Liquid silicone rubber injection molding (LSR) and liquid rubber over-molding (OLR) present distinct differences, particularly in their material delivery systems. While LSR employs a liquid injection mold, OLR utilizes a plastic gun for the injection process.
In the case of LSR, the injection-molded tool is introduced to a specialized injection molding machine designed for LSR. This machine comprises a dedicated silicone gun and an equipment control unit. The silicone gun is loaded with the desired silicone mold material, and a silicone line feeds it into the injection area. Here, liquid silicone is directly injected into the desired part, solidifying upon contact with the silicone mold. This method is suitable for over-molding parts that may not be compatible with traditional LSR injection molding.
Precision is crucial for the injection-molded tool to avoid damage to the molded surface or underlying components. Over-molded parts require removal, and the molding area is sanded down before the mold is ready for reuse.
In contrast, liquid rubber can be applied for over-molding using specific polyurethane material, which cures under pressure to form a durable over-molded part. The polyurethane bonds with the silicone mold and hardens instantly. Notably, liquid rubber cannot be over-molded independently without the aid of an injection-molded tool.
The process involves spraying a polyurethane gel onto the surface to be molded, penetrating the polymer and creating a semi-hard silicone seal. This seal ensures instantaneous hardening when applied over the mold. For effective silicone injection molding, a small amount of silicone rubber or polyurethane, elevated heat, and precise temperature control are essential. The amount of silicone injected determines the speed of hardening upon contact with the silicone gel.
LSR injection-molded parts must be produced with attention to the specified number of silicone injections to prevent leakage or deformation in the finished product.
The versatility of the injection-molding process extends to various applications, including cosmetic products like handbags, jewelry, shoes, bags, gloves, water bottles, and other items. Through the combination of liquid rubber and silicone, this manufacturing method opens up possibilities for creating intricate and durable molded parts across diverse industries.