Metlab, a commercial heat treater in Wyndmoor, Pa., recently quenched a fabricated 47,000-pound gear. The gear measured 12 feet in diameter and has a 30-inch face width. The customer left approximately 0.050 inch of grind stock on the gear for clean-up. With proper fixturing, handling and shimming, the typical taper on a gear this size is about 0.030 inch. The material was 18CrNiMo6-7. The required case depth was a nominal 0.275 inch with a surface hardness of HRC 58-62. The carburizing time to achieve the required case depth is about 10 days in the furnace at 1725°F (940°C). After lowering the temperature of the furnace and gear to 1550°F (843°C), it is quenched in oil. The transfer time from the pit furnace into the quench tank is less than one minute.
After quenching, the gear will be double-tempered, sand-blasted and prepared for shipment to the Midwest customer for final grinding. Metlab is expecting two smaller 37,500-pound gears for similar heat treatment within the month.
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