Spruing advice for small kinda intricate lost foam project

Discussion in 'Lost foam casting' started by Chassy, Aug 13, 2022.

  1. Chassy

    Chassy Copper

    I'm experimenting with casting some flaming bocce pallinos* and need some advice on the best way to sprue them up. They're 1.6" hollow spheres with a spindle inside around which I'm going to wrap a kevlar wick. I want advice because there's so much about these that is pushing the edge of what lost foam can do - they're small, with a large surface to volume ratio, and the path for the metal to flow around them is far from direct. A centrifugal casting setup would probably be best, but all I have is a bucket of fine sand. (BTW, they will also be coated with a thin layer of drywall compound.) My current plan is to make sure I have a long sprue to create more hydraulic pressure and to pour hot.

    Aside from wanting general advice, I have some specific questions:
    • The ideal sprue for lost foam is straight down. But is there a way I could gang these up for a single pour without causing too much of a chance of defects?

    • Regardless of if I gang them together or not, how far apart should they be? In the past, I think I've encountered some defects from hot gas from one pour messing with a nearby foam form in the same sand bucket. I'd prefer to avoid the extra work of setting these up in separate buckets of sand.

    • How well will dry sand flow into them? Should I take the extra step of making some green sand to pack in and around them? I have a gut feeling that this would give the pattern some extra stability, but maybe at the cost of permeability.

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    * A pallino is the little ball that's tossed out first during a game of bocce. Each person / team then alternates turns tossing their balls and trying to get them as close as possible to the pallino, or maybe to knock their competitors' balls away from it. I'm thinking it would be kinda fun for the pallino to be on fire, thus the hollow sphere with a wick on the inside.

    Thanks!
     
  2. Al2O3

    Al2O3 Administrator Staff Member

    Dry sand should flow and pack well, just make sure they are vibrated. 2-3” spacing should between them should be adequate and they can be ganged to a runner and fed from a single sprue.

    Best,
    Kelly
     
  3. Chassy

    Chassy Copper

    Just finished the project! Given that I'm very new to lost foam casting, I'm happy with the results - success with two out of the four pallinos. For the two failures, I'm guessing that there were areas that were just too tight for the aluminum to flow through. I think my drywall compound coating could also have been a little bit thicker. I'm also thinking that if I do this again, I could really use a vibratory tumbler for smoothing and polishing the exterior.


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  4. Petee716

    Petee716 Gold Banner Member

    The ones that turned out look really good. They should clean up pretty good. I’m not sure what happened but here’s something to consider:
    The liquid is going to take the path of least resistance. If it starts by moving first toward the failed side, partially fills, and then hits some resistance (like the downward gate), it will stop flowing that way and then start moving toward the successful side until it’s full. Then it tries to finish filling the first side but the gate is plugged by already solidified metal. That plugging solidification can happen in an instant. The horizontal flow may be the culprit here. Hotter metal might help, but in this case controlling the direction of flow might do the trick. I think melterskelter wrote a good description of this recently but I couldn’t find the thread.

    Pete
     
  5. Al2O3

    Al2O3 Administrator Staff Member

    More heat!

    Best,
    K
     

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