1) The midpoint is gray in color
After some glass is tempered, the surface in contact with the roller conveyor will appear grayish. This situation will result in a decrease in the transparency of the glass, often occurring in the middle of the glass. There are two main reasons for this situation: ① The roller temperature inside the heating furnace is too high. This situation often occurs on the first two furnaces of glass when the tempering furnace is first used. In this situation, it is advisable to increase the pressure of the heat balance blowing or reduce the empty furnace time to ensure continuous glass production Excessive use of SO gas. If SO is used too much or too frequently as a protective gas for glass, it can cause the glass surface to appear gray.
2) The problem of excessive stress spots
Tempered glass produced by physical tempering methods will exhibit stress spots, which are determined by the production principle of physical tempering and cannot be avoided. Sometimes this phenomenon is also used to identify whether glass is tempered glass, but when the stress spot is too heavy, especially under specific lighting conditions, this phenomenon becomes a problem of appearance quality defects.
The problem of excessive stress spots is usually caused by the following three reasons: ① Excessive wind pressure during the rapid cooling process. This high-pressure, high-speed airflow blowing onto the nearly softened hot glass will increase the stress spots on the tempered glass. This situation can be avoided by adjusting the parameters of wind pressure; ② When the glass has just entered the cooling chamber from the heating chamber and has started to blow air for rapid cooling, the swing of the air grille or the rotation of the roller conveyor is stopped, causing the air nozzle of the air grille to only blow air towards one part of the glass. When this situation occurs, the swing of the wind grille or the rotation of the roller conveyor should be restored in a timely manner to synchronize with the blowing; ③ When starting to blow air for rapid cooling in the cooling room, the distance between the air grille nozzle and the glass is too close. When this situation occurs, the height of the air grille can be appropriately increased by adjusting the parameters without affecting the particle size and other quality requirements of the glass.
3) Rainbow phenomenon of tempered glass
The iridescence phenomenon of tempered glass is an optical phenomenon. During the forming process of float glass, harmful substances such as oxygen and water enter the tin bath. At high temperatures, they undergo oxidation reactions with tin, generating SnO and SnO. Among them, Sn and Sn penetrate the lower surface of float glass through tin solution and form a thin tin containing layer rich in Sn and Sn. When this type of float glass with high tin infiltration is tempered, the SnO on the surface of the glass is oxidized to SnO after being heated in the tempering furnace, resulting in an increase in its volume and causing small wrinkles on the glass surface. Under the irradiation of light, light interference occurs.
Therefore, the iridescence phenomenon of tempered glass is not only related to the quality of float glass as the original glass, but also to the tempering process. In the production of tempered glass, in addition to selecting excellent float glass as the raw material, it is also necessary to adjust the heating temperature and heating time parameters of the tempering furnace to adapt to the actual situation of different raw glass sheets