S.s Mig ?

[fun4now]

if i want to MIG SS do i still back gas with strait argon, even if i MIG with try-mix ? or should i be back gassing with try-mix?
looking to try a little MIG on SS and want to know what all i need for best results. i have strait argon, strait Co2, and an empty 80 tank. so i was planing on filling with try-mix for SS and started thinking about what would be best for my back gas?????
so whats the best option ???
thanks guys

[fabricator]

ONLY pure argon or nitrogen.or you will get poor results.

[Glenn B]

Tri Mix

The best Gas to MIG Stainless is a Tri Mix 90% Helium 7.5% Argon 2.5% Co2
For TIG Pure Argon
I don't think nitrogen would work for either process.

[sparx]

Just a little clarification....while the 'best' gas for welding stainless is a 90/7.5/2.5 blend, this is true for short arc only. for higher voltages and thicker materials, blends like 90%AR/8%CO2/2%O2, and for pulse welding, 66.1%AR/33%He/.9%CO2 work very well.
As for Tig stainless, look into a Hydrogen blend of 2% for thinner material and 5% for heavier. This applies only to 300series stainless steels. The Hydrogen is a reducing gas that increases fluidity in the puddle, reduces oxides, increases heat input for faster travel speeds, and the appearance is beautiful. I will see if I can find my camera and post a pic or two of some of my tig welds using an Argon/Hydrogen Blend.
As for purging...pure argon works pretty much the best.
another option to purging is using a backing paste. The only problem with using something like Solar B flux, is cleaning it afterwards is a bit of a pain.

Hope it helped.

[SundownIII]

For your mig (MM 135--Short Arc) tri-mix is the best gas for welding.

100% Argon is the best gas for purging (back gassing).

[fun4now]

thanks SundownIII & sparx.

[sparx]

I found an older picture on my computer of a tig weld done with 2% Hydrogen on 316 plate. notice the heat affected zone is pretty small compared to those of argon welds. I did a 'speed' test with an outside corner weld on 3/16 ss plate, no filler, 20 seconds of arc/travel time. The pure argon got me about 4" of travel, the 2% H2 blend got about 6-1/2" of travel, and the 5% H2 blend, I ran out of material (10" long coupons) so I figured I would get about 11 or 12" of travel with the 5% H2/Argon.