Friends who often operate glass tempering furnaces know that heating and cooling are two key points to ensure the quality of tempering. If improper control will cause serious quality problems, then the author will say today: heating can not reach the tempering temperature, and the tempering section is released. When the surface compressive stress is formed, the glass may crack or break; if the temperature is too high, the glass wave will be deformed, and the surface will have pitting problems; the temperature should not only be controlled within a certain range, but also be uniform. If the temperature is not uniform, according to the author's observation and summary of long-term production practices, there will be different consequences:
1). The glass is warped upwards (ie, the front end and the tail end of the glass are upturned)
Cause: When the glass exits the furnace and enters the cooling section, the upper surface temperature of the glass is higher than the lower surface or the air pressure at the upper part of the cooling section is lower than the lower one.
Correction method: If the air pressure balance is within the quenching range, the temperature at the bottom of the furnace should be raised. If the furnace temperature setting is correct, the top air volume can be increased and the bottom air volume can be reduced to correct.
2). The glass is bent downward (ie, the middle portion of the glass is raised upward )
Cause: When the glass exits the furnace and enters the cooling section, the upper surface temperature of the glass is lower than the lower surface or the air pressure at the upper part of the cooling section is higher than the lower one.
Correction method: If the air pressure balance is within the quenching range, the temperature at the bottom of the furnace should be lowered. If the furnace temperature setting is correct, the top air volume and the bottom air volume can be reduced to correct.
3). The edge of the glass is upturned or tilted:
Cause: The intermediate temperature of the glass is lower than the edge temperature.
Solution: Increase the central furnace temperature by changing the temperature profile. By changing the heat balance pressure, the air convection in the furnace is adjusted to keep the glass straight and increase the heating time.
4). The tempered glass has a large waveform
Cause: The temperature is too high when the glass comes out of the furnace.
Solution: Reduce the furnace temperature or reduce the heating time.
The glass must be heated to a temperature higher than normal for the following reasons:
-------- Glass edging is not good.
-------- There are sharp grooves on the glass, a lot of cutting and drilling.
--------The raw materials are defective, especially the art glass.
--------The thickness of the glass is not uniform and is damaged in the tempering section.
5). Spot (pitting)
Cause: When the glass comes out of the furnace, it is too hot, or a lot of impurity particles accumulate on the surface of the silicon roller.
Solution: Reduce the furnace temperature or heating time and clean the quartz silicon roller.
6). There are white lines or optical distortions in the center of the glass.
Cause: First, after the glass is bent upwards around the furnace, the center pressure of the glass in contact with the silicon roller is too large, resulting in white line or optical deformation (the glass bending is usually caused by the excessive silicon roller temperature, and the silicon roller is in the glass). The heat released from the lower surface is fast, and this is heated too fast only when the center of the glass contacts the silicon roller. At the end of the heating cycle, the center becomes soft and will be deformed. Secondly, the amount of sulfur dioxide is insufficient.
Solution: Increasing the temperature of the upper surface of the glass by heat equilibrium pressure or furnace temperature, optical distortion usually occurs in the first two pieces, due to the excessive heating of the silicon roller to properly increase some sulfur dioxide. (When the silicon roller is too dirty, it is easy to cause a trace on the glass surface.)
7). Micro-cracks on the surface of tempered glass
Cause: When the glass comes out of the furnace, the glass has become too cold.
Solution: Increase the furnace temperature or heating time.
8). The glass is rotten in the furnace
Causes: There are several reasons for the glass rotten-----------the glass itself has cracks----------- the edge is not good, it is easy to produce micro-cracks----- ------When tempered thick glass, the furnace is too hot and the temperature difference between the center of the glass and the surface is too large.
(When the glass has been tempered, it should not be tempered again. The tempered glass has a high internal stress, and the stress easily breaks beyond the strength of the glass during heating.)
Solution: When the glass is heated, there is a temperature difference between the glass surface and the center. There is also a temperature difference between different parts of the glass. These temperature differences generate stress. If the stress is too high, the glass is easily rotted.
9). Glass is bad in the tempering section
Cause: The glass can not withstand the cooling, in the tempering section, there are mainly the following ------------ raw materials are defective, the glass has sand or micro cracks -------- ----The heating time is too short, the glass temperature is too low or uneven ------------The glass edge and the drilling and cutting parts are not processed well (the edging or chamfering is not good).
------------The tempering wind pressure is too high, especially for thick glass, the wind pressure should be relatively small,
Too high a tempered wind pressure creates a very high temperature gradient between the center of the glass and the surface, which tends to cause the glass to burst.
-------------The tempered windshield is plugged, dust may enter the fan impeller, which blocks the nozzle hole. When the tempered glass is used, some area is not fully cooled. Other areas around this area cool very quickly, causing uneven stress on the glass, causing the glass to burst.
Solution: Especially for thin glass, it is cooled quickly in the tempering section, which can enhance the stress of the glass. On the other hand, for thick glass, even if it is slowly cooled, a high temperature gradient is required at the center of the glass. The surface of the glass will be stressed by these temperature differences, and if the stress is high, the glass will burst. (In any case, the rotten glass should not be left in the furnace, the furnace should be cleaned as soon as possible, the glass on the lower heater will affect the furnace temperature or damage the silicon roller.)
10). Other glass surface impressions:
This kind of situation is easy to appear after washing the furnace. If the silicon roller is not wiped clean when washing the furnace, obvious roller road impression will appear on the glass surface. At this time, some SO2 gas can be put into the heating furnace, SO2 gas To the role of lubricating the silicon roller and protecting the lower surface of the glass. SO2 gas is only used when necessary. When there is no impression after tempering several furnaces, SO2 gas should be shut down immediately. Because too much SO2 gas will make the glass blue, affecting the optical properties of the glass and corrosive to the furnace. . In addition, if the fiber roller path in the ceramic roller or the grille of the heating furnace is not clean, the glass will be scratched; if the quality of the edging glass is not good, the glass will burst; in winter and summer, the same wind pressure glass The degree of tempering is also different, and so on, all factors will affect the quality of tempered glass.
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