(388f) Minimizing Surface Turbulence in Casting

Surface turbulence is a leading cause of defects in casting. This turbulence is distinct from traditional turbulence that occurs in bulk fluids and indicates the increased surface area that develops from wavy fluid surfaces and droplets pinching off. In liquid metal at elevated temperature, in contrast to water, these surface react (e.g., forming oxides or carbides) to form thin surface layers that invaginate or pair to bilayers. These bilayers are recognized as a leading source of bulk defects that decrease material properties of metals formed by casting processes. In this talk, we explore staggered posts along the edges of tilt cast molds as a means of reducing surface turbulence. The development of surface turbulence is controlled by the Weber number, the product of fluid density, a length scale (here the width of the mold), and local fluid velocity divided by the surface tension. We find that surface turbulence develops when the Weber number exceeds six. The posts reduce the Weber number by attenuating the velocity more so than the side runner also explored. The presentation highlights development of a 3D printed test platform, computational fluid dynamics modeling of the tilt casting process, and quantitative comparison of their results.