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As Campbell stated in 2006, “the use of entrainment models to optimise filling systems designs for castings has huge commercial potential that has so far being neglected by modellers”. In this paper a methodology using computational modelling to define entraining events and track the entrained oxide films is presented. Research has shown that these oxide films present within the casting volume are highly detrimental to casting integrity, thus their entrainment during mould filling is especially undesirable. The method developed for the modelling of oxide entrainment has been validated against previously published data by Green and Campbell (1994) [31] . The validation shows good quantitative correlation with experimental data. However there is scope for further development which has the potential to both improve the accuracy and further validate the technique.

The entrainment of oxide films into the bulk material has been shown to have a detrimental effect on casting integrity. A number of mechanisms have been shown to initiate the entrainment of oxide films, including: returning waves, plunging jets, bubble trails and fountains. Therefore, the assessment of the casting system for these features by the foundry engineer is critical in improving casting quality. The use of computational fluid dynamics software packages, which are now widely available to the foundry engineer, has allowed the foundry engineer to improve casting system design by using qualitative parameters. Optimization software is now an economically viable option for many foundries. However, optimization for casting integrity requires a quantitative casting integrity assessment technique, which allows the modeling and quantification of defects. Therefore, modeling and quantification of defects is becoming an ever more important research area to allow the optimization software manufacturers to meet the needs of industry. The current methods found in published literature for the modeling of casting defects have been described and critically reviewed, shedding light on the qualities and issues currently associated with the present available methods. However it is clear that further investigations and developments are still required to allow the accurate and efficient modeling of casting defects. The topics of research relating to the modelling of casting defects which require further investigation have been highlighted.

Entrainment defects occur frequently in aluminium alloy castings during mould filling, and are very detrimental to both mechanical properties and reliability. The formation mechanisms and influences of these defects have been discussed previously, but the behaviour of the defects in the liquid metal and their evolution during solidification has not been studied in detail. In this research, samples of Al-Si-Mg alloy A356 that contained entrainment defects were scanned using ultra-fast synchrotron-based X-ray tomographic microscopy at the TOMCAT beamline of the Paul Scherrer Institut. The samples were directly viewed at both room temperature and in a fully liquid state. The reconstructed images showed three different entrainment defect morphologies, namely, entrained pores, tangled double oxide films and closed cracks. The evolution of the morphology of the entrainment defects was studied to better understand morphological changes of the defects, and the relationship between entrainment defects and microporosity.

Anthropometric measurements were taken on 281 toddlers (24-48 mo old) in Linguère, Sénégal, to determine the prevalence of undernutrition. Blood samples collected from 271 of the toddlers were analyzed for retinol and carotenoids by HPLC. According to the National Center for Health Statistics reference values 30.2% of the population was undernourished. Serum retinol values were below the lower limit of the normal range in 71.5% of the children; 7.4% of this group had concentrations0.35 mumol/L, placing them at risk for xerophthalmia. Only 3% of the population had serum retinol valuesor = 1.0 mumol/L. Serum carotenoids were low (0.70 mumol/L) in 55% of the children. Retinol-binding protein values were low and measurable concentrations of retinyl palmitate were detectable in only 17% of the children. Undernutrition and poor vitamin A status were found to exist at a concentration that would endanger health.

Modelling of three common entrainment mechanisms in fluid flow, namely plunging jet, return wave and rising jet, that generating defects during casting were conducted and validated by A356 alloy. Previous research highlighted surface turbulence in liquid metals could result in the fold-in of surface films into bulk liquid and leave cracks or porosity in the solidified component. An algorithm applied face normals of free surface and their interaction to capture the entrainment of surface films was used in study. The model integrated the algorithm into CFD package FLOW-3D and was used to track the entrainment defects formation and distribution involved in different entrainment behaviours in casting process. The defects density in local volume plotted by the model was then employed as quantitative criteria to predict the reliability of castings. Directly observation of transient flows in moulds by real-time X-ray radiography showed good correlation between real filling scenario and simulation results. Fracture strength achieved by four-point bend tests on the samples from corresponding locations with models in castings showed some extent relationship between defects density and reliability of castings quantitatively. Studies also indicated the plunging jet mechanism usually leaded to high variation of mechanical properties due to intense turbulence and entrainment.