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Silicon Carbide Refractory Castable for Furnace Lining in Reducing Atmosphere

September 5, 2024September 3, 2024 by rsrefractorycastable

Silicon carbide refractory castable has stable properties and excellent corrosion resistance and wear resistance. It is not corroded by boiling hydrochloric acid, sulfuric acid, or hydrofluoric acid. SiC 75-80% castable. Silicon carbide refractory castable for reducing atmosphere furnace lining. It will not oxidize when used in a reducing atmosphere with a temperature of 1600°C, but oxidation will occur in an oxidizing atmosphere.

The Optimal Operating Temperature of Silicon Carbide Castables in Reducing Atmosphere Furnaces

Silicon carbide castable is used at a temperature of 800-1140℃, rather than 1300-1500℃. Because within the range of 800-1140°C, the oxide film formed by oxidation has a loose structure and cannot play the role of silicon carbide. Above 1140°C, especially between 1300-1500°C, the oxide film formed by oxidation covers the surface of the silicon carbide substrate, preventing oxygen from contacting the silicon carbide. Therefore, the antioxidant capacity is the best within the temperature range of 1300-1500°C. However, when the temperature exceeds 1500°C, the oxidation protective layer will be destroyed. At this time, the silicon carbide castable will be strongly oxidized and the matrix will be decomposed and destroyed.

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Application Advantages of Silicon Carbide Castables

Silicon carbide castable is a hard material with high hardness. It has good creep resistance, thermal shock resistance, and wear resistance, but has high thermal conductivity. However, silicon carbide castables also have different qualities, that is, different proportions of silicon carbide are added. However, no matter what type of castable it is, metal silicon powder must be added to adjust it to resist oxidative decomposition. Including refractory bricks, they must also be adjusted to prevent oxidation.

In fact, silicon carbide castable is a composite castable, which is made of alumina aggregate and powder, mixed with a certain proportion of silicon carbide and binder. So they are all composite.

Generally used in furnace linings with severe erosion. If the temperature is below 1300°C for the furnace lining, do not use silicon carbide refractory castables. Furnace linings in oxidizing atmosphere are also not suitable for this castable. Silicon carbide refractory castables are best used in reducing atmosphere furnace linings at 1300-1500°C.

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Silicon Carbide and Its Application in Refractory Materials

Silicon carbide can maintain high strength and high wear resistance at high temperatures. After adding a certain proportion of silicon carbide, refractory castables have good chemical stability and will not be corroded by acid and alkali solutions. Silicon carbide has a larger wetting angle with molten metal and slag. Compared with oxide refractory castables, it has good corrosion resistance to various furnace lining solids, liquids and gases.

Wear-resistant

The hardness of silicon carbide is second only to diamond, and it has strong wear resistance. It is an ideal material for wear-resistant pipes, impellers, pump chambers, cyclones, and linings of ore hoppers. Its wear resistance is 5-20 times that of cast iron and rubber, and it is also one of the ideal materials for aviation runways. Using a special process to coat silicon carbide powder on the inner wall of the turbine impeller or cylinder block can improve its wear resistance and extend its service life by 1 to 2 times.

Thermal shock resistance

Due to the high thermal conductivity and small thermal expansion coefficient of silicon carbide, silicon carbide refractory materials have good thermal shock resistance. The thermal shock resistance of silicon carbide products is also closely related to the type and nature of the bonding base material. In actual application, since silicate-bonded silicon carbide products can be observed to expand, crack, and deform after being subjected to thermal shock, the service life of the material can be easily predicted.

High thermal conductivity

Since silicon carbide itself has good thermal conductivity, refractory materials with high silicon carbide content have higher thermal conductivity. Most of their thermal conductivity exceeds 14.4W/(m·K). Used in heat exchangers, saggers, water-cooled walls of coal gasification furnaces, indirectly heated kiln furniture products, etc. During the use of silicon carbide products, the thermal conductivity of the particle surface will gradually become smaller. The properties of the bonding base material have a certain impact on the thermal conductivity of silicon carbide products. The thermal conductivity of silicon oxynitride bonded and silicon nitride bonded silicon carbide is higher, and the thermal conductivity of silicate bonded silicon carbide is smaller.

Anti-oxidation

Silicon carbide has good oxidation resistance. Oxidation is weak below 1300°C. Significant oxidation does not occur until the temperature is above 1300°C. The oxidation generates a SiO2 glass protective film, which can inhibit the oxidation of silicon carbide.

The oxidation resistance of silicon carbide refractory products also varies significantly with the type of binding base material. The lower oxidation resistance of silicon nitride-bonded silicon carbide products can be explained by their microstructural characteristics. Because the base material of silicon nitride combined with silicon carbide products is in the form of interwoven fibers and has high air permeability, it plays a small protective role on silicon carbide particles. In silicate bonded and silicon oxynitride bonded silicon carbide products, the surface of the silicon carbide particles is wrapped by a continuous base material. Therefore, it has strong antioxidant properties. The antioxidant properties of silicate-bonded silicon carbide and silicon oxynitride-bonded silicon carbide show similar properties in the above tests, but the differences between them can be clearly shown in long-term use.

Resistance to slag

SiC is a compound with strong covalent bonds and maintains high bonding strength at high temperatures. Therefore, SiC has good chemical stability and will not be corroded by most acid and alkali solutions. Silicon carbide has a larger wetting angle with molten metal and slag. Compared with oxide refractory materials, it has good corrosion resistance to various solids, liquids and gases. Such as Al2O3-SiC-C castables and products used in iron-making systems, silicon molybdenum bricks and silicon carbide-containing castables used in cement kilns, various acid-base reaction vessels, etc.

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Application of Carbonaceous Castables Containing Silicon Carbide Raw Materials in Blast Furnace Bottom

Blast furnaces are the basis for stable and smooth ironmaking production, and the most important ones are carbon bricks and water cooling systems. Carbon bricks and molten iron are not easily wetted and have strong corrosion resistance. Water cooling is the key to ensuring the longevity of carbon bricks. During the blast furnace bottom masonry process, after the water-cooling pipes are laid, the existing technology mostly uses carbon ramming material to level and fill the carbon brick joints. In order to ensure the water cooling effect, the carbon ramming material is required to have high thermal conductivity, a certain strength, and good construction performance. Since the performance of ramming materials is closely related to the construction process and quality, and there are many human-influenced factors, the thermal conductivity often fails to meet the expected requirements. In recent years, the results of analyzing carbon castables show that the thermal conductivity of castables mainly made of carbon raw materials is relatively low, and some are less than 10W·(m·K)⁻¹. The thermal conductivity of carbonaceous castables containing silicon carbide raw materials is greater than 15W·(m·K)⁻¹. Its construction is more convenient than ramming material, and its operation is simple. It only needs vibration forming and quick smoothing, which can save a lot of man-hours. Performance of carbonaceous castables containing silicon carbide raw materials in blast furnace bottoms.

(1) Carbonaceous castables using silicon carbide as the main raw material have higher strength. The compressive strength after 24 hours of insulation at 110°C is greater than 17MPa, and the compressive strength after 3 hours of insulation at 1450°C is greater than 70MPa. The thermal conductivity at 700°C measured using the laser method is 7.2W·(m·K)⁻¹. The compressive strength of imported carbon castables using carbon as the main raw material after being kept at 110°C for 24 hours is 18.3MPa. The compressive strength after being kept at 1450°C for 3 hours was significantly reduced. The thermal conductivity at 700℃ measured by laser method is 5.08W·(m·K)⁻¹. Its thermal conductivity is relatively low compared to the technical requirements of blast furnace bottom carbonaceous castables.
(2) After the sol-bonded carbon castable with silicon carbide as the main raw material is soaked in water, the compressive strength and volume density increase, while the shape remains unchanged. After soaking in 2% (w) hydrochloric acid solution, the compressive strength after 30 days decreased. After immersion in 2% (w) sulfuric acid solution, the compressive strength decreased after 30 days, and the decrease was smaller than that in hydrochloric acid solution. After soaking in 2% (w) sodium hydroxide solution, it was completely loosened into powdered materials in 30 days. Carbon castables made of silicon carbide as the main raw material are not resistant to immersion in alkali solutions. In an environment where alkali metal vapor may penetrate into the blast furnace bottom, such carbonaceous castables should be used with caution if there is cooling water leakage.

Rongsheng Refractory Castable Manufacturer is a powerful refractory material manufacturer. Rongsheng Manufacturer has an environmentally friendly, fully automatic unshaped refractory material production line. The refractory lining materials products of Rongsheng manufacturer 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, etc. We can customize refractory lining materials according to the actual working conditions of high-temperature furnace linings. To purchase high-quality silicon carbide refractory materials, please choose Rongsheng Refractory Castable Manufacturer.

Castable Low Cement Lining With Silicon Carbide

July 2, 2024 by rsrefractorycastable

Low cement silicon carbide refractory castable is a special refractory material. Made of low cement ratio, silicon carbide aggregates and powders, ultrafine powder, CA-70 cement and antioxidants. It is suitable for thermal equipment such as power generation boilers, non-ferrous metallurgical furnaces and incinerators. It has low linear expansion coefficient, high thermal conductivity, high strength and good wear resistance. Low-cement silicon carbide refractory castables can improve the fire resistance and thermal efficiency of the equipment under reasonable proportions and use under appropriate conditions, and the application effect is good.

Rongsheng Low Cement Silicon Carbide Castable (Al2O3-48%,SiC-30%) — Rongsheng Castable Low Cement Lining With Silicon Carbide

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Low Cement Silicon Carbide Refractory Castable

Low cement silicon carbide refractory castable is a special refractory material suitable for thermal equipment such as power generation boilers, non-ferrous metallurgical furnaces and incinerators. This silicon carbide refractory castable has the following characteristics:

Low coefficient of linear expansion. As the main refractory aggregate and powder, silicon carbide has a low coefficient of linear expansion, which can reduce the possibility of thermal stress.
High thermal conductivity. Silicon carbide has good thermal conductivity and can effectively conduct heat and improve the thermal efficiency of the equipment.
High strength. The use of low cement ratio and reasonable binder can improve the strength of the castable and increase its compression and flexural resistance.
Good wear resistance. Due to the use of silicon carbide with SiC greater than 97% as refractory aggregate, the castable has excellent wear resistance.

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Raw Material Composition of Low Cement Silicon Carbide Refractory Castable

The preparation of low cement silicon carbide refractory castable includes the following ingredients:

Refractory aggregates and powders mainly use silicon carbide with SiC greater than 97%, which has excellent refractory properties.
Ultra-fine powder. Adding SiO2 ultrafine powder can improve the density and refractoriness of the castable.
Binder, using CA-70 cement as the binder, can ensure that the castable has a certain strength and durability.
Antioxidants. Metallic silicon antioxidants are used to prevent the oxidation of silicon carbide.

The performance test results of the castable at different temperatures are as follows:

After drying at 110℃, the bulk density is 2.5g/cm³, the compressive strength is 45MPa, and the flexural strength is 9MPa.
After firing at 1000℃, the linear change is -0.2%, the compressive strength is 107MPa, and the flexural strength is 24MPa.
After firing at 1450℃, the linear change is +0.3%, the compressive strength is 130MPa, and the flexural strength is 54MPa.
The thermal conductivity at 400℃ is 12.2W/(m·K).

In summary, low cement silicon carbide refractory castable has a low linear expansion coefficient, high thermal conductivity, high strength and good wear resistance. Through reasonable proportions and the use of appropriate materials, the fire resistance and thermal efficiency of the equipment can be improved. The castable has good application results in thermal equipment such as power generation boilers, non-ferrous metallurgical furnaces, and incinerators.

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Low Cement Mullite Corundum Castable

Low-cement mullite-corundum refractory castables use sintered or electro-fused mullite, brown corundum, alumina-based corundum and white corundum as refractory bone powder. Sometimes special-grade alumina clinker powder is also used, and ultra-fine powder is mixed with α-Al2O3 and silica fume. It is formulated with aluminate cement as binder and additional dispersant. This material is used for steel rolling heating furnace lining, water cooling pipe wrapping and burner bricks. The use effect is good on thermal equipment such as tundish slag weir, medium and small blast furnace tap trough and electric furnace cover.

Does Low Cement Castable Need to Add Steel Fiber when Used in Settling Chamber?

When low-cement castables are used in settling chambers, steel fibers are usually not required. When the design of the settling chamber is unreasonable, the discharge opening of the cone section is too small and the smoke dust needs to be beaten. At this time, steel fibers can be added to the low cement castable to enhance wear resistance and extend the service life. Under special circumstances, the settling chamber can be lined with clay bricks or high-aluminum castables with high-voltage electrical porcelain added.

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If low-cement castables are used in settling chambers, there is generally no need to add steel fibers.

If the lower opening of the cone section of the settling chamber is too small and needs to be beaten during use, just add steel fibers to the low-cement castable used in the cone section to increase traction, wear resistance, and erosion resistance. However, if the discharge port of the settling chamber is reasonable, and the size of the settling chamber and the rotary kiln are also reasonable, there is no need to add steel fiber to the castable.

The temperature of the settling chamber is not high, and it mainly plays the role of dust removal. The dust has fallen to the bottom before the flue gas flows out of the settling chamber, and is collected by the ash hopper at the bottom of the settling chamber. The unsettled dust is brought out with the flue gas. General low-cement castables can be used.

Generally, it is common to use high-aluminum castables and low-cement castables. However, clay bricks are also used as linings for settling chambers. There is also the use of high-aluminum castables with a certain proportion of high-voltage electrical porcelain added to the castables to create a glazed surface to facilitate the fall of smoke and dust.

Adding steel fibers to low-cement castables is rarely used in settling chambers. In recent years, the settling chambers of some white ash rotary kilns and zinc volatilization kilns are often lined with clay bricks. However, the size design of some settling chambers is not reasonable. If the settling chamber is too small, and the cone section discharge opening is also too small, there will be a situation of beating during the production process to make the smoke and dust sink. This will speed up the service life of the cone section lined with clay bricks or low-cement castables.

Therefore, under special circumstances, a reasonable proportion of steel fibers is added to the low-cement castable to increase the wear resistance of the cone section and extend its service life.

Iron Ditch Anti-Scouring Silicon Carbide Refractory Castable

January 15, 2024 by rsrefractorycastable

The blast furnace tap trough system consists of a main tap trough, branch troughs, and slag troughs. It is an important system to realize the separation of molten iron and slag in the blast furnace. With the enlargement of iron-making blast furnaces and the development of high-temperature and high-pressure technology, higher requirements have been placed on the service life and iron flux of the blast furnace tap trough. The trough material is the main factor affecting the performance of the blast furnace tap trough. Its high-temperature resistance, thermal shock resistance, erosion resistance, erosion resistance, and other properties directly affect the iron flux and service life of the blast furnace tap channel. This in turn affects the production cost and labor intensity of the entire production process.

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Refractory Material Al2O3-SiC-C Castable for Tap Trough

At present, the refractory materials used in the blast furnace tap trough are mainly Al2O3-Si C-C castables. Although it has the advantages of good high-temperature mechanical strength, good resistance to slag erosion and permeability, good thermal shock resistance, and small changes in reburning. However, in the face of technological advancements such as increased molten iron temperature, increased iron tapping volume, prolonged iron tapping time, and faster-molten iron flow rate caused by modern large-scale blast furnace smelting. The original iron trench materials cannot meet production needs. Therefore, improving Al2O3-SiC-C castables or developing new refractory materials for blast furnace tap troughs are the research directions of many scholars.

Aluminum silicon carbide carbonaceous castables, which are unshaped refractory materials, are often used in blast furnace tap troughs, so they are also called trough castables. The blast furnace tap trough castable is made of fused corundum (or sintered corundum, special high-aluminum clinker) and silicon carbide. It is a high-performance refractory castable containing 90%-95% fixed carbon (or flake graphite), binder, and various admixtures.

Aluminum silicon carbide carbonaceous castable. The aggregate part can be made of one or two types of fused or sintered corundum, brown corundum, spinel, and bauxite clinker. Carbonaceous raw materials can be asphalt, coke, graphite, or electrode powder. The binding agent can be bonded clay, oxide micro powder or ultrafine powder, and pure calcium aluminate cement with good dispersion properties.

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The blast furnace tap trough is a channel through which high-temperature molten iron or molten slag flows. Its refractory lining should have the following characteristics. These features are complementary to each other and should be compatible with each other.

① Strong resistance to erosion and erosion from molten iron and slag.
② Good thermal shock resistance and small change in volume after reheating.
③ Strong antioxidant capacity.
④ Easy to construct, can be baked quickly without bursting, and is easy to repair and dismantle.
⑤ When used, it does not produce harmful gases, does not stick to slag iron, and has a long service life.

Iron trench castable is a high-tech refractory castable with exquisite preparation technology and excellent performance, which can significantly increase the service life of the trench lining. The key issue is that the amount of construction water must be strictly controlled, operated carefully, and maintained carefully to achieve the expected purpose.

At the same time, the specific selection of tap trough castables also depends on the size of the blast furnace. Generally speaking, high-aluminum silicon carbide carbonaceous castables can be used for the main ditch, slag ditch, and slag line of small blast furnaces. Corundum silicon carbide carbonaceous castables can be selected for medium and large blast furnaces.

Wear-Resistant Corundum Silicon Carbide Castable

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Erosion-resistant Molten Iron-Clad Aluminum Silicon Carbide Castable

Spheroidized ladle castable is an unshaped refractory material with high aluminum and silicon carbide materials as the main raw materials and refractory cement as the binder. It is widely used in molten running ladles, launders, and working linings of kilns. It has high strength and refractory resistance and has good impact resistance, corrosion resistance, wear resistance, and other properties. It has a long service life, convenient construction, and easy maintenance. It is suitable for the overall lining of ladles and is the refractory material of choice for spheroidized ladles.

Molten iron and slag react with the castable, resulting in chemical slag sticking. According to ASTM C01-91 Al2O3-SiO2 series castables, those with CaO content >2.5 are traditional cement-bound castables. The CaO content between 1.0% and 2.5% is low cement castable. The CaO content <1.0% is cement-castable. The lower the CaO content, the higher the temperature at which the liquid phase appears, and therefore the higher the fire resistance. The CaO content of the existing castable is 3.78%, which is a traditional high cement content castable. Aluminum silicon carbide castables are erosion-resistant, heat-exchange-resistant, refractory castables, and ladle castables.

The liquid phase of this material appears at a low temperature, about 1300°C. The temperatures of molten iron and slag are generally >1300°C, and the interface is prone to reaction at this time. For example, the components in the refractory material, especially the liquid phase in the matrix, easily react with CaO, SiO2, Fe2O3, etc. in the slag to form Al2O3-SiO2-CaO-Fe2O3 series low-melting materials. The molten iron, molten slag, and refractory materials are melted together to form sticky slag. The sticky residue that occurs in this form is strong and difficult to clean.

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Development of Aluminum Silicon Carbide Refractory Castables for Tap Trench

Al2O3-SiC-C castable is the most widely used iron trench refractory material in my country. Improving the quality of Al2O3-Si C-C castables is an important factor in reducing the cost of molten iron and achieving efficient production. RS Unshaped Refractory Castable Manufacturer puts forward several suggestions based on the current development situation.

(1) Different companies have different compositions of molten iron and slag. The reasons why molten slag and molten iron corrode the iron trench materials should be analyzed based on the actual situation to achieve “prescribing the right medicine”.

(2) Using slag or other industrial waste residues as raw materials to prepare Al2O3-Si C-C castables has extremely high added value. At the same time, it can also solve problems such as waste residue accumulation and environmental pollution.

(3) Improve the production of Al2O3-Si C-C castables in the direction of green and environmental protection, and remove or replace toxic and harmful components in the raw materials. It not only achieves green production but also protects the health of workers.

(4) Many new Al2O3-Si C-C castables have been applied in enterprise blast furnace production, achieving mutual benefit and win-win results between scientific research and enterprises.