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Safety glass is a type of glass which is designed to resist breaking, and to break in a way which minimizes the risk of injuries in the event that the glass cannot withstand the forces which are exerted on it. Car windows are classically made from safety glass to promote safety in collisions, and this type of glass can also be used in regular house windows, eyeglasses, laboratory glassware, and a wide variety of other products. As its name would seem to imply, safety glass is meant to be safer than ordinary glass.
There are two ways in which safety glass can work: tempering or laminating. Tempered glass is made by treating the glass very carefully as it is heated and cooled to increase its tensile strength, making it hard to break. If tempered glass does break, it snaps apart into rounded chunks, rather than breaking up into jagged pieces which could potentially be very dangerous. People who have seen a broken side window in a car have probably seen an example of tempered safety glass. We are looking queries majorly from North India.
Toughened or tempered glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering creates balanced internal stresses which cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards. The granular chunks are less likely to cause injury.
As a result of its safety and strength, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.
Toughened glass is physically and thermally stronger than regular glass. The greater contraction of the inner layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass. For glass to be considered toughened, this compressive stress on the surface of the glass should be a minimum of 69 mpa. For it to be considered safety glass, the surface compressive stress should exceed 100 mpa. The greater the surface stress, the smaller the glass particles will be when broken.
The term toughened glass is generally used to describe fully tempered glass but is sometimes used to describe heat strengthened glass as both types undergo a thermal 'toughening' process. There are two main types of heat treated glass, heat strengthened and fully tempered. Heat strengthened glass is twice as strong as annealed glass while fully tempered glass is typically four to six times the strength of annealed glass and withstands heating in microwave ovens. The difference is the residual stress in the edge and glass surface.
It is important to note that the tempering process does not change the stiffness of the glass. Annealed glass deflects the same amount as tempered glass under the same load, all else being equal. But tempered glass will take a larger load, and therefore deflect further at break.
Toughened glass is used when strength, thermal resistance and safety are important considerations. The most commonly encountered tempered glass is that used for side and rear windows in automobiles, used for its characteristic of shattering into small cubes rather than large shards.
Toughened glass is also used in buildings for unframed assemblies (such as frameless doors), structurally-loaded applications, and any other application that would become dangerous in the event of human impact.