Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume.
Liquid silicone rubber is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for production of parts, where high quality is a must. Due to the thermosetting nature of the material, liquid silicone injection molding requires special treatment, such as intensive distributive mixing, while maintaining the material at a low temperature before it is pushed into the heated cavity and vulcanized.
Chemically, silicone rubber is a family of thermoset elastomers that have a backbone of alternating silicon and oxygen atoms and methyl or vinyl side groups. Silicone rubbers constitute about 30% of the silicone family, making them the largest group of that family. Silicone rubbers maintain their mechanical properties over a wide range of temperatures and the presence of methyl-groups in silicone rubbers makes these materials extremely hydrophobic, making them suitable for electrical surface insulations.
Typical applications for liquid silicone rubber are products that require high precision such as seals, sealing membranes, electric connectors, multi-pin connectors, infant products where smooth surfaces are desired, such as bottle nipples, medical applications as well as kitchen goods such as baking pans, spatulas, etc. Often, silicone rubber is overmolded onto other parts made of different plastics. For example, a silicone button face might be overmolded onto a Nylon 6,6 housing.
Rubber molds are mainly used in the process environment that needs to strengthen the molding pressure or transfer the molding pressure. The rubber mold is very useful when it is difficult for the vacuum bag to enter the recessed area of the complex cavity. For example, when the vertical parts on the stiffened plate are formed, the expansion of the rubber mold causes the side surfaces of the vertical parts in the part to be subjected to process pressure. The application of rubber molds has two basic forms, namely fixed volume and variable volume.
In the fixed volume method, the parts and rubber materials are completely enclosed in a turnable metal frame, and the expansion of the rubber can effectively make the parts subject to a uniform fluid pressure. In the variable volume method, a vacuum bag or a soft flexible uniform pressure plate is covered on the rubber mold, so that it is no longer necessary to accurately calculate the volume of the rubber mold. The most basic way of a rubber mold is as a simple template between the vacuum bag and the part, or as a rubber backing plate for parts that are difficult to compact in the part.