Glass is made up of several oxides that when heated fuse and react with each other to create a glass. These include silica, sodium oxide and calcium oxide. Raw materials from which these materials are formed are sand, soda and limestone. Soda 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. Windshield glass also contains several other oxides: magnesium oxide, potassium oxide, and aluminum oxide.
The raw materials are weighed in the right amount and mixed with a small amount of water. Once made, it is sent to a large tank to be melted, performing the float glass process. First, the charge is heated to a molten state and then passed into a tank called a float chamber, which contains a bath of molten tin. At the entrance, the temperature of the can is around 1,835 degrees Fahrenheit, while at the exit, the temperature of the can is slightly cooler at 1,115 degrees Fahrenheit. In the float chamber, the glass does not dip into the can, but floats on it and moves through the tub like on a conveyor belt. The perfectly flat surface of the tin causes even the molten glass to become flat while the high temperatures clean the glass of impurities. The reduced temperature at the exit of the chamber allows the glass to harden sufficiently to be moved to the next chamber. After the glass leaves the float chamber, it is picked up by rollers and fed into a teaching furnace. In this furnace, the glass is gradually cooled to about 395 degrees Fahrenheit, after the glass leaves the gauge it cools to room temperature. It is now very hard and strong and ready to be cut.
cutting and tempering
The glass is cut with a diamond scriber. Diamond is used because it is harder than glass. Next, the cut piece needs to be shaped. The pane of glass is placed in a metal mold. The glass-filled mold is then heated in an oven to the point where the glass forms into the shape.
After this shaping step, the glass must be tempered in a heating step called tempering. First, the glass is heated to approximately 1,565 degrees Fahrenheit and then blasted with cold air jets. This process hardens the glass. As a result, the car glass can break into many small pieces of glass without sharp edges if damaged.
In this process, two panes of glass are bonded together with a layer of plastic. The lamination takes place in a special oven. The plastic layer is often tinted to act as a UV filter. When laminated glass breaks, the broken glass remains bound to the tear-resistant plastic layer and the broken pane remains transparent. In contrast to conventional safety glass, laminated glass can be further processed
Once laminated, the windshield is ready to be assembled using plastic molds so it can be mounted. This assembly process, known as encapsulation, is typically performed at the glass manufacturer. First, the windshield is placed in a mold. Next, molten plastic is injected into the mold which, when cooled, forms a plastic frame around the glass. The windshield is then shipped to the automaker where it is installed in a vehicle. Installation is through a process that uses a polyurethane adhesive to bond the windshield to the vehicle body.
This step includes checking the raw materials and checking the melt temperature. Special equipment is used in the manufacture of the glass to look for flaws in the glass. Other automated devices have been developed to measure dimensions and radii of curvature after the windshield has been formed.
Safety glass used in windshields must meet specific specifications for properties such as impact resistance and strength. Safety standards have been developed to ensure the quality of the glass.