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Refractory Ramming Mass Applied to the Inner Walls of Medium-Frequency Electric Furnaces

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Steelmaking furnaces, electric furnaces for non-ferrous metal smelting, and cement rotary kilns quietly sustain the workings of modern civilization through temperatures reaching thousands of degrees. Yet, lining the inner walls of this high-temperature equipment is an unassuming yet vital “armor”—a material that silently withstands searing flames, chemical corrosion, and thermal shock, safeguarding the safety and efficiency of the entire production system. This material is refractory lining. Today, we focus on a specific type: refractory ramming mass used for the inner walls of medium-frequency electric furnaces.

Dry Ramming Mix Material
Dry Ramming Mix Material

What is Refractory Ramming Mass?

Refractory ramming mass is composed of refractory aggregates, powders, binders, and additives mixed in specific proportions; it is applied using a ramming method, hence the name.

It offers excellent plasticity, filling capability, and application flexibility, along with resistance to high temperatures, scouring, chemical erosion, abrasion, and thermal shock. It maintains good volumetric stability at high temperatures and conforms tightly to the furnace structure. It does not require firing during installation and can be put into service after curing via baking. It is suitable for complex, irregularly shaped furnace sections.

The material is mixed on-site and compacted using pneumatic picks or mechanical rammers, with an air pressure of at least 0.5 MPa. Its drawbacks include slow installation speeds and high labor intensity. Refractory ramming mass is widely used for lining smelting furnaces, steelmaking furnace bottoms, induction furnace working linings, and electric furnace roofs. In recent years, carbon-containing refractory ramming masses have seen rapid development and are frequently used in thermal equipment such as blast furnace iron runners, slag runners, and large cupola furnaces.

Classification and Application of Refractory Ramming Masses

Refractory ramming mass is a type of unshaped refractory material that is compacted and formed through external ramming force. Ramming masses for medium-frequency furnaces are classified based on two dimensions—application area and material composition—with specific focuses for each scenario:

Classification and Application by Area of ​​Use

Furnace Lining Ramming Mass: Used for the core lining of medium-frequency furnaces, coming into direct contact with molten metal at high temperatures. Suitable for the main melting chambers of various furnaces, it requires high refractoriness and strong erosion resistance.

Furnace Mouth Ramming Mass: Specifically designed for the furnace mouth area to withstand mechanical impact from frequent charging, high-temperature oxidation, and molten metal splashing. It is ideal for operating conditions where the furnace mouth is prone to wear.

Tapping Spout Ramming Mass: Used for iron or steel tapping troughs to resist the erosive flow of molten metal and thermal shock (rapid heating and cooling). Suitable for medium-frequency furnace production lines involving continuous tapping.

Ramming Material for Intermediate Frequency Furnace
Ramming Material for Intermediate Frequency Furnace

Classification and Application by Material Type

Acidic Ramming Mass: Composed primarily of quartz sand or silica, offering stable chemical properties. Suitable for melting cast iron, ferrosilicon, ferromanganese, and other acidic or low-alloy steels.

Basic Ramming Mass: Composed primarily of magnesia or magnesia-alumina spinel, offering strong resistance to erosion by basic slag. Suitable for melting stainless steel, high-carbon steel, specialty steels, and non-ferrous metals such as copper and aluminum.

Neutral Ramming Mass: Composed primarily of high-alumina bauxite, corundum, or silicon carbide, offering good chemical stability. Suitable for use as a transition layer in multi-metal melting processes or for melting metals with complex compositions that cause moderate lining erosion.

As industrial technology advances, refractory ramming masses continue to evolve. Environmentally friendly ramming masses—featuring low-cement or cement-free bonding—have increasingly become the mainstream choice. These materials not only enhance refractory performance and erosion resistance but also reduce the emission of harmful substances during installation, aligning with the trend toward green industrial development.

Though seemingly ordinary, this humble ramming mass bears the critical responsibility of ensuring the stable operation of medium-frequency furnaces. Standing firm amidst scorching heat, it safeguards the safety and efficiency of every furnace with its robust performance, serving as an indispensable “refractory guardian” in industrial production.

Differences Between Refractory Ramming Masses and Refractory Castables

There are distinct differences between refractory ramming masses and refractory castables regarding production formulation, installation methods, and performance outcomes.

The production processes differ primarily in the type of binder used. Refractory castables typically utilize high-alumina cement as a binder. During installation, a specific amount of water is added; the material is mixed, poured into formwork, and consolidated using a vibrating rod. Castables exhibit good flowability and generally offer superior stability and durability compared to ramming masses. In contrast, ramming masses often employ liquid binders and possess high plasticity. “Bake-out-free” ramming masses utilize resin binders; they require no water addition and are installed using a high-force ramming technique.

The application areas for these two materials also differ. Ramming masses are used to fill gaps between furnace shell cooling equipment and the masonry, or for leveling masonry surfaces. Historically, they were used to fill the gap between the hearth carbon bricks and the cooling staves; however, due to installation challenges that could compromise gap filling, castables are now commonly used for these blast furnace gaps. Nevertheless, bake-out-free ramming masses remain the preferred choice for lining iron runners in front of the furnace. Refractory castables have a wider range of applications; the structural stability and durability achieved through vibration-based installation make them suitable for various furnace linings. Furthermore, the diversity of castable materials—ranging across different grades and composite compositions—allows them to meet a wide array of requirements for furnace lining projects.

In terms of current usage and development trends, refractory castables are employed more frequently than refractory ramming masses, primarily due to their stability and long service life.

 

Application of Corundum-Mullite Castables in the Emergency Repair of Critical Areas of Hot Blast Stoves

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Corundum-mullite castable is a high-performance material for repairing hot blast stoves. Unlike high-temperature sintered refractory bricks, this material—though unsintered—offers superior airtightness, making it particularly suitable for emergency repairs on critical sections of the stove.

When components such as hot blast outlets or combustion ports suffer collapse or damage, traditional repair methods using composite bricks involve multiple stages—including manufacturing and pre-assembly—and struggle to meet rapid repair requirements due to the wide variety of brick types and limited usage volumes. Utilizing corundum-mullite castable for repairs effectively shortens the repair cycle and enhances operational efficiency.

Corundum Mullite Castables
Corundum Mullite Castables

Emergency Repair Process for the Hot Blast Outlet

The hot blast outlet is a critical passage within the hot blast stove, and its structural stability directly impacts operational safety. When a collapse occurs in this area and requires urgent attention, the repair can be carried out using the following steps:

  1. Demolition and cleanup. Systematically remove the collapsed material to ensure the repair zone is clean and safe, thereby preparing the site for subsequent operations.
  2. Reconstruction of the insulation layer. Construct an insulation layer inside the hot blast branch pipe using lightweight bricks to create an effective thermal barrier.
  3. Monolithic casting. After installing the formwork, perform a monolithic cast using corundum-mullite castable material. This process not only enables rapid repair but also ensures a tight connection between the hot blast branch pipe and the hot blast outlet, significantly enhancing the system’s sealing performance.

Emergency Repair Process for the Combustion Port

The combustion port is highly susceptible to damage within the hot blast stove. While the repair process is similar to that of the hot blast outlet, it must meet specific structural angle requirements:

  1. Removal of damaged sections. Clear away collapsed or damaged areas to ensure the repair substrate is intact and solid.
  2. Insulation layer construction. Rebuild the insulation layer using lightweight bricks to maintain the thermal performance of the combustion port.
  3. Sectional formwork and casting.

Implement a two-stage formwork process in the composite brick zone and perform a monolithic cast. Upon completion of the casting, ensure the structure achieves a 25° inclination angle to meet the original design specifications.

Emergency Repair Procedures for Other Areas

Corundum-mullite castables can also be used for emergency repairs in areas such as the straight sections of the hot blast stove’s main wall, the composite brickwork of the hot blast dome, and the connection points between the hot blast branch pipe and the furnace shell. When localized deformation or burn damage occurs in these areas and affects normal production, the following repair methods may be employed:

  1. Removal of damaged structures. Remove the damaged heavy brickwork and ensure the repair area is clean and free of debris.
  2. Repair of the insulation layer. Reconstruct the original insulation layer using lightweight mullite bricks to restore thermal insulation performance.
  3. Surface treatment. Apply asphalt paint to the surface of the lightweight bricks to enhance corrosion and water resistance.
  4. Sectional monolithic lining installation. After erecting the formwork, install a monolithic lining in sections using corundum-mullite castable to complete the repair of the damaged upper sections of the hot blast stove.
Castable Refractory Construction
Castable Refractory Construction

Drying and Operational Management

Repaired areas—such as the hot blast outlet, combustion port, and hot blast branch pipe—must undergo a drying process strictly in accordance with the established drying curve. The drying procedure is crucial for fully realizing the performance potential of the corundum-mullite castable and directly impacts the service effectiveness of the repaired sections. Only after thorough drying can the repaired areas achieve optimal durability and stability, allowing for a transition to normal operation and ensuring the safe, efficient functioning of the hot blast stove.

How can the thermal shock resistance of corundum-mullite castables be improved?

Among high-temperature refractory materials, corundum-mullite castables are characterized by high load-softening temperatures and excellent creep resistance. However, pure corundum products exhibit suboptimal thermal shock resistance due to their high thermal expansion coefficients, whereas pure mullite products have lower thermal expansion coefficients and better thermal shock stability.

How can the thermal shock resistance of the castable be enhanced?

Corundum-mullite castables are composed of a composite of mullite and corundum. A mixture with a mullite-to-corundum mass ratio of 75:25 corresponds to the composition point in the SiO₂-Al₂O₃ phase diagram where a eutectic reaction occurs at 1840°C. Regarding thermal shock resistance, the mismatch in thermal expansion coefficients between mullite (which has a lower coefficient) and corundum (which has a higher coefficient) within the composite material generates micro-cracks. These micro-cracks increase the energy absorbed during fracture, thereby enhancing the castable’s thermal shock resistance.

While a composition at the eutectic point affects creep resistance, it is precisely at this ratio that the creep rate is minimized. When the mullite-to-corundum ratio is around 75:25, the aggregate significantly influences the product’s thermal expansion coefficient and the degree of thermal expansion mismatch. Under thermal shock stress, existing micro-cracks propagate, and transgranular fracture occurs within the aggregates, consuming a large amount of energy. This process inhibits the propagation of major cracks and influences the thermal shock stability of the corundum-mullite castable.

Improving the thermal shock resistance of castables

Of course, corundum castables can also exhibit excellent thermal shock resistance; differences in thermal shock stability arise from variations in the ratio of aggregate to binder. The coefficient of thermal expansion of corundum-mullite castables significantly influences their thermal shock stability; interestingly, micro-cracks resulting from thermal expansion mismatch can actually enhance the material’s thermal shock resistance.

In summary, a mullite-to-corundum ratio of 75:25 in the formulation yields optimal thermal shock stability. An apparent porosity of approximately 20% is highly beneficial for the thermal shock stability of the castable. Therefore, maintaining the apparent porosity of corundum-mullite castables at around 20% can further improve their thermal shock stability.

 

Why is Adhesive Tape Wrapped Around Metal Anchors Used for Refractory Castables?

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The primary purpose of wrapping tape (typically plastic electrical tape) around metal anchors used in refractory castables is to provide space for thermal expansion, thereby preventing the castable from cracking due to thermal stress during heating.

Key Reasons

Significant Difference in Thermal Expansion Coefficients: The coefficient of thermal expansion for metal anchors (such as Q235B steel or 310S stainless steel) is far higher than that of refractory castables. Metals expand significantly at high temperatures; if in direct, rigid contact with the castable, this expansion generates immense tensile stress, leading to cracking or even spalling of the castable.

Refractory Anchors For Furnace Lining
Refractory Anchors For Furnace Lining

Tape as a Temporary Expansion Gap: Wrapping the anchor with tape 1–5 mm thick (or applying a coating of asphalt, paraffin, etc.) creates an isolation layer during installation. During the furnace dry-out or initial heating phase, the tape (or coating) burns off or volatilizes, leaving a small void that allows the metal anchor to expand freely, thus preserving the structural integrity of the castable.

The thickness of the tape wrapping is determined by a combination of the furnace’s operating temperature and the anchor layout density, and it is closely related to the metal anchor’s high-temperature linear expansion coefficient.

Alternative methods include coating the metal anchors with asphalt paint or fitting them with plastic protective caps.

Installation of Refractory Anchors
Installation of Refractory Anchors

Why do kilns and furnaces constantly require repair?

In high-temperature industries such as cement, power generation, metallurgy, and chemicals, kiln and furnace maintenance is an unavoidable issue. Furnace linings suffer continuous wear and tear from high temperatures, dust, erosion, and frequent thermal shock. Consequences range from localized spalling requiring minor repairs to complete shutdowns and total relining. A single major overhaul can halt operations for days or even weeks, leading to a compounding of production losses, energy waste, and maintenance costs.

Many equipment and technical managers face a common puzzle: despite selecting “top-brand” refractory bricks, they still encounter problems like brick detachment, flame leakage, and service lives that fall short of expectations. The answer often lies not in the bricks themselves, but in the traditional masonry method—combining bricks with mortar—which inherently creates thousands of joints. These joints are precisely the weakest links in the entire lining. To fundamentally solve this problem, we turn to today’s featured solution: castables.

What are castables?

To put it simply: if refractory bricks are like “prefabricated panels,” then castable refractories are “high-temperature concrete” designed specifically for industrial equipment. Supplied as a mixture of loose aggregates and powders, the material is mixed with water on-site, then poured into molds or pumped directly to the installation area. After vibration for compaction and subsequent hardening and curing, it bonds firmly with the equipment to form a seamless, monolithic, high-temperature protective layer.

Technically speaking, castables are classified as “monolithic refractories.” Because they bypass the brick-pressing stage, they are not constrained by brick shapes and can be molded into structures of any complexity. They consist of four basic components:

  • Aggregates: Refractory particles such as high-alumina bauxite or corundum; these act as the “skeleton,” determining strength and erosion resistance;
  • Powders: Finely ground refractory powders that fill the voids between aggregates, increasing density;
  • Binders: Most commonly calcium aluminate cement; these react with water to bond the aggregates and powders into a solid, cohesive mass;
  • Additives: Small amounts of water reducers, dispersants, accelerators, anti-explosion fibers, etc., used to precisely tune construction and performance characteristics.
Construction of Furnace Lining Refractory Castable
Construction of Furnace Lining Refractory Castable

Principles of Industrial Refractory Castables

Core working principle: Transforming from “a bag of powder” into “a protective shell.” The process by which castables function can be summarized in three stages.

  • Step 1: Mixing and casting. Water is added according to the manufacturer’s specified ratio, and the mixture is mechanically mixed into a slurry. It is then poured into formwork or pumped to the installation site. An immersion vibrator is used to expel air, ensuring the material fills every corner and preventing the formation of voids or weak points.
  • Step 2: Curing and hardening. Upon contact with water, the calcium aluminate cement undergoes hydration; the resulting hydration products interlock, causing the slurry to harden gradually over a period ranging from a few hours to a day. After demolding, moisture-retention curing is required to allow full strength development—a step that lays the foundation for all subsequent performance characteristics.
  • Step 3: High-temperature sintering. Before the furnace is put into operation, the temperature must be raised slowly according to a specific heating curve to first drive off free and chemically bound water. As the temperature rises further, a ceramic-bonding reaction occurs between the powder and the binder, ultimately forming a stable, dense, ceramic-bonded structure capable of withstanding high temperatures.

The key to this entire process lies in “monolithic integrity.” Traditional brick linings are assembled from individual bricks, making the joints inherent weak points; shrinkage and cracking at high temperatures allow slag, molten aluminum, and alkali vapors to penetrate, often leading to brick detachment, aluminum seepage, and flame leakage originating at these joints. In contrast, castables are poured as a single, seamless unit. They offer superior sealing and structural integrity, allowing complex areas—such as furnace roofs, nozzle zones, corners, and pipe openings—to be formed in one piece without the need to cut and shape custom bricks.

Illustration of the monolithic lining after casting: seamless and uniformly dense.

Applications of Industrial Refractory Castables

Refractory castables are suitable for use across virtually all high-temperature industries:

  • Cement Industry: High-wear areas such as rotary kiln transition zones, kiln inlets/outlets, kiln hood assemblies, preheaters, and tertiary air ducts.
  • Power Industry: Cyclone separators, loop seals (return legs), refractory belts, and ignition burners in circulating fluidized bed (CFB) boilers.
  • Metallurgical Industry: Linings for aluminum melting/holding furnaces, heating furnace roofs and walls, ladle covers, and iron runners.
  • Chemical & Petrochemical Industries: Linings for reformers, cracking furnaces, and gasifiers.

A simple rule of thumb for determining suitability: if the operating temperature exceeds 600°C, the component geometry is complex, or the application requires a seamless, airtight structure, there is almost certainly a suitable castable solution available.

Summary of Refractory Castable Essentials

Composition: Castables consist of aggregates, fines, binders, and additives. As unshaped (monolithic) refractories, their primary advantage lies in seamless, monolithic installation—eliminating the joints found in brickwork.

  • Water Content is Critical: While excess water improves flowability, it causes a drastic drop in strength and abrasion resistance; strict adherence to the mixing ratio is mandatory.
  • Curing and Dry-out Are Essential: Do not remove formwork or apply loads before hardening is complete. Dry-out must follow a specific heating curve; otherwise, trapped moisture cannot escape, leading to explosive spalling during heat-up.
  • Selection Criteria: Consider three key factors—operating temperature, corrosive media, and operating conditions. For example, areas in frequent contact with molten aluminum require materials that are non-reactive with aluminum and resistant to aluminum penetration.
  • Common Misconception: “Higher grade” does not always mean “better”; the best material is the one that is best matched to the specific operating conditions.

 

Lime Kiln Models and Refractory Bricks for Key Components

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A lime kiln is a piece of equipment used for lime production; the specific models and the refractory brick materials employed vary depending on the production process and kiln structure. The following information outlines common lime kiln models, along with details regarding the refractory brick materials typically used in specific sections—including alumina content, bulk density, mass, and refractoriness.

Lime kiln refractory brick Construction
Lime kiln refractory brick Construction

Types of Lime Kilns and Refractory Bricks Used

Vertical Kiln

High-alumina bricks are typically used for the kiln lining. For instance, Grade I high-alumina bricks have a high alumina content (generally above 75%) and a relatively high bulk density (approximately 2.5–2.8 g/cm³). They are heavy, weighing around 4.6–4.9 kg per brick, and offer high refractoriness, capable of withstanding temperatures above 1790°C. Their advantages include high refractoriness, wear resistance, and erosion resistance, making them suitable for high-temperature environments. Disadvantages include a relatively high price, high thermal conductivity, and poor thermal insulation performance.

Lightweight insulating bricks can be used for the kiln roof. Diatomite bricks, for example, have a low alumina content (generally below 30%) and a low bulk density (approximately 0.6–1.0 g/cm³). They are lightweight, weighing around 1–2 kg per brick, with a lower refractoriness range of 1000–1300°C. Their advantages include excellent thermal insulation, effectively lowering roof temperatures and reducing heat loss. Disadvantages include low strength and poor wear resistance.

Rotary Kiln

High-alumina bricks or silica bricks are commonly used for the kiln lining. The alumina content and bulk density of the high-alumina bricks are similar to those used in vertical kilns. Silica bricks have a high silica content (generally above 93%) and a low bulk density (approximately 1.8–2.0 g/cm³). They are lightweight, weighing around 2–4 kg per brick, and offer high refractoriness, capable of withstanding temperatures above 1600°C. Their advantages include good thermal stability and the ability to withstand rapid temperature fluctuations. Disadvantages include a high price and poor resistance to alkalis.

Lightweight insulating bricks are generally used for the kiln roof. Alumina hollow sphere bricks, for example, have a high alumina content (generally above 60%) and a low bulk density (approximately 0.8–1.2 g/cm³). They are lightweight, weighing around 1–2 kg per brick, and offer high refractoriness, capable of withstanding temperatures above 1800°C. Its advantages include excellent thermal insulation, high refractoriness, and high strength; their disadvantage is the relatively high cost.

Sleeve Kiln

High-alumina bricks or mullite bricks are commonly used for the kiln lining. The alumina content and bulk density of high-alumina bricks are similar to those used in shaft kilns. Mullite bricks have a higher alumina content—typically around 70%—and a higher bulk density of approximately 2.6–2.8 g/cm³. They are heavier, weighing about 3–5 kg per brick, and offer high refractoriness, capable of withstanding temperatures above 1750°C. Their advantages are high refractoriness and good thermal shock resistance; their disadvantage is the relatively high cost.

Lightweight insulating bricks or ceramic fiber modules can be selected for the kiln roof. The properties of lightweight insulating bricks are similar to those used for rotary kiln roofs. Ceramic fiber modules have a lower alumina content (generally below 40%) and a lower bulk density (approximately 0.2–0.3 g/cm³). They are lighter, weighing about 0.5–1 kg per unit, with a lower refractory temperature rating (generally below 1200°C). Their advantages include excellent thermal insulation, light weight, and ease of installation; their disadvantages are lower strength and relatively high cost.

The national standards classify and define refractory bricks as follows:

  • Fireclay bricks: Aluminosilicate refractory materials containing 30%–48% Al₂O₃.
  • High-alumina bricks: Aluminosilicate refractory materials containing more than 48% Al₂O₃. Based on Al₂O₃ content, they are categorized into Grade I (Al₂O₃ > 75%), Grade II (Al₂O₃ 60%–75%), and Grade III (Al₂O₃ 48%–60%).
  • Silica bricks: Refractory materials containing more than 93% SiO₂.
  • Magnesia bricks: Refractory materials containing more than 80% MgO.
  • Special refractory bricks: Refractory materials with unique properties and applications, such as corundum bricks and silicon carbide bricks.

Parameters such as alumina content, bulk density, mass, and refractoriness vary among the different grades of high-alumina bricks.

It is important to note that the specific selection of refractory bricks should be based on a comprehensive assessment of the lime kiln’s actual conditions and operational requirements. Factors such as kiln operating conditions, fuel type, and production processes must be considered, alongside recommendations from the brick manufacturer. Furthermore, to ensure the safe operation and long-term stability of the lime kiln, the refractory lining should undergo regular inspection and maintenance, with damaged or worn bricks replaced promptly.

Magnesia-Alumina Spinel Bricks for Lime Kilns

Magnesia-alumina spinel bricks for lime kilns are high-performance refractory materials specifically designed for this application. Their primary constituent is magnesia-alumina spinel (MgAl₂O₄)—formed through the high-temperature reaction of magnesia and alumina oxides—though they may also contain specific amounts of other refractory oxides to enhance performance. Magnesia-alumina spinel offers excellent high-temperature resistance, corrosion resistance, and thermal shock resistance, making these bricks an ideal choice for critical sections of the lime kiln, such as the firing zone and preheating zone.

These bricks feature the following characteristics:

  • (1) High-temperature resistance: Magnesia-alumina spinel bricks possess exceptional refractoriness, enabling them to withstand the intense heat within the lime kiln and ensure stable kiln operation.
  • (2) Corrosion resistance: In the reducing atmosphere of a lime kiln, these bricks resist corrosion from kiln slag and furnace gases, thereby extending their service life.
  • (3) Thermal shock resistance: These bricks exhibit excellent thermal shock resistance, allowing them to withstand thermal stresses caused by rapid temperature fluctuations and preventing cracking or spalling.

Magnesia-alumina spinel bricks are primarily used in critical areas of the lime kiln—such as the firing and preheating zones—where refractory material performance requirements are extremely high. Their use can significantly improve both the operational efficiency of the lime kiln and the quality of the final product.

 

Installation Procedures for Ceramic Fiber Boards Across Different Industries

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Refractory ceramic fiber refers to man-made mineral fiber suitable for use as thermal insulation at temperatures above 800°C. Refractory ceramic fiber boards are rigid, flat products typically manufactured using a wet process and containing inorganic or organic binders. So, what are the characteristics of ceramic fiber boards, and how are they installed?

Characteristics of Ceramic Fiber Boards

1. Ceramic fiber boards are not only rigid in texture but also possess excellent toughness and strength, making them resistant to wind erosion. They offer very high compressive strength and a long service life. Additionally, ceramic fiber is an environmentally friendly material; it has low thermal inertia, allowing for precise control over heating response times.

2. Ceramic fiber boards are not brittle, which gives them good toughness; furthermore, precise manufacturing ensures excellent flatness. They are convenient to install and easy to cut. They dry very quickly—often achieving thorough, uniform drying within just a few minutes—and have a very low moisture content, ensuring high quality.

Rongsheng Ceramic Fiber Boards for Sale
Rongsheng Ceramic Fiber Boards for Sale

How to Install Ceramic Fiber Boards

1. First, clean the wall surface to remove loose dust, grease, and other debris. Scrape away any loose concrete or debris from cracks; repair any areas where the plaster or render has delaminated (hollow spots).

2. High standards of flatness are required for installing ceramic fiber boards; surface deviations must not exceed 4 mm. If the deviation is significant, grind down protruding areas. Fill in recessed areas with a repair layer at least 6 mm thick, ensuring that both internal and external corners remain square and true. Additionally, use specialized adhesive mortar and surface-specific bonding agents for the installation.

3. Mix the adhesive mortar at a water-to-mortar ratio of 1:5. Add water while mixing and continue for at least 5 minutes, ensuring consistent mixing intensity and moderate viscosity. Let the mixture rest for 5 minutes, then stir it again before application. Use the prepared mortar within one hour; using it within this timeframe maximizes the bond strength between the board and the mortar, ensuring a secure attachment.

Installation Procedures for Ceramic Fiber Boards Across Different Industries

Installation procedures for ceramic fiber boards vary depending on the industry in which they are applied. Therefore, it is crucial to avoid errors during installation, as mistakes can compromise the quality of the finished assembly.

Ceramic Fiber Insulation Board
Ceramic Fiber Insulation Board

Industrial Furnace Construction

1. Clean the surface of the area to be lined (including the substrate surface).

2. Adhesive mixing ratio: Mix the adhesive powder and sodium silicate (water glass) evenly at a 1:1.2 ratio (do not use water).

3. Use plastering tools to apply the adhesive evenly to the surface of the insulation board. Press the boards firmly together—both vertically and horizontally—to ensure a tight, secure bond.

Manufacturing and Heat Treatment Industries

1. Clean the concrete wall surface to remove loose dust, oil stains, debris, and areas with hollow spots (delamination).

2. Remove loose concrete fragments, inclusions, and hollow areas from the ceiling slab, then repair these spots.

3. The surface flatness deviation for bonding ceramic fiber boards must not exceed 4mm. If the deviation exceeds this limit, grind down protruding concrete areas and fill in recessed areas. For fill-in thicknesses exceeding 6mm, use 1:2.5 cement mortar; for thicknesses less than 6mm, use polymer bonding mortar. Ensure the overall wall flatness remains within 4mm, with square internal and external corners and straight vertical alignment.

4. The mortars used include a specialized bonding mortar and a high-temperature adhesive for the surface layer.

5. Mix the bonding mortar at a water-to-mortar weight ratio of 1:5. Add water while stirring; mix for at least 5 minutes to ensure thorough, uniform blending, achieving moderate consistency and appropriate viscosity.

6. After mixing, let the mortar sit for 5 minutes and stir again before use; the prepared mortar must be used within one hour.

7. To enhance the bond between the extruded board (XPS) and the bonding mortar, [treat the surface] prior to bonding the fiber board.

Construction Industry

For general renovation and interior finishing, the installation method is very simple. Since the board is primarily used for fireproofing and thermal insulation, leaving it exposed is generally not recommended; instead, installers should bond the ceramic fiber board tightly against the unfinished wall and secure it with mechanical anchors (nails). The exterior is then finished with wall cladding.

Therefore, when installing and using ceramic fiber boards across various industries, it is essential to strictly adhere to the correct installation procedures to ensure the highest quality of the installation.

 

Do You Know How the Brick Designations for Refractory Bricks are Indicated?

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Rongsheng Refractories specializes in the production of a wide range of refractory materials. Its product portfolio includes refractory bricks—such as high-alumina and fireclay bricks—as well as various refractory castables, including low-cement, high-alumina, lightweight, and wear-resistant varieties. The company has developed shaped products (including aluminum silicate, silica-based, basic, and lightweight insulating brick series) and other refractory materials tailored for industries such as coking, building materials, iron and steel, non-ferrous metals, and electric power.

Rongsheng Al₂O₃-SiO₂ Refractory Bricks
Rongsheng Al₂O₃-SiO₂ Refractory Bricks

Refractory Brick Designations

There is a wide variety of refractory brick designations, and the shapes and dimensions involved are quite complex; however, standardized designation codes have been established. These codes reveal the brick’s intended application, as well as its shape, dimensions, and weight. For instance, bricks with the “T” prefix are used in general industrial furnaces; this series ranges from “T-1” to “T-105,” comprising over 20 shapes and 105 specific designations (specifications)—such as the “T-3” standard brick, which measures 230 × 114 × 65 mm. Similarly, bricks with the “G” prefix are designed for blast furnaces; the “G-1” through “G-8” series includes two shapes and eight specifications. The table below lists several refractory brick designations and their applications:

Designations Uses Designations Uses
D-1~D-17 For electric furnaces C-1~C-27 Steel ladle lining brick
P-1~P-64 For open-hearth furnaces X-1~X-10 Steel ladle sleeve brick
G-1~G-8 For blast furnaces S-1~S-8 Steel ladle stopper brick
R-1~R-28 For hot-blast stoves ZH-1~ZH-9 Steel ladle nozzle brick
H-1~H-12 For cupolas Z-1~Z-6 Steel ladle well block
T-1~T-105 For general industrial furnaces L-1~L-6 Pouring funnel brick
ZG-1~ZG-4 Casting bricks for cast pipes ZL-1 Intermediate pouring funnel brick
ZX-1~ZX-23 Casting center bricks ZL-2 Intermediate pouring funnel nozzle brick
LG-1~LG-15 Casting runner bricks MD-1~MD-6 Ingot mold bottom brick

SK32, SK34, SK36, SK38, and SK40 Refractory Bricks

Refractory bricks are bricks capable of withstanding high temperatures exceeding 1580°C. They are produced by mixing refractory clay with grog (calcined and crushed clay), pressing the mixture into shape, drying it, and finally firing it. Other types include silica bricks and high-alumina bricks. Based on grade designations, they are classified as SK32, SK34, SK36, SK38, and SK40 refractory bricks. These bricks are primarily used for furnace linings, flues, and chimneys, and are categorized by shape and specification into two main types: standard and special-shaped. Standard refractory bricks measure 230 mm × 114 mm × 65 mm, while special-shaped bricks are either processed on-site to meet specific needs or manufactured using custom molds.

Based on their heat resistance, refractory bricks are classified into ordinary types (refractoriness of 1580–1770°C) and high-grade types (refractoriness of 1770–2000°C). Chemically, they are classified into three categories: acidic, basic, and neutral.

Rongsheng is a specialized manufacturer of refractory bricks, offering products such as the SK series, special-grade, first-grade, and second-grade refractory bricks, as well as special-shaped bricks. Rongsheng’s refractory bricks are characterized by wear resistance, corrosion resistance, spalling resistance, low creep, excellent thermal shock stability, and a long service life. They are primarily used for linings in blast furnaces, hot blast stoves, carbon baking furnaces, carbon calcining furnaces, coke ovens, steel ladles, casting systems, boilers, cement kilns, glass kilns, and various other industrial furnaces and thermal equipment. They serve industries such as metallurgy, machinery, building materials, casting, ceramics, electric power, petroleum, and chemicals.

Special Shaped High Alumina Bricks in Rongsheng Factory
Special Shaped High Alumina Bricks in Rongsheng Factory

Standards for Refractory Materials

The standard size for refractory materials is 230 × 114 × 65 mm. According to national standards, refractory bricks are classified into various types—commonly including straight bricks—suitable for different construction projects and industrial equipment. General-purpose refractory bricks refer to straight bricks, side-tapered bricks, edge-tapered bricks, end-tapered bricks, and skewback bricks used for masonry in the straight walls and arched sections of thermal equipment such as industrial furnaces and kilns. The dimensions for general-purpose refractory bricks (specifically the T-3 type) are 230 × 114 × 65 mm; national and ministerial standards are largely consistent. Dimensions (Length × Width × Thickness) and volumes are as follows: T-1 (172 × 114 × 65 mm, 1274.5 cm³), T-2 (230 × 114 × 32 mm, 839 cm³), T-3 (230 × 114 × 65 mm, 1704.3 cm³), and T-4 (230 × 172 × 65 mm, 2571.4 cm³). Among these, the standard refractory brick size is T-3 (230 × 114 × 65 mm) with a volume of 1704.3 cm³.

Refractory Brick Dimensions

Rongsheng Refractory Brick Manufacturer offers general-purpose refractory bricks—including models, specifications, and dimensions—suitable for industrial furnaces, kilns, and other thermal equipment.

Naming Convention for Refractory Brick Models and Codes

In the brick model number, the letter “T” represents the Pinyin initial for “General-purpose” (Tongyong). Following the hyphen is a sequential number.

In the code, the letters Z, C, S, K, and J represent the Pinyin initials for the brick types: Straight (Zhi), Side-wedge (Ce), Vertical-wedge (Shu), Wide-wedge (Kuan), and Arch-foot (Jiao). For straight bricks, the letter is followed by the hundreds and tens digits of the brick length (*a*), then the tens digit of the brick thickness (*c*). For wedge bricks, the letter is followed by the hundreds and tens digits of the distance (*b*) between the large and small ends, then the digits (tens place and above) for the large-end dimension (*a*) and small-end dimension (*a1*); the suffix “k” indicates a staggered-joint wide brick. For arch-foot bricks, the letter is followed by the hundreds and tens digits of the inclined surface length (*L*), then the tens digit of the inclination angle.

Specifications for refractory bricks include their model, shape, name, code, dimensions, and parameters.

In effect, every skewback brick incorporates a right-angled triangle; that is, the brick features two complementary inclination angles. For instance, a skewback brick with an inclination angle of 52° has a complementary angle of 38°; thus, a 38° skewback required for an arch with a central angle of 104° can utilize the complementary angle of a 52° skewback brick. This method of utilizing complementary angles is sometimes applied to furnace roof skewbacks with thicknesses of 380 mm and 440 mm. Consequently, standard inclination angles for skewbacks include 30°, 38°, 45°, 52°, and 60°. The length of the inclined face (L) of the skewback brick should match the dimension (b) between the large and small ends of the mating wedge brick; common values ​​for this dimension are 114, 230, 300, 380, and 440 mm.

The thickness (c) of the skewback brick should correspond to the effective thickness (c) of the mating wedge brick; for example, skewback bricks used with side-wedge bricks have a thickness of 230 mm, while those used with 230 mm vertical-wedge bricks have a thickness of 114 mm. To reduce weight, the thickness of skewback bricks with inclined face lengths of 300, 380, and 400 mm is halved to 75 mm. However, when constructing stepped inclined roofs, it is often observed that two skewback bricks laid side-by-side result in a combined thickness exceeding the 150 mm width of the arch brick ring. Due to the extra mortar joint, combined with positive dimensional tolerances and surface irregularities, the total thickness can reach 160 mm, creating significant difficulties for inclined roof construction. To rectify this issue, the standard thickness for skewback bricks was revised to 73 mm. While the dimensions of the two right-angle sides of the skewback brick can be calculated based on the inclination angle, specific standards are established to facilitate manufacturing, storage, and optimal performance.

 

Application of Silicon Carbide Refractory Bricks in Aluminum Electrolytic Cells

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The electrolytic cell is a crucial component in the aluminum electrolysis process, and the two main factors affecting its lifespan are the carbon cathode and the refractory lining. This section explores the application of silicon carbide refractory bricks in aluminum electrolytic cells and the current challenges they face.

Aluminum electrolytic cell linings can be categorized into bottom linings and side linings. The bottom lining functionally supports the cathode structure and provides insulation. The side linings primarily protect the steel outer shell from corrosion by the molten electrolyte.

Aluminum Electrolysis Cells
Aluminum Electrolysis Cells

Aluminum Electrolytic Cell

The side lining of an aluminum electrolytic cell is a crucial structural component. Modern concepts dictate that the sidewall material should possess the following important properties at high temperatures: high resistivity, good thermal conductivity, non-reactive to molten cryolite, low porosity, impermeability to electrolyte and aluminum, and resistance to air oxidation.

Since silicon carbide’s valence bond structure determines its superior properties, such as high strength, high hardness, high temperature resistance, oxidation resistance, high thermal conductivity, low thermal expansion coefficient, excellent thermal shock resistance, good chemical stability, and non-wetting by non-ferrous metals, and also exhibits good resistance to high-temperature chemical corrosion, it is particularly suitable as a refractory lining material for aluminum electrolytic cells.

With advancements in materials technology and the increasing capacity of electrolytic cells, the structure of the side lining material has evolved from the early double carbon block plus insulating brick structure to single-layer carbon blocks without insulating bricks, and ultimately to today’s single silicon carbide combined with silicon nitride materials.

Problems and Current Research Status

Silicon carbide refractory bricks are a new type of furnace-building material recently promoted and used in the non-ferrous metals industry, initially applied to a 320kA large prebaked aluminum electrolytic cell in an aluminum plant. In recent years, user experience has shown that regardless of whether pure silicon carbide refractory brick side blocks or composite side blocks are used, varying degrees of cracking and detachment have been commonly observed during production, with the silicon carbide layer in composite side blocks also exhibiting upward lifting.

Silicon Carbide Bricks
Silicon Carbide Bricks

Silicon Carbide Bricks

Temperature difference (with the upper edge of the artificial extension leg as the boundary) is the main cause of silicon carbide brick cracking. Although silicon carbide bricks have good thermal conductivity and a low coefficient of thermal expansion, because the products are fired at temperatures above 1450℃, forming a hexagonal ceramic structure, their resistance to thermal shock and temperature differences is poor. Under environments where repeated temperature differences are formed between the upper and lower parts of the silicon carbide refractory brick, it is extremely prone to cracking.

When the silicon carbide composite layer fractures, electrolyte seeps into the crack. When the electrolytic cell returns to normal temperature from the initial effect temperature, the electrolyte in the crack solidifies and shrinks, and new electrolyte enters and solidifies again. During the next effect, the solid electrolyte in the crack expands due to heat, pushing up the upper fractured block. When the cell temperature returns to normal, the electrolyte solidifies and shrinks again, forming a gap. Then, new electrolyte enters and solidifies again. During the next effect, expansion pushes the fractured block up again, and this process repeats, gradually raising the upper part of the fracture.

During aluminum electrolysis, the temperature approaches 1000℃. At this temperature, the erosion of the electrolytic cell lining mainly consists of three parts: the molten aluminum near the bottom, the molten electrolyte in the middle, and various corrosive gases (such as HF, AlN, and AlF4) in the upper part. Typically, in the electrolyte-alumina molten liquid, cation penetration is mainly Na+, and anion penetration is mainly F-.

Porosity, matrix phase, wettability, and other factors can all affect the erosion resistance of refractory materials. Materials with high porosity and large pore size generally have poor corrosion resistance because cryolite or molten aluminum can directly penetrate into the material’s interior. The limiting pore sizes of molten metal in refractory materials are 30 μm for molten steel, 5 μm for molten iron, and 0.5 μm for molten aluminum; therefore, molten aluminum has a very strong penetrating ability. A thin matrix phase results in good corrosion resistance, but its strength is directly affected; a thick matrix phase results in poor corrosion resistance. A large wetting angle between the material and molten aluminum leads to superior corrosion resistance.

The resistance of SiC materials with various bonding phases to electrolyte corrosion was studied. The results showed that, except for self-bonded SiC, Si3N4-bonded SiC materials exhibited the best electrolyte resistance. Although the Si3N4 bonding phase was wetted by the melt, the penetration was shallow and no decomposition occurred.

The results indicate that damage to Si3N4-bonded SiC products in the air interface is mainly due to the oxidation of Si3N4 and SiC. At the cryolite electrolyte-air interface, the vicious cycle of oxidation-erosion-penetration formed by chemical reactions results in the most severe corrosion. The dissolution of electrolytes in molten aluminum and the porosity of the sample structure itself are likely the main reasons for the corrosion of Si3N4-bonded SiC products in molten aluminum.

Silicon Nitride-Bound Silicon Carbide Bricks
Silicon Nitride-Bound Silicon Carbide Bricks

Silicon Nitride-Bound Silicon Carbide Bricks

The erosion behavior of silicon nitride-bound silicon carbide refractories with different silicon nitride contents in cryolite molten salt was studied. The results showed that corrosion mainly occurred before 25 hours. After 25 hours, the weight gain of the Si3N4/SiC material remained essentially unchanged, while the Si3N4/SiC material with a low Si3N4 content (13%) exhibited good resistance to cryolite melt corrosion.

The study found that during aluminum electrolysis, porosity and β-Si3N4 content significantly affected the erosion resistance of Si3N4-bound SiC refractories. Higher porosity or higher β-Si3N4 content resulted in more severe erosion. A SiC aggregate content between 80% and 85% showed good erosion resistance.

 

What are the Differences in the Refractory Materials Used for the Inner Lining of Electric Furnaces?

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An electric arc furnace is an electric furnace that uses the energy of an electric arc to smelt metals. Industrially used electric arc furnaces can be divided into three categories: The first category is the direct heating type, where the electric arc occurs between a dedicated electrode rod and the charge being smelted, with the charge directly receiving the heat from the arc. It is mainly used for steelmaking, and also for smelting iron, copper, refractory materials, and refining molten steel. The second category is the indirect heating type, where the electric arc occurs between two dedicated electrode rods, with the charge receiving the radiant heat from the arc. It is used for smelting copper, copper alloys, etc. This type of furnace is noisy and produces poor smelting quality, and has gradually been replaced by other types of furnaces. The third category is called a submerged arc furnace, which uses high-resistivity ore as raw material. During operation, the lower part of the electrodes is generally buried in the charge. Its heating principle utilizes both the heat generated by the resistance of the charge when current passes through it and the heat generated by the electric arc between the electrodes and the charge. Therefore, it is also called an electric arc resistance furnace.

Electric Arc Furnace Wall Structure

The electric arc furnace wall is divided into three parts according to its operating conditions: the main furnace wall, the slag line, and the hot spots.

  • ① In the main furnace wall of high-power and ultra-high-power electric furnaces, directly bonded magnesia-chrome bricks, pre-reacted magnesia-chrome bricks, and magnesia bricks are mainly used.
  • ② The hot spots are close to the electric arc and are subjected to high-temperature radiation and slag splash, resulting in particularly severe damage. Oil-impregnated magnesia bricks, directly bonded magnesia-chrome bricks, cast magnesia-chrome bricks, and magnesia-carbon bricks are mainly used.
  • ③ The slag line is severely corroded by molten steel and slag, and its operating conditions are harsh. Therefore, high-quality refractory materials similar to those used for the hot spots should be used.

Due to the different operating conditions of different parts of the furnace wall, single-material construction is rare. Most furnaces use a combination of various bricks to achieve balanced corrosion. In the upper part of the furnace wall, the slag line and hot spots are weak points due to uneven corrosion caused by heat load, chemical erosion, and mechanical action. These “hot spots” can even limit the service life of the furnace wall. To meet the needs of these harshly corrosive areas, magnesia-carbon bricks, which are resistant to corrosion, thermal shock, and have low linear expansion, are increasingly used in the high-corrosion zones of electric arc furnaces. They have become the preferred refractory material for the walls of UHP electric arc furnaces both domestically and internationally.

Magnesia Chrome Bricks
Magnesia Chrome Bricks

What are the differences in the refractory materials used for the inner lining of electric arc furnaces?

Initially, high-temperature fired direct-bonded magnesia-chrome bricks were used for electric arc furnace walls. In the 1970s, to meet the needs of large electric arc furnaces and the hot spots of UHP (Unified High-Performance) electric arc furnaces, a combination of fused cast magnesia-chrome bricks and rebonded magnesia-chrome bricks was tested. In 1976, “Corhart” fused cast magnesia-chrome bricks were widely used in UHP electric arc furnaces, with 90%–95% used in hot spots and some in the slag line area. Fused cast bricks have a high degree of direct bonding between the magnesia-chrome spinel and the slag, resulting in a dense structure.

The development of electric arc furnace steelmaking in the United States was rapid. A major development that effectively improved the productivity of electric arc furnace steelmaking was the development and use of magnesia-carbon bricks in the high-loss areas of the furnace wall, which had lower raw material and process costs but better performance. These magnesia-carbon bricks were produced from high-purity, high-density sintered magnesia sand with a CaO/SiO2 ratio of 3, containing approximately 10% carbon, with an apparent porosity of 3% and a bulk density greater than 2.95 g/cm³.

In the former Soviet Union, electric arc furnace walls were mostly made of magnesia materials. Reconstituted magnesia-chrome bricks, produced from fused periclase and chromite sand, were tested and used in the severely eroded areas above the taphole of 100t electric arc furnaces. These bricks had few low-melting-point mineral phases, good corrosion resistance, and performed well.

In the UK, electric arc furnace walls generally use ordinary chrome-magnesia bricks (70% chromite, 30% seawater magnesia), fired magnesia-chrome bricks (70% seawater magnesia, 30% chromite), and high-quality magnesia bricks made from seawater magnesia. High-temperature fired magnesia bricks prepared from seawater magnesia or fired magnesia bricks impregnated with pitch and tar were used in hot spots and slag lines, achieving good results.

In Japan, electric arc furnace walls used magnesia-chrome bricks and magnesia bricks. In hot spots, magnesia bricks, magnesia-carbon bricks, cast magnesia-chrome bricks, and carbon bricks were used.

In the 1980s, my country’s electric arc furnace steelmaking developed rapidly, evolving from ordinary power electric arc furnaces to ultra-high power electric arc furnaces. Advances in electric arc furnace (EAF) steelmaking technology are closely linked to the synchronous development of refractory material technology, promoting a steady increase in EAF lifespan and a gradual decrease in refractory material consumption per unit area. My country’s ordinary power EAFs employ two types of linings: one is a monolithic lining made of rammed mortar containing low- and medium-temperature binders in sintered magnesia and fused magnesia; the other is a lining constructed with tar-bonded magnesia bricks and magnesia-carbon bricks of various standards. Alkaline carbonaceous materials are the main materials for furnace wall linings, and magnesia-carbon bricks play a crucial role in EAFs.

Application and Damage Mechanism of Magnesia-Carbon Bricks in Electric Arc Furnaces for Steelmaking

The working environment of electric arc furnace linings is extremely harsh, posing a significant challenge to the lining refractory materials. The two most severe challenges are temperature variations within the furnace and changes in slag composition.

Ordinary electric arc furnace operations complete the melting, oxidation, and reduction stages within the furnace. However, UHP (Ultra-High Power) electric arc furnaces utilize forced melting to significantly increase the melting rate, while alloying is achieved after refining in an LF (Fuel-Fuel-Low Power) furnace. Therefore, the specific power level of UHP electric arc furnaces is generally above 600 kVA per ton of steel, and modern furnaces reach 1000 kVA per ton of steel. The relationship between power level, furnace temperature, and melting time is discussed.

service life of MgO-C bricks in large converters
Magnesia Carbon Bricks

The high power level of UHP electric arc furnaces results in a surface heat load of up to 1000 kVA/m² on the furnace lining. During the melting period, the furnace lining is rarely shielded, and combined with the highest radiation levels, this creates a hot spot on the lining opposite the electric arc. The minimum heat load occurs between phases, in the “cold zone,” and the difference in heat load between the hot and cold zones can reach 60%. This demonstrates the spatial unevenness of temperature within the electric arc furnace. Under these conditions, some hot zones can reach temperatures exceeding 2000℃. This is extremely detrimental to the slag resistance of magnesia-carbon bricks, as slag penetrates these hot spots and erodes the entire brick structure. Furthermore, temperature differences increase internal thermal stress within the brick, making it prone to spalling under the mechanical erosion of the slag.

Another characteristic of electric arc furnace steelmaking is the wide variety of steel grades produced. This variety results in diverse slag composition and properties, making the slag erosion on the MgO-C bricks of the furnace wall extremely complex. The intense boiling of molten steel and slag, the stirring, and the thermal shock from the electric arc cause the furnace lining to experience far more severe erosion than in a converter. Consequently, while the service life of MgO-C bricks in large converters reaches thousands or even tens of thousands of heats (using slag splashing protection technology), the service life of electric arc furnace walls remains only 300-500 heats. The composition of primary and final slag from smelting the same steel grade can vary significantly depending on changes in smelting parameters. The variation in composition is even more pronounced when smelting primary and final slag from different steel grades. Similar to the situation with slag in converter processes, the most significant variation is primarily in binary basicity.

Traditional electric arc furnace steelmaking processes encompass the entire melting-refining process, with each furnace lasting 3-4 hours. The composition of the slag and reducing slag varies significantly during the oxidation and reduction phases. For the furnace lining refractory materials, this involves alternating erosion by acidic and basic slags. For example, in 1Cr18Ni19Ti steel, the initial slag has a C/S ratio <1, while the final slag has a ratio >2. Electron probe microanalysis has been used to thoroughly study the phase combinations and chemical composition changes of the molten pool slag and splashed slag during different smelting cycles in traditional steelmaking processes. While the percentage content of each phase cannot be determined to estimate the overall slag composition, changes in phase chemical composition can still reveal variations in the overall slag composition. The melting and oxidation phases produce oxidizing slag; the refining and alloying phases produce reducing slag. Except for some characteristic elements of special alloy steels, the phase combinations in these slags follow normal patterns. However, the micro-regional composition of the phases allows analysis of their crystallization behavior. For instance, the banded structure and compositional changes of spinel in the molten pool slag are due to variations in slag composition during the smelting cycle. This also reflects the cation substitution during spinel nucleation and growth, changing from a high-chromium type to a high-alumina type, which is also a characteristic of the chromium return and deoxidation process. During the oxidation period, the spinel remains high-chromium, while during the refining-alloying period, it becomes high-FeOn type.

The erosion of magnesia-carbon bricks occurs under the alternating and cyclical action of various slag compositions. In each furnace run, for each heat of steel, and even at different smelting stages within a single heat, the erosion behavior of the magnesia-carbon brick working surface changes. From changes in slag basicity to changes in slag oxidizability, and even changes in slag fluidity, these changes all have different effects on the erosion of magnesia-carbon bricks.

 

Refractory Bricks Can be Divided into Five Categories According to Their Materials

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Refractory bricks, as the name suggests, are high-temperature resistant bricks, also known as fire bricks. They are refractory materials with specific shapes and sizes. Based on their manufacturing process, they can be classified into fired bricks, unfired bricks, electrofused bricks, and refractory insulating bricks. Based on their shape and size, they can be classified into standard bricks, ordinary bricks, and special-shaped bricks. According to their composition, refractory bricks can be divided into five main categories: silica-alumina series refractory bricks, basic series refractory bricks, carbon-containing refractory bricks, zirconium-containing refractory bricks, and insulating refractory bricks.

RS High Alumina Bricks for Sale
RS High Alumina Bricks for Sale

Silicon-Alumina Series Refractory Bricks

  1. High-Alumina Refractory Bricks: These are neutral refractory materials made from high-alumina bauxite clinker as the main raw material, soft clay and waste pulp as binders, and multi-grade particle size distribution. They are produced through high-pressure molding, drying, and high-temperature firing, resulting in an Al2O3 content greater than 75%. High-alumina bricks are classified into four grades based on Al2O3 content: extra-grade, grade 1, grade 2, and grade 3. Extra-grade high-alumina bricks have an Al2O3 content of no less than 80%, grade 1 no less than 75%, grade 2 no less than 65%, and grade 3 no less than 55%. High-alumina bricks are widely used in the steel industry, non-ferrous metal industry, and other industries.
  2. Clay Bricks: These are refractory materials made from clay clinker as aggregate and refractory clay as a binder, with an Al2O3 content of 30-48%. Clay bricks are typically made from hard clay as the main raw material, pre-calcined into clinker, then mixed with soft clay and molded using a semi-dry or plastic method, and fired at 1300-1400°C. They are commonly used refractory bricks in blast furnaces, hot blast stoves, heating furnaces, power boilers, lime kilns, rotary kilns, and ceramic kilns.
  3. Silica bricks refer to refractory bricks with a SiO₂ content of over 93%, and are a major type of acidic refractory brick. They are mainly used for lining coke ovens, and also in various glass, ceramic, and carbon calcining furnaces, and in high-temperature load-bearing parts of hot blast stoves. However, they are not suitable for use in thermal equipment with temperatures below 600°C and large temperature fluctuations.
  4. Corundum refractory bricks refer to refractory bricks with an Al₂O₃ content of not less than 90%, with corundum as the main phase. They are divided into sintered corundum bricks and fused corundum bricks.
Rongsheng Magnesite Brick
Rongsheng Magnesite Brick

Basic Refractory Bricks

Basic refractory bricks refer to refractory products with basic oxides and MgO and CaO as the main components. The main varieties include:

  1. Magnesia Refractory Bricks: Made from magnesite, with periclase as the main crystalline phase, and an MgO content of 80-85% or higher. Magnesia refractory bricks are the most important type of basic refractory brick, possessing high refractoriness and excellent resistance to basic slag and iron slag. They are mainly used in open-hearth furnaces, oxygen converters, electric furnaces, and for smelting of advantageous metals.
  2. Dolomite Bricks: A type of basic refractory brick produced using dolomite as the main raw material. Widely used in basic converters and can also be used as linings for certain ladle refining ladles.
  3. Forsterite Refractory Bricks: A type of refractory brick with forsterite (MgO-SiO₂) as the main component. Primarily used as checker bricks in open-hearth furnaces, ingot casting bricks, furnace bottoms in heating furnaces, and also showing good performance in copper smelting furnaces.

Carbon-Containing Refractory Bricks

Carbon-containing refractory bricks are made from carbon or carbon compounds.

  1. Carbon Bricks: High-temperature resistant, neutral refractory products made primarily from carbonaceous materials with the addition of appropriate binders. Carbon bricks are widely used for lining the bottom, hearth, belly, and lower part of blast furnaces.
  2. Graphite-Based Refractory Products: Refractory materials made from natural graphite as raw material and clay as a binder. These products mainly include graphite clay crucibles, cast steel stopper bricks, nozzle bricks, and steel ladle lining bricks.
  3. Silicon Carbide Refractory Products: High-grade refractory materials produced from silicon carbide (SiC). They have good wear resistance and corrosion resistance, high high-temperature strength, high thermal conductivity, low coefficient of linear expansion, and good thermal shock resistance. In iron and steel smelting, they can be used for steel ladle linings, nozzle stoppers, and blast furnace bottoms.
Fused AZS Bricks for Glass Kiln
Fused AZS Bricks for Glass Kiln

Zirconium-containing Refractory Bricks

Zirconium-containing refractory bricks are an acidic material made from natural zircon sand. Zirconium refractory bricks have good slag resistance, low thermal expansion coefficient, high load softening temperature, high wear resistance, and good thermal shock resistance.

  1. Zircon bricks: They exhibit good resistance to slag and molten steel corrosion and have good thermal shock resistance. They are used as linings for stainless steel ladles, continuous casting ladles, casting gate bricks, sleeve bricks, and high-temperature induction furnace linings.
  2. AZS fused alumina bricks, also known as fused corundum bricks, have become an important refractory material in key parts of glass furnaces. They have strong resistance to molten glass corrosion.
  3. Zirconium-mullite fused alumina bricks: Characterized by a dense crystal structure, high load softening temperature, good thermal shock resistance, high mechanical strength at both room and high temperatures, good wear resistance, good thermal conductivity, and excellent resistance to slag corrosion. They are used in the discharge ports of metallurgical heating furnaces, soaking furnaces, and calcium carbide furnaces.
Alumina Bubble Brick - Rongsheng Refractory
Alumina Bubble Brick

Insulating Refractory Bricks

Insulating refractory bricks, also known as lightweight refractory materials, refer to refractory materials with high porosity, low bulk density, and low thermal conductivity. They can be divided into:

  1. High-alumina insulating lightweight refractory bricks: These are lightweight insulating bricks with an alumina content of not less than 48%. They can be used for building insulation layers and in areas not subject to strong erosion or scouring from molten materials at high temperatures. The contact temperature should not exceed 1350°C.
  2. Mullite insulating refractory bricks: These are high-quality insulating refractory bricks made primarily from high-alumina bauxite clinker. A porous structure is formed through foaming or chemical methods. The mixture is then mixed with water to create a plastic mortar or slurry, which is extruded and fired at high temperatures. These bricks can be directly exposed to flames and exhibit high temperature resistance, high strength, and good energy-saving performance. They are used for linings in pyrolysis furnaces, hot blast stoves, ceramic roller kilns, and various resistance furnaces.
  3. Clay-based insulating refractory bricks are made primarily from refractory clay. They are produced by mixing refractory clay, cenospheres, and other binders with sawdust, followed by batching, molding, drying, and firing.
  4. Cenosphere bricks are insulating refractory products made primarily from cenospheres. Cenospheres are hollow aluminosilicate glass spheres floated from fly ash in thermal power plants. Cenosphere bricks can be formed using a semi-dry method.
  5. Alumina bubble bricks are made primarily from alumina hollow spheres and alumina powder, combined with other binders, and fired at 1750℃. The maximum service temperature is 1800℃. These bricks have high mechanical strength, several times that of general lightweight products. They are widely used in high-temperature and ultra-high-temperature kilns such as gasifiers in the petrochemical industry, reactors in the carbon black industry, and induction furnaces in the metallurgical industry, achieving very satisfactory energy-saving effects. Hollow alumina spheres have a refractoriness of over 1750℃, good thermal stability, low reheat linear change rate, durability, strong heat insulation properties, and low thermal conductivity.

 

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