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Tri-mix VS Bi-mix gas for 304SS welding

To All, So another SS welding job has come my way that would benefit, timewise, by using MIG instead of TIG. I have a Lincoln SP125 Plus welder and will be welding 1/16 maximum thickness 304SS for this job. According to Lincoln my welder should have no problem doing this weld as long as the right gas mix is used. C25 gas is about 1/3 the price of Tri-mix with 90% helium. I tried using flow gauges to mix C25 with pur argon in order to get a Bi-mix ratio of 98% argon, 2% CO2 which Lincoln recommends, but I wasn't real happy with the appearance of the welds. This could be because the flow gauges weren't accurate enough, or I couldn't set then accurately enough, or that the gasses didn't mix properly (which I doubt), or because I can't weld worth a shit. Or it could be because the welds would look crappy no matter who did the welding because 98% argon 2% CO makes crappy looking welds. I could try the mixing trick with the oxygen but I don't have a flow meter that is for a low enough flow. So I am thinking about buying a cylinder of 98% argon, 2% oxygen. Can anyone here give me good advice about how well the 304 will weld with .030 308lSi wire and 98%A, 2%O mixed gas? Thanks, Eric

Reply to
etpm
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I've welded 304 using a 90% He, 7% Ar and 3% CO2 mix using a mixing manifold. Keep in mind that stainless takes HEAT to get a nice weld. You will want to crank up the voltage and wire feed to raise the heat into the weld.

Reply to
Steve W.

Why won't pure argon work ? Is MIG that much different from TIG ? I've never used SS in my MIG machine , it interests me to know what to expect if and when I do . I have 2 "flow" guages , but only one is actually a flow gauge the other is a cheapie . I did try TIG with C25 once, it wasn't pretty . I think the SS takes up carbon from the CO2 .

Reply to
Terry Coombs

Greetings Terry, Pure argon won't work for MIG because the SS needs an "active" gas to get hot enough. When using TIG the heat is of course controlled by the arc between the tungsten and the work, but with MIG all the heat can only come from the actual arc between the filler metal and the work. I have tried pure argon with SS before I knew better and it doesn't work very well. Tri-mix with 90% helium works well partly because the helium doesn't carry the heat away as much as other gases. But it costs a lot and I won't be using it much so I would rather use a cheaper gas mix. Cheers, Eric

Reply to
etpm

OK , thanks . With the cost of SS MIG wire I'm probably not going to go there now that I have a TIG machine but it's good to know . -- Snag

Reply to
Terry Coombs

Yeah, the MIG wire is about 13 bucks a pound. But the faster speed of MIG over TIG will more than make up for any extra up front costs because I will be needing to buy wire. I do have SS MIG wire but not the correct alloy. The alloys I have don't have the extra silicon added. Lincoln recommends the silicon because it helps the weld bead wet out better. This morning I ordered an oxygen flow meter that has a low enough flow so I can accurately mix in the 2% oxygen to the 98% argon. I'm also gonna make a new gas mixing tube. Since I have oxygen here at the shop it will be easy to see if a bi-mix gas will work for me. Better than buying a cylinder full only to find out it won't work for me. Eric

Reply to
etpm

Eric, Just to clarify this: pure argon is okay to use when welding SS with TIG, right? I welded some SS with my Lincoln 175 TIG a few years ago, but can't remember any problems with the weld.

Reply to
Garrett Fulton

Ok , I 'm going to jump out on a limb here and guess - the only way I can see that this can work is to have flow controls that operate at the same pressure , and flow is controlled by something like a needle valve . That won't work with what I have , my cheapie is just a regulator with a pressure gauge calibrated (and not well at that) in "CFM" .

Reply to
Terry Coombs

Wiith TIG only pure argon for SS, with MIG mixed gasses. Eric

Reply to
etpm

The flow meter outputs will be connected to a manifold that is pressurized much lower than either flow meter because the manifold connects to the gas hose for the MIG torch. So I think as long as both flow meters show flow I'm OK. Eric

Reply to
etpm

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