Research of the Lifetime and Lubricant Properties of Greases for Rolling Bearings Operating in Space Conditions

In this study, the lubricating properties and relative service life of plastic lubricants for work in space were studied. Grease relative lifetime and lubricity test methods and testing equipment were developed. Commercially available VNII NP-274, AMETIST, NIKA, IZUMRUD, and EFELE SG-394 greases are tested. The test procedure is based on testing the rolling bearing with a limited amount of lubricant. Lubricity is evaluated by the value of the friction coefficient. The grease relative lifetime is assessed by the bearing operation time before the friction coefficient sharply increases divided by the lubricant mass. Tests are carried out in both normal climatic conditions and conditions close to those in space (vacuum of <10–4 bar and at a high temperature of 100°С). The bearing load is 2800 N and rotation frequency is 50 rpm. The test results show that VNII NP-274, NIKA, and EFELE SG-394 greases have a low friction coefficient and a high relative lifetime under normal climatic conditions. When tested in conditions close to space (in vacuum and at high temperatures), NIKA and EFELE SG-394 greases have a low friction coefficient and the highest relative lifetime. The relative lifetime of the studied greases decreases 6–20-fold (for VNII NP-274, up to 200-fold) during the transition from normal climatic to space conditions. The lifetime decrease is associated with the lubricant accelerated destruction in vacuum and during heating.