Initial Unbalance in Die Cast Rotor of Induction Motor

It is difficult to suggest solutions to an undefined problem.

It's like asking how to make a good cup of coffee without knowing how you are doing it now.

I'd suggest the expenditure of money to hire someone who can observe the present processes and conditions and recommend a solution, if there is one.

Perfection costs money and cannot be gained from an anonymous forum with nothing with which to work.

Break loose with a buck and hire a consultant.

An internet search might help: Die Casting Process, Defects, Design

Implementation of good engineering design and manufacturing practices coupled with a decent quality control on raw pre-production material selections will solve most of your issues /problems.

No known published standards!

Good luck with your search

Do the casting in outer space, where there is no gravity.

You can try to determine what is causing the imbalance. imperfections on dimensions of the laminated core, its centering, its channels etc, Al conductor casting air pockets, or some offset of outer connecting AL rings (I obviously assume you use Al conductor, the mainstream material for induction core rotors). There's no rule that says where a problem will happen, it depends on what specific compromises you had to make to keep cost down. S.M.

If a 50Hz rotor is operated on 60Hz supply(to stator)will there be unbalance?.

No. It will turn more slowly is all.

As you increase the RPM, which is related to the supply Hz, the vibration will increase with speed. If its unbalanced at 50Hz then its STILL unbalanced at 60Hz, the only difference is the vibrations increases with speed.

Due to bad form factor of applied voltage wave, due to harmonics,-ve sequence component etc will unbalance,in addition to vibration result?.

I think its a simple case of..you know about it, so do something in your pre-production to get rid of the problem!

I would start with your pattern/model maker, then look at the material you are using in the casing process, and your casting process. Maybe you are not removing ALL the air out of the mould as you cast.

Also you must remember that no cast will be truly balanced, so you will have to balance it. Something that many manufacturers forget or don't realise they have to do

If not the results of a non-balanced rotor can be severe. I was commissioning a 500HP 3.3Kv motor, and once we were satisfied that it was alined and no soft foot, we started it up. The vibration was off the scale. The motor was removed and the rotor checked, found to be out of balance, then balanced.. once assembled and fitted it run with almost zero vibration.

So if you know about, do your best to get rid of it!

Standards for this..... not sure, but common sense and the drive to deliver a good product should be your guide.

Dear All,

Thank you very much for your valuable suggestions.

Yes, we are looking in the process of Die casting in depth to get the clue of the High Initial Unbalance.

The purpose of this post is to understand if any standard / thumb rule available which can tell us the limits of Initial unbalance.

During the process of balancing this initial unbalance will be corrected to G2.5 (ISO 1940-1), but our efforts are to limit this initial unbalance.

Thanks a lot again.

Regards,

Vishram Lele

ISO 1940 is the standard used for balancing of rotors whether old or new. Although it is an old standard, it is still very much used.