This extra strength and resilience makes toughened glass ideal as “safety glass”, which is a variety of glass that (when broken) breaks into small pieces rather than large (and usually very sharp) fragments which pose a direct safety threat.
In domestic applications, such as shower screens and sliding doors in residential properties, toughened glass is the most suitable glass variety currently available. What’s more, it’s also used in a variety of other applications, such as automobile windows as well as a component in bulletproof glass, which is a testament to its superior strength.
How is Toughened Glass Made?
Toughened glass differs to regular glass, not only in its superior strength (both physically and thermally), but also in its production. While it starts as float glass, just like regular glass, it undergoes a strengthening process which makes it stronger and more resilient than other glass varieties. The toughening process is conducted before the glass has been given its final shape (for example, cut into a window pane), as any additional machining or working once the glass has been toughened would cause it to shatter.
This toughening process is called ‘tempering’ and involves heating the surfaces of the glass in a furnace to temperatures as high as 600°C. After the glass has been heated to the required temperature, it’s then cooled very quickly by blasting cool air over it for pre-determined periods (usually between three and ten seconds) of time. The tempering process takes just a few minutes and can be applied to most types of glass.
The result of the cool air meeting the hot glass causes the surfaces of the glass to shrink and tensile stresses to develop. The tensile stresses and the contracting of the glass result in what are known as ‘residual compressive surface stresses’ on the surface and ‘compensating tensile stresses’ in the interior. This creates a tension zone in the glass which takes up approximately 60% of its mass, resulting in superior thermal, physical and flexural strength to other glass varieties. However, the colour, clarity and chemical composition remain unchanged, as does its stiffness and transmittance.
Why Does It Crumble Rather Than Shatter?
Toughened or tempered glass is used as ‘safety glass’ because it shatters into a greater number of pieces (these pieces aren’t as sharp or as hazardous as glass shards) than regular glass when broken, but what makes it shatter this way?
It’s the compressive and residual stresses (these stresses contain higher amounts of energy) in toughened glass that cause it to crumble rather than shatter, as the more energy contained, the greater the number of stress points. The compressive stress in toughened glass must be at least 10,000 psi, and for it to be used as approved safety glass, the compressive stress of the surface must exceed 15,000 psi. If you want to observe the compressive stress of toughened or safety glass for yourself, you can use a pair of polarised sunglasses or a polarised light.
The Advantages and Disadvantages of Toughened Glass
For most domestic and commercial customers, the advantages of toughened glass outweigh the disadvantages. Nevertheless, it’s always good to be aware of both as this helps you to make informed decisions about the toughened glass products that you invest in at home or at work.
Advantages:
- The enhanced safety of toughened glass is one of its greatest advantages and the reason why it’s so widely used in domestic applications such as shower screens and doors, sliding doors, skylights and windows. Not only does it require greater force to break, but the small cube-like pieces into which it breaks when seriously damaged pose less of a safety risk.
- The physical strength of toughened glass offers a distinct advantage over other glass types. This makes it a better choice for a wide range of applications which require strong glass panes that won’t break easily.
Disadvantages:
- As toughened glass must be shaped and sized before it undergoes the toughening or tempering process, it can’t be worked on again once treated. This means that toughened glass panels can’t be reduced in size once they’ve undergone the toughening process.
- Toughened glass panes will break completely if the edges are damaged (its edges are, however, remarkably strong in comparison to regular glass), which means it requires a solid frame. However, with such a wide range of shower screen and door frames available, selecting a suitable frame won’t pose a problem for commercial or domestic customers.
As mentioned above, in most cases the advantages of toughened glass outweigh the disadvantages.
Toughened Glass Applications
Toughened glass is used in a variety of domestic and commercial applications, most notably applications in which safety, strength and thermal resistance are deemed to be important. This has resulted in toughened glass being used in the following, among many other, applications:
- Automobile windows. Toughened glass is most commonly used in side and rear windows in automobiles, though the glass used here must be safety glass (minimum 15,000 psi). Contrary to what many people think, the windscreens on cars and other automobiles are laminated glass, not toughened glass.
- Building components. After automobile windows, the next most common application for toughened glass is building components, such as shower screens, skylights, windows, sliding glass doors, etc. Depending on local building codes, toughened glass (10,000 psi) or safety glass (15,000 psi) can be used.
If you’re replacing the windows, shower screens, glass splashbacks or sliding doors in your home, you’ll be using safety glass which meets the rigid Australian requirements for domestic applications.
Rockingham Glass are glass experts with over 35 years’ industry experience backing us up. Whenever you’re in need of glass replacements (we also offer a 24-hour emergency glass replacement service) or glass products, including a wide range of shower screens, don’t hesitate to give Rockingham Glass a call. We look forward to assisting you with your toughened and safety glass requirements.
