Why tempered glass shatters

But it costs about twice as much as tempered glass. For safe handling of glass at home, he cautioned against stacking glassware, as that can chip the edges. But if needed, cushion each piece with cardboard or cloth.

To prevent more accidents, one person who is helping to design robots that can clean and scan glass panels for cracks is Mohan Rajesh Elara, an assistant professor of engineering product development at the Singapore University of Technology and Design. The idea is to have these robots alert the end users early so that they can take measures such as replacing a glass panel.

The robots use artificial intelligence to detect and classify cracks. But there are limitations at this time: Glass is transparent, so the robots might mistake elements in the surrounding environment for a crack.

To combat this, Mohan is working at adding acoustic and thermal sensing, as cracks reflect sound differently and retain more heat. This means the robots should be able to see, hear and feel. It will take about two years, however, before these robots can be deployed commercially. Watch this episode of Talking Point here.

The programme airs on Channel 5 every Thursday at 9. We know it's a hassle to switch browsers but we want your experience with CNA to be fast, secure and the best it can possibly be. To continue, upgrade to a supported browser or, for the finest experience, download the mobile app. Main navigation Top Stories. CNA Insider When glass suddenly shatters — why it happens and how to be on the safe side.

Bookmark Bookmark Share. Close Top Stories. CNA Insider When glass suddenly shatters — why it happens and how to be on the safe side There have been cases at home, and outside too; over the past decade, at least exterior glass panels were reported to have shattered.

The danger is that all it takes is a few drops of water for this to happen. Arulnathan John. Chan Luo Er. Joshua Lim posted this on social media. Dr Leonard Loh has spent a decade studying glass and its properties. Does your glassware have micro-cracks or small chips? It can shatter the whole glass. Even without the issue of safety, replacing toughened glass in inaccessible areas can be a major not to mention expensive inconvenience.

This is known as spontaneous glass breakage and is, in actual fact, generally triggered by one of four factors:. Minor damage during installation such as nicked or chipped edges that later develop into larger breaks. Overly tight binding of the glass in the frame, which causes stresses to develop as the glass expands and contracts due to thermal changes or deflects due to wind. While factors such as installation damage and incorrect fitting can be avoided to some degree by experienced glass technicians, avoiding glass that contains nickel sulphide is somewhat more difficult.

These inclusions are invisible to the naked eye and are almost impossible to completely avoid in the plate glass manufacturing process. During the tempering process, plate glass is heated up to its softening point, then rapidly cooled. The surface cools quicker than the internal glass, which creates the centre tension that gives toughened glass its increased strength.

However, any nickel sulphide inclusions that are present are frozen in an unstable state by the rapid cooling. Spontaneous glass breakage or exploding glass has been the cause of highly publicized incidents involving domestic cookware, furniture, glass doors, and windows. All have a soda-lime-silicate composition, and are treated with various strengthening methods. Glass cookware was originally made with borosilicate glass by Corning, which marketed their products under the brand Pyrex.

As early as the s, glass cookware was also made with soda-lime-silicate glass that was heat-strengthened to increase resistance to thermal stress. By when Corning licensed Pyrex to World Kitchen LLC, the popular cookware was made exclusively with heat-strengthened or tempered soda-lime-silicate glass. Borosilicate glass has a very high thermal stress resistance, whereas temperature changes within normal kitchen use can cause soda-lime-silicate glass to fracture.

There is usually a delay between the initiating thermal shock and glass failure, causing the fracture event to seem "spontaneous" Bradt Glass cookware fractures take the form of shards regardless of heat-strengthening or tempering, which indicates that the heat treatment is not sufficient for normal use; properly strengthened tempered glass fractures into small "dice" rather than shards. There are many compositions of soda-lime-silicate glass, each having different properties and thermal resistance.

Statistically, only a small fraction of glassware sold experiences catastrophic breakage, but the nature of the failures has caused public outcry and scrutiny of the materials, manufacturing processes, and regulation of these consumer products. Tempered plate glass is made by reheating panels of glass to about C F , then quenching in streams of cold air. As the outer surfaces of the panel rapidly cool they are put into compression, while the slowly cooling center is in tension.

Tempered glass is times stronger than conventional glass of the same thickness, and gains the characteristic of breaking into small equiaxed pieces in a fracture process known as dicing Konrad , Bradt During cutting, shipping or installation, tempered glass can be easily chipped or nicked on its edges. This may not cause immediate breakage, but it initiates internal stresses that increase over time with cycles of expansion and contraction.

Similarly, poorly fit frames or gaskets can cause internal stress which exceeds the strength of the glass, especially when subjected to expansion and contraction or wind deflection. In large pieces of sealed insulating glass, thermal stress can cause breakage if the installation method is too rigid; when the center of the tempered glass pane is hotter than the edges, the center expands and the edges are put under tensile stress.

Nickel-sulphide NiS inclusions can be present in plate glass as a result of virtually non-preventable impurities introduced during the float glass manufacturing process, most likely from stainless steel machinery containing nickel and fuel containing sulphur.

The inclusions usually range in size from 0. In tempered glass, NiS inclusions can expand over time because of an arrested phase transformation during quenching Swain If the inclusion is located in the center tensile zone of the glass panel, its expansion may cause enough stress to shatter the glass, leaving a characteristic "figure eight" or "butterfly" pattern.

The presence of NiS inclusions has been estimated to be 1 in every glass panels, with a fracture rate of 0. Failure has occurred most frequently years after installation, and none appear to happen beyond 30 years' time Karlsson Heat-soaking has been introduced as a measure to initiate or accelerate phase change in NiS inclusions, causing the glass to break before shipping.

Although manufacturers offer it, it is not a guarantee that spontaneous breakage will not occur, and it can reduce profits by destroying glass that may not have broken after installation.