Claims
- 1. A method of hardening the surfaces of closely spaced, successive protrusions and the connecting portions between said protrusions on a convoluted workpiece with a central core where the ratio of area to quench mass is substantially lower in said connecting portions than in said surfaces of said protrusions, said method comprising the following sequential steps of:
- (a) inductively heating for a first predetermined time period said surfaces of the convoluted workpiece;
- (b) interrupting said induction heating for a second predetermined time period such that step a followed by said second predetermined time period defines a preheat cycle;
- (c) repeating steps a and b until a predetermined number of preheat cycles have occurred with each preheat cycle having its own predetermined first and second time periods, to produce a heated circular band of an anticipated configuration interconnecting said connecting portions at an unstable temperature, said band at a temperature not less than that of said protrusions, said protrusions being at temperatures greater than the temperature of said core;
- (d) immediately inductively heating the surfaces of said convoluted workpieces to a hardening temperature at a radio frequency for a third time period less than that of step a; and
- (e) immediately quenching the surface of said convoluted workpieces by quenching liquid sprayed thereagainst.
- 2. The method of claim 1 wherein said induction heating in step a is less than 10 seconds; said time delay period in step b is greater than 10 seconds and said time period in step d is less than about 1 second and at least two preheat cycles are produced with said first predetermined time period of said first preheat cycle longer than said first predetermined time period of said second preheat cycle.
- 3. The method of claim 1 wherein said induction heating in step a occurs at an audio frequency.
- 4. The method of claim 1 wherein said temperature of said circular band in step c is at or near the critical hardening temperature of said surfaces of the convoluted workpiece.
- 5. The method of claim 1 wherein step d occurs before said circular band has substantially dissipated its heat.
- 6. The method of claim 1 wherein said inductive heating in step d occurs at a high power of at least about 100 KW.
- 7. A system of hardening the surfaces of closely spaced, successive protrusions and the connecting portions between said protrusions on a convoluted workpiece with a central core where the ratio of area to quench mass is substantially lower in said connecting portions than in said surfaces of said protrusions, said system comprising:
- (a) induction heating coil means closely surrounding said workpiece for heating said workpiece by induction;
- (b) power supply means connected to said induction heating coil means for supplying power to said induction heating coil means to cause said induction heating coil means to heat said workpieces;
- (c) microprocessor means connected to said power supply means for actuating said power supply means for a first predetermined time period followed by interrupting said power supply means for a second predetermined period, said first and second periods defining a preheat cycle, said microprocessor means effective to actuate a predetermined number of preheat cycles with each cycle having its own predetermined first and second time periods to produce a heated circular band of an anticipated configuration interconnecting said connecting portions at an unstable temperature not less than that of said protrusions, said protrusions being at temperature greater than the temperature of said core but less than the critical temperature of said workpiece;
- said microprocessor means further effective after applying a predetermined number of preheat cycles to actuate said power supply means for immediately inductively heating said convoluted surfaces with a radio frequency for a third time period, said third time period less than said first time period; and
- (d) quench means associated with said induction heating means and actuated by said microprocessor means after said third time period and before dissipation of said unstable temperature band for supplying quenching liquid as a spray against said surfaces of said convoluted workpiece for quenching said workpieces whereby a plurality of workpieces can be rapidly processed in succession.
- 8. The system of claim 7 wherein said induction heating coil means includes a first and second induction coil axially spaced from one another;
- said power supply means includes a first inverter operating at audio frequency to power said first induction coil and a second inverter operating at radio frequency to power said second coil;
- said system further including motor means associated with said workpiece to drive said workpiece from said first coil to said second coil;
- said microprocessor means being effective to actuate said motor means and move said workpiece to said second coil after completing said predetermined number of cycles; and
- said quench means is located within said second coil and is actuated by said microprocessor means to immediately quench said surfaces of said convoluted workpiece after said third period whereby grain growth in said surfaces of said convoluted workpiece is minimized.
- 9. The system of claim 7 wherein said predetermined number of cycles is at least two in number.
- 10. The system of claim 7 wherein said power supply means is capable of supplying a source of high power to said induction heating coil means of at least about 100 KW.
Parent Case Info
This is a continuation of application Ser. No. 106,537 filed Oct. 6, 1987, which in turn is a divisional application of U.S. Ser. No. 023,564, filed Mar. 9, 1987, which in turn is a divisional application of Ser. No. 878,186 filed June 25, 1986 now issued as U.S. Pat. No. 4,675,488 on June 23, 1987.
US Referenced Citations (12)
Divisions (2)
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23564 |
Mar 1987 |
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878186 |
Jun 1986 |
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Continuations (1)
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106537 |
Oct 1987 |
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