Page 106 - Mechanical Engineer's Data Handbook

APPLIED MECHANICS 95

2.9.1 Service factor for rolling bearings

The bearing load should be multiplied by the following
factor when selecting a bearing.

Uneven Moderate Heavy Very heavy
Type of load Even light shock shock shock shock
Service factor 1 .o 1.2-1.5 1.7-2.0 2.2-2.5 2.7-3.0

2.9.8 Coefficient of friction for bearings

Plain bearings - boundary lubrication Rolling bearings

P P
Mixed film (boundary plus Self-aligning ball 0.001&0.0066
hydrodynamic) 0.024.08 Rollers 0.00 124.0060
Thin film 0.084.14 Thrust ball 0.001 34.0060
Dry (metal to metal) 0.2M.40 Deep groove ball 0.0015-0.0050
Taper roller 0.00254.0083
Spherical roller 0.00294.0071
Plain journal bearings - oil bath lubrication
Angular contact 0.00 184.00 19
P
Velocity Pressure Pressure
Lubricant (ms-’) 7bar 30bar
Mineral grease 1.0 0.0076 0.00016
Mineral grease 2.5 0.0151 0.0027
Mineral oil 1 .o 0.0040 0.0012
Mineral oil 2.5 0.007 0.0020

2.10 Gears

Gears are toothed wheels which transmit motion and relative positions of the axes of the shafts (see table).
power between rotating shafts by means of success- Most teeth are of the ‘involute’ type. The nomen-
ively engaging teeth. They give a constant velocity clature for spur gears is given in the figures.
ratio and different types are available to suit different