Increasing the speed suitability of tapered roller bearings for use in main spindles

• Applicant: Professor Dr.-Ing. Christian Brecher
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 519602222

In main spindles for high performance cutting, spindle bearings are used to support the rotating shaft and transmit high cutting forces into the machine structure. Compared to spindle bearings tapered roller bearings have a much higher stiffness and load capacity but a significantly lower speed limit due to high friction of the line and rib-roller contact. However, tapered roller bearings can be a suitable alternative in these applications. The objective of this project is to increase the limited knowledge regarding the operational behavior of tapered roller bearings for high-speed applications and high loads. The obtained results will be combined in recommendations and guidelines for the design and operation of high-speed tapered roller bearings. In the first project period, the axial stiffness of tapered roller bearing was modeled. In particular, the critical influence of the rib-roller-contact was identified. In addition to this, a new bearing prototype with ceramic rollers, an optimized geometry and a lubricated rib at the outer ring was designed. However, the new bearing prototype doesn’t fulfill the requirements for high speed applications yet. The skewing of the roller caused by friction and an anisotropic thermal deformation of the rollers where identified as the reasons for bearing failure. By extending the existing model these influences can be taken into account. Besides that, the calculation of the radial stiffness should be enabled. In addition to this, the calculation with measured geometries of the roller should be integrated in the extended model, making it possible to evaluate the influence of manufacturing tolerances on the operational behavior. For confirm the assumed cause of failure of the bearing prototype, the roller skewing will be measured directly on a new test rig under radial loads. With the results of the failure analysis, a new prototype bearing will be developed. To evaluate the influence of the roller’s length on its skewing an additional test bearing with longer rollers will be evaluated. The new bearings with ceramic and steel rollers will be tested in short and long-term-tests under different load combinations with high radial forces. The test will show, if the adopted measures are expedient. Subsequent, the extensions of the simulation model will be validated with the measurements. Finally, the results of the research project will be summarized in form of recommendations for the design of the bearing geometry and the safe operation at high rotational speeds.

• DFG Programme: Research Grants