Experimental Study on the Lubrication Enhancement of Slider-on-Disc Contact by Stearic Acid Adsorption under Limited Lubricant Supply

The optimization of the lubricant supply quantity contributes to minimizing energy losses and wastage. To enhance the performance of hydrodynamic bearings running with limited lubricant supply (LLS), this study examined the effect of stearic acid as an additive. Stearic acid is commonly used for boundary lubrication as an organic friction modifier. How the stearic acid adsorption affects the hydrodynamic lubrication of a slider-on-disc contact under LLS was investigated using interferometry measurement and fluorescence observation in this study. Firstly, the oil reservoir of PAO10 with stearic acid adsorption was observed at the slider entrance. Secondly, the film thickness versus speed of PAO10 and PAO10 with 0.1% and 0.3% stearic acid, respectively, were measured. Finally, the morphology and surface properties of the glass and steel blocks with stearic acid adsorption were characterized by atomic force microscopy and Fourier transform infrared spectroscopy. The results show that the stearic acid adsorption layer weakens the wettability of the lubrication track and induces the ‘dewetting’ phenomenon of the lubricating oil. Thus, discrete oil distribution in the form of stripe or droplet can be generated, which leads to the accumulation of lubricating oil at the slider entrance to form a reservoir. An additional inlet pressure that is generated by the oil reservoir due to surface tension increases the oil film formation capacity. Furthermore, the morphologies of the adsorbed stearic acid layer on the glass and the steel blocks are, respectively, characterized by the nano-sized granular bulge and brush structure. This study reveals a new role of stearic acid adsorption in promoting LLS lubrication.