Toughened glass, otherwise known as safety glass or tempered glass, is used in applications where the chances of stress and damage are high. This type of glass is much, much stronger than ordinary glass and can be found in vehicle windows, glass table tops, kitchen appliances, mobile devices, countertops, shower doors, and more. Toughened glass can be made either with the use of heat and cold or with chemicals.
Glass Manufacturing Process
Thermal tempering process
Most toughened glass is manufactured through a thermal process that involves the heating of annealed glass to above 620 degrees Celsius as it moves through a heating oven or furnace. After it has been heated, the glass undergoes a rapid cooling process in which it is hit by high-pressure jets of cold air for several seconds. This rapid cooling causes the surface of the glass to cool down and harden much faster than the interior of the glass, which still flows for a time. The balance of the tensile stresses of the interior and the compressive stresses of the surface of the glass is what makes tempered glass so strong.
Chemical tempering process
This alternative manufacturing process makes use of certain chemicals and ion exchange to make annealed glass tougher. In this process, the glass is submerged in a bath of molten potassium nitrate. An exchange occurs between the sodium ions in the exterior of the glass and the potassium ions from the bath. The potassium ions are 30% larger than the sodium ions, which causes the exterior of the glass to go into compression and strengthens the glass.