The effect of Tin as solid lubricant dispersing Lithium grease in reducing friction coefficient and wear in dusty environments

摘要

The present work aims to develop the lubricating properties of lithium grease to withstand abrasion of surfaces contaminated by dust in cement industry. Tin in granulates was added to the grease. The effect of main components of white cement such as sand, kaolin and limestone contaminating lithium grease on friction coefficient and wear of steel test specimens was discussed. The tests were carried out using cross pin wear tester to determine friction coefficient and wear. Based on the experimental results it was found that tin proved to be effective as solid lubricant dispersed in lithium grease to decrease abrasion wear of the sliding surfaces. This behaviour might be attributed to the action of tin to cover the sliding surfaces as well as the contaminant particles and consequently decreased their ability to abrade the sliding surfaces. Friction coefficient showed relatively higher values when the grease was contaminated by sand particles compared to that observed for kaolin and limestone. Presence of sand particles showed the highest wear values. The effect of tin was more pronounced in the presence of sand particles at 5 wt. % content. It seems that adherence of tin into the surfaces of sand particles was quite effective to lessen their ability to abrade the sliding surfaces. Besides, the presence of tin on the steel surfaces decreased friction coefficient and facilitated the sand to slide more than to abrade. The action of tin to defeat abrasive wear increased with increasing tin content up to 3 wt. %. The easy separation of tin layers which are weakly bonded to each other was the reason for the lubricating effect of tin particles. The layers of the tin slid apart with minimal force giving tin its inherent softness and lubricity. Formation of tin layers on the sliding surfaces as well abrasive particles like sand, kaolin and limestone could decrease the friction in the contact area.