The structure of thermoset liquid silicone rubber (LSR) injection molds is generally similar to that used for thermoplastic rubbers, but there are a number of significant differences. For example, LSR compounds generally have a low viscosity, resulting in short mold filling times, even at very low injection pressures. In order to avoid air retention, it is crucial to have good air venting in the mold.
In addition, LSR compounds do not shrink in the mold as much as thermoplastic compounds; they tend to expand when hot and shrink slightly when cold. As a result, the product does not always remain on the convex side of the mold as desired, but rather is trapped in the mold cavity, which has a larger surface area.
1. Shrinkage
Although LSRs do not shrink in the mold, they often shrink by 2.5% to 3% after demolding and cooling. The exact amount of shrinkage depends to some extent on the formulation of the adhesive. However, from a mold perspective, shrinkage can be affected by several factors, including the temperature of the mold, the temperature of the compound when it is demolded, as well as the pressure in the mold cavity and the subsequent compression of the compound.
The location of the injection point also deserves consideration, as shrinkage in the direction of adhesive flow is usually somewhat greater than that in the direction of flow perpendicular to the adhesive. The external dimensions of the product also have an effect on the shrinkage, with thicker products generally having less shrinkage than thinner ones. If secondary vulcanization is required, additional shrinkage may occur.
2. Parting line
Determining the location of the parting line is one of the first few steps in designing a silicone rubber injection mold. Venting is mainly achieved by means of grooves located on the parting line, which must be in the area where the injected compound will finally reach. This helps to avoid internal air bubbles and reduces the loss of strength in the joint.
Due to the low viscosity of LSR, the parting line must be precise in order to avoid overspray. Even so, parting lines can often be seen on molded parts. Mold release is influenced by the geometry of the part and the position of the parting surfaces. Designing the part with a slight chamfer helps to ensure that the part has a consistent affinity for the desired other half of the mold cavity.
3. Venting
As LSR is injected, air trapped in the mold cavity is compressed when the mold is closed and then expelled through the vent grooves as the mold is filled. If the air is not completely discharged, it will be trapped in the rubber (which often results in a partially exposed white edge of the product). Ventilation grooves are generally lmm-3mm wide and 0.004mm-0.005mm deep.
Vacuuming inside the mold creates the best venting effect. This is achieved by designing a gasket on the parting line and using a vacuum pump to quickly evacuate all the mold cavities. Once the vacuum reaches the rated level, the mold is fully closed and injection molding begins.
Some injection molding equipment allows operation at variable closing forces, which allows the processor to close the mold at low pressures until 90-95% of the cavity is filled with LSR (allowing air to escape more easily), and then switch to a higher closing force to avoid silicone rubber expansion and overspray.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150A. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.