Influence of particle size distribution and circularity on the permeability of alumina refractory coating for lost foam casting

Abstract

In this article, the influence of particle size distribution and circularity of refractory alumina particles was evaluated in obtaining ceramic coatings with low, medium, and high permeability for the foam pattern (EPS) used in the production of SAE305 aluminum alloy parts by the lost foam casting (LFC) process. Refractory particles constitute about 90 %wt of the coating, forming the pore structure, whose permeability was evaluated using particles with different mean diameters (50 − 120 μm) and mean circularities (0.64 − 0.76). The perme ability constants of the Darcy and Forchheimer equations were obtained experimentally using a permeameter and compared with those estimated by the Kozeny-Carman and Ergun-Orning models, using the porosity determined through a pycnometer and the tortuosity estimated by a model that considers circularity. The For chheimer factor is used to determine the percentage deviation of the compressed air flow through the samples from the laminar regime about the Darcy equation. The permeabilities of the disc-shaped coating samples were compared with those of low, medium, and high permeability coatings for aluminum casting reported in the literature. Analysis of these results showed reasonable agreement. The best result for improving the surface quality of the casting was obtained with a coating made from fine particles with a mean diameter of 51.7 μm and a mean circularity of 0.76, classified as a low permeability coating.