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.
Main spindles and their bearings are of vital importance for the performance of machine tools and machining centers. Thus increasing demands on the machines' productivity and reliability directly affect the required bearing properties. The development and testing of rolling bearings in the speed range up to n x d m = 2,7 10 6 mm/min requires highly specialized test rigs to investigate the bearings' operating behavior. In such test rigs a customized telemetry system is used to continuously measure the test bearing's inner ring temperature. The system uses a shaft integrated bridge circuit with a Pt1000-temperature sensor. The temperature signal is made available as an analog and digital output. This system allows for a deeper understanding of the inner ring excess temperature which is of vital importance for the speed rating of high speed rolling bearings especially of such with small contact angles.
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