Thermal shock is the name of cracking or explosion of glass due to a rapid temperature change. Glass is particularly vulnerable to this because of its low toughness, low thermal conductivity and high thermal expansion. The thermal shock of the glass occurs when the thermal gradients cause the expansion of different parts of the glass by different amounts. When stress overcomes resistance, the glazing fails and the outer flap will explode due to the accumulation of heat pressure, or more often the inner glass will crack. Thermal cracking can only occur on low strength glass, so tempered or tempered glass can never be affected by heat shock.
There are a number of internal and external factors that contribute to thermal cracking such as:
- Shading caused by stickers, walls, trees or curtains.
- Intense reflection of the snow or the sea.
- Abrupt changes in temperature such as air conditioning or the rising sun.
"The Pittsburgh Plate Glass Thermal Service" has released several reports accusing the glass industry of glass shock incidents. We know that the temperature absorbed by the glass with a reflective silver window film would increase the temperature by about 5 ° C, compared to about 3 ° C if the curtains are used. A temperature increase of 5 ° C would produce only 500 psi (10% of the single glass resistance factor) resistance which is designed to withstand a resistance of 5000 psi. This is disregarding the reinforcement provided by the film itself. This means that thermal shock should not occur if the glazing has been cut to the correct standards.
The main factors that are attributed to the thermal shock of glass are the installation of films or curtains for windows. However, these are not the cause, they only contribute to this. Without a defective thermal thermal shock, it will not occur. Many windows have slight cracks around the edge of the glass that are hidden inside the frames, the thermal crack will occur from there. Even shaving a small screw head that enters the groove is enough to trigger the break. The age of the frame and the intensity of the differential radiation resulting from the shadows are also factors involved in thermal shock.
European glazing is more fragile than in the United States, 90% of the glazing in the United States is temperate, which means it will withstand changes of 150oC against 25oC for non-tempered glazings that are often found in Europe. This means that Europeans should be much more aware of the effects of thermal cracking.
Heat shock causes cracking on sub-standard or damaged windows, but these windows could have no problem for ten years, then a window film is installed and the window cracks in a few months. This is not a coincidence, although the window film did not cause the thermal shock crack, it contributed to it because it increased the heat absorption of the glass which Then crack formation, the crack will engage from a small crack hidden inside the frame due to a bad glass cut. The same can also be mentioned when installing curtains.
We do not advise the film of double glazed or triple glazed windows because of a high heat absorption between the windows, although low absorption films such as a light Reflective Silver 50 or Coolclear is fine. It is not recommended to install a film that has too high a absorption on the reflective glazing as this will increase the absorption parameters and could cause a thermal shock. Clearer films such as security film, clear or luxurious UV window film or one of the lighter dyes are also perfectly suited for installation, or any film can be Installed outside.
Things to watch out for before installing the window film:
- You should pay particular attention to rounded and divided trapezoidal windows or to another modern architecture
- Holes or places where fans are used.
- Be aware of the old and large glazing systems that have a frame that no longer guarantees the expansion tolerance as this also represents a risk of thermal shock.
- Adjustment film on wired glass is not recommended because iron wires absorb heat when driving and the edges of the glass are cut with clamps that leave chips that can become a source of cracks.
In summary, low-quality glass, edges, poor glass installation, appropriate window frames, external factors and shades that combine to cause thermal cracking glass. If the glazing is of the correct standard thermal cracking can never occur on a home or office window.