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Know more about tempered glass stress spot

  • Author:Shenzhen Jimy Glass Co., Ltd
  • Source:Original
  • Release on:2018-04-16

Tempered glass
also named toughened safety glass, ESG glass, reinforce glass etc. Stress spots are also called wind spots, which is caused by uneven heating and cooling during glass tempering. Different stress distributions occur on the glass plate surface. Optical path difference due to uneven stress distribution under polarized light irradiation. The phenomenon of light wave interference that is unique to stress spots. Stress spots are also caused by uneven stress. For example, in the heating process. The temperature difference between the hearth and the middle causes uneven stress. Stress spots are not yet completely eliminated, but well-designed tempering equipment and scientific processes can greatly reduce the visibility of stress spots.

1.Causes of stress spot formation

The phenomenon of stress spots produced by tempered and semi-tempered glass as anisotropic materials can be understood by light path diagrams. When a beam of polarized light passes through a tempered glass, there is a stress difference inside the glass, which causes the dense particles in the surface particles to be loose and each position is different. This beam of light has a larger angle of refraction at the relative light density, and refraction angle at the light sparse position. Relatively smaller, it will be decomposed into two polarized lights with different propagation speeds. When two lights formed at a certain point intersect with light beams formed at another point, there is a phase difference at the intersection of the beams due to the difference in the speed of light propagation. At this point, interference occurs between the two lights, when the two lights are When the amplitude direction is the same, the light intensity is strengthened, resulting in a bright field of view, ie, a bright spot; when the light amplitude is in the opposite direction, the light intensity is weakened, resulting in a dark field, a dark spot.

2.Heating effect on stress spots
The characteristics of the physical toughened glass is that the glass is heated first and then air-cooled to make the glass form the internal and external stress difference. At present, the mainstream tempering equipment is batch-type convection ovens (single chamber furnaces, dual chamber furnaces, and bending furnaces) and continuously produced radiant furnaces (continuous furnaces). Convection furnace glass is affected by convective wind pressure, heating wire and roller heat conduction. The ideal state is that the temperature of each point is the same at the end of the heating of the glass, or it is understood that the temperature field uniformity of the heating is Good. Because of the existence of these three factors, the change of any one of these factors will cause the change of the temperature field and directly affect the heating effect of the glass. If the temperature of the glass is not uniform, it will enter the same air-cooling system. Because of the difference of cooling shrinkage, the stress spot is obvious. Therefore, the primary factor for reducing the stress spot is to ensure uniform heating.

3. How to obtain a uniform temperature field

First of all, we must consider whether the power value of the heating furnace wire is even. The inspection method can be used to judge the intensity of the current through the furnace wire. Furnace aging during use, affecting the power to play, or using different manufacturers of furnace wire will also have a larger power deviation. The glass more thick, and the street spot will be more serious.

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