Cement-free refractory castables are cement-free, monolithic refractory materials (using ultrafine powder, activated alumina, and other binders). Their core advantages are excellent high-temperature performance and strong structural stability, making them suitable for a variety of demanding high-temperature operating conditions. Specific performance and applications are as follows:
I. Core Performance Characteristics of Cement-Free Refractory Castables
Excellent Volume Stability: They do not contain the cement found in conventional castables (cement hydration products are susceptible to decomposition and shrinkage at high temperatures). Their low line stability at high temperatures (typically ≤±0.5%) effectively prevents cracking and spalling of the lining caused by volume shrinkage, ensuring excellent structural integrity after long-term use. 2. High Strength and Stable High-Temperature Strength: 2◦1 Room-Temperature Strength: Relying on the agglomeration of ultrafine powder and the reaction of the active binder, room-temperature compressive strength reaches 40-60 MPa, meeting the strength requirements for construction and installation. 2◦2 High-Temperature Strength: Sintering densification further enhances strength at high temperatures (compressive strength ≥80 MPa at 1000°C), eliminating the "high-temperature strength decay" issue and far exceeding that of ordinary cement castables.
3. Strong Corrosion and Wear Resistance: A low CaO content (≤1%) reduces the formation of low-melting-point phases (such as anorthite) that react with slag and molten iron, significantly improving resistance to penetration by alkaline slag, acidic slag, and molten iron. The material also boasts high density and surface hardness, offering excellent resistance to material erosion and wear. 4. Excellent thermal shock stability: The microstructure contains a reasonable amount of micropores (pore size 1-5μm), which can buffer thermal stress caused by sudden temperature changes. Thermal shock stability (1100°C water cooling cycle) can reach over 30 times, making it suitable for working conditions with frequent temperature fluctuations (such as ladles and tapping channels).
5. Controllable construction and curing performance: The addition of dispersants can adjust fluidity, meeting the casting requirements of complex areas (such as special-shaped linings and pipe linings). Curing does not require cement hydration; only moisturizing curing for 72 hours at 20-25°C is required, avoiding the problem of poor hydration at low temperatures (<5°C).
II. Key Application Scenarios for Cement-Free Refractory Castables
The performance of cement-free refractory castables is well-suited to operating conditions characterized by high temperatures, severe corrosion, high wear, and large temperature fluctuations. Its core application areas are concentrated in the metallurgy and building materials industries:
1. Steel Industry (Core Application Areas)
1.1 Ladle Lining: Used in the permanent or working layer of the ladle, it resists corrosion from molten steel and slag, as well as sudden temperature changes (from tapping to empty ladle cooling), extending the ladle's service life to 150-200 heats.
1.2 Blast Furnace Casthouse: Used in the main taphole and slag skimmer working layer, it resists erosion from molten iron and slag, extending its service life by over 30% compared to conventional high-aluminum castables.
1.3 Converter/Electric Furnace Lining: Used in key areas such as the furnace mouth and taphole to withstand high temperatures and mechanical shock. 2. Non-ferrous Metal Smelting: Linings for copper and nickel smelting converters and anode furnaces, resisting corrosion from non-ferrous metal slag (such as ferrosilicate slag) and adapting to the high temperatures (1200-1300°C) and highly oxidizing environments encountered during the smelting process. 3. Thermal Power and Building Materials Industry: 3.1 Large Industrial Heating Furnaces: Used in load-bearing areas such as furnace roofs and walls, adapted for long-term high-temperature (1000-1200°C) operation, reducing lining maintenance frequency. 3.2 Cement Rotary Kilns: Linings for transition and cooling zones, resisting abrasion from cement raw material dust and corrosion from alkali metals (K and Na).
III. Key Construction Considerations for Cementless Refractory Castables
1. Mixing Control: Add pure water (or a special binder) strictly according to the mix ratio and mix for 3-5 minutes to ensure a uniform slurry without lumps. Avoid excessive water addition, which may reduce strength.
2. Vibration Compaction: Use an inserted vibrator to vibrate the material in layers (each layer ≤ 300mm thick) until no bubbles escape the surface to prevent internal pores from affecting corrosion resistance.
3. Baking System: After curing, bake the material in a gradient cycle: low temperature (50-100°C, 30-48 hours) → medium temperature (300-500°C, 50-72 hours) → high temperature (800-1000°C, 28-36 hours) to completely remove free water and prevent cracking during high-temperature use.
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