Rolling bearings, transfer lubrication

The general problem of resupplying a system with a solid lubricant is discussed elsewhere in this book, and various possible techniques are mentioned, but resupply by transfer from some form of reservoir is the most successful technique, and the only one which has been used commercially. It has been used in spacecraft, and in terrestrial applications for vacuum or for very high or very low temperatures, while rolling bearings lubricated by solid lubricant composite retainers or cages have been commercially available for over thirty years. 

According to the published reports the tests were generally satisfactory, but there appear to have been no operational uses of the technique, and little or no further testing in the intervening forty years. This may be partly due to the complication of arranging a suitable feed system, and partly to the satisfactory development of alternative techniques such as composite retainers and transfer films, and lead lubrication for rolling bearings in vacuum ... 

PTFE (e.g.. Teflon) is widely used in the form of composites as self-lubricating cages for ball bearings. A thin film of polymer is transferred from the cage to the rolling/rubbing surface providing continuous lubrication for the system. 

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