Tempered glass is a type of glass that is processed by treating the float glass, by applying controlled thermal and chemical treatments, so as to increase the strength. The light transmission and solar radiant properties of tempered glass are as same as float glass. Tempered glass is also called as safety glass or toughened glass.
Tempered or toughened 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, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, mobile phone screen protectors, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.
Properties of Tempered Glass
A glass is considered tempered when the compressive stresses on the surface of the glass have a value of minimum 69MPa. If this value exceeds 100Mpa, then the glass is considered safety glass. This characteristic of tempered glass makes it safe for high-pressure and explosion-proof applications. The important properties of tempered glass are:
1. Impact Resistance
The impact resistance of tempered glass is high compared to float glass. This helps to easily resist higher temperatures.
2. Versatility
Tempered or toughened glass can be made into different unique styles and creative applications for building interior design.
3. Strength
The strength of tempered glass is four to five times the strength of float glass. This, hence, can sustain high wind load or snow loads.
4. Fabrication of Tempered Glass
Cutting and resizing the tempered glass is not possible. Any fabrication required must be performed before tempering the glass panels.
5. Optical distortion of Tempered Glass
The tempered glass has a hazy and unclear vision because the tempering process causes optical distortions in tempered glass.
6. Failure of Tempered Glass
Here, the breaking pattern of the glass is considered, where it breaks into small blunt pieces. These pieces are not harmful and hence are used widely for the making of safety glass.
The outer surface of the tempered glass is subjected to compression and the inner surface is subjected to tension. This action is the reason why the tempered glass breaks into granular chunks instead of splintering as in the case of normal glass.
Manufacture of Tempered Glass
The manufacturing process of tempered glass is performed by heating a normal glass or float glass to a uniform temperature of 700-degree celsius. It is then cooled in the annealing lehr and finally, the tempered glass is produced. Hence, the process is time-consuming compared to normal glass and is therefore a costly material.
Compressive stresses are induced on the surface of the tempered glass and it is this compressive stress that provides the tempered glass increased strength.
Uses of Tempered Glass
The important uses of tempered glass in buildings are:
- Used as Balusters, escalator, staircase, handrails, etc.
- Used as a partition member for homes, airports, offices, and resorts.
- Used for sliding doors and windows.
- It is used as a decorative panel in interior design.
- The tempered glass can be used as a facade for buildings that add up aesthetics.
Disadvantages
Tempered glass must be cut to size or pressed to shape before tempering, and cannot be re-worked once tempered. Polishing the edges or drilling holes in the glass is carried out before the tempering 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 tempered 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.
Nickel sulfide defects can cause spontaneous breakage of tempered glass years after its manufacturing
