Super Precision Bearing Installation
To obtain the best possible performance of super precision bearings, installation must be performed very carefully, preferably in ultra clean conditions, and most likely with dedicated bearing installation tooling. Some main points of bearing installation are (this list is not exhaustive):
- Clean environment
- Appropriate bearing installation tooling
- Proper technique
- Well-designed assembly and pre-load strategy
- Appropriate tolerancing and surface treatment for the application
- Proper starting operation and break in procedure
The leading cause of premature precision bearing failure is contamination. To repeat, the number one cause of premature super precision bearing failure is contamination. The cleaner your shop can be the better your opportunity for a long bearing life. A separate room where there is no machining, no grinding, and no other debris being created is highly advisable. A clean work station is required at the bare minimum. Also, it is strongly advised to not open the sealed bearing delivery bag until immediately before installation. Note that even a human hair is contamination for a super precision ball bearing. Just a single human hair can easily decrease bearing life. Many facilities will utilize clean room attire such as gloves, aprons, hair nets, etc. to prevent bearing contamination. This must be taken into account during super precision bearing installation.
- It is common and advised to use tools that support both the inner and outer bearing races during installation.
Bearing installation tools are required to insure that the bearing races are not dimpled during installation using improper bearing support. If a bearing is pressed on to a shaft or inside a housing passing the installation press fit load through the bearing, plastic deformation – dimpling – can occur and greatly decrease the bearing life and running characteristics. As seen in the example picture, installation tools can press on a single race or both of the bearing races. Each installation can vary. If there is any uncertainty contact GMN USA engineering support for advice.
Proper technique overlaps with appropriate bearing tooling. However, technique goes much further to how tools are being used.
Heating of the bearing inner race utilizing an induction heater can support installation efforts. Within some applications, a heated bearing can be slid onto a shaft with ones hands. Note: A bearing should not be heated above; the lubrication limit, cage limit, seal limit, or potentially any associated material limits. An arbor press is recommended if an induction heater is not handy.
An Arbor press is recommended because the press can be done in a single motion. Stopping and starting a press along the shaft can increase opportunities for errors. Even though it is strongly advised against, if one must use a hammer be sure that it is a dead blow hammer. In no way use the dead blow hammer directly against the bearing, an intermediary tool is required (similar to press tools above). A ball peen or metal hammer can greatly increase the opportunity for precision bearing damage.
System Design and Pre-Load
A proper design and assembly strategy is required for a long super precision bearing life. Some key aspects are: proper pre-load strategy, bearing sizing, load capacities, duty cycles, etc. Click here for examples of bearing arrangements. Also click here for various techniques of precision pre-load options. Please contact GMN USA engineering support for further advice.
Tolerancing and surface treatments can have a large effect on super precision bearing life, especially in high RPM applications. Centrifugal forces are a concern for inner race lift off at high RPM’s. For this reason, correction factors need to be made for both RPM and thermal effects on materials. Generalities of a slight press on the inner race and slight gap on the outer race can often be made. Be cautious of being too general, this can open one up for an easily avoided issue. Please click here for more information on tolerancing and thermal effects on mating parts.
Precision Bearing Break In Procedure
A complete and thoughtful break in procedure can be the difference between a short and long precision bearing life. No matter what the lubrication medium, polishing effects occur during break in that improve the precision bearing performance. For this reason, a proper start up and break in procedure should not be underestimated even for oil lubricated bearings. ‘Grease Fling’ can cause a very short grease lubrication life, just the same as running a spindle before the oil jets are on can greatly reduce bearing life. Please click here for a proper break in procedure example and further information.