Experimental Observation of Single-Charging Grease Lubrication with Different Directions of Surface Motion

Using a ball-on-disc optical apparatus, the features of grease lubrication were experimentally investigated under different angles between the surface velocities of the two contact bodies. It was found that in the contacts with different surface velocities, there represented two typical features: inlet oil reservoir formation and asymmetrical film shape, which were different from traditional observations of grease lubrication. The film thickness and lubricating duration were significantly enhanced due to the presence of an inlet oil reservoir. Furthermore, this finding also indicated the incorrect use of classical inlet boundary conditions for numerical EHL with non-collinear surface velocities. The asymmetrical film shapes were mainly attributed to the non-uniform thermal properties of the sliding components. And moreover, asymmetrical films became pronounced under higher speeds and angles. The crossed lubrication tracks on two surfaces facilitated the lubricant replenishment, which was the main mechanism of inlet oil reservoir formation.