II SHOP TALK
Page 95
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Traditionally, if you wanted to bond pieces of metal together you had little alternative to using the techniques of welding, brazing and riveting so long as oil and grease were present. In the hands of craftsmen these techniques can produce excellent results, but there can be problems of distortion. Moreover, the cost of replacement welding plant may not always be justified for operators of fewer :han half-a-dozen vehicles.
In recent years adhesives have been leveloped which can be viable and cost effective alternatives to traditional monding methods, even where there is a isk of contamination from oil and grease. The new adhesives are high merformance-toughened materials. They ire both replacing welding and being effectively used to refurbish parts well mutside the scope of traditional metalwinding methods. As well as reducing the isk of distortion, they can make joints with fewer corrosion problems, better ;eating and more even stress distribution. Another advantage is that there is no woud weld to grind flush with the rest of he adjoining section. The surface is left ;mooth and if painting is required this can >e undertaken without prior preparation. Companies such as Ciba-Geigy, Bostik, 3ritish Petroleum and Loctite are heading he research. Among products that this 'esearch has produced are toughened ingle-part epoxy adhesives. These have leen found to absorb stresses effectively wing to their structural composition. Any ocalised cracking or damage that could ake place can be arrested due to the ubbery constitution of the matrix. A problem with metal is that, because If the uniform atomic structure, both atigue and stress-corrosion cracks spread hrough it very easily. Computer lodelling techniques are now used to stablish the stress and strain distribution t the joint area. Optimum dimension can e established to reduce localised stress oints and determine the most effective rea.
Considerable developments have taken lace with anaerobic adhesives which set metal in the absence of air. They are seful for sealing or locking threaded, seal nd turned parts.
Permabond has developed an acrylic rhich absorbs oil. This makes it suitable r bonding components used on oily nvironments, such as gears and earings. Also, British Petroleum has cently developed an adhesive polymer ailed Epoc, capable of absorbing oil from luminium and steel structures and binding into its chemical structure. The ampany is also collaborating with Harwell to the use of glass-reinforced plastic to ond steel.