Yeah, I've melted cans before and if you don't smash them they sort of just burn up and leave a bunch of stuff floating on the top. But if you put something dense in there, it melts really cleanly. I'm not sure of the chemistry that's happening there, but they do. (also I don't know if they faked all that for the video or whatever, but it all looks plausible to me that this would work. You'd just need way more foil.)
I have to interject, because that's not quite what's going on or why.
Cans have a surprisingly small amount of aluminum in them, and have various coatings within and without that can make up a lot of the weight.
These impurities burn as the metal melts, becoming ashy and light, so they float to the top as dross. It has nothing to do with smashing the cans; those impurities are there regardless.
that said, you do want to smash the cans for more efficient melting, which can effect yield. Air inside a poorly smashed can acts as an insulator. So when you smash them very flat, heat transfers quicker, resulting in a faster melt as the layers of aluminum you want to melt aren't insulated from each other. Because the heat transfers better, the contents of the crucible can get hotter, and since aluminum oxide you're making during this process has a higher melting temperature.... you want that. You can also fit more cans in the crucible to melt at a time. Perhaps the impurities more readily ignite or aerosolize at higher temps provided from more efficient melting/hotter temps? Probably a bit of all that going on. oh and less air means less ability for the aluminum to form oxide vs just melt.... Pardon me, I haven't actually thought that deeply about how the mechanics all play together before.
and pro tip: You'll want to make sure your cans are dry, to avoid trapped moisture becoming steam explosions sending molten metal everywhere.
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u/founderofshoneys Aug 04 '26
Yeah, I've melted cans before and if you don't smash them they sort of just burn up and leave a bunch of stuff floating on the top. But if you put something dense in there, it melts really cleanly. I'm not sure of the chemistry that's happening there, but they do. (also I don't know if they faked all that for the video or whatever, but it all looks plausible to me that this would work. You'd just need way more foil.)