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: ARTICLES : ABOUT MAGNETS (1 OF
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| About
Magnets |
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Modern magnets
are far more powerful than those of only a few years ago, which has
greatly increased their usefulness in a wide range of products. Magnets
are usually shipped from the factory to a manufacturer in the unmagnetized
state. There are a number of reasons for this. There are legal restrictions
on the shipping of active magnets. They may affect instruments, destroy
nearby delicate equipment, and erase magnetic tape and disk memory
information. Larger masses of magnets can be dangerous to personnel,
causing objects to fly at high speed, and pinching or crushing body
parts. In addition, magnetized magnets attract some kinds of dirt
particles, and they are extremely difficult to clean once they have
become contaminated. The new types of magnets can be made and used
in extremely thin sections, and materials are often brittle. Once
they are magnetized, additional forces are caused, which could greatly
increase breakage in shipment. For these reasons, it is usually preferable
to magnetize magnets in place in the final product, or just before
assembly.
Older magnet materials could often be magnetized by such means as
exposing them to a fixed magnetic field caused by other magnets, focused
through a steel pole structure, or by using a short time duration
current (perhaps a second) of rectified AC current directly from the
power lines into a fixture of many turns (and high inductance), among
other techniques. The newer high-coercivity magnets are much more
resistive to demagnetizing effects, and are correspondingly much harder
to magnetize. |
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