The induction heating frequency includes low, medium, and high frequencies. For the heat treatment of metals, high and medium frequencies are usually used.
Induction heating is to put the workpiece into the induction coil, the induction coil is generally input medium frequency or high frequency alternating current (300-300000Hz or higher) hollow copper tube. In the alternating magnetic field in the workpiece to produce induced current with frequency, the induced current distribution in the workpiece is not uniform, strong on the surface, and in the internal is very weak, the heart is close to zero, use the skin effect, can make the surface heating quickly, within a few seconds surface temperatures to rise to 800-1000 ℃, and the core temperature is small.
Therefore, according to the requirements of heat treatment and heating depth, select the induction heating frequency, the higher the frequency, the shallower the heating depth.
The heating depth of high frequency (above 10kHz) is 0.5-2.5mm, which is generally used for heating small and medium-sized parts, such as small module gear and small and medium-sized shaft parts.
Intermediate frequency (1~10kHz) heating depth is 2-10mm, generally used for shaft type with large diameter and large and medium modulus gear heating.
Power frequency (50Hz) heating hardening layer depth is 10-20mm, generally used for diathermic of large size parts, large-diameter parts (diameter of more than 300mm, such as roller) surface quenching.