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 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 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
- ASTM C1048 — United States Defines mechanical strength and fragmentation requirements for tempered and heat strengthened glass.
- EN 12150 — Europe Specifies performance criteria for thermally toughened soda-lime silicate safety glass.
- EN 1683 — Europe Specifies performance criteria for heat strengthened glass.
- AS/NZS 2208 — Australia & New Zealand Governs tempered and heat strengthened glass under safety glazing materials.
- 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.