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9 INTERNAL SELF-ALIGNING BALL & ROLLER BEARING UNITS

1. Basic load rating and life
Fig. 1 Nomograms for life calculation
rpm 10 100 1000 10000
15 20 30 40 60 80 150 200 300 400 600 800 1500 2000 3000 4000 6000 8000 15000 20000 30000 40000 60000
n
For ƒn 1.4 1.3 1.2 1.1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.28 0.21 0.22 0.18 0.16 0.14 0.12 0.09 0.082
1.49 1.0 0.20 0.10
Ball
Hour 200 1000 10000 80000
Bearings 300 400 500 600 700 800 900 2000 3000 4000 6000 8000 20000 30000 40000 60000
Lh
ƒh 0.75 0.80 0.85 0.90 0.95 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.5 3.5 4.5
0.74 1.0 2 3 4 5 5.4
rpm 10 100 1000 10000
n 15 20 30 40 60 80 150 200 300 400 600 800 1500 2000 3000 4000 6000 8000 15000 20000 30000 40000 60000
ƒn
For 1.4 1.3 1.2 1.1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.28 0.24 0.22 0.18 0.16 0.14 0.12 0.106
1.44 1.0 0.20
Roller
Hour 200 1000 10000 80000
Bearings 300 400 500 600 700 800 900 2000 3000 4000 6000 8000 20000 30000 40000 60000
Lh
ƒh
0.80 0.85 0.90 0.95 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.5 3.5 4.5
0.74 1.0 2 3 4 4.6
1.2 Adjustment of rating life 1.2.1 Reliability factor a 1

The basic rating life of bearings, may be obtained In the case where a high reliability level of more than 90%
through the formulas mentioned in Section 1.1, which is (or failure probability of less than 10%) is required, the
an arbitrary standard adopted for most applications. bearing life Ln may be found by the factor a1 given
However, when the bearing life of more than 90% in Table 2.
reliability is required, or when the life of bearing made of
bearing steel with improved method of manufacture or of Table 2. Reliability factor a1
materials other than standard bearing steel is required, or R A I L E - T I L I B Ln a 1
, Y %
when the bearing life is to be calculated in due consider 0 9 L 01 0 0 . 1
ation of lubricating and other conditions, the bearing life 5 9 L5 2 6 . 0
6 9 L4 3 5 . 0
can be given by use of the adjustment factors, 7 9 L3 4 4 . 0
established in ISO 281/1. 8 9 L2 3 3 . 0
9 9 L1 1 2 . 0
Lna = a1 a2 a3 (8)
C P
10 6 [ ]
60n1 P 1.2.2 Material factor a 2
where
Lna = adjusted rating life for material When the bearing is made of a material whose rolling
properties operating conditions and fatigue life has been improved or of materials other than
for a reliability of (100-n) %, standard bearing steel, the rating life may be adjusted by
million revolutions. the material factor a2. For instance, it has been proved
a1 = reliability factor that the life of vacuum degassed steel, which CBC uses
a2 = material factor for all their bearings is expected to increase by
a3 = operating condition factor approximately three times as compared with air melted
The Lna life is then multiplied by the appropriate life bearing steel.
adjustment factors that apply to the particular bearing The bearing (shown with the symbol “TS”) treated for
and application condition involved. In most applications dimensional stability at high temperature, is reduced in
however, it is difficult to have sufficient knowledge of hardness. The life of this bearing should consequently
every operating condition. In such a case it is necessary be found from formula (8), using the temperature factor
to refer to the field experiences on the life of bearing in Table 3.
used in the same machine (or under the same conditions)
and to adopt the factors a2 and a3, or to determine their
values. For cases under special conditions, CBC should
be consulted. It may not be assumed that a deficiency in Table 3. Temperature factors for high temperature
lubrication and mounting can be overcome by using an bearings
improved material. It is emphasized that indiscriminate M A . X O P E R A N I T G S Y M B O L T E M P E R A T U R E
use of the life adjustment factors in the equation may T E M P E R A T U R ˚ , E C F A C T O R
0 0 1 – 0 0 . 1
result in serious problems.
0 3 1 T S 1 5 9 . 0
0 6 1 T S 2 7 8 . 0
0 0 2 T S 3 8 6 . 0
0 5 2 T S 4 0 3 . 0
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