Study On Improving The Performance Of Rolling Bearing At Starved Lubrication By Porous PI

In the process of helicopter flight,when the lubrication system meets failure or the oil-tank is hit,the transmission system will enter the starved lubrication or dry running state.In this condition,transmission elements like bearings are most likely damaged.Therefore,it is significantly important to improve the performance of bearing under starved lubrication for improving the dry-running performance of transmission system and enhancing the safety and reliability of helicopter.Porous materials have been proved to be an excellent self-lubricating material,it can store and release lubricating oil due to its unique porous structure.Based on this,porous material was applied into retainers of rolling bearings and their effect on performance of bearings at starved lubrication was studied in this research.The results may help to provide experimental basis for improving dry running ability of transmission system of helicopter by using porous retainer.According to the limitations and shortcomings of existing research,this paper focused on the key index of porosity and prepared porous polyimide(PI)with different porosities.Their oil-containing and oil-supply properties as well as tribological properties were investigated.Also,porous retainers of rolling bearing were prepared and the friction and lubrication test of bearing was carried out.The whole contents and main conclusions are as follow:(1)Completed the preparation of porous polyimide with different porosities.The cold pressing and sintering method was used in the forming process.The results showed that the porosity of porous polyimide can be adjusted by controlling the pressure,sintering temperature and holding time.The porous structure of polyimide was observed.The results showed that porous samples have uniform pores,the larger the porosity,the more compactly the pores performed.(2)The oil-containing and oil-supply properties of porous polyimide were tested.The results showed that the porosity has a significant effect on the performance of oil store and oil supply.The larger the porosity,the higher the oil content ratio and oil supply content,the better the oil-containing and oil-supply properties performed.Based on the experiment and theoretical calculation,the oil-supply mechanism of porous polyimide was analyzed.The results showed that the thermal effect is the major cause,while the centrifugal force has little effect.(3)The tribological property of porous polyimide was systematically studied.The fiction and wear behavior of porous polyimide under different lubricating conditions(dry friction and starved lubrication),different porosity and different working conditions(temperature,speed,load).The results showed that porous structure has obvious improvement on the tribological properties of the polyimide at starved lubrication,and the porosity has a significant effect on the tribological properties.(4)Examined the effect of porous material on the starved lubrication performance of bearing by experiment.Porous polyimide retainers of two kinds of typically rolling bearings(thrust ball bearing and angular contact ball bearing)are manufactured by machine and the bearing lubrication tests were completed.The results showed that the porous polyimide retainer could supply the lubricating oil stably in the process of bearing operation,ensure good lubricating effect and prolong the life of the bearing.The larger the porosity of retainer,the better the anti-fiction and cooling effect showed.