The reason and identification method of self - explosion of tempered glass
Does the "butterfly spot" feature mean that the tempered glass must be self-exploding? How to define the self-explosion of tempered glass? How can we quickly tell if it's a self-detonation or a force impact? What are the causes of the self-explosion of tempered glass? How to reduce the self-detonation rate of tempered glass?
1
What kind of tempered glass rupture is considered a self-explosion?
Strictly speaking, only spontaneous rupture of tempered glass under no load is called self-detonation of tempered glass. In actual engineering, for the tempered glass without external impact, under normal service conditions, with typical self-detonation crack is also attributed to the tempered glass self-detonation.
2
How to quickly distinguish a self-detonation from an external impact?
Obvious "self-detonation", characterized by the initiation point "butterfly spot" smooth and flat, and there are impurities visible to the naked eye
Obvious external force impact, as the indoor side glass at the detonation point "butterfly spot" there are obvious glass debris.
"butterfly spot" can not determine whether the toughened glass self-explosion, but also combined with the characteristics of the fracture comprehensive judgment.
The fracture is smooth and flat, and there are impurity particles visible to the naked eye, basically can be determined as the tempered glass self-explosion; If there is obvious debris or other impact characteristics at the fracture, it is judged to be external impact.
3
What are the causes of the self - explosion of tempered glass?
There are many reasons for the self-detonation of tempered glass. The phase transition expansion of nickel sulfide particles in glass, the stress concentration caused by bubbles and stones, the excessive tempering, the uneven stress of tempered glass, the low processing quality of the glass edge and the size of tempered glass are mostly likely to cause the self-detonation of tempered glass.
The expansion of nickel sulfide (NiS) is the fundamental cause of the self-detonation of toughened glass. NiS is generally crystalline, and has a thermodynamic tendency to transition from α to β phase at room temperature, accompanied by volume expansion of 2%~3%. Under the corresponding dynamic conditions, the temperature change can cause the self-detonation of toughened glass.
Therefore, temperature change is the direct cause of the self-detonation of toughened glass, which is also the reason why self-detonation mostly occurs at the alternations of seasons and in the southward and westward direction of intense solar irradiation.
In addition, wind load and glass assembly will also change the stress distribution inside the toughened glass, and become a possible cause of the self-detonation of the toughened glass
4.
How to reduce the self-detonation rate of tempered glass?
According to the statistical analysis of studies, the diameter of the impurity particles causing the self-detonation of tempered glass is more than 95% in the range of 0.04mm ~ 0.65mm.
The national standard GB 11614-2022 "Flat glass" has the following requirements for spot defects of High quality processing grade flat glass.
Table 5 Appearance quality of high quality machining grade flat glass
Type of fault | Require | |
Spot fault | Dimension L | Allowable number limit Allowable number limit
|
0.3 mm ≤ L ≤ 0.5 mm | 1XS | |
0.5 mm< L ≤ 1.0 mm | 0.2XS | |
L>1.0 mm | 0 | |
Spot defect density
| Minimum spacing of spot defects with size L≥0.3mm is not less than 300 mm: no more than 3 point defects with size L> 0.1mm can be found in a 100mm diameter circle.
| |
Lines | Not allowed | |
Crack | Not allowed | |
Scratch | Allowance range | maximum number of allowed items
|
Width W ≤ O.2 mm,Length L ≤ 40mm | 2 X S | |
That is, the allowable number of spot defects with a diameter of 0.3~0.5 mm within one square meter is 2. Obviously, the impurities of nickel sulfide were not excluded, which determined that the possibility of self-detonation of toughened glass must exist, and we can only reduce the self-detonation rate.
The main ways to avoid the self-explosion of tempered glass are: 1) choose high-quality flat glass; 2) Moderate tempering; 3) Ensure uniform surface stress of toughened glass; 4) Improve the edge processing quality of tempered glass; 5) Limit the size of tempered glass 6) After tempered ,carry out heat soak process.
5
Analysis of self-explosion causes of toughened glass and interpretation of relevant regulations on reducing self-explosion rate of toughened glass on"Toughened Glass for Building Door, Window and Curtain Wall", contact hope create glass ,provide more specialized expound on tempered glass engineering .
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