Micropitting and Gear Lubrication

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Micropitting occurs on surface-hardened gears and is characterized by extremely small pits approximately 10 m (400 -inches) deep. Micropitted metal has a frosted or a gray appearance. This condition generally appears on rough surfaces and is exacerbated by use of low-viscosity lubricants. Slow-speed gears are also prone to micropitting due to thin lubricant films. Micropitting may be sporadic and may stop when good lubrication conditions are restored following run-in. Maintaining adequate lubricant film thickness is the most important factor influencing the formation of micropitting. Higher-speed operation and smooth gear tooth surfaces also hinder formation of micropitting. The following guidelines should be observed to reduce the onset of micropitting in gear units:

• Use gears with smooth tooth surfaces produced by careful grinding or honing.
• Use the correct amount of cool, clean, and dry lubricant with the highest viscosity permissible for the application.
• Use high speeds, if possible.
• Use carburized steel with proper carbon content in the surface layers.

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