Page 405 - Rollingbearings

Design considerations
Design Performance and operational reliability Four-point contact
depend on:
considerations ball bearings
• proper adjustment for single bearings
• the correct selection of clearance and Used as a thrust bearing
Single row angular preload for universally matchable bearings
If there is too much clearance in the
contact ball bearings bearing arrangement during operation, Four-point contact ball bearings are often
used as entirely thrust bearings, together
the load carrying capacity of the bearings with a radial bearing When used in this way,
Proper adjustment will not be fully utilized. Excessive preload the four-point contact ball bearing should be 3
produces more friction and higher operat- mounted with radial clearance in the hous-
Single row angular contact ball bearings ing temperatures, leading to a reduction in ing (ig. 12)
must be used (ig. 11): bearing service life.
• in combination with a cylindrical roller
• with a second bearing bearing:
• in sets Axial loads in one direction – the radial internal clearance of the cylin-
The bearings must be adjusted against drical roller bearing should be smaller
each other until the requisite clearance or When the axial load acts predominantly in than the theoretical radial internal
preload is obtained (Selecting preload, one direction in back-to-back and face-to- clearance of the four-point contact ball
page 186 face arrangements, unfavourable rolling bearing after both have been mounted
conditions for the balls of the axially – the theoretical radial clearance can be
Universally matchable bearings mounted unloaded bearing may occur, which can lead calculated from:
immediately adjacent to each other: to:
C = 0,7 C a
r
• require no further adjustment (Bearings • increased noise levels
for universal matching, page 385) • discontinuity in the lubricant ilm where
• obtain requisite clearance or preload by: • increased stresses on the cage C = theoretical radial internal clearance
r
– choosing bearings from an appropriate C = axial internal clearance (table 9,
a
clearance or preload class Under these circumstances, SKF recom- page 397)
– applying suitable its for the bearings on mends zero operating clearance, which can
the shaft and in the housing be attained by using springs. When springs – the outer ring of the four-point contact
are not suficient, using bearings with a 25° ball bearing must be able to accommo-
contact angle as a backup bearing may help date thermal movements
Therefore, it should not be clamped
axially, but a small gap should be main-
Load ratio tained between the outer ring and the
cover lange
• of F /F ≥ 1 is required by bearings in the – bearings with locating slots should be
a
r
70 B, 72 B(E) and 73 B(E) series used (ig. 12) to prevent the outer ring
• of F /F ≥ 0,55 is required by bearings in from turning
r
a
Fig. 12 the 72 AC and 73 AC series If clamping the outer ring cannot be
Bearing mounted with radial clearance in avoided, the outer ring must be carefully
the housing If the load ratio requirement is not met in centred during mounting
each case, bearing service life can be
reduced
Load ratio

For proper functionality, the balls should
contact only one inner ring raceway and the
opposite side of the outer ring raceway This
is the case when the load ratio is
F /F ≥ 1,27
a
r
A load ratio that is smaller than recom-
mended can reduce bearing service life

403