Page 336 - The Tribology Handbook

C8 Rol I i ng bearing I ubrication

OIL LUBRICATION
Oil viscosity selection

Generally, when speeds are moderate, the following To use Figure 8.3, starting with the right-hand portion
minimum viscosities at the operating temperatures are of the graph for the appropriate bearing bore and speed,
recommended : determine the viscosity required for the oil at the working
temperature. The point of intersection of the horizontal
cSt
Ball and cylindrical-roller bearings 12 line, which represents this oil viscosity, and the vertical line
Spherical-roller bearings 20 from the working temperature shows the grade of oil to be
Spherical-roller thrust bearings 32 selected. If the point of intersection lies between two oils,
the thicker oil should be chosen.
The oils will generally be HVI or MVI types containing Examples: Bearing bore d = 60 mm, speed n = 5000 rev/
rust and oxidation inhibitors. Oils containing extreme min (viscosity at working temperature = 6.8
pressure (EP) additives are normally only necessary for cSt), with working temperature = 65°C. Select
bearings where there is appreciable sliding, e.g. taper- oil S 14 (14 cSt at 50°C approx.)
roller or spherical-roller bearings, operating under heavy
or shock loads, or if required for associated components, Bearing bore d = 340 mm, speed n = 500 rev/
e.g. gears. The nomogram, Figure 8.3, shows how to select min (viscosity at working temperature = 13.2
more precisely the viscosity needed for known bore and cSt), with working temperature = 80°C. Select
speed when the operating temperatures can be estimated. oil S 38 (38 cSt at 50°C approx.)
If the operating temperature is not known or cannot be
estimated then the manufacturer's advice should be sought.

VISCOSITY
R" SI' cst 100 130 210°F 150 250400 d, mrn
2000 - 450 -
1500 50.0 -
1000 1000 30.0 - 260
800 80 0 -
600 20.0 - 170
600 - -
400 500 13.0 100 -
90
400
-
300 10.0 : 80 -
70
300 9.0 : -
8.0 : 60
200 7.0 : 50 -
200 -
40
150 -
150 30 -
-
-
-
100 -
90 100 20 1
80 90 - -
-
-
-
70 80 2.5 - -
60 70 2.0 : -
-
60 - 10 -
50 1.8 9-
8-
45 50 1.6 :
7-
1.5 :
45 6-
40
1.4 7 c
20 30 40 50 60 70 BO 90 100 110 12OoC 50 75100 200300 500 d.mm
R"= Redwood No. 1 seconds;
S" = Saybolt Universal seconds, SSU
E" = degrees Engler
CSt = centistokes
Figure 8.3 Graph for the selection of oil for roller bearings (permission of the Skefko Ball Bearing Co. Ltd). The
graph has been compiled for a viscosity index of 85, which represents a mean value of the variation of the viscosity of
the lubricating oil with temperature. Differences for 95 VI oils are negligible
C8.4