Materials • Processes • Finishes


such as gas detectors used in OEM, medical, laboratory and similar applications, as well as mass flow controllers, blood pressure cuff monitors, ventilators and oxygen concentrators. These valves are suitable for use on air or other gases that are clean or dry, non-corrosive and non-flammable. Other actuation applications have been seen in the


aerospace, automotive and other industries. The variable- geometry chevron, for example, is a shape memory alloy structure that reduces aircraft noise on take-off, then adopts a different shape in flight to cut noise and conserve fuel.


Superelasticity


As well as the shape memory effect, these alloys have another important characteristic: superelasticity, which is also referred to as pseudoelasticity. This occurs when an alloy is deformed slightly above its transformation temperature. The effect is caused by the stress-induced formation of some martensite above its normal temperature. For this reason, the martensite instantly reverts to undeformed austenite once the stress is removed, which manifests as a highly elastic effect in the bulk material, with elastic strains in the region of 10 per cent possible. Wires with this property will therefore extend well beyond the normal ‘elastic limit,’ springing back to their original shape very easily. Such materials have been used to make ‘unbreakable’ spectacle frames and were popular for antennas on early mobile telephones. But the medical industry remains the key market for shape


memory alloys because of the materials’ biocompatibility. To this end, Nitinol Devices & Components (NDC) is to establish a new research and development and manufacturing centre in Costa Rica later in 2010. “Costa Rica presented the best combination of operating cost, workforce talent and tax advantages for a low-cost manufacturing facility,” explained Jeff Lenigan, vice president of operations at NDC. This new plant will produce medical guide wires, using


NDC’s core expertise in Nitinol processing, combined with extrusion, coating, and assembly operations. The plant is situated in a Free Trade Zone in San Jose, which also hosts other medical device companies. In its first year of operation, NDC plans to hire 30 employees – rising to 200 in the long- term – and invest around $3.5 million. Mitchell Tatum, the plant’s general manager, commented:


“We plan to deliver product from the new plant by the first quarter of 2011.” NDC also offers a wealth of information about shape


memory alloys on its website: the ‘Nitinol University’ section includes technical papers and design tips – including a ‘stent calculator’ worksheet to help designers calculate parameters such as strut widths, lengths and foreshortening, as well as providing simple estimates of strain. Another company that is helping to make shape memory


alloys more accessible to new users is Johnson Matthey, which has developed an interactive online inventory tool so customers can find popular, in-stock sizes and obtain pricing and delivery information for products including its Nitinol superelastic tubing, wire and sheet. The inventory tools can be accessed via www.jmmedical.com. Johnson Matthey’s range of standard Nitinol products


includes superelastic alloys of various sizes, thicknesses and finishes. Each product type has its own inventory/ordering tool that can be accessed via the appropriate product line page. Nitinol tube, wire, sheet and machined parts are manufactured at the plant in San Jose, California, while micromachining takes place in San Diego. In 2009 SAES Memry – which is part of SAES Getters,


the Italian-owned shape memory alloy specialist – added Nitinol sheet to its portfolio of products for the medical device industry. The sheets, manufactured at the company’s facility in Germany, are available in a variety of alloy compositions, including some in the superelastic state. Each can be supplied in different conditions such as cold worked, flat annealed and shape annealed. Surface finish options include standard dark oxide, oxide-free, and ground or polished sheet surfaces. Biocompatibility means that many of the shape memory


alloys will continue to be attractive for use in medical devices, but there are countless other applications for which these unusual materials can deliver significant benefits. Designing components and assemblies to take advantage


of the shape memory effect or superelasticity requires some additional knowledge, and processing can be difficult using conventional machining operations, but support is often available from the suppliers and the advantages in terms of product performance can make the additional effort very worthwhile. l


Remelt capacity expanded S


apa Profiles UK Ltd is investing in the remelt facilities at its Tibshelf, Derbyshire, UK, plant.


The cost of this expansion is £5.4m and will raise capacity from 17k tonnes to 35k tonnes, making Sapa UK 60 percent self- sufficient for raw material billet supplies. The investment is aimed at providing first class consistent billet quality, thus ensuring the highest levels of profile quality to their customers. The ability to cast a full range of commercial alloys will also re-enforce the companies commitment to reduced lead


times and flexibility of supply. Environmental considerations are


another part of the investment ethos, as recycling is the ‘cornerstone’ of aluminium’s sustainability. Recycling aluminium saves up to 95 percent of the energy required for primary aluminium production. All Sapa customers are invited to take part in the recycling program and Sapa are more than happy to discuss the taking back of any scrap arising from customer processing.


This investment comes on the back


of the £6million spent by Sapa over the past two years on a new extrusion press line at Tibshelf, a recently built fabrication centre at Cheltenham, and the newly- acquired Redditch Application Centre, where customers and designers have the opportunity to make their products a reality utilising CAD and 3D software tools. l


Enter 27 or ✔ at www.engineerlive.com/ede


Sapa Profiles UK Limited is based in Cheltenham, Gloucestershire, UK. www.sapagroup.com


www.engineerlive.com 27


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