Thermal tempering

To increase the mechanical and thermal strength of glass, thermal toughening is available for glass thicknesses of around 3 mm or greater. This process involves uniformly heating the glass in an oven to in excess of 600°C and then quickly cooling it with cold air. This creates a compressive pressure zone on the surface of the glass which surrounds a tensile pressure zone within the glass core. The difference in these pressures gives toughened glass a mechanical and thermal strength that is 3–4 times greater than non-tempered glass.

Thermally toughened glass destructs into small glass particles. The glass has specific fracture patterns depending on the grade of thermal tempering. These patterns range from fine particled (tempered safety glass) to coarse and/or dagger-like (heat-strengthened glass).