Page 306 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

206 Major Process Equipment Maintenance and Repair

many small areas of damage can be practically invisible yet still very
harmful. Remove all nicks and burrs present by stoning or filing lightly.

Assembly

The first step in assembling a gear unit is to place the bearings and
rotating elements into the housing. Proper precautions should be taken
during this procedure. When the bearings and rotating parts are placed in
the housing, be sure all fits are correct and the bearings are properly
seated in the bores. Recheck tooth contact with the soft blue procedure.
Also, using the hard type of layout blue (spray or brush), coat three or
four teeth at three locations around the gear.
Next, apply a sealant to the machined split line of the housing. If a
silicone-type sealant is used, care must be taken to prevent the excess
from entering the oil system and clogging the orifices. If anaerobic seal-
ers are used, make sure that the jacking screws are installed, since it may
be very hard to disassemble the unit afterward. Do not use anaerobic ma-
terials for pipe threads or for stud locking on the split line since the
strength of these sealants may be so high that future disassembly may not
be possible without damage.
After applying the sealant, set the cover over the gearing, and insert
taper pins or locating devices. Snug down bolts and studs by hand, and
drive taper pins “home.” Check the alignment of the bores at the split line
to be sure any offset is minimal. If offset is present, raise the cover and
reassemble. An allowable amount of offset cannot be given since this
value varies with the size and design of the gear unit. If the offset present
seems too great and the unit cannot easily be rebored, correction can be
made by scraping or sanding the bore from the split line up (approxi-
mately 20 to 30”) to minimize the “pinch” on the bearings. Finally,
tighten all bolts completely, and add end caps and auxiliary equipment.
Before operating the reassembled gear unit, be sure to hand turn the
unit if possible and check the coupling alignment. After operating the
unit for a short time, check the tooth contact by observing the wear-off
pattern of the hard blue.
Use hands, ears, and available instrumentation to check for abnormal
temperatures, noise, or vibration, especially during the initial period of
operation. Observe the checklists for before and after start-up listed else-
where.

Roubleshooting
The most common gear problems are noise, overheating, vibration,
tooth wear, and tooth breakage. The following is a discussion of the most
common causes of and remedies for each type of problem.