Liquid silicone rubber flows easily at room temperature and begins cross linking at very high temperatures. In the molding process, this could be anywhere from 350-400F. The high temperature not only transforms the material into a cross-linked elastomer which can stretch up to 600%, but one of the material’s key properties is its high temperature resistance. Once molded, the liquid silicone rubber is able to withstand up to 600F prior to degradation.
There are several applications which are heat sensitive and require an elastic but resilient material. For example, if you needed to over mold or encapsulate a heat sensitive substrate such as a polypropylene insert, flexible electronics component, or a wearable device. Another example would be molding a silicone connector on Pebax medical tubing which has a Vicat softening temperature below 200F, meaning the traditional molding process would melt the tubing.
The current solution in the silicone industry is an RTV or room temperature vulcanizing material. The RTV material can take anywhere from 1-24 hours to fully cure. RTVs also have a short pot life or working time once the two parts of material are mixed. Hence RTVs are never recommended in the injection molding process.
Once cured, the RTV material does not have the same mechanical properties that a silicone elastomer would have. Apart from being the most expensive material per pound, the RTV material tends to have the longest cycle time with the worst properties. Below is a basic comparison of the properties:
