Induction Heating is a method of heating electrically conducting material by subjecting it to an alternating electromagnetic induction, where eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal. An inductor (the work coil), acting as a primary winding of a transformer, surrounds the material which is to be heated (the work piece), which acts as the secondary winding. Alternating (RF) current flowing in the primary coil induces eddy currents in the work piece and heats it up. The frequency of AC used depends on the object size, material type, coupling (between the work coil and the object to be heated) and the penetration depth, usually at frequencies between 100 and 500 kHz.

The frequency of the primary alternating current, along with the permeability and resisitivity of the material, decide the depth that the eddy currents penetrate and therefore the distribution of heat within the work piece. The particular design of the coils, along with temperature sensors and feedback controls, allows either the entire work piece or a specific area to be heated. The repeatability of the process is excellent. Oscillator circuits containing triodes are commonly used to generate the RF currents.

Applications of Induction Heating Technology

Induction heating allows the targeted heating of an applicable item for applications including surface hardening, melting, brazing and soldering and heating to fit. Iron and its alloys respond best to induction heating, due to their ferromagnetic nature. Eddy currents can, however, be generated in any conductor, and magnetic hysteresis can occur in any magnetic material. Induction heating has been used to heat liquid conductors (such as molten metals) and also gaseous conductors (such as a gas plasma). Few popular applications of induction heating technology are:

  • Induction Heating Furnace – An induction furnace uses induction to heat 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.
  • Induction Welding – Smaller-scale induction heating process is used for induction welding. Plastics may also be welded by induction, if they are either doped with ferromagnetic ceramics or by metallic particles.
  • Induction Cooking – In induction cooking, an induction coil in the cook-top heats the iron base of 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.
  • Induction Brazing – Induction brazing is often used in higher production runs. It produces uniform results and is very repeatable.
  • Induction Sealing – Induction heating is often used in cap sealing.
  • Induction Heating Treatment – Induction heating is often used in the heat treatment of metal items. The most common applications are induction hardening of steel parts, induction soldering/brazing as a means of joining metal components and induction Annealing to selectively soften a selected area of a steel part. Induction heating is often used to heat an item causing it to expand prior to fitting or assembly. Bearings are routinely heated in this way using mains frequency (50/60 Hz) and a laminated steel transformer type core passing through the centre of the bearing.