Elastohydrodynamic Lubrication With Herschel-Bulkley Model Greases

The analysis of grease-lubricated rolling element bearings is presented. Experimentally determined flow curves for grease are found to be well correlated by the Herschel-Bulkley model flow equation. A theory for predicting roller film thickness based on the assumed flow model is derived. Experimental results show that grease will develop a larger film thickness than the grease base oil at first, but the film thickness falls during rolling until it reaches a steady thickness usually lower than that of its base oil. This effect is shown to depend on the degree of shear degradation of the grease, its resulting flow curve, and the temperature rise due to shear in the inlet. The grease yield stress is found to have a negligible effect on EHL performance.