Maybe you have heard that pouring boiled water into a glass would cause it to shatter. What about the glass table, will it break in heat or cold weather?
The glass table is mostly made of annealed and tempered glass; annealed glass can withstand -20°C to 120°, and tempered glass can withstand -70°C to 300°C. Therefore, heat or cold is less likely to break the glass table as most climates can’t get that extreme temperature.
However, the temperature won’t cause the glass table to break, but the thermal stress caused by rapid temperature change does. Keep reading to know why.
How does thermal stress break glass?
Glass expands and contracts as the temperature changes. When a portion of it is heated, it will expand; however, because of uneven heating, another portion will not undergo the same degree of thermal expansion; thus, the glass will suffer internal stress.
The greater the temperature differential, the more rapid the rate of temperature change and the higher the thermal stress. The glass will shatter when the tension exceeds its limited strength.
The clear annealed glass can withstand temperatures from -20°C to 120°C, temperature difference at 40°C (150°F -180°F). After tempering, the tempered glass can survive severe heat and cold temperatures. It can withstand temperatures from -70°C to 300°C and temperature differences up to 250°C. The strong thermal stress breaks the glass table when the rapid temperature change reaches the limits.
Here is the data about the temperature differences and thermal stress resistance of different types of glass:
A volunteer standard requires tabletop to use tempered glass in the USA. As shown in the data, tempered glass has high thermal stress resistance, and it is unlikely that tempered glass tables will break due to excessive thermal stress.
For the tempered glass table, besides the thermal stress, some other factors will cause the glass to break.
Other potential causes of glass breakage
Nickel sulfide inclusions
Nickel sulfide inclusions are the most common internal defect in tempered glass. During tempered glass production, stainless steel machinery is used to make glass; nickel-containing stainless steel machinery and sulfur-containing fuels might leave inclusions in this process.
It is hard to avoid the inclusions from getting in. They are very small, and not easy to view them by eye. Furthermore, these inclusions do not mean the quality issue. According to ASTM C1036, it is acceptable if the size of float glass inclusions is between 0.5 to 2.5 mm (1/50 to 1/10 inch).
It is important to note that nickel sulfide inclusions do not always cause immediate glass breakage. These tiny impurities are commonly trapped in glass, and as time passes, they change the structure and grow, as well as expand and swell, creating internal stresses in the glass.
When it expands and swells, causing enough stress that exceeds the strength of the glass, it will break. If these inclusions are in the center of the glass, the force extending from the center to the surrounding area will cause the glass to break in a typical “figure of eight” or “butterfly” pattern. The image below is a typical NIS tempered glass broken image
Although NIS inclusions may be introduced during glass production, this does not imply that every piece of glass contains NIS inclusions, nor does it mean that glass breakage will occur.
There is approximately 1 NiS inclusion per 500 glass panes, and the breakage rate is 0.8%. (Napier and Blakely 2010). Failures are most prevalent between 2 and 7 years after installation and do not seem to occur after 30 years (Karlsson 2017).
Whether annealed or tempered glass, they both will break after dramatic impact. Annealed glass breaks at 6,000 impacts, but tempered requires a much higher value. Normally, tempered glass has a surface compression of 10,000 or higher and breaks around 24,000 psi.
Please read our other article for more information about the impact resistance of tempered glass.
Minor edge damage
When glass is tempering, ion exchange (chemical tempering) or rapid cooling (thermal tempering) pushes the edges away from the glass’s center, lowering the compressive and tensile stresses in these areas. This expansion leads to the edge of tempered glass being the most fragile part.
As a result, the edges of tempered glass are easily scratched or chipped during transportation, placement, and installation.
These small corner damages may not immediately break the glass. Temperature differences and other factors can cause the glass to expand or contract over time, and creating a stress concentration around the damaged edge that can break it.
Improper glass thickness
The thickness of the glass varies according to the furniture’s type, size, position, and functionality. The improper glass thickness is another potential cause of glass breakage.
A piece of thick glass is too heavy, pressing too much on the base might shorten the furniture base service life, then the whole piece of glass furniture collapse; but a piece of thin glass is not strong enough for daily use, and a slight impact may break it. It is important to get the right thickness of furniture glass.
Not enough gap for Binding in the frame
Glass expands and contracts with temperature changes, and some furniture styles are made with glass set into the frame. Along the glass keeps expanding due to the extrusion stress, if there is not enough expansion space in the frame, it breaks once it is over its withstand limits.
To solve this, place spacers in the frame or leave a sufficient gap. Do not hesitate to contact your supplier to ensure they have considered this.