Alt-BEAM Archive
Message #07296
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Tue, 02 Nov 1999 19:42:50 -0500
Subject: [alt-beam] Re: magnets
Timothy Flytcher wrote:
> >Timothy Flytcher wrote:
>
> >Most powerful magets come with 'keepers' that close the path of magnetic
> >flux, to protect the magnet when stored.
>
> Ok Bob, protect them from what???
Physical dammage, such as chipping and shock, from objects being drawn
to the poles by the field! It also protects objects from being effected by the
magnet.
> >A magnet stuck to the front of your refrigerator does not loose any
> >strenght
> >in the process of sticking there, for months or years.
>
> Yes it dose... try running a guise meter over a refrigerator door after you
> have removed them...
This is getting off topic, but a magnet hanging on the refrigerator does not
loose
any energy at all. A magnet floating over a supercondutor also does not loose
any energy while levitating.
In fact, when a bit of metal is drawn to a magnet, say a paperclip being picked
up off a desk, is not taking any energy from the magnet at all. Thats simply
not
how the physics of magnetic fields works. (in fact, the magnetized paperclip
hanging from the magnet is in a lower energy state than when it was sitting on
the desk!)
All the energy the magnet appears to use in drawing up the paperclip is payed
back, with interest, when you remove that paperclip. The same is true when you
remove
the magnet from the refridgerator.
You can also make magnets (like the spot where your fridge magnet hung) without
'taking' any energy or magnetism from the original magnet used to make the
second magnet. So just because your fridge has a magnetic spot left behind does
not mean that 'energy' was taken from the magnet, or that it 'used' any energy
while it hung there.
To do this, you simply place a bit of iron next to your magnet pole, and hammer
on the iron bit. Viberation from the hammering will realign the magnetic
moments
in the iron, and they will move into alignment with the field of your magnet.
In this case the energy used to magnetize the bit of iron came from the
hammering, not from the magnet. Thermal viberations will also do this over
time, depending on how long you let your fridge magnet hang, so will the motor
viberations, etc.
> >PM motors will loose efficiency if the armature becomes magnetized, which
> >happens much quicker if the motor overheats, and then cools again (this is
> >how
> >many mangets are made in the first place).
>
> This is how a few magnets are made...very few! it is simply too expensive!
Not according to many manufactuers. As most modern magnets are ceramic
based rare earth magnets, they have to be formed above their curie points
anyway.
A huge zap from a capacitor is dumped into a copper sheet around the form as its
quenched, and there you go...one supermagnet, ready to ship.
> Only end product magnets are shipped magnetized...I once worked for EB
> making guitar pickups. I can't remember the composition of the material but
> its qurie point was 530' a little high for the card stock that we used to
> mount the windings...And yes guitar pick-ups loose there strength with time
> and use... some say they mellow... I can and have reproduced this upon
> request... :)
Maybe pickups do age, I have no idea, but the reason why they age may not be
what you think it is. Bucking magnetic fields can also depoloarize magnetic
materials, and other materials can easily become saturated (like Mu metal).
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