Needle roller / cylindrical roller thrust bearings
These combined bearings:
consist of a radial needle roller bearing and a cylindrical roller thrust bearing
The cylindrical roller and cage thrust assembly is identical to the 811 series.
- are supplied without an inner ring
- can be combined with an inner ring (fig. 2), where the shaft cannot be hardened and ground (→ product table, must be ordered separately)
- can accommodate axial loads in one direction
- can locate the shaft in one direction only
can be mounted back-to-back (fig. 3) for short shafts and where changes in length due to thermal expansion are relatively minor
For these types of arrangements, SKF recommends preloading the thrust ball bearings with cup springs (Belleville washers). This elastic preload helps to prevent the balls from skidding if one of the thrust bearings becomes unloaded. Preload also improves performance of the thrust ball bearings while reducing noise levels.
- are separable (fig. 1)
- can be mounted separately from both the cylindrical roller and cage thrust assembly and the shaft washer
- should be oil lubricated, as oil facilitates an adequate supply of lubricant to the bearing
- have no stamped steel cover, as standard
have a stamped steel cover for bearings with designation suffix Z (fig. 4) that
- has no lubrication holes
- extends over the shaft washer of the cylindrical roller thrust bearing
- is firmly attached to the housing washer that is integral to the needle roller bearing outer ring
- makes these bearings non-separable
SKF supplies certain needle roller / cylindrical roller thrust bearings capped with a stamped steel cover over the thrust part of the bearing (fig. 4, designation suffix Z). The cover, which has no lubrication holes, forms a gap-type seal to retain the grease in the bearing.
When capped bearings must operate under certain conditions, such as very high speeds or high temperatures, some grease may leak. For bearing arrangements where this would be detrimental, appropriate actions could be taken.
The thrust part of combined needle roller bearings with the designation suffix Z is supplied greased as standard. They are filled with high-quality grease (table 1) under clean conditions.
The relatively large quantity of grease in the bearings means they can be operated for long periods before relubrication is required (→ Perform calculations). SKF recommends SKF LGWA 2 grease (table 1), if relubrication is required.
The needle roller bearing used in combined bearings has an annular groove with one lubrication hole in the outer ring.