Process for Lost Foam Ceramic metal casting explained?


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Thread: Process for Lost Foam Ceramic metal casting explained?

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    Default Process for Lost Foam Ceramic metal casting explained?

    Hello,
    I'm hoping I can get a basic or even better a detailed explanation of how Lost Foam Ceramic coated metal casting is done. The reason is my son is a last year at NorthEastern (Mechanical Engineer major) and has a elective class for welding and metal casting. His instructor wants them to do a "Multiples" casing of the same part. So the plan is to make a number of Positive masters from Foam and coat with ceramic for casting. The item is going to be a somewhat fancy shelve bracket. Since I have the CNC machine at my shop we are doing the machining of the masters . So allow me to kick this off with all the NooB questions. The better I understand the entire process I feel the better the foam master will come out: Rest assured I will NOT be doing the casting but will be done at the Mass Art Institute shop under proper supervision.

    1- What foam is normally used for this process. I was thinking Dow Hi-Load 100 or even 40. What about Core-cell?

    2- Are the foam masters machined with included pour tubes and vent tubes?

    3- How are the foam masters coated with Ceramic? What is the process? Dipped multi times, Brush on? Sprayed on?

    4- How are the coated masters supported for the pour process. Some kind of stand, jig? Master machined in one large unit for a large single pour?

    5- How is the foam removed once coated. Baked out with oven? Pour in acetone and melt? Let the hot liquid metal blow it out? Just curious.

    6- How is the ceramic removed after pour and cooled. Just beat it off with a hammer?

    I'm sure I have missed a lot but look forward to learn how this is done.

    Thanks

    Steve in Maine

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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    What material will it be cast in? I have cast aluminum using blue extruded polystyrene (XPS) coated in drywall mix, then suspended in sand.
    The foam can be joined with hot glue, and doesn't need to be removed from the plaster shell, it just burns out from the liquid metal.

    I learned what I know from LFMC After all these years, it's a pleasant surprise this website is still online.

    This website is what got me interested in CNC in the first place, building a cnc hotwire foam cutter for preparing the foam blanks.



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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    Thanks Alan for the reply. I checked out the website and was really good. After talking to my son I guess they have a ceramic slurry vat to dip the foam in. I'm excited to be part of this process. I'll post some pictures after we pour!

    Steve In Maine



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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    This method usually works by vaporizing the foam by pouring in hot metal, not by dissolving it with solvents. It requires a styrene-based foam, like the Dow products you linked to, but works best with low-density foam that has less material to burn. Under no circumstances should you use Core-cell foam, which produces toxic fumes containing cyanide when burned. It says this in the MSDS https://www.b2bcomposites.com/msds/ccp/212936.pdf Most hobbyists typically don't bother with the full ceramic shell method, but, as Alan advises, just apply a light coating of drywall mud, then support the pattern in a tub full of sand, and evaporate the foam by pouring the metal directly on it. The sprues and risers should be integral to the pattern.

    The ceramic shell process can be used, which involves baking the shell in a kiln, but it's important to provide adequate ventilation, even when using Styrofoam. It's usually a semi-automated process where the models are suspended from hooks in a line, lowered into the slurry tank, and coated with "stucco" - dry particles of ceramic - then redipped and recoated multiple times. Since foam models will tend to float, they'll need help to coat evenly. Then they are placed in a kiln to cure the shell, and poured when clean and empty.

    The ceramic shell can be removed by hammering to some extent, but must be painstakingly removed from deep cracks and fine details by hand if it doesn't separate cleanly. Production facilities use vats of molten salt to remove the residues, which is a lot easier.

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    Andrew,
    Great explanation! After talking to my son the shop he is taking the class has a Induced fan hood for the dipping process and a Autoclave for burning out the Foam. Then the normal sand flask pour process. I was surprised he is casing Brass. The class is at the Art Institute of Mass so they have a lot of brass on hand. They also have a Glass Bead Booth for aiding in removing the ceramic which is being stubborn. Sounds like they have all the proper safety protocol's in place. Can't wait to see the results. Thanks for the safety tip on Corecell.

    Steve in Maine.



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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    An autoclave won't really burn out the foam; it just melts it with steam. But that would reduce the volume significantly. Hopefully, they still use a kiln to cure the shell and vaporize the remaining plastic.

    I'm surprised about the brass as well; most art foundries use bronze. If they're really using brass, then they need to provide positive ventilation, since it produces a lot of white smoke when poured, that will make people sick (look up "zinc fume fever") .

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default Re: Process for Lost Foam Ceramic metal casting explained?

    Thanks Andrew,
    So I just checked with my son and you are correct, Bronze is what they are using. Not sure where brass came from? To be honest I'm new to all this and really on the outside looking in. Really just involved with the foam masters. I will be going to the school shop to watch and take pictures which I plan to post.

    As far as Zinc Fume I had that once from welding on galvanized pipe. Sick as a DOG! Safety protocol's have improved over the years thank god!

    Steve in Maine.



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Process for Lost Foam Ceramic metal casting explained?

Process for Lost Foam Ceramic metal casting explained?