Induction heating comes from Faraday's discovery of electromagnetic induction, in which alternating currents generate an induced current in a conductor, causing it to heat up.In 1890, Swedish technicians invented the first induction melting furnace -- slotted core furnace, and in 1916, Americans invented the closed groove core furnace, since then, induction heating technology gradually entered the practical stage.
The rapid development of power electronic devices and technology in the 20th century has greatly promoted the development of induction heating technology.
In 1957, the United States developed the thyristor as a milestone of power electronic devices, marking the beginning of modern power electronic technology, but also triggered the revolution of induction heating technology.In 1966, Switzerland and West Germany first used thyristors to develop induction heating devices, since then induction heating technology began to develop rapidly.
After 1980s, power electronic devices developed rapidly again, and GTO, MOSFET, IGBT, M-CT, SIT and other devices appeared successively.Induction heating devices also gradually abandoned the thyristor, began to adopt these new devices.Now more commonly used are IGBT and MOSFET, IGBT for higher power, and MOSFET for higher frequency.It is reported that IGBT can be used in foreign countries to make the induction heating device with power over 1000kW and frequency over 50kHz.MOSFET is more suitable for high-frequency occasions, usually used in a few kilowatts of small and medium power occasions, the frequency can reach more than 500kHz, even a few megahertz.However, foreign countries have also introduced high-power induction heating devices using MOSFET, such as the 2000kW /400kHz device developed in the United States.
The real application of induction heat treatment technology in China began in 1956, introduced in the former Soviet Union, mainly used in the automobile industry.With the manufacture of power supply equipment in the 20th century, induction quenching process equipment has also been followed by the development.At present, the domestic induction hardening process equipment manufacturing industry is also expanding, with more products. The equipment that used to be imported is gradually replaced by domestic products, which not only saves foreign exchange for the country, but also develops domestic related enterprises.At present, the service object of induction heating manufacturing industry is mainly automobile manufacturing industry. In the future, modern metallurgical industry will have great demand for induction heating.
I. Induction heating characteristics
Induction heating technology is fast, clean, energy-saving and easy to realize automation and online production, high production efficiency, etc, is an internal heat source, is a non-contact heating mode, can provide high power density, when there is a high degree of heating surface and the depth of the selectivity of flexible, can work in all kinds of carrier gas (air, gas, vacuum), the loss is extremely low, does not produce any physical pollution, accord with environmental protection and sustainable development policy, is one of the green environmental protection heating process.It has become the mainstream of heat treatment technology along with controllable atmosphere heat treatment and vacuum heat treatment with little oxidation.
Its main applications include:
(1) Smelting of non-ferrous metals in metallurgy, heat treatment of metal materials, diathermy production of profiles such as forging, extrusion and rolling, and welding seam production of welded pipes.
(2) Quenching of various mechanical parts manufactured by the machine, and heating of tempering, annealing and normalizing heat treatment after quenching;Diathermy before pressure machining.
(3) Sealing of light industry cans and other packaging, such as the famous tetra pak.
(4) Heating of vacuum degassing of electron tube.
(5) Special applications such as plasma, surfacing, etc.
Take FAW for example, in the production of medium cars, light cars and cars, there are nearly 200 kinds of parts need induction heating quenching treatment, from the shape and size of induction heating quenching parts, can be called a variety of sizes.With the continuous development of induction quenching technology, the induction quenching parts have risen to account for about 50% of all heat-treated parts.According to the relevant data, the application of induction heat treatment in China's automobile industry is entering the ranks of the world's advanced level.
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