These units consist of a bearing element and a housing, assembled to permit convenient mounting. All components are mounted in a single unit to ensure proper protection, lubrication, and operation of the bearing.
Lubrication is provided within the units and sealing elements retain the lubricant and exclude foreign material.
Ratings consider:
- Shaft mounting.
- Housing configuration.
- Heat dissipation.
Units from different manufacturers typically interchange and differ only in individual features.
Rigid premounted units require accurate alignment with the shaft. Therefore, overall cost may be higher than self-aligning types because of additional assembly labor.
Self-aligning units compensate for minor misalignment in mounting structures, shaft deflection, and changes which may occur after installation. Self-alignment in sleeve and some rolling types is accomplished by use of separate inner housings, into which the bearing element is assembled. A ball-and-socket action between inner and outer housings accommodates the misalignment. Some rolling bearings have spherical outer races which permit self-alignment within the bearing element.
Expansion bearings permit axial shaft movement in equipment where shafts become heated and increase in length at a greater rate than the structure on which the bearings are mounted. Under such conditions, sleeve bearings permit the shaft to move through the bearing.
Nonexpansion bearings restrict shaft movement relative to the mounting structure and keep shaft and attached components accurately positioned. They also serve as thrust bearings within their capacity. Nonexpansion sleeve bearings usually require collars attached to the shaft at both ends of the housing. Nonexpansion roller bearings are constructed with the bearing element or inner housing mounted in the outer housing to restrict lateral movement. The bearing element is secured to the shaft by conventional methods.
