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Is there anyone with a metallurgy background reading this? It's easy to melt aluminium at home, what are the properties of a billet cast with primitive tools vs

by roel_v 6y ago

Is there anyone with a metallurgy background reading this? It's easy to melt aluminium at home, what are the properties of a billet cast with primitive tools vs in a factory? Like, is it more brittle, or does it have cavities etc? What circumstances does a factory control better for to get a better product?

throwaway0a5e 6y ago
Casting is a massive pain in the ass. It's one of those cases where the difference is in all the sum of all the little things and refinements that only make sense at scale.
cwkoss 6y ago
For garage level, I built this charcoal aluminum forge with my friend and it works great for the price! https://www.youtube.com/watch?v=hHD10DjxM1g https://www.youtube.com/watch?v=hHD10DjxM1g It's relatively easy to re-cast aluminum at home at small scale. I think the biggest challenge for boat-sized would be the massive amount of energy needed to heat all that metal, plus the huge crucible and machinery to pour it. Another issue with home-cast aluminum is alumina (oxidized aluminum) which will make small inclusion defects in your print. I've had several casts fail because I wasn't able to properly separate the alumina and the high-alumina areas were very brittle. I think most aluminum foundries have the electrolysis capabilities to convert all the alumina back to aluminum, but this is an extremely high voltage hot process that does not seem feasible for garage-scale. (As an aside, aluminum cans have a ton of oxide because of the high surface area, so you get a ton of dross that must be skimmed off to use the molten aluminum. We would do it in two steps: first melt cans and pour in a muffin tin to make small ingots, then use those higher-purity ingots to cast the desired piece. Probably better in most circumstances to just start with lower-surface-area aluminum materials: better to pay for quality bar stock or ingots rather than spend the same on more charcoal for multiple runs.)
- cwkoss 6y ago
  Note: if anyone tries this, invest in safety! At minimum, you should have welding gloves, sturdy tongs and a face shield. You should understand what happens when molten aluminum comes in contact with moisture (wet concrete is extremely dangerous!), practice your pouring motion with a cold crucible, and keep a bucket of water and/or fire extinguisher nearby in case you start a fire. But please research casting safety yourself, I'm no expert. 1200+F temperatures significantly more dangerous than the high temperatures we interact with in our daily lives.

by roel_v 6y ago

throwaway0a5e 6y ago

Casting is a massive pain in the ass. It's one of those cases where the difference is in all the sum of all the little things and refinements that only make sense at scale.

cwkoss 6y ago

For garage level, I built this charcoal aluminum forge with my friend and it works great for the price! https://www.youtube.com/watch?v=hHD10DjxM1g https://www.youtube.com/watch?v=hHD10DjxM1g It's relatively easy to re-cast aluminum at home at small scale. I think the biggest challenge for boat-sized would be the massive amount of energy needed to heat all that metal, plus the huge crucible and machinery to pour it. Another issue with home-cast aluminum is alumina (oxidized aluminum) which will make small inclusion defects in your print. I've had several casts fail because I wasn't able to properly separate the alumina and the high-alumina areas were very brittle. I think most aluminum foundries have the electrolysis capabilities to convert all the alumina back to aluminum, but this is an extremely high voltage hot process that does not seem feasible for garage-scale. (As an aside, aluminum cans have a ton of oxide because of the high surface area, so you get a ton of dross that must be skimmed off to use the molten aluminum. We would do it in two steps: first melt cans and pour in a muffin tin to make small ingots, then use those higher-purity ingots to cast the desired piece. Probably better in most circumstances to just start with lower-surface-area aluminum materials: better to pay for quality bar stock or ingots rather than spend the same on more charcoal for multiple runs.)

cwkoss 6y ago
Note: if anyone tries this, invest in safety! At minimum, you should have welding gloves, sturdy tongs and a face shield. You should understand what happens when molten aluminum comes in contact with moisture (wet concrete is extremely dangerous!), practice your pouring motion with a cold crucible, and keep a bucket of water and/or fire extinguisher nearby in case you start a fire. But please research casting safety yourself, I'm no expert. 1200+F temperatures significantly more dangerous than the high temperatures we interact with in our daily lives.