Weird TIG arc instability

I have been TIG welding stainless long enough to get a hang of it but I
still consider myself a novice. I have bee quite successful last year making
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and now I am attempting to finish it.
I encountered the following arc behavior problem. Occasionally as I strike
the entire tip would be enveloped in a blush glow. The arc would strike but
initially it would not be concentrated on the tip but it would seem to be
coming from the entire front end of the electrode. Eventually it would drop
down and emerge from the tip. This behavior started last year and was rare
but now it is getting worse. Yesterday after some successful welding it came
back wit the vengeance. I could not get the stable arc at all. It would
buzz and hiss loudly and really jump around. The electrode would glow
noticeably brighter and it would wear rapidly. There would be sooty deposits
in the strike area. At its worst the arc would emerge as a jet of blush
reddish plasma from the entire cup destroying the lens in the process. There
would be copper deposits on the sides of the tip and in one spot on the side
tungsten looked really shiny. I took the torch apart and reassembled it. The
problem went away but is showing signs of coming back. Is this a classic
symptom of something or a weird combination of novice errors?
The machine is Lincoln Squarewave 175
The torch is T-9
average current is 80 - 125 A DCEN
The electrode is 3/32 Th
Here are the pictures of what the damaged tip and lens look like.
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Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
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Reply to
Boris Mohar
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It sounds just like what happens when you forget to turn on the argon. My guess is its a gas flow problem- either you forgot, or the valve was sticky, or there was some teflon tape in the hose, or a kink, or something along those lines.
Reply to
I have plenty of gas. I can feel it coming out and I have used half of the bottle without this problem.
Reply to
Boris Mohar
Cannot be. I used half of the bottle before it got this way.
Reply to
Boris Mohar
Sounds to me like you're getting discharge in places other than from tungsten tip to workpiece. That suggests a deposit of metal in the various parts of your torch, cup, lens, etc.
You might try gritblasting those parts where a discharge could occur from tungsten to metal deposit to workpiece.
You may need a new torch.
Reply to
Don Foreman
If there were conductive paths in the torch, he'd be getting zapped by the HF. Hmm, that does give me a thought, that his HF is turned up way too high. Some machines, like the bigger Lincolns, have so much HF that you can actually weld thin materials without any real welding current. The HF does tend to hop around a lot, too. But, the horrible mess of his electrode and the total melting of the gas lens is not something the HF system could do. Maybe if he was resting the torch or gas lens cup against the workpiece, the welding current could jump to the dirty cup and then to the work. That would almost certainly shatter the cup within seconds, though. And, there'd be obvious arcing from the cup to the work.
There is nothing in the torch handle that is grounded. There couldn't be, or the HF would arc to it for sure.
Reply to
Jon Elson
I looked a the gas lens and indeed there were signs of brass melting around the periphery. There also copper deposits in the tungsten in the region where it emerges from the lens. I cleaned out all the threads on the inside of the torch. When I was reassembling the torch I saw that there is a spot for the wrench on the lens and I have been installing it only finger tight. So now I made sure the lens is in snug. The wild arc behavior is gone. Thanks for all the help.
Reply to
Boris Mohar
Not if the conductive material were only in and around the cup, not extending anywhere near where the user holds the torch. This seems to be the most likely region of contamination.
Reply to
Don Foreman

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