What is self-align ball bearing?

Self-aligning ball bearings are recommended for applications where aligning the shaft and housing is difficult or where the shaft may bend, such as transmission shafts. The outer ring has a spherical raceway and its center of curvature coincides with that of the bearing, allowing the axis of the inner ring, balls, and cage to rotate freely around the bearing center. Pressed steel cages are typically used for this type.

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Since they have a small contact angle, self-aligning ball bearings have low axial load capacity. Permissible dynamic misalignment is approximately 0.07 to 0.12 radian (4 to 7 degrees) under normal loads; however, such angles may not be allowable depending on the surrounding structure.

Features

• Correct for misalignment
  The inner ring, balls, and cage rotate freely around the bearing center, allowing permissible dynamic misalignment of about 0.07 to 0.12 radian (4 to 7 degrees) under normal loads.
• Ideal for difficult mountings
  Self-aligning ball bearings suit applications where shaft bending occurs and where it is difficult to align the shaft and housing (transmission shafts, etc.)

Applications

By Joyce Laird, Contributing Editor

What is different about self-aligning bearings vs. basic bearings?

In a self-aligning bearing, the inner ring has two raceways and the outer ring has a single spherical raceway with its center of curvature coincident with the bearing axis. This allows the axis of the inner ring, balls and cage to deflect around the bearing center to automatically correct misalignment caused by housing and shaft machining or installation error.

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Paul Brda, Application Engineer, NSK Americas explains, &#;Whereas a ball bearing only has one raceway groove on both the inner and outer ring and is the most common type of rolling bearing.&#;

Why would you choose to use self-aligning bearings?

A self-aligning bearing is recommended when the alignment of the shaft and housing is difficult or when the shaft may bend during operation. Brda notes that similar to deep groove ball bearings, most self-aligning ball are for general use.

Can they interchange with standard ball bearing assemblies?
Depending on the series, most self-aligning bearings can be interchanged with standard ball bearing assemblies. ( and have direct interchanges with the and series). &#;However, if this is not possible, the self-aligning bearing may be wider or can have a tapered bore,&#; Brda explains.

Selection and Installation tips

According to Brda, the bearing would be selected based on the load, speed and space constraints of the application. Also, the misalignment and/or shaft bending amount should be considered when specifying bearing type.

Normal mounting and handling procedures for a cylindrical bore bearing should be followed. For the tapered bore, special care must be taken to ensure the bearing is driven up the taper the appropriate amount. Because matching the bearing to the specific application is critical, it is important to verify your application need with your selected vendor.