Impact, recoil and splashing of molten metal droplets

We studied the impact and solidification of molten tin droplets on a stainless steel surface. Droplet impact velocity was varied from 1.0 to 4.0 m/s and substrate temperature from 25 to 240°C (above the melting point of tin, 232°C). We photographed droplet impact and measured splat diameter and liquid–solid contact angle from these photographs. Substrate temperature under an impacting droplet was measured using a fast response thermocouple. Thermal contact resistance at the droplet–substrate interface was calculated by matching measured surface temperature variation with an analytical solution. A simple energy conservation model was used to predict the maximum spread of droplets during impact. Predictions agreed well with measured values. Instabilities were observed on the periphery of the droplet, which led to the formation of fingers. A model based on the Rayleigh–Taylor instability was used to predict the number of fingers around the periphery of the droplet.