Soot around a tack weld

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Started noticing it a while ago, but it's inconsistent. After I tack sometime I get soot that when it cools I can actually wipe away. Everything welds fine, but can't be right. Going to change the pre flow today to see if it goes away. Guys seen this or have any other ideas ?
Reply:It happens sometimes!  It's no big deal, just wipe it away.  I think it's caused by contaminates on the metal surface or oxidized or dirty filler wire, or insufficient gas coverage.  I haven't found any one thing that eliminates it, especailly on aluminum.  Just have to try a combination of things untill it goes away, which sometimes it doesn't.  Holding the torch closer to the work, use a bigger nozzle/cup, turn up the gas flow, turn up the pre-flow time, don't lift the torch away too quickly, don't hold the torch at too much an angle to the work,  clean the metal good, clean the filler wire, anything you can think of.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:What kind of material/gas are you using?Last edited by BrianNye Welding guy; 12-20-2009 at 05:12 PM.
Reply:MS mostly and noticed it on the 304 this morning.
Reply:What process are you using; MIG, TIG, Stick, O/A ? I know sometimes I get that with TIG, but as desertrider said, not a big deal. Just wipe or wire brush it off before completing the weld. I think when it happens to me it is either from contaminants in or on the base metal, or I have too much angle on my torch causing insufficient gas coverage."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Sorry, it's tig. Using a 347 rod with 304 material and pure argon. I upped the pre flow to .5, and I'm at 13 cfm for 35ish amps.
Reply:Try 308 rod. That's all I use for 300 series stainless (except 316)."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Probably a little oil or something on the metal. I find I get soot on machined parts because of the cutting oil. Even if I wipe it with a clean rag some of the oil remains in the metal. Just enough to make some soot, not enough to be a problem.