Page 119 - The Tribology Handbook

A20 Selection of rolling bearings

Oil lubrication
Oil lubrication is used when operating conditions such In the figure d = bearing bore diameter mm
as speed or temperature preclude the use ofgrease. Fig. 20.6 n = rotational speed rev/min
gives a guide to suitable oil viscosities for rolling bearings An example is given below and shown on the graph by
taking into account the bearing size and operating tem- means of the lines of dashes.

E
T T po.0

30.0
20.0
500- 500 15.0 n, rev/min
400-
400
300- 10.0
300 8.0
200- 6.0 \
200
150- 5.0
150 4.0 \
100-
100 3.0
80 - \
70- 80 2.5
\
70
60- \
2.0
60
50- 1.8 \
45- 50 1.6
\
1.5
45
40- \
1.4 -
3
- Operating temperature, "c - mm
d,
Fig, 20.6.

Generally the oil viscosity for medium and large size bearings should not be less than 12 centistokes at the operating
temperature. For small high-speed bearings less viscous oils are used in order to keep friction to a minimum.
Example: A bearing having a bore diameter d = 340mm and operating at a speed n = 500 revlmin requires an oil having
a viscosity of 13-2 centistokes at the operating temperature. If this operating temperature is assumed to be 70°C an oil having
a viscosity of 26 centistokes at 50°C should be selected.
Acknowledgement is made to SKF (U.K.) Limited for permitting the use of graphical and tabular material.

A20.6