Fused cast AZS block is an important component of glass furnace. Its quality has a significant impact on the service life of glass furnace. This article makes a simple discussion on the relationship between the quality of fused cast AZS block and the service life of glass furnace.

Fused cast AZS block is an indispensable key furnace building material used in important parts of glass furnace. It has more unique physical and chemical properties than other types of refractory materials; especially high temperature resistance (load softening degree above 1700℃), dense internal crystal structure, low porosity, high mechanical strength, strong chemical stability and corrosion resistance, good thermal stability above 1200℃, high glass phase precipitation temperature (above 1400℃), etc. It is precisely because of the above characteristics that it is recognized and widely used in glass industry production. Whether the quality of fused cast AZS block is good, whether the variety is complete and matching, is not only directly related to the quality of molten glass and the economic and technical indicators such as the melting capacity, fuel consumption, and thermal efficiency of glass furnace, but also directly related to the service life of glass furnace.

China‘s fused cast AZS refractory materials began to be produced in the mid-1960s with fused cast mullite bricks, and later developed into zircon mullite bricks (ZrO2 content is about 8%). At this time, the chemical composition and internal crystal structure of zircon mullite bricks are unstable, the glass phase precipitation temperature is low (about 1200℃), the porosity is high, and the service life in the glass furnace is only 1-3 years. In addition, the melting temperature of the glass furnace is low (below 1550℃), the fuel consumption is high, the thermal efficiency is low, the glass melting quality is poor, and the production of the glass industry is basically stagnant. In the past thirty years, with the deepening of reform and opening up, scientific and technological progress, the introduction and digestion of foreign advanced technology, scientific and technological personnel, prompting China‘s fused cast AZS refractory materials have a rapid development, high quality, new varieties of fused cast AZS products continue to emerge. The previous reduction production process has been basically eliminated, and the advanced oxidation production process has taken the product quality to a new level. The ZrO2 content of the product has increased from 8% to 33%-46%, and the corrosion resistance, chemical stability, glass phase precipitation temperature and other characteristic indicators have been greatly improved. The glass furnace has been changed from partial insulation to full furnace insulation; the melting temperature of the glass furnace has been increased from less than 1550°C to 1600°C; The melting rate of glass is increased from below 1.5t/m‘-d to more than 3t/m‘-d; the thermal efficiency is increased from about 20% to nearly 50%, and in some cases even more; glass quality is close to and reaches the advanced foreign level; the service life of glass furnaces is increased to 5-8 years, and some are even more than 10 years.

Due to the rapid development of fused cast AZS block materials in recent years, the quality has been continuously improved. It is undeniable that it has promoted the comprehensive and rapid development of the glass industry, and the improvement of the technical level of glass production depends to a large extent on the technological progress and innovation of fused cast AZS block materials. Fused cast AZS block materials are used in the highest temperature part of the flame space in the melting tank part of the glass furnace. For example: crown, breast wall, port, front crown and gable wall. There are also parts that are directly in contact with high-temperature molten glass. The bottom of the melting tank, the side wall, the throat and the high-temperature chimney on the upper part of the regenerator are all touched. These parts are characterized by high temperature, large flame scouring, and severe erosion of the alkaline steam atmosphere in the glass furnace; the convection erosion of the high-temperature glass liquid due to the temperature difference and the thermal shock phenomenon generated during the operation of the glass furnace have a direct impact on the service life of the glass furnace. Of course, there are also the quality and variety of other types of refractory materials in the glass furnace body and their supporting use. The quality of the glass furnace masonry, the operation quality of the glass furnace during operation, the control level in production operation, etc. are all related to the service life of the glass furnace. However, the key role is still the quality of the fused cast AZS block material.
                                                                    
With the development of the glass industry, high-quality, new varieties of glass products cannot meet the market demand at present, especially with the increasing demand for high-end deep-processed glass and other special glass. How to improve the quality of fused AZS refractory materials, reduce the fuel consumption of glass furnaces, improve thermal efficiency, and extend the service life of glass furnaces is an important task and topic that we will continue to work hard to explore now and in the future. Although in recent years, the quality of fused AZS refractory products has made great achievements and the service life of glass furnaces has been continuously extended, there is still a big gap with the advanced level of foreign countries and the requirements of high-quality products produced by the glass industry. Based on our many years of production practice experience, should we improve the quality of fused AZS refractory materials from the following aspects, further maintain the high-quality and safe operation of glass furnaces, and achieve the purpose of further extending the service life of glass furnaces.

1. Improving the stability of the chemical composition of the product is an important guarantee for the quality of fused cast AZS block materials

The chemical composition of fused cast AZS block materials is one of the key factors that determine its crystal structure and physical and chemical performance indicators. Therefore, effectively controlling the chemical composition of the product is very important for stabilizing and improving the quality of fused cast AZS products.

High-purity raw materials should be selected from the source, especially the main components such as AL2O3, SiO2 , ZrO2 and NaO2. Harmful impurities such as Fe2O3, Ti02, CaO and MgO should be minimized or eliminated. Only in this way can the crystal structure of the product be optimized, and the physical and chemical performance indicators can meet the role of glass furnace in resisting erosion and scouring at high temperature.

Any change in the composition will change the change of its reasonable crystal structure. For example, if the SiO2 content is too high, it will generate mullite crystals with AL2O3 in an alkali-free environment, and this crystal will reduce the glass phase and corundum phase of the crystal structure in the product, thereby destroying the high-performance mineral rock phase structure of the product, making its rock phase structure loose and not tight. Baddeleyite and corundum are exposed and scattered, causing serious erosion of the glass furnace body. Another example is the problem of too high ZrO2 content. ZrO2 has the characteristics of high temperature resistance, high mechanical strength, strong resistance to glass erosion, and good chemical stability, but its thermal stability is very poor at 1000-1200℃. Some people think that a higher ZrO2 content is better, but this may not be the case from the perspective of glass furnace use practice and glass production process. We know that the resistance to glass liquid erosion is not only related to the ZrO2 content, but more importantly depends on the material microstructure, that is, whether the eutectic formed by baddeleyite and corundum is tightly arranged. If the structure is tightly arranged, the erosion resistance is good. Too high ZrO2 will cause the crystal phase structure to be loose, and baddeleyite will scatter into the glass liquid to pollute the molten glass, causing defects in the glass. Such as stones, streaks, bubbles, sand particles, etc., the glass furnace is seriously damaged and the service life is shortened. Therefore, the ZrO2 content in the product is not proportional to the resistance to glass liquid erosion. On the other hand, the high ZrO2 content increases the difficulty of high-temperature melting in the production process of AZS products. It not only increases the melting temperature, but also increases the viscosity of the solution, which adds difficulties to the casting process, and the product is prone to cracking and shrinkage cavities.

In addition, the instability of Na2O composition will also affect the quality of fused cast AZS block products. In particular, harmful components such as Fe2O3, TiO2, CaO, MgO, S, P, etc. are not allowed to exist in the product. The mechanism of its influence on product quality is no longer elaborated. These harmful impurities will affect the changes in the crystal structure of the product, reduce its unique physical and chemical properties, and cause great damage to the glass furnace during use. Therefore, the stability of the chemical composition of the product is not only the premise of quality assurance of fused cast AZS block products, but also an important condition for extending the service life of the glass furnace.

2. The use of advanced product preparation technology, equipment and automatic control means is an important link in improving the quality of fused cast AZS block materials

The crystal phase composition of fused cast AZS block is the concentrated embodiment of its excellent physical and chemical properties. Its crystal phase composition is baddeleyite, corundum and the eutectic of the two. The glass phase generated by this is closely arranged in a beaded shape. Different products have different crystal phase compositions and different physical and chemical properties. This generation process is formed by high-temperature melting in an arc furnace, so that the melt reaches excellent composition homogenization and strict temperature control during casting and annealing. In this important link, China‘s production enterprises currently use oxidation melting method for production. This melting process solves the problem of high carbon content in the product produced by the reduction method used in the past. The high carbon content of the product will increase the porosity of the product, reduce the bulk density and the precipitation temperature of the glass phase, and also reduce the corrosion resistance of the product. At the same time, it increases the bubbles in the glass during the use of the glass furnace, pollutes the glass, and reduces the quality of the glass. The oxidation method is now used to overcome the disadvantages of unstable product quality caused by backward technology in the reduction method, improve the quality of fused-cast AZS products, and correspondingly ensure the service life of the glass furnace.

In addition, in the entire process of preparing fused AZS refractory materials, each process such as mold making, raw material preparation, arc furnace melting, casting and annealing should have strict and scientific operating procedures and standards. Problems in each process and link will have a great impact on product quality. For example, in the oxygen blowing process of high-temperature melting of batch materials in the arc furnace, it is necessary to strictly operate according to process parameters such as oxygen blowing angle, oxygen blowing time, pressure, flow rate and oxygen gun insertion depth. If improper operation occurs in a small link, it will cause the product crystal phase to change and affect the product quality. Others are not elaborated one by one. At the same time, each process should continuously design and adopt advanced automatic control detection means, such as: the batch of raw materials that react in a short time combined with isotope low-energy emission spectrometer and electronic weighing batching system, the detection data of molten liquid, temperature digital controller, melting process TV monitor, high-efficiency batch mixing equipment, mold integration production equipment, mechanized casting equipment, controlled annealing device, etc. A series of high-tech detection means and equipment play an important role in stabilizing and improving the quality of fused cast AZS products. The large-scale adoption of modern high-tech monitoring and testing methods and equipment is a necessary way for the fused cast AZS block products to move towards standardization, integration and modernization.
                                                                     

3. The preparation of high-precision fused cast AZS block product dimensions is also an important condition to ensure the service life of the glass furnace.

The accuracy of the structural dimensions of the glass furnace according to the design requirements is closely related to the accuracy of the fused cast AZS product dimensions, in addition to the quality of the masonry construction. If the product dimensions cannot be guaranteed, the structural dimensions of the glass furnace cannot be guaranteed. During the masonry process of the glass furnace, defects such as skewness, excessive brick joints, uneven brick plane bite, rough surface, and unmatched assembled bricks are prone to occur. This will cause accidents or serious erosion during the glass furnace baking and normal operation of the glass furnace, as well as serious consequences of glass pollution, affecting the service life of the glass furnace. For this reason, the fused cast AZS products must be cold processed. This requires the introduction of new high-efficiency and high-precision cutting machines, plane, bevel and curved surface grinding machines, and drilling and other supporting processing equipment to meet the requirements of the glass furnace structure size for the refractory material dimension accuracy, realize the precise assembly and matching of fused cast AZS products, and provide them to customers according to the requirements of the design drawings.

                 

In order to meet the needs of various high-end glass products in the glass industry, and to narrow the gap with foreign advanced fused AZS products as soon as possible, we still need unremitting hard work, in-depth research and exploration, especially in the basic theory, in-depth research and experiments are needed, especially the optimization composition of fused cast AZS refractory products, melting reaction process, annealing crystallization process, glass phase content, lead corundum segregation mechanism, product damage mechanism under different operating environments, etc., a lot of meticulous and hard work needs to be done. In order to improve our current production process as soon as possible, further improve product quality, develop new varieties and reasonable and scientific matching and use of glass furnaces, extend the service life of glass furnaces, and improve the quality of glass products, provide a scientific and reliable basis.

In short, the quality of fused AZS refractory materials and the service life of glass furnaces are interdependent. Although it is related to other factors, the use of fused AZS products in the high temperature zone of the melting part of the glass furnace is the only choice at present and in the future. The high temperature zone of the melting part is the key to the service life of the glass furnace, so both should be given equal attention. We firmly believe that high-quality and multi-variety new refractory materials made from fused cast AZS block materials will surely be presented to people and make positive contributions to the greater development of the glass industry.

Henan SNR Refractory Co., Ltd. is dedicated to the manufacturing research and development of fused cast AZS refractory materials and bonded refractory materials for the glass industry. Meanwhile, SNR can provide total solutions and services for glass furnace design, glass furnace construction, renovation, and upgrading. Please contact me if you have any requirements.

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