Toughened glass, also known as tempered glass, is a type of safety glass that has undergone a controlled thermal process to increase its strength over standard annealed glass. This process significantly increases the glass’s resistance to breakage and shattering, which is critical for a variety of applications where glass strength and safety are essential.
Toughening involves heating the glass to over 1200°F (650°C) and then rapidly cooling it with air blasts. This causes tension on the surface, while tension stresses form within the glass. The compressed surface layer increases the strength of toughened glass, making it roughly four times stronger than regular annealed glass of equal thickness. Toughened glass’s unique fracture pattern contributes to its increased safety. When broken, it breaks into small harmless granular chunks rather than jagged shards like annealed glass.
Toughened glass is widely used in buildings, vehicles, and other industries where impact and thermal resistance are required. Understanding its manufacturing process, properties, and applications is critical to ensuring maximum safety and performance.
How Is Toughened Glass made?
The toughening process for glass requires precise heating and cooling cycles.
- First, the annealed glass is inspected to ensure there are no flaws or impurities that could cause cracking or breakage.
- The glass is then placed in a high-temperature furnace and heated to approximately 1200°F (650°C), far exceeding its annealing temperature of 1000°F (538°C). At this point, the glass is soft and malleable.
- The heated glass is then removed from the furnace and transferred to a cooling cabinet. Strong blasts of ambient air from air jets or nozzles quickly cool the glass’s exterior surfaces.
- As a result, the inner part stays temporarily heated and expands, while the outer surfaces contract and solidify first. As the inner section attempts to contract, the now-rigid outer surfaces prevent inward movement. This creates balanced compressive and tension forces within the glass.
- The compressed outer layer increases the strength of toughened glass by up to 4-5 times that of regular annealed glass. Meanwhile, the inner tension region prevents surface defects from spreading inward.
- After quenching, the glass is inspected again for optical or surface defects. Properly toughened glass has a compressed surface, which makes it more scratch resistant than untreated glass.
This entire process must be carefully conducted, keeping in mind its precise temperatures, cooling rates and glass compositions to achieve the best version of the glass.
Properties of Toughened Glass
- Increased Strength: Toughened glass is most notable for its significantly higher strength, which is approximately 4-5 times greater than annealed glass of the same thickness and composition. This increase in strength is caused by the compressed surface layer formed during the quenching process.
- Resistance: In addition to increased strength, toughened glass is more resistant to impact forces and thermal loads. It can withstand more force before cracking or breaking.
- Safety: When toughened glass breaks, it crumbles into small, relatively harmless granular chunks rather than dangerous shards. This significantly lowers the risk of serious cutting injuries.
- Thermal Resistance: Toughened glass can withstand higher temperature differences between the surface and edge than annealed glass before cracking occurs. This thermal resistance is useful in applications like fireplaces.
- Surface Compression: Toughened glass’s surface is compressed, making it more resistant to scratches, abrasion, and weathering than annealed glass.
However, once produced, toughened glass cannot be reworked or reheated because it will shatter. Prior to toughening, any necessary cutting, drilling, or edging must be completed. Additionally, because of its higher surface compression, it is more prone to handling flaws and edge damage.
Advantages of Toughened Glass
Safety and security aspects
Toughened glass provides superior safety and security benefits over regular annealed glass. It is less prone to break from impacts, wind loads, and other forces thanks to its improved breakage resistance, which is attributable to the increased strength obtained during the thermal toughening process. However, if toughened glass breaks, it fragments into small, relatively harmless granular chunks rather than sharp shards, significantly lowering the risk of serious cutting injuries. Toughened glass is an excellent choice for applications that prioritise human safety, such as door glass, overhead glazing, and vehicle windscreens, etc.
Longevity and environmental impact
Toughened glass provides significant benefits in terms of durability and environmental impact. The higher surface compression caused by the toughening process improves the glass’s resistance to scratches, abrasion, and weathering. This extends its service life significantly. Furthermore, toughened glass’s ability to withstand higher thermal loads reduces the risk of cracking or fracturing caused by temperature differences, adding to its durability. Toughened glass is fully recyclable at the end of its useful life, which contributes to sustainability.
Energy efficiency
Toughened glass provides significant energy efficiency benefits. It can be treated with low-emissivity (low-E) coatings to improve its thermal insulation properties. Toughened low-E glass helps minimise heat transfer in energy-efficient windows and glazing systems, which lowers heating and cooling energy costs. Furthermore, toughened glass’s ability to withstand temperature changes without cracking makes it suitable for use in passive solar building designs, where it can effectively harness and retain solar energy while minimising heat loss.
Toughened Glass Uses
Architecture and Building Construction
Toughened glass is widely used in the architecture and building construction industries due to its exceptional strength, safety, and durability. It is widely used in glazing systems such as curtain walls, skylights, overhead glazing, and interior divisions. Toughened glass’s enhanced impact resistance makes it an excellent choice for applications where glass breakage is a concern, such as high-traffic areas, storefronts, and entryways. Furthermore, toughened glass is commonly used in the manufacture of safety glass for doors, windows, and balconies, providing an important barrier against accidental breakage and ensuring safety.
Automotive industry
The automotive industry is a major consumer of toughened glass, particularly for windscreens and side windows. Toughened glass’s increased strength and impact resistance are critical in protecting passengers in vehicles in the event of a collision or other impact. When shattered, toughened glass fragments into small, relatively harmless granular chunks, it reduces the possibility of getting serious injuries. This distinct fracture pattern is an important safety feature, especially for windscreens, which are intended to remain intact during a collision and protect people from getting harmed.
Electronics and Home Appliances
Toughened glass is widely used in the electronics and home appliance industries because of its increased strength, safety, and aesthetic appeal. It is widely used in the production of smartphone and tablet screens, as it is more scratch and impact resistant than regular glass. Toughened glass is used in home appliances, such as oven doors, refrigerator shelves, and microwave windows, providing increased thermal resistance and durability. Furthermore, the sleek and modern appearance of toughened glass adds to the aesthetic appeal of electronic devices and appliances.
Conclusion
Toughened or tempered glass outperforms regular annealed glass in terms of strength, safety, and durability. Toughened glass is expected to see increased use in industries that value safety, security, and resilience as technology advances. Understanding this high-performance glass material is critical for applying its properties to modern design and engineering solutions. Toughened glass is guaranteed to fulfil its potential benefits through proper handling, quality control, and regulatory compliance.
FAQ’s
- What is the difference between toughened glass and normal glass?
Toughened glass is heat-treated to increase its strength and breaks into small granular chunks when broken, whereas regular glass breaks into sharp shards.
- Is toughened glass unbreakable?
No, toughened glass is not unbreakable, but it is approximately 4-5 times stronger than standard annealed glass of the same thickness.
- How do you check if glass is toughened or not?
There are several methods for determining whether glass is toughened: look for surface roughness/distortion, tap the glass, or inspect the internal stress patterns with polarised light.
- Which is better tempered or toughened glass?
Toughened and tempered are two terms used to describe the same type of heat-treated safety glass, which is equally strong and performs well.