Did you know, that in the building of a bus, about 250 kgs of adhesive is needed?, and that the manufacturers of the adhesives are, among other things, working on optimising their weight? Think about it, the using of this amount, can mean the achievement of as much as 20 percent weight-saving with new developments, this can, after all, amount to as much as 50 kgs. One additional (slender) passenger could be carried.
The polyurethane based adhesives must be so chemically neutral, that they don't pose a danger for the people working with them. Modern adhesives of this type don't even need to carry any respective warning markings. These are single-component adhesives, which harden chemically, depending on the surrounding humidity and temperature. Of course this and the type of skin-formation is also dependent on the application amount.
Other demands made on the bondings may interest you. The adhesive may never harden or lose it's softening agent completely. At the same time, it must maintain the connection of metal to glass under all conditions, since this stabilizing bonus has already been calculated into total construction. These adhesives don't have much problems with temperatures, they can easily stand -50°C or lower, and 150°C or mostly even higher temperatures.
Adhesive bonding can be used well on metals, glass-fibres and carbon fibres, which makes them more suitable for the future than welding seams. Hole-drilling is no longer necessary, indeed particularly pointless in the case of carbon fibres. High temperatures do not occur during the assembly either. Therefore however, sometimes the construction must be thus adapted, that the area next to the adhesive seam is not exposed to higher demands.
These are not the only demands to which the adhesive is exposed. On the edges of the windscreen it should feel like rubber. To do this, like rubber, it also contains soot, which when constantly exposed to UV-rays, can lead to unsightly smearing. Neither the bus-driver nor his boss would be happy with smeared windscreens and definitely not with additional visits to the car-wash. This is why modern adhesives contain ingredients to prevent such smearing.
No, as far as demands are concerned, we're not finished yet. Give a thought to the always growing safety standards. There are the multiple-layer, enormously heavy windscreens to be installed and, mostly when refitting, the possible unevennesses which have to be ironed out. Here it also depends on how the adhesive surface can be shaped or smoothed. Since this type of vehicle is mostly found in the upper price segment.
This is only one example of the application of adhesives. There are hundreds of thousands of applications and just as many different types. In this case, the 'all-purpose universal adhesive', is rather a compromise. Most conspicuously, for the type of adhesive described here, is in the construction of modern high-rise buildings, where thousands of glass windows, either double- or triple-paned and/or bullet-proofed, are kept in place purely by adhesives. 07/13