Medium-frequency induction heating furnaces operate based on the principle of electromagnetic induction. When an alternating current flows through an induction coil, it generates an alternating magnetic field of the same frequency. This magnetic field induces an electromotive force and generates eddy currents within the metal workpiece placed inside the coil; the heat produced by these eddy currents overcoming the workpiece's electrical resistance results in heating. The induction heating process involves the skin effect, proximity effect, and ring effect. Among these, the skin effect determines the depth of current penetration into the conductor; for forging heating temperatures exceeding 800°C, the skin depth Δ can be simplified to the formula Δ = 503(ρ/f)¹/² (in meters).
The main circuit typically employs an "AC-DC-AC" conversion system-such as the KGPS-type thyristor-based medium-frequency power supply-comprising a three-phase fully controlled bridge rectifier circuit, a filter circuit, and a parallel inverter circuit. The frequency of the converted medium-frequency power supply generally ranges from 500 Hz to 20 kHz.