How can I verify gas flow?

Brett · Sun Jul 01, 2012 9:31 pm

Hi all,

I'm a hobbyist with no formal training, but I have welded occasionally over the past couple decades... the most complicated project being a set of mild-steel headers for a corvette.

I have a Lincoln Precision TIG 185 I bought about six years ago, but haven't used for two or three. I just tried to weld some aluminum, and made a hell of a mess; couldn't keep the welds from being contaminated. At first I thought, "Man, I am REALLY rusty!", and that may be part (or all) of the problem. For the hell of it, I switched to Argon/CO2 & DCEN and tried a bit of mild steel, with similar results. I started to suspect that I wasn't getting a good gas shield (even though it sounded like the valve was opening at the machine), so I disconnected the torch and tried blowing through it... and yes, I waited for it to cool first! I could force air through, but it wasn't exacly easy; but I have no idea what's normal. With the torch connected, I held the torch away from everything and pressed the pedal, but couldn't hear anything specifically flowing from the cup (and I'm NOT about to put it up to my ear!) I even directed it toward some loose bristles on a paint brush, and saw a bit of movement whether I was pressing the pedal or not, but no change when I did.

How can I confirm that I am actually getting sufficient airflow at the cup? Any ideas or suggestons?

Thanks,
Brett.

Sun Jul 01, 2012 9:59 pm

Disassemble the torch. i.e. take the cup, collet-body or gas lens off, tungsten out, put the back-cap back on. Trigger the welder again. With the flow at normal (about 15-20 CFH) or above, you should clearly hear it hissing at the torch head, and there should be more than enough argon to extinguish a small flame. I recently switched to a 1/8" gas lens, and had a similar problem. Turned out the gas lens was clogged somehow. If the machine's been idle a while, it's hard to say where a blockage might be, but I suspect you have one, or perhaps a split in the line.

BTW, Ar/CO2 is for MIG. TIG on carbon, stainless, aluminum, is 100% argon, with few exections (Ar/He for thick Al, for example)

Steve

Brett · Mon Jul 02, 2012 12:16 am

Thanks for the suggestions; I'll try going down that path tomorrow and see what I find. I'm glad to hear that it's (probably) not my imagination. I really like the flame suggestion!

Of course you're right about the CO2/Argon thing; after all the messing around, I ran out of Argon and decided to try the mixed gas from my mig welder... didn't really think about the fact that it wasn't appropriate. So my test on steel was invalid anyway. Like I said, it's been several years and I was never a frequent welder to begin with...

Brett · Mon Jul 02, 2012 11:58 pm

Problem resolved! I tried the flame test with the cup on: not a flicker. I removed the cup, collet, etc. and tried again: instantly out! I inspected the collet, electrode, etc and didn't find anything obvious, but cleaned them up with acetone anyway. Reassembled and ran the flame test again: instantly out.

I can't say for sure what the problem was, but it seems likely that either the act of disassembly cleared the blockage, or shooting gas through without the collet pushed the blockage out (I'm assuming the collet prevented the blockage from moving before...).

At any rate, I was then able to run some decent (for me) beads in aluminum, so I'm back in business... thanks for the help, and especially the flame test tip. That really helped with the troubleshooting.

Brett.

Tue Jul 03, 2012 5:57 pm

Good for you!

Pay attention to the sound of normal gas flow, and you'll recognize a similar problem immediately if it happens again.

Steve