China Henan Rongsheng Xinwei New Materials Research Institute Co., Ltd Company News

Currently, refractory materials made from andalusite generally include the following four types: Fired bricks Unfired bricks Refractory fibers Unshaped refractory materials, such as castables, ramming materials, and casting sands. In China’s metallurgical industry, most Al₂O₃-SiO₂ series refractories experience volume shrinkage under high-temperature conditions. This shrinkage limits their performance and lifespan under high-temperature loads, thermal shock, and slag corrosion. However, the slight expansion property of andalusite improves these weaknesses, enhancing their durability.   Additionally, while China is rich in high-alumina bauxite resources, their high impurity content often leads to melting under high temperatures. Adding andalusite to bauxite increases the mullite phase, altering the matrix mineral composition and microstructure, thereby raising the load-softening temperature of the material. Consequently, refractory materials made from andalusite are primarily used in the metallurgical industry, specifically in the following areas: Blast Furnaces: Used for furnace tops to resist CO corrosion. Hot Blast Stoves: For furnace walls, checker bricks, furnace tops, and combustion chambers. Iron Tapholes: Includes taphole clay for sealing and coatings or ramming materials for the iron trough. Mobile Torpedo Ladles: For lining permanent layers and working layers with fired and unfired products, ensuring the optimal performance of andalusite-based SiO₂-C composite working layers. Iron Ladle Cars: For lining permanent and working layers. Tundishes: For permanent linings and replaceable linings, as well as for preparing low-cement and ultra-low-cement refractory castables containing finely crushed andalusite. Reheating Furnaces: For furnace walls and roofs using plastics and ramming materials. Auxiliary Equipment: Includes bricks for steel casting nozzle bases, blowing stopper heads, stirring tuyere bricks, anchoring blocks, and burner bricks for reheating furnaces, along with protective refractory coatings and low-cement refractory castables for burners.   Unshaped refractories with general purposes (including materials requiring high stability and cement based on andalusite) form mullite at relatively low temperatures (1350°C), which creates a "strong welding" effect on product surfaces.   Additionally, andalusite-based high-temperature materials find widespread applications in: Aluminum Industry: Pre-baked anode cells Glass Industry: Reheating furnaces Ceramic Industry: Kiln furniture Cement Industry: Rotary kilns   Andalusite is also used in the production of multiphase composite materials (e.g., andalusite-silicon carbide composite materials) and insulating ceramics.

Currently, the common methods to reduce the high-temperature erosion of magnesia-carbon bricks can be summarized as follows:   1. Using High-Quality, Stable Materials Select stable, high-quality materials to enhance erosion resistance, thermal shock resistance, and structural spalling resistance.   Use high-purity and premium fused magnesia, which features large grains, high density, low chemical activity, and excellent erosion resistance. It also resists self-destructive reactions with carbon at high temperatures, thereby suppressing slag erosion on MgO particles.   Increase MgO content while reducing impurities, especially limiting SiO₂ content, to minimize silicate phases in the structure. This reduces high-temperature side reactions, such as the reaction between SiO₂ and graphite, preventing carbon oxidation.   Improve the crystallinity of MgO to prevent grain boundaries from transforming into liquid phases at high temperatures, thus stopping slag penetration into magnesia-carbon bricks. Similarly, increasing the purity of graphite can enhance slag resistance. Higher-purity graphite improves thermal shock resistance and high-temperature flexural strength. Typically, graphite with more than 95% carbon content is used. Higher purity results in fewer silicate phases, which reduces decarburization reactions and the formation of low-melting phases in the presence of alkaline slag.   Add appropriate amounts of antioxidants and select high-quality thermosetting binders to improve the high-temperature performance of magnesia-carbon bricks. 2. Optimizing Slag Composition Increase MgO content in the slag to saturation levels to minimize the dissolution of MgO. As MgO is an alkaline oxide, increasing slag alkalinity reduces the chemical reaction between slag and magnesia, thereby mitigating chemical erosion.   Reduce FeO and other elements in the slag that may react chemically to limit oxidation of MgO and graphite . 3. Adopting External Protective Measures Form a protective layer on the surface of magnesia-carbon bricks to prevent contact with slag, thereby inhibiting the physical penetration and chemical erosion of molten steel/slag into the refractory. Techniques like slag splashing can protect the furnace. Utilize external fields, such as electric fields, magnetic fields, or ultrasonic fields, to protect magnesia-carbon bricks. Among these, the cathodic protection method using external electric fields is a novel technology for combating high-temperature erosion by molten steel/slag, which has garnered significant attention from researchers in recent years.

The hearth and bottom of a blast furnace should adopt a structure made entirely of carbon bricks or composite carbon bricks, using high-quality carbon bricks for construction. For large blast furnaces, the use of carbon bricks and SiC bricks is crucial for extending furnace lifespan. With the adoption of copper cooling walls, the weak point for longevity has shifted from the lower furnace body, belly, and waist to the hearth area. Therefore, prolonging the hearth's lifespan has become a key focus in achieving a long service life for blast furnaces.   In recent years, several blast furnaces in China have experienced increased water temperature differences or even burn-through in the hearth, requiring comprehensive measures to address these issues. High-quality carbon bricks and blocks used in blast furnaces should meet conventional performance standards while also fulfilling requirements for thermal conductivity, permeability, oxidation resistance, alkali resistance, and resistance to molten iron erosion.   The tuyere area is recommended to use a composite brick structure, typically corundum-mullite bricks, brown corundum bricks, or hot-pressed carbon bricks like NMA or NMD. Common causes of erosion in the hearth include mechanical abrasion from coke and slag, chemical corrosion, oxidation by water vapor, attack from zinc and alkali metals, and thermal stress damage. To address these issues, blast furnaces can adopt microporous carbon bricks with high thermal conductivity and strengthen cooling measures on the hearth’s cooling wall. This ensures that the solidification temperature of slag and molten iron (1150°C) remains within the carbon bricks, keeping it away from the cooling wall. Currently, there are three basic structures for hearths and bottoms in domestic and international blast furnaces: Large carbon bricks with a ceramic pad. Hot-pressed small carbon bricks with a ceramic pad. Large or small carbon bricks with a ceramic cup at the bottom. All three structures have proven to enhance furnace lifespan. High thermal conductivity carbon bricks, microporous carbon bricks, and ceramic pad structures have been widely adopted.   In high coal-injection blast furnaces, operations emphasize maintaining an active hearth center while ensuring an appropriate bottom center temperature. As a result, attention has shifted to the thermal resistance of the ceramic pad and improving its lifespan to achieve suitable bottom center temperatures.   Theory of Solidified Layer Formation via Enhanced Cooling: The use of refractory materials with high thermal conductivity (18.4 W/(m·K) at 600°C, 60-80 W/(m·K) at 20°C) on the hearth sidewall, combined with intensive cooling, prevents slag and molten iron penetration. These materials also offer high alkali resistance, absorb thermal stress, and rapidly transfer heat to the cooling water through an efficient water-cooling system. This creates a stable solidified protective layer on the hot surface of the refractory lining (with isothermal lines above 1150°C), forming an "iron shell" on the hearth bottom and resisting sidewall erosion caused by "elephant foot" effects.   The key to hearth longevity lies in the thermal conductivity of the hearth sidewall materials. The focus is on selecting materials with excellent thermal conductivity, impermeability, and resistance to annular cracking. Proper maintenance emphasizes cooling effectiveness, monitoring water temperature differences on the cooling wall, and injecting grout into porous areas.   The integrated bottom with cooling is considered a reasonable structure. It includes carbon ramming material above the cooling pipes and 2-3 layers of carbon bricks. Different parts require carbon bricks with specific properties. Below the tap hole, microporous carbon bricks with high impermeability should be used, while SiC bricks with high thermal conductivity should be used for the furnace bottom's lowest layer. Other areas may use standard or microporous carbon bricks.   Incorporating longer carbon bricks below the furnace bottom perimeter beneath the tap hole enhances resistance to molten iron and alkali metal penetration and erosion. The gaps between bricks should be reduced to less than 0.5 mm for construction.   Regarding the "ceramic cup" structure, academic opinions are divided. Some argue that the ceramic cup plays a significant role and should be strengthened, while others believe it will eventually deteriorate, leaving the carbon bricks as the primary structure. High-density, hot-pressed small carbon bricks with resistance to molten iron penetration and high thermal conductivity can also be used on the hearth sidewall.   Both approaches have advantages and disadvantages, and either can achieve a long furnace lifespan, though with differing economic costs. The adoption of high-quality microporous and ultra-microporous carbon bricks, as well as hot-pressed small carbon bricks, has significantly improved the lifespan of blast furnaces in China. Most medium and large blast furnaces in China have abandoned ramming carbon material bottoms and self-baking production processes.

Purchasing the right refractory castables requires careful consideration of multiple factors. Below are some key steps and recommendations: Understand the Application Environment Identify the equipment or process where the refractory castables will be used, including operating temperature, chemical environment (e.g., acidity or alkalinity), and mechanical stresses. Select appropriate refractory aggregates, powders, and binders based on the application. For example, high alumina bauxite is suitable for high-temperature zones, while magnesia is ideal for alkaline environments. Determine Process Requirements Choose castables based on physical properties like particle size and density according to the specific process requirements. Consider the characteristics of the casting method, such as self-flowing, vibration, or compaction, to select suitable materials. Consider Material Costs Refractory castables vary widely in price. Balance cost considerations with durability and service life for long-term economic benefits. Avoid focusing solely on price; prioritize materials that offer better performance and longevity. Inspect Material Quality Check the shelf life and manufacturing date of the refractory castables to ensure they are within the usable period. Examine the material’s appearance, including color, texture, and gloss, as reputable brands typically exhibit consistent quality standards. Verify particle size, shape, and strength to ensure they meet usage requirements. Choose Reputable Brands and Suppliers Opt for well-known brands and suppliers with a strong market reputation to ensure quality and reliable after-sales service. Assess the supplier’s technical support capabilities and responsiveness to address potential issues during use. Refer to Experience and Case Studies Leverage past experience and successful case studies from similar equipment and processes to inform material selection and casting solutions. This approach can improve accuracy, reduce trial-and-error costs, and increase success rates. Consider After-Sales Service Select vendors offering excellent after-sales services, including effective quality guarantees and technical support. Reliable after-sales support can ensure optimal material performance, construction quality, and timely resolution of issues. In summary, purchasing the right refractory castables involves evaluating the application environment, process requirements, material costs, quality, brand reputation, experience, and after-sales service. A thorough assessment and strict quality control ensure that the selected materials perform excellently under high-temperature conditions, meeting the demanding requirements of industrial production.

Extending the service life of castables is key to ensuring the long-term and stable operation of kilns and other equipment. Here are some effective measures and methods: 1. Proper Material Selection and Design Choose materials based on the operating environment: Different working conditions of kilns (e.g., temperature, chemical erosion, physical impact) require refractory materials with specific properties. In highly corrosive environments, select refractory materials with high corrosion resistance. For areas subject to significant mechanical impact, use materials with high toughness. Opt for low-expansion coefficient raw materials: The thermal expansion coefficients of aggregates and matrix materials should match the working conditions of the kiln to reduce thermal stress caused by temperature fluctuations. 2. Optimizing Construction Quality Maintain a clean construction environment: Before construction, ensure the work environment, tools, and equipment are clean to prevent contamination of the refractory materials. Follow construction instructions strictly: Adhere to the specified guidelines for refractory castable installation. Prepare the site and required tools and materials according to design dimensions. Focus on construction methods: Key steps include uniform mixing, appropriate vibration, accurate casting, and proper curing to ensure the density and uniformity of castables. Use specialized mixing equipment and control mixing time to avoid material wear or unevenness. Vibrate using a vibrating rod to eliminate air bubbles and increase the density of the castables. Minimize construction joints: During construction, reduce the occurrence of joints. If necessary, design sectional joints in a stepped shape to minimize stress concentration. 3. Enhancing Curing and Baking Proper curing: Curing allows the binder in the castable to set and harden, achieving sufficient initial strength. Curing methods include natural curing and steam curing, depending on the type of binder and construction environment. Appropriate baking: Baking removes excess moisture from the castables and promotes sintering at high temperatures, enhancing physical properties. The baking process should follow a specified heating curve to avoid excessively fast or slow temperature changes. 4. Implementing Protective Measures Apply anti-expansion asphalt: Coat metal components in contact with or encased by castables with anti-expansion asphalt to allow the metal to expand freely without exerting pressure on the castables. Surface protection: Applying waterproof coatings prevents moisture penetration. Additional surface protection measures can be implemented as needed to extend the service life of castables. 5. Regular Inspection and Maintenance Inspection items: Regularly check the surface condition of castables, the stability of anchoring components, and the sealing of joints. Maintenance actions: Address any issues promptly, such as repairing cracks, replacing damaged anchoring components, or resealing joints. 6. Controlling Kiln Operating Conditions Reduce start-stop cycles: Minimize the number of kiln start-stop cycles to reduce thermal shocks to the castables. Control temperature changes: During start-up and shutdown, heat up slowly to avoid drastic temperature changes that may cause thermal fatigue in the castables. Control the chemical environment: Regulate the kiln’s chemical environment to prevent damage to refractory materials caused by chemical erosion. In conclusion, extending the service life of castables requires efforts in material selection and design, construction quality, curing and baking, protective measures, regular inspection and maintenance, and controlling kiln operating conditions. By implementing these measures, the long-term stable operation of kilns and other equipment can be ensured.

1. Blast Furnace and Iron Ladle for Blast Furnace Iron (1) Blast Furnace The blast furnace is a thermal equipment used for accumulating, storing, and maintaining a constant temperature (1250–1300°C) while uniformly mixing iron components. The blast furnace is lined with refractory materials. The primary cause of damage to the refractory lining is the infiltration of molten iron into the cracks between bricks, along with brick lifting, slag erosion, and spalling. Depending on the slag’s alkali content, magnesia bricks, magnesite olivine bricks, or high-alumina bricks with high alumina content are used. When the slag has a low alkali content, aluminosilicate products are used. When the slag contains Na₂O > 2%–3%, aluminosilicate products become porous and are damaged. In such cases, magnesia bricks or magnesite olivine refractory materials are used. Special attention must be given to the life of fire clay, which should have the ability to make brick joints dense. Acidic blast furnace linings are generally made of silica bricks. (2) Iron Ladle for Blast Furnace With the increase in steel production, the blast furnace, as a storage vessel for molten iron, has lost its specific function and is replaced by the blast furnace type iron ladle, as shown in Figure 11-2. The operating conditions for refractory materials in the iron ladle are similar to those in the blast furnace. From the perspective of stress on the ladle material, it involves the even distribution of load across two supporting beams. Even a slight bending of these beams can cause mechanical load stress of 0.2 MPa or higher on certain areas of the lining. This condition results in creep limitations for the applied refractory materials. It is suggested that under a 0.2 MPa load at 1300°C, the creep rate should not exceed ≥0.03%/h. When using tar-impregnated refractories, the lifespan of the ladle lining is significantly improved. The ladle lining generally consists of three layers: working layer, protective layer, and thermal insulation layer. With the development of molten iron pretreatment technology, the blast furnace-type ladle is used not only as a tool for transporting liquid iron from the blast furnace to steel-making equipment but also as a container for out-of-furnace refining, including desulfurization of molten iron. Lime is used as the desulfurizing agent, which is blown into the molten iron and mixes with the subsequent gas in the nitrogen stream. In such cases, magnesia or alumina-silicon carbide refractories are used for the lining of the iron ladle. When using calcium carbide for desulfurization of molten iron, a tar-bonded, non-burning magnesia-calcium product lining is used, yielding good results. In Japan, desulfurization, dephosphorization, and desiliconization are performed inside the ladle using Al₂O₃-SiC-C products with good results. In China, high-alumina bricks impregnated with pitch, or those with added SiC or C, or both, are used to enhance resistance to erosion and thermal shock. Some use dolomitic refractories.   2. Coke Oven The coke oven has a complex refractory masonry structure. The most critical part of the masonry is the combustion chamber wall. It operates under the following conditions: during coking, the temperature is about 1300°C with minimal variation; the coking temperature starts at 500–600°C during the coking cycle and rises to 1200–1250°C at the end of coking. At the same time, the temperature at the center of the coke cake reaches 1100°C. The chamber width is 400–450 mm, and the coking period lasts for 14–17 hours. For normal operation of the coke oven, it is essential to maintain high gas tightness of the walls and furnace masonry. The refractory masonry also bears compressive stress due to both the mass of the masonry itself and the weight of the coal charging cars on top of the furnace. Only silica bricks may meet these conditions. Coke ovens that use silica bricks may last up to 40 years. However, silica bricks have relatively low thermal conductivity under coking temperatures, approximately 1.9 W/(m·K), and due to their high volatility, the temperature should not exceed 1250°C. More efficient refractory materials to replace silica bricks are currently in the development stage. For example, there are proposals for magnesia-silica products for wall structures, and experiments with silicon carbide bricks, corundum refractories, and iron-containing silica bricks are underway. Refractory castables (large wall panels) are also used to replace complex-shaped small block products.   3. Direct Ironmaking Refractories The process of directly producing iron from ore results in sponge iron, granular iron, or liquid iron, which is heated in a reducing gas medium (H₂, CO), mainly to reduce iron oxide to metallic iron. The production of sponge iron is carried out at temperatures below 1000°C in a vertical furnace. Ordinary clay refractories can be used in these furnaces. The reduction gas is produced using natural gas (CH₄) and converted in a specialized gas heater based on a regenerative principle. The gas heater, structurally similar to a blast furnace hot blast stove, uses nickel as a catalyst for natural gas conversion. The grid of the gas heater plays a key role as a catalyst and operates under variable temperatures and gas media, working under conditions that transition from oxidation to reduction. The issues that arise here involve the thermal shock resistance of refractories and their chemical stability with respect to the catalyst. According to relevant data, Al₂O₃-C bricks and MgO-Cr₂O₃ products show better performance. Since the molten iron smelting process is a new technology still under development, the refractory materials used are also being explored.   4. Iron Ore Sintering Furnace Refractories In order to enhance metallurgical production, various methods have been adopted, including the configuration of equipment for the pre-heat treatment of iron ore raw materials: conveyor belt-type sintering machines and roasting machines; grate plate-tube furnaces-ring coolers. Combined equipment includes vertical furnaces, fluidized bed furnaces, and other thermal equipment. Furnace linings are primarily made of high-alumina products with an Al₂O₃ content of 85%, various compositions of refractory castables, and insulating materials such as mullite, silica boards, perlite bricks, or refractory fibers. Damaged refractory linings are repaired and patched using spray methods to extend their lifespan.

(1) Operating Conditions for Refractory Materials Electric arc furnaces, which use the arc between the electrode tip and the charge material as the heat source for steelmaking, are characterized by unique conditions for refractory material usage. The development of direct current (DC) arc furnaces, high-power operation, bottom gas stirring, and bottom tapping have been introduced in recent years. The furnace roof is built with magnesia-chrome or magnesia-spinel refractory materials, which exhibit excellent stability against basic slags, metals, and silicate melts. However, the operating conditions for refractories in this environment are quite severe, dictated by the specifics of arc melting.   The arc melting process is approximately twice as fast as the open-hearth process, subjecting refractories to frequent temperature changes and prolonged high temperatures. During the charging phase, the furnace roof is removed, exposing it to uneven heating, with the temperature at the center significantly higher than at the periphery. This uneven heating is exacerbated by the irregular nature of the working arc. Consequently, the center of the roof deteriorates quickly. For instance, in a 100-ton furnace, the central roof section erodes at a rate of 4 to 4.4 mm per heat, compared to 2 to 2.6 mm per heat at the edges. This uneven wear leads to uneven bulging of the roof and, occasionally, brick spalling.   In DC arc furnaces, the single-electrode design eliminates hot spots, and the water-cooled roof area is expanded, slightly improving refractory conditions. However, as furnace capacity increases and specific power rises, the working conditions for the roof become even harsher. Furnace roofs are circular and often built using fan-shaped arches or ring bricklaying techniques. Bricks are laid without binders or cement, secured by metal spacers with sharp ends. Openings for electrodes, gas extraction, and oxygen injection reduce the roof's weight. In some cases, the areas around these openings are cast using high-alumina cement or phosphate-bonded castables. Measures are also taken to eliminate electrical short circuits.   The service life of furnace roofs for furnaces with capacities below 100 tons is typically 60–120 heats, while larger furnaces with capacities above 100 tons achieve 60–80 heats. Total refractory consumption for an electric furnace per ton of steel is approximately 10–12 kg, with the roof accounting for 6–7 kg. (2) Selection of Roof Refractories The choice of refractory materials for electric arc furnace roofs is still evolving. Although MgO-Cr₂O₃-based refractories offer high resistance to slag and metals, their load-softening temperature is relatively low. Another drawback of basic refractories is their significant thermal expansion at high temperatures, which can cause brick joints to crack and the roof to deform. To prevent joint cracking, a mix of fired and unfired bricks is used, allowing shrinkage to offset the expansion of fired bricks. Some literature suggests combining fired and metal-coated unfired magnesia-chrome products.   Innovative refractory materials for furnace roofs are being tested, including corundum-chromite, mullite-corundum, and combinations of basic and high-alumina materials. Special attention is paid to chromium-containing refractories, as spalling of chrome bricks may introduce chromium into the steel, which is not permissible for certain grades of steel.   With advancements in metallurgical technologies such as atomic energy furnaces, continuous casting machines, and large electric arc furnaces, the role of electric furnaces in steelmaking is expected to grow significantly. Electric furnaces offer advantages over open-hearth and converter furnaces, including flexibility in adjusting steel composition and producing various steel grades. This expansion is also economically favorable due to the continuous increase in scrap metal availability.   In China, high-alumina bricks are commonly used for furnace roofs, with ramming mixes applied around the center and electrode holes of smaller furnace covers. However, with the development of large ultra-high-power electric furnaces, the service life of high-alumina bricks has declined, prompting further use of basic bricks.   (3) Application of Water-Cooling Technology The development of modern electric steelmaking is closely linked to the adoption of high-power transformers, ensuring unit power levels of 600–800 kV·A/t during the melting phase. Preheating of charge materials, oxygen injection into the molten bath, and heating the furnace with gas-oxygen burners are among the advanced features. Artificially cooled components are increasingly used to replace portions of refractory linings.   During intensive oxygen supply to the molten bath, dust formation (15–40 g/m³) increases the optical density of the gaseous medium, turning its blackness close to 1. This nearly completely obscures the molten bath and furnace roof, reducing the roof temperature. Slag-forming roofs and walls incorporate various water-cooled structures, with movable cooling shields protecting wall hot spots.   The introduction of artificially cooled components has led to new electric arc furnace designs, reducing the ratio of refractory lining surface area to metallic surface area. Improved heat exchange conditions lower the heat load on the molten bath, which increases as the refractory lining is reduced or eliminated. Structures with adjustable lining development allow for horizontal water-cooled roofs that can move downward along water-cooled walls as the melting process progresses.   The use of artificial cooling in steelmaking furnaces removes limitations imposed by thermal loads and lining temperatures, creating conditions for intensified smelting. Although water-cooled structures slightly increase electricity consumption, the reduction in downtime and increased productivity enhance overall economic efficiency. Refractory material consumption is significantly reduced (almost to the minimum), electrode consumption per unit is lowered by 15%, and the heavy manual labor associated with refractory bricklaying is reduced.   Experimental development of furnaces with water-cooled lining components has shown that the energy and cost savings in related industries (refractory production, transportation, electrode manufacturing, etc.) exceed the additional energy costs associated with water-cooled equipment.

The Reasons Why Refractory Bricks Can Withstand High Temperatures The ability of refractory bricks to resist high temperatures can be analyzed from the following aspects: 1. High Refractoriness of Raw Materials The raw materials used to produce refractory bricks are typically natural minerals, such as bauxite, silica, and magnesite. These materials inherently have high refractoriness, forming the foundation for manufacturing refractory bricks. Bauxite: Processed bauxite is used to produce aluminosilicate refractory bricks. Its main component, alumina, has a refractoriness of up to 1780°C, along with strong chemical stability and excellent physical properties. Silica: The raw material for silica refractory bricks is silica, with SiO₂ as the main component. Higher SiO₂ content correlates with higher refractoriness. Silica bricks are made by combining natural silica with a small amount of mineralizer, then firing at high temperatures to achieve high strength at elevated temperatures. Magnesite: Magnesite, the main raw material for producing magnesia refractory bricks, primarily consists of MgO. Magnesium oxide has excellent refractory insulation properties and, after high-temperature calcination, forms crystalline structures with refractoriness exceeding 2000°C. 2. Characteristics of Inorganic Non-Metallic Materials As inorganic non-metallic materials, refractory bricks derive their functionality from the inherent properties of their raw materials. These materials are typically characterized by high compressive strength, hardness, resistance to high temperatures, and corrosion resistance. These traits ensure that refractory bricks remain stable in high-temperature environments, resisting softening, deformation, or melting. 3. Influence of Manufacturing Processes The production process plays a significant role in determining the high-temperature resistance of refractory bricks. Key stages include shaping, drying, and firing. High-Temperature Sintering: During the firing process, refractory bricks undergo high-temperature sintering to form a dense structure with enhanced mechanical strength. Generally, higher firing temperatures and longer durations improve the high-temperature performance of refractory bricks. However, excessively high temperatures or prolonged firing can alter the crystalline structure, potentially impacting performance. Process Control: Precise control of manufacturing processes and parameters is crucial for ensuring the excellent thermal resistance of refractory bricks. 4. High-Temperature Treatment of Finished Products The finished bricks are subjected to high-temperature treatment in tunnel kilns, reaching temperatures above 1500°C. This process further enhances the thermal resistance of the refractory bricks by densifying their structure, enabling them to better withstand erosion in high-temperature environments.   In conclusion, the ability of refractory bricks to resist high temperatures relies on the high refractoriness of raw materials, the properties of inorganic non-metallic materials, the influence of manufacturing processes, and the high-temperature treatment of finished products. These factors work together to ensure that refractory bricks remain stable and perform well in high-temperature environments.

Refractory Materials for Furnace Construction Refractory materials for furnace construction are essential components for building industrial kilns and furnaces. They can withstand high temperatures while maintaining the structural integrity and thermal efficiency of the furnaces. Below is a detailed introduction to these materials: 1. Classification Refractory materials for furnace construction are primarily divided into two categories: shaped refractory products and unshaped refractory materials. Shaped Refractory Products: These include refractory bricks and blocks, which come in fixed shapes and sizes, ready for direct use in furnace construction. Unshaped Refractory Materials: These include refractory castables, plastics, spray coatings, and ramming materials, which can be cast, rammed, or sprayed on-site to form the desired refractory layer. 2. Common Materials and Applications Refractory Bricks Fireclay Bricks: Widely used for general furnace linings, walls, floors, and flues, with an operating temperature range of 1250–1400°C. High Alumina Bricks: Suitable for high-temperature, abrasion-resistant areas or load-bearing sections of furnaces, burner blocks, and other special areas, with a temperature range of 1300–1450°C. Insulating Firebricks: Available in fireclay and high-alumina types, these are used for furnace linings not exposed to molten slag or corrosive gases, with operating temperatures of 1150–1300°C and 1200–1300°C, respectively. Unshaped Refractory Materials Dense Unshaped Refractory Materials: Refractory castables are used for furnace linings exposed to flame, pre-cast hangers, and more. Steel-fiber-reinforced castables offer excellent thermal stability, mechanical impact resistance, and abrasion resistance, with operating temperatures of 1000–1200°C. Pure calcium aluminate cement castables are suitable for temperatures up to 1650°C, often used in secondary reformer linings. Heat-resistant, abrasion-resistant castables are designed for specific furnace sections requiring high temperature, abrasion, and erosion resistance, with temperatures up to 1250°C. Insulating Unshaped Refractory Materials: Silicate and aluminate cement insulating castables are used as insulation layers in uniquely shaped furnace linings. Refractory ceramic fiber materials, such as castables, sprays, and plastics, feature low thermal conductivity, lightweight, and good volumetric stability, making them ideal for furnace backing layers and hot air duct linings. 3. Material Selection When selecting refractory materials for furnace construction, factors such as operating temperature, atmosphere, slag properties, and furnace structure must be considered. For example: In highly reducing atmospheres, materials with strong reduction resistance should be chosen. For areas subject to mechanical impact and abrasion, materials with superior wear resistance and mechanical impact properties are ideal. 4. Construction and Maintenance Proper construction and maintenance of refractory materials are critical to the performance and lifespan of furnaces. During construction, ensure accurate mixing, casting, ramming, or spraying of materials following relevant standards. For maintenance, regularly inspect refractory layers for wear and erosion, and promptly repair or replace damaged sections.   In conclusion, refractory materials for furnace construction come in a wide variety. Selecting the right materials, adhering to proper construction techniques, and ensuring routine maintenance can guarantee the safe and efficient operation of furnaces.

Magnesia-Alumina-Iron Spinel Bricks: Characteristics and Performance Characteristics High-Quality Raw Materials: Magnesia-alumina-iron spinel bricks are made using high-purity magnesia, fused magnesia, and iron-alumina spinel as the primary raw materials, supplemented with free Al₂O₃ and Fe₂O₃. The excellent physical and chemical properties of these materials provide a solid foundation for the high performance of these bricks. Specialized Manufacturing Process: The production process involves high-pressure molding and high-temperature sintering, ensuring the product’s density and strength. These techniques also contribute to superior microstructure and overall performance. Performance Outstanding Corrosion Resistance: The magnesia and iron-alumina spinel components exhibit high chemical stability, effectively resisting erosion by silicate melts at high temperatures. Additionally, a dense Fe-rich layer forms around the iron-alumina spinel particles, further enhancing the corrosion resistance. Excellent Thermal Shock Resistance: The differences in thermal expansion coefficients among the various phases create a network of microcracks within the brick. These microstructures absorb and release thermal stress, significantly improving resistance to thermal shock. This ensures high stability and prolonged service life under high-temperature conditions. Superior Coating Formation: Magnesia-alumina-iron spinel bricks react with cement clinker during operation, forming a dense layer of calcium aluminate on their surface. This protective layer prevents further penetration of the liquid phase and enhances resistance to clinker erosion. Additionally, the brick's microstructure supports "mechanical anchoring" by allowing molten kiln materials to infiltrate, thereby stabilizing and strengthening the coating layer. Low Thermal Conductivity: Compared to directly bonded magnesia-chrome bricks, these bricks exhibit lower thermal conductivity. This reduces heat loss through the kiln lining and minimizes heat transfer to the kiln shell, thereby lowering the shell surface temperature. These properties enhance kiln efficiency and contribute to energy savings. Environmentally Friendly: Magnesia-alumina-iron spinel bricks eliminate chromium-related pollution in cement production. They do not release harmful substances during manufacturing or use, making them environmentally friendly. In conclusion, magnesia-alumina-iron spinel bricks offer exceptional corrosion resistance, thermal shock resistance, excellent coating performance, low thermal conductivity, and eco-friendly properties. These advantages make them indispensable high-performance refractory materials for cement kilns and other high-temperature industrial furnaces.