Designs and variants
Bearings with a two-piece inner ring incorporate a large number of large balls, giving the bearing its high load carrying capacity, especially in the axial direction.
Bearings in the 33 D series (fig. 2) are separable, i.e. the outer ring with ball and cage assemblies can be mounted independently of the inner ring halves.
Bearings in the 33 DNRCBM series (fig. 3) are non-separable. They have a snap ring groove with a snap ring in the outer ring, enabling simple and space-saving axial location in the housing. Bearings in the 33 DNRCBM series have been designed specifically for centrifugal pumps, but can also be used in other applications.
SKF double row angular contact ball bearings are equipped with two cages. Depending on the bearing design, series and size, the cage design varies (table 1).
The lubricants generally used for rolling bearings do not have a detrimental effect on cage properties. However, some synthetic oils and greases with a synthetic oil base and lubricants containing EP additives, when used at high temperatures, can have a detrimental effect on polyamide cages. For additional information about the suitability of cages, refer to Cages and Cage materials.
SKF supplies the most common basic design bearings capped with a contact seal or shield on both sides. For information about the suitability of seals or shields under various conditions, refer to Sealing solutions.
Bearings capped on both sides are lubricated for the life of the bearing and should not be washed or relubricated. The bearings are considered virtually maintenance-free. If they are to be hot mounted, an induction heater should be used. SKF does not recommend heating capped bearings above 80 °C (175 °F). However, if higher temperatures are necessary make sure that the temperature does not exceed the permissible temperature of either the seal or grease, whichever is lowest. During start-up, grease may leak at the inner ring. For bearing arrangements where this would be detrimental, special design steps must be undertaken. For additional information, contact the SKF application engineering service.
Shields are made of sheet steel. SKF supplies shields in two designs. The shields used in smaller bearings have an extension in the shield bore to form a long, narrow gap with the inner ring shoulder (fig. 4). The shields used in larger bearings and in all SKF Explorer bearings extend into a recess on the inner ring (fig. 5).
SKF double row angular contact ball bearings with a shield on both sides are identified by the designation suffix 2Z.
Contact seals (fig. 6) are made of NBR and are reinforced with a sheet steel insert. These seals, which are fitted in a recess on the outer ring, make good, positive contact with the recess. The seal lip exerts light pressure against the recess on the inner ring to provide an effective seal.
SKF double row angular contact ball bearings with a contact seal on both sides are identified by the designation suffix 2RS1.
Greases for capped bearings
Capped double row angular contact ball bearings are filled with one of the following greases (table 2):
- The standard grease is GJN.
- In Europe, MT33 is commonly used and widely available.
- SKF Energy Efficient angular contact ball bearings are filled with the low-friction grease GE2.
- Other greases listed in table 2 can be supplied on request.
The standard grease is not identified in the bearing designation (no designation suffix). Other greases are indicated by the corresponding grease suffix.