Bearing OD Fits or Anti-Rotation Features 1

[fsincox]

I have a current in-place design that uses a pin and mating machined slot on the bearing OD to prevent rotation. From the historical record it appears to be this feature was added as an after thought.
My questions are:
Are proper bearing fits, tolerances and finishes sufficient to control rotation in a properly designed bearing application?
Are these not most likely the rexult of bad designapplication, balancing or is this common in some cases?
These are high grade, grease packed, radial ball bearings running at around 30000 RPM.

 

[caoimhin1]

For general applications...yes, fits as recommended by the manufacturers are fine. For general industrial applications for ball bearings, this is usually H6 fit for the housing and k5 for the shaft. 30000 rpm is quite fast, although it depends on the size of the bearing. A precision ball bearing and precision fits may be needed.
If rotation in the housing is a problem (due to an aluminium housing for example, or an out of balance load), its best not to reduce the fits. Common practice is to use rubber O-rings in the housing...or if spending money on a special bearing isn't a problem, use a lock pin in the bearing OD.

 

[fsincox]

rubber o-rings?

 

[caoimhin1]

Yes. For example:

http://www.nskeurope.com/cps/rde/xchg/eu_en/hs.xsl/innovative-creep-free-bearings.html

These ones are fitted to the bearing by the bearing manufacturer. Unless using large volumes, its usually more cost effective to machine the grooves in your housing, fit o-rings yourself and then use standard bearings.

 

[electricpete]

I don't know your application, but in some applications a floating bearing must be able to move axially within the housing to accomodate thermal growth. In that case special things like O-rings might inhibit that motion.



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(2B)+(2B)' ?

 

[fsincox]

Yes, thank you both, electricpete one of the bearings is a floating bearing, the floating bearing is actually in a thin sleeve for assembly purposes and therefore there is clearance to assemble the sleeve. I suspect also allows the sleeve to expand and that aggravates the ability of the bearing fit to do its job. Shouldn't high grade bearing seats generally be ground when specifying IT5 & IT6?
Frank

 

[Hidromar]

Hi!

"Just adding"

1) We produce rotary polymer seals. Some of them are made for high speed rotating. In these cases, an O-ring on the "static" part of the seal is, also, the part we use on these seals in order to avoid self-rotation of the seal, as soon as housing don't allow to install another kind of seal more adequate for this work!

2) Ticona has a good document on tribology (about plastics -that's my field) showing different behaviours on the same plastic against metals with different finishes. I assume tribolgy on metal-to-metal should be similar

http://www.hidromar.es