Page 302 - The Tribology Handbook

Selection of lubricant twe CI

3 2 3 4 5 10 20 30 40 50 100 200 300 400500 1000 2000 300040005000 10000
LIFE, h
Figure 1.4 liemperature limits for greases. In many
cases the grease life will be controlled by volatility or The effective viscosity of a lubricant in a bearing may be
migration. This cannot be depicted simply, as it varies different from the quoted viscosity measured by a standard
with pressure and the degree of ventilation, but in test method, and the difference depends on the shear rate
general the hnits may be slightly below the oxidation in the bearing.
limits

Shear rate in bearings may - 2
Shear rate in
-5 200 -- - standard test -
._ methods is low I be high
al
c
W I
r
r
W
I
i !
I 1 1
Typical SA€ 20/50 mineral oil at 10OoC
\I
I
I
30 20 10 0 10 2030405060708090100 120 .Typical SA€ 30 mineral oil at 100°C 1-
Temperature, 'C 100 1000 10000 100000 lO0OC 0
Shear rate (s-' )
Figure 1.5 Viscosit y/temperature characteristics of
various oils Hgure 1.6 Variation of ViSMIsity with shear rate
C1.3