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Needle roller / thrust ball bearings

SKF needle roller / thrust ball bearings com­bine a radial needle roller bearing and a thrust ball bearing. SKF supplies these bearings in the following two series:
  • NX series (fig. 1), with a full comple­ment thrust ball bearing
  • NKX series (fig. 2), with a thrust ball bearing with a cage
SKF supplies the bearings of both series without an inner ring. In applications where the shaft cannot be hardened and ground, the needle roller bearing can be combined with an inner ring (fig. 3). Appropriate inner rings are listed in the product table and must be ordered separately.
Needle roller / thrust ball bearings can accommodate axial loads in one direction and can, therefore, locate the shaft in one direction only. For short shafts and where changes in length as a result of thermal expansion are relatively minor, two bearings can be mounted back-to-back (fig. 4). For these types of arrangements, SKF recommends elastically 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.
NX series

Needle roller / full complement thrust ball bearings in the NX series (fig. 5) are suitable for applications where there are moderate radial loads and lighter, single direction axial loads. Their extremely low sectional height enables shaft centrelines to be positioned close together like for multi-spindle drills. For axial support, the bearings can be mounted with a snap ring or against a shoulder in the housing bore. The snap ring groove in the outer ring provides a cost-effective and axially space-saving solution (fig. 6). The appropriate snap rings are listed in the product table.

Needle roller / thrust ball bearings in the NX series have a stamped steel cover. It extends over the shaft washer of the thrust ball bearing and is firmly attached to the radial needle roller bearing. The cover makes these bearings non-separable. Most often they are oil lubricated, as the cover has lubrication holes. Therefore, SKF supplies these bearings without grease.

Needle roller / thrust ball bearings in the NX series with the designation suffix Z (fig. 7) have a stamped steel cover without lubrication holes and should be grease lubricated.

NKX series

Needle roller / thrust ball bearings in the NKX series combine a radial needle roller bearing and a thrust ball bearing with a ball and cage thrust assembly identical to the 511 series. They permit relatively high-speed operation. The outer ring flange locates the bearings axially in one direction.

Needle roller / thrust ball bearings in the NKX series (fig. 8) do not have a cover over the thrust ball bearing. Therefore, both the ball and cage assembly and shaft washer can be mounted separately from the rest of the bearing. These bearings, without the designation suffix Z, should be oil lubricated whenever possible, as there is no cover that retains the grease in the bearing.

Needle roller / thrust ball bearings in the NKX series with the designation suffix Z (fig. 9) have a stamped steel cover without lubrication holes. The steel cover extends over the shaft washer of the thrust ball bearing. It is firmly attached to the housing washer that is integral to the needle roller bearing outer ring. The cover makes these bearings non-separable.

Cages

Depending on their design, series and size, SKF needle roller / thrust ball bearings are fitted with cages shown in 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.

Sealing solutions

SKF supplies certain needle roller / thrust ball bearings capped with a stamped steel cover over the thrust part of the bearing (fig. 7, fig. 9). The cover, which has no lubrication holes, forms a gap-type seal to retain the grease in the bearing. These bearings are identified by the designation suffix Z.

Greases for capped bearings

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 under clean conditions.

The relatively large quantity of grease in the bearings means they can be operated for long periods before relubrication is required. SKF recommends SKF LGWA 2 grease, if relubrication is required.

The technical specifications for the initial grease fill and the grease for relubrication are listed in table 2.

Relubrication features

Depending on the design and size, SKF supplies needle roller bearings with different features to facilitate efficient lubrication and relubrication.

The needle roller bearing of all combined bearings has an annular groove with one lubrication hole in the outer ring.

Needle roller / full complement thrust ball bearings in the NX series without the designation suffix Z have a cover with lubrication holes over the thrust part of the bearing (fig. 5). Most often they are oil lubricated and, therefore, SKF supplies these bearings without grease.

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