Metal Casting Zone

I used to make a lot of parts using investment casting.

Now I am experimenting with using plaster for the part of the mold that the metal shrinks away from and Petrobond where the metal would grab a core.

The part I am showing here is a headlight stand for a 1936 Chevy passenger car.

The two upper halves of the mold are made of (metal casting) plaster.

When the part is poured, the metal doesn't grab the plaster sections.

The lower part is rammed up with Petrobond, the the pattern is removed and casting is done as usual.

This molding system is very eaqsy to do and captures good detail.

This is the mold box with the plaster. It is turned upside down and then the Petrobond is put in.
A pressure board on top of the Petrobond holds it in place while you turn the mold upright.

This is the mold box with the pattern installed, ready for the petrobond.

This looks interesting, I'm not sure where I would use it but I'll keep it filed away.

Will there be a core in this?

And, what are you referring to, when you say "Metal casting plaster"?
Is it a mix of plaster and clay and/or Silica sand, or something totally different?

It is a metal casting plaster that I buy from IGC in Milwaukee.
They used to go by the name Industrial Gypsum Co.
It is $63.00 per 80 pound bag that they split into 2 40 lb. boxes.
It accepts multiple pours before chipping out.