aluminum prep question

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hi guys great forum,i have a question on how i should prepare aluminum a/c hoses and lines for welding. these lines are exposed to all the contaminates under the hood, plus the freon and oil running through them. how can i insure these containments do not effect the weld? these welds must also be air tight. i can see leak dye penetrating welds from time to time. even steel lines that have been brazed have shown this failure (not as often). welds seem to have pin holes some times many (like a sponge). thanks mikeany a/c questions?
Reply:A search turned up this Arcal Chemicals product they call Weld-O, that uses hydrofluoric and nitric acids.Hydrofluoric acid!  Really, really bad *** stuff.  I believe this is the acid used to etch glass.  You absolutely can not get this on you, apparently it will go through your skin to the bone and break down the calcium.  Not too sure, but sounds serious and painful, and maybe dismembering (no more welding).  It takes a special substance called calcium gluconate to treat skin contact.This is the site, read the MSDS! http://www.arcalchem.com/
Reply:i have tryed to weld a/c  lines  and  had every little luckit tends to be too contaminated from the oil  i would  just replace the hose/line  rather than go through ::the weld--pressure test system, install freon and hope it don't leak would price a new line/hose oh  a lot of pressure  on the high side of system
Reply:Originally Posted by prop-doctori have tryed to weld a/c  lines  and  had every little luckit tends to be too contaminated from the oil  i would  just replace the hose/line  rather than go through ::the weld--pressure test system, install freon and hope it don't leak would price a new line/hose oh  a lot of pressure  on the high side of system
Reply:If you use carb cleaner let it dry. Then preheat it with a propane torch. to burn off the rest of the oil.Don't over heat it. Let it cool back down then spray it again with carb cleaner steel-wool it.Wipe clean with a clean cloth.Steel-wool the tig wire also.Good Luck