On grease leakage from rolling bearings

The leakage of grease from shielded rolling bearings is usually caused by grease being pushed out by ball or cage motion, centrifugal force, or grease flow due to high temperature. However, we have discovered two other mechanisms that cause significant leakage: (1) slippage of the grease lump caused by adhesion forces to the shield plate and inner race which typically occurs in case of slippery grease on the surface, and (2) the thixotropic flow of grease due to alternate grease deformation which could occur when the shaft has precession motion or inclines against the bearing.