Date: Wed, 20 Oct 1999 15:54:06 -0600

Author: Jerry DiMarco

Subject: Re: Magnet Storage

Post:

Patrick,

I'm a little behind on mail because I went to my 25th(!) college
reunion last weekend. Please bear with me while I catch up.
Magnets in storage usually get demagnetized because of:
1) being close to opposing, strong magnetic fields,
2) contact with ferromagnetic bodies (applies to steel and most alnicos
only, sides are more sensitive to this effect than ends),
3) storage near ferromagnetic material (e.g. painted metal shelf).
According to reference books on this topic I've read, the best way to
store magnets is in a non-magnetic tray with spacers inbetween. To that
end, I have made storage boxes for the magnets used in labs that have a
thick piece of pink foam board with holes every 3", that hold bar magnets
in a vertical orientation. Over in the demo room is a box that holds bar
magnets horizontally with spacers inbetween. Spacer width is determined by
magnet strength, and varies from 3" to 12". The big radar magnets are on a
separate, MUCH lower shelf, spaced a foot or more apart. The shelves are
made of wood.
Disk and other flat magnets with polar faces can be stacked because the
poles just combine to make a longer magnet. Bar magnets can be stacked end
to end too. It is just the opposite of the broken magnet demo. Flat
magnets with poles on the circumference will align with opposites together,
and I'm not sure how this will turn out. I'm inclined to think it is a bad
arrangement. Does anyone else know for sure?
Horseshoe magnets have their poles in close proximity, which can cause
them to lose strength over time as noted in #1 above. This is why
horseshoes always come with keepers. Keepers reduce the field in the space
around the magnet. The field is concentrated in the keeper, preventing
mutual demagnetization of the poles. Horseshoes with keepers should be
stored apart like bar magnets.
That about covers the major types of magnets. Let me know if you have
further questions...

Jerry


At 10:00 AM 10/13/99 -0500, you wrote:
>Hi!
>How do you all store your magnets?
>
>- Patrick


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Jerry DiMarco, Instructional Lab Supr. ph: 406-994-6161
Physics Dept., Montana State Univ. fax: 406-994-4452
Bozeman, MT 59717-3840 e-mail: dimarco@physics.montana.edu

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