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Evaluation of the Scuffing Resistance of Isotropic Superfinished Precision Gears

By: P.W. Niskanen, Alion Science and Technology, B. Hansen, Sikorsky Aircraft Corporation and L. Winkelmann, REM Chemicals, Inc.

Technical Papers and White Papers

The high performance required from aerospace gears places stringent requirements upon the metallurgical quality, geometry, and surface finish of mating parts. In an effort to meet their mission requirements, aerospace gears are often engineered to operate near the upper bounds of their theoretical design allowables. Due to this, scuffing is a primary failure mode for aerospace gears.

It was previously shown that specimens having an isotropic superfinish using chemically accelerated vibratory finishing had an improved performance in Rolling/Sliding Contact Fatigue (R/SCF) testing. Isotropic superfinishing improved R/SCF resistance up to nine times that of baseline test specimens. These tests also demonstrated the ability to successfully carry 30 percent higher loads for at least three times the life of the baseline samples.[1]

A study was then conducted on actual gears having an isotropic superfinish. This study showed isotropic superfinishing technology increased a gear’s resistance to contact fatigue by a factor of three, and increased bending fatigue resistance by at least 10 percent. [2] This increase in gear performance translates to reduced operation and sustainment costs, and also offers the potential for weight reduction in new transmission designs.

The present paper will discuss an additional study which is underway to determine and compare the scuffing resistance of isotropic superfinished aerospace gears to that of baseline ground gears. Sample gears were made from case carburized SAE 9310. These tests were conducted using a method that progressively increases lubricant temperature until scuffing occurs, rather than the traditional load increasing method used in FZG testing rigs. The results of the current testing reveals that isotropic superfinished SAE 9310 specimens show at least a 40° F higher lubricant temperature at the point of scuffing compared to as-ground baseline gears. Based on these results and the previous studies, it was concluded that this isotropic superfinishing technology should be incorporated in all future aerospace gear designs. A later paper will report on similar scuffing testing performed on AMS 6308 gears due to run-outs achieved by both the baseline and isotropic superfinished samples during the current procedure.

Copyright © 2005


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