The specific film thickness: calculated minimum elastohydrodynamic film thickness divided by the combined roughness of the two flanks. Below about 1 the teeth run in boundary lubrication with heavy asperity contact, between 1 and 3 in mixed lubrication, and above about 3 in full film. Low lambda drives micropitting, wear and scuffing, and it is raised by higher viscosity, lower temperature, higher speed or smoother surfaces.
Lambda ratio's about 0.6 at full load and low speed, no wonder it's micropitting, we need smoother flanks or thicker oil.
Also heard as
- specific film thickness
- lambda
- film thickness ratio
Related terms
Micropitting
Very fine surface fatigue pits, too small to see one by one, that give tooth flanks a dull gray look.
Superfinishing
Polishing ground gear teeth to a mirror-like finish, chemically assisted, to cut friction and surface fatigue.
Scuffing
Sudden adhesive damage where tooth surfaces weld and tear apart because the oil film broke down.
Flash temperature
The brief spike in surface temperature where teeth slide over each other under load, used to predict scuffing.