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Material
Glass is made up of several oxides that fuse and react with each other when heated to form a glass. These include silica, sodium oxide and calcium oxide. The raw materials from which these substances are made are sand, soda ash and limestone. acts as a soda ash flux; Simply put, it lowers the melting point of the batch composition. To increase the hardness of glass, lime is added to it. Glass designed for windscreens also contains several other oxides: magnesium oxide, potassium oxide and aluminum oxide.
Process
The raw material is weighed in the right quantity and mixed with a small amount of water. Once made, it would be poured into a large tank to melt, applying the float glass process. Initially, the batch is heated to a molten state, and will then be poured into a tank known as a float chamber, which contains a bath of molten tin. At its entrance, the temperature of the tin is approximately 1,835 °F, while at the exit the temperature of the tin is slightly cooler at 1,115 °F. In the float chamber, the glass does not sink into the tin, but floats on top of it, moving through the tank, like a float on a conveyor belt. The perfectly flat surface of the tin also allows the molten glass to become flat, while the high temperature washes away the impurities in the glass. The lower temperature at the exit of the chamber allows the glass to harden enough to pass into the next chamber. After the glass exits the float chamber, rollers pick it up and feed it into a furnace called a lehr. In this furnace the glass is slowly cooled to about 395 °F, after the glass exits the laver it cools to room temperature. It is now very hard and strong and ready to be cut.
chopping and tempering
The glass is cut using a diamond scribe. Diamond is used because it is harder than glass. Next, the cut piece must be molded into shape. The glass sheet is placed in a metal mold. The glass-filled mold is then heated in a furnace to the point where the glass takes shape in the mold.
After this shaping step, the glass must be hardened in a heating step called tempering. First, the glass is heated to about 1,565 degrees Fahrenheit, and then blasted with a blast of cold air, a process that hardens the glass. This allows the auto glass to break into many small pieces of glass without sharp edges when it is damaged.
laminating
In this process two sheets of glass are joined together with a layer of plastic. Lamination takes place in a special oven. The plastic layer is often colored to act as an ultraviolet filter. When laminated glass breaks, the broken pieces of glass remain bonded to the tear-resistant plastic layer, and the broken sheet remains transparent. Unlike conventional safety glass, laminated glass can be further processed
molding
After laminating, the windscreen is ready to assemble with plastic molds being made to fit it. Known as encapsulation, this assembly process is usually performed at the glass manufacturer. First, the windscreen is set in a mould. Next, molten plastic is injected into a mold, which when it cools forms a plastic frame around the glass. The windscreen is then shipped to the car manufacturer, where it is fitted to the vehicle. Installation is done by a process that uses polyurethane adhesive to attach the windscreen to the vehicle body.
quality control
This step includes testing the raw material and checking the melting temperature. As glass is made, special equipment is used to look for defects in the glass. Other automated tools have been developed to measure the amplitude and radius of curvature after the windscreen has been shaped.
Safety glass used in windscreens must meet certain specifications with respect to properties such as impact resistance and strength. Safety standards have been developed to ensure the quality of the glass.
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