After the glass is broken, its broken starting point presents a typical "butterfly spot" shape, see above. It is clear from the direction of its thickness that there is a stone present in the middle of the thickness direction, it can be concluded that the breakage of the glass is due to the "blew phenomenon" of the tempered glass and does not belong to external damage.
Tempered glass blew is due to the production of tempered glass inside the original film there are some stones caused by the phenomenon of glass broken. At the beginning of the toughening of the tempered glass, there will be nickel sulfide stones, these nickel sulfide in the production of tempered glass will be high-temperature crystalline "frozen" and retained at room temperature. Because this high temperature crystalline state is not stable at room temperature, it will gradually change to room temperature crystalline , accompanied by a certain volume expansion; if the stone happens to exist in the tempered glass stress zone (the middle of the direction of the thickness of the glass plate), then this phase change process will often lead to sudden collapse of tempered glass, that is, we usually call the glass "blew" phenomenon. Under normal circumstances, due to the reasons for the original glass tempered glass there is a certain rate of blasting, from a technical point of view, you can control the quality of the original glass or secondary heat treatment can greatly reduce the rate of tempered glass, but can not completely eliminate the tempered glass Of the blew. Under normal circumstances, when the tempered glass by the impact of external friction and broken, such as small stone splash, etc., in the glass tipping point "butterfly" will find the impact of the glass surface is not smooth, there are some glass powder and pits, which is Because the glass by the external energy caused by the energy. And blew the tempered glass in the tipping point inside and outside the surface is very smooth.