magnets was [CAD_CAM_EDM_DRO] Re: Why do stepper motors lose their magnetism when disassembled?

I have to jump in here. My qualifications are that I designed spindle motors, and voice coil magnet assemblies for hard disk drives.

The are many different types of magnets out there - take a look at Wikipedia for more information. Commonly you might run across:

Alnico - used to be very common, not so much any more. They require a keeper. In a magnetic circuit, they are stable, even at high temperatures.

Barium Ferrite and Strontium Ferrite - these two are very similar "cheap" magnets. The powder is often mixed with plastic and injection molded into various shapes, including refrigerator magnets. These are next to impossible to demagnetize, do not require a keeper, and are stable at high temperatures. They are not very powerful magnets.

Samarium Cobalt - expensive, very powerful, stable at high temperatures, do not require a keeper.

Neodymium Iron Boron - not expensive, very powerful, easy to demagnetize with higher temperature (in some cases less than 150°F). They do not require a keeper. Invariably, if a NdFeB magnet looses strength it is due to temperature - a keeper or lack there of has no effect.

Nigel F Misso, PE
http://www.linkedin.com/in/nigelmisso

----- Original Message -----
From: carbonsteelsam
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Saturday, December 13, 2008 10:26 AM
Subject: [CAD_CAM_EDM_DRO] Re: Why do stepper motors lose their magnetism when disassembled?


If the magnets are of the rare-earth "super" variety (neodynium,
boron etc) they absolutly do not need a keeper. I have purchased
several hundred of these magnets of various shapes & sizes a couple
of years ago and they were never shipped with keepers, nor did the
vendor advise using them. Older, iron-nickle magnets do need a
keeper. BTW, it is impossible to remagnetize a rare-earth magnet
without a collossal piece of equipment, which would propably dim the
lights of a small town.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jim Register
<jtregister@...> wrote:
>
> Yahoo wrote:
> > I figured it was something like that. I suppose if you had an
iron plug the
> > same size as the rotor you could slide it in as you remove the
rotor and
> > maybe not ruin the motor.
> > --
> > Phil Mattison
>
> The rotor is the permanent magnet; you'd need an iron/steel tube
to
> slide it into, I think.
>
> Jim Register
>


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