Below is a comparison of the four types of channel refractory materials currently in widespread international use, along with their advantages and disadvantages:
Fused silica is currently the most widely used lining material for flow channels in large and medium-sized aluminum plants and foundries.
Performance Characteristics:
It has a thermal expansion coefficient approaching zero (making it extremely resistant to cracking at temperatures up to 1000°C), offers exceptional thermal shock resistance, and is non-wetting to molten aluminum.
Extremely high thermal shock resistance: Suitable for intermittent production involving frequent start-ups, shutdowns, or alternating hot and cold cycles.
Low thermal conductivity: Provides good thermal insulation, reducing the temperature of molten aluminum.
Smooth surface that does not adhere to aluminum: Ensures good flow of molten aluminum and makes cleaning up residual aluminum dross very easy.
Prolonged use at temperatures above 750°C can cause a phase transformation, leading to material embrittlement and breakage. The material has relatively low strength and is not resistant to strong mechanical impacts (such as blows from tools during cleaning).
Exceptional aluminum non-stick properties: Molten aluminum forms highly rounded beads on the surface with absolutely no penetration.
Long service life: Its resistance to erosion and corrosion far exceeds that of fused quartz, significantly reducing the frequency of downtime for replacement.
High thermal shock resistance and high-temperature strength: Excellent long-term operational stability.
Expensive, with high initial procurement costs. Prone to solid-phase decomposition in the medium-temperature range of 900°C–1100°C.
3. Anti-Wetting Low-Cement/Cement-Free Castables (Anti-Wetting Castables - LCC/Sol-Bonded) — The preferred choice for long-distance and complex, irregularly shaped flow channels.
Made with high-alumina or mullite aggregates, combined with anti-wetting agents (such as BaSO₄ and AlF₃) and silica sol bonding technology, these materials are cast on-site or manufactured as precast components.
High mechanical strength: Resistance to molten aluminum erosion and mechanical impact from tools is far superior to that of fused quartz.
Suitable for complex shapes: Suitable for complex flow channel systems, such as those with long distances, multiple bends, and diverter boxes.
Moderate cost: Offers excellent cost-effectiveness compared to aluminum titanate.
Thermal conductivity is higher than that of fused quartz and aluminum titanate, requiring a thick backing insulation layer (such as nano-boards).
If the wetting inhibitor fails at high temperatures, molten aluminum may penetrate the material, leading to corundum nodule formation.
4. Silicon nitride-bonded silicon carbide (Si3N-SiC)—A specialized material for high-erosion and critical components, primarily used in aluminum outlet ports of flow channels, diverter valve cores, control gates, and key areas directly exposed to the impact of falling molten aluminum; it is rarely used as a complete structure for long flow channels.
Performance Characteristics: Extremely high hardness, wear resistance, and thermal conductivity.
Advantages: Superior erosion resistance, extremely high dimensional accuracy, and exceptional wear resistance.
Disadvantages: High thermal conductivity (poor thermal insulation), heavy weight, and high cost.
Composite Flume Structure Design (From the Inside Out)
To balance the requirements of “non-stick properties with aluminum, erosion resistance, extreme low-temperature performance, and shell safety,” modern aluminum plants generally adopt a multi-layer composite lining structure:
Working layer (in contact with molten aluminum): Fused quartz or alumina titanate precast components (approximately 40–80 mm thick).
Filler/Transition Layer: Lightweight high-alumina castable or aluminosilicate refractory plastic, serving as a buffer layer between the precast components and the insulation layer.
Backing Insulation Layer: Nano-microporous insulation boards (Microporous Board) or AES soluble eco-friendly fiber boards (thickness 10–20 mm), which maintain the steel shell temperature below 80°C.
Shell: Carbon steel shell.
