Tim Williams wrote:
"JohnM" wrote in message
...

wrote:
As Roy said, use a heavier mold to start with and use a better quality
of scrap. Stuff like beer cans is very inneficient scrap, even when done
on industrial levels with baled or briquetted cans. The bottom half of
the cans is good stuff, but the tops are a crummy alloy that you'll
probably find to be quite slushy.


Nah, the cans overall melt to approx. 3% Mg, balance Al. Which... really
isn't very useful anyway. Burn out 1-2% of the magnesium, add 1-2% copper
and 10% silicon and you've got yourself a skookum casting alloy. Just need
to find silicon...

Or.. you could start with a different alloy;-)


There's a *lot* of metal in cans, more than you'd think. I mean, individual
cans are ****-poor on metal, but more than half the slag still contains
metal. To get it out, you need to add a flux. Salt is a good flux for
aluminum, or better yet, a lower-melting mixture such as half and half NaCl
+ KCl (potassium). Throw it on, stir, wait for the salt to melt, add enough
that it becomes a soupy mess, then pour everything. If you want aluminum
oxide for any reason, it can be seperated from the salt by soaking in water.

Again, I think I'd start with heavier chunks.. although the oxide might
be useful. Seems a can is about an ounce, and there's a lot of surface
area there to oxidize..



If your mold gets too hot the aluminum will bond with it, either through
warpage or like brazing.


I'd be more inclined to call it soldering.. it's a pretty weak bond.
'Course it won't get a bond in the first place if your steel is rusty or
covered in scale, which is why you need to char your steel items before any
contact with aluminum.

Maybe a coating of carbon from a torch? Careful with the rusty steel, a
little water makes for impressive results. The aluminum foundry I worked
in had some fairly large water cooled sow molds, around 600lb. ingots..
when they'd accidentally pour a wet mold the aluminum would hit the roof
pretty hard, about 20' above. The help would scatter amidst considerable
verbal abuse directed at whoever slipped up, the aluminum would continue
to run, etc. It was sort of a hoot, when nobody got burned.



Even iron, given some time, will dissolve in aluminum


Doesn't take much time, pure aluminum eats non-charred soup cans for
breakfast. At 1450°F, aluminum has about 4% solubility for iron (which
later comes out as brittle Al13Fe4 or if silicon is present, a three
component AlFeSi intermetallic).

Now that you mention it, I remember a guy who liked to throw coathangers
and or banding in the melt when the iron content was adequately low and
they were waiting to bring the alloy to spec., didn't take long for them
to dissolve. The point was simply to increase the number of pounds in
the furnace cheaply.



and I think what you're getting is your ingots effectively
brazed to the muffin tins. A heavier mold won't get to as high a
temperature and you'll likely get better results.


My 1/4" thick angle iron regularly gets red hot, the problem is how clean
the interface is. I use the damn rustiest angle in my scrap pile and there
ain't a damned thing gonna stick to it.

With small ingots I think you're onto something. Again, most of my
experience is with ingots of 25lbs. and up- these have adequate size to
shrink considerably, relative to the mold, and would come out of a clean
mold fairly well. Usually..

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms