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Thread: Casting lead questions

  1. #71
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    Default Re: Casting lead questions

    Quote Originally Posted by Small boats rock View Post
    Another sealant which can handle molten lead temperatures is silicone, the stuff used for sealing up roof gutters etc.
    Construction grade silicone won't take the heat. There is one readily available high temperature gasket silicone that might be OK here.

    I was about to say that you would have to go to something like Pelseal liquid Viton because no silicone could handle the temperature. As much as I hate being wrong, one more check came up with Permatex 81160 High-Temp Red RTV Silicone Gasket Maker that is supposed to be OK to 650F while Pelseal is only rated for 450F. Between the high price, difficulty finding it and potential for toxic fumes, Pelseal is not the best bet.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  2. #72
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    Default Re: Casting lead questions

    Your first test will reveal a lot of information to you. But my guess, based on some experience, is that the lead won't release easily. If it doesn't, you'll have to build in draft or make two sides removable to aid release. I don't think you need to use furnace cement. A simple dab of plasticine clay will do the trick and is easily done before each pour. The first pour will heat the mold and you'll be good to go from there on.

    Jeff

  3. #73
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    Default Re: Casting lead questions

    I live and drink rum where other people vacation.

  4. #74
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    Default Re: Casting lead questions

    Quote Originally Posted by MN Dave View Post
    Construction grade silicone won't take the heat. There is one readily available high temperature gasket silicone that might be OK here.

    I was about to say that you would have to go to something like Pelseal liquid Viton because no silicone could handle the temperature. As much as I hate being wrong, one more check came up with Permatex 81160 High-Temp Red RTV Silicone Gasket Maker that is supposed to be OK to 650F while Pelseal is only rated for 450F. Between the high price, difficulty finding it and potential for toxic fumes, Pelseal is not the best bet.
    When I did my big pour, much of the lead was old roof flashing. Lots had big lumps of silicone stuck to it where attempts had been made to fix roof leaks. I thought it would just burn up, but no, it didn't burn, didn't melt, didn't change at all. The lead melted away and the silicone retained its original shape as though nothing happened. Later when everything was cool I picked up those bits of silicon and found it still nice and rubbery, stretchy, flexible, just as it is meant to be. I have not previously sealed a mould with it, but next time I pour some lead I will incorporate some silicone to see what happens, and will heed your caution about fumes by standing to windward.

  5. #75
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    Default Re: Casting lead questions

    Quote Originally Posted by Woxbox View Post
    Oh no, my secret plan revealed. It's true, I'm planning for the Waterworld future, where I'll be shaving bits of gold from the bottom of my ballast castings to survive the lawless, sunken planet.


    I live and drink rum where other people vacation.

  6. #76
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    Default Re: Casting lead questions

    Quote Originally Posted by Small boats rock View Post
    When I did my big pour, much of the lead was old roof flashing. Lots had big lumps of silicone stuck to it where attempts had been made to fix roof leaks. I thought it would just burn up, but no, it didn't burn, didn't melt, didn't change at all. The lead melted away and the silicone retained its original shape as though nothing happened. Later when everything was cool I picked up those bits of silicon and found it still nice and rubbery, stretchy, flexible, just as it is meant to be. I have not previously sealed a mould with it, but next time I pour some lead I will incorporate some silicone to see what happens, and will heed your caution about fumes by standing to windward.
    Good information. Thanks. I wouldn't count on any real strength at temperature, but as a plug for a very small leak, it sounds like it should work.

    I meant that any fumes from Pelseal were a problem. It is a fluorocarbon, so it can release HF and other really nasty things if it gets too hot. Most silicones are not fluorinated so the fumes, if any, wouldn't be as bad. I never met a fume I liked, but some are a lot worse than others. Avoid them all. There are fluorosilicones, but I doubt you can find them in a retail store.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  7. #77
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    Default Re: Casting lead questions

    Quote Originally Posted by Sailor View Post
    Could you not just pour some sand into that cavity so the lead can't get in? I'd consider packing sand all around the mould as well, to keep the lead in the shape required.
    Don't do it! The sand will float up all through the lead making it impossible to work with edged tools. Even drill bits.
    Don't ask how I know this...

  8. #78
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    Default Re: Casting lead questions

    Ha ha, reminds me about my concrete mould. Tried to make a weak cement mix by having a fair amount of sand in it. Well some places evidently had a bit too much sand, so when the ballast keel emerged it had patches with sand embedded on the surface. The fix was a cheap electric plane which I didn't really like anyway. Fairly hacked up the blades which had to be sharpened every 10 minutes. Got the job done ok.

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