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George D

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Reply with quote  #1 
There's an IRD document that, I believe, many of us have entitled "Balance Quality Requirements of Rigid Rotors - The Practical Application of ISO 1040/1".  I'd post a copy, but am reluctant to as it may be proprietary?

One section of the document gives a recommendation for how to allocate unbalance tolerances for "Overhung and Narrow Rotors".  It divides these tolerances into "static" and "couple" elements.  This makes sense to me... as a narrow rotor may require a heavy couple correction across narrow correction planes, where the same couple unbalance force on the bearings would be corrected by a much lighter weight if wider correction planes were available.

So... the document provides formulas for "Uper static", and "Uper couple" based on the configuration and dimensions of the rotor under attention.  And... finally... my question:

Are these "static" and "couple" Uper allocations cumulative, or can they be dealt with individually?  That is... once the static and couple elements of a rigid rotors balance condition is known, is a rotor's balance condition acceptable if it eats up the entire allowable value for both "static" and "couple"?  Or... are these Upers designed to be used cumulatively, such that once you use up the entire static Uper (for example) no further margin remains for the couple?

My intuition is that they must be dealt with in a cumulative manner... such that each of the static and couple Uper calculations account for the entire allowable unbalance.  If you're dealing with a combination of the two (which is always the case), it becomes necessary to somehow weight each of the two allocations to a combined Uper.

Hope that made sense?... thanks, in advance, for everybody's insight and expertise.  This may have already been covered on this board?  If so... appreciate everybody's patience...

George
JB1

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Reply with quote  #2 
From IRD

http://www.irdbalancing.com/assets/balance_quality_requirements_of_rigid_rotors.pdf
OLi

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Reply with quote  #3 
It is not ISO 1940-1 anymore it changed number and got upgraded so a smaller Q or G value exist as the smallest I think, it is ISO 21940-11 from 2016-11-15. ISO standard will after selection of grade, speed etc. give you a accepted residual unbalance per plane expressed in a number of ways. If rotor is not symmetrical you may have different result in the planes, slightly higher in heavier end. When you are under that spec. when balancing you are good and it is the combination of static and coupled it does not care what the residual consist of. I will find the new ISO standard number(21940-11) it is hard to reprogram that worn out memory position(in my brain). Your rotor/machine may care of what your residual consist of but that is another story.
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John from PA

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Reply with quote  #4 
Quote:
Originally Posted by OLi
It is not ISO 1940-1 anymore it changed number and got upgraded so a smaller Q or G value exist as the smallest I think, it is ISO 21940-11 from 2016-11-15.


I have the 2nd edition of 1940/1 and it is dated 2003.

Browse to https://www.iso.org/obp/ui/#search and put 21940 in the search box, then check off standards you will get a summary of the many "parts" of 21940 that are available.
OLi

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Reply with quote  #5 
Here is the revision notice re ISO 1940-1  https://www.iso.org/standard/27092.html


And here are the specifics of the ISO 21940-11      https://www.iso.org/standard/54074.html


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John from PA

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Reply with quote  #6 


ISO has gotten pricy.  I see the part 11 you reference is 138 CHF (Swiss francs).  That is about USD$138...and that is for just one part of many!
OLi

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Reply with quote  #7 
Yes, meetings must be expensive?
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RustyCas

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Reply with quote  #8 
I don’t see a problem with posting links - or even the files - as long as they are readily available on the web - for free - from the copyright owner, and are unmodified.

ISO standards seem expensive to me as a small-business owner, but I’m sure they don’t care. I suppose ISO is generally a good thing, but I always wonder how much the “movement” is driven by those who are profiting from it. Same with safety and reliability.

I’ve always been biased toward the “doers” - I usually cast a wary eye towards the “talkers” unless they are talking their walk.

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