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Dan Timberlake

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Reply with quote  #46 
The standard ball and roller bearing L10 life calculations relate life inversely to the load raised to a power. The exponent of the life equation = 3 for ball bearings and = 10/3 for roller bearings .
http://www.skf.com/us/products/bearings-units-housings/principles/bearing-selection-process/bearing-size/size-selection-based-on-rating-life/bearing-rating-life/index.html

So reducing the load on the bearing to 1/2 would theoretically increase life of a ball bearing 2³ = 8 times.

There are flaws, or at least limitations, to the argument that reduced vibration due to improved balancing will affect bearing life in that same ratio .

1 - Unbalance is not the primary load on most bearings. Rotor weight often is greater than the unbalance force, and belt loading can be even higher, so  the unbalance forces can be kind of insignificant in the scheme of things.

2 - Most bearing manufacturers are willing to publish a "fatigue load limit" .  >>If<< the bearing loading is below that limit, the L10 life is darn near infinite, as long as a few not-so-insignificant conditions are met.                              http://www.skf.com/us/products/bearings-units-housings/principles/bearing-selection-process/bearing-size/size-selection-based-on-rating-life/fatigue-load-limit/index.html

3 - Similar to Item 1, overload due to imbalance or any other cause is pretty low on most all the pie charts that various interested organizations publish about such things.
     http://www.lubricationsystems.ltd.uk/user/gimage/Why-Bearings-Fail_400_264.jpg
vibecuador

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Posts: 3
Reply with quote  #47 
Greetings,
I found an article that mentions the relationship between load and vibration level. It doesnt provide good reference to where did they got the data. 

http://www.iosrjournals.org/iosr-jmce/papers/vol1-issue2/I0124754.pdf?id=2670 
http://www.royalpurpleindustrial.com/assets/Reliability_Magazine.pdf

Best wishes for the upcoming year.

Regards,
Alejandro
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