The Glass Process
Virtually all commercial glass is manufactured as float glass. The Float Process was invented by Sir Alastair Pilkington in 1952, allowing larger and more consistent panels of glass to be manufactured than ever before. All the glass that White Metal supply for our balustrades is toughened, or toughened and laminated. View our Balustrade Glass Range here.
There are 6 main steps in manufacturing float glass:
- Melting and refining
- Float bath
- Cutting to order
As all the glass White Metal supplies is either toughened or toughened and laminated, the cut float glass then goes through one or two more processes.
- Toughening/tempering the glass
Annealed glass is a basic product formed from the annealing stage of the float process. The molten glass is allowed to cool slowly in a controlled way until it reaches room temperature. Without this controlled slow cooling, glass would crack with relatively little change in temperature or slight mechanical shock. Annealed glass is used as a base product to form more advanced glass types.
Once the glass is annealed, it can be cut into shaped panels. All holes and notches have to be cut into it at this stage.
Tempered or Toughened Glass
This is the most common type of glass used in balustrades or similar structural applications. Annealed glass is heated to about 700 degrees Celsius. The cooling process is accelerated by a uniform and simultaneous blast of air on both surfaces. The different cooling rates between the surface and the inside of the glass produces different physical properties, making it four to five times stronger and safer than annealed or untreated glass.
The counteracting stresses or surface compression gives toughened glass its increased mechanical resistance to breakage, and when it does break, causes it to produce small, regular, typically square fragments rather than long, dangerous shards that are far more likely to lead to injuries.
The most commonly used finished product is two sheets of toughened glass, laminated together with a 1.52mm thick Polyiynil Butyral (PVB) interlayer.
Lamination significantly increases the safety and security of the glass. Rather than shattering on impact, laminated glass is held together by the interlayer. This reduces the safety hazard associated with shattered glass fragments.
If a glass panel breaks or shatters it is highly unlikely that both laminated panels will break at the same time, which means that the remaining panel and interlayer will support the broken glass and keep it in place as edge protection until it is replaced or secured suitably.
Another increasingly common interlayer is the SGP Interlayer. The product offers 5 times the tear strength and 100 times the rigidity of standard PVB. SGP offers an enhanced impact performance and greater protection against severe weather.
A variety of other interlayers are available which apply a range of other technologies to the application. Coloured interlayers can be used for privacy or decorative purposes. Other properties such as sound dampening and fire resistance can also be incorporated into the interlayer.