RTV Silicone
Room Temperature Vulcanizing or RTV silicone was first developed in the late 1930’s as an insulating material which could withstand the heat produced by smaller engines, but it is used today primarily to make durable, easy to construct and use molds suitable for a wide range of casting materials. It is also used today in the electronic industry for potting and encapsulation because of its superior ability to maintain its properties through a wide variety of environmental conditions.
The entertainment industry has risen to new heights thanks to the scenes and characters that come alive on television and movie screens, in theme parks, and haunted houses everywhere thanks to the development of RTV soft “skin” silicone rubbers specifically formulated at the request of special effects studios. The platinum cure silicone is also used in the medical field for prosthetics and other specialized uses.
An ideal mold-making rubber perfectly suited for making strong, flexible custom resin molds with good directional stability and good elongation and tear strength, this silicone rubber accurately duplicates the finest of details and is great for undercut parts. RTV silicone is available in both condensation (tin catalyzed) and addition cure (platinum catalyzed) formulations, both of which are comprised of two-components which must be mixed for activation. Some sulfur-containing clays can inhibit the cure of tin (condensation) cure silicone.
The two components of RTV silicone are usually referred to as Part A, the silicone component, and Part B, the catalyst component. Part A is a liquid medium with a medium viscosity. Side B, the catalyst, is usually of a different color—it is fully mixed when there are no more streaks.
Because of the complexity of creating some custom molds, it is good operating procedure to fully read the manufacturer’s instructions and complete as much of the mold-making construction and process as possible before mixing the two components.
The uses of RTV silicone rubber can be further enhanced with optional additives. Silicone thinner is a clear silicone fluid that lowers the viscosity of the RTV silicone when added. This makes it thinner and is used to create a bubble-free skin coat prior to adding thick coats of the silicone rubber. It is important to follower manufacturer recommended ratios, and it should be noted that the thinner will increase the working time even as it reduces the final hardness and tear strength of the mold.
Sometimes it is necessary to brush the silicone rubber on to the artifact being molded, rather than pouring it. Mixing in a thixotropic additive will increase the viscosity of the silicone from a slow flowing liquid into a paste with the consistency of peanut butter. This allows it to be brushed on vertical surfaces and to be used for glove molds.
ResinObsession carries a full line of RTV silicone rubbers for your custom mold-making needs. All of the RTV silicone formulations carried by ResinObsession’s online store are easy to use, have a 10:1 mix ratio, low viscosity, which means fewer bubbles, and do not require vacuum degassing. The open and demolding times vary by formulation to suit the time requirements of different projects. http://http://www.resinobsession.com/silicone-mold-rubber-putty-c-31.html
