A REPORT

ON

INDUCTION FURNACE

BY

Akash Khaitan 08DDCS547

AT

NIKITA METALS, KALYANESHWARI, BURDWAN, W.B.

An Internship Program-II station of

Faculty of Science & Technology, ICFAI University

26th May-17th July, 2010

A REPORT

ON

INDUCTION FURNACE

BY

Akash Khaitan 08DDCS547 CS

Prepared in partial fulfilment of the

IP201 Internship Program-II course

AT

NIKITA METALS, KALYANESHWARI, BURDWAN, W.B.

An Internship Program-II station of

Faculty of Science & Technology, ICFAI University

26th May-17th July, 2010

iii

Acknowledgement I would like to express my gratitude to Prof. R.C.Ramola Center Head FACULTY OF SCIENCE AND TECHNOLOGY, Prof. Nesa Moorty IP Coordinator FACULTY OF SCIENCE AND TECHNOLOGY and towards all the faculty members for allowing me in taking the industrial training according to our curriculum and to bring about industrial awareness .This training at NIKITA METALS gave me an opportunity to realize the ways the industries work and the problem it faces during the course. I also thank Mr. Brahmanand Agrawal (Director), Mr. Arman Ali, M.r Sumant Chaudhary and Mr. S.R Mishra of Nikita Metals who tried their best to provide us all the facilities needed by my team and cooperated in all possible. Special thanks to Mr. Ajay Kumar Khaitan (A Scientist and a world record holder) who gave us his precious time and helped us in understanding the technical details about the each and every component of the industry. I thank our faculty in charge Prof. Ranjan Mishra who has helped us all throughout with his guidance and also helped us in the completion of this report.

Faculty of science & Technology, ICFAI University

Station: NIKITA METALS Center: BURDWAN

Duration: 55 days Date of Start: 26th May,2010

Date of Submission: 16th July,2010

Title of the project: NIKITA METALS

ID No./Name(s)/Discipline(s)/of the student(s) :

08DDCS547 Akash Khaitan CS

Name(s) and Designation(s)Of the expert(s):

Mr Sumant Chaudhary (Technical Incharge),

M.r Arman Ali (Factory Incharge)

Name of the

IP Faculty: Mr. Ranjan Mishra

Key Words: Induction Furnace

$Project Areas: Industrial Training

Abstract: This project deals with Induction Furnace Technology employing high frequency magnetic heating.

Signature of Student Signaure of IP Faculty

Date Date

Table of Contents

1 Introduction 1

2 Induction Furnace 2

2.1 Induction Furnace Diagram 3 - 4

3 Furnace Making 5

4 Hydraulic System 6

5 Magnetic Shielding & Analysis of an Induction Furnace 7

6 Final Product 8

7 Induction Heating 9

8 Induction Heating Requirements 10

8.1 Series resonant tank circuit 10

8.2 Parallel resonant tank circuit 11

8.3 Impedance matching 11

9 The LCLR work coil 12

10 Water Treatment Unit 13

10.1 Water Purification 14

10.2 Water Cooling Tower 15

11 Power Control Methods 16

11.1 Varying the DC link voltage 16

11.2 Varying the duty ratio of the devices in the inverter 16

11.3 Varying the operating frequency of the inverter 17

11.4 Varying the value of the inductor in the matching network 17

11.5 Impedance matching transformer 18

11.6 Phase-shift control of H-bridge 18

12 Chemical Lab 19

12.1 Sample Carbon Test 20

13 Air Pollution Control Unit 21

13.1 Electronic Precipitator 22

13.2 The Plate Precipitator 23

14 Recommendations xxiv

15 References xxv

16 Glossary xxvi

1

1. Introduction

Induction Furnace: It is the most important Unit that helps in melting the iron. Power Control System: It consists of the sets of practical circuits that is responsible for the effective power control in order to melt the metal Water Treatment Unit: Water is an important component in the induction furnace plant. The main purpose of water is in the regulation of a particular temperature that is it works as a coolant in the induction furnace plant. Air Pollution Control Unit: As the name suggest it is required in order to keep the plant pollution free and thus better efficiency. Chemical Lab Test: It is done in the chemical lab to test the % of each component present in the raw material and to decide whether the raw material is applicable for the plant or not. Raw Material Control Unit: Consists of experienced labors who purchase raw material required for the plant Transportation Unit: Controls the transportation section of the industry.

The complete induction plant consists of series of individual units which are assembled and are synchronized together in order to work as a complete induction furnace plant. The units are as follows:

Induction Furnace Power Control System Water Treatment Unit Air Pollution Control Unit Chemical Lab Test Unit Raw Material Control Unit Transportation Unit

Fig 1.1Complete Plant Overview

2

2. Induction Furnace

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. The advantage of the induction furnace is a clean, energy-efficient and well-controllable melting process compared to most other means of metal melting. Most modern foundries use this type of furnace and now also more iron foundries are replacing cupolas with induction furnaces to melt cast iron, as the former emit lots of dust and other pollutants.

.

Induction furnace capacities range from less than one kilogram to one hundred tones capacity, and are used to melt iron and steel, copper, aluminum, and precious metals. The frequency of operation of induction furnace also varies. Usually it depends on the material being melted, the capacity of the furnace and the melting speed required. A high frequency furnace is usually faster to melt a charge whereas lower frequencies generate more turbulence in the metal, reducing the power that can be applied to the melt. When the induction furnace operates it emits a hum or whine (due to magnetostriction), the pitch of which can be used by operators to identify whether the furnace is operating correctly, or at what power level.

Fig 2.1 Induction Furnace

Features of induction furnace:

Highest chemical durability. Lowest alloy losses. Leading to highest metal quality

with respect to impurities. High refractoriness. Available in various sizes. Comes in different capabilities

Fig 2.2 Induction furnace (molten metal)

3

2.1 Induction Furnace Diagram

Fig 2.1.1 Induction Furnace Diagram An induction furnace system has an active induction coil surrounding a crucible. A passive induction coil also surrounds the crucible. The passive induction coil is connected in parallel with a capacitor to form an L-C tank circuit. A source of ac current is provided to the active induction coil to produce a magnetic field that inductively heats and melts an electrically conductive material in the crucible. The magnetic field also magnetically couples with the passive induction coil to induce a current in the passive induction coil. This induced current generates a magnetic field that inductively heats and melts the material. The resistance of the L-C tank circuit is reflected back into the circuit of the active induction coil to improve the overall efficiency of the induction furnace system. The crucible may be open-ended to allow the passage of the electrically conductive material through the crucible during the heating process. The three phase A.C. electric power is converted into D.C. power with the help of high voltage/high current rectifiers and the A.C. ripple components are removed with the help of large size inductors and capacitors. Now these rectified D.C. power is applied to the

4

high power thyristors/IGBT. Now high frequency switching signal is applied to the controlling gates to obtain very frequency current which passes through the coil surrounding the induction furnace crucible. Because of the high frequency oscillations around the crucible magnetic fields are generated. Hence the ferrous materials inside the crucible start melting The crucible contains about 7-9 tons of scrap iron which melts within 30 minutes. The temperature rises about 1400-1600 degree centigrade A huge amount of smoke and gases comes out which is collected and sent to the ESP (Electro Static Precipitator) for purification.

Fig 2.1.2 Wave Forms at different places

Fig 2.1.4 Control Panel with Inductor

Capacitor (LC) Set up at Nikita Metals

Fig 2.1.3 Large Set of Capacitors

at Nikita Metals

5

3. Furnace Making

It is done with the help of ramming mass which is a refractory that can withstand high temperatures. The furnace outer wall is already present and the inner wall of the furnace is to be constructed. Furnace inner wall making is done in following ways:

Ramming mass is put at the bottom square of the container

The cylindrical shaped iron flask (which is thinner than container)is put in the

container The gap in between the iron flask and the container is filled with the ramming

mass Now we get a cylindrical shaped hole The raw material to be melted is put inside it and the induction process is started.

As the induction continues the iron flask, the raw materials gets melted and only the ramming mass is left with a hole of the flask shape

This furnace obtained is used 10-15 times and after that the refractory material is

broken and the whole steps is repeated again

Fig 3.2 Iron Flask at Nikita Metals

Fig 3.1 Top View Of the Furnace

6

4. Hydraulic System

Fig 4.1 Hydraulic System in the induction furnace

Fig 4.2 D.C Motor (which controls hydraulic system)

Fig 4.3 A tilted furnace

(with the help of dc Motor & hydraulic system)

The hydraulic system present in the induction furnace works with the help of a dc generator. The hydraulic system with dc generator helps in the tilting the furnace. The hydraulic is such built that it provides facility for the workers to control the degree of rotation on a particular axis from 0 to 90 degree. The furnace’s hydraulic system provides motive power to perform a number of other functions including opening/closing the furnace cover, tilting the furnace and pushing out the lining.

Fig 4.4 Hydraulic System control at Nikita Metals

Fig 4.5 Tilted Furnace at Nikita Metals pouring

molten iron

7

5. Magnetic Shielding & Analysis of an Induction Furnace

Fig 5.1 Coil surrounded by iron core

An induction furnace is an electrical furnace in which the current is generated within the metal by induction heating and the heat generated by the electric resistance that melts the metal. The magnetic iron cores around the coil are used to protect the coil from being damaged. The magnetic iron cores also prevent the flux leakage so that the steel sheet outside the iron cores will not be heated. The magnetic flux density distribution with and without the iron core. The flux leakage of the furnace with iron core is lower than that of the furnace without iron core. So the steel sheet outside the iron core is protected from being heated. The Joule loss of the molten metal with and without iron core. The Joule loss of the furnace with iron core is about 5% more than that of the furnace without iron core. The molten metal is heated efficiently with iron core.

Fig 5.4 Coil of induction furnace surrounded by iron core at

Nikita Metals

8

6. Final Product

Fig 6.2Tilted Furnace Ready to pour molten

metal

The final product produced is the ingot which is prepared as a result of dried molten metal. The molten metal in the furnace after getting prepared is allowed to fall from the funnel to the refractory material A series of ingot cover which are put together gets filled up from bottom to top ensuring no air gap is present Finally the molten metal is dried inside the iron cover and thus the ingot is obtained.

Fig 6.3 Molten Metal being poured to Refractory

Fig 6.4 Ingot at Nikita Metals

Fig 6.5 Final Product(Ingot)

Fig 6.1 Molten metal pour opening(Funnel)

9

7. Induction Heating

Electromagnetic induction, simply induction, is a heating technique for electrical conductive materials (metals). Induction heating is frequently applied in several thermal processes such as the melting and the heating of metals. Induction heating has the important characteristic that the heat is generated in the material to be heated itself. Because of this, induction has a number of intrinsic trumps, such as a very quick response and a good efficiency. Induction heating also allows heating very locally. The heating speeds are extremely high because of the high power density. The principle of induction heating is mainly based on two well-known physical phenomena: 1. Electromagnetic induction 2. The Joule effect Electromagnetic induction The energy transfer to the object to be heated occurs by means of electromagnetic induction. It is known that in a loop of conductive material an alternating current is induced, when this loop is placed in an alternating magnetic field When the loop is short-circuited, the induced voltage E will cause a current to flow that opposes its cause – the alternating magnetic field. This is Faraday - Lenz’s law

Fig 7.1 Electromagnetic induction Joule Effect If a ‘massive’ conductor (e.g. a cylinder) is placed in the alternating magnetic field instead of the sort circuited loop, than eddy currents (Foucault currents) will be induced in here (see Figure 7.2). The eddy currents heat up the conductor according to the Joule effect.

Fig 7.2 Induction of eddy currents

10

8. Induction Heating Requirements

3 things are essential to implement induction heating:

1. A source of High Frequency electrical power, 2. A work coil to generate the alternating magnetic field, 3. An electrically conductive workpiece to be heated,

Practical induction heating systems are usually a little more complex. For example, an impedance matching network is often required between the High Frequency source and the work coil in order to ensure good power transfer. Water cooling systems are also common in high power induction heaters to remove waste heat from the work coil, its matching network and the power electronics. The control electronics also protects the system from being damaged by a number of adverse operating conditions.

In practice the work coil is usually incorporated into a resonant tank circuit. This has a number of advantages. Firstly, it makes either the current or the voltage waveform become sinusoidal. This minimizes losses in the inverter by allowing it to benefit from either zero-voltage-switching or zero-current-switching depending on the exact arrangement chosen. The sinusoidal waveform at the work coil also represents a more pure signal and causes less Radio Frequency Interference to nearby equipment.

We will see that there are a number of resonant schemes that the designer of an induction heater can choose for the work coil:

8.1 Series resonant tank circuit

The work coil is made to resonate at the intended operating frequency by means of a capacitor placed in series with it. This causes the current through the work coil to be sinusoidal. The series resonance also magnifies the voltage across the work coil, far higher than the output voltage of the inverter alone.

The inverter sees a sinusoidal load current but it must carry the full current that flows in the work coil. For this reason the work coil often consists of many turns of wire with only a few amps or tens of amps flowing. Significant heating power is achieved by allowing resonant voltage rise across the work coil in the series-resonant arrangement whilst keeping the current through the coil (and the inverter) to a sensible level. The main drawbacks of the series resonant arrangement are that the inverter must carry the same current that flows in the work coil. In addition to this the voltage rise due to series

11

resonance can become very pronounced if there is not a significantly sized work piece present in the work coil to damp the circuit.

The tank capacitor is typically rated for a high voltage because of the resonant voltage rise experienced in the series tuned resonant circuit. It must also carry the full current carried by the work coil, although this is typically not a problem in low power applications.

8.2 Parallel resonant tank circuit

The work coil is made to resonate at the intended operating frequency by means of a capacitor placed in parallel with it. This causes the current through the work coil to be sinusoidal. The parallel resonance also magnifies the current through the work coil, far higher than the output current capability of the inverter alone. However, in this case it only has to carry the part of the load current that actually does real work. The inverter does not have to carry the full circulating current in the work coil. This property of the parallel resonant circuit can make a tenfold reduction in the current that must be supported by the inverter and the wires connecting it to the work coil. Conduction losses are typically proportional to current squared, so a tenfold reduction in load current represents a significant saving in conduction losses in the inverter and associated wiring. This means that the work coil can be placed at a location remote from the inverter without incurring massive losses in the feed wires.

Work coils using this technique often consist of only a few turns of a thick copper conductor but with large currents of many hundreds or thousands of amps flowing. (This is necessary to get the required Ampere turns to do the induction heating.) Water cooling is common for all but the smallest of systems. This is needed to remove excess heat generated by the passage of the large high frequency current through the work coil and its associated tank capacitor.

Fig 8.2.1 Parallel resonant tank circuit

8.3 Impedance matching

This refers to the electronics that sits between the source of high frequency power and the work coil we are using for heating. Impedance matching is the practice of designing the input impedance of an electrical load or the output impedance of its corresponding signal source in order to maximize the power transfer and minimize reflections from the load.

12

9. The LCLR work coil

This arrangement incorporates the work coil into a parallel resonant circuit and uses the L-match network between the tank circuit and the inverter. The matching network is used to make the tank circuit appear as a more suitable load to the inverter.

The LCLR work coil has a number of desirable properties:

1. A huge current flows in the work coil, but the inverter only has to supply a low current. The large circulating current is confined to the work coil and its parallel capacitor, which are usually located very close to each other.

2. Only comparatively low current flows along the transmission line from the inverter to the tank circuit, so this can use lighter duty cable.

3. Any stray inductance of the transmission line simply becomes part of the matching network inductance (Lm.) Therefore the heat station can be located away from the inverter.

4. The inverter sees a sinusoidal load current so it can benefit from ZCS or ZVS to reduce its switching losses and therefore run cooler.

5. The series matching inductor can be altered to cater for different loads placed inside the work coil.

6. The tank circuit can be fed via several matching inductors from many inverters to reach power levels above those achievable with a single inverter. The matching inductors provide inherent sharing of the load current between the inverters and also make the system tolerant to some mismatching in the switching instants of the paralleled inverters.

Another advantage of the LCLR work coil arrangement is that it does not require a high-frequency transformer to provide the impedance matching function.

13

10. Water Treatment Unit

Fig 10.2 A Complete Water Treatment Unit

Water is essential component as it helps to regulate the temperature in the plant. The water treatment unit consists of two sub unit:

Water Cooling Water Purification

The main purpose of the water cooling Unit is to make the hot water colder and pass it on The water purification is done to make the water free from any type of impurities

Fig 10.1 Water Cooling Tower

14

10.1 Water Purification

Water Cooling

Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion exchangers'.

Typical ion exchangers are ion exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, and soil humus. Ion exchangers are either cation exchangers that exchange positively charged ions (cations) or anion exchangers that exchange negatively charged ions (anions). There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions can be more efficiently performed in mixed beds that contain a mixture of anion and cation exchange resins, or passing the treated solution through several different ion exchange materials.

Ion exchangers can be unselective or have binding preferences for certain ions or classes of ions, depending on their chemical structure. This can be dependent on the size of the ions, their charge, or their structure. Typical examples of ions that can bind to ion exchangers are:

H+ (proton) and OH− (hydroxide) Single charged monoatomic ions like Na+, K+,

or Cl− Double charged monoatomic ions like Ca2+ or

Mg2+ Polyatomic inorganic ions like SO4

2− or PO43−

Organic bases, usually molecules containing the amino functional group -NR2H+

Organic acids, often molecules containing -COO− (carboxylic acid) functional groups

Biomolecules which can be ionized: amino acids, peptides, proteins, etc.

Ion exchange is a reversible process and the ion exchanger can be regenerated or loaded with desirable ions by washing with an excess of these ions.

Fig 10.1.1Ion exchanger

Fig 10.1.2 Ion exchange resin beads

Fig 10.1.3 Water Purification Unit at

Nikita Metals (Ion Exchanger)

15

10.2 Water Cooling Tower

Water cooling is a method of heat removal from components. A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The generic term "cooling tower" is used to describe both direct (open circuit) and indirect (closed circuit) heat rejection equipment. A direct, or open-circuit cooling tower is an enclosed structure with internal means to distribute the warm water fed to it over a labyrinth-like packing or "fill." The fill may consist of multiple, mainly vertical, wetted surfaces upon which a thin film of water spreads. In a counter-flow cooling tower air travels upward through the fill or tube bundles, opposite to the downward motion of the water. In a cross-flow cooling tower air moves horizontally through the fill as the water moves downward. Cooling towers are also characterized by the means by which air is moved. Because evaporation consists of pure water, the concentration of dissolved minerals and other solids in circulating water will tend to increase unless some means of dissolved-solids control, such as blow-down, is provided. Some water is also lost by droplets being carried out with the exhaust air (drift). Cooling towers are also characterized by the means by which air is moved. Mechanical-draft cooling towers rely on power-driven fans to draw or force the air through the tower. A fan-assisted natural-draft cooling tower employs mechanical draft to augment the buoyancy effect. The high voltage current cables used in the furnace is covered by a water cable that is water flows in between the current cable and water cable .

Fig 10.2.1 Cooling Tower Design

Fig 10.2.2 Cables Surrounded by Water Cables

Fig 10.2.3 Water Cooling Tower at Nikita

Metals

16

11. Power control methods

It is often desirable to control the amount of power processed by an induction heater. This determines the rate at which heat energy is transferred to the work piece.

The power setting of this type of induction heater can be controlled in a number of different ways:

11.1 Varying the DC link voltage

The power processed by the inverter can be decreased by reducing the supply voltage to the inverter. This can be done by running the inverter from a variable voltage DC supply such as a controlled rectifier using thyristors to vary the DC supply voltage derived from the mains supply. The impedance presented to the inverter is largely constant with varying power level, so the power throughput of the inverter is roughly proportional to the square of the supply voltage. Varying the DC link voltage allows full control of the power from 0% to 100%.

However, that the exact power throughput in kilowatts depends not only on the DC supply voltage to the inverter, but also on the load impedance that the work coils presents to the inverter through the matching network. Therefore if precise power control is required the actual induction heating power must be measured, compared to the requested "power setting" from the operator and an error signal fed back to continually adjust the DC link voltage in a closed-loop fashion to minimize the error. This is necessary to maintain constant power because the resistance of the work piece changes considerably as it heats up.

11.2 Varying the duty ratio of the devices in the inverter

The power processed by the inverter can be decreased by reducing the on-time of the switches in the inverter. Power is only sourced to the work coil in the time that the devices are switched on. The load current is then left to freewheel through the devices body diodes during the dead time when both devices are turned off. Varying the duty ratio of the switches allows full control of the power from 0% to 100%. However, a significant drawback of this method is the commutation of heavy currents between active devices and their free-wheel diodes. Forced reverse recovery of the free-wheel diodes that can occur when the duty ratio is considerably reduced. For this reason duty ratio control is not usually used in high power induction heating inverters.

17

11.3 Varying the operating frequency of the inverter

The power supplied by the inverter to the work coil can be reduced by detuning the inverter from the natural resonant frequency of the tank circuit incorporating the work coil. As the operating frequency of the inverter is moved away from the resonant frequency of the tank circuit, there is less resonant rise in the tank circuit, and the current in the work coil diminishes. Therefore less circulating current is induced into the work piece and the heating effect is reduced.

In order to reduce the power throughput the inverter is normally detuned on the high side of the tank circuit’s natural resonant frequency. This causes the inductive reactance at the input of the matching circuit to become increasingly dominant as the frequency increases. Therefore the current drawn from the inverter by the matching network starts to lag in phase and diminish in amplitude. Both of these factors contribute to a reduction in the real power throughput. In addition to this the lagging power factor ensures that the devices in the inverter still turn on with zero voltage across them, and there are no free-wheel diode recovery problems.

11.4 Varying the value of the inductor in the matching network

The power supplied by the inverter to the work coil can be varied by altering the value of the matching network components. The L-match network between the inverter and the tank circuit technically consists of an inductive and a capacitive part. But the capacitive part is in parallel with the work coil's own tank capacitor, and in practice these are usually one and the same part. Therefore the only part of the matching network that is available to adjust is the inductor.

The matching network is responsible for transforming the load impedance of the work coil to a suitable load impedance to be driven by the inverter. Altering the inductance of the matching inductor adjusts the value to which the load impedance is translated. In general, decreasing the inductance of the matching inductor causes the work coil impedance to be transformed down to a lower impedance. This lower load impedance being presented to the inverter causes more power to be sourced from the inverter. Conversely, increasing the inductance of the matching inductor causes a higher load impedance to be presented to the inverter. This lighter load results in a lower power flow from the inverter to the work coil.

The degree of power control achievable by altering the matching inductor is moderate. There is a also a shift in the resonant frequency of the overall system. The L-match network essentially borrows some of the capacitance from the tank capacitor to perform the matching operation, thus leaving the tank circuit to resonate at a higher frequency. For this reason the matching inductor is usually fixed or adjusted in coarse steps to suit the intended work piece to be heated, rather than provide the user with a fully adjustable power setting.

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11.5 Impedance matching transformer

The power supplied by the inverter to the work coil can be varied in coarse steps by using a tapped RF power transformer to perform impedance conversion. Although most of the benefit of the LCLR arrangement is in the elimination of a bulky and expensive ferrite power transformer, it can cater for large changes in system parameters in a way that is not frequency dependent. The ferrite power transformer can also provide electrical isolation as well as performing impedance transformation duty to set the power throughout.

Additionally if the ferrite power transformer is placed between the inverter's output and the input to the L-match circuit its design constraints are relaxed in many ways. Firstly, locating the transformer in this position means that the impedances at both windings are relatively high. i.e. voltages are high and currents are comparatively small. It is easier to design a conventional ferrite power transformer for these conditions. The massive circulating current in the work coil is kept out of the ferrite transformer greatly reducing cooling problems. Secondly, although the transformer sees the square-wave output voltage from the inverter, it's windings carry currents that are sinusoidal. The lack of high frequency harmonics reduces heating in the transformer due to skin effect and proximity effect within the conductors.

Finally the transformer design should be optimized for minimum inter-winding capacitance and good insulation at the expense of increased leakage inductance. The reason for this is that any leakage inductance exhibited by a transformer located in this position merely adds to the matching inductance at the input to the L-match circuit. Therefore leakage inductance in the transformer is not as damaging to performance as inter-winding capacitance.

11.6 Phase-shift control of H-bridge

When the work coil is driven by a voltage-fed full-bridge (H-bridge) inverter there is yet another method of achieving power control. If the switching instants of both bridge legs can be controlled independently then it opens up the possibility of controlling power throughput by adjusting the phase shift between the two bridge legs.

When both bridge legs switch exactly in phase, they both output the same voltage. This means there is no voltage across the work coil arrangement and no current flows through the work coil. Conversely, when both bridge legs switch in anti-phase maximum current flows through the work coil and maximum heating is achieved. Power levels between 0% and 100% can be achieved by varying the phase shift of the drive to one half of the bridge between 0 degrees and 180 degrees when compared to the drive of the other bridge leg.

The power factor seen by the inverter always remains good because the inverter is not detuned from the resonant frequency of the work coil, therefore reactive current flow through free-wheeling diodes is minimized.

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12. Chemical Lab

Nikita metal consists of a big chemical lab with a number of chemical and testing tools in order to perform all the required chemical tests.

Fig 12.1 Chemical lab at Nikita Metals

Chemical tests are done at Nikita metals to maintain a particular composition of metals in the final product (ingot). A sample is tested and all the percentage composition of all the constituents are found in the sample and accordingly the sample is mixed with other samples to maintain a particular ratio of each constituents. The chemical test ensures a better quality product and is an essential component of metal based industry.

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12.1 Sample Carbon Test At Nikita metals we were illustrated with a sample carbon test that is the aim was to find the carbon content in the given sample

The apparatus used at Nikita Metals during the test are shown below

Following are steps performed for the chemical test for carbon:

1 gm of sample is taken using beam balance (35 % carbon approx) Lead Oxide is added to the sample

The product was kept in the heating furnace in order to melt the sample Initial reading with iron is taken Final reading without iron is taken

Carbon content = final reading-initial reading

Fig 12.1.3 Beam Balance & Digital Beam Balance

Fig 12.1.1 Heating Furnace &

Chemicals

Fig 12.1.2 Reading Taker

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13. Air Pollution Control Unit

Air pollution can be defined as the harmful particles present in the air which can have dangerous impact on the surroundings. Air pollution control unit is an important unit as it is directly related to health of the labors and the environment. Air pollution control in the induction furnace plant is done using Electrostatic precipitator popularly known as ESP technology.

Fig 13.1 Complete Process of Air Pollution Control

Air Pollution Control Unit consists of the following: Steam Generator: The dust particle that comes out as a result of combustion of metals, get mixed with steam and passes on to the Electronic precipitator Electro Static Precipitator: An Electro Static Precipitator (ESP),or Electro Static air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream

22

13.1 Electro Static Precipitator

Electrostatic precipitation removes particles from the exhaust gas stream of an industrial process and sends a particle free gas to the chimney. Often the process involves combustion, but it can be any industrial process that would otherwise emit particles to the atmosphere.

Six activities typically take place in the electronic precipitator:

Ionization - Charging of particles Migration - Transporting the

charged particles to the collecting surfaces

Collection - Precipitation of the charged particles onto the collecting surfaces

Charge Dissipation - Neutralizing the charged particles on the collecting surfaces

Particle Dislodging - Removing the particles from the collecting surface to the hopper

Particle Removal - Conveying the particles from the hopper to a disposal point

The major precipitator components that accomplish these activities are as follows:

Discharge Electrodes Power Components Precipitator Controls Rapping Systems Purge Air Systems Flue Gas Conditioning

Fig 13.1.1 Electro Static Precipitator (Design)

Fig 13.1.2 Electronic Precipitator at Nikita Metals

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13.2 The Plate Precipitator

Fig 13.2.1 Plate Precipitator with Hopper (Dust Collecting System)

The Plate Precipitator present inside electronic precipitator works as follows:

Particles suspended in a gas enter the precipitator and pass through ionized zones around the high voltage discharge electrodes.

The electrodes, through a corona effect emit negatively charged ions into the gas.

The negatively charged gas field around each electrode charges the particles

causing them to migrate to the electrodes of opposite polarity, i.e. the collecting electrodes.

The charged particles gather on the grounded collecting plates. Rappers dislodge

the agglomerated particulate, which falls into the collection hoppers for removal.

xxiv

Recommendations

Some of the suggestion we would like add for the betterment of the industry are as follows:

Steel sheets covering the industry should be replaced by transparent sheet in order to insure better light in the industry

The furnace should have an opening at the top so that the slag can come out

automatically and no worker is required for the same purpose.

The furnace wall presently made up of refractory material can be used 10 to 15

times should be replaced by an alloy comprising of niobium, hafnium and titanium.

Proper neatness should be maintained in the industry

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References http://www.google.com http://www.wikipedia.org http://www.richieburnett.co.uk/indheat.html http://www.furnace-design.com/Induction-Furnace.html http://www.neundorfer.com/knowledge_base/electrostatic_precipitators.aspx Mr. Ajay kumar Khaitan (Scientist)

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Glossary

Control Panel: To control the current, voltage and temperature etc Cooling Tower: The water cooling system Crucible: The refractory tub where metals are melted ESP: Electro Static Precipitator for air pollution control Hopper: The waste collector of Electro Static Precipitator Hydraulic Jack: The jack to tilt the crucible to pour the melted metals I.G.B.T: Insulated gate bipolar transistor is a three-terminal power

semiconductor device, noted for high efficiency and fast switching. Induction Furnace: Based on high frequency heating to melt metals Ingot: Final solidified product from the melted metal Ion Exchange: Based on Anion & Cation Resins to remove water harness LC Tank: Inductor & Capacitor circuits to create electrical Oscillations Moulds: The dies in which molten metals are casted & shaped Oscillator: The LC circuit to create AC signals Ramming Mass: The refractory material, which can withstand high temperatures Rectifiers: The semiconductor device to convert AC power into DC power Thyristors: The 3-Terminal semiconductor device, controlled by gate for

switching electric power.