Lubrication Characteristics of Porous Oil-containing Polyimide and Friction and Wear Analysis of Their Compatibility with Silicon Nitride
Porous polyimide (PPI) has become the main material for aerospace bearing cages due to its excellent self-lubrication. To investigate the self-lubricating properties of PPI and its anti-friction and lubrication effect on silicon nitride (Si3N4) ceramic materials,PPI was impregnated with polyimide of different viscosities,and α-Two types of PPI oil containing samples were obtained from olefin oil PAO 4 and PAO 10. Centrifuge and vacuum oven were used to conduct centrifugation and heating tests on PPI oil containing samples,to explore the oil storage performance of PPI oil containing samples at different speed and temperature. A Retc ball/disc friction and wear testing machine was used to conduct sliding friction and wear tests at different temperature and load under immersion and dry friction conditions. After the test was completed,the wear and lubrication mechanisms of the samples under different lubrication conditions were analyzed with a Taylor roughness meter and a 3D laser confocal microscope. The results showed that immersing different viscosity poly (alpha olefin) oils into PPI samples resulted in a stable oil content of 17％ to 18％ for the PPI samples,indicating that PPI samples had a wide range of applications for lubricating oil viscosity. At a speed of 3000 r/min,the sample had good oil retention and almost no oil spills;As the temperature continued to rise,the oil output of the sample gradually increased;The main factor affecting the oil yield of PPI oil containing samples was temperature. Within the scope of test and research,the friction coefficient between two PPI oil-bearing samples immersed in PAO 4 and PAO 10 and Si3N4 was 0.04-0.124,showing a stable friction coefficient. Under dry friction conditions,the friction coefficient between PPI samples and Si3N4 was 0.343-0.452,showing a fluctuating friction coefficient. The friction coefficient and wear rate under oil immersion conditions were significantly lower than those under dry friction conditions,And the PPI oil containing sample maintained continuous and stable lubrication during the test period;During the sliding friction process,the lubricating oil in the PPI oil containing sample gradually moved towards the surface of the sample due to temperature and pressure,forming a lubricating oil film,preventing direct contact between the friction pairs,keeping the friction coefficient in a continuously low state,providing good lubrication and protection for the PPI sample,and extending the service life of the PPI sample;With the increase of temperature and load,the viscosity and output of lubricating oil changed,leading to the change of the quality of lubricating oil film,which made the friction coefficient of PPI fluctuate under the condition of oil immersion. Excessive temperature can reduce the performance of lubricating oil,while excessive load can damage the adsorption film on the working surface and cause significant wear. Appropriate temperature and load are conducive to forming a complete and stable lubricating oil film,achieving good lubrication effect. Therefore,reasonable control of temperature and load can achieve the best friction reduction and lubrication effect of PPI,providing guidance for its lubrication as a cage material in Si3N4 all ceramic bearings.
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