page_title: Tempered glass
section_title: Manufacturing
hierarchical_section_title: Tempered glass / Manufacturing
caption_attribution_description: English: Meat case filled with frozen turkeys with a broken tempered glass window. Picture taken from a Winn-Dixie supermarket.
context_page_description: Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tension. Such stresses cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards as plate glass does. The granular chunks are less likely to cause injury.
  As a result of its safety and strength, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, mobile phone screen protectors, bulletproof glass components, diving masks, and various types of plates and cookware.
context_section_description: Tempered glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it well above its transition temperature of 564 °C (1,047 °F) to around 620 °C (1,148 °F). The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time.
  An alternative chemical toughening process involves forcing a surface layer of glass at least 0.1 mm thick into compression by ion exchange of the sodium ions in the glass surface with potassium ions (which are 30% larger), by immersion of the glass into a bath of molten potassium nitrate. Chemical toughening results in increased toughness compared with thermal tempering and can be applied to glass objects of complex shapes.
caption: Tempered safety glass which has been laminated often does not fall out of its frame when it breaks – usually because an anti-splinter film has been applied on the glass, as seen in this grocery store meat case.
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