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Toughened Glass

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Toughened or tempered glass is a type of safety glass processed by controlled thermal treatments to increase its strength compared with annealed glass. Tempering puts the outer surfaces into compression and the interior into tension. This stress causes the glass (when broken) to crumble into small blunt cubes instead of splintering into jagged shards as annealed glass does.

There are two main types of heat-treated glass: heat-strengthened and fully tempered. Heat-strengthened glass is roughly twice as strong as annealed glass, while fully toughened glass is typically four times the strength of annealed glass.

However, the tempering process can cause problems if the float glass used has microscopic inclusions within it. Nickel sulphide particles formed in the production of the glass will cool down at a different rate to the rest of the glass. This can result in the toughened glass shattering, seemingly spontaneously.

The heat soaking process serves to identify any problematic sheets of toughened glass . At Ravensby Glass we have two Torgauer heat soaking ovens which allows us to heat soak glass in accordance with the European Standard EN14179. The use of heat soaked tempered glass is recommended where the risk of spontaneous breakage would cause difficulty, either from a replacement point of view or where falling glass fragments may be unsuitable, such as roof or high level glazing, balustrades, screens and high level curtain walling.

Heat Strengthened

If tempered glass breaks, it disintegrates into small pieces, which qualifies it as a safety glazing material. Because of the high level of stress in tempered glass, it is subject to rare “spontaneous breakage”, where the glass will break for no apparent reason. Upon breakage, it may void the opening. Heat Strengthened glass is approximately twice as strong as regular annealed glass
of the same thickness. Heat strengthened glass is used primarily to provide additional glass strength to prevent breakage in applications where high thermal stress is a concern. It breaks, like regular annealed glass, into relatively large pieces that will tend to remain in the glazing system. This feature makes it more suitable than tempered glass for locations where even the remote chance of spontaneous breakage is of concern.

Maximum sizes

Approx. 2050mm x 3100mm*

* 1 edge must be below 2050mm

We produce toughened glass up to 19mm thick, all certified to BS EN 12150.