The Basics of Liquid Injection Molding

June 14, 2023

Liquid injection molding is an industrial fabrication method that molds stock materials into a range of components and products. It differs from the standard reaction injection molding process in that it relies on mechanical mixing rather than pressurized impingement mixing, and it focuses specifically on liquid silicone rubber and similar elastomeric materials. It is capable of efficiently producing a large number of versatile items, including seals, o-rings, isolators, and electronic contacts.

A large part of liquid injection molding’s versatility derives from the material properties of liquid silicone materials. These silicones exhibit a high degree of heat and flame resistance, tensile strength, and flexibility. Also, silicones provide beneficial formability characteristics, allowing for coloring or transparency in the finished product. Depending on their chemical composition, these materials can also serve as insulators or conductors. The liquid injection molding process used to fabricate liquid silicone is a precise and distinct method, capable of producing highly accurate results.

The Liquid Injection Molding Process
Liquid injection molding focuses on the apportioned mixing and dispensing of plastic-based materials via a series of plungers. Usually, one plunger contains the base forming plastic, which can be reinforced with additives and fibers, while the other plunger holds a catalyst that activates the mixing reaction. The compounded material is then injected directly into a sealed mold, and after hardening, the nearly finished component is ejected from the molding machine.

Silicones and acrylics are the materials most commonly involved in liquid injection molding. To help prevent machine hardware from becoming clogged with liquid plastic, a spring-loaded pin nozzle can be used for the injection stage. Spring-loading allows the injection pressure to be higher than that of the extruder barrel, thus keeping the channel unblocked. Computer-aided design tools are also helpful for making the molding process more efficient. Computer programs can run simulations to determine the most effective processing conditions, as well as evaluate results and monitor integrated devices. Thermal imaging technology also has the potential to identify production errors, such as molding flaws or design inconsistencies.

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