Re: pour finish on aluminum.


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Posted by bpfink on November 05, 19100 at 11:56:55:

In Reply to: pour finish on aluminum. posted by John T on November 01, 19100 at 20:25:24:


I'm not sure what you mean a 'pour finish'.

Or is it a misspell and means a 'poor finish'?

In either case, a "metal casting plaster" of course is not just a special plaster name but a combination of molding plaster with approximately 60% fine sands or sand flour (looks like plaster also but if mixed with water it will not set up of course).Straight 100% plaster will not work at all due to the need for the 'burnout' as it will craze and crack up into many small pieces. That is one of the reasons for the sand addition making it a 'cement' with better strength and degassing attributes.

So if you are then talking of 'drying' it or 'heating it up enough' what do you refer to?

In all cases you have to remove both the mechanical water that made it flow, AND the chemically combined water that let it set up. (This is somewhere between 700 degree F for a long time, or a higher temperature for a lesser time). The later H2O amount is very small but if not removed or reduced to a very low level hot metal flowing into the mold will release it and cause steam gas and either blow the metal back out, or at least cause it to boil and pit and screw up on the surface. The metal does not boil, it's the moisture being released.

SO if these are the things you refer to, read on and do a Search on our files for 'burnouts', 'investments', 'kilns' , etc.

It is all here and explained in great detail.

Or are you talking about an open faced mold and the lack of a depth for gravity is just not taking a good impression?

This isn't rocket science, but is akin to alchemy and you will love what you find. bpfink

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