Oil release mechanisms in porous polyimide bearing cages: A multiphysics modeling study

Porous polyimide bearing cages are widely used in space applications for their excellent self-lubricating capability. However, the oil release mechanisms still need to be further elucidated. This study develops a multiphysics coupled model to investigate oil release mechanisms under centrifugal, thermal and mechanical loading. The model incorporates thermal expansion, viscosity-temperature effect, and poroelastic coupling, and is validated through centrifugal fluorescence imaging and static heating experiments. The results reveal that centrifugal oil release follows a preferential flow-dominated mechanism. Lubricant exits exclusively through the outer surface while pocket surfaces exhibit inward flow, risking oil starvation at ball-cage contacts. The decoupling analysis demonstrates that viscosity reduction dominates thermally enhanced oil release, while thermal expansion plays a minor role. Moreover, solid-phase thermal expansion and poroelastic effects cannot be neglected; otherwise, the lubricant release can be overestimated by up to 82 %. In addition, ball-cage collision is found to induce transient flow with spatiotemporal hysteresis. These findings suggest that gradient porosity design and lubricant selection based on viscosity-temperature characteristics are more effective strategies for space bearing applications.