An Investigation of the Fundamental Properties of Grease-Lubricated Bearings

摘要

Grease is used as a lubricant for large numbers of bearings in everyday use; but the non-Newtonian rheological properties of these thixotropic gels, and their effect upon journal-bearing performance, are not well understood. To initiate a program in grease lubrication, we reactivated a concentric-cylinder journal-bearing test apparatus used by Smith and Fuller. This particular configuration has been treated extensively by theoreticians for constant viscosity lubricants, and to a considerably lesser extent for non-Newtonian lubricants. Smaller amounts of experimental data exist for both types of lubricants. The journal-bearing test apparatus was operated first as a concentric-cylinder viscometer, and the shear viscosity of SAE 10 oil measured. Subsequently, the apparent shear viscosity of a lithium-based grease (Sears and Roebuck) was measured as a function of rate of strain and of temperature. Performance of the grease-lubricated journal bearing was characterized by experimental determination of the coefficient of friction as a function of the bearing number ZN/p. As expected, the high shear viscosity of the grease (with corresponding high bearing number) was found to permit operation at lower RPMs.