1. The principle of induction electric heating of hot forging.Under the action of the alternating magnetic field generated by the induction of the alternating current, alternating eddy currents are generated inside the metal blank. The metal blank is heated directly due to eddy currents and magnetization heating (below the magnetic transition point).

When the blank is heated by induction hot forging, the current density generated inside is unevenly distributed along the cross-section, the center current density is small, and the surface current density is large. This phenomenon is called the skin effect. As a result, the surface metal is mainly heated by the passing of the current, and the core metal is heated inward by the heat of the outer layer. For large-diameter blanks, in order to increase the heating speed, a lower current frequency should be selected to increase the current penetration depth; while for small-diameter blanks, due to the smaller cross-sectional size, a higher current frequency can be used, which can improve the electrical conductivity. efficiency.

2. The principle of contact electric heating of hot forging.  The principle of contact electric heating is to directly pass a low voltage and a large current to the metal blank. Due to the certain resistance of the metal, the passing of the current will generate heat, thereby heating it.

For the hot forging of a blank of a certain size, a certain amount of heat needs to be generated to heat it to a specified temperature. The resistance value of the general metal is relatively small, in order to improve productivity and shorten heating time, it is necessary to pass a large current into the blank. In order to avoid short circuits, the method of reducing the voltage is often adopted to obtain a large current with a low voltage. Therefore, the no-load voltage of the secondary terminal of the transformer used for contact electric heating is only 2-15V.

The characteristics of contact electric heating of hot forging are fast heating speed, less metal burning loss, unlimited heating temperature range, high thermal efficiency, low power consumption, low cost, simple equipment, and convenient operation. However, the surface roughness and shape and size of the blanks are strictly required, especially since the ends of the blanks must be regular without distortion. In addition, the measurement and control of the heating temperature are also difficult. Suitable for global or local heating of long blanks.

Through the above introduction and analysis of two principles of hot forging, hope it helps you.