30 Aug 2015, 00:28
Theoretically, it is possible to re-polarize these with a rare-earth magnet, but in practice, it is very difficult to get BOTH the strength, polarity, AND field orientation correct. Originally, these were done in what is called a gap-magnet; a type of electromagnet shaped rather like a ring with a small section missing (the "gap"). The part to be magnetized is placed in the gap (in this case, in a very specific orientation), current is applied, and a powerful field is briefly established. Power is then shut off, and the part is now (more or less) permanently magnetized. The Pulsar setting magnets are all sintered AlNiCo V (5), an aluminum-nickel-iron alloy, made by mixing powdered metals, heating them to just under the melting point, and pressing them under tons of pressure into shaped molds. The "D"-shaped (P3) and half-D (P4) magnets were apparently done in individual molds; the "C" type was done as a long bar, and sliced (loaf-of-bread style) into individual magnets...the curved lines left by the cutting saw are clearly visible on both sides (variations with rounded and more squared-off corners exist). Though these were the best "permanent" magnets that could be made at the time, they were still susceptible to loss of field strength by either mechanical shock, or exposure to strong external magnetic fields.