Impact of molten metal droplets on the tip of a pin projecting from a flat surface

We photographed impact of molten zinc and tin droplets on a flat steel surface from which the tip of a small pill was projecting. The height of the pin and its distance from the droplet center vas varied. A three-dimensional model of droplet impact and solidification was used to predict splat shapes formed by droplets after they had spread and frozen. The model calculated velocity and pressure distributions in droplets and the growth of solid layers. When the offset distance of the pin was less than the droplet radius liquid flowed over the pin so that it had relatively little impact on the final splat shape. At larger offset distances a liquid sheet jetted from under the droplet after impact and impinged on the vertical surface of the pin. If the pin height was sufficiently large, approximately the same as the final splat thickness, it obstructed flow of liquid so that the solidified splat had a V-shaped notch in it. If pin height was made less than the average splat thickness liquid flowed over it and the final splat was circular, but the pin reduced flow velocity and suppressed growth of fingers along the edges of the splat that passed over the pin. Reduced velocities also resulted in faster growth of the solidified layer around the pin. (C) 2004 Elsevier Inc. All rights reserved.