Porous Retainers for Rolling Bearings

A theoretical analysis is made for the lubrication of ball bearing retainers made of porous material. The results show that at low Sommerfeld reciprocals, the eccentricity ratio tends to unity with a high coefficient of friction. At a certain critical value of the reciprocal, a minimum friction occurs, thereafter followed by hydrodynamic operation. The critical value depends on the permeability parameter of the porous matrix and increases with its porosity. Experiments suggest that at low Sommerfeld reciprocals or with the oil supply coming only from the retainer pores, mixed film lubrication occurs, friction being less than that obtained theoretically. Such a lubrication regime would still allow sufficient oil to be carried by the balls to the races for their lubrication.