Induction heating is mostly used for industrial induction heating: the workpiece is placed in the inductor, and the inductor is usually a hollow copper tube that is input to an intermediate frequency or high frequency alternating current (300-300000 Hz or higher). The alternating magnetic field generates an induced current of the same frequency in the workpiece. The induced current is uneven in the distribution of the workpiece, strong on the surface, and weak inside, to the core close to 0, using this skin effect The surface of the workpiece can be heated rapidly, and the surface temperature rises to 800-1000 ° C in a few seconds, while the temperature rise of the core is small.