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Key words: glass bottles; high white materials; air bubbles; absorption method Bubbles are common defects in glass, which are caused by many reasons, such as lack of melting ability, insufficient temperature, elimination of fining defects, and generation of refractory materials. There is also the improper feeding operation during molding. This article discusses the elimination of air bubbles in the production of high white glass bottles in our No. 1 glass furnace.
Bubble Generation and Elimination Process No. 1 glass kiln is a coal-fired regenerator horseshoe flame tank furnace. The design uses a small momentum ratio, inclined floor furnace structure, deep clarification pool, inclined rising flow hole and rising material. Road, no work pool, the furnace cold modified after the production of high-white glass bottles, put into production found on the product with bubbles, there are round, oval and surface thin skin bubbles, the number of 0 23/! Seriously affect the appearance of the product quality. At first, we take measures according to the discharge method: increase the melting temperature, reduce the melting rate, the flame space radiation temperature is gradually increased, the amount of discharge is also reduced, the resulting increase in the number of bubbles to 523/!, Diameter increase The increase in the number of bubbles in large skins, the increase in the gas ratio of the batch, the increase in the amount of fining agent, and the increase in the gas rate, but the bubbles have not decreased; and the increase in the amount of flux introduced has still had no significant effect. Faced with more and more bubbles on the products, we Realize that the idea of ​​"absorption method" may be correct. Then, reduce the number of bubbles after reducing the melting temperature. Afterwards it was reduced to 0 23/!, and then improved feeding machine to achieve thin layer wrapped feed, continue to reduce the melting temperature, the discharge control is appropriate, the final bubble number is stable, the diameter decreases.
The bubble elimination mechanism in the glass melting process The melting process is a complex physical and chemical reaction process that includes the silicate formation stage, the glass formation stage, and the clarification homogenization stage, in which the clarification stage is the bubble elimination process. In this process, As the temperature rises, the viscosity of the glass decreases, the gas in the bubbles, the gas in the kiln establishes a balance with the physically dissolved and chemically bonded gases in the glass, and the visible bubbles float on the surface of the glass to eliminate them. Visible in the clarification process The elimination of bubbles occurs in the following two ways:
1 The volume of the bubble increases and accelerates, and it disappears after floating out of the glass surface.
2 The gas components in the small bubbles dissolve in the glass and the bubbles are absorbed and disappear.
The size of the bubble and the viscosity of the glass are the determinants of whether or not the bubble can float. According to Stokes' law, the rising speed of the bubble is proportional to the square of the radius of the bubble and inversely proportional to the viscosity of the glass.
Calculate the viscosity of the glass at different temperatures according to the composition of the high white glass, and compare it with a green glass formulation of our company. The glass float temperature at the clarification position and the bubble floating distance are used to calculate the floating time of different diameter bubbles.
Increasing the melting temperature can increase the floating speed of bubbles with a diameter of 0.2 mm or more, and reduce the time required for floating. However, bubbles with a diameter of less than 0.2 mm are difficult to eliminate by floating. It is necessary to adjust the temperature so that the small bubbles are in the glass. Absorbed and eliminated.
In the process of cooling glass liquid, as the gas becomes colder, the gas bubble will become smaller under the same gas pressure. Due to the surface tension of the glass, the pressure in the bubble increases due to the decrease of the radius. When the temperature decreases, the gas in the glass liquid will decrease. The saturation pressure is lower than the pressure of the gas in the gas bubble. The gas in the gas bubble is released into the glass liquid. As the gas is released, the gas bubble radius is reduced. The surface tension of the glass liquid further increases the pressure in the gas bubble until the gas bubble is completely covered with glass. Liquid absorption.
In the process of clarification, the two phases of the large bubble discharge and the small bubble absorption are indispensable. The former requires the necessary temperature and duration, and the latter requires a certain temperature gradient, if one of these conditions cannot be achieved. Will make the product with air bubbles.
Kiln structure and the given process conditions to eliminate the impact of air bubbles 1. Furnace structure The kiln structure has two characteristics: First, the small furnace with a large inclination angle and small momentum ratio, the second is a sinking deep clarifier structure This structure allows the flame to have a higher speed and rigidity, the flame is close to the glass surface, and there is a forward thrust on the material pile. According to the measurement, when the melting temperature is insufficient and the discharge volume is large, the material pile is moved. Some of the batch materials had not completely melted before they reached the clarification department, which took up the clarification time and caused the fining to be insufficient. The bubbles that should have been discharged remained in the molten glass and entered the cooling stage. The bubbles above 0.2 mm in diameter on the products were Forming.
Different diameters of bubbles rise at different speeds and time. The fining distance in the direction of the kiln length is short, the clarification time is relatively insufficient, and the discharge of large bubbles is sometimes insufficient. From the analysis of the clarifier structure, the so-called deep clarifier sinking is also limited. Compared to the sinking deep pool in the past, the glass liquid in the vertical direction The distance to cool down is shortened, the time is reduced, and the temperature reduction is small. The time for the downward clarification of the glass liquid is short, small bubbles cannot be completely dissolved in the glass liquid, and the glass liquid entering the uptake channel has both bubbles with a diameter of 0.2 mm or more. There are also ash bubbles below 0.2mm in diameter.
There is a cooling process from the bottom of the rising channel to the top of the material channel to the vicinity of the material basin. Due to the high heat-intensity of the rising channel, the gradient of temperature drop during this stage is small, and the temperature of the glass at the top is high. With large cooling air volume, the glass liquid is rapidly forced to cool, and the glass at the skin surface is affected by the absorption of small bubbles due to excessive cooling. This causes the phenomenon of uneven distribution of small bubbles on the product. In order to fully play the glass liquid into the flow hole After this process absorbs the effect of small bubbles, we reduce the insulation strength of the rising channel and remove the insulation brick. The measurement results show that the temperature of the glass at the top of the rising channel decreases, and the rotation speed of the temperature-regulating fan decreases. As a result of this treatment, the diameter of the bubbles on the product becomes smaller and the number becomes smaller.
2. Feeder modification, control of the discharge capacity of the feeder equipped with the kiln can not achieve the thin layer feeding, the proportion of broken glass is only %7, the height of the batch material floating on the glass surface after entering the furnace is large, this gives the flame The blow increases the area of ​​action, the thrust increases the speed of the drift faster. Compared to the green material with a large proportion of broken glass (partially wrapped into the material), the height of the pile floating on the liquid surface is small, the phenomenon of heap pile forward is not Obviously, the improved feeder reduces the discharge port, and the feeder is moved down so that the added batch material is immersed in the glass. The thickness of the pile is reduced, the bearing area is reduced, and the distance to the stack is reduced. Help prevent runaways and increase clarification time.
3. Melting temperature In general, increasing the melting temperature is the most direct measure to solve the bubble, it is to speed up the melting speed of the batch material, increase the temperature of the glass, reduce the viscosity, and thus facilitate the discharge of bubbles. For this example After the melting temperature is increased, there are several direct effects.
1Increase the flame ejection speed and flame length. The role of flame speed increase is to increase the thrust of the material pile. The result of flame lengthening is the hot spot advance. The hot spot advance shortens the cooling section, which is not conducive to small bubble absorption.
(2) The temperature of the glass liquid is increased, the solubility of the gas in the glass liquid is reduced, and the amount of gas evolved increases. When the fining time is not sufficient, the effect of reducing the air bubbles is not achieved but the opposite occurs.
3 reduce the viscosity of the glass. Viscosity reduction on the one hand is conducive to the discharge of large bubbles, on the other hand to reduce the resistance of the forward drift of the pile to reduce the more easily run out of material, deteriorate the clarification quality, is not conducive to bubble discharge. Observed situation is The phenomenon of a lot of bubbles is more serious, which shows that the second aspect has a great effect.
4 The bubble diameter becomes larger. These growing bubbles cannot enter the cooling section as soon as they are discharged from the molten glass, but they become difficult to absorb.
When the melting temperature is appropriately lowered, the flame jetting speed decreases, the viscosity of the glass increases, and it is not easy to run the material, and the hot spot retreat clarification time is prolonged. The solubility of the gas in the glass is improved, and bubbles can be reduced or eliminated. Of course, the temperature is not lower. Well, when the temperature drops to a certain degree, the problem will go to the opposite side. Not only will the bubbles be reduced, the stones will also appear.
4. Influence of the gas rate on the number of bubbles in the recipe Increasing the gas rate can shorten the melting time and prolong the clarification time, but this effect is negative compared to the gas ing rate requiring a longer clarification time. The increase in the rate also increases the cost of batching materials, which is uneconomical, so in the end we will reduce the gas rate.
5. Effect of Glass Viscosity In order to study the effect of glass viscosity on running material, we compared the temperature and viscosity of the glass solution at the feed port of another green material furnace. The difference in the viscosity of the two materials was related to the drift rate of the material stack. The influence is very obvious, and it can be seen from the difficulty of manually selecting the material. This can explain that when the same furnace is used to produce green material, it is difficult to discharge material when the output of green material is large, and it is easy to run when the output of white material is small. The reason for the material.
Summarizing the idea of ​​solving the bubble problem comes from the theory that the solubility of most gases in the glass liquid is inversely proportional to the temperature. It is used in the production practice. By taking measures to lower the temperature, the solubility of the gas in the glass liquid is increased, and the quality of the appearance of the product is greatly affected. The bubbles are absorbed by the glass.
In fact, there is a balance between the melting temperature and the quantity of discharged material and the number of bubbles in the production of high-white glass bottles in this kiln. That is, the melting temperature can be appropriately reduced when the discharge amount is reduced. When the discharge amount increases, the melting temperature increases. Should be properly increased, but not excessively high. Using this law to guide production, can make the number of product bubbles within the allowable range.
Abstract : According to the theory that the solubility of gas in molten glass is inversely proportional to the temperature, the influence of the furnace structure and process conditions on the elimination of bubbles is discussed, and the equilibrium relationship between the melting temperature of the furnace, the discharge amount and the number of bubbles is found. Used to guide production.