Investigating surface entrainment events using CFD for the assessment of casting filling methods

The reliability of cast components is dependent on thequality of the casting process. This can be characterised by the robustness (repeatability) and specific fluid flow characteristics within the running system and mould cavity. During this highly transient filling phase the prevention of free surface turbulence and consequential oxide entrainment is critical to assure the mechanical integrity of the component. Past research has highlighted a number of events that lead to entrainment of surface oxides, including plungingjets, waterfalls and returning backwaves. Using FLOW-3D, flow structures that result in surface entrainment events have been simulated and an algorithm developed that allows entrainment and defect motion to be tracked. This enables prediction of the quantity and motion of oxide film generated from each event. The algorithm was tested experimentally using real-time X-ray radiography to directly image transient liquid metal flows. A quantitative criterion is proposed in order to be able to assess the damage of each type of event. Complete running systems have also been studied in order to understand how they could be assessed for quality of filling based on the geometric features of the flows within them.