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However, due to the lack of understanding of the characteristics of the people, when the glass is damaged, it is considered that the glass has "self-explosion". However, if the glass is not subjected to external stress, it will not break, that is, the so-called "self-explosion" phenomenon. In fact, we should call it: glass breakage. Due to its crystal structure, glass has no yielding process before it suddenly ruptures. Therefore, people generally think that glass has produced "self-destruction." Because glass is non-durable and fragile. The cracking of all glass is the result of tensile stresses greater than compressive stress and surface defects, and is never the cause of pure compressive stress.
The glass will be damaged after the surface compressive stress layer is penetrated. Although the glass edge and surface scratches and microcracks and other defects do not completely penetrate the compressive stress layer, these fine damages are at a temperature over time. Under the repeated action of changes such as changes and wind loads, it will slowly become effective and become larger, which will lead to the "self-explosion" of the glass. Because there is no obvious reason before the glass breaks, it often makes people feel unexpected. It is the reason of the glass manufacturer. It should be compensated by the glass manufacturer. This is not the case.
Since glass is a poor conductor of heat, dangerous pressure is created when the glass encounters sudden changes in temperature. At this time, the temperature difference between the glass surface and the inside of the glass may cause the glass to break. For very obvious reasons, the risk of sudden heating is less than sudden cooling. Sudden heating increases the compressive stress on the glass surface, and sudden cooling increases the tensile stress on the glass surface, causing the glass to break. The thermal conductivity of the glass gradually decreases as the temperature decreases. At temperatures above 39 ° C, the radiant conductivity of the glass increases significantly. When the glass is at noon in summer, the surface temperature will reach about 80 °C, and the heat transfer of the thick glass to the thin glass is obviously enhanced, so the thick glass is prone to thermal cracking.
◆◆◆Analysis of glass breakage
1. Design reason The design strength of the glass is lower than the allowable strength value, which can cause damage to the glass. The glass structure design is unreasonable, resulting in damage caused by excessive local stress of the glass, such as: triangular, convex and concave, digging holes and other structures, which will cause local stress concentration of the glass. The thermal cracking of the glass during design is not considered or considered insufficient. Glass, especially heat-absorbing glass and heat-reflecting glass, when exposed to sunlight, due to factors such as curtain effect, the glass surface will form a non-uniform temperature field, thereby forming thermal stress in the glass, when this thermal stress exceeds the strength of the glass. In the range, thermal cracking occurs, and the glass appears in a curved state when it is thermally exploded. When the glass thickness is too thin or the deflection is large during design, after the glass is subjected to the wind load or the wind pressure, the deflection of the glass sealant is caused by the deflection, and the glass in contact with the frame is damaged.
2, the impact on the production, transportation and handling of the glass in the production, transportation and handling, if the glass is not properly protected, it will cause serious scratches, blasts, abrasions and other defects on the surface or edge of the glass, It will cause local stress concentration on the glass. Causes damage to the glass.
3. The stress generated during installation causes the broken glass of the glass to be deformed due to the difference of the error between the building and the glass. When the glass is deformed, additional stress is generated on the glass, which may cause damage to the glass. Due to the hardness of the glass block and the improper selection of the position and quantity, the stress on the edge of the glass may be concentrated or excessively large, causing damage to the glass. The broken state is a straight shape.
4. The uneven settlement of the building caused the glass to be damaged. A large curtain wall enterprise in China once measured and measured the installation of a building curtain wall. The settlement of the building reached 12mm. Exceeding the allowable flexural strength of the glass, it is bound to cause damage to the glass. The photograph below shows the amount of deformation of the point support member in the horizontal direction, which is also sufficient to cause damage to the glass.
5, the cause of man-made glass in the state of use, people intentionally or unintentionally damage the glass. When the glass is mounted, the smashing and knocking of the edge of the glass may inadvertently cause damage to the glass. Or people are unintentionally damaged by the impact of the glass when they are active. Intentional: When manufacturing ice cracked glass, artificially damage the glass. Or people's active impact on the glass is broken.
6. Causes of natural disasters Typhoons, hail, sandstorms, etc. cause damage to the glass.
7. The reason for the “self-explosion†of glass The national standard “Safety glass for construction Part II: Tempered glass†Appendix A.2 of GB15763.2-2005 has a clear description of the self-explosion of tempered glass: due to the presence of tiny nickel sulfide in the glass In the stone, after the heat treatment, a part of the stone will change crystal state with time, and the volume will increase, causing micro cracks inside the glass, which may cause the tempered glass to self-explosion.
◆◆◆Three ways to reduce this self-explosion
1. Use the original film containing less nickel sulfide stones, that is, use high quality original film.
2. Avoid excessive steel stress.
3, hot dip / detonation / homogenization. Special attention: avoid the furnace temperature exceeding 320 degrees during hot dip / detonation / homogenization, and the surface temperature of the glass exceeds 300 degrees. In fact, the tempered glass causes a "self-explosion" phenomenon, in addition to nickel sulfide, there are also single polycrystalline silicon, aluminum oxide, Na2Al2Si5O10 and the like. However, the hot dip/detonation/homogeneous process only acts on the "self-explosion" caused by nickel sulfide, but has no effect on the "self-explosion" caused by other substances. Therefore, the "self-explosive" profile of tempered glass: three thousandths of compensation. However, a famous foreign processing enterprise promised that after the hot dip of tempered glass, the “self-explosion†rate should not exceed five thousandths. In fact, Australian technicians tracked 12 buildings for 12 years. In a total of 17,760 pieces of glass, a total of 306 pieces of glass "self-explosive" occurred. The statistics showed that the glass self-explosion rate was 1.72%. The "self-explosion" of tempered glass has its own unique shape, namely the "butterfly spot" phenomenon. Only in the presence of glass: nickel sulfide, elemental polycrystalline silicon, aluminum oxide, Na2Al2Si5O10, etc., and the external stress exceeds the compressive stress on the glass surface, the so-called "self-explosion" phenomenon occurs in the tempered glass.
In summary, there are many reasons for glass breakage, and the phenomenon of "self-explosion" is only one of them. If the glass is not subjected to external stress, there is no glass breakage. Therefore, when the glass is damaged, it is necessary to analyze it from many aspects to confirm the cause and determine the responsibility. If the glass is not damaged, it is claimed that the glass is “self-explosiveâ€, and the glass manufacturer is required to take responsibility.