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Reasons For The Self-explosion Of Tempered Glass

- Aug 01, 2017 -

1, the rate of self explosion of manufacturers is not uniform, from 3%~0.3%. General self-explosion rate is based on the number of units, not considering the size of the glass and glass thickness, it is not accurate, and can not be more scientific comparison. In order to calculate the self explosion rate uniformly, the unified hypothesis must be determined. Uniform Conditions: Each $number ton of glass contains a nickel sulfide that is sufficient to cause the explosion; the average area of each piece of toughened glass is 1.8mm; nickel sulfide evenly distributed. The calculated self detonation rate of the tempered glass with 6mm thickness is 0.64%~0.54%, that is, the self detonation rate of the 6mm tempered glass is about 3‰~5‰. This is consistent with the actual value of the domestic high level processing enterprises. Even if completely according to the standard production, also cannot completely avoid the tempered glass self explosion. Large buildings can easily use hundreds of of tons of glass, which means that the glass nickel sulfide and heterogeneous impurities exist in a large rate, so tempered glass although hot-dip treatment, the explosion is still inevitable.


2, the reason for the uncontrollable self-explosion of tempered glass--the source of the uncontrollable self explosion of nickel sulfide (NIS) and heterogeneous granular glass is not only the traditional knowledge of NIS particles, but also many other heterogeneous particles. The crack germination and expansion in glass is mainly due to the residual stress produced near the particle. This kind of stress can be divided into two kinds, one is the phase change stress in the process of phase change expansion, the other is the residual stress caused by the mismatch of thermal expansion coefficient. Nickel sulfide (NIS) and heterogeneous phase granules. The glass contains nickel sulfide impurities, in the presence of small crystal states, in general, will not cause glass breakage, but because tempered glass reheated, changed the phase of nickel sulfide impurities, the high temperature α state of nickel sulfide is frozen when the glass is cold, they may take years to be restored to beta, because the low temperature β-state nickel sulfide impurity will produce the volume increase, the local stress concentration inside the glass, then the tempered glass will happen. However, only relatively large impurities will cause a self-destruct, and only when the impurity is at the core of the tensile stress can the tempered glass explode. NIS is a crystal, there are two kinds of crystalline phase: high-temperature phase Α-nis and low-temperature phase Β-nis, Phase change temperature is 379 ℃, glass in tempering furnace heating, because the heating temperature is much higher than the phase change temperature, NIS all changed to α phase. However, in the subsequent quenching process, Α-nis too late to convert to Β-nis, which was frozen in the tempered glass. At room temperature, the Α-nis is unstable and has gradually changed into Β-nis trend. This transformation is accompanied by the expansion of the volume of about 2~4%, which allows the glass to withstand a huge phase change tensile stress, thus causing a self-destruct. A scanning electron microscope photograph of Nis stone extracted from a self exploding glass fragment can be seen as uneven and rough on the surface. The heterogeneous particles cause the tempered glass to explode, and can rupture the source of glass fragments in the cross-section of the photo to see, a spherical micro-particle caused by the first crack marks and two times the fragmentation of the boundary zone.


3, how to identify the self explosion of tempered glass first see the initiation point (tempered glass crack is radial, there are starting points) whether in the middle of the glass, such as on the edge of glass, generally because the glass has not been inverted angle grinding edge treatment or glass edge damage, resulting in stress concentration, crack gradually developed; if the initiation point is in the middle of the glass, see if there are two small pieces of polygon in the initiation point that resemble two butterfly-wing patterns (butterfly spots), If there is a careful observation of the common edge of two small polygons (the trunk part of the butterfly) should be visible to the naked eye of small black particles (nickel sulfide stones), it can be judged to be self explosive, otherwise it should be external damage. The typical characteristic of the self explosion of glass is the butterfly spot. The glass fragments are radially distributed and the center has two pieces of glass shaped like butterfly wings, commonly known as "butterfly spots". The NIS stone is located on a two-piece "Butterfly Spot" interface.


4, the Theory of self-explosion of tempered glass discussion on the stress of the r≥a tangential stress r≥a the interface between the particles and the glass in the glass matrix, the temperature of the cooling process is negative, so the radial stress around the particle is the pressure and the tangential stress is the tensile force. Glass middle layer spherical elemental silicon particle scanning electron microscope image and edge extrusion morphology, the radial stress around the particle is pressure, tangential stress is the tensile force, so tangential stress is the root of crack initiation.


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