Published on February 22, 2014
INTRODUCTION Toughened glass is also know as Tempered glass. 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 puts the outer surfaces into compression and the inner surfaces into tension. Such stresses 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. 2
HISTORY The first patent on tempered glass was held by chemist Rudolph A. Seiden, born in 1900 in Austria. Though the underlying mechanism was not known at the time, the effects of "tempering" glass have been known for centuries Its popularity has increased in recent decades because of its use in the automobile and construction industries, as well as in microwaveable glassware. Among the most common current uses are for side and rear windows and windshields in automobiles, display cases, patio doors, and shower doors. 3
PROPERTIES 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 Any cutting or grinding must be done prior to tempering. Cutting, grinding, sharp impacts and sometimes even scratches after tempering will cause the glass to fracture The strain pattern resulting from tempering can be observed with polarized light or by using a pair of polarizing sun glasses. 4
STEPS INVOLVED IN MANUFACTURING OF TOUGHENED GLASS Steps involved in making tempered glass are as follows: 1. Cut the glass into the desired shape first. 2. Inspect the glass for imperfections 3. Sand the cut edges smooth 4. Wash the glass 5. Heat the glass in a tempering oven 6. Quench the glass to cool it 5
SPECIFICATIONS & SIZES OF TOUGHENED GLASS Glass type Thickness (mm) Toughened glass 2.8 3 4 5 6 8 10 12 15 19 22 25 Monolithic types Transparent, Bodily colored, Colorfully glazed, Film plated and Toughened glass Combination types Toughened insulating glass, Toughened laminated glass and Toughened insulating laminated glass Max size possible (mm) 5100 x 3200 Min. size possible (mm) 300 x 300 6
SAFETY Through the quenching process , the inside of toughened glass possesses the compressive stress , it will with stand the impact force to certain extent, even though it encountered greater load of impact and broke, its fragments seemed to lot of tiny particles with obtuse angle that hardly would do any harm to human body. While with the fragments of ordinary glass, they are similar to large size broken sharp pieces easily causing serious injuries to the people. 7
APPEREANCE OF FRAGENTS 8
USES 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 It is used for its characteristic of shattering into small cubes rather than large shards and is sometimes referred to as safety glass in this context 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. 10
ADVANTAGES The term "toughened glass" is generally used to describe fully tempered glass but is sometimes used to describe heatstrengthened glass as both types undergo a thermal "toughening" process. There are two main types of heat-treated glass: heatstrengthened and fully tempered. Heat-strengthened glass is twice as strong as annealed glass while fully tempered glass has 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 undergoes a similar deflection compared to tempered glass under the same load, 11
DISADVANTAGE Toughened glass must be cut to size or pressed to shape before toughening and cannot be re-worked once toughened. Polishing the edges or drilling holes in the glass is carried out before the toughening process starts. Because of the balanced stresses in the glass, damage to the glass will eventually result in the glass shattering into thumbnail-sized pieces. 12
NOTE: Steps involved in the manufacturing process of TOUGHENED GLASS can be seen in my next upload. For any mistakes and suggestion’s feel free to text here Mail id: email@example.com 13
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