Glass is made up of various oxides that fuse together and react with each other when heated to create a glass. These include silica, sodium oxide, and calcium oxide. The raw materials from which these materials are formed are sand, soda ash and limestone. The soda ash acts as a flux; Simply put, it lowers the melting point of the batch composition. Lime is added to increase the hardness of the glass. Glass designed for windshields also contains several other oxides: magnesium oxide, potassium oxide, and aluminum oxide.
The raw materials are weighed out in the correct amounts and combined with a small amount of water. Once manufactured, it will be fed into a large tank for melting, implementing the float glass procedure. The batch is initially heated to a molten state and then fed into a tank known as a float chamber, which contains a bath of molten tin. At the entrance, the temperature of the can is about 1,835 degrees Fahrenheit, while at the exit the temperature of the can is a little cooler, 1,115 degrees Fahrenheit. In the float chamber, the glass does not sink into the can but floats on top of it, moving through the tank as if on a conveyor belt. The perfectly flat surface of the can causes the molten glass to also become flat, while the high temperatures clean the glass of impurities. The decrease in temperature at the exit of the chamber allows the glass to harden enough to pass to the next chamber. After the glass leaves the float chamber, it is picked up by rollers and fed into a furnace called a Lehr. In this furnace, the glass gradually cools to about 395 degrees Fahrenheit, after the glass leaves the Lehr, it cools to room temperature. It is now very hard and strong and ready to be cut.
Cut and Tempered
The glass is cut with a diamond scribe. Diamond is used because it is harder than glass. Next, the cut piece needs to 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 conforms to the mold.
After this forming step, the glass must be hardened in a heating step called tempering. The glass is first heated to approximately 1565 degrees Fahrenheit and then blown out with jets of cold air; this process hardens the glass. This allows the car glass, when damaged, to break into many small pieces of glass with no sharp edges.
In this process, two sheets of glass are bonded together with a layer of plastic. Lamination is done in a special oven. The plastic layer is often tinted to act as an ultraviolet filter. When laminated glass breaks, the broken pieces of glass are bonded to the tear-resistant plastic layer and the broken sheet remains transparent. Unlike traditional safety glass, laminated glass can be processed more
After lamination, the windshield is ready to be assembled with plastic molds for placement. Known as encapsulation, this assembly process is usually done at the glassmaker. First, the windshield is placed in a mold. Molten plastic is then injected into the mould, when it cools it forms a plastic frame around the glass. The windshield is then shipped to the automobile manufacturer, where it is installed on a vehicle. Installation is done through a process that uses a polyurethane adhesive to bond the windshield to the vehicle body.
This step includes raw material testing and melting temperature verification. As the glass is made, special devices are used to look for defects in the glass. Other automatic devices have been developed to measure the dimensions and radius of curvature after the windshield has been shaped.
Safety glass used in windshields must meet certain specifications for properties such as impact resistance and strength. Safety standards have been developed to ensure the quality of the glass.