Barry, Three types of iron-based materials are used in magnetics. The "Reference Data for Radio Enfineers" has a rather complete table of metallic core materials. The "soft iron" variety is almost pure iron, with up to 10% silicon. The cobalt iron alloys are about 50% cobalt, and have a high saturation curve. The vast majority of choices, which includes the several of the "permalloy" alloys, run from 50 to 80% nickel, and provide the highest permeability but lower saturation. But for many applications low-silicon (4%) soft iron is the best bet. Its advantage is that it can be stamped or cold forged, as are the poles in speaker magnets, where you can see the stamping streaks in the edges of the soft-iron donuts. I am using soft iron washers as poles for the magnets for the new NSF instrument. (I have posted the magnet design). In general, I try to design around bought hardware, since few people have a lathe or mill. McMaster has a large selection of large OD/ID by 1/4" thick washers. The cyclotron I worked on had a 13 ton magnet with 30" poles and was made with 1" slabs of low silicon soft iron, which will not saturate until about 20 kgauss (we ran at about 15 kgauss). But if you dismantle a transformer, the laminates are most likely a grain-oriented silicon alloy, which is tempered and stamped; bend it once and it becomes very soft at the bend. The transformers I modify to be the poles of the VRDT displacement transducer will not re-assemble if any of the laminates have been bent because they cannot be straightened. Regards, Sean-Thomas __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>