Rhodia Silicone Rubber

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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.