Basics of Glass Tempering and Heat Strengthening
On a daily basis you encounter glass in all shapes, sizes, and compositions. Glass is used in many applications ranging from the glass for your cell phone screen to your car’s windshield. You can also find glass in impact and explosion resistant lighting applications in demanding environments like coal mines and oil rigs. In all these applications, glass must be able to withstand a certain level of abuse and still maintain performance. In this video we review the basics of glass tempering and how this process results in a stronger glass product.
Tempered glass, commonly referred to as safety glass is used for intense, demanding applications. Glass can be strengthened using a controlled heating and cooling process. This makes it more resistant to mechanical and thermal stress over standard annealed glass. Tempering does not alter other important characteristics such as light transmission, specific gravity, or the coefficient of expansion.
Tempering is accomplished by first heating the glass above its strain temperature but below its deformation temperature. Next, the external surface of the glass is rapidly cooled or quenched. Because the inner material cools at a slower rate compared to the outer material, thermal differential creates compressive stress on the glass surface. The internal tensile stress is controlled by the compressive stress of the surface. This compressive stress must be neutralized before catastrophic failure can occur.