Page 108 - Rollingbearings

B.3 Bearing size
Guideline values for Requisite Checklist after the
static safety factor, s bearing size is
0 minimum load

The static safety factor s is given by determined
0
In applications where the bearing size is
s = C /P determined by factors other than load – for
0
0
0
example, shaft diameter constrained by crit- When you have worked through this section
where ical speed – the bearing may be lightly and determined bearing size, before contin-
s = static safety factor loaded in relation to its size and carrying uing to the section on Lubrication, page 110,
0
C = required basic static load rating [kN] capacity. Where there are very light loads, check the following by referring to the prod-
0
P = equivalent static bearing load [kN] failure mechanisms other than fatigue, such uct sections:
0
as skidding and smearing of raceways or
Alternatively, you can calculate the required cage damage, often prevail. To provide satis- • grease life for capped bearings
basic static load rating C . factory operation, rolling bearings must • allowed axial/radial loads and F /F ratios
a
r
0
Guideline values for the static safety factor always be subjected to a given minimum • minimum load
s , based on experience, are listed for ball load. As a general rule, minimum loads of • adjusted reference speed and limiting
0
bearings in table 7, and roller bearings in 0,01 C should be imposed on ball bearings speed
table 8. The s values given for continuous and 0,02 C on roller bearings. More accurate • misalignment
0
motion relate to the inluence of permanent minimum load requirements are given in the • stabilization class
deformation on bearing performance – product sections.
ranging from noticeable friction peaks, The importance of applying a minimum
vibrations and reduced fatigue resistance load is greater in applications where there
(for the lowest s values), to no inluence on are rapid accelerations or rapid starts and
0
friction, vibration or fatigue life (for the high- stops, and where speeds exceed 50% of the
est s values). The certainty of load level limiting speeds listed in the product tables
0
relects how well the actual bearing load is (Speed limitations, page 135). If minimum
known and/or can be predicted. load requirements cannot be met, potential
improvements are:
• Use a bearing with a smaller dimension
Bearing size • Consider special lubrication or running-in
series.
procedures.
• Consider NoWear coated bearings,
page 1060.
B.3 • Consider applying a preload (Selecting
preload, page 186).

Table 7
– for continuous and/or occasional
Guideline values for the static safety factor s 0
loads – ball bearings
Certainty of load level Continuous motion Infrequent motion
Permanent deformation Permanent deformation
acceptance acceptance
Yes Some No Yes

High certainty 0,5 1 2 0,4
For example, gravity loading
and no vibration
Low certainty ≥ 1,5 ≥ 1,5 ≥ 2 ≥ 1
For example, peak loading

106