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Background of the development of induction heating

Electromagnetic induction discovered by Michael Faraday in 1831 is the basis of all induction heating.

Based on the phenomenon that the change of current in the primary coil can generate induced current in the adjacent closed secondary coil, he created the concept of modern induction heating.

The essential feature of induction heating is that the alternating current in the primary coil causes the change of magnetic flux in the closed secondary coil. About a hundred years ago, this principle has been used in motors, generators, transformers and radio communications, but any thermal effect in either the circuit or the magnetic circuit is considered a harmful side effect.

For this reason, in order to minimize harmful eddy current heating, engineers use a laminated structure for the magnetic core of the transformer and motor, so that the magnetic resistance is lower in the direction parallel to the winding axis, and the magnetic core circumference perpendicular to the magnetic flux direction has a higher resistance. Following Faraday’s research work, many laws were later proposed, such as Lenz and Neumann’s laws.

These laws show that the magnetic flux of the induced current opposes the original magnetic flux, and the opposing effect is proportional to the frequency of change of the original magnetic flux. In 1868, Foucault proposed the eddy current theory, and Heaviside published a paper entitled “Induction of Current in the Iron Core”, which discussed the problem of energy transmission from the winding to the solid iron core. At the same time, Thomson also contributed to the theory of induction heating.

At the beginning of this century, suggestions for using coreless induction furnaces for medium-frequency smelting were proposed in France, Sweden and Italy, and the idea of ​​using capacitors to compensate for reactive power was also proposed. Dr. Northrup developed a medium-frequency induction furnace for industrial application. Since then, due to the lack of suitable motor-AC generator sets and capacitors with sufficient capacity and reliable performance, medium-frequency smelting furnaces have stagnated at the development level of the early stage of induction heating applications.

By 1927, the British Electric Furnace Company (EFCO) installed the first medium-frequency furnace in Sheffield. Since then, a large number of various types of induction heating devices have been steadily developed. At the same time, it was also recognized that induction heating is also applicable to local heating of forging and metal brazing.

During World War II, further developments showed that induction heating has the following advantages: extremely precise heating depth and heating surface area; no external heat source is required, so heat loss is low and the working environment is clean; the heated object does not need to be in contact with the inductor and high power density is easy to achieve, so the heating time is very short; the combination of the above factors is ideally suitable for automation of production processes