How to troubleshoot the reentrant bubbles in the production of float glass? How to solve it effectively?
After the 800t/d float glass production line of a certain unit was ignited and put into production, it mainly produced high-quality float glass with a thickness of 4-15mm and a qualified plate width of 4880mm. However, after 3 months of production, continuous bubbles appeared on the board. Because it is shaped like an ellipse or a circle, and it folds back and forth in the longitudinal position of the glass plate surface, it is called "return bubble". The fold back bubbles occasionally appear, burst out suddenly, and appear frequently every three to five. Its diameter is variable, and the horizontal position is uncertain. The bubbles are on the upper surface of the glass. The hand touch has obvious concavity and convexity, and the upper surface can be heard crisply after the upper surface is broken when you touch it with your fingernail. The sound. The impact time of the foldback bubbles is variable. The short 0.5h disappears, and the long one is more than 24h; the core diameter is as small as 1.0mm, and some as large as 5mm, and even more than three foldback bubbles appear at the same time in the transverse area of ??the board. Table 1 is a statistical table of reentrant bubbles in June of a certain year. Aiming at the fold-back bubble, a comprehensive comparative analysis was carried out on the process, and a series of solutions were formulated to solve the fold-back bubble.
Judgment of the cause of the fold back bubble
According to the characteristics of the folded back bubble, it is preliminarily determined that the bubble is generated in the medium and low temperature zone of the float furnace. As a result, targeted adjustments and investigations were carried out for the following locations, and the law of bubble change was observed according to the adjustment situation to help further confirm the cause and location of the cause.
1.1 Inspection of runner gate bricks
Each time the foldback bubble appears, the foldback bubble can temporarily disappear by adjusting the temperature of the flow channel greatly and quickly. Combining the above characteristics, it is preliminarily judged that the location of the reentrant bubble generation may be the runner gate. Replace the runner ceramic gate. After the runner gate is replaced, the reentrant bubble has not disappeared. Make sure that the reentrant bubble is not generated at the position of the runner gate.
1.2 Inspection of runners and runners
A long-term power outage caused by a transformer failure of the enterprise substation caused serious damage to the structure of the kiln, flow channel and other structures. Opening the recirculation zone seal found that the lip brick had four cracks, and the bottom of the cracked lip brick leaked glass water, and two of the leaks were serious. Therefore, it is judged that the gap between the runner and the runner may be further pulled apart and the runner bricks are eroded seriously, leading to the generation of fold back bubbles. In addition, the lip brick leaked serious glass water, and the glass plate surface also had defects such as under-plate devitrification and under-plate blistering, so it was decided to replace the lip brick. Begin to replace the lip brick, and successfully lead the head after 19 hours, but the fold back bubble still did not disappear, indicating that the position where the fold back bubble was generated is not in the runner runner.
1.3 Further investigation by adjusting the neck agitator
After removing the blisters generated at the runner gate and the runner position, move the target to the cooling part. Because the diameter of the foldback bubbles is above 1.0mm, and they are all oval-shaped bubbles on the board, they can make a crisp sound when they break, indicating that the foldback bubbles come from the area after the clarification. Observing the neck area for a long time, no bubbles were found floating, so it was preliminarily determined that the bubbles came from the cooling part.
First, when the foldback bubble appears, adjust the horizontal stirrer from 3 turns/min to 5 turns/min, and try to change the glass flow in the cooling part by adjusting the stirring speed of the stirrer. After 5h, it was found that after the stirring speed of the stirrer was changed, the fold back bubble changed significantly in the lateral position of the plate surface. Then restore the stirrer speed to 3 turns/min. After 5 hours, the bubble is folded back and returned to the position where the plate surface appeared before the adjustment. In order to confirm that the foldback bubble comes from the cooling part, adjust the different number of turns of the horizontal agitator to observe the change of the foldback bubble. It can be found that the change of the foldback bubble coincides with the time of the agitator adjustment, further verifying that the foldback bubble may come from the bottom of the cooling part. .
1.4 Analysis of bubble composition
In order to further verify whether the folded back bubble is generated in the cooling part, the gas composition analysis of the folded back bubble was carried out. Cut two pieces of 100mm×100mm folded back bubble samples with different diameters and send them to Shahe Glass Research Institute for analysis of bubble composition. The analysis equipment is GIA522 bubble analysis mass spectrometer.
From the analysis results, it can be seen that the composition of SO? in the bubbles is less than 0.003%, almost no. It can be judged that the bubbles are not clear bubbles from the melting part, nor are they caused by the falling of the neck or the condensate of the cooling part. In addition, the gas composition of the three fold-back bubble samples is basically similar, and the gas composition of the fold-back bubble is very close to that of air (the nitrogen content in the air component is about 78%, the oxygen content is about 21%, and the rare gas is about 0.93%). Moreover, the large diameter of the bubbles proves that the thermal history of the bubbles in the kiln is relatively short. It further proves that the reentrant bubbles are located in the middle and low temperature area of ??the furnace. Because some bubbles are distributed in the middle and lower part of the glass plate, it is confirmed that such bubbles may come from the cooling part. Cracks in paving tiles at the bottom of the pool. Because the individual paving tiles at the bottom of the cooling pool are eroded by the glass liquid or the gaps are opened when the paving tiles are baked in the kiln, the glass liquid intrudes into the large clay brick refractories at the bottom of the pool. At this time, the closed pores of the refractory materials are opened, and the pores in the pores are opened. The gas enters the molten glass to form bubbles. Or the holes or joints of the refractory material suck in air, and the air enters the glass liquid to form bubbles. Due to the fluctuation of the reflux of the glass liquid, the position of the bubble is shifted.
solution
Through the judgment and analysis of the causes of bubbles, this type of bubbles from the bottom of the cooling part can only be completely solved by cold repair, but the cold repair of the kiln will take some time. It can be effectively alleviated by adjusting the working conditions: reduce the bottom temperature of the cooling part, and thicken the immobile layer of the bottom glass. Take the following measures to adjust and control.
2.1 Adjust the depth of the neck water bag
Adjust the pressing depth of the card neck water bag, and gradually adjust the pressing depth from 420mm to 460mm (the depth of the card neck water bag is 480mm). During the adjustment, there is no situation of insufficient clarification leading to the generation of microbubbles. After the adjustment, the bottom temperature of the cooling part 1# dropped from 950°C to 942°C; the frequency of foldback bubbles decreased, from once three or two days before adjustment to once after five or six days after adjustment. From the analysis of the adjustment results, the adjustment direction is correct. However, considering that the continuous adjustment of the card neck water ladle is likely to cause major changes in the glass flow in the kiln, which will affect the overall melting conditions and lead to fluctuations in the plate surface quality, so we did not continue to press the card neck water ladle.
2.2 Remove the thermal insulation bricks at the bottom of the cooling part
From the analysis of the effect of adjusting the neck water bag, lower the temperature of the bottom of the cooling part, the frequency of foldback bubbles can be reduced, and it can be determined that the foldback bubbles come from the bottom of the cooling part. So continue to remove the first to fifth rows of insulation bricks in the cooling part. After the thermal insulation bricks were removed, the bottom temperature of cooling part 1# dropped from 942°C to 917°C. Significantly lower the bottom temperature of the cooling part, and the frequency of reentrant bubbles also drops drastically. They only appear once in ten days or even longer, and all the reentrant bubbles appear are smaller than 2.0mm. Through this adjustment, the fold back bubble has been effectively controlled, but it is still not completely resolved.
2.3 Increase iron content
(1) Increase iron content and improve clarification efficiency
In the float glass production process, a certain amount of iron content plays a certain role in the clarification and redox performance of the float glass melting process. A certain amount of iron, Glauber's salt and carbon powder undergo a series of complex chemical reactions at high temperatures, which are four stages:
At 350℃: 2Fe?O?→4FeO+O?
At a temperature of 600°C: 2C+O?→2CO?
When the temperature is 700~850℃: C+CO?→2CO, Fe?O?+2CO→2FeO+CO?
When the temperature is above 1200℃: 2FeO+Na?SO?→Fe?O?+SO?+Na?O
It can be seen from the above reaction that the FeO produced by adding a certain amount of iron powder helps the decomposition of Glauber's salt to release SO? gas, which is conducive to clarification.
(2) Increase the iron content and reduce the bottom temperature of the pool
In order to increase the immobile layer at the bottom of the pool, after technical demonstration, the iron content in the ingredients was gradually increased from 0.072% to 0.092%, and iron powder was added in three stages to further reduce the bottom temperature of the cooling part and increase the clarification capacity. Observe the return bubble The change. After adding iron powder to increase the iron content of the glass, the ferric ions of the glass liquid increase, the thermal conductivity of the glass liquid decreases, the heat permeability of the glass is reduced, and the temperature difference between the upper layer of glass liquid and the bottom layer of liquid glass is increased, so as to reduce the pool. The purpose of the bottom temperature. The bottom temperature of cooling part 1# dropped from 917°C to 910°C. After that, the fold-back bubble was fully controlled. It occasionally appeared once or twice a month, and it appeared for a short period of time, and disappeared automatically in one or two hours. Even if it does not disappear for one or two hours, the temperature of the flow channel will disappear quickly after adjusting the temperature of 2 ℃ up and down, and the detection rate of the first-class product by the detector is stable at more than 90%. In addition, the time when the reentrant bubble appears is mainly the night shift with large changes in temperature between day and night or when the temperature changes greatly. Although the reentrant bubble can be effectively controlled after the iron content is increased, the glass performance is sacrificed, such as the B value and light transmittance of the glass are reduced.
Conclusion
In the production process of float glass, there are many reasons for the generation of bubbles, which is also a long-term problem for glass enterprises. Therefore, grasping the principle of bubble generation and the analysis of bubble composition, combined with actual production conditions, can accurately determine the cause and location of float glass bubbles, which has a multiplier effect on effectively controlling bubbles and solving bubble problems. The practice of the causes and solutions of reentrant bubbles on the float glass production line can be promoted and applied to other float glass companies for reference, and provide valuable technical experience for speeding up the elimination of bubbles on the float glass surface and improving the glass quality and yield.
