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electricpete

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Reply with quote  #16 
Oli - Sorry, I didn't read carefully. I knew we had discussion about non-synhronous instability in another thread and when I saw you talking about instability and babbit bearing I though it was intended for the other thread.  But now I understand you were talking about rolling bearing that experienced a failure that effectively turned it into a sliding bearing (maybe the bearing froze up and inner ring started spinning on shaft).
John from PA

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Reply with quote  #17 
Quote:
Originally Posted by OLi

No it was an answer to Alex, it actually did that and it was a ball bearing to start with and complaint was that wheel was touching inlet cone as dimensions changed some during this process.....
If it can be defined as over or under lube I don't know.



So perhaps the symptoms were more like those expected from a rub.   Under the right set of circumstances, if operating speed is sufficiently well above a critical speed then a sub-synchronous frequency may occur at a sub-synchronous frequency equal to the critical speed.

OLi

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Reply with quote  #18 
Well as remember it was no multiples I normally see and it did look like a peak that could be from instability in about the correct freq. range, yes the inner ring was rotating on the shaft with a lot of clearance and a lot of grease and the rest was seized but it is just a one off exception not connected to the original question.

What about the idea to add some grease to solve if it is lack of it or to much? You normally get a change and if it is to much it will leak out after a while when it get hot and runny. Rarely they seize, if you dd cold grease to a hot bearing it is not good it may seize.

You can also look at the zerk if it's dry it's not greased if it's greasy then wait a while for it to dissipate.

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Alex

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Reply with quote  #19 
Yes of course, adding some grease and measuring the difference is standard procedure but I would like to concentrate to the vibration analysis. You don't have the possibility every time to add grease. When you are measuring one big route you need to record as much data as possible and you can't do the analysis for every single machine on the site.

Is it possible the difference between under and over-greased bearing could be in the ˝Fuji˝ frequency zone? However the metal to metal contact principle is very different between those two cases. There should be some difference noticed somehow. 

Overgreased = sliding, skidding, friction....
Undergreased = metalic rolling
John from PA

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Reply with quote  #20 
The content doesn't exactly address vibration related effects but SKF has a good article on over/under greasing.  See http://evolution.skf.com/us/grease-lubrication-mechanisms-in-rolling-bearing-systems/.
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