Liquid silicone molding is a highly automated process that utilizes low viscosity liquid silicone rubber to mold and cure high-precision molded items. It offers the advantage of shorter cycle times than traditional injection molded thermosets such as polyurethane, natural rubber and peroxide-cured silicone. These features can help reduce manufacturing costs while increasing part quality, reliability and durability.
The key to liquid silicone molding is a closed-loop system that combines equal portions of two primary liquid silicone elastomer components. These meter/mix systems are often referred to as “closed dispensing machines.” This allows for less handling of the raw material, greatly decreasing the chance of contamination. It is also possible to add color pigment to the mixture in this closed-loop system, which makes it ideal for medical applications such as nipple protectors produced for nursing mothers.
A typical LSR injection molding system begins with the two primary liquid silicone materials, typically a catalyst and base forming silicon, stored in separate pails or drums (known as a kit). The kits are then connected to a metering unit that pumps both the A and B compounds through a static mixer. Depending on the application, color pigment can be added to the mixture as it exits the mixer. The mixed compound is then pushed through the cooled runner system and into a heated mold cavity through a nozzle that frequently has an automatic shut-off valve to prevent leaking and overfilling.
Once in the mold, the LSR undergoes a rapid curing process. This is the result of heat generated by the injection molding machine’s screw and the reaction between the liquid elastomer and the hardeners that are incorporated into the formulation. This results in a tough, durable rubber that is resilient and can hold its shape in most environments.
While conventional thermoplastic elastomers lose flexibility at extreme temperatures, LSRs remain flexible at lower temperatures and will not creep or crack over time. These properties make LSRs an excellent choice for automotive and heavy-duty applications, such as seals and gaskets, which must withstand high pressure and temperature extremes.
LSRs are also biocompatible, chemical resistant and can be sterilized. They offer a wide operating temperature range, good electrical insulation and a sustainable life span.
Medical applications of LSR include nipple protectors, breast pads and reusable surgical gloves. LSR is easy to inject into tight-tolerance, high-precision parts. It flows easily into tight radii and thick/thin features, making it an ideal alternative to solid silicone-rubber injection molding processes such as thermosets and hot-melts.
The resulting silicone molded products are safe for human contact, non-toxic and odorless. They are durable, flexible and highly customizable. These properties have made them an industry standard for many types of medical applications, including nipple protectors and other maternity-related silicone items. The molded products can also be sterilized or cleaned with chemicals, which is beneficial for hospitals and other medical facilities. This is because the nipple protectors and other medical products can be reused, saving money and resources for healthcare institutions.
