Influence of external vibration and frictional surface roughness on friction-reduction performance of granular flow lubrication

Purpose This study aims to reveal the impact of external vibration and frictional surface roughness on the friction-reduction of granular flow lubrication, to further enhance the lubricating effect of granular media, and to promote the wide application of granular flow lubrication technology in industrial fields. Design/methodology/approach The test of vibration-assisted granular flow lubrication with different friction surfaces were conducted on a homemade linear reciprocating vibration friction tester. Based on the test results, the effects of vibration frequency and amplitude on the friction reduction performance of granular flow lubrication were analyzed. Meanwhile, the morphology, size and wear rate of the wear scar on the friction test sample were measured using a white light interference microscope, and the improvement effect of vibration-assisted granular flow lubrication on the anti-wear performance of the friction sample was analyzed. Findings The results indicate that, under the condition of vibration-assisted granular flow lubrication, both ordinary and roughened samples exhibited a significant anti-wear effect. As the vibration frequency was increased, the friction coefficient and the wear amount of the lower specimen initially decreased and then increased. In contrast, with increasing amplitude, both parameters demonstrated a continuous downward trend. Compared with the no-vibration condition, the average friction coefficients with ordinary and roughened samples under vibration-assisted condition were reduced by 16% and 24%, respectively, and the wear rates of the lower specimens were reduced by 20% and 57%, respectively. The result shows that, a roughened surface can store granules, and external vibration facilitates the entry of granular media into the friction interface. Based on the synergistic effect of two above factors, the lubricating effect of granular flow was significantly enhanced. Originality/value This research can enrich the theory of granular tribology, improve the friction reduction effect of granular flow lubrication and ultimately provide theoretical and practical references for the wide application of this technology.