Page 594 - Rollingbearings

7 Needle roller bearings
Needle roller / cylindrical NKXR series bearings • have a stamped steel cover for bearings
roller thrust bearings • are separable with designation sufix Z (ig. 34) that
• can be mounted separately from both the – has no lubrication holes
SKF supplies needle roller / cylindrical roller cylindrical roller and cage thrust assembly – extends over the shaft washer of the
thrust bearings in the NKXR series (ig. 31) and the shaft washer cylindrical roller thrust bearing
These combined bearings: • should be oil lubricated, as oil facilitates an – is irmly attached to the housing washer
adequate supply of lubricant to the that is integral to the needle roller bear-
• consist of a radial needle roller bearing bearing ing outer ring
and a cylindrical roller thrust bearing • have no stamped steel cover, as standard – makes these bearings non-separable
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
(ig. 32), where the shaft cannot be hard-
ened and ground (product table,
page 658, must be ordered separately) Fig. 31 Fig. 32
• can accommodate axial loads in one Needle roller / cylindrical roller thrust NKXR ‥ Z bearing with an inner ring
direction bearing
• can locate the shaft in one direction only
• can be mounted back-to-back (ig. 33) 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 Belleville washers (cup
springs) This elastic preload helps to pre-
vent the balls from skidding if one of the
7 thrust bearings becomes unloaded
Preload also improves performance of the
thrust ball bearings while reducing noise Fig. 33
levels NKXR series bearings arranged back -to -back, incorporating Belleville washers

Fig. 34 Fig. 35
Needle roller / cylindrical roller thrust Inner rings
bearing

NKXR ‥ Z IR LR

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