Inclusions are the most prevalent defects in casting production. For a long time, the industry has adopted multiple traditional processes to block impurities, including high-quality furnace charge selection, slag skimming before pouring, slag collectors covering ladles, bottom-pour or teapot ladles, closed gating systems, and slag traps/channels on horizontal runners. However, these methods deliver limited interception performance against micron-scale fine inclusions.

Metal melt filtration technology was developed in the 1970s and went through three generations of products: woven filter screens, extruded straight-hole ceramic filters, and the third-generation ceramic foam filters (CFF). Featuring outstanding purification capacity, CFF has been widely popularized across the global foundry industry, serving as a core process to boost casting quality, cut production costs and strengthen international competitiveness of cast products.

I. Manufacturing Principle & Product Advantages of Ceramic Foam Filters

Ceramic foam filter, abbreviated as CFF (Ceramic foam filters), is produced by dipping polyurethane foam carriers into ceramic slurry, squeezing out excess slurry, then high-temperature sintering. The polyurethane framework fully decomposes under high heat, forming a 3D interconnected porous ceramic structure.

Compatible with all casting alloys such as ductile iron, gray iron, cast steel and aluminum alloy, CFF has achieved standardized and commercialized production. In industrially developed countries across Europe and America, filtration technology has been fully deployed as the simplest and most efficient standardized solution to eliminate blowholes and slag inclusions and upgrade mechanical properties of castings.

II. Five Core Application Advantages of Ceramic Foam Filters

1. Greatly Save Molten Metal & Improve Process Yield

   Traditional slag retention solutions rely on enlarged and lengthened horizontal runners as well as expanded slag traps to capture impurities, which consumes large volumes of molten metal inside the gating system and reduces casting yield.

   Taking ductile iron front hub castings from a foundry as an example: the process yield stood at 65.3% without filters, and rose to 71.5% after adopting CFF, cutting molten iron consumption by 6 percentage points. Based on an annual output of 80,000 tons of ductile iron castings, the foundry can reduce molten iron smelting by 5,000 tons every year, slashing raw material and energy consumption while maintaining full production capacity.

2. Reduce Machining Allowance & Optimize Machinability

   Inclusions tend to accumulate at the upper section of molds during pouring. Traditional processes require an extra-large machining allowance of 6–8 mm for machined surfaces facing upward, pushing up overall machining costs.

   Molten metal purified by ceramic foam filters boasts remarkably enhanced cleanliness, eliminating the need for excessive machining allowance. The filters trap incompletely melted inoculants to remove hard spots inside castings, cutting hardness deviation of a single casting by 50%.

   Significant benefits for machining: Tools need replacement every 4 hours at most 8 hours for unfiltered castings; after filtration, tools can run for 8–16 hours before replacement, extending tool service life by 2–4 times and greatly lowering machining consumable costs.

3. Improve Fluidity of Molten Metal & Dramatically Reduce Scrap Rate

   (1) Boost melt fluidity and forming quality

   Filters remove non-metallic inclusions and dissolved gases to lower melt viscosity. Purified metal melt requires higher undercooling for nucleation, accelerating crystallization and shortening solidification time by 10%. This improves mold filling and feeding capacity, drastically reducing misruns and cold shuts. When applied to automotive ductile iron front hubs, slag traps can be canceled, runners shortened, and riser height halved.

   (2) Control slag, sand and blowhole defects to cut scrap losses

   Cylinder heads feature complex thin-walled structures with strict sealing requirements and require higher pouring temperatures. Even with multiple traditional slag-blocking structures including closed gating and flow restrictors, the scrap rate caused by inclusions remained around 12%. After installing ceramic foam filters, stable pouring conditions significantly reduce leakage, keeping inclusion-related scrap rate below 3%.In the batch trial of 4,000 rear bracket castings with 1,000 pouring tests, filtration fundamentally minimizes slag defects and transforms defect modes.

   (3) Production comparison between 2nd and 3rd-generation filters

   Under identical production conditions, the overall scrap rate was 6.58% with 2nd-generation extruded ceramic filters, and dropped to 3.58% with 3rd-generation ceramic foam filters. Scrap related to filtration defects decreased from 3.62% to 1.79%, proving the superior purification performance of CFF.

4. Refine Metallographic Structure & Fully Upgrade Mechanical Properties

   Non-metallic inclusions break the continuity of metal matrix and trigger stress concentration at inclusion boundaries, easily leading to intergranular fracture. Ceramic foam filters capture micro-inclusions smaller than 2 μm and remove dissolved gases to fundamentally raise melt purity.

   Tests on HT150 gray iron show that filtered melt nucleates graphite at lower temperatures, producing finer, denser and more evenly distributed graphite that weakens its matrix-cutting effect, alongside refined and uniform pearlite. Under identical conditions, tensile strength rises by 16%, bending strength by 5.4%, and hardness by 10%. Elongation sees particularly prominent improvement.

5. Simplify Gating Systems & Boost Pattern Plate Utilization

   In ductile iron production, uneven spheroidizer/inoculant dispersion or low molten iron temperature causes particle segregation, triggering hard spots and inverse chill defects. Conventional countermeasures adopt complex oversized closed gating systems that occupy massive space on pattern plates.

   Ceramic foam filters efficiently trap fine scattered slag particles and greatly simplify gating layout, cutting space occupied by runners on pattern plates. A plate originally holding 4 casting patterns can accommodate 1–2 extra cavities, lifting pattern plate utilization and single-batch production efficiency simultaneously.

III. Industrial Promotion Significance: Empower Domestic Foundries to Upgrade Quality & Expand Overseas Markets

Practical application data demonstrates wide-ranging benefits of ceramic foam filtration technology: scrap rate of castings with slag, sand and blowhole defects drops by approximately 70%, process yield rises by 10%, and overall production cost reduces by 6%. Meanwhile, machinability and mechanical properties are optimized, delivering remarkable economic and eco-friendly social benefits. Low investment with immediate quality improvement, ceramic foam filters are essential technology for foundries to upgrade product quality, cut production loss and strengthen core competitiveness in export business, with extremely high industrial promotion value.

As downstream industries raise higher standards for casting material quality and reliability, molten metal purification has become a mandatory process for manufacturing high-end castings.

XINDA Ceramic Foam Filters are manufactured with mature sintering technology and stable 3D porous filtering structure, compatible with all ductile iron, gray iron, cast steel and aluminum alloy production lines. Integrating high-efficiency slag removal, degassing and metallographic refinement functions, XINDA CFF delivers sharp scrap reduction, higher casting yield, less tool consumption and comprehensive mechanical property upgrades with low upfront investment.

Choose XINDA Ceramic Foam Filters to fully eliminate slag inclusions, blowholes and hard spots in castings. We support domestic foundries to produce premium castings aligned with international standards, expand global sales channels, and drive the sustainable, low-loss and green development of the whole foundry industry.