Molecular Dynamics Simulations of Lubricant Outflow in Porous Polyimide Retainers of Bearings

The retainer of a space rolling bearing widely made of porous polyimide (PI) materials is oil-impregnated and can continuously release lubricants for lubrication. Understanding the lubricant supply mechanism in porous polyimide retainers is important to improve the lubrication performance of space bearings and therefore extends the bearing life. In this work, molecular dynamics simulations are adopted to model the lubricant outflow process from the pore of the PI material. Coarse-grained models are constructed to investigate the lubricant migration behaviors with different pore sizes and radii of rotation. At rest, a lubricant within the pore fails to outflow due to the capillary effect, which decreases with the increase of the pore size. However, for the rotating pores, if the inertial forces generated by the rotational motion exceed the capillary forces, the lubricants will begin to accumulate and some of the lubricants will flow out. Furthermore, the lubricant in the larger pore is easier to outflow due to the smaller capillary forces. This study quantifies the inertial effect and reveals that the centrifugal force is the main mechanism of lubricant outflow from the pores.