In glass melting furnace, in addition to the contact with flame as we mentioned before, the entire furnace pool from melting part, cooling part to forming part is in contact with high-temperature glass liquid. The temperature of glass liquid ranges from 1200-1600℃, is in a convection state, presents a variety of flow modes, and the flow rate of each part is different. The combustion airflow flows above the glass liquid surface. Therefore, it has strong erosion performance. The bricks in contact with this part can be divided into pool wall, pool bottom, feeding pool, cooling part (or working part), flow channel, etc.
(2) Pool bottom bricks
The conditions of the pool bottom bricks are that the glass liquid temperature is low and the flow is weak. It has the following three damage characteristics.
① Downward drilling: Metal impurities (mainly iron, the order of metal corrosion intensity is: Sn, Pb, CuA1, Zn) brought in by the batch (mainly broken glass) and the molten metal obtained by glass reduction sink to the bottom of the pool, forming spherical or flat ring-shaped melts. Due to their large surface tension, they form a wedge-shaped mouth between the glass liquid and the pool bottom bricks, resulting in downward drilling erosion, especially drilling into the seams of the pool bottom bricks. While drilling, erosion occurs and extends to the corrosion-resistant parts of the pool bottom bricks (such as clay bricks, or even lightweight insulation bricks). In severe cases, most of the pool bottom bricks (under the paving bricks) can be hollowed out.
② Upward drilling: When the glass liquid and metal liquid melt the brick seam material and penetrate into the cushion layer under the paving bricks, the cushion layer is corroded and damaged. The glass liquid and metal liquid erode the paving bricks vertically upward in a pit-like shape, that is, upward drilling. Attack from top to bottom until the paving bricks are melted through.
③ When the bottom of the pool is insulated due to mechanical wear, the bottom glass liquid is in a convection state. The circulating liquid flow damages the bottom of the pool, especially the feeding area, where the convection is intense and the wear is heavy.
In view of the above damage characteristics, the pool bottom bricks are required to be wear-resistant and have integrity. Now a multi-layer composite pool bottom structure is mostly used. Generally, a protective layer is built under the bottom bricks (clay bricks), and zircon sand ramming material or fused zircon corundum ramming material is set on the top of the clay bricks. The latter is better. This layer of ramming material and the pool bottom are sintered into a whole. It is required not to shrink or expand, without cracks, and very dense, which can prevent the leakage of glass liquid to the maximum extent and form a solid bottom structure with sufficient strength.
The paving bricks are in direct contact with the slag glass liquid, which can well protect the ramming material pool bottom. Commonly used are fused AZS bricks with good corrosion resistance and wear resistance (high-quality sintered AZS bricks can also be used, but the disadvantage is that the size is small and there are many brick joints). The effect of the composite pool bottom structure is: reducing heat loss, extending the life of the pool bottom and improving the quality of glass liquid.
(3) Bricks for charging pool
Bricks for charging pool are subject to erosion by powder and glass liquid, wear of material layer, scouring of liquid flow and flame, so they are seriously damaged, especially corner bricks for charging pool. The protruding corners are subject to strong abrasion and scouring. There is a large temperature difference between the inner and outer surfaces of the bricks, which produces large mechanical stress. In addition, this part has a certain temperature fluctuation, so it is very easy to be damaged. It is regarded as one of the weak parts of the pool kiln. High-temperature wear-resistant and corrosion-resistant materials must be used. Commonly used are fused zirconium corundum bricks containing ZrO2:41% without shrinkage cavities, and the brick thickness is increased to strengthen air cooling. Except for corner bricks, other parts can use ordinary cast AZS-33 bricks.
(4) Bricks for cooling section
The cooling section is the melted and clarified glass liquid, which has entered the later stage of the melting process. It must not cause any defects (including stones, streaks, bubbles) to the glass liquid. Since the temperature of the glass liquid here is lower than that of the melting section, the erosion of the bricks is lighter. The cooling part needs to use AZS-33 bricks produced by oxidation method, which has a high glass phase precipitation temperature and will not bring bubbles to the glass liquid.
(5) Bricks for flow channel
The flow channel uses fused AZS-3 bricks or fused α-A1203 bricks. These materials have fine-grained and dense structures, with very little glass phase filling between crystals, which causes the least pollution to the glass liquid. Their corrosion resistance is better than that of AZS bricks below 1300℃. Flow channel and flow trough bricks (11001200℃, glass liquid flow rate 0.83~1.67m/min or even higher) are very easy to wear, and high-quality materials must be used. Practice has shown that sillimanite bricks and mullite bricks can also be used for flow channels, because they have a dense fine-grained structure and are not easy to cause bubbles in the glass liquid.
Damage characteristics of each part and commonly used materials.
(1) Pool wall bricks
At present, the pool wall bricks are mainly made of fused zirconium corundum bricks. The damage mechanism of this brick is the melting process of multi-phase materials. The damage process can be roughly divided into three steps:
① High-temperature glass phase seepage The melting of fused AZS bricks depends on the high-temperature glass phase seepage temperature (1320~1420℃C). The glass phase seepage in the brick forms a high-viscosity glass liquid with the nearby glass liquid, which prevents the brick from being further eroded. However, holes are left in the fused bricks. Since the surface tension of the fused bricks is smaller than that of the glass liquid, the fused bricks are always wetted by the glass liquid. The melting rate depends on the glass phase seepage temperature, the amount of glass phase and the viscosity of the melted material.
②) Due to the flow and scouring of the glass liquid, the high-viscosity glass liquid layer on the surface of the fused brick leaves its original position and enters the glass liquid. The holes left are exposed
③ After the glass liquid infiltrates the fused layer, the new glass liquid infiltrates the exposed new surface and holes, reacts with the phases around the holes, and continues to melt the fused bricks. First, the mullite in the structure is decomposed to form aluminum oxide and new glass phase, and then the baddeleyite and corundum fine particles in the structure are dissolved, and finally the brick structure is completely disintegrated. The penetration rate depends on the diffusion rate and the organizational structure of the brick (such as the size, shape, number and distribution of pores).
The above three-step process is repeated continuously, so that the fused brick is continuously corroded. When the temperature of the glass liquid increases, the corrosion will accelerate. When the outer surface of the pool wall brick is cooled by blowing air, the corrosion will slow down. The corrosion situation varies with different glass components. For example, when using Glauber's salt, there will be "nitrate water" on the liquid surface, which will aggravate the corrosion of the pool wall brick. When it contains fluoride, the corrosion is very fast.
The brick seams of the pool wall brick are very easy to be corroded, which is due to the flow of glass liquid and the upward drilling. This is also the interface of gas, liquid and solid. The bubbles on the interface promote the stirring of the liquid phase, accelerate the dissolution of the solid phase, and the reaction layer is easily washed away by the slope glass liquid. As the material of the pool wall brick, it is required to be resistant to corrosion, not cause any defects to the glass liquid (such as streaks, stones, bubbles), not color the glass liquid, and have a certain degree of thermal shock resistance and low thermal conductivity. The ideal pool wall brick is fused zirconium corundum brick. The melting part pool wall usually uses fused AZS bricks containing 41% zirconium oxide, and the cooling part uses fused AZS bricks containing 33% zirconium oxide. For fused AZS products, attention should be paid to the abnormal volume change accompanied by crystal transformation at 1050-1150℃ when baking the kiln.
Some companies also choose to use α-β-fused corundum products. This product is composed of tightly staggered α-alumina (53%) and β-alumina (45%) fine particles, and the space between the crystals is filled with glass phase (2%). It can be used as a large brick for vertical laying of the cooling part pool wall and a bottom brick and seam cover brick for the cooling part. Among the materials for the upper structure, a β-fused corundum product is also launched. It is composed of large β-alumina grains. There is a certain amount of pores inside the brick body, but there is almost no glass phase. Therefore, this brick has excellent resistance to thermal shock and alkali vapor erosion.
Damage characteristics and selection of refractory materials in contact with glass liquid in glass melting furnace
In glass melting furnace, in addition to the contact with flame as we mentioned before, the entire furnace pool from melting part, cooling part to forming part is in contact with high-temperature glass liquid. The temperature of glass liquid ranges from 12001600℃, is in a convection state, presents a variety of flow modes, and the flow rate of each part is different. The combustion airflow flows above the glass liquid surface. Therefore, it has strong erosion performance. The bricks in contact with this part can be divided into pool wall, pool bottom, feeding pool, cooling part (or working part), flow channel, etc.
(2) Pool bottom bricks
The conditions of the pool bottom bricks are that the glass liquid temperature is low and the flow is weak. It has the following three damage characteristics.
① Downward drilling: Metal impurities (mainly iron, the order of metal corrosion intensity is: Sn, Pb, CuA1, Zn) brought in by the batch (mainly broken glass) and the molten metal obtained by glass reduction sink to the bottom of the pool, forming spherical or flat ring-shaped melts. Due to their large surface tension, they form a wedge-shaped mouth between the glass liquid and the pool bottom bricks, resulting in downward drilling erosion, especially drilling into the seams of the pool bottom bricks. While drilling, erosion occurs and extends to the corrosion-resistant parts of the pool bottom bricks (such as clay bricks, or even lightweight insulation bricks). In severe cases, most of the pool bottom bricks (under the paving bricks) can be hollowed out.
② Upward drilling: When the glass liquid and metal liquid melt the brick seam material and penetrate into the cushion layer under the paving bricks, the cushion layer is corroded and damaged. The glass liquid and metal liquid erode the paving bricks vertically upward in a pit-like shape, that is, upward drilling. Attack from top to bottom until the paving bricks are melted through.
③ When the bottom of the pool is insulated due to mechanical wear, the bottom glass liquid is in a convection state. The circulating liquid flow damages the bottom of the pool, especially the feeding area, where the convection is intense and the wear is heavy.
In view of the above damage characteristics, the pool bottom bricks are required to be wear-resistant and have integrity. Now a multi-layer composite pool bottom structure is mostly used. Generally, a protective layer is built under the bottom bricks (clay bricks), and zircon sand ramming material or fused zircon corundum ramming material is set on the top of the clay bricks. The latter is better. This layer of ramming material and the pool bottom are sintered into a whole. It is required not to shrink or expand, without cracks, and very dense, which can prevent the leakage of glass liquid to the maximum extent and form a solid bottom structure with sufficient strength.
The paving bricks are in direct contact with the slag glass liquid, which can well protect the ramming material pool bottom. Commonly used are fused AZS bricks with good corrosion resistance and wear resistance (high-quality sintered AZS bricks can also be used, but the disadvantage is that the size is small and there are many brick joints). The effect of the composite pool bottom structure is: reducing heat loss, extending the life of the pool bottom and improving the quality of glass liquid.
(3) Bricks for charging pool
Bricks for charging pool are subject to erosion by powder and glass liquid, wear of material layer, scouring of liquid flow and flame, so they are seriously damaged, especially corner bricks for charging pool. The protruding corners are subject to strong abrasion and scouring. There is a large temperature difference between the inner and outer surfaces of the bricks, which produces large mechanical stress. In addition, this part has a certain temperature fluctuation, so it is very easy to be damaged. It is regarded as one of the weak parts of the pool kiln. High-temperature wear-resistant and corrosion-resistant materials must be used. Commonly used are fused zirconium corundum bricks containing ZrO2:41% without shrinkage cavities, and the brick thickness is increased to strengthen air cooling. Except for corner bricks, other parts can use ordinary cast AZS-33 bricks.
(4) Bricks for cooling section
The cooling section is the melted and clarified glass liquid, which has entered the later stage of the melting process. It must not cause any defects (including stones, streaks, bubbles) to the glass liquid. Since the temperature of the glass liquid here is lower than that of the melting section, the erosion of the bricks is lighter. The cooling part needs to use AZS-33 bricks produced by oxidation method, which has a high glass phase precipitation temperature and will not bring bubbles to the glass liquid.
(5) Bricks for flow channel
The flow channel uses fused AZS-33 bricks or fused α-A1203 bricks. These materials have fine-grained and dense structures, with very little glass phase filling between crystals, which causes the least pollution to the glass liquid. Their corrosion resistance is better than that of AZS bricks below 1300℃. Flow channel and flow trough bricks (11001200℃, glass liquid flow rate 0.83~1.67m/min or even higher) are very easy to wear, and high-quality materials must be used. Practice has shown that sillimanite bricks and mullite bricks can also be used for flow channels, because they have a dense fine-grained structure and are not easy to cause bubbles in the glass liquid.
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