Contamination ?? help appreciated

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All of a sudden my welds are very crappy. In the past I tigged HR steel with acetone cleaning only and acceptable results. Here' the first 2 pix the hot rolled steel was acetone cleaned only. The arc sparkled but the tungsten stayed intact. The third one the hot rolled steel was ground to a shine and acetone cleaned. No sparkle and a decent arc, but still that black sooty deposit.I tried two different gas cylinders, checked all piping and torch for leaks, nothing.Inverter tig. 1/4" steel, 130 amps, 3/16 thoriated and gas lens, 14 cfh,All comments appreciated. Attached Images
Reply:Did ya check your tungsten after all that crap spit up on it?Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Yeah that's what I was thinking also.....Never had too much luck tig welding Hot Rollunless it was sanded clean.....Still didn't like it....Mig works much better on Hot Roll..Maybe some Acetone residue of something left from grinder?  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Looks like CO2 contamination to me.Miller Dynasty 200DXMiller Spectrum 250DMiller Millermatic 200Bunch of old blue dinosaurs....
Reply:Shovelon> Funnily enough the tungsten electrode was not affected after doing the welds on the unground HR.Jon> As for Co2 contamination where would that come from? the ground plate was very well wiped with acetone till the towel came off clean.
Reply:Bad sheilding gas.Try a bottle from another supplier.Make sure you're not trying to weld in a breezeMiller Dynasty 200DXMiller Spectrum 250DMiller Millermatic 200Bunch of old blue dinosaurs....
Reply:Check the screen on your gas lens, after all the spatter from the HR mill scale ( really you guys need to clean that sh$t off first or it's a worthless endeavor) it may have spatter on the screen. Also would be running a little more gas, around 20-25 cfh if you are seeing contamination problems, but even small spatter on a gas lens will give you an unshielded area of the weld. "Anybody can talk $h!t behind a monitor, I let the quality of my work speak for itself"Lincoln Square Wave 255 and 355 Tig Lincoln 255 Power-Mig w/ spool gun Koike 5 x 10 CNC plasma Hyd-Mech DM-10 bandsaw Ineco QB-76 NC tube bender
Reply:Originally Posted by CoupebuilderCheck the screen on your gas lens, after all the spatter from the HR mill scale ( really you guys need to clean that sh$t off first or it's a worthless endeavor) it may have spatter on the screen. Also would be running a little more gas, around 20-25 cfh if you are seeing contamination problems, but even small spatter on a gas lens will give you an unshielded area of the weld.
Reply:Thanks for the tips, I have spent some time trying different things and decided that since I always wanted to buy a dynasty 200dx, now is the time to do that. It is already on the UPS truck from Indianapolis to be delivered on Monday.When I started a welding course last year at a technical college, I bought a weldall 256 tig/stick/plasma not wanting to make a big investment before knowing if welding was for me. The experience has been mixed, and the first welder was defective ( for plasma) on arrival, but it was replaced at zero cost for me. Now I have many projects to do, it's time to get serious tools. A hypertherm is next, and then I will put up my Longevity for sale.I ordered the dynasty with the contractor kit and a second torch (wp20), so the whole setup will be new except for the gas cylinders. It would be funny if after all my two gas cylinders turn out bad.
Reply:Originally Posted by yul m6All of a sudden my welds are very crappy. In the past I tigged HR steel with acetone cleaning only and acceptable results.
Reply:Originally Posted by Fat BastardNo you didn't.
Reply:GTAW on Hot Rolled steel with out removing the mill scale will lead to the scale dislodging from the base metal and attempting to incorporate is self within the weld metal. That is a fact. During the detachment phase some of the scale will   attach to the electrode.One should consider including scale into a GTAW weld unacceptable.Last edited by Fat Bastard; 05-19-2012 at 01:55 PM.