1. Causes of rainbow streaks First, we analyze rainbow streaks from the perspective of glass materials and optics.
The original float glass sheet before tempering belongs to an amorphous structure with irregular atomic arrangement and belongs to isotropic materials, that is, the physical and chemical properties in all directions are macroscopically the same. Before the tempering of glass, the atomic arrangement of the glass was chaotic at the micro level, which led to the physical and chemical isotropy at the macro level. As a result of the isotropy, when the light passes through the glass, there is always a suitable path for the light to pass through. Therefore, the well-annealed original float glass sheet has the same speed of light passing in all directions, and there is no change in the outgoing light and incident light, and the phenomenon of rainbow streaks will not appear.
Tempered glass will form compressive stress on the surface layer of glass and tensile stress inside the glass. There is a difference in the density of the same surface layer from the surface to the center. The relatively irregular atomic arrangement on the macro level causes the tempered glass to become an anisotropic material. When a beam of polarized light passes through toughened glass, this makes the path through which visible light passes a tortuous route. Due to the difference in optical density inside the glass, this beam of light will be broken down into two polarized lights with different propagation speeds. That is, one beam is light with a relatively fast propagation speed, and one beam is light with a relatively slow propagation speed. When two beams formed at one point intersect with beams formed at another point, there is a phase difference at the intersection of the beams due to the difference in light propagation speed. At this point, the two beams will interfere with each other. When the amplitude direction of the light is the same, the light is strengthened, and a bright field of view is generated visually, that is, rainbow streaks. Therefore, the more uneven the stress distribution of tempered glass, the more obvious the rainbow streaks on the surface.
2. Process control methods to avoid and mitigate rainbow streaks Through the above analysis, it can be clear that the culprit that causes rainbow streaks in tempered glass is caused by uneven stress distribution of glass after tempering. The smaller the rainbow markings appear.
2.1 Glass heating To avoid and reduce rainbow streaks after tempering the glass, the temperature of each area of ??the glass must be highly uniform before air cooling, otherwise the internal tensile stress generated by the relatively high temperature area of ??the glass is large and the surface The compressive stress is small, the internal tensile stress generated in the region where the glass temperature is relatively low is small, and the external compressive stress is large, resulting in unevenly distributed stress on the glass surface. The main reason for the uneven heating of glass is the inconsistent furnace temperature in various regions of the heating furnace.
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