It consists of charging, melt down period and refining. The large baskets containing heavy and light scrap are preheated through the exit gas. Burnt lime and spar are added to help early slag formation. Iron one or mill scale may also be added if refining is required during melt- down period.
The roof is swung off the furnace, and the furnace is charged. Some furnaces are equipped with continuous charging. Hot metal is also charged as per the requirement.
In the meltdown period, electrodes are lowered and bored into the scrap. Lower voltages are selected in order to protect the roof and walls from excessive heat and damage from the arcs. Once the arc is shielded by scrap, voltage is increased to form molten metal pool to reduce the meltdown period. During meltdown period, silicon, manganese and carbon oxidizes. Also oxidizing and limy slag is produces which promotes dephosphorization as well. Melt- down time depends on
Arc conditions: larger arc requires lower current and lower heat losses
Deep or shallow bath: deep bath shortens the meltdown period.
Refining continues even during melting. Removal of phosphorus must be complete before the rise in temperature and carbon boil.
The single oxidizing slag practice is employed when removal of sulphur is not required. When both P and S are required to be removed double slag practice is used. In double slag practice, oxidizing slag is removed and reducing slag is formed after deoxidation with ferrosilicon or ferromanganese or aluminum. Reducing slag helps to avoid loss of alloying elements.
Once the bath chemistry and its temperature are attained, heat is deoxidized and finished for tapping.
Comparison with oxygen steelmaking
EAF
Oxygen steelmaking
Source of energy
Electric + chemical energy
Chemical energy; Autogeneous process
Iron–containing raw material
Hot metal + directly reduced iron + scrap in the suitable proportion as per practice
Hot metal + 20 – 30% scrap
Operating procedure
Oxygen lancing is to promote decarburization, scrap melting and post combustion.
Oxygen supply is continuously done to refine hot metal to steel. A three phase dispersion of slag/metal/gas forms to accelerate the refining rates.
Slag foaming is induced to shield refractory lining from the heat of arc.
Carbon injection is done to induce foamy slag practice
