Tempered glass is a type of safety glass. It is processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into conpression and the inner surfaces into tension. Such stresses cause the glass, when broken, to crumble into small granular chunks, The granular chunks are less likely to cause injury. As a result of its safety and strength, it has a high ability of pressure resistance, heat-resistance,and shock resistance.
Toughened glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it well above its transition temperature. The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time. During the cooling process, the surface is faster in cooling and solidifying than inner side of the glass,and when the inner side continues its cooling shrinkage, the tension stress comes up to increase the strength and heat-resistance of the glass.