The Shop > Metal Stuff
Lost Foam Casting: a Crankcase in Zinc Alloy
vtsteam:
One other problem, as I see it with the solvent-foam idea is that it doesn't actually get rid of the polystyrene. And that is the problem here.
Unless you had a way of removing the dissolved polystyrene it will simply move with the acetone to the bottom of the mold, where the acetone will evaporate (hopefully to avoid explosion when pouring) and leave the polystyrene as a hardened sludge, And possibly impregnate both into the investment.
Actually I bet it would be a long wait until all of the acetone disappeared by evaporation inside a mold. Like maybe weeks.
My guess is that acetone won't be an advantage to the problem I'm seeing which is polystyrene entrapment. Not failure to fill the mold. I could be wrong. You never know until you try.
Lost wax methods -- with a kilned mold make sense to me -- that truly does get rid of the pattern material.
And high temp metals evaporate/incinerate foam creating a gas which escapes easily through the porosity of a very thin investment and loose sand, so the lost foam method also works.
Zinc seems marginal to poor for lost foam -- as a guess, in a zinc pour, polystyrene liquefies but doesn't gasify sufficiently in a small casting like mine. And remains trapped.
My guess is aluminum creates the minimum pour temp for good results on this scale.
mattinker:
It could be worth a try, true lost polystyrene depends on the molten metal replacing the foam with molten metal with nothing but dry sand to hold it in place! The thing about dissolving out the polystyrene is that one would have to be able to pour off the "sludge" before filling with the dry sand.
Plaster for a mold that size could be baked in a largish foundry!
Regards, Matthew
vtsteam:
I'm starting to think in terms of feral die casting.
feral, not ferrous. Ahwooooo!
werewolves of london
mattinker:
--- Quote from: vtsteam on August 09, 2014, 10:52:17 PM ---I'm starting to think in terms of feral die casting.
--- End quote ---
What's feral die casting? Google revealed nothing!
PekkaNF:
Maybe VT is going to have animals to raise the dies? Feral dies? Or maybe just good sense of humor. Normally dies are made of steel for zinc, maybe he is thinking of using non ferrous metal? Would aluminium have problem with molten zinc?
I'm following this thread it is really interesting. I have been reading some experiments of vax coated styrofoam used as lost wax methods, but can't remember how it ended. Typically less steps you have less room for errors there is.
My brother used styroxfoam as a plug to make smooth engine intake. He laminated glass/epoxy on top of it and then dissolved foam off. Can't remember what he used but options were gasoline or MEK, had something to do in getting it all out.
Pekka
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