Metal Casting Zone

Hi Everyone,

I'm soon to start casting aluminium alloy and I have a few questions. I want to try a simple investment casting just to see how it works. Was thinking of using a 50/50 mix of plaster of paris and sand around the wax. Surface finish at this point is of little importance. My main question is in regard to how thick should the layer of sand and plaster be and will I need to fire it for a while after the wax has burnt out to drive off any excess moisture to hopefully prevent a steam explosion. WHat type of temp/time profile is normal for this sort of thing?

When making the slurry is it best to mix the sand and plaster at once or keep them seperate, apply plaster to the wax then pour sand over the wet plaster? How many coats?

Thanks
Splint

Keep in mind that plaster is not the greatest of materials to use.

Even if it's been setting for a few weeks drying, it can still hold quite a bit of moisture ( enough for steam pockets to form ), and if you heat it up above 600* or so, it starts to chemically break down back into gypsum.

Greg H. wrote:
Keep in mind that plaster is not the greatest of materials to use.

Even if it's been setting for a few weeks drying, it can still hold quite a bit of moisture ( enough for steam pockets to form ), and if you heat it up above 600* or so, it starts to chemically break down back into gypsum.i agree. i tried plaster at first but what a fizzle!!!!! fiz...fizzzzzz.....if you know what i mean