Research Progress on the Tribological Properties of Porous Oil-Impregnated Polyimide for Bearing Cages

Porous oil-impregnated polyimide (iPPI) combines the functions of oil storage, oil supply, and oil reabsorption, offering significant potential for applications in space bearings and under starved-oil lubrication applications. This Review focuses on research progress in the tribological properties of porous polyimide (PPI), systematically elaborating on its structural characteristics, liquid storage behavior, self-lubricating antiwear mechanisms, and performance optimization methods. The formation mechanism, the structural characteristics, and their impact on the oil and mechanical properties of pores are highlighted. Research progress in lubrication models, friction-contact types, PPI modification, structural optimization, preparation technology optimization, and lubricant medium optimization is summarized. The results indicate that the tribological properties of iPPI are determined by the pore structure, the properties of the lubricating medium, and its dynamic migration behavior within the pores and are significantly influenced by the service conditions and the counterpart materials. Research in this field is progressively shifting from single-parameter adjustment toward collaborative design and predictable design for complex service requirements.