How to deal with the shrinkage of the silicone rub...

Silicone rubber is a kind of rapid molding materials, which are widely used in the RPM technology, and it can replicate products of large quantities. Silicone rubber can be used in a wide temperature range of-50~350℃, and has a natural mold release properties, not easily bonded with other materials.   As a flexible mold, silicone rubber also has certain application in RTM. Compared with the traditional mold, silicone rubber mold has a short processing cycle (usually a day can be completed), low cost, high accuracy, more easy to release (without considering the draft angle), etc., but there are disadvantages of low intensity, low-turnover times, easy to shrink and other shortcomings. In this article, we make some exploration about how to deal with the shrinkage of the silicone rubber.     Some dates prove that the shrinkage of the silicone rubber vulcanized at room temperature can be controlled within 1%, but in the practical process, we found that the shrinkage of the silicone rubber is about 1.8% or so. At the same time, in contrast to the shrinkage of the silicone, the phenomenon of expansion will be also occurred in the interior of the mould in some occasions, such as pouring unsaturated polyester into the silicone rubber mold. So, what on earth is affecting the shrinkage of the silicone rubber? There are mainly the following three factors.   1. The amount of the curing agent Mold silicone rubber generates a low molecular weight alcohol during vulcanization, which is the fundamental cause of shrinkage of the silicone rubber. Meanwhile, the excess curing agent can escape from the mold, so, the mold shrinkage increased. Therefore, the larger the amount of curing agent, the shrinkage of the silicone is quicker. For this situation, you should deal with shrinkage of the silicone by adjusting the proportion of catalyst determined by the size of product, the ratio of silicone rubber, and operating temperature. Usually, we add 2 g curing agent into 100 g silicone rubber under room temperature 25℃. If the dosage is too little, silicone rubber can't meet normal levels of vulcanization. While, adding too much catalyst, it will meet a decline in the strength of silicone rubber and increase in the shrinkage of the silicone rubber.   2. Type of diluents The shrinkage of the silicone rubber is also affected by all kinds of diluents. When used, it is often necessary to add a certain amount of diluents. Silicone oil is a good material to lower the viscosity of silicone rubber, and can ensure stability of the size of mould. However, someone use mineral oil or toluene solvent to dilute the viscosity of the silicone rubber in order to reduce costs, it will cause large size shrinkage of the silicone rubber. As mineral oil and silicone rubber has low compatibility, which is likely to precipitate, the more the amount added, the greater the shrinkage. In the process of mould making, we cannot use the material such as white oil, toluene instead of silicone oil to dilute silicone rubber; otherwise it will lead to the shrinkage of the silicone rubber mold.   3. Swelling behavior of silicone rubber mold If we use the unsaturated polyester resin to turn over a rabbit model, with the increase of modulus, the rabbit's ears will gradually become smaller and thinner. The reason is that silicone rubber is in constant expansion, resulting in the cavity space is slowly getting smaller. But if you use the plaster or paraffin to perfusion, such a problem does not occur. Therefore, in actual operation, you should promptly release once the resin hardened to reduce the contact time of mold and styrene. Also, please note that there is a certain time for mold to rest to make the solvent escaped from the mold, which is also an effective way to deal with mold expansion and shrinkage of the silicone rubber.   If you want to get more information about how to deal with the shrinkage of the silicone rubber, please contact us at e-mail: info@szrl.net or tour our website:http://www.szrl.net, thank you!