Evaluation of hybrid spindle bearings with nitriding raceway steels under high rotational speeds

Abstract

The further development of high-precision bearings regarding higher speeds and load-carrying capacity is becoming increasingly challenging. One approach to meet the increased requirements is to use new high-performance raceway steels. Particularly for a highly stressed lubricant film, where seizure may occur, the bearing material properties can make a key contribution in increasing the lifetime. In the following, the test results of hybrid spindle bearings of type 7008 made of nitriding steel are analysed. The bearings were tested in an endurance run for a constant speed parameter of 2.5 million ndm and a maximum contact stress of 2,900 MPa at the inner ring contact. The operational behaviour was validated based on the bearing outer ring temperature and the acceleration level in the test rig. A further sample test in endurance runs with an increased speed parameter of 2.8 million ndm and a maximum contact stress of 3,200 MPa at the inner ring shows that the performance limit of the bearing is even higher than initially assumed. The microscope analyses of the bearing steels after the test show low wear. An analysis of the test conditions in terms of contact stresses, lifetime and the pv value illustrates that the bearings can run far above standard conditions. The experimental results show that the operational limits of hybrid spindle bearings with a raceway made of nitriding steels are significantly higher than expected.