Compactness of Magnesia-Aluminum Spinel Rich in Magnesium Oxide

Application of magnesia-alumina spinel bricks in cement kilns. At present, the chromium-free measures taken by the new dry process cement kiln are mainly to replace magnesia-chrome bricks with magnesia-dolomite bricks, magnesia-alumina spinel bricks, and magnesia-iron-alumina spinel bricks (referred to as magnesia-iron bricks). Its kiln lining performance is very outstanding, and it is the best material to replace magnesia-chrome bricks in domestic cement kilns.

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The magnesia-alumina spinel bricks produced by introducing ferroalumina spinel into magnesia refractory materials provide a new lining concept for cement rotary kilns. Its good structural flexibility and excellent kiln lining performance provide it with high adaptability. In recent years, magnesia-alumina spinel bricks have been fully used in the high-temperature zone of cement rotary kilns. Rongsheng refractory manufacturer can provide high-quality magnesia refractory brick products for cement kilns, including magnesia-dolomite bricks, magnesia-alumina spinel bricks, and magnesia-alumina spinel bricks. Contact Rongsheng for a free quote.

Material Properties of Magnesia-Alumina Spinel

Magnesia-alumina spinel is one of the most important refractory materials in the steel and cement industries. It has gradually replaced chromium spinel and is also a popular refractory material in the above fields. However, magnesium-chromium alloys and Al2O3-chromium alloys are gradually decreasing due to the environmental hazards of hexavalent chromium. Magnesium-alumina spinel has excellent refractory properties such as high refractoriness, moderate thermal expansion, thermal shock stability and resistance to slag erosion.

The densification of spinel by primary firing requires very high temperatures (>1700℃) because the oxide composition is accompanied by a 7% volume expansion during the spinel formation process. On the other hand, the expansion during the spinel formation process is beneficial for Al2O3-MgO-C (AMC) bricks. Because the expansion during the in-situ spinel formation process minimizes the gaps between bricks and prevents metal infiltration.

The formation and sintering of spinel have been studied by different researchers by changing the raw materials and processing steps. Mansour et al. pointed out that the most spinel is formed when the calcination temperature of raw materials MgCO3 and Al(OH)3 is 900℃ and 1100℃ respectively. Gray believes that hydroxide contributes to the formation of spinel and the densification of magnesium-aluminum spinel. Kostic et al. found that fine grinding of raw materials will increase its specific surface area and increase its structural defects, which will lead to the formation of low-temperature spinel.

Magnesia-Rich Magnesia-Alumina Spinel

Magnesia-rich magnesia-alumina spinel is mainly used in cement kilns because of its compatibility with the products of cement formation process. Compactness of MgO-rich magnesia-aluminum spinel. Alper in the study of MgO-Al2O3 binary system showed that the solubility of MgO in the spinel phase was 39%. Bailey et al. found that the presence of excess MgO in the spinel phase would restrict the growth of spinel grains and promote sintering. Cooper et al. found that 40% MgO in magnesia spinel bricks would improve its thermal and corrosion properties. India has a large reserve of magnesia ore, which contains impurities such as CaO, SiO2 and Fe2O3 that limit its application at high temperatures. In the present study, natural magnesia ore has harmful impurities SiO2 and CaO. As a magnesia-rich magnesia-alumina spinel aggregate, it was developed and compared with the aggregate prepared by synthetic calcined magnesia.

Dense Magnesium Aluminate Spinel

Through various experiments, researchers have a unique understanding of dense magnesium aluminate spinel bricks.

1) The density of sintered spinel generated by Salem magnesite (SS) increases sharply between 1400℃ and 1500℃, followed by a slight decrease at higher temperatures due to liquid phase sintering. The spinel generated by caustic magnesia (NS) densifies slowly below 1500℃, followed by an improvement in density at 1600℃. The NS sample is densified by solid phase sintering.

2) X-ray diffraction analysis of the SS sample sintered at 1600℃ shows that spinel and periclase are the main phases, and forsterite is the secondary phase. This is because SiO2 exists in natural magnesite, while the NS sample only contains periclase and spinel phases.

3) As the temperature increases from 1500℃ to 1600℃, the flexural strength of the NS sample increases due to its more compactness. However, compared with the SS sample sintered at 1500℃, the flexural strength of the SS sample sintered at 1600℃ is lower, which is due to the presence of the low melting point phase and the uneven particle size distribution.

Manufacturer of Magnesia Alumina Spinel Bricks for Cement Kilns

Magnesia-alumina spinel bricks are made of high-purity magnesia sand and pre-synthesized magnesia-alumina spinel as the main raw materials and are made after reasonable grading, high-pressure molding, and high-temperature firing. Rongsheng is a manufacturer of magnesia-alumina spinel bricks for cement kilns. Magnesia-alumina spinel bricks are characterized by high purity, high strength, corrosion resistance, low linear expansion coefficient, and good thermal shock resistance. They are ideal refractory materials for the transition zone of cement rotary kilns.

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Production of Magnesium Aluminum Spinel Bricks

The amount of magnesium aluminate spinel added to the ingredients of magnesium aluminate spinel brick production is not the more the better. With the increase of spinel amount, the thermal shock resistance becomes better. However, due to mismatched expansion, the strength (especially flexural strength) will decrease. Taking Al2O3 as the standard, the Al2O3 in the product should not be greater than 15%~20%, and 10%~18% is preferred. The main impurity in magnesium aluminate spinel bricks is SiO2, which should not be greater than 1.5%.

Over the past thirty years, people have been pursuing technologies to replace magnesium chrome bricks to eliminate hexavalent chromium pollution, and first placed their hopes on periclase spinel bricks. When spinel bricks entered China with the introduction of six new dry kilns at a price of more than $1,000 per ton, China saw a fever for spinel bricks. The initial reports were optimistic, but gradually different news came from the cement plants: “It can’t hold the kiln skin.” It turns out that the eutectic temperature of spinel bricks and cement is close to (slightly lower) the firing temperature of cement, which is fatal. Therefore, spinel bricks retreated 15~20m in the lining of Chinese cement kilns and reached the upper transition zone. They occupied the position of high-alumina bricks or ordinary magnesia-chrome bricks.

Regardless of M-A series or M-K series products, the academic community agrees that Fe2O3 affects the product’s resistance to atmosphere changes. One of the explanations for the superiority of spinel bricks over magnesia-chrome bricks in the upper transition zone is that the Fe2O3 content is lower than that of M-K series products. However, Yoshiki Tsuchiya of Japan added 4% Fe2 O3 to spinel bricks to improve the brittleness of the bricks. The expansion rate is only 1.13% at 1000℃, the flexural strength is 12MPa, and the wear is 30mm in 8 months in the area of ​​3840m of φ5.0SP kiln. The wear of commonly used spinel bricks is 80~120mm, and it is said that this high iron brick can hang on the kiln skin when used in the firing zone.

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Performance Advantages of Spinel Bricks

Spinel bricks are better than ordinary magnesia-chrome bricks in thermal shock resistance, R+ alkali corrosion resistance, acidic gas corrosion resistance, and atmosphere change resistance. However, for refractory bricks used in transition belts and unloading belts on cement kilns, should also have low thermal conductivity, good wear resistance, and high shear fracture resistance. It determines the availability of spinel bricks. China has been using spinel bricks for about 20 years. The most basic problem exposed is the high cylinder temperature. The cylinder temperature of a 200~220mm thick kiln lining will rise to 350℃ or even close to 400℃ within 100 days of operation. The wear resistance is poor, and it is rare to be able to operate stably for more than 8 months on a 2500t kiln.

The ingredients of periclase spinel bricks in my country use sintered high-purity magnesia sand, medium-grade magnesia sand, and synthetic spinel sand (SiO2 0.6%~2.0%). The thermal shock resistance index is generally more than 10 times, and the best ones are more than 20 times. However, the high-temperature flexural strength is low (1400℃, 0.5h), which is roughly 23MPa, and most products are less than 3MPa. This is a technology that spinel bricks need to improve. Spinel bricks for cement kilns. Magnesium-aluminum spinel bricks for cement kilns.

The advantages of spinel bricks are good thermal shock resistance. During use, they react with clinker to form a very thin calcium aluminate protective layer on the surface of spinel bricks. It makes the liquid phase difficult to penetrate, and the anti-stripping performance is better than that of directly bonded magnesia-chrome bricks. When used in the cooling zone and transition zone of the cement kiln, the service life is doubled compared to that of directly bonded magnesia-chrome bricks. However, it is slightly inferior to directly bonded magnesia-chrome bricks in terms of corrosion resistance. At the same time, spinel bricks are easy to hydrate, have a large thermal conductivity, and the kiln shell temperature is higher than when using directly bonded magnesia-chrome bricks.

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Application of Rongsheng Magnesium Aluminum Spinel Brick in the Transition Zone of Cement Rotary Kiln

Magnesium aluminum spinel brick is a product made of high-purity magnesia sand and pre-synthesized magnesium aluminum spinel as the main raw materials, after reasonable grading, high-pressure molding and high-temperature firing. It is characterized by high strength, corrosion resistance, low linear expansion coefficient, and good thermal shock resistance. It is an ideal refractory material for the transition zone of cement rotary kiln.

Bauxite-based sintered magnesium aluminum spinel uses high-quality alumina with an Al2O3 content of more than 76% and high-quality light-burned magnesium powder with an MgO content of more than 95%. After a multi-stage homogenization process, it is sintered at a high temperature of more than 1800°C in an ultra-high temperature tunnel kiln. It has a large volume density, a high mineral phase content, good grain development, uniform structure, and stable quality. Magnesium aluminum spinel has good erosion resistance, strong corrosion and spalling ability, good slag resistance, abrasion resistance, good thermal shock stability, and high temperature resistance. It is a magnesium aluminum spinel brick for the high temperature zone of the rotary kiln for producing cement. It is also an ideal raw material for refractory products such as ladle lining bricks and ladle castables. Magnesium-aluminum spinel is widely used in refractory materials, steel smelting, cement rotary kilns and glass industrial kilns.

It has good erosion resistance, abrasion resistance and thermal shock stability. Its main uses: First, it replaces magnesia-chrome sand to make magnesia-aluminum spinel bricks for cement rotary kilns, which not only avoids chromium pollution, but also has good spalling resistance. Second, it is used to make ladle castables, which greatly improves the erosion resistance of steel plate linings. It is widely used in refractory materials for steelmaking.

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Product Characteristics of Rongsheng Magnesium Aluminum Spinel Bricks

1. Excellent kiln skin performance.
2. Low thermal conductivity (1000℃, 2.27w/m·k), small thermal expansion coefficient.
3. Excellent structural flexibility. The alkali salts of K2SO4, Na2SO4, NaCl, and KCl decomposed from cement materials have strong anti-corrosion and anti-penetration capabilities.
4. High load softening temperature and excellent thermal shock resistance. Suitable for key parts of SP and NSP kilns with high kiln temperature, fast rotation speed, strong alkali corrosion ability, and heavy mechanical load. It can effectively extend the life of the furnace lining and maintain a low kiln shell temperature.

Rongsheng Magnesium Aluminum Spinel Brick for Sale from Manufacturer

Rongsheng Refractory Manufacturer, Magnesium Aluminum Spinel Brick is a refractory material with a high melting point, small thermal expansion coefficient, low thermal conductivity, good thermal shock stability and strong corrosion resistance. Magnesium aluminum spinel brick belongs to isometric crystal system minerals, and high-purity magnesium aluminum spinel brick is colorless. Magnesium aluminum spinel crystals formed under natural conditions have good chemical stability, so they are commonly found in drifting sand deposits. Magnesium aluminum spinel crystals with pure composition do not hydrate or react with acid. Magnesium aluminum spinel bricks are made of light-burned magnesium powder, industrial alumina, or high-quality inkstone clay, and are made after cooperative melting, cooling and crushing. The advantages of magnesium aluminum spinel bricks are good crystal development, large grain size, dense structure, and strong corrosion resistance. To purchase high-quality magnesium aluminum spinel bricks for cement rotary kilns, please contact Rongsheng for free samples and quotations.

How Castable Gunmix Does Furnace Patching and Maintenance

In industries that rely heavily on high-temperature operations, such as steel manufacturing, foundries, and cement plants, maintaining the integrity and efficiency of furnaces is crucial. Over time, the intense heat, thermal cycling, and exposure to corrosive materials can cause wear and tear on the furnace linings. To ensure that these furnaces continue to operate efficiently and safely, regular maintenance and patching are essential. One of the most effective solutions for this is the use of Castable Gunmix. In this blog post, we’ll explore how Castable Gunmix is utilized for furnace patching and maintenance, and why it is an indispensable tool for industries dealing with high-temperature processes.

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What is Castable Gunmix?

Castable Gunmix is a type of refractory material specifically designed for repairing and maintaining high-temperature industrial furnaces. Refractories are materials that can withstand extremely high temperatures without degrading. Castable Gunmix is a mix of refractory aggregates, binders, and additives that can be applied using a gunning machine, making it easier to repair worn-out or damaged areas in a furnace lining.

Unlike traditional refractory bricks, which require precise cutting and placement, Castable Gunmix can be applied directly to the affected areas, ensuring a quick and efficient repair process. This method of application not only saves time but also reduces labor costs and minimizes downtime, which is crucial in industries where furnace availability is key to production.

The Role of Castable Gunmix in Furnace Patching

Furnace patching is a vital part of furnace maintenance, as it addresses localized damage that, if left untreated, could lead to more extensive repairs or even complete furnace failure. Castable Gunmix plays a critical role in this process due to its unique properties and application method.

Flexibility in Application: Castable Gunmix can be applied to various furnace linings, including those with complex shapes and hard-to-reach areas. The gunning process allows for precise application, ensuring that the material adheres well to the existing lining and forms a strong bond. This flexibility is particularly important for patching cracks, spalls, and other localized damage that may not warrant a full lining replacement.

High-Temperature Resistance: One of the most important characteristics of Castable Gunmix is its ability to withstand high temperatures. Depending on the specific formulation, Castable Gunmix can resist temperatures well above 1000°C (1832°F). This makes it suitable for use in furnaces operating under extreme conditions, where other materials might fail.

Thermal Shock Resistance: Furnace linings are often subjected to rapid temperature changes, which can cause thermal shock and lead to cracking or spalling. Castable Gunmix is designed to have excellent thermal shock resistance, meaning it can absorb and dissipate the stresses caused by sudden temperature fluctuations. This property helps extend the life of the furnace lining and reduces the frequency of repairs.

Abrasion and Corrosion Resistance: In many industrial processes, furnace linings are exposed to abrasive materials, molten metals, and corrosive gases. Castable Gunmix is formulated to resist these harsh conditions, ensuring that the patched areas remain intact and functional for longer periods. This resistance to abrasion and corrosion is particularly valuable in industries like steelmaking, where furnace linings are constantly under attack from molten slag and other aggressive substances.

Ease of Installation: The gunning process for applying Castable Gunmix is relatively straightforward and can be performed by trained personnel with minimal disruption to the furnace operation. This ease of installation is a significant advantage, as it allows for quick repairs that minimize downtime and keep the furnace running at optimal capacity.

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The Maintenance Benefits of Using Castable Gunmix

Regular maintenance of industrial furnaces is essential to ensure their longevity and efficiency. By incorporating Castable Gunmix into the maintenance routine, industries can reap several benefits:

Extended Furnace Life: By addressing minor damages promptly with Castable Gunmix, industries can prevent small issues from escalating into major problems that require costly repairs or even furnace replacement. Regular patching with Castable Gunmix helps extend the overall life of the furnace lining, reducing the need for frequent and expensive overhauls.

Reduced Downtime: Downtime in industrial operations can be incredibly costly. The quick and efficient application of Castable Gunmix allows for repairs to be completed in a fraction of the time compared to traditional methods. This means that furnaces can be back in operation sooner, minimizing production losses and maximizing efficiency.

Cost-Effective Solution: Castable Gunmix offers a cost-effective solution for furnace maintenance. The material itself is relatively inexpensive, and the gunning process reduces labor costs and the need for extensive preparation. Additionally, the longer lifespan of the repaired linings translates to lower maintenance costs over time.

Improved Safety: A well-maintained furnace is a safer furnace. By using Castable Gunmix to patch and maintain furnace linings, industries can reduce the risk of catastrophic failures that could lead to accidents, equipment damage, or even loss of life. Regular maintenance with Castable Gunmix ensures that the furnace operates safely and reliably.

Importance of Furnace Maintenance

In high-temperature industries, the importance of furnace maintenance cannot be overstated. Castable Gunmix provides an efficient, cost-effective, and reliable solution for patching and maintaining furnace linings. Its unique properties, including high-temperature resistance, thermal shock resistance, and ease of application, make it an indispensable tool for industries that rely on continuous furnace operation.

By incorporating Castable Gunmix into their maintenance routines, industries can extend the life of their furnaces, reduce downtime, lower maintenance costs, and improve overall safety. As the demands on industrial furnaces continue to increase, the role of Castable Gunmix in furnace patching and maintenance will only become more critical. Whether you are in steel manufacturing, cement production, or any other high-temperature industry, investing in regular maintenance with Castable Gunmix is a smart choice that will pay off in the long run.