Abstract

Induction furnaces utilize the phenomena of electromagnetic induction to produce an electric current in the load or workpiece. This current is a result of a varying magnetic field created by an alternating current in a coil that typically surrounds the workpiece. Power to heat the load results from the passage of the electric current through the resistance of the load. Physical contact between the electric system and the material to be heated is not essential and is usually avoided. Nonconducting materials cannot be heated directly by induction fields.

The efficiency of an induction furnace installation is determined by the ratio of the load useful power to the input power drawn from the utility. Losses that must be considered include those in the power converter transmission lines, coil electrical losses, and thermal loss from the furnace. A unique capability of induction heating is apparent in its ability to heat the surface of a part to a high temperature while the interior remains at room temperature. Induction heating is used to heat steel reactor vessels in the chemical process industry. Induction melting applications almost always contain the liquid metal charge within a hearth formed by a suitable refractory material. Coreless furnaces derive their name from the fact that the coil encircles the metal charge but the coil does not encircle a magnetic core. Channel induction furnace is one in which the energy for the process is produced in a channel of molten metal that forms the secondary circuit of an iron core transformer. The primary circuit consists of a copper coil which also encircles the core.