Green sand cores.

Discussion in 'Sand Casting' started by Ironsides, Oct 10, 2021.

  1. Ironsides

    Ironsides Silver

    I watched this very interesting video about casting a iron cooking pot. They used a green sand core and never bothered to put in vents in that green sand core. I have used only two green sand cores in the past and worked well. Seeing how large this core was it would make no sense to make it out of epoxy resin because the casting is emptied from the mold while very hot, so there is very little time for the epoxy resin to burn out plus green sand can be reused over and over again.
     
  2. Lots of graphite washed onto the mould before it can be used. I wonder, if the pot casting gets contraction damage if they let it cool in the mould.
     
    Last edited: Oct 10, 2021
  3. Chazza

    Chazza Silver

    Most interesting!
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Great video. Every move was refined and perfected.

    This is the first casting I’ve seen where the sprue becomes an essential feature of the casting. Also the dam ring to catch overflow was interesting. My guess as to why the core was dumped/shoveled out with the casting still hot is that leaving the core in longer just allows it to cook harder and make it more difficult to remove and makes the core pieces crispier and harder to crush for reuse.

    Denis
     
  5. Petee716

    Petee716 Gold Banner Member

    I’m still trying to figure out the significance of the divot the guy dug into the bottom of the core at the 1:00 minute mark.
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Good question. Did it give better ventilation for outgassing to dig into softer core and also give more surface area for outgassing? Was that also why he scored the top around 1:45 and then lightly smoothed it? That core has a lot of volume and only the top and bottom to outgas.

    Denis
     
  7. Ironsides

    Ironsides Silver

    So am I and I cannot figure out why he dug out the top and then smoothed it over.
     
  8. Petee716

    Petee716 Gold Banner Member

    I figured he flattened the top of the core in order to give the vessel a flat bottom inside or maybe to thicken its cross section. They could just change the core pattern if that were the case, but depending on what's involved in making those patterns they may have decided flattening the core manually was a better tradeoff. They certainly dont waste time.
    The hole does expose alot of surface area and he made no effort to smooth it, so that would make sense, but how much heat penetration does that core really get?
    After viewing the video again, it gets alot!
     
    Last edited: Oct 14, 2021
  9. Melterskelter

    Melterskelter Gold Banner Member

    The core itself is quite massive and it is exposed to a relatively thin shell of molten iron. But a fair bit of surface area is exposed and that is 20 to thiry pounds of molten iron which contains quite a bit of heat energy. So, the entire core may not heat up as much as a lot of cores that are smaller in proportion to the iron that surrounds them. Still and all, there is a fair bit of gas generated and, large core or not, that gas must be allowed to escape. By peeling off the hard and less pervious shell of the core in those areas, those gases escape more easily and do not cause possible bursting of the core. So, that is my best guess.

    Man, would it be nice to get that question answered for certain.

    Denis
     
    Last edited: Oct 15, 2021
  10. Melterskelter

    Melterskelter Gold Banner Member

    So, who knows what the white powder is that is layered onto the core and then heated with the propane weed burner?

    Denis
     
    Last edited: Oct 15, 2021
  11. DavidF

    DavidF Administrator Staff Member Banner Member

    Possibly aluminum oxide, or titanium dioxide
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    Why do you think that? Why did they fire it?

    Denis
     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    I think that because either of the two can take the temperature of iron. Firing might be to drive out moisture, or there may be some sort of binder in it.
    Could have been some sort of fire clay, but even the high fire porcelain clays I've seen aren't that white before firing..
     
    Melterskelter likes this.
  14. Ironsides

    Ironsides Silver

    I found another green sand core video, very interesting to watch.
     
    Petee716 likes this.

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