Locating/non-locating bearing system
A locating/non-locating bearing system in a typical industrial application is designed to accommodate thermal expansion and contraction of a shaft. In this system, the bearing arrangement at one end of the shaft must be able to locate the shaft axially. This is accomplished by securing one bearing axially on the shaft and in the housing. The bearing arrangement on the opposite end of the shaft is non-locating and is designed to accommodate thermal displacements of the shaft relative to the housing to avoid induced internal loads.
For the locating bearing position, radial bearings that can accommodate combined (radial and axial) loads are used. These include deep groove ball bearings, double row or matched 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 bearing arrangement in the locating position can consist of a combination of two 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.
The bearing that locates the shaft axially must not be located radially and is typically mounted with a small radial gap in the housing.
There are two ways to accommodate thermal displacements of the shaft at the non-locating bearing position. The first is to use a bearing that only accommodates radial loads and enables axial displacement within the bearing. These include CARB toroidal roller bearings, needle roller bearings and cylindrical roller bearings that have one ring without flanges. The other method is to use a radial bearing mounted with a small radial gap 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 systems 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 system 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 bearing system.
For bearing systems 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: