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Types of RTV Silicone Rubbers

rtv silicone rubber

Condensation-curing RTV silicone rubbers (Tin catalyst)

These cure at room temperature after addition of catalyst, volatile alcohols being liberated during the reaction. Shrinkage occurs, which is completed after about a week. Although heating can speed up the vulcanising process, this is not very effective. The temperature should under no circumstances exceed 70 oC. It is also most important that freshly made moulds, i.e. which still contain the alcohol produced during the curing reaction, are not subjected to temperatures higher than 80 oC, since this would cause a loss of elasticity and softening or stickiness of the RTV silicone rubber (see also Mould pre-treatment).

 

Addition-curing RTV silicone rubbers

These vulcanise without the formation of reaction products, so that there is practically no shrinkage. The cured rubbers can therefore be used immediately after they are fully cured. Vulcanisation can also take place at higher temperatures (up to 200 oC), which greatly reduces the required curing time. In this case however, one must take the high coefficient of thermal expansion of silicone rubber into account.

 

Note: Cleanliness is especially important when processing addition-curing RTV silicone rubbers, since the platinum catalyst can lose its power through contamination. Catalysts used for condensation-curing silicone rubbers, for example, can interfere with vulcanisation already in small amounts. Furthermore, vulcanisation of addition-curing rubbers can be delayed or completely prevented if they are in contact with certain materials such as natural and synthetic rubbers, PVC, amine-cured epoxy resins, plasticine, adhesives, soldering tin etc. Preliminary tests are therefore vitally important.