Page 40 - needle bearings

Bearing Fits
Shaft and Housing Design
NTN
NTN

7. Shaft and Housing Design

Even if the bearing to be used is selected correctly, it
can not fulfill its specific function unless the shaft/housing
on/in which it is installed is designed correctly.
Particularly for needle roller bearings the shaft and the
housing must be designed under special consideration
because the bearing ring thickness is thinner than that of
other rolling bearings.

7.1 Design of bearing installing portions
Where a needle roller bearing with cage is used as an
individual and is guided in axial direction directly by shaft
shoulder (Fig.7.1), the shaft shoulder with which the cage
side face comes in contact must be finished accurately
and also is not allowed to have any raiser thereon. For a
needle roller bearing subjected to high speed running, its
contact surface is hardened and thereafter fine-finished
by grinding. Fig. 7.1 Bearing fixing by thrust ring
When a snap ring is used for axial guide of the cage
(Fig.7.1), a thrust ring is inserted between the cage and
the snap ring to prevent the cut section of the snap ring
from contacting directly the cage. NTN shaft snap ring
WR type specially designed for NTN needle roller
bearings is available as the snap ring intended for axial
guide of bearing cage. (Refer to Dimensions Table on
page B-227.)
On other hand, radial needle roller bearing can move
freely in axial direction so that a ball bearing or a thrust
bearing is used at single side for axial positioning of the
shaft. Where axial load is less and, in addition, rotational
speed is not so high(Ex. idle gear in a gear box), a thrust
ring is fitted on the shaft, as illustrated in Fig. 7.2 and a
sliding bearing is formed between the thrust ring and the
outer ring or the housing end face for the purpose of axial
positioning. In such a design, good care must be
exercised so the guide surface is fully lubricated. Fig.7.3
illustrates an example of the above thrust ring with oil
groove on its guide surface. The boundary between this Fig. 7.2 Bearing fixing in axial direction
oil groove and the plane area must be chamfered for
deburring.
In general, for proper installation of needle roller
bearing the inner ring and outer ring are both positioned
in axial direction so that the bearing displaces in axial
direction while running.
0.6ʙ1mm 5ʙ6mm

Round a corner

Fig. 7.3 Design of thrust ring guide surface

A-36