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Casting Blanks

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Posted by Stephen Campbell on January 27, 2001 09:18:11 UTC

I am currently in the design stage of a casting kiln, i have found some useful information on the web relating to this subject. it will be constructed as follows: casting chamber 25" x 25" x 6" deep, 3000F rated firebrick enclosure,kanthal heating elements(all elements on top above mold),digital pyrometer,programmable microprocessor controlled temp control(important for annealing)firebrick will be covered on the outside with aluminosilicate fiber,and the whole firebrick enclosure will be inside a sheet metal box.
Pyrex has the viscosity of cold honey at 2,192F,after several hours at this temperature it will conform to the shape of the mold,im trying to figure out if this kiln design can produce a maximum 2350F with the elements running on 120v ac at around 25-30 amps, the depth of the chamber is only 6", and if properly insulated it might just work. i know that the depth of the firing chambers on all glass fusing/casting/annealing kilns are around 6"-9".
i plan on using either pyrex 7740 rod, or sheet cut into strips and loaded into aluminosilicate mold,in fact i might even start off with soda-lime glass which has a working point of 1832F just to practice with.
One thing ive been having trouble finding info about is the construction of the aluminosilicate fiber mold, i found suppliers of this material,but can't find any mold making info.
I realize annealing is the hard part of casting blanks,the annealing "range" is around 1049F, and the temp is reduced by 0.5 degree per minute over a period of several hours,other problems are devitrification,bubbles, and straia which i have yet to research.
I have decided to put-off building a vacuum coating system for awhile,seems a little too difficult and parts are hard to find, for now im going to put all my effort into building a casting kiln.

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