Designs and variants
SKF standard assortment
- bearings in the 32 A and 33 A series (fig. 1)
- bearings in the 33 D series
- capped bearings
- open bearings (that are also available capped) that may have recesses in the ring side faces
Bearings in the 52 and 53 series are no longer available and have been replaced with 32 A and 33 A series bearings, which are dimensionally interchangeable. Only size 3200 A is different, and has a width of 14 mm instead of 14,3 mm.
- have different tolerances and performance capabilities compared with SKF Explorer bearings
- incorporate a larger number of balls, and have a larger contact angle, giving the bearing its high load carrying capacity, especially in the axial direction
- are separable in the 33 D series (fig. 2), i.e. the outer ring with ball and cage assemblies can be mounted independently of the inner ring halves
are non-separable in the 33 DNRCBM series (fig. 3)
- have a snap ring groove with a snap ring in the outer ring, enabling simple and space-saving axial location in the housing
- have been designed specifically for centrifugal pumps, but can also be used in other applications
SKF supplies the most common basic design and SKF Explorer bearings capped with a contact seal or shield on both sides. For additional information, refer to Integral sealing.
Shields (designation suffix 2Z, fig. 4)
- are made of sheet steel
- extend into a recess on the inner ring
Contact seals (designation suffix 2RS1, fig. 5)
- are made of NBR
- are reinforced with a sheet steel insert
- are fitted in a recess on the outer ring and make good, positive contact with the recess
- have a lip that exerts light pressure against the recess on the inner ring to provide an effective seal
When capped bearings must operate under certain conditions, such as very high speeds or high temperatures, grease may appear between the inner ring and capping device. For bearing arrangements where this would be detrimental, appropriate actions should be taken.
Greases for capped bearings
Bearings capped on both sides are lubricated for the life of the bearing and are virtually maintenance-free. They are filled with one of the following greases (table 1):
- as standard → GJN
- in Europe → MT33 (commonly used and widely available)
- low-friction grease → GE2
- other greases (table 1) 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.
Grease life for capped bearings
- is presented as L10, i.e. the time period at the end of which 90% of the bearings are still reliably lubricated (diagram 1)
- the operating temperature
- the ndm value
- grease performance factor (GPF) (table 1)
- horizontal shaft
- inner ring rotation
- light load (P ≤ 0,05 C)
- operating temperature within the green temperature zone of the grease (table 1)
- stationary machine
- low vibration levels
Where the operating conditions differ as described below, the grease life obtained from the diagrams should be adjusted:
- vertical shafts → 50% of the obtained value
- heavier loads (P > 0,05 C) → apply reduction factor (table 2)
SKF double row angular contact ball bearings are as standard equipped with either a cage made of PA66 or of stamped steel, among others, as shown in table 3.
When used at high temperatures, some lubricants can have a detrimental effect on polyamide cages. For additional information about the suitability of cages, refer to Cages.