MIGing 304L stainless - what gas?

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Hey guys - got a standard Argon/CO2 tank for mild steel.  Building an exhaust with 304L and want to weld it best I can.  Going to pick up 308L wire but what gas should I use?Thanks,Jon
Reply:A tri-mix gas. I don't remeber what the % of blends are. I have herd of using 75/25 in a pinch, but your better off using a tri mix blend that is ment for stainless.Ya gotta spend money to make money!
Reply:It sounds like it is thin, the "standard" stainless tri-mix for short-circuit is 90%He, 7.5%Ar, and 2.5%CO2It can be pretty expensive
Reply:Argon +3 CO26 Miller Big Blue 600 Air Paks2 Miller 400D6 Lincoln LN-25's4 Miller Xtreme 12VS2 Miller Dimension 812 4 Climax BW-3000Z bore welders Hypertherm 65 and 85Bug-O Track BugPair of Welpers
Reply:Thanks guys - went to the LWS and grabbed Trimix
Reply:how much did that cost you and for what size bottle if you don't mind me asking.
Reply:I just grabbed a 320 Cf of trimix.   I think I paid $75 for it.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:100% Argon for me...C02 for stainless?A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:Originally Posted by Awelderiam100% Argon for me...C02 for stainless?
Reply:Originally Posted by ExpatWelderBy adding a reactive gas such as oxygen or CO2 to the argon, it stabilizes the arc and increases the arc energy, gives you less weld oxidation and provides a tighter, more directional arc which improves weld fusion-------much less erratic and much easier to control.--Matt
Reply:I've never had any luck using anything but 100% Argon on all of my stainless. I do use a tri-mix on carbon steel the CO2 lowers the Mn to limit hardness spots within the weldment. There again I mainly use Tig for any stainless but have found good results with my new pulse-arc power mig 300.A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:Originally Posted by shovelonYes, and I believe the max CO2 is 15%. Personally I switched to 90/10 argon-CO2 as recommended by SundownIII.You could bleed pure argon into you existing CO2 mix to get under 15%CO2.
Reply:I've always used 100% argon. I'll have to grab a bottle of the tri-mix next time it's appropriate. Unfortunately tigging thin stainless isn't something I do often.IW Local 580 NY, NY
Reply:Originally Posted by con_fuse9Careful, I don't think Sundown ever recommended 10% CO2 for stainless.  Sundown is a big fan of a tri-mix blend.There was a report on the web that the corrosion resistance of 304 stainless drops off quickly after about 5% CO2.  That seems to be consistent with Ed Craig's recommendation of about 2-4% on thin stainless.
Reply:Originally Posted by shovelonYes, and I believe the max CO2 is 15%. Personally I switched to 90/10 argon-CO2 as recommended by SundownIII.You could bleed pure argon into you existing CO2 mix to get under 15%CO2.
Reply:Originally Posted by ExpatWelderBy adding a reactive gas such as oxygen or CO2 to the argon, it stabilizes the arc and increases the arc energy, gives you less weld oxidation and provides a tighter, more directional arc which improves weld fusion-------much less erratic and much easier to control.--Matt
Reply:Originally Posted by BlueArcI've always used 100% argon. I'll have to grab a bottle of the tri-mix next time it's appropriate. Unfortunately tigging thin stainless isn't something I do often.
Reply:Originally Posted by DSWDid you really mean to type "tigging" since the OP was interested in MIG? Big difference in what gas you use if you are doing TIG rather than MIG.
Reply:Originally Posted by sn0border88Im not sure how you reason that adding o2/co2 to the shield gas reduces the oxidization potential at the weld?
Reply:con_fuse,Believe me when I say, you only have to redo ONE JOB to realize how inexpensive it is to use the right gas/filler combo.Do the job right and the customer will tell two of his friends.  Do the job wrong and the customer will tell everyone he knows.Just the way it isLot of BS put out on the internet by people who've never performed a given task/procedure.  It "must be true" because I read it on WW.Last edited by SundownIII; 11-27-2011 at 02:13 PM.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:I think the addition of CO2 causes a higher heat when welding on Carbon steel but not sure of its effects on stainless.Last edited by Awelderiam; 11-27-2011 at 04:35 PM.A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:^^^ Off topic:A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:I actually heard that from my Dad some 20+ years ago.......We were welding on a 6" gas line and I asked him how to make the bottom look like the top and that was his answer....... He used to also walk up and look at my welds then look towards the sky......I asked what he was doing....he said looking for the bird that crapped on my weld!!!!.. Man I miss him.......A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:For doing exhaust should it be back gassed too?JoeMiller 140 Autoset (2010)Miller Syncrowave 250 (1996)
Reply:Assuming 16 gauge 304 stainless, if you have perfect fitup and fussion weld, you don't need purge.  Basically you don't get full penetration, but its an exhaust pipe, not a structural piece.  However, If you ever have to add filler - even a little, the gap was too wide and the back side will have a nasty looking booger that is basically oxidation (my understanding).  The stuff is hard and needs to be ground out (which is tough to do on the inside of an exhaust pipe).Now if you are putting 4" exhaust on a Honda Civic HF - who cares.  If you putting dual 2" or similar on a big V-8, you might.If you are building a competitive race vehicle, then absolutely.Solar Flux might be an acceptable compromise.You don't need to purge to tack weld.Use aluminum foil tape or even masking tape to block off openings.  Masking tape burns, aluminum foil tape's glue melts away.  IMHO easier to clean up.BTW, a good purge is 6x the volume of the area being purged.  Exhaust pipes use a lot of argon....Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DXOriginally Posted by con_fuse9Assuming 16 gauge 304 stainless, if you have perfect fitup and fussion weld, you don't need purge.  Basically you don't get full penetration, but its an exhaust pipe, not a structural piece.
Reply:Sorry for the slow reply.If you have butt joint, with the back side exposed, you can get away without purging if you just fuse the parts together.A couple of assumptions.1) This is an exhaust pipe - nothing structural, no safety issues.2) There are lots of other parts on the car that aren't stainless.  Bottom line the exhaust system only has to outlast the rest of the car.3) 16 Gauge 304L.  About .060 thick.I have a 12" sanding disk so I can typically get mating surfaces to be really really close up to about 4" exhaust pipe.Shoot for a gap that is about .015" (thickness of typically staple).  You can get away with zero gap, just need to be fast with your tack welds.  Tack one side and before it cools you need to tack the other.  zero gap with a material like stainless runs the risk of the metal bumping into each other and moving up and down relative to each other.When you fusion weld, you use just enough heat to melt the two halves together - you will effectively undercut both sides of the weld.  On the back side you should still see the parting line between the two pieces (not complete penetration), on the front side you see bead - a bit concave.  Coloration on both sides should be acceptable.  If is gray, you used to much heat or your gap was too big.If you want to polish the exhaust pipe, make a second pass with filler.  Again, really really low heat.If, as you are dragging the puddle around (fusion welding) and you ether can't get the puddle to move fast enough, or you are tempted to add filler rod etc.  You will be putting in too much heat - you will have sugaring on the back side.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX