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Thread: DIY Refractory Compositions

  1. #21
    It should be fine up to bronze temps, it'll probably glaze a bit. The red clay might have some iron content, and it and the perlite are fluxes at higher (iron-ish) temps, which means they help the more refractory compounds melt at a lower temp. (Not an exact explanation, I'm sure, Anon can help me out here with the chemistry...) As long as it fired hard with no cracking, it should do great.
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  2. #22
    Administrator Site Admin Anon's Avatar
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    Clay straight out of the ground could have who-knows-what in it (there's a process by which clay is separated from sand, silt, some of its soluble salts, and organic matter--essentially it's dissolved in water, filtered, and then settled out with the water poured off and evaporated), so it may or may not melt at operating temperature. Worth a try.
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  3. #23
    Senior Member Robert's Avatar
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    After reading all this I am left wondering what materials are in commercial castable refractories that work so well. I have used dense (Mizzou) and insualating (Kastolite) castables. They look and feel alot like cement when working them. Do they have Portland in them? Is it possible to duplicate their product or come close?
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  4. #24
    Administrator Site Admin Anon's Avatar
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    The binder in commercial refractories is calcium aluminate, and they can be grogged with all manner of stuff (usually high alumina, since calcium aluminate contributes some flux to the mix). Kyanite is used to counteract firing shrinkage, and most commercial products expand very slightly on full firing in order to be able to fill cracks and such.

    If you can get the calcium aluminate, then yes, it's possible. It will take a bit of ceramic chemistry knowledge to get a workable near-zero-shrinkage recipe, and probably a bit of experimentation as well if you want a specific set of properties, but it's doable.
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  5. #25
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    I'm looking to do a little bit of research for personal and school reasons. I think a decent experiment would be creating 4-5 "minifoundries" small paint cans rammed with refractory made with the same ingredients, but different proportions. Would this recipe be ok for manipulation?
    Alumina
    Fireclay
    Foam

    (Fireclay could be substituted with EPK or similar)

    Working on a small scale, very high temperatures could be reached, but before I get into this, I guess I should ask what the clay-alumina sintering temp is. I have one hell of a propane burner, so that certainly wouldn't be the issue. The reason I want to use alumina as opposed to different proportions of sand, foam, perlite, fireclay, portland etc, is because that's a process I've done before, and I think this micro-experimentation could pave the way for some much needed refractory progress.
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  6. #26
    Administrator Site Admin Anon's Avatar
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    That sounds like a great experiment, and I'd be very interested in hearing of the results. It's one of the things I've been needing to run some tests on before I can finish the second edition of my book.

    Another, related experiment I've been dying to try for a while is alumina + a small amount of bentonite. It takes very little bentonite (5% or so) to hold together a fine powder in its plastic state, and with all the alumina around, the fluxes contributed by the bentonite should be pretty negligible. I'm hoping that it can be rammed up more like molding sand instead of shaped like clay, then speed-dried without so much shrinkage or cracking.

    "Sintering temperature" is ill-defined. You're looking at cone 18 or so in terms of heat work, which can be done with propane quite easily. It takes a lot of fuel to fire stuff, though, so be warned.
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  7. #27
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    Anon-
    So pleased you think so. I hope you'll be able to supply me with the intermittent spot of info I may need to do this successfully.
    Cone 18, I haven't been able to find a fahrenheit conversion other than,
    "Dude, that's really F*****g hot"
    Regardless, I think for a project more suitable for producing a huge amount of data is the one for me.
    My independent variable would be: Proportion of Alumina to Fireclay
    My Dependent variable would be: Temperature reached in (given amt of time).
    I have all of the materials at my disposal, thanks to a great ceramics store just out of town. (Clay People, look it up). Pretty much I need to measure out very exact numbers, get some large volumetric measuring devices.
    Would it be at all possible for you to answer the questions that come to me? Is there a thread you check often? In return for the mentorship, I'd publish all of my data tables for the good of the forum, as well as some neat graphs.

    For Now:
    Fahrenheit for Cone 18? Or should I stop worrying, and go buy some cones?
    What would an appropriate thickness for my concocted refractory be, if I'm using my micro foundry shells. If they're 6 5/8 inches in diameter, the standard 3 inch method will not work.

    http://www.emptypaintcans.com/1gallo...ids34case.aspx

    Thank you so much! After this project, I'd be happy to experiment with the bentonite-alumina method. I'm sure to have a lot of leftovers.
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  8. #28
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  9. #29
    Gomeltsomething, rather than volumetric measuring you might think of picking up one of those cheap kitchen scales and mix by weight. Other than the foam you should be able to get reproducible recipes this way. For the foam slight variances should not matter much so using a measuring cup and volume will get you awfully close.

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  10. #30
    Administrator Site Admin Anon's Avatar
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    Foam should be measured by volume because it's so light (hint: for accuracy, try looking into methods of ensuring it's compacted the same way every time when you measure the volume), but everything else is traditionally measured by mass because mass measurements will be more easily made accurate. I'd recommend a 0-2000g scale with resolution of 1g or better. If you don't have one, you can probably borrow one from your school's science department. Digital is easier to use, but a beam balance works fine.

    What I've estimated is about cone 18 (precision isn't really required for me, but you'll want to be consistent, which means using cones) is a ramp-up to as hot as I can get, maybe 2900 F, at a rate of maybe 1000 F/hr, a 30-minute soak, and a somewhat faster cool-down.

    Things that could be tested: Strength of the pieces (bending is probably easiest, as the compressive or tensile strength of a piece of un-foamed ceramic is rather large), rate of heat conduction through the pieces, flux resistance, thermal expansion at different temperatures (this one would take some precision to measure, but would be invaluable), and so on. You'll note that some of these tests end up being destructive, so you might want to fire several bars of each sample instead of a single furnace-shaped piece.

    I check the entire forum pretty regularly, so getting in contact shouldn't be a problem. I'd be glad to answer your questions on this.
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