Appliance Design - March 2009 - (Page 28)

METALS cut sheets, blanks, 3D components, blocks, and sandwich constructions with solid metal panels surrounding a metal foam core. Some are available preassembled. Porvair’s MetFlame burner emitters, for instance, can be purchased cut-to-size and assembled in a stainless steel frame that can be dropped into place. Metal foams can also be fabricated into custom shapes. While the benefits of metal foam have established it as a viable choice for designers, the suppliers say that the material cost is greater, in some cases twice the cost, and this discourages use of the material. A lack of knowledge was also cited as a reason that metal foams have not yet found a wider audience, but the suppliers point out that it is still a relatively young industry. As the benefits of metal foam become wider known, and suppliers work to improve these benefits and bring down costs, more applications for a lightweight metal material are expected. < For more information, email: Fraunhofer: thomas.hipke@iwu.fraunhofer.de FPE Fischer: info@fpe-fischer.de M-pore: info@m-pore.de Porvair Advanced Materials: mheamon@selee.com ShApE MEMory FoAMS A new metal alloy with shape memory attributes has been developed by researchers at Boise State University, Boise, Idaho, and Northwestern University, Evanston, Ill., that may lead to smaller, lighter, and more precise pumps and other devices. Shape memory alloys change shape when subjected to an external stimulus such as temperature or magnetic fields. While the material changes shape, it still has the memory of its original shape and will return to that form when it is exposed to a different stimulus or if the original stimulus is removed. Temperature is considered too slow for many uses. Magnetic shape change, on the other hand, can change shapes almost as soon as the field is engaged. One material that is especially appropriate for shape memory applications in magnetic fields is a nickel-manganesegallium alloy (Ni-Mn-Ga), says Peter Mullner, a professor and alloy expert at Boise State. The alloy is especially good for devices that require very precise, repeatable, and rapid positioning such as pumps, sonar devices, microscopes, and medical devices. For relatively large samples such as a 6 mm length, a length change of 10 percent (0.6 mm) could be achieved within less than a millisecond. In pumps, for example, the magnetic shape memory alloy (MSMA) would control the position (on/off) of a valve. The advantage is that with MSMA, the on/off positions can be attained very precisely and in very short time. Compared to devices using solenoid technology, the frequency may see an improvement by a factor of 10 (given the same amount of stroke). A single crystal of the Ni-Mn-Ga alloy deforms by 10 percent when subjected to the magnetic field. It will retain its new shape when the field is turned off and return to its original shape when the field is rotated 90 Deg. Shape change is more pronounced with a single crystal because its internal structure is oriented in the same direction throughout the entire piece and will move predictably. However, single crystals are expensive and time consuming to make. Because of cost considerations, most of the alloys used are polycrystals, which contain many smaller crystals. Polycrystals have a grain structure pointing in every direction and as they The magnetic shape memory alloy (MSMA). Photo credit: P. Mullner, M. Chmielus, and S. Donovan, Boise State University, and D. Dunand and Y. Boonyongmaneerat, Northwestern University. move in various directions, the individual movements mutual obstruct each other. By foaming the polycrystalline alloy, crystals have more room to grow and expand, says Mullner. To create the foam, molten Ni-Mn-Ga is poured into a mold of porous sodium aluminate salt. After cooling, the salt is leached out with acid. In testing, samples of the foam were exposed to a 1-Tesla magnetic field that rotated at 12,000 rpm, while a laser system measured the induced strain. The shape change was only about 0.12 percent, which was significantly less than a single crystal, but better than polycrystals, and a cause for optimism. Since then, Mullner says they have gotten significantly better results, but declined to give actual numbers until new results are published in a scientific journal later this year. Mullner says that the foam structure may not get to 10 percent deformation as with a single crystal, but because of cost tradeoffs, he believes the material will find many applications. Any device such as an actuator, pump, valve, positioning tool, shutter, etc., that requires a fast and precise motion is a potential application. If long stroke and lightweight is important, the advantages of magnetic shape memory foam become even more relevant. < 28 applianceDESIGN March 2009 www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - March 2009

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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