elementcollector1
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Aluminum Casting!
(If there is a topic already like this, my apologies to the mods - I did search, but it's possible I missed something.)
Anyway, I was outside melting some aluminum cans today. Forge was charcoal briquette-based, with a hairdryer on a steel pipe to blow air in, and a
steel waterbottle used as crucible. I had some fairly large chunks of aluminum from the few times I had done this before, so I tossed those in and
waited.
2 hours later, they were mostly molten, so I started tossing soda cans and the like into the melt from a bag of 50 or so. Parents come out, tell me to
finish up. I douse the flames with water, flip the crucible over, and a teensy dribble of aluminum comes out. Peering into the slightly glowing-red
slag, I was surprised to find most of it (~95%!) was still there, in some sort of solid matrix. It was still shiny aluminum - but I bet whatever dross
and slag was in there was somehow 'holding' it.
What can I do to alleviate this problem? I am sure that there is much, much more aluminum to recover from this slag - earlier runs with lesser amounts
of cans yielded more than this joke. Should I add sodium chloride as a flux?
Yield of pourable aluminum metal was 73.7 grams, from (by my estimate) about 1 kg of material.
Elements Collected:52/87
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WGTR
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If at first you don't succeed; flux, and melt again.
It's not unusual to have a semi-molten pot of crud before the flux is stirred in. What it does is not only protect the melt from
the atmosphere, but it also dissolves the aluminum oxide into the molten salts. The fluidity of the melt can improve quite
dramatically with this treatment.
You've probably already figured this one out by now, but alkali salts are the best ones for fluxing aluminum. One time I used
a eutectic mix of KCl-NaCl-CaCl2 just because I had it laying around. But a KCl-NaCl eutectic mix is commonly used.
Whatever is used, the idea is to use a mix of salts that remain molten at the temperature of your melt. The CRCT database
is your friend.
Another thing, if detailed castings are being done, aluminum needs to be de-gassed before pouring it. Hydrogen (from
traces of water) is somewhat soluble in it at molten temperatures, but not in solid aluminum. This could give a
casting with porosity.
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elementcollector1
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The castings are absolutely not detailed, thankfully - about as simple as it gets.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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Fantasma4500
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ive made a 600g aluminium bar with .. well several bags of aluminium cans stomped flat and acetylene - oxygen burner
in a somewhat thickwalled iron rectangle closed off at the end
ive heard nitrates are added (KNO3 i guess?) to remove this suspension of aluminium caught in the slag, as it will heat up instantly due to chemical
reaction and put the aluminium to a boil
i guess you could just take a piece of metal (that can last the temperatures) and run through the molten aluminium in the crucible to get the slag to
get stuck at it, then whip it off at the ground or whatever
when burning off cans i found something very weird.. it smelled like H2S, but very very weakly, and there was a small amount of yellow on the slag
(zinc?)
the slag you can smash apart with a hammer and take the more pure aluminium pieces and dump back into the aluminium melt
its tricky and frustrating to melt aluminium cans, perhaps take apart some computer HDD's? the frame is made of aluminium, i have yet to try and melt
this down with air supplied charcoal fire in order to achieve a bulk of magnalium some day (:
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MrHomeScientist
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EC1: I've done a bit of aluminum can melting myself, and my setup is almost identical to yours. I also have similar problems, though
I'm usually able to get more metal per pour than that. It definitely helps to crush the cans beforehand, to reduce the amount exposed to air and thus
lessen oxidization. I also used a stainless steel crucible (camping cup), but that didn't last very long. After 3 melts (roughly 70 cans total), it
ended up with holes melted right through the bottom. Luckily I didn't have any disastrous spills, because the slag had also welded to the bottom!
I'll second the idea of fluxing. Once I get a new crucible, I was going to experiment with 50:50 NaCl:KCl as flux, to dissolve and fluidize slag. My
question, though, is how much flux to add? And when to add it?
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Muffn Man
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Metal casting site
This is not a chemistry site but they have tons of information on building furnaces, crucibles, burners and other stuff. Check out http://www.backyardmetalcasting.com/
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Fantasma4500
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infact about casting it, you should be able to mix up gypsum and sand 1:1 then mix with water and heat it up to drive off any water in the gypsum,
otherwise it might result in bubbling and even cracking when you pour in the aluminium
http://www.youtube.com/watch?v=jBVa2bw3r_k
i used simple gypsum packed in layers of aluminium foil and plastic to keep it together as i made lead/zinc fist
https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-frc3/t1/s7...
https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-frc3/s720x...
https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-frc3/s720x...
although it had significantly lower melting point than aluminium, meaning it would most likely get entirely wrecked by aluminium, but the sand:gypsum
sounds like a really good solution if youre willing to put effort in making the gypsum anhydrous before use
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