Tempered Glass

tempered-glass

Tempered glass is made from annealed glass which is regular glass, also referred to as “non-tempered” glass. Annealed glass is placed onto a roller table, taking it through a furnace which heats it 620 degrees Celsius, which is well above its transition temperature of 564 degrees Celsius in which it changes from a hard material into a soft rubber material. The glass is soon after rapidly cooled with forced air. The inner portion remains free to flow for a short time whilst the outer portion hardens quickly. 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 toughening and can be applied to glass objects of complex shapes

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