Induction heating

Induction heating is the process of heating a metal object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal. An induction heater (for any process) consists of an electromagnet, through which a high-frequency AC current is passed. Heat may also be generated by magnetic hysteresis losses.

Applications of induction heating

Induction heating allows the precision heating of an applicable item, for applications from surface hardening to melting. Often, iron and its alloys respond best to induction heating, due to their ferromagnetic nature. Eddy currents can, however, be generated in any metallic conductor, and magnetic hysteresis can occur in any magnetic material.

Induction furnace

An induction furnace uses induction to heat a metal to its melting point. Once molten, the high-frequency magnetic field can also be used to stir the hot metal, which is useful in ensuring that alloying additions are fully mixed into the melt. Most induction furnaces consist of a tube of water-cooled copper rings, surrounding a container of refractory material. Induction furnaces are used in most modern foundries, as a cleaner method of melting metals than a reverbatory furnace or a cupola. Sizes range from hundreds of kilograms capacity, to ten tonnes capacity. Induction furnaces often emit a high-pitched whine or hum when they are running, depending on their operating frequency. Metals melted include iron and steel, copper, aluminium, and precious metals.

Induction welding

A similar, smaller-scale process is used for induction welding. Plastics may also be welded by induction, if they are either doped with ferromagnetic ceramics (where magnetic hysteresis of the particles provides the heat required) or by metallic particles.

Induction cooking

in induction cooking, an induction coil in the cook-top heats the heavy iron base of special cookware. The heat induced in the base is transferred to the food via conduction. Benefits of induction cookers include efficiency, safety (the induction cook-top is not heated itself) and speed. Drawbacks include the fact that non-ferrous cookware such as copper, aluminium and glass cannot be used on an induction cook-top, and if an induction cook-top is installed in a home and the owners wish to move, a choice must be made to either take the whole induction cooking set with them, or leave it all behind. However, portable induction cookers are available.

Heat treatment

Induction heating is often used in the heat treatment of metal items.

See also

• Magnetism, for a starting point on why induction heating is possible