Choosing the right injection technology for LSR molding is key to a successful part, especially in the case of directly gated components (no sprue). The two most popular systems involve open nozzle systems and valve gates.
For Two Shot Molding, a multi-shot mold is needed. There are several types of multi-shot molding available, such as over-molds, core-back, and multi-station molds. The right mold selection depends on part geometry, volume, quality, and molder capacity/capability.
In 2-Shot injection molding, a polymer is injected over a molded plastic insert to combine the best features of different materials while reducing or eliminating additional assembly operations. This reduction or elimination of post-processing steps is one of the biggest economical advantages of the 2-Shot silicone injection moulding process. For this kind of silicone injection moulding, a multi-shot mold is needed. There are several types of multi-shot silicone injection moulding available, such as over-molds, core-back, and multi-station molds. The right mold selection depends on part geometry, volume, quality, and molder capacity/capability.
An informative presentation of the silicone liquid rubber curing incorporating the degree of cure is the Time-Temperature-Transformation (TTT) diagram, developed by Enns and Gillham. It can be used to relate the material properties of thermosets, such as Silicone Liquid Rubber (LSR), as a function of time and processing temperature. The diagram visually presents various lines representing constant degrees of cure. The curve labeled c=,c-g. represents the gel point and c=1 represents the fully cured resin.
The density, or its reciprocal, the specific volume, is a commonly used property for polymeric materials. Density is primarily used as a material control tool, as well as to compare the buoyancy of different materials, but it can also be used to calculate the mass of rubber required to produce a given volume of material. The density of compounds with fillers or different materials can be computed at any temperature using the rule of mixture. Density measurements are performed following the standard tests ISO 1183 and ASTM D792. The density of Liquid Silicone Rubber (LSR) is typically in the range of 1.10 – 1.50 g/cm3 (density of natural rubber: 0.92, EPDM: 0.86 g/cm3), so it will sink in water (density of water: 1 g/cm3).