Glass toughening is the use of physical or chemical methods to form a compressive stress layer on the surface of glass and a tensile stress layer inside; When the glass is subjected to external forces, the compressive stress layer can partially offset the tensile stress, avoid glass breakage, and thus achieve the goal of improving the strength of the glass. Moreover, the microcracks on the glass surface become more subtle under this compressive stress, which also improves the strength of the glass to a certain extent.
The commonly used physical tempering method at present is to heat the glass to the softening point (around 650 ℃), at which time the glass can still maintain its original shape, but the particles in the glass have a certain migration ability. Structural adjustments are made to quickly eliminate the internal stress, and then the glass is blown and suddenly cooled. When the temperature is balanced, compressive stress is generated on the surface of the glass and tensile stress is generated on the inner layer, That is, glass generates a uniform and regularly distributed internal stress, which improves the tensile strength of glass as a brittle material, thereby improving its bending and impact resistance. At the same time, due to the existence of uniform stress inside the glass, once the glass is partially subjected to an impact that exceeds its strength and ruptures, it self explodes into small particles under the action of internal stress, improving its safety. Therefore, tempered glass can also be referred to as prestressed glass or safety glass.
During the process of glass tempering in a glass furnace, wind and stress spots are generally generated. Wind spots are formed during the cooling process due to uneven cooling, resulting in uneven stress on the glass. When viewed from a special angle, the surface of the glass shows alternating light and dark stripes. Stress spots are also caused by uneven stress, such as the temperature difference between the edge and middle of the furnace during heating, which leads to uneven stress. At present, stress spots cannot be completely avoided, but well-designed tempering equipment can minimize the visibility of stress spots.
