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Mu-metal or steel - how to tell easily?

I'm a scrounge. I work with computers. I pull magnets from dead hard drives - they typically have one or two really strong rare earth magnets which are handy for various purposes. I've recently begun to wonder if the sheilds or pole pieces around those magnets (the ones that sit on the back side of the head apparatus to position it) are plain steel, which I've pretty much assumed would be the case (cheap) or if that sheild might just be mu-metal.

If there is either an easy way to tell, or if somone on here knows in general or specific cases from the manufacturing end, I'd like to know.

Thanks,

Reply to
Ecnerwal
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The mu-metal I've seen was thin, maybe 20 ga. and a nice deep gray color with a very slight texture. Unfortunately physically deforming it will destroy it's shielding properties so it is difficult to salvage and reuse

Reply to
Jim Stewart

Gnaw... mu metal has much too low saturation for that. I've got to believe those magnets are at least that strong. Probably silicon steel, or maybe something with nickel in it.

Tim

Reply to
Tim Williams

To be re-used, it needs to be annealed at a very high temperature.

Jim

Reply to
jim rozen

I always thought it wasn't very hot, maybe orange hot (about like annealing steel), but it has to be done under hydrogen reduction.

Tim

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Reply to
Tim Williams

Yes. We used to get it done by a company called Klock in CT, they would fire them under H2. I remember the temperature was hot enough that a couple of runs would burn out the elements in the H2 furnaces at work so they didn't like to anneal mu metal. I want to think about 1200 or 1250 C or thereabouts.

Shields have to be annealed after fabrication or their attenuation is reduced.

Jim

Reply to
jim rozen

Definitely not mumetal (or any of the fancy nickel iron alloys).

The only important magnetic characteristic for these pole pieces is reasonably high saturation flux density. This means that there is no advantage in using anything more exotic than mild steel or soft iron.

Jim

Reply to
pentagrid

I case some of you were not aware, the magnets in a hard drive usually come attached to a plate that has a few holes suitable for screwing to the overhead with a drywall screww. These will easily hold about any size hammer you might use above your workbench or a half dozen wrenches each. A 4lb hand drilling hammer has to be pulled off of one above my bench, they are that strong.

Reply to
bamboo

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