As we all know, the operation of a glass tempering furnace greatly affects the appearance of tempered glass. Only by mastering the correct operating methods can these problems be avoided. Many friends have reported encountering various problems when operating tempering furnaces, with many relating to optical aspects. Today, we will briefly introduce these issues.

　　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: Gray Central Area

　　After tempering, some glass shows a hazy phenomenon on the surface contacting the roller table. This reduces the transparency of the glass and often occurs in the middle of the glass. There are two main reasons for this:

　　① Roller temperature in the heating furnace is too high. This often occurs in the first two batches of glass after the tempering furnace is initially used. In this case, you can increase the pressure of the heat balance air blowing or reduce the empty furnace time to ensure continuous glass production;

　　② Excessive use of SO2 gas. SO2, as a protective gas for glass, can cause graying on the glass surface if used excessively or too frequently.

　　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: Excessive Stress Spots

　　Stress spots will always appear in tempered glass produced by physical tempering methods. This is determined by the production principle of physical tempering and is unavoidable. Sometimes, this phenomenon is used to identify whether the glass is tempered glass. However, when stress spots are too heavy, particularly under specific lighting conditions, this becomes an appearance quality defect.

　　Excessive stress spots are usually caused by the following 3 reasons:

　　① Excessive air pressure during rapid cooling. This high-pressure, high-speed airflow blowing onto the nearly softened hot glass will increase the stress spots in the tempered glass. This can be avoided by adjusting the air pressure parameters;

　　② When the glass enters the cooling chamber from the heating chamber and the rapid cooling blowing has begun, if the movement of the air baffle or rollers is stopped, causing the air nozzle of the air baffle to blow only on one part of the glass. In such cases, it is necessary to restore the synchronization of the air baffle movement or roller rotation with the air blowing;

　　③ When the rapid cooling air blowing begins in the cooling chamber, the air nozzle of the air baffle is too close to the glass. In this case, the height of the air baffle can be appropriately increased by adjusting the parameters without affecting the grain size and other quality requirements of the glass.

　　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: Iridescence in Tempered Glass

　　Iridescence in tempered glass is an optical phenomenon. During the forming process of float glass, harmful substances such as oxygen and water enter the tin bath, and at high temperatures, they react with tin to generate SnO and SnO2. Sn2+ and Sn4+ seep into the lower surface of the float glass through the tin liquid and form an extremely thin tin-containing layer rich in Sn2+ and Sn4+. When such float glass with high tin content is tempered, the SnO on the glass surface is oxidized to SnO2 after heating in the tempering furnace. Its volume increases, causing microscopic wrinkles on the glass surface, which, under the irradiation of light, produce light interference. Therefore, iridescence in tempered glass is related to both the quality of the float glass as the original sheet and the tempering process. In glass tempering production, in addition to selecting high-quality float glass as the original sheet, the heating temperature and heating time parameters of the tempering furnace must also be adjusted to suit the actual situation of different original sheet glasses.

　　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: White Streaks on the Bottom Surface of Tempered Glass

　　White streaks in tempered glass are due to slight wear on the glass surface. The heating methods for the top and bottom surfaces of the glass in the heating furnace are different. The top surface mainly relies on radiation, while the bottom surface relies on both conduction and radiation. When the glass enters the heating furnace initially, due to the combined effect of the two heating methods, the bottom surface obtains a higher temperature in the same amount of time compared to the top surface. In severe cases, the glass will bend upwards, and due to the friction between the bottom surface of the glass and the roller table, white streaks appear.

　 　To solve this problem, we can use the following 4 methods:

　　1. Adjust the heating parameters and appropriately reduce the lower temperature of the heating furnace. If necessary, reduce the lower power;

　　2. Correspondingly increase the upper temperature of the heating furnace;

　　3. When white streaks appear in the middle of the glass, increase the heating balance value; when white streaks appear at the edges, reduce the heating balance value or change the heating curve;

　　4. Continuous production must be ensured during the production process to avoid empty furnace operation.

　　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: Scratches on the Surface of Tempered Glass

　　Although scratches on the surface of tempered glass are considered appearance defects, they can disrupt the uniform distribution of surface stress, leading to reduced mechanical strength. This is usually caused by the following 3 reasons:

　　1. Hard foreign matter sticking to the rollers. In this case, the furnace temperature must be lowered, and the foreign matter on the rollers must be cleaned;

　　2. Slipping of ceramic rollers or cooling rollers. In this case, each roller’s transmission device needs to be checked, and the transmission device needs to be tightened, or the damaged rollers repaired;

　　3. Broken glass may be stuck in the upper and lower air baffles. In this case, check the air baffles and thoroughly remove any broken glass stuck in the air baffles.

　 　Tempered Glass Optical Problems in Glass Tempering Furnace Operation: Pinholing in Tempered Glass

　　Pinholing is another appearance defect in tempered glass, generally classified into two types: one is dense. Pinholing is usually concentrated in an orange peel pattern, caused by excessive heating time or temperature. This can be resolved by adjusting the heating time or temperature parameters; the other is dispersed. Individual pinholes are distributed in a star-like pattern, caused by uncleanliness on the top plate or roller table, or unclean rollers under the air baffle. To reduce pinholing, companies can establish a roller cleaning system and clean the roller table regularly.

　　The above is a summary of questions and measures regarding the operation and optical aspects of glass tempering furnaces, compiled by our editor. For more information, please continue to follow us.