shielding gas for stainless mig

By saxdoc Date 03-08-2003 19:40

Hi everyone, great forum! I have a lincoln weld pak 100 I bought a mig conversion for it. My question is I want to weld 3/4" diameter stainless steel pipe with it and I am trying to decide what to use for shielding gas.
I know that the best choice for stainless short circuit transfer would be a mix of 90% helium, 7.5% argon,and 2.5% co2, but that mix will be difficult to get in my area, also I want to set this up as economically as possible. Is there another gas I could use with stainless which would also work for mild steel welding? Is it possible to weld stainless using co2, or argon only? what about 75%argon, 25% co2 ( this is readily available to me) Any help would be greatly appreciated.
saxdoc

By brande

Date 03-09-2003 04:56

The old 75/25 mix will weld stainless. The only problems are that this mix tends to give a "ropey weld" and greatly compromises the corrosion resistant properties as well.Especially on multi-pass.

As far as operation with a easily available gas, Stargon, or argon tri-mix might be a choice. This gas can still compromise the corrosion resisting properties to some extent.

In corrosion critical weldments, my choice has been a 97% argon/3% CO2. CO2 under 4% have little effect on stainless corrosion resistance.
This gas will short arc or spray as needed.

Do stay away from the helium tri-mixes. The high helium content (the 90/8/3 mixes) increases heat (by increased arc voltage)to the weld, regardless if in short arc or spray.The last thing we need on gauge thickness stainless is heat.

While I know that spray arc is not available on a machine of your size, and if your requirements are basically lo-tech-I would go with the Stargon or argon tri-mix. You will find this mix very helpful on thin gauge carbon steel as well.

Good Luck

brande

By saxdoc Date 03-09-2003 17:40

Hi Brande,
Thanks for your informative response I will probably try the argon, 3% co2, bottle. I think I can get that fairly easily and though this project is not high tech, I do want the welds to be sound, and corrosion resistant, as well as have as good an appearance as I can produce. I also found some great info at the weldreality.com site your advise seems right in line with theirs as far as steering away from the helium mixes cheers,saxdoc

By ScottV

Date 03-10-2003 04:01

Brande,My friend runs a welding store,and was welding some stainless with some tri mix gas,023 wire,using a sp135 plus 120 volt welder.He turned up the wire feed,and voltage,and got that little lincoln to spray arc.It really shocked him it that it was posible to do with a 120 welder.He also told me that 98% argon/2% co2 was good for a tiny little weld bead in short-arc.My friend has welded with about every machine out there,and this was impressive.I can spray-arc with 90/10 with .023 ER70-6 wire with my sp175 plus,and almost with .030 wire but not quite.

By Michael Sherman (***)

Date 03-10-2003 12:11

Sax, have you considered running stainless flux core wire? I use it exclusively for all GMAW applications. It is easy to use, aesthetically appealing and the recommended gas is 75/25.

Mike Sherman
Shermans Welding