The problem of poor flatness of flat tempered glass. There are mainly five types of such problems:
(1) Glass deformation caused by temperature difference between the upper and lower surfaces during heating
① The tempered glass panel is curved upwards. This phenomenon is due to the situation where the temperature of the upper surface of the glass is higher than that of the lower surface after being heated in the heating furnace. The glass that maintains this temperature state enters the cooling chamber for cooling. During the cooling process, when the cooling temperature and wind pressure of the upper and lower surfaces of the glass are the same, due to the high temperature of the upper surface of the glass, the shrinkage of the upper surface after cooling is greater than that of the lower surface, resulting in upward bending and deformation of the glass surface.
In this situation, the temperature at the bottom of the heating furnace can be increased to minimize the temperature difference between the upper and lower surfaces of the glass.
② The tempered glass surface bends downwards. This phenomenon is due to the temperature of the lower surface of the glass being higher than that of the upper surface after being heated in the heating furnace. The glass that maintains this temperature state enters the cooling chamber for cooling. During the cooling process, when the cooling temperature and wind pressure of the upper and lower surfaces of the glass are the same, due to the high temperature of the lower surface of the glass, the shrinkage of the lower surface after cooling is greater than that of the upper surface, resulting in the downward bending and deformation of the glass surface. In this situation, the temperature at the bottom of the heating furnace can be lowered to minimize the temperature difference between the upper and lower surfaces of the glass.
(2) Glass deformation caused by temperature difference between the middle and edges during heating
After being heated in the heating furnace, if the temperature of the middle part of the glass is higher than that of the edges, the shrinkage of the middle part with higher temperature on the glass will be greater than that of the edges with lower temperature during the cooling process. When the glass is cooled to room temperature, the size of the edges of the glass will be larger than that of the middle part, forming a large compressive stress at the edges of the glass, resulting in the phenomenon of downward bending and deformation of the glass surface. Similarly, if the temperature of the edge of glass is higher than that of the middle part after being heated in the heating furnace, the shrinkage of the middle part with higher temperature on the glass will be greater than that of the edge part with lower temperature during the cooling process. When the glass is cooled to room temperature, the size of the middle part of the glass will be larger than that of the edge part, forming a large tensile stress at the edge of the glass, resulting in upward bending deformation of the glass surface.