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Thread: Making ceramic crucibles

  1. #11
    Administrator Site Admin Anon's Avatar
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    I'm guessing it's just under the melting point of the clay and grog, so about 3000 F. This temperature is probably held for at least 24 hours.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

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  2. #12
    My homemade crucible 2 bit the dust the other day.
    My fault really as it was a little too big for my furnace and I had to turn it just right to get it in & out.

    The wires I had put in it did as I wanted and kept it together so I did get it out without spilling a lot of Al.
    Heat them up, mold them out.

  3. #13
    Eh, no wonder they're expensive. There must be a lot of fuel costs wrapped up in the price.
    No man really becomes a fool until he stops asking questions.

  4. #14

    wow

    Wow I had no idea this subject would spark so much intrest.

    Thats so cool on the silicon carbide issue. I had no idea.

    I also had no idea the graphite was to make it more heat conductive. Surely there has to be a good cheap source of graphite.

    I wonder if ground up carbon would do any good in the mix. I got some very large carbon rods from a surpluss store that came from a carbon arc spotlight. may fit the bill huh???

    also what other materials may be a high temp material??? crushed quarts maybee?? Just shoting in the dark here I am no chemist or geologist lol.

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  5. #15
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    I'm not sure if they actually use bona fide graphite dust in clay/graphite crucibles (I think they also use some bituminous material, probably for green strength or something), but finely ground amorphous carbon (e.g. charcoal dust) would probably do as well, or nearly so. Coarser amorphous carbon (depending on the source) will likely have too much air in it to be an effective thermal conductor.

    Your "large carbon rods" are probably synthetic graphite, and likely low-grade, but I'd wager they would be fine for crucibles.

    Other candidates in the grog department would be silica sand of varying mesh, alumina (mullite crucibles, maybe?), and crushed firebrick (or the remains of cracked crucibles . . . ).

    The most critical component is the clay: it's easy to find stuff that doesn't melt at 3000 F, but not quite as easy to find stuff that sticks together and still doesn't melt at 3000 F. A good kaolin ought to do nicely.

    There's no way a hobbyist could match the firing schedules of a commercial crucible factory, but it may not be necessary. A good hour's soak time at 2800 F won't make SiC to any significant degree, but it will make a very nice sintered-clay crucible.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

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  6. #16
    Stockcar92,
    Are you aware of the gingery book regarding making crucibles? It's where Ron & I gathered our information. its a simple process & the only real expense is firing them.



    The left one is fired & the right one is green. (#4 crucibles)I have yet to cast iron in my home made ones but they are holding up fine to brass so far.

    http://www.lindsaybks.com/dgjp/djgbk/cruc/index.html
    This thing will melt Iron with kitchen matches.......http://i32.photobucket.com/albums/d10/tmoto/fish003.jpg

  7. #17
    I'm slipping !

    Look at the .pdf of makeing Shopmade Crucibles.

    http://www.copperstarways.com/freebies.cfm
    Heat them up, mold them out.

  8. #18
    I was wondering the same thing about grog. You can buy ready-made grog (vitrified fire clay) from ceramic supply places, as well as alumina, silica, and coarse mullite. (SiC, too, but it's very expensive.) All struck me as good possibilities for crucible grog. But if there's no major difference among them I'd be inclined to go with the cheapest one, which seems to be silica sand.
    No man really becomes a fool until he stops asking questions.

  9. #19
    I've been considering making a crucible out of graphite powder mixed with porcelain clay, since that is the highest temperature clay I can think of that I know I can get. True Porcelan is a very short clay, it does better using slip-casting than it does with throwing, but I have worked with it before at times.

    One of my first crucibles was a plain stoneware clay, it actually held three aluminum pours before the uneven heat from my forge cracked it.
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  10. #20
    Regarding graphite or carbon, does anyone know if the graphite or carbon from used water filters (like Brita or Pur) would be usable? I wonder if any of the material trapped by the filter would cause problems?

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