Tempered Glass Self-explosion Solution

Reduce stress value
The distribution of stress in tempered glass is that the two surfaces of the tempered glass are under compressive stress, the core layer is under tensile stress, and the stress distribution on the thickness of the glass is similar to a parabola. The center of the glass thickness is the vertex of the parabola, that is, the maximum tensile stress; the two sides close to the two surfaces of the glass are under compressive stress; the zero stress surface is approximately 1/3 of the thickness. By analyzing the physical process of tempering and rapid cooling, it can be seen that the surface tension of tempered glass and the maximum tensile stress inside are roughly proportional in value, that is, the tensile stress is 1/2 to 1/3 of the compressive stress. Domestic manufacturers generally set the surface tension of tempered glass at around 100MPa, and the actual situation may be higher. The tensile stress of tempered glass itself is about 32MPa to 46MPa, and the tensile strength of glass is 59MPa to 62MPa. As long as the tension generated by the expansion of nickel sulfide is 30MPa, it is enough to cause self-explosion. If its surface stress is reduced, the tensile stress of the tempered glass itself will be reduced accordingly, which will help reduce the occurrence of self-explosion.
The American standard ASTMC1048 stipulates that the surface stress range of tempered glass is greater than 69MPa; semi-tempered (heat-strengthened) glass is 24MPa~52MPa. The curtain wall glass standard BG17841 stipulates that the semi-tempered stress range is 24<;δ≤69MPa. The new national standard GB15763.2-2005 "Architectural Safety Glass Part 2: Tempered Glass" implemented in China requires that its surface stress should not be less than 90MPa. This is 5MPa lower than the 95MPa specified in the old standard, which is conducive to reducing self-explosion.
Uniform stress
The uneven stress of tempered glass will significantly increase the self-explosion rate, which has reached a level that cannot be ignored. The self-explosion caused by uneven stress sometimes manifests itself very concentrated, especially the self-explosion rate of a specific batch of curved tempered glass will reach an alarming severity, and may occur continuously. The main reason is the uneven local stress and the displacement of the tension layer in the thickness direction, and the quality of the original glass itself also has a certain impact. Uneven stress will greatly reduce the strength of the glass, which is equivalent to increasing the internal tensile stress to a certain extent, thereby increasing the self-explosion rate. If the stress of tempered glass can be evenly distributed, the self-explosion rate can be effectively reduced.
Hot dip treatment
Hot dip treatment is also called homogenization treatment, commonly known as "detonation". Hot dip treatment is to heat the tempered glass to 290℃±10℃ and keep it warm for a certain period of time, so that nickel sulfide can quickly complete the crystal phase transformation in the tempered glass, so that the tempered glass that may explode after use is artificially broken in the factory's hot dip furnace in advance, thereby reducing the self-explosion of tempered glass in use after installation. This method generally uses hot air as the heating medium, which is called "Heat Soak Test" abroad, abbreviated as HST, which literally means hot dip treatment.
Difficulty of hot dip. In principle, hot dip treatment is neither complicated nor difficult. But in fact, it is very difficult to achieve this process indicator. Studies have shown that there are many specific chemical formulas of nickel sulfide in glass, such as Ni7S6, NiS, NiS1.01, etc. Not only are the proportions of various components different, but other elements may also be doped. The speed of its phase change is highly dependent on the temperature. Studies have shown that the phase change rate at 280°C is 100 times that at 250°C, so it is necessary to ensure that each piece of glass in the furnace experiences the same temperature system. Otherwise, on the one hand, the glass with low temperature cannot completely change phase due to insufficient insulation time, which weakens the effectiveness of hot dip. On the other hand, when the glass temperature is too high, it may even cause the reverse phase change of nickel sulfide, causing greater hidden dangers. Both of these situations will lead to the heat dip treatment being futile or even counterproductive. The uniformity of temperature during the operation of the hot dip furnace is so important, and the temperature difference in the furnace of most domestic hot dip furnaces during hot dip insulation is even up to 60°C, and it is not uncommon for the temperature difference of foreign imported furnaces to be around 30°C. Therefore, although some tempered glass has been treated with hot dip, the self-explosion rate remains high.
In fact, the hot dip process and equipment have been continuously improved. The German standard DIN18516 stipulates that the holding time is 8 hours in the 1990 edition, while the prEN14179-1:2001 (E) standard reduces the holding time to 2 hours. The effect of the hot dip process under the new standard is very significant, and there are clear statistical technical indicators: after hot dip, it can be reduced to one case of self-explosion per 400 tons of glass. On the other hand, the hot dip furnace is also constantly improving its design and structure, and the heating uniformity has also been significantly improved, which can basically meet the requirements of the hot dip process. For example, the self-explosion rate of the glass treated by the hot dip of CSG Group has reached the technical indicators of the new European standard, and the performance in the 120,000 square meters Guangzhou New Airport super-large project is extremely satisfactory. Although hot dip treatment cannot guarantee that there will be no self-explosion, it does reduce the occurrence of self-explosion and actually solves the self-explosion problem that has troubled all parties in the project. Therefore, hot dip is the most effective method recognized by the world to completely solve the self-explosion problem.