Lubrication of Radial Loaded Tapered Roller Bearings Under High Rotational Speeds

To improve the manufacturing accuracy in the machining process, the stiffness of the machine tool spindle must be increased. One approach is to replace the conventionally used spindle bearings by tapered roller bearings to achieve a higher stiffness and load carrying capacity. However, the speed capability of this bearing type is limited, though can be enhanced by sufficient lubrication, especially in the critically loaded rib-roller-contact. The objective of this paper is to validate the lubricant influence on the speed capability of radially loaded tapered roller bearings. In various speed step runs, the operating behavior of the bearings under oil-air and grease lubrication was evaluated based on the outer ring temperature and the vibration level in the test rig. With oil-air lubrication, a speed parameter up to 900,000 mm/min could be achieved, whereas with grease lubrication, a speed parameter of 540,000 mm/min could be reached. In comparison, the setup with spindle bearings can achieve the highest investigated speed parameter of 900,000 mm/min with both grease and oil-air lubrication. For grease lubricated ball bearings, significantly higher temperature fluctuations are present with variation of the radial load. In the case of oil-air lubrication, the steady-state temperature improved with increasing oil viscosity.