Appliance Design - March 2009 - (Page 25)

METALS uids. The two different structures provide different mechanical properties that make them suitable for different applications. Closed-cell metal foams are typically used in structural, load-bearing applications, or as an impact-absorbing material, similar to the polymer foams found in a bicycle helmet because they provide higher strength, says David Dunand, professor at Northwestern University, Evanston, and an expert on metal-foam architecture. Dunand says that metal foams, especially open-cell foams, feature the mechanical strength, stiffness, and energy absorption that are much greater than those of polymer foams. As compared to polymers, they are more thermally and electrically conductive and they maintain their properties at much higher temperatures than polymers. The open-cell foams do have a structure similar to open-celled polyurethane foams, he adds. This structure provides metal foams with very high specific surface areas, which are good for fluid-flow applications. Their spongelike architecture is linked by ligaments, called struts, and it is these struts that create the additional surface area. In one application, for instance, a solid metal panel was replaced with a metal foam panel in a computer case and the computer’s internal temperature decreased by approximately 20 DegC. The cellular structure of metallic foams can be created through a number of techniques, including casting methods. Some of the more obvious methods include bubbling a gas through the molten metal, or mixing in a foaming agent. Another technique is to inject gas into a liquid metal under pressure, then slowly relieving the pressure, allowing MetFlame open cell reticulated metal foam from Porvair Advanced Materials. www.applianceDESIGN.com AD01084AmerN.indd 1 applianceDESIGN March 2009 25 12/10/07 11:26:17 AM http://www.americannickeloid.com http://www.americannickeloid.com http://www.appliancedesign.com

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Appliance Design - March 2009 Contents Editorial Shipments/Forecasts News Watch Transmitting Power Wirelessly Promises to Reduce the Ever-Growing Tangle of Cords and Cables Found in the Modern Home. There Are Different Technological Approaches for Achieving this Goal, and Some Are Already on the Market. Electrochemical Capacitors Can Provide an Extra Peak-Power Boost in Battery-Operated Appliances, Allowing Product Designs to Have Smaller Battery Packs. Metallic Foams Put the Properties of Metals into Lightweight Packages. Applications for this Emerging Technology Include Gas Burners, Heat Exchangers, and Electronics Housings. Hall-Effect Switches Are Compact and Provide a High Degree of Reliability and Durability as They Virtually Eliminate Mechanical Wear, Shock, and Contact Oxidation. Blowing Agents for Polyurethane Foam Insulation Face Increased Scrutiny Due to Global Warming Concerns, but Alternatives with Lower GWP Values May Provide Solutions to Meet These Challenges. Design Marts Association Report: AHAM Advertisers' Index

Appliance Design - March 2009

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