Лако-красочные материалы — производство

It has often been observed that the application of adhesives to metal fabrication, in common with many other technological innovations, was pioneered by the aircraft industry. It is ironic that this industry, in which safety and reliability command paramount attention, should lead the departure from traditional methods of joining. Today adhesives are used to bond critical parts in commercial and military aircraft and helicopters, spacecraft, rockets, missiles and the US Space Shuttle. The American Primary Adhesively Bonded Structure Technology (PABST) Programme, which ran from 1976-81, was an imaginative attempt to advance significantly the use of bonded structures in aircraft. The project involved the construction and testing of an entire adhesively-bonded fuselage section of a military aircraft.

The earliest structural adhesive application was made during the First World War for bonding the wooden frames of Mosquito aircraft; strength was adequate but, by today’s standards, moisture resistance was poor. Structural adhesive bonding of metal parts began in the early f940s with the introduction of Ciba Geigy’s Redux 775, phenol formaldehyde-polyvinyl formvar (the trade name is a composite of Research and Duxioxd airfield), to bond metal honeycomb to metal skins. The de Haviland Comet jet airliner was one of the first civil aircraft to make significant use of structural bonding with Redux 775, followed by the Trident, Nimrod and VCfO, and this adhesive is still in use today on the British Aerospace European Airbus; indeed, no other adhesive has such a good and well-proven track record. However, a cure temperature of 150 °С and pressures between 0.2 and 0.7 MNm~2 (25 and fOO psi) are required, and this spurred the development and use of alternative products. For example, epoxy-based filmic adhesives are commonly used which require lower curing temperatures and pressures, making the use of autoclaves and the cure cycle less expensive than with the phenolics.

The motivation in the aerospace industry to replace mechanical fasteners with adhesives stems from the desire to prolong aircraft life and to reduce costly maintenance. Rivet holes, for example, are points of weakness where fatigue cracks can form, and metal fasteners can corrode or loosen. Equally important is that aircraft are now designed to include a large amount of composite materials, and the fabrication of honeycomb sandwich panels frequently involves connecting dissimilar materials for the skin and core. The Fokker Friendship F27 airliner employed large amounts of adhesive in both load-bearing and secondary structures, the wing assemblies being tested up to 14.5 million cycles of reverse loading (Fig. 1.1).

The use of material combinations has continued in aircraft such as the Boeing 747, McDonnell Douglas DC10, Lockheed Tristar and Concorde, as designers recognised the high stiffness to weight ratio that can be achieved with these components. The sheet metal skin materials are predominantly aluminium alloys, although titanium and stainless steels are also used for special purposes. The honeycomb material is often aluminium foil but paper, laminated nylon paper and phenolic impregnated glass fibre are alternatives. As much as

50% of the airframe of modern military aircraft may be carbon fibre reinforced plastic (cfrp) composite, with adhesives being used for primary structural bonding. It is worth noting also that helicopter rotor blades are complex structures which are highly stressed and of limited fatigue life, and are wholly dependent upon adhesive to join the extruded aluminium spar, nomex core, grp skin and aluminium trailing edge.

Honeycomb structures are susceptible to physical damage because of their location and their weakness to loads, applied normal to the skin forces. Airlines and Air Forces are, therefore, developing repair techniques which they can carry out themselves in preference to purchasing expensive replacement components. For in situ repairs alternative techniques in terms of surface preparation, adhesive type and curing regime have to be used to those employed during initial manufacture. Surface preparation is vitally important bearing in mind that a typical airliner operating temperature range is from —80 °С to +80 °С, and for many aircraft salt spray conditions may
be severe. For the same reason the choice of adhesive is critical. Cold-cure products may be the only alternative for repair work despite their performance disadvantages. Finally, use of the correct curing temperature and pressure is important.