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Powder separated molds

I’ve been experimenting many problems when separating molds with the
cutting system,I’m no good with the knife and I’m sick and tired of
messing up molds specially with the parting line,the wax seems to get
trapped once it’s injected and difficulting its extradition. Can
somebody please explain in more detail the powder separation system?
Do I have to add the talcum to the first half when the model is in
place or before to put the model? Thanks


Hello Marco; You might try working with the “silicone” type mold
rubbers. These are like a putty (not like the sheet rubber), and you
pack them into the mold frame. You use “locater buttons” which are
small brass cones with little prongs on the bottom. You pack the
mold frame half full with the mold compound, then stick a locator
button in each of the corners, dust the surface with parting powder
or talc, press your metal model down halfway into the rubber, and
pack the mold full to the top of the frame. Then you vulcanize at
350 degrees farenheit for about 45 minutes per inch of mold
thickness. When the mold is cured and cooled down, simply pull the
two halves apart. This is a bit of an oversimplification, but you
can get the material from any supplier of Castaldo products and
usually there is an instruction sheet accompanying the material. I
believe we have a representative of the Castaldo company who posts on
Orchid, and I’m sure if he reads this he will be intersted in
directing you to a solution to your problem. Good luck.

David L. Huffman

Marco, I assume you are using heat vulcanized molding materials. If
so, I have found the best results when I use the putty type rubber
(vs the firmer “regular” material) and I make the first half, push
the piece into the putty to the level you want it with the filling
unit going to the outside of the rubber, dust, push the second half
of the rubber onto the first and over the partially piece and filling
unit and vulcanize.

After having said that, I would HIGHLY recommend that you look into
RTV molding materials. We have the vulcanizing equipment and all but
only use RTV materials now.

My 2� worth!!!
John Dach

Marco, David is right.I have been using a product called moldex.It is
sold through Contenti Company in Providence,RI.Their # is
1-800-343-3364.I rarely have to cut a mold except in cases that have a
lot of undercuts.Best J Morley Coyote Ridge Studio.

It’s hard to improve on the always excellent info provided by Dan
Grandi, but I have to weigh in as a light-weight. The absolutely most
wonderful tool for a female with small hands is that silicone rubber.
Never again would I use the old type. Now, I just wish manufacturers
would get it and supply those of us who don’t have man-size hands
with safe to use smaller heat-proof gloves. The giant ones are
hazardous for me to use. But I’ll never have to worry about scalpel
cuts. Thanks to you all for taking precious time to help the
less-knowledgable. Pat @Pat_Hicks

Hi Pat, Thanks for the ego boost… you mentioned

     Now, I just wish manufacturers would get it and supply those
of us who don't have man-size hands with safe to use smaller
heat-proof gloves. The giant ones are hazardous for me to use. But
I'll never have to worry about scalpel cuts. 

I don’t use gloves at all… We use a wide , bent heavy duty plaster
scraper to loosen and remove the mold from the vulcanizer. We do use
the special wax paper that comes with the contenti rubber on both
sides of the frame so that the rubber does not get stuck to any metal
on the vulcanizer. We always cut the paper slightly larger than the
frame so that when we remove the frame and put it on the table, we use
the scraper to hold down the frame , then we pull the paper off the
frame on one side, flip it with the spatula, remove the other piece of
paper, then with the scraper,pick up the frame and dunk it in water.
Heat cured silicone rubber has more tear strength if you open the
mold when it is cold…Also… easier to deal with.

Also, we use the scraper to remove the exess rubber before
vulcanizing and after the paper is removed, I use the scraper to
scrape any excess rubber that may have oozed onto the frame during
vulcanization. Pres down reasonably hard with the sharp edge bearing
down on the aluminium frame and push across the frame… you will see
that the scraper removes all the excess and leaves you with a clean
top and bottom to your frame.

Next, use the scraper to slide down the inside edge of the frame …
all the way around . this will break the seal of the rubber against
the inside of the frame and make it easy to push the rubber out. I use
a thin , flaxible scraper for this last operation.This is also done
when the frame is cold.

If you do use the paper supplied with the rubber, make sure to put
the shiny side against the rubber, or the paper will stick to the
rubber. If the shiny side sticks to the rubber and is difficult to
remove, check your vulcanizer temperature as it may be to hot.

Daniel Grandi