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RustyCas

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I have a theory (concept?) of machinery failure that I have developed over time that goes something like this:

There are a number of factors in machinery design & operation (bearings, lubrication, coupling, alignment, balance quality, stiffness, fasteners, belts tension, support design, etc) that, in the best case, are optimized.  Over time, some (or many) of these factors start to "diverge" from the best case due to a number of either inherent (design) or "created" (operations, maintenance, modification) problems.  At some point in time these divergent factors, if not detected and corrected in a timely manner, will "converge" to become a machine failure.   The failure is usually a combination (convergence) of factors, most of which would not cause a failure if there were no other divergent factors.  In essence, failures are rarely due to "one thing"

This is not meant to be a scholarly or academic statement, but rather just what I have observed over the years.  A customer wants me to do a "precision maintenance" class for their maintenance staff and I want to open it by driving home the point that, "Most everything matters, and matters more than you think."  Since most failures are multi-factored, we have to minimize the divergence of as many factors as possible.

This is all a bit wordy, maybe obtuse even.  I'd welcome your comments or ideas (subtractions or additions). Am I on point here, or have I wandered off into the weeds?

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Noknroll

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Reply with quote  #2 
Rusty I  think you are definitely on track, just haven't heard it expressed that way before and sounds like a good opener for your class.
Jon1990Fitz

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In my original training with Pruftecknic they opened with a very similar statement that multiple issues cause a unit to fail that usually start with one issue but tend to spread through out to a machine.  
Danny Harvey

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I like it as an illustration of what I find almost every time I am asked to balance a fan because it shakes.

Sometimes I balance them, but most often, I correct looseness, misalignment, belt defects, resonance...


Danny Harvey

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...and I think it's a message that is essential for all people involved in maintenance and repair.

Just make sure it's delivered so that it doesn't imply that they don't already know it.
Shurafa

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Reply with quote  #6 
Quote:
Originally Posted by RustyCas
In essence, failures are rarely due to "one thing".


This is foundational for any proper fault analysis. However, despite that this concept or fact is tought in classes and during OJT, many people fail to practice it consistently.

My favorite example of this kind of argument is that most of severe traffic accidents take place because of two or more simultaneous reasons.

I guess there is a known mathematical theory of the same name.

Regards- Ali M. Al-Shurafa
arie mol

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Reply with quote  #7 
Rusty,
Another 'concept':
What I have seen over the decades, a main reason for premature rotating machinery failure is resonance. A resonant condition does not diverge or converge. It is existent from day 1 and - going undetected - it is waiting very patiently to inevitably run the most vulnurable component into failure one day.
RustyCas

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Quote:
Just make sure it's delivered so that it doesn't imply that they don't already know it.
Very good point Danny. It's hard to do that when they really know so little about it.

Quote:
A resonant condition does not diverge or converge.
 Arie, I agree in principal, but unless a machine is very well built (and most today are not), the resonant frequency will change. For many lighter built, less stiff machines today, resonance is indeed lurking right around running speed.  As system stiffness changes (broken welds, loose bolts, etc) so does the resonant frequency, shifting usually it seems towards running speed.

And yes, resonance is a big part of the training, particularly when discussing welding vs bolting in high vibration areas, fasteners, foundations, changes in operating speed, etc.

What is a good, simple way to effectively demonstrate resonance?




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