Hi folks,
I am thinking of stepping up my lost foam casting. Standard packaging and insulation foam gives a pretty crappy finish of my parts, so I have researched how professional grade lost foam casting is made.
First thing, the right foam. After watching some DIY videos for foam duck decoys, I believe I can cut out a mold for the foam and expand my own shapes. I did find a supplier of non-expanded polystyrene beads specially formulated for lost foam casting. And the last thing I need is a slurry for a smooth finish.
I suppose I can do my initial tests without the slurry, and use either loose sand for a more coarse finish, or some greensand for a fine finish.
However I do want to achieve a small batch (lets say 50 pieces) production process with the lowest possible costs, so that takes greensand out of the question, and a slurry is needed.
the LFC process does not burn out the investment and leave a hollow shell as in the Lost wax, so the slurry shell does not need to be very thick and strong. It just needs to be able to stick to the styrofoam well enough, provide good finish, have gas permeability, and withstand transportation once applied to the foam models.
I'm not planning to do large scale casting by myself, so I need to transport my foam models to a foundry. That is why I need it to be relatively strong in order to survive transportation (provided the slurry covered foam models are well packaged).
I was thinking of a thin coat of plaster sprinkled with silica sand, however I am not sure if the plaster won't cause problem with air permeability.
Would love to hear any good recipes for a slurry.