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Thread: Working Silicone Bronze?

  1. #1
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    Default Working Silicone Bronze?

    I want to make an "L" bracket from some 1/4" silicone bronze I have. (alloy 655) Strength is the goal, I want it to anchor 1/3 of a three point internal lifting bridle to launch a #4500 boat. First question: is this too much to ask of this material? Second question: Hot bend or cold bend? (Ideal external radius would be about 1/2") My local Makerspace has press brakes that could do it cold, but would the material be tougher with a cold bend or a hot bend? In either case, would I need to re-temper it? And how?

    Please advise,

    Ken

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    Default Re: Working Silicone Bronze?

    Cold bending depends a lot on the temper. H01 has good elongation, 30% for a 1mm sheet. H02 drops to 17% and H04 it is only 8%. That pretty much says that you should anneal it first (900 to 1300F) That will bring the elongation up to 50%. The yield strength will be in the 20-30ksi range. Annealed stainless runs around 30ksi yield if that helps. Hot working should be done between 1300 and 1600F. The book says it has excellent hot and cold forming properties. Most bronzes are going to crack easily if you forge outside the correct temperature range. There is no heat treatment to increase strength. This alloy is hardened by rolling and stretching only. (ASM Handbook Vol 2, 1990, p. 335)
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  3. #3
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    Default Re: Working Silicone Bronze?

    You could cut the pieces and have them welded. You could get a sharper bend that way.

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    Default Re: Working Silicone Bronze?

    My bending rule of thumb has always been: Minimum inside bend radius= 1.5X Material Thickness. If you want that .500 outside radius I'd weld in a couple of gussets to reinforce. To be taken with a grain of salt as I have no experience with bronze, but that pretty safely applies to steel and aluminum.

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    Default Re: Working Silicone Bronze?

    All things considered, including the weight you're talking about, I'd seriously consider making up a pattern with good sized fillets and have the fittings cast. Port Townsend Foundry may have something on the shelf, for that matter. The old Navy motor whaleboats used to have hellacious bronze pads and shackles fastened to the top of their keels for lifting purposes. Those were beautiful castings.

  6. #6
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    Default Re: Working Silicone Bronze?

    All things considered, including the weight you're talking about, I'd seriously consider making up a pattern with good sized fillets and have the fittings cast.
    +1. That sounds like a lot of boat to hang off of 1/4" bronze, especially if the bracket has been annealed for working.

    I don't remember any such brackets in the PTF pattern library, but that doesn't mean they aren't there. The library is pretty huge. That said, if you're considering making the bracket from bent sheet, it'd probably be pretty straightforward to build a pattern if PTF doesn't have something you like.

    Alex

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    Default Re: Working Silicone Bronze?

    Quote Originally Posted by MN Dave View Post
    Cold bending depends a lot on the temper. H01 has good elongation, 30% for a 1mm sheet. H02 drops to 17% and H04 it is only 8%. That pretty much says that you should anneal it first (900 to 1300F) That will bring the elongation up to 50%. The yield strength will be in the 20-30ksi range. Annealed stainless runs around 30ksi yield if that helps. Hot working should be done between 1300 and 1600F. The book says it has excellent hot and cold forming properties. Most bronzes are going to crack easily if you forge outside the correct temperature range. There is no heat treatment to increase strength. This alloy is hardened by rolling and stretching only. (ASM Handbook Vol 2, 1990, p. 335)
    Thanks for the research and reply! It looks like I need to go back to them and find out what the temper is as supplied. This came from Atlas Metal sales which has sometimes advertised in WB mag. Short of melting it, is there a downside to overheating prior to a bend? Would I expect colors similar to mild steel when heating? Your post says that it doesn't temper by heat, I have a dim memory that in general bronzes harden when cooled very slowly, the opposite of carbon steel. No?

    Ken

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    Default Re: Working Silicone Bronze?

    Quote Originally Posted by kbowen View Post
    Thanks for the research and reply! It looks like I need to go back to them and find out what the temper is as supplied. This came from Atlas Metal sales which has sometimes advertised in WB mag. Short of melting it, is there a downside to overheating prior to a bend? Would I expect colors similar to mild steel when heating? Your post says that it doesn't temper by heat, I have a dim memory that in general bronzes harden when cooled very slowly, the opposite of carbon steel. No?

    Ken
    There are some bronzes that might harden some when slowly cooled, but which and how much would take some digging, and I would probably come up empty handed after hours of looking. There are very few that can normally be hardened by heat treatment.

    There are easily found tables of bend factors for aluminum that tell you how thick, what temper, and how sharp the bend, but I can't find one for bronze. Maybe somewhere on the copper development association web site.

    One thing to remember is that the metal will bend more without cracking across the rolling direction than when the axis of the bend is in the rolling direction. Your best bet is to cut some small pieces and bend them to see when or if it cracks and how sharp you can bend it.

    These links are to forums where people with the same books as I have have done the work and come up with some information, but not a definitive answer:
    Good information on Si bronze:
    http://cr4.globalspec.com/thread/634...Silicon-Bronze
    I had to grab this bit:
    POST #26: The reason is that wooden boats are still primarily high end boat examples primarily due to the fact that in spite of the quality and performance ability of competing materials like composites wood has an aesthetic quality that is highly prized.

    http://www.newenglandblacksmiths.org/tips_&_tricks.htm
    Find the part about forging bronze (cda 655)

    As so often happens, some of the best information is on this forum:
    http://forum.woodenboat.com/showthre...de-bronze-rod&
    http://forum.woodenboat.com/showthre...g-bronze-in-NC
    --which links to http://www.sawmillcreek.org/showthre...ting-in-Bronze
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  9. #9
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    Default Re: Working Silicone Bronze?

    I have done quite a bit of forging and weldment work with Silicon Bronze and it cold works very well, you just need force.
    A simple die set will do wonders.
    You could "bend" up something like this with a hammer die.
    (The math for 1/4" plate is pretty straight forward. I would want it so that any one of them would hang your boat with a bit to spare)

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