MIG welding SS

You say the torch / gun is on DCEN. With MIG you need to be on DCEP? TIG is DCEN. I never got an explanation, but while for TIG DCEN is super penetrative, you can damn' well see for stick/SMAW that DCEP is more penetrative. Never had a chance to try MIG on DCEN - never had the time on a machine which offers means to change polarity (rare).

'nother thing. I have tried Stainless MIG with pure Argon - "TIG gas". There is 2/10's of not-a-lot of penetration. MIG stainless - you have to add a smidgeon of oxygen to give it any "bite" / penno. As I have heard. Only MIG stainless I met was testing out making road sweepers. They had Ar / He / O2 mix. As good as you get. Pity their welding wasn't. They did pause in their telling us nonsensical weld practices they demanded when, seeing the way things were going - to the door - I put in a small neat spray bead which did the job so much better. Really really looked the part. I've repeatedly ensured you know how little experience I have of this. Hope what I've mentioned helps.

Here's some basic stuff on SS

stainless behaves quite differently from plain steel. It's a terrible heat conductor and it burns up easier. I always marvel at a well done stainless weld job, no matter what the process is.

"Snag" wrote in message news:so4bph$5e8$ snipped-for-privacy@dont-email.me...

I'm getting a start on fabbing a new exhaust for my truck (currently down for an engine rebuild/hopup) . This morning I set my Lincoln Weldpak 100 up to run a couple of beads on the header collector adapters , and it wasn't at all pretty . The wire is .023 ER309L , shield gas is argon at varying flow rates , electrode negative . First thing I noticed is that this wire sure seems to burn a lot faster than ER70S6 , so I bumped the feed speed up . Still ain't right , so I drop the amps a notch (this machine has 4 settings for current) and it's a bit better but still too hot . Drop it another notch and the wire isn't burning back so fast but there's zero penetration and the bead is very narrow and tall . Drop the wire feed and it's still too cold . I'm totally lost here , I was hoping MIG welding the joints would be fast and easy but ... I ended up using the TIG to flow the welds and got things looking less like pigeons crapped on my weld seam , but that has problems too . I have no means (yet) to purge the back side of welds in tube . I did get the inside cleaned up with die grinders and flap wheels , but that ain't going to work on a 6 or 7 foot long piece of exhaust tube ! I sure could use some tips on MIG welding SS ! I hesitate to use ER70S6 or flux core since the tubing is stainless , but it may come down to that to get a decent weld .

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On the welding salesman's recommendation I used 312 rod to stick weld 1/16" sheet stainless into the bucket on the front end loader I made for my Sears garden tractor. Although the weld area is discolored the stitched beads were neat and strong enough to survive years of ramming into snow, ice and occasionally rocks and trees. Road salt didn't seem to affect the unshielded back side of the welds.

My thanks to all who responded . I think I'll just figure out a way to shield the back side of my welds and TIG it all together . I'll have the bed off the truck for an axle gearing change , that might make it easier . Or I could just MIG it with ER70S2 ... Now hold on thar ! I just discovered (browsing a car forum) a product called Solar Flux . Paint it on the back side of your weld area and it forms a shield as it gets melted by the weld heat . Just exactly what I needed , considering the forums I was browsing are pretty emphatic about NOT using ER70 to weld SS exhaust tube . The recommended filler is ER308L , which I happen to have on hand . I was concerned about sugaring causing flow problems ... this has been an exhausting discussion !

Paint on flux is a new one on me, but it makes perfect sense. I was just going to comment that if you plug the ends with just a small weep hole you really do not use that much gas in a piece of pipe the size you mention. The weep hole is two fold. To allow you to actually purge the air, and to make sure you do not pop your plugs out when the gas inside the tube starts to expand from heat.

Oh, yeah, and I have to ask. Is exhaust using an pipe expander so the joints can slide together totally out of vogue now?

I recently figured out the reason the expander I have doesn't work . The threads are stripped . It was a gift , so I can't complain too much . One of these days I'll make new parts for it and see how it works . Maybe .

Tig it and back gas with dry ice - a lot easier than flowing welding gas just tape up the "bottom" and throw in a few chunks of dry ice - it will back purge perfectly and no clinkers inside the pipe.

That is clever. I was not aware pure C02 was good for shielding stainless.

I recently figured out the reason the expander I have doesn't work . The threads are stripped . It was a gift , so I can't complain too much . One of these days I'll make new parts for it and see how it works . Maybe .

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I recently reduced the diameter of a tailpipe expander from the 1970's (not a recent import) and found that the plain cone under the head was case-hardened and needed carbide but the bars and the internally threaded, faceted cone cut easily with HSS.

Perhaps you could machine a harder faceted cone from an impact socket and a grade 8 nut. You could anneal the socket if necessary without softening the nut.

That is clever. I was not aware pure C02 was good for shielding stainless.

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I wanted to suggest using CO2 if you have a tank of it for steel, but a fairly brief Google search only returned advice not to, without describing bad experiences.

IIRC CO2 isn't recommended as a shielding gas for stainless as it can compromise the corrosion resistance, as a purge gas it may be fine as it's not exposed to the arc. I've known people that have used it for steel body repairs and had good results but it's not as nice a weld and more spatter apparently but has the advantage of better penetration, all those I know who have used CO2 had mates down the pub that could get bottles pinched as necessary at the time. The UK pub suppliers have apparently clamped down on that as they can match CO2 consumption to the drinks requiring it and flag up inconsistencies. The only time I have tried Argon for steel MIG it didn't work well, the depot had no BOC Argoshield light at the time and they thought Argon would do it OK but didn't so later in the day they had Argoshield light back in stock and swapped the bottle FOC and all was good again. I've MIG  welded stainless with 0.6mm and 1.0mm wire with the Argoshield light and all went well. Argoshield light is apparently 93% Argon with 5% CO2 and 2% O2, maybe not the best for stainless but it's what I have.

100% effective at eliminating oxygen from the hot joint. Maybee niot as good as tri-mix - ot ideally Argon but better than plain atmosphere at stopping "sugaring". You can't use co2 as sheilding gas but I've seen it used as a back purge. (Wouldn't use it on a Nuke installation, but it's better than a mild steel MIG weld on exhaust pipes - and I;ve seen a LOT of that!!!

I've seen lots of pictures of what it looks like down the road ... which is why I want to do it with SS filler . Too bad the MIG experiment didn't work out for me , but I gots TIG and plenty of 308L filler . Also got some of that Solar Flux coming - the dry ice idea is intriguing , but I'm not aware of any place near here to get some . I do have a bottle of CO2 for the MIG , but wasn't sure if it was suitable for a back purge . Now I know !

I think some grocery stores have dry ice... or used to. We used to get it at Thrifty Drug back in the day (40+ years ago.)