Counter Gravity Casting : Any one achieved it??

Discussion in 'Sand Casting' started by Dazz, Jan 7, 2022.

  1. Dazz

    Dazz Copper

    Hi
    Reading John Campbell's book. He is a strong advocate for counter gravity casting. This is where the molten metal flows from the bottom of the crucible out to the mold, against gravity. There are various methods of achieving this in a commercial foundry.

    The aim is to avoid pouring all of the dross and other contaminates floating on the melt. It is a method that can be applied to any metal.


    What I find interesting is that some methods use current passing through the melt to pump the metal. The current flow generates a force at 90 degrees to the current direction. This is a super elegant solution but commercial systems would be out of reach $$$ of DIY.

    I know this method of pumping molten metal with just current was applied in a research nuclear reactor that used liquid sodium metal as a coolant. The sodium was contained in steel pipes. Two terminals were welded to the pipe (one each side of the pipe) and a large current passed through the terminals. The liquid sodium is a much better conductor than the steel pipe, so most of the current passed through the sodium, not round the pipe.

    If the pipe is an insulator (eg. alumina ceramic) then a half turn coil can apply the magnetic force to the molten metal. Contact with electrons is not required.

    So conceptually, pumping molten metal is not that difficult but possibly beyond the reach of DIY.

    Has anyone achieved counter gravity casting in a DIY Home Foundry????
     
  2. It would be easier to have a bottom pour crucible like the steel foundries use or a teapot crucible that pours metal from the bottom to get closer to counter gravity casting. By the way those liquid metal pumps were first developed by a young student named Albert Einstein and his supervising professor, using potassium metal as the active liquid which would melt from resistive and inductive heating before pumping refrigerant gases of the day like ammonia and sulphur dioxide. The idea was to have a sealed compressor pump to prevent gases leaking as fridges of the day were gassing families in their apartments as they slept at night. They were making money by selling the rights to appliance manufacturers who would promptly file them away unused.
     
    Dazz likes this.
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    +1

    I haven't read any of Campbell's recent papers on the subject but when he first proffered the idea of counter gravity casting, it was a method to tranquilly fill molds without imbedding surface oxides from turbulent or suboptimal feed system. This is essentially the same thing that the naturally pressurized gating systems attempts to do but in practice, I don't think the result was ever as perfect as imagined......thus the counter gravity as an extension of concept following from bifilm theory.

    Best,
    Kelly
     
  4. Dazz

    Dazz Copper

    Hi
    Hi

    I was thinking along the lines of the Cosworth casting process. I have seen commercial race engine items cast with this process, and they were very very impressive. Large aluminium engine transmission casings with a wall thickness of 1.6mm.

    I don't think the Cosworth process could be readily simplified and adapted for the DIY foundry. It would require at least the availability of a low cost metal pump.

    I am interested to learn of any attempts to gain the benefits of counter gravity pouring. For example, has anyone considered adding a teapot spout to a crucible to draw metal from under the dross???
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There was a member here (Oldironfarmer) that was using steel tee-pot style crucibles, but bottom pour crucibles are commercially available. Are you familiar with them? Morgan offers them and I'm sure many others.

    Bottom Pour Crcible.jpg

    Best,
    Kelly
     
  6. Dazz

    Dazz Copper

    Hi
    I am only aware of crucibles with a hole in the base that is plugged until the pour.
    I looked in the Morgan catalogue. I did not find bottom pour crucibles. I can only find open topped spouts. There is the possibility of placing a tile on the inside of the crucible to partly block the spout so that metal was mostly drawn from the bottom of the crucible. That would achieve many of the benefits of counter gravity casting.

    Where I live, I would need to import a spouted crucible, and that would be $$$$$.
     
  7. Melterskelter experimented with a refractory biscuit on a normal crucible to function like a teapot crucible, I think it worked fine for him: it at least kept dross from going into the mould.
     
  8. Dazz

    Dazz Copper

    I wonder how he held it down to stop it floating?
    Would a stainless steel version work?
     
  9. Stainless steel will eventually dissolve in the aluminium, it might be ok to test the concept. I have a couple of dead crucibles I could probably cut a section from with a grinder and use with metal clips to hold in position.

    https://forums.thehomefoundry.org/i...er-that-mounts-to-my-trolley.1270/#post-30213
     
  10. Dazz

    Dazz Copper

    I was thinking of using stainless steel as a consumable item for cast iron. I need to consider the consequences of leeching chromium to the CI melt.

    I am also thinking of using stainless steel to create a pot lid for the crucible in the furnace. The idea being to keep the highly reactive combustion gases away from the melt. The theory being that the lid will contain a relatively stable, less-reactive and still layer of gases above the melt.
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

  12. Nickel and chrome at high enough levels will give you "White Iron" a super hard wear resistant material, If I could actually get 316 stainless to dissolve in grey iron, a 50-50 mix would be ideal for hard wear resistant castings.
     
  13. Dazz

    Dazz Copper

    Nice
    I have argon but no plans to use it with cast iron. I am working to the theory that any gas trapped under the lid may start being reactive, but it soon won't be, and will then effectively be inert. I think that should reduce, but not eliminate, the oxidation of the melt, improving overall efficiency. Less oxidation = more metal to pour.
     
  14. Dazz

    Dazz Copper

    I could think of some really good applications for such a material, but it also sounds like the perfect recipe for unmachineabilium.
    I was hoping that the stainless steel would not spend enough time in the melt to seriously affect the melt properties. That theory needs testing with some reality.
     
  15. Billy Elmore

    Billy Elmore Silver

    I have started using a vertical runner that side feeds the casting from the bottom to the top. About as close as I can get with the existing machinery we use. We have had astonishingly good results with this type of system and have begun converting many of our existing patterns to these types of gating systems. I think there are multiple advantages with these types of systems. One is that you are pooling your metal in the bottom of the runner and greatly reducing the velocity at the ingate which reduces sand wash inclusions and if done properly you can also reduce turbulence and reduce oxide defects. Having the ingate on the side means you are not pushing the iron through all of the loose sand you created when putting the molds together and so forth...meaning less loose sand defects. The metal enters the ingate under the top of the melt flow thus feeding good clean iron from under the dirty iron being pushed toward the top of the runner. The runner feeds hot iron throughout the pour which greatly reduces streaks and cold iron issues. We can use much thinner ingates as they are less pressurized and reduce the risk of slag and oxide defects. There are a few cons to this system however. Yield is typically not as good. The ingates are typically longer which means more grinding. They are depressurized gating systems so any disturbance during the pour may result in an incomplete casting...the pour needs to be uninterrupted to maintain a constant flow rate. If you do not have the ingate as close to the bottom of the casting as possible you may generate oxides inside the casting due to a vortex being created by a low pressure spot where the metal has to back fill under the ingate. I will see if I can put some videos together that show you some examples later.
     
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  16. Billy Elmore

    Billy Elmore Silver

    I believe white iron comes from the devil...LMAO.....shatters like glass in thin wall applications. Sure there could be some uses for it but not in anything that may break.
     
  17. Chazza

    Chazza Silver

    White cast iron was typically used in plough discs and scarifier points. Very good wear resistance to soil abrasion.
     

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