Steel fiber-reinforced castable is made using premium bauxite clinker as aggregate, high-quality bauxite clinker and corundum fine powder as matrix, and various composite materials such as ultrafine powder as binders and additives, plus stainless steel heat-resistant fibers. Furthermore, the addition of steel fibers significantly enhances the overall strength of the furnace wall after casting.
Applications of Steel Fiber Reinforced Castables
Steel fiber-reinforced castables are mainly used in the following areas:
- Linings for various thermal equipment.
- Thermal insulation for flues and large-diameter metal chimneys.
- Linings for industrial boilers, with particularly noticeable effects on furnace roofs.
- Thermal insulation for low-temperature air (≤1200℃) pipelines.
- KT-J impermeable carbon fiber castable for muffle-less carburizing furnace linings.
- Various standard and custom-shaped precast components to meet specific user requirements.
- Backing insulation layers for various low-temperature furnaces with interface temperatures ≤1050℃ (including furnace walls and roofs).
- For industrial furnaces using flat-flame burners, providing sealing and insulation for the furnace roof, with superior sealing performance compared to any other material.
- Linings for resistance furnaces with operating temperatures ≤1200℃; heating elements can be exposed or embedded.
- This type of furnace lining is particularly suitable for applications with minimal mechanical vibration and large temperature variations, such as bell-type furnaces and movable lids of removable aluminum melting furnaces.
- HS-J ultra-low temperature refractory fiber castable, ML-J polycrystalline mullite fiber castable, and L80-J alumina fiber castable can be used for industrial furnace linings with operating temperatures of 1300-1450℃.
- This type of furnace lining, including furnace walls and roof, is suitable for various fuel furnaces with operating temperatures ≤1250℃. Composite linings made from different types of refractory fiber castable offer a stable structure, are economical and reasonable, and are easy to construct.
Performance of Steel Fiber Refractory Castables
The heat-resistant steel fibers used in common steel fiber-reinforced refractory castables should be selected according to the operating conditions of the thermal equipment, and the appropriate dosage should be determined. The preparation process is as follows: First, weigh the refractory aggregate, powder, binder, and admixtures, and dry mix for 1 minute. Next, add water and wet mix, evenly sprinkling the steel fibers into the mixture, ensuring no lumps form. Finally, mix for 1 minute before discharging; the total mixing time should not be less than 5 minutes. When using a vibratory rod for molding, the vibration direction should be staggered to ensure proper steel fiber orientation, which can improve performance.
The performance of steel fiber-reinforced refractory castables and high-strength clay-bonded refractory castables uses refractory aggregates and powders made from grade III and grade I bauxite clinker, respectively. To improve matrix performance, fused brown corundum powder, active SiO2 ultrafine powder, and admixtures are added. CA-50 cement is used as an accelerator. Fused calcium aluminate cement-alumina-magnesia refractory castable uses dense fused corundum as aggregate, alumina and high-purity sintered magnesia powder as refractory powder, and also incorporates ultrafine powder and composite admixtures. Low-cement bauxite-mullite refractory castable uses first-grade bauxite clinker and mullite as refractory aggregate, high-grade bauxite clinker powder or corundum powder as refractory powder, and CA-70 cement as binder, while also incorporating ultrafine powder and composite admixtures. Low-cement special alumina corundum refractory castable also incorporates a small amount of admixtures. This type of high-quality refractory castable is used at higher temperatures; therefore, 330 heat-resistant steel fiber with an equivalent diameter of 0.5 mm and a length of 20 mm is selected, with a dosage of 2% and water dosage of 6%~7%. According to the selected mix proportions, all raw materials are weighed, mixed, and then molded. After molding, it is naturally cured and must not be wetted. After curing for 24 hours, remove the mold and continue natural curing for another 48 hours before testing the performance.
What role do steel fibers play in refractory castables?
When added to refractory castables in a certain proportion, steel fibers provide tensile, compressive, crack-resistant, and drop-resistant properties. Furthermore, the addition of steel fibers enhances the overall integrity of the refractory castable, making it less prone to deformation.
Steel fiber castables have a wide range of applications, showing significant effectiveness in industrial kilns with furnace lining temperatures below 1350℃. This is due to their long service life and high tensile strength. The steel fibers added to the refractory castable are arranged in a staggered pattern; the special shape of the fibers strengthens the bond strength of the refractory castable and also resists drop during temperature fluctuations.
Refractory castables with added steel fibers exhibit high strength, thermal shock resistance, and resistance to flue gas erosion. They not only withstand high temperatures and wear but also prevent the aggregate in the refractory castable from expanding at high temperatures and prevent stress damage caused by large temperature gradients during furnace start-up and shutdown.
Steel fibers can be added to any type of refractory castable, such as corundum refractory castable, high-alumina low-cement refractory castable, steel fiber reinforced wear-resistant castable, and high-strength castable. In short, adding steel fibers can enhance the tensile strength, crack resistance, and bond strength of any refractory castable.
Adding steel fibers to steel fiber castable increases the overall strength of the refractory castable. However, the proportion must be reasonable; too little will have no effect, while too much will have the opposite effect. The general proportion is 1-1.5%. Steel fiber castable can only be used at temperatures below 1350℃. Above 1350℃, even with added steel fibers, the temperature exceeds the critical point, and the effect is minimal.
Differences between Steel Fiber Castable and Steel Fiber Wear-Resistant Castable
Key Difference: Introduction of Silicon Carbide. Steel fiber wear-resistant castable, in addition to the above, introduces silicon carbide with a particle size of 0.5- 3 mm and a purity ≥90% (8-15% addition). Silicon carbide (SiC) has high hardness (Mohs 9.2) and a low coefficient of thermal expansion, forming a “hard core” skeleton within the material. This allows the SiC particles to bear the stress first when the surface layer is subjected to erosion from coal powder, incandescent ash, or clinker, thus significantly reducing the wear rate of the matrix.
Steel fiber castables and steel fiber wear-resistant castables both belong to the fiber-reinforced series and have the same construction methods. The only difference lies in whether silicon carbide is introduced. By adhering to the selection principle of “wear first, oxidation last” and strictly controlling the production and construction processes, safe, long-life, and economical furnace lining operation can be achieved in thermal equipment below 1350℃.
