Spherical Roller Bearings: A Look Inside
Spherical roller bearings are self-aligning and can handle both radial and thrust loads. Take a look at the structure behind these bearings that allows them such versatility.
Spherical roller bearings are self-aligning and can handle both radial and thrust loads. Anti-friction bearings are named for their rolling element. With spherical roller bearings, the rollers are spherical shaped, as opposed to the more common ball shape. They have an inner and outer ring of similar race profiles.
Spherical bearings have two rows of rollers. This helps them handle a high radial load capacity and a moderate axial load capacity. In addition to this, spherical bearings can also handle a small amount of misalignment.
Through-hardened, 52100 steel is the most common material used for the rings and rollers of a spherical roller bearing. Occasionally, E3310 case-hardened steel is used, generally for application specific uses, such as paper mills.
Spherical roller thrust bearings combine the capacity for heavy thrust with moderate radial loading. Such designs will accommodate some dynamic misalignment. An exceptional advantage of the spherical roller bearing is its ability to handle both static and dynamic misalignment.
The outer race of the bearing has a spherical shape. The complete profile for the outer race and the complete profile of the roller both make a perfect sphere. The interaction between these two spheres is what allows for misalignment. When misalignment happens, the roller and inner assembly will automatically self-center inside the outer ring. This allows the load to be distributed through the center of the roller. This design feature aids in eliminating edge loading of rollers typically seen with other bearing types during misaligned conditions.
Another design feature of spherical bearings is line contact. This gives these bearings excellent radial load capacities. The profiled surface and symmetrical shape allow loads applied through the inner or outer ring to be distributed outward from the roller center. There are many other special features of spherical roller bearings. Super precision variations, for example, offer improved radial runout. Radial runout is the difference between the maximum and minimum distance between the surface of the bearing from the axis of rotation that occurs over one revolution. Another special feature is advanced metallurgy such as hardened cases, special coatings (thin, dense, and chrome), solid lubrication, and sealed bearings.
As mentioned previously, steel is often used as cage material on a spherical roller bearing. Steel cages come in two designs: CJ and YP. The CJ cage is a two piece, stamped steel, roller riding cage. This design is lightweight, low cost, and will sometimes accommodate either more or larger rollers than the machined brass cages. The YP design is a pin type, high capacity cage. YP’s are low volume and application specific. They use hardened steel pins and require two large cage rings and two small cage rings. The advantages of the YP design is they allow for either increased roller size or additional rollers to be added for increased load ratings.
Spherical bearings are used in countless industrial applications, where there are heavy loads, moderate speeds and possibly misalignment. Some common application areas are gear boxes, wind turbines, marine propulsion and offshore drilling.