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I. Material Properties and Technical Characteristics
Lightweight insulating castables are a type of unshaped refractory material with lightweight aggregates as the core and composite binders as the carrier. Their technical characteristics can be analyzed from the following dimensions:
1. Physical Properties
Low-density structure: The bulk density ranges from 0.6 to 2.0 g/cm³, which is 40%-70% lower than that of traditional heavy castables.
Low thermal conductivity: The thermal conductivity at room temperature is 0.15-0.75 W/(m·K); for some models (e.g., alumina hollow sphere castables) at 800℃, it can be controlled below 0.3 W/(m·K), which is more than 60% lower than traditional materials.
Compressive strength: The strength after drying ranges from 1 to 18 MPa, and the strength retention rate at high temperatures (1000℃) exceeds 90%, meeting the dual requirements of metallurgical equipment for load-bearing and erosion resistance.
2. Thermal Properties
High-temperature stability: The long-term service temperature covers 800-1500℃. For example, lightweight mullite castables can stably serve at 1350℃, while alumina hollow sphere castables are suitable for extreme environments above 1500℃.
Thermal shock resistance: After 100 cycles of 1000℃→room temperature, the strength loss is less than 10%, which is significantly better than traditional heavy materials.
Refractoriness: Most products have a refractoriness of more than 1790℃, and some high-purity models can reach 1850℃, meeting the requirements for direct contact with high-temperature melts.
3. Chemical Properties
Corrosion resistance: The acid resistance is over 95%, and the strength retention rate after alkali erosion is ≥70% (YB/T 4197 standard), showing excellent performance in strongly corrosive media such as steel slag and molten iron. For example, acid-resistant castables even show increased strength after immersion in concentrated acid, making them suitable for composite environments in chemical and metallurgical industries.
Anti-permeability: The apparent porosity is ≤18% (GB/T 2997 standard), effectively inhibiting the penetration and damage caused by molten steel and slag.
II. Core Applications in the Metallurgical Industry
1. Blast Furnace System
Furnace lining insulation layer: Lightweight mullite castables (with a thickness of 80-150mm) can reduce the furnace shell temperature by 30-50℃, decrease heat loss by 30%-50%, and save more than 2,000 tons of standard coal annually.
Hot blast stove dome: Alumina hollow sphere castables (with a thermal conductivity of 0.25 W/(m·K)) used in the dome lining can increase the hot blast temperature by 50-80℃ and reduce fuel consumption by 8%-12%.
2. Steelmaking Equipment
Permanent layer of ladles: High-strength lightweight nano-micron castables (density 1.1-1.3 g/cm³) replacing traditional silica-calcium boards can reduce the ladle wall temperature from 350℃ to 200-240℃, lower the tapping temperature by 15℃, and save 6 kWh of energy per ton of steel annually.
Tundish lining: The composite structure of lightweight castables and nano-insulation boards (thickness 50-150mm) can reduce the molten steel temperature drop rate from 5℃/min to 2℃/min, increasing the continuous casting billet qualification rate by 5%-8%.
3. Steel Rolling Heating Furnaces
Furnace roof and walls: Integrally cast lightweight mullite castables (bulk density 1.2-1.3 g/cm³) improve furnace temperature uniformity to ±5℃, reduce unit energy consumption by 8.2%, and extend service life to 8-10 years.
Regenerators: The "lightweight layer + reflective layer" double-layer design reduces the overall heat transfer coefficient by 15% and increases heat storage efficiency by 20%.
III. Key Applications in the Foundry Industry
1. Hot Metal Ladles and Steel Ladles
Insulation layer optimization: Lightweight castables (thermal conductivity 0.25 W/(m·K)) combined with Y-type stainless steel anchors (spacing 200-300mm) can reduce the ladle shell temperature by more than 130℃ and lower the molten iron temperature drop rate from 8℃/min to 4℃/min.
Composite structure of working layer: The combination of insulating magnesia-carbon bricks (thermal conductivity 5 W/(m·K)) and lightweight castables reduces the back temperature of the working layer from 1500℃ to 1400℃, extending the service life of nano-insulation boards by 3-5 years.
2. Casting Molds and Distribution Systems
Aluminum rod casting distribution plates: Lightweight castables (density 1.35-1.45 g/cm³) treated with BN coating exhibit significant aluminum-non-sticking properties, with a service life of 9-12 months, 3 times longer than traditional alloy liners.
Copper-nickel matte smelting electric furnaces: Lightweight castables (temperature resistance 1380℃) used in furnace linings increase matte separation efficiency by 15% and extend furnace maintenance cycles to 18 months.
3. Melting Furnaces and Heat Treatment Furnaces
Aluminum melting furnace linings: Lightweight castables (bulk density 1.0-1.2 g/cm³) in direct contact with aluminum melt control furnace temperature fluctuations within ±10℃, reducing aluminum melt burning loss by 2%-3%.
Heat treatment furnace trolleys: Lightweight castable precast parts (compressive strength ≥8 MPa) reduce trolley weight by 40%, increase heating rate by 30%, and save 150,000 yuan in natural gas costs annually per 100m³ furnace.
IV. Construction Technology and Performance Assurance
1. Material Proportion Control
Aggregate gradation: A dual-gradation system of "coarse aggregates (expanded perlite) + fine powders (mullite micropowder)" is adopted, with porosity controlled at 45%-60% to balance strength and insulation.
Binder selection: The dosage of aluminate cement is ≤8%, combined with silica fume (3%-5%), which can reduce water demand by 15% and improve fluidity by 20%.
2. Optimization of Construction Parameters
Mixing process: Mixing in a forced mixer for 3-5 minutes to avoid aggregate sedimentation, ensuring the density uniformity deviation is ≤5%.
Vibration molding: Vibrating with a high-frequency vibrator (frequency 50-60 Hz) until surface bleeding occurs, with compactness ≥90% to avoid concentrated pores.
Curing system: Curing in an environment with humidity >60% for 72 hours, followed by drying at 110℃ for 24 hours to ensure early strength development.
3. Anchoring System Design
Anchor selection: Y-type stainless steel anchors (spacing 200-300mm) are used in high-temperature zones, while ceramic bolts can be used in low-temperature zones, with shear strength ≥5 MPa.
Anchoring depth: Penetrating 100-150mm into the furnace shell, with a hook angle ≥90° to ensure mechanical interlocking with the castable.
V. Economic Benefits and Industry Value
1. Energy-Saving Benefits
A case study of a steel enterprise's heating furnace transformation shows that the application of lightweight castables reduces unit energy consumption by 8.2%, saving 2,000 tons of standard coal annually, equivalent to a cost reduction of 1.5 million yuan.
After optimizing the ladle insulation layer, energy consumption per ton of steel is reduced by 6 kWh. For a steel plant with an annual output of 5 million tons, this translates to annual electricity cost savings of 24 million yuan.
2. Reduction in Maintenance Costs
Improved thermal shock stability extends furnace lining life from 5 years to 8-10 years, reducing maintenance frequency by 30%-50% and lowering overall maintenance costs by 40%.
The service life of casting molds is extended to 9-12 months, reducing annual replacement costs by 800,000 yuan per production line.
3. Environmental Benefits
A case study of an aluminum company shows that unit product carbon emissions are reduced by 12%, meeting the requirements of the EU Carbon Border Adjustment Mechanism (CBAM) and enhancing international market competitiveness.
Dust emissions during the construction of lightweight materials are reduced by 60%, improving the working environment and complying with the “Ultra-Low Emission Transformation Plan for the Iron and Steel Industry”.
Conclusion
Lightweight insulating castables, with their excellent thermal performance and structural stability, have become core materials for energy conservation and consumption reduction in the metallurgical and foundry industries. In the future, with the in-depth integration of intelligent, functional, and green technologies, these materials will continue to play an irreplaceable role in high-temperature industrial fields, driving the industry toward high efficiency, low carbon, and sustainability.
