Cage Friction in High-Speed Spindle Bearings

Abstract

Friction-induced heat is one of the main reasons for the upper speed limit of high-speed angular contact ball bearings (spindle bearings). One source of friction inside the bearing is the cage. In this article, it is shown through experimental results that the frictional losses due to the cage are of significant magnitude. Based on measurements, a new, simple calculation model is proposed to estimate the cage induced frictional losses in spindle bearings under high rotational speed with minimal lubrication. The cage is assumed to rotate eccentrically around the bearing's axis and to be in contact with the outer ring at just one position. One single ball at the same position is assumed to drive the cage. Thereby, the friction between the cage and the outer ring is transformed in a breaking torque for the inner ring and the shaft. Both the cage outer ring contact and the ball cage contact are handled according to Coulomb's law of friction. Despite its simplicity, this model shows a close correlation with experimental results. Consideration of the centrifugal and thermal expansion provides insight into the relation between cage clearance and cage friction and hence allows for the development of new cage designs. Finally, the design and experimental results of optimized cages made of polyether ether ketone (PEEK) are presented.