Toughened or tempered glass is glass that has been processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. It will usually shatter into small fragments, rather than sharp shards, when broken.Compared with normal glass, toughened glass is strong, has enhanced thermal resistance, and breaks into small cuboids fragments rather than irregular shards of glass and therefore is less likely to cause injury.
Production Process: Toughened glass is 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 to above its annealing point of about 600 °C. The glass is then rapidly cooled with forced drafts of air while the inner portion of the glass remains free to flow for a short time.
An alternative chemical process involves forcing a surface layer of glass at least 0.1mm thick into compression by ion exchange of the sodium ions in the glass surface with the 30% larger potassium ions, 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 shape.
.jpg)
