Steel molds for zinc-aluminum gravity casting?

Look into investment casting. It's probably the ideal solution for you if you are into limited production. You make a plug from which you make urethane or plastisol molds into which you pour wax, remove from mold, put waxies on a tree, dip in ceramic slurry, cure, melt wax from mold, fill with molten metals as hot as required for steel if you want. Break away the ceramic and you have perfect, seamless reproductions.

Wayne

Graphite?

Harry C.

"Spencer" wrote in news:1116622401.700055.37570 @g44g2000cwa.googlegroups.com:

GOOD grade of H13 is what is used in many gravity aluminum molds.

There's been some confusion over the years about permanent-mold casting because the use of terminology has changed. Permanent molds have been used for aluminum and zinc casting for many decades.

Originally, the molten metal was poured in through a tall sprue, made of clay or ceramic, and it typically was 3 feet or more high. Early on, they started calling this "low pressure die casting."

Then, sometime later, they started actually using some pressure, and the term was switched to that method. The gravity method is now usually called "gravity permanent mold casting." My basis for saying this is that I had to research it once for an article, and I had access to an excellent old engineering library at the time.

Many permanent molds actually were made of cast iron. Others were made of steel, of various grades. One of the more dramatic examples of permanent mold casting, using the tall sprue, was the B-O-P V8 engine block, made in the very early '60s. They located the cast ribbed steel cylinder liners in the mold and cast the block around them, in place. My vague recollection is that the molds were made of cast steel.

I have read that they smoked new molds to keep them from sticking. You can do that very quickly with an acetylene torch, with the oxygen turned off.

-- Ed Huntress

For lead casting, bullets and model soldiers, we used to use a candle to put a smoke carbon release layer on the mold surface, it worked well. For "Spencer's" situation a candle should work too since he mentions the part will only be the size of a hocky puck. Also a note on molds, besides steel and cast Iron, brass or copper should work too.

---------------------------------------------------- Plain old hot rolled steel will work fine for short run permanent molds. Some preheating of the mold is helpful to get started so that the castings won't freeze short. Once the die temp has reached equilibrium no extra heat is required. Die casting spray release will help too. Don't forget to leave

2 to 3 deg.of draft. It might be easier to buy 100 lbs of petro-bond and sand cast. It gives great detail.

Donald Warner

Don't let the facts interfere with your prejudices

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I didn't try it, but anti spatter spray might*) work too (and be less expensive and easy to obtain).

*) The one used for MIG/MAG welding

Nick