Annealed or float glass when broken forms large jagged sharp shards which can cause injury. Glass toughening is the process of heating and then cooling float glass. This heating and cooling process alters the chemical structure of the glass and results in the glass becoming 5 times stronger and resistant to impact. The properties of the glass when it does break are also different, toughened glass shatters into many very small and generally less sharp or dangerous fragments. Toughened glass is sometimes referred to as tempered glass or safety glass. Security glass is not the same thing as toughened glass, although security glass is similar in that it has been chemically or thermally treated to significantly increase its strength, security glass is manufactured for specific requirements such as to be blast proof or bulletproof etc.
Toughened glass is made from annealed glass treated with a thermal tempering process. A sheet of annealed glass is heated to above its “annealing point” of 600°C; its surfaces are then rapidly cooled while the inner portion of the glass remains hotter. The different cooling rates between the surface and the inside of the glass produce different physical properties, resulting in compressive stresses in the surface balanced by tensile stresses in the body of the glass. These counteracting stresses give toughened glass its increased mechanical resistance to breakage, and are also, when it does break, what cause it to produce small, regular, typically square fragments rather than long, dangerous shards that are far more likely to lead to injuries. Toughened glass also has an increased resistance to breakage as a result of stresses caused by different temperatures within a pane.
Toughened glass has extremely broad applications in products for both buildings and, automobiles and transport, as well as in other areas. Car windshields and windows, glass portions of building facades, glass sliding doors and glass partitions in houses and offices, glass furniture such as table tops, and many other products typically use toughened glass. Products made from toughened glass often also incorporate other technologies, especially in the building and automotive and transport sectors.