Induction heat treatment began to be used in China in the 1950s when the process was called “high frequency quenching”.This new heat treatment process USES coil electromagnetic induction heating to quickly reach the quenching temperature of the workpiece, and then rapid cooling so that only the surface layer to obtain the quenching structure. It has the characteristics of high heating speed, good working conditions, high surface strength, and small deformation, and is quickly accepted and developed by heat treatment workers.
1.Thyristor (SCR) intermediate frequency power supply
Early induction heating power supply is mechanical if generator, low electrical efficiency, 70% ~ 75%, has been phased out of the induction heating range, replaced by thyristor if power supply, also known as SCR of power supply. Thyristor power supply frequency is 2.5 ~ 8kHz, the application range is greatly expanded. By the early 1990s, it was fully mature and some of its technical indicators had reached the international advanced level. Compared with mechanical intermediate frequency, it has the advantages of small volume and light weight.No mechanical movement, low noise; Can start and stop instantly; Frequency is automatically tracked during the operation of the workpiece. Disadvantages are low overload capacity, high failure rate, high price.
2. High frequency power supply of vacuum tube
The high frequency power supply of the vacuum tube is simple to tune and easy to use. Although the frequency is high, its application range is wide. The disadvantage is low electrical efficiency, about 50%; The working voltage is too high and the safety is poor.
3. Transistor UHF and HF power supplies
After the 1990s, transistor high-frequency power supply (SIT high-frequency power supply, MOSFET high-frequency power supply, IGBT super audio power supply, etc.) began to develop.
The static Induction Transistor SIT(StaticSIT Induction Transistor) is actually a junction fET.SIT electrostatic induction transistor power supply, set large current, high voltage and high-frequency characteristics in one, but because the SIT power supply due to a small single tube power and other shortcomings is difficult to overcome, foreign companies have stopped research and development and production, domestic production has been dozens of, but due to the lack of spare parts, has been scrapped.
MOSFET (Field effect transistor circuit) is a voltage type hf majority carrier device. The domestic transistor MOSFET hf power supply F =50 ~ 200kHz can be produced with power up to 200kW.
The IGBT/Insulating Gate Polartransistor is a combination of MOSFET and GTR that provides both high input impedance of MOSFET and low conduction voltage drop in GTR.GTR has a lower saturation voltage and higher carrying current density, but higher driving current.MOSFET drive power is small, switching speed is fast, but the conduction voltage drop is large, carrying current density is small.IGBT combines the advantages of the above two devices, with low drive power and low saturation voltage.IGBT super audio power in China in 90 years of development success, at present domestic IGBT power, has been very mature, the frequency can achieve several hundred kilohertz.
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