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Re: [hobbicast] Glass & Aluminum

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  • Daniel C Postellon
    I have just cast obsidian in place in molten aluminum. It may have worked due to a low coefficient of expansion of obsidian, which is a fused silica natural
    Message 1 of 14 , Aug 22, 2006
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      I have just cast obsidian "in place" in molten aluminum. It may have worked
      due to a low coefficient of expansion of obsidian, which is a fused silica
      natural glass. Some obsidians are "hydrated" (contain a lot of water) and
      might explode with this technique. I would seriously try a test piece, to
      see if you can cast the aluminum around the glass. The aluminum cools
      rather quickly, even in molding sand, and it might not heat the glass
      quickly enough to damage it.
      I would worry about electrolytic corrosion if you poured lead into aluminum.
      You could also try using a zinc-based alloy, or some metal that melts at an
      even lower temperature. Some of these have a lower melting point than lead.
      >
      >
      > Greetings,
      >
      > I am designing a sign that I am going to cast out of Aluminum.
      >
      > Instead of having it "stenciled" I am going to cut the outlines of
      > the letters (from foam) then insert glass (hand casted) pieces
      > slightly smaller than the aluminum openings so that I can fill the
      > gap with lead or some soft metal so that the glass won't shatter from
      > the difference in coefficiency.
      >
      > Questions: If I warm the glass to around 800F, would it be safe to
      > just pour lead in to fill the gap between my glass and aluminum
      > without shattering the glass? Would the lead will be adequate to keep
      > the glass from shattering? If not, how can I cast glass in aluminum
      > openings properly? I imagine if I heat the glass to 800F and keep the
      > pouring temperature around 800F I should not even have to anneal the
      > glass again.
      >
      > Any and all thoughts and advice is welcome....
      >
      >
      > Thanks,
      >
      > Jeshua Lacock, Owner
      > <http://OpenOSX.com>
      > phone: 877.240.1364
      >
      >
      >
    • Jeshua Lacock
      ... Thanks for the advice! Hmmm. Yes I am aware that I can experiment - I was hoping someone could offer some advise so I could minimize that process. Obsidian
      Message 2 of 14 , Aug 22, 2006
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        On Aug 22, 2006, at 7:37 AM, Daniel C Postellon wrote:

        > I have just cast obsidian "in place" in molten aluminum. It may
        > have worked
        > due to a low coefficient of expansion of obsidian, which is a fused
        > silica
        > natural glass. Some obsidians are "hydrated" (contain a lot of
        > water) and
        > might explode with this technique. I would seriously try a test
        > piece, to
        > see if you can cast the aluminum around the glass. The aluminum cools
        > rather quickly, even in molding sand, and it might not heat the glass
        > quickly enough to damage it.
        > I would worry about electrolytic corrosion if you poured lead into
        > aluminum.
        > You could also try using a zinc-based alloy, or some metal that
        > melts at an
        > even lower temperature. Some of these have a lower melting point
        > than lead.


        Thanks for the advice!

        Hmmm. Yes I am aware that I can experiment - I was hoping someone
        could offer some advise so I could minimize that process.

        Obsidian is very different from soft glass, and is much closer to
        Quartz than the soft glass (eg bottle glass). I have poured aluminum
        directly on quartz without even heating it without any problems -
        don't try that with soft glass!). The closer glass is to quartz, the
        less you have to worry...

        My main concern is that I if I pour aluminum directly to the (warmed)
        soft glass, in the Winter or Summer it might shatter. I am planning
        on doing a lot of work for the sign, and without letting some tests
        sit outside for a year or many months, I have no idea if the glass
        will break from thermal expansion. Or is the coefficient of Glass and
        aluminum similar enough that I needn't worry about it? I am surprised
        nobody has done this before?

        How do they seal the windows on the space shuttle I wonder - actually
        I guess glass plates are mounted between metal plates? They certainly
        do not use rubber....


        Thanks,

        Jeshua Lacock, Owner
        <http://OpenOSX.com>
        phone: 877.240.1364
      • Jeshua Lacock
        ... Thanks for the advice! Hmmm. Yes I am aware that I can experiment - I was hoping someone could offer some advise so I could minimize that process. Obsidian
        Message 3 of 14 , Aug 22, 2006
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          On Aug 22, 2006, at 7:37 AM, Daniel C Postellon wrote:

          > I have just cast obsidian "in place" in molten aluminum. It may
          > have worked
          > due to a low coefficient of expansion of obsidian, which is a fused
          > silica
          > natural glass. Some obsidians are "hydrated" (contain a lot of
          > water) and
          > might explode with this technique. I would seriously try a test
          > piece, to
          > see if you can cast the aluminum around the glass. The aluminum cools
          > rather quickly, even in molding sand, and it might not heat the glass
          > quickly enough to damage it.
          > I would worry about electrolytic corrosion if you poured lead into
          > aluminum.
          > You could also try using a zinc-based alloy, or some metal that
          > melts at an
          > even lower temperature. Some of these have a lower melting point
          > than lead.


          Thanks for the advice!

          Hmmm. Yes I am aware that I can experiment - I was hoping someone
          could offer some advise so I could minimize that process.

          Obsidian is very different from soft glass, and is much closer to
          Quartz than the soft glass (eg bottle glass). I have poured aluminum
          directly on quartz without even heating it without any problems -
          don't try that with soft glass!). The closer glass is to quartz, the
          less you have to worry...

          My main concern is that I if I pour aluminum directly to the (warmed)
          soft glass, in the Winter or Summer it might shatter. I am planning
          on doing a lot of work for the sign, and without letting some tests
          sit outside for a year or many months, I have no idea if the glass
          will break from thermal expansion. Or is the coefficient of Glass and
          aluminum similar enough that I needn't worry about it? I am surprised
          nobody has done this before?

          How do they seal the windows on the space shuttle I wonder - actually
          I guess glass plates are mounted between metal plates? They certainly
          do not use rubber....


          Thanks,

          Jeshua Lacock, Owner
          <http://OpenOSX.com>
          phone: 877.240.1364
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