Experimental Studies On The Friction Torque Of Ball Bearing Used In Space Mechanism Under Several Lubrication Conditions

Flexible operation, and low friction torque are advantages of ball bearings, so they has a wide range of applications, and is also common in the space agency. Only reasonable lubrication was established, those advantages existed, otherwise the friction torque is easy to become large, unstable and bearings even be stuck. The vacuum environment in space makes lubrication very difficult. So it is necessary to study the friction torque of ball bearings in vacuum. At home and foreign, there are many researches about Space tribological and ball bearing friction torque, but little about the friction torque of ball bearings used in space mechanism. In this kind of case, this article does the following works.The vacuum and different temperature environment as required is provided by setting up the vacuum friction experiment system. Lubrication method of space is discussed. Selectting MoS2-sputtered film, PFPE (perfluoropolyethers) grease and their combination used as lubrication, and the case of no lubrication as the contrast group. Analysing the influence of space environment upon the friction torque of ball bearings, choosing vacuum and temperature as key factors, and speed, load as additional factors, test the friction torque of ball bearing, analyse the of friction and wear.The experiments about the friction torque of ball bearing have been done. The results show that:for ball bearings treated with MoS2-sputtered film, the friction torque is small and stable, not sensitive to temperature, first a growth then a decrease with the increased speed, linear growth with load, much smaller in vacuum than atmosphere; for ball bearings without lubrication, the friction torque is bigger and more unstable, usually not sensitive to temperature and speed, but increase sharply as temperature or speed get high enough, usually linear growth with load, but Sharply increase as load is bigger enough in vacuum; For ball bearings lubricated by PFPE grease, start friction torque is large, and has a long adjust period. Friction torque has a continued decrease with the increase of temperature, first a slight decrease then a linear growth with the increase of load, first a growth then a decrease with the increased speed. The friction torque is larger in vacuum than the atmosphere. For ball bearings lubricated by modified PFPE grease, the friction torque usually is smaller than that of ball bearings lubricated by PFPE grease, especially at low temperature or heavy load. The friction torque first has a slight increase then a continued decrease with the increase of load or speed. For ball bearings having Mixed lubrication, the temperature characteristics of friction torque is similar to that of ball bearings lubricated by PFPE grease, but more gentle. The load characteristics and the speed characteristics of friction torque are similar to those of ball bearings lubricated by modified PFPE grease. The results of SEM and EDS show that:MoS2-sputtered film of solid lubricating ball bearing has been destroyed, but the ontology of bearing wears light. Ball bearing without lubrication got serious wear. Ball bearings PFPE grease lubricating by PFPE grease or modified PFPE grease wear light, and the latter is slighter. The destruction of MoS2-sputtered film in ball bearings having mixed lubrication is also very serious, and the ontology of bearing wears light.Based on the results of experiments, come to a conclusion. In space mechanism, when required light load, and short lifetime, we should choose ball bearing lubricated by solid film. When required heavy load, long lifetime, choose ball bearing lubricated by proper grease.