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.

► Unknown grease leakage mechanisms from shielded rolling bearings were revealed.
► One is grease lump rotation due to the torque caused by grease adhesion to shield plate and inner ring surface.
► The other is due to thixotropic flow in the grease resulting from the alternate grease deformation in the bearing.