What is Toughened Glass and How is It Made?

Toughened glass is everywhere, although we may not realise it. Toughened glass – also sometimes called “tempered glass” or “safety glass” – is used in our cars, in public buildings, furniture, shelving, bathroom fittings, windows and much more, thanks to its increased strength and protective ability compared to ordinary glass.

It’s important enough that we at the Glass Warehouse have dedicated our company to producing the best quality toughened glass on the market, making sure that safe, strong, functional and beautiful glass is always available to those who need it.

The toughened glass on offer from The Glass Warehouse is much stronger than ordinary annealed glass, and is suitable for safety applications in a variety of industries and settings – if you would like to know more about the specifications of our toughened glass or what we can do for you, you can get in touch with us at any time by calling us on 020 8500 1188 or using the contact form on this page to send us a message – the glass experts at our head office will be happy to answer any questions you may have, or help you to place an order!

What is Toughened Glass?

Toughened glass is a type of glass used where greater strength or safety is needed. As clear and transparent as ordinary untreated or “annealed” glass, safety glass is up to 6 times harder to break, and can resist impacts that would shatter ordinary glass panes. In addition to this, if the glass does break, patterns of stress within the glass sheet make sure that it breaks into many small, round or cube-shaped pieces, each around the size of a thumbnail. By contrast, ordinary glass breaks in large, sharp, jagged shards when it shatters, many of them with extremely sharp edges, which presents a serious risk of injury to those nearby.

It is the small, rounded pieces that toughened glass shatters into that give it the name “safety glass” – not just the greater toughness or difficulty to break.

Annealed glass can be made into toughened glass via thermal tempering or by chemical reactions – both of these processes produce the same end result in the toughened glass, by different mechanisms, with one introducing differential stress by rapid heating and cooling, while the other introduces the same patterns of stress via chemical action.

What is Toughened Glass Used For?

Thanks to its excellent physical properties, greater safety compared to annealed glass, and superior strength, toughened glass is used in thousands of applications, in every industry. From the reinforced windows of high-rise offices and apartments to safe glass shower screens, and safer car windows, bus shelter windows that won’t form a hazard if broken, glassware that is tougher and safer than ordinary glasses, refrigerator trays, mobile phone screens and screen protectors, bulletproof glass and diving masks, toughened glass can handle any number of demanding and safety-intensive applications.

What are the Advantages of Toughened Glass?

Toughened glass is, first and foremost, harder to break than ordinary float glass or “annealed” glass. With a strength six or even seven times greater than that of ordinary glass, the toughened glass from The Glass Warehouse is suitable for use in situations where greater glass strength is imperative – and can even be used in architectural glass doors, tables and shelves.

In addition to the increased strength and resistance to shattering, if safety glass does shatter, it will break into many small, granular chunks, instead of the long, jagged shards most commonly seen in ordinary glass. This prevents a hazard from occurring when the glass shatters, and greatly reduces the risk of injury due to broken glass.

How is Toughened Glass Made?

Toughened glass can be made in two ways, but both methods rely on the fact that glass is much, much stronger under compression than it is under tension. By placing the exterior surfaces of the glass into compression, these toughening methods mean that any attempt to break the glass must first overcome the often considerable compressive forces before the glass may be broken.

Tempering Glass with Heat and Cold

Most safety glass is made by tempering, which involves heating ordinary annealed glass up to around 620°C and keeping it there for a time, before rapidly cooling the outside of the glass with jets of cold air. This forces the outside into compression while the inside remains free to flow for a time.

The end result is glass which is under compressive strain on the outside, and under tension on the inside. Glass is much, much stronger under compression than under tension, so in order to break the glass, the compressive force must first be exceeded – making the toughened glass from The Glass Warehouse up to 6 or 7 times stronger than ordinary annealed glass!

An extra benefit conferred by this process is the differential stress patterns throughout the glass, which cause it to break into tiny, blunted pieces if broken.

Toughening Glass with Chemical Reactions

Chemically strengthened glass is made stronger by ion exchange, when the glass is submersed in a bath containing a potassium salt at 300°C. Since the salt is dissolved, this means that it has separated into its constituent ions, freeing the charged potassium ions to replace the sodium ions in the surface of the glass. As sodium ions leave the glass to enter the solution, the gaps they leave behind are filled with comparatively larger potassium ions.

Potassium ions are 30% larger than sodium ions, so the result of this process is the outer surface of the glass being forced under compression as its molecules “grow”, while the interior remains the same, placing it under tension. With both surfaces of the glass now under compression, the force needed to break the glass increases – it must first exceed the compressive forces.

However, when chemically toughened glass does break, it breaks into the same long, sharp splinters that annealed glass does, meaning that while it is a toughened glass, it cannot be called a safety glass unless it is laminated, preventing the sharp splinters from coming free when the glass breaks.

Contact the Glass Warehouse Today!

If you would like more information on the toughened glass available from The Glass Warehouse, its uses, or how it is made, you can get in touch with us at any time by calling our head office contact number, 020 8500 1188, or sending us an email on info@egw.co.uk. We’ll be happy to answer any questions you might have, provide any advice you need on choosing the perfect toughened glass for your needs, and can provide a quote or recommendation whenever you need it.

Get in touch with us today – our expert staff can help sort the perfect toughened glass solution for you!

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