Here is an experiment on ‘Induction Furnace’ especially written for school and college students.
Aim of the Experiment:
Study of Induction furnace.
Objective:
The students may be familiar to study of induction furnace by visiting an industry.
Material Required:
High frequency induction furnace, raw scraps material, high frequency ac source.
Theory:
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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 around which water cooled magnetic coils are wound. The advantage of the induction furnace is 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 lot 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 etc. The one major drawback to induction furnace usage in a foundry is the lack of refining capacity; change material must be clean of oxidation products and of a known composition.
Operating frequency range from 50 or 60 Hz to 10 KHz, usually depending on the material being melted, the capacity of the furnace and melting- speed required. A higher frequency furnace is usually faster to melt a charge. A lower frequency generates more turbulence in the metal, reducing the power that can be applied to the melt.
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The furnace contains crucible surrounded by a water-cooled coil. The coil represents the primary to which a high frequency current of 1000 Hz or higher is supplied by electronic solid state converter. By induction, the secondary called eddy currents are produced in the crucible charge. The flow of these currents is motivated by potential difference between the various parts of charge. Resistivity of metal causes current losses, which are dissipated into heat energy thereby melting the metal. In case of ferrous metals, in which, the loss due to hysteresis produces extra heat. Vary temperatures can be obtained by this method of melting.
Induction furnaces are two types, viz. cored and coreless. The cored furnace carries an induction coil, which is immersed within the metal bath and acts as core for the eddy currents to flow. The electromagnetic induction effect causes the liquid metal to move through the channel around the coil and simultaneously secondary currents, which cause heating, are induced in the liquid metal around the core. The core furnace is largely used for melting non-ferrous metals on a relatively long run basis.
Coreless induction furnaces, on the other hand, do not have any induction coil or core and secondary currents or eddy currents are induced in the charge itself by electromagnetic induction. Such furnaces are designed particularly for ferrous metals.
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Induction furnaces are built in capacities varying 100 kg to 30 tonnes, though, for foundry use, a capacity in the range of 1 tonne to 5 tonnes is found most suitable. The present trend in cast iron and alloy cast iron melting is more and more towards the use of induction melting. The approximate power consumption of these furnaces is about 650-750 kWh per tonne of metal induction furnaces have largely been of the high frequency type, the frequency of current ranging as high as 100,000 Hz. However, medium frequency or main frequency induction furnaces, which have proved ideal for melting. Cast irons have also come in use they work efficiently and melt rapidly is a small quantity of molten left in the furnace after tapping. Stirring action is also better in these furnaces.
In order to melt 1350 kg steel power supply of 600 kW, 300 Hz is required.
An operating induction furnace usually emits a hum or whine the pitch of can be used by operators to identity weather the furnace is operating correctly.
Melting Procedure for High Frequency Induction Furnace:
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Procedure:
1. Take the charge for melting from a specially selected scrap and suitable alloy additions so as to give the required composition.
2. The scrap is charged into the furnace with plate scrap at the bottom.
3. As the steel melts, a pool of molten metal forms at the bottom of the furnace, and the remaining charge in the upper portion slips down into it until all of it is melted.
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4. Add extra scrap, as the melting proceeds fill the required metal temperature is reached.
5. The power is then switched off and alloys are added to adjust the composition of the metal.
6. Now finally deoxidizers i.e., ferro silicon are then added with the help of ladle.
7. When the alloy additions have been absorbed by the metal and the reactions are complete, a small amount of slag produced is removed.
8. The metal is then tapped into ladle by tilting the furnace.
Precautions:
1. Keep the furnace full as for as practicable
2. Avoid rusty, ocly scrap
3. Minimize slagging
4. Minimum periods of no power
5. Avoid heat wastage.