The structure of the injection mold for thermosetting liquid silicone rubber (LSR) is generally similar to that of the mold used for thermoplastic materials, but there are also many significant differences. For example, LSR rubber materials generally have low viscosity, so the filling time is very short, even at very low injection pressures. It is crucial to install a good exhaust device in the mold to avoid air retention.

In addition, LSR rubber does not shrink like thermoplastic rubber in the mold, and they often expand when exposed to heat and contract slightly when exposed to cold. Therefore, its products do not always remain on the convex surface of the mold as expected, but rather remain in the mold cavity with a larger surface area.

1. Shrinkage rate
Although LSRs do not shrink within the mold, they often shrink by 2.5% -3% after demolding and cooling. As for the exact amount of shrinkage, it depends to some extent on the formula of the adhesive. However, from the perspective of the mold, the shrinkage rate may be influenced by several factors, including the temperature of the mold, the temperature at which the material is demolded, as well as the pressure inside the mold cavity and the subsequent compression of the material.
The location of the injection point is also worth considering, as the shrinkage rate in the direction of the rubber material flow is usually larger than that in the direction perpendicular to the rubber material flow. The external dimensions of a product also have an impact on its shrinkage rate, and thicker products generally have a smaller shrinkage rate than thinner ones. If secondary vulcanization is required, there may be an additional shrinkage of 0.5% -0.7%.