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Liquid injection molding uses liquid silicone rubber mixed with an activation catalyst to mold products. The process involves injecting the mixture into a heated mold, resulting in highly accurate and predictable results. The equipment used includes tanks, a dosing unit, a mixing unit, an injection nozzle, and the mold. Silicone rubber compounds have excellent characteristics for producing seals, baby products, medical equipment, and tableware.
Liquid injection molding is a process that uses premixed liquid silicone rubber to mold products rather than the thermoplastic resins used in other methods. In this process, inert liquid silicone rubber is mixed with an activation catalyst outside the mold prior to injection into the mold cavity. The activated silicone compound then hardens in the heated mold at which point the finished product is ejected. The liquid injection molding process produces highly accurate and predictable results in a medium that possesses special physical properties.
The liquid injection molding process is similar to other injection molding methods in its basic principles. A flowable material is forced or injected into a closed mold under pressure where it cures or hardens and then dropped or ejected from the open mold. The major differences between this particular technique and others include the materials used to manufacture the finished product and the external processes used to prepare the material. The silicone rubber used for liquid injection molding is a low viscosity inert fluid that remains in this state until mixed with an activating agent or catalyst, then heated or cured. Once activated and heated, the compound undergoes a chemical reaction that causes it to solidify to form the final production material.
The equipment used to facilitate liquid injection molding consists of two or more tanks or plungers, a dosing unit, a mixing unit, an injection nozzle, and the mold itself. One tank contains the inert base material and the other the catalyst agent. Further additives or colorants will then be contained in further tanks. The discharges from all the raw material tanks lead to a doser which maintains a constant ratio between the materials. The mixing station thoroughly combines all the various materials and then feeds the mixed compound to the injection nozzle under pressure for injection into the mold.
Molds are usually preheated to ensure uniform filling and to complete the curing or curing process. Compounds mixed in the feed section of the system are held at a lower temperature to prevent full cure and the resulting blockages. The injection nozzle is usually equipped with an automatic shut-off system to prevent leaks and overfilling of the mold. Nozzle assemblies can also have a spring loaded pin design to maintain higher injection pressures which further helps keep the extruder channel free from clogging. Given the low viscosity of the materials used in liquid injection molding, all parts of the system must be tightly sealed to prevent leaks.
Silicone rubber compounds have excellent tensile strength, flexibility and heat resistance characteristics. Additionally, unique forming capabilities are possible with these materials that allow for broad coloration and transparency options in the finished product. These characteristics are ideal for the production of seals, smooth surface flexible baby products such as soothers and bottle nipples, medical equipment and tableware.
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