Weird TIG arc instability

Hello,
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
this
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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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Regards,
Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
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void _-void-_ in the obvious place

Reply to
Boris Mohar
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I have had a similar problem over the years. I find it has to do with the quality and type of tungstens and how happy your high frequency unit is.
Try Cold Scratching.
Every time a TIG arc is created, a certain amount of vaporized metal ions are trapped in the arc stream. When the arc collapses, these ions will cling to the surface of the tungsten, creating a very thin layer of metal oxides. This layer of oxides acts as a perfect insulator, preventing the arc from re-initiating.
By scratching the tungsten on a piece of metal with no current running, you can break this oxide, thus allowing the arc to initiate.
Get in the habit of cold scratching before each weld and you should have much improved arc starting.
BTW try switching to Lanthanated tungstens for all AC and DC TIG.
Reply to
Ernie Leimkuhler
Ernie,
Are you saying that lanthanated tungsten are preferred over regular tungsten? I am trying to learn something here.
Thanks
Reply to
knowone
AH!!! That explains a similar problem Iv been having. THANKS!!
I did at your advice year or so ago..makes a hell of a difference.
Gunner
"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist
Reply to
Gunner
Sounds like your HF is leaking somewhere in the cup.
Boris Mohar wrote:
Reply to
RoyJ
2% lanthanated (blue) is suppose to be the "best" for DC.
i experienced your issue using blue. taking off the cup i noticed burn marks on the copper collet... odd, seems as if the arc was jumping off the collet and skinning down the outside of the tungsten. i cant figure it out. i did however notice that more gas flow seems to make it happen less....
Reply to
Kryptoknight
also make sure your gas line is purged and you have some argon pre flow set to purge the weld area (mine is set at 1 sec. preflow)
Reply to
acrobat ant
Re place the cup.
Reply to
James R. Freeman
Yes.
2% Thoriated (red) tungstens are "ok", but only OK, not great. Plus Thoria dust is a radioactive alpha emitter, which may or may not cause lung cancer. Also Thoriated tungstens only work well on DC. With AC they erode rapidly and make for an erratic arc.
Pure (green) tungstens, the traditional choice for AC TIG, ...SUCK. Yep they just plain suck eggs. Don't waste money on them.
1% (black), 1.5% (gold) or 2% (blue) Lanthanated tungstens will work on AC or DC and do both better than almost any other tungsten out there.
The only kind of tungsten, other than lanthanated, that I buy are zirconiated (brown). Zirconiated tungstens are specifically for very high amperage AC.
The only other AC/DC tungsten available is Ceriated (orange), but they are more for very low amperage work. At higher amperages they don't work so well.
Reply to
Ernie Leimkuhler
Thanks, Ernie.
Doggone, I wish that you would write a book. Anyone else wish this? I am standing back for the flood of replies.
Reply to
knowone
"Ernie Leimkuhler" wrote
I ordered the 1.5% in 2 sizes and it makes my welds look like I know what I'm doing. I also got a box of 1/16 ceriated, but havent welded anything really thin yet. What about the percentages? Why would you chose one over the others?
Reply to
Stupendous Man
Higher percentages of doping agents should increase the heat resistance of the electrodes.
Reply to
Ernie Leimkuhler
I did, years ago, about welding for theatrical scene construction. I couldn't get a single publisher interested.
If I do write a book it will be self published.
Viva La Internet.
Reply to
Ernie Leimkuhler
Had something similar going on. Believe it is poor contact between the tungsten and the copper collet. I buff the oxide off the tungsten with a wire wheel-seems to help greatly. using the more expensive polished finish tungsten would also help.
Reply to
glockdoc

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