The structure of the thermosetting liquid silicone rubber (LSR) injection mold is generally similar to that of the thermoplastic compound, but there are also many significant differences. For example, LSR compounds generally have a low viscosity and thus a short filling time, even at very low injection pressures. In order to avoid air retention, it is essential to set up a good exhaust device in the mold.
In addition, LSR adhesives do not shrink in the mold like thermoplastic adhesives, they tend to expand in response to heat and shrink slightly in response to cold. Therefore, its products are not always left on the convex surface of the mold as expected, but remain in the mold cavity with a larger surface area.

1 Shrinkage rate
Although LSRS do not shrink in the mold, they often shrink by 2.5-3% after demoulding and cooling. The exact amount of shrinkage depends to a certain extent on the formulation of the compound. However, from the perspective of the mold, the shrinkage rate may be affected by several factors, including the temperature of the mold, the temperature at which the rubber is demoulded, and the pressure in the mold cavity and the subsequent compression of the rubber.

The location of the injection point is also worth considering, as the shrinkage in the direction of the flow of the compound is usually greater than the shrinkage in the direction of the vertical flow of the compound. The size of the product also has an impact on its shrinkage rate, and the shrinkage rate of the thicker product is generally smaller than that of the thinner one. If secondary vulcanization is required, an additional 0.5% to 0.7% shrinkage is possible.