Physics and Technology
Tempered glass is produced by heating annealed float glass to around 620–650°C and then rapidly cooling it with high-pressure air. This cooling process is also known quenching. This process creates compressive stress on the surface and tensile stress in the core, making the glass four to five times stronger than ordinary annealed glass. When fractured, it breaks into small, blunt fragments rather than sharp shards, reducing injury risk.
Heat strengthened glass is produced by heating annealed float glass to approximately 620–650°C, similar to the tempering process, but then cooled at a slower rate. This controlled cooling creates surface compressive stress that is lower than tempered glass but higher than annealed glass. As a result, heat strengthened glass is about twice as strong as ordinary annealed glass. It has less optical distortion due to lower stress level. When fractured, it breaks into larger fragments compared to tempered glass, which is advantageous in laminated applications where retention of fragments is desired.
International Standards
To ensure safety and reliability, Glaspedia tempered and heat strengthened glass comply with most global standards.
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ASTM C1048 (United States)
Defines mechanical strength and fragmentation requirements for tempered and heat strengthened glass.
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EN 12150 (Europe)
Specifies performance criteria for thermally toughened soda-lime silicate safety glass.
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EN 1683 (Europe)
Specifies performance criteria for heat strengthened glass.
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AS/NZS 2208 (Australia & New Zealand)
Governs tempered and heat strengthened glass under safety glazing materials.
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IEC Standards (International)
Govern tempered glass use in Building Integrated Photovoltaics (BIPV) applications.
Aesthetics
The tempering or heat treating process can introduce optical effects that influence design. Roller wave, bow, or warp may cause reflections to appear uneven, particularly on large façades. Anisotropy, visible as rainbow-like patterns under polarized light, results from stress distribution within the glass. While not defects, these phenomena affect visual uniformity.
South Star mitigates distortion and anisotropy through advanced inspection systems, Osprey 10 Complete by LiteSentry®, and optimized cooling processes, ensuring heat treated glass meets both functional and aesthetic expectations.
Glaspedia tempered and heat strengthened glass exemplifies the balance between physics, safety, and design. Its strength and compliance with international standards make it indispensable, while careful management of optical effects ensures it remains a material of choice for modern architecture and technology.
What is the main difference between tempered and heat strengthened glass?
Tempered glass is cooled rapidly (quenched) making it 4-5 times stronger than annealed glass and breaks into small, blunt fragments. Heat strengthened glass is cooled slower, making it about twice as strong as annealed glass, and breaks into larger fragments which is ideal for laminated applications.
How is tempered glass manufactured?
It is produced by heating annealed float glass to approximately 620–650°C, followed by a rapid cooling process using high-pressure air, which creates compressive stress on the surface and tensile stress in the core.
What global standards does Glaspedia safety glass meet?
Glaspedia glass complies with major international standards including ASTM C1048 (United States), EN 12150 and EN 1683 (Europe), AS/NZS 2208 (Australia & New Zealand), and various IEC Standards for BIPV applications.
Does the tempering process affect the optical clarity of the glass?
Yes, the heating and cooling process can introduce optical effects such as roller wave, bow, warp, or anisotropy (rainbow-like patterns under polarized light). While these affect visual uniformity, they are inherent to the process and are not considered defects.
How does South Star improve the visual quality of heat treated glass?
South Star minimizes optical distortion and anisotropy by utilizing optimized cooling processes and advanced inspection systems, such as the Osprey 10 Complete by LiteSentry®.
Why choose heat strengthened glass over tempered glass?
Heat strengthened glass has less optical distortion due to lower stress levels. Furthermore, when it breaks, it forms larger fragments, which is highly advantageous in laminated glass applications where you want the broken glass pieces to be retained safely.