What Is Base Oil Viscosity?
Base oil viscosity is the most critical property of a bearing lubricant. It determines the thickness of the hydrodynamic oil film that separates the rolling elements from the raceways. Measured in mm2/s (centistokes, cSt) at 40C per ISO 3104, it must be matched to the bearing's speed and load.
Selection Method
Calculate the speed factor (n x dm, where n = RPM and dm = mean bearing diameter in mm). Cross-reference with the manufacturer's viscosity chart to find the minimum required kinematic viscosity at operating temperature. The Grease Selection Guide provides the complete SKF methodology with worked examples.
Frequently Asked Questions
How do I choose the right base oil viscosity for my bearing?
Use the bearing manufacturer's speed factor (n x dm) to determine the minimum required viscosity at operating temperature. For high speeds, use lower viscosity (ISO VG 22-68). For slow, heavy loads, use higher viscosity (ISO VG 220-460). The viscosity ratio kappa must be >= 1 for adequate film formation.