Page 297 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Power Transmission Gears 277

3. Monthly Maintenance
a. Check operation of auxiliary equipment and/or alarms.
b. Clean air breather.
c. Check tightness of foundation bolts.
d. Clean oil filter.
4. Semi-Annual Maintenance
a. Check gear tooth wear.
b. Check coupling alignment.
c. Check zinc pencils in heat exchanger.
5. Annual Maintenance
a. Check heat exchanger for erosion, corrosion, or foreign mate-
rial.
b. Check bearing clearance and end play.
c. Check tooth contact pattern.
d. Check condition of oil and change if necessary.

Journal Bearing Maintenance
The most commonly used journal bearings in high speed gear units are
split, steel or bronze backed, babbitt-lined journal bearings; however,
when operating speeds or loads make oil-whirl possible, the manufac-
turer can use pressure dam journal bearings or some other type of stabi-
lized bearing such as tilting pad journal, elliptical bore, or longitudinal
groove bearing. The pressure dam bearing is designed for a particular
direction of rotation; therefore, care should be taken at assembly to as-
sure correct placement. The pressure dam grooves are normally found on
the pinion bearings only. However, the gear bearings on some of the
smaller units may also require pressure dam grooves in some cases. The
grooves are positioned on the unloaded side of the bearing journal as shown
in Figure 6-35.
To axially locate the gear train and to take any nominal thrust created
by external loads, the manufacturer normally uses flat face thrust bear-
ings with radial grooves, tapered land, Kingsbury, ball, or tapered roller
thrust bearings. In units with double helical or herringbone gearing, only
one thrust bearing is required to locate the gearset as this type of gearing
generates no external thrust. The thrust bearing is usual€y placed on the
low speed shaft allowing the pinion to center itself with respect to the low
speed gear. Where single helical, spiral bevel, or other types of gearing
that generate external thrust loads are used, thrust bearings must be posi-
tioned on each shaft.
Carefully inspect bearings and journals for uneven wear or damage. If
required, polish journals using belt-type crocus cloth and remove high