Liquid Silicone Moulding
LSR (liquid silicone rubber) injection molding is used to produce a wide range of durable, flexible silicone parts and products. It is an alternative to the traditional reaction injection molding (RIM) process and a more efficient production method for mass quantities of high-performance silicone rubber.
Unlike RIM, which uses a pressurized impingement mixing process to blend two-component platinum-cured LSR material compounds together that flow into a mold cavity, the liquid silicone molding (LIM) manufacturing process utilizes a mechanical mixer that blends the primary raw materials into a consistent viscous state that can be delivered into a designated mold. Depending on the application, color pigment may be added during this mixing process as well.
The raw uncured silicone materials are shipped in separate containers – Barrel A, which holds the base forming material, and Barrel B, which contains the catalyst. These two raw materials connect to a metering unit that simultaneously releases both components at a one-to-one ratio, as well as any pigmentation additives. This metering unit also connects to an automated injection-molding machine – with settings for temperature, pressure and pistons that are customized to match the design of the customer part.
Liquid silicone is injected into a heated, closed mold through a nozzle that is sized to precisely fit the part’s design. The resulting injection molding process produces a fully cured silicone product with no stress, strain or shrinkage. The liquid silicone can be injected into the mold at relatively low injection pressures, typically between 200 to 1200 psi.
After the molded product is clamped together in a mold, it remains closed until it cures, which can take as little as 30 seconds. The result is a high-quality silicone component that has excellent elongation, tensile and tear strength, superior flexibility, and a hardness range of 5 to 80 Shore A.
Other advantages of the liquid injection molding process include tight control over dimensional tolerances. As the injection molding process occurs with the mold’s tooling closed, it is possible to achieve very close tolerances in cross-section dimensions and plan view dimensions. In addition, the ability of the liquid silicone to easily accommodate variations in wall sections can virtually eliminate flash.
Durability and Performance
Silicone is a highly resilient material that resists extreme temperatures and can endure the heat of an automobile engine, making it ideal for automotive applications under the hood. It can also withstand harsh chemical solutions and is highly resistant to oxidation, water and many acids and alkali.
For medical applications, molded silicone is sterilizable via steam autoclaving, ethylene oxide, gamma, e-beam and numerous other methods commonly used in the manufacture of surgical devices, catheters and other healthcare equipment. Its low viscosity makes it a good choice for flexible medical implants, nipple protectors and other medical accessories. It is odorless, non-toxic and hypoallergenic. It can also be used to make food-grade silicone and cosmetics, and it can withstand sterilization temperatures that are often higher than those used for other elastomeric materials.