In the glass manufacturing industry, the same glass products and the same glass kiln have different maintenance times, repair parts, and kiln service life. What are the causes of corrosion of fused AZS refractory brick pool walls in glass furnaces? Normal material erosion is within the designed use time range of the material, while abnormal material erosion is a malignant condition that occurs in a location that is not necessarily fixed and within the designed service life of the material. The hidden negative effects of these situations are huge, affecting not only the economic interests of glass companies. To a certain extent, it also affects and restricts the healthy development of the entire glass industry.
Harmful Components and Corrosion Mechanisms in Fused AZS Refractory Bricks
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Glass phase
The phase composition of fused cast azs refractory products is baddeleyite, corundum, a small amount of mullite, glass phase, and pores. In the manufacturing process of fused cast azs refractory bricks, in order to reduce and eliminate residual thermal stress, a certain amount of glass phase is required in the product as an absorbent to buffer thermal stress. However, the existence of the glass phase also brings some disadvantages. In terms of the resistance of refractory materials to the erosion of glass liquid, the glass phase is the weak link. During the erosion process, the glass phase first precipitates and is replaced with the high-temperature glass melt, thereby accelerating the erosion of the crystal. Under high-temperature use conditions, the glass phase will also ooze out and release bubbles, thereby contaminating the glass melt.
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Carburizing
Generally, zirconium corundum fused cast refractories brick products produced by the reduction method have serious carburization. According to literature reports, the corresponding carbon content can be judged according to the color of the cross-section of the refractory material: light gray 0.03%~0.06%, off-white <0.03%, gray 0.08%~0.18%, dark gray 0.15%~0.19%. Even products produced by advanced oxidation methods (long arc and oxygen blowing) contain some carbon (<0.01%). Carburizing exists in the form of carbides, mixed nitrogen compounds, sulfides, solid carbon, and residual reducing gases. When used under oxidizing conditions, gas is released, causing the glass phase to seep out and the temperature to decrease. When the AZS refractory brick contains a large amount of glass phase (#33 is generally about 20%), it will soften and ooze out at temperatures above 1100°C. And as the temperature increases, the loss intensifies. The exudation of the glass phase is related to the carbon, carbide, low-priced iron and titanium, and other impurities present in the brick. When there is an oxidizing atmosphere in the kiln, oxygen diffuses to the bricks and reacts with these impurities to release CO2, SO2, and other gases. These gases squeeze out the molten glass phase and form nucleation bubbles on the surface. The crystalline phase is lost due to the loss of the combination of the glass phase. This is the cause of the erosion of AZS refractory bricks.
The entry of harmful components in the production process of fused AZS refractory bricks
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Sand inclusion and other foreign matter enter the product
For the casting model produced by adding quartz sand and water glass, the sand inclusion phenomenon refers to the high-temperature molten liquid gradually rising in the model during pouring, similar to that of pool wall bricks. The part not covered by the melt undergoes high temperature, and the sand on the surface breaks away in lumps and falls into the melt, forming a sand inclusion phenomenon. Due to the high temperature of 1750℃, the added sand skin exists in the glass state inside the product. In addition, there is a flat material program during the melting process. The flat material tool is a cast steel drill. If the steel drill is exposed to high-temperature molten liquid for a long time, its texture will soften. When prying the unmelted material block, the steel drill may break. The broken steel drill may be completely melted in the melt, increasing the iron content in the product. It is also possible that it is not completely melted and enters the product during pouring.
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Oxidation uniformity of fused AZS refractory bricks
The degree of oxidation or uniformity of oxidation of fused AZS refractory bricks is one of the key indicators of whether the quality of the product is excellent. Each manufacturer has complete system requirements in formulating the oxygen-blowing process, but most of them have defects in setting the position of the oxygen lance. It is an inevitable phenomenon that the oxygen lance hole is blocked during oxygen blowing. Oxygen guns generally have seven oxygen outlets distributed around or at the bottom of the ball head. When one or several oxygen outlets are blocked, uneven oxidation of the product will occur. It can be seen if it is serious, but it is difficult to judge intuitively if it is not serious. Even on a single brick, there will be color inconsistency. Dark color indicates a large amount of carburization, and light color indicates a small amount of carburization. The clogging of the oxygen lance hole directly leads to poor oxidation effect of the product and increased carburization of the product. When the glass furnace is operating, the glass phase is precipitated along with bubbles, mostly carbon dioxide gas.
The formation of gaps in glass furnaces
1 Grinding or masonry kiln
When the product is processed and ground, the flatness of the machine tool surface cannot meet the requirements after aging, causing the product to be convex or recessed in the middle. During pre-assembly, the gap is evened up and down, making it seem that the gap is not large. During the kiln masonry construction, due to foundation flatness errors or defects in the bottom of the product, the builder’s negligence caused the bottom of the product to be elevated. When the final kiln is baked, the expansion of the product may not be shaped according to the uniform gap, which may cause the gap at the bottom or upper part of the pool wall brick to be significantly enlarged.
2 Kiln sill specification design
In a glass kiln, improper arrangement of kiln sill bricks will also cause the kiln sill to be deformed due to the impact of glass liquid. Since the kiln ridge bricks must withstand the impact of the molten glass turning over, the kiln ridge must have sufficient thickness and support. The height of the supporting bricks needs to exceed 1/2 of the height of the kiln sill bricks for more effective support. When the kiln sill bricks are deformed by the impact of glass liquid, the gap between the bricks will become wider.
3 kiln deformation
In the temperature range of the kiln, the zirconium component in the fused AZS refractory brick transforms from the monoclinic phase to the tetragonal phase at 1100°C. Some volume changes will occur at this time. The temperature decrease when the temperature is unstable will cause some volume changes in the opposite direction. This temperature fluctuation causes the reverse volume change of the zirconium component, which is the fundamental reason for the explosion of the product. When baking the kiln, a heat preservation stage is usually set at 1100°C to fully convert the volume of the fused AZS refractory bricks.
To sum up,
the reasons for the erosion of the fused AZS refractory brick pool wall in glass furnaces are as follows. Listed here for reference by refractory material manufacturers and glass production companies to choose a suitable solution for their own glass furnace refractory lining. Reduce maintenance costs, increase production capacity, and create more economic benefits.
- (1) The glass liquid is seamless. The gaps between the products will cause mechanical erosion of the glass liquid backflow. When glass precipitates in the gaps, it is accompanied by the precipitation of bubbles, which intensifies the erosion of the gaps in the product. When accepting the entire kiln, the stricter the requirements for gaps, the better.
- (2) When constructing the kiln, ensure that the foundation is stable and there must be no overhead products. The expansion joints should be reserved reasonably or the masonry personnel should strictly control their work.
- (3) The height and width specifications of the inner protective bricks of the kiln sill bricks should be appropriately increased. The protective bricks must effectively play a supporting role.
- (4) The production process of fused AZS refractory bricks requires effective system management to determine whether the oxygen lance outlet holes are blocked. The position of the oxygen lance should be set to facilitate observation of the status of the oxygen lance outlet hole.
- (5) For sand molds made of quartz sand and water glass, the proportion of water glass should not be less than 8%. A small amount of water glass will cause the surface sand to fall off during pouring, which will bring inherent hidden dangers to the product. It is best to choose fused AZS refractory bricks made from resin sand models.
