Ceramic Foam Filters (CFF) are frequently used during the filtration of aluminum (Al) melts to produce high-quality products. In the present study, the physical and hydraulic characteristics of alumina (Al2O3)-based CFF from three different suppliers (A, B and C) have been thoroughly investigated. The filters’ porosity and pore diameter, i.e., Window and Cell Feret diameters, were measured and the permeability of the different filters calculated based on pressure drop experiments. The comparison of the classification systems of CFF, i.e., Grade and PPI (Pore Per Inch) numbers, using statistical analysis of permeability and Window Feret diameter showed significant variations between the morphological and hydraulic properties of some CFFs of identical Grade and PPI numbers. Moreover, the Fanning friction factor was plotted as a function of interstitial Reynolds numbers (Rei), and laminar, transient, and turbulent flow regimes were identified. The relationship between the Fanning friction factor and the interstitial Reynolds numbers of all the filter samples investigated was processed using regression analysis, and a model equation developed to calculate the pressure drop over the CFF using the Window Feret diameter. The correlation between the experimental pressure drop values and the derived model equation indicates that empirical expressions for calculating the pressure drop over CFFs should be derived based on experimental measurements carried out at the velocity range of the application of the CFF, which is about 10 mm·s−1 for aluminum filtration.

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The purpose of the present study was to investigate the effect of different grain refiners' additions on structure and electrical conductivity of commercially electrically conductive (EC) grade 1370 aluminium alloy. A series of controlled lab scale experiments were carried out by addition of 0.1 wt. percentage Al-5Ti-1B, Al-3Ti-1B, OPTIFINE, TiBloy, and Al-3Ti-0.15C, grain refiners to molten aluminium at 730 ± 5 °C. The macro structural analysis showed that 0.1 Wt % of TiBloy, Al-5Ti-1B, Al-3Ti-1B, and OPTIFINE did not grain refine commercial EC grade aluminium. The Al-3Ti-0.15C master alloy showed, however, good grain refining performance, giving an equiaxed structure. Fading effect was observed in the samples grain-refined by Al-3Ti-0.15C master alloy. The electrical conductivity of all the grain-refined samples decreased between 0.02-0.75 ± 0.3 % IACS, compared to the reference samples of commercial pure aluminium. However, the electrical conductivity increased slightly by holding the melt, after the addition of the grain refiners, for 90 minutes, that might be due to settling of the particles by grain refiner additions.

The filtration efficiency of Ceramic Foam Filters (CFFs) of grades 50 and 65 has been quantitatively evaluated using a hydraulic water system. Distilled water seeded with Polystyrene Microsphere particles with a distribution of 20 and 50 µm. The polystyrene particles were illuminated during the filtration step by a continuous laser sheet placed before and after the filter. Images of the illuminated particles were acquired, and their number automatically distinguished and counted by the use of the image processing software. The filtration efficiency was further calculated based on the ratio of counted particles before and after the filter. Based on the obtained results the potential of the present method is discussed for evaluating the filtration efficiency of CFFs as the filtration media for molten aluminium.

Filtration using Ceramic Foam Filters (CFFs) is a method widely used to separate inclusions from molten aluminium. In the present work, the specific permeability and form drag coefficients of nominal 50 mm thick commercial Al2O3-based CFFs, of grades 30, 50, 65 and 80, have been calculated from pressure drop experiments using high (60-500 mm•s-1) and low (0.2-10 mm•s-1) water velocities. Moreover, 2D axial symmetric Computational Fluid Dynamic (CFD) models have been developed, using COMSOL Multiphysics ® to validate the experimental results. The empirically obtained values were defined as global parameters used to model the pressure, as well as the velocity fields in the water pipes and in the CFFs. The modelled pressure drop over the filter thickness for the high water velocity experiments showed < ±1 % deviation from the corresponding experimental results for all CFF grades. Moreover, the developed model also showed good agreement with the experimental results obtained from the low water velocity experiments, where the deviation of the pressure drop for the CFF samples of grade 30, 50 and 65 were ≤ ±4.6 % and for CFF samples of grade 80 ≤ ± 13.4 %.