Radial floating bearing for high speed applications

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In machine tool main spindle an axial movable and radial stiff bearing is necessary to reach highest rotational speed. State of the arts floating bearings show specific disadvantages like the thermal clamping of cylindrical roller bearings or the complex design with additional machine elements when using spindle bearings. Therefore, no optimal solution exists. This research project aims to develop and investigate a new radial floating bearing which meets to named criteria reliably and is easy to apply. The Floating Roller Ball bearing (FRB) combines the characteristics of a cylindrical roller bearing and an elastically mounted multi contact point bearing in a new roller geometry. In the first research period several aims were archived: First, the fundamental calculation methods to design FRB bearings and describe their operational behavior where developed. Second, a first prototype was designed. Third, the prototype was investigated in test runs and compared to reference bearings. Finally, optimization approaches for the calculation methods where identified. The computational analysis shows a high potential, since the FRB bearing shows a high stiffness with a low sensitivity of the operational behavior to rotational speed and load in comparison to spindle and cylindrical roller bearings. The experimental investigation confirms the functionality of the bearing concept and shows that the speed limit of FRB bearings exceeds that of similar cylindrical roller bearings. Nevertheless, wear detected on the grooves and cage indicates a strong tilting and skewing motion of the rollers. The aim of the second research period is to identify an optimized bearing geometry for highest rotational speeds. The first challenge is to investigate and describe the problems detected during the first research period caused by critical operation conditions like low preload, tilting of the movable outer ring or unsuitable lubrication. The second challenge is to find design features and operational conditions to prevent these problems. The project consists of four working packages. The aim of the first working package is to model the skewing motion of the roller. The second working package aims to design different test geometries. In the third working package the objective is to enhance the understanding of the operational behavior of both reference and FRB bearings, while the fourth working package aims to characterize critical operation conditions. The results regarding friction, skewing, wear mechanisms and lubrication can be transferred to other bearing types and enhance the basic knowledge of the operational behavior of high speed bearings in general. With the help of derived design recommendations the findings can be transferred to practical applications and form the basis of a transfer project.