Large scale castings are also tricky. You can't cast a rectangular prism and get good results. As the metal freezes (solidifies), it shrinks. You'd end up with a very poor surface finish at best, and chunks missing at worst. The shrinkage needs to be made up for with some additional molten metal.
The fix is pretty simple though. You need directional solidification, meaning the freezing starts on one end and moved towards the other. If you apply a draft angle of 1 degree or so to the parallel faces, you will have enough difference in dimensions to get directional solidification working fine.
>That way you don't need any special equipment and you can use whatever Aluminium you can get your hands on. Hell, you can even recycle Aluminium cans.
I'd advise against mixing alloys, but you may still be alright to get something, but it will be worthless if you try to recycle it again. Mixed scrap fetches far less than sorted scrap when you try to sell it. E.g. Some alloys might allow 1-2% copper, while others require <0.01% copper. Each pound of type 1 mixed with type 2 requires lots of pig (pure aluminum, no alloying elements) to be added to get the proportions back to something you can legally call whatever alloy you're targeting.
Aluminum cans aren't a wonderful source for things like this because they contain a thin plastic film on the inside to prevent the liquid contained from having its flavor tainted. Normal recycling processes handle this fine, but cannot handle the plastic labels added on many small brewery cans. Those should be cut off prior to recycling.
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Side note - It is incredibly energy intensive to mine bauxite, refine it through an electrolysis process into alumina, and finally alloying it into your preferred type of aluminum. It recycles incredibly well though. Recycling 1 ton of aluminum saves about 95% of the energy compared to new aluminum. This 95% savings is about 14,000 kWh. The energy intensity is part of why Iceland houses 4 smelters. With nearly 100% of electricity production coming from hydroelectric, they have incredibly cheap electricity, and it's economically viable for the likes of Alcoa, Rio Tinto, and Century Aluminum to haul bauxite ore from around the world to a tiny country with almost no manufacturing base, process it, then haul it around the world to its final destination.
Iceland's electricity production mix seems to be typically about 70% Hydro and 30% Geothermal (which does not change the overall point - just interesting).
Ah, good catch! I was rusty on my numbers from a year and a half ago when I wrote a paper on this for school. Back in the 80's they were nearly 100% hydro.
Just a note about aluminum recycling. Humans tend to trash things instead of recycling. Out here in the desert where people dump things I have noticed old steel cans rusted to nothing mixed with aluminum cans which seem to not degrade over time.
Arguably if you are worried about the environment and account for human laziness steel cans are better for the environment IMO
I've read around 75% of the aluminum ever produced is still in use today. If you machine a new surface on aluminum, it will form an aluminum oxide layer in a matter of hours. I believe (but am not certain) this effectively prevents it from degrading the way steel does over time.
Aluminum can recycling rates tend to be higher in states that offer deposit programs. Back when they were getting introduced in the 80's, $0.05/container had a lot more buying power than it does today. It's enough of an annoyance now, they'd be best off eliminating it or increasing it to ~$0.15 or so. Or since this is HackerNews, maybe we could use block chain technology to verify each can is properly recycled and reimburse with bitcoin.
A classmate of mine in college made all of his sculptures out of plywood and Bondo, reasoning that they were likely to last much longer than anything made out of metal due to having no scrap value.
The fix is pretty simple though. You need directional solidification, meaning the freezing starts on one end and moved towards the other. If you apply a draft angle of 1 degree or so to the parallel faces, you will have enough difference in dimensions to get directional solidification working fine.
>That way you don't need any special equipment and you can use whatever Aluminium you can get your hands on. Hell, you can even recycle Aluminium cans.
I'd advise against mixing alloys, but you may still be alright to get something, but it will be worthless if you try to recycle it again. Mixed scrap fetches far less than sorted scrap when you try to sell it. E.g. Some alloys might allow 1-2% copper, while others require <0.01% copper. Each pound of type 1 mixed with type 2 requires lots of pig (pure aluminum, no alloying elements) to be added to get the proportions back to something you can legally call whatever alloy you're targeting.
Aluminum cans aren't a wonderful source for things like this because they contain a thin plastic film on the inside to prevent the liquid contained from having its flavor tainted. Normal recycling processes handle this fine, but cannot handle the plastic labels added on many small brewery cans. Those should be cut off prior to recycling.
------
Side note - It is incredibly energy intensive to mine bauxite, refine it through an electrolysis process into alumina, and finally alloying it into your preferred type of aluminum. It recycles incredibly well though. Recycling 1 ton of aluminum saves about 95% of the energy compared to new aluminum. This 95% savings is about 14,000 kWh. The energy intensity is part of why Iceland houses 4 smelters. With nearly 100% of electricity production coming from hydroelectric, they have incredibly cheap electricity, and it's economically viable for the likes of Alcoa, Rio Tinto, and Century Aluminum to haul bauxite ore from around the world to a tiny country with almost no manufacturing base, process it, then haul it around the world to its final destination.