... A.High frequency induction heating machine:frequency from20 to 80KHZ Application: all classes of machine parts heattreating(quenching,anneal, ... , and so on. B.Medium frequency induction heating machine:frequency:1.5-20KHZ 1. series resonance medium frequency ... and so onC.ultrahigh frequency induction heating machine:frequency:100-500KHZ Application: machine parts quenching, depth of quenching less than ...