Locating/non-locating bearing arrangements
Conventional locating/non-locating bearing arrangements (fig. 1) are designed to accommodate thermal elongation of the shaft. In these arrangements, the non-locating bearing must be able to move axially on its seat in the housing.
SKF housings can accommodate bearings in both the locating and non-locating positions. Most standard housings have a bearing seat that is sufficiently wide to enable axial displacement of the non-locating bearing (fig. 2, "s"). When these housings are used in the locating position, locating (stabilizing) ring(s) should be used to secure the bearing axially in the housing (fig. 3).
Some SKF housing series are available with a wide bearing seat for axial displacement, designation suffix L, and a bearing seat that matches the width of the bearing to locate it axially, designation suffix F (fig. 4).
The SKF self-aligning bearing system
To accommodate misalignment and shaft deflections, conventional self-aligning bearing arrangements use spherical roller or self-aligning ball bearings in both the locating and non-locating bearing positions (fig. 1). To accommodate thermal elongation of the shaft in these arrangements, the non-locating bearing must be able to move axially on its seat in the housing. Any wear or damage to the housing seat results in a “stick-slip” condition that induces axial loads, friction, and heat into the bearing arrangement.
A better solution is to use a CARB toroidal roller bearing in the non-locating position (fig. 1). CARB bearings accommodate misalignment and shaft deflections. They also accommodate thermal elongation of the shaft within the bearing, with virtually no friction, to avoid induced axial loads.
Because CARB bearings do not accommodate axial loads, these bearings must always be secured axially in the housing, with either locating (stabilizing) rings or by using a housing variant with an F (or RA for some housings) in its designation suffix.
Compared to conventional self-aligning bearing arrangements, replacing the non-locating bearing with a CARB bearing increases the load carrying capacity of the bearing arrangement, enabling a more compact, and therefore lighter, bearing arrangement to be used. By virtually eliminating induced axial loads, vibration levels and temperatures are reduced and less grease is consumed, resulting in less maintenance. The solution contributes to improved reliability and extended bearing service life.
Typical shaft-bearing combinations
Bearings in SKF housings can be mounted either directly on a shaft or on a sleeve on the shaft. There are four typical combinations (table 1):
- plain shaft with bearing on an adapter sleeve
- stepped shaft with bearing on an adapter sleeve
- stepped shaft with bearing on a withdrawal sleeve
- stepped shaft with bearing on a cylindrical seat