The appearance of rainbow spots in the production does not affect the quality of the tempered glass itself. No matter whether it is the reflection effect of the glass (mainly refers to the phenomenon of glass surface reflection distortion), the strength of the glass, or the light transmission effect of the glass, it will not cause rainbows. Because of the appearance of spots, the National Standard GB 15763.2-2005 for the toughening of glass doors and windows does not impose restrictions and requirements on the phenomenon of rainbow spots on tempered glass. However, the appearance of relatively obvious rainbow markings will inevitably cause customer dissatisfaction.
1. Causes of Rainbow Stripes First, we analyze the phenomenon of rainbow stripe from the perspective of glass materials and optics.
Before the tempering, the original float glass sheet is an amorphous structure with irregular arrangement of atoms, belonging to the isotropic material, that is to say, the physical and chemical properties in all directions are the same in the macroscopic. Because the atomic arrangement of the glass before the tempering is microscopically disorganized, resulting in macroscopic physical and chemical isotropy. As a result of the isotropic effect, when light passes through the glass, there is always a suitable path through which light can pass. Therefore, in an annealed float glass original film, the speed of light passing through is the same in all directions, and there is no change in the emitted light and the incident light, and no rainbow streak phenomenon occurs.
The tempered glass forms a compressive stress on the surface layer of the glass, and a tensile stress is formed inside the glass. There is a difference in the density of the surface layer from the surface to the center of the same surface layer. The macroscopically irregular arrangement of atoms causes the tempered glass to be anisotropic. When a polarized light passes through a tempered glass, this makes the path through which visible light passes a tortuous path. Due to the difference in optical density inside the glass, the light is split into two polarized lights with different propagation speeds. That is, one beam is light that travels relatively fast, and one beam is light that travels at a relatively slow speed. When two light beams formed at a certain point intersect with a light beam formed at another point, there is a phase difference at the intersection of the light beams due to the difference in the light propagation speed, and at this point, the two light beams will produce an interference phenomenon when the two beams When the direction of the light's amplitude is the same, the light is strengthened, resulting in a visually bright field of view, i.e. rainbow streak. Therefore, the more uneven the stress distribution of the tempered glass is, the more pronounced is the rainbow speckle phenomenon produced on the surface.
2. Process control methods for avoiding and alleviating rainbow markings Through the above analysis, it can be clearly identified that the culprit leading to the occurrence of rainbow markings in tempered glass is caused by the uneven stress distribution after glass tempering. If the stress distribution of glass after tempering is more uniform, The smaller the rainbow stripes appear.
2.1 Glass heating In order to avoid and reduce the rainbow markings after glass tempering, the temperature of the glass in each area of the glass before the air cooling must be uniform, otherwise the internal tensile stress generated in the relatively high temperature area of the glass is large. The compressive stress is small, the internal tensile stress generated in the region with a relatively low glass temperature 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 the glass is that the furnace temperatures in the various zones of the furnace are inconsistent.