About Magnets
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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