In casting processes, oxidized slag, molten slag and sand inclusions within molten metal constitute the primary causes of casting defects such as slag entrapment, leakage and substandard mechanical properties. Featuring a dual-layer filtration mechanism and matched gating system design, ceramic foam filters effectively improve the cleanliness of molten metal and reduce defect formation. They are widely applied in the production of ductile iron, gray iron and other castings.

Ⅰ. Filtration Mechanism and Process Adaptation

The purification of ceramic foam filters is achieved in two stages: mechanical sieving and cake filtration. Mechanical sieving relies on interconnected internal pores to directly trap inclusion particles and impurity agglomerates larger than the pore size. As impurities accumulate at the inlet surface of the filter, a filter cake gradually forms, which can capture fine oxidized inclusions smaller than the pore size to realize deep purification of molten metal.

This filter component is compatible with mainstream molding processes including clay sand horizontal parting and vertical parting. For horizontal parting production lines, rational installation clearance and draft angle shall be reserved for filter arrangement to prevent sand scraping and sand dropping during production. For vertical parting production lines, a gating system adopting the "first closed then open" principle is used, combined with bottom ingates and mold cavity venting structures. This stabilizes the flow velocity of molten metal and lowers risks of sand erosion, re-oxidation of molten iron and porosity, so as to guarantee stable filtration performance.

Ⅱ. Engineering Application Cases

Case 1: 400kg RUT450 Casting — Efficient Slag Removal and Balanced Mold Filling for Large-Tonnage Castings

The casting weighs 400kg, and a 15 ppi ceramic foam filter is installed in the runner with a symmetrical dual-piece layout. Large-tonnage casting involves high molten metal flow. This scheme efficiently intercepts molten slag generated during melting and pouring, balances molten metal flow on both sides, eliminates turbulence caused by overfast single-side filling, stabilizes the filling process, reduces slag inclusion risks in heavy-section castings, and ensures uniform overall microstructure.

Case 2: 240kg Ductile Iron Axle Housing — Balanced Inclusion Filtration and Feeding for Castings

Axle housings are heavy-load safety-critical castings that impose stringent requirements on internal cleanliness and density. For this 240kg ductile iron axle housing, a 10 ppi ceramic foam filter is symmetrically arranged and matched with a gating structure with side riser ingates. The filter removes fine inclusions from molten metal to avoid internal slag defects. Meanwhile, the complete gating system realizes stable flow and feeding, optimizes the solidification process of castings, reduces shrinkage porosity, and meets the high strength and reliability standards for heavy-load components.

Case 3: HT300 Volute — Process Modification for Castings with High Rejection Rate

Under the original production process of HT300 volutes, re-oxidized slag and minor sand inclusion were prominent issues, leading to a slag inclusion rejection rate higher than 30%. Massive scrapped castings pushed up production costs. After adopting high-porosity ceramic foam filters for process optimization, fine oxidized slag and suspended sand particles can be effectively captured to control inclusion defects at the source. After modification, the slag inclusion rejection rate of castings dropped below 1.0%, greatly cutting material waste and rework, and significantly improving process stability.

Silicon carbide ceramic foam filters are suitable for molten metal filtration under working temperatures up to 1500℃. When the molten metal temperature exceeds 1450℃, the load-bearing capacity of the filter declines. Sufficient safety factors shall be reserved at the process design stage, and small-batch trial production verification shall be carried out. Shockproof and moisture-proof protection must be ensured during product storage and transportation. Product dimensions shall be rechecked before installation, and floating sand in mold cavities shall be cleaned, to avoid molten metal bypass caused by dimensional deviation and prevent filtration failure.

The casting industry continues to advance toward precision manufacturing. As a key procedure to control the intrinsic quality of castings, molten metal purification gains growing importance. Xinda ceramic foam filters feature stable impurity interception capacity and adapt to production demands of castings of different weights and materials. Supported by mature process matching experience, Xinda provides reliable process solutions for foundries to resolve inclusion-related defects and stabilize product quality.

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