Page 300 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

280 Major Process Equipment Maintenance and Repair

steel wool or crocus cloth for polishing. Repeat the checking process un-
til the contact area is satisfactory.

Flaklng of Babbitt

Flaking of babbitt in the loaded area of the bearing is caused by vibra-
tion or shock loading of the bearing material, which causes the babbitt to
fatigue and break loose from the steel shell. Not only do the flakes cause
scoring as they pass through the bearing, but they also contaminate the
oil. In the advanced stages of flaking, the load-carrying area of the bear-
ing is destroyed, and the bearing must be replaced. However, if flaking is
caught in the early stages, the bearing may be repaired by scraping and
polishing. Whatever the case, the cause of vibration or hammering
should be corrected before the unit is put back into service.

Scoring
Scoring is the scratching, or marring, of the bearing babbitt or the
journal riding in the bearing, or both. It is caused by dirt or metal parti-
cles present in the oil that passes through the bearing. A little scoring is
not serious, and the bearing may be polished with fine steel wool to re-
move any rough edges caused by scoring. Any foreign particles imbed-
ded in the babbitt which could score the journal should be carefully
picked out, and that area should then be polished smooth. Scoring be-
comes serious when it significantly reduces the bearing area. In this case,
the bearing should be replaced, and the gear unit drained and flushed out
with a solvent.

Wiplng
Wiping is the melting and wiping away of a spot or area of the babbitt
due to the bearing temperature rising above the pour point of the babbitt.
Abnormally high bearing temperatures can be caused by one or more of
the following conditions: insufficient bearing clearances, insufficient oil
pressure, excessively high oil temperature in the bearing, a high spot in
the bearing, extreme bearing loading caused by poor bearing contact, or
a gear mesh failure. If wiping is localized in a small spot, the bearing
may be repaired by scraping and polishing the spot until it blends in with
the remainder of the bearing; otherwise, the bearing must be replaced.
Before replacing a wiped bearing, determine the cause of the wipe and
take corrective measures. If new bearings are necessary, the following
precautions should be taken: