An electric arc furnace uses an electric arc to melt materials, typically metals. It has a shell with a domed bowl, electrodes, and a refractory hearth. AC or DC power sources can be used, and additives are often used to promote chemical balance. Arc furnaces offer flexibility, quick shutdown and restart, and are cheaper to install and operate per ton of finished product.
An arc furnace, also known as an electric arc furnace (EAF), is an installation that uses an electric arc to heat materials, typically metals, to their melting point. A typical arc furnace melts material, or “charge” as it’s known, by passing an electric current through the charge via a series of electrodes. A combination of the heat generated by the passage of current and the arc on the charge surface melts the material. EAFs are found in research and dental laboratories, iron foundries, and steel manufacturing plants, and can have internal capacities ranging from a couple of pounds to 400 tons or more. Arc furnaces have several distinct advantages over other types of furnaces.
An electric arc furnace typically consists of a shell with side walls and a domed bowl at the bottom. A retractable roof section, through which the graphite electrodes are lowered, covers the furnace. The bowl section of the shell is lined with a layer of refractory material known as a hearth. The tap or spout used to discharge the molten metal is fitted to the side of the shell or the bottom of the bowl. Electrodes are usually round in cross section and made up of threaded sections allowing new sections to be added as the electrode burns.
Alternating current (AC) or direct current (DC) power sources can be used in an arc furnace. The steel mill’s medium arc furnace operates on 400 to 900 volts at 44,000 amperes or more supplied by transformers rated approximately 60,000,000 volt-amperes (60 MVA). An arc furnace of this type can produce about 80 tons of molten steel per hour. Arc furnaces range in size from small units used in research laboratories that hold about a pound of charge to massive steel mill installations capable of melting hundreds of tons of material. The largest of these furnaces have capacities exceeding 300 tons and use power supplies of 300 MVA or more.
The arc casting process is quite simple. Once the vat or furnace hearth has been filled with raw material, the electrodes are lowered until they come into contact with the charge. Electric current is then applied, typically at lower voltages to start the process. The current flow through the charge in combination with the radiant energy from the arc increases the heat in the charge to a point where it melts. Once the charge is completely melted, its temperature and chemical composition are controlled using remote probes or lances; if everything is correct, the molten metal can be tapped or poured.
The raw materials used in the kilns are often accompanied by the addition of pig iron, burnt lime and dolomite. These additives promote proper chemical balance in the molten steel and form surface slag that floats impurities and isolates the charge. Arc furnace installations offer much more flexibility than other types of furnaces; they can use an exclusive supply of waste material and their production can be varied according to demand. Arc furnaces can also be quickly shut down and restarted, which is not the case with blast furnaces. They are also cheaper to install and use less energy to operate per ton of finished product.
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