During the processing of tempered glass, various parameters are unreasonable, which may cause the tempered glass to bend and other appearance quality. Here we summarize some frequently encountered bending reasons and how to solve the tempered glass quality problems of glass tempering furnace.

1.Bend towards upper side

Reason: When the glass is out of the furnace chamber, the upper surface temperature of the glass is higher than the lower surface temperature; the upper surface temperature of the glass lose faster than lower side; at the quenching section, the upper air pressure is lower than the lower air pressure.

Solution: Increase the bottom temperature of the furnace and lower the upper temperature appropriately. If the furnace temperature is stable, the pressure of the air grid can be adjusted. When the height of the air nozzle is unchanged, the upper pressure is greater than the lower pressure.

2.Bend towards lower side

Reason: When the glass is out of the furnace chamber, the lower surface temperature of the glass is higher than the upper surface temperature; the lower surface temperature of the glass lose faster than upper side; at the quenching section, the lower air pressure is lower than the upper air pressure.

Solution: Increase the upper temperature of the furnace and lower the lower temperature appropriately. If the furnace temperature is stable, the pressure of the air grid can be adjusted. When the height of the air nozzle is unchanged, the lower pressure is greater than the upper pressure.

3. Roller print

Reason: The heating time of the glass in the furnace is too long, the temperature in the furnace is too high, and the rotation speed of the ceramic roller is too slow when the glass is released from the furnace.

Solution: Shorten the heating time, lower the furnace temperature, and speed up the glass release speed.

4.Curved glass

Reason: The temperature in the middle of the glass is lower than the edge temperature.

Solution: Change the heating temperature control mode to increase the middle temperature; reduce the overall furnace temperature and extend the heating time.

5.Glass marks

Reason: The furnace bottom temperature is too high, the surface of the ceramic roller is dirty, and the glass is heating time is too long.

Solution: Reduce the heating time, clean the ceramic rollers, and lower the furnace bottom temperature.

6. The center of the glass is dark (gray) and optical defects

Reason: The edge of the glass bend towards upper side after entering the furnace, resulting in excessive pressure on the surface of the glass facing the ceramic roller to cause this defect, or the surface temperature of the ceramic roller is too high and is in contact with the glass surface, or the swing speed of the ceramic roller is too fast.

Solution: Increase the heat balance time of the empty furnace time, increase the temperature of the upper surface of the glass, reduce the time of the empty furnace, ensure that the glass is continuously fed into the furnace, and reduce the swing speed of the ceramic roller after the glass enters the furnace.

7. Cracks on the surface of tempered glass

Reason: The heating time of the glass in the furnace is too short, or the temperature of the furnace is too low.

Solution: Increase the furnace temperature and extend the heating time.

8. Glass broken in the furnace chamber

Reason: There are the following situations:

1. There is a crack in the glass (the tempered glass must be absolutely free of cracks). At the end of the crack, the accumulated stress is released and cracked.
2. The edging is not good, leaving a slight crack.
3. When tempering thick glass, the furnace temperature is too high, and the temperature difference between the surface and the center is too large.
4. The glass has been tempered or thermally strengthened, and absolutely cannot be tempered twice. The inherent stress of tempered glass is extremely high. During heating, the tensile stress can easily exceed the glass strength.
5. There are impurities, bubbles, stones in the float glass. When the glass is heated, the tensile stress surface contacts the above impurities and breaks.

Solution: The tension generated by reducing the furnace temperature will be very small. Carefully check the quality of the float glass sheet and the glass pre-processing quality before tempering.

9. Glass broken in the quenching section

Reason: Breaking in the quenching section is usually because the glass can’t stand the cooling:

1. Defects in float glass and impurities inside.
2. The edges or holes are not well ground.
3. The heating time is too short, the glass temperature is too low or uneven.
4. The wind pressure is too high, especially for thick glass. The wind pressure should be very small. If the cold wind is too high, it will form a higher temperature gradient on the surface and center of the glass and break the glass.
5. The quenching section is blocked, and the cold wind pressure of the glass is uneven and broken.
6. The glass is placed too close to the wind nozzle, and it will break when swinging.

Solution: Appropriately reduce the wind pressure (if the particles reach the national standard), appropriately increase the distance of the glass, prolong the heating time or increase the furnace temperature, and check whether the edge of the hole is smooth.

10. Collapse angle

Reason: The temperature is too high when the glass enters the furnace, the edge of the hole is too close to the edge of the glass or the edge of the glass is cracked.

Solution: Reduce the furnace temperature and open the stress groove closed to the edge of the glass when glass drilling.

11. Spontaneous Explosion

Reason:

1. The glass has a poor internal quality such as stone like impurities, nickel sulfide particles, bubbles, etc.
2. The scratches, nick, deep micro cracks left on the glass during glass processing due to improper operation may lead to stress concentration or spontaneous explosion.
3. The uneven stress distribution due to uneven heating or cooling is likely to cause spontaneous explosion.
4. The higher stress inside the glass and the higher tempering level, the higher percentage of spontaneous explosion it will has.

Solution: Appropriately reduce the tempered wind pressure (in the case of particles reaching the national standard).

12. What should I do if the glass is broken in the furnace and the door cannot be opened without a gas source?

Solution: The shaft of the furnace door has a shaft head to be used outside the furnace body. In an emergency, you can use a tool to forcibly open the furnace door directly.If the glass is shattered too much, clean it till the furnace cools down.

13.Why does the tempered glass produce white lines, white haze, white channels?

Reason: The main reason for the white haze in the tempered glass is the setting issue of the tempering process, that is, the temperature setting of the lower heating zone is too high. When the glass enters the tempering heating section, the glass is upturned, and the glass contact surface is rubbed on the ceramic roller. After the heating time, the resulting surface wear and tear on the glass surface (white haze, white lines, white channels) is actually a scratch on the glass surface.

Solution:

Change the process:

① The lower temperature remain unchanged and the upper temperature is increased.

②The upper temperature remains unchanged, and the lower temperature decreases. Adjust the upper and lower temperature according to the actual situation of tempered glass, in short, the glass has no white haze.

14. Tempered glass fragments are too large

There are three reasons:

1. We sometimes found that the whole batch glass had large fragments during the tempered glass process. At this time, we found that there was a problem in setting the blowing process. The problem is that when the tempered glass exits the furnace and enters the cooling section, the wind pressure has not reached the required maximum cooling air pressure, but the glass has been cooled, so the toughened glass will produce excessive fragments that do not meet the standard.

The solution has the following three points:

①Select different wind pressure settings according to the glass thickness.

② The starting time of the cooling blower is advanced.

③ Improve the air-running speed of the blower.

2. Artificial factors

Operation mistakes, sometimes the operator forgets to adjust the glass thickness and wind pressure during the tempered glass process. If thin glass wind pressure tempered glass is used, the thick glass fragments are too small and the self-detonation rate is too high. If thick glass wind pressure is used to toughen the thin glass, fragments are too large to meet the requirements. This phenomenon is actually a problem that often occurs. If the operation error is changed, the ideological awareness of the operator should be strengthened, and the technical level of the operator should be improved. Operators carefully read the actual process instructions of tempered glass when tempering different products, and perform tempering operations according to process requirements.

3. Uneven heating

The phenomenon of excessive glass fragments caused by uneven heating of tempered glass is directly related to the following aspects:

① The heating temperature is set at the same temperature in the upper zone, and the same temperature is set at the lower zone.

② Inaccurate thermocouple detection

③ Solid-state relay is disconnected, and the partial zone is not heated.

④ The solid-state relay goes directly into the furnace, the local temperature is too high.

⑤ Sometimes the individual resistance wire breaks, and the partial zone is not heated.

How to change the above matters:

When setting the heating temperature, first consider that the glass is the equilibrium temperature value of the external environment when the glass enters the furnace through the loading table. When the glass in the cold state enters the heating furnace, the glass absorbs heat extremely, and the glass absorbs heat while entering the furnace. From the first glass to the last piece of glass, it must be heated by the resistance wire of the front furnace. The temperature drops sharply, the front glass is heated faster than the rear glass, and the temperature of the front furnace is lower than the temperature of the rear furnace. According to this reason, when the heating process is set again, the heating temperature of the front furnace increases, the temperature of the middle furnace increases, and the temperature of the rear furnace decreases, which can directly change the uneven heating.

1. The setting temperature of each heating zone (6 mm glass temperature setting) is for reference only.

2. Thermocouples are frequently checked, repaired and replaced.
3. Check and replace the solid state relay.
4. Check and repair the resistance wire.

15. Uneven wind blowing matters

In the process of tempered glass, the wind pressure from the quenching section appears that some wind sections have high wind pressure, and some wind sections have low wind pressure, which results in different sizes of tempered glass fragments and poor glass flatness.

Reason: It is mainly used in the tempering furnace for many years. Some paper scraps, dust and sludge are blown into the air knife by the blower, causing the air knife to be blocked，which decreases the air pressure lower and makes each air knife blow unevenly.

Solution: clean the blower, bellows and air knife, which can have a certain effect.

16. Matters of tempered glass for lamination

Factors: The flatness of the tempered glass is bad.

Solution:

①Adjust the heating process. Lower the temperature slightly under the condition of normal setting temperature value.

②The heating time is reduced accordingly.

③ Increase the wind pressure accordingly.

④ Paired tempered glass. Prepare several glass racks and place the glass in the relative position of the first batch and so on to place glass in the same position of the second batch.

17. Bending tempered glass matching matters

In the process of bending and tempering, the tempered glass has a poor fit, and the tempered glass with the same radius has deep and shallow.

Reason: The main reason is that the upper and lower air outlets of the bellows are not synchronized when blowing. When blowing, one is turned on first, and the other is turned on later. The lower air outlet opens first, and the glass has a deep upward radius; the upper air outlet opens first, the glass radius becomes shallower, and does not form an arc according to the actual radius.

Solution: Adjust the synchronous structure fastening process.