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9 INTERNAL SELF-ALIGNING BALL & ROLLER BEARING UNITS

1. Basic load rating and life

1.1 Basic dynamic load rating and life
The basic rating life of a group of ball or roller bearings Table 1. Lh Bearing Life
is defined as the number of revolutions (or hours at
R E C O M M E N D E D F I L E H O U R S H O U R S
some given constant speed) that 90% of the group of
M y l t n e u q e r f n i s e n i h c a d e s u 0 0 5
bearings will complete or exceed before the first evidence p i u q E m t n e t t i m r e t n i r o f t n e e c i v r e s 0 0 0 4 o t 0 0 0 8
n o i t p u r r e t n i – e l b i s s i m r e p
of fatigue develops, namely the life estimated with 90%
t n e t t i m r e t n I e c i v r e s m s e n i h c a 0 0 0 8 o t 0 0 0 0 2
reliability. – m i y l t n e d n e p e d t n a t r o p
M s e n i h c a d e s u 8 s r u o h r e p y a d 0 0 0 0 2 o t 0 0 0 0 3
The basic dynamic load rating is that constant stationary C s u o u n i t n o e c i v r e s p i u q e m t n e 0 0 0 0 5 o t 0 0 0 0 6
p i u q E m r o f t n e s u o u n i t n o c e c i v r e s 0 0 0 0 0 1 o t 0 0 0 0 0 2
load which a group of bearings with stationary outer ring d n a m m i x a u m y t i l i b a i l e r
can endure for a rating life of one million revolutions of
In the case when some bearings are used in an equipment,
the inner ring. It refers to pure radial load for radial
it is often decided that failure of any one of them impairs
bearings.
the function of the equipment, the total life of the assembly
The relationship between the bearing basic dynamic load is to be given by the following formula (6):
rating, the bearing load and the basic rating of spherical
roller bearings is given by the following formula (1): 1
L = 1 1 1 1 / (6)
]
[ L1e + + + Lr1e e
...
L2e
C P
L10 = [ ] (1) where
P
L = total life of the whole bearing assembly, h
where
L1, L2, ..., Ln = rating life of bearings 1, 2, ..., n, h
L10 = basic rating life in millions of e = 9/8 – for roller bearings
revolutions e = 10/9 – for ball bearings
C = basic dynamic radial rating, N
P = dynamic equivalent radial load, N
p = 10/3 – for spherical roller bearings In the case where load and the number of revolutions
p = 3 – for ball bearings. change at regulated intervals, after finding the rating life L1,
L2, ..., Ln under conditions of n1, Pr1; n2, Pr2; nn, Prn, the
built-in life Lm can be given by formula (7);
When the running speed of a bearing is fixed, it is
L1 =
C P
convenient to calculate the basic rating life in terms of 10 6 [ ]
operating hours rather than the number of revolutions, L2 = 60n1 P1
10 6 C P
using the following procedure: 60n2 [ ]
P2
Ln =
10 6 C P
L10h = 500fh P (2) 60nn [ ]
Pn
Cr
1
Pr
fh = fn (3) Lm = Ø1 Ø2 ... Øn -1 (7)
33.3 1
fn = [ ] / P (4) where [ L1 + + + Ln ]
L2
n
where L1, L2, ..., Ln = rating life under condition 1, 2,...,
n, h
L10h = basic rating life in hours of = number of revolutions under
operation, h n1, n2, ..., nn
fh = life factor condition 1, 2,..., n, h, rpm
fn = speed factor P1, P2, ..., Pn = equivalent radial load under
n = operating speed, rpm condition 1,2,..., n, N
Ø1, Ø2, ..., Øn = ratio of condition 1, 2, ..., n
accounting for the total
operating time
Formula (2) may also be expressed as formula (5):
Lm1 = in-built life, h
C P
L10h = 10 6 [ ] (5)
60n P
The rating life of spherical roller and ball bearings can be
obtained from the nomograms in Figure 1. Table 1 shows
the bearing life (Lh). Figures in hours generally required
in the selection of bearings for various types of machines.
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