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Thread: Properties of high tin bronze?

  1. #1
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    Properties of high tin bronze?

    Hi all,

    Does anybody have any info on properties of high tin bronze, over 10 percent tin? And up to 30 or so?
    I am having trouble casting my little coins in regular bronze. The problem seems to be fluidity of the bronze. The bronze is not getting in the gates well. Now that its cold in my work area i think the temperature difference is having some effect. That and my gates are tiny. I mean tiny!

    My coins are usally an inch across by 1.5mm thick and i try to keep the gates as small as poss because it saves work later on , cutting the gates, and filing them down. So the gates are about 1cm long and only slightly wider than the coin. I know bigger gates would might solve it but its a major hassle on the finishing end. Its a bit delicate work so have to use small files so as not to ruin the features on the coins.

    I was messing around today and having failure after failure of the bronze not entering the mold. So i decided to try some pewter in with the bronze. (I sometimes add a tiny bit of silver to lower the melt temp as well) but with the pewter added, maybe 10-20 pecent, it poured so easily and had no probs entering the tiny gates. Ive yet to cut the gates and finish working the coins. But i know that when i tried the same thing with zinc, the metal mecame so brittle as to be unusable. It cracked while hack-sawing the sprues or when filing the edges of the coins. So, im afraid this new high tin bronze will be too good to be true, but rreally hope not, the brassy gold color is just what I need in some cases, but mostly i will be putting heavy patina on it so it doesnt really matter.

    Anyone ever work high tin bronze with hand tools? Cant find anything on the copper manufactures web pages of such high tin content. Thanks for reading my ebook this far 😉

    Ming

  2. #2
    Senior Member HT1's Avatar
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    Read this and then search for an alloy that meets your needs...

    https://www.slideshare.net/coremater...-molten-metals


    Just an FYI coins generally are not cast because they are too thin. but if you insist, you will probably need to incorporate jeweler techniques such as centrifugal casting to get good results

    V/r HT1

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    Senior Member Spelter's Avatar
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    The standard metal for european bells is a Sn22 Cu78 bronze. I poured a few, no apparent difference from my usual 1 tin to 8 copper bronze, though the books say it should be more fluid, harder, lower melt, more brittle. The bells I cast were about 8 pounds.

    Before glass mirrors were developed, mirrors were usually cast metal. The usual alloy was a very high tin bronze, maybe 60% tin, ballance copper. Never fooled with that one, but I'd guess hard and brittle given that it polished well. Should be fairly low melt temp.[Edit: found an abstract that puts composition at 32% Cu, trace zinc and lead, ballance tin; describes it as a quasi-crystaline alloy. https://link.springer.com/article/10...o-access=true] ]
    "The former lives of objects need not interfere with their current use."

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    Thanks guys for the detailed information, greatly appreciated!
    About cast coins, they were still casting into the 1900s in china and late 1800s in japan, both the genre I work in.
    Right now ive got an alloy mix of 85 bronze, 14 pewter, 1 silverthat is working well.
    Will try a small hand mirror using the euro bell metal recipe as well, thanks!

    Edit wrong metals
    Last edited by Ming; 01-27-2018 at 05:23 AM.

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