Fusor grid material

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Anthony Marshall
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Fusor grid material

Post by Anthony Marshall » Sun Mar 10, 2019 4:41 pm

I was curious if anyone here has ever used tungsten rods for tig welders as the material for building fusor grids.

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Bob Reite
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Re: Fusor grid material

Post by Bob Reite » Sun Mar 10, 2019 6:03 pm

Yes! Doug Coulter makes his grids partially out of tungsten tig welding rods, with end caps out of graphite, which can stand very high temperatures as long as it's in a reducing atmosphere (which it will be if you are flowing D2) or good vacuum.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

ian_krase
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Re: Fusor grid material

Post by ian_krase » Tue Mar 12, 2019 1:50 am

Note that Doug uses unusual cylindrical grids.

A more common trick is making grids out of tungsten wire, which isn't too expensive on eBay, though it's insanely springy and easy to break.

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Richard Hull
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Re: Fusor grid material

Post by Richard Hull » Tue Mar 12, 2019 4:35 am

Almost any of the high temperature grid materials made of wire will not retain any springiness once run in a fusor for a protracted number of runs. Hydrogen/deuterium embrittlement will ultimately make the the wire hold its shape to the point that if any attempt to straighten or adjust the used grid in most any way will have it break like glass. The constant thermal cycling, (expansion and contraction), can also tend to work harden the grid wires, as well. This doesn't mean it is more delicate to handle. It means don't expect to take it out and adjust it in an attempt to make it more symmetrical.

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ian_krase
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Re: Fusor grid material

Post by ian_krase » Thu Mar 14, 2019 6:58 am

Yes. IDK if it's hydrogen or something else, but no tungsten that has been incandescent will ever be ductile again (to the degree that tungsten is ever ductile).


Interesting, copper wire has exactly the opposite effect. If copper is heated to glow even dull red hot (which a demo fusor will do easily), when it cools down it will be extremely soft and bendable, to the degree that it may not really want to support its own weight without bending. However, you can bend it back, and it will be a bit more normally-stiff after a bit of cold bending.

(this was a problem when I built my own spot welder.)

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Trent Carter
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Re: Fusor grid material

Post by Trent Carter » Wed Sep 04, 2019 8:58 pm

Yes. We have made many successful cathodes out of tungsten welding rods. Most in the 1mm diameter realm. Buy several from several sources. Some are fragile like glass rods, break no bend. Some bend fine. Use those. I have dropped a glass like tungsten cathode that took a day to make and had it shatter like glass. Not good.

To mount them you can drill holes slightly smaller than the rod and work them into place. You can tap the end daps fine but you are not threading tungsten. It’s harder than your threading tool.

As for the end caps; I recommend stainless or nickel. Yes the melting temps are lower, and they get red hot, but they hold. The tungsten takes the majority of the heating. The end cap connected to the cathode needs to be a great temp conductor.

Trent

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