BEARING HOUSINGS - CBC Bearings

9
INTERNAL SELF-ALIGNING BALL & ROLLER BEARING UNITS
1. Basic load rating and life
For
Ball
Bearings
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
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
Hour 200 1000 10000 80000
Lh
300 400 500 600 700 800 900 2000 3000 4000 6000 8000 20000 30000 40000 60000
For
Roller
Bearings
ƒh
0.74 1.0 2 3 4 5 5.4
rpm 10 100 1000 10000
n
ƒn
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
15 20 30 40 60 80 150 200 300 400 600 800 1500 2000 3000 4000 6000 8000 15000 20000 30000 40000 60000
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
Hour 200 1000 10000 80000
Lh
300 400 500 600 700 800 900 2000 3000 4000 6000 8000 20000 30000 40000 60000
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
The basic rating life of bearings, may be obtained
through the formulas mentioned in Section 1.1, which is
an arbitrary standard adopted for most applications.
However, when the bearing life of more than 90%
reliability is required, or when the life of bearing made of
bearing steel with improved method of manufacture or of
materials other than standard bearing steel is required, or
when the bearing life is to be calculated in due consider
ation of lubricating and other conditions, the bearing life
can be given by use of the adjustment factors,
established in ISO 281/1.
Lna = a1 a2 a3 (8)
10 6 C P
[ ] 60n1 P
where
Lna = adjusted rating life for material
properties operating conditions and
for a reliability of (100-n) %,
million revolutions.
a1 = reliability factor
a2 = material factor
a3 = operating condition factor
The Lna life is then multiplied by the appropriate life
adjustment factors that apply to the particular bearing
and application condition involved. In most applications
however, it is difficult to have sufficient knowledge of
every operating condition. In such a case it is necessary
to refer to the field experiences on the life of bearing
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
lubrication and mounting can be overcome by using an
improved material. It is emphasized that indiscriminate
use of the life adjustment factors in the equation may
result in serious problems.
1.2.1 Reliability factor a 1
In the case where a high reliability level of more than 90%
(or failure probability of less than 10%) is required, the
bearing life Ln may be found by the factor a1 given
in Table 2.
Table 2. Reliability factor a1
RELIABILIT-
Y, %
90
95
96
97
98
99
1.2.2 Material factor a 2
Ln a 1
L10
L5
L4
L3
L2
L1
1.00
0.62
0.53
0.44
0.33
0.21
When the bearing is made of a material whose rolling
fatigue life has been improved or of materials other than
standard bearing steel, the rating life may be adjusted by
the material factor a2. For instance, it has been proved
that the life of vacuum degassed steel, which CBC uses
for all their bearings is expected to increase by
approximately three times as compared with air melted
bearing steel.
The bearing (shown with the symbol “TS”) treated for
dimensional stability at high temperature, is reduced in
hardness. The life of this bearing should consequently
be found from formula (8), using the temperature factor
in Table 3.
Table 3. Temperature factors for high temperature
bearings
MAX. OPERATING
TEMPERATURE,˚ C
100
130
160
200
250
SYMBOL
–
TS1
TS2
TS3
TS4
TEMPERATURE
FACTOR
1.00
0.95
0.87
0.68
0.30
183