Page 298 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

278 Major Process Equipment Maintenance and Repair

PINION GEAR
REDUCER
ERG. LOAD
A. CW ROTATION

B. C’CW ROTATION

INCREASER

C. C’CW ROTATION

D. @ CW ROTATION

Figure 6-35. Pressure dam bearing groove location.

spots. Sleeve and thrust bearings should be thoroughly inspected for cor-
rect clearance, high spots, flaking of babbitt, scoring, and wiping using
the following procedures.

Bearing Clearance
The journal bearings used in high-speed gears must have clearance be-
tween the shaft journal and the bearing. The amount of clearance neces-
sary depends on the oil viscosity, the journal speed, and the bearing load-
ing. Manufacturers’ engineers consider each of these parameters in
calculating a bearing clearance that will produce hydrodynamic lubrica-
tion as well as a flow of oil sufficient to cool the bearing. The required
clearance for your particular unit may be found in the technical data fur-
nished with the unit or may be available from the manufacturer. A rough
rule of thumb (when better data are not available) is .001 in. per in. of
journal diameter plus .0015 in. up to 9OOO ft per minute journal velocity.
Above this speed, clearance should be .002 in. per in. of journal diame-
ter for shafts larger than 2.5 in.