[modeleng] Re: RE Magnetic Chucks going OT - sorry guys!
- From: "R.L. Roebuck" <rlr20@xxxxxxxxxxxxxxxx>
- To: modeleng@xxxxxxxxxxxxx
- Date: Thu, 23 Feb 2006 10:31:44 +0000 (GMT)
As it was explained to me, it is easy for the magnets to drive the field
around the system when you have the motor or chuck assembled, but when you
dissasemble it you force the magnets to drive the field though a large
expanse of air (which is a lot more effort than driving it through metal).
In the same way that if a human tries to push a load up too steep a hill,
the magnets suffer from their equivalent of a hernia!
Reassembly and a trip to the remagnitisers will normally sort it out (for
the magnets that is).
As far as the use of keepers is concerned, I'm assuming that these have to
be purpuse built for the job, and have to be inserted before the armature,
or whatever else you are removing is taken out (rather like Indiana Jones
when removing precious artifacts which are sat on a trip switch).
Is that of any use?
Yours,
Rich.
On Wed, 22 Feb 2006, John Pagett wrote:
>
>
>> What is the mechanism that keeper provides? On the face of it, why should
>> an increase in reluctance lead to the domains re-arranging? It's one of
>> those things that I know happens, but don't understand why!
>
> Peter,
> A nice man at a magnetics course told me why, but I didn't take much notice
> because he was talking about Alnico magnets and I was interested in Samarium
> Cobalt, which isn't nearly so badly affected by removing the keeper.
>
> Do you know about B-H curves? They are the diagrams showing applied and
> "generated" magnetic field, and always show hysteresis between the two.
>
> When the magnet is in place with the keepers, you are at the point on the
> B-H curve where the curve crosses the y axis somewhere above the origin.
> When you remove the keeper the effect is to push you down the B-H curve.
> When you replace the keeper you would come back up the B-H curve BUT there
> because of the hysteresis so you don't end up with as much magnetism as you
> had before. As to what happens to the domains, I'm not really sure.
>
> It's one of those things that you think you understand....until you have to
> explain it to someone!
>
> Regards,
>
> JohnP
>
>
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