What metal are beer bottle tops made from?
September 20, 2017 6:08 AM   Subscribe

What metal are beer bottle tops made from?

Specifically those on stubbies in Australia, but if you have an exhaustive beer bottle top metallurgy guide, that'd be (weird and) great too.
posted by pompomtom to Technology (16 answers total)
Best answer: I don't know about Australia, but ours in the States stick to magnets, so I figure they must be steel. What kind of steel, I couldn't say.
posted by egregious theorem at 6:15 AM on September 20, 2017 [2 favorites]

Best answer: Ones I've encountered have been magnetic, probably thin sheet steel. A googling of the internets shows aluminum is also used sometimes, but I've never encountered it (and I have no data on Australia).
posted by AzraelBrown at 6:16 AM on September 20, 2017

Best answer: Wikipedia says "steel" but also "citation needed", so we can't be certain. They certainly behave like steel.
posted by ubiquity at 6:18 AM on September 20, 2017

Response by poster: Ta all. Don't know why I didn't check with a magnet in the first place...
posted by pompomtom at 6:22 AM on September 20, 2017

Confirmation from the US: I have a wall mounted bottle opener in my kitchen with a couple of magnets that I attached underneath it to catch the caps, and in the many years since I've had that and people have used it with different bottles, we have never encountered a non-steel cap, at least to my knowledge.
posted by ernielundquist at 6:32 AM on September 20, 2017

Note that they're not super-high quality stainless steel, they do rust. (and as the alloy blend increases non-iron content, they stop being magnetic)
posted by aimedwander at 8:00 AM on September 20, 2017

Response by poster: I was hoping for aluminium. Suspect a backyard forge won't do iron.
posted by pompomtom at 8:56 AM on September 20, 2017

Um. To possibly derail, what are you trying to do with a backyard forge? Backyard forges for blacksmithing steel are common and not mad expensive.
posted by stet at 9:22 AM on September 20, 2017

Note, the bottom of the cap is generally coated in a plastic so the cap doesn't rust.
posted by advicepig at 1:09 PM on September 20, 2017

Best answer: Do you mean "furnace" rather than forge? Backyard casting of aluminum is common, backyard casting of steel is going to be a bit more intense than most would want, including neighbors, but it can be done.
If you need good aluminum for casting, broken up auto cylinder heads from the junkyard are a good alloy. "Beer can" is almost pure aluminum and doesn't have much strength.
posted by rudd135 at 3:09 PM on September 20, 2017

Response by poster: Indeed, I mean furnace. Thinking about doing lost-PLA casts.
posted by pompomtom at 9:02 PM on September 20, 2017

Best answer: I have read that small pieces of aluminium such as cans and what bottle caps would be if they were aluminium is not good for casting. They have great surface area to mass ratio and so oxidise readily when heated. They are also made from aluminium alloys suited to extrusion rather than casting. Pieces that were originally cast like alloy wheels are supposed to be better. Just don't get magnesium alloy or you'll have a bigger fire than expected.
posted by deadwax at 11:55 PM on September 20, 2017 [2 favorites]

Best answer: They are cut from sheets of steel. YouTube video of a production line

I have always heard that aluminum caps exist, but I've never encountered one in the wild.
posted by Lame_username at 12:33 PM on September 21, 2017

Best answer: They're definitely steel. If you want aluminum to cast with, you are better off getting cans. There are lots of videos on Youtube of people doing this that you can refer to; you probably want to shred (best) or crush (better than nothing) the cans first, so you can get them into the crucible to melt.
However, broken-up automotive parts—engine parts, typically not wheels because of the alloying materials—are definitely better, but will cost you.

The reason they'll cost you is because they're less contaminated with plastic, which is the same reason commercial scrappers and recyclers (and, down the supply chain, aluminum smelters) want them.

You can melt cans, but definitely do it outside since it will produce some nasty stuff as the interior coating (beverage cans are coated—the beverage doesn't actually touch metal internally) and labeling melt and burn off.
posted by Kadin2048 at 1:05 PM on September 21, 2017 [1 favorite]

Response by poster: Ta all, again. Strength is not a huge issue, reckon I'll be doing ornamental things first until I work this all out. Tinnies are a problem, because we don't do tinnies (aka cans, sorry). Stubbie tops we have in spades.

Thanks for the auto-parts suggestions. Hadn't thought of that, and have local options.

Crucible arrived today, and I have a store of apparently useless steel tops. Might just start off with lead.
posted by pompomtom at 5:22 AM on September 22, 2017

From a safety point alone I would just buy a few ingots of a premade pewter to start with. Some have a low enough melting point that you can actually cast in PLA (or maybe ABS) and as an added bonus it is non-toxic. Using lead will mean that you will be increasing your lead xposure and also increasing the exposure for people around you. You're not likely to run into any problems, but for the cost of some pewter you can make things that you could give to a kid to hold and not have to worry about them eating it.
You can get it for 10 cents a gram so it isn't that expensive.
posted by koolkat at 9:08 AM on September 22, 2017

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