Toughened glass, also known as tempered glass is made through a process which involves controlled high temperatures or chemical treatments in a special tempering oven. This process gives the glass a special feature (balanced internal stress) which strengthens the glass. It is more than 5 times stronger than a normal glass sheet of the same thickness.
In the case of abnormal tension or pressure which exceeds its strength, the glass will simply crumble down into small cubes unlike other window glass which breaks into sharp pieces that can cause serious injuries. Its fragments are less likely to cause serious injuries. This qualifies toughened glass to be categorized as a safety glass.
Controlled thermal treatment in the tempering oven mainly involves heating stress free, annealed glass to a temperature between the glass softening point and a transition temperature and then rapidly cooling it using air jets while it is still very hot. As a result, the glass surface freezes while its interior is still in molten form.
Consequently, a wide temperature differential exists across the glass thickness when made. Scientifically, the hotter core section will contract at a faster rate than the outer core. The process is repeated several times until an isothermal state is achieved.
Initial stages of sudden cooling induce ‘tensile stress’ or pressure on the outer core. This effect is reversed in the latter stages. The final glass produced can thus withstand stress on its surface. If the stress exceeds its strength, it will safely shatter into small fragments.
The toughened glass produced will have the following important features:
- Superior strength that can withstand abnormal stress to a certain point
- In case of accidents, the glass will safely shatter into small cubes
- Ability to resist chemical reactions
- Reacts with hydrofluoric acid
- Thermally strong-Can withstand very high temperatures
There are two distinct types of toughened glass:
Fully tempered and heat strengthened. Fully tempered glass is stronger compared to heat treated and the annealed glass. It can withstand high temperatures used in ovens and baking appliances. Heat strengthened glass is relatively stronger than window glass but less so than fully treated glass. The difference arises as a result of residue stress effect on the glass surface and its edges.
Note that: The toughening process will not alter the stiffness of annealed glass. Both will undergo the same deflection under the same load before shattering. The only difference is that toughened glass can deflect further when extra pressure is applied instead of breaking.
Magic Glass is a reputable Australian glazier company offering 24-hour emergency glass repair, replacement, installation and other professional glazier services in Sydney. Call us now on 18 000 GLASS for a complimentary consultation.