On 25.09.16 13:11, Danny Miller wrote: > Some of our folks built a metal kiln and we tried to melt some aluminum > swarf the neighboring metalshop discarded, at least what we thought was > aluminum (no confirmation, but it wasn't steel). We got almost no metal, > just inches of dross. No inert gas or flux there, in fact the metal was > exposed to combustion gases.
It is some years back now, but I made a number of Al castings, using scrap, and had no difficulty filling a 2 litre crucible with liquid metal. That produced about a centimetre (call it 3/8") of dross, but that much is just surface oxide from the significant proportion of drink cans which went in. To really bring the dross to the surface, it is necessary to stir in some flux - then you get a good layer. (I've read of common table salt being used as flux, but I bought a commercial product.) The other thing which should be done is to plunge and stir a degassing tablet (I just held it in a pair of domestic fire tongs, slightly rusted, and well carbonised, to minimise iron contamination. You could whitewash them instead.) That drives off bubbly amounts of dissolved hydrogen, which will otherwise come out of solution on cooling, causing cavities in the casting. And, of course, add a couple of % of copper, early on, to make the casting machinable. (Who wants a casting made of toffee?) A little bit of zinc helps to make the alloy age-hardening, I found, and those castings are still sound 40 years later. (The zinc I used came from scraps of pot-metal, or "die-cast" as it's called down under. So all I know is that 1% or 2% of Zn, or something like that, went in.) (If you have a tub of accumulated brass swarf, not enough to make a useful brass casting, then it is a source of both Cu and Zn, ideal for Al alloying, I figure. Mine is exclusively hard brass, which is around 60:40, IIUC. The ductile stuff is 70:30, I think. Also near enough.) I would expect a good layer of dross from swarf, as there's a lot of surface area. And there must be some further loss of metal when all that dross is scraped over the side of the crucible, as it burns as bright as the sun when it falls onto the charcoal fuel I used. It is possible that a deep layer of charcoal, and only gentle forced ventilation from a speed-controlled DC fan, contributed to a reducing (or at least only mildly oxidising) atmosphere, but I kept the lid on the crucible except when charging with fresh (PRE-DRIED!) metal. Erik ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
