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Bearing Arrangement, Back to Back and Face to Face

When bearings are overloaded see what happen to them.

By: Cyrus

When bearings operate beyond the rated design, the bearing are overloaded. The greater the overload the shorter the bearing life. Bearings are an essential part of rotating equipment. The final load, whether it be axial or radial, is finally grounded with the help of bearings. Bearings may be considered analogous to ground connection in the case of electrical circuit. Bearings can be classified depending on various criteria such as the design, loading conditions, arrangements, type of lubrication and so on. Proper selection of the bearing is important, but not as important as proper installation. Following the correct assembly procedure while installing the bearings is paramount to achieving the intended service life of the bearing.

Understanding duplex bearing arrangements during selection as well as assembly is important. Incorrect installation and a failure to understand what the application is could result in problems while running the equipment, such as skidding or overheating.

The aim of this article is to present the underlying factors and what happens when bearings are preloaded.

Duplex bearings are a set of two bearings that attain greater radial and axial rigidity when arranged on a shaft with the inner and outer rings clamped together with preload. Single-row angular contact ball bearings and tapered roller bearings are generally preloaded axially by mounting them against a second bearing of the same type and size in a back-to-back (load lines diverge) or face-to-face (load lines converge) arrangement.

As mentioned above, these different types call for the different faces of the bearings to come in contact, causing preload. These arrangements are typically used in connection with angular contact ball bearings and tapered roller bearings. The preloading is achieved either by closing the gap between outer-race faces or inner-race faces, depending on the type of arrangement.

Types of Bearing Arrangements

This include:

• Back to back arrangement:(O arrangement) It gives maximum stability and rigidity. In this arrangement, inner ring faces are designed to touch each other to achieve preload.

     Understanding Back to back bearing Arrangement

In this arrangement the outer races are radially and axially restricted completely. the internal clearance of the bearing will be closed when the inner races of the two bearings touch. That is called preloading. When preloading, the inner races of the bearings are being pushed toward one another.

• Face to face arrangement:(X arrangement) this type of arrangement can accommodate misalignments and can not support moment load very effectively as the back to back arrangements.

When misalignment cannot be avoided between the bearing positions, face-to-face bearing arrangements are recommended.

                             Understanding face to face bearing arrangements

The reaction load lines in this arrangement are converging inside reducing the distance L as to the back to back arrangement. The point to note here is that the inner races are touching each other at the face and the gap is initially present at the outer races. In this arrangement the preload is achieved by closing the gap between the outer race.

Since the movement of the inner races is completely confined, there will be a reaction force arising inside out, i.e., the reaction will be given by the inner races against the applied force. This is due to the load lines will come closer to reducing the length L. The reaction force coming from the shaft (inner races) reduces the stiffness of the arrangement and then it can tolerate some misalignments.