Jochem Sauer discovers some demanding applications for epoxy,
polyurethane and acrylic adhesives, which demand total reliability and
long term durability
Adhesive bonding is often the best alternative or indeed the only way to
join plastic or composite materials to one another or to components made
from other materials. Contrary to mechanical fixing methods, adhesives
avoid the local concentration of stresses while bonding generally results
in superior joints with regard to fatigue resistance. Adhesives also
provide a smooth appearance, uncluttered by protruding fasteners.
A key factor in the development of innovative construction vehicles, for
example, was the advantages gained from using plastic materials for body
parts and casings - a pleasing design, improved ergonomics and
substantial cost savings, compared with traditional metal parts. In this
case a two-part methacrylate adhesive bonds an ABS plastic cover to the
steering column and attaches local metal reinforcements and hinges on
external ABS surface. The benefits include excellent adhesion and
durability, minimal surface preparation and fast curing. Some
methacrylates provide a lap shear strength as high as 22MPa and a peel
strength of 11N/mm, and can reach an initial green strength of more than
1MPa in as little as four minutes, allowing fixing clamps to removed
early in the production cycle.
The aerospace industry is another big user of structural adhesives. The
thermoplastic components of civilian and military aircraft, such as
interior fittings and panels, are often bonded using high performance,
two-part polyurethane adhesives, which can be used on a wide range of
materials, including polycarbonates, ABS, acrylics, PEEK and so on, and
usually a wipe-down with isopropanol is all that is required by way of
surface preparation. In the case of acrylic panels, polyurethane
adhesives also offer a high degree of elasticity to avoid cracking during
the wide temperature fluctuations sustained by modern aircraft.
One of the latest applications of UV-curable acrylic adhesives is to bond
the protective polycarbonate layer to the aluminium treated data storage
area of the second polycarbonate section of Digital Versatile Disks
(DVDs). Curing (which has to be fast to keep up with production) is
achieved in just 1.5 seconds. The author’s company developed a special
product for this application, which also features high optical purity and
a refractive index equal to that of polycarbonate.
Two-part epoxy and polyurethane adhesives are also used suitable for
bonding composite materials. There are many examples, but among the more
demanding applications are wind turbine blades, civil engineering
constructions and exterior locomotive panels. The author’s company has
supplied both types for the bonding of wind turbine rotor blades
comprising GRP vanes and an epoxy matrix. A special epoxy with a lap
shear strength of 30MPa is used to meet the high loads placed on
blade/hub joint. Meanwhile, the longest composite bridge in the world -
the nine year old 113m long Aberfeldy bridge - has GRP pultrusions bonded
with a thixotropic, gap-filling epoxy adhesive, and an epoxy is also used
to bond GRP sandwich structures forming the rounded front cabs of Lok
2000 locomotives, many of which are used by Swiss Federal railways.
Jochem Sauer is international market development manager, Ciba Specialty
Chemicals, Basel, Switzerland. you can find out more about the companies
adhesives and tooling products by visiting www.ciba-araldite.com
Back to Fasteners and Adhesives June 2000
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