Silicone Mold: Silicone Rubber Properties Explained

Mold making is an expensive business. This makes it all the more important to have precise knowledge of the available moldings, their properties and processing. If you have read this information, choosing the right epoxy resin casting compound is no problem.

Mechanical Properties

Vulcanized products made from RTV / NV and HB silicone rubber have only moderate mechanical strengths. This property should be taken into account when designing the shape.

Very strong undercuts, which lead to overstretching during demolding, must therefore be avoided. With correct construction and careful handling of the molds, very long service life can be guaranteed.

Physiological Properties

Silicone rubber RTV is chemically inert and physiologically harmless so that no special precautionary measures need to be taken when handling the rubber and the vulcanizates.

Since silicone rubber crosslinkers contain organometallic compounds, direct contact (of the crosslinker) with the eyes or mouth must be avoided in any case.

Storage of Silicone Rubber

If possible, silicone rubber RTV and silicone rubber crosslinkers should be stored in their original containers up to a maximum of 25 ° C. RTV silicone rubber that has been stored for longer than the specified time can still be used in most cases. However, it is advisable to test the functionality with a small amount before use. Do not use gelled crosslinker anymore. In the case of long-term storage, the filler can settle in the case of low-viscosity types, but this can be easily remedied by stirring well with a clean tool.

Adhesion And Bonding

Silicone rubber RTV adheres very well to a vulcanizate of the same type with a dry and clean surface. Only silicone adhesive (one-component silicone rubber) is suitable for bonding vulcanized RTV silicone rubber to another material. The parts to be connected are coated thinly with it and pressed together.

The bond is resilient after approx. 24 hours. Damage to molds made from RTV silicone rubber can also be repaired with a silicone rubber of the same type. To do this, the damaged area is poured in with silicone rubber RTV containing crosslinking agents or the parts are glued together. The parts to be connected must be cleaned with a solvent before gluing.

Separation Of Silicone Rubber RTV From Silicone Rubber RTV

Very often it is necessary to pour or coat objects made of silicone rubber RTV vulcanizate with fresh silicone rubber RTV without any adhesion between the two parts (e.g. multi-part casting molds). To prevent this, the surface of the hardened vulcanizate is coated thinly and evenly with Vaseline or mold release agent from Hobby-Time. Then the next molding can be painted or poured on immediately. Demolding is then problem-free.

Removal Of Silicone Rubber RTV

Since unvulcanized residues are difficult to remove, care must be taken to work correctly. Drip residues can be vulcanized, after which they can be easily removed from the vessels. It is advisable to wear suitable work clothing when working with RTV silicone rubber.

Processing And Vulcanization Times

The processing and vulcanization time depends on the silicone rubber RTV type, the amount of crosslinker and the room temperature. Guide values ​​at 20 ° C.


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