What makes a car's windshield stronger?
The front windshield of a car is a piece of glass used to keep out the rain and foreign matters on a high-speed moving car.
Compared with the door glass, the front windshield of a car is stronger. This is mainly because the windscreen is a three-layer structure: two layers of glass, in the middle of which there is a thin film to firmly stick them together. Even if they are broken, they will firmly stick to the fragments and will not fly out to hurt people.
This amazing film is PVB film.
Structure diagram of windshield
PVB is polyvinyl butyral, which is a kind of polymer material produced from petroleum. It is non-toxic, odorless, non corrosive, with excellent transparency, good insulation, impact resistance and tensile properties, as well as light resistance, cold resistance, aging resistance and other excellent comprehensive properties. Because it has a good adhesion to inorganic glass, and has transparent, heat-resistant, cold resistant, moisture-resistant, high mechanical strength characteristics, it is the best material for manufacturing safety glass in the world.
This is the production process flow chart of PVB.
PVB production process flow chart
The common thickness of PVB film is 0.38mm and 0.76mm. Of course, Japanese companies also have thicker products (such as 1.14mm and 1.52mm). The thickness of the intermediate film used in laminated glass for different purposes is different. To prevent foreign objects and theft, at least two layers of 0.38 film should be used, while bulletproof glass should use at least three layers of 0.76 or six layers of 0.38 film.
Before PVB film is used in automobile windscreens, it needs to be heated, stretched and cooled once to make the film reach the radian of automobile glass. This kind of heating stretching is the heating roller, while the cooling shaping is the conical cooling roller.
The temperature required for heating and drawing is not high. It is 90-120 ℃ according to different requirements, but the roller has higher requirements for temperature uniformity, usually ≤± 2 ℃. If it can be controlled within ± 1 ℃, the product quality can be further improved. At the same time, this kind of processing is carried out in a clean room with a level of 100000 or above. Therefore, the best choice here is to use electromagnetic heating roller.
Cooling setting also has requirements for temperature uniformity. The more uniform the temperature is, the better the product consistency is. Because of the defects of the structure of the common cooling roller, the temperature difference of the roller surface must be very large. Due to the requirement of temperature uniformity, this kind of roller emerges as the times require, that is, non condensation cooling roller, whose surface temperature uniformity is far better than that of ordinary cooling roller.
Heating roller + common cooling roller
Electromagnetic heating roller + cooling roller without condensation
With the combination of electromagnetic heating roller and non condensation cooling roller, the product performance has been greatly improved. At present, Xinyi Glass, a domestic automobile glass giant, has adopted this method. It has replaced dozens of sets of heat-transfer oil heating rolls + ordinary cooling rolls in the group with the combination of electromagnetic heating rolls + non condensation cooling rolls, which greatly improves the product performance.
It is because of PVB film that two pieces of glass are firmly adhered together that the strength of automobile windshield can be greatly improved, so it is also more solid.