Liquid Silicone Rubber (LSR) is often utilized for seals, valves and diaphragms, due to its high elongation (between 400 and 700% at room temperature) and tensile strength over a wide temperature range. The tensile properties of thermoset rubbers and thermoplastic elastomers need to be measured/tested in order to verify that the quality control standards of Silicone Rubber Liquid are met, as well as to determine whether or not the material is fit for its purpose. The test should be performed according to ASTM D412, which describes two test methods: A and B.
The density or its reciprocal, the specific volume, is important for the shrinkage during processing and is greatly affected by temperature and pressure. The specific volume is often plotted as a function of pressure and temperature, in what is known as a pvT diagram (see image on the left below for an example of a pvT diagram). The measurement is defined in ISO 17744.
Injection molding of Liquid Silicone Rubber (LSR) has existed and evolved over the past 20 years. Due to the thermosetting nature of the material, injection molding of liquid silicone rubber requires special treatment, such as uniform distributive mixing; in addition, the material must be maintained at a constant temperature up until it is pushed into the heated cavity and vulcanized.