Purification Mechanisms of Foam Ceramic Filters

I. Sieving-Filter [https://www.beihaicomposite.com/filter/] Cake-Deep Bed Filtration Mechanism

1. Sieving (Screening): This mechanism follows the principle of traditional fiberglass mesh filtration, acting like a sieve to block inclusion particles and their agglomerates larger than the filter's surface pores from passing through.

2. Filter Cake Filtration: Many inclusions larger than the filter's pores are captured at the filter's inlet end through sieving. As the number of captured inclusions increases, a "filter cake" composed of large impurities forms on the filter's inlet surface. This "filter cake" refines the liquid, causing even inclusions smaller than the filter's pore size to be partially captured on the "filter cake."

Sieving and filter cake filtration are two stages of the same mechanism, and their duration depends on the amount of inclusions in the liquid and the size of the filter's pores.

3. Deep Bed Filtration: Inside the foam ceramic [https://www.beihaicomposite.com/customized-ceramic-foam-aluminum-foam-ceramic-alumina-high-temperature-resistant-filtration-product/] filter, the melt flows along a tortuous path. In small areas, there are even instances of cross-flow reversal. This primarily serves to increase the probability of inclusion particles contacting the filter greatly. Smaller diameter inclusions, as they flow with the melt, can be trapped in a corner after colliding, thus being captured.

II. Floating Separation Mechanism

When a foam ceramic filter [https://www.beihaicomposite.com/ceramic-foam-filter/]is correctly designed and placed in the gating system, the resistance to metal flow increases, causing the liquid metal to fill the gating system and thereby fully utilize the slag-retaining function of the gating system. Simultaneously, the liquid flow injected from the sprue is throttled by the filter, causing the metal liquid to temporarily dwell in the sprue. This allows less dense slag to float and separate, achieving the advantages of a bottom-pouring gating system. As the metal liquid continues to be poured through the Foam ceramic filter, on one hand, less dense slag floats up, and on the other hand, turbulence is effectively reduced or eliminated.

III. Adsorption Mechanism

When the filter is placed in the runner or ingate of the mold cavity, as the first stream of liquid reaches the filter's inlet surface during pouring, an adsorption phenomenon occurs between the liquid flow and the foam network. This adsorption is primarily a non-selective, multi-molecular layer physical adsorption, where inclusions are adsorbed layer by layer onto the filter's network until blockage occurs.

IV. Rectification Mechanism

Studies on the sources of inclusions in castings reveal that secondary oxidation inclusions account for 83% of total inclusions, inclusions caused by mold material erosion account for 13%, and only 4% are due to incomplete slag removal before pouring. This indicates that most inclusions within castings are formed during the pouring process, and using filters to purify the metal achieves significant purification effects. During the pouring process, in most cases, the metal liquid fills the mold cavity in a turbulent state, especially during the initial stages when it enters the cavity from a certain height. Due to the tortuous and winding flow paths within the foam ceramic filter, it has a strong ability to rectify the liquid metal from turbulent to laminar flow. As a result of the filter's rectifying action, the highly turbulent metal liquid transforms into a laminar state after passing through the filter. When it flows past the filter, it requires a longer transition zone to revert to its original turbulent state. Within this transition zone, the liquid flow does not have enough time to develop into turbulence or significant turbulence, thereby preventing secondary oxidation of the metal and erosion of the mold, and thus acting as a "slag barrier" to prevent the formation of secondary oxide inclusions.

Image: https://ecdn6.globalso.com/upload/p/566/image_other/2025-07/purification-mechanisms-of-foam-ceramic-filters.jpg [https://www.beihaicomposite.com/ceramic-foam-filter/]

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