Electric induction furnaces are the highly used
furnaces for melting iron and non ferrous alloys. As compared to other
cupola furnaces, these furnaces are pollution free and have outstanding
metallurgical control. They are available in capacity ranging from a few
kilograms to 75 tonnes.
Principle :
Firstly the high voltage is passed in the primary coil, which induces
low voltage and high current across the metal charge which acts as a
secondary coil. Due to electrical resistance, electrical energy is
converted into heat which fuses the charge. Once the metal is in its
molten state the magnetic field yields a stirring motion. The stirring
rate is determined by the applicable power and frequency. This rate is
controlled to lower the temperature gradients in the charge and to
assure entire melting of charge and adequate mixing of alloy and fluxing
materials. On the other side, excess stirring can raise lining damage,
oxidation of the alloys, high amount of slag, inclusions and gas
pick-up.
Types :
The two most common electric induction furnaces are :
- Coreless furnace: In this furnace, the refractory-lined
crucible is entirely surrounded by a water-cooled copper coil which
deters the primary coil from overheating. These furnaces are
available in the range of 5 tonnes to 10 tonnes.
- Channel furnace: Also used as holding furnace, in channel
furnace, the coil is surrounded by an inductor. This furnace can
have a capacity of over 200 tonnes.
Usage :
Electric induction furnaces are available in varied sizes. Efficient as
well as durable, these furnaces are capable to melt a vast range of
metals, still little refining of the metal is possible. Due to reduced
refractory wear, the operating costs of them are very less. The melting
time of metal is very small thus metal is delivered at small and regular
intervals. Along with ease of simplicity, they need very small
quantities of metal composition which can be easily melted in very less
time. Around 60% of the energy supplied to the furnace is transferred to
the charge. The efficiency of an induction furnace installation is
determined by the ratio of the load useful power to the input power
drawn from the utility. The overall fuel consumption in the furnace is
over 2000 kWh/ tonne.
Electric
induction furnaces require much better cleaner scrap as compared to
other furnaces.
The
start up and capital costs are higher.
Approximately
30% of the energy is lost to the cooling water, 7% is lost from
radiation and convection losses and the remainder is
lost in the
furnace electrical system.
Electricity
has to be regenerated for achieving high utilization factors and energy
consumption.
The
efficiency is around 40%.
Electric
Induction Furnaces
