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I am planning to melt and cast aluminium from soda cans. I went to quora page that deals with "burning" aluminium can, which can release toxic gases as the cans are coated with plastic inner lining. So my question is if melting aluminium has the same effect? If so can the affects be mitigated by melting aluminium in the open and wearing respiratory masks (not sure if they are rated for plastic related fumes)?

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    $\begingroup$ It is my understanding that all aluminium cans used to store carbonated beverages have a spray-on coating/liner to prevent the liquid and metal from interacting. As you heat the cans to melt them, you are likely to start burning that lining which may produce dark smoke, acrid odors, and many other things. The type of mask that would be suitable is hard to know just from internet research. If you do this in the open, don't you risk having some annoyed neighbors? $\endgroup$
    – J. Ari
    May 17 '20 at 15:03
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    $\begingroup$ Metallic aluminum is always covered by an invisible, colorless, thin and continuous layer of aluminum oxide. If you heat soda cans above 660°C, the metal will melt, and not the alumina. So the liquid will stay imprisoned in a mantle of aluminum oxide. You may have difficulty to get it out of this protective varnish. $\endgroup$
    – Maurice
    May 17 '20 at 15:15
  • $\begingroup$ @J.Ari I am glad you mentioned If you do this in the open, don't you risk having some annoyed neighbors? I wont be doing this in vicinity of other people due to potential cancerogen fumes. Im just trying to protect myself and a helper who would be only one in the vicinity. I guess I really need to search for proper respiratory masks then. $\endgroup$
    – gfdsal
    May 17 '20 at 15:54
  • $\begingroup$ @Maurice I am not sure I understood well. Dont people skim the alumina and other dross by simply using a spatula? I am more concerned in ensuring if the fumes can cause significant damage if I melt say 100 cans. My understanding is that since the protective film is very small and the hazard to being exposed to the fumes is negligible but I have to be sure as I will have a friend help me as well. $\endgroup$
    – gfdsal
    May 17 '20 at 15:58
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    $\begingroup$ Youtube, honestly? ;-) (Btw. I meant tin, not zinc.) $\endgroup$
    – Karl
    May 17 '20 at 18:03
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There will be some organic coatings that will burn ,producing -who knows what? You will have little success melting aluminum cans in air , they will basically oxidize. Aluminum cans were not worth anything as scrap until years ago commercial melting began in inert ( non-oxidizing) atmospheres. I have seen the remains aluminum tank trucks ( gasoline) that burned , only steel is left , no melted puddles of aluminum. Apparently, the burning gasses carry away most of the alumium oxides produced.

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  • $\begingroup$ This makes sense. I was gonna melt them properly in a small homemade furnace as here. Are you suggesting that most of the aluminium will oxidize and we will be left with uncommercially small aluminium? $\endgroup$
    – gfdsal
    May 17 '20 at 16:39
  • $\begingroup$ They will if you have any oxygen present in the atmosphere. Aluminium will react with Nitrogen above 850C too. $\endgroup$
    – Waylander
    May 17 '20 at 18:19
  • $\begingroup$ @Waylander alright thanks for the tip. I did see too many tutorials on youtube where the yield from melting soda cans is sufficient. Roughly 50 cans yield 2kgs of Aluminium. I assume that the combustion of the fuel inside the furnace uses up all the oxygen. $\endgroup$
    – gfdsal
    May 17 '20 at 20:04
  • $\begingroup$ please do care to look at this $\endgroup$
    – gfdsal
    Aug 3 '20 at 16:18
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In addition to the problems listed in the other answer (typically you get very low yield because most of the aluminum oxidizes, and you have to burn off a toxic plastic coating), aluminum cans are made out of aluminum sheet, which is rolled (hot/cold rolled) and not cast. The alloys used are not especially suited for casting, (the obviously named) cast aluminum alloys are way better. You find cast aluminum often in car parts such as pistons, other engine parts, and some wheels. Since these are in big chunks instead of sheets, they won't oxidize nearly as badly, either.

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  • $\begingroup$ This makes so much sense. Are you suggestion that aluminium alloy in sheets is not good for casting (apart from low yield and oxidizing) because the alloy has other elements that make casting less desirable? Someone suggested me exactly what you mentioned about car parts but I want to use what is avaialble to me. $\endgroup$
    – gfdsal
    May 17 '20 at 20:01
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    $\begingroup$ Aluminum casting alloys usually contain silicon, up to 12 %. $\endgroup$ May 17 '20 at 20:01
  • $\begingroup$ @blacksmith37 yes and a quick search also reveals the soda can has 1% magnesium, 1% manganese, 0.4% iron, 0.2% silicon, and 0.15% copper along with aluminium. I am assuming they are there to make aluminium more malleable to be formed into cans using punching dye's as well as make them recycling friendly. source $\endgroup$
    – gfdsal
    May 17 '20 at 22:02
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    $\begingroup$ It's not that you can't cast with sheet aluminum, just that cast aluminum alloys works better, it has a lower melting point, flows better, and has a lower tendency to 'hot crack' in the mold. But aluminum alloy is cheap enough (or easy to find scrap for) that it might be better to work with a more suitable alloy. (ASIDE: I'd also worry a bit about the coating on cans forming some aluminum carbide in the melt.) $\endgroup$
    – AlaskaRon
    May 18 '20 at 21:55
  • $\begingroup$ please do care to check this out $\endgroup$
    – gfdsal
    Aug 3 '20 at 16:16

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