About RTV-2 Silicone Rubber

Considerations for making a mold

1. RTV silicone rubber is white flowing liquid with general hardness of 22-40A° after curing.
2. If the mold makers want to make large products and large size molds, the mold should be made of silicone rubber with high hardness. On the contrary, if the products require fine and precision pattern reproduction, it should be made of silicone with low hardness.
3. The amount of the curing agent depends on the actual requirements of the customer. If molding requires fast drying and demold, more curing agent is needed. Contrarily, for molds requiring slower drying and demold, less curing agent is needed.
4. It doesn't hurt to add silicone oil into silicone rubber. If a special soft silicone mold or fine detailed and complex patterned products are required, 5-10% silicone oil can be added to soften the mold for easy demolding.

Advantages and disadvantages

Advantages

RTV silicone rubber has the best release properties of all the mold rubbers, which is especially an advantage when doing production casting of resins (polyurethane, polyester and epoxy). No release agent is required, so there is no post-production cleanup. Silicones also exhibit good chemical resistance and high temperature resistance (205 °C, 400 °F and higher). High temperature resistance makes silicone the only mold rubber suitable for casting low melt metals and alloys (e.g. zinc, tin, pewter, and Wood's metal). The combination of good release properties, chemical resistance and heat resistance makes silicone well-suited for production casting of resins. RTV silicone rubber can capture fine details of any surfaces, and the RTV silicone mold can be reused for hundreds of times.

Disadvantages

RTV silicone rubbers are generally high in cost - especially platinum-cure. They are also sensitive to substances (sulfur clay 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 thanlatex). 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.