Ceramic Foam Filter CFF with 10-20 PPI 30-50 PPI and 50-80 PPI for Molten

Product Specification

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:

• Oxides: (Al₂O₃) from surface oxidation during melting and transfer.

• Spinel: Complex oxides often containing magnesium.

• Carbides: From linings or tools.

• Refractory particles: Erosion from furnace linings and troughs.

• Clusters: Agglomerations of these particles.

If not removed, these inclusions lead to:

• Poor surface finish.

• Reduced mechanical properties (strength, ductility).

• Porosity and defects in final products.

• 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):

• A robust steel box heavily lined with refractory cement or pre-cast refractory panels.

• Designed to hold molten aluminium and withstand thermal shock and chemical corrosion.

• Has an inlet well (where metal enters) and an outlet well (where filtered metal exits).

• Often includes a heating system (gas or electric) to prevent metal freeze-up.

2. The Ceramic Foam Filter (CFF):

• The heart of the system. It is a three-dimensional, open-cell foam structure made from materials like:

  • Alumina (Al₂O₃)

  • Zirconia (ZrO₂)

  • Silicon Carbide (SiC)

• It is characterized by its Pores Per Inch (PPI):

  • 10-20 PPI: Coarse filtration for roughing applications.

  • 30-50 PPI: The most common range for general casting (e.g., extrusion billets, foundry ingots).

  • 50-80 PPI: Fine filtration for high-quality products like aerospace sheet, foil, and critical castings.

• The filters are brittle and must be handled carefully before use.

3. The Filter Gasket and Sealing System:

• A high-temperature ceramic paper gasket is placed between the filter and the box ledge.

• 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:

• Large inclusions and clusters are physically blocked on the surface of the filter because they are larger than the filter's pore openings. This is the initial stage.

2. Depth Filtration:

• As a cake of inclusions builds up on the surface, it itself becomes a filter layer.

• Smaller inclusions are trapped within the complex three-dimensional network of the filter's cells through mechanisms of:

  • Interception: Particles touch and adhere to the filter walls.

  • Brownian Diffusion: Very fine particles drift and collide with the cell walls.

  • Gravitational Sedimentation: Particles settle onto cell walls.

  • Inertial Impaction: Particles cannot follow the tortuous flow path and impact the ceramic material.

This combination provides extremely high filtration efficiency, often >95%.