Wednesday 1st February, 2017
Whenever you walk down a street, sit in an office, drive a car, go into a shop, or even relax at home, the chances are you will encounter products made from toughened glass.
Toughened glass is everywhere – shop doorways, bus shelters, oven doors, glass furniture, car windows, even some mobile phone screens are made from toughened glass. It really has become one of the most widely used glass products in the world.
But what is it about toughened glass that makes it so useful?
As the name suggests, toughened glass is much stronger than standard annealed glass. Around four to five times stronger in most cases.
This is thanks to the thermal tempering process, during which the glass is heated past its transition temperature of around 650°C. As the glass begins to soften at these high temperatures, it is then rapidly cooled by a blast of cold air.
The surface of the glass cools more quickly than the internal area, causing it to shrink at a faster rate. As the rest of the glass cools, residual compressive stresses develop in the already solidified surface. The interior develops compensating tensile stresses.
The balance of these stresses is what makes toughened glass so strong.
As well as an increase in mechanical strength, toughened glass also has a higher thermal shock resistance than ordinary float glass. In fact, it can withstand temperature changes up to 250°C, as compared to about 32°C for standard annealed glass.
This thermal strength makes toughened glass ideal for use in applications such as cookware, laboratory equipment and fire doors.
As well as being less prone to breakage, toughened glass is also safer when it does break.
The balance of internal stresses mean that when the glass does break, it crumbles uniformly into small dull pebbles across the entire pane. These pebbles are far less likely to cause injury than the razor-sharp shards left when standard glass breaks. They are also easier to clear up, as the small fragments can be safely swept up and thrown into a rubbish bag.
With the many benefits of toughened glass, it’s easy to see why its use has become so widespread. But are there any disadvantages to using it?
Depending on the situation, toughened glass’s strengths can actually be its weakness. The fact that an entire pane will crumble on breaking means it can be dangerous to use toughened glass for applications such as overhead glazing. If the glass shatters and falls from its frame, anyone who stands underneath it could receive some nasty injuries.
For these reasons, architects often opt to specify toughened laminated glass for overhead glazing, as lamination will keep the shattered glass in place until it can be replaced.
Toughened glass must also be cut to size before it undergoes the tempering process. Once toughened, any reworking, cutting or drilling will cause it to shatter.
Commercial glass suppliers Peterlee Glass are specialists in the manufacture and supply of toughened glass. See our website for more information on our toughened glass products, including glass floors, glass balustrades, glass canopies, glass splashbacks and other forms of architectural glass.