[modeleng] Re: RE Magnetic Chucks going OT - sorry guys!

John Paget said:
>When you remove the keeper the effect is to push you down the B-H curve.<

First question is why? I suppose if you think of it in electrical analogy 
terms (which is how I managed to understand magnetics enough to pass ONC - 
dear me, that WAS a long time ago!) you can imagine the keeper as a low 
reluctance (low resistance) which maintains the flux density 
(webers/sq.metre in MKS) for a given AT/m (voltage in electrical terms). 
What I don't see is what causes the loss in AT/m when you remove the 
keeper, since I imagine the magnet itself consisting of the aligned 
magnetic domains, which I thought required some energy to disturb them - 
such as hammering, heating etc.

I presume that a material with a very square B-H curve could show very 
little effect, but I'm still puzzled as to why the domains 'disalign' 
themselves. I can see why the hysterisis is a problem - incidentally, I 
was taught that the hysterisis occurs because of the reluctance of the 
domains to move readily.

Peter Chadwick (still puzzled in San Diego!)

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