When you buy tempered glass
The stress distribution in tempered glass is that the two surfaces of the tempered glass are compressive stress and the core layer is tensile stress. The stress distribution in the thickness of the glass is similar to a parabola. The center of the glass thickness is the apex of the parabola, that is, the place where the tensile stress is the greatest; the two sides close to the two surfaces of the glass are compressive stress; the zero stress surface is located at about 1/3 of the thickness. By analyzing the physical process of tempering and quenching, it can be known that the surface tension of tempered glass and the maximum internal tensile stress 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 about 100MPa, but the actual situation may be higher. The tensile stress of the tempered glass itself is about 32 MPa to 46 MPa, and the tensile strength of the glass is about 59 MPa to 62 MPa.As long as the tension produced by the expansion of nickel sulfide is 30MPa, it is enough to cause spontaneous explosion. If the surface stress is reduced, the inherent tensile stress of the tempered glass itself will be reduced accordingly, thereby helping to 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 "Safety Glass for Building
Part 2: Tempered Glass" implemented by China requires that its surface stress should not be less than 90MPa. This is 5 MPa lower than the 95 MPa stipulated in the old standard, which helps reduce self-detonation. Uniform stress The uneven stress of tempered glass will significantly increase the rate of spontaneous explosion, which has reached a level that cannot be ignored. The spontaneous explosion caused by uneven stress sometimes appears very concentrated. In particular, the spontaneous explosion rate of a specific batch of bent tempered glass can reach an alarming severity, and spontaneous explosion may occur continuously. The main reason is the uneven local stress and the deviation of the tension layer in the thickness direction, and the quality of the original glass itself also has a certain influence. The 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-detonation rate. If the stress of the tempered glass can be evenly distributed, the spontaneous explosion rate can be effectively reduced.
The hot dip treatment is also referred to as homogenization treatment, commonly referred to as "detonation". Hot-dip treatment is to heat the tempered glass to 290℃±10℃ and keep it for a certain period of time to promote the rapid completion of the crystal phase transformation of nickel sulfide in the tempered glass, so that the tempered glass that may explode after use is artificially broken in advance in the factory. In the hot dip furnace, the self-explosion of the tempered glass used after installation is reduced. This method typically uses hot air as the heating medium. It is called "Heat Soak Test", or HST for short, literally translated as hot dip treatment. Difficulties in hot dip. From the principle point of view, the hot dip treatment is neither complicated nor difficult. But in fact it is very difficult to reach this technological index. Studies have shown that there are many specific chemical structural formulas of nickel sulfide in glass, such as Ni7S6, NiS, NiS1.01, etc., not only the proportions of various components are different, but also other elements may be doped. The speed of the phase change is strongly temperature dependent.Studies have shown that the phase transition 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 regime. Otherwise, on the one hand, the low-temperature glass will not be able to completely phase change due to the insufficient holding time of the glass, which will weaken the effect of hot dip. On the other hand, when the glass temperature is too high, it will even cause reverse phase transformation of nickel sulfide, causing greater hidden dangers. Both of these conditions will cause the hot dip treatment to be laborious or even counterproductive. The temperature uniformity of the hot soaking furnace is so important when it is working, and the temperature difference in the furnace during the hot soaking and holding of most domestic hot soaking furnaces can even reach 60℃, and it is not uncommon for foreign imported furnaces to have a temperature difference of about 30℃. Therefore, although some tempered glass is hot-dipped, the spontaneous explosion rate is still high. In fact, the hot dip process and equipment have also been continuously improved. The German standard DIN18516 stipulated in the 90th edition that the holding time was 8 hours, while the prEN14179-1:2001(E) standard reduced the holding time to 2 hours. The effect of the hot dipping process under the new standard is very significant, and there are clear statistical technical indicators: after hot dipping, it can be reduced to one case of spontaneous explosion per 400 tons of glass. On the other hand, the hot dip furnace is 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 heat-dipped glass processed by CSG Group has reached the technical indicators of the new European standard, and it has performed extremely well in the 120,000-square-meter Guangzhou new airport super project. Although hot dipping treatment cannot guarantee that there will be absolutely no self-detonation, it does reduce the occurrence of self-detonation, and actually solves the self-detonation problem that plagues all parties in the project. Therefore, hot immersion is the most effective way to completely solve the problem of self-detonation that is universally recognized in the world. Note packaging Products should be packed in containers or wooden boxes. Each piece of glass should be packed in plastic bags or paper, and the space between the glass and the packaging box should be filled with light and soft materials that are not easy to cause glass scratches and other appearance defects. Specific requirements should comply with relevant national standards. Packaging logo The packaging signs should comply with the relevant national standards, and each packaging box should be marked with words such as "face up, handle with care, be careful of broken, glass thickness, grade, factory name or trademark". transport The various types of transportation vehicles and transportation rules used for the products shall comply with relevant national regulations. During transport, wooden boxes should not be placed flat or inclined and their length direction should correspond to the direction of movement of the transport vehicle and measures such as rain should be taken. The product should be stored vertically in a dry room.
GB / T 531-92 "Test method for Shore A hardness of vulcanized rubber"
GB 1216-85 "outer micrometer"
GB 4871-1995 "Ordinary Flat Glass"
GB 5137.2-1996 "Test method for the optical performance of automotive safety glass"
GB 11614-89 "float glass"
JC / T 677-1997 "Test method for simulating an evenly distributed static load wind pressure in glass buildings"