The zone between boundary and full-film lubrication in which the fluid film carries part of the load and the high points of the surfaces carry the rest, with lambda ratios of roughly 1 to 3. Many gears and rolling bearings spend much of their lives here, which is why both viscosity and additive chemistry matter and why surface finish has such a strong effect on fatigue life.
With the sump at 85 C that pinion is in mixed lubrication, so either cool the box down or step up a grade.
Also heard as
- mixed-film lubrication
- partial EHL
Related terms
Boundary lubrication
Regime where surfaces touch through the oil and protection comes from chemical surface films, not fluid pressure.
Elastohydrodynamic lubrication
Film regime in rolling contacts where huge pressure stiffens the oil and elastically flattens the metal.
Lambda ratio
Oil film thickness divided by the combined roughness of the two surfaces, used to judge the lubrication regime.
Stribeck curve
Plot of friction against viscosity times speed over load, showing the boundary, mixed and full-film regimes.
Micropitting
Fatigue damage made of tiny pits, about 10 to 20 microns deep, that turns gear and bearing surfaces dull gray.