1. Causes of rainbow markings
First, we analyze the phenomenon of rainbow markings from the perspective of glass materials and optics.
The original float glass before tempering is structurally an amorphous structure with irregular atomic arrangement and belongs to an isotropic material, that is, the physicochemical properties in all directions are macroscopically identical. Because the atomic arrangement of the glass before the tempering is microscopically disordered, resulting in the macroscopic physicochemical isotropic, the result of isotropic is that when the light passes through the glass, there is always a suitable passage for the light to pass. Therefore, the original glass sheet with good annealing has the same speed of light passing through in all directions, and there is no change in the emitted light and incident light, and there is no rainbow marking phenomenon.
The tempered glass forms a relatively long compressive stress on the surface layer of the glass, and a longer tensile stress is formed inside the glass, and there is a difference in density from different positions of the same surface layer from the surface to the center. The macroscopically irregular atomic arrangement causes the tempered glass to become an anisotropic material. When a bundle of polarized light passes through the tempered glass, this makes the path through which the visible light passes a tortuous path. Due to the difference in optical density inside the glass, the light is split into two polarized lights of different propagation speeds. That is, one beam is light that travels relatively fast, and one beam is light that travels relatively slowly. When two beams formed at a certain point intersect with a beam 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, the two beams will interfere, when the two beams When the amplitude of the light is in the same direction, the light is reinforced, creating a bright field of view, i.e., rainbow markings. Therefore, the more uneven the stress distribution of the tempered glass, the more obvious the rainbow marking phenomenon on the surface.
2. Process control method for avoiding and reducing rainbow markings
Through the above analysis, it can be clarified that the main cause of the rainbow streak phenomenon in the tempered glass is caused by the uneven stress distribution after the glass tempering. If the stress distribution of the glass after tempering is more uniform, the rainbow markings appearing are smaller.
2.1 heating of glass
In order to avoid and reduce the rainbow marking after glass tempering, the temperature of each area of ??the glass must be uniform and uniform before the glass is air-cooled. Otherwise, the internal tensile stress generated by the relatively high temperature of the glass is large, and the surface compressive stress is small. The inner tensile stress generated by the relatively low glass temperature region is small, and the external compressive stress is large, resulting in uneven distribution of stress on the glass surface. The main factor in the uneven heating of the glass is that the furnace temperatures in the various areas of the furnace are inconsistent.
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