How does an Electric Arc Furnace for Electrode Handling work in the Steel Process?
Structure of the Arc Furnace
The Electric Arc Furnace is a thick, cylindrical boiler made of reinforced steel plates. It consists of a refractory-lined vessel covered with a retractable roof, and through which one or more graphite electrodes enter the furnace. The furnace is normally divided into three sections:
1. Shell, which consists of the sidewalls and lower steel “bowl”;
2. Hearth, which consists of the refractory that lines the lower bowl;
3. Roof, which may be refractory-lined or water-cooled, and can be shaped as a section of a sphere, or as a frustum (conical section).
Separate from the furnace structure is the electrode support and electrical system, and the tilting platform on which the furnace rests.
A typical EAF is powered by a three-phase electrical supply and therefore has three electrodes. Electrodes are round in section, and typically in segments with threaded couplings, so that as the electrodes wear, new segments can be added. The arc forms between the charged material and the electrode, the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc. The furnace is built on a tilting platform so that the liquid steel can be poured into another vessel for transport.
The scrap is loaded into baskets. Heavy melt is placed on top of a light layer of protective shred, on top of which is placed more shred. The scrap basket is then taken to the melt shop, the roof is swung off the furnace, and the furnace is charged with scrap from the basket. After charging, the roof is swung back over the furnace and meltdown commences. The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. To speed up the process, metal charging, burnt lime, slag formation and spar are added to the basket.
Once heated, the meltdown processes begin. Electrodes are lowered down into the scrap to produce the arc in a low voltage condition. Once the arc is formed, the voltage is increased to speed up the melting process while simultaneously oxidising manganese, silicon and carbon. As melting continues, the refining process begins.