- Types of Glass
- 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 interior into tension. Such stresses cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards as plate glass (a.k.a. annealed glass) does. The granular chunks are less likely to cause injury.
As a result of its safety and strength, toughened glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, mobile screen protectors, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.
Toughened glass is physically and thermally stronger than normal 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 megapascals (10,000 psi). For it to be considered safety glass, the surface compressive stress should exceed 100 megapascals (15,000 psi). As a result of the increased surface stress, if the glass is ever broken it only breaks into small circular pieces as opposed to sharp jagged shards. This characteristic makes tempered glass safe for high-pressure and explosion proof applications.
It is this compressive stress that gives the toughened glass increased strength. This is because annealed glass, which has almost no internal stress, usually forms microscopic surface cracks, and any applied tension gets magnified at the surface, reducing the applied tension needed to propagate the crack. Once it starts propagating, tension gets magnified even more easily, causing it to propagate at the speed of sound in the material. Consequently, annealed glass is fragile and breaks into irregular and sharp pieces. Any cutting or grinding must be done prior to tempering. Cutting, grinding, and sharp impacts 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.
Toughened glass is used when strength, thermal resistance, and safety are important considerations. Passenger vehicles, for example, have all three requirements. Since they are stored outdoors, they are subject to constant heating and cooling as well as dramatic temperature changes throughout the year. Moreover, they must withstand small impacts such as from road debris such as stones as well as automobile accidents. Because large, sharp glass shards would present additional and unacceptable danger to passengers, toughened glass is used so that if broken, the pieces are blunt and mostly harmless. The windscreen or windshield is instead made of laminated glass, which will not shatter into pieces when broken while side windows and the rear windshield is typically toughened glass.
Other typical applications of toughened glass include:
Shower doors and bathroom areas
Exhibition areas and displays
Computer towers or cases
Buildings and structures
Household electrical appliances
Solar energy industry
Toughened glass is also used in buildings for unframed assemblies (such as frameless glass doors), structurally loaded applications, and any other application that would become dangerous in the event of human impact. Tempered and heat strengthened glass can be three to seven times stronger than annealed glass. Building codes in the United States require tempered or laminated glass in several situations including some skylights, near doorways and stairways, large windows, windows which extend close to floor level, sliding doors, elevators, fire department access panels, and near swimming pools.
Tempered glass is also used in the home. Some common household furniture and appliances that use tempered glass are frameless shower doors, glass table tops, replacement glass, glass shelves, cabinet glass and glass for fireplaces.
Cooking and baking
Some forms of tempered glass are used for cooking and baking.
Most touchscreen mobile devices use some form of toughened glass, as do some aftermarket screen protectors for these devices.
An alternative chemical toughening process involves forcing a surface layer of glass at least 0.1 mm thick into compression by ion exchange of the sodium ions in the glass surface with potassium ions (which are 30% larger), by immersion of the glass into a bath of molten potassium nitrate. Chemical toughening results in increased toughness compared with thermal toughening and can be applied to glass objects of complex shapes.
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 any portion will eventually result in the glass shattering into thumbnail-sized pieces. The glass is most susceptible to breakage due to damage to the edge of the glass, where the tensile stress is the greatest, but shattering can also occur in the event of a hard impact in the middle of the glass pane or if the impact is concentrated (for example, striking the glass with a hardened point).
Using toughened glass can pose a security risk in some situations because of the tendency of the glass to shatter completely upon hard impact rather than leaving shards in the window frame.
The surface of tempered glass does exhibit surface waves caused by contact with flattening rollers, if it has been formed using this process. This waviness is a significant problem in manufacturing of thin film solar cells. The float glass process can be used to provide low-distortion sheets with very flat and parallel surfaces as an alternative for different glazing applications.
Float glass: clear float glass &tinted/colored float glass: euro grey float glass, light grey float glass, dark grey float glass, light blue float glass, dark blue float glass, ford blue float glass, euro bronze float glass, golden bronze float glass , pink float glass, black float glass, euro grey reflective float glass, light grey reflective float glass, dark grey reflective float glass, light blue reflective float glass, dark blue reflective float glass, ford blue reflective float glass, euro bronze reflective float glass, golden bronze reflective float glass , pink reflective float glass, low e glass
Clear patterned/figured/rolled glass, tinted patterned/figured/rolled glass
Pattern: nashiji, flora, kasumi, mistlite, karatachi, mayflower masterlite, millennium,aqualite, baroque, bubble, wood etc.
Acid etched glass, frosted glass, sandblast glass etc.