Alumina ceramic foam filter plate is essential for improving the quality of molten aluminum alloy. It largely determines the subsequent processing performance and the quality of final products. Therefore, the purification of aluminum melt has attracted great attention across the global industry.

The contamination of molten aluminum comes from multiple sources. During melting, aluminum in molten or semi-molten state is exposed to furnace atmosphere. It is susceptible to oxidation and hydrogen absorption through reaction with water vapor, generating various non-metallic inclusions such as furnace lining debris, chlorides and carbides from fluxes, as well as coarse intermetallic particles. Meanwhile, return scraps have complex sources, including process wastes from internal production procedures and externally purchased scraps, which introduce various non-aluminum impurities. These impurities cause blowholes and inclusion defects in cast billets, reduce melt cleanliness, and impair processing performance, mechanical properties, corrosion resistance and surface quality of finished products.

Alumina ceramic foam filter plate can efficiently remove micron-scale fine inclusions from molten aluminum, convert turbulent metal flow into stable laminar flow and optimize mold filling performance. Featuring a unique mullite-corundum structure, the product boasts high mechanical strength, favorable chemical stability and excellent erosion resistance against molten aluminum. Its pore size and open porosity are strictly controlled to achieve stable filtration results. A sealing ceramic fiber gasket is fitted around the filter plate to realize sealing inside the filter box and prevent unfiltered molten metal from bypassing through gaps.

I. Main Application Fields

1. Melt purification process for aluminum and aluminum alloy production;

2. Filtration for copper alloy casting. Non-ferrous melts such as brass, bronze, zinc and tin are prone to oxidation and non-metallic inclusion formation during casting, leading to high reject rates. Ceramic foam filter plates can significantly reduce reject rates. Cordierite-grade filters with pore sizes of 20 PPI or 30 PPI are generally selected for copper alloy filtration;

3. Catalyst carrier for automotive exhaust purification. Ceramic foam has a large specific surface area, good thermal stability, wear resistance, anti-poisoning performance and low density, making it a mainstream carrier for exhaust catalysts. Installed on the exhaust pipe of gasoline engines, it converts harmful gases including CO, HC and NOₓ into carbon dioxide, water and nitrogen with a conversion rate of over 90%. For diesel engines, the purification rate of carbon particles can exceed 50%. After carbon particles accumulate on the filter element, regeneration can be realized by catalytic oxidation or electronically controlled combustion for continuous use;

4. Special high-temperature fields. With excellent thermal radiation performance, it is applied to heat transfer enhancement and porous medium combustion technology. It can also serve as a photocatalyst carrier loaded with nano titanium dioxide. Excited by ultraviolet light, it degrades organic substances and microorganisms to purify air. Additionally, it can be used as packing for chemical towers, gas distribution materials and energy-saving burner plates for gas stoves.

II. Filtration Mechanism

1. Filter cake effect. The three-dimensional porous structure of ceramic foam mechanically intercepts slag. When molten metal flows through, inclusions larger than the surface pores are trapped and accumulated on the inlet side to gradually form a filter cake. The filter cake further narrows flow channels and captures finer impurities. Slits and dead zones inside the ceramic body can also trap inclusions, producing the filter cake effect internally;

2. Surface adsorption effect. Molten metal is split into fine streams by the porous structure, raising the contact chance between inclusions and filter media. The surface of the filter plate features micro-concave-convex structures of 1~10 μm, which capture impurities by electrostatic adsorption and adhesion;

3. Rectification effect. After the melt stream is split, the equivalent flow diameter decreases and the Reynolds number drops, turning the flow into laminar flow. Under laminar conditions, the density of inclusions is far lower than that of molten aluminum, allowing sufficient time for inclusions to float upward and separate. The filter plate increases flow resistance, reduces melt velocity in the runner, promotes slag floating and retains slag on the upper part of the runner to assist slag blocking.

III. Application Benefits

Purified molten aluminum brings remarkable benefits to aluminum processed products such as sheet, strip, foil and profiles. For the production of 6063 aluminum alloy profiles, the advantages are listed as follows:

1. Higher extrusion capacity. After filtration, the extrusion speed rises by about 20%, and the overall productivity increases by nearly 15%;

2. Longer service life of dies and fewer die maintenance times;

3. Lower extrusion pressure. The extrusion pressure is reduced by more than 3% compared with unfiltered molten aluminum;

4. Greatly improved surface quality of aluminum profiles.

In casting applications, it effectively reduces inclusion defects, improves the cutting performance of castings, lessens tool wear and cuts production costs.

IV. Installation and Operation Guidelines

Filtration efficiency is closely related to installation. The adoption of filter plates cannot replace basic impurity removal procedures such as melting, in-furnace refining and casting. Re-contamination of purified molten aluminum should also be prevented.

1. Proper selection. The dimension and PPI pore density of the filter plate shall match the casting flow rate, maximum molten aluminum level, total filtration volume and cleanliness of raw aluminum melt;

2. Pre-treatment of melt is indispensable. Complete regular slag skimming, furnace cleaning and in-furnace refining. An on-line degassing unit is essential, as it reduces hydrogen content and removes part of inclusions;

3. Match with square refractory filter box to ensure sealing, prevent molten aluminum from flowing out through gaps and avoid filter plate floating and failure;

4. Preheat before use. Preheat by electric or gas heating for about 15 minutes to remove moisture and guarantee stable initial filtration;

5. Do not remove slag, knock or vibrate the filter plate during filtration. Keep the launder full of molten aluminum to reduce liquid level turbulence;

6. Drain residual metal in the launder and filter plate after casting. A vibrator can be used for 1 minute to shake off approximately 75% of retained molten aluminum;

7. Clean the surroundings and take out the filter plate after residual metal solidifies.

V. Product Features

1. Excellent thermal shock resistance and resistance to molten metal erosion and impact, suitable for high-temperature working conditions;

2. Advanced production process, supplying filter plates in various sizes and pore densities to meet demands of aluminum processing enterprises;

3. Strict dimensional tolerance control, compatible with automatic filter loading production lines;

4. Manufactured with high-purity alumina as raw material, featuring uniform pores, high temperature resistance, good thermal stability, wear resistance and stable chemical properties. Widely used in casting, water treatment, chemical industry and environmental protection. It is the preferred material for molten aluminum filtration and catalyst carriers, and can also be applied for sound insulation and heat insulation. Custom shapes, sizes and PPI pore densities are available.

VI. Product Specification Table

Note: Custom special-shaped products can be supplied upon customer request.

With stable and reliable purification performance, alumina ceramic foam filter plate is a core consumable for molten metal quality control and yield stabilization in aluminum alloy and non-ferrous alloy casting. Xinda can flexibly select proper specifications and pore densities according to customers' on-site casting process, pouring flow rate and product requirements, provide customized filtration solutions, and help foundries continuously improve casting quality and reduce production costs.