Why does tempered glass self-explode after tempering?
The reason is actually very simple, because in the process of glass production, some nickel-containing impurities are mixed in the molten materials such as raw materials or refractory materials, and these impurities use each other to form nickel sulfide crystals during the glass melting process.
Nickel sulfide crystals are in the α-phase state at high temperatures exceeding 380°C, and are in the β-phase state at room temperature. When the nickel sulfide crystal changes from the α phase to the β phase, the volume of the crystal will change by 2-4%, and the average diameter of the nickel sulfide crystal that causes the self-explosion of the tempered glass is about 0.2mm.
When the glass factory is forming the original glass, it needs to go through a slow annealing process, and the nickel sulfide crystal will basically not affect the strength of the glass. But the situation is quite different when tempering glass.
Because tempered glass adopts quenching process. Under the action of the cooling wind, the cooling speed of the glass is very fast. When the glass is cooled to room temperature, after the structure is completely fixed, the α-phase nickel sulfide crystals have no time to convert into the low-temperature β-phase, but are still in the high-temperature α-phase state. exist. If nickel sulfide crystals appear in the tensile stress area of tempered glass, as long as there is a crystal transformation, self-explosion will definitely occur.
Due to the uncertain time of crystal transformation, the self-explosion of tempered glass at room temperature is also completely uncertain.
The detonation treatment reduces the probability of self-explosion. The solution to the self-explosion of tempered glass is to homogeneously process the tempered glass (that is, to reheat the tempered glass to 280-300°C, and then keep it warm for 2-4 hours, so that the tempered glass that is conditional to self-explode can be processed in this process. burst).
The homogeneity of tempered glass is also called detonation treatment of tempered glass or heat soaking treatment of tempered glass. According to the analysis of the glass factory, after strict homogenization treatment, the probability of self-explosion of tempered glass will be greatly reduced, and the rate of self-explosion of a piece of glass per 10,000 square meters of glass within a year is only less than 1%. Such tempered glass can be called real safety glass
What is glass tempering
There are two types of glass tempering, chemical tempering and physical tempering:
Glass tempering can be divided into physical tempering and chemical tempering. Physical tempering is more common. Glass is obtained after passing high temperature in a physical tempering furnace.
Physical tempering is very effective for glass with a thickness of 3mm and above. Semi-tempered treatment, semi-tempered glass has a very small hardness and strength compared to fully tempered glass, but its safety factor will also be lower. If the glass with a thickness below 2cm can achieve the effect of full tempering, it must be tempered by chemical tempering. .
Chemical tempering is a simple low-temperature ion exchange of glass in an alkali salt solution at about 400°C. The principle of chemical tempering is different from that of physical tempering.
Physical tempering is mainly used to strengthen glass with a large thickness, while chemical tempering is used to strengthen glass with a thin thickness. Among them, the products that are often used in chemically toughened glass include mobile phone glass, scanner glass, display glass, printer glass, plasma TV glass, etc.
Chemical toughening does not necessarily have to be toughened thin glass, and thick glass can also be better. Tempering, the advantage is that tempering is flexible, suitable for glass of different sizes, shapes, and thicknesses, and the glass processing range is 0.3-19 mm. Compared with physical tempering, its surface is smoother, the light transmittance is better, and there is no self-explosion. Phenomenon.