Spherical roller bearings have the advantage that they provide a much larger load capacity than ball bearings and can accommodate axial force. One of the features that makes an Extreme Bearing unit stand out is its ability to accommodate axial displacement. The bearing seats in the housings are sufficiently wide to allow axial displacement of the bearing and to accommodate for thermal expansion and contraction of the shaft due to high or low temperatures. Temperature variations are therefore not a problem.
Self-alignment in a traditional bearing versus an Extreme Bearing
Traditional ball bearing design subject to axial displacement.
The traditional bearing unit portrayed in the drawing contains ball-bearing inserts fitted with a spherical outer ring (marked in red). The idea is that the bearing is self-aligning. However, this is not always the case. What usually happens is that the force (F) holds the outer ring of the insert firmly in the housing, making it difficult or even impossible for the insert to adjust itself. If the bearings are subject to excessive axial loading, the forces generated penetrate through the bearing, causing damage to the balls, inner ring, ball race and even the housing. Ultimately, the insert has to be replaced, while the bearing housing is also damaged permanently in many cases.
An Extreme Bearing does not use an insert with a spherical outer ring, but instead has a flat outer ring with a concave raceway. The concave raceway in combination with the spherical rollers operate over a wide range of contact angles thus the rollers align themselves correctly with the shaft and assembly without causing undue stress on the rest of the bearing assembly.
Room for axial displacement
Suitable for expansion and contraction of the shaft
The seats of an Extreme Bearing are machined to a tolerance to provide a loose fit. The bearing seats in the housings are sufficiently wide to allow axial displacement of the bearing and to accommodate for thermal expansion of the shaft due to high temperatures, such as on a baking conveyor belt.
The Extreme Bearing blocks can absorb expansion of the shaft because there is an adjustment or locating ring in the bearing housing. The locating ring can be removed from a bearing block of a pair placed opposite each other so that axial displacement is possible.
Allow for thermal expansion and contraction
There is a total clearance available for thermal expansion that is equal to the thickness of the location ring. The expansion and contraction of material must be considered in order to maintain the clearance that is required to operate the bearing well. In the diagram, the clearance for contraction by cooling is indicated by C and the clearance for expansion by heating is indicated by B. The table shows the maximum values for C and B depending on the diameter of the shaft.
Calculate the maximum shaft length depending on the temperature in your application. In case you need to mount a long shaft, it is necessary to calculate the thermal expansion or contraction and adjust the bearing position to take this into account. As an example, a stainless steel shaft of 1 metre will become 0.023 mm longer when the temperature rises by 1°C and a carbon steel shaft of 1 metre will become 0.016 mm longer when the temperature rises by 1°C. The table shows the maximum shaft length depending on how the temperature changes during operation after the time of installation.