Hi, Is there some compound or liquid that I can spray or rub on between parts that will keep them from fusing from the heat of nearby welding?
I'm welding three pieces of tubing to a structure, and they have to line up precisely, so I've got to have a shaft holding them in place. The problem is that the heat causes the shaft to get stuck. I don't think that I'm welding through the side (I'm quicker than that) but something is fusing it in place. Any help for this?
It probably won't stop the sticking but a high temp anti-seize would at least keep it from galling together when you go to take it out.
If done properly the weld won't be sticking to the shaft. However every time you weld the tube you shrink it and pull it out of alignment with the others. There's not really anything that can be done about this since it's the nature of welding to shrink stuff.
The key to this job is the put the shaft in there. Lightly tack all of the pieces in place (preferable in about 4 places 2 top and 2 bottom). Then remove the shaft and do the welding.
Afterwards if the pieces that go in the tubes are a good fit before welding you'll likely have to ream the holes in order for them to fit again. This is why you need some clearance on a job like this preferably .010" or more.
My guess is that the welding distorts the tubing, which causes the shaft to get stuck. Even if the opening stays round, the welded metal shrinks when it gets cold, so that could use up all the clearance. If you had a smaller diameter shaft with more "Play" you might be able to avoid the problem. Even 0.010 inch more clearance might be enough to enable you to remove the shaft after welding. I would probably try for 0.020 inch clearance before welding, but I am not sure that is enough.
If you cannot live with that much clearance you might want to use the shaft to get the initial alignment, then clamp the tubing externally and remove the shaft after welding.
Yet another approach would be to make an alignment bushing or whatever that you would plan to leave in place after the weld, so it would not matter if you could not extract it. If absolute accuracy was needed, this could be the way to go. Perhaps the bushing could be internally threaded, so you could position the bushing with a threaded rod (Only engaged a couple of turns) and then unscrew the threaded rod.
Whatever, you will need to experiment until you figure out what will work, before you start trying to build the final product.
Max, I can't add anything to the other posters, they are all excellent answers. I've been there/ done that. How about letting us know how you finally solve your problem. Hey, maybe you can teach US something with a new approach to an old problem. Bill.
I'll almost gurantee that you are distorting BOTH the bushings them selves as well as the alignment between the bushings. If your 'bushings' are really thin tube, double that.
You might want to experiment with just one tube, use your rod through the center, weld on one side, pull the rod out, measure the resulting inner diameter. Expect to find the tube egg shaped in the .030" range, and bent by .020"to .050" over a couple of inches.
First, I would use anti-splatter-spray (you use that for MIG/MAG/TIG). But second, I would check how the current flows. I guess it's going through that shaft. Of course, I always have a copper hammer that solves many problems like these without leaving a trace. :-)
If the shrinkage is causing the stuckage, could you cut a couple wide slots in the shaft? That would make it more like a spring, letting you drive it out. Maybe use a pipe instead of a shaft? Easier to cut the slots that way.
On 11 Dec 2005 11:56:01 -0800, with neither quill nor qualm, firstname.lastname@example.org quickly quoth:
I'll ditto Bill here but add that if you're arc/tig/mig welding, you need to watch how you ground the parts. Grounding to the loose tube might arc it to the other parts. If OA welding, perhaps a couple of thin, non-metallic shims between the parts would do the trick in case of welding deformations. I've seen thin phenolic sheet which might work when used as narrow shimstock. It would provide clearance even if you had to break it out after the welding.
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