Characteristics of tempered glass, semi tempered glass, and homogeneous tempered glass
1. What are tempered glass and semi tempered glass? What are their characteristics?
Tempered glass: By heating and quenching the glass, the surface of the glass exhibits uniform compressive stress and the interior exhibits uniform tensile stress, thereby improving the flexibility and strength of the glass by several times. Visually speaking, the upper and lower surfaces of tempered glass are like a spring net that contracts towards the middle, while the inner middle layer is like a spring net that stretches outward. When the glass is bent, the spring on the outer surface is stretched, allowing it to bend a larger arc without breaking, which is the source of toughness and strength. If for some reason the tension balance of the tempered glass mesh is disrupted, it will disintegrate and break into small particles. Figure 1 is a photo of the tempered glass shattered by external force.
Tempered glass has the following characteristics:
Safety: The strength of tempered glass is 3-4 times that of ordinary glass, and it appears as small particles after crushing. It can minimize the damage caused by glass falling or splashing after crushing, so it belongs to safety glass.
Thermal stability: Tempered glass has good thermal stability, and can have a temperature difference of 200 ℃ on the same piece of glass without thermal cracking.
Disadvantages: There is a phenomenon of self explosion, which is the phenomenon of tempered glass breaking when placed naturally, and the tempering process can affect the flatness of the glass.
Figure 1 Photos of tempered glass shattered by external force. jpg
Figure 1 Photos of tempered glass shattered by external force
Semi tempered glass: It is a type of glass that falls between ordinary glass and tempered glass. Its strength is about twice that of ordinary glass, and the fragments after crushing are relatively large (Figure 2), so it is not considered safety glass; The cracks of semi tempered glass that break will not intersect. Although it is not a safety glass, it still has a certain degree of safety when being clamped and installed on all four sides, even if each fragment is broken, it is fixed by the edges; Its thermal stability is weaker than tempered glass, and it can withstand a temperature difference of 100 ℃ without generating thermal cracking; The biggest advantage is that there is no defect of self explosion. It should be noted that glass with a thickness of less than 8mm can be processed into semi tempered glass, while glass with a thickness of more than 12mm is difficult to process into semi tempered glass.
Figure 2 Photos of Half Tempered Glass After Breaking. jpg
Figure 2 Photos of Half Tempered Glass After Breaking
2. What is self explosion of tempered glass? What is the self explosion rate of tempered glass?
Self explosion of tempered glass refers to the cracking caused by internal stress in the glass without external force. The main reason for self explosion is the increase in volume of nickel sulfide (NiS) crystals in the glass during phase transformation or the expansion of hard silicon crystals, which causes the tensile stress to be greater than the tensile stress, disrupting the balance between tension and tension and causing the glass to break. There are obvious signs of "butterfly spots" after self explosion. (See Figure 3)
Due to the inability of existing online detection equipment in float glass production lines to detect nickel sulfide or hard silicon crystals with particle sizes of several micrometers, self explosion is unpredictable. Therefore, self explosion is called an inherent property or defect of tempered glass.
Figure 3 Photos of Tempered Glass After Self Explosion. jpg
Figure 3 Photos of tempered glass after self explosion
The self explosion rate is a post event statistical data that has no scientific basis and only commercial significance. It is scientifically reasonable to infer the self explosion rate of glass based on the amount of impurities contained in glass materials using big data.
Accumulated statistical results over the years have shown that approximately 4-8 tons of glass may contain one NiS crystal that can cause tempered glass to break. Taking an average of 6 tons containing one impurity, calculated based on the commonly used glass size for curtain walls, which is 6mm thick and 1.2m * 2.6m, each 1000 pieces of glass weighs about 47 tons. These glasses may contain 8 NiS crystals that can cause self explosion. It can be inferred that the self explosion rate of tempered glass of this size is about 0.8%. The thicker and larger the glass, the higher the content of NiS or hard impurities, thus the higher the self explosion rate. Assuming a tempered glass weighing 6 tons, it is estimated that it will definitely self explode, but of course, there is no glass of such a large size.
3. What is homogeneous tempered glass? What are its advantages?
Homogeneous tempered glass is a product obtained by homogenizing tempered glass, and there is currently a national standard for this product. Homogenization treatment process is to place tempered glass in a homogenization furnace, maintain a heating rate of no more than 1.5 ℃/min, and continue to heat up to around 298 ℃ for several hours, causing NiS transformation or hard impurities inside the tempered glass to expand and cause glass breakage. After gradually cooling, the intact glass is taken out. This process is also vividly referred to as detonation treatment.
The history of homogeneous processing technology internationally is not long, and sufficient data has not been accumulated to accurately predict the self explosion rate after processing. However, based on existing cases at home and abroad, it is completely guaranteed that the self explosion rate of conventional size glass is less than 0.1%. It should be noted that current technical methods cannot detect whether tempered glass has undergone homogenization treatment. The most effective way is to require manufacturers to provide homogenization curves or send personnel to supervise the production of homogenized tempered glass at the factory.