To All,
Does any one out there have a quick reference chart showing the standard in ips, RMS, or Peak to Peak to use as a quick reference for acceptance to confirm or to hold an electric motor rebuild shop to? Baldor Electric uses one half of NEMA’s standard for rotor balance but does not use a standard for a completed assembly.

A standard would bring problems like cocked bearings, misaligned end bells, and bad “new “ bearings to the repair shop’s attention before the motor leaves their shop. It is my hope each motor will be bench tested before it is sent to us to prevent animosity, finger pointing, or any other ill will by agreeing on standards we both can live with. Bad rebuilds happen it’s a fact of life.
Thanks In Advance for Your Assistance,

noisemakr

Go to the following site and download the NASA Building and Equipment Commissioning Guide. There is a section on motors that can be used as a guide along with the EASA document on what information you want from a rebuild shop. If they have a problem complying, find another shop.

http://www.hq.nasa.gov/office/codej/codejx/Assets/Docs/RCB&EGuideJUL04.pdf

Ken Culverson

Thanks Ken!

We just had a large vertical motor whose lower bearing failed (very bad inner race spall) less than two years after being rebuilt. We have 8 of these motors on site operating for almost 20 years and never had another lower bearing failure. I participated in teardown inspection - there was nothing obviously wrong with the lubrication. Shaft and housing fits as-found were good. Load pattern on the removed bearing did not show misalignment.

The timing of the failure stronagly suggests it was related to motor rebuild. We are left with the conclusion that it is an infant mortality. Perhaps the bearing was bad from the factory or had been mishandled during storage/handling or had unusual trauma during installation.

There is not much that can be done about this except to watch for unexplained non-sync frequencies during the shop run and make them part of an acceptance standard. Someone had suggested to me a limit of 0.01 ips on unexplained non-sync frequencies. I guess you also need to specify an Fmax with that to tell them how far out they have to look. I will read the NASA document with interest to see if they have any recommendations.

I think you all will like the NASA document. There are a lot of guidelines in there relating to vibes, balance, alignment, and such. I have used them for guidelines for a while now. Unless the customer requests a specific ISO, I tell em I use rocket science
Be prepared though, you aint gonna read that in one sitting. That is about 350 pages of some of the driest readin you'll do.

Dave

Another consideration beyond numbers: use high sensitivety, high resolution transducers with super low noise cables. This will help avoid arguements. In some instances (frequency depentant) 0.01 IPS may be too high for new acceptance for a motor on an test bed.

Sam,
The 0.01 level applied only to non-synchronous vibration. I think that is achievable on a new motor.
Now, to further discuss the original thread,
RSS-Dave - I think the NASA spec, especially for motors is poor at best. It will open a huge bag or worms in a warranty situation. All of the acceptable limits for in service are TBD.
It also discusses bearing frequencies and other fault frequencies as needed to be so low they are not identifiable! In this day of the 90 dB dynamic range analyzer, I can find peaks that will line up with something that is non-synchronous. Are they a problem? No.
The best spec I have come across in years was put together by General Motors about 8 years ago. I will try to locate it, but it addressed everything, from motors to fans to gearboxes. Very well thought out and realistic.

Got it! Let's see if she goes.

GMVibeStandard.doc (1,678 Kb, 54 downloads)

The GM document is great! I have heard about it but never have been able to get my hands on a copy. Thanks Ron!

Folks,
Do me a favor. Only use this PDF formatted version. GM was not opposed to me having it or handing it out, but if someone changes the original document and still leaves GM's nameplate on the front, there will be reprocussions.

GMVibeStandard.pdf (361 Kb, 43 downloads)

Ron,

I agree with you on the GM spec. We used it quite a bit for motor shops. GM defined the rubber to be used under a motor very well, and it gave very good results if someone asked for a standard. Otherwise, a piece of conveyor belt works very well.
The thing I like about the NASA standards is it is an all encompassing document that attempts to standardize not just vibrations, but thermo., oil sample, and just about everything else in a maintenance environment
I just think it is a very good overall document.
I used their band alarms for some time.Now I guess I use my own. When comparing them many years ago, I don't think there was a whole loot of difference between the two (NASA and GM). However, I do think GM updated their numbers, I'm not so certain of NASA

Have a good one.

Dave

Speaking of the rubber/resilient mount - I have one beef with NEMA MG-1 vibration standards: they allow you to test on either resilient mount or ridig mount and in fact they give you a higher vibration limit (0.15) if you are resiliently supported than if rigidly mounted (0.12ips).

But if it's a NEMA frame 2-pole motor, you will often find the 2LF vibration is much higher when bolted to rigid base (due to imperfect foot conditions I guess).

So the same motor that easily passes the test with 0.06 ips on rubber pads (limit 0.15 ips) might miserably fail the test if rigidly bolted with 0.25 ips (limit 0.12 ips). And when you install it in your plant you are more likely to get a result similar to the rigid mount (0.25 ips). And if you didn't do a rigid mounted test at the shop, installation in the plant would the first time you find out about it... not a good situation.

Therefore my preference for 2-pole motors is to shop test them bolted to a rigid base.

Is there a more recent version of the GM standard? Does GM mind other people having it or just you? It is the type of document that they might share with vendors (confidentiality agreement?).

Do you know of other GM standards that would be legally available? It looks like they put some thought into this.

Bill,

I got this version (1999) when I was doing some work at GM during the IRD days. The Engineer that gave it to me didn't seem to mind that he was giving it out, as he said I could keep it and use it where ever. I know his word is a far cry from the court, but at the time I didn't feel like he was winking at me as he said it.

Dave

GM_Vibration_Spec_V1.0a-1999.pdf (894 Kb, 31 downloads)

The GM spec (1999 version) was the basis for the vibration spec at NASA Ames Research Center and others. At the time, GM made the spec publicly available on a web site. When we adapted their spec, we gave credit to GM but did modify the text to meet the needs of the center. There was a series of documents that were used at the center to specify performance levels in contractural documents. Internally at least, they were designed to be a 'cut-and- paste' operation for our design engineers to put in purchasing documents to ensure we got what we required.

Ken Culverson

Thanks Ken,

SOme one else told me that same thing, the GM spec was used in developing the NASA spec.
I just wasn't sure who told it to me. I ran into it when we (Entek/IRD)bid on installing monitoring for the LOX pumps (I think) for the shuttle. Took us a while to read through everything.
Thanks again for clarification,

Dave

William,

You wrote
"Is there a more recent version of the GM standard? Does GM mind other people having it or just you? "

Is this intended as humor? If so, good one.
Obviously, GM wrote the specification so that their many vendors understood what they expected from new and rebuilt equipment. How do they accomplish that without giving the document out? The reason for the PDF file (they only had it in a Word doc when I received it) is so that the specs remain as GM intended them.
RRS-Dave, Thanks for the update.

To All
This is great. I truly have a living document to present to various local repair shops, and for more than just electric motors.
Thank you all for your support and information.