Hi Terry and Ted
Thank you very very much for your detailed answer. Really a fantastic info
and help to me. It is not the quality of the various RTV-Rubber´s that
gives me problems, but the amount of work involved creating such molds
combined with the constant fear of poor results due to "underbleeding" or
poor fit of the resulting mold parts.
I wish to produce 54 mm and 70 mm figurines for a special collector´s
market. Nothing unusal but I have to cast the figures in "one piece" not
like the available multi-part resin model kits of figurines. I am aiming for
a injection cast look of my figurines just like the soft plastic products of
various makers on the toy market.
I finally solved the beginner´s problems of pressure- and vacuum-casting as
well as mold design. Promising results so far but the RTV-molds still do not
really suit my needs. I also tried blockmolds which I cut to create the two
mold halfs, tried clear RTV for that as well but given the amount of work
and the prices of various rubbers - it still does not give me the results I
am searching for. I do not spincast my molds. My "masterplan" would look
like this: Creating a square mold of a master figurine in the vulcanisr (a
table model like Romanoff´s since working space is a issue as well) than
cast 6-10 copies, leaving the venting sprues etc. intact and do another mold
of those figures which will hold 6-10 figurines. Thus resulting in a
economic and affordable "mass-production-mold(s)".
I will give another variant a try this week. I constructed a wooden mold
frame , top plates made of steel and a simple hydraulic press. I will try
and use some kneadable dental rubber on this project trying to simulate the
vulcanising effect. I will "sandwich" the master between two talc dusted
portions of the rubber inside the wooden frame, put the steel plates on
bottom and top of the mold frame and apply pressure, I drilled small hole
into the wood frame to evacuate surplus rubber from the mold . So far for
the theory, no idea if it will work and how the rubber will react with the
resin but I will give it a try .
Thank you for your help
Von: Terry Wellman [mailto:mwhirailer@...
Gesendet: Mittwoch, 2. März 2005 07:22
Betreff: Re: [casting] Re: materials question
We spin resin in vulcanized molds on a regular basis. Despite the learning
curve, it is entirely do-able. The main concern is the quality, condition,
and geometry of the prototypes that you wish to reproduce.
We have used several brands of rubber and silicone disc sets before settling
on Chardan Ltd. of Attleboro, MA for our organic rubber discs. They have
several black organic rubbers that work well. I like their 100, 145, and 180
series organics. I am awaiting a sample of their 300 series to try out this
week. It is a softer more supple rubber that works well with high detail
prototypes. I'll let you know how it works on the parts that I want to try
it with. Chardan's number is 1-508-226-2708. Charles Katsanos is the owner
and Lee is his sales rep. Good people to deal with.
We tried the Millenium brand of silicone discs with some success. They're ok
but I like the Romanoff Silcast silicone discsets better. The Milleniums
seem to have a sweet odor that tends to permeate the shop. Yecch! ;-) The
Red Silcast works well.
At some point we'll try the Nicem line of silicone discs. I like to try
different products in order to stay on top of things and find the best
materials to handle our requirments. Once we find something good, we tend to
stick with it. Contenti Company carries Nicem. 1-800-343-3364.
We vulcanize 9" and 12" molds in several different frames. I believe that
our current frames are 1", 2", and 4" for 12" discsets along with 1", and 2"
for 9" discsets. Normally we vulcanize between 310 and 320 degrees F for 60
minutes. I usually preheat the frames before dropping the discs in.
We also make spin molds with RTV too for more difficult and fragile parts.
The issue here is labor as you now have to clay in the parts, make sure that
you've got clean parting lines, registration nuts, pour, wait 8-12 hours,
flip it over, clean out the clay, spray with Parfilm 4 as a protective
barrier coat then pour the second part of the mold, wait yet another 8-12
hours, pry open, demold the masters, spray both halves with Parfilm 4 again,
heat up the halves, then spin. Of course this is the simplified version.;-)
Typically we're spinning them between 75-450 RPM, 80 PSI, 5 minute cycles
with two minute post cure settings on the spinner. For resin, we're spinning
with Alumilite's RC-3. It mixes very well and pours like cream into the
spinner. With a 3-5 minute gel time, it works very well for us in this
application. There are other resins out there to spin with. This is our
preference. Be careful spinning filled resins. One company advertises
aluminum filled resin for spinning. As this is a centrifugal operation, any
filler is likely to find its way to the outer edges of the mold cavities
while leaving the inner edges to just resin. There is a misnomer out there
about spinning with fillers. Yes, it can be done but you need to spin at a
slower RPM. You might find that you need higher RPM to completely fill your
cavities depending upon their geometries of course.
When spinning resin, you won't need the pour funnel on the top of your
machine as you don't need to worry about aiming the metal into the center
gate. Resin pours pretty straight into the machine.
One issue to keep in mind is the pressure level on the spinner. You want to
insure that you have enough pressure to keep the two mold halves sealed in
order to reduce the chance of resin spraying our of the seam onto the wall
of the spin caster. Ask me how I know this! ;-) We have had times where we
didn't have enough pressure on a mold during its first cycles and could hear
the resin hitting the wall of the tub. It's like a short but heavy
Hope this helps,
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