Rhodia Silicone Rubber
Rhodia’s Room
Temperature Vulcanizing, or RTV Silicone Rubbers are used
extensively for applications where a flexible mold material
is required. Silicone rubber compounds, by nature, are not
only flexible, but are also self-releasing and therefore
make an excellent choice for a variety of mold
applications.
Known throughout the industry for its quality and
consistency, Rhodia’s line of silicone systems features low
shrinkage, high heat resistance, outstanding
wear-resistance, and excellent tear strength and elongation
properties which ensure a more accurate, longer lasting
tool than most competing lines.
There are two types of silicone rubber: addition cure
rubbers, which are platinum catalyzed, and condensation
cure rubbers, which are tin catalyzed.
Our most popular addition cure rubber is
Rhodia V-340, which offers a choice of
catalyst for either a 45 or 55 shore A hardness.
Typically harder in durometer than condensation cure
rubbers, these materials feature an unlimited library life,
very low shrinkage, and are often the easiest rubbers to
create molds from, which is why they are demonstrated
extensively in our instructional videos.
They do, however, experience a greater cure inhibition with
materials like sulfur-containing clays, vinyl, and woodsap,
which we will demonstrate here, with a circular dam of
non-sulphuric clay built on top a block of sulphuric clay.
After pouring V-340 in this mold, we allow it to cure
overnight. Upon demolding, notice how most of the rubber
has cured, including that which came into the contact with
the non-sulphuric clay. The bottom, however, is still wet.
And even after sitting an additional day, it still fails to
cure, proving that proper sealing and releasing of
sulphuric clay, vinyl, and wood is essential when using
addition cure rubber.
Freeman also offers five other Rhodia addition cure rubbers
to meet various hardness and wear resistance requirements,
including V-3040, a translucent rubber
ideal for
creating molds with complex parting lines.
The other type of silicone rubber, condensation cure
rubber, is typically softer in durometer, which makes it
ideal for molds with deep undercuts.
Here you see V-1065, our most popular of the
seven formulations. This rubber can be accelerated
chemically and is less prone to cure inhibition when
being poured against materials like clay, vinyl, and
woodsap.
However, unlike addition cure rubbers, these materials do
have a limited library life, so a mold that was created two
years ago won’t have the same tear resistance as a newly
created mold.
Also, you do need to be careful when pouring certain
urethanes into molds made from these materials. To
demonstrate, we’ve made a mold out of V-1065 and in it
we’ve poured our FMSC 1040 flexible urethane.
The next day, we get a clean release, but the surface of
our part is sticky and the surface of our mold is still
wet. Even the following day, the part still hasn’t cured,
and in fact will never fully cure.
Most urethanes will work fine with condensation cure
rubbers, but since these exceptions do exist, we normally
recommend this chemistry for polyester castings and we
recommend addition cure rubber for urethane castings.