Every summer, multiple regions across the country enter the "barbecue mode". Recently, it has been learned that many cities have frequently reported incidents of tempered glass explosions in high-rise building glass curtain walls. So is it really like the glass exploding on a high-temperature barbecue mentioned in the news. Let's take a look at the causes of self explosion of tempered glass.
In fact, since the birth of tempered glass, it has been accompanied by the problem of self explosion. Self explosion of tempered glass can be described as the phenomenon of tempered glass breaking automatically without external direct action. Tempered glass self explosion can occur during the processes of tempering, storage, transportation, installation, and use.
The self explosion rate in China varies among manufacturers, ranging from 3% to 0.3%. The self explosion rate is generally calculated based on the number of pieces, without considering the area and thickness of a single piece of glass, so it is not accurate enough and cannot be compared more scientifically. To uniformly calculate the self explosion rate, it is necessary to establish a unified assumption. Set a unified condition: every 5-8 tons of glass contains one nickel sulfide sufficient to trigger self explosion; The average area of each tempered glass is 1.8 square meters; Nickel sulfide is uniformly distributed. The calculated self explosion rate for 6mm thick tempered glass is 0.64% to 0.54%, which means the self explosion rate for 6mm tempered glass is approximately 3 ‰ to 5 ‰. This is basically consistent with the actual value of domestic high-level processing enterprises.
Even if produced entirely according to standards, it cannot completely avoid self explosion of tempered glass. Large buildings can easily use hundreds of tons of glass, which means there is a high probability of nickel sulfide and heterogeneous impurities in the glass. Therefore, although tempered glass is subjected to hot dip treatment, self explosion is still inevitable.
Self explosion mechanism of tempered glass
Self explosion can be divided into two types based on different causes:
One is self explosion caused by visible defects in the glass, such as stones, sand particles, bubbles, inclusions, notches, scratches, edges, etc;
The second is the self explosion of tempered glass caused by nickel sulfide (NIS) impurities and heterogeneous particles in the glass. The diameter of nickel sulfide that causes self explosion ranges from 0.04 to 0.65mm, with an average particle size of 0.2mm. Now there are also new discoveries of tempered glass self explosion caused by heterogeneous particles.
These are two different types of self explosions, which should be clearly classified, treated differently, and handled using different methods. The former is generally visually visible and relatively easy to detect, so it is controllable in production. The latter is mainly caused by the volume expansion of small nickel sulfide particles in the glass, which cannot be visually inspected and is therefore uncontrollable. In practical operation and handling, the former can generally be removed before installation, while the latter continues to exist due to inability to be inspected, becoming the main factor causing self explosion of tempered glass in use. The difficulty of replacing nickel sulfide after self explosion is high, and the handling cost is high. At the same time, it will be accompanied by significant quality complaints and economic losses, causing dissatisfaction and even more serious consequences for the owner.
There are other factors that contribute to the self explosion of tempered glass, such as unreasonable glass slotting and drilling, poor quality of glass raw materials, uneven thickness such as embossed glass, and uneven stress distribution such as bent tempered glass and regional tempered glass.
How to identify the self explosion of tempered glass
Firstly, check whether the initiation point (the crack in tempered glass is radial and has a starting point) is in the middle of the glass. If it is at the edge of the glass, it is generally due to the glass not being chamfered or the glass edge being damaged, causing stress concentration and gradually developing cracks; If the detonation point is in the middle of the glass, check if there is a pattern similar to two butterfly wings formed by two small polygons at the detonation point (butterfly spot). If there are black small particles visible to the naked eye on the common edge of the two small polygons (butterfly's trunk), it can be determined that it is self detonating; Otherwise, it should be caused by external forces. The typical feature of glass self explosion is butterfly spots. The glass fragments are distributed radially, with two glass blocks resembling butterfly wings at the center of the radiation, commonly known as "butterfly spots". The nis stone is located at the interface between two butterfly spots.
So how should we defend against such self destructions?
1. Use laminated glass:
Sandwiched between the glass with PVB intermediate film, processed under high temperature and high pressure. The toughness of PVB film is very good. When laminated glass breaks under external force, it can absorb a large amount of impact energy and quickly decay, making it difficult for laminated glass to break through and maintain excellent integrity. This allows buildings that use laminated glass to remain within the door and window frames even if the glass breaks during explosions, wind disasters, earthquakes, and other situations, protecting people inside and outside the building from the hazards of flying glass fragments. It is also difficult for wind, rain, and other foreign objects to cause damage to the interior. The shortcomings are:
(1) The weight and thickness of glass increase the building's load-bearing capacity and load;
(2) Not conducive to escape and rescue in the event of a fire;
2. Apply a film to the glass:
Stick high-performance polyester film on glass. Polyester film, commonly known as safety explosion-proof film, can adhere to glass fragments to prevent splashing when glass breaks due to various reasons, protecting people inside and outside the building from the harm of splashed glass fragments. It is also difficult for wind, rain, and other foreign objects to cause damage indoors. The safety explosion-proof film can be connected to the frame edge system together with organic adhesive to form a glass film protection system to prevent falling. Advantages: Easy processing, without changing the glass specifications and layout. Shortcomings: Increasing construction costs.
3. Install enclosure design:
Set up guardrails and other measures in densely populated areas to prevent damage caused by glass breakage.
4. Select ultra white tempered glass:
Good thermal stability, high strength, low self explosion rate (approaching 0), safe use, high light transmittance, good permeability, high-end, high technical content, and wide application range.