Although glass is heavy, it is an inexpensive material, it has very good melting properties and is easy to work with. What distinguishes it, is it's relatively resistant surface, especially against chemical influences. Nowadays, apart from its optical features, glass is also used as an element in car bodies. When bonded, it strengthens considerably. There are already cars in which the windscreen merges seamlessly into the roof.
Glass can be isolating and reflects the rays of the sun, UV-and X-rays. Coatings on and between the glass layers contain still unimaginable possibilities. One can generate current with glass or achieve a colour toning, dependent on the flow of current. Bullet-proof glass can protect the passengers against criminals, indeed, this increases the curb weight substantially. Even as simple laminated glass it can hardly be surmounted. Optical glass-fibres can transport enormous amounts of data quickly, and is also already being used in cars.
The first glass findings, glass melts, glass vessels and even spectacles, date back to before the birth of Christ. 4000 years earlier, in Mesopotamia the gaffers- (glaziers) blowpipe (figure 2) had already been discovered, this is an iron pipe with a wooden handle in which liquid glass is taken up and by turning, appropriate blowing and perhaps the application of a special form, the specific production of vessels and even of smaller flat-glass pieces was possible. It was not until the middle ages, that the window pane arrived in Europe and it wasn't until the 19th century, that flat glass could be produced industrially.
Glass is made up of about 75% silica sand. The rest is mostly sodium sulphate and calcium. The components are complemented by recycled glass and melted at approx. 1600°C. They are then cooled down in shallow troughs which are filled with tin. Due to the slow cooling down process, the molecules are not closely packed - as is common with metals - into crystals. It is also not completely liquid when it is cast and only takes on it's form as flat glass slowly in the troughs.
The curvature of the glass is produced by repeated heating, this time however, only to approx. 600°C. It is pretensioned through quick cooling down of specific areas using ventilating fans. This glass is used for side- and also mostly for rear windows. Through the pretensioning it is more stable, however, it is also more sensitive to punctate forces and the chipping off of small shards. This type of glass-pane can, e.g., be more easily destroyed by using a light hammer with a small head than a heavy one with a large impact area. When ruptured, it disintegrates into harmless, small blunt-edged fragments. Heating filaments or aerial wiring can only be integrated from the inside using the silk screen printing process containing a certain proportion of silver.
Laminated glass must always be cooled down slowly after each heating process. After being roller-milled, the panes are thinner and are made into multi-layer sheets which are interlaid with transparent foil. By the way, before the sheets are heated they are opaque, only after the bonding of the individual layers and when all the air has been extracted between the foil and the panes, does it become completely transparent.
For over 30 years now windscreens have to be built in this way. The use as side- and rear windows is possible and more favourable for the passengers, it also offers more protection against theft. Heating- and/or aerial wiring can be integrated into the foil and of course, the toning of the glass also poses no problem. Up to 500 extremely thin foils (0.01 micrometers) are possible. They can now be had in five layers, as an optional extra in the VW-Passat. Even more interesting, is the prospect of no longer having to scrape ice off the winscreen, even without the benefit of a garage. At the moment, the Fraunhofer-Institute is developing a coating of indium- tin-oxide, which not only keeps the screen warmer, it also makes it more resistant to scratches.
Recently, glass can also have a foil-like characteristic, it can be flexible and, e.g., can have a thickness of 0,1 millimeter, of course, then it's also no longer very heavy. It is created, when the molten glas is allowed to overflow to both sides of a gutter, after a certain distance, the two sides are brought together again. The result is, that both sides have a perfectly flat and smooth surface, differnt than if one of them had been cooled in a tin-bath. Through specific application of a salt-bath at relatively high temperature, do the surfaces become hard and scratch-resistant. One can now produce sheets up to the size of LCD-TV-screens, also the ability to be able to be used as computer touch-keys and touch-screen-monitors, doesn't seem to be far away either. 01/12