Measurement of air entrainment during pouring of metal castings

Understanding and reducing air entrainment in liquid metals is important for improving casting filling systems and liquid metal transfer processes. Air entrainment generates oxide inclusions that reduce mechanical performance of metals. This study presents air entrainment measurements for a jet of liquid aluminum alloy A356 plunging into a pool and examines the results of similar experiments performed with ASTM 216 WCB steel alloy. Measurements are performed in argon and air atmospheres for a range of jet fall heights. The volume ratio measured of entrained gas to liquid aluminum poured in the argon atmosphere is 0.43 for an average jet impact velocity of about 3.8 m/s. This ratio is of a similar magnitude as water under the same jet parameters. For the corresponding aluminum experiments in air, the measured volumetric ratio is only 0.16. It was not possible to measure the volume of air entrained by a plunging jet of liquid steel. The expansion of the gas due to thermal radiation of the steel jet greatly affected the volume of air entrained measurements for the experiments with steel. It is found that nearly 50% of the volume of oxygen entrained is consumed by oxidation when pouring A356, but this alone does not account for the difference between the volume ratio measurements in inert and oxidizing atmospheres for A356. Instead, the ratio air is so low because during some portion of the experiment no air was entrained. In contrast, all the oxygen in the entrained air is consumed by oxidation when pouring a steel alloy. The onset velocity for gas entrainment for a plunging jet of liquid A356 in an air atmosphere is found to be 3.9 m/s and is 3.4 m/s in argon, with the difference attributed to the effect of the oxide film on the jet surface in air. The onset velocity for gas entrainment for a plunging jet of liquid WCB steel is found to be 3.8 m/s in both air and argon environments. These are about three times greater than the onset velocity previously measured for water.