Manufacturing Process
The manufacturing process of heat treated glass begins with glass melts being created from raw materials such as silica sand, soda ash, limestone, and recycled flat glass at high temperatures ranging between 2400 °C to 2600 °C in a furnace. This melts down the materials and forms a liquid that can be manipulated. The liquid glass is then poured into molds or sheets and allowed to cool slowly in an annealing oven at a precise rate known as the glass transition temperature. This annealing process relieves internal stresses in the glass.
Thermal Strengthening
Heat Treated Glass annealing is complete, the glass can undergo thermal strengthening. This process involves reheating strengthened glass to just above its transition temperature, which is around 550°C, and then rapidly cooling the surfaces while maintaining the core of the glass at a higher temperature. This causes compression stresses to develop at the surfaces and tension stresses in the inner portion of the glass. The uneven cooling and resulting internal stresses make the glass up to 4 times stronger and more resistant to impact and flexural stress than regular annealed glass.
Heat Soak Testing
Prior to installation, some thermally strengthened glass undergoes a heat soak testing process. This involves heating the glass to around 300°C for several hours. The heat causes any nickel sulfide inclusions, which pose a slight risk of spontaneous breakage, to stress relieve without breaking. Any glass containing inclusions that may have broken during use is identified and replaced before installation. This additional step ensures the glass will perform safely as intended.
Chemical Strengthening
An alternative to thermal strengthening is chemical strengthening, also known as chemical tempering. This involves submerging annealed glass in a molten salt bath of potassium salts. Ions in the bath are then exchanged for smaller sodium ions in the glass surface. This induces additional compression stresses in the glass surfaces and tension in the interior through ion exchange. Chemically strengthened glass can be up to 10 times stronger than regular annealed glass and has additional advantages like reduced breakage from impact and rigidity.
Advantages
Safety
One of the key advantages of heat strengthened and chemically strengthened glass is improved safety performance compared to regular annealed glass. In the event of breakage, heat treated glass fractures into small pieces rather than large, jagged shards like standard annealed glass. This significantly reduces the risk of serious cuts and lacerations. The internal stresses also make it more resistant to impacts and force, allowing it to maintain its integrity under more stress before breaking completely.
Durability
The increased strength and rigidity of heat treated glass means it can withstand more abuse and damage than standard annealed glass without breaking or needing replacement. Thermally and chemically strengthened glass is much less prone to chipping or damage from everyday wear and tear, weathering, and minor impacts. This extended performance and lifespan make it a durable option appropriate for high-traffic areas.
Scratch Resistance
Glass manufacturers have also found that chemical strengthening creates a layer of compression on the glass surface that enhances its resistance to abrasion and scratching. Tests have shown chemically strengthened glass can withstand abrasive forces up to 10 times greater than regular float glass before visible damage occurs. This durability against scratches makes chemically strengthened glass well-suited for applications such as retail storefronts.
Architectural Flexibility
The ability to manufacture larger pieces of heat treated glass has expanded architectural design possibilities. Thermal and chemical strengthening allow for larger glass panels, doors, skylights and other glazing applications that were not possible with standard annealed glass which is limited to smaller sizes due to strength and safety concerns. This has enabled much more open interior spaces, expansive views through glass, and innovative building designs with floor-to-ceiling windows and structural glass elements.
Through heat treatment and other manufacturing enhancements, glass has vastly improved strength and safety properties compared to ordinary annealed glazing. The capability to produce rigid, long-lasting pieces has significant benefits for both consumer protection and architectural freedom. While possessing some increased brittleness upon breakage, strengthened glass provides greater durability, impact resistance, and reliability as a building material. Its use allows greater design creativity while helping ensure structural integrity and user security.
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Ravina Pandya, Content Writer, has a strong foothold in the market research industry. She specializes in writing well-researched articles from different industries, including food and beverages, information and technology, healthcare, chemical and materials, etc. (https://www.linkedin.com/in/ravina-pandya-1a3984191)
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