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9 INTERNAL SELF-ALIGNING BALL & ROLLER BEARING UNITS

1.
1. Basic load rating and life Basic load rating and life

1.2.3 Operating condition factor a 3 In addition to the theoretical (calculated) load, bearings are
In general, when lubrication is satisfactory, a3 = 1. often subjected to additional dynamic loads caused by
Values of a3 greater than 1 may be considered in vibration, shock, etc. Generally, however it is difficult to
application where the lubrication is particularly favour- determine such additional loads and hence, it is a
able and other factors to the bearing are also normal and common practice to multiply the calculated load by one of
satisfactory. Reduction of a3 values should be considered the experience based factors, as given in formula (10) and
for example, in applications where the lubrication is so Table 3b.
unfavourable as the lubricant film on contact surfaces of . (10)
F = Fw Fc
the rings and rollers is not formed sufficiently. For
where
instance, where the viscosity of lubricant is less than
F = bearing load, N,
2
20mm /s for roller bearings at the operating temperature
and/or where the rotational speed is exceptionally low Fw = load factor
Fc = theoretical force, N,
.
(dpw n<10000mm-rev/min).
Table 3b. Load factor Fw
1.3 Basic static load rating
L O A D C O N O I T I D N S F A C T O R E X A M P L E
The basic static load rating is defined as the static load c i r t c e l E m , s r o t o
t h g i L e c i v r e s 0 . 1 o t 2 . 1 C o m , s r o s s e r p
which corresponds to a total permanent deformation of
R y r a t o . s n l i k
the rolling elements and raceways at the most heavily R g n i l l o , s k c o t s
stressed contact point of 0.0001 times the diameter of R g n i l l o , s l l i m
P r e p a m g n i k a m , s e n i h c a
the rolling element. This degree of permanent deforma- M e t a r e d o k c o h s 2 . 1 o t 5 . 1 P o w s n a r t r e , s n o i s s i m
tion is not supposed to affect the performance of ordinary e c i v r e s M l a t e w g n i k r o
m , s e n i h c a s e n a r C
machines and this basic static load rating is taken as the P u e n m c i t a , s e s s e r p
permissible limit for the load a given stationary bearing R r e b b u g n i x i m . s l l o r
can be subjected to. The maximum load that is A l a r u t l u c i r g m , s e n i h c a
C n o i t c u r t s n o p i u q e m , t n e
practically permissible with a bearing under various H y v a e k c o h s e c i v r e s 5 . 1 o t 0 . 3 , s r e h s u r C
service conditions is to be determined from formula (9) g n i t a r b i V , s n e e r c s
l e e t S . s d n a t s l l o r l l i m
and Table 3a with the safety factory “So” taken into due
consideration.
1.5 Equivalent load
While, as mentioned above, the basic load rating for a
Cor
So = (9) spherical roller bearing is in terms of pure radial load, in
p or max
where practical services they are often subjected to a
= static safety factor combination of radial and axial load or to a pure axial
So
p = maximum static equivalent load, N load. In such a case it is essential to have the load
or max
= basic static load rating, N converted into the corresponding radial load by formulae
Cor
(11) and (12).
Dynamic equivalent load (11)
Table 3a. Safety factor So
Pr = XFr + YFa
S E R C I V E C O N O I T I D N S O
g i H h o i t a t o r l a n o i s i c e r p n e r q e r i u d 5 . 1 o t 0 . 2 Static equivalent load (12)
B e g n i r a e t c e j b u s d o t o i t a r b i v k c o h s / n 2 . 1 o t 5 . 2
O y r a n i d r g n i n n u r o c o i t i d n n 0 . 1 o t 2 . 1 Por = Fr + Y0Fa
R g r a l r e h t a e p r e m a e n t n d r o f e m o i t a n 5 . 0 o t 0 . 1
p r e e l b i s s i m where
Pr = dynamic equivalent radial load, N
Por = static equivalent radial load, N
1.4 Loads acting on bearings
Fr = radial load, N
In general, the load applied to a bearing includes the Fa = axial load, N,
inherent weight of a rotating body, loads produced by a X = radial load factor
machine itself, forces transmitted from belt and/or gear Y = axial load factor
and moment loads. Y0 = static axial load factor.
Values of X, Y and Y0 are given in Section 9 tables 18
and 19.

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