Mu-metal
Moderators: pompeiisneaks, Colossal
Mu-metal
Anyone have an idea what temperature you have to bend Mu-metal so it will retain it's magnetic/austenetic properties? I'd hate to bend some to fit only to realize it i let out the magic vapor.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
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Tony Bones
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- Joined: Thu Oct 30, 2014 8:24 pm
Re: Mu-metal
The idea is that it needs to be fully annealed after bending, which amounts to heating it in an oven to some temp after bending and then letting it cool slowly.
I don't know what the magic temperature is, but it's almost certainly hotter than the oven in your kitchen will go.
I don't know what the magic temperature is, but it's almost certainly hotter than the oven in your kitchen will go.
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martin manning
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Re: Mu-metal
Thanks for the reference Martin,
Looks like over 2000° is required, and in an oxygen free kiln at that. No carbon, sulphur, etc. can be present
From what i can deduce, some of the other high nickel metals will allow a modicum of shaping without much loss of effectiveness. Apparently they are not as good as the formulation for Mumetal though.
One surprising fact was that steel is more effective for larger magnetic fields. In a high strength field, surrounding the source with steel, then shielding the sensitive circuitry with Mumetal gives the best protection. The type of steel matters also to a degree, with electrical steel, (like the steel in transformer laminations) having the edge.
Looks like over 2000° is required, and in an oxygen free kiln at that. No carbon, sulphur, etc. can be present
From what i can deduce, some of the other high nickel metals will allow a modicum of shaping without much loss of effectiveness. Apparently they are not as good as the formulation for Mumetal though.
One surprising fact was that steel is more effective for larger magnetic fields. In a high strength field, surrounding the source with steel, then shielding the sensitive circuitry with Mumetal gives the best protection. The type of steel matters also to a degree, with electrical steel, (like the steel in transformer laminations) having the edge.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
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Tony Bones
- Posts: 228
- Joined: Thu Oct 30, 2014 8:24 pm
Re: Mu-metal
Think of magnetic shielding as channeling the flux around what ever you're shielding more than blocking it. By that I mean that it won't work to put up a wall hoping it will leave a "shadow" free of flux. You need to make a full enclosure; the flux enters the shield on one side, stays in the high mu material as it travels around the shielded area, then leaves on the other side. There needs to be a path all the way around the shielded area.
Multiple layers with significant space between them is more effective than a single layer. Each one needs to provide its own path for the flux. Think of a small can inside a larger can.
Large radius corners are better than sharp corners. A sphere is better than a cube. That's true after annealing, but even more true if you don't plan to anneal after bending; a gentle bend will disrupt the grain structure less than a sharp one.
Multiple layers with significant space between them is more effective than a single layer. Each one needs to provide its own path for the flux. Think of a small can inside a larger can.
Large radius corners are better than sharp corners. A sphere is better than a cube. That's true after annealing, but even more true if you don't plan to anneal after bending; a gentle bend will disrupt the grain structure less than a sharp one.