29 Nov 2006, 00:56
On the contrary, this is precisely the sort of information that should be shared. It is the reason this forum exists. It is certainly the reason I am here. There are those who derive a misplaced sense of personal satisfaction in the mindset of "I know something you don't know" [I daresay those individuals know who they are]. I find no rational purpose in this. Future collectors depend on us, and what we do now, to make sure there is something left to collect in the years to come, and they will judge us on our actions, or inactions. I intend to be among those they praise, rather than condemn, for having been here.
Back to the magnets... The originals were an alloy called AlNICo 5, an aluminum-nickel-iron-cobalt combination, presumibly the fifth in a series of similar alloys. These metals do not blend well by melting, so they are powdered, mixed, and placed under enormous pressure and heat [very high, but below the melting point of any of them], until they compress into a solid mass [this process is called "sintering"]. It can still leave occasional small voids in the metal [often visible on the "C"-shaped magnets as dark areas]. This was about the best permanent-magnet material available in the 70s. Modern rare-earth magnets [primarily neodymium-boron-iron], have five to eight times the field-density strength of AlNICo, and can easily be used to repolarize them. At the factory, the initial polarization was done in an electromagnet [called a "gap" magnet, because of its' nearly circular shape, with a small opening, or gap, at the top]. The blank magnet was placed in the gap, in the necessary orientation, power was applied, and the blank was appropriately magnetized. A similar effect can be achieved by pulling your magnet across the face of a rare-earth magnet in the proper direction. It will take a bit of trial-and-error to get the orientation correct, but once you find the right combination, you can do it routinely.