Welding Tungsten

You definitely need a controlled atmosphere, inert at minimum. A reducing atmosphere (hydrogen) would be better, but is obviously very dangerous unless you know exactly what you're doing. With enough fussing you *might* be able to fuse the two pieces with one held in a TIG torch running an inert shielding gas and the other grounded. Don't even think about trying this with hydrogen.

Why do you need to join them?

Ned Simmons

On 10 Feb 2007 19:36:50 -0800, with neither quill nor qualm, snipped-for-privacy@volcanomail.com quickly quoth:

You'll need biflux and use at least a 1.21 gigawatt flux capacitor with to deal with the temporal instabilities of tungsten, Andy.

- Inside every older person is a younger person wondering WTF happened. ---

Please try it with hydrogen! And have a spectator with a video camera. Id love to see the tape.

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

Thanks for replys, I am attempting to make a super high temperature, (and super cheap !!) heating element. I though I could weld about 10 of the bars in a square spiral shape and simply apply power. Can W bars similar to the electrodes but twice or 3 times as long be purchased anywhere? Is there anyway I could join the electrodes together without welding. If I had thicker bar or cube of W. Drill holes at right angles to each other the same (similar) size to the electdroes and simply join my (10 or so) electrodes together by inserting them into the holes. I would end up with my 'square spiral'. It sounds a bit hair brained. I would drill the holes using the electrodes themselves in a drill press and abrasive slurry with a dashing of patience.

Andy

How hot is "super high temperature?"

Even below the temps a common heat treat furnace reaches (~2000F) you'll need a controlled atmosphere to protect the element, as tungsten oxidizes quite readily. Nitrogen will work at moderate temperatures (up to 1200-1400F, IIRC), and hydrogen is the norm beyond that, though I imagine inert gas would also work.

Mechanical joints of the sort you describe are often used when fabricating large elements. Tungsten is machinable with carbide, but it's no fun. Moly (see my comments re moly below) is easy by comparison, with a few caveats.

Tungsten, though very brittle at room temperature, can be formed at only a few hundred degrees F. Google, "brittle to ductile transition temperature" tungsten, or, BDTD tungsten, for more info. W is available as wire, so you could bend up your element with no joints.

All of this also applies to molybdenum, which is cheaper and much easier to work with, and is good up to at least 3500F in the proper atmosphere.

Ned Simmons

I spend almost all my time working for a plant that runs dozens of hydrogen atmosphere furnaces. While it's rare enough that I've never been in the factory when it's happened, it's not unheard of that a furnace will aspirate a charge of air with the predictable result. The furnaces have blow-out doors that act like a pressure relief to minimize damage to the furnace, but I've heard the boom can be loud enough to knock the dust off the roof beams all through the very large factory.

Ned Simmons

temperature"tungsten, or, BDTDtungsten, for more info. W is available as wire, so you

Thanks Ned, . I want to go to 1800C that's 3300F (approx) I did not realize that W oxidises so easily. Thought I could go to

1800C without inert gas or H2. How hot could you heat W before it oxidezes rapidly do you know. I might as well go with carbon rods if I have to use an inert atmosphere. Looked at they have lots of wire. I did not realize it was so easily available. Do you think I could use Propane as a protection atmosphere (reducing) instead of H2 or inert gas.

Cheers, Andy

temperature"tungsten, or, BDTDtungsten, for more info. W is available as wire, so you

I'm working from memory here, but I think W will start developing a black oxide coating somewhere around a red heat, perhaps 1000F. A little hotter and you'll get a greenish powdery oxide on the surface.

My knowledge is admittedly limited, but I doubt propane is going to work, and will still be dangerous if your furnace sucks in any air. (At what temp does propane dissociate? Will the tungsten have an affinity for the carbon? -> tungsten carbide?) If there was an economical alternative to H2 I expect my customer would be using it in at least some applications.

There are some potential problems when picking refractories at these temps in a reducing atmosphere, which you may be able to avoid with inert gas.

I'm afraid I don't have any direct experience with carbon or SiC elements.

Ned Simmons

Have a look at Kanthal. They should have what you need under the SiC-heating-elements section.

Nick

This may help:

Kanthal will got to 2300 F at in a ceramic kiln at 200 fet above sea level. I have done it hundreds of times with no failures.........

at

and search in the archives for a thread mentioning them and MoSi2

Thanks for replys all. I have been aware of the MoSi2 elements but have assumed they would be very expensive and hard to get . I well look into it

Andy

at

>and search in the archives for a thread mentioning them and MoSi2

If it helps the thread name was "Moly furnace" IIRC and mid December

2005. Easily found with google.

you might try contacting an element manufacturer to see if they have something off the shelf.

regards, charlie