Industrial seal self study guide - SKF.com

Troubleshooting (cont...)
Causes
Such hammer damage can be caused by using a steel hammer on the
seal housing during installation.
B
A
Shaft-to-bore misalignments (left)
and dynamic run-out (right) both
cause early lip leakage (fig. 9d).
STBM
Misaligned components in a power train
create Shaft to Bore Misalignment (STBM)
and leaks. The seal lip will appear worn
on one side and relatively untouched on
the other. Shaft alignment should always
be checked before installing a new seal
(fig. 9e).
DRO
Dynamic Run Out (DRO) is the result of a
bent, unbalanced or misaligned shaft. The
sealing lip will be severely worn around
the entire diameter. A dial indicator
attached to the bore or housing while the
shaft is rotated through 360˚ will reveal
DRO. (fig. 9f).
Corrective Actions
Never hammer directly on the seal. Seals which are to be flush with
the outside of the housing should be pressed in with an installation
tool larger than the seal O.D. or with a block of wood. In this case it is
acceptable to use a steel hammer, a dead blow hammer or soft-faced
hammer on the wooden workpiece.
When the blow is going through steel (such as a bearing ring), use
a soft-faced or dead-blow hammer or mallet. This type of tool, like
a block of wood, absorbs the shock wave created by the tool’s impact.
A hammer blow without any material to absorb the shock wave can
dislodge the garter spring from its proper operating position. Once
the spring is out of position, the seal will fail. It may even interfere
with the action of the seal lip, or find its way into the bearing.
Shaft-to-Bore-Misalignment Dynamic Run-Out
Early lip leakage, excessive (uneven) lip wear on one side of the seal,
and/or excessive but consistent lip wear all around are symptoms of
shaft-to-bore-misalignment or dynamic run-out.
Causes
Shaft-to-bore-misalignment (STBM) is a condition of excessive
misalignment created by inaccurate machining, shaft bending, lack of
shaft balance or worn bearings (fig. 9d and fig. 9e). Dynamic run-out
(DRO) is a similar condition where the shaft does not rotate around
its true center (fig. 9d and fig. 9f).
If you find a leaking seal with a wide wear band on one side, but a
narrow band on the other, you can suspect high STBM (unless O.D.
markings indicated the seal was cocked). The lip area with the greatest
wear indicates the direction of shaft misalignment.
Initial leakage will generally occur in the area that shows little or no
seal wear. This is because of inadequate lip contact. But as the worn
side is hardened from excess pressure and heat, it may crack and
cause additional leakage.
Corrective Actions
Check the shaft-to-bore alignment, and adjust it. Inspect the shaft and
bore before installing the replacement seal. Replace worn bearings.
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