DIY recipe for lost foam slurry

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.

Quote:

---

Originally Posted by zeox

I did find a supplier of non-expanded polystyrene beads specially formulated for lost foam casting.

---

Do you have a link I could check out? Also feel free to join us over at the Alloyavenue forums. I do not get around to posting much, however I do tend to read a lot. The knowledge base there is immense and someone should have some ideas for you. :D

Sure thing, here you go :)

https://www.alibaba.com/product-deta...0.0.xZ8PO7&s=p

Alibaba of course. You can find everything in China :)

I will place an order for a 25kg bag in the coming few days, but I will have to wait for about 2 months to get it because I will be using maritime shipping (I intend to combine the shipping of those beads with some engine parts that I have ordered and will be shipped soon. My partner in China will order them and pack everything together in a crate).

Anyways I'll have plenty of time to prepare :)

As for the Alloyavenue forum.... Well Google already took me there :) Been browsing it a lot lately. Still not registered though.

In order to expand your pellets into foam shapes, you need a heated metal mold. Have you made one?

Casting solid parts like duck decoys takes a lot of metal, and anything more than about an inch thick starts to have severe problems with shrinkage porosity. An optimal thickness for aluminum is about 1/4".

I have no idea what you're trying to cast, but I wouldn't rule out sand-casting unless it has a lot of undercuts. It's a fairly economical process, and you only have to make a single pattern board to cast a whole lot of parts. Making all those styrofoam shapes, gating them up, coating and transporting them without damage sounds like a lot more more expense and difficulty.

Well I still haven't done the molds for foam expansion. But as I said, I have plenty of to time for this.
As for the parts I'm about to cast, various holders, flanges etc.
I would also try casting larger shapes with LFC. but for now I'm good with small parts.

I am already working with greensand. However I see huge potential in LFC, and if my expectations prove to be correct, I might transition completely to LFC.

Time will show.
For now I am still looking for a good slurry recipe :)