Re: Air-set sand


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Posted by bruce paul fink on September 21, 1999 at 22:31:44:

In Reply to: Air-set sand posted by John Odom on September 21, 1999 at 16:57:00:

I'm sure you already know about this John, may just not recognize the term.

I'm not sure what he meant as his specific "air-set sand" either but assume it was a sand that used a binder that did not need any Carbon dioxide gas or heat or plaster or whatever to set it up for the sand binder.

Of these there are many.

One would be an acid catalyst mixed in with the dry sand and then remixed with an oil that would harden (due to the acid) and become the binder.

The one I use at times like this is Kensett by brand name but goes under many other brand names also. It is fast. To mull or mix in about a 5 gallon amount it takes about 2 minutes to electrically churn in the catalyst, and then another 3 or so minutes to churn in the oil and then you have about 10 to 20 minutes (depending on the amounts used and the temperature of the sand) to pack it around the piece before it sets up. I let it set up several hours to make sure it is fully hardened.

If doing a styrofoam model you can proceed with a direct pour in those standard directions like I know you already do,

or if it is a wax you can burn it out in your low heat oven like he mentioned. Don't use the kitchen oven though unless it is a throw-a-way and set outdoors... It's a real stinker.

It can be a little tricky. If the sand is heated too high it will also burn out the binder and become sand again but not by 400F. I believe there will still be a strong residue of wax in the cavity and it will be soaked into the sand investment now but you will get a pour with the hotter metal forcing it out the sand walls. We used to burn these out for a full day before pouring but don't let that heat get over 400. I don't do this system anymore as it is very polluting and stinks and really needs an afterburner in the exhaust stack as well, but does work... kind of... with some gas or porosity able to form in the metal from that less than totally gone wax residue in the sand .

I do use the sand binding system though and after being cast and when the molds are ready to be thrown away (by most others) I put the sand hunks in a steel bucket and fill some spaces in the next kiln firing at 900F with a plaster investment and burn off that oil (is now just more fuel really) and reclaim the sand... which is now also highly dry and ready for another mold. Hey this stuff can go for $15 to $25 per 100 lb. delivered if you are buying a good fine grade and why toss it out or even worse pay for some disposal charge to get rid of it.

There are other room temperature setting binders for this process also.

Sodium Silicate (also know as water glass and used once to dip eggs in to preserve them... this must date me for sure) can be mixed in with dry sand also and after being packed around the model gased with CO2 (we used to use a long horse sized hyperdemic needle gotten from a veterinarian). This also hardens the sand mold and feels like a rock. We never burned wax out of these but it must work, I don't know it's temperature breakdown range.

This sand system can also take higher temperatures for the pour so cast iron is also able to pour in these. I believe the molds used in the photos of the Southern University College web page you mentioned show those air set / oil hardened based molds for their cast iron pours. (They have a web page that shows the cupolette at work putting iron into moulds at the

web page. Go to Arts and Sciences, then Art, then Sculpture, then foundry.)

Hope this helps, there are others but maybe someone else with first hand usage can comment on them.


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