Purge gas 304 SS

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I am working on a project where I am making an aluminum smelting crucible for a friend. I found some 3.5" .250 wall 304 SS tubing lengths that I need to weld together then weld a bottom on to. I know that in order to keep the weld from 'sugaring' I need to back it with argon. Trouble is, I don't have a dual regulator. I do have a second tank for my MIG Welder, but that is using MIG Mix (75% argon, 25% Co2). Can I use the MIG Mix (or even straight CO2) as a backing shielding gas? This isn't sanitary welding, but the pipe will take a great deal of heat. If that won't work, What about putting a T and a valve into my pure Argon tank and running a line to use as the back purge, then adjust the flow rate?James AHP 200X TIGMillerMatic 175DaytonaMIG 135Chinese O/A
Reply:Argon or nitrogen for backing. Nothing with carbon or oxygen will work.Long after the price is forgotten, the quality will remain.Both of my Poppy's 1954 Short Hoods -Third generation to weld with it and teaching a fourthSA 2## - Bought and sold more than I can remember or care to list, 8 in the shop right now
Reply:Originally Posted by Adam ArcArgon or nitrogen for backing. Nothing with carbon or oxygen will work.
Reply:Go to your welding supply and get a tee with valves for a gas line. they will have it. Pretty common. I've used it plenty of times. Although its not as accurate as a dual flowmeter/regulator, it will get the job done for a fraction of the price.Lincoln Idealarc Tig 300/300, Lincoln ranger 8, Lincoln LN-25, Miller Sidekick (keeps rockin!), Oxy/Acy torch, Miller XMT-304 with a Miller 60 series wire feeder and high freq. box, Profax positioner 8" chuck, Aaronson 3500# positioner 15" chuck
Reply:Just my 2 cents but wouldnt copper make a better crucible? Maybee Im missing something. I would be interested in seeing what your making. I would like to see something that uses a welder to smelt. I think a 200 amp buzzbox would work depending on the quantity of aluminum. Just a thought.
Reply:Originally Posted by tigerstripe40That's what I was afraid of. What about the Tee and valve idea to provide purge argon?One other question. when watching welding videos(MrTig, weldingTipsAndTricks), I see that all of the TIG torches have nice clean alumina cups on them. Mine don't stay clean, they tend to get carbon build up on them... Am I doing something wrong or are the guys on video putting on new cups before TIG Welding?
Reply:I've cleaned new 304 SS pipe and had issues with dark welds and contamination. Depends on the quality and country of origin. Sent from my iPhone using TapatalkLong after the price is forgotten, the quality will remain.Both of my Poppy's 1954 Short Hoods -Third generation to weld with it and teaching a fourthSA 2## - Bought and sold more than I can remember or care to list, 8 in the shop right now
Reply:Originally Posted by InsanerideJust my 2 cents but wouldnt copper make a better crucible? Maybee Im missing something. I would be interested in seeing what your making. I would like to see something that uses a welder to smelt. I think a 200 amp buzzbox would work depending on the quantity of aluminum. Just a thought.
Reply:Budget Crucibles is a place to price one out. I know it's done but I don't want a couple of pounds of something 1100° leaking out.
Reply:If you're going to fabricate these crucibles, instead of cutting a disk for the bottom, I'd use these instead...http://www.mcmaster.com/#45605k591/=zsznohJust out of curiosity, how deep are these crucibles going to be?If they are not too deep, and  (if) you (can) weld the inside as well as the outside, you wouldn't need to purge them. After you weld the outside, flap wheel ( or carbide burr) the inside clean, then run a bead around the inside.With those weld-on end caps, the seam will be up 2" from the bottom as opposed to the absolute bottom.RichLast edited by steelsurgeon; 11-14-2015 at 06:46 AM.
Reply:With something 1/4" thick you shouldn't have a sugaring issue if you have good fit up. You only need to back gas if you are getting the back of the weld above critical temp. I doubt you are going to pump enough heat into 1/4" stock to melt all the way thru unless you are setting up a beveled open root joint. You can simply bevel partially on say the front to give you some where for the weld to go and weld away. The tech school teaches basic SS tig using 1/4" stainless so that the kids don't need to worry about back gassing at that point.You could also use Solar flux if you wanted vs back gassing if you really felt you absolutely had to.As far as themite, you are way too worried. The reaction doesn't work like that..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by steelsurgeonIf you're going to fabricate these crucibles, instead of cutting a disk for the bottom, I'd use these instead...http://www.mcmaster.com/#45605k591/=zsznohJust out of curiosity, how deep are these crucibles going to be?If they are not too deep, and  (if) you (can) weld the inside as well as the outside, you wouldn't need to purge them. After you weld the outside, flap wheel ( or carbide burr) the inside clean, then run a bead around the inside.With those weld-on end caps, the seam will be up 2" from the bottom as opposed to the absolute bottom.Rich
Reply:If you go with a cut disk, flat bottom, you could cut it @ 4" diameter, so that it overhangs the pipe 1/4" all around.Then, weld a 1/4" fillet all around the pipe (minimum of at least 2 layers of weld). Welding the inside would be unnecessary.How short are these pieces of pipe that you have to weld them together to achieve a 5" depth?Man....the guy you are doing this for is cheap!Rich
Reply:Originally Posted by steelsurgeonHow short are these pieces of pipe that you have to weld them together to achieve a 5" depth?Rich