Posted by bpfink on December 24, 1998 at 20:18:27:

In Reply to: Re: I need help with casting with Zinc!!! posted by Dee on December 24, 1998 at 20:01:08:

Dee

I looked further at your site suggestion. From what I could guess at... it would be doing the original in either an oil based clay or the like and then making a mold of that. I would guess the mold would be in plaster. Then the clay removed and the plaster (now a negative) sealed with a good wax surface or positive sealer.

Then a urethane rubber mold made from that (this is again just like the original as a positive). This rubber mold model could include the feeder sprues and any vents that would later be needed in the final hard sand molds.

The reasons for all this is a savings of time and a low cost of media so far. It also gives one a flexible rubber positive.

Now ... forget the green sand (too risky for great detail unless being an experienced mold maker) and go to a hard binding sand.

The oil / acid or catalyst type would be my first choice and you could buy the dry sand in 80 to 100 lb. bags as just silica sand. Mix it with some finer silica flour sand about (3 sand to 1 flour... an educated guess ). Of course other dry sands could be used for zinc casting, even beach sand that has been sifted and dried.

Then mix it with the oil and when fully blended, add the acid or catalyst. These are all materials you could get from any foundry supply and normally comes in 1 to 5 gallon sizes. The amount of catalyst is small in proportion so get the smallest size you can get there. Five gallons of the oil will go along way. Exact proportions will be on the manufacturers labels.

Make an oversized wooden frame around the rubber mold to serve as a sand or mold flask (this can be reused over and over as well),

spray the rubber with a protective release spray,

pack the sand on it and let set overnight or till hard (depends on the temperature and the mix).

Turn over and remove the rubber master (which can be used over and over probably hundreds of times.)

Now lay in a flexible rubber or foam sheet that is the thickness you want the casting to be and make the back half of the resin / sand mold. Be sure to put in keys joints or such

so the two line up exact again later and also put over it a layer of seal wrap or saran wrap so there is a definite parting plane to open on.

Open again when that side is set hard,

remove the 1/8th to 3/16th inch space sheet (depending on what thickness you want the zinc to be cast in) and finish any vents, sprues or metal feeding channels.

Again, there are many other tricks of the trades that can not be included here. Many gaps to this road map but this may give you an idea of the route.

The zinc can be plated in any other pure metal such as copper or silver but that is probably a process to send out. Too complex for me to get into here.

You may also want to just look into spray metalizing or having your originals and molds done by you and for someone else to do the spraying. This can then be done in any metal such as

bronzes or alloys composed of combinations of metals. Makes for a much richer patina when getting to the natural coloring.

Good luck.

Let us know how it works out or what your choices and discoveries include. bpfink

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