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,

--
Cats, Coffee, Chocolate...vices to live by

Ecnerwal wrote:

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.

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

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

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

"Ecnerwal" wrote in message
...
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,

--
Cats, Coffee, Chocolate...vices to live by

In article , Jim Stewart says...

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

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

Jim


--
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please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
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"jim rozen" wrote in message
...
To be re-used, it needs to be annealed at a very
high temperature.

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

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

In article , Tim Williams says...

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

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

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


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On Fri, 04 Mar 2005 18:39:16 GMT, Ecnerwal
wrote:

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,

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

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.