When aluminium is exposed to the atmosphere, the top surface is covered by a thin layer of aluminium oxide. This reaction can also be achieved industrially in a controlled process.
The anodic oxidation (called 'anodisation' in French and 'eloxieren' in German) is an electrochemical process that consists of adding an additional layer on the surface of the part.
One of the methods is called sulphuric acid anodising: the part is plunged into an acid bath and electric current is applied simultaneously. The electrolysis enables the growth of the aluminium oxide layer while the acid creates local nanopores that keep the reaction going.
The layer obtained industrially is thicker than the natural process and varies generally between 5 to 50microns depending on the final application requirements. The layer prevents further oxidation and offers good resistance to wear and temperature.
Additionally this top layer can be coloured and in fact the top surface is porous and easily accepts dyes. A huge palette of colours is available. The final process consists of sealing these pores and fixing the colours by immersion in a bath.
Lemo is a designer and manufacturer of precision custom connection solutions. The company's high quality push-pull connectors are found in a variety of challenging application environments including medical, industrial control, test and measurement, audio-video, and telecommunications.
Lemo manufactures connectors made out of a vast range of materials in order to offer solutions in various environments. For instance, marine applications such as shipping, offshore oil, power plants and coastal industrial plants will require connectors resistant to salt water.
Special coatings can be applied to the surface of the connector: stainless steel or nickel aluminium bronze can be used to prevent rapid oxidation of the connector. For nuclear applications, materials are exposed to high energy radiations that will eventually alter the properties of materials. In this case Lemo uses stainless steel to reduce the ageing of the connector.
Today aviation applications, such as mil-aero, avionics and space, require high density interconnect and lightweight devices. The advantage of the high density connector is relative low mass for an important number of I/O pins that fulfil the requirements of commercial and military aviation sectors.
Lemo's new M series connector is focused on the designer that requires a MIL-38999 type of connector but in a much smaller and lightweight package, giving up none of the vibration, RFI, water ingress or corrosion specifications. These connectors use crimp contacts, which require more investment for assembly equipment (crimping tools rather than a simple solder iron). However on the long term and in case of large contact volumes that need to be assembled on wire, crimping the contacts rather than soldering is the solution.
"Connectors manufactured from aluminium raw material can be up to two times lighter than conventional brass connectors. To fulfil the RoHS (2002/95/CE) requirements, LEMO now uses exclusively eco-friendly aluminium completely lead-free," says Roger Vonlanthen Laboratory Manager with Lemo connectors.
After anodising, the material keeps its metallic aspect and offers a nice aesthetic finish. Finally, for those who want to reduce their ecological impact, aluminium is 100 per cent recyclable without any loss of its natural qualities, it melts at about 660°C. Recycling of aluminium requires only about 5 per cent of the energy initially necessary for its production.
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Serge Buechli is Product Manager, LEMO SA, Ecublens, Switzerland. www.lemo.com