Electric furnace is a device for providing heat by electrical means. It consists of a chamber that receives the electric current, which is used to raise the temperature of the materials placed in the furnace. The material to be heated is called the charge.
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 °F. to 2800 °F. (540 °C to 1500 °C). 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 °F. (1100 °C). Silicon carbide elements permit operations up to 2800 °F. (1500 °C). The temperature of an electric arc may exceed 6000 °F. (3300 °C). Arc furnaces may heat the charge to temperatures limited by the melting point of the furnace lining, perhaps up to 3000 °F. (1600 °C).
