Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume.
[2] 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.
Typically, a molding machine requires a metered pumping device in conjunction with an injection unit—a dynamic or static mixer is attached.
Biocompatibility: Under extensive testing, liquid silicone rubber has demonstrated superior compatibility with human tissue and body fluids.
The material can be sterilized via a variety of methods, including steam autoclaving, ethylene oxide (ETO), gamma, e-beam and numerous other techniques, meeting all required approvals such as BfR XV, FDA 21 CFR 177.2600, USP Class VI.
[4] Durable: LSR parts can withstand extreme temperatures, which makes them an ideal choice for components under the hood of cars and in close proximity to engines.
Mechanical properties: LSR has good elongation, high tear and tensile strength, excellent flexibility and a hardness range of 5 to 80 Shore A.
This attribute makes it possible to produce colorful, custom, molded products[5] Liquid silicone rubbers are supplied in barrels.
In contrast, hard silicone rubbers are processed by transfer molding and result in less material consistency and control, leading to higher part variability.
Liquid silicone has a very low viscosity index and requires perfect seals of the mould cavity in order to guarantee a burr-free finished product.
[6] From the metering section of the injection molding machine, the compound is pushed through cooled sprue and runner systems into a heated cavity where the vulcanization takes place.
A chiller supplying cold water to jacketed fittings is typically used to retard the curing process prior to the materials introduction to the mold.
In a cold deck scenario, the 1 to 1 mixed compound is pumped through cooled sprue and runner systems into a heated cavity where the vulcanization takes place.