[China Glass Network] Improving the quality of glass clarification is always the eternal theme of glass manufacturing technology. The factors affecting the quality of glass clarification are multifaceted, physical, chemical, and physicochemical, and there is a complex internal relationship between the three, so that solving the clarification problem can not be too simplistic. In order to ensure the quality of the glass liquid, reduce and avoid the quality accidents in the production, the company should gradually establish a practical and relatively standardized production operation management system, optimize the production process elements, in order to produce high quality, low cost glass products.
This paper systematically reviews the source of gas in the bubble, the mechanism of bubble generation and disappearance, and the relationship between the glass bubble and the production factors of the raw material and the kiln, in order to eliminate the glass bubbles and improve the clarification quality to find a feasible clue.
1. Mechanism of glass bubble generation and disappearance
To study glass bubbles, first analyze the source of gas in the bubble, the interaction between the gas and the glass, and the effect of the physical and chemical properties of the glass on the process of bubble generation or disappearance.
The gas in the glass bubble usually comes from the following aspects:
(1) Gas in the gap between the raw material particles and gas adsorbed on the surface of the raw material
In the initial stage of compounding, such gas will continuously volatilize or evaporate, and large bubbles will float up during the ascending process to escape the glass liquid, which generally does not directly cause visible bubbles in the glass product. Unless the particle size of the raw material is improperly controlled, the batch of the batch is not sufficiently melted and the gas cannot be discharged.
(2) Gases liberated by salt
There are a large amount of carbonates, sulfates and nitrates in the batch. These salts are decomposed by heat and produce a large number of tiny bubbles. The amount of gas generated by the decomposition of salts is about 15-20% of the weight of the batch. Compared with the formed glass liquid, the volume is many times larger, and the large release and continuous movement of these gases promotes the heat exchange efficiency, accelerates the melting of the batch material, and improves the uniformity of the glass composition and the uniformity of the temperature. However, the bubbles formed by such gases are not eliminated in time to form glass bubbles.
(3) Gas generated by external factors
Gases generated by refractory materials, harmful impurities and gases generated by the action of glass liquid, glass bubbles formed by these gases disappear in normal production for a long time, and it is difficult to disappear, but this situation is relatively rare.
The glass liquid is cooled too fast or the temperature fluctuates greatly, or for various reasons, the redox state of the glass fluctuates greatly. These factors act together to cause the solubility of various gases in the glass to fluctuate, releasing a large amount of tiny Secondary bubble. Such bubbles are characterized by a small diameter and a large number.
Sometimes due to the calculation of the material side or the feeding error during the execution of the material, the glass composition in the kiln greatly fluctuates, and the solubility of the gas in the glass fluctuates, resulting in a large amount of glass bubbles.
There are two ways to disappear the glass bubbles in the clarification process: one is that the small bubbles continue to grow into large bubbles, and the bubbles continue to rise due to the difference in density, and disappear out of the glass. The other is microbubbles. As the temperature decreases, the solubility of the gas in the glass increases. Due to the surface tension, there are several components of the gas in the bubble. Due to the small diameter of the bubble and the high pressure, the gas is quickly absorbed by the glass. As the diameter becomes smaller, the bubble pressure rises and the gas in the final bubble dissolves into the glass. The small bubbles disappear completely.
2, the elements of the glass bubble
2.1, temperature
The temperature of the glass directly affects the viscosity of the glass, the surface tension, and the solubility of the gas in the glass.
In the glass melting furnace, the glass clarification process is carried out in a high temperature hot spot region, and large bubbles continue to grow and float upward, and small bubbles are continuously reduced and absorbed by the glass liquid. There are many control methods for glass hotspots, and a longitudinal temperature distribution curve is formed in the longitudinal direction of the melting furnace to form two large circulating convections, the melting rate, the fluctuation of the discharge amount, the distribution of the fuel and the structure of the burning flame, and the glass. Factors such as redox state can significantly affect the temperature of the hot spot and the stability of the temperature. In addition, the use of bubbling technology or electric fluxing technology can significantly improve the hot spot of the glass and promote the clarification of the molten glass.
2.2, time <br> <br> large bubbles and float glass in the disappearance of the absorption process and the process of small bubbles of molten glass, must be completed within a specific temperature range and a specific time frame.
Some factors in the melting process, such as the depth of the molten glass, the temperature of the glass at the bottom of the pool, the melting rate, the convection of the glass, the redox state of the glass, the electric flux at the bottom of the pool or the bubbling at the bottom of the pool can obviously affect The disappearance of glass bubbles. If the bubble disappears for a short time, it will remain in the glass to form a glass bubble.
2.3, redox state of glass
The choice of clarifying agent has a great influence on the redox state of the glass, and the clarifying agent promotes the disappearance of the glass bubbles above 1300 °C.
In recent years, with the enhancement of people's awareness of environmental protection and the improvement of the grade of glass products, many complex clarifiers have been developed. Due to different functions and prices, enterprises have diversified choices of clarifying agents.
The daily detection and control of the COD value of the glass batch material, the stability control of the valence state of the valence metal in the glass liquid, affects the temperature of the bottom of the pool and the redox state of the glass, and ultimately affects the solubility of the gas in the glass.
3. Control of raw material quality
Strengthening the daily detection and management of batch ingredients, moisture, COD value and batch uniformity is one of the effective ways to stabilize the quality of glass clarification. Once there is a problem in production, this work can find clues to problems in time.
Strengthening the daily inspection and data processing of glass density is one of the important links in the production process control. There is a lot of technical information hidden in the glass density data. According to the statistical analysis of the production of glass density, the density of glass is not only related to the glass composition, but also related to the thermal history of the glass. The structure of the furnace, the scale of production, the size of the melting rate and other factors all affect the thermal history of the glass product. In addition, the type and amount of clarifying agent are different and can be reflected in the glass density data. Some people have done statistical analysis of production. Under the same production process conditions, the use of bubbling and not using bubbling can reflect the density value of glass. It can be seen that the statistical analysis results of the glass density data can directly guide the adjustment of the production process parameters.
If the compound contains sulfate, the change of iron content and valence state in the glass can directly affect the solubility of SO3 in the glass. Therefore, the daily detection and control of the iron oxide and iron valence state in the glass, and the clarification quality of the stabilized glass are Significant positive effect.
Strengthen the control of raw material particle size. In addition to the raw material composition, crystal phase structure, moisture and impurity content control, the average diameter of the raw material particles and the uniformity of the particle-level matching batch, the melting speed and the clarification speed have a direct influence. Excessive raw materials are not conducive to melting and mixing homogenization, but too fine raw materials will increase the cost of raw materials, and will also cause the agglomeration of raw materials, affecting the melting and clarification. In addition, the volatilization and adhesion of the powder will directly lead to the glass components. Fluctuations and changes in compositional uniformity.
Strengthen the control of the redox state of the raw materials. The glass raw materials mainly use mineral raw materials, and a small amount of chemical raw materials contain some impurity components, which have a direct influence on the redox state of the glass liquid, the glass color, the bottom temperature, the melting speed and the clarification speed. At present, some companies have begun to face up to this problem, testing and controlling the raw material COD value of various raw materials, and controlling the COD value and the clarification quality of the glass liquid.
For certain glass products, due to the different scale of production, kiln structure, and melting process, the volatilization of the compound during the melting process, as well as the valence of the oxide, will change the control requirements of the raw materials.
The effect of the redox state of the glass on the temperature at the bottom of the cell and the solubility of the gas in the glass, all of which ultimately affect the clarifying quality of the glass. Therefore, some companies have begun to pay attention to strengthening the control and management of the content of valence oxides and the change of valence state in glass.
4. Control of melting process parameters of kiln
Strengthen the control of hot spots. To strengthen the vertical glass liquid circulation convection, the following process measures are usually taken: one is to control the fuel distribution and combustion process in the furnace, control the longitudinal temperature gradient of the furnace, and promote the circulation convection. The second is to ensure that the glass has a certain depth to form a stable circulating convection. The third is to increase the discharge amount under the condition that the melting area is constant. The fourth is to use bubbling or electric fluxing at the hot spot to highlight the temperature at the hot spot. The longitudinal convection of the glass liquid promotes the homogenization of the glass composition and temperature, improves the heat exchange efficiency, and lowers the temperature of the flame space. Save fuel consumption.
Strengthen the rational distribution management of fuel in the kiln and control of the combustion process. The distribution of fuel in the kiln and the combustion conditions affect the temperature and temperature distribution within the kiln. If the fuel is not burned sufficiently, the reducing carbon black will be absorbed by the glass to form a large amount of microbubbles or brown stripes. Since the structure of the furnace and the structure of the combustion flame are different, even if the glass of the same composition, the volatilization loss of the oxide in the batch material is different.
Bottom bubbling of the kiln plays a special role in the melting process. Bubbling points are distributed in different locations and play different roles. The bubbling point is distributed at the hot spot and can play a special hot spot. Evenly distributed between the feeding port and the hot spot can improve the temperature and homogenization of the glass liquid at the bottom of the pool, and promote the melting of the batch material and the clarification process of the glass liquid. In the bubbling mode, there are two types of continuous bubbling and pulse bubbling. Obviously, the adjustment effect of the latter is more reasonable, and the bubble frequency can be controlled at 5 to 10 per minute. The bubbling material can be made of an expensive platinum-rhodium alloy or a ceramic material resistant to high temperatures and corrosion.
In addition to raw material factors, the uniformity of glass composition and temperature and the design of the furnace structure, the distribution of fuel in the furnace and the conditions of combustion, the structure and length of the material channel, and the level of management of the melting process are inseparable. These factors are ultimately reflected in product quality, cost, and forming efficiency.
5. Improvement of kiln structure design
As we all know, the structural design of glass melting furnace has great influence on heat exchange efficiency, energy consumption and glass liquid quality. Due to different design schemes, energy consumption can be different by 30%. The improvement of heat exchange efficiency not only reduces energy consumption, but also saves production costs, and also promotes the formation of reasonable circulating convection of the molten glass and improves the clarification quality of the molten glass.
In recent years, people have a deeper understanding and understanding of the glass melting process, and environmental awareness is constantly increasing. Countries around the world have strengthened environmental protection legislation to limit the emissions of dust, NO-SO: and F: in glass furnace flue gas. In order to meet these environmental standards, some companies use flue gas treatment methods for traditional kiln to reduce the concentration of dust and harmful components and meet environmental emission standards. Some companies use new technology, such as improving glass formulation and glass composition, limiting sulfur content in fuels, using low NOx combustion technology, using pure oxygen combustion technology, using full fused technology or electric fluxing technology, etc. Advanced technology has promoted the improvement of glass technology to a certain extent.
In recent years, a new type of pool furnace structure has emerged abroad, separating the melting process from the clarification process. The batch material is melted into the cold-top all-electric bath furnace, and the batch material is melted into glass and then enters the flame melting furnace for high temperature. Clarification of homogenization, combining the advantages of an all-electric melting furnace and a flame kiln. This type of kiln prevents the batch from coming into contact with the flame, reduces dust and volatile components, reduces blockage of the lattice, and reduces the interaction between the melting process and the clarification process to a lesser extent.
Glass fiber kiln, advanced pool bottom electric fluxing technology and application of various bottom bubble technology, advanced combustion technology application, boron-free fluorine-free glass formulation, these technologies are directly or indirectly improved The stability and uniformity of the composition of the glass liquid promotes the improvement of the liquid liquid w+.
The uniformity of the temperature of the glass liquid is inseparable from the structural design of the channel and the temperature adjustment method. In order to uniformly reduce the clarified glass liquid to the required forming L: art temperature, the upper space is adjusted with a gas premixed combustion temperature to make the temperature uniformity of the glass liquid better, and the channel K degree is usually above s meters. . At present, many glass fiber channels, glass wool channels, glass pipe channels, and some glass products are used in this temperature regulation.
In summary, there are many ways to improve the quality of glass clarification. The quality control of raw materials and batch materials, the control of furnace melting process parameters, the improvement of kiln structure design and the design improvement of combustion system, strengthen the exploration and summary of these aspects, and promote the reduction of glass manufacturing cost and product quality.
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