Casting a windmill gear in grey iron

Discussion in 'Sand Casting' started by Mister ED, Nov 17, 2018.

  1. Mister ED

    Mister ED Copper Banner Member

    For what its worth, keep in mind that I did leave a bit of machining + shrinkage allowance. So, surface finish is not a big deal.
     
  2. Melterskelter

    Melterskelter Silver Banner Member

    I guess I forget the original story on the pattern. Is it out of the question to print a new pattern with a couple degrees of draft? Seems like that would make life so much simpler.

    Denis
     
  3. PatJ

    PatJ Silver Banner Member

    But then we would never know if it was possible to pull the straight pattern from resin-bound sand.
    Hopefully we will have the answer to that question today.

    .
     
    Tobho Mott likes this.
  4. MortyNTenon

    MortyNTenon Copper

    There is a point with the SS/catalyst sand when it has a hard skin but is still somewhat flexible. Might be when you want to pull the pattern.
     
  5. PatJ

    PatJ Silver Banner Member

    I am not using SS for these molds, but rather resin binder.
    I have two types, and I will try the older material I have first in an attempt to use it up so that it is not wasted.
    Should the older material not mix/harden well with a test mold, then I will use the newer binder.

    SS sand seems to be the worst about sticking to the pattern.
    Resin-bound sand does not seem to be as bad.

    There is a "set" time, and a "strip" time for bound sand, and the trick is to pull the pattern during the strip time, early enough that the pattern does not get permanently glued into the sand, but late enough that the sand has enough strength not to tear out in the weaker places.

    There is a period after the set time where the sand has not reached its maximum hardness, and generally right after the set time, the sand may be at only 25% hardness.
    There is a bit of an art to picking exactly the right time to pull the pattern, but with the resin binder I have been using, I have gotten good at picking the right time, and thus the reason I would like to use the resin binder again, since I am very familiar with it.

    Pressing on the bound sand with a fingertip gives a good indication of the level of cure/strength/hardness.
    If you can easily make an indentation in the sand with your fingertip after the set time, then the mold is not ready for stripping the pattern.
    As soon as the mold becomes hard enough to pass the finger indentation test (pressing the sand with the fingertip without creating an indentation), then that is a good time to strip the pattern.

    The mold is still not totally hard at this point, so it has to be kept on a flat surface, else it will move slightly and distort.

    After about two hours, the resin-bound sand will be completely rigid, and can be handled without danger of warping.

    .
     
  6. joe yard

    joe yard Silver

    I am wondering about a thin coating of the part with say a 5 weight or lighter oil.
    I know that polyurethane “Gorilla Glue” does not like oil at all.
    I am also wondering if Gorilla Glue would work well as a foundry sand binder?
    I have played with it and sand. It takes on very good detail however I have not tried to use it when pouring metal.
    Joe
     
  7. PatJ

    PatJ Silver Banner Member

    I would be afraid that an oil residue would combust and cause problems, but then again there is Petrobond, which is an oil-based sand, so maybe not.

    There has been some experimentation with epoxy as a sand binder, but I am not sure how that turned out.
    I think epoxy would probably work given it is similar in nature to resin binder (it may be about the same thing chemically; I am not sure).
    From a cost standpoint, epoxy is not cheap, and the big thing about resin-bound sand is the ability to control and vary the set time, which I don't think you would be able to do with standard epoxy 1:1 mixes.

    I think there are many off-brand uses of materials that could work, but the bigger question to me is "Would it be cost effective?".
    Nothing seems to be cheap these days.

    .
     
  8. MortyNTenon

    MortyNTenon Copper

    There are so many types of epoxy, unless you have tried or know of someone who has used a specific one its a long shot. And then you'd want to know if they used it at iron temps or not.

    Your findings with resin bound sand setting mirrors my experience with SS/catalyst. I find that when SS sand sticks to the pattern I'm pulling it to soon.

    Good luck with the molding.
     
  9. Chazza

    Chazza Copper

    The same question I ask, which is why I use greensand bonded with soluble-oil. The oil, like any oil, is expensive but I use so little in re-constituting the burnt sand, that it can be largely discounted when considering the profit I can make in an hour.

    It also bonds so well, that I would never use water as a binding agent again, because there is rarely any wash of sand into the moulds and a mould made in May, will still be viable if left unused, at Christmas,

    Cheers Charlie
     
  10. Melterskelter

    Melterskelter Silver Banner Member

    So, Charlie, what makes soluble oil especially
    desirable for binding sand compared to other less expensive oils?

    Denis
     
  11. Petee716

    Petee716 Silver Banner Member

    And additionally, what formula do you use?

    Pete
     
  12. Chazza

    Chazza Copper

    Good question about other oils – my answer is that I do not know, because I have not used anything else. I wonder if it is poor flammability, because it always surprises me that it doesn't catch fire when the metal hits it. It has a very distinctive smell and I do know that the last commercial foundry I walked past in Perth in the 1990's was using it. A pattern-maker put me onto using it in 1986.

    The formula is absurdly simple; add the oil to dry sand and mix it thoroughly – I do all of my mixing by hand and store it in 20 litre drums – test the bonding by squeezing handfuls of sand into the palms of your hands. If the lump created can be broken in half and holds its shape reasonably well, the amount of oil is pretty good; repeat this test several times to make sure all of the mix is good. If the lump crumbles easily add more oil and re-mix. If you over do the oil – this is most easily seen by patterns that will not release, or sand sticking to the pattern – add dry sand and re-mix until the test works out well.

    If you have a muller the same technique applies, except that through experience it would be easy to work out exactly how much oil should be added, to each 20 litre drum of sand.

    After I have poured the castings and everything has cooled, I strip the burnt sand out with a small trowel and let it fall through a grid into and empty drum; this saves me having to remix all of the sand. The unburnt sand is returned to the drums and when the burnt-sand drum is full, I re-constitute it with oil.

    The drums have wooden lids to keep out foreign objects. I use dry sand rather than parting powder and that works extremely well and I clean the patterns with Prepsol before each mould is made, to remove any traces of oil,

    Cheers Charllie
     
    Melterskelter likes this.
  13. PatJ

    PatJ Silver Banner Member

    A pretty long and apparently somewhat straight pull on this mold at 1:30.
    And notice the silver "Zip Slip" type material on the pattern or corebox.

    Lots of neat tricks in this video if you look closely.

     
  14. PatJ

    PatJ Silver Banner Member

    Nice iron bridge and foundry.

     
    joe yard likes this.
  15. Melterskelter

    Melterskelter Silver Banner Member

    I think the pattern had normal draft at 1:30 though you only get 1 second to look! It was an easy pull—-no draw spikes.
    They are adding an inoculant at 2:40—likely FeSi though it could be a “fancier” mix.
    Fun vid to watch.

    Denis
     

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