The injection molding of liquid silicone rubber is a new technology rising in rubber processing in recent years. The characteristic of this process is that it can produce silicone rubber products at high speed. Here in this article, we overview the introduction to liquid silicone rubber injection molding and process of LSR injection molding from start to finish.
Liquid silicone rubber has existed since the late 1970s and has become the preferred material for manufacturing rubber parts and products. The unique quality of liquid silicone injection molding makes it different from traditional high consistency silicone molding and other thermoplastic injection molding processes.
Liquid silicone rubber injection molding is a thermoset process that cools the material delivery system, while heating the mold tool to cure silicone material into parts. The liquid silicone injection molding process is highly automated with short cycle times to reduce the silicone part price. Liquid silicone injection molded parts are elastic with a high degree of chemical, electrical and thermal resistance. In addition, the parts are biocompatible and can be subjected to sterilization. They are used in a variety of industries, including healthcare, automotive, infant care, general industrial markets, aerospace, electronics and many other professional industries.
Here are steps of silicone rubber injection molding process from start to finish:
1. The uncured liquid silicone starts in two containers – Compound A and Compound B, which connects to the pumping system. Barrel A holds the base-forming material, and Barrel B contains a catalyst. A metering unit automatically releases the two substances at a constant one-to-one ratio, as well as any pigmentation additive.
2. The molder can program and customize the automated injection- molding machine and have the injection setting deliver the appropriate shot size for each job. The platens and pistons that align and close the mold have settings for the temperature, pressure, injection rate, and cycle time-adjusted in accordance with the customer’s specifications.
3. After finishing the setting, the molding machine heats the mold to the a proper temperature and applies the appropriate clamping force. The mold is closed in coordination with the machine’s injector, pump, and supply. The injection mechanism then pushes the material into the mold and cavities.
4. A combination of heat and pressure applied to the liquid silicone rubber cures the material until it solidifies. After the cycle is completed, the mold opens and the part and flashing can be removed automatically or by a workers. Then close the mold and repeat the process.
5. After the removal of the item from the mold, the post-molding process may include de-flashing, post-curing, inspection, and packaging.
6. As the production molding run comes to a close, the liquid silicone injection molding process must be prepared for a new material for different part designs. It is unacceptable to purge out the system with the new silicone which will result in the parts having the last production runs silicone in them. Therefore, everything must be cleaned up, which can easily take a day to clean depending on which injection mold press is used.
Instead of some of the advantages of liquid silicone rubber tooling, some of the benefits over plastic injection molding tools are superior ability to accommodate deviations in wall sections and it has almost no sink characteristics. The ability to create undercuts where the parts can easily be removed from the tooling injection from the tool does not require ejector pins, the parts are easily removed, operator or grippers pulling the mold off the tool, silicon parts require small gates compared to injection molded parts.