Direct Arc Furnace
In direct arc furnace, arc is struck between the electrodes and charge.
When the arc is struck between the electrodes, the current passes through the charge.
This current produces heat as I2Rt joules.
H = I2Rt joules.
I —> Current flowing through charge in Amperes.
R —> Resistance of charge in ohms.
t —> Time in seconds.
Construction of direct arc furnace is simple. It consists of arc chamber with refractory lining.
Total structure of furnace is on the basis of steel frame work, Carbon or graphite electrodes are used.
Arc is maintained due to ionisation of air. Ionised air acts as current carrying conductor.
Current passing through the charge causes heating of the charge.
Application of direct arc furnace is in the production or steel.
The steel obtained by this method is more pure than other methods.
Indirect Arc Furnace
In indirect arc furnace single phase A.C, supply is applied across the graphite electrodes.
The arc is struck by separating the electrodes manually or automatically,
The heat is transferred to the charge top layer and refractory lining through radiation and from top layer of charge to other portion of charge through conduction.
The charge is uniformly heated by rocking arrangement (stirring arrangement).
This type of furnace has two electrodes and capacity of furnace is limited upto 3 tonnes.
The power factor is about O.85 lagging and power consumption of the furnace is about 400 kWh per tonne.
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