There are three important factors for
proper bearing installation. First, you should use an arbor press to press-fit
the bearings. This is the most efficient installation method and will preserve
the integrity of the bearing. For example, if you use a hammer, the
installation of the bearing might be uneven.
Next, ensure your bearing housing has a chamfer-plastic bearing manufacturer, igus, recommends 25-30 degrees for its bearings-and that it is press-fit with the outside chamfer of the bearing against the housing chamfer (for flange bearings, the sleeve portion will have this).
Conducting quality checks on the bearings after installation can be done many ways. One way is to use a pin-gauge test, also called a "go/no-go" test after press-fitting the bearing into the smallest specified housing-bore dimension. This will make sure the bearings are within specifications and will work properly once in service. Specifically, a "go" signifies the pin falling through the bearing under its own weight, while a "no-go" occurs when the pin does not fall through the bearing, or "sticks".
A pin-gauge test is the most accurate quality check because the pin acts like the shaft used in a real-world application and it reveals the inner diameter of the bearing at the smallest points, which is most critical to the application.
When using a plastic bearing, a pin-gauge test works especially well because the peaks and valleys of the bearing are irrelevant as long as the recommended shafts are able to pass through the bearing. Over time, as the bearing's self-made lubrication fills in the peaks and valleys of the shaft and the bearing, an ideal sliding surface is achieved.
While there are other tests that can be used to quality-check a bearing, problems can arise when applying these methods to plastic bearings. In particular, the use of a caliper should be avoided. Calipers, depending on the level of accuracy, are generally acceptable for only hurried quality checks. However, depending on the amount of pressure applied by the caliper or the location of the measurement, it is possible the numbers will not read correctly. It is more reliable to use a pin-gauge test to avoid unforeseen problems.
A common post-installation problem is the bearing showing signs of material shave-off at installation. If this occurs, check to make sure the housing has the recommended chamfer of 25-30 degrees. If using a sleeve bearing (which typically has only one end with an outside chamfer), match up the bearing's outside chamfer with the housing-bore chamfer. If using a flange bearing, the sleeve portion (installed) has the outside chamfer already. In both instances, also check the housing bore to ensure it is not undersized.
Another problem that can occur is when the bearing is press-fit into the housing bore is that the ID after-press-fit is smaller or larger than the recommended tolerances. If this problem arises, the following points need to be assessed:
- Confirm that the housing bore matches the recommended tolerances (generally an H7 housing bore).
- If the housing bore is comprised of a softer metal, like aluminum or plastic rather than steel, it is possible that the bearing is pushing into the housing bore. To compensate, try using a thicker-walled housing.
- Check your shaft tolerances to confirm that your pin gauges determined during the QC process are accurate.
- If the ID of the bearing is undersized, make sure shavings are not in between the bearing and the housing.
Tom Miller is Bearings Unit Manager, North America for igus Inc. He can be reached at [email protected]