Experimental Investigations of the Depth Filtration inside Open‐Cell Foam Filters Supported by High‐Resolution Computed Tomography Scanning and Pore‐Scale Numerical Simulations

Abstract

The removal of nonmetallic inclusions from metal melts is a crucial step in producing high‐quality castings that have to meet strict requirements regarding strength, toughness, and machinability. To separate the unwanted impurities, the liquid metal is usually passed through ceramic foam filters (CFF), in which the inclusions adhere to the surface of a complex strut network. The development of improved CFF structures requires a good understanding of the physical phenomena involved in the filtration process. In this respect, an experimental investigation of the real system is challenging, due to the opacity of the melt, high temperature, and the presence of a protective atmosphere. Therefore, the present study relies on water model experiments, which are conducted for different pore counts and flow velocities. To achieve a high degree of similarity to the real system, the wetting properties of the filters and particles are adjusted accordingly. Experimentally evaluated filtration efficiencies are compared with predictions obtained from a detailed numerical model that considers the CFF geometry, which is digitized using 3D X‐Ray micro‐computed tomography, and previously measured particle adhesion forces. The results suggest that a considerable fraction of particles does not remain attached after collision with the CFF struts.

Atomic Force Microscopy Investigation of the In Situ‐Formed Oxide Layer at the Interface of Al2O3−C/Steel Melt in Terms of Adhesion Force and Roughness in a Model System

“…If a CP particle hits one of these microbubbles, such large capillary forces arise after film breakage, where the full distance of the Z-scanner (10 μm) is not sufficient to let the particle detach from the refractory sample surface. In the case of capillary forces with such optically visible microbubbles, it can be said quite confidently on the basis of the results of Hoppach et al [34] that the inclusions remain trapped on the refractory materials during filtration because the flow-induced shear forces are not sufficient to redisperse them. Therefore, areas without microbubbles are of particular interest.…”

Large Eddy Simulation of Turbulent Flow and Inclusion Transport during Filtration of Liquid Steel inside Open‐Cell Ceramic Foams

“…Another difficulty arises from the transitional nature of the turbulence, which develops as the melt advances through the filter and is also expected to be largely heterogeneous due to the strong variation in the flow velocity, commonly observed inside ceramic foams. [ 6 ]…”