Help With Reducing Adhesion With Casting Tooling for Zinc & Aluminum

[blueandwhiteg3]

I am trying to prepare some casting tooling to cast zinc and/or aluminum. My goal is to cast a shallow parabolic dish, approximately 70 cm diameter. I have at my disposal a friend who's an expert metalworker, but he doesn't know casting, and I'm not entirely sure what I want them to produce to meet my goals.

My thought is to produce something similar to two identical and very heavy weight parabolic dishes with a small spacer around the rim equal to the thickness of the finished dish. We would pre-heat them both, pour molten metal into the lower half, then set the top half on top of the bottom half and allow it to cool very gradually.

We've tried simulating this using smaller steel commercial parabolic dishes, but we found the metal would adhere... to the point where it basically soldered the dishes together.

What kind of surfaces should I be looking at as a casting surface for zinc and aluminum? A specific steel? Stainless steel? How smooth should I make it? What about release agents?

 

[arunmrao]

What is the die mold material? You can use cast iron. If there is an issue of metal sticking or adhering to the die. You are advised to contact nearest foundry consumablee dealer. Dykote or some such trade name material is available. You need to apply this on the surface of the die before pouring liquid metal onto it.

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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[unclesyd]

Take a look at products from ZYP or better yet give them a call.

http://www.zypcoatings.com/

 

[EdStainless]

The surface does not need to be very smooth, just not rough enough to trap metal. A coating is the only way to do this. Generally they use ceramic slurry for the coating. You coat and then dry.
Unless your part is very thin you shouldn't need much pre-heat. Put the two parts together and then pour the molten metal into the gap. You will have trim the top edge afterward.

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Plymouth Tube

 

[btrueblood]

Try some boron nitride powder. You can buy it in spray cans from McMaster-Carr.

 

[ornerynorsk]

Mica powder is used as a release agent for die casting. Aluminum has a greater propensity to scavenge iron from the mold than do zinc alloys.