Vacuum heat treating eliminates distortion

Solar Atmospheres of Souderton, Pa., says its vacuum heat treating process helps to eliminate distortions caused by oil quenching heat-treated metal parts, while matching stringent heat treating specifications.

These helicopter carrier parts were vacuum heat treated by Solar Atmospheres at its Hermitage, Pa. facility for Triumph Gear.


Solar Atmospheres of Souderton, Pa., says its vacuum heat treating process helps to eliminate distortions caused by oil quenching heat-treated metal parts, while matching stringent heat treating specifications.

Solar Atmospheres successfully used its vacuum gas pressure heat-treating process for two parts of a helicopter in development.

The components — called carriers — were made by Triumph Gear, of Macomb, Mich. They needed to be finished to BAC specifications but with minimal metal distortion. The parts were needed for bench testing of an experimental gearbox design.

Instead of the usual oil quenching or martempering, Solar Atmospheres used gas pressure quenching under a quenching-media exception to a BAC specification.

The helicopter components are made of 4340M alloy steel. They weigh 407 pounds and are 26-inches high and 24-inches in diameter and have a 1.562-inch cross-sectional thickness. The parts support the internal planetary gears in the helicopter's transmission. Solar Atmospheres preheated the components to 1,400 F and held that for 30 minutes based on readings from thermocouples placed inside test pieces. The gas was circulated by a 300-horsepower motor, and pressure quenched at 10 bar helium. Final austenitizing processing was done at 1,600 F, ±25 degrees, and held for 105 minutes. The work was done at the company's facility in Hermitage, Pa.

After being cooled to room temperature, the parts were tested at 62 HRC hardness and dimensionally checked. Subsequent inspection confirmed minimal geometry change on the components. They were then doublevacuum tempered and returned to Triumph Gear for final grinding.

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