Steel Bearing
Inserts
When idler rolls are used in high temperature environments, there
are many concerns. One concern is due to the expansion of metals
as a result of temperature and especially the different rates of
expansion for dissimilar metals.
When an aluminum dead shaft roll is bored for bearings, the bearing
bore must be precise. The bore must have just enough press fit to
hold the bearing but not too much so as to compress the bearings
internal clearances.
As the aluminum roll fit with a steel bearing heats up, the aluminum
will expand at a rate that is twice that of the steel bearing. At
some point, the bearing bore grows to where the press fit is gone
and the bearing may fall out of the roll. This may happen at temperatures
as low as 125° F.
In this case, Webex recommends the use of steel bearing inserts.
Steel sleeves are put into each end of the roll using a heavy shrink
fit. The fit is designed so that it will remain an interference
fit even through elevated temperatures. Since the bearing and the
insert are of like materials, they will expand at the same rate
and the relative bearing fit will be maintained.
Steel inserts are also used in aluminum rolls when a more robust
design is desired. For example, if routine bearing replacement is
a possibility, steel inserts would be recommended.
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