Tempered Glass Introduction

What is tempered glass?

Tempered glass is often used in applications where using standard glass could pose a potential danger. Tempered glass is stronger than standard glass and does not shatter into large shards when broken. This is important, because it can greatly minimize potential danger in the case of a break. Manufactured through a process of extreme heating and rapid cooling, tempered glass is much harder than normal glass.

In the case that tempered glass does break, it shatters into small pebbles that are void of dangerous, sharp edges. As tempered glass is considered to be much safer than normal glass, you may often here it referred to as safety glass or toughened glass. Tempered glass has a wide variety of uses that you’ll find just about everywhere. In fact, the shower doors in your bathroom or the side glass on a motor vehicle are examples of tempered glass.

Another benefit of tempered glass is the ability to stand up to moderate heat (470°F). The process that creates this strengthened glass also makes it heat-resistant. This makes tempered glass a great solution for a situation where there is a danger of the glass breaking due to impact or moderate heat. Tempered glass is often used for fireplace doors (not woodstoves), on masonry and prefabricated fireplaces. If tempered glass is exposed to higher temperatures, it gradually weakens the structure of the glass thus making it more susceptible to breakage.  Tempered glass is not recommended in wood burning applications.

Tempered glass is about four times stronger than annealed glass.The greater contraction of the inner layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass. Fully tempered 6-mm thick glass must have either a minimum surface compression of 69 MPa (10 000 psi) or an edge compression of not less than 67 MPa (9 700 psi).For it to be considered safety glass, the surface compressive stress should exceed 100 megapascals (15,000 psi). As a result of the increased surface stress, when broken the glass breaks into small rounded chunks as opposed to sharp jagged shards.

Tempered glass is used when strength, thermal resistance, and safety are important considerations. Passenger vehicles, for example, have all three requirements. Since they are stored outdoors, they are subject to constant heating and cooling as well as dramatic temperature changes throughout the year. Moreover, they must withstand small impacts from road debris such as stones as well as road accidents. Because large, sharp glass shards would present additional and unacceptable danger to passengers, tempered glass is used so that if broken, the pieces are blunt and mostly harmless. The windscreen or windshield is instead made of laminated glass, which will not shatter into pieces when broken while side windows and the rear windshield have historically been made of tempered glass. Some newer luxury vehicles have laminated side windows to meet occupancy retention regulations, anti-theft purposes, or sound-deadening purposes.

typical applications of tempered glass include:

• Balcony doors

• Athletic facilities

• Swimming pools

• Façades

• Shower doors and bathroom areas

• Exhibition areas and displays

• Computer towers or cases

• Mobile phone screen protectors

Buildings and structures

Tempered glass is also used in buildings for unframed assemblies (such as frameless glass doors), structurally loaded applications, and any other application that would become dangerous in the event of human impact. Building codes in the United States require tempered or laminated glass in several situations including some skylights, glass installed near doorways and stairways, large windows, windows which extend close to floor level, sliding doors, elevators, fire department access panels, and glass installed near swimming pools.

Household uses

Tempered glass is also used in the home. Some common household furniture and appliances that use tempered glass are frameless shower doors, glass table tops, glass shelves, cabinet glass and glass for fireplaces.

Food service

"Rim-tempered" indicates that a limited area, such as the rim of the glass or plate, is tempered and is popular in food service. However, there are also specialist manufacturers that offer a fully tempered/toughened drinkware solution that can bring increased benefits in the form of strength and thermal shock resistance. In some countries these products are specified in venues that require increased performance levels or have a requirement for a safer glass due to intense usage.

Tempered glass has also seen increased usage in bars and pubs, particularly in the United Kingdom and Australia, to prevent broken glass being used as a weapon. Tempered glass products can be found in hotels, bars, and restaurants to reduce breakages and increase safety standards.

Touchscreen devices

Most touchscreen mobile devices use some form of toughened glass (such as Corning's Gorilla Glass), but there are also separate tempered screen protectors for touchscreen devices sold as an accessory.

Manufacturing of tempered glass

Tempered glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it well above its transition temperature of 564 °C (1,047 °F) to around 620 °C (1,148 °F). The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time.

An alternative chemical toughening process involves forcing a surface layer of glass at least 0.1 mm thick into compression by ion exchange of the sodium ions in the glass surface with potassium ions (which are 30% larger), by immersion of the glass into a bath of molten potassium nitrate. Chemical toughening results in increased toughness compared with thermal tempering and can be applied to glass objects of complex shapes.

Disadvantages of tempered glass

Tempered glass must be cut to size or pressed to shape before tempering, and cannot be re-worked once tempered. Polishing the edges or drilling holes in the glass is carried out before the tempering process starts. Because of the balanced stresses in the glass, damage to any portion will eventually result in the glass shattering into thumbnail-sized pieces. The glass is most susceptible to breakage due to damage at its edge, where the tensile stress is the greatest, but can also shatter in the event of a hard impact in the middle of the glass pane or if the impact is concentrated (for example, the glass is struck with a hardened point).

Using tempered glass can pose a security risk in some situations because of the tendency of the glass to shatter completely upon hard impact rather than leaving shards in the window frame.

The surface of tempered glass does exhibit surface waves caused by contact with flattening rollers, if it has been formed using this process. This waviness is a significant problem in manufacturing of thin film solar cells.The float glass process can be used to provide low-distortion sheets with very flat and parallel surfaces as an alternative for different glazing applications.

Is tempered glass breakable?

Tempered glass is a unique type of glass created to be stronger and, if it does shatter, it shatters safely. When tempered glass is broken, it will break into thousands of small pieces as opposed to large sharp shards of glass.

Is tempered glass better than glass?

Tempered Glass is about four times stronger than regular class and is known for its safety. And, unlike regular glass, tempered glass fractures into small, relatively harmless pieces. This is possible because during the annealing process the glass is cooled down slowly, which makes the glass much stronger.

Can tempered glass just explode?

Exploding glass is a phenomenon by which toughened glass (or tempered) may spontaneously break (or explode) without any apparent reason. The most common causes are: ... Binding of the glass in the frame, causing stresses to develop as the glass expands and contracts due to thermal changes or deflects due to wind.

What is clear tempered glass?

Tempered glass, also known as toughened or safety glass, is scratch and impact resistant while breaking into small pieces devoid of harmful sharp edges. To further prevent injury, a pane of this clear glass also disintegrates in its entirety, but you can't rework, reshape or cut it as it'll form inline cracks.

How is tempered glass made?

Tempered glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it well above its transition temperature of 564 °C (1,047 °F) to around 620 °C (1,148 °F).

What is the differences between tempered and non-tempered glass?

Unlike standard glass, tempered glass is cooled much more slowly during the annealing process which allows it to be much more sturdy and strong than its non-tempered cousin. This glass won't break as easily, and if it does, it will shatter into much smaller pieces with fewer sharp edges.

Wallkingdon Glass provides first-class products and services to exceed customer expectations. No matter what your project needs—from external high-rise windows to large-capacity glass in storefronts or showrooms, please contact us through the following ways: enquiry@wallkingdonglass.com