The effectiveness of PTFE nanoparticle powder as an EP additive to mineral base oils

This paper describes experiments using a four-ball tester to evaluate the extreme pressure (EP) and wear reduction properties of AISI 52100 steel balls with several mineral oils with and without additive. The lubricants studied include PTFE nanoparticle powder as an additive in different percentages with SN-350 and Bright Stock as mineral base oils with very different viscosities (9 and 32.4 cSt, respectively, at 100 °C). Plots of wear scar diameters versus applied loads, load wear indexes and weld points are given for all the lubricants that were tested. The contact angle for the different oils tested both with and without additive is estimated experimentally in order to provide some understanding of the behaviour described in the results. Results indicate a reduction of the average scar in the three lower balls and an increase of the Welding Point for both oils. They also point to an increase in the load wear index (LWI) in line with increasing percentages of additive. The oil specimens with EP antiwear additive had higher welding loads, higher load wear indexes and smaller scars for the same load. The topography and surface chemistry of the ball-bearing specimens were examined using scanning electron microscopy and LINK techniques, respectively, thereby highlighting the protection mechanism of the additive, which works either by mechanical deformation or by filling the micro-cracks.