rsrefractorycastable, Author at Rongsheng Refractory Castable Cement for Sale Manufacturer and Supplier

Basis for Selecting Castable Refractory for Flue Lining

December 16, 2025October 29, 2025 by rsrefractorycastable

The most important consideration for flue lining is the erosion and corrosion caused by acidic gases. Acidic gases necessitate the use of acid-resistant castables or acid-resistant bricks for the lining. However, flues can be vertical or horizontal; for vertical flues, weight must be considered. If they are too heavy or the chimney is too tall, installation and assembly will be extremely difficult.

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Flue Lining Using Castable Refractory

Flue temperatures are not high, but the gas pressure is high, and the flue gas volume is large. The lining is susceptible to acid erosion and water erosion due to the generation of water vapor. Therefore, careful consideration is needed when choosing castable refractory or refractory bricks for the lining.

For example, roasting furnace flues can be vertical or horizontal, and the vertical and horizontal structures are often connected. Therefore, when selecting materials for the lining, both weight and erosion must be considered. If acid bricks are used, the mortar joints will result in poor airtightness. If heavy acid-resistant castable refractory is used, it will be too heavy. If lightweight acid-resistant castable refractory is used, its erosion and scouring resistance is insufficient, which is not suitable for flue lining applications. Furthermore, since the flue lining temperature is not high, insulation is generally not required.

Therefore, semi-heavy acid-resistant castable refractory should be considered. Semi-heavy refractory has a bulk density of around 1.5, which provides resistance to erosion and scouring while also offering some insulation. Another reason is that the weight issue is also alleviated. Currently, considering market conditions and chimney characteristics, semi-heavy acid-resistant castable is an ideal material for flue linings. It is particularly suitable for use in large-diameter flues.

What is the thickness of the castable lining for a chimney?

Fluid ducts typically have small inner diameters. If acid-resistant castable lining is used, the thickness is generally less than 100mm, resulting in a significant weight reduction. However, the small diameter of the lining can cause unnecessary difficulties during construction. For flues with a diameter of less than 2 meters, using a coating material is a better alternative, as semi-heavy coating materials can be 30-50mm thick. This reduces the weight by approximately 50% compared to castable lining. For vertical flues, this further reduces the potential for excessive weight. It also facilitates construction in small-diameter flues. Therefore, semi-heavy acid-resistant coating materials are an ideal choice for small-diameter flues.

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Construction of Flue Lining with Castable Refractory

The construction of flue lining with castable refractory can be carried out after installation or after the lining is installed. When constructing the flue lining with castable refractory, a 3mm gap should be left between each cast section for expansion joints. The process involves applying sealant to adjacent sections of the castable refractory before pouring the next section.

Construction of Flue Lining with Castable Refractory Before Installation

Constructing the lining after installation is generally preferable. Large-diameter flue linings are easier to construct with castable refractory. However, if the large-diameter pipe is heavy, lining before installation will significantly increase the pipe’s weight, increasing installation risk and making component welding difficult. Large-diameter flue linings are best constructed after installation.

The construction of flue lining with castable refractory before installation is suitable for small-diameter flue linings due to its lighter weight. Pre-installation construction reduces the difficulty of high-altitude operations, as the refractory lining is poured on the ground, resulting in lower labor intensity and higher construction efficiency. The disadvantage is that the lining construction cannot be carried out continuously, and expansion joints are difficult to handle.

Safety is the primary concern during construction.

The primary concern in constructing flue linings using refractory lining is safety, followed by the welding of anchors and the refractory pouring method. For large-diameter flues, the anchor nails are welded first, and then the anchors are painted before proceeding with the construction in sections. Sectioning involves constructing two sections within a 180° radius, then rotating the pipe 180° to construct the third and fourth sections. If there is an insulation layer, the insulation refractory lining is constructed first, followed by the working layer of the wear-resistant refractory lining. Additionally, if two types of refractory lining are used, the construction must also be carried out in four sections. However, a 12-hour break must be observed after each section is completed before proceeding to the next section. The lower half is poured first, and then the flue is rotated on the ground to pour the remaining half.

Lining Construction on the Ground

If lining construction is carried out on the ground, pipe openings must be straightened and anti-deformation measures implemented. This is to prevent pipe opening deformation due to weight differences during construction and rotation. Areas prone to deformation during refractory lining construction should not be constructed initially; lining should be applied to these areas after other parts are completed.

For pipe bends, expansion joints, and valves, refractory lining should be applied in sections, with expansion joints reserved in both horizontal and vertical directions. For lower-lying areas, inclined formwork can be used for refractory lining, followed by vibration to ensure compaction, and excess material should be removed tangentially. In areas with limited space or high construction joints, refractory lining should be applied using a flat butt joint, with a 3mm high-temperature resistant ceramic fiber felt sandwiched within the joint before welding.

What Type of Refractory Castable is Best for a Kiln Operating at 1500℃?

When the operating temperature of a kiln is 1500℃, corundum castable should be selected based on the temperature. However, many users don’t understand this and think that because it’s expensive, they should choose general high-alumina castable.

However, if the operating temperature is directly at 1500℃, general high-alumina castable is not suitable. Brown corundum castable is required to meet the requirements. Some users have suggested using steel fiber castable. However, this is also not an option because steel fibers begin to melt above 1300℃. Therefore, steel fiber castable cannot be used.

However, some users suggest using stainless steel, but this is also not suitable. Because the lining only uses rust as an anchor, it does not provide high-temperature resistance or corrosion resistance. Corundum castable is characterized by the highest bulk density, the lowest apparent porosity, and good high-temperature resistance, corrosion resistance, and thermal shock resistance. Moreover, the characteristics of corundum castable are fully realized at 1500℃. If steel fiber castable is used, it cannot withstand temperatures up to 1500°C. General high-alumina castables, however, can be used at temperatures of 1300°C-1400°C.

However, for different kilns with varying gas fields and degrees of corrosion, corundum wear-resistant castables or high-strength wear-resistant castables can be selected. This provides both high-temperature resistance and corrosion resistance. For example, in waste incinerators, the temperature is not high, but the degree of corrosion is strong, sometimes involving both acid and alkali corrosion. In such cases, corundum castable is unsuitable because the temperature is too low for the corundum to be fully utilized. Using clean, wear-resistant castables can resist acid or alkali corrosion. Moreover, they are cheaper than corundum castables, making them cost-effective and suitable for the special conditions of incinerators.

In short, regardless of the material of the refractory castable chosen, it is essential to select the appropriate refractory castable based on the specific kiln, temperature, and degree of corrosion.

Application of Dry Ramming Refractory Material in Electric Furnace Bottom

October 14, 2025 by rsrefractorycastable

Currently, the working layer of high-power and ultra-high-power electric furnaces is commonly constructed using magnesia dry ramming refractory materials. The working layer, made of refractory materials, comes into direct contact with molten steel and slag, bearing the high-temperature heat load and slag erosion. The erosion of molten steel, the mechanical impact of scrap steel, and the high-temperature oxidation and reduction processes within the furnace cause slag to penetrate the furnace floor, resulting in a thinning of the furnace floor. During discontinuous operation, the dicalcium silicate in the slag absorbs atmospheric moisture and disintegrates, reducing the material’s durability and service life.

Magnesia Refractory Ramming Mass Material from Rongsheng — Refractory Ramming Mass Material from Rongsheng

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Common dry ramming refractory materials use high-iron, high-calcium synthetic magnesia and fused magnesia as aggregates, with the synthetic and fused magnesia powders used as fine powders, with a critical particle size of 5-6 mm. C2F (dicalcium ferrite) in the synthetic magnesia is used as a sintering aid, without the addition of any binders, and are produced using a multi-stage batching process. Through vigorous ramming, the resulting density is guaranteed, allowing it to sinter into a solid, integral structure at the appropriate temperature. Its service life is several times longer than that of previous knotting and bricklaying methods. The dry ramming mass used in medium frequency furnaces has higher quality requirements. Some scholars have studied the use of fused corundum, white corundum, plate-shaped corundum, and magnesia as granular materials, magnesia fine powder and corundum fine powder as powder, adding high-temperature sintering agents and boric acid as admixtures. The various raw materials are mixed evenly and the particle size distribution is adjusted to produce dry ramming mass.

Dry Ramming Material for Electric Furnace Bottom Construction

Before applying dry ramming refractory material for electric furnace bottoms, be sure to clean away any foreign matter such as permanent layer residue, dust, wire, and plastic sheeting. Calculate the knot size; the actual knot thickness is the desired knot thickness multiplied by 1.09. Prepare a sufficient amount of ramming material based on the required furnace slope and bottom dimensions. Upon receipt, inspect the ramming material for debris and moisture. Remove any debris and do not use damp material. Prepare ramming tools such as a rammer and jackhammer.

For specific construction steps, refer to the following plan:

After shoveling the material flat and laying it flat, tamp it down with your feet to remove any air. After tamping, insert a steel chisel into the material and shake it repeatedly, then tamp it down further with your feet. The ideal thickness for each layer of ramming refractory material is 150-200mm. Then, use a knotter to tamp the material three times in a spiral motion from the perimeter to the center.

The quality of the knot is usually checked by placing a 5mm diameter round steel bar on the ramming layer and pressing it down with a 10kg pressure to a depth of no more than 30mm. During on-site construction, you can forcefully insert the chisel, but the depth should not exceed 30mm.

The method for knotting the furnace slope is the same as for the furnace bottom: first tamp it down with your feet, then tamp it with a knotter. The maximum angle between the slope and the furnace bottom should not exceed 40°. This is to prevent rolling or collapse caused by excessive slopes.

In areas where molten steel is agitated and eroded, such as the taphole base bricks and the furnace door, ramming should be more vigorous and appropriate thickness may be added to maximize the service life of the refractory material in these damaged areas.

After ramming, a 5-10mm thick steel plate is placed on the ramming refractory material to prevent the scrap from damaging the furnace bottom or piercing the ramming material layer, which could cause steel leakage. If steelmaking cannot be carried out in time, a 100-200mm thick layer of lime is placed on the iron plate to prevent the ramming material from hydrating.

When knotting the ramming material, strict adherence to construction requirements is crucial to ensure its density. Failure to do so will result in significant shrinkage during use, leading to numerous cracks and spalling, shortening its lifespan. The first furnace smelting is crucial. During oxygen decarburization, the oxygen lance must not be inserted too deeply, as this can cause the ramming material to flip upwards and create large pits at the furnace bottom. During the first furnace smelting, a layer of lime can be applied to the furnace bottom. This not only prevents scrap steel from directly impacting the furnace bottom, but also prevents the ramming material from hydrating and prematurely forming slag.

Generally, dry ramming refractory material has a lifespan of over 300 furnaces. This can be extended to 500-600 furnaces through hot repair, with some commercially available products even exceeding 600 furnaces.

Repair of ramming material at the bottom of an electric furnace

After a certain period of use, the ramming refractory material at the bottom of an electric furnace will be damaged to varying degrees due to various reasons. Therefore, the lining should be repaired according to the damage of the lining.

(1) Hot repair is carried out at regular intervals during smelting, but the bottom dynamics must be closely monitored after each batch of steel is discharged. If a pit with a depth greater than 150mm is found, it must be repaired.
(2) Before repairing, use oxygen (immediately after the steel and slag are discharged) to blow the surface to be repaired to completely remove the residual steel and slag in the area.
(3) Hoist the ramming material to the top of the area to be repaired and drop it down. Move the crane to distribute it reasonably.
(4) Hoist iron blocks or other heavy objects and compact them.
(5) It should be emphasized that if a large area of the furnace bottom or furnace slope is hot-repaired, in order to ensure the service life after the repair, shorten the number of repairs, and reduce the consumption of dry ramming refractory material per ton of steel, the first batch of steel after hot repair can be smelted in accordance with the “Operation Requirements for Smelting New Furnaces”.

Bauxite Calcination Process

September 30, 2025 by rsrefractorycastable

We are a professional manufacturer of calcined bauxite aggregate, offering a comprehensive range of products including lumps, aggregates, and fine powders. We process and sell a wide range of aggregates and fine powders (containing 60-90% aluminum) and can also customize them to meet customer needs. Particle sizes include: 0-1mm; 1-3mm; 3-5mm; 5-8mm; 8-15mm; and 80-325 mesh. Our aggregate products are high-quality and competitively priced. Contact us for free samples and a quote.

Calcined Bauxite Aggregate Material Can be Applied to Make Monolithic Refractory — Calcined Bauxite Aggregate Material of Rongsheng

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Bauxite Calcination Process

The bauxite calcination process follows: raw materials entering the factory → crushing → screening → calcination → crushing → finished product delivery.

Equipment for Calcining Bauxite

In the process of producing calcined bauxite aggregate clinker, the calcination of bauxite has a great influence on the quality of the clinker. Therefore, it is very important to choose a kiln for calcining bauxite. The main equipment for calcining bauxite includes downdraft kiln, rotary kiln, tunnel kiln, etc.

(1) Downdraft kiln is an intermittent kiln. Its name is derived from the flow of flame. The flames generated by combustion all rise from the fire nozzle of the combustion chamber to the top of the kiln. Since the kiln top is sealed, the flames cannot continue to rise. In the absence of an air outlet at the top of the kiln, they are pulled downward by the suction force of the chimney. After passing through the gaps in the sagger columns, they enter the branch flue and the main flue from the fire-absorbing hole at the bottom of the kiln and are finally discharged from the chimney. Because hot gases are light in weight and always float on the surface, people are accustomed to calling the flames flowing from bottom to top “shun”. The flames flowing from top to bottom are called “reverse”. This is the origin of the name “downdraft kiln”.

The advantages of the downdraft kiln are that the kiln volume can be large or small, which is flexible in production and can produce high-quality products. The construction investment cost is low and the metal material consumption is low. The disadvantages are that it is intermittent operation and the exhaust gas temperature is very high when it leaves the kiln, so the fuel consumption per unit product is high. The production scale is small and the working conditions are poor. The mechanization level is low, the operation and control are difficult, and the production efficiency is low. The environmental performance is poor. Generally, the thermal efficiency of the downdraft kiln is only 6.48%, while the coal consumption per ton of finished product is as high as 1.456 tons.

Rotary Kiln for Bauxite Calcining Production

(2) The rotary kiln refers to a rotary calcining kiln, which originated in cement production. Rotary kiln equipment is now widely used in many production industries such as building materials, metallurgy, chemical industry, and environmental protection to perform mechanical, physical or chemical treatment on solid materials. Most rotary kilns for calcining bauxite have changed from heavy oil as fuel to coal powder as fuel. The coal consumption for calcining 1 ton of high-bauxite is 200-250kg. The characteristics of rotary kilns are: simple structure, few vulnerable parts, easy to control the production process and high operating rate. It is easy to mass produce and easy to realize automatic control, and the product quality is stable.

(3) Tunnel kilns are modern continuous firing thermal equipment, widely used in the roasting production of ceramic products, and also used in metallurgical industries such as abrasives. Tunnel kilns are mainly used for the firing of products. The refractory industry can be divided into three types according to the different operating temperatures. Low-temperature tunnel kilns are mainly used for roasting skateboard bricks, etc., with a firing temperature of about 1000℃. Medium-temperature tunnel kilns are mainly used for firing ordinary alkaline bricks, clay bricks, high-alumina bricks, silica bricks, etc., with a firing temperature of 1300℃-1650℃. High-temperature tunnel kilns are mainly used for firing mid-range magnesia bricks, high-purity magnesia bricks, magnesia-alumina and corundum products, with a firing temperature greater than 1700℃, generally between 1800℃-1900℃. The labor intensity is high, the production efficiency is low, the heat consumption is high, and it is difficult to realize automatic control.

At present, for calcined bauxite aggregate, large-scale bauxite calcining production systems at home and abroad all use rotary kiln equipment and technology.

Advantages and Disadvantages of Ceramic Aggregates and High-Alumina Aggregates

As two important refractory and construction materials, ceramic aggregates and high-alumina aggregates each possess unique advantages and disadvantages. Below is a detailed comparison of their advantages and disadvantages:

Ceramic Aggregate

Advantages

Reduced Density: Compared to traditional concrete aggregates, ceramic fine aggregate has a lower density, effectively reducing the overall density of concrete, thereby reducing the load on the building itself.
Increased Strength and Durability: Ceramic fine aggregate has higher strength and hardness, effectively improving the compressive strength and durability of concrete, making it stronger and more durable.
Reduced Environmental Pollution: Traditional concrete production produces large amounts of carbon dioxide and other pollutants, while ceramic fine aggregate concrete can effectively reduce environmental pollution and improve production efficiency.

Disadvantages

Higher Cost: Because the production cost of ceramic fine aggregate is higher than that of traditional aggregates, the cost of ceramic fine aggregate concrete is also higher, increasing the overall cost of concrete structure construction.
Difficult Construction: The construction of ceramic fine aggregate concrete is relatively difficult, requiring high technical requirements and construction experience, as well as special construction techniques and equipment.
Poor Seismic Resistance: Due to its lower density, ceramic fine aggregate concrete has inferior seismic performance compared to traditional concrete.

High-Alumina Aggregate

Advantages

High Strength and Hardness: High-alumina aggregates offer high strength and hardness, capable of withstanding high temperatures and mechanical stress, ensuring a stable and safe production process.
High-Temperature Resistance: High-alumina aggregates, calcined bauxite aggregates are primarily made from bauxite calcined at high temperatures. They contain a high proportion of aluminum oxide, resulting in excellent high-temperature resistance.
Chemical Stability: High-alumina aggregates exhibit excellent chemical stability at high temperatures and are resistant to reactions with acids and alkalis, maintaining excellent stability in aggressive media.
Wide Applications: High-alumina aggregates are widely used in ceramics, metallurgy, and the chemical industry. They are an indispensable raw material for applications such as refractory bricks, castables, and gunning mixes.
Thermal Insulation: High-bauxite aggregates are rich in alumina and have low thermal conductivity. They reduce indoor heat loss in winter and block external heat conduction in summer, providing greater building comfort and contributing to energy conservation and environmental protection.
Durability: Due to its high content of alumina, high-alumina aggregates are impervious to deliquescence, moisture, and water erosion, and are also resistant to acid and alkali corrosion. This extends the lifespan of buildings and reduces maintenance costs.

Disadvantages

High Cost. Due to the complex production process and high raw material costs, high-alumina aggregates command a relatively high market price.
High production equipment and processes are required. The production of high-alumina aggregates requires advanced equipment and processes to ensure product quality and performance.

In summary, ceramic aggregates and high-alumina aggregates each have their own unique advantages and applications. Choosing which aggregate to use requires careful consideration based on the specific project requirements and budget.

Monolithic Refractories in Various Shapes, Such as Powder, Granular, Mortar, and Block

September 17, 2025September 15, 2025 by rsrefractorycastable

Monolithic refractories, also known as bulk refractories, are made by mixing refractory aggregates and powders of a specific grade with binders and admixtures. These refractory linings materials are used directly without undergoing forming and firing processes. Rongsheng Castable Refractory Factory, a manufacturer of unshaped refractory materials, operates an advanced, environmentally friendly, fully automatic monolithic refractory production line with an annual output of 80,000 tons. They primarily produce monolithic refractory products, including refractory castables, refractory plastics, refractory ramming materials, refractory clay, high-temperature mortar, refractory cement, and prefabricated refractory blocks. These products provide reliable support for the integral lining of high-temperature industrial furnaces.

Refractory Castables

Refractory castables are a new type of refractory material that exhibits excellent fluidity after mixing with water without calcining. They are an important type of amorphous refractory material. They are a mixture of refractory aggregate, refractory powder, and binder (or admixtures) in a specific proportion. They can be shipped in bulk form or prefabricated.

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The composition of castable refractory is as follows:

Refractory aggregate is the main component of refractory castables and functions similarly to the crushed stone and sand in conventional building concrete. Refractory aggregate can be obtained from calcined clinker of various refractory materials (clay, high-alumina, siliceous, magnesian, etc.) or from various waste bricks that have been crushed to a certain degree. Aggregate particle size significantly impacts product quality. Coarse aggregate (5-20 mm) generally accounts for 35%-45% of the mix, while fine aggregate (0.15-5 mm) accounts for 30%-35%.
Binders: These act as a bonding and hardening agent, imparting a certain strength to the product. Common binders include ordinary Portland cement, alumina cement (high-alumina cement), magnesia cement, water glass, and phosphoric acid. To ensure refractoriness and minimize volume shrinkage during use, the binder dosage should be kept as low as possible, generally 10% to 25%. Furthermore, the binder and aggregate should not form excessive low-melting products.
Admixtures: To improve the physical and chemical properties and workability of refractory castables, appropriate amounts of these additives are often added. These include plasticizers, dispersants, accelerators, retarders, dilution agents, and gelling agents. For refractory castables exposed to high mechanical forces or intense thermal shock, adding an appropriate amount of stainless steel fiber can significantly increase the material’s toughness. Adding inorganic fiber to insulating refractory castables not only enhances toughness but also helps improve thermal insulation.

Refractory Mortar

Refractory mortar, composed of refractory aggregate, binders, and admixtures, is used as a joint material for shaped products. It is delivered in dry or wet form. During construction, a mixing liquid (water or other liquid) is added to the mortar to a specified consistency. Masonry or pouring is then performed using a trowel or specialized machinery (such as a pressure grouting machine).

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Refractory mortar is divided into two categories: heavy and light. Based on the binder, it can be categorized as phosphate slurry, water glass slurry, and organic binder slurry. Based on the material, it can be categorized as clay, high-alumina, magnesia, silica, or carbonaceous slurry. Its components are as follows:

01 Refractory Powder

Refractory powder is typically fine particles of refractory materials such as high-alumina, silica, and magnesia, and determines the basic properties of the refractory mortar.

02 Binder

Binders, such as Portland cement, phosphate, and water glass, are used to allow the refractory mortar to harden and develop a certain strength after application.

03 Admixtures

Admixtures are added according to specific application requirements, such as setting accelerators, setting retarders, and plasticizers.

Performance Characteristics

Excellent Adhesion: Securely bonds refractory bricks and other refractory materials, forming a tight masonry structure and preventing the penetration of high-temperature gases and slag.
High Refractoriness: Remains stable at high temperatures without softening or melting, maintaining masonry stability.
Suitable Plasticity: Facilitates construction and can fill brick joints and irregularities.
Excellent Volume Stability: Minimal volume change at high temperatures, preventing expansion or contraction that could damage the masonry structure.

Refractory Precast Blocks

Precast blocks, which cannot be mass-produced for certain reasons, are typically prefabricated refractory block products composed of refractory aggregate, refractory powder, binders, and admixtures.

Precast Shapes with Refractory Anchor Bricks for Heating Furnace Top — Precast Shapes with Refractory Anchor Bricks for Furnace

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01 Refractory Aggregates

Refractory aggregates, such as high-alumina bauxite, corundum, and mullite, form the primary skeleton of precast blocks. They determine their refractoriness and high-temperature strength.

Refractory powder: Refractory powder has a finer particle size and fills the gaps between aggregates, increasing the density and strength of the precast blocks.

02 Binders

Common binders include cement, phosphate, and water glass. They are used to bind the aggregate and powder together, ensuring sufficient strength after curing under certain conditions.

03 Admixtures

Additional additives, such as accelerators, retarders, and explosion-proofing agents, are added as needed to improve the construction and performance of precast blocks.

Performance Characteristics

Excellent refractory properties: Maintains structural stability in high-temperature environments without softening or melting. High refractoriness and refractoriness under load.
Good mechanical strength: Through a rational formulation and manufacturing process, the precast blocks possess high compressive and flexural strength, capable of withstanding mechanical loads at high temperatures.
High-dimensional accuracy: Prefabricated in the factory, dimensional deviations can be strictly controlled, facilitating installation and ensuring the quality and tightness of the masonry.
Easy and convenient construction: The precast blocks can be transported directly to the construction site for installation, reducing on-site construction time and workload. They are particularly suitable for the construction of complex structures such as large industrial furnaces.
Good thermal stability: They can withstand rapid temperature fluctuations without cracking or flaking, ensuring safety during furnace startup and shutdown.

Refractory Cement

Refractory cement, also known as aluminate cement, is a specialty cement with high refractory properties. It is used as a binder in refractory materials for the production of refractory bricks, refractory castables, and refractory spray coatings. It enables refractory materials to maintain excellent strength and integrity at high temperatures. It is also used in the linings of various industrial furnaces, such as those used in steelmaking, cement, and glassmaking.

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01 Composition

It is primarily composed of calcium aluminate minerals, such as monocalcium aluminate (CaO·Al₂O₃) and monocalcium dialuminate (CaO·2Al₂O₃). It may also contain small amounts of dicalcium silicate (2CaO·SiO₂).

Performance Characteristics

High refractoriness: It maintains structural stability in high-temperature environments, resisting softening and melting. Its refractoriness generally exceeds 1580°C.
Early Strength and Rapid Hardening: It exhibits a high rate of early strength development, achieving high strength in a short period of time, facilitating rapid construction.
Excellent Corrosion Resistance: Strong resistance to corrosive media such as slag and molten salt at high temperatures.
Excellent Thermal Stability: Minimal volume change with temperature fluctuations, making it less susceptible to cracking and flaking.

Can Lightweight Castables Used as Insulation Layers for Industrial Furnaces Reduce Heat Consumption?

August 31, 2025 by rsrefractorycastable

Lightweight castables have lower thermal conductivity than heavy castables and significantly reduce the weight of the furnace lining. The diffusion rate of combustion temperature in industrial furnaces can be reduced by about 30% compared to heavy castables. Therefore, using lightweight insulating castables as insulation layers can effectively reduce the heat loss of industrial furnace linings.

Lightweight Castable Refractory for Furnaces

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Lightweight Castables as Insulation for Industrial Furnaces

Lightweight castables are the first layer of material that adheres to the furnace shell in the kiln lining. High-end lightweight castables, such as hollow alumina sphere castables and lightweight mullite refractory castables, can also be used directly as a working layer on the lining of some lightweight kilns. This reduces furnace weight, lowers heat consumption, and saves energy costs.

The thickness of lightweight castables used as insulation should be 80mm-150mm. Thicknesses below 50mm will result in poor installation and ineffective insulation. Using lightweight castables for lining pipes and chimneys is also a poor choice. Castables with a specific gravity of approximately 1.5 can serve as both an insulation layer and a working layer. This reduces weight while meeting the requirements for chimney and pipe linings.

Lightweight castables are used at different temperatures: low temperatures (600-900°C), medium temperatures (900-1200°C), and high temperatures (1200°C). High-temperature insulation layers require high-quality lightweight materials, such as lightweight mullite and hollow alumina sphere castables. Commonly used materials include vermiculite, perlite, and ceramsite. These materials have an operating temperature of approximately 1000°C and cannot be used at high temperatures. Lightweight mullite and corundum-mullite castables can be used at temperatures between 1350°C and 1500°C, allowing for direct use in the working layer.

Lightweight castables lack the refractoriness, compressive strength, and flexural strength of heavier castables. However, their low thermal conductivity provides excellent insulation. Choosing the right lightweight material for different temperatures and kiln linings can effectively insulate and reduce energy consumption.

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Significant Features of Low Thermal Conductivity Castables

Low thermal conductivity castables are unique refractory materials that maintain low bulk density and low thermal conductivity even at high temperatures, while also offering excellent thermal insulation. Unlike conventional lightweight castables, whose bulk density increases with increasing temperature, low thermal conductivity castables maintain a low bulk density even at high temperatures. Their light weight effectively reduces the weight of equipment, which is crucial for the installation and operation of large-scale industrial equipment. Furthermore, their excellent thermal insulation properties ensure more uniform furnace temperature distribution, thereby saving energy and reducing production costs.

In terms of technical performance, low thermal conductivity castables offer the dual advantages of low bulk density and high refractory strength, a true innovation in themselves. They offer strong overall performance, excellent spalling resistance, a long service life, and can be repaired and processed into various shapes as needed. They can also be used to construct integral furnace linings, greatly facilitating the maintenance and construction of industrial furnaces.

Wide Application Areas and Energy-Saving Advantages

Low thermal conductivity castables have a wide range of applications across numerous industries. They are widely used in industrial furnaces and thermal equipment in industries such as metallurgy, machinery, power generation, chemicals, and petroleum. Compared to conventional lightweight castables, using low thermal conductivity castables can achieve energy savings of over 20%, a significant saving for energy-intensive industries. Especially in applications such as petroleum and petrochemical furnaces, where material performance requirements are more stringent, low thermal conductivity castables require a lower bulk density and adhere to stricter quality standards. Therefore, compared to lightweight castables used in other industries, low thermal conductivity castables for petroleum and petrochemical furnaces are of higher quality and relatively higher price. However, the energy-saving benefits and equipment protection they provide are well worth the effort.

Easy Construction

Low thermal conductivity castables are relatively easy to apply. Manufacturers carefully select the aggregate particle size. An appropriate particle size helps enhance the compressive strength of lightweight castables. Excessively large particle sizes can negatively impact the construction process. By optimizing the particle size, low thermal conductivity castables can be constructed more smoothly, reducing difficulties and problems during construction, improving construction efficiency, and ensuring construction quality.

Considerations for Lightweight Castable Pipe Installation

Lightweight castables provide insulation. For pipe use, their bulk density generally must be no less than 1.2 kg/m³. Specific gravity of 1.5 is more common. When used in pipes, installation is limited by the pipe diameter, making it difficult for workers to work within the pipe.

1. Pay attention to the insulation layer.

Applying the insulation layer to the insulation is also challenging. The pipe insulation in the image above is applied irregularly, and the anchors are not suitable for use. Anchors must be painted. If not, plastic caps must be placed on them. Otherwise, rust will occur, shortening their lifespan.

If this occurs, there is a remedy: apply a layer of plastic film to the surface of the insulation. This prevents moisture from penetrating the insulation during baking after the lightweight castable is applied. If moisture seeps into the insulation, even after drying, the insulation’s effectiveness will be reduced.

2. Pay attention to the proportions added during construction.

When applying lightweight materials, the water ratio must be carefully considered. If too little water is added, some of the base materials, due to their light weight, will be difficult to apply and will not set easily. Adding too much water will affect the strength of the material in the final application.

3. Mix the aggregate and powder before construction.

During on-site construction, first mix the aggregate and powder, then add the binder. Then, strictly follow the manufacturer’s water ratios and mix the lightweight castable. After mixing, verify that the castable has good fluidity before vibrating. Generally, the water content for lightweight castables is 15-17%. Some manufacturers, due to the light weight of the lightweight castable, may sprinkle some water during production to facilitate production control.

High Temperature Performance of Silicon Carbide Refractories

August 18, 2025August 16, 2025 by rsrefractorycastable

SiC is widely used in key areas of the steel and nonferrous metallurgy industries due to its stable high-temperature chemical properties, excellent high-temperature strength, high wear resistance, and good thermal shock resistance. Examples include blast furnace tuyere, inner wall, ceramic cups, various furnace wall linings, and kiln furniture. Compared to metals and intermetallic compounds, silicon carbide refractories have higher high-temperature strength and creep resistance. Compared to oxide ceramics, they have higher thermal conductivity and thermal shock resistance. The high-temperature properties of silicon carbide refractories are as follows:

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High-Temperature Oxidation Resistance of SiC Refractories

Although SiC offers excellent performance, it is susceptible to oxidation during long-term use. Extensive research has been conducted on the oxidation process of SiC. Results indicate that high-temperature oxidation of SiC can be divided into two types: passive oxidation and active oxidation. When the O₂ partial pressure is below 10⁻⁴Pa, SiC undergoes active oxidation, with the product being SiO₂ gas and the net weight decreasing. When the O₂ partial pressure is above 10⁻⁴Pa, SiC undergoes passive oxidation, with the product being SiO₂ and the net weight increasing. The formation of a SiO₂ protective film prevents further oxidation. However, at oxidation temperatures above 1473K, SiO₂ converts to cristobalite at high temperatures. This volume expansion destroys the structure of the oxide film, causing cracks, which in turn leads to internal oxidation, severely shortening the service life of the SiC material. Therefore, improving the oxidation resistance of SiC materials is an essential consideration in the design and preparation of SiC refractories.

The high-temperature oxidation behavior of a self-bonded SiC material with a porosity of 11.5% in air at 1573K was studied. Research results show that the amorphous SiO2 formed during the initial oxidation process can passivate pores and crack tips within the material, resulting in an increase in the room-temperature strength of the material with increasing oxidation time. The refractory material achieved its highest strength, reaching 293 MPa, at an oxidation time of 22.5 h. As oxidation time continues, the amorphous SiO2 crystallizes to form cristobalite, destroying the structure of the oxide film and generating new surface cracks during cooling, resulting in a decrease in the room-temperature strength of the material.

The effects of adding varying amounts of calcium oxide, aluminum oxide, and zirconium oxide to SiC on its oxidation resistance at different temperatures were investigated. Experimental results show that a 2 wt% aluminum oxide addition yields the best oxidation resistance. Mullite coatings were generated on recrystallized SiC materials of varying particle sizes using a sol-gel method. The effects of coating thickness and particle size on the high-temperature oxidation behavior of the recrystallized SiC at 1773 K were investigated. Results show that the formation of mullite coatings significantly improves the high-temperature oxidation resistance of the recrystallized SiC. Furthermore, increasing coating thickness increases the oxidation resistance of the recrystallized SiC material. Al₂O₃, SiO₂, and Mullite coatings were applied to SiC whiskers using a sol-gel method. Anti-oxidation experiments showed that all three coatings improved the oxidation resistance of SiC.

In summary, while silicon carbide refractories possess relatively good oxidation resistance, oxidation to a certain degree can be fatal to the material’s structure. Therefore, studying the mechanism and control of the oxidation process in silicon carbide refractories, as well as its impact on the material’s structure and properties, is of great significance.

Silicon Carbide Lining Refractory for Furnaces

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Thermal Shock Resistance of SiC Refractories

As an important high-temperature industrial structural material, silicon carbide refractories have high requirements for thermal shock resistance. The thermal shock resistance of SiC materials is not only related to their microstructure, grain size, and the shape and distribution of internal defects, but also to physical properties such as strength, elastic modulus, thermal conductivity, thermal expansion coefficient, Poisson’s ratio, and porosity. Improving and enhancing the thermal shock resistance of SiC materials is crucial for their safe and stable use.

The Effect of Different Bonding Methods on the Thermal Shock Resistance of SiC Kiln Furniture. Si2N2O-bonded SiC kiln furniture exhibits superior thermal shock resistance to mullite- and Si3N4-bonded SiC kiln furniture. When the Si2N2O content is ≤20%, the thermal shock resistance of Si2N2O-bonded SiC samples improves with increasing Si2N2O content. When the Si2N2O content exceeds 20%, the thermal shock resistance of the samples decreases.

Si3N4-SiC and Sialon-SiC materials were prepared by reaction sintering. The results show that the in-situ formation of Si3N4 or Sialon bonding phases can increase the toughness of SiC materials, influence crack propagation, and modulate stress distribution at high temperatures, improving the material’s plastic deformation capacity at high temperatures and, consequently, enhancing the thermal shock resistance of SiC materials.

The thermal shock resistance of reaction-sintered SiC materials was also studied. The results show that materials with low residual Si content and small SiC particles exhibit superior thermal shock resistance to materials with high residual Si content and large SiC particles.

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SiC Refractories’ Resistance to Cryolite Attack

SiC is used as the bottom material for aluminum electrolytic cells because it is non-wettable by molten aluminum and exhibits high thermal conductivity, chemical stability, and excellent oxidation resistance. Aluminum smelting typically uses cryolite (Na₃AlF₆) as a flux, and is carried out by electrolytic reduction of aluminum oxide in the electrolytic cell at a temperature typically between 1173 and 1273 K. Therefore, studying the resistance of SiC materials to cryolite attack is of great practical significance.

The attack of cryolite on various non-oxides, such as BN, SiC, Si₃N₄, Al₁N, and TiN, was studied. The results showed that these non-oxides exhibited good resistance to cryolite attack. Cryolite melt enters the pores of Si₃N₄-bonded SiC refractory materials and reacts with the binder phase. Erosion of the binder phase causes SiC particles to fall into the cryolite melt, resulting in corrosion of the material.

The crucible method was used to study the cryolite melt corrosion resistance of Si3N4-bonded SiC refractory materials. The results showed that after 20 hours of corrosion at 1273K, only a small amount of corrosion was observed on the inner wall of the crucible of the Si3N4-bonded SiC refractory prepared in an air atmosphere. This indicates that the material has good cryolite corrosion resistance.

The static crucible method was also used to study the cryolite corrosion resistance of alumina-based Sialon-bonded corundum-SiC composite refractory materials at 1273K. The results showed that under these conditions, cryolite erosion of the composite material was minimal, with an erosion layer thickness of approximately 1mm, and the erosion product being NaAlSiO4. The penetration layer depth was approximately 6mm, and the penetration rate decreased with increasing Sialon content.

In summary, silicon carbide refractory materials have excellent cryolite corrosion resistance. The corrosion mechanism suggests that corrosion primarily occurs between cryolite and oxides in the binder phase. Reducing or eliminating the oxide content in the binder phase could further improve the cryolite corrosion resistance of silicon carbide refractory materials.

To purchase high-quality silicon carbide refractory materials, please contact Rongsheng Refractory Materials Factory for free samples and quotes.

Importance of Refractory Aggregate in Refractory Castables

August 1, 2025 by rsrefractorycastable

Refractory aggregate is a key component of refractory castables. Its type, grade, and particle size distribution are key factors influencing various castable properties.

Performance Requirements for Refractory Aggregates

High-Temperature Stability

Refractory aggregates must exhibit excellent chemical stability at high temperatures, resisting chemical reactions with the melt and gases within the furnace and maintaining their structure and properties. They must also possess a low coefficient of thermal expansion and good thermal shock resistance to withstand rapid temperature fluctuations without breaking.

Most refractory aggregate particles are multiphase and polycrystalline. Therefore, their shape is influenced by the crystal structure, crystallization behavior, and impurity content of the various phases in the material, as well as the processing methods used.

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For example, mullite produced by the electric fusion process, because it precipitates from the melt, is mostly euhedral. Therefore, due to its crystallization behavior, mullite often forms columnar polycrystalline aggregates. During crushing, the grains fracture along the longitudinal direction, where the bonding strength is poor, resulting in the formation of columnar polycrystalline particles.

Mullite produced by sintering, however, has crystal growth that is constrained by the surrounding environment. This results in morphologies such as needles, columns, plates, and granules, with irregular interlacing growth. Consequently, the crushed particles have irregular shapes, including flakes, needles, columns, and fusiform shapes.

The morphology of crushed refractory aggregate particles also depends on the density of the material and the crushing method. For example, for ultra-dense and high-density high-alumina clinker, impact or extrusion crushing methods often produce flake or fusiform aggregate particles. Grinding crushing methods often produce irregular granular or nearly spherical shapes. Therefore, to produce aggregate particles that are most suitable for monolithic refractory materials, a more appropriate crushing method should be selected.

Mechanical Strength

Under high-temperature operating conditions, refractory aggregates must withstand the impact, abrasion, and pressure of the furnace charge. Therefore, they must possess sufficient mechanical strength, including compressive strength, flexural strength, and wear resistance.

Particle Size Distribution

A reasonable particle size distribution is crucial to the performance of refractory materials. Typically, refractory aggregates are composed of particles of varying size grades to form a tightly packed structure, enhancing the material’s density and strength.

In the production of monolithic refractory materials, refractory aggregates are generally divided into coarse, medium, and fine aggregates. The particle size ranges of coarse, medium, and fine aggregates are related to the critical particle size (i.e., particle size) of the aggregate.

For example, if the aggregate particle size is 8 mm, the coarse aggregate particle size range is 8-3 mm, the medium aggregate particle size range is 3-1 mm, and the fine aggregate particle size range is 1-0.088 mm. Particles smaller than 0.088 mm are not considered aggregates but are instead called powder (or matrix).
For example, if the aggregate particle size is 3.5mm, the coarse aggregate particle size range is 3.5-1.5mm, the medium aggregate particle size range is 1.5-0.5mm, and the fine aggregate particle size range is 0.5-0.074mm.

The ideal aggregate particle size distribution should achieve the most compact packing. That is, the gaps left by the coarse particles are filled by the medium particles, and the tiny gaps left by the medium particles are filled by the fine particles, thus forming a skeleton. The remaining gaps are filled by the powder. However, due to the irregular shape of refractory aggregate particles, achieving an ideal aggregate particle size distribution is difficult in actual production. Aggregate gradation is usually determined through experiments, and the typical ratio of coarse, medium, and fine aggregate is (35-45):(30-40):(15-25).

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Refractory Aggregates for Refractory Castables

Castable performance can be improved through refractory aggregate grading.

The refractory aggregate grade, impurity content, sintering quality, and storage time of the raw materials also affect castable performance. As the Al₂O₃ content increases, the castable’s refractoriness and refractoriness under load also increase. When the post-firing linear change decreases, or when the material is underfired or contains a high impurity content, the refractoriness and refractoriness under load decrease, and the post-firing linear shrinkage increases.

Before making refractory castables, it is important to select well-sintered, high-purity bauxite and carefully grade the refractory aggregate to improve the various properties of the castable.

The particle size of the refractory aggregate is determined by the thickness of the lining.

The more irregular the shape of the refractory aggregate particles, the better. Avoid using long, flake-shaped particles. The particle size is determined by the thickness of the lining.

The Importance of Refractory Aggregates in Refractory Castables.

The grade, impurity content, sintering quality, and raw material quality of the refractory aggregate significantly influence the density of the castable. These are the most basic principles that must be followed when determining the aggregate particle size gradation. The values may change after adding cement and powder, but the basic principles remain the same.

When high-alumina cement is added to the castable, the material fluidity remains the same, but the water requirement is different. A better aggregate particle size gradation reduces water usage, increases bulk density, and reduces apparent porosity. Furthermore, the compressive strength at room temperature and after firing is also higher. When fine aggregate is present in larger quantities, its particle surface area increases, requiring the addition of more cement and powder to encapsulate the aggregate and prevent the aggregate from becoming densely packed. While a higher cement content also requires more water, encapsulation is crucial. Therefore, a proper mix ratio is crucial to avoid compromising the performance of the refractory castable.

Refractory aggregate particle grading is generally a three-level gradation, with a high-quality gradation characterized by larger particles at the ends and smaller particles in the middle. When crushing refractory aggregate, the ratio of large, medium, and small particles should be controlled to prevent segregation of oversized particles, thereby creating a denser castable.

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Applications of Refractory Aggregates

Refractory aggregates are widely used in high-temperature industries such as steel, nonferrous metallurgy, glass, cement, and ceramics. The following are some specific application examples:

In Steelmaking

High-alumina refractory aggregates are commonly used in the shaft and waist of blast furnaces to withstand the erosion of high-temperature molten iron and slag, as well as the impact of furnace charge. Magnesia refractory aggregates are often used in electric furnace linings. Their excellent slag resistance and high-temperature resistance effectively extend the service life of electric furnaces.

In the Glass Industry

Silica refractory aggregates are the primary material for kiln refractory linings. For example, the tin baths in float glass production lines use refractory materials made from high-quality silica refractory aggregates, which can withstand temperatures up to 1600°C and resist the erosion of molten glass.

In Cement Production

The firing zone of rotary kilns typically utilizes refractory materials made from magnesia-chromium refractory aggregates to withstand the abrasion and chemical attack of high-temperature clinker.

In tunnel kilns in the ceramic industry

Refractory bricks made from mullite refractory aggregate are used in the kiln roof and walls, ensuring long-term stability and energy efficiency.

In short, refractory aggregates, as a crucial component of refractory materials, play an irreplaceable role in ensuring the safe and efficient operation of high-temperature industries. Continuous in-depth research and innovation in the performance, preparation processes, and applications of refractory aggregates will provide strong support for the development of high-temperature industries.

What Should You Do if the Refractory Plastic Cannot be Cured?

July 17, 2025 by rsrefractorycastable

Recently, a user of Rongsheng Refractory Material Factory consulted that a batch of refractory plastics purchased before could not solidify after ramming, and wanted to ask what was going on. Rongsheng Factory, based on years of production, sales, and construction experience, analyzed from the following aspects to help customers solve the problem. Rongsheng Refractory Castable Factory, a professional technical team, and an environmentally friendly fully automatic amorphous refractory production line provide material guarantees for the overall refractory lining of high-temperature industrial furnaces. Contact Rongsheng to get free solutions and quotes for refractory linings.

Phosphate Bonded High Alumina Refractory Plastics — Rongsheng Refractory Plastics

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As we all know, the components of refractory plastics are made of granular and powdered aggregates, plastic clay, and other binders and plasticizers, and then a small amount of water is added. After fully mixing, it is a hard mud-paste-like amorphous refractory material that maintains high plasticity for a long time.

What aggregates and binders are refractory plastic components divided into?

According to the type of aggregate, it can be divided into clay, high aluminum, mullite, corundum, chromium, silicon carbide, and zirconium-containing refractory plastics. According to the type of binder, it can be divided into refractory plastics combined with aluminum sulfate, phosphoric acid, phosphate, water glass and resin.

The plasticity index of refractory plastics requires that the amount of water added must be limited when adding binders

Plastic clay is an additional binder for plastics. It only accounts for 10%~25% of the total weight of plastics, but it has a great influence on the bonding strength between plastics and their hardened bodies, the plasticity of plastics, the volume stability and refractoriness of plastics and their hardened bodies.

The plasticity of refractory materials is related to the characteristics of clay, the amount of clay used and the amount of water. It mainly depends on the amount of water, which increases with the increase of water. However, too much water will bring adverse effects, generally 5%~10% is appropriate.

Necessity of adding appropriate amount of plasticizer to refractory plastic

In order to control the amount of clay in plastic and reduce the amount of water, it is necessary to add appropriate amount of plasticizer. Its plasticizing effects mainly include: increasing the hygroscopicity of clay particles. Dispersing clay particles and wrapping them with water film. Dispersing humus in clay and making clay particles sol. Increasing the electrostatic repulsion between clay particles in clay-water system. Stabilizing sol. Excluding ions that hinder solification from the system as insoluble salts, etc.

Considering the hardening and strength of plastic, it is necessary to correctly select the binder

Plastic without any added chemical binder is called ordinary plastic. This kind of plastic has very low strength before sintering, but as the temperature rises, water escapes and the strength increases. After high-temperature sintering, the cold strength increases. But the hot strength at high temperature decreases with the increase of temperature.

The strength of plastic with sodium silicate increases faster with the increase of temperature after construction, and the mold can be removed faster after construction. However, during the drying process, this binder may migrate to the surface of the structure or product, preventing the smooth removal of moisture and causing stress and deformation of the surface.

Aluminum phosphate is the most widely used thermosetting binder in plastics. After construction, it can obtain high strength after drying and baking.

In order to improve the shortcomings of plastics with soft clay as binder, such as slow hardening after construction and low strength at room temperature, it is often chosen to add an appropriate amount of air-hardening and thermosetting binders and their polymers.

High-quality plastics also need to have excellent thermal shock resistance

The good thermal shock resistance of plastics mainly depends on the following aspects: Plastics made of aluminum silicate refractory raw materials as granular and powdered materials will not produce serious deformation caused by crystal transformation during heating or when used at high temperatures. The mineral composition near the heating surface is fine crystals of mullite and cristobalite, with less glass, and transitions along the heating surface to the low-temperature side. The structure and phase of the plastic are gradual rather than drastic. Due to the uniform porous structure in the plastic component, the expansion coefficient and elastic modulus are generally low.

Correct construction method of refractory plastics

The construction of plastics requires a tamping machine or manual tamping. The thickness of each addition is 80~100mm. After tamping, the surface is loosened, and then the material is added to continue tamping until it is completed. According to the type of binder, temperature and humidity conditions, the plastic should be naturally dried for a period of time before demolding. Because demolding too early will cause cracks on the stress surface of the anchor brick. When the temperature is around 25℃, the plastic combined with phosphoric acid should be demoulded after 48 hours of natural drying. The plastic combined with aluminum sulfate and clay should be demoulded after 72 hours of natural drying.

The shelf life of refractory plastic should not be too long

Refractory plastic generally has a shelf life of 15 days. Experienced manufacturers do not use hydraulic binders to ensure that the plasticity of plastic does not decrease significantly during its shelf life. Rongsheng Refractory Material Manufacturers recommends that users use up the products in one construction within 3-5 days after the arrival of the goods, and do not store them for a long time.

Rongsheng Refractory Material Manufacturer recommends that you purchase high-quality refractory plastic products and read the instructions for the construction and use of refractory plastic in detail. Strictly follow the construction instructions for construction. Choose a professional construction team to carry out the construction of the refractory furnace lining. After the construction is completed, reasonable maintenance of the refractory furnace lining can effectively extend the service life of the furnace lining.

Thermodynamic Properties of Al2O3-SiC-C Castables

June 30, 2025June 26, 2025 by rsrefractorycastable

Al2O3-SiC-C castables have excellent thermal shock resistance and slag resistance, and are widely used in blast furnace tapping channels, ladle linings, and slag lines of mixed iron furnaces. Al2O3-SiC-C (hereinafter referred to as ASC) castables mostly use ultra-low cement bonding systems composed of alumina micropowder, silica micropowder, and a small amount of calcium aluminate cement. Compared with ultra-low cement bonding, calcium aluminate cement bonding without silica micropowder and cement-free bonding have the characteristics of high purity and small amount of liquid phase generated at high temperature. Therefore, it has excellent high-temperature mechanical properties and slag resistance.

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Bonding Methods of ASC Castables

For a long time, people have been accustomed to the ultra-low cement bonding method and the application of silica powder in ASC castables. Therefore, there are few applications and research on calcium aluminate cement bonded ASC castables without silica powder. Common cement-free bonding methods for castables mainly include silica powder agglomeration bonding, hydrated alumina bonding and sol bonding. The shortcomings of silica powder agglomeration bonding are low body strength, hydrated alumina bonding body strength, poor burst resistance, etc., which make these two bonding methods less used in ASC castables. In recent years, with the development of silica sol bonded castable technology, a small amount of silica sol bonded ASC castables have appeared on the market. With the development of alumina sol bonding system, alumina sol bonded ASC castables that replace hydrated alumina may have better performance.

It is well known that the good thermal conductivity of silicon carbide and carbon in ASC castables gives the material better thermal shock resistance, and the non-wettability of carbon and slag gives the material better slag resistance. Carbon plays a key role in the structure and performance of ASC castables. However, carbon is easily oxidized at high temperatures, which deteriorates the material structure and performance. Carbon can be oxidized by oxygen in the atmosphere and by the material’s own oxide components, such as SiO2. When SiO2 and carbon coexist, the generation and escape of SiO2 gas at high temperatures will consume the carbon in the material, increase the porosity of the material, and thus deteriorate the performance of the material. It can be seen that as far as ASC castables are concerned, the SiO2 component may have an adverse effect on its performance. Based on the above analysis, this work studied the changes in phase composition and chemical composition of four common bonding methods of ASC castables: silica sol, silica-free micropowder cement, hydrated alumina and ultra-low cement, and conducted thermodynamic analysis.

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Thermodynamic Properties of Al2O3-SiC-C Castables

(1) After calcination at 1350℃, the mass of all samples with different bonding methods increased significantly. Compared with the samples calcined at 1350℃, the mass change rate of the samples calcined at 1500℃ decreased significantly except for the pure calcium aluminate cement bonding method without silica powder.

(2) Thermodynamic analysis showed that under the carbon coexistence calcination conditions in the Si-O-C-N system, SiO2 is a stable phase when the temperature is below 1431℃, and SiC is a stable phase when the temperature is above 1431℃. Si and SiC in Al2O3-SiC-C castables are oxidized by CO at low temperatures, which increases the C and SiO2 contents in the castables.

(3) Under the carbon coexistence calcination conditions, the stability order of SiO2-containing compounds is: cristobalite < mullite < anorthite. Under the condition of 1500℃ carbonization, both cristobalite and mullite can be reduced by C, while anorthite can only be reduced by C when there is enough Al2O3 around it. When the temperature does not exceed 1550℃, Si can prevent C from being oxidized by SiO2-containing compounds, and SiC can only prevent C from being oxidized when the temperature is lower than 1431℃.

(4) When the SiO2 content in the material is high, more SiO gas will escape from the reaction, which will lead to a reduction in sample mass and unstable structure. Considering that silica can promote the formation of SiC, the amount of silica powder added to ASC castables should be minimized.

Low Cement Silicon Carbide Castable in RS Factory

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Low Cement SiC Refractory Castable

Low cement SiC refractory castable is characterized by low linear expansion coefficient, high thermal conductivity, high strength and good wear resistance. It has been applied in thermal equipment such as power generation boilers, non-ferrous metallurgical furnaces and incinerators, and the use effect is good. Low cement SiC refractory castable uses silicon carbide with SiC greater than 97% as refractory aggregate and powder, adds SiO2 ultrafine powder and metal silicon antioxidant, uses CA-70 cement as binder and adds polyphosphate water reducer. The main properties of this material are SiC of 85%, 110℃ drying bulk density, pressure resistance and flexural strength are 2.5g/cm3, 45MPa and 9MPa respectively. After burning at 1000℃, the linear change, pressure resistance and flexural strength are -0.2%, 107MPa and 24MPa respectively. After firing at 1450℃, the linear change, compressive strength and flexural strength are +0.3%, 130MPa and 54MPa respectively, and the thermal conductivity at 400℃ is 12.2W/(m·K).

Rongsheng Refractory Castable Manufacturer

Rongsheng Refractory Castable Manufacturer, advanced environmentally friendly fully automatic amorphous refractory production line, specializes in providing refractory products for high-temperature industrial furnace linings. Rongsheng’s refractory products have been sold to more than 120 countries and regions around the world, including South Africa, Chile, Egypt, Colombia, Uzbekistan, Italy, Indonesia, Ukraine, Hungary, Spain, Kenya, Syria, Zambia, Oman, Venezuela, India, Peru, the United States, Ethiopia, Iran, Iraq, Israel, etc. If you need to buy high-quality silicon carbide refractory castables, low-cement silicon carbide refractory castables, Al2O3-SiC-C castables, please contact Rongsheng manufacturers. Get free samples and quotes.

How to Prevent Oxidation of Al2O3-SiC-C Castable?

June 17, 2025June 5, 2025 by rsrefractorycastable

Technological progress. Rongsheng monolithic refractory manufacturer, environmentally friendly fully automatic monolithic refractory production line, specializes in providing high-quality refractory products for high-temperature industrial furnace linings. After years of hard work, Rongsheng’s refractory products have been sold to more than 120 countries around the world, such as South Africa, Chile, Egypt, Colombia, Uzbekistan, Italy, Indonesia, Ukraine, Hungary, Spain, Kenya, Syria, Zambia, Oman, Venezuela, India, Peru, the United States, Ethiopia, Iran, Iraq, Israel, etc. Rongsheng’s iron trough castable, Al₂O₃-SiC-C castable, has also improved its oxidation resistance compared to before. Contact Rongsheng for detailed information. So, how does Al₂O₃-SiC-C castable prevent oxidation?

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Preferential Oxidation of Carbon Source

Antioxidants are added to the castable material of the iron trough. The main principle is that the affinity of the antioxidant with oxygen is greater than the affinity of carbon with oxygen. The added antioxidant reacts with oxygen before carbon to achieve an anti-oxidation effect. Anti-oxidation mechanism of adding borides, Si and Al:

(1) The additive itself undergoes oxidation reaction before carbon.
(2) Part of the low-melting phase is generated during the high-temperature process, which blocks the porosity inside the material and increases the density of the material, resulting in the material having good anti-oxidation properties.

The effect of the amount of metal silicon powder added on the performance of the iron trough castable. From the cross-section, as the amount of metal silicon powder added increases, the area of the darker color area in the cross-section increases, indicating that the anti-oxidation effect is better. During the sintering process of the sample, the anti-oxidation mechanism of metal silicon powder as an antioxidant is as follows:

anti-oxidation mechanism 1

In the same time, as the amount of metal silicon powder added increases, the amount of carbon reduced in the sample increases. At the same time, the more SiO2 is generated by the reaction, of which SiO2 is in the liquid phase, which can close the pores and increase the density. In this way, the anti-oxidation performance and comprehensive mechanical properties of the castable are improved.

Figure 1 Cross-section of samples with different amounts of metal silicon powder added after oxidation

Adding metal Al powder to carbon-containing refractory materials can have an antioxidant effect. This is mainly because during the heat treatment process, Al reduces CO to C(s) and generates Al2O3, which inhibits the oxidation of C. The reaction formula is as follows:

Volume expansion will occur during this reaction process, increasing the density of the material structure, thereby hindering the oxidation of carbon. However, metal Al will react with carbon above 1 000°C to generate Al4C3. And Al4C3 will react with water vapor during the reaction process:

The material will have a significant volume expansion, seriously deteriorating the comprehensive performance of the material.

During the oxidation process at 1100°C and 1500°C, the antioxidant is BN, and its reaction equation is:

This shows that BN has an antioxidant effect. In addition, the generated B2O3 promotes the sintering of the sample, blocks the pores of the sample, and makes the structure of the sample denser. But the generated N2 will also cause the volume expansion of the sample.

In addition, B4C was added to Al2O3-SiC-C castable to study the effect of B4C on its mechanical properties. B4C will undergo oxidation reaction in air atmosphere:

The generated B2O3 liquid phase can promote sintering and improve the anti-oxidation effect of the material. The improvement of anti-oxidation property also further inhibits the oxidation of carbon-containing materials such as SiC, and also has a positive effect on the high-temperature flexural strength of the sample.

It can be seen that the anti-oxidation mechanism of CaB6 is the same as that of B4C and BN. They all react with O2 to generate liquid phase, and then this liquid phase further promotes the sintering of the sample. Improve the density of the material, and then improve the anti-oxidation effect of the material.

Reaction to form a protective layer

Unlike additives that preferentially oxidize carbon sources, some low-melting-point additives form a liquid phase with oxygen or components in the material at high temperatures. The generated liquid phase forms a protective layer on the surface of the material and fills the pores inside the material to prevent oxygen from entering the material, thereby achieving a certain anti-oxidation effect.

Si3N4-Fe was added to Al2O3-SiC-C castables and its effect on material properties was studied. The experiment found that when Si3N4-Fe was added to Al2O3-SiC-C castables, Si3N4 in Si3N4-Fe was first oxidized, and SiO2 was generated on the surface of the sample, which formed a low-melting phase with Al2O3 or impurities in the material, and further formed a glass phase film on the surface of the sample. It prevented O2 from entering the sample, thereby achieving a certain anti-oxidation effect.

ZrB2 was added to Al2O3-SiC-C castables. It was found that the thickness of the oxide layer gradually decreased with the increase of the amount of ZrB2 added. In the presence of carbon, carbon is first oxidized to CO, and CO continues to react with ZrB2 as follows:

On the one hand, it hinders the oxidation of carbon. On the other hand, the generated B2O3 liquid phase and the liquid phase generated by the reaction of B2O3 and CaO form a protective layer on the surface of the material. It hinders O2 from entering the interior of the sample and further prevents the oxidation of carbon.

The effects of andalusite particle size, composition and addition amount on the performance of aluminum silicon carbide refractory materials were studied. The experiment found that when andalusite was added to Al2O3-SiC-C castables, the silicon-rich glass phase generated blocked the pores inside the material due to the transformation of andalusite into mullite. In addition, the generated glass phase formed secondary mullite with the original matrix and aggregate of the material, which enhanced the dense structure of the material. Both of these help to prevent O2 from entering the material. The effect of andalusite particle size and purity on the anti-oxidation effect of Al2O3-SiC-C castables. The anti-oxidation effect of andalusite with a particle size of 1 to 3 mm is better than that of 5 to 8 mm and 3 to 5 mm. This is because the smaller the particle size of andalusite, the lower the purity, and the faster the mullite transformation rate. Based on the fact that andalusite has a certain anti-oxidation ability. Replace part of the antioxidant in the castable with andalusite. The experiment found that replacing part of the antioxidant silicon in the castable with andalusite has a better anti-oxidation effect than the antioxidant silicon powder. At present, there have been many studies on the addition of andalusite to Al2O3-SiC-C castables. The anti-oxidation effect of andalusite on castables mainly comes from the high-temperature phase transformation of andalusite to produce mullite and silicon-rich glass phase. As an aluminosilicate mineral, kyanite also has high corrosion resistance and good mechanical properties when converted into mullite after calcination. By adding kyanite powder to Al2O3-SiC-C castables, it was found that mullite phase was detected in the sample with kyanite powder added, and the formation of liquid phase reduced the apparent porosity of the sample and increased the density.

Add calcium aluminotitanate to the iron ditch castable. Replace the brown corundum in the iron ditch castable with calcium aluminotitanate, and the content of Al2O3, CaO and TiO2 in the sample increases. During the high-temperature reaction process, CaO, SiO2 and Al2O3 in the matrix react to generate low-melting phases such as CaSi2Al2O8 and mullite, which increases the density of the sample, hinders O2 from entering the material, and improves the anti-oxidation effect. However, when the substitution rate of calcium aluminate titanate is too high, the increase in the amount of low-melting phase and mullite generated causes the volume expansion of the sample, leading to the proliferation and expansion of cracks, which in turn reduces the anti-oxidation effect and mechanical properties of the sample.

Optimizing the Form of Carbon Source

Common carbon sources for iron trough castables include high-temperature modified asphalt, spherical asphalt, flake graphite, etc. Researchers are trying to find a way to modify graphite, that is, to optimize the form of carbon source to improve the anti-oxidation effect. At present, one way to optimize the form of carbon source is to add a coating on the surface of graphite so that oxygen cannot directly react with carbon. The first thing to consider when choosing a coating is whether the thermal expansion coefficient between the coating and the carbon-containing refractory material matches. The most commonly used coatings are silicon nitride and silicon carbide, which have similar thermal expansion coefficients to the carbon matrix and good chemical compatibility. According to the actual use environment of the coating, the following factors should also be considered when formulating the coating:

(1) Diffusion rate of oxygen.
(2) Fluidity of the coating raw material at high temperature.
(3) Chemical stability.

The second form is to change the carbon source by adding modified graphite, such as composite carbon source form, granulated graphite, carbon black, etc. Carbon oxidation is reduced by increasing the fixed carbon content of the carbon source and reducing the carbon volatility. The effect of the amount of granulated graphite added on the properties of Al2O3-SiC-C castables was studied. Granulated graphite with a carbon mass fraction of 35% was used as the carbon source, and its effect on the anti-oxidation properties of Al2O3-SiC-C castables was investigated by changing its addition amount.

Al2O3-SiC-C castables have been widely used in castables for iron troughs, and currently have excellent use effects. However, how to further extend the service life of the material and improve the performance of the material depends to a large extent on its anti-oxidation effect. Al and Si powders will undergo hydration reactions. Although the liquid phase generated by low-melting phase additives will block the pores inside the sample and increase the density. However, excessive liquid phase causes the volume expansion and crack propagation of the sample. At the same time, the liquid phase generated by the additives during the heat treatment process will form a thin film on the surface of the material to prevent oxygen from entering the material and reduce the oxygen partial pressure inside the material. Secondly, adding a coating on the surface of the carbon source, although this achieves a certain anti-oxidation effect, there are also problems such as deterioration of material performance and cumbersome production. In order to further improve the anti-oxidation technology of Al2O3-SiC-C iron trough castables and extend the service life of iron trough castables, studying low-cost anti-oxidation technology that can simultaneously improve the anti-oxidation effect and material performance is one of its important development directions.

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