Jul 09 , 2025
The NR-80 high density calcium silicate board is specifically engineered to provide exceptional resistance to molten aluminum, thus significantly extending the lifespan of furnace linings and components, and drastically reducing maintenance downtime in casting processes.
NR-80 high density calcium silicate boards employ a combination of material science principles and specific formulations to achieve their remarkable resistance to molten aluminum:
1. Non-Wetting Property: This is the most crucial characteristic. The surface of these boards is inherently non-wetting to molten aluminum. Unlike many traditional refractories, molten aluminum does not spread or adhere readily to the board's surface. This minimizes the contact area and prevents the aluminum from "sticking" and building up (dross formation) or penetrating into the material's pores. This non-wetting behavior is often attributed to:
o Surface Tension Control: The chemical composition and microstructure of the board create a high contact angle with molten aluminum, meaning the aluminum prefers to bead up rather than spread out.
o Lack of Reactivity: The constituents of the calcium silicate board are carefully selected to be chemically inert or have very low reactivity with molten aluminum. This prevents the formation of undesirable compounds (like aluminum silicates or carbides) at the interface, which could otherwise degrade the material or facilitate penetration.
2. Dense and Fine-Pored Structure: High-density calcium silicate boards possess a very compact and fine-pored microstructure. This significantly limits the pathways for molten aluminum to physically penetrate the material via capillary action. Even if some wetting occurs locally, the dense matrix acts as a formidable barrier.
3. Reinforcement with Fibers (e.g., Carbon Fiber): NR-80 incorporate reinforcing fibers, such as carbon fibers or high-purity glass fibers, within the calcium silicate matrix. These fibers provide:
o Enhanced Mechanical Strength: They significantly boost the board's compressive and flexural strength, making it more resistant to erosion, abrasion, and mechanical damage during operation and cleaning.
o Improved Thermal Shock Resistance: The fibers help to distribute thermal stresses, preventing cracking and spalling when the material experiences rapid temperature changes, which are common in foundry operations. Carbon fibers are particularly effective in offering "pseudoplastic" fracture behavior, where cracks lose energy and propagate slowly, preventing catastrophic failure.
o Additional Non-Wetting Effect: In some cases, the fibers themselves can contribute to the non-wetting characteristics or improve the overall integrity of the non-wetted surface.
4. Carefully Controlled Chemical Composition: The primary constituents of calcium silicate are calcium oxide (CaO) and silicon dioxide (SiO2). The precise ratio of these components, along with the absence of certain impurities, is critical. For instance, specific mineral phases like xonotlite (6CaO⋅6SiO2⋅H2O) are known for their high-temperature stability and resistance. The material is typically asbestos-free and free from other harmful substances, ensuring no contamination of the aluminum melt.
5. Hydrothermal Curing Process: Calcium silicate boards are manufactured through a hydrothermal reaction under high temperature and pressure. This process creates a stable crystalline structure (e.g., tobermorite or xonotlite) that is highly resistant to thermal degradation and chemical attack, ensuring long-term performance in high-temperature aluminum environments.
1. Superior Non-Wetting to Molten Aluminum: This is the primary defense. The material's surface discourages the molten aluminum from adhering, preventing build-up and initial penetration. This significantly reduces dross formation and keeps the contact surfaces cleaner.
2. High Density and Low Porosity: The high density (typically 800-1200 kg/m³) means a compact structure with minimal open pores, physically impeding the molten aluminum from infiltrating the bulk material.
3. Exceptional Thermal Shock Resistance: The fiber reinforcement (especially carbon fiber) provides outstanding resilience against rapid temperature changes, preventing thermal cracking and spalling that could expose inner layers to the molten metal. This is crucial for furnace components that experience fluctuating temperatures during casting cycles.
4. High Mechanical Strength and Durability: The high compressive and flexural strength of NR-80 allows it to withstand mechanical stresses, abrasion from cleaning tools, and the impact of molten metal flow, ensuring structural integrity over time.
5. Chemical Inertness to Aluminum: The carefully balanced chemical composition of calcium silicate makes it largely non-reactive with molten aluminum. This prevents detrimental chemical reactions at the interface that could lead to material degradation, such as the formation of corundum (Al2O3) or other brittle intermetallic phases.
6. Dimensional Stability at High Temperatures: NR-80 exhibits very low shrinkage even at high operating temperatures (up to 1000°C continuous use). This dimensional stability prevents cracking due to thermal expansion/contraction mismatches with surrounding furnace structures and maintains the precise geometry of intricate components like hot top rings or spouts.
7. Precision Machinability: Despite its high density and strength, NR-80 can be precisely machined (often CNC machined) into complex shapes with tight tolerances. This allows for the creation of intricate components that fit perfectly, minimizing gaps where molten aluminum could otherwise accumulate or penetrate.
In essence, NR-80 high-density calcium silicate boards provide a robust, multi-faceted barrier against the challenging environment of molten aluminum, leading directly to the extended service life of critical furnace linings and components, and ultimately, significant reductions in maintenance downtime and operational costs for aluminum casting and refining operations.
