The development direction of refractory materials for glass kiln

According to a report from the European Glass Association, global flat glass production was 52 million tons in 2014, approximately 10,000 tons per week. China's production accounts for 50% of the world's production, and other major producers are located in countries and regions such as Europe, North America, ASEAN, Japan, CIS, and South Africa.

Since the reform and opening up, China's raw material industry has developed rapidly, and the output of steel, cement and flat glass industries has grown rapidly. Around 2012, the steel, cement, and glass industries have successively experienced overcapacity problems. After 2012, the output of flat glass, cement, and steel no longer increases or even decreases, which means it has entered the “new normal”.

The steel, cement, and glass industries are major users of refractory materials. Because steel, cement, and glass companies have repeatedly pushed down prices and defaulted on payment, many refractory companies are in a difficult situation. Therefore, refractory companies need to work hard to innovate, improve the quality of existing products, improve the level of after-sales service, and develop new products in order to win the leadership of negotiations and the right to speak in sales.

On the one hand, the traditional market is no longer growing; on the other hand, traditional technology is also difficult to improve. For traditional materials with few opportunities, there is still room for improvement. Through market segmentation, in-depth analysis, precise positioning, etc., we will open up a promising “blue ocean” in the “red ocean” where refractory materials for glass kilns are highly competitive.

2 Brief introduction of the development of refractories in China

Due to differences in raw material, fuel, power, and labor costs, the price of refractories in China is only one-third that of Japan and one-half that of the United States. If the quality is not much different, domestic refractories can replace foreign ones. Even if the quality is different, foreign materials can be used in the key parts of the kiln, and domestic materials can be used in other parts, so that the cost can be greatly reduced without affecting the service life. For this reason, on the one hand, foreign companies frequently initiate anti-dumping; on the other hand, they strengthen research and development, trying to occupy the commanding heights of science and technology, and lead the development of refractory materials.

In the 1980s, some foreign factories realized a high degree of automation and preliminary intelligence. For example, a plant with an annual output of 50,000 tons of Refra has only 100 employees and uses computer-aided formulation design. With the development of IT, foreign companies are more adopting CAX (CAD computer-aided design, CAE computer-aided engineering analysis and CAM computer-aided manufacturing) to improve the manufacturing level of refractory materials. In the 1990s, the China Institute of Building Materials analyzed the refractory materials used in Jidong and Handan Cement Plants. The results show that: (1) The quality of imported materials is stable, and almost all properties meet the requirements; the quality of domestic materials is unstable, some performances meet the standards, and some do not meet the standards; 2) The imported materials have accurate external dimensions and almost no internal damage; domestic materials the dimensions are inaccurate, and a few have hidden cracks.

In recent years, Chinese refractory companies have greatly improved their equipment. In the manufacturing process of refractory materials, important links such as ingredients, forming and firing have gradually been automated, and the quality of refractory materials has been significantly improved. In the future, it is necessary to strengthen the online inspection and sorting of bricks and brick materials. In addition, Chinese-funded enterprises need to improve the level of using CAX, such as the research and development of non-standard refractory equipment. General equipment can be purchased in the market, but special equipment needs to be developed by itself. At present, China has made great progress in computer-aided process design, not only has published many papers, but also published monographs. With the help of a computer, the information in the test and production data can be extracted, through modeling, analysis and optimization of the process, and find the problems in the production, thereby improving product quality.

3 Fused cast refractories for glass kilns

3.1 Overview of casting materials

The world-renowned manufacturers of fused cast refractories include Saint-Gobain's Syrp, RHI A and Asahi Glass. SIP has acquired Cohart of the United States, Toshiba Monofrax of Japan, and has two subsidiaries, CUMI and Beijing SIP, in India and China. RHI AG owns two brands, Monofrax (USA) and Refl (I). As a large number of refractories made in China enter the world market, the profit margins of foreign fused cast refractories have been squeezed. The fusion cast AZS material was the most affected, followed by the fusion cast Al2O3, and the fusion cast ZrO2 material was also affected. On the one hand, fusion casting is less restricted by molds, which facilitates the manufacture of large-scale products, which is beneficial to reduce the erosion of brick joints and along brick joints; on the other hand, the apparent porosity of fusion casting materials is very low, and it is difficult for molten glass to penetrate into the material. Therefore, the fusion casting material has incomparable corrosion resistance than ordinary sintered refractory materials. However, the corrosion resistance of different fused refractory materials is still very different, and the refractory materials should be used reasonably according to the kiln location and material properties. Below 1400 ℃, the corrosion rate of all casting materials is very small; above 1400 ℃, the order of corrosion resistance is: Cr2O3- Al2O3, 41#AZS, 36#AZS, 33#AZS, α-Al2O3, α-β -Al2O3. Due to the coloring properties of Cr2O3, the melting part of the glass furnace adopts 33", 36" and 41" fused cast AZS bricks for comprehensive masonry. Generally, 41# fused cast AZS is used for harsh parts, 36# fused cast AZS is used for eroded middle parts, 33# Fusion-cast AZS is used in relatively mild parts; the breast wall of the cooling part can be made of β-Al2O3 bricks, and the pool wall and bottom tiles of the cooling part can be made of α-β-Al2O3 fused-cast bricks. In recent years, domestic and foreign manufacturers, especially foreign companies, have greatly improved the fusion casting The ZrO2 content of the wrong corundum material, such as increasing the ZrO2 content of 33#AZS to 34% -35% (w); increasing the ZrO2 content of 36#AZS to 37% ~ 39% (w); increasing the ZrO2 content of 41*AZS To 43% -45% (w).


3.2 The relationship between the composition, structure and performance of the fused cast zirconium corundum material

In the fused-cast zirconia corundum material, zirconia has the effect of improving the corrosion resistance; the glass phase has the effect of helping the melting when melting, relaxing the thermal stress and reducing the harm of zirconia phase transformation when cooling. The key point of the process of fusing and casting zirconium corundum refractories is to evenly distribute the primary zirconia with suitable particle size and shape in the glass phase with suitable composition and quantity, so that the primary zirconia and the glass phase can cooperate with each other and protect each other; this can make the melting and casting Corundum refractories have higher zirconia content, lower glass phase content and higher manufacturing qualification rate. For this reason, it is necessary to improve the automation level of equipment and optimize the molding, melting, casting and annealing processes.

3.3 New varieties of fused cast refractories

With the promotion of oxy-fuel combustion technology, the concentration of alkali vapor in the flame space of the glass furnace has increased greatly, which severely corrodes the refractory materials in the upper space of the glass furnace. Corroded refractories enter the molten glass in the kiln, causing stones, streaks and bubbles, which affect the quality of the glass. Therefore, low-exudation fused cast refractories have been developed, and their performance indicators are shown in Table 1.

It can be seen from Table 1 that the content of Na2O in 36# AZS is 0.4% (w) lower than that of 33# AZS, so the glass phase content is reduced from 21% to 14% (w). Therefore, it is necessary to add more expensive desiliconized zirconium in the batching, increase the smelting temperature when melting, and control the cooling rate of the bricks when cooling. These measures significantly increased production costs, but the amount of glass phase exudation was only reduced from 1.5% to 0.7% (w). However, ER2001 adopts the opposite technical route, which greatly reduces the content of ZrO2, increases the content of A12O3, and especially increases the content of Na20. Since the content of ZrO2 was reduced from 33% to 17% (w), the manufacturing cost was greatly reduced; the amount of glass phase exudation was reduced from 1.5% (w) to 0, which greatly improved the anti-exudation performance. According to the Al2O3-SiO2-ZrO2 ternary phase diagram, when cooling, ER 2001 first precipitates corundum, and secondly, corundum and mullite are precipitated at the corundum-mullite connection; however, because of Na2O3. The content is relatively large, only corundum is precipitated; finally corundum and oblique zircon are precipitated at the lowest eutectic point. Due to the incomplete crystallization of zirconia, the remaining zirconia can increase the viscosity of the glass phase; because the fine zirconia is distributed in the glass phase, the flow of the glass phase is restricted. Therefore, the amount of glass phase exudation is zero.

3.4 New molding process of flame casting refractories

Recently, domestic manufacturers of fused cast refractory materials have transplanted the casting industry to improve the manufacturing level of fused cast refractory materials, such as resin sand, investment mold, lost foam and V method casting.

Resin sand adopts phenolic resin or suranic resin as binding agent. For example, raw sand is mixed with thermoplastic phenolic resin, urotropine, calcium stearate, etc. to form coated sand, which is molded and heat-treated to form a model. The advantages of resin sand molding are: high production efficiency, high model strength, high model accuracy, and few casting surface defects; disadvantages: high resin prices and environmental pollution.

Investment casting and lost foam casting are suitable for manufacturing special-shaped casting materials. Investment casting is also called "lost wax casting": paraffin wax is made into castings, coated with refractory materials, after solidification, the wax is poured out after heating, and then heat treated to form a model. In the case of lost foam casting, the foam is used to make a mold, and the refractory is dipped into a sand box that can be vacuumed. The foam is filled and compacted with molding sand, and then covered with a plastic film and vacuumed. When casting, the foamed plastic is heated to vaporize quickly, the vapors are pumped away, and the melt is cooled to form refractory materials. Because the melt contacts the plastic during casting, the lost foam is not suitable for manufacturing zirconia corundum materials.

The V method is a molding method named after Vacuum’s initials, that is, the vacuum sealing molding method. The V method was born in Japan in the late 1960s and was introduced to China in 1974. At present, hundreds of foundries in China have used the V method for production. The advantages of the V method:
1) High surface accuracy of castings;
2) Small machining allowance for castings, which is conducive to saving processing man-hours, power consumption and material consumption;
3) Saving raw materials and labor costs, the recovery rate of molding sand can reach 95%, power And the labor consumption is about 60% of wet molding;
4) Because the gas generated during molding and casting is pumped away by the vacuum pump, the pollution is small and the working environment is improved.

.Silicon refractory materials for glass kiln

In the 1980s, China introduced the manufacturing technology of advanced silica bricksfor glass kilns from the United States. In order to be different from the original products, the products manufactured with imported technology are called high-quality silica bricks. After adopting the oxy-fuel combustion technology, the service life of silica bricks has been drastically reduced from 5 to 10 years to 2 to 3 years. Rat holes and erosion are the main causes of damage. The rat hole is caused by the alkali in the leaking gas from the kiln condensing on the joints of the bricks to corrode the silica bricks. The methods to improve the life of silica bricks are as follows:

(1) Improve the dimensional accuracy of the bricks. The cracks between the bricks are narrowed, the kiln air leakage is less, the erosion is light, and the mouse hole is also small.

(2) Reasonably design the kiln lining structure so that the condensation temperature section of the alkali is moved to the sealing layer behind the silica brick.

(3) Use low-calcium silica bricks or high-purity silica bricks with good corrosion resistance.

5Alkaline refractory materials for glass kiln

5.1 The configuration of refractory materials in the regenerator of the glass furnace

Generally, the uppermost layer of the regenerator lattice body uses high-grade magnesia bricks, w(MgO) >97%; the upper layer uses medium-grade magnesia bricks, w(MgO) is about 95% -96%; the middle layer uses directly combined with magnesia bricks; the lower layer uses Low-stomata clay bricks.

The important properties of the lattice body are corrosion resistance and creep resistance. To improve the creep resistance, it is necessary to use high-purity, low-iron, low-porosity and large-grain raw materials, and use high temperature to fully sinter. The stability and heat exchange effect of cylindrical checker bricks are better than those of bar checker bricks. For example, the specific heat transfer area of ​​cylindrical bricks is 16 m", while that of bar bricks is only 10.4~12.7 m".

6 Conclusion

Both the glass industry and the refractory industry are traditional industries, but neither are they sunset industries. Therefore, the research and development of refractory materials for glass kilns should be carried out from the following aspects:

(1) Market segmentation. The fused cast refractories were divided into materials for pool bottom, pool wall and upper structure, and found the insufficiency of previous research on upper structure materials, and developed low exudation fused cast corundum refractories°

(2) In-depth analysis. Analyze the damage mechanism of the silicon bricks on the road roof, find out the mechanism of the formation of rat holes, and lay the amorphous refractory layer and insulation layer behind the silicon bricks, thereby greatly improving the life of the road roof.

(3) Precise positioning. Improve the purity of the substrate, introduce little CaO, Fe2O3 for mineralization, and prepare high-purity, high-performance silica bricks.

(4) Transplant hybridization. Introducing the vacuum sealing molding method in metal casting into the manufacture of fused cast refractory materials has achieved good results.

(5) Use new technology. Using information technology, through continuous efforts, the computer-aided process optimization method has been developed, which has greatly improved the quality management and R&D level.

(6) Seize the opportunity. According to the fact that glass companies have adopted petroleum coke as an alternative fuel, which has caused a significant decrease in the service life of refractory materials for glass kilns, research and development of new refractory materials for regenerators.

In short, we must seize all opportunities, take all methods, strive to improve technology, improve product quality, increase research and development efficiency, improve after-sales service, gradually build product popularity and reputation, establish a strong brand, and finally realize China Refractory The transformation and upgrading of the materials industry.