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Thread: Gold ingots cracking while rolling

  1. #1
    Join Date
    May 2021
    Posts
    2

    Default Gold ingots cracking while rolling

    Hi, Ive been trying to melt my own gold ingots and roll them out into sheets but they keep cracking. Sometimes in the middle of the surface, sometimes from the sides, sometimes both. They are 20k gold, and Iíve tried three batches- two from bits of older sheets (that were made by someone else) and one using fresh gold. I thought the older batches might be contaminated so i went with some new gold. The old ones had some combination of copper/ silver/ some master alloy, but i alloyed the fresh batch with just copper. Im really not sure what Iím doing wrong. They always seem to crack when i put them in the roller after annealing around thrice. There are no signs of cracks before this. I anneal to a dull orange, Ive tried quenching and air cooling after annealing, i tried hammering down the ingot around 15% after making it before rolling, and even annealing after just 3 passes through the roller (only rolling it down like 0.3mm), but it cracks every time. The ingot mould is i think as hot as i can get it- i heat it up first and then place it behind the crucible while melting so the torch flame continues to supply it with heat. I first tried the process with sterling silver and it came out fine (i didnít end up making a thin sheet, but passed it many more times through the roller than the gold, without it developing cracks). I think ive tried around 10 times but had no success. any idea what i could be doing wrong/ try differently? Thank you

  2. #2
    Join Date
    Dec 2009
    Location
    Central London
    Posts
    8,397

    Default

    When molten metal cools, it becomes crystalline.
    Try gently and persistently hammering a freshly poured ingot. Then re-anneal and roll twice, re-anneal and hammer etc. It should gradually respond to the mill without cracking as it gets thinner. Dennis.

  3. #3
    Join Date
    Dec 2014
    Location
    South Australia
    Posts
    1,601

    Default

    To add to what Dennis said, adding Silver will create a softer metal and will be easier to work.

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