Re: CRT magnetic screens: Mumetal?


Ed Breya
 

It's not about degaussing, it's a problem with losing the grain orientation that was imparted during annealing.

Annealing it is very difficult since the temperature is quite high - like approaching its melting point, and the hydrogen atmosphere is very risky. It occured to me once to maybe try an oxy-hydrogen torch with an over-rich flame, but then the problem is what do you do about the opposite side, and the transition region from flame to not, and hot to cold. It really needs to be in a uniform environment.

If you buy raw sheet stock, it may be un-annealed, so won't work as well as that in a finished piece that definitely would have been. If the stock is labeled so or known to be annealed, then it's good stuff to keep around.

Ed

--- In TekScopes@yahoogroups.com, Peter Hildebrandt <petertech99h@...> wrote:

Hi Steve,

Can you save a dropped shield with a AC degauss coil?  How high a temperature
was needed to anneal the Mu metal?
A local guy over here is sitting on a little stock of Mu, maybe I'll get it for future
use! you never know!

see ya

Peter
 
 




________________________________
From: Steve <ditter2@...>
To: TekScopes@yahoogroups.com
Sent: Wednesday, June 19, 2013 5:05:53 PM
Subject: [TekScopes] Re: CRT magnetic screens: Mumetal?



 
--- In TekScopes@yahoogroups.com, "John S" <John@> wrote:


I've always assumed that the blue screen around the CRT on Tek scopes (400 series etc) was made of Mumetal. Is this actually true?

John
Yes.

Tek fabricated them from raw stock. After they were cut, bent and spot welded, they went into an oven to be annealed (mu metal loses its shielding properties if physically bent or modified (drilling holes etc.) after annealing. If you drop a shield on the floor and the corner bends - throw it away.) The ovens operated at high temperature in a pure hydrogen (reducing) atmosphere. Opening an oven door before it had cooled posed an explosion hazard. To minimize the danger, Tek used several small ovens, each could only contain about 4 or 6 shields.

- Steve

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