From Limtech

Liquid silicone rubbers (LSR or LIM) are a family of thermoset elastomers. They are two-component silicone compounds which are used to mold flexible components by means of injection molding. The two-components (A & B) are low enough in viscosity that they can be pumped from their containers in the proper ratio (typically one to one), pushed through a static mixer, and injected into the mold cavities. One of the components contains the catalyst, typically platinum based.

Processing

Pigments as well as other additives can be added before the components enter the static mixer. In the static mixer, the A & B components, the pigments and the other additives are well mixed prior to being injected through a cooled sprue and runner system into heated mold cavities where the vulcanization takes place. The mold cavities are heated to a temperature typically between 140 and 230 degrees Celsius and the vulcanization takes place fairly rapidly. The rapid vulcanization results in fast cure cycles and excellent productivity. In addition, the rapid vulcanization reduces flash.

Shrinkage

Liquid silicone shrinks as it cures. This shrinkage is dependent on the grade of material and is typically in the range of 2.7% for non post-cured parts and 3.5% for post-cured parts.

Post-Cure

Post-curing liquid silicone parts increases shrinkage, and drives off volatile elements of the silicone. Limtech has developed post-cure processes for food contact components which allow these components to meet the European 0.5% weight loss specification.

Post-curing may also improve some mechanical properties such as compression set.