... heating products, the mainly situations are as follows: 1,workpiece through hot, such as: high strength bolt ... mm more than the application of intermediate frequency (0.5-10 KHz) 2,heat treatment, shaft, ... : hardening layer0.2-0.8mm applicable UHF 100-250 KHz, high-frequency 1.0-1.5mm applicable 40-50 Khz ... high-frequency, super-audio1.5-2.0mm applicable VHF 20-25 Khz 2.0 ...