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As we all know, ordinary white glass is mainly used in the field of construction and is also the main product of many float lines. Its product characteristics are that the glass transmittance is between 67% and 89% (the value varies with the thickness of the glass), and the iron content is About 1000ppm; and ultra-white glass is a kind of ultra-transparent low-iron glass, also known as low-iron glass, high-transparent glass; it is a high-quality, multi-functional high-end new glass, the transmittance is generally above 91.5%, iron The content is generally controlled below 150ppm; the high white glass mentioned in this article is a variety between ordinary white and ultra-white glass, the transmittance is generally controlled between 89.5% and 91.5%, and the iron content is controlled between 200ppm and Between 400ppm, its purpose is to be processed into handicraft glass to meet the requirements of market decoration.

The process characteristics of three different transmittance glasses.

The process control of glass varieties with different transmittances is determined by their process characteristics. The following is a comparison of the glass composition of ordinary white glass, high white glass and ultra-white glass (%):

The biggest difference between the three glasses with different transmittances is that the Fe2O3 content is different, and the difference is large. The Fe2O3 content of ordinary white glass is about 8 times that of ultra-white glass, and the high-white glass is 2 to 3 times that of ultra-white glass. Therefore, when switching between three glass varieties with different transmittances, it is mainly considered that the change of Fe2O3 content affects the heat permeability of the glass. The different glass heat permeability will affect the heat transfer during the glass melting process, which will cause the entire furnace The change of the horizontal gradient and the vertical gradient of the molten glass temperature will affect the reflux of the molten glass in the entire furnace, which will affect the quality of the glass to a certain extent. Therefore, when switching from ordinary white glass to high white glass, and from high white glass to ultra-white glass, it is necessary to formulate a suitable process system and process control process according to the difference in the heat permeability of the glass, and modify it during the implementation process to obtain melting Comparable quality glass meets the needs of users.

Fe2O3

Fe2O3 

The process control of three kinds of glass with different transmittance.

In the actual production process, when switching from a glass with a lower transmittance to a glass with a higher transmittance, the heat permeability of the glass will gradually increase; according to the above, the heat conduction of high white glass and ultra-white glass The rate will be higher, the heat transfer of the molten glass in the vertical direction in the furnace is faster, so the bottom temperature of the pool will rise. However, due to the high transmittance of high white glass and ultra-white glass, the emissivity of the molten glass in the furnace will decrease, which determines that the heat released after the fuel is burned will be absorbed by the molten glass to a certain extent. The heat radiated to the furnace body and the heat taken away with the flue gas will increase, which causes the higher the heat permeability of the glass, the more difficult the melting will be, the higher the energy consumption per unit of glass; in addition, the transmission rate The higher the heat permeability of the glass, the better. During production, the temperature of the molten glass at the bottom of the pool will be higher, resulting in a higher average temperature of the molten glass, but the temperature of the surface glass is lower, and the molten glass is convective in the horizontal direction. The strength increases, the residence time of the forming circulation in the clarification zone is shorter, and the clarification of the glass liquid is very likely to be poor. At the same time, for three glasses with different transmittances, the order of the vertical temperature gradient and viscosity in the depth of the pool is plain glass, high white glass, and ultra-white glass. The upper and lower temperature difference of the glass liquid decreases, and the convection will also Correspondingly weakened, the degree of difficulty of bubble discharge will also vary greatly. Because of the large upper and lower temperature gradient of ordinary white glass, the discharge of bubbles is relatively easy. Due to the heat permeability of ultra-white glass, the upper and lower temperature gradient is small, and the discharge of bubbles is more difficult. Between ordinary white and high white glass, the first thing to be solved in the production of high white glass and ultra white glass is clarification.

The glass transmittance online detector

The glass transmittance online detector

Above we have analyzed the essential difference between the three different transmittance glasses. Therefore, in the actual production process, when switching between the above three different transmittance glass varieties, it is necessary to formulate an appropriate process control system according to its process characteristics. The following is the process control process of switching from the production of plain white products to high white products or ultra-white products: 

(1) Glass cullet rate: The current float production line generally has a relatively high yield when producing plain white glass, so the resulting return fragmentation There is less glass. Generally, the cullet rate of ordinary white glass production line is maintained at about 10%. However, when switching to high white glass and ultra-white glass, due to the difference in heat absorption and clarification, in order to produce high-quality glass, To increase the cullet rate to a certain extent, the cullet is generally increased to between 20-30%, which is beneficial to enhance the melting and clarification process of the molten glass. 

(2) Adjustment of the heat load of the melting process: the production of high-white and ultra-white glass is mainly to solve the problem of clarification of glass liquid, so the heat load of 1#, 2#, 3# small furnaces should be reduced, and the clarification circuit 4#, The heat load of 5# and 6# small furnace, but the heat load to the small furnace should not be increased too much, otherwise the return glass liquid under the forming flow has been absorbed by the glass liquid and the microbubbles will easily rise to the surface flow to cause secondary Air bubbles are also likely to aggravate the erosion of the refractory material at the bottom of the pool, and cause the refractory material to precipitate bubbles. 

The heat load of the melting processing

The heat load of the melting processing

(3) Adjustment of auxiliary equipment related to the melting furnace: First, when switching from ordinary white products to high-white and ultra-white products, the depth of the deep-layer water bag of the card neck into the molten glass should be appropriately increased to strengthen the molten glass in the clarification part to the hot spot The reflux of the glass liquid increases the temperature of the clarification part, which is beneficial to the discharge of microbubbles; the second is to avoid the use of a neck agitator, which can effectively prevent the possibility of secondary bubbles; the third is to adjust the bubbler appropriately to enhance the furnace The convection of the molten glass in the vertical direction of the furnace accelerates the discharge of bubbles. 

(4) Optimization of the furnace process: 

① Optimize the flame of each small furnace, including the rigidity and angle of the flame; 

② Adjust the ratio of Glauber's salt and carbon powder content; 

③ Adjust the redox atmosphere of each small furnace Make adjustments; 

④ Adjust the thermal expansion coefficient of glass adaptively; 

⑤ Adjust the thickness of the material layer.

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