Simulation of Fluid and Inclusions Dynamics during Filtration Operations of Ductile Iron Melts Using Foam Filters

Abstract

The use of ceramic foam filters in ductile iron foundries to reduce the number of inclusions that reach the casting has been widely accepted. However, the exact mechanisms contributing to foam filter effectiveness are not yet known; this limits the ability to maximize filter performance and inclusion reduction. The objective of this work is to qualify and quantify the effects of the foam filter structure on inclusion retention. This has been accomplished through the development of a three-dimensional (3-D) mathematical model, based on physical water modeling and mathematical simulations. It was found that the casting rate and inclusion density play minor roles in the capture ratio, while inclusion size is the most influent variable. One mechanism for capturing inclusions involves the direct impact of an inclusion on the web wall and its adhesion after crossing over the liquid film. Two additional mechanisms involve the entrainment of inclusions by buoyancy-lift forces into low-velocity fields and the ulterior adhesion through buoyancy effects. The second mechanism is the entrainment of inclusions into microrecirculating flows; the inclusions remain in these flows for times that exceed the mold filling time. The latter mechanism has limited intensity for inclusions approximately 30 to 100 lm in size. In order to enhance the effects of this mechanism in this range of sizes, the vorticity magnitude in the microfree shear flows in the filter's pores must be increased, through changes in the structure geometry of this device.

Authors’ Reply to Discussion of “Simulation of Fluid and Inclusions Dynamics during Filtration Operations of Ductile Iron Melts Using Foam Filters”

“…Certainly, what our Figures 15(a) through (c) and 16(b) indicate are potential sources of melt oxidation for this specific filter print, which would lead to the formation of CO blowholes or, eventually, to the precipitation of slag. (4) This point raised by Professor Campbell is in complete disagreement with the experimental results provided by References [1] and [3] and, of course, with our theoretical analysis. Therefore, no further commentaries are necessary in this regard.…”

Non‐Isothermal Simulations of Aluminum Depth Filtration

“…This assumption is valid for low particle concentration. [3,12] 6) Monodisperse spherical particles are considered, but their interaction with each other and their agglomeration are disregarded. [3,12] 7) A simplified adhesion model is used, where each particle in contact with a solid surface is captured and remains attached.…”

“…[3,12] 6) Monodisperse spherical particles are considered, but their interaction with each other and their agglomeration are disregarded. [3,12] 7) A simplified adhesion model is used, where each particle in contact with a solid surface is captured and remains attached. [12] The contact is established, when the distance of a solid surface from the center of a particle is less than or equal to its radius.…”

“…Davila-Maldonado et al [12] modeled the ductile iron filtration, employing a commercial FVM code, comprising a turbulence model for solving the 3D fluid flow. A similar approach was also used by Damoah and Zhang [13] in order to study the melt flow during aluminum filtration.…”

“…[10,11,14,15] The trajectories of inclusions are most often determined by numerically solving the equation of motion for the particles. [3,4,[8][9][10][11][12][13][14][15] In the present work, both fluid flow and heat transfer during the aluminum depth filtration are considered. In particular, the influence of local temperature variation on the fluid flow and the particle deposition due to temperature-dependent density and viscosity of the melt is investigated.…”