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What is Silicone Injection Molding?

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  • Written By: Ron Davis
  • Edited By: C. Wilborn
  • Last Modified Date: 21 September 2016
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Silicone injection molding is an economical and widely used industrial process for manufacturing a wide range of goods made of silicone. These include seals for aero-space applications, sealing membranes for industrial use, electrical connection insulators, and even baking pans and spatulas. Silicone rubber products are mass produced using machines of various sizes.

The main types of silicone rubbers are liquid silicone rubber (LSR), flourosilicone rubber (FSR), high consistency silicone rubber (HCR), and fluoro-liquid silicone rubber (F-LSR). While all variants of this family of thermoset elastomers are used with the injection molding process, LSR and F-LSR can be formed only by injection molding. Silicone injection molding is used to make products for a wide variety of industries, including agricultural, aviation and aerospace, energy, and medical and health care.

The basic idea in any injection molding process is that a machine will mix together two component resins along with a catalyst and, often, a coloring agent. The machine will then force the mixture into the mold where it will cure, setting into the shape of the mold. Typical machines used for silicone injection molding have six essential parts: injectors, metering units, supply drums, mixers, a nozzle, and the mold clamp.

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Injectors push the silicone rubber into the pumping section under pressure. The operator can adjust the pressure and pumping rate to the best level for the product being made. Metering units pump the component resins in carefully controlled portions, releasing them simultaneously at a constant ratio. Supply drums contain the resins; often another drum will contain pigment.

The components are pumped into the mechanical mixer, where they are mixed. After mixing, the LSR or F-LSR is forced through the nozzle into the mold. Nozzles usually have automatic shut off valves to prevent over-filling or leaking. The mold clamp is a device that is triggered in coordination with the injector, pump, and supply units. It secures the mold in place and opens it when the product is cured.

Silicone injection molding provides several benefits to the manufacturer and the consumer. Products made from silicone remain stable when exposed to weather, ozone, and ultraviolet rays. In contrast, organic elastomers tend to become brittle and crack after prolonged exposure to the environment. Silicone rubber products can function properly at temperatures as low as -140° F (-100° C) or as high as 600° F (316° C). They remain good electrical insulators and retain a high proportion of their flexibility and resilience across most of that temperature range.

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