Changing over to Gas, Need some help...

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I have a lincoln SP 175 and am currently using it with flux cored wire. I'm considering changing over to gas. I'd like to be able to work with three materials, mild steel, stainless and aluminum. I know aluminum requires 100% argon, but what about mild steel and stainless? Will pure CO2 work on mild steel? What is used on stainless?I'm just a hobbiest and I can only justify having two bottles. Am I going to be able to work with these three materials? Can somebody post the refill cost of pure CO2, 25% CO2/75% argon and 100% argon?
Reply:I use C-25 for steel, !00% Argon is recommended by Miller for aluminum, however I have been told to try helium. The helium I have been told will help preheat the aluminum work so you get a little better penetration.  Miller recommends Tri-Mix (90% helium, 7.5% Argon, 2.5% CO2) for stainless.  My 40CF C-25 costs $30 to refill.Millermatic 135Miller Big 40Lincoln 225AC
Reply:http://www.weldingsupply.com/cgi-bin...UNDEF:OR:H::PH that's a pretty good price reference, i pay $23 for 80cf swapsStangnetShop Full Of Stuff. Joey
Reply:The cheapest way to go for mild steel is CO2.  20 pounds will last you through a 10 pound roll of wire.  For aluminum, 100% argon.  For stainless, a tri-mix is recommended (90% He, 7.5% Ar, 2.5% CO2).  C-25 (75% Ar/25% CO2 is also a steel mix that runs cooler with less spatter.If you want to weld mild, stainless and aluminum, you're kinda stuck with three bottles.  And if you want to spray-arc mild steel, it's bottle #4 for 98/2.As far as fill cost, it varies with location.  Get the largest tanks you canafford.  The fill cost is nearly the same for 80CF of argon as 150CF.HankLast edited by hankj; 12-27-2004 at 01:31 PM.
Reply:If cost is not an issue, can Argon be used for all three? A good friend owns a metalworking shop and says thats all he uses for everything. He doesnt weld much though, mainly machine work.The expensive fill ups would probably be cheaper then the cost of having two bottles considering how much i weld.
Reply:Some will tell you yes; some will say no.  I've tried short-arc on mild steel with 100% Ar and did not like the welds, but I'm told that in high-current applications, argon works OK.  Certainly, you should try it.  You WILL need 100% Ar to weld aluminum, so make that your first gas purchase and try the rest.  Nothing to loose!Hank
Reply:While I was down at my local welding supplier looking at a MM175 I asked the guy what he thought about using argon for all three metals. He expalined to me that using argon for mild steel is a bad idea because your welds will have poor penetration. Using C02 increases the penetration of the weld in mild steel. Andrew
Reply:also pure argon won't stabalize the arc on a 175 machine. the steel also needs a small amount of oxy (less then 5%) usually supplied by the breakdown of the CO2. You have three metals with three differnet needs...your choice to do it right or not.You might consider starting with one can of C25 and E70 solid wire (.030) and then still use coated wire for the other jobs.