Advantages and disadvantages
RTV silicone rubber has excellent release properties compared to mold rubbers, which is especially an advantage when doing production casting of resins (polyurethane, polyester, and epoxy). No release agent is required, obviating post-production cleanup. Silicones also exhibit good chemical resistance and high-temperature resistance (205 °C, 400 °F and higher). For this reason, silicone molds are suitable for casting low-melt metals and alloys (e.g. zinc, tin, pewter, and Wood’s metal).
RTV silicone rubbers are, however, generally expensive–especially platinum-cure. They are also sensitive to substances (sulfur-containing modelling clay such as Plastilina, for example) that may prevent the silicone from curing (referred to as cure inhibition). Silicones are usually very thick (high viscosity), and must be vacuum degassed prior to pouring, to minimize bubble entrapment. If making a brush-on rubber mold, the curing time factor between coats is long (longer than urethanes or polysulfides, shorter than latex). Silicone components (A+B) must be mixed accurately by weight (scale required) or they do not work. Tin catalyst silicones shrink somewhat and do not have a long shelf life. Certain types of RTV release acetic acid during the curing process, and this can attack solder joints, causing the solder to detach from the copper wire.
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