ABB DC motors are equipped with front and rear balancing discs. I have noted recently that many are bent and some have as many as 8 screws (Probably a couple of ounces) in one spot on the ring which is about 8" to 10" in diameter.

I was always of the understanding that motor manufacturing was a pretty tightly controlled process and as such shouldn't need too much balancing. At the normal operating speed of about 1500 rpm that is about 32 lbs of force due to imbalance in a rotor of probably no more than 200 lb. (That is only estimated and doesn't take into effect the rear balancing disc which I can't see.)

Does that seem excessive to anybody else?

Any experience making corrections with the discs?

I am thinking that if I find significant axial wobble, I will correct that first and check again. After that it may be one of those situations where you are best off removing everything and starting from scratch.

We used to see problems with vane-axial fans on navy ships. These had cast rotor with little "fins" on each end of the motor casing that were trimmed off for balancing. Sometimes, we'd see a motor where all the little fins were trimmed off on both ends from one side. This was a sure indication of problems because it meant that the rotor had been cast off-center. It might be balanced when they were done with it, but the gap between the rotor and stator was eccentric.

Jon
Spintelligent Labs

Dear Danny,

If your ABB DC Motor does not vibrate presently with the existing balancing discs as they are, do not worry about it.

As you say, they are small discs in diameter and the corresponding motor rotor must be of fair size as well. All is very proportional, I would think.

But, to be on the safe side, do as you say and check for wobble on the discs.

By the way, did the motor come with the discs and the corrections on it ? If so, worry not ! The folks at ABB know what they're doing, I know ! I have worked for their Canadian branch for 15 years in the field of design and balancing.
However, if the motor underwent further trim balancing, I would wager that, yes... the discs may be overly loaded, weight wise.

Have a good day !

MarkoLeo

MarkoLeo,

The motors in question do have some problems, although fairly minor.

One of the worst is the one with the bent disc and the vibration spectra are just what one would expect.

The next worse case is the one with 8 screws in the disc.

I'll get some phase data next time I'm there and get them to straighten the bent disc at the nest outage.

I read your other post and was wondering if it was a coincidence that the two subjects came up at the same time. I have to say that you are so correct about devices like that being underused, that neither I nor the Maintenance Supervisor knew for sure what the discs were. I thought they were probably balancing discs, but had to go to the ABB website to find out for sure.

Regards,