s rating, usually

by a formula) and a bed with a fixture to guide and hold the work-piece. The grinding

head can be controlled to travel across a fixed work piece or the workpiece can be

moved whilst the grind head stays in a fixed position. Very fine control of the grinding

head or tables position is possible using a vernier calibrated hand wheel, or using the

features of numerical control.

Grinding machines remove material from the workpiece by abrasion, which can

generate substantial amounts of heat; they therefore incorporate a coolant to cool the

workpiece so that it does not overheat and go outside its tolerance . The coolant also

benefits the machinist as the heat generated may cause burns in some cases. In very

high-precision grinding machines (most cylindrical and surface grinders) the final

grinding stages are usually set up so that they remove about 200 nm (less than

1/100000 in) per pass - this generates so little heat that even with no coolant, the

temperature rise is negligible.

Types

These machines include the:

1. Belt grinder, which is usually used as a machining method to process metals and

other materials, with the aid of coated abrasives. Sanding is the machining of

wood; grinding is the common name for machining metals. Belt grinding is a

versatile process suitable for all kind of applications like finishing, deburring,

and stock removal.

Applications

Belt grinding is a versatile process suitable for all kinds of different applications. There

are three different applications of the belt grinding technology:

Finishing: surface roughness, removal of micro burrs, cosmetic finishes, polishing

Deburring: radiusing, burr removal, edge breaking

Stock removal: high stock removal, cleaning (e.g. of corrosion), eliminating mill or

tool marks, dimensioning

http://en.wikipedia.org/wiki/Belt_grinder

http://en.wikipedia.org/wiki/Belt_grinding

http://en.wikipedia.org/wiki/Stock_removal

http://en.wikipedia.org/wiki/Surface_roughness

http://en.wikipedia.org/wiki/Burr_(metal)

http://en.wikipedia.org/wiki/Stock_removal

http://en.wikipedia.org/wiki/High_stock_removal

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2. Bench grinder, which usually has two wheels of different grain sizes for

roughing and finishing operations and is secured to a workbench or floor stand.

Its uses include shaping tool bits or various tools that need to be made or

repaired. Bench grinders are manually operated.

3. Cylindrical grinder, which includes both the types that use centers and

the centerlesstypes. A cylindrical grinder may have multiple grinding wheels.

The workpiece is rotated and fed past the wheel(s) to form a cylinder. It is used

to make precision rods, tubes, bearing races, bushings, and many other parts.

Applications

The cylindrical grinder is responsible for a plethora of innovations and inventions in the

progression of science and technology. Any situation in which extremely precise

metalworking is required, the cylindrical grinder is able to provide a level of precision

unlike any other machine tool. From the automotive industry to military applications, the

benefits the cylindrical grinder have given us are immeasurable.[1]

4. Surface grinder which includes the wash grinder. A surface grinder has a "head"

which is lowered, and the workpiece is moved back and forth past the grinding

http://en.wikipedia.org/wiki/Bench_grinder

http://en.wikipedia.org/wiki/Cylindrical_grinder

http://en.wikipedia.org/wiki/Lathe_center

http://en.wikipedia.org/wiki/Cylindrical_grinder#cite_note-lewis-0

http://en.wikipedia.org/wiki/Surface_grinder

421

wheel on a table that has a permanent magnet for use with magnetic stock. Surface

grinders can be manually operated or have CNC control

5. Tool and cutter grinder and the D-bit grinder. These usually can perform the

minor function of the drill bit grinder, or other specialist toolroom grinding

operations.

6. Jig grinder, which as the name implies, has a variety of uses when finishing jigs,

dies, and fixtures. Its primary function is in the realm of grinding holes and pins. It

can also be used for complex surface grinding to finish work started on a mill.

Applications

The most important factor on a jig grinder is the dual-spindle configuration. The main

spindle is roughly positioned with between 1" or 2" of travel for setup, and then the .100"

of outfeed is used during machine operation to outfeed into the work. A spacer bar may

be used between the grinder and main spindle, allowing large (9" radius or larger) work

to be completed. The main spindle has a wide range of speeds to ensure proper grinder

feed rates are maintained.

7. Gear grinder, which is usually employed as the final machining process when

manufacturing a high precision gear. The primary function of these machines is to

http://en.wikipedia.org/wiki/Tool_and_cutter_grinder

http://en.wikipedia.org/wiki/Toolroom

http://en.wikipedia.org/wiki/Jig_grinder

http://en.wikipedia.org/wiki/Gear_grinder

422

remove the remaining few thousandths of an inch of material left by other

manufacturing methods (such as gashing or hobbing).

Applications

The old method of gear cutting is mounting a gear blank in a shaper and using a tool

shaped in the profile of the tooth to be cut. This method also works for cutting internal

splines.

Another is a pinion-shaped cutter that is used in a gear shaper machine. It is basically

when a cutter that looks similar to a gear cuts a gear blank. The cutter and the blank

must have a rotating axis parallel to each other. This process works well for low and

high production runs.

Q 133) Note on grinding wheel selections and specifications.

Name: Chetan Dattatray Niladhe.

Branch:Mechanical R No: 340

SELECTION OF GRINDING WHEELS

It is customary for grinding wheel manufacturers to provide, through their literature,

information on the selection and use of grinding wheels, but it may not always be possible or

convenient for users to take advantage of such consultative service. The need for ready to use

general guide on grinding wheels has been keenly felt and the Indian Standard (IS: 1249-1958)

gives recommendations on the general considerations which should guide the selections of

grinding wheels for different applications.

In selecting a grinding wheel there are four constant factors and four variables given table:

Constant factors Variable factors

1.Material to be ground 1.Wheel speed

2.Amount of stock to be removed 2.Work speed

3.Area of contact 3.Condition of the machine

4.Type of grinding machine 4.Personal factor

Grits: The grain or grit number indicates in general way the size of the abrasive grains

used in making wheel, or the size of the cutting teeth, since grinding is a true cutting

http://en.wikipedia.org/wiki/Shaper

423

operation .Grain size is denoted by a number indicating the number meshes per linear

inch (25.4 mm) of the screen through which the grains pass when they are graded after

crushing. The following list ranging from very coarse to very fine, includes all the ordinary grain

sizes commonly used in the manufacture of grinding wheels :

COMMON ABRASIVE GRAIN TYPE AND SIZE

Grain size or grit

Coarse 10 12 14 16 20 24 -

Medium 30 36 46 54 60 - -

Fine 80 100 120 150 180 - -

Very fine 220 240 280 320 400 500 600

Grade: The term ‘ rade’ as a lied to a rindin heel refers to the tenacity or hardness

with which the bond holds the cutting points or abrasive grains in a place. It does not

refer to the hardness of the abrasive grain. The grade shall be indicated in all bonds and

process by a letter of the English alphabet ‘A’ denotin the softest and ‘Z’ the hardest

rade. The term ‘soft’ or ‘hard’ refer to the resistance a bond offers disr tion of the

abrasive. A wheel from which the abrasive grains can easily be dislodged is called soft,

whereas one which holds the grains more securely is called hard .The grades are

denoted as:

GRADE OF GRINDING WHEELS

Soft A B C D E F G H - -

Medium I J K L M N O P - -

Hard Q R S T U V W X Y Z

Structure: Abrasive grains are not packed in the wheel but are distributed through the

bond . The relative spacing is referred to as the structure and denoted by the number

of cutting edges per unit area of wheel face as well as by number and size of void spaces

between grains. The primary purpose of structure is to provide chip clearance and it

may be open or dense. The structure commonly used is denoted numbers as follows:

STRUCTURE OF GRINDING WHEELS

Dense 1 2 3 4 5 6 7 8

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Open 9 10 11 12 13 14 15 Or higher

Q 134) Write a note on lapping.

NAME:SHRIKALP POKHARKAR

ROLL NO: 347

Lapping is an abrading process that is used to produce geometrically true surfaces,

correct minor surface imperfections, improve dimensional accuracy ,or provide a very

close fit between two contact surfaces. Very thin Layers of metal are removed in lapping

and it is, therefore, evident that lapping is unable to correct substantial errors in the form

and sizes of surfaces. It is, however, low efficiency process and is used only when

specified accuracy and surface finish cannot be obtained by other methods.

Abrasive powders such as emery, corundum, iron oxide, chromium oxide, etc, mixed

with oil or special pastes with some carrier are used in lapping. The face of a lap

becomes “charged” with abrasive particles. Charging a lap means to embed the

abrasive grains into its surface. Laps are made of soft cast iron, brass, copper, lead or

soft steel. When the lap is once charged, it should be used without applying more

abrasive until it ceases to cut. Laps may be operated by hand or machine, the motion

being rotary or reciprocating.

There are three important types of lapping machines. The vertical axis lapping

machine laps flat or round surfaces between two opposed laps on vertical spindles. The

centreless lapping machine is designed for continuous production of round parts such

as piston pins, bearing races and cups, valve tappets and shafts. The abrasive belt

lapping machine laps bearing and cam surfaces by means of abrasive coated clothes.

425

Q 135) Write a note on honing

-By VIVEK SINGH

Roll No: Me353

Ans: Honing is grinding and a abrading process mostly for finishing round holes by

means of bonded abrasive stones, called hones. Honing is therefore a cutting operation

and has been used to remove as much as 3 mm of stock but is normally confined to

amount less than 0.25 mm. So honing is primarily used to correct some out of

roundness, taper, tool marks, and axial distortion. Honing stones are made from

common abrasive and bonding materials, often impregnated with sulphur, resin, or wax

to improve cutting action and lengthen tool life. Materials honed rang from plastic, silver,

aluminium, brass, and cast iron to hard steel and cemented carbides. This method is

mostly used for automobiles crankshaft journals.

When honing is done manually tool is rotated, and the workpiece is passed back and

forth over the tool. For precision honing, the tool is given a slow reciprocating motion as

it rotates. Honing stones may loosely held in holders, cemented into metal shells which

are clamped into holders, cemented directly in holders, or cast into plastic tabs which

are held in holders. Some stones are spaced at regular intervals around the holder,

426

while others are interlocking so that they present a continuous surface to the bore. A

typical honing toolhead shown in Fig.16.1.

The honing tool may be so made a floating action between the work and tool prevails

and pressure exerted in the tool may be transmitted equal to all sides. Coolants are

essential to operation of this process to flush away small chips and to keep temperature

uniform.

Honing is done for general purpose machines, such as the lathe, drill press, and

portable drills, as an expedient. But more economical results can be obtained by honing

machines for production work. There are two general types of honing machines:

Horizontal and Vertical. A honing machine rotates and reciprocates the hone inside

holes being finished. The two motions produce round and straight hole that have a very

fine surface finish of random scratches. Vertical honing machines are probably more

common. Horizontal honing machines are often used for guns and large bores.

Q136)Write a note on burnishing

Ans):-Burnishing is a polishing and work hardening of a metallic surface. This process

will smooth and harden the surface, creating a finish which will last longer than one that

hasn’t been burnished. This is a desirable characteristic in clockmaking and

watchmaking since the major determining factor in how long a clock or watch will run is

the degree to which the bearings will wear over time. Long-lasting bearing surfaces,

like pivots and pivot holes, will greatly increase the length of time that a clock or watch

will perform as expected. Although this article is primarily targeting the burnishing

process for clocks, the same methods may be applied to watches with the

understanding that jewel holes need not, nor can they be, burnished.Burnishers can be

427

purchased for use as either right-handed or left-handed .The distinction is the shape in

the profile of the burnisher. A burnisher will usually have an edge, which is relieved to

allow for clearance against the shoulder, so as to provide a sharp transition between the

pivot and shoulder. A right-hand burnisher will allow the clockmaker to burnish the pivot

from underneath with the piece being held and rotated from their left. A left-hand

burnisher will allow burnishing from underneath while being held on the right. If the

preference is to burnish from over-the-top, a left-hand burnisher is used with the piece

being held on the left and a right-hand burnisher with it held on the right . This can add

confusion as to which burnisher to purchase. Since most machinists will machine with

the piece being held in a lathe headstock on their left whether they are right- or

lefthanded, it should first be decided whether burnishing will be done from underneath

or over-the-top.

The types of burnishers are as follows:

1. File/Burnisher Combo: Some burnishers come mated to a pivot file (fig 10). These

can shorten the time it takes to polish and burnish a pivot since it only takes a flip of

the tool to transition from polishing with the pivot file to burnishing. This eliminates

the time it takes to put down one tool and pick up another.

2. Steel Burnishers: Most commercially made burnishers are made of high quality

steel and are capable of many years of burnishing, often outlasting the user (fig 11).

These are available in either right- or left-hand versions and are easily re-surfaced

when they become worn.

3. Carbide Burnishers: Carbide is a type of steel which is harder than the steel used in

mostclocks. This characteristic is advantageous since a burnisher made from

carbide will polish and burnish in one step. Although not commercially available, a

hand held carbide burnisher can be made at a minimal cost.

4. Morgan Pivot Polisher

This is a lathe attachment that has a carbide wheel which burnishes as it polishes.

Although more costly than a hand-held steel or carbide burnisher, this tool will

increase the speed and accuracy with which a pivot can be burnished.

5. Smooth Broach: This tool is specifically designed to burnish pivot holes. Full sets

are available which will cover most pivot hole sizes encountered in clockmaking (fig

14). Some smooth broach sets come with handles attached but with others, it will be

necessary to attach them to a handle in order to use them.

6. Pegwood: Although not used to burnish metal, pegwood is necessary for burnishing

the pivot holes in wooden works. An inexpensive source of pegwood is round

toothpicks .

written by : Krishna vatwani

Q 137) Write a short note on Buffing.

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Vishal Walawalkar Roll No. : Me-359 BUFFING - Refers to the abrasive being formulated with binders into a cake, tube, paste, or liquid form. The term “buffing” means the practice of producing a uniform finish by means of a revolving buffing wheel “charged” with buffing compound in contact with the work surface. Assuming that the work piece surface is smooth enough to buff out imperfections or if needed, has been leveled through a polishing wheel or belt operation, “buffing” can generally be divided into two operations referred to as (1.) “cutting down” and (2.) “coloring”.

1. “Cutting Down” is the preliminary step performed with a coarse cutting abrasive

buffing compound. In many cases this one “cutting down” operation may be all that’s necessary to secure a bright enough, satisfactory appearance.

2. “Coloring” is light-duty buffing intended to bring up a luster on work surfaces that do not require an initial “cutting down” operation. "Coloring" compounds are formulated using finer mesh size abrasives than those used in making “Cutting” compounds. “Coloring” compounds are also used when a secondary re-buffing

operation is desirable to enhance and brighten the appearance left from a “cutting down” operation. Compounds that serve the dual purpose of both cutting and coloring are referred to as “Double-duty” compounds.

LIQUID BUFFING COMPOUNDS - The abrasives and binders used in formulating liquid/paste buffing compounds are virtually the same as those used in solid compounds. The difference being the ingredients are carried in a water base, emulsified, fluid form intended for spray or brush application. COMPOUND SHELF LIFE - Except for Satin-Glo® greaseless polishing compound and Liquid Spraymax, our compounds can be stored indefinitely without deteriorating. BUFFING WHEELS - Buffing wheels serve two main functions: (1.) To carry the

abrasive particles across the work surface to perform a cutting and/or coloring action. (2.) Where required, to generate sufficient frictional heat to permit plastically flowing or burnishing the work surface. It is to perform these two principal functions that buffing wheels are produced in a range of designs, buffing fabrics and constructions. The nature and shape of the work piece and the ultimate finish desired dictate the styles best suited for that specific application.

http://www.formaxmfg.com/buffing-wheels-for-a-sparkling-finish

http://www.formaxmfg.com/buffing-wheel-bar-compounds

http://www.formaxmfg.com/polishing-compounds-premium-grade-compounds




http://www.formaxmfg.com/liquid-compounds

http://www.formaxmfg.com/greaseless-polishing-compounds

http://www.formaxmfg.com/buffing-wheels-for-a-sparkling-finish

429

Q.138 Note on selection of remelting furnances

Sandeep yadav roll no. 361

FURNACE SELECTION PROCESS

Step 1

The furnace capacity selection is the most common question bothering for the buyer/prospects.

Sometimes it creates confusion, because different manufacturers suggest different combinations.

How should one select the furnace (Kw/KG/Hz) which fitted to one's requirement technically

and commercially as well?

So we suggest every one to follow the furnace selection process step by step.

• Which metal or alloy do one's want to melt and at what pouring temperature?

• Melt rates or melting speed is different for different metal & alloys at particular applied kw,

this is due to difference in specific heat of different metal.

• At the same time due to different latent heat of each metal, superheating of each molten metal

will be different, so different melt rate at particular applied kW.

For Example

For Different Metal

At particular kW Furnace Compare Brass & Steel Melting

For Steel Melting

1000 Kgs / Hour @1600ºC

Where as, Brass Melting will be, 1900 Kg / Hr @11000ºC

Summary

So At same kW, different metals, different Melt rate

For super Heating case:

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At particular kW for steel melting:

At 15000ºC the melt rate will be 1000 Kgs / Hour

At 16000ºC the melt rate will be 925 Kgs / Hour

Summary

For Same metal, At particular applied kW, Different Pouring Temperature, Different melt

rate.

Once you configure your requirement i.e. melt rate @ temperature degree centigrade ºC

according to step one, Now switch to step 2.

Step -2

You must specify the liquid metal requirement in tons or in Kgs, per month with working hours

in a day.

( A ) For Steel Ingot

Suppose you required 1200 Tons / Month of M.S. Steel Ingot @ 1600ºC what the Furnace size

should be?

• 1st consider working days - 25 days

• 2nd 1200 Tons 1 25 days gives 48 Tons of liquid metal Day out of 24 Hrs working.

• 3rd 48 Tons 1 24 Hrs i.e melt rate will be (48/24 = 2) 2 Tons per hour

• 4th Now consider the unproductive time of cycle, i.e. time for deslagging, charging, sintering,

lining etc. so the furnace utilization will be 80 % thus

• 2 tons 1 hr divided by 0.8. is 2.0 ÷ 0.8 = 2.5 Tons / Hour should be the required furnace melt

rate at 1600ºC .

• 5th Now refer the furnace specification table. You will find the nearest melt rate can be

achieved by 1500 kW 1 3 Tons Furnace i.e. 2.6 Tons 1 Hour Melt rate.

• We have considered here 1500kw means 1500 KVA – Exclusive power at the furnace Input.

So the Answer is By 1500 KW 13 Ton furnace you can produce 1200 Tons of M.S. Steel

Ingots @ 16000C per month.

B) For Castings (Step -2)

Suppose you want to make 300 Tons / Month of finished steel casting, with an average yield of

65% and utilizing of furnace is about to 75%.

Then what should be the furnace capacity? Pls suggest.

• So now 300 Tons ÷ yield (0.65)

431

• Gives total monthly molten metal requirement for casting is 465 Tons / month.

• Now 465 Tons divided by 25 working days gives 18.6 Tons of molten metal per day of 24

hours working.

• 18.6 Tons again divided by 24 hours gives required melt rate of molten metal is 775 kgs /

Hour. Now considering the utilization of the furnace is 75 %, is due to sintering, lining

deslagging, recharging, composition setting etc.

• Thus actual molten metal requirement will be 775 ÷ 0.75 i.e. 1033 Kgs / Hour.

• Next step now you refer the table & from the table the nearest suitable furnace, which can give

1033 Kgs/ Hour melt rate is FER 1.

• So you should select 600kW & 1 Ton Induction Furnace, which will give you the suitable melt

rate.

• Another main factor which one foundry men has to be decided is, what should be the batch

size?

• The batch size will be depending upon the molten metal weight you required.

For Example

If you required 600 Kgs, 750 Kgs, 1000 Kgs, metal at a time then you can select 600 kw solid

state M.F. Power source with 1000 Kgs crucible or otherwise, if your molten metal requirement

is around 500 Kgs or less, then you can select 300 kw x 2 Nos solid state M.F. Power Source

with 500 Kgs crucible. Which will cost you more, compare to buy 600 kw one unit.

Step – 3

Now what should be the right frequency?

Normally frequency selection is not available, and is not an important constraint too. There are

many combinations of Kw and Kgs available at different frequencies.

Basically frequency is one parameter which affects stirring.

In a coreless Induction furnace stirring is produced by magnetic forces acting on a molten metal

because of interaction between the coil current and the current flowing in the molten metal bath.

The force is the strongest at middle part of the coil so metal is forced at the central side of the

bath from where it is resolved to upward and downward. Metal moves up because of upward

resolved force. The upward movement of the metal in the center creates meniscus a unique

characteristic know as a stirring effect is measured by h/D ratio (h by D ratio).

Stirring effect is depending upon the power frequency applied, the induction coil & molten bath

as well as density and viscosity & molten metal. The three major variable which Effect stirring

are

432

1) Power 2) Frequency 3) Furnace Size

Stirring can be change with charging anyone of the major variable.

WHAT IS EFFECT OF STIRRING

INADEQUATE STIRRING CAUSE

1. Insufficient Mixing of Alloys

2. Temperature difference in molten metal bath

3. difficulty to melt light weight scrape

EXCESSIVE STIRRING CAUSES

1. Frequent lining erosion

2. Metal oxidized and splashing of metal

3. Lining or slag inclusions in casting found

• Once you decide the kW/Kgof the furnace & according to your mixing or alloying

requirement, metal properties, operating frequency can be decided.

Role of Frequency in Melting

High power density melting allows better utilization of the equipment, minimizing the amount of

time needed to perform a melt. This also improves the efficiency since the energy loss due to

heat conduction and radiation is also minimized because the molten metal is not kept in the

furnace for a long time. This method of quick high power density melting and complete

emptying of a furnace became known as "batch" melting. The older technique, called "heel"

melting, involved large furnaces which were only partially emptied and then topped by a load of

solid metal charge. The batch melting method requires larger power supplies operation on higher

frequencies.

High power density i.e. produced melting power kw/kg or per ton of charge, gives better

utilization of the furnace, and so takes less time to melt the metal in particular batch size. This

too improves the overall effective of the melting operation as energy loss due to conduction of

heat through lining and radiation loss is reduced, reason is less holding time of molten metal in

the furnace. The lining life of the furnace is also gone up and so over all efficiently of the

melting operation is gone up so the melting cost per kg totality has to be reduced. This method of

quick high power density melting or hatch melting requires larger power supplies (kw/kg) on

high frequency.

Because produced melting power or power density is a function of the product of sensitivity of

the metal and the operational of frequency metal.

Pm = Const × resistivity of metal × Frequency

Plays significant role for effective melting at a particular power on a particular batch size.

HOW TO CALCULATE THE FURNACE.EFFICIENCY

FURNACE

EFFICIENCY

THEORETICAL TOTAL HEAT REQD FOR MELTING (H T) IN KWH.

FOR THE MELTING OF THE METAL IN KWH

433

= --------------------------------------------------------------------------------------------

ACTUAL CONSUMED ENERGY BY THE FURNACE FOR MELTING

OF THE METAL IN KWH (H A)

THEORETICAL HEAT REQD FOR MELTING:

H.1 IN KWH

=

W X SPECIFIC HEAT OF THE METAL X ( T2- T1) + LATENT HEAT

OF

THE METAL XW

--------------------------------------------------------------------------------------------

3600 ( 3600 KJ = 1KWH)

H2 IN KWH = HEAT REQD FOR SLAG TO.HEAT AND MELT WILL

BE 1.65X WSLG X3.6 ( WHERE 3.6 MJ = 1 KWH)

WHERE

W = WEIGHT OF THE METAL TO MELT

T2- = MELTING FINAL TEMP OFTHE METAL.

T1 = INITIAL OR CHARGING TEMP OFTHE METAL.

WSLG = WEIGHT OF SLAG GENERATED IN OPERATION.

HERE,

H T = H1 + H2

AND

• ACTUAL CONSUMPTION OF THE MELTING CAN BE MEASURED FROM THE INPUT

BUSBAR OF THE FURNACE PANEL IN KWH. (H A IN KWH) WHICH IS HIGHER

THAN H.T.

• SO DIFFERENCE BETWEEN HA AND HT (HA - HT) IS LOSS DUE TO CONDUCTION

RADIATION AND OTHER LOSSES,

• AND SO FURNACE EFFICIENCY IS RATIO OF THEORETICAL HEAT REQD FOR

MELTING IN KWH TO ACTUAL CONSUMED HEAT IN KWH.

i.e.,

FURNACE

EFFICIENCY

=

HT

--------------------------------------------------------------------------------------------

HA

434

55% TO 65% (MAX) OVERALL ENERGY EFFICIENT FURNACES ARE AVAILABLE.

FOR M.S. SCRAP

SPECIFIC HEAT = 0.682 KJ / KG DEG CENTI.

LATENT HEAT = 272.0 KJ / KG

SPECIFIC HEAT REQD TO MELT 1000KGS OF M.S SCRAP WILL BE, @ 1650ºC

= 100 × 0.682 × (1650 - 30)

-------------------------------------- KWH

3600

= 307 KWH

LATENT HEAT REQD,

272 × 1000 / 3600

76 KWH.

HEAT FOR SLAGE

1.6 × 25 / 3.6

12 KWH.

TOTAL KWH THEORETICALLY REQD FOR MELTING IS 395 KWH.

APPROX 400 KWH REQD TO MELT M.S OF 1000KGS TO 1650DEG CENTIGRADE.

IF THE FURNACE CONSUMES 625 KWHITON THAN THE FURNACE IS OVERALL

ENERGY EFFIECIENT 65%.

[ i.e. 400 ÷ 625 = 64 % ]

DISTRIBUTION OF LOSSES IN INDUCTION FURNACE:

LOSSES IN INDUCTION FURNACE

The theoretical energy require to melt one Ton of steel is 385 TO 400 KWH / Ton. However in

actual practice, the specific energy consumption is remarkably higher to 550 KWH / ton to 950

KWH / ton.

Top

THE POWER LOSS IN INDUCTION FURNACE SYSTEM

1. Power loss in generator / panel 2% to 4%

2. Power loss in capacitor Bank 1.0% to 3%

3. Power loss in Crucible

(Water cooled cables, Bus bar, change over switches) 18% to 25%

http://www.furnacesupplier.com/furnace_selection.html

http://www.furnacesupplier.com/furnace_selection.html

435

4. Radiation loss 7% to 9%

Above figures can vary according to

1. Manufacturer of furnace.

2. Size of the furnace.

3. Scrap quality.

4. Plant operational specific issue.

FACTORS EFFECTING THE FURNACE EFFICIENCY.

In foundry the tool or unit of efficiency measurement is kwh/ton.

In foundry most of the power is consumed by the induction furnace is around 65% of the power.

The factors, which effects the furnace efficiency are as under;

1. Wrong selection of the furnace & operational practice:

i. Small power supplied unit & big crucible.

ii. furnace top extension and relative slow charging.

iii. wrong lining thickness.

Results:

a / slower melting

b / reduced lining life

c / poor utilization of power due to increase in furnace losses.

d / poor power transfer/coupling increase melting time.

Optimum furnace size, approximately to be;

For up to 1000 kw -1.5 times the kw applied

Above 1000 kw furnace - 2.0 times the kw applied.

2. Furnace down time:

(1) molt sintering and pateching.

Higher sintering & patch in g increases the cost of production and reduces the efficiency.

3. Break down time :

due to poor maintenance the total production stops sometimes.

Higher breakdown results in increasing the' cost of production

4. Low supplied power :

some time supplied voltage is low, so furnace draw less power. Causes slow melting &

inefficient operation resulting; increase cost of production

436

5. Wrong lining :

some time lining material selection is wrong with respect to metal.

Basic lining is better conductor of heat compared to acidic lining

Wrong lining selection increases breakdown,

Furnace down time and furnace losses,

Resulting in inefficient operation.

Besides above all points some more factors which can also effect the energy consumption

per MT are:

A ) poor coordination between melting staff & contractor

B ) absence of material handling equipment

C ) poor molding efficiency so furnace on hold

D ) poor quality scrap, reducing lining life, takes more time to melt.

E ) absence of thermal insulation between lining & coil.

Total absolute energy required to turn 1 Ton of different. Solid metals to

melt @ different molten temperature.

Type of metal Specific heat require Latent heat require Total require

kwh/Ton

Mild steel @

1650ºC Melting

temp.

1000 x 0.682 x 16200C

÷ 3600

∆T=1650-30

Speci heat = 0.9 kj/kg0C

= 307 kwh

272 x 1000 ÷ 3600

kwh

Latent Heat = 272

kj/kg

= 76 kwh

307 + 76 = 376 kwh

Aluminum @

710ºC Melting

temp.

1000 x 0.9 x 6800C ÷

3600 kwh

∆T=7100C-300C

Speci heat = 0.9 kj/kg0C

= 170 kwh

396.9 x 1000 ÷ 3600

kwh

Latent Heat = 396.9

kj/kg

= 110 kwh

170 kwh + 110 kwh =

180 kwh

Copper @ 1130ºC

Melting temp.

1000 x 0.386 x 11000C

÷ 3600 kwh

∆T=11300C-300C

Speci heat = 0.386

kj/kg0C

= 118 kwh

212 x 1000 ÷ 3600

kwh

Latent Heat = 212

kj/kg

= 59 kwh

118 kwh + 59 kwh =

117 kwh

Gold @ 1130ºC

Melting temp.

1000 x 0.131 x 11300C

÷ 3600 kwh

∆T=11300C-300C

Speci heat = 0.131

67.62 x 1000 ÷ 3600

kwh

Latent Heat = 67.62

kj/kg

36.38 kwh + 18.78

kwh = 56 kwh

437

kj/kg0C

= 36.38 kwh

= 18.78 kwh

Q 139) Construction and working of cupola advt& limitations

Ankush Roy

Roll no.363

Ans: Preparation of cupola

– Leftovers of the previous charging removed from the bottom opening

– Lining is repaired and bottom opening is closed

– Founding sand is rammed over the bottom door with downhill slope

towards tap hole.

Working

• Lighting the cupola

– Dry wood pieces placed on the rammed sand

– Coke bed placed on the wood stack

– Wood stack ignited through tap hole (torch/spark)

– Air enters through wind box and aids combustion

438

– Coke bed is added with fresh coke through the charging door

• Charging the cupola

– Alternate layers of coke (fuel) the bottom layer, limestone(flux) middle

layer & top layer of metal (pig iron 30%, new scrap iron 30% & returns

40%)

• Melting

– Soaking period initially for an hour

– Air blast is turned ON for next 10 minutes

– Molten iron starts accumulating at the tap hole

• Slagging and tapping

– Slag is opened first and slag skimmed

– Tap hole is opened and molten metal ladled

– Cupola is kept charging coke, limestone and metal

– Intermittent slagging & tapping happens

• Dropping down the bottom

– Near the end of the heat, charging is stopped

– Air blast is shut off and the charge is allowed to be consumed

– Bottom door knocked open and remains are quenched

– Segregated metal is reused for next heat

Advantages

• Remelting of scrap and or pig iron

• Economical for Cast Iron family castings

• Can be used to remelt Cu alloys

• Good grade low sulphur coke is fuel

• Operates at longer cycle times

• Molten metal obtained is not uniform

439

• Simple design and low initial cost

• Ease of operation and maintenance

• Less floor space

• Continuous operation for many hours possible

• Poor control over chemical composition of the molten metal

• Close temperature control is not possible

Q 140 construction and working of reverberatory furnace with advantages and disadvantages?

Moosa kazi

Reverberatory furnace

A furnace or kiln in which the material under treatment is heated indirectly by means of a flame deflected downward from the roof. Reverberatory furnaces are used in opper, tin, and nickel production, in the production of certain concretes and cements, and in aluminum. Reverberatory furnaces heat the metal to melting temperatures with direct fired wall-mounted burners. The primary mode of heat transfer is through radiation from the refractory brick walls to the metal, but convective heat transfer also provides additional heating from the burner to the metal.

The advantages provided by reverberatory melters is the high volume processing rate, and low operating and maintenance costs.

The disadvantages of the reverberatory melters are the high metal oxidation rates, low efficiencies, and large floor space requirements. A schematic of Reverberatory furnace is shown in Figure:-

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Figure: Schematic of a Reverberatory Furnace

reverberatory furnace, in copper, tin, and nickel production, a furnace used for

smelting or refining in which the fuel is not in direct contact with the ore but heats it by a

flame blown over it from another chamber. In steelmaking, this process, now largely

obsolete, is called the open-hearth process. The heat passes over the hearth, in which

the ore is placed, and then reverberates back. The roof is arched, with the highest point

over the firebox. It slopes downward toward a bridge of flues that deflect the flame so

that it reverberates. The hearth is made dense and impervious so that the heavy matte,

or molten impure metal, cannot penetrate into and through it, and the walls are made of

a material that resists chemical attack by the slag. The process is continuous in the

reverberatory furnace: ore concentrate is charged through openings in the roof; slag,

which rises to the top, overflows continuously at one end; and the matte is tapped at

intervals from the deepest part of the ore bath for transfer to a converter

Q.141 A note on the zones in Cupola

Daanish Mukadam

ME-337

Zones of Cupola

Well

• Zone where the molten metal is collected before tapping

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Superheating/combustion/oxidizing

• Oxygen from air blast is consumed here

• Exothermic reactions add to the heat

• Heat is supplied from here to other zones

Reducing/protective

• Protects the molten metal from oxidizing

• Endothermic reactions aid reducing action

Melting zone

• Receives the heat from oxidizing zone

• Iron melts in this zone

• High temperature zone

Preheating zone

• Hot exhaust gases from combustion zone CO, CO2, N2 being lighter travel to the

charge upwards and preheat the same and make it form a distinguished melting

zone

Stack or exhaust zone

• From above the preheating zone up to the spark arrester

Q142 CONSTRUCTION AND WORKING OF ROTARY FURNACE

WITH ADVANTAGES AND LIMITATIONS

- Faaiz

Kazi

- Me 322

Ans:

Since air furnace for making malleable cast iron is difficult to operate and wasteful in

fuel , a rotary furnace is used.

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CONSTRUCTION -

A rotary furnace consists of a horizontal cylindrical steel shell lined with refractory

material and mounted on rollers for rotating or rocking purposes. The cylindrical shell

revolves completely at about 1 r.p.m. The refractory lining may be renewed after 200

to 300 heats .

WORKING-

1) Due to rotation of the furnace the metal gets heat from the walls and is melted more

efficiently and faster. The melting time is reduced to half that of a stationary furnace.

2) Rotary furnace is charged form one of its conical ends after removing burner or

exhaust box temporarily.

3) The burner at one end burns the fuel and the resulting high temperature flame melts

and superheats the metal charge lying in the shell.

4) Since the molten metal does not come in contact with the fuel there is no danger of

carbon or sulphur pick up. The furnace atmosphere can be controlled within limits.

5) The slag floating on the molten iron, protects the metal and its constituent elements

(like Si , Mn ,etc) from oxidation.

6) Unlike cupola, in rotary furnace , a sample of molten metal can be drawn before

pouring and analyzed regards its chemical composition which subsequently can be

accurately controlled by additions if required.

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7) Charge in rotary furnace can be super – heated to high temperatures.

8) Cheap and light scrap like steel clippings or cast iron borings which cannot be used

in cupola, may be added in the charge without affecting the melt quality. This offsets the

higher melting cost of rotary furnace when compared to cupola.

9) After the melting is complete, the initially plugged tap hole is opened and the furnace

is rotated slowly until the tap hole reaches the level of molten metal in the furnace,

when the same can be poured into a ladle.

10) In case the tap hole is not provided in the cylindrical body, the liquid metal can be

tapped from the other end of the furnace. Besides tapping, this end is used for charging

, slagging and evacuating the products of combustion.

11) The products of combustion may be sent to a preheater or recuperator unit where

they may heat the cold air to be used subsequently in the rotary furnace.

12) Rotary furnaces find applications in producing high duty cast irons having alloying

elements such as Mo , Ni, Cr, etc. which if added in cupola will suffer a loss.

13) Metals previously melted in cupola can be held and superheated in rotary furnaces.

Advantages of Rotary Furnace include :-

- Short melting periods

- Low exhaust gas volumes

- Properly mixed melt

- Flexible operations

- Low investment and operating costs

- Easy dust removal

- Highly reproducible analysis

- Low fuel consumption

- High melting efficiency

- Improved waste-gas quality

Q.143]Construction and working of open hearth advantages & limitations.

S.E.AUTO

Roll.no.304

Ashwin dhawad.

Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other

impurities are burnt out of pig iron to produce steel. Since steel is difficult to manufacture

444

owing to its high melting point, normal fuels and furnaces were insufficient and the open

hearth furnacewas developed to overcome this difficulty.

The actual process of operation with an open hearth furnace makes it possible to position the

pig iron so that the combination of open flames and the hot air generated within the furnace

can trigger the chemical activity necessary to produce the steel. Sometimes known as a

reverberatory melting furnace, the flames pass over the material while the hot air aids in

intensifying the heat within the hearth to the desirable level.

*Working:-

The furnace is first inspected of possible damages. Once it is ready or repaired, it is charged

with light scrap, such as sheet metal, shredded vehicles or waste metal. Once it has melted,

heavy scrap, such as building, construction or steel milling scrap is added, together with pig iron

from blast furnaces. Once all steel has melted, slag forming agents, such as limestone, are

added. The oxygen in iron oxide and other impurities decarburize the pig iron by burning the

carbon away, forming steel. To increase the oxygen contents of the heat, iron ore can be added

to the heat. Preparing a heat usually takes 8 h to 8 h 30 min to complete into steel. As the

process is slow, it is not necessary to burn all the carbon away as in Bessemer process, but the

process can be terminated at given point when desired carbon contents has been achieved. The

furnace is tapped the same way a blast furnace is tapped; a hole is drilled on the side of the

hearth and the raw steel is let to flow out. Once all the steel has been tapped, the slag is

skimmed away. The raw steel may be cast into ingots; this process is called teeming, or it may

be used on continuous casting for the rolling mill. The regenerators are the distinctive feature

of the furnace and consist of fire-brick flues filled with bricks set on edge and arranged in such a

way as to have a great number of small passages between them. The bricks absorb most of the

heat from the outgoing waste gases and return it later to the incoming cold gases for

combustion.

* Structure of open hearth furnace:-

A modern open hearth furnace consists of following principal parts:-

1) Reaction chamber

2) Right and left ports.

3) Air and gas slag pockets.

4) Air and gas regenerators with checkerwork.

5)flues for air and combustion products.

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6)a change-over system.

7)a stack.

An open hearth furnace is a symmetrical unit i.e. its rights and left sides are mirror images

of each other.The fuel gas and air for its combustion enter the open hearth furnace

alternatively from

right and left sides. When fuel and air are supplied from right, combustion products are

exhausted to left.

Open hearth furnaces are provided with valves and slide gates to reverse the flow of fuel and

air,

this operation being called the change-over.

*ADVANTAGES:-

Owing to its merits, the open hearth process will long remain the topmost in steel manufacture.

1)Basic open hearth furnace are capable of processing iron of almost any chemical composition.

2)the process is suited to handle any amount of low-cost steel scrap.

3)open hearth furnace can operate on any kind of fuel.

4)The quality of open hearth steel is highest among commercial steel making processes.

5)The process is far slower than that of Bessemer converter and thus easier to control and take

samples for quality control.

*LIMITATIONS-

1)it has lower productivity than oxygen-convertor process.

2)Modern open hearth furnace are not suited to intensification by blowing the bath with large

amount of oxygen.

3)there is a necessity to provide slag pockets and regenerators which makes the furnace

complicated.

4)The making and running of open hearth furnace is costly.

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Q.144) Differntiate Between Acidic and Basic Open Hearth Furnace.

ANS

Acidic Open Hearth Furnace Basic Hearth Furnace

1) It Uses Acid Furnace lining(Silica Firebricks) and utilizes acid slags for metal refining. a) Since excess phosphorous or

silicon cannot be removed by an acid slag,the amount of these elements charged into the open hearth furnace should be controlled.

1) It uses basic lining(ie., of dolomite, crushed magnesite etc.)

a) Steel scrap and pig iron of low grades can be charged into the basic lined furnaces because impurities such as excessive amounts of phosphorous and sulphur are successfully eliminated.

2) Metal charge should contain low phosphorous and low sulphur pig iron and scrap. Limestone is required to keep the slag fluid.

2) Metal charge consists of pig iron and scrap iron. Limestone needed to form slag. Iron ore(Iron Oxide) may be added to burn excess carbon if present.

3) Acid Refractories are Cheaper compared to basic refractories.

3) Basic refractories are more costly.

Name: Bradley D’Souza, Roll No.: ae306

Q145 Construction and working of Converter Furnace. Give its advantages and

limitations.

Ans: INTRODUCTION

Converters are actually those furnaces which do not melt steel rather they

are steel making units.

Converter are of two types (a) Bessemer or Bottom blow in which blast of

cold air is blown from the bottom and, (b)Torpenus or side blow converter

in which blast of cold air is blown from side of the converter.

447

A converter actually converts pig or cast iron into steel by blowing air

through (Bessemer) or over (side blown) molten iron.

The side blown converter is more suitable then the Bessemer converter in

foundries producing steel casting.

Aside blown converter can produce high temperature molten steel (3200-

3300°F) which are required to pore in thin sectioned steel casting.

The producing of steel casting by the converter method however is not

widely employed.

WORKING:

The metal charge is melted in a cupola and it is brought to the converter for

refining the same.

The converter is tilted down; the molten cupola iron is given a desulfurizing

treatment in the ladle and is transferred to the converter which is then tilted

back to the upright position.

Cold air is blown through tuyers located in the side (of the converter) over

the molten iron at a pressure of about 5lb. pre inch sq (about 0.35kg/cm sq).

The oxygen of the cold air burns (oxidizes) Mn and Si to form slag ; the

carbon is oxidized out of the charge (melt) and produces CO and CO2 .

This oxidizing reaction are exothermic and thus no fuel is required for

heating purpose; rather the heat generated by these reaction raise the

temperature of the metal to about 1700°C which is sufficient for pouring

purposes.

448

The cold air blown is continued (only) until carbon is reduced to about 0.1-

0.2%.

The colour and the length of the flame originating from the converter nose

gives an indication of the rate of oxidation and the order of oxidation of the

elements (like C, Si and Mn). Photoelectric devices can be used to mark the

end of the air blast.

Recarbonizers (Ferro alloys of carbon) , Ferro-Silicon and Ferro-Manganese

can be added to the molten metal as it is being tapped into a pouring ladle ,

in order to adjust metal to required composition.

Addition of Al to deoxidize the melt makes the metal ready for pouring.

name KISHOR.S.GUNJALKAR

rollno=AE310

Q146. Differentiate between bessemer and side-blow converter furnaces?

ANS

Bessemer Converter

It is similar in construction to the side-blow converter , the bessemer converter differs

from the side-blow converter in that the tuyeres are located in the bottom instead

of at the side. The Bessemer process for making steel depends upon the ability of

oxygen in air to oxidize silicon, manganese, carbon, and some phosphorous more

readily than it oxidizes iron at high temperatures. Sulphur cannot be oxidized and

remains in the steel. The chemical reactions are the same as those used in the open-

hearth process. The converter is filled with molten pig iron by tilting it to about the

horizontal position. Then a blast of air is turned on through the tuyeres in the bottom,

and the converter is rotated to its upright position. An air-blast pressure of 20-25 psi is

sufficient to keep the metal from entering the tuyeres Bessemer converters have

capacities ranging from 20 to 40 tons and are generally considered capable of

producing about 1 ton of steel per minute of operation. Since the initial cost of the

equipment is relatively low, this is an economical method for making some steels.

Side-Blow Converter:

In foundries which produce steel castings, the side-blow converter is more suitable than

the Bessemer converter. The air blast from tuyres, located at the side, impinges on the

surfaces of the molten pig iron, oxidizing the undesirable elements. An air-blast

pressure of about 5 psi is used. Here the carbon is burned largely to carbon dioxide,

creating more heat than with the bessemer process. This produces higher-temperature

449

molten steels(3200 to 3300deg.F), which are needed to pour steel castings in this

section. Side-blow converters are normally smaller than bessemer converters ,holding

from 1 to 4 tons of steel.

name :Ajay Kashyap Roll.No.:318.

Q 147 ) Construction &Working of Crucible Furnace? Advantages & limitations

Name: Amit Khairaokar

Roll no: 319

Branch: Automobile

CRUCIBLES

Introduction

-Metal has been melted in cruciable for thousand of years Throughout

this period cruciable melting has survived all the onslaught of social

economic and technological change to emerge

materials and it can withstand high temperature

lener and fitter, ready to meet any challenge. The major reason for

its survival has been the progressive development of cruciables with

their unipue combination of properties

1. Refractoriness-the ability to withstand high remperatures;

2. Resistance to thermal shock-the ability to withstand rapid changes

of temperature

3. Resistance to erosion by the solid charge, and by molten metal

swirling around in the cruciable

4. Resistance to chemical attack by metals, fluxes and slag.

5. High thermal conductivity, to ensure the rapid transfer of heat

from the fuel to the metal charge.

6. Resistance to oxidation from the atmosphere and metal oxides.

7. Retention of thermal conductivity.

8. Good mechanical strength to withstand rough handling in foundry conditions

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Advantage

1. Uniform heating of charge.

2. No contaminantion of the charge by production of combustion

3. Flexibility. The ability to change alloys

4. Low melting losses.

5. Low capital and installation costs.

Cruciable Production

- Modern cruciable manufacturing has developed from what was an

ancient industry to a highly sophisticated one which encompasses many

technological disciplines. The combustion system of the multi-fuel

fired kilns depend upon the latest microprocessor regulators to attain

high thermal efficiency and eliminate environmental pollution

- All manufacturing industries strive to achieve consistent high

quality in their products. For cruciables, this not only means a heavy

dependence upon equipment control, but also intensive inspection

techniques at each stage of manufacture from the preparation and

selection of the "raw" materials so the final pre-despatch check

- Cruciables are made from mixtured of several raw materials, the principals ones being graphite, silicon carbide, and various types of clay. In addition, pitches and resins are used as binders. - There are various ways in which the prepared mixtures are formed to the final cruciable shape. Very small cruciable, such as those used in laboratory are pressed, whereas the majority of larger cruciable are

451

formed in rotation moulds or by isostatic pressing. CRUCIABLE FURNACES

1) In a cruciable furnace the metal charge is placed and melted in a cruciable

2) A cruciable is made up of silicon caraide, graphite refracetory

3. A cruciable furnace is though mainly used for melting of non

ferrous metals and alloys, it has been and is being used for melting

cast and steel also

4. A cruciable furnace consist of steel shell provided with refractory

lining inside.

a) advantages of cruciable furnace

- Low initial cost

- Easy to operate

- Low cost of fuel

b) types of cruciable furnace

1. Pit cruciable furnace 2. Cruciable furnace of bale-out type.

3. Cruciable furnace of titling type

4. Gas and oil fired cruciable furnace

5. Cock fired cruciable furnace

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1. Pit cruciable furnace a) A pit furnace has cruciable placed in a pit below the ground level b) It may be coke oil of gas fired furnace, but usually it is fired with coke c) Enough coke is packed around and above the cruciable pot so as to melt and superheat the metal charge 2) Cruciable furnace of bale-out type. a) Unlike pit furnace, cruciable of a bale-out type furnace rests above the ground level. b) Such furnace are normally fired by oil or gas. c) Bale-out type furnace are made cylindrical so that flame may sweep

454

around and uniformly heat the cruciable.

2. 3) Cruciable furnace of titling type a) As compared to stationary furnace, titling type furnace are preferred where larger amount of metal. 4) Stationary gas or oil fired cruciable furnace a) It has an outer shell having a refractory lining inside. b) As explained under titling furnace, the flame swirls around the outside of cruciable containing the charge and melts the same.

5) Stationary coke furnace

a) It differes from pit furnace in the sense that it is above the floor level.

b) In oceration it resembles coke fired pit furnace.

Advantages of an oil or gas fired cruciable furnace over a coke fired furnace

a) Oil and gas heat more quickly than coke provide a fast a making rate

b) A coke fired furnace needs an enclosed ash pan whereas nothing like

that is required in oil is gas fired furnace

455

c) Floor space can saved by using an oil or fired furnace

d) Any oil or gas fired furnace required less labour as compared to a

coke fired furnace

e) Recoking in a coke fired furnace accompanies with it a drop in the

temperature of the melt.

Q148 . Write a note on types of crucible furnaces with diagrams and applications.

Name : ImranKhan

Class: S.E.(AUTO)

Roll no. AE 320

Ans:

(1) In a crucible furnace, the metal charge is placed and melted in crucible.

(2) A crucible is made up of silicon carbide, graphite or other refactory materials.

(3) A crucible furnace is though mainly used for melting of non ferrous metals and

alloys, it has been and being used for melting the cast and steel also

(4) A crucible furnace has the following advantages:

-Low initial cost

-Easy to operate

-Low cost of fuel etc.

457

(1) PIT CRUCIBLE FURNACES:

458

(a) A pit furnace has crucible placed in a pit below the ground level.

(b) It may be coke, oil or gas fired furnace, but usually it is fired with coke.

(c) Enough coke is packed round and above the crucible pot so as to melt

and superheat the metal charge.

(d) Since molten metals does not come in contact with fuel, there is no pick

up of elements by the metal from the coke and a very little composition

occurs in the metal charges.

(2) CRUCIBLE FURNACE OF BAIL OUT TYPE:

(a) Unlike pit furnaces crucible of the bail out types furnace rests above

ground level. Such furnaces are normally fired by oil or gas.

(b) Bale out type furnaces are made cylindrical so that flame may sweep

around and uniformly heat the crucible.

(c) The forced draft is provided usually by a fan.

(3) CRUCIBLE FURNACE OF TILTING TYPE:

(a) As compared to stationary furnaces, tilting type furnaces are preferred

where larger amounts of metal are melted.

(b) In a stationary furnace, the crucible can be taken out from the furnace and

moved to the place of pouring whereas in tilting type of furnace the

crucible is permanently cemented in place.

(c) Thus unlike of stationary furnace, in a tilting furnace the molten metal is

poured into preheated ladle from the crucible by tilting the furnace.

(d) Against stationary furnaces of capacities up to 100 kg, tilting furnaces

may have capacity upto 500 kg of metal or more.

(e) A tilting crucible furnaces consists of an outer cylindrical shell having a

refractory lining inside.

459

(4) STATIONARY GAS OR OIL FIRED CRUCIBLE FURNACES:

(a) It has an outer shell having a refractory lining inside.

(b) As explained under tilting furnaces, the flame swirls around the outside of

the crucible containing the charge and melts the same.

(5) STATIONARY COKE FIRED FURNACE

(a) It differs from pit furnace in the sense that it is above the level.

(b) It operation it resembles coke fired pit furnace.

ADVANTAGES:

(1) Oil and gas heat more quickly than coke and provide a fast melting rate.

(2) Unlike coke fired furnace, in an oil or gas fired furnace, the furnace heating

can be immediately stopped when desired or when the charge has been

melted. This saves a lot of fuel.

460

(3) A coke fired furnace needs an enclosed ash pan whereas nothing like that is

required in oil or gas furnaces.

(4) Floor space can be saved by using oil.

(5) Any oil or gas fired furnace requires less labour as compared to a coke fired

furnace.

(6) An oil or gas fired furnace associates with it an improved and easier control

of temperature.

Q.149) Construction and working of pot furnace advt and limitations.

Ans-

Construction and working-

1.Like a crucible furnace a pot furnace is usually an indirect flame furnace . However some

constructions of pot furnaces are approach direct flame conditions.

2.A pot furnace consists of cast iron or steel pot in which metal chage is placed and the pot is

heated by the gas,oilor electricity.

3.Metals commonly melted in pot furnaces are magnesium, aluminium, zinc,lead,tin and other

low melting point metals and alloys.

4.As the metal is melted it is ladled from the pot for distribution to the molds.

5.Pot furnaces are often used with permanent mold amd die casting machines for producing

small castings.

ADVANTAGES-

A tilting pot furnace may accommodate upto 1500 kg of metal.

DISADVANTAGES-

The capacity of a pot furnace is of few hundreds of kg.

461

Q150.Construction And Working of Electric Furnance Advantages and

Limitations.

Ans:

Introduction:

1.Electric furnances are employed for moulding metals in high quality casting,because:

_losses by oxidation can be eliminated,

_alloying element can be can be added without any loss (due to oxidation)

_composition of the melt and its temperature can be accurately controlled.

2.Electric furnance are used to melt steel(including alloy steel i.e,tool steels and

stainless steel) high-test and alloy cast iron,brasses,etc.

3.As compared to other furnances, the cost of operation of electric furnance is high;

however this has to be borne when castings of finest quality are demanded.

4.capacity of electric furnances ranges from 250kgs to 10tons.

5.More than 30% of yearly tonnage of castings in U.S.A are produced in electric arc

furnances.

462

Types:

(a)Direct arc furnance.

(b)Indirect arc furnance.

(c)Resistence heating type.

(d)Coreless type(or High Frequency)induction furnance.

(e)Core type(or Low Frequency)induction furnance.

DIRECT ARC FURNANCE

Introduction:

1.It is the most widely used used remelting unit in steel foundries.

2.It remelts steels of widely differing compositons.

3.The largest direct arc furnances have capacities of 125 tons

4.Direct arc furnance has its diameter upto 6 meters.

5.Rating of transformer supplying power to the arc ranges from 800 kVA to 400 kVA.

6.A 50 ton direct arc furnance may require arc current of the order of 2500 Amps and

arc voltage is about 250 volts.

Construction:

1.A direct arc furnance consists of heavy steel sheel linked with refractory brick and

silica for acid lined furnances and magnesite for basic lined furnances.

_acid lining is preferred when good steel scrap low in sulphur and phosphorous is

available so that removal of these two elements is not required;the heats are produced

much faster.

_a basic lined furnance is advantageous because inferior scrap may be used to

make good steel; the basic process removes S & P from the metal.However the heats

takes longer time than in acid lined furnances.

2.The roof of the direct arc furnance consists of a steel roofing in which silica brics are

fixed in position.

463

_The direct arc furnance may be charged either from charging door or from the

furnance roof which is made to lift off and swing clear of the furnance.

_A few spare roofs can be made available at all times as the roofs does not have a

very long life.

3.Depending upon whether it is a two phase or three phase electric furnance,two or

three graphite electrodes are inserted through the holes in the roof into the furnance.

4. All the arc furnances rest in bearings on their two sides and bearings in turn are

mounted in trunnious;thus arc furnances can be tilted backward or forward for

charging,running off the slag and pouring the molten metel into the ladle.

Operations:

1.The interior of the furnance(i.e,refactory lining ,etc )is preheated before placing the

metal charge in the furnance.

2.The furnance is charged either by swinging over the roof or through the charging door.

3.Once the cold charge has been placed on the hearth of the furnance, electric arc is

drawn between the electrodes and the surface of the metal charge by lowering the

electrodes down till the current jumps the gap between the electrodes and the charge

surface.

4.The arc gap b/w the electrode and the charge is regulated by automatic control which

raise or lower the electrode and maintained the desired arc gap by maintaining constant

arc voltage.

5.Three arc burning simontaneously produces temperature of 11000 deg.F,and the

readly made flux,sand and the metal scrap.

6.Before pouring the liquid metal into the ladle, the furnance is tilted backward and the

slag is poured of from the charging door.

7.The furnance is then tilted forward and the molten metal is empited into ladels.

8.Hearth,side walls and roofs of the furnancearc repaired with the help of the suitable

refactory materials after each heat.

Advantages of direct arc furnance

1.Unlike crucible furnances,direct arc furnance take a nite metal refining sequence.

2.Electric furnance lend themselves to close temperature and heat control.

3.Analysis of melt can be kept to accurate limits.

464

4.Direct arc furnance has athermal efficiency as high as about 70%.

5.It is not difficult to control the furnance atmosphere above the molten metal.

Limitations

Heating costs are higher than for other furnances.this is however can be adjusted to

some extent by using low cost scrap turnings or boring as metal charge.

Name:Rahul Mishra

Roll no.327

Q151.Construction and working of direct arc furnace advantages and limitations.

ANS

DIRECT ARC FURNACE

Introduction

1. It is the most widely used remelting unit in steel foundries.

2. It remelts steels of widely differing compositions.

3. The largest direct arc furnaces have capacities of about 125 tons.

4. Direct arc furnace has its diameter up to 6 metres.

5. Rating of the transformers supplying power to the arc ranges from 800 KVA to

40000 KVA.

Construction

1. A direct arc furnace consists of a heavy steel shell lined with refractory brick and

silica for acid lined furnace and magnesite for basic lined furnace.

2. The roof of the direct arc furnace consists of a steel roofing in which silica bricks

are fixed in position. The arc furnace may be charged either from the charging

door which also serves for removing slag from the molten metal or from the

furnace roof which is made to lift off and swing clear of the furnace. A few spare

roofs can be made available at all time as the roof does not have a very good life.

3. Depending upon whether it is a two phase or three phase electric furnace, two or

three graphite electrodes are inserted through the holes in the roof into the

furnace. Electrodes can be raised up and down. For a 50 ton furnace, each

electrode carries a current of the order of 25000 amperes.

465

Electrodes guides placed on the furnace roof are water cooled to dissipate

damaging heat.

4. All arc furnaces rest in bearings on their two sides and bearings in turn are

mounted in trunnions;thus arc furnace can be tilted backward or forward for

charging, running off the slag and pouring the molten metal into the ladle.

Operation

1. The interior of the furnace is preheated before placing the metal in the furnace.

- Preheating is done by alternatively striking and breaking the arc

between the electrodes and used electrodes pieces kept on the

hearth.

- After preheating, the electrodes pieces placed on the hearth are

removed

2. The furnace is charged either by swinging over the roof or through the

charging door.

- For melting cast iron a large proportion of the metal charge consist of

cast iron foundry scrap having sand adhered to it.

3. Once the cold charge has been placed on the hearth of the furnace, electric

arc is drawn between the electrodes and the surface of the gap between the

electrode and the charge surface.

4. The arc gap between the electrode and the charge is regulated by automatic

controls which raise or lower the electrode and maintain desired arc gap by

maintaining constant arc voltage.

- Smaller arc lengths produce more intense heat, however there is a

little fear of contaminating molten metal with graphite.

466

5. Three arcs burning simultaneously produce a temperature of the order of 11000

F, and readily melt flux, sand and the scrap.

6. Before pouring the liquid metal into the ladle, thefurnace is tilted backward and

the slag is poured off from the charging door.

7. The furnaceis then tilted forward and the molten metal is emptied into ladles.

8. Hearth, sides walls and roof of the furnace are repaired with the help of

suitable refractory materials after each heat.

Advantages of Direct Arc Furnace

1. Unlike crucible furnace, direct arc furnace undertake a definite metal refining

sequence.

- Additions to the charge are made so as to form slags which have a

refining action on the metal.

2. Electric furnace lend themselves to close temperature and heat control.

3. Analysis of melt can be kept to accurate limits.

4. A direct arc furnace has a thermal efficiency as high as about the 70%

5. It is not difficult to control the furnace atmosphere above the molten metal.

6. Alloying elements like Cr, Ni and W can be recovered from the scrap with little

losses

7. It can make steel directly from pig iron and steel scrap.

8. An arc furnace is preferred for its

- Quicker readiness for use,

- Longer hearth life,

- Ease of repair,

- Greater independence of the quality of the charge.

Limitations

1. Heating costs are higher than for other furnaces. This however can be adjusted

to some extent by using low cost scrap turning or borings as metal charge.

Name=Akshay.D.Mohite

Roll no=328

Q.152) Construction and working of indirect arc/rocking furnace advt&

limitations.

ANS

467

Introduction.

Has a capacity ranging from few Kgs. to 2 tons.

Preferred for producing smaller melts as compared to direct arc furnace.

It is of rocking type since it moves back and forth during melting process. The

metal thus comes in contact with the hot refractory lining and picks up heat for

melting the linings.

Used for melting:

Cast Iron

Steel

Copper and its alloys.

Obtains Lower temperatures and has less efficiency compared to a direct arc

furnace.

Construction:

It consists of a barrel type shell made up of steel plates, having refractory lining

inside.

There three openings,

Two for Graphite electrodes

Third is the charging door for feeding the metal charge into the furnace.

Pouring spout is built up with the charging door.

468

The Furnace is mounted on the rollers which are driven by a rocking drive unit to

rock the furnace back and forth during melting.

While furnace rocks-

Liquid metal washes over the heated refractory lining and absorbs

heat from them.

The metal charge constituents get mixed thoroughly.

Rocking of furnace

Speeds up melting

Stirs the molten metal

Avoids refractory linings from getting over-heated

Thus increasing its life.

The angle of rocking of furnace is adjusted in such a manner that the liquid

metal level remains below the pouring spout.

Operation:

First, pig Iron is charged in the furnace.

Above pig Iron Scrap is placed.

Electric Power is turned on,

Graphite electrodes are brought nearer till the current jumps and an electric arc is

set up between them.

Heat generated in the arc melts the charge.

Now the furnace is set to rock to and fro.

Rocking helps in better heat exchange between refractory linings, molten metal

and solid metal.

Rocking of furnace and adjustment of arc gap between the graphite electrodes is

automatically controlled.

When the melting is complete,

The furnace is tilted mechanically farther than the rocking level

Liquid metal is poured out through the pouring spout into the ladle.

Advantages:

Metal Charge does not form a part of electrical circuits.

Low cost scrap metal canbe used in an indirect arc furnace

Operation and the control of the furnace are simple.

Alternative design: The arc is replaced by Resistance heating of a single electrode.

This electrode has : Reduced diameter at its centre producing greater resistance thus producing high

heats.

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Operates Noiselessly. Furnace involves high Operational costs.

Name: Shreenath Nair , RollNo. Ae 330

Q153) Construction and Working CORELESS (high freq) INDUCTION FURNACE

advt. & limitations.

Name :- Kalpesh E. Patil

Roll no :- 335

Branch :- SE Automobile

What is Furnace?

Furnaces are the Devices which are used to produce the molten metal from

the raw material.

Induction Furnace:

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An induction furnace is an electrical furnace in which the heat is applied by

induction heating of a conductive medium (usually a metal) in a crucible

placed in a water-cooled alternating current solenoid coil.

Construction of Coreless Induction Furnace:

A high frequency induction furnace consist of refractory

crucible placed centrally inside water cooled copper coil and

packed into position by ramming dry refractor tightly between

the crucible and the copper coil.

A high frequency induction furnace can of two types as,

1) A tilting type

2) A lift coil type in which the furnaces shell along with the

coils can be lifted up to leave aside crucible in its position.

Working Principle of Coreless Induction Furnace

The Furnace works on the principle of a transformer in which the copper coil acts as

primary and the charge (steel scraps) as secondary.

When a high frequency electric current is passed through the primary coil, a much

heavier secondary current is induced in the charge. Heat is generated due to the

resistance of the metal causing it to melt.

The liq id metal nder oes a stirrin action d e to the ‘edd c rrents’ ind ced b the

EMF ( Electromagnetic Force) that is concentrated in the center of the circular primary

coils. This stirring action is beneficial in uniform distribution of temperature and alloy

chemistry in the melt. But on the other hand, if stirring action is excessive, dross or

surface impurities is drawn into the melt.

471

When the molten metal has reached the desired temperature, the metal is deoxidized

and tapped into ladles for pouring into moulds.

Advantage of Induction furnace:

1) An induction furnace can melt relatively small quantities (from 1.5 kg

up to 12 tons) of a wide variety of metals and alloys quickly,

conveniently and cleanly.

2) Magnetic stirring of the melt produces excellent uniformity of the melt

composition.

3) Rate of energy input can be readily controlled.

4) Furnace atmosphere can be easily controlled.

5) High frequency induction furnaces do not need a warming up time.

Limitations of Induction furnace:

1) The initial cost of the furnace and its auxiliary equipments being high, it

is limited to melting high quality metals and in smaller quantities.

2) Due to the speed with which the process of melting is completed, there is

little time available for analysis the melt composition.

3) Thus, the melt charger should be carefully selected and it should be of

required chemical composition.

Coreless Induction Furnace Diagram

473

Q154) Construction and working of Core type (low frequency) induction furnace

Advantages and Limitations?

ANS

A core type induction furnace operates as an ordinary transformer.

The furnace uses an AC supply of 60 cycles per second.

Secondary currents (having high current values at low voltage) arc induced in the metal

bath around the core and the heat is generated ary currents.

Channel of molten metal around the coil connects to the main metal container above,

which holds the metal charge.

The metal in the channel gets heated, circulates through and stirs the metal in the

container and thus the melting process (of the metal charge) proceeds.

Once the melt reaches the required pouring temperature it can be ladled out from the

pouring.

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Advantages

A core type induction furnace is most effcient of the induction melting furnaces.

It has thermal efficiency of about 80%,

Melting is rapid and clean,

Since melting is rapid and no combustion products are present, oxidation losses are at

a minimum.

Melt can be accurately controlled as regards its composition and temperature.

Magnetic stirring of the melt ansures uniformity of the metal.

The furnace operation is economical.

Limitations

Furnace cannot be operated on solid metal charge, furnace operation can be started

only after filling the channels with molten metal procured from some other furnace.

If once by chance metal gets solidified in the channels, it cannot be remelted by the

heat created in the secondary coil.

furnace

AE337 PRASHANT R.

PATIL

Q155) Explain DUPLEX and TRIPLEX of remelting process?

ANS

They are used to refine the liquid metal.

DUPLEXING PROCESS

1. A duplexing process makes uses of two furnaces.

2. A duplexing process may use cupola for melting the iron and then molten iron

may be refined in an electric furnace.

3. As an other example, if PHOSPHORUS and SULPHUR inherent in the bessemer

process are objectionable, an air furnace may use end product of bessemer

converter and reduce S and P content. This is quite time saving because all the

impurities except S and P have already been removed from the melt.

4. Duplexing is especially suitable and is being used for producing in large

quantities, the molten metal required for continuous pouring in mass production

foundry.

475

TRIPLEXING PROCESS

1. It makes use of three furnaces one after the other in order to alter or

improve the properties of metal.

2. Triplexing process is especially used in the production of low carbon irons.

Iron is melted in cupola, carbon is reduced in a converter and final refining of molten

metal is carried out in an electric furnace.

NAME: DEEPA REMULKAR

ROLLNO.:AE340

Q 156) What is s pattern? What are its functions?

A pattern is a model or the replica of the object(to be casted).

It is embedded in molding sand and suitable ramming of molding sand around the

pattern is made.

The pattern is then withdrawn for generating cavity (known as mold) in molding sand.

Thus it is a mould forming tool.

Pattern can be said as a model or replica of the object to be cast except for the various

allowances a pattern exactly resembles the casting to be made.

Defination :-[It may be defined as a model or form around which sand is packed to give rise to a

cavity known as mold cavity in which when molten metal is poured, the result is the cast object

]

When this mould/ cavity is filled with molten metal, molten metal solidifies and

produces a casting (product).

So the pattern is the replica of the casting.

Pattern mey also possess projection known as core prints for producing extra recess in

the mould for placement of core to produce hollowness in casting.

It may help in establishing seat for placement of core at locating points on the mould in

form of extra recess

It establishes the parting line and parting surface in the mold.

It should have finished and smooth surfaces for reducing casting defects.

Runner,gates and risers used for introducing and feeding molten metal to the mold

cavity may sometimes form the parts of the pattern.

The first step in casting is pattern making.

The pattern is made of suitable material and is used for making cavity called mould in

molding sand or other suitable mould material.

476

When this mould is filled with molten and it is allowed to solidify, it forms a

reproduction of the, pattern which is known as casting.

Functions of pattern:-

1. Pattern prepares a mould cavity for the purpose of making a casting.

2. Pattern possesses core prints which produces seats in form of extra recess for core

placement in the mould.

3. It establishes the parting line and parting surfaces in the mould.

4. Runner, gates and riser may form a part of the pattern.

5. Properly constructed patterns minimize overall cost of the casting.

6. Pattern may help in establishing locating pins on the mould and therefore on the

casting with a purpose to check the casting dimensions.

7. Properly made pattern having finished and smooth surface reduce casting defects.

Name:- Manoj Sharma, roll no:-342

Branch :- [SE]Automobile engineering

Q157) DIFFERENCE BETWEEN PATTTERN AND CASTING

ANS

The main difference between a pattern and casting is as regards their dimensions. A

pattern is slightly large in size when compared to casting because as a pattern:

1. Carries shrinkage allowance, it may be order of 1 to 2 mm/100cm.

2. Is given a machining allowance to clean and finish the required surface.

3. Carries a draft allowance of the order 1 to 3 degree for external and internal surfaces

respectively.

4. Carries core prints.

In addition

5.A pattern may not have all the holes and slots which the casting will have.Such holes

and slots unnecessarily complicate the pattern. Therefore it can be drilled in the casting

after it been made.

6.A pattern can be of 2 or 3 pieces whereas casting is in 1 piece.

477

7. A pattern and casting can also differ as regards the material with which they are

made.

MIHIR .R .TALREJA ROLL NO 348

Q158) State different pattern material used with their advantage, limitation and

application

Ans:

1) Wood

a. Shisham

It is dark brown in color having golden and dark brown stripes. It is very

strong and durable.

b. Kail

It has many knots. It can be very well painted. It is very hard and durable.

c. Deodar

It is white in color when soft but hard, its color turns toward light yellow. It

is strong and durable. It is easy workable and its cost is also low.

d. Teak Wood

It is hard, very costly and available in golden yellow and dark brown color.

It is very strong. It can maintain good polish.

Advantages of wooden patterns 1. Wood can be easily worked. 2. It is light in weight. 3. It is easily available. 4. It is very cheap. 5. It is easy to join. 6. It is easy to obtain good surface finish. 7. Wooden laminated patterns are strong. 8. It can be easily repaired.

Disadvantages

1. It is susceptible to moisture. 2. It tends to warp. 3. It wears out quickly due to sand abrasion. 4. It is weaker than metallic patterns.

2) Metal

Cast Iron

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It is cheaper, stronger, tough, and durable and can produce a smooth surface finish. It also possesses good resistance to sand abrasion. The drawbacks of cast iron patterns are that they are hard, heavy, brittle and get rusted easily in presence of moisture. Advantages

1.It is cheap 2. It is easy to file and fit 3. It is strong 4. It has good resistance against sand abrasion 5. Good surface finish Disadvantages

1 It is heavy 2 It is brittle and hence it can be easily broken 3 It may rust Brasses and Bronzes

These are heavier and expensive than cast iron and hence are preferred for manufacturing small castings. They possess good strength, machinability and resistance to corrosion and wear. They can produce a better surface finish. Brass and bronze pattern is finding application in making match plate pattern Advantages 1. Better surface finish than cast iron. 2. Very thin sections can be easily casted. Disadvantages

1. It is costly 2. It is heavier than cast iron. Aluminium Alloys Aluminium alloy patterns are more popular and best among all the metallic patterns Because of their high lightness, good surface finish, low melting point and good strength. They also possesses good resistance to corrosion and abrasion by sand and there by enhancing Longer life of pattern. These materials do not withstand against rough handling. These have poor repair ability and are preferred for making large castings. Advantages

1. Aluminium alloys pattern does not rust. 2. They are easy to cast. 3. They are light in weight. 4. They can be easily machined. Disadvantages 1. They can be damaged by sharp edges. 2. They are softer than brass and cast iron. 3. Their storing and transportation needs proper care. White Metal (Alloy of Antimony, Copper and Lead) Advantages

1. It is best material for lining and stripping plates. 2. It has low melting point around 260°C 3. It can be cast into narrow cavities. Disadvantages

1. It is too soft.

479

2. Its storing and transportation needs proper care 3. It wears away by sand or sharp edges.

Roll no ae349

Q 159) What are the different types of patterns?

By Prashant S. Vishe

roll no. AE-353

Drawn milling types of pattern:-

1] Single piece or solid pattern

2] Split Pattern

3] Match plate pattern

4] Sweep pattern

5] Loose piece pattern

6] Gated Pattern

7] Cope and drag

1] Single piece or solid pattern

A pattern made without joints is known as single piece pattern

This pattern is cheaper and of simple shapes.

480

2] Split Pattern

Pattern consist of two or more parts which are properly by means of dowel pins

This pattern is made by two different moulding boxes each box produces half of the

part.

Advantage of this pattern is to make process easier.

3] Match plate pattern

When split patterns are mounted with one half on one side of box nad the other half

directly on the other side of plate, the part called as a match pattern.

4] Sweep pattern

A template of wood which pivots at one end and shapes a mould in the moulding sand is

called as a sweep.

It saves material as well as time to construct pattern.

481

5] Loose piece pattern

Some patterns are made as assemblies of loose pieces.

These pieces are use to create different part of pattern

This type is use to create complicated parts of pattern

A loose piece is attached to main pattern with help of a anchor pin

The pattern is placed on the mould board and moulding sand is rammed upto the loose

piece. Then sand and pins are removed.

482

6] Gated Pattern

Gating is a provision for passage of flowing molten metal into mould.

In mass production a number of castings are produced in a multicavity mould by joining

a group of pattern with a gating system.

Gated pattern are made of either wood or metal and are used for mass production of

small castings.

7] Cope and drag

When large and heavy castings are to be produced this patterns are used.

The patterns are made in two halves on a convenient joint line

Then cope and drag patterns are built separately and mould on plates.

Q 160)A note on design of pattern and hence explain various pattern allowances

A: A good pattern may produce a sound casting but a bad pattern will always result in a poor

casting. Therefore, in order to construct a good pattern, the factor listed below must be taken

into consideration while designing a pattern.

i. A pattern should be accurate as regards its dimensions and possess very good surface

finish.

ii. Proper material for making the pattern should be selected. Metallic pattern last longer

as compared to wooden once but are expensive

iii. A pattern should carry all those allowances which are essential to simplify the molding

operations and impart accurate dimensions to the final casting.

483

iv. In case of split patterns, the parting surface should be such that the maximum parting of

the pattern remains in the drag, offset parting is beneficial.

v. All sharp edges and corners should be rounded. It help removing the pattern from the

molding box, permits a smooth flow of the metal into the mold cavity, minimizing

casting stresses and strains and produces good castings.

vi. Changes in section thickness should be smooth, gradual and uniform. It will reduce

stress and strains and minimize the changes of crack formation in the castings.

Various pattern Allowances

a) Shrinkage Allowance

i. Almost all cast metals shrink or contract volumetrically after solidification and

therefore the pattern to obtain a particular sized casting is made oversize by an

amount equal to that of shrinkage or contraction.

ii. Different metals shrink at different rates because shrinkage is the property of

the cast metal or alloy.

iii. The metal shrinkage depends upon:

1. The cast metal or alloy.

2. Pouring temperature of the metal or alloy.

3. Casting dimensions

4. Casting design aspects.

5. Molding conditions

iv. Shrinkage allowance for various cast metals is as follows;

1. Gray Cast iron 6.95 to 10.4mm/metre

2. White cast iron 20.8

3. Malleable cast iron 10.4

4. Steel 20.8

v. Cast iron poured at higher temperatures will shrink more than that poured at

low temperature.

vi. Harder grades of cast iron shrink more than the softer grades of cast iron.

b) Machining Allowance

A casting is given an allowance for machining, because

i. Casting get oxidized in the mold and and during heat treatment and scales etc.

thus formed need to be removed.

ii. It is intended to remove surface roughness and other imperfections from the

castings.

iii. It is required to achieve exact casting dimensions.

iv. Surface finish is required on the casting.

484

The above factors necessitate the provision of extra metal on the casting or the

machining/finishing allowance.

How much extra metal or how much machining allowance should be provided,

depends upon the factor listed below:

i. Nature of metal i.e. ferrous or non-ferrous .ferrous metal gets scaled

whereas nonferrous one do not.

ii. Size and shape of the casting. Longer casting tends to warp and need

material (i.e. allowance) to be added to ensure that after machining the

casting will be alright.

iii. The type of machining operation to be used employed by cleaning the

castings. Grinding removes much lesser metals as compared to turning.

iv. Number of cuts to be taken. Machining allowance is directly proportional to

cuts required for finishing the casting.

v. The degree of surface finish desired on the cast part.

c) Draft or taper allowance

i. It is given to all surface perpendicular to the parting line.

ii. Draft allowance is given so that the pattern can be easily removed from molding

material tightly packed around it without damaging the mold cavity

iii. Amount of taper depends upon

1. Shape and size of the pattern in the depth direction in contact with the

mold cavity.

2. Molding method.

3. Mold material.

iv. Draft allowance is imparted on internal as well as external surface; of course it is

more on internal surfaces.

v. Shown two patterns—one with taper allowance and the other without it.it can

be visualized that it is easy to draw the pattern having taper allowance, out of

485

mold without damaging mold walls or edges.

d) Distortion Allowance

A Casting will distort or wrap if:

i. It is of irregular shape.

ii. All its part do not shrink uniformly i.e., some parts shrink while others are

restricted from doing so,

iii. It is U or V shaped,

iv. It has long, rangy arms as those of the propeller strut for the ship,

v. It has long flat casting,

vi. The arms possess unequal thickness,

vii. One portion of the casting cools at a faster rate as compared to the other, etc.

e) Shake Allowance

486

i. A pattern is shaken or rapped by striking the same with a wooden piece from

side to side. This is do so that the pattern is loosened a little in the mold cavity

and can be easily removed.

ii. In turn, therefore, rapping enlarges the mold cavity which result in a bigger

seized casting.

iii. Shake allowance is normally provided only to large castings because it is

negligible in case of small castings and is thus ignored.

iv. The magnitude of shake allowance can be reduced by increasing the tapper.

v. The amount of rapping varies with the molder doing the same and therefore the

foundry supervisor must be consulted while fixing this allowance

Name:Swapnamurti.B.Wagh roll no:AE354

Q161: What are cores? What are its functions?

A: cores are separate shapes of sand that are generally required to from the hollow

interior of the casting. Sometimes cores are also used to save those parts of the tasking

that are not otherwise practically or physically obtainable by the mould produced directly

from the Pattern. The core is left in the mould in casting and is removed after the

casting.

Functions of cores

i. For hollow castings, cores provide the means of forming the main internal

cavities.

ii. Cores may form a part of green sand mood.

iii. Cores may provide external undercut features.

iv. Cores may be employed to improve the mold surface.

v. Cores may be inserted to achieve deep recesses in the castings.

vi. Cores may be used to strengthen the molds.

vii. Sometimes the mold may be completed simply by assembling the core-pieces or

cores.

viii. Cores may be used to form the gating system of large size molds.

Name: Swapnamurti. B.W

Roll no: 354(Automobile)

Q 162) Cores and types of core and its classification

487

Akshay bhivshet

Roll no AE359

What is core ?

A core is a body of specially prepared sand which has been moulded in a core box and then

baked in oven. Cores can be made in many shapes by ramming core sand in core boxes.

Cores can be classified according to:

A) The state or condition of core

1) Green sand core

2) Dry sand core

B) The nature of core material employed

3) Oil bonded cores

4) Resin bonded cores

5) Shell cores

6) Sodium silicate cores

C) The types of core-hardening process employed

7) Co2 process

8) The hot box process.

9) The cold set process.

10) Fluid or castable sand process.

11) Nishiyama process.

12) Furan N0-bake process.

13) Oil-no-bake process.

D) The shape and position of the core

14) Horizontal

15) Vertical core

16) Hanging or cover core

17) Balanced core

488

18) Drop core or stop off core

19) Ram up core

20) Kiss core

1) Green sands cores

(a) Green sand cores are formed by the pattern itself.

(b) A green sand cores is a part of the mold .

(c) A green sand core is made out of the same sand which the rest of mold has been made

that is the molding sand

2) Dry sand cores

a) Dry sand cores, unlike green sand cores are not produce as a part so the mold

b) Dry sand cores are made separately and independent of the mold

c) A dry sand core is made up of core sand which differs very much from the sand out of

which the mold is constructed.

d) Core sand core is made in a core box and it is baked after ramming.

e) A dry sand core is positioned in the mold on core-seats formed by coreprints on the

patterns.

f) A dry sand core is inserted in the mold before closing the same.

3. Oil bonded cores

a) Conventional sand cores are produced by mixing silica sand with a small percentage of

linseed oil

b) Oil bonded cores base themselves on the principle of the oxidation and polymerization of a

combination of oils containing chemical additives which, when activated by an oxygen bearing

material, set in a pre-determined time

4. Resin –bonded cores

a) Phenol resin bonded sand is rammed in a core box.

b) The core is removed from the core box and baked in a at 375 to 475 degree F to harden the

core

5. Shell cores

489

Shell cores have been discussed under section 9.4

6. & 7. Sodium silicate –CO2 cores

a) These cores use a core material consisting of clean, dry sand mixed with a solution of sodium

silicate

b) The sand mixture is rammed into the core box.

c) The rammed core while it is in the core box is gassed for several seconds with carbon-di-

oxide gas. As a result a silica gel forms which binds sand grains into a strong, solid form

Na2SiO3 + co2 NA2CO3 + SiO2 (SILICA GEL)

d) Cores thus formed usually need no baking

e) Cores thus formed posses more strength than the oil/resin bonded ones

f) Unhardened cores are not handled so there is no chance of breaking or sagging of cores

g) core-dryer is not required

h) Cores formed by co2 process are used in the production of cast iron, steel, aluminum and

copper base alloy castings

i) The used sand mixture however cannot be recovered and re-used.

8. The hot box

a) It uses heated core boxes for the production of cores.

b) the core boxes is made up of cast iron ,steel or aluminum and possesses vents and ejectors

for removing core gases and stripping core from the core box respectively.

c) Core box is heated from 350 to 500 degree F

d) Heated core boxes are employed for making shell cores from dry resin bonded mixtures.

e) Hot core boxes can also be used with core sand mixture employing liquid resin binders and a

catalyst.

9. The cold set process

a) While mixing the core sand, an accelerator is added to the binder

b) The sand mixture is very flow able and is easily rammed

490

c) Curing begins immediately with the addition of accelerator and continuous until the core is

strong to be removed from the core box.

d) A little heating of core hardens it completely.

e) Cold set process is preferred for jobbing production

f) Cold set process is employed for making large cores.

10. Cast able sand process

a) A setting or hardening agent such as dicalcium silicate is added to sodium silicate at the time

of core sand mixing.

b) The sand mixture process high flow ability and after being poured in the core box, it chemical

hardens after a short interval of time.

c) as compared to co2 process , where it may not be possible to gas the full core uniformly and

to obtain uniformly hardened cores, castables sand process produces much better annually

from results.

d). castable sand process is best suited to large jobbing work

11. nishiyama process

a) nishiyama process uses sodium silicate bonded sand, which is mixed with 2% finely powered

ferrosilicon.

b) Hardening occurs because of exothermic reaction of silicon with NaOH produced by

hydrolysis in the solution of sodium silicate.

c) Cores thus made possess short bench life.

12. furan-no-bake system

a) the cores sand mixtures contain washed and dried sand with clay content less than 0.5%

,furan no –bake resin 2% and activator (phosphoric acid ) 40%.

b) The basic reaction between the furan resin and phosphoric acid results in an acid

dehydration of the resin.

c) The core sand mixture has high flow ability and needs reduced rodding (to handles the cores)

491

d) Uniform core hardness, exact core dimension, better fitting cores, lower machining and

layout costs, and reduction of oven baking are some of the good characteristics of cores made

by furan-no-bake system.

13. Oil –no-bake process

a) The process employs a synthetic-oil-binder which when mixed with basic sands and activated

chemically, produces cores that can be cured at room temperature.

b) The sand mix may consist of:

Washed and dried sand 500 kg.

Oil-no-bake binder and catalyst 7 kg.

Oil-no-bake cross linking agents 1.4 kg

c) In oil-no-bake process, the polymerization reaction results in a complete and uniform setting

of the complete core –sand mass.

d) This process assures better depth of set, fast baking, easier core-withdrawal and lower

production costs as compared to furan or oil bonding process

14. Horizontal core

a) Fig. shows horizontal core.

b) A horizontal core is positioned horizontally in the mold.

c) A horizontal core may have any shape, circular or of some other section depending upon the

shape of the cavity required in the casting.

d) A horizontal core is supported in core seats at both ends.

e) Uniform sectioned horizontal cores are generally placed at the parting line

f) A horizontal core is very commonly used in foundries

492

Horizontal core

15. Vertical core

a) Fig. shows a vertical core.

b) On the cope side, a vertical core needs more taper so as not to tear the sand in the cope

while assembling cope and drag.

c) A vertical core is named so because it is positioned in the mold cavity with its axis vertical.

Vertical core

d) The tow ends of the vertical core are supported in core seats in cope and drag respectively.

e) A big portion of the vertical core usually remains in the drag

f) A vertical core is very frequently used in foundries

When horizontal and verticals premade cores of different sizes are kept in the stores for ready

use, they are termed as stock cores.

16) Hanging or cover core

493

a) A hanging core is supported from above and it hangs vertically in the mold cavity.

b) A hanging core has no support from bottom

c) Fig shows a hanging (cover core)

d) A hanging core is provide with a hole through which molten metal reaches the mold cavity

e) Hanging cores can be made up of either green or dry sand.

f) It is known as hanging core because it hangs; it is also called cover core if it covers the mold

and rests on a seat made in the drag. Ref to the fig given below

g) A simple hanging core is one which is not supported on any seat. Rather it hangs from the

cope with the help of wires.etc

Hanging core

494

Balanced core

17. Balanced core

a) Fig. shows a balanced core.

b) A balanced core is one which is supported and balanced from its one end only.

C) A balanced core requires a long core seat so that the core does not sag or fall into the mold.

d) A balanced core is used when a casting does not want a through cavity.

e) A balanced core may be supported on chaplets.

18 Drop or stop off core

a) Fig. shows a stop off core.

b) A stop off core is employed to make a cavity (in the casting) which cannot be made with

other types of cores.

c) A stop off core is used when a hole, recess or cavity, required in a casting is not in line with

the parting surface; rather it is above or below the parting line of the casting.

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Drop or stop off core

d) Depending upon its shape and use, a stop off core may also be known as tail core, saddle-

core, chair core, etc.

19 Ram-up –core

a) A ram-up core is one which is placed in the same along with pattern before ramming the

mold.

b) A ram-up core cannot be placed in the mold after the mold has been rammed.

c) A ram-up –core is shown in fig

d) A ram-up-core is used to make internal or external (surface) details of a casting.

Ram-up-core

20. Kiss Core

a) Kiss core is shown in fig.

b) A kiss core does not require core seats for getting supported

c) A kiss core is held in position between drag and cope due to the pressure by cope on the

drag.

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d) A number of kiss cores can be simultaneously positioned in order to obtain a number of

holes in a casting.

Kiss core

Core application

A) Cores and core forms greatly increase the versatility of molding and casting operation.

B) Besides being used for forming recesses and holes in the castings, cores are also

employed:

1) As, strainer, gates, and pouring cups.

2) As riser cores.

3) For making moulds.

4) As core mould in centrifugal casting process.

5) As slab core for increasing castings output from one mould.

6) For increasing production from match plate moulding.

Q.163) Note on Core Baking Ans: Core baking

Once the cores are prepared, they will be baked in a baking ovens or furnaces.

The main purpose of baking is to drive away the moisture and hard en the binder, thereby giving strength to the core.

The core drying equipments are usually of two kinds namely core ovens and dielectric bakers.

The core ovens are may be further of two type’s namely continuous type oven and batch type oven.

The core ovens and dielectric bakers are discussed as under.

1) Continuous type ovens

Continuous type ovens are preferred basically for mass production.

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In these types, core carrying conveyors or chain move continuously through the oven.

The baking time is controlled by the speed of the conveyor.

The continuous type ovens are generally used for baking of small cores.

2) Batch type ovens

Batch type ovens are mainly utilized for baking variety of cores in batches.

The cores are commonly placed either in drawers or in racks which are finally placed in the ovens.

The core ovens and dielectric bakers are usually fired with gas, oil or coal.

3) Dielectric bakers

These bakers are based on dielectric heating.

The core supporting plates are not used in this baker because they interfere with the potential distribution in the electrostatic field.

To avoid this interference, cement bonded asbestos plates may be used for supporting the cores.

The main advantage of these ovens is that they are faster in operation and a good temperature control is possible with them.

After baking of cores, they are smoothened using dextrin and water soluble binders.

Roll no ae349

Q164) What is a core box ? Explain its types with diagrams ?

AE337 PRASHANT R. PATIL

ANS

A core box is basically a pattern for making cores.

core boxes are employed for ramming cores in them.

Core boxes impart the desired shape to the core sand.

Range from simple wooden structures to precision metal assemblies for long life.

Types of core boxes

1. Half core box

It can make cylindrical cores.

Half portion of the core is made in the core box, at one time.

Later-on, after a number of half core portion have been made and asked, they

are cemented together to make full cylindrical cores.

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2. Slab or dump core box

It resembles half core box as regards its construction.

It makes full core at a time.

It is employed for making rectangular, square or trapezoidal cores.

3. Split core box

Unlike dump and half core box, a split core box is in two parts.

The two portions of the split core box can be aligned and temporarily joined

together with the help of dowels

For making the core, first of all the two portions of the split core box are

temporarily joined and then the sand is rammed.

Rammed core can be removed by splitting the core box again into two halves.

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4. Left and right hand core boxes

They are used to make cores for producing pipe bends.

Half of the pipe bend core is made in each core box.

Two halves of a pipe bend thus rammed are baked and then cemented together

to make the full core.

5. Strickle core box

Sand is rammed in a dump core box.

The top portion of the core in the core box is given a desired shape or contour

with the help of a strickle board cut and finished to the desired shape. A strickle

board strikes off excess sand (from the core box) not confirming to its shape.

A strickle board may be made up of wood and any shape.

This method of producing irregular core surfaces cost less as compared to other

methods.

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6. Gang core box

It contains a number of core cavities so that more than one cores can be rammed

at one time.

7. Loose piece core box

It resembles half core box,

Unlike half core box, loose piece core box can produce two halves of a core,

which may be neither identical in size nor in shape.

This is achieved by inserting loose wooden pieces in the core box whenever

necessary.

The insertion of loose pieces in the core box will naturally alter the symmetry of

the rammed half core.

After they are baked, the two unidentical halves of the core can be pasted

together.

Q165. What are the functions of Core Making Machine?

ANS:

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1. Core making operation is performed by machine similar to those used for making

molds.

2. Suitability of a particular type of machine (or method) is influenced by the factors

mentioned below

- Quantity to be produce

- Type of core

- Size of core

- Intricacy and complexity of machine

3.various machines utilised for core making are as follows:

a) Jolt machines-(i)Jolt squeeze machine,(ii)jolt squeeze roll over pattern

b) Core roll-over machine

c) Sand slinger

d) Core extrusion machine or Continuous core making machine

e) Core blowing machine

f) Shell core machine

a) Jolt machine

- A jar or jolt machine consists of a rugged base cylinder and piston which is attached

to the machine table.

- The table along with pattern plate, flask and sand in it is repeatedly lifted by an air

pressure directed against the piston from below and is then permitted to drop under

gravity. Inertia of the sand consolidates the sand in contact with the face of the pattern.

- The operation is very rapid and some of the jolt machines employed for remaining

small molding boxes give more then a 100 jolt/min

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- Jolt machines give greatest density of sand at the deepest portion of the sand that is

near the pattern. The sand density progressively decreases towards the top of the flask

were the packing of sand is negligible.

- Sand near the top of the flask may also be rammed hard by placing weight freely

resting on top of the molding sand during jolting operation.

- limiting capacity of a jolt machine=W=pie/4*d^2*P

P=air line pressure

d=diameter of jolt cylinder

Commercial machines possess jolt capacities of the order 250 kg to several tons.

Advantages-

1. Jolt machines can handel many size of moulding boxes and are suitables for casting of various sizes but are particularly useful for large works.

2. Jolt machines are in more general use than in squeezed machines. 3. A jolt machine is preferred for ramming horizontal surface.

Limitation-

1. Sand density varies from bottom to top of the moulding box. 2. Jolt operations are noisy. 3. Jolt ramming is hard on equipment; molding box etc., should be sufficiently strong

as they are lifted and dropped repeatedly. (i)Jolt-squeeze machine:

-It combines in single machine the operating principle of the jolt and squeeze

machine.

-Combination of jolting and squeezing produces beneficial compaction effect on

sand density and thus a more uniform hardness throughout the mold is attained.

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-A jolt-squeeze machine makes use of match plate molding .

-In match plate molding, a complete mold is produce in an operation whereas

otherwise, cope or drag is to be made separately.

Match plate pattern may be made up of aluminium, magnesium or plywood plates.

(ii)Jolt-squeeze roll-over pattern draw molding machine:

-Unlike the jolt-squeeze machine explained earlier, in a jolt squeeze roll-over

machine, flasks are rolled over mechanically and by the same mechanism, pattern is

withdrawn by either raising the cope pr lowering the drag away from the pattern.

-The machine consists of a table actuated by two pistons in air cylinder, one

inside the other.

-Inner piston raises and drops the table repeatedly and is thus responsible for

jolting whereas outer larger piston pushes the table upward to squeeze the sand in the

flask against the squeezer or squeeze head at the top

-A vibrator is attached to the machine too loosen th pattern so that it may be

easily withdrawn without damaging the mold.

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(b)Core roll-over machine:

1. It is similar to mold roll-over machine.

2. Core box is rammed with sand using the jolt principle.

3.Core box is then rolled over, the core is withdrawn and sent to baking oven.

(c)Sand slinger:

1. The sand slinger consist of a base; a sand bin, a bucket elevator, a swinging or

movable arm, a belt conveyor and the sand impeller.

2. Prepared sand lying in the sand bin is picked up by the elevator bucket and is

dropped in to the belt conveyor which takes the same to the impeller head.

3. Inside the impeller head, a rapidly rotating cup shaped blade picks up the sand

and throws it downward in to the molding box as a continuous stream of sand with

machine gun rapidly and great force.

4. The sand is discharge into the molding box at the rate of 300 to 2000 kg/min.

this force is great enough ram the mold satisfactorily.

5. In molding boxes, sand is filled and rammed at the same timing.

6. The density of sand which is the result of sands inertia is uniform throughout

the mold.

7. A sand slinger simply packs the sand into the mold and therefore it is often

operated together with other system such as that of roll-over and pattern drawing.

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(d)Core extrusion machine:

1. simple cores of regular shapes and uniform cross section can be extruded easily on a

core extrusion machine.

2. cores of square, round, hexagonal and oval section are produced rapidly on a core

extrusion machine.

3. A core extrusion machine has a hopper through which the core sand is fed to a

horizontal spiral conveyor.

4. As the spiral conveyor is rotated, it forces core sand through a die of specifed shape.

5. long cores thus produced can be cut to the desired length.

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(e)Core blowing machine:

1. core blowing machine provides a rapid method of producing small and medium

sized cores.

2. A core blowing machine makes use if compressed air ro blow the sand in to the

core at high velocity.

3. The sand carrying compressed air stream is responsible for filling the core box

and ramming the core .

4. The air incoming with sand is exhausted through vents provided in the core-box.

5. small core blowers are of bench type whereas big core-blowing machines of

either vertical or horizontal construction are floor mounted.

(f)Shell core making:

1. (i) Shell core can be made manually.

(ii) shell cores can also be produced on machines.

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Rohit dalvi

Q166)Explain in brief the various steps involved in core making

Ans: 1. Core making operation is performed by machine similar to those used for

making molds.

2. Suitability of a particular type of machine (or method) is influenced by the factors

mentioned below

- Quantity to be produce

- Type of core

- Size of core

- Intricacy and complexity of machine

3.various machines utilised for core making are as follows:

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a) Jolt machines-(i)Jolt squeeze machine,(ii)jolt squeeze roll over pattern

b) Core roll-over machine

c) Sand slinger

d) Core extrusion machine or Continuous core making machine

e) Core blowing machine

f) Shell core machine

a) Jolt machine

- A jar or jolt machine consists of a rugged base cylinder and piston which is attached

to the machine table.

- The table along with pattern plate, flask and sand in it is repeatedly lifted by an air

pressure directed against the piston from below and is then permitted to drop under

gravity. Inertia of the sand consolidates the sand in contact with the face of the pattern.

- The operation is very rapid and some of the jolt machines employed for remaining

small molding boxes give more then a 100 jolt/min

- Jolt machines give greatest density of sand at the deepest portion of the sand that is

near the pattern. The sand density progressively decreases towards the top of the flask

were the packing of sand is negligible.

- Sand near the top of the flask may also be rammed hard by placing weight freely

resting on top of the molding sand during jolting operation.

- limiting capacity of a jolt machine=W=pie/4*d^2*P

P=air line pressure

d=diameter of jolt cylinder

Commercial machines possess jolt capacities of the order 250 kg to several tons.

Advantages-

4. Jolt machines can handel many size of moulding boxes and are suitables for casting of various sizes but are particularly useful for large works.

5. Jolt machines are in more general use than in squeezed machines. 6. A jolt machine is preferred for ramming horizontal surface.

Limitation-

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4. Sand density varies from bottom to top of the moulding box. 5. Jolt operations are noisy. 6. Jolt ramming is hard on equipment; molding box etc., should be sufficiently strong

as they are lifted and dropped repeatedly. (i)Jolt-squeeze machine:

-It combines in single machine the operating principle of the jolt and squeeze

machine.

-Combination of jolting and squeezing produces beneficial compaction effect on

sand density and thus a more uniform hardness throughout the mold is attained.

-A jolt-squeeze machine makes use of match plate molding .

-In match plate molding, a complete mold is produce in an operation whereas

otherwise, cope or drag is to be made separately.

Match plate pattern may be made up of aluminium, magnesium or plywood plates.

(ii)Jolt-squeeze roll-over pattern draw molding machine:

-Unlike the jolt-squeeze machine explained earlier, in a jolt squeeze roll-over

machine, flasks are rolled over mechanically and by the same mechanism, pattern is

withdrawn by either raising the cope pr lowering the drag away from the pattern.

-The machine consists of a table actuated by two pistons in air cylinder, one

inside the other.

-Inner piston raises and drops the table repeatedly and is thus responsible for

jolting whereas outer larger piston pushes the table upward to squeeze the sand in the

flask against the squeezer or squeeze head at the top

-A vibrator is attached to the machine too loosen th pattern so that it may be

easily withdrawn without damaging the mold.

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(b)Core roll-over machine:

1. It is similar to mold roll-over machine.

2. Core box is rammed with sand using the jolt principle.

3.Core box is then rolled over, the core is withdrawn and sent to baking oven.

(c)Sand slinger:

1. The sand slinger consist of a base; a sand bin, a bucket elevator, a swinging or

movable arm, a belt conveyor and the sand impeller.

2. Prepared sand lying in the sand bin is picked up by the elevator bucket and is

dropped in to the belt conveyor which takes the same to the impeller head.

3. Inside the impeller head, a rapidly rotating cup shaped blade picks up the sand

and throws it downward in to the molding box as a continuous stream of sand with

machine gun rapidly and great force.

4. The sand is discharge into the molding box at the rate of 300 to 2000 kg/min.

this force is great enough ram the mold satisfactorily.

5. In molding boxes, sand is filled and rammed at the same timing.

6. The density of sand which is the result of sands inertia is uniform throughout

the mold.

7. A sand slinger simply packs the sand into the mold and therefore it is often

operated together with other system such as that of roll-over and pattern drawing.

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(d)Core extrusion machine:

1. simple cores of regular shapes and uniform cross section can be extruded easily on a

core extrusion machine.

2. cores of square, round, hexagonal and oval section are produced rapidly on a core

extrusion machine.

3. A core extrusion machine has a hopper through which the core sand is fed to a

horizontal spiral conveyor.

4. As the spiral conveyor is rotated, it forces core sand through a die of specifed shape.

5. long cores thus produced can be cut to the desired length.

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(e)Core blowing machine:

1. core blowing machine provides a rapid method of producing small and medium

sized cores.

2. A core blowing machine makes use if compressed air ro blow the sand in to the

core at high velocity.

3. The sand carrying compressed air stream is responsible for filling the core box

and ramming the core .

4. The air incoming with sand is exhausted through vents provided in the core-box.

5. small core blowers are of bench type whereas big core-blowing machines of

either vertical or horizontal construction are floor mounted.

(f)Shell core making:

1. (i) Shell core can be made manually.

(ii) shell cores can also be produced on machines.

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( SHAILESH SAH)

(SE –MECHANICAL)

Q167.What is core print ?what are its functions?

ANS: Castings are often required to have holes, recesses, etc. of various sizes and

shapes. These impressions can be obtained by using cores. A core is a device used in

casting and molding processes to produce internal cavities and reentrant angles. So

where coring is required, provision should be made to support the core inside the mold

cavity. Core prints are used to serve this purpose. The core print is an added

projection on the pattern and it forms a seat in the mold on which the sand core

rests during pouring of the mold.

The core print must be of adequate size and shape so that it can support the weight of

the core during the casting operation. Depending upon the requirement a core can be

placed horizontal, vertical and can be hanged inside the mold cavity. A typical job, its

pattern and the mold cavity with core and core print is shown in fig

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(SHAILESH SAH)

(SE-MECHANICS)

Q168) What is a MOLD? What are its characteristics?

ANS

MOLD

Prepared molding sand is packed rigidly around the pattern and when the pattern

is withdrawn, a cavity corresponding to the shape of the pattern remain in the

sand and is known as (MOLD or) MOLD CAVATY.

Thus a MOLD is a sort of container which when poured with molten metal

produces a casting of the shape of the mold.

The process of making molds is referred to as MOLD-MAKING.

CHARACTERISTICS OF MOLD

A mold must:

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A process refractoriness to bear the high heat of the molten metal,

Process strain to hold the weight of molten metal,

Produces a minimum amount of mold gases,

Be able to resist the erosive action of the molten metal being poured,

Resist metal penetration into the mold wells.

NAME: HIMANSHU VIJAY KALE

ROLL NO.: AE 314

Q.169 Explain in brief the various types of molds ?

Name: Aditya Kallianpur

Roll no: Me 319

Types of molds

1. Green sand mold

2. Dry sand mold

3. Skin dried mold

4. Air dried mold

5. Core sand mold

6. Loam mold

7. Shell mold

8. Cement bonded sand mold

9. Metal molds or Dies

10. Ceramic mold

11. Plaster mold

12. Graphite mold

13. Sodium silicate-CO2 mold

14. Investment mold

15. Suction molding

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A typical sand mold

1. GREEN SAND MOLD

i. Green sand is a sand which is in damp condition and contains free water

ii. It contains clay –binder

iii. In a green sand mold ,molten metal is poured while it is in the green state i.e. the

undried condition.

iv. A green sand mold possesses lower strength and lower permeability.

v. Intricate shapes can be produced in green sand molds.

vi. Green sand mold offers less resistance to the solid shrinkage of casting and thus

the casting do not crack or tear while solidifying

vii. Green sand molds are suitable for producing small and medium sized castings .

2. Dry sand molds(and its comparison with green sand molds)

i. In sand molds sand is used for making dry sand molds, certain binders are

added which harden when heated.

ii. Dry sand molds are actually made with molding sand in green condition and

then the entire mold is dried in oven (at temperature 300 to 6500 F),before the

molten metal is poured in them.

iii. Dry sand mold possesses higher strength as compared to green sand molds.

iv. They are more expensive and consume more time in making as compared to

green sand molds .

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v. They generate less mold gasses than green sand molds.

vi. They posses higher permeability than green sand molds.

vii. They employ finer sands and hence produce smoother casting surfaces.

viii. They are preferred for large size casting.

ix. Dry sand molds are used when green sand molds prove to be unsatisfactory.

3. Skin-dried molds

i. sand used for making skin dried molds contain certain binders like linseed oil

which harden when heated.

ii. The mold is made with the molding sand in the green condition and then the skin

of the mold cavity is dried with the help of gas torches or radiant heating lamps.

iii. Unlike dry mold, a skin dried mold is dried only upto a depth varying from 6mm

to 25 mm.

iv. A skin dried mold possesses strength and other characteristics in between green

and dry sand molds.

v. If a skin-dried mold is not poured immediately after drying, moisture from green

backing sand may penetrate the dried skin and make the same ineffective .

4. AIR DRIED MOLDS

i. They resemble skin dried mold in the sense that their skin is dried, of course not

be heated with a gas or torch or so.

ii. After the mold has been made in the green state, it is kept open to the

atmospheric air for a certain period of time, during which some of the moisture

from the mold surface gets evaporated and consequently the mold skin dries and

thereby increases the strength and hardness of mold surface .

iii. Large pit molds get dried in this manner because they remain exposed to

atmosphere for quite some time while they are being made.

5. Core sand molds

i. A core sand mold is made by assembling a number of cores made individually in

separate core boxes and baked.

ii. The cores are made with recesses and projection so that they can be fitted

together to make the mold .

iii. A core sand mold is poured without a molding box surrounding the same .

iv. As compared to green ,dried and skin dried molds ,core sand possesses high

collapsibility, baked strength and hardness .

v. Core sand molds are more expensive (because of cost of binders etc.)as

compared to green and dry sand molds .

6. Loam molds

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i. No pattern is required to make a loam mold.

ii. A loam mold takes a considerable time to make it .

iii. A loam mold is preferred for making large castings.

7. Shell molds

i. Shell molds are produced with the help of heated iron or steel patterns .

ii. A mixture of fine sand and phenolic resin is used to produces shells

iii. Shells are assembled to form the mold which is poured with molten metal.

iv. Shell molds produce exceptionally good surface finish and dimensional accuracy.

Shell molding process

1. Sand resin in a box, 2. Mix dumped over a heated pattern, 3. Shell formed

over the pattern, 4. Shell stripped from pattern, 5. Shells joined together to form a

complete mold.

8. CEMENT BONDED SAND MOLD

i. Cement bonded sand mold material consists of 85.5% clean silica sand,

10% portaland cement and 4.5% of water.

ii. The mold sand mixture does not need much ramming.

iii. Cement-bonded sand molds develop strength and hardness owing to the

setting action of Portland cement.

iv. The pattern is withdrawn from the sand only after it is set a little.

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v. Further the mold is permitted to continue setting, drying or curing for

about 72 hours, before the separately made cope and drag molds are

assembled for pouring.

vi. Molds should be porous and contain suitable distributed vent holes so that

stream generated, owing to the water of crystallization of the cement

during hot metal pouring, should be able to escape from within the molds.

vii. Cement bonded sand molds can produce accurate and smooth surfaced

casting

viii. Cement bonded sand molds can be used for making small and preferably

large size castings.

ix. Most of the sand used for making cement bonded sand molds may be

reclaimed for use

9. Metal molds or dies

i. Metal molds are also know as permanent molds.

ii. They are generally made up of grey cast iron or steel .

iii. A metal mold is made in two parts to facilitate the removal of the cast

object.

iv. A metal mold is manufactured by casting and consequent machining of

the mold cavity.

v. Metal molds are preferred for casting non-ferrous metals and alloys (i.e,

Al, Mg, Zn and Pb base alloys) Aluminum alloy pistons are cast in metal

molds .

vi. Metal molds are employed in the following casting processes

a) permanent mold casting

b) pressure die casting

c) centrifugal casting.

vii. metal molds produce surface with

a) Fine grain structure

b) High dimensional accuracy and

c) Very good surface finish.

viii. Metal molds are preferred for mass production of the castings.

10. Ceramic molds

i. Ceramic mold is a variation of investment mold.

ii. If instead of an investment molding mixture, a slurry composed of re

factory sand grains and ceramic binder is poured on the wax pattern ,it

results in ceramic thin wall shell.

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iii. Wax is removed in the same manner as in investment mold.

iv. A ceramic mold

1) can cast very intricate objects.

2) can produce thin sections for high melting point metals and alloys.

3) can cast higher melting point alloys to accurate dimensions .

4) produces casting which do not need machine.

11. Plaster molds

i. A plaster mold is prepared in the following way:

a) use a pattern of metallic or some other moisture resistance material.

b) Make a slurry of mixture of gypsum or plaster of paris .

c) Ingredients listed above and other, control contraction characteristics of

the mold and setting time .

d) The slurry is poured over the pattern and is allowed to preset.

e) Pattern is taken out and the preset mold is heated in an oven for about

6000 F for several hours. It removes moisture from the plaster mold.

f) Cope and drag are made separately by the method described above

and are assembled for pouring.

ii. Plaster molds are employed for producing non-ferrous casting.

iii. Plaster molds impart good surface finish and dimensional accuracy to the

castings.

iv. Plaster molds however do not possesses high permeability.

12. Graphite molds

i. They are used to make titanium alloy castings.

ii. Graphite molds are prepared by squeezing the graphite mold material

around the pattern at 4 to 8.5 kg/cm2 pressure.

iii. The mold is dried and fired at 1800 to 20000 F in a reducing atmosphere in

order to obtain solid mold.

iv. Solid molds are assembled and poured in vacuum in order to avoid

atmospheric contamination of titanium alloys.

v. For obtaining permanent graphic molds .the mold cavity is machined in

solid block of graphite.

vi. Such molds are given a surface coating of ethyl silicate.

vii. Graphic molds have been used for casting raidroad car wheels.

viii. Graphite mold liners are employed for centrifugally casting brass and

bronze bushings and sleeves.

13. Sodium silicate-CO2 molds

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i. Such molds are made using clean, dry silica sand and sodium silicate(as

binder).

ii. The molding mixture thus obtained is rammed around the pattern and

gassed with carbon-di-oxide.

iii. The mold material gets hardened and as soon as the pattern is removed

the mold is ready for pouring.

14. Investment Molding

This process of making casting is often referred to as "lost wax process" and "precision

casting process". Casting can be made to very close tolerances in this process and do

not require subsequent machining. It mainly consist of two stages .

Investment molding in

stages.

1. Making the pattern,

2. Making cast wood,

3.prelimenaries of casting

process, 4. Separating

and cleaning the castings.

First a master pattern is made

of wood or metal around which a mould is formed. It consist of gelatin or an alloy of low

melting point which is poured over the master pattern. This master consist of two

sections and thus can be opened. It is used for making the "lost pattern".

The pattern mould is then filled with liquid wax, with a thermoplastic material liquified by

heating or with mercury. The heated materials become solid when they are cooled to

normal room temperature. If mercury is used, the master mould must be cooled down

to about -600 to become solid. The expandable wax pattern is coated with slurry

526

consisting of silica flour and small amounts of kaolin and graphite mixed with water. This

process is referred to as the "investment" of the pattern.

However, the pattern is then used to make up moulds similar to those used in

conventional molding process, but the pattern within the mould is not taken out of the

mould which is not opened after molding process. This is the reason why a high

precision is achieved in casting .

The finish mould is dried in air for 2 to 3 hours and baked in an oven for about 2 hours

to melt out the wax. At a temperature of 1000 to 1200 C the wax melts and runs through

a hole in the bottom plate into a tray, thus providing a cavity of high dimensional

accuracy for casting process. After this the mould is sintered at about 10000C to

improve its resistivity. Finally, it is cooled down to a temperature between 9000C and

7000C for casting.

Investment castings produced by this process have a good surface finish and are exact

reproduction of the master pattern. This is used for casting turbine plates , parts of

motor car, calculating machines etc.

Advantages of the process are

Machining can be largely reduced or eliminated since tolerances close to + or -

0.1 mm and surface finish of around 1-5 micron are possible.

Extremely thin section, to the extent 0.75mm, can be process can be cast

successfully.

Complex shaped parts that cannot be obtained by other process can be

conveniently made.

sound and defect-free castings may be obtained.

Suitable for mass production of small-sized castings .

The limitations of the process are

Unsuitable for castings of more than about 5kg weight.

Precise control is required in all stages of casting .

Expensive in all respects.

15. Suction Molding

In this method, a vacuum is created by withdrawing air from the mould space.

Subsequently molding sand is sucked in, and cavity is filled up. The sand can thereafter

be rammed in the pattern. The process is used for casting iron, steel and aluminium.

The weight of casting ranges from 200 gm to 120 kg .Mould is used once and is made

from wet artificial crashed sand . The process is different from vacuum molding where

plastic sheet is vacuum molded to the contour of the pattern, back filled with fine

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grained binder free quartz sand sealed with another plastic sheet. The mould is

constantly connected to a vacuum source before, during and after casting.

suction molding

Advantages of suction molding process are

Optimum mould compaction around the pattern.

Decreasing hardness of compacted sand from inside to the outside.

High surface quality.

Dimensionally stable casting.

Reduced cleaning.

Limitations of the process are

High cost of manufacturing .

Change-over time high.

Q170. Explain various molding process.

PRATHAMESH SHRIKANT MORE

ROLL NO: 29

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Ans: The different molding processes are:

(a)Green sand molding-

(1)It is most widely used molding process.

(2)The green sand used for molding consists of silica sand, clay, water and other

additives.

(3)One typical green sand mixture contains 10 to 15% clay binder, 4 to 6% water and

remaining silica sand.

(4)Green sand molding is preferred for making small and medium sized casting.

Advantages:

(1)Green sand molding is adaptable to machine molding.

(2)No mold drying and baking is required.

(3)Time and cost associated with mold baking or drying is eliminated.

(4)There is less mold distortion than in dry sand molding.

(b)Dry sand molding-

(1)Dry molding sand differs from the green molding sand in the sense that it contains

binders (like clay, bentonite, molasses etc.) which harden when the mold is heated and

dried.

(2)A typical dry sand mixture (for making non-ferrous casting) consists of floor sand

40%, new silica sand 30%, coal dust 20% and bentonite 10%.

(3)A dry sand mold is prepared in the same manner as a green sand mold; however it

is baked at 300 to 700* C for 8 to 48 hours depending upon binders used and the

amount of sand surface to be dried.

Advantages:

(1)Dry sand molds possess high strength.

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(2)They are more permeable as compared to green sand molds.

(3)Casting produced from dry sand molds possess clean and smooth surfaces.

(4)As compared to green sand molding, dry sand molding turns out casting with less

defects.

(c)Skin-dried molding-

(1)A skin dried mold is intermediate between green sand mold and dry sand molds.

(2)Whereas a dry sand mold has its entire surface dried, a skin dried mold has its (6 to

25 mm) skin dried.

(3)Moisture from the skin is removed either by storing the mold for some time or with

the help of gas torches.

(4)Skin dried moldings possess partially the advantages of both green and dry sand

molding.

(5)Large molds and molds of pit molding are skin dried.

(d)Air dried molds-

(1)They resemble skin dried molds in the sense that their skin is dried, of course not

be heating with a gas torch or so.

(2)After the mold has been made in the green state, it is kept open to the

atmospheric air for a certain period of time, during which some of the moisture from

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the mold surfaces gets evaporated and consequently the mold skin dries t and thereby

increases the strength and hardness of mold surfaces.

(3)Large pit molds get dried in this manner because they remain exposed to

atmosphere for quite some time while they are being made.

(e)Core sand molds-

(1)A core sand mold is made by assembling a number of cores made individually in

separate core boxes and baked.

(2)The cores are made with recesses and projections so that they can be fitted

together to make the mold.

(3)A core sand mold is poured without a molding box surrounding the same.

(4)As compared to green, dried and skin dried molds, core sand molds possess high

collapsibility, baked strength and hardness.

(5)Core sand molds are more expensive as compared to green and dry sand molds.

(f)Shell molds-

(1)Shell molds are produced with the help of heated iron or steel patterns.

(2)A mixture of fine sand and phenolic resin is used to produce shells.

(3)Shells are assembled to form the mold which is poured with molten metal.

(4)Shell molds produce exceptionally good surface finish and dimensional accuracy.

(g)Cement bonded sand mold-

(1)Cement bonded sand mold material consists of 85.5 % clean silica sand, 10%

Portland cement and 4.5% water.

(2)The mold sand mixture does not need much ramming.

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(3)Cement-bonded sand molds develop strength and hardness owing to the

setting action of Portland cement.

(4)The pattern is withdrawn from the sand only after it is set a little.

(5)Further, the mold is permitted to continue setting, drying or curing for about 72

hours, before the separately made Cope and Drag molds are assembled for pouring.

(6)The mold should be porous and contain suitably distributed vent holes so that

the steam generated, owing to the water of crystallization of cement during hot metal

pouring, should be able to escape from within the mold.

(7)Most of the sand used for making cement bonded sand molds may be reclaimed

for reuse.

(h)Ceramic mold-

(1)Ceramic mold is variation of the Investment mold.

(2)If instead of an investment molding mixture, slurry composed of refractory sand

grains and ceramics binder is poured on the wax pattern.

(3)Wax is removed in the same manner as in investment molds.

(4)A ceramic mold,

A. Can cast very intricate objects.

B. Can produce thin sections even for high melting point metals and alloys.

C. Can cast high melting point alloys to accurate dimensions,

D. Produces casting which do not need machining.

(i)Plaster molds-

(1)Plaster molds are employed for producing non-ferrous castings.

(2)Plaster molds impart good surface finish and dimensional accuracy to the

castings.

(3)Plaster molds however do not possess high permeability.

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(j)Graphite molds-

(1)They are used to make titanium alloys castings.

(2)Graphite (temporary) molds are prepared by squeezing the graphite mold

material.

(3)The mold is dried and fired at 1800 to 2000* F in a reducing atmosphere in order

to obtain solid mold.

(4)For obtaining permanent Graphite molds, the mold cavity is machined in solid

block of graphite.

(5)Graphite molds have been used for casting railroad car wheel.

(6)Graphite mold liners are employed for centrifugally casting brass and bronze

bushings and sleeves.

(k)Sodium silicate-CO2 mold

(1)Such molds are made using clean, dry silica sand and sodium silicate (as binder).

(2)The molding mixture thus obtained is rammed around the pattern and gassed

with carbon-di-oxide.

(3)The mold material gets hardened and as soon as the pattern is removed the

mold is ready for pouring.

Q 171) Write a short note on hand molding equipments.

Ans SANMESH S. WAGHMARE

SE-Auto Roll no-361

Various hand tools are used in a foundry for making moulds. A brief description of various

hand tools is given as follows:-

1) Shovel :- It consists of a square iron blade fitted with a D-shaped wooden handle, as

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shown in fig. It is used for transferring sand to a sand mixer and pouring sand in the molding

flask.

2) Strike-off bar :- It is a wooden or metallic bar having a true edge, as shown in fig. It is

used for removing for removing the surplus sand after the ramming has been completed.

3) Handle Riddle :- It is also known as a sieve. It consists of a wooden frame fitted with a

screen of a standard wire mesh at its bottom. It is used for removing foreign material such

as nails, short metals, splinters of wood, etc from the molding sand. Different types of

riddles are denoted by different numbers like 8, 10, 12, etc. Riddle no.8 has an opening of

1/8 inch approx.

4) Vent Wire :- It is a thin steel rod or wire having a pointed edge at one end and a wooden

handle or a bent loop at the other end as shown in fig. It is used for making small holes,

called vents in the rammed sand moulds to permit easy escape of gases and steam

generated during cooling of the heated metal.

5) Trowels :- Trowels are made of iron and are provided with wooden handle. The three

types of commonly used trowels are-

a) Finishing trowel

b) Square end trowel

c) Heart shaped trowel

Trowels are used for -

a) Finishing flat surfaces of moulds

b) Cutting ingates

c) Making joints

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d) Repairing moulds

e) Giving shape

6) Slicks :- Slicks are used for repairing and providing finishing to mould surface and edges

after the pattern has been withdrawn. The commonly used slicks in a foundary are shown in

fig.

a) Heart and leaf slicks

b) Square and heart slick

c) Spoon and bead slick

d) Heart and spoon slick

e) Leaf and spoon slick

7) Lifter / Cleaner:- The lifters as shown in fig are made up of thin sections of steel of

various widths and lengths, with one end bent at right angles. The lifter is a finishing

tool used for patching deep sections of a mould and removing loose sand from pockets

of the moulds. The Yankee lifters is very commonly used in an average sized foundary.

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8) Rammers :- Rammers are used for packing and ramming the sand in the moulding box.

Depending upon the type of casting and the nature of work, there are many types of

rammers. Rammers are generally made of wood or steel. The commonly used rammers in a

foundary are:-

a) Pein rammer

b) Hand rammer

c) Floor rammer

d) Butt rammer

e) Pneumatic rammer

Pneumatic Rammer :- A pneumatic rammer is shown in fig.It is an automatic rammer

operated by compressed air. It is fitted with long or short shafts according to the

requirements with open or flat ends. It is used for ramming sand in large moulds. It saves

considerable labour and time in moulding.

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9) Swab :- Simple swabs are shown in fig. It is a small brush having long hemp fibres.

A swab is used for applying water around the edges of a pattern. This prevents the the sand

edges from crumbling when the pattern is removed from the mould. A bulb swab that has a

rubber bulb to hold the water and a soft hair brush at the open end.

10) Sprue pin :- A sprue pin is also known as a rubber peg. It is a tapered wooden or iron

rod, which when embeded into top part of the mould, known as cope, and later withdrawn ,

produce a cavity known as down gate or runner. Through the runner, the molten metal is

poured into the mould.

11) Drawn spike :- As shown in the fig. It consists of a tapered steel rod having a loop or ring

at one end and a sharp point at the other. It is used to draw a pattern from the mould.

12) Draw screw and Rapping plate :- The draw screw is a straight mild steel rod carrying a

loop or ring at one end and a wood or machine sprue at the other. It is always used in

conjunction with a rapping plate for rapping and withdrawing a pattern from the sand. The

rapping plate or lifting plate is provided with several threaded and rapping holes, as shown

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in the fig. Threaded holes accomodate either a wood screw type or machine screw type

draw screws. Rapping holes are provided to accomodate seperate rapping rods so that the

threaded holes are not damaged.

13) Smoother and Corner slicks :- These are tools used for finishing and repairing of

a) round and square corners and edges

b) round and flat surface.

According to their use and shape, they are given different names. Most commonly used

tools for giving finishing and repairing are inside square, flat, pipe, button, half round corner

and egg shaped.

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14) Clamps :- Clamps are made of steel and are used for holding and clamping the moulding

boxes in proper position. Commonly used clamps are shown in fig.

Q 172) Write a note on ramming moulding boxes?

Kushboo Gupta

AE 311

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Ans:- Rammers are used for compacting sand in the mould . The peg or pin rammer

applies force downwards as well as side ways and is used for primary ramming. The

butt rammer applies force downwards and is used for finish ramming. The rammers may

be operated by hand or with pneumatic pressure.

Method of ramming molding boxes?

The different method of ramming flasks along with their characteristics are given below.

Hand ramming

1- It is done by hand using rammer

2- It is laborious, slow and time consuming

3- It involves low initial cost

4- It produces variables(i.e. ,non-uniform) hardness

MACHINE RAMMING (MOLDING)

Squeezing

1-Flask is filled with loose sand.

2-a platen which can closely enter the flask, constants the upper surface

of the loose sand filled in the flask.

3- A air pressure is applied with the help of the piston cylinder arrangement.

The platen moves down, presses the sand filled in the flask and compacts it.

4-Squeezing is preferred for ramming shallow flasks.

5-squeezing is suitable for relatively small works only.

6-sand is more compact in the upper portion of the flask as compared to it LOW

PORTION.

Jolting

1-flask is filled with loose sand.

2-flask is fastened on the platen which is raised to certain height

And allowed to drop under its own weight against a solid bed plate.

3- the action of raising and dropping the molding box continuous till adequate

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Mold hardness is achieved

4-jolting is best for remaining horizontal surfaces.

5-it,however, produces uneven density of rammed sand.

6-sand is more compact in the bottom position of the flask as compared

To its upper portion.

7-jolting proves hard on equipment

Sand slinging

A sand slinger does,

1-fast ramming

2- uniform ramming ,but involves

3- high initial cost.

Sand slinger

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1- The sand slinger consists of a base, a sand bin, a bucket elevator, a swimming

or movable arm, a belt conveyor and the sand impelle

(ramming head)

2-prepared sand lying in the bin is picked up by the elevator

Buckets and its dropped on to the belt conveyor which take the same to the

impeller head.

3-inside the impeller head, a rapidly rotating cup shaped blade picks up the

Sand throws it downward into the molding box as a continuous stream

Of sand with machine gun rapidity and great force.

4-the sand is discharged into the molding box at a rate of 300 to 2000kg/min. this

force is great enough to ram the mold satisfactorily.

5-in molding boxes, sand is filled and rammed at the same time.

6-the density of sand which is the result of sand’s inertia is uniform

Throughout the mold

7- a sand slinger simply packs (i.e. fills and rams )the sand into the mold and

therefore it is often operated together with other system such as those of roll-over

and platter drawing

8-sand slinger of several different types such as given below are in use:

(a) Stationary slinger

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The operator rides in a special seat located above the ramming or impeller

head.

The operator observes the ramming and controls ramming head movement

by a joysticks which hydraulically operates the translational

movement of the ramming head for filling the molding box.

slinger remains stationary, but molding boxes to be filled (with sand) and

rammed pass on a conveyor under the remming head.

(b) Tractor sand slinger

It picks up sand, reconditions it, and feeds it back to the ramming head

which travels behind.

The tractor slinger can ram up molds which are within the reach of the

ramming head.

(c) Motive slinger

Motive sand slinger moves on rails and can ram molds anywhere within the

reach of the arc of slinger-head rotation

Motive slinger is generally used for producing medium and larger sized

casting (floor and pit works)

Advantages

1-mold is filled with sand and rammed at the same time.

2-mold hardness can be controlled by regulating the speed of impeller

3-sand slinger deliver larger quantities of sand rapidly and are thus beneficial

for ramming big molds.

4-irrespective of the size or shape of the mold,the mold produced are of uniform

density throughout.

Q173.Write a note on gating system requirements, purpose, functions

Ans- Purpose:-

1- a gate is a channel which connects runner with the mold cavity and through

which molter metals flows to fills the mold cavity

2- A gate should feed liquid metal to the casting at a rate consistent with the rate

of solidification.

3- The size of the gate depends upon the rate of solidification

4- A small gate is used for a casting which solidifies slowly and vice-versa.

5- More than one gate can be used to feed a fast freezing casting.

6- A gate should not have sharp edges as they(i.e edges) may break during

pouring and(sand pieces) thus be carried with molten metal with the cavity.

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7- Moreover, sharp edges may cause localized delay in freezing, thus resulting

in the formation of voids and inclusions in the cast objects.

8- A gate may be built as a part of the or it may be cut in the mold with the help

of a gate cutter.

9- A gate basin preferably performed to act as a reservoir or store for molten

metal.

10- A gate basin traps loose sand and other undesirable particles and thus stop

them from entering the mold cavity.

11- A gate basin prevents turbulent liquid metal from entering the gate.

Requirements:-

1- The mould should be completely filled in the smallest time possible without

having to raise the metal temperatures or use higher metal heads.

2- The metal should flow smoothly into the mould without any turbulence. A

turbulent metal flow tends to form dross in the mold.

3- Unwanted material such as slag, dross and other mold material should not

be allowed to enter the mold cavity.

4- The metal enter to the mold cavity should be properly controlled in such a

way that aspiration of the atmospheric air is prevented.

5- A proper thermal gradient should be maintained so that casting is cooled

without any shrinkage cavities or distortions.

6- Metal flow should be maintained in such a way that no gating or mold

erosion takes place.

7- The gating system should ensure that enough molten metal reaches the

mold cavity.

8- The gating system design should be economical and easy to implement

and remove after casting solidification.

9- Ultimately, the casting yield should be maximized.

Function:

1- The molten metal introduce should be with lest turbulence.

2- There should be a prevention of the slag and dross present in the

poured metal from reaching the mould cavity.

3- Gating system should facilitate complete filling of the mold before

solidification.

4- There should be proper temperature gradient.

5- There should be maximum yield development.

6- The flow of metal should be controlled. The entering velocity of the

metal should be low.

7- The erosion in the metal should be low.

8- It should be economical to use.

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Q174) Construction and woking of pot furnace advt and limitations.

Ans-

Construction and working-

1.Like a crucible furnace a pot furnace is usually an indirect flame furnace . However

some constructions of pot furnaces are approach direct flame conditions.

2.A pot furnace consists of cast iron or steel pot in which metal chage is placed and the

pot is heated by the gas,oilor electricity.

3.Metals commonly melted in pot furnaces are magnesium, aluminium, zinc,lead,tin and

other low melting point metals and alloys.

4.As the metal is melted it is ladled from the pot for distribution to the molds.

5.Pot furnaces are often used with permanent mold amd die casting machines for

producing small castings.

ADVANTAGES-

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A tilting pot furnace may accommodate upto 1500 kg of metal.

DISADVANTAGES-

The capacity of a pot furnace is of few hundreds of kg.

Name-Nitin P. Mali

Branch-Automobile

Roll no.-325

Q 175) What is a gate? Explain the types of gates & give its advantages,

limitations & applications.

-Dhaval Patel

Roll no. 34(A.E.)

Ans:

A gate is a channel which connects runner with the mould cavity & through which

the molten metal flows to fill the mould cavity.

Characteristics:-

A gate should feed liquid metal with the casting at a rate consistent with the rate

of solidification.

The size of the gate depends upon the rate of solidification.

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A small gate is used for a casting which solidifies slowly & vice-versa.

More than one gate may be used to feed a fast freezing casting.

A gate should not have sharp edges as they may break during pouring & (sand

pieces) thus be carried with the molten metal in to the mould cavity.

Moreover, sharp edges may cause localized delay in freezing, thus resulting in

the formation of voids & inclusions in the cast objects.

A gate may be built as a part of the pattern or it may be cut in the mould with the

help of a gate cutter.

A gate basin preferably is provided to act as a reservoir for molten metal.

A gate basin traps loose sand & other undesirable particles & thus stops them

from entering the mould cavity.

A gate prevents turbulent liquid metal from entering the gate.

Types of Gates:-

The major types of gates are,

A. Top Gate

B. Bottom Gate

C. Parting Line Side Gate.

A. Top Gate:-

1) A top gate is sometimes also called Drop gate because the molten metal just

drops on the sand in the bottom of the mould.

2) In top gate, a stream of liquid metal impinges against the bottom of mould cavity

until a good pool is formed & this is kept in a state of agitation until the mould is

filled.

3) Edge gate avoids the forceful impinging action of the molten metal stream onto

mould cavity.

4) Pencil gate though does not reduce the severity of turbulence of metal entering

the mould; it does control the rate of metal flow. Moreover, slag gets removed

from the liquid metal in the pouring cup. Pencil gates may be used for massive

iron castings.

5) Gate with strainer core. A strainer core is a perforated disc of core sand or pro-

fined refractory placed. The strainer core arrests the major inclusions & reduces

velocity & turbulence on the system by breaking the force of the liquid metal

stream.

6) Wedge Gate:-

Wedge gates,

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a) are used on stove plate castings & bath,

b) are in series & deliver metal rapidly form an elongated pouring basin,

c) help keeping slag back,

d) are easily broken from the solidified casting.

7) Finger Gate:-

Finger gate,

a) is a modification of wedge gate,

b) is more easily broken than the wedge gate.

8) Ring Gate:-

Ring gate,

a) uses a core to break the fall of liquid metal,

b) retains slag etc.,

c) sends the molten metal in the mould in proper position.

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Advantagesof Top Gating:-

1) The dropping liquid metal stream erodes the mould surface.

2) Dropping the metal does cutting action, lifts portions of the surface & causes

scab.

3) Splashing of molten metal associated with the liquid metal stream increases

chances of oxidation.

4) There is lot of turbulence & pick-up of air & other gases.

5) Top gate is not suitable for alloys which are sluggish or prone to rapid oxidation.

6) Top gate is not favoured for non-ferrous castings (Al & Mg) because of the

tendency of dross formation.

Applications of Top Gating:-

1) Top gates are used for grey iron castings of simple designs,

2) Castings with heavy bosses (like railway driving wheel carriers) & hollow

cylinders employ top gates.

3) Moulds made up of erosion resistant materials such as performed refractory tiles

employ top gates.

Improving Top Gating:-

1) In order to break the force of stream & to keep the slag floating in the pouring

cup, a cup strainer core maybe used.

2) The use of a large sized pouring basin will reduce the force of metal stream &

prevent dross & loose sand particles from entering the mould.

3) Variations in simple top gate remove many shortcomings of a simple open top

pour gate.

B.Bottom Gate:-

1) A bottom gate is made in the drag portion of the mould.

2) In a bottom gate, liquid metal fills rapidly the bottom portion of the mould cavity &

rises steadily & gently up the mould walls.

3)

a) A horn gate resembles the horn of a crow.

b) The mould can be made in cope & drag only; there is no need of check.

c) The pattern which forms horn gate is withdrawn from the drag portion of

the mould.

d) A horn gate tends to produce a fountain effect in the mould cavity.

e) A horn gate avoids the necessity of a core for the gate.

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4) In another type the core forms the bottom gate.

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5) Down gate is at a lower level than the in-gate & being curved backwards forms a

trap for slag, splashes of cold metal, dirt etc.

6) Bottom gate with a skim bob

a) The mould cavity is made using three flasks.

b) This type of bottom gate possesses a slag trap above the bottom gate & a

kink in down gate.

7) Bottom gate with Drown-in-Runner

a) Mould is prepared in three flasks.

b) This gate has a taper in a direction opposite to born gate.

c) The gate is tangentially placed on castings so that a spinning action is

imparted to incoming liquid metal.

d) The swirling action tends to move the scum & slag to the centre of the roll

from where it ascends into the riser & thus chances of slag, etc. being

trapped in the casting are eliminated.

Advantages of Bottom Gating:-

1) There is no scouring & splashing in the bottom gate.

2) As compared to top gate, a bottom gate involves little turbulence & meal erosion.

3) Bottom gate produces good casting surfaces.

Disadvantages of Bottom Gating:-

1) In bottom gates, liquid metal enters the mould cavity at the bottom. If freezing

takes place at the bottom, it could choke off the metal flow before the mould is

full.

2) A bottom gate creates an unfavourable temperature gradient & makes it difficult

to achieve directional solidification especially when the bottom gate has a riser at

the top of the casting.

3) A bottom gate involves greater complexity of moulding.

4) The liquid metal cools as it raises the mould walls & results in cold metal & cold

mould near the riser & hot metal & hot mould near the gate. Rather, the riser

should contain hottest metal so that it is last to solidify & can continuously feed

metal to all other comparatively colder, solidifying portion of the casting.

These difficulties can however be overcome by:-

a) Using excessive padding of casting sections towards risers so that they do

not cool fast.

b) Using extra-large risers.

c) By pouring some hot metal from the ladle directly into top risers.

d) By using blind rises.

e) By employing side risers.

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- When using side riser, the hot metal fills the riser first & then the mould cavity

and thus the gate hot spot occurs in the riser where it promotes directional

solidification.

- On the contrary with a top riser, HOT SPOT occurs at the gate entrance which if

not avoided, results in shrinkage.

Overheating of sand at a place can be minimized bathe use of more than one

ingates.

Applications of Bottom Gating:-

1) A bottom gate is employed for steel castings in order to

a) reduce erosion,

b) reduce gas entrapment,

c) prevent splashing which otherwise may create cold shots.

2) A bottom gate can be used for heavy castings.

C. Parting Line Side Gate:-

1) In parting line side gates, the liquid metal enters the mould cavity from the side of

the mould at the parting line separating cope & drag at or the level of mould joint.

2) Parting line gate can be made by the pattern itself or it can be cut afterwards.

3) As regards fluid flow, parting line gates stand in between top & bottom gates

4) A parting line gate has sprute formed in the cope.

5) A recess is generally provided at the base of the sprue to avoid the cutting of

sand at this place.

6) Gate with skim bob & choke

a) A skim bob or a recess is provided in the cope to trap slag.

b) A choke is provided in between the in-gate.

c) A choke is a restriction which controls the rate of liquid metal flow.

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7) It prevents molten metal to enter the mould in the form of a jet thus minimises

sand erosion.

8) Gate with strainer core

a) Strainer core filters the liquid metal of impurities.

b) Strainer core traps slag.

c) Strainer core reduces mould erosion.

d) If the liquid metal does not possess adequate fluidity, the use of strainer

core may introduce defects in the castings. These defects are owing to the

slow rate of flow of molten metal through the strainer core to the mould

cavity.

9) Gate with shrink bob

a) A shrink bob serves as a metal reservoir to feed the casting as it shrinks.

b) A shrink bob on the runner, thus, prevents shrinkage defect from occurring

in a casting in front of an ingate.

10) Branch gate

a) This arrangement ensures clean castings.

b) Slag & liquid metal flow in the runner & rise up in the riser.

c) Thus all the slag goes to the top portion of the riser.

d) Because of the angle of ingates, the clean liquid metal enters the mould

cavities & produces sound castings.

11) Swirl gate

a) In swirl gate, centrifugal forces assist in separating slag from liquid metal.

b) Slag along with other lighter impurities is forced to the centre of swirl from

where they move up the riser & thus help produce a casting free of slag &

dross.

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Advantages of Parting Line Gate:-

1) Parting line gates are simple to construct.

2) Parting line gates are very fast to make.

3) Parting line gates produce very satisfactory results when drag is not very deep.

4) Parting line gating makes best compromise between moulding convenience &

the ideal gating arrangement.

5)

a) A parting line gate proves to be very advantageous when it can be fed

directly into the riser.

b) In this system, the hottest metal reaches the riser, thereby promoting

directional solidification.

c) Cleaning costs of castings are reduced by gating into risers, because no

additional gate is required to connect the mould cavity with riser.

Disadvantages of Parting Line Gate:-

1) In case the parting line is not near the bottom of the mould cavity or the drag

position is deep, some turbulence will occur as the liquid metal falls into the

mould cavity.

2) Cascading of molten metal from a height in the mould cavity will cause erosion or

washing of the mould.

556

3) Cascading in non-ferrous metals will promote dross & air pick-up by the liquid

metal & thus result in an inferior casting.

4) Turbulence created by cascading can be reduced by slowing down the rate of the

molten metal flow with the help of a choke.

Q 176)Explain in brief the Design considerations in gating systems.

PRIYANK NANDU AE 332

For proper functioning of a gating system the following fators need to be controlled

1. type of pouring equipment,such as ladles,pouring basin etc.

2. temperature/fluidity of molten metal

3. rate of liquid metal pouring.

4.type n size or spure.

5. type n size of runner.

6. Size,number and location of gates connecting runner and casting.

7. position of mould during pouring and solidification.

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POURING BASIN

a.sometimes the spure is closed with a ball fixed on the end of the rod.the ball is lifted

when the pouring basin is full,this reduces turbulence.

b.a dam may be builtso that the kadke operator can acquire an optimum flowing speed

before the liquid metal entyers the spure.

c.indirect pouring minimizes the turbulence, vortexing and thus the air entrapments at

spure enterance.

SPURES

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a. a round spure has minimum surface exposed to cooling and offers lowest resistance

to flow of metal.

b. there is less turbulenve in rectangular spure.

GATES

a. A small is gate is used for a casting which solidifies slowly n vice-versa.

b. more then one gate may be used to feed a fast freezing casting.

c. Edge gates avoids the forceful impinging action of the molten metal stream to mould

cavity.

d.pencil gate may be used for massive iron casting.

e.gate with strainer core may be used. the strainer core arrests major inclusions and

reduces velocity and turbulence by breaking the force of liquid metal stream.

f.the use of large sized pouring basins will reduce the force of molten metal stream and

prevent dross and loose sand particles from entering the mold.

g.use of bottom gates prevents scouring and splashing.bottom gate produces good

casting sufaces.

h.gate with skim bob n choke helps controlling the rate of metal flow .it prevents molten

metal to enter the mould in the form of jet and thus minimizes sand corrosion.

i.Branch gate ensures clean casting.

j. centrifugal forces in swirl gate assist in separating slag from liquid metal.

RISERS

1. Using excessive paddling of casting sections towards riser so that metal do not cool

fast.

2. Using extra large risers.

3. By pouring some hot metal from the ladle directly into top riser

4. by using blind risers.

5. By employing the side risers.

RATE OF FLOW OF MOLTEN METAL

1. normally the gating design aims aims at reducing the turbulence rather than eliminating it completely

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2. the flow of fluids in ducts is related ny their Reynolds number R = Mean velocity of flow*diameter of duct*density of liquid

Kinamatic velocity of liquid

3. A liquid with Reynolds no. less than 2000 experiences true streamline flow

4.turbulent flow occurs when reynold’s no. goes above 2000.

5.ordinary gating system experience reynold’s no. ranging from 2000-20,000.

Calculations made above are not very accurate.

DESIGN CRITERIA FOR POURING BASIN

1. the pouring basin should be designed such that proper uniform flow system as under full flow condition, is rapidly established.

2. It should be easy and convienient to fill the pouring basin. 3. the pouring basin should avoid splashing.

DESIGN OF SPRUE

1. vortexing is minimized by tapering the sprue.in a properly tapered sprue,the liquid metal lies firmly against its walls during cascading and reduces turbulence and eliminates aspirations.

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DESIGN OF RUNNER AND GATES

1.in a good runner and gate design

a. abrupt changes in sections and sharp corners which create turbulence should be avoided.

b. A suitable relation ship must exist between the cross-sectional area of several ingates,gates and runner and runner and sprue.

c. Ingates should be properly located to feed to the casting. d. Air aspirations should be avoided e. Mould erosion n dross are minimized. f. Favourably reduced metal flow is achieved. g. Meatl pulling from mould walls is eliminated.

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Q.177 Explain the concept of Gating Ratios.

ANS

The most important characteristics of gating system besides sprue ,are the

shape and dimensions of runners and gates which affect the rate and type of flow

and determine the position at which the liquid metal enters mold cavity

The dimensional characteristics of gating system is ‘Gating Ratio’

It refers to the proportions of cross sectional area between the sprue,runner and

ingates

Denoted as a : b : c

Where a =cross-sectional area of sprue

b =cross-sectional area of runner

c = cross-sectional area of ingates

Depending on choke area there are two types of gating system:-

Unpressurized gating system

A non –pressurised gating system having choke at the sprue base, has

total runner area and ingate areahigher than the sprue area.

In this system there is no pressure existing in the metal flow system and

thus it helps to reduce turbulence.

This is particularly useful for casting drossy alloys such as aluminium

alloys and magnesium alloys.

When metal is to enter the mould cavity through multiple ingates, the

cross section of the runner should accordingly be reduced at each of a

runner break-up to allow for

equal distribution of metal through all ingates.

Typical gating ratio is 1:3:3

Pressurized gating system

In the case of pressurised gating system normally the ingates area is the

smallest, thus maintaining a back pressure throughout and generally flows

full and thereby, can minimize the air aspiration even when a straight

sprue is used.

It provided higher casting yield since the volume of metal used up in the

runners and gates is reduced.

Because of turbulence and associated dross formation, this type of gating

system is not used for light alloys but can be advantageously used for

ferrous castings.

Typical gating ratio is 1: 0.75: 0.5

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Use of pressurized and unpressurized system of gating depends on the metal

being cast

Eg. Gating ratio of aluminium

Aluminium a : b : c

Pressurized system 1 : 2 : 1

Unpressurized system 1 : 3 : 3

- Kaustubh Raul

Roll no: AE339

Q 178 ) Differentiate between Pressurised and Non- pressurised gating

Ajit Prabhakaran AE 358

Pressurised Gating Systems

Unpressurised Gating Systems

1. Gating ratio may be the order of 1 : 0.75 : 0.5

1. Gating ratio is 1 : 3 : 3

2. Back pressure is maintained on the gating system by a fluid flow restriction at the gates.

2. Primary restriction to fluid flow is near the sprue.

3. This back pressure keeps sprue full of metal, reduces metal pulling from mold walls and minimises air aspirations.

3. Unless designed very carefully sprue and runner may not run full and may give rise to metal pulling and air aspiration.

4. Volume flow of liquid from every ingate is almost equal.

4. Volume flow of liquid from every ingate is different.

5. They are smaller in volume for a given flow rate of metal. Therefore he casting yield is higher.

5. They are larger in volume because they involve large runners and gates as compared to pressurised systems and thus the casting yield is reduced.

6. Owing to high metal velocity, severe turbulence may occur at corners etc., if they are not streamlined.

6. Lower metal velocities. Turbulence is reduced. Stream lining of junction between runner and gates with runner size reducing at each gate is desirable.

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Q179) STATE PRACTICAL RULES FOR GOOD GATING SYSTEM

NAME: SREYAS.S.ERANDE

CLASS: SE- AUTO

ROLL NO : 307

Q179.state practical rules for good gating system

ANS:-

PRACTICAL RULES FOR GATING SYSTEM ARE:-

Irrespective of the technique being adopted, a number of general principles for making gating

systems to obtain sound castings are given below,

1) A gating system should be rammed hard so that its sand is not dislodged by the molten

metal.

2) A gating system should be kept free of loose sand or other foreign matters which if enter the

mould will produce defective casting.

3) Facing sand if employed should be used both for mould cavity and the gating system

4) The various components of the gating system should be smooth, rounded and streamlined to

minimize turbulence and mold erosion.

5) Streamlining of casting design and gating system minimises the danger of VENA CONTRACTA,

a local constriction of liquid metal stream which may cause air or gas aspiration and turbulence.

6) The gating system should have an appropriate gating ratio.

7) In case of a multigate system, the runner should extend a little beyond the gate farthest

frosprue to trap any slag dross etc., coming with the 1st flow of metal.

8) The direction of ingates should be such , so as to avoid direct impingement of the liquid

metal against mold surface.

9) Gating should enter the heavier systems of the casting.

10) The gating system may be reinforced against erosion by the use of pre-molded refractory

sleeves and files or with thw help of high strength cores.

11) It is much better if a runner core containing part or whole of the gating system is used.

This makes molding simple, intoduces well consolidated liquid, metal passage walls and

ensures close control of the dimensions of the gating system.

12) Pouring basins of the offset type prove atleast tageous over the simple pouring cup because

they suppress,

7. High metal velocities also cause turbulence (in mold cavities), mold corrosion, dross formation and air entrapment.

7. Spurting of metal into the mold cavity is reduced.

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-Turbulence

-Fluctuations in pouring

-Air entrapment, and secure steady flow.

13) Liquid metal should be poured at normal temperature

Low temperature may cause misruns etc,

High temperature may

-Increase the gas content of the metal,

-Produce more dross, and

-Badly affect directional solidification.

14) The type of gating system to be used depends upon

-Susceptibility to oxidation,and

-Fluidity of the alloy to be cast.

15) Light metal alloys like aluminium bronzes and high tensile brasses require bottom gates or

(reversed)horn gates.

-Highly pressurised system is not recommended for these alloys.

16) Cast iron, phosphour,bronze and gun-metal are gated by a variety of methods including top

gating.

17) Steel, because it freezes prematurely and can cause excessive mold rerosion, should have

gates at points low in the mold(i.e. bottom gating)

18) Alloys susceptible to oxidations and to formation of strong surface films need quite and

progressive mold filling with least division of the liquid metal stream.

Q 180) Explain the concept of slag and dross removal in gating system design?

Ans.

Elimination of Slag and Dross:

(1). Slag and Dross are oxides or other reaction products of metal being cast.

(2). Slag may also include other non-metallics from the melting operation.

(3). Foreign materials may also generate owing to faulty pouring of molten metal.

(4). These foreign materials may generate in the gating system itself.

(5). These foreign materials or ipmurites being lighter than the ferrous or copper alloys

come to the surface of the molten materials.

(6). Since there is not much difference between the specific gravities of these impurities

and molten light metal alloys, the problem of removing slag or dross from the melt is

more complicated.

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(7). Dross formation takes place in the early stages of pouring.

(8). If dross and slag along with the liquid metal reach the mold cavity they get included

in the casting and make it unsound.

(9). To prevent slag and dross inclusions in the castings, they are removed from the

molten metal before it reaches the mold cavity.

(10). The different methods adopted to avoid dross and slag from entering the mold

cavity are as follows:

(A). For Copper Or Ferrous Alloys

1.Slag and Dross should be skimmed from the molten metal in the ladle before pouring.

2. Molten metal may be poured with the help of a bottom pouring ladle.

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3. Pouring basin should be employed in place of a pouring cup.

4. Pouring basin with a DAM works still better.

5. Strainer cores may be used to filter the molten metal.

6. Runner may be employed beyond the farthest gate to catch the slag accompanying

the first poured metal.

The slag being lighter comes on the top of molten in the ladle and gets poured into the

gating system along with the first or initially poured molten metal. The metal coming

later which fills the mold cavity is free from slag.

7. The use of large runners increased runner area reduces metal velocity and as the

liquid metal flows through the runner, slag etc. Float on the liquid metal surface of the

runner.

8. A swirl gate may be used to separate slag from molten metal centrifugally.

9. Since slag etc. Float onto the surface of liquid metal, a gating system with runner in

the cope and gates in the drag will clean the liquid metal, because only slag free metal

from the gates which are at bottom.

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Name: Tanmay Adiwarekar.

Class: SE- Auto.

Roll No.: 301

Q 181 )WHAT IS RISER? WHAT ARE IT’S FUNCTION?

NAME:- KUNAL B PATIL

ROLL NO. :-336

BRANCH :- AUTOMOBILE

(i) A riser or a feeder head is a passage of sand made in the cope (mold)

during ramming the cop.

(ii) The molten metal rises in the feeder head after the mold cavity is filled up.

(iii) This metal in the feeder head (or riser) compensates the shrink-age as the

casting solidifies.

FUNCTION OF A RISER

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1. (a) Metals and their alloys shrink as they cool and solidify. It creates a partial

vacuum within the casting.

(b) Partial vacuum leads to a shrinkage void.

(c) This shrinkage void will grow and form shrinkage cavity if extra liquid metal

from outside the mold (cavity) is not supplied.

(d) The primary function of the riser (attached with the mold) is to feed metal to

the solidifying casting so that shrinkage cavities are get rid of.

Shrinkage is a very common casting defect.

2. A riser permits the escape of air and mold gases as the mold cavity is being filled

with the molten metal.

3. A riser full of molten metal indicates that the mold cavity has already been

completely filled up with the same.

4. A casting solidifying under the liquid metal pressure of the riser is comparatively

sound.

5. Risers promote directional solidification.

Q182 Differentiate between open and blind riser

ANS

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OPEN RISERS

1. The top end of the open riser is open i.e. exposed to atmosphere

2. the liquid metal in the riser is fed to the solidifying casting under the force of gravity and atmospheric pressuretill the top surface of the riser solidifies and thereafter gravity is the only feeding force.

3. an open riser is connected a. either at the top of cope. b. Or on the side at the parting

line.

4. An open riser is generally cylindrical

5. LIMITATIONS a. open riser is not placed in the

drag

b. open riser is generally larger than a comparable blind riser.

c. An open riser is more difficult to

BLIND RISERS

1.A blind riser is closed at the top.

2. A vent or a permeable core at the

top of the riser may be provided to

have some exposure to atmosphere

otherwise the vacumn created

between the top of the riser and the

liquid metal level in the riser may not

permit proper feeding of liquid metal

from the riserto the casting.gravity is

the only feeding force.

3.A blind riser is connected

a. either at top of cope

b.or on the side of the casting

atparting line or drag

4.A blind riser is a rounded cavity

and has the minimum practical ratio

of surface area to volume and thus

associates a slow cooling rate and is

more difficult.

5.ADVANTAGES

a. blind risers can be placed at any

positions.

b. a blind riser is smaller then a

comparable open riser

c. a blind riser can be removed more

easily than an open riser

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remove from casting as compared to blind riser

d. Being exposed to atmosphere, the liquid metal in the top portion of the riser starts solidifying immediately after the mould filling is completed, because there is major heat loss to the atmosphere by radiation.

e. Its height is determined not by feeding requirements but by the depth of moulding box used.

6. ADVANTAGES a. An open riser is easy to mould

as compared to a blind riser. b. An open riser is open to

atmosphere thus it ensures that unlike a blind riser it will not draw metal from the casting as a result of partial vacumn in the riser.

d. being surrounded by moulding

sand from all sides the metal in riser

cools slowly.

e.blind risers promote directional

solidification better than the open

risers.

6.LIMITATIONS

a.it is difficult to mold a blind riser

b.a blind riser may draw liquid metal

from the solidifying casting.

Priyant nandu

Roll no ae332

Q 183 How Riser Aids Directional Solidification?

Ans Aamir ae322

DIRECTIONAL SOLIDIFICATION

Directional solidification and progressive solidification describe types

of solidification within castings. Directional solidification describes solidification that

occurs from farthest end of the casting and works its way towards the sprue. Directional

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solidification is solidification that starts at the walls of the casting and progresses

perpendicularly from that surface.

RISER

A riser, also known as a feeder, is a reservoir built into a metal casting mould to

prevent cavities due to shrinkage. Most metals are less dense as a liquid than as a solid

so castings shrink upon cooling, which can leave a void at the last point to solidify.

Risers prevent this by providing molten metal to the casting as it solidifies, so that the

cavity forms in the riser and not the casting. Risers are not effective on materials that

have a large freezing range, because directional solidification is not possible. They are

also not needed for casting processes that utilized pressure to fill the mold cavity. A

feeder operated by a treadle is called an underfeeder.

Carbon steel experiences shrinkage of about 3% during solidification. Additional

volume reduction occurs during the cooling of the liquid metal after pouring. These

contractions will create internal unsoundness (i.e., porosity) unless a riser, or liquid

metal reservoir, provides liquid feed metal until the end of the solidification process.

The riser also serves as a heat reservoir, creating a temperature gradient that induces

directional solidification. Without directional solidification, liquid metal in the casting

may be cut off from the riser, resulting in the development of internal porosity. Two

criteria determine whether or not a riser is adequate: 1) the solidification time of the riser

relative to that of the casting, and 2) the feeding distance of the riser. To be effective, a

riser should continue to feed liquid metal to the casting until the casting has completely

solidified. Thus, the riser must have a longer solidification time than the casting. Since

the critical factor affecting solidification time is heat loss, minimizing heat loss from the

riser is an important consideration

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Q184) HOW TO PROMOTE DIRECTIONAL SOLIDIFICATION OF CASTING.

.Directional solidification and progressive solidification describe types of solidification within

castings. Directional solidification describes solidification that occurs from farthest end of the

casting and works its way towards the sprue. Progressive solidification, also known as parallel

solidification]is solidification that starts at the walls of the casting and progresses

perpendicularly from that surface.

Directional solidification of casting.

Theory:

Most metals and alloysshrink as the material changes from a liquid state to a solid state.

Therefore, if liquid material is not available to compensate for this shrinkage a shrinkage defect

forms.[3]

When progressive solidification dominates over directional solidification a shrinkage

defect will form.[2]

http://en.wikipedia.org/wiki/Solidification

http://en.wikipedia.org/wiki/Casting

http://en.wikipedia.org/wiki/Sprue_(manufacturing)

http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Alloys

http://en.wikipedia.org/wiki/Alloys

http://en.wikipedia.org/wiki/Directional_solidification#cite_note-2

http://en.wikipedia.org/wiki/Directional_solidification#cite_note-chastain104-1

http://en.wikipedia.org/wiki/File:Directional_solidification.svg

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The geometrical shape of the mold cavity has direct effect on progressive and directional

solidification. At the end of tunnel type geometries divergent heat flow occurs, which causes that

area of the casting to cool faster than surrounding areas; this is called an end effect. Large

cavities do not cool as quickly as surrounding areas because there is less heat flow; this is called

a riser effect. Also note that corners can create divergent or convergent (also known as hot spots)

heat flow areas.[4]

In order to induce directional solidification chills, risers, insulating sleeves, control of pouring

rate, and pouring temperature can be utilized.[5]

Directional solidification can be used as a purification process. Since most impurities will be

more soluble in the liquid than in the solid phase during solidification, impurities will be

"pushed" by the solidification front, causing much of the finished casting to have a lower

concentration of impurities than the feedstock material, while the last solidified metal will be

enriched with impurities. This last part of the metal can be scrapped or recycled. The suitability

of directional solidification in removing a specific impurity from a certain metal depends on the

partition coefficient of the impurity in the metal in question, as described by the Scheil equation.

Directional solidification is frequently employed as a purification step in the production of

multicrystallinesilicon for solar cells.

Q185) GENERAL PRINCIPLES IN RISER DESIGN

ans

(1)FREEZING TIME

Riser should freeze at a slower rate than the casting so that liquid metal can fed to the

casting till it solidifies completely .Therefore the freezing time for the risers can be exceed that

for casting by a safe margin

(2)FEEDING RANGE

When a casting becomes large and complicated , the number of parallel sections in it also

increase. The total feeding range thus cannot be covered by a single riser and for this reason

more than one risers are employed to feed molten metal depending upon the effective feeding

range of each riser. A casting should be sub-divided into different rones so that each rone can be

http://en.wikipedia.org/wiki/Heat_flow

http://en.wikipedia.org/wiki/Directional_solidification#cite_note-stefanescu68-3

http://en.wikipedia.org/wiki/Chill_(casting)

http://en.wikipedia.org/wiki/Riser_(casting)

http://en.wikipedia.org/wiki/Directional_solidification#cite_note-4

http://en.wikipedia.org/wiki/Partition_coefficient

http://en.wikipedia.org/wiki/Scheil_equation

http://en.wikipedia.org/wiki/Polycrystal

http://en.wikipedia.org/wiki/Polycrystal

http://en.wikipedia.org/wiki/Solar_cells

http://en.wikipedia.org/wiki/File:Casting_solidification_conditions.svg

http://en.wikipedia.org/wiki/File:Casting_solidification_conditions.svg

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fed by a separate riser . Risers may be shared by a number of castings as well. Risers should be

attached to heavy sections since they are generally last to solidify in a casting

The shrinkage happens because no matter freezing time is equal in two castings the plate

is much larger than the cube and therefore it demands more metal from the riser. The riser must

have sufficient volume of liquid metal to feed the casting. The liquid metal in the riser gets

consumed in two ways firstly a part of the liquid metal solidifies in the riser itself. Secondly the

rest of the metal flows into the casting to compensate liquid and solidification shrinkages

I.F Caine proposed a method to calculate riser sizes. His method was based on

experimently determined hyperbolic relationship between relative volume and relative side

The relationship is X=(a/y-b ) +c

X= freezing ratio

Y= volume ratio

A= freezing characteristics constant

B= liquid-solid solidification contraction

C= relative freezing rate of riser and casting

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Curves similar to (a) and (b) can be plotted for different values of a,b,c depending upon a

wide variety of castings, riser shapes and sizes

Caines method described that ,if the freezing rates of riser and casting are identical the

feeder should be infinitely large the riser needed be infinite

But if the casting solidifies increasingly rapidly relative to riser the necessary riser

volume decreases to the shrinkage level. Caines curves has been use many years by steel

founders.

Adams and Taylor later on suggested corrections which could be applied to values pf

surfaces area used in caines curve for local differences in cooling rate . A factor of 2.2 is used for

chills employed in the casting of steel and that of 0.6 for gypsum insulation in conjunction with

bronzes .they predicted riser behaviour from fundamental thermal and solidification constants

(1-B)VB/VC=AB/AC +B

RISER LOCATION AND RISER FEEDINF DISTANCE

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(1) IN ADDITION TO ITS ADEQUATE SIZE, A RISER MUST BE PROPERLY

LOCATed to obtain a sound casting

(2) A riser should have adequate metallostatic head and must maintain positive of liquid

metal on all portions of the solidifying casting

(3) Risers can be located on the top of the casting or in the side of the same

(4) Should be placed on a flat rather than the surface because a riser on the flat surface

the need for sculptuer in the fettling shop

(5) Should be large but few because the collective 1:4 ratio is large in this and hence

the risers will experience delayed freezing

(6) The riser is placed in direct contact with the behavior sections of casting

Ravi Yadav Roll no 356

Q 186) State and explain the classification of casting defects and their causes

Ans:

(A) patterns and molding Box equipment

(a)Mismatch or Mould Shift

CAUSES

(1) WORN OR LOOSE DOWELS IN PATTERN MADE IN HALVES

(2) WORN OUT, LOOSE,BENT OR ILL-FITTING MOLDING BOX CLAMPING PIN

REMEDIES

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Remedies involve removing the causes listed above

(b)Variation in wall thickness of the casting

Causes

(1)Worn core boxes giving oversize core dimensions

(2)worn core prints allowing a core to float or move

(c) FINS, FLASH AND STRAIN

Causes

(1)These may occur when bottom boards are too flexible

(2)pattern plates are not sufficiently rigid to keep straight ramming

(3)top part boxes inadequately weighted permit the top to lift eligibility when poured

thereby causing flash

(d)Crush

Causes

(1)Excessive weibhting of the green sand mold

(2)core print too small for the core

(3)core too large for the core print

(B)Defects caused due to improper molding and core-making materials

(a)Blowholes

Causes

(1)excess moisture in the molding sand

(2)low permeability and excessive fine grain sands

(3)cores neither properly baked nor adequately vented

REMEDIES

Remedies involve removing the causes promoting a defest

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(b)Drop

Causes

(1)low green strength

(2)low mold hardness

(3)insufficient reinforcement of sand projections in the cope

(c)Scrab

Causes

(1)too fine a sand

(2)sand having low permeability

(3)uneven mold ramming

(d)Pin-holes

Causes

(1)sand with high moisture content

(2)sand containing gas generating ingredients

(3)faulty metals

(e)Metal penetration and rough surface

Causes

(1)high permeability

(2)large grain sized sands

(3)soft ramming

(C)Defects due to improper sand mixing and distribution

Improper sand mixing and distribution give rise to faulty sand conditions and various

defects which result ,have been discussed earlier under section

(D)Defects caused by molding, core-making, gating

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Causes

(1)Too cold molten metal

(2)too thin casting section

(3)too small gates

(4)metal lacking in fluidity

(E)Defects due to improper mold drying and core baking

(1)A layer of moisture collected under the impervious layer of mold paint will cause sand

and paint scab and ped with the result that casting shoes,

(1)sand washes

(2)scabs

(3)blowholes

(2)Oil sand cores, if under-baked, absorb moisture from atmosphere

(1)core sand wash

(2)Core blow, and blow holes

(F)Defects occurring while closing and pouring the molds

(a)shift or mismatch of the cope and drag at the mold joint

Causes

Faulty molding box equipment

Faulty molding

REMEDY

(1)PROPER MOULDING

(2)molding sands should posses adequate hot strength

(3)skimming off or screening of molten metal before pouring

Ravi Yadav

Roll no 356

581

auto

Q 187) Write a note on solidification of Casting?

solution:

The mechanism of solidification of casting and its control for obtaining sound casting is

the most important problem of foundry men. The proper understanding of the

solidification mechanism is essential for preventing defects due to shrinkage of metals .

The metallographic structure consist of

1) Grain size, shape and orientation,

2)Distribution of alloying elements

3)Underlying crystal structure and its imperfection

Also soundness implies the degree of true metallic continuity and the and the casting

will be sound if volume shrinkage accompanying the change of state.

Solidification occurs due to:

a) By the nucleation of very small grains.

b) Which grown under the thermal and crystallographic conditions existing during

solidification obtained from a flat mould wall.

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Sound casting can be obtained also by Progressive , Directional solidification and control

of solidification

It can be specified as-

a)Progressive solidification is a product of freezing mechanisms. It implies growth of

partially solid and partially liquid zone from the outside to the interior of casting Short

liquidious to solidifying metal results high degree of progressive solidification

b) A solidification which is made to occur directional i.e. in a particular direction is

known as directional solidification . The direction of solidification in the casting is made from

the thinnest section towards the heavier section.

The fig. below shows the various process of Progressive and directional solidification.

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If sound casting with no shrinkage voids along the centre line are to be obtained , the

following requirement should be met

a)The solidification should be progressive ,directional and must proceed from most

distant points towards riser/risers

b)Temperature gradient should be step and properly directed so that metal can reach

the solidification section to compensate for the shrinkage (of the solidifying metal) as it occurs

at the centre line)

Production Processes I

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