INDUCTION HEATING

method of raising the temperature of an electrically conductive material by subjecting it to an alternating electromagnetic field. The electric currents induced in the object (although it is electrically isolated from the source of the field) bring about dissipation of power in the form of heat. Induction-heating methods are applied most widely in metalworking to heat metals for soldering, tempering, and annealing. The method is also employed in induction furnaces for melting and processing metals. The principle of the induction-heating process resembles that of the transformer. A water-cooled coil, or inductor, acting as the primary winding of a transformer, surrounds the material to be heated (the workpiece), which acts as the secondary winding. Alternating current flowing in the primary coil induces eddy currents in the workpiece, causing it to become heated. The depth to which the eddy currents penetrate, and therefore the distribution of heat within the object, depends on the frequency of the primary alternating current and the magnetic permeability, as well as the resistivity, of the material. Induction hardening, widely used to increase the resistance of steel objects to wear, can be effected by brief exposure to a high-frequency field. The related method of producing heat in nonconductors is called dielectric heating.