Appliance Design - January 2008 - (Page 50)

SHIELDING/EMI Cho-Seal 6371 molded parts. Soft-Shield 3500 consists of nickel-plated nylon wrapped around a urethane foam core. that 10 or more years ago, appliances were essentially robust electromechanical pieces of equipment whereas today they typically contain large amounts of complex and sensitive digital and analog circuitry. Couple this to a general trend of more demanding operating conditions — especially for portable appliances designed for outdoor use — and one is faced with a fairly demanding set of criteria combined with a strong need for good EMI shielding. When addressing the shielding aspect of appliance design, it makes good sense for OEMs to try and work closely with EMI shielding material manufacturers. This will enable the OEMs to draw upon the knowledge and experience of people whose focus is entirely on shielding solutions. This is especially true if custom parts are being considered, but still valid even when standard, off-the-shelf parts are able to do the job adequately. An individual appliance is likely to have several areas that require some form of EMI shielding. In order to make the right choice of material for each, the designer will need to consider several factors, including the shielding performance required, mechanical considerations such as the closure forces and tolerance build-up, whether the mating parts are dynamic or static, and physical aspects. For example, the material may be exposed to high shear or compressive forces, environmental concerns such as exposure to moisture and humidity, and perhaps resistance to extreme heat or flame. Thought should also be given to the manufacturability and ease of assembly of a particular shielding solution. This is especially true for appliances produced in high volume. The trend for manufacturing to move to low labor cost countries in Asia and Eastern Europe is a clear indicator of how important reducing assembly costs is to appliance OEMs. Material options The EMI shielding materials that appliance designers have at their disposal can be broken into five broad groups: metal gaskets; molded or extruded elastomers; foam-based gaskets; conductive plastics; and adhesives, inks and coatings. Metal Gaskets. All-metal EMI shields and gaskets have been in existence the longest of all materials developed to combat electrical noise. They are still relevant for a large number of applications, particularly www.applianceDESIGN.com 1/3/07 12:29:46 PM For more Information Enter 116 50 applianceDESIGN AD02074BTM.indd 1 January 2008 http://www.tog-l-loc.com http://www.tog-l-loc.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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