BY MIKE SANTORA
A self-aligning cylindrical roller bearing
is a cylindrical roller bearing inside a spherical bushing, which allows the bearing to accommodate misalignment and axial growth of the shaft. However, the addition of the spherical ring limits the radial capacity of the bearing by reducing the diameter of the rollers that can be incorporated into the predefined design envelope (smaller rollers equating to less load capacity).
The toroidal bearing is the best known and has been the prevalent design. It was introduced in the early 1990s and was first to provide combined axial float and dynamic misalignment capability. It uses highly profiled inner and outer rings and rollers to deliver this dual functionality. However, the functions are not independent of one another, and therefore, maximum misalignment cannot be achieved at the same time as maximum axial float. In addition, comparatively high radial internal clearances are required for acceptable misalignment and float performance in demanding applications.
The toroidal bearing is typically installed with an inner ring offset such that the rings become approximately aligned when the shaft reaches normal operating temperature. This means that bearing operation may be compromised during the critical warm-up period while the rings are offset. This operating condition might introduce roller skew and the potential for bearing lockup.
In the full-complement versions of these bearings (no cage or roller retainer), there is the risk of rollers falling out during handling and installation. This can result in damaged rollers. Sometimes a snap ring is used on one side of the bearing to help retain the rollers, but extra care must be taken to correctly orient the ring at installation. Incorrect orientation can lead to the snap ring contacting the rollers in operation as the shaft expands.
Thus, the ideal bearing would combine the full axial float characteristics of a cylindrical roller bearing, the excellent static and dynamic misalignment capability of a spherical roller bearing, and a contained or unitized roller set that facilitates simple, straightforward installation and maintenance.