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Prese tatio o Nuts a d olts ,Belts, Pulleys,Gear,Chain,Bearings, Boilers and

“tea Ge eratio

CHITKARA UNIVERSITY CHITKARA SCHOOL OF

MECHANICAL ENGINEERING

;HARVINDER SINGH

FASTENERS

The act of holding together the different parts of a

machine is called fastening. Fastening can be of three

kinds;

1. Temporary 2. Semi-permanent 3. Permanent.

Temporary Fastening:- When parts of a machine are

joined in such a way that these can be dismantled or re-

assembled again easily, it is called temporary fastening.

The device used are;

Shank Head

Diameter 1

Bolt:- This is one of the most widely used fasteners.

Bolt is made of a thin rod of metal. Different types of

Heads are made to fix them. On the remaining part,

shank, threads are cut. Diameter of bolt is measured at

threads as shown in figure. They are made of Mild

Steel. Nuts are used with bolts to fasten any

component.

‘T’ Head bolt:- This bolt with ‘T’ head is

used with machine table. Some portion

below the ‘T’ head is kept square.

Hexagonal head bolt:- This is the most

commonly used bolt which is shown in

figure above.

4

Taper headless bolt:- This bolt does not

have head. Whole shank is made taper

of 3/8” TPF. This bolt is used for

clamping machine shaft.

Grooved nut:- This is a hexagonal nut with the

lower part made cylindrical on the cylindrical

surface. There is a recessed groove in which a

set screw is used to lock the nut.

Locking plate:- For preventing the nut from

loosening locking plates are fixed on the

outside of the hexagonal nut.

Tab washer:- Tab washers can be used for

locking the nuts which are located near an

edge or corner.

Spring washer:- Spring washers are

available with a single or double coil. These

are placed under a nut in the assembly as

washers. The stiff resistance offered by the

washer against the surface of the nuts serves

to prevent loosening.

Hook bolt:- Head of this bolt is made

hook shaped. Square neck is provided

below this head which restrict the bolt to

be turned. This bolt is used for lifting

machines.

Eye bolt:- Head of this bolt is made

round shaped by bending the round bar.

They are threaded to whole length. A

hook or bar is passed through its hole to

lift any component. This bolt is also

used for lifting machines and

components.

Cup / Round head bolt:- Head of this

bolt is made round. Snug is provided

below this head which restrict the bolt to

be turned during the fitting. This bolt is

used generally for wood working.

Cheese head bolt:- Head of this bolt is

made cylindrical shaped. A pin is

fastened below the head to lock the

position of bolt. This bolt is used where

a spanner can not be used due to narrow

space. Fastening offered by this bolt is

comparatively weak.

Counter head bolt:- Head of this bolt is

made countersunk. This bolt is also used

where the head of bolt above the surface

is objectionable. Square snug is

provided below the head to lock it.

Nut:- Nuts are used in conjunction with Bolts to clamp

the components. Nuts of different types are used

depending on the requirement of the assembly.

Hexagonal nut:- This is the most

commonly used type of nut in structural

and machine tool building. Thin

hexagonal nuts are used as lock-nuts.

Square nut:- Square bolts are provided

with square nuts. In coach building

mostly square nuts are used.

NUT

T-nut:- T-nuts are used along with studs on

machine tools for fixing holding devices

or work pieces.

Stud

T-Nut

Slotted and castle nut:- These nuts have

special provision in the form of slots for

fixing split pins for locking the nuts.

Slotted nuts are hexagonal shaped

throughout. In the case of castle nuts, the

top part of the nut is cylindrical in shape.

Wing nut:- These nuts are used in light duty

assembly which require frequent removal and

fixing. These are available as hot forged / cast

and cold forged. Example of this nut is, used

in Hacksaw.

Knurled nut:- Knurled nuts (thumb nuts) are

used in place where frequent adjustment is

required. They are suitable in places where

finger tightening is enough. They are available

as Type-A & Type-B.

Cap nut:- Cap-nuts are used to protect the bolt

end threads from damages and they also act as

protector for safe working. They also provides

a decorative appearance.

Hexagonal nut with collar:- These nuts

have a machined collar on one end. This

provides additional bearing surface in

assembly. The collar act like a washer and is

useful where frequent tightening and

loosening is necessary.

Hexagonal weld nut:- These nuts are used

for welding on plate work. They have

projected legs on one side.

. Round nut:- These nuts are used with special

types of wrenches to turn it like hook wrench,

pin wrench, face wrench, etc.

Slotted and castle nut:- The position of the nut

can be locked using a split pin. Split pins are

used for locking slotted nuts, castle nut,

hexagonal nut, clevis pins etc. and are used in

different ways.

Sawn nut:- In this type of locking, a slot is cut

half way across the nut. A screw is fitted with

a clearance hole on the top part and matching

threads on the lower part of the nut.

Grooved nut:- This is a hexagonal nut with the

lower part made cylindrical on the cylindrical

surface. There is a recessed groove in which a

set screw is used to lock the nut.

Keys

• A key is define the piece inserted in a axial direction between a shaft and hub to prevent

relative rotation but allow sliding movement along the shaft if required.

• Keys are temporary fastening and are always made of mild steel because they are subjected to shearing and compressive stresses caused by the

torque they transmit.

• a keyway is the groove cut in the shaft or hub to accommodate a key. Key ways can be milled

horizontally or vertically .

Keyways milled

Classification of keys

• Saddle keys » Hollow saddle key

» Flat saddle key

• Sunk keys » Taper sunk keys

» Parallel sunk keys

» Father keys

– Woodruff key (adjustable key)

• Round keys » Parallel pin

» Taper pin

Saddley keys

• Saddle key are taper keys which are sunk into the hub only.(note: a taper key in uniform in width but tapered in thikness on one side, usually 1:100 and is used where no axial movement along the shaft is required).

• Saddle key is suitable for light duty, since they rely on a friction deive alone and are liable to slip on the shaft under load.

Type of the saddle key

• Hollow saddle key:

– this key has its underside hollow out so that it can be placed on the curved surface of the shaft. The keyway is cut in the mating piece (hub) only. Hollow saddle key is used for light duty.

• Flat saddle key:

– In this the flat surface is made on the shaft over which the key is placed in position . In this , holding force is comparative large than the hollow saddle key. It is used for light duty.

Hollow saddle key

Flat saddle key

Sunk keys • Sunk keys are sunk into the shaft and into the hub. These

keys are suitable for heavy duty since they rely on positive drive.

Sunk taper key

Parallel sunk key

It is uniform in width and thickness throughout. It is thus taper less and is used where the pulley or other mating piece is required to slide along the shaft. It may be rectangular or square cross-section and their ends may be squared or rounded.

Feather keys

It is a key attached to one member of a pair and permitting relative motion axial movement thus it is particular kind of parallel key which permits axial moment . A feather key is secured either to the shaft or to the hub, the key being a sliding fit in the keyway of the moving piece.

Woodruff keys

It is an adjustable sunk key. It

is in the form of a semi-circular disc of uniform thickness. The key fits into a semi-circular keyway in the shaft and the top of the key fits into a plain rectangular key way in the hub of the wheel. Since the key and the key seat bear the same radius , it has the advantage of adjusting itself to any taper of the slot of the hub or boss of wheel.

Spline shaft and hub

• A spline shaft is used when the hub is required

to slide along the shaft. These shafts are used

mostly for sliding gear application as in

automotive gear box and propeller shaft of

aircraft.

• A spline shaft in which are cut equiangular

longitudinal groove, the metal between these

groove forming splines or feathers of uniform

depth. – By this means the power transmitted is equally divided

amongst the number of keys giving great strength and security

against total failure than by using a single key.

Spline shaft

Bearing

FUNCTION OF A BEARING

• The main function of a rotating shaft is to transmit power

from one end of the line to the other.

– It needs a good support to ensure stability and

frictionless rotation. The support for the shaft is

known as bearing .

• The shaft has a running fit in a bearing. All bearing are

provided some lubrication arrangement to reduced

friction between shaft and bearing.

Bearings are classified under two main

categories:

– Plain or slider bearing : -

• In which the rotating shaft has a sliding contact with the bearing which is held stationary . Due to large contact area friction between mating parts is high requiring greater lubrication.

– Rolling or anti-friction bearing : -

• Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.

Rolling or anti-friction bearing

Ball and roller bearings due to low rolli g fri tio these eari gs are aptly alled a tifri tio eari g.

• Frictional resistance considerably less than in plain bearings • Rotating – non-rotating pairs separated by balls or rollers

• Ball or rollers has rolling contact and sliding friction is eliminated and

replaced by much lower rolling friction.

• In plain bearing the starting resistance is much larger than the running resistance due to absence of oil film.

• In ball and rolling bearings the initial resistance to motion is only slightly more than their resistance to continuous running.

• Hence ball and rolling bearing are more suitable to drives subject to frequent starting and stopping as they save power.

• Owing to the low starting torque, a low power motor can be used for a line shaft running in ball bearing.

Ball and Roller bearing

Races and balls are high carbon chrome steel (to provide resistance to wear)

machined and ground to fine limits of 0.0025 mm, highly polished and hardened.

The cages are made of low-carbon steel, bronzes or brasses, though for high

temperature application case-hardened and stainless steels are used.

Inner ring or race which fits on the shaft.

Outer ring or race which fits inside the housing.

Ball and roller arranged between the surfaces of two races. These provide rolling action between the races. the radius of the track for balls is

slightly greater 5 to 10 % than that of the ball themselves.

Note that the rotating surfaces rotate in opposite directions.

Cage which separates the balls or rollers from one another.

The disadvantage of the ball and roller

bearings are high cost, they cannot be

used in half, and greater noise.

The ball and roller bearing consists

of following parts:

Types of bearing

Types of ball bearings

SLIDING CONTACT BEARING

Classification of the sliding contact bearing

Collar thrust bearing

Footstep bearing Journal bearing

• Journal bearing – in this the bearing pressure is exerted at right angles to the axis of the axis of the shaft. The portion of the shaft lying within the bearing in known as journal. Shaft are generally made of mild steel.

• Foot step or pivot bearing – in this bearing the bearing pressure is exerted parallel to the shaft whose axis is vertical. Note that in this case the end of the shaft rests within the bearing.

• Thrust bearing – in this bearing supporting pressure is parallel to the axis of the shaft having end thrust. Thrust bearing are used in bevel mountings, propeller drives, turbines, etc. note here the shaft ,unlike foot-strep bearing passes through and beyond the bearing.

– Thrust bearings also known as collar bearing .

Journal bearing

• Simple journal or solid bearing

– It is simply a block of cast iron with a hole for the

shaft providing running fit. An oil hole is drilled at

the top for lubrication.

– The main disadvantage of this type of bearing are

– There is no provision for wear and adjustment on account of

wear.

– The shaft must be passed into the bearing axially, i.e. endwise.

– Limited load on shaft and speed of shaft is low.

Solid bearing

• Bush bearing

– In this the bush of soft material like brass or gun

metal is provided and the body or main block is

made of cast iron. Bush is hollow cylindrical piece

which is fitted in a housing to accommodate the

mating part. When the bush gets worn out it can

be easily replaced.

Bushed bearing

Note that the insertion of the shaft in this bearing is endwise.

BELTS, CHAINS, AND GEARS

FLAT BELT DRIVES WITH PARALLEL SHAFTS


FLAT BELT DRIVES WITH PERPENDICULAR SHAFTS


CROWN ON PULLEY


V-BELT AND PULLEY


LOCATION OF IDLER PULLEYS


ROLLER CHAIN TERMINOLOGY


SPROCKETS


CHAIN DRIVE WITH LONG CENTER DISTANCE


GEAR-TEETH TERMS


MESHING OF GEAR TEETH


WORKING DRAWING OF A SPUR GEAR


BEVEL GEAR

NOMENCLATURE


WORKING DRAWING

OF A BEVEL GEAR


BEVEL GEAR ASSEMBLY


WORM GEARS AND WORMS

General Introduction

• It is a closed vessel in which water is firstly heated, then

vaporized & finally converted into steam.

• The pressure at which steam generated is always higher than

the atmospheric pressure.

• The energy which is used to produced steam is “Heat Energy” & it is measured in calorie.

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Simple Figure of Steam Boiler 68

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Steam & Its Uses

• Steam: It is simply the water vapor, which is formed when

water boils.

• Basically, steam is the gaseous phase of water.

• Steam is used for various purposes:

In Power Generation.

In Industrial Process.

Heating.

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Boilers Classification

• According to their relative position.

• According to water circulation.

• According to its position.

• According to the steam pressure.

• According to its use.

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Fire tube and Water tube Boiler 71

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Mountings in Boiler

• Safety Valves.

• Pressure gauge.

• Feed Check Valve.

• Fusible Plug

• Feed Pipe.

• Steam Stop Valve.

• Water Level Indicator.

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Simple Figure of Steam Boilers Mounting

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Boilers Accessory

• Economizer.

• Super-heater.

• Air –pre heater.

• Steam Injector

.

• Feed-pump.

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Draught in Boilers

• It is defined as the pressure difference due to which the flow of gases inside in a boiler takes place.

• The pressure difference is very small.

• It works in such a way that it sucks the air from furnace and discharged the hot flue gases in atmosphere.

• It is of two types:

i. Natural Draught.

ii. Artificial Draught.

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Working of Draught 76

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BOILERS ACT

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