Pilot-Scale Investigation of Liquid Aluminum Filtration through Ceramic Foam Filters: Comparison between Coulter Counter Measurements and Metallographic Analysis of Spent Filters

International audienceA pilot has been designed to study the mechanisms associated with liquid aluminum filtrationthrough ceramic foam filters (CFFs). Before entering the filtering bowl, the liquid metal isseeded with massive artificial inclusions. A theoretical analysis of the filtration of massiveinclusions shows that there are two preponderant deposition mechanisms, i.e., direct interceptionand sedimentation, which explain qualitatively the effect of the operating conditions on themeasured filtration efficiency. Furthermore, it is observed that the filtration efficiency measuredby two Coulter counters reaches a minimum value for a diameter close to 30 µm. This nonmonotonoustrend can be explained by the coexistence of two populations of inclusions,intentionally added massive ones and oxide films. It is expected that oxide films are the mostnumerous inclusion type for diameters less than 25 µm and have an apparent volume muchlarger than their absolute volume (contrary to massive inclusions), leading to a higher filtrationefficiency. In addition, a metallographic analysis of spent filters shows that the density of thecaptured massive inclusions decreases exponentially between the filter inlet and the filter outlet.The initial filter coefficient can be derived, which is equal to 25 m^-1 for a 30-ppi filter grade(with a specific surface area of 1610 m^-1), SiC inclusions 50 µm in diameter, and a filtrationvelocity of 0.9 cm.s^-1