System for hardening gears by induction heating

An apparatus for hardening the radially, outwardly facing surfaces of a generally circular toothed workpiece adapted to rotate about a central axis generally concentric with said outwardly facing surfaces, said surfaces defining an outer circle by the tips of said teeth of said workpiece, said apparatus comprising:

• (a) first and second induction heating coils having inner circular surfaces generally matching and slightly larger than said outer circle of said workpiece;
• (b) motor means adapted to be associated with said workpiece for locating said workpiece concentrically in said first induction heating coil;
• (c) first power means associated with said first coil for energizing said first induction heating coil with a first alternating frequency current of less than about 5.0 KHz and a first power level greater than 100 KW;
• (d) microprocessor means associated with said first power means for activating said first power means to energize said first coil for a time period less than about 10.0 seconds and deenergize said coil with said workpiece therein for a first time delay period of at least about 10 seconds;
• (e) said microprocessor means effective to again actuate said first power means to energize said first induction heating coil with a second alternating frequency current of less than about 5.0 KHz and a second power level at least as great as said first power level and for a second time period substantially less than said first time period to produce an unstable temperature band located radially inwardly from said tips, said tips being at a higher temperature than the core of said workpiece but less than the critical temperature of said workpiece;
• (f) said motor means controlled by said microprocessor means effective to said workpiece concentrically into said second induction heating coil after a second delay time no more than about 1.0 seconds;
• (g) second power means associated with said second coil and actuated by said microprocessor means for energizing said second induction heating coil with a radio frequency current of more than 200 KHz at a third power level over 100 KW said microprocessor means further effective to actuate said second power means for a third time period of less than about 1.0 seconds;
• and,
• (h) quench means within said second induction heating coil controlled by said microprocessor means for immediately spraying a quenching liquid against said surfaces after said third time period while said workpiece is in said second induction heating coil to quench said workpiece without adverse grain growth.