Re: Investment for lost foam


Bramblebush ForumsFAQ

Posted by bpfink on January 28, 19100 at 07:46:55:

In Reply to: Investment for lost foam posted by Jeff Krueger on January 27, 19100 at 23:23:57:


Better just read down the listing here a little while longer.

Straight plaster will not work at all since it will crack up in the burnout and give you so much flashing that the piece will be worthless at best. Roughly a 50 % / 50% plaster sand mix is needed and there are hundreds of more precise formulas for exactly what the percents and sand types should be.

How are you planning to get rid of the foam? In a lost foam pour there will be lots of gas and fumes to burn out so a plaster based mold is not the best unless it is first burned out.

You do know you have to burn it out yah? Even if it is a mold that opens to remove the model form the moisture in the plaster will turn to steam and violently blow that metal right back into the air (and maybe hit the ceiling and splatter your whole studio like molten rain). And please don't think that the feel-good-dry or sun baked system is really dry since it is the chemically combined water that is going to be the blow out surprise steam critter. The burnout needs to be at least 500 F but I personally consider 700 F the minimum. The plaster based investments are not porous like the green sand or bonded sand systems so a little moisture potential is a bad thing here... it can NOT be exhausted out the sides of the investment body like with those open porous sands.

You are playing with some potential major dangers in this process so don't be too enthusiastic until you are better versed with the whole process... and it is covered right here on these pages but you better do the reading.

Good luck bpfink

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