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The CraftSil-750
series come as a two component system Part A base and a Part B accelerator
which after mixing in the proper ratio cure at ordinary room temperatures
to a flexible, strong RTV (room temperature vulcanizing) silicone
rubber. CraftSil-750
is what is known as a tin-catalyzed, condensation-cure RTV system.
After mixing they gel in one to two hours and cure within 24 hours. The properties that attract most users to silicone is that
it does not shrink as it cures. It also can be cast quite thickly and is
safe, often used in medical applications. It has the ability to retain very fine detail. Fortunately
most solvents do not attack silicone. However one of the most important
features is that almost nothing will stick to silicones. This simplifies the mould making procedures in that no
release agents or model pre-preparation are usually necessary. In fact the only reason why you would not use silicones
for most of your mould making functions is cost. If your silicone costs are
high, examine the use of polyurethane as an alternative. What can you
cast into a silicone mould?
Silicone moulds can be used for casting polyester resins,
plaster, hot melt vinyl, cement, wax, and special types can be used to cast
low temperature melting metals such as pewter or lead. For reasons of cost,
plaster and cement are almost never used with silicone moulds. It is also the preferred mould material for casting polyurethane
plastic resins such as CraftCast
but should be left for a week before using. Safety
Silicones are safe to use if directions are followed.
Avoid contact with your skin or eyes as irritation may develop. In case of
eye contact flush with water for 15 minutes and then see a doctor. Use in
well ventilated areas. |
How to prepare
the model
Sealing a porous model: Although silicones will
not usually stick to other materials, some porous materials such as plaster
or wood need sealing to prevent silicone embedding itself in wood
pores and preventing mould removal from the model. Seal porous models with several coats of CraftSeal an
acrylic based aerosol spray. Release agents: Release agents are not usually
required when making silicone moulds from properly sealed models.
However if in doubt lightly smear the model with petroleum jelly (Vaseline)
being careful to leave no fingerprints. We use CraftRelease
20 which is petroleum jelly dissolved in a solvent that allows
us to spray on the release- which evaporates rapidly and leaves a
thin layer of petroleum jelly. Some surfaces will inhibit the cure of silicones such as sulphur based modeling clays. It is
always a good idea to make a test if the surface of your model is in doubt. Making the mould
Weigh the two parts accurately before mixing. Slowly and
thoroughly. The colour will indicate
when you have an even mix. Scrape the sides and bottom of the container. Do
not mix air into the mixture with a whipping or up and down motion. Pour the silicone over the model in a thin stream
from as high as is comfortable and let it flow over the model. Air bubbles
will break up if you pour in a thin stream. Break any bubbles that surface with a pin or needle. Allow
the silicone to sit undisturbed for 12 to 24 hours. Making a mould
by brushing silicone
Silicone can be used to brush on a skin mould over a model
by thickening with CraftThix to a non-sag viscosity. This is sometimes used
as a cost saving alternative to a solid pour. Casting
Release agents are not usually required when using
silicone moulds. You can purchase CraftSil-750 on our Ebay store. Click here for more information |
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Copyright 2006 Aldax industries Pty Ltd
www.aldax.com.au