When it comes to assembling a thin section bearing, you must account for the following: its type, orientation, direction and amount of applied loads, the maximum gap inside the bearing, the maximum friction torque it can handle, shaft and housing tolerances, the operational conditions, and which of the two rings rotate. With this in mind, there are several types of thin section bearings, most of which will be covered in this blog.
Radial Bearings (C-Type)
are used in applications where radial loads are applied. When two bearings are mounted on the outside of a long shaft, one of the two bearings should be free in an axial direction. This is especially important to avoid the thermal expansion of the shaft or its housings, ultimately resulting in axial thrust on the radial bearing.
Four-Point Contact Bearings (X-Type)
Four-point contact bearings are implemented where axial loads or a combination of axial and radial loads are present. If two bearings are mounted on the exterior of a long shaft, one of the two bearings must be radial (C-type) in design and should be free in an axial direction. It is important to note that two four-point contact bearings should not be used on the same shaft.
A single four-point contact bearing has the ability to absorb axial loads in both directions and tilting movements. Moreover, this type of bearing has a higher friction rating than radial bearings (C-type) and angular contact bearings
(A-type) with the same construction parameters. If radial and four-point contact bearings are used together, operators should follow the manufacturer’s recommendations regarding the shaft and housing tolerances. By following these steps, bearings will not be preloaded after installation, which can affect service life and performance.
Pairing the aforementioned bearings together, or any other coupling, is only valid if the bearings have the same standard gap, operational and environmental tolerances, and are constructed with compatible materials. Using different materials can affect assembly tolerances, produce excessive friction torque, or generate an unprecedented preload. When it comes to friction-and high-speed sensitive applications, pairs of angular-contact bearings can be used in place of a single four-point contact bearing.
Angular-Contact Bearings (A-Type)
Angular-contact bearings are the last type of bearing we will be covering. This bearing has the ability to absorb axial loads (thrust) in a single direction. As such, these bearings are typically used in combination with other bearings. Versatile in their capabilities, angular-contact bearings can be used in a back-to-back (DB) or a face-to-face (DF) configuration. When these bearings are combined, they can be used with certain axial preloads to reduce backlash and increase stiffness.
If these bearings are purchased individually, registering the preload during installation is important. When bought in pairs, the preload is executed in the factory. Angular-contact bearings are designed with inner and outer rings that must be fixed. For bearings with an axial preload, providing a gap between the bearing and the shaft is recommended. If a third bearing is used on the other end of a shaft, it is advised that one also utilizes a single radial pair or a face-to-face pair (DF).
As previously explained, thin-section ball bearings
are extremely sensitive to shaft and housing parameters. In general, bearings tend to take the shape of the shaft and housing, so the planarity of the bearing seat is critical. The bearing seat’s planarity tolerance should match the axial eccentricity of the combined bearing’s ring. Additionally, the planarity tolerance of the shaft and housing should have the same radial eccentricity as the mounted bearing’s ring.
To facilitate assembly, the shaft and housing should contain a shallow edge on the rings, and the radius of the bearing seats should be smaller than that of the bearing’s chamfer. If an interference assembly needs to be used, heating or cooling the bearing to facilitate assembly is possible, proceeding only when all components are at a set environmental temperature. The use of an interference assembly necessitates a uniform amount of pressure to be placed on the entire bearing.
With regard to proper preload settings for bearings, the optimal preload necessary for certain bearings depends on the application at hand. As preload increases, deflection under load decreases while bearing stiffness and natural frequency rise. Keep in mind that preload increase causes a higher friction torque as well.
Properly mounting your bearings ensures the optimal functionality of your applications; thus, using clamping flanges or plates on all bearings is recommended. Clamping flanges can provide a protective shield, keeping contaminants out while maintaining ample lubrication. For bearings utilized in harsh environments, using external seals can also protect the bearing.
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