Ceramic Foam Filter
A Molten Aluminium Filtration Box is a refractory-lined chamber integrated into the molten metal flow path (typically between the furnace and the casting unit). Its core component is a Ceramic Foam Filter (CFF), a porous ceramic plate designed to physically trap non-metallic inclusions (impurities) as molten aluminium is poured through it.
This system is a critical and standard piece of technology in modern aluminium foundries and casthouses for producing high-quality, defect-free cast products.
1. Purpose and Why it's Necessary
Molten aluminium always contains solid impurities called inclusions. These include:
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Oxides: (Al₂O₃) from surface oxidation during melting and transfer.
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Spinel: Complex oxides often containing magnesium.
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Carbides: From linings or tools.
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Refractory particles: Erosion from furnace linings and troughs.
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Clusters: Agglomerations of these particles.
If not removed, these inclusions lead to:
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Poor surface finish.
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Reduced mechanical properties (strength, ductility).
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Porosity and defects in final products.
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Catastrophic failure in high-integrity applications like aerospace or automotive parts.
The CFF box is the most efficient and widely used method to remove these inclusions.
2. Key Components of the Filtration System
A typical system consists of three main parts:
1. The Filter Box (or Filter Casse):
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A robust steel box heavily lined with refractory cement or pre-cast refractory panels.
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Designed to hold molten aluminium and withstand thermal shock and chemical corrosion.
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Has an inlet well (where metal enters) and an outlet well (where filtered metal exits).
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Often includes a heating system (gas or electric) to prevent metal freeze-up.
2. The Ceramic Foam Filter (CFF):
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The heart of the system. It is a three-dimensional, open-cell foam structure made from materials like:
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Alumina (Al₂O₃)
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Zirconia (ZrO₂)
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Silicon Carbide (SiC)
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It is characterized by its Pores Per Inch (PPI):
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10-20 PPI: Coarse filtration for roughing applications.
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30-50 PPI: The most common range for general casting (e.g., extrusion billets, foundry ingots).
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50-80 PPI: Fine filtration for high-quality products like aerospace sheet, foil, and critical castings.
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The filters are brittle and must be handled carefully before use.
3. The Filter Gasket and Sealing System:
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A high-temperature ceramic paper gasket is placed between the filter and the box ledge.
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A hold-down beam or refractory clamp is used to press the filter down onto this gasket, creating a seal that forces all the molten metal to flow through the filter, not around it.
3. How It Works: The Filtration Process
The process is primarily deep bed filtration, involving two main mechanisms:
1. Mechanical Sieving:
2. Depth Filtration:
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As a cake of inclusions builds up on the surface, it itself becomes a filter layer.
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Smaller inclusions are trapped within the complex three-dimensional network of the filter's cells through mechanisms of:
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Interception: Particles touch and adhere to the filter walls.
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Brownian Diffusion: Very fine particles drift and collide with the cell walls.
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Gravitational Sedimentation: Particles settle onto cell walls.
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Inertial Impaction: Particles cannot follow the tortuous flow path and impact the ceramic material.
This combination provides extremely high filtration efficiency, often >95%.
Product Tags:
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Ceramic Foam Filter CFF with 10-20 PPI 30-50 PPI and 50-80 PPI for Molten Aluminium Filtration Images
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