Arrangements and their bearing types
A bearing arrangement supports and locates a shaft, radially and axially, relative to other components such as housings. Typically, two bearing supports are required to position a shaft. Depending on certain requirements, such as stiffness or load directions, a bearing support may consist of one or more bearings.
- locating/non-locating bearing arrangements
- adjusted bearing arrangements
- floating bearing arrangements
Locating/non-locating bearing arrangements
- The locating support provides axial location of the shaft relative to the housing.
- The non-locating support accommodates axial displacements that occur when thermal expansion of the shaft relative to the housing changes the distance between the two bearings. Additionally, it compensates for the accumulation of tolerances of the components, which affects the distance between the two bearings.
Radial bearings that can accommodate combined (radial and axial) loads are used for the locating bearing support. These include:
- deep groove ball bearings
- two universally matchable single row angular contact ball bearings, arranged back-to-back or face-to-face
- double row angular contact ball bearings
- self-aligning ball bearings
- spherical roller bearings
- matched tapered roller bearings, arranged back-to-back or face-to-face
- cylindrical roller bearings with flanges on both rings or cylindrical roller bearings mounted with an angle ring (thrust collar)
The locating bearing support can consist of a combination of bearings. For example (fig. 2):
- To accommodate the radial load, a cylindrical roller bearing that has one ring without flanges may be used.
- To provide the axial location, deep groove ball bearing, a four-point contact ball bearing, or a pair of angular contact ball bearings may be used.
The outer ring of the axial locating bearing must be mounted radially free and should not be clamped. Otherwise, this bearing can be subjected to unintended radial loads.
There are two ways to accommodate axial displacements at the non-locating bearing support:
Use a bearing type that enables axial displacement within the bearing (fig. 3):
- cylindrical roller bearings with flanges on one ring only
- needle roller bearings
- CARB toroidal roller bearings
When these bearings are rotating, they accommodate axial displacement and induce almost no axial load on the bearing arrangement. You should use this solution where an interference fit is required for both rings.
- Use a loose fit between one bearing ring and its seat. Suitable bearing types include:
When using other bearing types, you may need to take additional design considerations into account.
From the large number of possible locating/non-locating bearing combinations, the following are the most popular.
For bearing arrangements where the axial displacement is accommodated within the bearing
Conventional bearing arrangements in which limited angular misalignment occurs include:
- deep groove ball bearing / cylindrical roller bearing (fig. 4)
- double row angular contact ball bearing / NU or N design cylindrical roller bearing (fig. 5)
- matched single row tapered roller bearings / NU or N design cylindrical roller bearing (fig. 6)
- NUP design cylindrical roller bearing / NU design cylindrical roller bearing (fig. 7)
- NU design cylindrical roller bearing and a four-point contact ball bearing / NU design cylindrical roller bearing (fig. 8)
SKF self-aligning bearing systems, which can compensate for more misalignment, are:
- spherical roller bearing / CARB toroidal roller bearing (fig. 9)
- self-aligning ball bearing / CARB toroidal roller bearing
For bearing arrangements where the axial displacement is accommodated between a bearing ring and its seat
Adjusted bearing arrangements
In adjusted bearing arrangements, the shaft is located axially in one direction by one bearing support and in the opposite direction by the other (cross-located). Adjusted bearing arrangements require proper adjustment of clearance or preload during mounting.
These bearing arrangements are generally used for short shafts, where thermal expansion has only a little effect. The most suitable bearings are:
Floating bearing arrangements
In floating bearing arrangements the shaft is cross-located, but is able to move axially a certain distance between the two end positions (i.e. “float”). When determining the required "float" distance , consider thermal expansion of the shaft relative to the housing and tolerances of the components, which affect the distance between the two bearings.
With this arrangement, the shaft can also be axially located by other components on the shaft (e.g. a double helical gear). Most common bearings are: