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The principle of induction heating is that when the light flows through the inductor, due to electromagnetic induction, an alternating magnetic field is generated in the workpiece in the inductor, and the alternating magnetic field generates an induced potential that forms a current, that is, a eddy current, in the workpiece. The density of the eddy current is extremely unevenly distributed in the workpiece. The closer to the surface of the workpiece, the larger the current is, and the higher the frequency is, the larger the surface current is. Therefore, when the workpiece is inductively heated, the power is concentrated on the surface layer of the workpiece, so the surface temperature of the workpiece rises most. fast. As the surface temperature of the workpiece increases, the resistivity of the workpiece increases. When the temperature reaches the Curie temperature (768 ° C), the electric power is concentrated on the inner layer.
Therefore, induction heating is a layer-by-layer heating process, and the correct selection of heating power, operating frequency and heating time can achieve the required quenching temperature.
According to the different depth of quenching, it can be divided into three types:
High frequency heating equipment
It has a set of devices that convert power frequency 50 cycles/second AC to high frequency (70000~1000000 cycles/second) (usually using a tube high frequency generator) with a quenching depth of less than 3 mm.
2. Intermediate frequency heating equipment
It also has a set of equipment that converts power frequency 50 cycles/second into intermediate frequency (500~10000 cycles/second), usually medium frequency generator (low power factor) and thyristor inverter, with quenching depth of about 5 mm. .
3. Power frequency induction heating equipment
The power frequency of the inductor is the same as the frequency of the grid, ie 50 cycles/second, so the energy can be extracted directly from the grid, and the quenching depth is above 10 mm. The downside is that the power factor is too low.
Advantages and types of induction heating
Compared with general electric furnaces, induction heating has the advantages of fast heating speed, small deformation of workpiece and high surface hardness.