Understanding Scuffing and Micropitting of Gears

Abstract : This paper describes the results of basic research, both theoretical and experimental, on scuffing and micropitting of gears used in naval and aerospace applications. Scuffing experiments have been carried out under severe conditions of load, sliding speed and temperature using typical gear steels with different surface treatments including case-carburising, nitriding, superfinishing, and super-hard coatings. The results of this work demonstrate the importance of surface finish not only in improving scuffing resistance, but also in reducing contact friction and energy losses. Theoretical work on microelastohydrodynamic lubrication shows the importance of surface roughness in terms of high pressures generated at surface asperities on gear teeth and the effect this has upon the distribution of stress very close to the tooth surface. Some new microelastohydrodynamic parameters, derived from this work, are of potential use in discriminating between different types of gear finishes in terms of their tendency to generate extremes of pressure and film thinning which are of direct relevance to micropitting.

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