Bramblebush ForumsFAQ
Posted by bruce paul fink on January 03, 1999 at 11:55:55:
In Reply to: Ceramic Mold posted by Mark on December 28, 1998 at 22:26:26:
Not familiar with that mix. If you don't get a response here soon more info on it might give us an idea of it's nature. Got a URL for the company, product, etc.?
Meanwhile... the Petrobond can give a very fine detail but this all depends on the methods of casting, moldmaking, etc. as well. The fineness of the sand will start to be the key but I have used very course backup sand (brick sand... air dried... able to degas any residues of the model much better as they can escape right out the investment body)
with a fine direct contact sand and
even a fine surface facing of a silica, clay, flour mixed with alcohol and surface sprayed, or brushed (but this can leave brush marks so spraying is better) to give very fine detail surfacing.
Next thing to consider:
is this an open working mold system (such as might be found in a relief casting or a parted mold than could be opened to remove the model) where you can surface spray the alcohol mix and then stick a match to it to flash dry it...
or is it a closed / burnout mold where you have sprayed or brushed (no brush marks this way as the sand backs up the marks) the finner alcohol seal on the model body (NO flash burn this time).
AND YES you can burnout Petrobonded sand but NOT with the regular high 900 to 1400 F temperatures of plaster or ceramic shell molds. I have done it quite often when necessary but would prefer the other investments over this if possible, they are more forgiving.
To burn out an oil / resin bonded investment you can not raise the temperature to any point over the bonding resin abilities or you will be back to a pile of sand. Actually, before the pile comes there will be a general surface breakdown and there goes your detail again. So all-in-all I will not recommend this system to the beginner, but I do use it often myself.
If you do try this, the wax or foam plastic body will not be totally removed as the temperatures must remain nearer to 400F or slightly above, and it means that a wax residue will be still in the sand, and that is okay to a limit as the sand is a more forgiving gas release body and the metal will tend to chill and not blow back out...
see the new conditions that become challenges... but it does work. Just takes a lot more understanding of the brew that is hidden below the surface.
And here we go gang... COMMENTS ANYONE?
this is a great open forum for all those other tried and true and worked and failed experiments beyond what the manufacturers will have promoted. And what is this CERAMACAST 673????
bpfink
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