Appliance Design - January 2008 - (Page 51)

SHIELDING/EMI in rack-mounted equipment where individual circuits may need to be periodically removed and replaced. Beryllium-copper fingerstock gaskets combine high levels of EMI shielding effectiveness with spring-finger wiping and low closure force properties. Berylliumcopper’s high tensile strength and superb electrical conductivity are ideal for shielding over a broad frequency range. Supplied in either standard or custom lengths for high-volume applications, strips are available in a wide variety of cross-sections. For low-compression grounding contacts, individual fingers are available with pressuresensitive adhesive for convenient peel-andstick application. Although the standalone electrical conductivity of fingerstock is unrivaled, other factors such as the dimension and number of slots in the fingerstock and surface contact area in an assembly can affect the final shielding performance with the result that elastomer approaches may actually provide better performance. Other metal gaskets such as PCB card cages, connector and panel shields, and knitted wire mesh exist to provide a solution for static applications that require good shielding performance without any environmental sealing. Molded and extruded elastomers. By combining an elastomer with a conductive filler such as nickel/graphite, a material can be created that provides both EMI shielding and an environmental seal. These materials lead to the even dispersion of the conductive filler within the elastomer to provide uniform physical and electrical performance. The elastomeric binder and the dispersed conductive filler can be manufactured into almost any shape using molding, extrusion or die-cutting processes. It is also possible to overmold the material onto plastic or metal components to provide a one-piece shielded housing that can speed and simplify assembly of an appliance sub-assembly. Although several elastomers can be used, silicone is usually the material of choice due its ability to compress at low closure forces and its excellent compression set performance across a very wide temperature range. Designers can expect to achieve shielding effectiveness in the region of 80 dB from 100 MHz to 10 GHz (Chomerics Cho-Seal 6371) using these types of materials. www.applianceDESIGN.com AD09074Web.indd 1 Extruded conductive elastomer gaskets can be supplied in a wide range of solid and hollow cross-section configurations. With a hollow section, conductive elastomers require even lower force in order for them to be compressed, and they also have larger deflection ranges. This makes them ideal for use in applications such as appliance door sealing where it is often difficult or inconvenient to generate high closure forces and where there may be significant tolerance build up over long lengths. Foam-based gaskets. A more recent development in the EMI shielding market has been the emergence of wrapped foam gaskets. These materials have been developed to provide economical shielding in highvolume applications. Typical uses include shielding and sealing of doors, faceplates and backplanes. Flexibility “Good enough” just won’t cut it in competition – whether you’re playing a sport or trying to win market share. Performance that is just “good enough” won’t set your appliance apart from all the others. Weber Knapp offers the flexibility and skill to design a hinging solution around your specific requirements. So you’re not boxed into using an “off-the- shelf” hinge that is just “good enough”. We bend over backwards to give you something better! Let us perform for you! 800.828.9254 www.weberknapp.com sales@weberknapp.com For more Information Enter 117 applianceDESIGN January 2008 51 6/28/07 10:20:27 AM http://www.weberknapp.com http://www.weberknapp.com http://www.appliancedesign.com

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Appliance Design - January 2008 Contents Editorial Shipments/Forecasts News Watch Makers of Commercial Refrigeration Equipment Turn to Variable-Speed Motors to Improve Energy Efficiency. New Motor Design and Control Scheme Makes Brushless Motors More Economically Feasible for a Wider Range of Applications. External Gas Molding, a Relatively New Technique, Solves Many of the Challenges Associated with the Injection Molding of Large Plastic Parts. Plastic Housings Offer Many Benefits: EMI Protection Isn't One of Them. But, New Materials and Techniques are Solving that Problem. Choosing the Optimal Strategy for Effective EMI Shielding Depends on Both Mechanical and Electrical Requirements Ethernet-Enabled Microcontroller Makes Networking Schemes Easier and More Cost Effective to Implement The Ever-Changing Array of Microcontroller Memory Options Makes it Imperative to Keep Abreast of What's Available to Determine the Optimal Choice for an Application. A Vast Range of Components and Finished Products will be Exhibited at the Country's Preeminent HVAC/R Show, AHR Expo, which is Scheduled for Jan. 22-24 in New York. Advertiser's Index Association Report: PRBA

Appliance Design - January 2008

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