Tempered glass is a type of glass that is processed with thermal or chemical treatments, which increase its strength. The process of tempering leaves the outer surface of glass in a state of compression, and the interior in a state of tension. Due to these mechanical stresses, tempered glass breaks into granular pieces instead of shards with sharp edges, reducing the chance of injury. Tempered glass is also known as toughened glass or safety glass.
Due to its safety and strength, tempered glass is used in many industries and applications, which include construction projects. Some uses for tempered glass include vehicle windows, shower doors, refrigerator trays, architectural components, cell phone screens and cookware.
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Tempered Glass Properties
Tempered glass is both physically and thermally stronger than conventional glass. As previously mentioned, tempered glass is treated to create exterior and interior stress in the material. The compressive surface stress of tempered glass is balanced by the tensile stress in the body.
For glass to be classified as tempered, its surface must have a minimum compressive stress of 69 megapascals (10,000 psi). Then, for a tempered glass to be considered a safety glass, its surface compressive stress must exceed 100 megapascals (15,000psi). If tempered glass breaks, the increased surface stress will result in small circular pieces instead of sharp shards. This property makes tempered glass suitable for high pressure and explosion proof applications.
Tempered glass gets its strength from the compressive stress on its surface. On the other hand, annealed glass has almost no internal stress, making it very fragile - it forms microscopic surface cracks that break under tension. Tempered glass does not have these surface cracks, and this prevents propagation or expansion when breaking.
The main properties of tempered glass are summarized below:
- Versatility: Tempered glass can be shaped into different forms and styles to meet various applications.
- Impact resistance: The impact resistance of tempered glass is very high compared with float glass. This helps withstand extreme conditions and temperatures.
- Strength: Tempered glass can be 3 to 7 times stronger than annealed glass, making it suitable for more demanding applications with high environmental loads.
- Optical distortion: Tempered glass is not as clear as float glass, since the tempering process causes some optical distortions.
- Fabrication: Any cutting or grinding must be done before tempering, since these processes will cause fracture once the glass is tempered.
Applications of Tempered Glass
Tempered glass is used in applications that require thermal resistance, strength and safety. Passenger vehicles are a great example with the three conditions:
- Since they are often parked outdoors, vehicles are subject to constant heating and cooling (thermal resistance).
- Vehicles must also resist small impacts from road debris (strength).
- Sharp shards of glass represent an additional hazard if an accident occurs, and tempered glass does not break into shards (safety).
The properties of tempered glass make it suitable for construction projects and many industrial applications.
Tempered glass has many applications in the construction industry, which include commercial building envelopes and facades. Tempered glass can also be used in unframed assemblies such as frameless glass doors. Tempered glass is suitable for structurally loaded applications in general, and any application where glass can be a hazard in the event of human impact:
- Partitions for homes, offices, hotels and other commercial buildings.
- Doors and windows
- Decorative panels in interior design
Building codes demand the use of tempered or laminated glass in several cases. These include skylights, doorways, stairways, elevators and fire department access panels. Consider that specific requirements change depending on local codes.
Tempered glass is also used in homes. For example, some types of furniture and household appliances have tempered glass parts:
- Glass tabletops
- Frameless shower doors
- Glass shelves
- Glass near fireplaces
Tempered glass products can be found in restaurants, hotels, bars and other foodservice applications. They increase safety standards in these applications, by reducing the chance of glass-related accidents. Some types of tempered glass are designed for cooking and baking, which means they can be used safely in ovens and other cooking devices.
Disadvantages of Tempered Glass
Tempered glass is very useful in construction and other demanding applications. However, like any construction material, it has limitations that must be considered.
Tempered glass must be cut, pressed, polished and drilled before tempering, since it cannot be reworked later. Due to the balanced mechanical stresses in the glass, any damage will cause the glass to shatter. In spite of its high strength, tempered glass can break when exposed to certain conditions, and it is especially vulnerable to damage along the edges. However, a concentrated impact with enough strength in the middle of the glass can also cause shattering.
The safety implications must always be considered when using any type of glass. While tempered glass is safer than conventional glass, it can still shatter.