Surface-initiated rolling contact fatigue in which vast numbers of microscopic cracks and pits form on hardened gear teeth or bearing races running in a thin, mixed film. To the eye it shows as dull, satin-gray patches, hence the names gray staining and frosting. Micropitting can stabilize, but it also changes the tooth profile, raises noise and often seeds macropitting. Higher viscosity, smoother surfaces and micropitting-resistant gear oils reduce it.
High-speed pinion is showing micropitting, those gray bands weren't there at the last borescope.
Also heard as
- gray staining
- grey staining
Do not mix it up with
- Pitting: Micropits are microns deep and show as a gray sheen; classic pitting leaves craters you can see and feel.
Related terms
Frosting
Shop name for the dull, satin-gray sheen of early micropitting on gear teeth or bearing races.
Pitting
Rolling contact fatigue that leaves visible craters on gear teeth or bearing races.
Mixed lubrication
Transitional regime where the load is shared between a partial fluid film and asperity contact.
Lambda ratio
Oil film thickness divided by the combined roughness of the two surfaces, used to judge the lubrication regime.