Physics and Technology
🔥 Tempered Glass
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 as 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
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 lower than tempered glass but higher than annealed glass. It is about twice as strong as ordinary annealed glass, with less optical distortion. When fractured, it breaks into larger fragments — advantageous in laminated applications where retention of fragments is desired.
International Standards
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US
ASTM C1048 — United States
Defines mechanical strength and fragmentation requirements for tempered and heat strengthened glass.
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EU
EN 12150 — Europe
Specifies performance criteria for thermally toughened soda-lime silicate safety glass.
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EU
EN 1683 — Europe
Specifies performance criteria for heat strengthened glass.
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AU
AS/NZS 2208 — Australia & New Zealand
Governs tempered and heat strengthened glass under safety glazing materials.
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IEC
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.
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.
Frequently Asked Questions
What is the difference between tempered glass and heat strengthened glass?
Tempered glass is cooled rapidly after heating, making it 4–5 times stronger than annealed glass and causing it to break into small, blunt fragments. Heat strengthened glass is cooled more slowly, making it approximately twice as strong as annealed glass while breaking into larger pieces — beneficial in laminated applications.
What temperature is used in the tempering process?
Both tempered and heat strengthened glass are produced by heating annealed float glass to approximately 620–650°C. The key difference lies in the cooling rate: rapid quenching for tempered glass and a slower controlled cooling for heat strengthened glass.
Which international standards does Glaspedia glass comply with?
Glaspedia tempered and heat strengthened glass comply with major global standards including ASTM C1048 (USA), EN 12150 and EN 1683 (Europe), AS/NZS 2208 (Australia & New Zealand), and relevant IEC standards for BIPV applications.
What causes anisotropy in tempered glass and is it a defect?
Anisotropy appears as rainbow-like patterns visible under polarized light and is caused by the internal stress distribution created during the tempering process. It is not considered a defect but can affect visual uniformity, particularly on large glass facades.
Why is heat strengthened glass preferred in laminated glass applications?
When heat strengthened glass fractures, it breaks into larger fragments compared to tempered glass. In laminated applications, these larger fragments are held together by the interlayer, helping to maintain structural integrity and retain the glass in place — which is critical for safety and overhead glazing.
How does Glaspedia control optical distortion in heat treated glass?
Glaspedia (South Star) uses advanced inspection technology, including the Osprey 10 Complete system by LiteSentry®, combined with optimized cooling processes to minimize roller wave, bow, warp, and anisotropy — ensuring the glass meets both performance and aesthetic standards for modern architecture.