How Automotive Glass Works

Tempered Glass

Tempered glass is just as important to a vehicle's safety as laminated glass, but it differs greatly in both form and function. This type of glass is used for the surrounding windows of car (also called the sidelites) and the back window (or backlite). Tempered glass is created by heating and then rapidly cooling the glass to room temperature by ushering it through a system of blowers.

The surface of the glass cools much faster than the center of the glass and contracts, causing compressive stresses, while the center of the glass expands because of its temperature, producing tensile stresses. What does that mean? Imagine a piece of glass that could be pulled or stretched to a certain length (tensile stress), while being pushed down and compressed (compressive stress) simultaneously. Both the pulling and pushing stresses achieved through the heating and cooling process give tempered glass its tensile and compressive strength. The differences between these two give the glass 5 to 10 times the amount of strength it originally had.

The edges on a typical piece of tempered glass are very weak. This is caused in part by the rapid release of heat during the cooling phase of the tempering process. To help compensate for this weaker area, the glass is ground down on the edges. When tempered glass breaks, it shatters into small, dull pieces. The differences between the compressive and tensile stresses are what enable the glass to break in this way. The pulling and the pushing of the glass produce a significant amount of energy during the tempering process. When the glass breaks, this energy is released and causes the glass to break into small pieces [source: AIS Glass Solutions].

Because of its strength, tempered glass can withstand the daily use of automobile driving. Without it, our cars would be filled with glass every time we encountered a pothole, got into a fender bender or closed a door.