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Injection Molding: Liquid Silicone Rubber

Liquid silicone rubber injection molding is the most recent addition to Jefferson Rubber Works, Inc.'s molding operations. The faster cycle times and improved performance properties of liquid silicone rubber make it a good choice for a variety of molded components. Liquid silicone rubber (LSR) remains flexible and elastic beyond -70°F and retains its properties up to 450°F which makes liquid silicone rubber a good candidate for gaskets, seals, boots, bellows, medical devices and other applications where outdoor conditions are demanding. Cured liquid silicone rubber does not out-gas volatiles and plasticizers as other rubber compounds do - which has made it friendly to various assemblies that were formerly required to be 'silicone free'.

A key advantage of liquid silicone rubber over gum based molding silicone compounds is the cycle time. Depending on the catalyst and cross-section of the molded component, the cycle times for liquid silicone molded parts range from 30 seconds to three minutes - with our average cure time of 25 to 50 seconds. In contrast, gum base silicones may take from 3 to 5 minutes total cycle time in a traditional silicone mold. Therefore, a single or two cavity injection mold will out-produce a multi-cavity mold. With fewer cavities needed to support production, tooling costs and lead times are reduced as well as part costs.

Liquid Silicone Compound Suppliers

Liquid silicone molding compounds are purchased in Part A and Part B components from the major silicone producers. These compounds are usually mixed in a one to one ratio, with pigment added during the mixing process prior to the cure. Elevated temperature and molding pressures of the liquid silicone injection molding process enhance the cure. Liquid silicone rubber is supplied to us in airtight containers, pumped from the mix metering units into the tooling without exposure to the environment - therefore humidity is not a concern and generally this liquid silicone injection molding process is more consistent than traditional molding.

Tooling considerations for Liquid Silicone Injection Molding

Liquid silicone molding involves room temperature compounds mixed and pumped into a hot mold. Tooling designs are simplified as liquid silicone rubber flows readily into very thin cross sections, tight radii and thick / thin features. Tooling surfaces do not have to be highly polished, and draft angles are not required to facilitate removal of the finished component from the tooling. When the cure cycle is complete, the molded silicone gasket can be removed without concern of distortion or tearing as the silicone is fully cured.

Silicon Rubber or Silicone Rubber? Silicone Rubber Molding or Silicone Molding?

We see silicon rubber or liquid silicon rubber called out frequently. Although silicon is often called out on prints, silicone is the widely accepted terminology used among in the synthetic rubber industry. Similarly, we see the terms liquid silicone rubber molding, liquid silicone rubber injection molding, liquid silicone molding, silicone liquid molding, liquid silicone injection molding, silicone injection molding, and silicone molding all used frequently and mostly interchangeably.

Jefferson Rubber Works, Inc. is a manufacturing agent building rubber & silicone products company inc and silicone rubber bulb seal.