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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I was thinking about using some 0.01" thick "Multipurpose Flame-Retardant Garolite G-10/FR4 Sheets and Bars" from McMaster Carr.
I wonder: What would be the best way to cut this stuff? If it's only 0.01" thick would scissors work, or would it chip and/or crack? Or maybe a glass cutter?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
You could use your least favorite scissors. Or score it, preferably with a tool shape & orientation that removes material, then break. Either way, the edge won't be pretty under a microscope, but can be deburred with sandpaper.
Why not use plastic film (e.g. acetate, Mylar) -- too hot? Or fish paper or a manila folder -- going to get wet?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Hey thanks klugesmith and johnf for the ideas.
While researching Kapton, fishpaper and mylar, I came across PEEK film and Ultem PEI film, both of which seem to have fairly good characteristics. Of these two, Ultem seems to be cheaper and more readily available, so I am leaning toward that material.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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A few years ago when I was researching insulation systems for HV transformers, I came across a few papers that touched on the aging of kraft paper, and I discovered that it's subject to several time and temperature dependent chemical processes (oxidation and hydrolysis or something like that) that cause it to eventually break down. And IIRC the breakdown process releases moisture, making it auto-catalytic.
I realize that in my low-duty application this would probably not be a factor, but being the semi-perfectionist that I am, the thought of it bothers me. So while it would probably suffice for most people, I don't like it.
(Moreover, the thought of cutting up paper bags to add to one of my transformers, also offends my gentle semi-perfectionist sensibilities :).
2Spoons wrote ...
Whats wrong with plain old paper? So long as you have a way to measure the thickness ( every engineer should have access to a micrometer or vernier gauge!) you can use any paper you have laying about.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
You might be amazed how many insulating parts inside pole- and pad-mounted electric utility transformers are made from paper or wood. Might be epoxy-impregnated paper in recent decades.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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I know paper is widely used. And I'm sure it would work fine in my application as a spacer for a ferrite core transformer. I just don't like the idea of using it.
Another example is teflon, which I also considered. I know it's prone to cold flow (more so than other plastics) so I found a data sheet with a graph showing total deformation under various levels of compressive loading, at 100 degrees C. And I concluded that it would probably not cause a problem for me.
But the idea that the teflon sitting there squeezed between two pieces of ferrite will slowly extrude from the gap - maybe only a few nanometers per day - nevertheless irritates me, so I have to reject it.
So the problem isn't really the materials, but my idiosyncrasies...
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What material is everyone using these days to gap ferrite double U cores?
