design, manufacturing and testing of controlled stir casting furnace

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DESIGN, MANUFACTURING AND TESTING OF INDUCTION FURNACE A PROJECT REPORT Submitted by FRANCIS. T (103378044) GIPSON PEREIRA (103378049) MOHAMED ASHIQ.M (103378086) MANIVANNAN.N (103378077) in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY In MECHANICAL ENGINEERING 1

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Design, Manufacturing and Testing of controlled Stir Casting Furnace

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DESIGN, MANUFACTURING AND TESTING OFINDUCTION FURNACE

A PROJECT REPORT

Submitted by

FRANCIS. T (103378044)

GIPSON PEREIRA (103378049)

MOHAMED ASHIQ.M (103378086)

MANIVANNAN.N (103378077)

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGY

In

MECHANICAL ENGINEERING

BHARATHIYAR COLLEGE OF ENGINEERING ANDTECHNOLOGY KARAIKAL

PONDICHERRY UNIVERSITY: PUDUCHERRY 605014

APRIL 2013

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BHARATHIYAR COLLEGE OF ENGINEERING AND TECHNOLOGY

KARAIKAL

DEPARTMENT OF MECHANICAL ENGINEERING

BONAFIDE CERTIFICATE

Certified that this project report “DESIGN, MANUFACTURING AND TESTING OF INDUCTION FURNACE” is the bonafide work of

FRANCIS. T (103378044)GIPSON PEREIRA (103378049)MOHAMED ASHIQ.M (103378086)MANIVANNAN.N (103378077)

who carried out the project work under my supervision.

SIGNATURE SIGNATURE Prof .S.RAVICHANDRAN Mr. S . GUNABALAN HEAD OF THE DEPARTMENT SUPERVISOR

Mechanical DepartmentBharathiyar College of EngineeringAnd Technology, Karaikal

Submitted for the university examination held on..........................................

INTERNAL EXAMINER EXTERNAL EXAMINER

PONDICHERRY UNIVERSITY: PUDHUCHERRY APRIL 2013

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Associate professor Mechanical DepartmentBharathiyar College of EngineeringAnd Technology, Karaikal

ACKNOWLEDGEMENT

We would like to acknowledge all the people who have contributed to a great extent towards the initialization, the development and success of our project.

Our sincere thanks go to Dr. Jayaraman, Principal, Bharathiyar College of Engineering & Technology, Karaikal for extending the college facilities for the successful completion of our project and for his kind patronage.

We also thank Prof .S.Ravichandran, Professor & Head of the Department, Department of Mechanical Engineering, Bharathiyar College of Engineering & Technology, Karaikal for extending the excellent laboratory facilities, ideas and encouragement towards our project.

We cordially thank Mr. S. Gunabalan, Associat Professor of Mechanical Department, Department of Mechanical Engineering, Bharathiyar College of Engineering & Technology for providing innovative ideas and expert guidance for the successful completion of our project.

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ABSTRACT

Aluminum are the important structural material in aerospace and car industries, as

well as in some other areas. Their main characteristics are small specific weight, good

mechanical properties, good processing and resistance to corrosion. Based on great marketing

interest of Aluminum, the investigation of technological parameters of workout of Aluminum

on a laboratory and pilot-plant scale is carried out. In this project a part of results on design

and definition of melting, alloying and casting conditions of aluminum are presented. These

investigations involve alloying temperature, alloying time, amount of alloying elements, and

sequence of their adding and casting temperature on the chemical composition,

microstructure and mechanical properties are investigated.

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INTRODUCTON

Metal melting is the process of producing a liquid metal of the required composition

at the required rate, and with required amount of superheat while incurring the minimal cost.

It is one of the most important foundry practices, as it decides the quality of the casting.

There are number of methods available for melting foundry alloys such as pit furnace, open

hearth furnace, rotary furnace, cupola furnace, etc. The choice of the furnace depends on

several factors, primary among them are the compositional range of the material to be melted,

the fuel or energy used to melt the charge, the degree of refining and control over the process

and type and size of the melting unit.

Induction heating is widely used in metal industry because of its good heating efficiency,

high production rate, and clean working environments. The development of high-frequency

power supplies provided means of using induction furnaces for melting metals in continuous

casting plants.

Rather than just a furnace, a coreless induction furnace is actually an energy transfer device

where energy is transferred directly from an induction coil into the material to be melted

through the electromagnetic field produced by the induction coil. A typical parallel resonant

inverter circuit for induction furnace . The phase controlled rectifier provides a constant DC

current source. The H-bridge inverter consists of four thyristors and a parallel resonant circuit

comprised capacitor bank and heating coil. Thyristors are naturally commutated by the ac

current flowing through the resonant circuit

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FURNACE

A furnace is a device used for heating. The name derives from Latin fornax, oven. In American English and Canadian English usage, the term furnace on its own refers to the household heating systems based on a central furnace (known either as a boiler or a heater in British English), and sometimes as a synonym for kiln, a device used in the production of ceramics. In British English, a furnace is an industrial furnace used for many things, such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns.

The term furnace can also refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, and is part of the standard English names for many metallurgical furnaces worldwide.

The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces.

A furnace is a device that produces heat. Not only are furnaces used in the home for warmth, they are used in industry for a variety of purposes such as making steel and heat treating of materials to change their molecular structure.

Central heating with a furnace is an idea that is centuries old. One of the earliest

forms of this idea was invented by the Romans and called a hypocaust. It was a form of

under-floor heating using a fire in one corner of a basement with the exhaust vented through

flues in the walls to chimneys. This form of heating could only be used in stone or brick

homes. It was also very dangerous because of the possibility of fire and suffocation.

Furnaces generate heat by burning fuel, but early furnaces burned wood. In the

seventeenth century, coal began to replace wood as a primary fuel. Coal was used until the

early 1940s when gas became the primary fuel. In the 1970s, electric furnaces started to

replace gas furnaces because of the energy crisis. Today, the gas furnace is still the most

popular form of home heating equipment.

Wood and coal burning furnaces required constant feeding to maintain warmth in the

home. From early morning to late at night, usually three to five times a day, fuel needed to be

put in the furnace. In addition, the waste from the ashes from the burnt wood or coal must be

removed and disposed.

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RAW MATERIALS

Today's modern furnace uses stainless steel, aluminized steel, aluminum, brass,

copper, and fiberglass. Stainless steel is used in the heat exchangers for corrosion resistance.

Aluminized steel is used to construct the frame, blowers, and burners. Brass is used for

valves, and copper in the electrical wiring. Fiberglass is used insulate the cabinet.

DESIGN

The original gas furnace consisted of a heat exchanger, burner, gas control valve, and

an external thermostat, and there was no blower. Natural convection or forced air flow was

used to circulate the air through large heating ducts and cold air returns to and from each

room. This system was very inefficient—allowing over half of the heated air to escape up the

chimney.

Today's gas furnace consists of a heat exchanger, secondary heat exchanger

(depending on efficiency rating), air circulation blower, flue draft blower, gas control valve,

burners, pilot light or spark ignition, electronic control circuitry, and an external thermostat.

The modern furnace is highly efficient—80-90%, allowing only 10-20% of the heated air to

escape up the chimney.

When heat is requested from the thermostat, the burners light and throws heat into the

primary heat exchanger. The heated air then flows through the secondary heat exchanger

(90% efficient furnace only) to the exhaust flue and chimney. The average furnace has three

heat exchangers each producing 25,000 BTUs for a total of 75,000 BTUs. A flue draft blower

is placed in the exhaust flue to supercharge the burners and increase efficiency. The heat

exchangers perform two functions: transfer heated air from the burners to the home and allow

dangerous exhaust

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THE MANUFACTURING PROCESS1. The primary heat exchanger is formed from two separate pieces of 409

stainless steel sheet. Each half is formed into shape by a 400 ton hydraulic press. The two halves are then fused together by a 25 ton hydraulic press.

2. The secondary heat exchanger is formed from 29-4°C stainless steel tubing and fins. The fins are welded to the tubing to form a radiator type configuration.

3. The primary heat exchanger is crimped to the secondary heat exchanger through a transition box. The flue draft blower is attached to the secondary heat exchanger.

4. The burners are constructed of aluminized steel and arrive at the plant preformed. They are then attached to a plate on the input side of the primary heat exchanger. There is one burner for each heat exchanger in the furnace.

5. The vendor supplied gas control valve is mounted to the heat exchanger and burner assembly. It is connected to the burner through a pipe.

6. The air circulation blower housing is formed through the same hydraulic press formation as the primary heat exchanger. The vendor supplied motor and squirrel cage rotor are connected and attached to the blower housing with brackets.

7. A plate is then attached for mounting the blower assembly to the heat exchanger assembly. Another mounting plate containing the vendor supplied furnace control circuitry and transformer are attached to the blower housing.

8. The air circulation blower assembly is then mounted to the heat exchanger assembly with screws and nuts.

9. The cabinet consists of two doors and the cabinet housing. The cabinet housing is supplied as a flat pre-painted sheet of steel and placed in a hydraulic press to form a three sided configuration. Sheets of fiberglass insulation are glued to the sides of the cabinet.

10. The cabinet is installed around the furnace assembly and secured with screws and nuts. The doors are installed on the front of the cabinet assembly. The completed assembly is boxed and prepared for shipment.

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QUALITY CONTROL

Each completed furnace undergoes an extensive series of tests. Checks for proper

operation of the flue draft and air circulation blowers are performed. The gas valve is checked

for proper operation. The heat output of the furnace in BTUs is measured. A dielectric test is

performed for shorts.

By products/Waste

Scrap metal from cutting and forming operations are collected and sent to recycling

plants for reclamation. Any excess piping is either reused or discarded. Defective steel sheets

can be sent back tot he manufacturer and reformed, depending on the extent of the damage.

The majority of the components of the furnace are able to be recycled.

Furnaces can also be classified according to the molten metal ;

1. Gray Cast Iron

Cupola

Air furnace

Rotary furnace

Electric arc furnace

2. Steel

Open hearth furnace.

Electric furnace.

Arc furnace

High frequency induction furnace

Converter

3. Non-ferrous metals

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Crucible furnaces (Al ,Cu)

Pit type

Tilting type

Non-tilting or bale out type

Electric resistance type (CU)

Pot furnaces (fuel fired) (Mg & Al)

Stationary

Tilting

Reverberatory furnaces (fuel fired ) (Al & Cu)

Stationary

Tilting

Rotary furnaces

Fuel fired

Electrically heated

Induction furnaces (Al & Cu)

Low frequency

High frequency

Electric Arc furnaces (Cu)

TYPE OF FURNACE

1. Induction furnace

2. Cupola furnace

3. Open Hearth furnace

4. Electric furnace

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Common Types of Metal Melting Furnaces Furnace Type

Raw Materials Outputs Process

Induction Furnace Scrap iron or non-ferrous metals

Molten iron or non-ferrous metals

Induction furnaces are the most common type used by both ferrous and non-ferrous foundries. Copper coils heat the metal using alternating currents. The flux reacts with impurities.

Cupola FurnaceIron ore, scrap iron, lime, coke

Molten iron

Alternative layers of metal and coke are fed into the top of the furnace. The metal is melted by the hot gases from the coke combustion. Impurities react with the lime and are separated.

Open Hearth Non-ferrous metals, flux

Molten non-ferrous metals

Reverberatory furnaces melt

metals in batches using a pot-shaped crucible that holds the metal over an electric heater or fuel-free burner.

The flux reacts with impurities

Electric Furnace Scrap iron, flux Molten iron and steel

Electric arcs from carbon electrodes melt the scrap metal. The flux reacts with impurities.

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1. INDUCTION FURNACE

Introduction

The development of Induction Furnaces starts as far back as Michael Faraday, who

discovered the principle of electromagnetic induction. However it was not until the late

1870’s when De Ferranti, in Europe began experiments on Induction furnaces. In

1890,Edward Allen Colby patented an induction furnace for melting metals. The first

practical usage was in Gysinnge, Sweden,by Kjellin in 1900 and was similar to the Colby

furnace with the primary closest to the core. The first steel made in an induction furnace in

the United States was in 1907 in a Colby furnace near Philadelphia. The first induction

furnace for three –phase application was built in Germany in 1906 by Rochling-Rodenhauser.

Original designs were for single phase and even two phases were used on the three phase

furnace. The two basic designs of induction furnaces, the core type or channel furnace and

the coreless, are certainly not new to the industry. The channel furnace is useful for small

foundries with special requirements for large castings, especially if off-shift melting is

practiced. It is widely used for duplexing operations and installations where production

requirements demand a safe cushion of readily available molten metal. The coreless induction

furnace is used when a quick melt of one alloy is desirable, or it is necessary to vary alloys

frequently. The coreless furnace may be completely emptied and restarted easily, makes it

perfect for one-shift operations. Induction furnaces have increased in capacity to where

modern high-power-density induction furnaces are competing successfully with cupola

melting. There are fewer chemical reactions to manage in induction furnaces than in cupola

furnaces, making it easier to achieve melt composition. However, induction melting is

more sensitive to quality of charge materials when compared to cupola or electric arc furnace,

limiting the types of scrap that can be melted. The inherent induction stirring provides

excellent metal homogeneity. Induction melting produces a fraction of the fumes that result

from melting in an electric arc furnace (heavy metal fumes and particulate emissions) or

cupola (wide range of undesirable gaseous and particulate emissions as a result of

the less restrictive charge materials).

A new generation of industrial induction melting furnaces has been developed during the last

25 years. The development of flexible, constant power-tracking, medium-frequency induction

power supplies has resulted in the widespread use of the batch melting methods in modern

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foundries. These power units incorporate heavy duty silicon-controlled rectifiers that are able

to generate both the frequency and the amperage needed for batch melting and are able to

achieve electrical efficiency levels exceeding 97%, a substantial improvement over the

85% efficiency typical of induction power supplies of the 1970s. The new designs allow

maximum utilization of furnace power throughout the melting cycle with good control of

stirring .Some of the largest commercial units are capable of melting at nearly 60 tons per

hour and small furnaces with very high power densities of 700 to 1,000 kWh/ton can now

melt a cold charge in 30 to 35 minutes.

INDUCTION HEATING:

Induction heating is a form of non-contact heating for conductive materials.

The principle of induction heating is mainly based on two well-known physical phenomena:

1. Electromagnetic induction

2. The Joule effect

1) ELECTROMAGNETIC INDUCTION

The energy transfer to the object to be heated occurs by means of electromagnetic

induction. Any electrically conductive material placed in a variable magnetic field is the site

of induced electric currents, called eddy currents, which will eventually lead to joule heating.

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2) JOULE HEATING

Joule heating, also known as osmic heating and resistive heating, is the process by which the

passage of an electric current through a conductor releases heat.

The heat produced is proportional to the square of the current multiplied by the electrical

resistance of the wire.

Induction heating relies on the unique characteristics of radio frequency (RF) energy

- that portion of the electromagnetic spectrum below infrared and microwave energy.

Since heat is transferred to the product via electromagnetic waves, the part never

comes into direct contact with any flame, the inductor itself does not get hot and there

is no product contamination.

Induction heating is a rapid, clean, non-polluting heating. The induction coil is cool

to the touch; the heat that builds up in the coil is constantly cooled with circulating

water.

FEATURES OF INDUCTION FURNACE

An electric induction furnace requires an electric coil to produce the charge. This

heating coil is eventually replaced.

The crucible in which the metal is placed is made of stronger materials that can resist

the required heat, and the electric coil itself cooled by a water system so that it does

not overheat or melt.

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The induction furnace can range in size, from a small furnace used for very precise

alloys only about a kilogram in weight to a much larger furnaces made to mass

produce clean metal for many different applications.

The advantage of the induction furnace is a clean, energy-efficient and well-

controllable melting process compared to most other means of metal melting.

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 tonnes

capacity, and are used to melt iron and steel, copper, aluminium, and precious metals.

The one major drawback to induction furnace usage in a foundry is the lack of

refining capacity; charge materials must be clean of oxidation products and of a

known composition, and some alloying elements may be lost due to oxidation (and

must be re-added to the melt).

A. Domestic Steel Sector Scenario

1) Present Scenario : After 2 years of depressed market, the steel market has suddenly shown

Competitiveness. It is noted that induction-melting furnaces in various parts of the country

are at present operating to near capacity. However, the power is not supplied to the units

fully. Revolution is taking place to make steel in India by utilising various technologies. India

is therefore, emerging as a country with innovative idea to make steel, which is not followed

by other countries in the world. In the first decade of twenty first century, major existing

integrated steel plants will face a challenge in producing Long products from Induction

Furnaces in producing steel economically and efficiently.

The iron and steel sector has been experiencing a slowdown in the last few years. The major

reasons for the slow growth in the steel sector during the last few years include:-

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(a) Sluggish demand in the steel consuming sectors

(b) Overall economic slowdown in the country

(c) Lack of investment by Government/private sector in major infrastructure projects. sector

investment is yet to materialise in the core sectors of the economy. This has also contributed

to slowing down demand for steel.

(d) Cost escalation in the input materials for iron and steel.

In the national steel policy recently announced by the Govt. of India, it is expected

that FDI in the steel industry along with domestic investment will take place in large

integrated steel plants. So, all the focus and of the steel policy is on the Primary Steel Sector

while completely ignoring the Secondary Steel Sector.

Induction melting furnaces in India were first installed to make stainless steel from

imported SS Scrap. Butin years 81-82 some entrepreneurs, who were having small size

induction furnaces making stainless steel, experimented in making mild steel from steel

melting scrap, they succeeded. More firms in northern India produced steel (Pencil Ingots) by

using 500 kg to 1 tonne induction furnaces. The power consumption was found to be about

700 kWh/tonne, which was nearly 100 units less than EAFs. Bigger size Induction furnaces

were then installed first in North India and then in other states of India. By 1985-86, the

technology of making mild steel by Induction Furnace route was mastered by Indian

Technicians. Induction furnace manufacturers saw the potential and started manufacturing

bigger size/capacity furnaces. By 1988-89 period 3 tonne per charge induction furnaces were

installed (became standard) all over India. The chemistry of melt was adjusted by adding mill

scale, if opening carbon of bath was more. Good quality of steel melting scrap was used. In

1991-92, the Government license and control on steel making and rolling was removed. Then

more induction furnaces were installed all over India. The use of sponge iron made it possible

to adjust chemistry of melt. Thus good quality of Mild Steel pencil ingots are being produced

with no tramp elements.

2) Ferrous Scrap: The word “Ferrous” comes from the Latin word “Ferrum”. Most people

associate scrap with waste or rubbish. However, our Industry prefers to refer to ourselves as

“Recyclers”, who play a very important role, in not only feeding the Steel Industry but also

protecting the environment by converting waste into wealth for society.

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Indian Steel Mills mainly import Shredded or Heavy Melting grades only. HMS is nearly

65% of the imports.

3) Global Requirement For Scrap: With global steel production at 1 billion tonne mark,

merchant scrap requirement is estimated in the current year at 318 million tonnes. By the year

2010, requirement for merchant scrap is likely to go up to 388 million tonnes. As the GDP

grows in developing countries, the generation of merchant scrap will increase and additional

processing capacities and scrap yards will have to be installed to meet the demand for quality

scrap needed for the increasing steel demand.

INDUCTION ELECTRICAL SYSTEM CONFIGURATION:

Induction furnaces require two separate electrical systems: one for the cooling system,

furnace tilting and instrumentation, and the other for the induction coil power. A line to the

plant’s power distribution panel typically furnishes power for the pumps in the induction coil

cooling system, the hydraulic furnace tilting mechanism, and instrumentation and control

systems. Electricity for the induction coils is furnished from a three-phase, high voltage, high

amperage utility line. The complexity of the power supply connected to the induction coils

varies with the type of furnace and its use.

A channel furnace that holds and pours liquefied metal can operate efficiently using

mains frequency provided by the local utility. By contrast, most coreless furnaces for melting

require a medium to high frequency power supply. Raising the frequency of the alternating

current flowing through the induction coils increases the amount of power that can be applied

to a given size furnace. This, in turn, means faster melting. A 10 ton coreless furnace

operating at 60 Hz can melt its capacity in two hours. At 275 Hz, the same furnace can melt

the full 10 ton charge in 26 minutes, or four times faster. An added advantage of higher

frequency operation is that furnaces can be started using less bulky scrap and can be emptied

completely between heats. The transformers, inverters and capacitors needed to “tune” the

frequency required for high-efficiency induction furnaces can pose a serious electrical hazard.

For this reason, furnace power supplies are housed in key-locked steel enclosures, equipped

with safety interlocks.

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CONSTRUCTION AND WORKING

Current flowing in one direction in the induction coil induces a current flow in the opposite direction in the metal charge. This current heats the metal and causes it to melt

Combustion furnaces and induction furnaces produce heat in two entirely different

ways.In a combustion furnace, heat is created by burning a fuel such as coke, oil or natural

gas. The burning fuel brings the interior temperature of the furnace above the melting point of

the charge material placed inside. This heats the surface of the charge material, causing it to

melt.

Induction furnaces produce their heat cleanly, without combustion. Alternating

electric current from an induction power unit flows into a furnace and through a coil made of

hollow copper tubing. This creates an electromagnetic field that passes through the refractory

material and couples with conductive metal charge inside the furnace. This induces electric

current to flow inside the metal charge itself, producing heat that rapidly causes the metal to

melt. Although some furnace surfaces may become hot enough to present a burn hazard, with

induction, you heat the charge directly, not the furnace.

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Induction Electrical System Configurations:

Induction furnaces require two separate electrical systems: one for the cooling system,

furnace tilting and instrumentation, and the other for the induction coil power. A line to the

plant’s power distribution panel typically furnishes power for the pumps in the induction coil

cooling system, the hydraulic furnace tilting mechanism, and instrumentation and control

systems. Electricity for the induction coils is furnished from a three-phase, high voltage, high

amperage utility line. The complexity of the power supply connected to the induction coils

varies with the type of furnace and its use.

A channel furnace that holds and pours liquefied metal can operate efficiently using

mains frequency provided by the local utility. By contrast, most coreless furnaces for melting

require a medium to high frequency power supply. Raising the frequency of the alternating

current flowing through the induction coils increases the amount of power that can be applied

to a given size furnace. This, in turn, means faster melting. A 10 ton coreless furnace

operating at 60 Hz can melt its capacity in two hours. At 275 Hz, the same furnace can melt

the full 10 ton charge in 26 minutes, or four times faster. An added advantage of higher

frequency operation is that furnaces can be started using less bulky scrap and can be emptied

completely between heats. The transformers, inverters and capacitors needed to “tune” the

frequency required for high-efficiency induction furnaces can pose a serious electrical hazard.

For this reason, furnace power supplies are housed in key-locked steel enclosures, equipped

with safety interlocks.

A. Safety Implications:

Typically, the induction coil power supply and the other furnace systems are energized

from multiple electric services. This means that foundry workers cannot assume that the

power to the furnace coil has stopped because service has been interrupted to the furnace’s

cooling system or hydraulic pumps. Review the lock out/tag out section provided in this

safety guide.

B. Input And Output Parameters Of The Induction Furnaces:

In order to study the prevailing practices in steel plants using Induction Furnaces, the

following parameters have been identified as

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1) Raw Material: Induction Furnaces are using Steel melting scrap, Sponge Iron & Pig

Iron/Cast Irons. On an average the ratio of these items is 40% sponge Iron + 10% Cast Irons

or Pig Iron. The technology of melting these input materials varies according to the

availability of raw materials and location of the plant and inputs of sponge iron consumed is

as high as 85 % as charge mix on bigger furnaces.

2) Power Supply: An A.C.current from the transformer is fed to the rectifier of the furnaces

electronic circuit. This converts A.C. to D.C, voltage is smoothed out by a D.C. choke, and

then fed to the inverted section of the furnace. Here the D.C is converted to a high frequency

A.C. current and this is fed to the coil.

3) Refractory Lining: The material used for lining is crushed quarts. This is a high purity

silica material. The linings are of two types, acidic lining and basic lining.

4) Water: The cooling system is a through-one-way- flow system with the tubular copper

coils connected to water source through flexible rubber hoses. The inlet is from the top while

the outlet is at the bottom. The cooling process is important because the circuit of the furnace

appears resistive, and the real power is not only consumed in the charged material but also in

the resistance of the coil. This coil loss as well as the loss of heat conducted from the charge

through the refractory crucible requires the coil to be cooled with water as the cooling

medium to prevent undue temperature rise of the copper coils.

5) Molten Metal : The molten metal is the desired output of the Induction furnace. The

quantity depends upon the capacity of the furnace, and the quality depends upon the raw

material and alloy composition. The tapping temperature depends upon the type of steel, as

well as the distance of end use of the molten metal.

6) Waste Heat: The surface of the molten metal bath is exposed to atmosphere. This results in

the major thermal energy loss through radiation. The Coils of furnace are water cooled this

also results in heat loss.

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7) Slag : During the operation of electric induction melting furnaces, non metallics are

produced from the various sources described earlier. Depending on the specific process being

used and the type of iron or steel being melted, the composition of the slag will vary.

8) Slag Composition: The composition of furnace and ladle slags is often very complex. The

slags that form in electric furnace melting are the results of complex reactions between silica

(adhering sand on casting returns or dirt), iron oxide from steel scrap, other oxidation by

products from melting, and reactions with refractory linings. The resulting slag will thus

consist of a complex liquid phase of oxides of iron, manganese, magnesium and silicon,

silicates and sulphides plus a host of other compounds, which may include alumina, calcium

oxides and sulphides, rare earth oxides and sulphides and spinel’s and fosterites.

ADVANTAGES OF INDUCTION FURNACE:

Induction furnaces offer certain advantages over other furnace systems. They include:

Higher Yield. The absence of combustion sources reduces oxidation losses that can be

significant in production economics.

Faster Start-up. Full power from the power supply is available, instantaneously, thus

reducing the time to reach working temperature. Cold charge-to-tap times of one to two hours

are common.

Flexibility. No molten metal is necessary to start medium frequency coreless induction

melting equipment. This facilitates repeated cold starting and frequent alloy changes.

Natural Stirring. Medium frequency units can give a strong stirring action resulting in a

homogeneous melt.

Cleaner Melting. No by-products of combustion means a cleaner melting environment and

no associated products of combustion pollution control systems.

Compact Installation. High melting rates can be obtained from small furnaces.

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Reduced Refractory. The compact size in relation to melting rate means induction furnaces

require much less refractory than fuel-fired units

Better Working Environment. Induction furnaces are much quieter than gas furnaces, arc

furnaces, or cupolas. No combustion gas is present and waste heat is minimized.

Energy Conservation. Overall energy efficiency in induction melting ranges

from 55 to 75 percent, and is significantly better than combustion processes.

DISADVANTAGES OF INDUCTION FURNACE

1. Refining in Induction Furnace is not as intensive or effective as in Electric Arc Furnace

(EAF).

2. Life of Refractory lining is low as compared to EAF.

3. Removal of S & P is limited, so selection of charges with less impurity is required.

TYPES OF INDUCTION FURNACE

CORELESS INDUCTION FURNACE

CHANNEL INDUCTION FURNACE

a) Coreless Induction Furnaces:

The coreless induction furnace is a refractory lined vessel with electrical current carrying

coils surrounding the refractory crucible. A metallic charge consisting of scrap, pig iron and

ferroalloys are typically melted in this vessel.

b) Channel Furnaces :

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In a channel furnace, induction heating takes place in the “channel,” a relatively small and

narrow area at the bottom of the main bath. The channel passes through a laminated steel core

and around the coil assembly.

CORELESS INDUCTION FURNACE:

A coreless induction furnace is actually an energy transfer device where energy is

transferred directly from an induction coil into the material to be melted through the

electromagnetic field produced by the induction coil.

The coreless induction furnace consists basically of a crucible, inductor coil, shell,

cooling system and tilting mechanism. The crucible is formed from refractory material,

which the furnace coil is lined with. This crucible holds the charge material and subsequently

the melt. The choice of refractory material depends on the type of charge, i.e. acidic, basic or

neutral. The durability of the crucible depends on the grain size, ramming technique, charge

analysis and rate of heating and cooling the furnace .

Principles are:

26

The principle of induction heating is based on the following two laws:

1. Electromagnetic induction

2. The joule effect

The high frequency induction furnaces use the heat produced by eddy currents generated

by a high frequency alternating field. The inductor is usually made of copper in order to limit

the electric losses. Nevertheless, the inductor is in almost all cases internally water-cooled.

The furnace consists of a crucible made of a suitable refractory material surrounded by a

water cooled copper coil. In this furnace type, the charge is melted by heat generated from an

electric arc. The coil carries the high frequency current of 500 to 2000 Hz.

The alternating magnetic field produced by the high frequency current induces powerful

eddy currents in the charge resulting in very fast heating. Various configurations are

available, with two or three electrodes high melting capacity (25 to 50 tons/hr) and they are

used primarily for casting steel.

These currents also provide certain amount of agitation to the melting charge resulting in

efficient mixing. Molten metal can be poured by tilting the furnace.

Advantages:

• Induction furnace does not need electrodes like electric arc furnace.

• Better control of temperature

• Better control of composition of the melt

Disadvantages:

• An induction installation usually implies a big investment that must be considered and

compared to alternative heating techniques.

• Induction heating is preferably used for heating relatively simple shapes.

27

Materials to be casted:

• Steel

• Steel alloys

CHANNEL INDUCTION FURNACE;

The channel induction furnace consists of a refractory lined steel shell which contains

the molten metal. Attached to the steel shell and connected by a throat is an induction

unit which forms the melting component of the furnace.

The induction unit consists of an iron core in the form of a ring around which a

primary induction coil is wound.

This assembly forms a simple transformer in which the molten metal loops comprises

the secondary component.

The heat generated within the loop causes the metal to circulate into the main well of

the furnace.

The circulation of the molten metal effects a useful stirring action in the melt.

Channel induction furnaces are commonly used for melting low melting point alloys

and or as a holding and superheating unit for higher melting point alloys such as cast

iron.

2.CUPOLA FURNACE

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For many years, the cupola was the primary method of melting used in iron foundries.

The cupola furnace has several unique characteristics which are responsible for its

widespread use as a melting unit for cast iron.

Cupola furnace is employed for melting scrap metal or pig iron for production of

various cast irons. It is also used for production of nodular and malleable cast iron. It

is available in good varying sizes. The main considerations in selection of cupolas are

melting capacity, diameter of shell without lining or with lining, spark arrester.

Shape

A typical cupola melting furnace consists of a water-cooled vertical cylinder which is lined

with refractory material.

Construction

29

The construction of a conventional cupola consists of a vertical steel shell which is

lined with a refractory brick.

The charge is introduced into the furnace body by means of an opening approximately

half way up the vertical shaft.

The charge consists of alternate layers of the metal to be melted, coke fuel and

limestone flux.

The fuel is burnt in air which is introduced through tuyeres positioned above the

hearth. The hot gases generated in the lower part of the shaft ascend and preheat the

descending charge.

Various Zones of Cupola Furnace

Various numbers of chemical reactions take place in different zones of cupola. The

construction and different zones of cupola are :

1. Well

The space between the bottom of the tuyeres and the sand bed inside the cylindrical shell

of the cupola is called as well of the cupola. As the melting occurs, the molten metal is get

collected in this portion before tapping out.

2. Combustion zone

The combustion zone of Cupola is also called as oxidizing zone. It is located between the

upper of the tuyeres and a theoretical level above it. The total height of this zone is normally

from 15 cm. to 30 cm. The combustion actually takes place in this zone by consuming the

free oxygen completely from the air blast and generating tremendous heat. The heat

generated in this zone is sufficient enough to meet the requirements of other zones of cupola.

The heat is further evolved also due to oxidation of silicon and manganese. A temperature of

about 1540°C to 1870°C is achieved in this zone. Few exothermic reactions takes place in

this zone these are represented as:

C + O2 → CO2 + Heat

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Si + O2 → SiO2 + Heat

2Mn + O2 → 2MnO + Heat

3. Reducing zone

Reducing zone of Cupola is also known as the protective zone which is located between

the upper level of the combustion zone and the upper level of the coke bed. In this zone, CO2

is changed to CO through an endothermic reaction, as a result of which the temperature falls

from combustion zone temperature to about 1200°C at the top of this zone. The important

chemical reaction takes place in this zone which is given as under.

CO2 + C (coke) → 2CO + Heat

Nitrogen does not participate in the chemical reaction occurring in his zone as it is also the

other main constituent of the upward moving hot gases. Because of the reducing atmosphere

in this zone, the charge is protected against oxidation.

4. Melting zone

The lower layer of metal charge above the lower layer of coke bed is termed as melting

zone of Cupola. The metal charge starts melting in this zone and trickles down through coke

bed and gets collected in the well. Sufficient carbon content picked by the molten metal in

this zone is represented by the chemical reaction given as under.

3Fe + 2CO → Fe3C + CO2

5. Preheating zone

Preheating zone starts from the upper end of the melting zone and continues

up to the bottom level of the charging door. This zone contains a number of alternate

layers of coke bed, flux and metal charge. The main objective of this zone is to

preheat the charges from room temperature to about 1090°C before entering the metal

31

charge to the melting zone. The preheating takes place in this zone due to the upward

movement of hot gases. During the preheating process, the metal charge in solid form

picks up some sulphur content in this zone.

6. Stack

The empty portion of cupola above the preheating zone is called as stack. It provides the

passage to hot gases to go to atmosphere from the cupola furnace.

Charging of Cupola Furnace

Before the blower is started, the furnace is uniformly pre-heated and the metal and

coke charges, lying in alternate layers, are sufficiently heated up.

The cover plates are positioned suitably and the blower is started.

The height of coke charge in the cupola in each layer varies generally from 10 to 15

cms. The requirement of flux to the metal charge depends upon the quality of the

charged metal and scarp, the composition of the coke and the amount of ash content

present in the coke.

Working of Cupola Furnace

32

The charge, consisting of metal, alloying ingredients, limestone, and coal coke for

fuel and carbonization (8-16% of the metal charge), is fed in alternating layers

through an opening in the cylinder.

Air enters the bottom through tuyeres extending a short distance into the interior of

the cylinder. The air inflow often contains enhanced oxygen levels.

Coke is consumed. The hot exhaust gases rise up through the charge, preheating it.

This increases the energy efficiency of the furnace. The charge drops and is melted.

33

Although air is fed into the furnace, the environment is a reducing one. Burning of

coke under reducing conditions raises the carbon content of the metal charge to the

casting specifications.

As the material is consumed, additional charges can be added to the furnace.

A continuous flow of iron emerges from the bottom of the furnace.

Depending on the size of the furnace, the flow rate can be as high as 100 tones per

hour. At the metal melts it is refined to some extent, which removes contaminants.

This makes this process more suitable than electric furnaces for dirty charges.

A hole higher than the tap allows slag to be drawn off.

The exhaust gases emerge from the top of the cupola. Emission control technology is

used to treat the emissions to meet environmental standards.

Hinged doors at the bottom allow the furnace to be emptied when not in use.

Type of Molten Metal

Cupola is employed for melting scrap metals or (over 90 %) of the pig iron used in the

production of iron castings.

Gray Cast iron, nodular cast iron, some malleable iron castings and some copper base

alloys can be produced by Cupola Furnace.

Heat Energy Source

34

The cupola is a tubular furnace which produces cast iron by melting scrap and alloys

using the energy generated from the oxidation (combustion) of coke, a coal derivative.

Advantages

It is simple and economical to operate.

A cupola is capable of accepting a wide range of materials without reducing melt

quality. Dirty, oily scrap can be melted as well as a wide range of steel and iron. They

therefore play an important role in the metal recycling industry

Cupolas can refine the metal charge, removing impurities out of the slag.

From a life-cycle perspective, cupolas are more efficient and less harmful to the

environment than electric furnaces. This is because they derive energy directly from

coke rather than from electricity that first has to be generated.

The continuous rather than batch process suits the demands of a repetition foundry.

Cupolas can be used to reuse foundry by-products and to destroy other pollutants such

as VOC from the core-making area.

High melt rates

Ease of operation

Adequate temperature control

Chemical composition control

Efficiency of cupola varies from 30 to 50%.

Less floor space requirements comparing with those furnaces with same capacity.

Limitations

Since molten iron and coke are in contact with each other, certain elements like si, Mn

are lost and others like sulphur are picked up. This changes the final analysis of

molten metal.

Close temperature control is difficult to maintain

35

3. OPEN HEARTH FURNACE

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 owing to its high melting point, normal fuels and furnaces were insufficient and

the open hearth furnace was developed to overcome this difficulty.

In 1865, the French engineer Pierre-Émile Martin took out a license from Siemens and first

applied his regenerative furnace for making steel. Their process was known as the Siemens-

Martin process, and the furnace as an "open-hearth" furnace. Most open hearth furnaces were

closed by the early 1990s, not least because of their slow operation, being replaced by

the basic oxygen furnace or electric arc furnace.

While arguably the first primitive open hearth furnace was the Catalan forge, invented in

Spain in the eighth century, but it is usual to confine the term to certain nineteenth century

and later steelmaking processes, thus excluding bloomeries (including the Catalan

forge), finery forges, and puddling furnaces from its application.

Open hearth working

36

A. gas and air enter

B. pre-heated chamber

C. molten pig iron

D. Hearth

E. heating chamber (cold)

F. gas and air exit.

The open hearth process is batch process and a batch is called a "heat". The furnace is

first inspected for possible damage. 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.

The process is far slower than that of Bessemer converter and thus easier to control and take

samples for quality control. 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

37

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.

4. ELECTRICAL FURNACE

Electric arc furnaces (EAF) are often used in large steel foundries and steel mills. The metal is

charged into the furnace, with additives to make recovery of slag easier, and heat to melt the metal is

produced with an electric arc from three carbon or graphite electrodes. The electric arc furnace is

lined with refractories which slowly decompose and are removed with slag. Electric arc furnaces also

usually employ air emissions equipment to capture most air pollution . Furnace operations are

discussed in detail below.

Furnace Operations

The electric arc furnace operates as a batch melting process producing batches of molten steel known

as "heats". The electric arc furnace operating cycle is called the tap-to-tap cycle and is made up of the

following operations:

Furnace Charging

The first step in the production of any heat is to select the grade of steel to be made. Preparation of the

charge bucket is an important operation, not only to ensure proper melt-in chemistry but also to ensure

good melting conditions. The scrap must be layered in the bucket according to size and density to

promote the rapid formation of a liquid pool of steel in the hearth while providing protection for the

sidewalls and roof from electric arc radiation. Other considerations include minimization of scrap

cave-ins which can break electrodes and ensuring that large heavy pieces of scrap do not lie directly in

front of burner ports which would result in blow-back of the flame onto the water cooled panels. The

charge can include lime and carbon or these can be injected into the furnace during the heat. Many

operations add some lime and carbon in the scrap bucket and supplement this with injection.

38

The roof and electrodes are raised and are swung to the side of the furnace to allow the

scrap charging crane to move a full bucket of scrap into place over the furnace. The

bucket bottom is usually a clam shell design i.e., the bucket opens up by retracting two

segments on the bottom of the bucket. The scrap falls into the furnace and the scrap

crane removes the scrap bucket. The roof and electrodes swing back into place over the

furnace. The roof is lowered and then the electrodes are lowered to strike an arc on the

scrap. This commences the melting portion of the cycle. The number of charge buckets

of scrap required to produce a heat of steel is dependent primarily on the volume of the

furnace and the scrap density. Most modern furnaces are designed to operate with a

minimum of back-charges. This is advantageous because charging is a dead-time where

the furnace does not have power on and therefore is not melting. Minimizing these

dead-times helps to maximize the productivity of the furnace. In addition, energy is lost

every time the furnace roof is opened.

Melting

The melting period is the heart of EAF operations. Melting is accomplished by

supplying energy to the furnace interior. This energy can be electrical or chemical. Electrical

energy is supplied via the graphite electrodes and is usually the largest contributor in melting

operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the

scrap. Usually, light scrap is placed on top of the

Principle of Metal Casting

39

charge to accelerate bore-in. Approximately 15 % of the scrap is melted during the

initial bore-in period. After a few minutes, the electrodes will have penetrated the scrap

sufficiently so that a long arc (high voltage) tap can be used without fear of radiation

damage to the roof. The long arc maximizes the transfer of power to the scrap and a

liquid pool of metal will form in the furnace hearth. At the start of melting the arc is

erratic and unstable. Wide swings in current are observed accompanied by rapid

movement of the electrodes. As the furnace atmosphere heats up the arc stabilizes and

once the molten pool is formed, the arc becomes quite stable and the average power

input increases.

Chemical energy is supplied via several sources including oxy-fuel burners and oxygen

lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxygen and air.

Heat is transferred to the scrap by flame radiation and convection by the hot products of

combustion. Heat is transferred within the scrap by conduction. Large pieces of scrap

take longer to melt into the bath than smaller pieces. In some operations, oxygen is

injected via a consumable pipe lance to “cut” the scrap. The oxygen reacts with the hot

scrap and burns iron to produce intense heat for cutting the scrap. Once a molten pool

of steel is generated in the furnace, oxygen can be lanced directly into the bath. This

oxygen will react with several components in the bath including, aluminum, silicon,

manganese, phosphorus, carbon and iron. All of these reactions are exothermic (i.e.,

they generate heat) and supply additional energy to aid in the melting of the scrap. The

metallic oxides that are formed will end up in the slag. The reaction of oxygen with

carbon in the bath produces carbon monoxide, which either burns in the furnace if there

is sufficient oxygen, and/or is exhausted through the direct evacuation system where it

is burned and conveyed to the pollution control system.

Refining

Refining operations in the electric arc furnace have traditionally involved the removal

of phosphorus, sulphur, aluminum, silicon, manganese and carbon from the steel. In

recent times, dissolved gases, especially hydrogen and nitrogen, have been recognized

as a concern. Traditionally, refining operations were carried out following meltdown

i.e., once a flat bath was achieved. These refining reactions are all dependent on the

availability of oxygen. Oxygen was lanced at the end of meltdown to lower the bath

carbon content to the desired level for tapping. Most of the compounds which are to be

removed during refining have a higher affinity for oxygen than the carbon. Thus the

40

oxygen will preferentially react with these elements to form oxides which float out of

the steel and into the slag.

In modern EAF operations, especially those operating with a "hot heel" of molten steel

and slag retained from the prior heat, oxygen may be blown into the bath throughout

most of the heat. As a result, some of the melting and refining operations occur

simultaneously.

Phosphorus and sulphur occur normally in the furnace charge in higher concentrations than

are generally permitted in steel and must be removed. Unfortunately the conditions

favourable for removing phosphorus are the opposite of those promoting the removal of

sulphur. Phosphorus removal is usually carried out as early as possible in the heat. Hot heel

practice is very beneficial for phosphorus removal because oxygen can be lanced into the

bath while its temperature is quite low. Early in the heat the slag will contain high FeO levels

carried over from the previous heat thus aiding in phosphorus removal. High slag basicity

(i.e., high lime content) is also beneficial for phosphorus removal but care must be taken not

to saturate the slag with lime. This will lead to an increase in slag viscosity, which will make

the slag less effective. Sometimes fluorspar is added to help fluidize the slag. Stirring the bath

with inert gas like argon is also beneficial because it renews the slag/metal interface thus

improving the reaction kinetics.

FURNACE ATMOSPHERE

The surrounding in the thermal enclosure (furnace) is termed atmosphere. The atmosphere

consists of gases and is usually air. However, in some heat treatment, thermo‐mechanical

processing, sintering etc special type of atmosphere is required to

Prevent oxide formation, if the heating material is prone to oxidation.

Decarburize steel.

Control the surface chemistry of steel which means the elements must not be oxidized

or reduced during heating.

Produce “blueing” effect in steel. The blueing effect imparts a wear‐resistant and

oxidation‐ resistant surface finish.

41

reduce oxides formed on the surface.

Make the surface hard by allowing carburizing or nitriding.

PROTECTIVE ATMOSPHERE APPLICATION

Composition(vol%)

42

Atmosphere Lean exothermic

N2 86.8

CO2 10.5

CO 1.5

H2 1.2

CH4 Dew point 4.5

Applications. Bright annealing of Cu, sintering of ferrites

Rich exothermic

71.5 5.0 10.5 12.5 5 10 Bright annealing low C steel, silicon steels/Cu brazing, sintering

Dissociated NH3

25 ‐ ‐ 75 ‐ 50 to ‐+60

Brazing sintering bright annealing

Endothermic 40 45‐ 0 0.5 ‐ 20 34 40‐ 0.51 10 to ‐+10

Hardening, carburizing with CH4, sintering brazing

Nitrogen H2

99.9 99.9 ‐60 ‐ 68 Natural for annealing

Reducing, sintering

Ar or He : These are pure and inert gases and are used to prevent oxidation during welding

of stainless steel , aluminum etc. and heat treatment of special steels.

ATMOSPHERE VOLUME REQUIREMENTS It depends on

43

Type and size of furnace

Environment and presence of draft

The nature and size of work pieces

Metallurgical process involve

Presence or absence of curtains at entrance and exit

44

APPLICATION FOR INDUCTION FURNACE

Induction heating is used for an ever-widening range of industrial and scientific

applications: material joining processes such as brazing, soldering and curing; material

processes applications including hardening, forging, annealing and melting; and component

assembly applications such as epoxy bonding and heat staking metal into plastic. Our

engineers have also applied the technology for catheter tipping, hot heading and other

component manufacturing processes.

1. Annealing

Annealing and tempering are used to soften metal for improved ductility and

machinability, as well as to relieve residual stress. In contrast to hardening, annealing

involves a much slower heating step followed by gradual cooling of the metal. Tempering

refers to a reheating and slow cooling of metal which has become too brittle as a result of a

hardening process.

2. Bonding

Flexible, epoxy-based gaskets can be bonded to metal or other conductive material

without a third bonding agent. Our Epoxy Bonding Systems are ideal for this application.

Induction heating has been used for bonding gaskets to metal automotive parts, thermoplastic

composite bonding, and rubber washer/bumper assemblies.

3. Brazing

45

Brazing is the process of joining two or more pieces of metal or ceramic material with a

molten filler metal such as silver, aluminum alloy or copper. Brazing requires a higher

temperature than soldering but produces a very strong bond which withstands shock,

vibration and temperature change. Brazing in a controlled vacuum or in an inert protective

atmosphere can significantly improve overall part quality and eliminate costly part cleaning

procedures. Please visit The Brazing Guide section of our website for in-depth information

about brazing processes, materials, filler metals and equipment.

4. Forging and Hot Forming

Industrial forging and hot forming processes involve bending or shaping a metal billet or

bloom after it has been heated to a temperature at which its resistance to deformation is weak.

Blocks of non-ferrous materials can also be used.

5. Fusing Nickel-Based Alloys to Steel

This application involves heating a steel boiler tube assembly to fuse a nickel-based, hard-

surfacing alloy which has been applied as a spray. The tube is coated with the alloy to

provide corrosion resistance during use; wear-resistant nickel alloys are applied to new parts

where wear or corrosion is anticipated, or to worn parts to replace metal lost through wear.

6. Hardening Steel

Steel hardening consists of heating the material to a temperature over 723ºC (austenitic

temperature) and then cooling the steel quickly, often with a quench of industrial water. The

aim is to transform the structure of the steek in order to increase its hardness, its yield

46

strength, and its breaking tension. The steels that are normally hardened with induction

heating contain from 0.3% to 0.7% carbon.

7. Heat Staking

When one piece of metal is designed to be inserted into a second piece, induction heating

can be used to "shrink fit" the two pieces together. The first or larger piece containing the

opening is heated to expand the size of the hole. The second piece is then inserted into the

opening, and as the first piece cools and shrinks back to its original size, the resulting

pressure holds the two pieces together in a strong bond.

8. Heat Setting

This medical application involves heating nitinol stents to set

proper size. The stents are slid over a correctly-sized mandrel, to which

induction heating is then applied. Precise temperature control is

required for this process.

9. Melting

Hard metals can be melted with an induction heating furnace. The metal is placed on a

non-conductive crucible; when induction heating power is applied, the eddy currents

circulating within the metal effectively stir the molten mass as it melts. Very high quality,

uniform melting can be achieved with precious metals, high quality steels and non-ferrous

alloys.

10. Pre-Tinning

Induction heating can be used to quickly pre-tin solder paste in a copper electrical

connector. With the right combination of induction coil and temperature, the solder paste can

be melted within 10 seconds.

47

11. Soldering/Desoldering

Induction soldering is similar to induction brazing, but soldering is done at a lower

temperature and the bond strength is not quite as high. One unusual application involves

desoldering and removing a stainless steel lid which had previously been soldered to a

stainless steel box.

12. Susceptor Heating

A susceptor is a conductive metal material that is used to transfer heat to another

piece of metal or non-conductive material. Susceptors are often made from graphite

because it is highly resistive and very machinable, or alternatively from stainless steel,

aluminum, or other materials.

13. Pre-Heating for Welding

Induction heating can be used very effectively to preheat conductive materials for

forging, welding, hot forming and hot heading. For example, the tips of turbine engine blades

can be placed in a specially designed induction coil and heated to the desired temperature for

welding repairs. The induction preheating step improves cycle time and reduces stress on

the rest of the blade.

48

DESIGN ANALYSIS

49

LOAD APPLIED

DISPLACEMENT

50

MESHING

RESULT OF APPLIED LOAD

51

ELECTROMAGNETIC & THERMAL ANALYSIS

MESHEING

52

ELECTROMAGNETISATION

HEAT GENERATION

53

JOULE HEAT GENERATION

MAGNETIC FLUX GENERATION

54

55

PRODUCTION DRAWING

56

57

58

59

60

61

PHOTOGRAPHY

62

Assembly

Crucible

63

CONCLUSIONS

Transient Thermal analysis of mock-up induction furnace is

being carried out in this study which is highly important for

operation and control of the process.

Preliminary model : it will aid in improving the design.

The studies reveal that Aluminium -liner is effective in reducing

the electromagnetic coupling between the coil and the vessel

and thus prevents vessel from getting heated up by this effect.

The coil temperatures are above the acceptable temperature of

copper material, hence different cooling technique is to be

adopted.

These results will be compared with the experimental results

which will be obtained during the operation of mock up facility.

64

REFERENCES

[1] E. J. Davies and P. G. Simpson, Induction Heating Handbook. Maidenhead, U.K.:

McGraw-Hill, 1979.

[2] D. A. Lazor, "Induction Related Considerations in Investment Casting", Modern

Investment Casting Technical Seminar, pp 1-14, Pittsburg USA, March 27-29, 2001.

[3] K.C. Bala, "Design Analysis of an Electric Induction Furnace for Melting Aluminum

Scrap", AU Journal of Technology, vol(9), No(2):, pp83-88, Oct. 2005.

[4] P. Dorland, J.D. Wyk, and O.H. Stielau, "On the Influence of Coil Design and

Electromagnetic Configuration on the Efficiency of an Induction Melting Furnace", IEEE

Trans on IA, Vol. 36, No. 4, July/Aug. 2000.

[5] J. Lee, S. K. Lim, K. Nam and D. Choi, "Design Method of an Optimal Induction Heater

Capacitance for Maximum Power Dissipation and Minimum Power Loss Caused by

ESR", 11th IFAC Symposium on automation in Mining, Mineral and Metal processing,

Nancy, France, September 2004.

[6] A. K. Sawheny, A Course in Electrical Machine Design, J.C. Kapoor, 1981.

[7] Lloyed H. Dixon, Jr. "Eddy Current Losses in Transformer Winding and Circuit Wiring",

Texas Instruments Incorporated, 2003.

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