sodium fluoride

Hi All
I'm researching info on argon-arc welding of aluminium and aluminium
alloys using flux powders of sodium fluoride for a school project.
could someone tell me please when and why sodium fluoride flux would
be used and what type of manufacturing is it used in - I'm getting
some mixed info from the web and don't know whats what....
jpm
Reply to
gozman
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For argon arc welding of aluminium you don't need flux, thats what the argon is for. I don't know the flux constituents but is you are using a flux then that sounds like gas welding aluminium. For some related info see the thread "seamless metalworking" on rec.crafts.metalworking
gozman wrote:
Reply to
David Billington
Aluminium needs to have its oxide film disturbed and prevented from re-forming. When electric welding the mechanical stirring effect of the arc is enough to break it up, and the shield gas (MIG or TIG) stops it forming again.
Flux is used for gas welding, or for brazing. These are quite agressive fluxes compared to those for brazing steel and they're based on fluorides (watch the toxicity hazard of hot fluorides). A flux is needed because gas welding doesn't have the stirring effect of the arc, and there's no shield gas even if the atmosphere around the flame is reducing (i.e. oxygen starved)
Reply to
Andy Dingley
thank you that helps clarify things - is it true that sodium fluoride paste can be used to 'clean' an aluminium surface of oxides prior to arc-welding? and would this be a common practice? jpm
Reply to
gozman
The fluoride isn't especially active. But when you heat it, it forms an active mixture, including hydrofluoric acid which is the toxic part. Used cold it's ineffective.
There are lots of aluminium pickles that are used before some processes (particularly anodising), but I'm not aware of any before arc welding. However I'm not an aluminium welder, so there may well be.
Reply to
Andy Dingley

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