Factors Affecting Flatness of Tempered Glass and Treatment Countermeasures
[China Glass Net] Tempered glass with poor flatness will cause optical distortion of the glass on the one hand after installation, which will greatly affect the appearance quality of the doors and windows and the curtain wall. On the other hand, it will also cause optical distortion of the glass, further affecting the doors and windows. The visual effect of the curtain wall, in addition, the tempered glass with poor flatness will also affect the installation effect, so it is very important to control the flatness of the doors and windows and the tempered glass of the curtain wall.
The kiln furnace roller problem causes poor flatness after glass tempering
The causes of the roller which cause poor flatness of the glass mainly include: the bending deformation of the heating section roller and the air-cooling section, the wear of the heating section roller and the air-cooling section.
1. Deformation of the ceramic roller in the heating section of the tempering furnace in the heating section of the tempering furnace and the air-cooling section. The use of low-quality ceramic rolls in the heating section of the tempering furnace affects the flatness of the glass. The ceramic roll in the heating section of the tempering furnace is made of fused silica and ceramic materials, which has good thermal shock resistance and thermal stability, but low quality. The unevenness of the internal microstructure of the ceramic roller causes the roller track to be thermally deformed at a high temperature, and the thermal deformation causes the roller path to bend, and the thermally deformed roller path causes deformation when carrying the drive glass.
Deformation of the air-cooled section roller. Since the glass is quickly transferred from the heating section of the tempering furnace to the air-cooling section, the glass is still in a softened state at this time, so the roller path of the air-cooling section must also be straight and free from bending, and the roller conveyor is smooth and has no jumping phenomenon. Otherwise it will also affect the flatness of the glass.
2. Wear of the heating section of the tempering furnace in the heating section of the tempering furnace and the roller section of the air-cooling section. In order to prevent the appearance of pitting on the surface of the glass, in the actual production, we will polish the ceramic roller in the heating section, and polish the surface of the ceramic roller with fine sandpaper to clean away the impurities adhered to the surface of the ceramic roller. Repeating the cleaning of the roller path several times may result in uneven wear of the roller table, causing uneven thickness of the same roller path or eccentricity of the roller table. In addition, sometimes the roller table and the roller table are replaced at different times, and the degree of wear of the new and old rollers is different, which causes unevenness between the roller and the roller. All of the above, whether the thickness of the same roller is uneven or the eccentricity of the roller, or the unevenness of the thickness of the different rollers, will result in unevenness of the surface of the roller, and the unevenness of the glass after heating to the softening temperature The surface of the roller table is driven, which will inevitably cause deformation of the glass itself and affect the final flatness of the tempered glass.
Wear of the roller table in the cooling section of the tempering furnace. The surface of the roller table of the cooling section of the tempering furnace is generally wrapped with heat-resistant asbestos rope or heat insulating material, and the long-term use of asbestos rope or heat insulating material is inevitably worn. Due to the abrasion of the asbestos rope or the heat insulating material, the unevenness of the driving surface of the cooling section roller is caused, thereby affecting the final flatness of the glass.
3. Control method When replacing the ceramic roller of the tempering furnace, the ceramic roller with better quality should be selected as much as possible. Before the glass enters the heating section of the tempering furnace, the ceramic roller must have sufficient time for preheating, so that each roller roller Part of the heat is even, eliminating stress and reducing the thermal deformation of the roller.
When grinding and cleaning the surface of the ceramic roller, it is necessary to uniformly polish the entire surface of the roller. It is not only necessary to polish the part to which the impurities are bonded, and the roller should be rotated without grinding, so that the parts of the roller are evenly worn and regularly Check the height of the adjustment roller so that all the rollers are in the same plane when moving. For the roller path of the air-cooled section, the nylon rope or insulation material wound on the surface of the roller table should be inspected regularly. Once it is found to be cracking, it should be replaced in time.
Poor glass flatness caused by improper temperature control
The main reason for the poor glass flatness caused by improper glass heating is that there is a temperature difference between the upper and lower surfaces of the glass when heated, and there is a temperature difference between various parts of the glass surface.
1. There is a temperature difference between the upper and lower surfaces when the glass is heated. The glass is heated in the heating furnace by conduction, radiation and convection. When the glass is transferred to the heating roller, the lower surface of the glass directly contacts the ceramic roller. At this time, the lower surface of the glass is directly heated by heat conduction, and the upper surface of the glass is heated by means of heat radiation. The heat transfer rate of the glass is higher than the heat radiation speed. If the upper and lower furnace temperatures in the heating furnace are set to the same and the heating balance in the furnace is not turned on for convection heating, the temperature of the lower surface of the glass will be higher than the upper surface of the glass. Since the coefficient of thermal expansion of the glass is high, once there is a temperature difference between the upper and lower surfaces of the glass, the expansion speed of the lower surface of the glass will be higher than that of the upper surface of the glass, which will cause the periphery of the glass to warp upward from the roller path, forming only the middle portion of the glass and The roller path contacts the weight of the entire glass. When the glass continues to be heated, the portion of the glass that is in contact with the roller path first reaches the softening temperature, which causes the plastic deformation of the glass intermediate portion to appear on the roller path. When the temperature difference between the upper and lower surfaces of the glass is subjected to air-cooling and quenching, the side of the higher temperature shrinks more than the side of the lower temperature. If the temperature of the lower surface of the glass is higher than the upper surface, the glass will be bent downward.
2. There are temperature differences in various parts of the glass surface. The temperature difference between the glass surface is mainly: the temperature of the middle part of the glass is higher than the edge, the temperature of the edge of the glass is higher than that of the middle part, and the temperature of the glass surface is irregular.
The temperature in the middle of the glass is higher than the edge. Before the glass exits the furnace and enters the air-cooling section, if the middle temperature of the glass is higher than the edge temperature, the shrinkage of the middle part will be higher than that of the edge during the cooling process, which will result in the edge of the final glass being larger than the edge. The intermediate size creates a large compressive stress at the edges of the glass. To balance this unbalanced stress, the glass is ultimately saddle-shaped.
The temperature at the edge of the glass is higher than the middle. If the temperature of the edge of the glass is higher than the central temperature of the glass before the glass exits the furnace and enters the air-cooling section, then the hot side shrinkage of the glass during cooling will be greater than the shrinkage of the middle, and the edge size of the glass will Less than the middle dimension, a large tensile stress is formed at the edge of the glass, which results in a shape of the bottom of the glass which is convex and changes in two directions.
The irregular temperature distribution of the glass surface is uneven. The condition of the equipment in the heating section of the tempering furnace is poor, the local furnace wire is damaged, or the power of the local furnace wire is degraded, the temperature sensor is distorted, the position of the glass sheet is unreasonable, etc., and the glass is unevenly heated. When the glass is heated unevenly, the amount of cooling shrinkage in different regions of the glass is different when air-cooling is performed, resulting in poor flatness of the glass.
3. Control method A method for controlling the poor flatness of the glass due to the temperature difference between the upper and lower surfaces of the glass. Before the formal production, the test furnace production is carried out. When the glass is bent upwards, the shrinkage of the upper surface of the glass is greater than that of the lower surface, that is, when the glass is air-cooled, the temperature of the upper surface is higher than that of the lower surface. It is necessary to appropriately lower the upper furnace temperature of the heating furnace, in order to keep the heating temperature of the entire glass constant, and to lower the temperature of a part of the upper furnace, and to appropriately raise the temperature of the lower furnace. When the glass is bent downward, it indicates that the temperature of the lower surface of the glass is higher than the upper surface of the glass, indicating that the temperature of the lower surface of the glass is higher than that of the upper surface. At this time, the temperature of the lower furnace is appropriately lowered, and the temperature of the upper furnace is appropriately increased.
Fdy Yarn,Polyester Fdy,Polyester Fdy Yarn,Polyester Dope Dyed Yarn
XINFENGMING GROUP , https://www.xfmgroupexport.com