Question about stainless welding flux

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I'm taking a mig/tig class in preparation for building a hotrod this summer.  I actually earn my living as a computer geek.  Anyway, my wife broke a handle off an expensive stainless cookpot, and it seems like a waste not to weld it back together.  It was originally spotwelded, so I know the alloy is weldable.  Since my only access to a welder is at school, I don't have any way to back gas the weld; so, I looked around for a backing flux.  I can't find any nearby.  The closest can of stainless backing flux is 20 miles away in St Louis, and it's $30.  The local welding supply store tried to sell me some silver brazing flux.  The instructions on the can said it was good for stainless brazing, and the flux was active between 800 and 1600 degrees F.  My question is, is this flux good enough to work as a backing flux?  I'm a little worried about sugaring the weld because the lid is fairly thin, on a WAG (Wild-A$$ Guess) I'd say about 12 gauge.  I'm not worried about discoloring the metal as long as I can polish it out.Thanks in advance.StonebreakerGraduate of the John Wayne School of Linguistics
Reply:You don't need the backup flux for that weld.  Due to the unknown alloy of the pot, use 309L filler rod as it is compatible with most 300 series stainless alloys.If you want to use the backup flux anyways, it is certainly worth the 20 mile trip to pick it up.  Even if you only plan to do stainless this once, it works just as well on mild steel.  I use Solar Flux Type B.  It makes it nearly impossible to burn through, which is handy when welding sheet metal.Last edited by 76GMC1500; 04-15-2006 at 04:41 PM.
Reply:OK, I'll get the Solar Flux if I have to, but will the brazing flux do the job?  That's only 8 bucks and on the way to work.  If she hadn't inherited that pot from her mom, I'd just buy her a new one...(guess who runs my house? )StonebreakerGraduate of the John Wayne School of Linguistics
Reply:No, brazing flux is an acid used to break up the oxide on the surface of the weld.  Backup flux protects the back side of the weld from air just like inert gas or the flux on a stick electrode.  It also supports the molten puddle, but that is just a benefit to using it and not a primary function.  Because the backside of your weld isn't entirely exposed to air, the shielding gas will cover the entire area, the flux isn't necessary.
Reply:[QUOTE=76GMC1500]It also supports the molten puddle, but that is just a benefit to using it and not a primary function.  Another way to support thin material is to clamp a copper bar to the back side of your pot wall.  The copper absorbs any excessive heat and offers physical support in case the material is going to melt through.  A small copper bar is a welder's best friend.
Reply:Thanks for the idea about the copper strip.  I'll see if they have any at school.  If not, I guess I'm driving to St Louis tomorrow.StonebreakerGraduate of the John Wayne School of Linguistics
Reply:What's that aphorism?  If you are a carpenter, every problem looks like a nail?As one who really enjoyed taking a TIG class a few years ago, I can relate to your wanting to tackle the pot handle as a TIG problem.  But isn't that overkill?  Neglecting for the moment your desire to apply your new skills, I think silver solder is the ideal solution for this problem.  Much lower temperature than TIG, but plenty of headroom above any possible operating temperature.  Ability to completely fill the interface.  Way more strength than required for the task.  Easy to get a very neat finished appearance with a nice fillet.  Negligible risk of burn-through or other thermal damage to the base metal other than a little discoloration that is easily polished out. Have fun.awright