Balacing of rotor with strong magnetic coupling. 3

[BjarneEng]

I’m working for a company that is developing a new pump with a magnetic coupling.
Magnetic couplings are novel to me and my company so I’m interested in finding industrial partners that know how to handle strong magnetic fields.
Are there firms in Europe that is specialized in balancing rotors with strong magnets attached?

 

[MikeHalloran]

You couldn't just slap a keeper on it?


Mike Halloran
Pembroke Pines, FL, USA

 

[BjarneEng]

Hi Mike,
I dont whant to add any extra weight to the rotor while balancing.
It might be that im overly concerned with the magneic forces but as I do not know all the pit falls I would like to talk to a vendor that has met these challanges before.

 

[Strong]

Can you balance the two parts independently prior to assembly? What balance criteria or specifications are you trying to meet? Have you made any vibration measurements yet that indicate balancing as necessary? Magnetic couplings designed to transmit torque typically do not transmit much dynamic force in the radial direction, so even if they are assembled, it should be possible to balance each hub as a separate unit. Can you provide a drawing or photo of the components in question? Can you identify operating speed and horsepower or torque during normal operation? What type of magnet circuit is used; opposing magnets for synchronous rotation or magnets with induction disc for asynchronous operation? My crystal ball is broken, so I cannot guess anything more about what you are trying to do! I recently designed a system to balance magnetic induction-type couplings currently sized up to 500 hp.

Walt

 

[BjarneEng]

Valide points there Walt.
This is an R&D job so the coupling is under development never been tested before.
Its an synchronous coupling with a male and female shaft. Im primaraly concerend with the male shaft/rotor as the magnetic field reaches outwards butting quite stringent demands on handling. Im not trying to balance the male and female together. Speed 6000rpm, Torque 2000Nm, shaft size Ø100mm. The steel shaft has thrust collar for thrust bearing attached.
I want to balance the unit as an assembly not needing to dismantle later. For my development unit I would like to achieve balancing grade of G1 according to ISO1940.
Im not allowed to provide drawings or pictures as the project is still R&D.

My concern is handling. I need to know if there are special balancing vendors out there that has handeled strong N48 neodymium magnets and know how to conduct them selfs.

 

[Strong]

You might discuss magnet handling practices on the Magnetics Forum:

http://www.eng-tips.com/threadminder.cfm?pid=340

A wood work bench might be slightly better than a steel one! A nonmagnetic rugged sleeve (wood, plastic, Fiberglas) to protect the rotor magnets could be used for handling coupling hub-shaft until it is mounted on the balance machine/spinner. Consider using drilled-tapped holes for set screws as balance weights. It is possible to control balance weight to a few hundredths of a gram with this scheme.

Walt

 

[CouplingGuru]

BjarneEng,

I will let you in on a little secret, the last step in the process of manufacturing a magnetic coupling is activating the magnets.
There are highly specialized machines that activate strong magnets required in a magnetic coupling design. The key is to get all balancing and machining done prior to activating the magnet. Look up "Capacitive Discharge Magnetizing".

And ISO G1.0 for a rotor at that size and speed is a fairy tale balance. That balance spec is meant for hard drive spindles, it has been misapplied so often in rotating machinery.

Good luck

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[BjarneEng]

Hi CouplingGuru
The magnetic layout of my coupling the magnets needs to be magnatized before they are assembled into the rotor.

 

[CouplingGuru]

BjarneEng,

That sounds intriguing. Depending on a lot of factors (misalignment ability, torque density, and slip lag) you may find you will need a much stronger magnet than originally anticipated. Consequently eventually assembly can get so un-manageable, especially if they are close together, that magnetizing after assembly is the only option. Plus if you are looking for a ISO balance grade of that precision, it lends me to believe you have a higher speed application. These high speed applications can be quite dangerous with magnetic couplings, because they tend to get extremely hot very quickly.

Good luck, post some pictures when you have it complete, I sure would like to see it.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM