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Liquid silicone rubber molding

Liquid silicone rubber molding

Silicone rubber molding

Silicone rubber molding is a process used to produce parts from silicone rubber, which is a flexible, durable, and biocompatible material. Silicone rubber is different from organic rubbers because it is a synthetic elastomer made from a crosslinked polymer, which is reinforced with silica. 

This molding process is often used to produce seals, gaskets, buttons, medical devices, kitchenware, and other products that require high-temperature resistance, flexibility, and non-reactivity.

1. Process

In this method, a pre-measured amount of silicone rubber compound is placed directly into the mold cavity. The mold is then closed, and pressure is applied, forcing the material to fill the mold cavity. The mold is typically heated, which causes the silicone to cure and take the shape of the cavity. After curing, the mold is opened, and the part is removed.

Similar to compression molding, transfer molding involves loading the silicone material into a chamber outside the mold cavity. Once the mold is closed, pressure is applied, and the material is transferred through a sprue into the mold cavity where it cures.

Liquid silicone rubber (LSR) is often used for injection molding. LSR is a two-component material, where the A and B components are kept separate until just before entering the injection barrel. These components are mixed, heated, and then injected into the mold cavity. Heat within the mold causes the silicone to cure rapidly, and the part can then be ejected. This method is especially suitable for high-volume production of precision parts.

This involves molding silicone rubber over a different material, typically a plastic or metal substrate. This process can create parts with combined properties, such as a rigid component with a soft-touch exterior.

2. Advantages

Silicone rubber can withstand high temperatures without degrading, making it suitable for applications requiring heat resistance.

Certain medical-grade silicones are biocompatible, making them ideal for medical devices and implants.

Silicone parts are flexible, resistant to compression set, and have excellent longevity.

Certain silicone formulations can be clear, which can be useful for applications like lenses or medical devices.

Silicones can be excellent insulators, making them valuable in electronics and electrical applications.

3. Challenges

Silicone rubber can be more expensive than some other materials.

Some silicone parts may require a post-curing process to achieve their final properties or to ensure removal of any uncured components, especially in medical applications.

Silicone’s inherent stickiness can sometimes make mold release challenging. Special mold treatments or release agents may be necessary.

Summary

In summary, silicone rubber molding is a versatile process that caters to the unique properties of silicone rubber. It allows for the production of parts that can withstand harsh conditions, remain flexible over time, and be safe for various applications, including those in the medical field.

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