Лако-красочные материалы — производство

Automobile construction is subdivided into the manufacture of passenger cars, trucks, buses and motor homes.

In the future, weight reduction will become increasingly important both in passenger car construction and industrial vehicle construction, although this may not be gathered from the development which has taken place in the past, in particular in passenger car construction. A reduction in fuel consumption through the further optimization ofaerodynamics is essentially no longer possible and, in many cases, is not necessary because cars are mostly driven at speeds less than 80 km h~1 in town and in light traffic, and air drag is not important under such operating conditions. With regards to traffic development, driving conditions between 80 and 0 km-1 (traffic jam) will probably increase. Important reductions in fuel consumption have been achieved by optimization of the drive train, yet the vehicle weight was not reduced for a variety (including fashion) reasons. With regards to foreseeable traffic scenarios and the resultant consumer behavior, these reasons will surely not persist, however.

While passenger cars continue to be built the way they are today, there will be very little room for weight reduction in the bodywork and chassis. Moreover, as vehicle history and development teaches us, the use of steel as the predominant material in self-supporting bodies, and of welding as the predominant joining technique, will surely continue. Although, lightweight metals or plastics may be used instead, from the point of costs the use of light metals (especially aluminum alloys) would require a drastic reduction in the number of components. This may be achieved by means of special body framings and simplification ofthe assembly process, such that a higher materials cost will be compensated by a lower production cost. Bonding alone, or in combination with riveting, is required when joining largely preshaped and pre­developed components. Although the recycling of aluminum materials is essential mainly for energy reasons, it is gratifying to realize that bonded aluminum con­structions will continue to be recycled in years to come.

Today, recycling problems are the main reasons for not opting for the structural use of plastics. Although purely thermoplastic components — which are predominantly welded rather than bonded — may be recycled several times, fiber-reinforced plastics —

which are generally required to produce high-strength components — still encounter recycling problems that, as yet, have not been solved. There is, therefore, much reason to believe that steel in particular — being a ‘good-natured’ and low-priced, recyclable construction material — will continue to predominate passenger car construction, especially as the often-referred-to corrosion problems may be solved, or have already been solved. Again, the use of bonding may result in a weight reduction in the structural steelwork, because it offers more versatile design options compared to welding. During manufacture, the joints need not be accessible from both sides, and the minimum sheet thickness may be less than the 0.6 mm otherwise required by spot welding. A further reduction in weight may be obtained by using ‘sandwich structures’ for large-surface components, such as the roof or the underbody. In contrast to welding, bonding may simplify the production process, because the final assembly of a body — that is, fitting the underbody or placing the roof — is the final operation sequence, when all other processes such as surface finishing have been completed. Hence, the production conditions would be clearly improved.

For many years, fully bonded steel bodies have been tested to trial stage, without any problems. Compared to their welded competitors, their properties are surpris­ingly favorable, with the low strength values of adhesives complying with the requirements of hem flange bonding or the joining of glass and steel, because the surfaces being bonded are relatively large. The damping performance and fatigue strength of bonded steel bodies are considerably better than those of welded ones. Likewise, their deformation behavior — that is, the energy storage in case of imposed deformation, or accident safety — is extraordinarily positive (see Section 8.2.2.1).

Due to limitations in the production sequence, the processing conditions play an important role alongside those purely mechanical viewpoints when choosing the correct adhesive. For example, adhesives may show a good adherence to nontreated sheets, or at least be sufficiently resistant to ‘washing away’ in dip-painting baths.

Structural bonding must be performed without any special pretreatment on sheets coated with corrosion-protection oil, but this no longer presents any problems. Although bonding is produced ‘against all the rules’ here, the results have been successful, with even glued windscreens contributing considerably to the rigidity of the car body nowadays. Only one problem remains to be solved, namely the development of a simple, suitable technology for bonding in a repair shop in addition to bonding for manufacture. At present, very few cases exist where bonding can be successfully used for repair purposes, an example being the repair of a windscreen damaged by flying stones. If the windscreen cannot be repaired by means of adhesive setting by UV irradiation, then several alternative adhesives are available for gluing-in a replacement screen, with the final join retaining the original, factory, quality.

Repair technology will be developed further since it is expected that, in the near future, fully bonded vehicles made from steel sheets or perhaps even aluminum will enter the market. If bonding technology is consistently applied in bodywork construction, it is probable that structural weight reductions of 20% can be achieved.

This means a saving of about 60 kg on the body-in-white of a medium class vehicle weighing about 300 kg.

Nerf bars, spoilers, hand straps, hooks and mirrors are all bonded by using pressure — sensitive adhesives (PSAs) in the form ofhigh-performance foamed acrylic adhesive tapes, or thermally postcuring, pressure-sensitive self-adhesive structural tapes (e. g. mirrors bonded onto windscreens). Seals (e. g. in doors) are increasingly bonded by means of special foamed adhesive tapes owing to a noise reduction and simplification of the assembly process. In the production of seats, a variety of adhesive materials are employed, for example in the upholstery and seat covers.

Another interesting field of application are commercial vehicles, or vehicles used by public authorities such as taxis, police cars and municipal vehicles. Rather than being coated with a uniform paintwork, they are provided with a film adhesive applied on the original paintwork, which may be removed after the intended service life, increasing the resale value owing to the protection of the original paintwork.

Truck manufacture is an important area where adhesive bonding is also increas­ingly used. Here, many trailers are constructed from fully bonded sandwich structures that are self-supporting, torsion-resistant, and have excellent insulation properties as no fasteners are employed which may build up heat bridges.

Even safety-relevant components such as seat belts may be bonded to the sidewalls of the vehicle, as long as the adhesive force ofthe material used is higher than the stability of the sidewalls. As in the passenger compartments of cars, various bonded compo­nents are utilized in trucks, such as the floor coverings and seats. Bonding is used not only for joining but also for vibration damping and sealing; for these purposes, foamed polyurethane (PU) tapes and other high-build materials are employed.

Closed-top containers, as might be used in furniture vans, are manufactured by joining beams to sidewalls by means of high-build adhesives. Two-part epoxy resin adhesives are used for bonding planks, or foamed adhesive tapes for vibration damping. In the majority of cases, the optical results achieved with bonding are better than those possible with riveting. In addition, the outer wall ofthe truck can be used as an attractive advertising surface, by using film adhesives with large-area prints that are strongly visible even at twilight and in the dark, owing to their retroreflecting properties.

The manufacture ofbuses also relies on the bonding of strips, hinges, fabrics, seats and whole sidewalls, as well as various foils. The front screens, side windows and rear windows are glued to the body using moisture-setting PU adhesives. High-build adhesives may also be used here as sealing and vibration-damping materials.

Owing to the use of efficient, low-priced production techniques, a well-equipped motor home may cost the same as a ‘superclass’ vehicle with simple equipment, despite lower serial production quantities. As the cost factor is very important here, the manufacturers generally use glass fiber-reinforced plastics and other types of plastic that can be joined with adhesives in order to create the body shell. Other examples include the bonding of strips and damping/insulation material such as Styrofoam.

Adhesives are also increasingly used for the bonding of electronic components and identification labels or nameplates on the vehicle. By using high-performance adhesives, bonded joints can even be produced in motor cars that are exposed to important thermal and mechanical stresses.