terry sullivan on wed 7 may 03
There is a technique using comprssed air, not vacuum, for quick release
of plaster mold pieces. One blows the clay form out of the mold
regardless of how wet the plaster mold is.
This is basicaly a derivation of systems used for Ram Pressing.
I'll give the system here and, if you email me personaly, I will lead
you through it.
This process allows the casting of the plaster mold and almost immediate
press molding of multiple units.
The process:
1. Make the clay positive of the tile or shallow relief piece out of
wet clay.
2. Make a frame out of 2x4, or larger, to fit a square around the piece
with at least 2 inches extra on all sides. Just screw this together with
long deck screws.
3. Drill a hole through one side of the frame to accept the threads of a
standard compressed air fitting. These fittings have a "female" screw
side opposite the snap on pressure side. It isn't made to screw into
wood but it will. Just screw it into the wood from the outside with the
snap on fitting projecting out of the frame.
4. Place the frame over the tile, or shallow form, with equall clearance
on all sides. About 1-2 inches will do.
5. Make a wire mesh cover over and around the piece . Use 1/4 inch wire
mesh. This will be suspended over the tile about 1/4 to 1/2 inch
clearance from the tile, and inside the frame. An easy way to do this
is to put little finnish nails into the frame on the inside that the
mesh can be supported by .
6. Now one takes a special product which is a 3/8 inch cotton rope that
is hallow, it is a tube. Starting at the middle of the mesh, you hot
glue gun the cotton tube in a spiral from the center to the outside to
the mesh ( I'll give information on this cotton tube later). Lastly; you
stick the end of the cotton tube into the hole drilled through the frame
that has the pressure fitting on the outside and hot glue it to the
frame.
Ok, what you have is, say, a clay tile wet or leather hard, on the
base. A frame of wood around it with about 1-2 inches clearance. A
suspended metal mesh over the piece ( you want it to be about 1/2 inch
above the piece all around) . And this cotton tube glued to the mesh and
leading into the hole in on side of the frame to the pressure fitting.
7. Now you pour plaster into this frame mold and "skreed" it flush with
the top of the frame. You have now invested the original tile, or
shallow bowl, along with the wire mesh and the cotton tube.
8. As soon as the plaster has taken its set and is hard but still quite
warm; you couple an air hose to the outside fitting and apply about 20
lbs. pressure. Turn the mold/frame on its side over a sink so that the
water bubbling out of the mold can flow and drain and wash it with clear
water using a light soft sponge.
Every minute, or so, increase the air pressure by 10 lbs. and continue
to wash off the surface of the mold with water. The originanal clay
piece will have popped out of the mold on the first step. Keep up
this process until the pressure is about 60 lbs. air pressure. This
all takes about 15 minutes.
9. You now have a plaster mold that is clean.
10. Now you can set the mold upright and press mold the tile in fresh
clay into it right away. You can pound in the new clay and skreed off
the excess. Use all the pressure you want to press the clay into the
new wet plaster mold.
11. Once the new clay piece, usually a tile, is pressed into the mold
and the bottom has been skree'd off, just flip over the mold and apply
about 40-60 lbs. of air to the fitting and the piece will pop out when
you lift the mold off the casting.
I have used this process to make a tile, make the pressure mold, and
make multiple castings all in an afternoon. Doesn't matter that the
plaster mold is wet from previous clay castings as the air pressue
releases each piece no matter how wet the plaster mold is.
This is a "low tech" version of the high tech ram press mold process. I
have personaly used this to form 60 tiles from a single mold in an
afternoon.
The one item is finding the hallow cotten tubing. I've got about 60
feet of the stuff and will have to look through my records for the
supplier.
Yours, Terry Sullivan
Nottingham Arts
Personal email address: go2tms@cox.net
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