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

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%.

Founded in January 2003,Jinan HYDEB Thermal Tech Co., Ltd. is located in Jinan High-tech Development Zone.

Hydeb mainly produces molten aluminum refining and degassing units, molten aluminum transfer ladles and holding crucible furnaces, which are sold to well-known corporations in the industry at home and abroad, meeting their high requirements for product safety and advancement.

Focusing on the aluminum casting industry, the Company takes “Technology, Quality and Service” as its base of enterprise, aimed at meeting all the needs of customers. Being “Safe, Practical, Reliable, Efficient and nice-looking”, its products are well unanimous recognized by the customers, with its brand “HYDEB” gaining high popularity in the industry.

To meet the increasingly high requirements for aluminum casting products, HYDEB gives full play to its technological superiority and engages industry experts as technical directors, developing products urgently needed in the market such as the counter (low) pressure casting holding crucible furnaces and molten aluminum refining and degassing units. It has also established long-term and friendly partnerships with a number of large-scale Chinese integrated equipment suppliers, sustaining its annual supply level of more than 80 sets.

“Taking the lead and creating a brand name in the industry”. We will continue to advance on the path of professional development and continually improve our products and services to further meet our customers’ development needs and support their creation of greater values.