Micropitting occurs on
surface-hardened gears and is characterized by extremely
small pits approximately 10 µm (400 µ-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.
