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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi all. I did find a way to make glass/metal feedthroughs. What you do is get your glass sphere, bowl etc, heat the spot to be fed through to red heat with a convenient blowlamp.. Then position it so the metal feedthrough is pressing on the red hot area and then microwave it until it is correctly set It relies on the conductivity of hot glass :)
Best to use a preheated (convection) combination microwave then slowly cool to prevent the glass shattering.. Also it might work for holding tungsten welding electrodes for spark gaps etc.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
Cool application of microwaves! I read a W Beaty article on "unwise microwave experiments" and melting glass with microwaves was mentions, I never thought it could have any practical use.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I have a contact in Russia who is able to supply high current fusible glass feed-throughs. This leaves the constructor with only problem of fusing glass to glass, rather than the problem of trying to seal round a metal rod, with all its co-efficient of thermal expansion problems.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
What kind of glass and what kind of metal are you using?
I was trying to seal stainless into boro glass, which isn't supposed to work because the expansion coefficients are too different. One seal looked like it worked for a while, but of course cracked later because I don't have an annealing oven.
For soft soda glass you can seal copper, stainless, kovar, nickel, a variety of materials, but the trouble here is obtaining lab quality soft glass because the distributers sell boro for the most part.
You could probably get away with sealing the glass like Harry is saying, but I think the whole must be annealed due to possible stresses. I have seen in my books that when you're doing an operation like this, the glassblower wraps the leading tube with asbestos tape to prevent heat transfer to the sensitive area. Now asbestos tape really isn't available so much these days, but you might be able to find some fiberglass cloth and make a tape out of that to prevent heat transfer.
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Glass feedthroughs..
