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: ARTICLES : ABOUT MAGNETS (2 OF
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| About
Magnets |
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| The method
used to magnetize a part is to send a very short (perhaps a thousandth
of a second) pulse of electric energy at very high voltage and current,
through a fixture which converts the electrical pulse into a magnetic
pulse. Whenever electric current flows through a wire, a magnetic
field is set up in a circular field (no poles) around the wire, the
direction of the field being at right angles to the direction of current.
By properly shaping wire conductors, often with steel (or other magnetically
permeable) pole material used both to support the wires, and also
to help concentrate and direct the magnetic flux, a fixture can be
made which holds the part and causes it to assume the required magnetic
pole pattern. The currents in the fixture are usually so high that
it would overheat, burn out its insulation, and even melt or vaporize
the wire, if the power were allowed to be on too long. The magnetization
of the part is accomplished in an extremely short time, once the required
coercive field is attained (millionths of a second), and so the field
does not need to be present very long. This is fortunate, since otherwise
the extremely high currents needed to produce the required field could
not be achieved in the space available.
If a number of magnets are placed together, they tend to line up
end-to-end. In a magnet, individual atoms (or small groups of atoms)
also tend to line up within small regions called DOMAINS, producing
tiny local magnetic regions. In an unmagnetized part, these domains
exist everywhere, but they have fields which point in different
directions, and they cancel each other out so that the average resulting
field is zero. |
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