TIG furnace for tungsten welding

Tricks of the trade

TIG furnace for tungsten welding

Postby Doug Coulter » Sun Mar 27, 2011 2:05 pm

Tungsten is hard to weld, no big surprise. There are a couple of ways to get it done, one being a capacitive discharge spot welder with close control on energy, and another is to just have a place where it's hot enough to melt tungsten -- no small requirement.

The need in my case arose as I decided to have some type C thermocouples to monitor evaporations and things in my fusor -- it alone will handle the temperatures I want. But it is an absolute bear to weld. Spot welding it tends to weld it nicely to the welder electrodes for example (still searching for the ideal welder electrode material for that) and it's hard even with a specialized spot welder -- forget the Harbor Freight one, even with a variac, you just can't control it well enough.

But for the case where you just need to make a junction between two twisted wires, there's an easier and better way. Set up a jig that holds a TIG arc and contains the shield gas, and just stick the wires in the fire -- done, works great, it's easy.
TIGFurnace.jpg
TIG furnace jig


This jig, made of 2" box steel, is the trick that makes it really easy. Nothing special really. I made a bushing on the lathe that fits the ceramic tip on the welding head to hold that end of things, and another out of copper that clamps a fat TIG rod, which gets the ground clamp. I also drilled a small hole in the side to introduce your thermocouple wires through. Just put them in the arc for a second or so, and pull them back out (but keep them inside the box till they cool off).

I suspect this toy could also be used with a crucible to get things really hot as well. You could use this upside down from the way it is in the picture and put the crucible down in the pipe where it would be in the shield gas too. Haven't tried this for any length of time -- I might have to replace some of the brazed in bushings with something else that will hack more heat for that to be really practical. It will definitely melt quartz -- stat.

Here is where you get type C wire. Nanmac. I have found it good for filaments for electron emission as well. The rhenium in the alloy makes the tungsten live longer when there is water around, and increases the electrical resistance as well. I coat it with yttria for that use which gives it emission similar to thoriated tungsten at similar temperatures, but avoids the complications of radioactivity and is more resistant to air and ion bombardment in the bargain.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Return to Shop tips and kinks

Who is online

Users browsing this forum: No registered users and 2 guests