Silicon molding services produce molded components made from silicon. Silicone rubber is a two-component, synthetic, flexible rubber like material made from silicone elastomers that can be cured at room temperature into a solid elastomer used in molding. It is heat resistant, durable and free of allergens or leachable chemicals. Liquid silicone is similar to normal silicone, but has different processing characteristics. It is purchased as a two-part raw material with a grease-like viscosity. Nowadays injection molding of liquid silicon rubber is becoming increasingly important. One reason for this is the increased performance requirements of the finished articles. In addition, more and more producers of rubber parts are seeing benefits in the high level of automation and productivity.
Various ways of silicon molding:
Molding processes used by providers of silicon molding services include cast molding, compression molding, dip molding, injection molding, reaction injection molding, rotational molding and transfer molding. Whereas in the cast molding process, liquid material is poured into an open mold, in compression molding a slug of silicone is pressed between 2-heated mold halves. On the other hand dip molding is a process similar to hot dip coating, in which the finished product is the fused plastisol stripped from the dipped mold. However in injection molding liquid silicone is forced into a cooled mold under tremendous pressure. In the Reaction Injection Molding (RIM) process two or more reactive chemicals are mixed at high speed as they are being injected into a mold. In rotational molding hollow molds filled with silicone material are secured to pipe-like spokes that extend from a central hub. In transfer molding, the two mold halves are clamped together and silicone is forced by pressure into the mold.
Why the preferred use of silicon rubber in injection molding Silastic silicon rubber is a shear material and so its viscosity depends on shear rate. As the shear rate rises the product becomes lower in viscosity. It is this effect that is very favourable for the injection molding process. At the beginning of the injection process the injection speed profile should be programmed in such a way that the volume flow is high enough for the liquid silicon rubber not to begin to vulcanize before the cavity is filled, in order to avoid scorch of the material. Thus liquid silicon rubber is widely used for the process of injection molding due to its following characteristics:
- Solvent less with low and versatile viscosity.
- Easy mixing and pigmentation
- Rapid processing compared to solvent dispersion and usually allows a complete coating to be applied in a single pass
- Prime less adhesion to glass and some other substrates.
- Meter mixed silastic liquid silicon rubber can be dip coated or fed to a crosshead for supported extrusion coating.
To sum up
Silicon rubber molding has come a long way over the past two decades. From its roots in a few specialty applications where premium physical properties counted more than the premium price, this thermo set carved out a small but solid niche in the medical and automotive fields. Now, among a proliferation of new applications, that niche has begun to burst at the seams.
