Abstract
Interactions between multiple splats landing on a substrate was studied experimentally by photographing deformations of droplets as they land and freeze on the substrate, or previously solidified splats. Uniform-size molten tin droplets (550 µm diameter) were produced using a drop-on-demand generator. To achieve high impact velocities the stainless steel coupons used as substrates were mounted on the rim of a rotating flywheel and heated using cartridge heaters to vary substrate temperature. To hit a falling droplet with the substrate and photograph its impact, a timing circuit was used to synchronize the ejection of a droplet, triggering of the camera and a flash to provide illumination. The substrate temperature and substrate roughness significantly affected splat impact dynamics. Droplets hitting a smooth cold substrate splashed extensively whereas those hitting a hot substrate spread in the form of a smooth disc. The final splat shapes were dependent on the offset distance between the impacting droplet and the previously solidified splat. The size of fingers around the splat edge increased with the offset distance. Large pieces of metal detached from the droplet rim when the droplet hit a rough substrate whereas droplets hitting previously solidified splats splashed in a star-like shape with extremely long fingers.
