Re: No good ideas here


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Posted by David Sherman on Saturday, August 30, 2008 at 11:06:14 :

In Reply to: Re: No good ideas here posted by Fleabag on Saturday, August 30, 2008 at 04:34:08 :

I have never had good luck with that stuff. You have to heat the aluminum almost to its melting point, and then rub the not-quite melted rod vigorously on the aluminum in order to scrub through the oxide layer. It's very easy to get a perfect-looking "weld" bead that falls right off. On something simple that's out in the open where you can be very careful with the heat and really work the rod into the metal, it's worth a try, but most of the time it either doesn't stick or you melt the workpiece. For thread repair, you'd have to get it to stick all the way down inside the hole, which is impossible because you can't scrub it onto the surface like that. You need a flux that will make it flow into a hole. On cast iron or copper alloys, borax will do it, but the only thing that will cut aluminum oxide is hydrofluoric acid, which is not something you want to work with. As I recall, the soft solder I mentioned had some kind of flux that released hydrofluoric acid when heated. Any acid will quickly dissolve zinc, which means it'll ruin most die-casting alloys. Basically I think you're stuck with mechanical repairs rather than welding/brazing/soldering for die cast.

At least carburetor and fuel pump castings aren't made out of the same alloy they used for die-cast parts on old radios in the 1920s and 1930s. They actually grow with age, and then crumble apart with a mass of fine cracks. I've seen some very bizarre results.



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