Industrial seal self study guide - SKF.com

Cut Seal Lip
Ever-so-slight seal leakage is evidence that there may be a small nick
or cut in the sealing lip (fig. 9k).
Causes
It may have been caused by a burr on the keyway, spline or shaft end.
Corrective Actions
Follow these steps to correct and prevent cuts on the seal lip:
• Use a deburring tool or emery cloth to remove any burrs. Use
correct mounting tools to protect the seal lip from sharp edges. Be
sure to tape the keyway or spline. Handle seals carefully. Keep seals
packaged during storage or while in transit.
A nicked seal lip also causes lip
leakage (fig. 9k).
Lube Breakdown
Sludge or varnish-like deposits on the seal lip and/or shaft are
symptoms of lube breakdown (fig. 9l).
Causes
Sometimes heat is high enough to break down the oil, but not enough
to harden the lip. In this case, sludge accumulates and is deposited on
the seal lip.
Corrective Actions
Reduce operating temperature if possible, or use a seal designed
for high temperatures (fluoroelastomer type). Be sure to use proper
lubricant for the seal. It also helps to change the oil regularly.
Heat Checking
Heat checking or cracking is another common sealing problem.
This may be evidenced by a hardened seal lip or fine cracks that show
up in the seal lip surface (fig. 9m).
Causes
These problems with the seal may be caused by an operating
temperature greater than the lip material maximum. Other
reasons for heat cracking are excessive surface speeds or insufficient
lubrication at the seal lip.
Corrective Actions
One possible solution is to reduce the temperature or select a seal
material with a higher temperature range. In the other cases, change
the lip material to one that is compatible with the lube or provide
proper lube for the seal. For high pressure applications, be sure to
use a seal designed for that purpose, such as CRWA5.
Sludge deposits on the seal lip
indicate lube breakdown (fig. 9l).
Fine cracks in the seal lip are
visible signs of excess heat or
pressure (fig. 9m).
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