The influence of polymer fillers in a grease lubricant on the tribological performance of friction nodes operating under mixed friction conditions

The paper presents the results of a study upon the influence of the type of polymer filler in a lithium grease lubricant on the lubrication performance of steel friction pairs operating under mixed friction conditions. Grease compositions based upon the 1S lithium grease and powders of three polymers, i.e. polytetrafluoroethylene (PTFE), polyoxymethylene (POM) and PA6 polyamide were analysed. For the sake of comparison, compositions with an anisodesmic filler (graphite) and metallic filler (tin) were also tested. The tribological testing was carried in agreement with the guidelines of the PN-76/C-04147 standard using a four ball apparatus. The effectivity of the tested lubricants was evaluated using three criteria: the ball wear d, the limiting wear load Goz and the limiting load Fg. It was found that a polymer featuring good tribological properties (when used as material for sliding bearings) might not always be equally efficient when used as filling powder. POM or PA powders used as fillers for the 1S lithium grease do not improve the effectivity of lubrication. A modification of the same grease with 6 wt % of PTFE powder results with an effective grease composition.