tech talk
Learn more at www.igus.com/info/plain-plastic-bearings
Part One: Why do bearings move out?
If the housing is not to their liking, plastic bearings
do not hesitate to move out. To keep them in for a
longer stay, users must better secure the bearings
or change the bearing material.
How to properly secure bearings
What causes bearings to move out?
Bearings will move out of the housing if the press
fit is lost and there is no additional axial securing.
Typically, plain bearings are installed with an arbor
press. The holes they are fit into are slightly smaller
than the outer diameter of the plain bearings.
Therefore, the bearing is kept in place and secured
by mechanical tension. If this tension is lower than
the push out force generated by the load and
movement of the pivot point, the bearing moves
out of the mounting hole. The result: a metal shaft
surface scraping away at a metal housing—and a
plastic plain bearing torn to pieces.
arbor press used to press-fit a plain bearing during installation
Two reasons for loss of press-fit are high temperatures and high loads. If the temperature in the bearing
position rises above the material specific threshold, the material begins to loosen, as it cannot maintain
the mechanical tension. The other root cause for losing press-fit is an overly high load that stays over
prolonged periods. This is also a material-specific value and describes a concept called "creeping," which
is a slow process of deformation where the material starts to give in to the load. This deformation can also
lead to loss of press fit and bearings moving out.
Another more inconsequential (but actually more frequently encountered) issue can be the housing bore
being out of tolerance. In that case, if the press fit is too loose due to an oversized housing bore, it can be
even more likely that the bearing will move out.
