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Thread: Re-Temper bronze screws?

  1. #1
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    Default Re-Temper bronze screws?

    please direct me if this has been covered: I have a bunch of bronze hardware from my late father, some of the bronze screws possibly came from a boat that burned. I can easily bend these 1/4" x 4" wood screws with my bare hands. Can these be re-tempered to be useful? At a new retail price of about $3.50 each,it seems worth my while to figure this out. I have an enameling kiln that I could heat them in. Please advise. Ken

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  2. #2
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    Default Re: Re-Temper bronze screws?

    Heat is used to aneal brass and makes it more malleable. So using the kiln is probably out.

  3. #3
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    Default Re: Re-Temper bronze screws?

    The short practical answer is no. Few copper alloys can be heat treated. The ones used for fasteners are not heat treatable. They are work hardened by wire drawing or rolling. any heat treatment after that can only soften them.

    For the few heat treatable alloys, you would have to know the exact alloy that you were heat treating since the temperatures will be different for each alloy. Short of having a friend with an XRF gun, it will be had to identify the alloys.

    This is as good a summary as I have in my collection of links: http://www.totalmateria.com/Article71.htm
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  4. #4
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    Default Re: Re-Temper bronze screws?

    As above, you can't reuse them. BUT I've been saving all my stripped / broken / bent silicon bronze fasteners and hardware, and at some point hope to visit either a foundry or someone who can make me something out of the material. We'll just have to see if that ever happens, but I love seeing the products made by the Port Townsend Foundry - http://www.porttownsendfoundry.com/

    "The enemies of reason have a certain blind look."
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  5. #5
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    Default Re: Re-Temper bronze screws?

    ^Chesapeake Bay Maritime Museum is putting on a bronze casting class in March…
    Steve Martinsen

  6. #6
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    Default Re: Re-Temper bronze screws?

    Could be useful for metal riveting (the plain shank part) as they need to be annealed before use, the rest to scrap
    the invisible man........

  7. #7
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    Default Re: Re-Temper bronze screws?

    Ok,so I was accepting all this depressing news, but then I started wondering, how the heck do they cast a bronze pad-eye or any other bronze fitting with any kind of a decent temper if one can't re-temper bronze? Does it have to come all the way from a liquid state to achieve a hard temper? I remember a metalworker telling me once that one can temper bronze by cooling it very slowly. Is there no hope?

    Ken

  8. #8
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    Default Re: Re-Temper bronze screws?

    Padeyes and other deck hardware don't require hardness. Strenght can be increased by increasing material thickness. Corrosion resistance is given a higher priority over wear resistance.

  9. #9
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    Default Re: Re-Temper bronze screws?

    Quote Originally Posted by kbowen View Post
    Ok,so I was accepting all this depressing news, but then I started wondering, how the heck do they cast a bronze pad-eye or any other bronze fitting with any kind of a decent temper if one can't re-temper bronze? Does it have to come all the way from a liquid state to achieve a hard temper? I remember a metalworker telling me once that one can temper bronze by cooling it very slowly. Is there no hope?

    Ken
    << Edit: I skipped the direct answer. The castings are not stronger. See Post #8, they are thicker than the screws. The only way to increase the as-cast strength is to increase the cooling rate of the casting, which isn't easy. >>

    You might get as much as $1.85 per pound. This link is the first hit on google. I have no idea how reliable it is.
    https://rockawayrecycling.com/metal/bronze/

    This is the common silicon bronze wrought alloy. https://alloys.copper.org/alloy/C65500 The only thing that changes the annealed strength other than cold work is grain size, and that is a time temperature relationship. More time and temperature increases grain size and lowers strength. This shows up in the link in the Mechanical Properties table under flat products.

    Here is a reading list on silicon bronze: https://www.copper.org/search.html?q...&submit=Search Somewhere in this long list there may be something about using heat treatment to refine grain size. I don't think it will work. If it is possible, it will probably be something like heat to 1600°F and quench in water several times. Bottom line would be that the scrap price is your best option.

    This is a guide to heat treating Ni-Al Bronze. It is not the same alloy, but shows a little more of what you are up against.
    Lots of good cast copper information:
    https://www.copper.org/publications/...t/pdf/7014.pdf
    https://alloys.copper.org/alloy/C87610
    Last edited by MN Dave; 02-17-2018 at 01:08 AM.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  10. #10
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    Default Re: Re-Temper bronze screws?

    I'm sure there is a metallurgical explanation for this but the cast items seem to have a natural rigidity that the wrought or extruded item doesn't. Compare cast iron vs mild steel, cast aluminium vs extruded aluminium. I've worked a lot with bronze over the years. LG2 bronze castings can be worked a little, tried to bend some parts of a G1 casting, very little success and you are always frightened it will break. The extruded bronzes seem to behave normally, anneal then work and hardens from the working, particularly silicon bronze.
    the invisible man........

  11. #11
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    Default Re: Re-Temper bronze screws?

    Manganese Bronze is used for props and fittings that need strength.
    Jay

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