The glass tempering furnace uses physical or chemical methods to form a compressive stress layer on the surface of glass and a tensile stress layer inside the glass. When the glass is subjected to external forces, the compressive stress layer can offset part of the tensile stress and avoid glass breakage, so as to improve the strength of glass. Moreover, the microcracks on the surface of glass become more fine under this compressive stress, and the strength of glass is improved to a certain extent. In production, when the glass tempering furnace needs to heat the glass whose shape is close to the square, it is suggested to adopt the heating method of low temperature and long time. This is because the endothermic process of glass in the furnace is gradually transferring from the edge of the glass to the middle. If the heating time is short, it will cause insufficient heat absorption in the middle part of the glass. One case is that the glass bursts after discharge, and the other case is that the glass bends in a spherical shape after tempering. What are the defects and corrective methods of glass sheet which is easy to be produced when it has just entered the glass tempering furnace?

　Because of the contact with the roller, the expansion speed of the lower surface of the glass is faster than that of the upper surface, and the glass will bend upward. The glass plate is hanging around but only the middle part contacts the roller, which results in the glass heating of the contact roller is faster than that of the suspended part (the reason for heat conduction). The suspended part around the roller will not continue to absorb heat until the glass plate is fully softened, and at this time the contact roller will continue to absorb heat. The heat in the middle part of the glass plate is much larger than that at the edge of the glass, which results in the serious distortion of the middle part of the glass plate due to the excessive temperature, thus forming the optical distortion.

　At this time, the convective fan speed of the upper part of the glass tempering furnace should be properly enlarged or the upper and lower furnace temperature should be adjusted so that the glass can flatten rapidly in the furnace to correct this problem. As for the basic principle of setting the temperature of glass tempering furnace, the thinner the tempered glass is, the higher the temperature is required, the thicker the glass is, the lower the temperature is required, and the glass of various thicknesses has a certain heating rate.