Entering the Age of Aluminum
We finally melted some aluminum!
We're not ready with our plaster molds, but we decided to just fire up the kiln and make some ingots out of the aluminum we had collected.
The melting point of aluminum is 660° celsius, but we had to get the pyrometer reading up to about 930° C before the metal in our tin-can crucible (not really tin, not much of a crucible either) would melt.
So we figured it's just the difference between what the pyrometer is reading—placed perhaps a little too high up in the kiln, with the hot air rushing by and out of the vent up top—and what temperature the metal is actually at, down below. A bit more of a spread than we had figured, but metal doesn't lie: it melts at 660° C and don't you try telling it otherwise.
Unless of course it's not pure aluminum. But the heat sinks from the computer are—almost 99.5% pure, in fact.
They melted down beautifully and easily. As did the scraps of aluminum from the guide-rail of a pocket door that I had. They formed some very nice ingots.
The pop cans were another story, though.
We crushed them down as flat as possible, and dropped them in.
The cans produced a small bit of aluminum, but the majority of what you end up with is dross. It seems that the impurities on the can—namely, the paint—affect the melt, so you end up with a lot of... crap (a semi-technical term).
But the main culprit is the amount of oxygen in the mix. Aluminum is quite reactive, and so when it melts down it reacts with the oxygen in the kiln to produce aluminum oxide. And that produces a lot of... crap. (Dross is the technical term. Dross is kind of like the low-temperature equivalent of slag. Slag and dross. Saying it over and over made me think it should have been the name of a Berlin Dada magazine from the 1920s.)
But I digress.
Here's what we're gonna do! No idea if it will work, but we thought that if we could reduce the amount of oxygen all around the crushed cans in the crucible, we might get a better melt. So to do that, next time we have our session, we're going to fill the crucible with charcoal. The charcoal should act as a reducing agent, and maybe, maybe, we'll get more aluminum.
Or else we'll end up with even more crap then before, a nice dark black colour.
I did some research on this first melt of ours and one common suggestion to reduce dross was to try to establish a small amount of molten aluminum in the crucible and then push each subsequent can into that liquid, so that the can melts with less exposure to oxygen. But nowhere did I read anything about charcoal. I got the idea from some bronze-smelting I did with Danny Z. ages ago.
I suppose if I knew more about chemistry and combustion I'd know if this will work or not. But I don't. And in any case it's more fun to try it out and see for ourselves. We'll keep you posted.
 |
| The kiln, loaded up. |
We're not ready with our plaster molds, but we decided to just fire up the kiln and make some ingots out of the aluminum we had collected.
The melting point of aluminum is 660° celsius, but we had to get the pyrometer reading up to about 930° C before the metal in our tin-can crucible (not really tin, not much of a crucible either) would melt.
 |
| The soup-can crucible fared much better when the flame wasn't blasting it straight on. |
So we figured it's just the difference between what the pyrometer is reading—placed perhaps a little too high up in the kiln, with the hot air rushing by and out of the vent up top—and what temperature the metal is actually at, down below. A bit more of a spread than we had figured, but metal doesn't lie: it melts at 660° C and don't you try telling it otherwise.
Unless of course it's not pure aluminum. But the heat sinks from the computer are—almost 99.5% pure, in fact.
They melted down beautifully and easily. As did the scraps of aluminum from the guide-rail of a pocket door that I had. They formed some very nice ingots.
The pop cans were another story, though.
 |
 |
| A very strange perspective of Jorge loading the crucible. (Could those really be his legs?) |
The cans produced a small bit of aluminum, but the majority of what you end up with is dross. It seems that the impurities on the can—namely, the paint—affect the melt, so you end up with a lot of... crap (a semi-technical term).
 |
| A small bit of aluminum on the end there. |
 |
| The dreaded dross. Aka crap. |
But the main culprit is the amount of oxygen in the mix. Aluminum is quite reactive, and so when it melts down it reacts with the oxygen in the kiln to produce aluminum oxide. And that produces a lot of... crap. (Dross is the technical term. Dross is kind of like the low-temperature equivalent of slag. Slag and dross. Saying it over and over made me think it should have been the name of a Berlin Dada magazine from the 1920s.)
 |
Here's what we're gonna do! No idea if it will work, but we thought that if we could reduce the amount of oxygen all around the crushed cans in the crucible, we might get a better melt. So to do that, next time we have our session, we're going to fill the crucible with charcoal. The charcoal should act as a reducing agent, and maybe, maybe, we'll get more aluminum.
Or else we'll end up with even more crap then before, a nice dark black colour.
I did some research on this first melt of ours and one common suggestion to reduce dross was to try to establish a small amount of molten aluminum in the crucible and then push each subsequent can into that liquid, so that the can melts with less exposure to oxygen. But nowhere did I read anything about charcoal. I got the idea from some bronze-smelting I did with Danny Z. ages ago.
 |
| (Back in 2006. There are tin and copper oxides in that there crucible. Topped with charcoal.) |
I suppose if I knew more about chemistry and combustion I'd know if this will work or not. But I don't. And in any case it's more fun to try it out and see for ourselves. We'll keep you posted.
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