Sealed Track Bushings Wear
In early hours, the wear patterns on Sealed
Track bushings should be very similar to
those shown for Sealed and Lubricated
Track. However, as varying amounts of
internal wear takes place, the external wear
pattern will change positions and acceler-
ate, thus reducing its life due to greater
interference loads with the sprocket and
greater sliding motion against the sprocket.
Measurement Technique
The small caliper must be used to measure
the wear at the minimum diameter of the
bushing regardless of the position with
respect to vertical and forward or reverse.
This is because the Sealed Track bushing
must have sufficient strength to resist
cracking after the turn. This remaining
strength is largely affected by wear before
the turn. Also, the Sealed Track bushing
receives most of its load in the later part of
its wear life in the same position where the
maximum wear is.
For a discussion on the possible errors
which can be made using the caliper to
measure bushings, see the section entitled
“Sealed and Lubricated Track Bushing
Wear Measurement Technique — Caliper
Method.”
Wear Limits
As mentioned above, wear limits for
Sealed Track bushings are determined not
only on the basis of remaining strength
before and after the turn but also the
external wear in late hours. Therefore, the
allowable wear for Sealed Track external
bushing is considerably less than for the
Sealed and Lubricated Track bushing. The
lesser allowable wear to the service point is
0.12" (3.1 mm). The greater allowable
wear to the service point is 0.19" (4.8 mm).
Wear limits should always be chosen on
the basis of degree of expected impact, not
on the basis of abrasiveness or desired life.
Wear charts for Sealed Track bushings
have the built-in effect of (a) approxi-
mately twice as fast expected wear rate
after the bushing case depth is worn
through and (b) a faster yet expected wear
rate (approximately three times) after a
significant amount of internal wear would
have further accelerated wear due to
greater interference loads and relative
motion between the bushing and the
sprocket.
How to Interpret Wear on
Sealed Track Bushings
Since the successful turnability and total
life of Sealed Track pins and bushings is a
function of both internal and external
wear, interpretation of external bushing
wear alone will not accurately determine if
and when to turn. However, the type and
degree of external bushing wear is a good
indicator of abnormal problems. Also,
knowledge of these patterns, the potential
life to the service point of the critical
position and the causes of each will help
determine the applicability and advantages
of Sealed and Lubricated Track in the
same or similar conditions.
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SEALED TRACK PINS & BUSHINGS
General Information