Re: I need help with casting with Zinc!!!

Posted by bruce paul fink on December 24, 1998 at 09:16:12:

In Reply to: I need help with casting with Zinc!!! posted by Dee on December 23, 1998 at 22:10:25:

Casting in Zinc you say? Best bet is to find some hands on experience as this is a

question with many directions and multiple answers.

I assume an alloy of zinc so it has better properties for strength and smaller

crystallization and ductility. You will probably find it under the heading of 'white metal'

and can be located in any scrap yard as many machine and automotive small parts were

cast in it (prior to plastics taking over more). It will be easy to melt and handle however.

Another question I would have is why Zinc? It will be harder to finish and patina and if

painting is the solution, why not others such as fiberglas casting, or etc. where molds can

be used more often and details can be precisely controlled. Open faced rubber molds

and silicone molds also come into play here.

For Zinc temperatures, I believe closed silicone molds could work but material costs may

be too high. I say this with reservations and will let others respond to this direction..

Almost any mold system you use for aluminum or bronze casting will work but of course

that is also more than is needed and again raises the question of why zinc over say

aluminum?. Check out all the posts relating to those mold systems for starters.

I normally do not cast it so anything I say here is open to and welcome for revisions by

others but since Zinc is such a low melt temperature in comparison you could get away

with simpler sand mold systems as well. This will probably be determined by the detailing

degree you're after.

As a minor introduction of some directions... you might look into these.

Either green sand (which is a fine sand mixed with a little powdered clay and a faint

amount of water for a moisture bonding, available at most foundry supply locations), or

resin or oil bonding or sodium silicate bonding sands will also work well.

The Resin bonding types usually require a good mixer (bigger foundries use a Muller)

such as a 1/2 inch drill and a good paddle or barrel type mixing shaft. This will handle

about 5 to 10 gallons worth at a time in a strong 30 gallon sized plastic garbage pail (or

equivalent). An ideal RPM on the drill is about 900 (plaster mixing drill by Milwaukee,

approx. $150.) but I also have success with one set up to 1200 (also by Milwaukee

Tools but in the form of a 1/2 inch Hole Haug drill that has both 300 and 1200 RPM

options, approx. $280.).

The resin / catalyst type mix in with the sand and then sets hard to a near rock like

quality. This can then be opened to remove the master model and closed again to pour.

If you want to save on sand, also put 1" open chicken wire in the mold body when

ramming it up. Also a plywood backing can save sand quantities.

The sodium silicate / sand mix is again a mulled mix but it will not harden until you inject it

with CO2 gas. We used to do that using a long hypodermic needle (on an air hose

coming from the tank of gas) the kind that you would use for veterinarian injections so it is

6 to 8 inch long and able to put down deep into the mold sand (which is soft on the way

in, hardens and leaves a fine air hole on the way out). Costs of this setup may be too

much unless you intend to do it often. Time to work with it can be an advantage

however.

And of course any of the ceramic shell, plaster /sand compositions, etc but these all need

a burnout and some knowledge of spruing and venting.

If you add further questions to your post you may be able to get more precise answer

directions. Good luck bpfink

http://www.fink.com/bpfink

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