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What caused the glass to burst suddenly?

1. The self-explosion rate is different among domestic manufacturers, ranging from 3% to 0.3%. Generally, the self-explosion rate is calculated according to the number of pieces, without considering the area size and thickness of single glass, so it is not accurate enough and cannot be compared with each other in a more scientific way. In order to calculate the self-explosion rate uniformly, the uniform hypothesis must be determined. A uniform condition is established: every 5 ~ 8 tons of glass contains a nickel sulfide sufficient to cause spontaneous explosion; The average area of each piece of tempered glass is 1.8mm. Nickel sulfide is uniformly distributed. The calculated self-explosion rate of tempered glass with 6mm thickness is 0.64% ~ 0.54%, that is, the self-explosion rate of tempered glass with 6mm thickness is about 3‰ ~ 5‰. This is basically consistent with the actual value of domestic high-level processing enterprises. Even if completely according to the standard production, can not avoid the steel glass self - explosion. Large buildings can easily use hundreds of tons of glass, which means that there is a high rate of nickel sulphide and heterogeneous phase impurities in the glass, so although tempered glass is treated by hot immersion, self-explosion is still inevitable.

tempered glass (12)

2. The cause of uncontrollable self-explosion of tempered glass - ni sulfide (NiS) and heterogeneous particles. Crack germination and propagation in glass are mainly caused by residual stress in the vicinity of particles. This kind of stress can be divided into two kinds, one is the phase change stress in the process of phase change expansion and the other is the residual stress produced by the mismatch of thermal expansion coefficient. Nickel sulfide (nis) and heterogeneous particles. Inside the glass containing nickel sulfide impurities, exist in small crystal state, in general, will not result in a broken glass, but because of toughened glass reheating, changed the nickel sulfide phase behavior of impurity, the high temperature of nickel sulfide alpha state in glass quenching were frozen, they are back to the beta state may take years, because of the low temperature beta state of nickel sulfide impurities will produce volume increase, local stress concentration inside the glass, toughened glass explosive will occur. However, only relatively large impurities will cause self-explosion, and only when impurities are at the core of the tensile stress can the tempered glass self-explosion occur. Nis is a kind of crystal, there are two kinds of crystalline phases: high temperature phase alpha beta nis nis and low temperature phase, the phase transition temperature is 379 ℃, when the glass tempering furnace heating, due to the heating temperature is far higher than the phase transition temperature, the nis all into alpha. In the subsequent quenching process, however, it was too late for them to transform into actin-nis, and thus they were frozen in the tempered glass. At room temperature, they were not stable, and gradually transformed into calf-nis. This transformation is accompanied by an expansion of about 2-4% of the volume, which makes the glass subject to a huge phase change tensile stress, thus causing self-explosion. As can be seen from the scanning electron micrograph of nis calculi extracted from the glass fragments after the explosion, its surface is undulating and very rough. A cross-sectional photograph of the glass fragment at the source of the fracture shows the boundary between the first crack and the second fracture caused by a spherical particle.

3. How to identify the self-blasting of tempered glass first to see whether the starting point (tempered glass cracks are radial and all have starting points) is in the middle of the glass. If it is at the edge of glass, it is generally because the glass has not undergone chamfered edge grinding or glass edge is damaged, resulting in stress concentration and crack gradually developing. If the detonation point is in the middle of the glass, see if the detonation point has a pattern like two butterfly wings composed of two small polygons (butterfly spots). If carefully observe the common edge of two small polygons (the body part of the butterfly), there should be black small grains (nickel sulfide stones) visible to the naked eye, then it can be judged as self-detonation. Otherwise, it should be damaged by external forces. Glass self - explosion characteristic is the butterfly spot. The glass fragments were distributed radially, and there were two pieces of glass shaped like the wings of a butterfly, commonly known as "butterfly spots". Nis calculi are located on the interface of two "butterfly spots".

4. In the theory of self-explosion mechanism of tempered glass, the stress at the interface between particles r greater than or equal to a and particles r greater than or equal to a was investigated. For heterogeneous particles in the glass matrix, the temperature during the cooling process was negative. Scanning electron microscopy images and edge extrusion morphology of the spherical mono-silicon particles in the middle layer of glass, the radial stress around the particles is pressure, and the tangential stress is tension, so the tangential stress is the root of the crack initiation.