Shielding Gas

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I've been running my Millermatic 180 on C25 and am real happy with the results.      What is the downside to using straight CO2?  Is it harder to get a good bead?  I was told to stick with C25 but wasn't told why CO2 would be a problem.  Comments??
Reply:to ME it just make a nicer bead. not as spattery if you will.6G zirconium 702 GTAW 2" xxheavy6G P.E.D. carbon steel GTAW 2" xxheavy3G titanium Gr. 2 - Gr. 7 GTAW up to 3/4" 3G 316L stainless GTAW up to 1" 3G carbon steel GTAW up to 1" 3G Hastalloy GTAW up to 3/4"1G tantalum GTAW up to .060"
Reply:I feel the same way about it as Welder 155.   Except with my Millermatic Passport.  That machine seems to be set up specifically for C02, it makes very nice welds on C02 .MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I use CO2 for most GMAW.  Cheaper and lasts a lot longer in the same size bottle.  It will have a LITTLE bit of spatter compared to C25, but still very acceptable and easy to knock off.C25 really shines for thin material (< 20-ga.) and also cleaner at higher amperages, but for most of the stuff in the middle, CO2 saves a fortune.
Reply:Originally Posted by MAC702I use CO2 for most GMAW.  Cheaper and lasts a lot longer in the same size bottle.  It will have a LITTLE bit of spatter compared to C25, but still very acceptable and easy to knock off.C25 really shines for thin material (< 20-ga.) and also cleaner at higher amperages, but for most of the stuff in the middle, CO2 saves a fortune.
Reply:C/25 for the small stuff, Co2 for the bigger stuff.  If you have adjustable inductance, Co2 is better yet.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Also note, that the shielding gas used should be appropriate for the metal being welded AND the wire used.  The metallurgical properties of the weld can be influenced, sometimes strongly, by the shielding gas that is used.  And Yes, that difference can be evident in CO2 versus C25 or C8 on mild steel.For Code or critical work, you -must- use the appropriate and specified gas.And don't use straight argon for GMAW on steel.
Reply:moonrise.  I'm not contradicting you, but could you explain why it's not acceptable to use pure Argon for GMAW welding on mild steel?  I know the penetration is better with pure CO2 or Ar/CO2 mixtures.  But I've often wondered, for the hobbyist who uses MIG and TIG, if using pure argon when MIG welding wouldn't be simpler?  It's one less cylinder of gas you have to pay for...What's your rationale?Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Why no pure argon for GMAW on steel?Poor penetration, incorrect metallurgy of the weld, no (and I mean NO) supplier or manufacturer of the electrodes will or does OK or bless or condone such.Especially for short-circuit transfer with GMAW, where you are already using a low-energy (relatively) welding method, the penetration profile is apt to be really-really-really inadequate.I've tried the rationale of 'Just use pure argon on steel so that you only need one bottle and then can do GTAW or GMAW on anything, steel or aluminum or whatever'.  Well for GTAW that is pretty much true.  But for GMAW on steel, you need that bit of CO2 to help stabilize the arc and get the weld to be 'right'.  Even if you are using C8 or even C5 (on stainless), GMAW -needs- that bit of CO2.I even had some folks from Lincoln cross checking some Charpy impact data and the apparent correlation of CO2 percentage versus impact strength at low temperatures, and they flat out said you MUST have some CO2 in there for GMAW.(and I've seen -some- GMAW welds that were done with straight argon on mild steel.  Not quite right is being generous regarding the condition of the welds.)So me, I'll go with the recommended argon-CO2 mix(es) for GMAW on steel.  Or plain CO2.  But not plain argon.
Reply:I did a test with pure argon.  It doesn't work.  Some use it and claim its great.  For those few, go ahead.Think of this.  TIG is at around 11 to 13 volts.  The voltage is that because that is what it takes to get the arc to happen in  a cloud of pure argon.  Adding Co2 raises the arc voltage which makes for more heat.  The wire penetrates deeper the more Co2 you add to the mix until you get to pure Co2.  Mig welding is from 16 to 23 volts.  This wont happen with pure argon.  The arc happens before you reach welding voltage.  The molten metal just lays on top of the plate.  Look at any gas or welding website.  They do not recomend pure argon for short circuit.Here is one of the tests.  Look for the pic of pure argon.  Note the voltages.http://weldingweb.com/vbb/showthread.php?t=16984DavidLast edited by David R; 04-29-2008 at 07:12 PM.Real world weldin.  When I grow up I want to be a tig weldor.
Reply:I have tried straight argon on short circuit mig on mild steel.  It does not work very well.  I had to turn the voltage way way up to get any kind of penetration at all.    It might work on sheetmetal, not good for anything much thicker than that.Oxygen can be substituted for CO2 in the mix.  I use 98% argon, 2% oxygen to spray mig steel.  Works good.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by DesertRider33...Oxygen can be substituted for CO2 in the mix.  I use 98% argon, 2% oxygen to spray mig steel.  Works good.
Reply:the bead will not wet out with 98/2 or 100% Ar. There is NO penetration with these gases and it should not be used for short arc on mild steel. . It did not work with the pure and on 98/2 there was mass amounts of undercut, and there was a high bead profile that would not wet out when I turned up the settings. Also I tried to pulse and spray with those gases. 98/2 worked ok on spray but I did not like it on pulse. 100% Ar for spray and pulse is crappy.  For spray and pulse I like 90/10.Last edited by ace4059; 04-30-2008 at 02:45 AM.