Locating/non-locating bearing arrangement
A locating/non-locating bearing arrangement in a typical industrial application is designed to accommodate thermal expansion and contraction of a shaft. In this bearing arrangement, the locating bearing support at one end of the shaft provides axial location of the shaft relative to the housing. The bearing support on the opposite end of the shaft is non-locating and is designed to accommodate axial displacements due to thermal elongation of the shaft relative to the housing. This avoids induced internal loads.
For the locating bearing support, radial bearings that can accommodate combined (radial and axial) loads are used. These include deep groove ball bearings, double row or universally matchable single row angular contact ball bearings, self-aligning ball bearings, spherical roller bearings, matched tapered roller bearings, NUP design cylindrical roller bearings, or NJ design cylindrical roller bearings mounted with an HJ angle ring.
Alternatively, the locating bearing support can consist of a combination of bearings:
- A radial bearing that only accommodates radial load, such as a cylindrical roller bearing that has one ring without flanges.
- A bearing that provides axial location, such as a deep groove ball bearing, a four-point contact ball bearing, or a double direction thrust bearing.
To ensure that this bearing does not accommodate radial load, it is typically mounted with its outer ring having radial and axial clearance in its housing (Four-point contact ball bearing used as a thrust bearing).
There are two ways to accommodate axial displacements due to thermal elongation of the shaft at the non-locating bearing support:
- Use a bearing type that only accommodates radial loads and enables axial displacement within itself. These include CARB toroidal roller bearings, needle roller bearings and cylindrical roller bearings where one of the rings is without flanges.
- Use a radial bearing mounted with a loose fit in the housing so that the outer ring is free to move axially.
From the large number of locating/non-locating bearing combinations, the popular ones are listed in the following.
For stiff bearing arrangements requiring “frictionless” axial displacement within a bearing, the following combinations should be considered:
- deep groove ball bearing / cylindrical roller bearing (fig. 1)
- double row angular contact ball bearing / NU or N design cylindrical roller bearing (fig. 2)
- matched single row tapered roller bearings / NU or N design cylindrical roller bearing (fig. 3)
- NUP design cylindrical roller bearing / NU design cylindrical roller bearing (fig. 4)
- NU design cylindrical roller bearing and a four-point contact ball bearing / NU design cylindrical roller bearing (fig. 5)
For the bearing arrangements listed above, angular misalignment of the shaft relative to the housing must be kept to a minimum. If this is not possible, SKF recommends a self-aligning bearing system that consists of either:
- spherical roller bearing / CARB toroidal roller bearing (fig. 6)
- self-aligning ball bearing / CARB toroidal roller bearing
The ability of this bearing arrangement to accommodate angular misalignment of the shaft relative to the housing, as well as axial displacement of the shaft within the CARB bearing, avoids induced internal axial loads in the bearings.
For bearing arrangements with a rotating inner ring load, where changes in the shaft length are to be accommodated between the bearing and its seat, axial displacement should take place between the bearing outer ring and its housing. The most common combinations are: