Investigation on Grease Elastohydrodynamic Lubrication

Lubrication as a friction reduction technique has been used in variety of mechanisms and machines. The contacting surfaces depart from each other by the pressure produced in lubricant due to surface wedge shape. In some applications pressure is such high that deforms the contacting surfaces and more space is provided for the lubricant. Increasing the film thickness leads to misestimating of friction coefficient. Greases are usually used when the lubricating area is unreachable easily or there is not enough space for oil recirculation. In this paper, Herschel–Bulkley's model was used for isothermal non-Newtonian grease lubrication under point contact elastohydrodynamic condition. A good agreement between experimental and simulation results is shown. The effect of different type of grease is compared according to lubricant film thickness and friction coefficient. Results show that threshold yield stress does not significantly affect tribological parameters but the power law exponent does. Higher load and lower entraining velocity cause thinner film as well as higher friction coefficient in spite of the grease type.