ELECTRIC FURNACE

heating chamber with electricity as the heat source for achieving very high temperatures to melt and alloy metals and refractories. The electricity has no electrochemical effect on the metal but simply heats it. Modern electric furnaces generally are either arc furnaces or induction furnaces. A third type, the resistance furnace, is still used in the production of silicon carbide and electrolytic aluminum; in this type, the furnace charge (i.e., the material to be heated) serves as the resistance element. In one type of resistance furnace, the heat-producing current is introduced by electrodes buried in the metal. Heat also may be produced by resistance elements lining the interior of the furnace. Electric furnaces produce roughly two-fifths of the steel made in the United States. They are used by specialty steelmakers to produce almost all the stainless steels, electrical steels, tool steels, and special alloys required by the chemical, automotive, aircraft, machine-tool, transportation, and food-processing industries. Electric furnaces also are employed, exclusively, by mini-mills, small plants using scrap charges to produce reinforcing bars, merchant bars (e.g., angles and channels), and structural sections. The German-born British inventor Sir William Siemens first demonstrated the arc furnace in 1879 at the Paris Exposition by melting iron in crucibles. In this furnace, horizontally placed carbon electrodes produced an electric arc above the container of metal. The first commercial arc furnace in the United States was installed in 1906; it had a capacity of four tons and was equipped with two electrodes. Modern furnaces range in heat size from a few tons up to 400 tons, and the arcs strike directly into the metal bath from vertically positioned, graphite electrodes. Although the three-electrode, three-phase, alternating-current furnace is in general use, single-electrode, direct-current furnaces have been installed more recently. In the induction furnace, a coil carrying alternating electric current surrounds the container or chamber of metal. Eddy currents are induced in the metal (charge), the circulation of these currents producing extremely high temperatures for melting the metals and for making alloys of exact composition.