Tempered glass, or toughened glass is obtained by heating the glass at a temperature up to 700-740 C0, then quickly cooling down its surface, this way the glass becoming five times more resistant, while preserving its flexibility.
Thanks to this process, should tempered glass break, it crumbles into small granular chunks, thus reducing the risk of injury.
The essential factor to reduce probability of glass sheets breaking during the tempering process is the careful glass edge processing. It is widely acknowledged that the edgework quality can affect both the quality and the mechanical features of the final product.
Tempered glass is used for glass walls, double glazing or laminated windows, etc. - mainly applications that require the following:
- greater resistance to mechanical shocks (glass doors, glass panels with point fixings such as glass balustrades, etc.).
- increased thermal stress resistance (glass panels exposed to intense sunrays or placed near heat like in glass cladding, etc.).
- a type of breakage that reduces the risk of injury.
There is still a risk that thermally tempered glass may accidentally break or spontaneously break without external pressure. It is therefore recommended to submit tempered glass to an additional thermal treatment called HEAT-SOAK TREATMENT test.
The inclusions of nickel sulphide (NiS) usually contained by any type of glass increase their volume under high temperatures. Thus, the balance of pressures inside the tempered glass can be affected, leading to the so-called spontaneous breakage. According to the type of application in which the tempered glass is to be used, the ‘heat soak’ treatment may be used to reduce the risk of human injury. Thus, once it has been toughened, the glass is placed in a furnace under a constant temperature of approximately 290°C for about 4-8 hours. This is intended to cause glass containing nickel sulfide inclusions to break in the heat soak chamber, thus reducing the risk of potential breakage in the field.
The tempering technology complies with European Standards EN 12150 and EN 1863, which regulate the processing of float glass with thicknesses between 4 to 19 mm and sizes of 2400x4200 mm and of special glass like reflexive or Low-E glass.