Electric Furnace

Electric furnaces are used to heat materials to great temperatures in order to produce useful products. For example, heat is used to melt different metals so that they can combine to form an alloy. Electric furnaces are also used to improve the quality of steel and glass by heating and cooling them at controlled temperatures below the melting point. Special types vulcanize rubber, mold plastic, and dry and bake other materials.

The chamber of an electric furnace is usually lined with a brick that can withstand high temperatures. An insulating material usually surrounds the brick to keep in the heat. A protective shell covers the insulation.

Resistor furnaces provide heat by passing an electric current through resistance heating coils that surround the charge. In a resistance furnace, electrodes are placed in contact with the charge, and the electric current passes through the charge itself. In an induction furnace, the charge is heated by electric induction, without any electrical contact with the charge (see Induction, Electric). Indirect-arc furnaces have an electric arc between electrodes near the charge, but direct-arc furnaces have an electric arc from the electrodes directly to the charge.

The temperature in an electric furnace is accurately controlled by varying the strength of the electric current. In resistor furnaces, temperatures may range from 1000 ºF. to 2800 ºF. (540 ºC to 1500 ºC). The maximum temperature is determined by the melting point of the resistor material. Resistor elements made of nickel-chromium alloy produce furnace temperatures up to 2000 ºF. (1100 ºC). Silicon carbide elements permit operations up to 2800 ºF. (1500 ºC). The temperature of an electric arc may exceed 6000 ºF. (3300 ºC). Arc furnaces may heat the charge to temperatures limited by the melting point of the furnace lining, perhaps up to 3000 ºF. (1600 ºC).

Contributor: Donald W. Novotny, Ph.D., Prof. of Electrical and Computer Engineering, Univ. of Wisconsin.

See also Electric Arc.

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