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Types of Silicone Molding

February 15th, 2018

Author: Krissy Dempsey, Marketing Manager - Saint-Gobain Life Sciences Medical Components

There are a variety of types of medical component molding.  These types can be categorize by the type of material being converted, part size, volume, molding technology, just to name a few. In this post, we’ll focus specifically on silicone molding.

There are two types of moldable silicone raw materials: High Consistency Rubber (HCR) and Liquid Silicone Rubber (LSR).

High Consistency Rubber (HCR)

HCR has the consistency of peanut butter.  The catalyst can be platinum or peroxide and is compounded with the base via a two-roll mill.  HCR can be molded via compression molding or transfer molding. With compression molding, material is placed between two plates. The heated plates are compressed, and the excess seeps out along the parting line.  This is an older technology but can still be a cost effective method for low volume parts.  Transfer molding differs from compression molding in that the press transfers the material through a runner, sprue and gate system into the cavity of the mold. Transfer molding can be a preferred processing method for silicone parts requiring unique material properties or low to mid-range annual volumes.

Liquid Silicone Rubber (LSR)
The most recent processing technology in silicone molding is liquid injection molding (LIM), which uses LSR material. LSR is the consistency of corn syrup, is supplied in drums, and uses a platinum catalyst. Within LIM molding, there are a variety of sub-categorizations and associated technologies including overmolding, two-shot molding and micromolding.

Overmolding involves molding silicone over, or onto, a substrate such as a thermoplastic part, titanium part or perhaps a silicone tube.  In this process, a robot or an operator places the first component into the silicone mold.  The silicone is then molded onto the initial component thereby resulting in a combined, overmolded, single part. This capability only requires an LSR molding machine and appropriate tooling. Training of operators is essential in this operation as there is a risk of misplacement of the insert which could result in damage to the tooling.

Two-shot silicone-thermoplastic molding is similar in that it is combining silicone and thermoplastic materials. However, with two-shot molding, it is done simultaneously. The initial thermoplastic component is molded in one half of the mold while the other half is overmolding the silicone onto the previously molded thermoplastic. When the mold opens, the silicone overmolded parts are removed, and the thermoplastic parts are rotated or transferred to the silicone overmold side of the tool. This technology requires specific equipment, a high-temperature thermoplastic material, a self-bonding grade LSR material, and a high level of experience and understanding of shrink and thermodynamics within each half of the mold as these materials are essentially opposites in regards to cure methods (thermoset heated and thermoplastic cooled).

Finally, micromolding of LSR is rising in demand within the medical device component space as devices continue to get smaller and smaller.  Using high precision tooling, an appropriate press (shot size, screw and barrel size, etc.), robotics, and more, silicone parts with a mass of 0.01g are manufacturable. Some examples include integrated seals, soft tips for surgical tools, or micro-valves.

For more information on molding types or specific capabilities of Saint-Gobain Medical Components, please contact us today.

Krissy Dempsey - Marketing Manager - Saint-Gobain Life Sciences Medical Components

Krissy Dempsey is the Marketing Manager for Saint-Gobain Life Sciences Medical Components.  She has been with Saint-Gobain’s Medical Components business for over 10 years in various roles. She works closely with sales and applications engineering to support new projects and opportunities, analyzes and develops product strategy and pricing.  She enjoys long walks on the beach and a good laugh every now and again!

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About Saint-Gobain

Saint-Gobain designs, manufactures and distributes materials and solutions which are key ingredients in the wellbeing of each of us and the future of all. They can be found everywhere in our living places and our daily life: in buildings, transportation, infrastructure and in so many industrial applications.

 

Saint-Gobain Performance Plastics' group of businesses gather solutions to save energy, provide protection, improve comfort and sustain the environment for a variety of markets.

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Saint-Gobain’s medical products are distributed exclusively to medical device manufacturers for use in the manufacture, assembly or distribution of their medical devices. Saint-Gobain cannot authorize the sale of its medical products directly to device user facilities (e.g. hospitals, surgery centers, nursing home, clinics, etc.), nor directly to end users (e.g. patients, patients’ caregiver, prescribing physician, nurse, pharmacist, etc.), including distributors serving device user facilities and end users directly. In accordance with every jurisdiction globally, Saint-Gobain’s customers are responsible for determining that any medical device they manufacture and market that incorporates a Saint-Gobain’s medical product, is compliant with each country-specific medical device regulations and has received proper country-specific clearance, certification or registration authorizing the sale of this medical device.


Saint-Gobain’s medical products offer covers:
- Medical Components [21 CFR 820.3(c)], intended for processing or use in the manufacture or assembly of medical devices before the finished medical device is packaged/labeled; Medical Components are intended to be included as part of the finished, packaged, and labeled device [21CFR820.3(c)].
- Finished Devices [21CFR820.3(l)] made on behalf of medical device manufacturers [21 CFR 807.20(a)(2)] under contract-manufacturing agreement. In accordance with the United States’ jurisdiction, Saint-Gobain complies with the FDA’s requirements for contract manufacturers of finished devices.

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