Why Does Tempered Glass Explode?

With the rapid development of society, glass has become an inseparable material in our lives, the variety of glass is rich and colorful, such as our more common tempered glass, tempered glass is a kind of safety glass, tempered glass is actually a kind of prestressed glass, in order to improve the strength of glass, usually use chemical or physical methods to form compressive stress on the glass surface, When the glass bears external force, the surface stress is first offset, thus improving the bearing capacity, and enhancing the glass's own resistance to wind pressure, cold and heat, impact, etc. But tempered glass will also self-explosion, some friends ask Xiaobian tempered glass in the absence of any external influence why will self-explosion? Next Xiaobian with everyone's questions to talk about, let's understand it together!

Tempered glass in the absence of direct mechanical external force under the automatic cracking called tempered glass self-explosion, according to industry experience, ordinary tempered glass self-explosion rate of about 1 to 3‰. Self-detonation is one of the inherent characteristics of tempered glass.

There are many reasons for self-explosion, which can be summarized as follows:

The effect of glass quality defects

1, there are stones in the glass, impurities, bubbles: impurities in the glass is the weak point of tempered glass, but also the stress concentration. In particular, if the stone is in the tensile stress area of the tempered glass, it is an important factor leading to the explosion crack. Calculi exist in glass and have different expansion coefficient from vitreous body. After glass tempering, the stress concentration in the crack area around the stone increases exponentially. When the expansion coefficient of the stone is smaller than that of the glass, the tangential stress around the stone is in a tension state. Crack growth associated with stones is very easy to occur.

2, the glass contains nickel sulfide crystals

Nickel sulfide inclusions generally exist as small crystalline spheres, with a diameter of 0.1-2 ㎜. Metallic in appearance, these impurities are Ni3S2, Ni7S6, and NI-XS, where X= 0-0. 07. Only Ni1-XS phase is the main reason for the spontaneous breakage of tempered glass.

The theoretical NIS is known at 379. In C, there is a phase transformation process, from the high-temperature α-NIS hexagonal system to the low-temperature β-Nis trigonal system, accompanied by 2.38% volume expansion. This structure is preserved at room temperature. If the glass is heated later, an α-β state transition may occur rapidly. If these impurities are inside the tempered glass under tensile stress, the volume expansion will cause spontaneous cracking. If A-NIS is present at room temperature, it will slowly transition to the β state after several years or months, and the slow increase in volume during this phase transition may not necessarily cause internal rupture.

3, the glass surface due to processing or improper operation caused by scratches, holes, deep explosion edge and other defects, easy to cause stress concentration or lead to tempered glass self-explosion.

(1) The stress distribution in tempered glass is uneven and offset

The temperature gradient along the direction of glass thickness is uneven and asymmetrical when glass is heated or cooled. The tempered products have a tendency to self-explosion, and some produce "wind explosion" when they are chilled. If the tensile stress zone is offset to a certain side of the product or offset to the surface, the tempered glass forms a self-explosion.

(2) The influence of the degree of tempering, the experiment has proved that when the degree of tempering is increased to 1 level /cm, the number of self-explosion can reach 20% to 25%. It can be seen that the greater the stress, the higher the degree of tempering, the greater the amount of self-detonation.