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The DIRECT ARC FURNACE ( ELECTRIC PROCESS IN STEEL MAKING )

The direct arc furnace consists of a steel shell lined with refractory bricks and a removable roof through which carbon or graphite electrodes ( about 2m long ) pass. Graphite electrodes offer less resistance to current and are considered to be more durable at high temperature but they are more expensive than the carbon electrodes. The number of electrodes correspond to the number of phases.




The electrodes are lowered into the furnace and the current is switched on. The heat generated by a powerful spark between the electrodes and the metallic charge on the hearth melts the charge. The charge usually consists of steel scrap and iron oxide in the form of iron oxide ore. Pig iron is not directly treated in electric furnaces, though sometimes it is partly purified in an open hearth furnace and then transferred to electric furnaces for final treatment and alloying. When the furnace is in operation, the electrodes are consumed and they become shorter. So a definite distance must be maintained between the electrodes and the charge by raising or lowering them by automatic controls. whenever necessary, a new electrode id built up (screwed) on top of the old one. 

Modern arc furnaces are built in 0.5 to 80 tons capacity but most favored are those with capacities of up to 80 tons. A melt is produced in 6 to 8 hour for an arc furnace 30 to 35 tons in capacity. 

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