Appliance Design - May 2008 - (Page 25)

ELASTOMERS A medical device that has been overmolded with ELASTOSIL® silicone rubber from Wacker, which gives the tool a soft touch and improved ergonomics. Colored silicone from Dow Corning that can be made to enhance aesthetics in appliance applications. molding companies around the country who are using silicone elastomer in a multi-shot production environment. The company molds thermoplastic materials in one process, and then in the second shot, molds that part with a silicone elastomer to get the best performance characteristic for a particular application. For instance, a gasket may need to be soft for sealing, but may have to endure mechanical stresses that would require a particular hardness level. With the multishot process, a gasket could be made of a hard thermoplastic material, and then have a soft silicone elastomer overmolded over the core gasket, providing something that is stiff on the inside, soft on the outside. To date, Phillips has used silicone elastomers in conjunction with high heat resistant grades of PC, PBT and PA. The thermoplastics that can be used in a multishot process with the silicone elastomer must have heat resistance of at least 300 DegF to 350 DegF. Wolgemuth says that using the material in a multi-shot environment cuts down on part costs and assembly issues. Multi-shot parts reduce assembly operations, as one multimaterial unit eliminates the need for fastening www.applianceDESIGN.com separate parts made of different materials. It can also provide a stronger bond and better seal between the two materials. For parts that are difficult to produce in a one-shot process such as an complex gasket or diaphragm or a “fish hooked shaped” part, the two-shot method can often provide a solution. In addition, the silicone material allows for “violations” of accept- ed molding rules. Variations of thick to thin wall sections are not an issue as silicone cures and expands to fill, as opposed to thermoplastics that will shrink and cause sink marks. Radii, drafts and undercut designs can have a greater amount of flexibility, typically not requiring a separate movement in the tool design. Blemishes caused by gating are also eliminated, he says. “With a thermoplastic you usually have to use a gate large The NORMAQUICK® V2 quick connector for fuel lines was developed by Norma-Group using two-component molding and Momentive’s new FFSL. The molded-in silicone eliminates the need for O-rings or seals. Photo: Momentive Performance Materials applianceDESIGN May 2008 25 http://www.appliancedesign.com

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Appliance Design - May 2008 Contents Editorial Shipments/Forecasts News Watch New and Notable Displays & Indicators Elastomers Quality & Standards Indoor Air Quality IHHS Highlights New Products Classifieds Design Marts Advertiser’s Index Association Report: PSMA

Appliance Design - May 2008

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