Shielding gas question

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hello all!I'm fairly new to welding.. About a year under my belt of actually doing and observing TIG and MIG. I currently own a Lincoln SP125 Plus.. nice welder with an infinite voltage control and wire speed. Gets the job done nicely.I work on automotive exhausts and intercooler systems etc.. nothing too heavy. What my question/problem is:I do a lot of stainless steel welding (409) and mild steel.. I do stainless to stainless and stainless to mild and mild to mild.. I need to know which gas would be best to run for my applications if there is such a gas mix that would be adequate for all of those welding jobs.. Also which wire would be best then for it? I've been out to the local welding place but they are telling me I will need to use a helium trimix what they call 529 for the stainless jobs and then I will need to use argon mix 75/25 co2 for the mild.. I don't really want to have to run 2 bottles though.. I've been told by other people that 75/25 will work just fine for all of it.. or even 98 argon 2% ox... I need a gas that will result in good looking welds as well.. I can't have a customers intercooler pipe welds look like crap or rust on me.. If I MUST get 2 seperate bottles then I will, I'm not going to sacrifice quality.. but I'm looking to avoid that expense if possible.Thanks!
Reply:You can't use 98/2 for stainless.  Its a reactive gas.  C/25 doesn't carry an arc for TIG of stainless, but works for Mig.  Again, Co2 is a reactive gas.  Works fine for short arc.  98/2 is for spray arc.  Pure Argon is for Stainless.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:If you want to limit your gas supply get some 98/2 Ar/O, this is for MIG only, TIG uses Argon or Helium straight or a mix of the two only. C25 will cause rust to develop on the welds.
Reply:Here is good info on MIG gasses.http://files.aws.org/wj/2006/02/wj20...j200602-46.pdf
Reply:I use a mm135 for stainless steel welding in kitchens.  I went to my weldding supplier and inquired within.  I use a commercial tri-mix made by air-gas (argon - co2 - and a small amount of o2).  Clean before and after and the welds look neat and professional.
Reply:Dude, step #1 is to RTFM!   Seriously, read the manual for your machine.  There's probably a table or chart in there with recommended settings and wires and gases for most of the common weld tasks within the capabilities of your machine.  No the manual doesn't cover everything, just the common stuff.Next, search or look through the manufacturer's website for info and recommendations.  Lincoln's website has a LOT of info there, but you have to do a little digging to get it (it's not the most easy site to browse through).  And then go to some of the other big welding manufacturers' websites as well and browse through them.  Miller and ESAB have tons of info on their sites as well.The little SP125 is just going to be able to do short-circuit MIG or FCAW on steel.  (On aluminum it -may- be just able to nudge into spray transfer when running flat-out).  So you really don't have to look up gases or parameters for spray transfer, cause the machine ain't gonna do that.The recommended gas for short-circuit MIG (especially with the little 120V machines) on 'plain' steel is C25 (25% CO2 and 75% Argon).  Maybe C20, or C18, or C15, or etc, etc.  You get the idea, mostly argon with some CO2 mixed in.  You can also use straight CO2, but that changes the weld behavior and parameters a bit.  You get a little more penetration and a little more spatter with CO2 than C25.For stainless steel MIG, tri-mix can usually be used, but the recommended gas for general stainless in your machine is 98-2 (98% argon and 2% O2).  If you use a gas with more than just a tiny bit of CO2 to weld stainless, you end up with a not-stainless weld because the metal picks of carbon from the CO2 and that changes the chemistry of the bead.If you weld stainless to mild steel, the weld will most likely also not be stainless.  You said you didn't want the welds to rust, well stainless to mild means the weld is no longer stainless so it will rust more than the clean stainless.If you only want one gas to do it all, then you want 100% argon and TIG/GTAW as the welding process.  Mild steel, stainless steel, aluminum, titanium, etc, etc, all use 100% argon when you TIG weld.  (note that argon-helium mixes may be used to TIG some materials).For MIG, you'll need two gases.  One for stainless steel, and one for mild steel.  The gas mix for stainless steel should be 98-2 Ar-O2 (per your machine's manual in Table B.1).  Tri-mix may be too hot of an arc for stainless sheet metal thicknesses and the SP125 might not have to voltage availability to properly drive an arc on tri-mix; tri-mix needs about 6 more volts in the arc than 98-2 and I don't know if the SP125 can or cannot drive that much voltage.  The gas for mild steel welding can be straight CO2 (you'll need the CO2 regulator, the stock regulator is for argon blend gases) or an Ar-CO2 blend like C25.And the recommended filler for welding 409 stainless is a 409 electrode (surprise).  Lincoln makes a 409 wire, Outershield MC-409, but the smallest size listed is a 33 lb spool of 0.045 wire, which is too big in spool size and diameter to run through the SP125.
Reply:Ok, I went to another local welding supply place today and talked to a rather knowledgeable guy there.. this is what he told me.He said I can use C25 for my stainless jobs with no problem using 308 wire.. he recommended using 308LSI though.. The place I buy my wire from only had 308L though.Either case, he told me that the weld will brown but I can buff it out using a wire wheel and the weld won't rust.For right now at this point in time the C25 is my best bet to get my jobs done and have decent welds. If my business picks up and continues to grow I will get a better setup.. but at a 120 dollars per 40cu cylinder .. I just don't want to invest 240+ into this just yet. As long as I can weld stainless to stainless with C25 and 308L wire and the welds won't rust I'm good. That is my main job concern right now because I use 409 for the intercooler piping so I want that to look good. After I weld the pipes up I can buff to get rid of the browning .. not a big deal.
Reply:Sorry, but c25 and 308L make a rough weld that begins to fracture rather quickly....I've been down this road too.  Straight argon is your friend and if you're not working with thick materials it makes a very nice bead and will provide good fusion of the base metals provided you prepped your material well (grind for fill/V-groove etc.).  I have 2 gasses that I use now.  Straight Argon (TIG all and MIG for stainless and thin Carbon Steel) and then I use my kegorator C02 tank when I want to MIG thicker mild steel (filled at the paintball house for $9 with Zero issues in quality so far).  Sometimes it gets to be a tough choice though when the tank gets low....Beer or Delayed Projet???  Good luck Sir!
Reply:So Pickled, you are saying to mig my stainless pipe and thinner steel that I should use just straight argon with the 308L wire still?
Reply:Try it...I don't think that you will be disappointed.  I've been running it for years now and just be sure to start looking for a "Paintball" or "Beer" set-up for clean welds on thicker mild steels.  I think that IOC (Ebay- Indiana Oxygen Company) could hook you up with a 5lb Co2 tank for under $60.  It takes a male regulator to run the CO2 into your mig, but it works darn good for mild steels.  Just realize that when you start combining mild and stainless there WILL be oxidation (read as rust) in the weld area at some point regardless of the gas that you use.GO make some $$$$$ so you can get an awesome TIG now!
Reply:I use C02 with my SP175+ Lincoln. It works very well on mild steel. I have a 20 pound tank which is equivalent to 160 cu. ft of gas. It's very inexpensive relative to C/25.Miller Millermatic 252Miller Syncrowave 200Liincoln AC-DC 225Victor O-A Set
Reply:Especially on 16-ga. - 3/16" CO2 is my favorite GMAW gas, too.  I usually save the argon for thin sheet metal and 1/4"
Reply:Ok well, I did some stainless welds last night with c25.. Then I let the pipe sit out side to get rained on.. and today there a spots of rust around the welds.. so apparently too much CO2.. My only concern is that if I go with straight argon.. With my lincoln 125 will I have enough juice to get good penetration on thicker metal.. like 1/4"?I mostly do thinner metal like exhaust pipe.. so that won't be a problem to get penetration there.With C25 on this 409 exhaust pipe I have to turn the voltage down to a little under half power on the dial or I'll melt through the pipe.. I know that with a helium based trimix, the helium is going to add more heat.. so I'd probably have to run even less voltage.. My local welding supply hut only has trimix in 80cu/ft cylinders or larger.. but it only costs like 22 dollars to fill.I guess if I need to do thicker metals at some point I'll have to get another bottle like straight CO2 or C25, which they charge me 18 dollars to fill a 60cu/ft cylinder with. But I guess if I go with straight CO2 I'll get great penetration.. Ahhh damn this!!! lolI guess I will just go with straight argon.. I have a bunch of stainless exhaust and intercooler jobs coming up and I can't have my welds/pipe rusting and I know my 125 has enough power to do the job with straight argon.
Reply:If you want to run thicker metals with your 125+ just get the grinder out. Chamfer and multi-pass.Anything worth doing is worth doing RIGHT
Reply:That is true.. Alright I guess straight argon I shall try. I will report back with my results
Reply:Straight argon is NOT a recommended gas for MIG on steel, mild or stainless.  A small-to-moderate (or in the case of straight CO2 on mild steel, a LOT of) amount of reactive gas is usually needed to get the proper arc-filler-base metal-etc interaction to get proper MIG welds on steel.Straight argon is the correct gas for MIG on aluminum, magnesium, titanium, or other GMAW-able reactive metals, sometimes Ar-He might be used as well.Straight argon is THE recommended gas for almost anything done with TIG, sometime Ar-He mixes may be used.And about the C25 on stainless making it rust?  I told you so.  I'm glad you did the experiment yourself and could see that even after just one night of rain on the stainless welds done with C25 you had rust.If you really-really-really want to only use one gas for mild and stainless welding, you could use a recommended gas for stainless on the mild steel.  It looks like 98-2 Ar-O2 or 98-2 Ar-CO2 or the tri-mix Ar-He-CO2 can be used on stainless or mild steel.  Running a CO2-blend gas on stainless, you have to watch out for carbon pick-up from the CO2 into the stainless and that usually is a problem around 2-5% CO2.The problem with the 'one-gas' approach is that the gas blends for MIG on stainless are usually more expensive that what you can use for MIG on mild steel.  But if an 80 ft3 tank of tri-mix is only costing $22, I'd say use that!And if you are trying to use the little 125 welder on 1/4 inch material on a regular basis, you are pushing the machine to the limits.  A bigger more powerful machine really is needed to do 1/4 inch material.The helium mix uses more voltage in the arc, and also makes a different heat profile in the arc, so helium usually produces a deeper weld penetration than a similiar gas without helium.  So if you are using a helium-mix gas, you will have to turn the voltage UP on the machine to form the arc and then turn the wire speed DOWN to reduce the amperage and the heat going into the weld.
Reply:Well, I also used a regular carbon steel wire wheel to clean the stainless welds I did with the C25.. that didn't help much.I just did a stainless weld with straight argon on the 409 pipe I use.. It was an interesting arc.. At first I was building a ridge of weld on the pipe so I turned the voltage up a little bit more and started to get a nice flat weld.. However, if I moved too slow I started to blow right through the pipe.. I think the straight argon will work just fine for my application. I don't/won't be using this 125 to do 1/4 on a daily basis however I have used it to make a hitch before on a car and it worked just fine.. Several passes.. and if I need too I could always pre-heat with a torch. But if I need to do thicker welds I can go to my buddies machine shop and use his 220 mig or tig machine.I cleaned the pipe up that I just welded with a stainless wire wheel.. so I won't be embedding any carbon steel into the pipe now either.The first set of this 409 pipe that I did a few months ago I tacked on the car with the 125 and mild wire.. and then I took it to the shop and used the TIG machine and stainless rod.. well guess what.. around the welds the pipe started to rust... because I used a carbon steel wire wheel to clean them up!You learn something new every day. As for the straight argon it seemed to work pretty well for this application. I wet the pipe down and it's sitting outside and if there is no rust tomorrow.. woohoo.
Reply:If you tracked carbon from the wire wheel job on your weld you can use veggie oil and a new scotch brite pad to pull the embedded carbon from the surface of the metal.  In my former life we had a job where the vendor for the tanks cross contaminated mild to stainless by using the same grinder back and forth from the structure (mild) to the tanks 304 SS.  All of the weld areas started to flash rust. They had to treat all of the weld areas with the veggie oil.  It worked.  Now if the carbon pickup is from the gas this may not do it all as the pickup could be through the weld (not just the surface)If you are going to weld both materials the best thing to do is segregate tools.  At least grinding wheels, flap disks and wire wheels.  Getting stainless wire wheels can be tricky sometimes.I am in the middle of buying mig tanks and it's expensive ~$300 for tank and fill (240 cu ft K tank). I am just going to start off with a C25 and do what little stainless I get into with the Tig welder.My advice is to go with the stainless mix and get your second tank (C25) as soon as you can.Don
Reply:I'm not sure if anyone has mentioned it but to stick together Mild and SS you need to use a 309L wire. This is the preferred wire for sticking the two together.  The 309L ensures a crack resistant weld between the two metals. Here is some: http://www.airgas.com/browse/product...62&WT.svl=7562John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Ya Micro, I've been told that at the local welding hut.The straight argon is working alright.. the welds aren't rusting.. I welded up a piece of pipe last week and it's been sitting outside every day since with no rust.. They are a bit sloppy though and it's tough to get the right voltage and wire speed dialed in.. I bought a stainless wire wheel for 18 dollars.. ouch.. and I agree with the segregating of tools.
Reply:Originally Posted by StephenKI bought a stainless wire wheel for 18 dollars.. ouch.. and I agree with the segregating of tools.
Reply:Originally Posted by David RYou can't use 98/2 for stainless.  Its a reactive gas.  C/25 doesn't carry an arc for TIG of stainless, but works for Mig.  Again, Co2 is a reactive gas.  Works fine for short arc.  98/2 is for spray arc.  Pure Argon is for Stainless.David
Reply:Use argon/CO2 or Argon/O2 mix gas for mild steel MIG....MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op