Liquid silicone injection molding process

Liquid silicone injection molding process
Material preparation: Liquid silicone is usually supplied in two-component form, namely component A (base rubber) and component B (curing agent). Before use, the two components must be accurately measured and mixed according to product requirements and material properties. The accuracy of the mixing ratio has a significant impact on the curing effect and final performance of silicone. For example, for a medical-grade liquid silicone, components A and B must be mixed strictly in a 1:1 mass ratio. The mixing process must be sufficient to ensure that the two components are evenly dispersed, which can be achieved with the help of mechanical stirring or static mixers.
Equipment preparation: Injection molding equipment is mainly composed of an injection system, a clamping system, a hydraulic system, and an electrical control system. Before production, it is necessary to check the operating conditions of each component of the equipment and set parameters such as injection pressure, speed, time, and mold temperature. For example, when producing mobile phone buttons, the injection pressure and speed must be adjusted according to the size, shape, and fluidity of the buttons to ensure that the silicone fills the mold evenly.
Mold installation and preparation: Install the designed and processed mold on the injection machine, clean the mold surface, apply a release agent (as needed), and preheat the mold to an appropriate temperature. Appropriate mold temperature is conducive to the flow and filling of liquid silicone, and can also accelerate the curing speed. For example, when making silicone sealing rings, preheating the mold to 80-100℃ can improve molding efficiency and product quality.
Injection and filling: The mixed liquid silicone is pushed by the screw or plunger of the injection machine and injected into the mold cavity through the barrel and nozzle. During the injection process, the high pressure makes the silicone fill the mold quickly. The injection speed and pressure need to be controlled to prevent problems such as lack of material and flash. For molds with complex structures, multi-stage injection may be required, with different speeds and pressures set at different stages.
Curing molding: After the liquid silicone fills the mold, it is heated and cured in the mold. The curing temperature and time depend on the type of silicone and the requirements of the product. Generally, it is cured at 120-180℃ for several seconds to several minutes. For example, when making silicone tableware, it needs to be cured at 150℃ for 3-5 minutes to ensure that the silicone is completely cured and has good physical properties.
Demolding and post-processing: After curing is completed, the mold is opened and the product is pushed out through demolding mechanisms such as ejectors and push rods. Be careful to avoid damage to the product during demolding. After demoulding, remove burrs and overflows from the product. Some products may require secondary vulcanization to further improve performance, such as hardness and aging resistance.