Induction Furnace

Table of Contents 1. Introduction 2. Induction Furnace 2.1

Induction Furnace Diagram

3. Furnace Making 4. Hydraulic System 5. Magnetic Shielding & Analysis of an Induction Furnace 6. Final Product 7. Induction Heating 8. Induction Heating Requirements 8.1

Series resonant tank circuit

8.2

Parallel resonant tank circuit

9. The LCLR work coil 10. Water Treatment Unit 10.1

Water Purification

10.2

Water Cooling Tower

12. Chemical Lab 13. Recommendations 14. References 15. Glossary

1. Introduction

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 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.

2. INDUCTION FURNACE

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. 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.

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.

2.1 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 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.

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.

4. 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.

5. MAGNETIC SHIELDING & ANALYSIS OF AN INDUCTION FURNACE 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. 5.1 Comparison Between With and Without Core Furnace

Fig.5.2 Induction Furnace With Iron Core

6. FINAL PRODUCT

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.

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. The eddy currents heat up the conductor according to the Joule effect.

Fig.7.2 Induction of Eddy Currents

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 zerocurrent-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 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

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.

10. Water Treatment Unit

Water is essential component as it helps to regulate the temperature in the plant. Water Cooling The main purpose of the water cooling Unit is to make the hot water colder and pass it on.

Fig.10.1 Water Cooling Tower

10.1 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 opencircuit 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.

Fig.10.2.1 Cooling Tower Design

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 naturaldraft 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.

Fig10.2.2 Water Cooling Tower

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.

Chemical tests are done 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. Steel Melting Shop (SMS): In the SMS plant the material is melted in an Electric Arc Furnace. The slag is removed automatically in the Arc furnace to achieve precision control of chemistry of the molten metal. The hot molten metal is checked for its chemical composition. Depending upon the composition required, various ferroalloys are added to it. The molten steel with requisite chemical composition from Electric Arc Furnace is sent to the continuous casting unit for casting billet. Continuous Casting Machine (CCM): The billets thus produced are first visually inspected for the surface condition and then tested for its chemical composition. If any surface discontinuity is observed in the material it is then sent to SMS unit for recycling. The tested billet is then sent to the Rolling Mill raw material yard with a proper batch number. Rolling Mill: The Billets are then taken for production in the Rolling Mill. During the production process, inspection is done at various stages. The non-conforming products are identified and segregated properly for recycling. The finished product is then subjected to final inspection (visual inspection & physical property) and a Lot Number is allotted to it before being stored in the finished product yard.

13. TYPES OF INDUCTION FURNACE