The filtering theory of ceramic foam filters 

The mechanism of ceramic foam filter plate filtering and purifying aluminum melt is generally described as diffusion interception and inertial collision interception or screening mechanism, sedimentary layer, and deep bed filtration mechanism. The State Key Laboratory of Tsinghua University has established a three-dimensional physical model and a two-phase flow model for the filtration mechanism of the ceramic foam filter and carried out simulation calculations, which are very helpful for our research on the filtration and purification of molten aluminum. The process of filtration and purification of molten aluminum by ceramic foam filter plate is very complicated, which is a complex process of high-temperature physical chemistry and metallurgical dynamics. As for screening, collision, sedimentation, interception, and filtration, it is relatively easy to understand. We have conducted a comprehensive analysis of many parameters obtained in the process of filtering aluminum melt with ceramic foam filters, and put forward the following insights:

(1) Through sieving collision interception, diffusion interception, friction, sedimentation, and other mechanical filtration, the filtration efficiency is proportional to the mesh aperture of the ceramic foam filter plate. The smaller the mesh, the stronger the interception ability of small particles of impurities.

(2) The effect of the deposition layer or filter cake layer, along with the deposition of impurity particles in the melt and the curved interconnected and uneven grid support in the filter plate, the ability to capture impurity phase particles is improved.

(3) The rough surface formed by the gaps on the surface of the network scaffold increases the interfacial energy between the aluminum liquid flow and the ceramic body surface and promotes the flow of impurity particles in the aluminum liquid flow to be more disordered, which is conducive to the capture of solid particles. deposited.

(4) Due to the microscopic cracks and pinholes on the surface of the network scaffold, a fluoride flux with a strong affinity for alumina particles is pre-deposited, which promotes a complete filter cake layer effect and strong chemical adsorption, and makes it possible to capture the retained impurity phase particles. capacity is enhanced.

(5) During the metal smelting process and the temperature field effect of the heat transfer process, the concentration difference of the alloy solute will inevitably form, and the metal melt will redistribute - integrate - redistribute - and integrate again, which is also a good alloying process. Some high melting point metal phases and compounds re-aggregate and grow up, and the fine impurity phase aggregates and grows up, which is beneficial to be captured by filtration. This can be explained from the changes in the concentrations of H, Al2O3, Fe phase, and Ti phase before and after filtration. In particular, the effect of double-stage filtration or pore gradient thick plate filtration is more obvious. Therefore, under the same conditions, the new generation of ceramic foam filter plates has a high removal rate of impurity phase in the aluminum melt, the change of static pressure difference before and after filtration changes more with time, and the change of hydrogen content in aluminum melt before and after filtration Also obvious. Of course, the smaller the pores of the selected ceramic foam filter plate, the better the cleanliness of the aluminum melt.