Browsing by Author "Green, N. R."

Now showing 1 - 7 of 7
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    Assessment of casting filling by modeling surface entrainment events using CFD
    (The Minerals, Metals and Materials Society, 2010-05-31) Reilly, C.; Jolly, Mark R.; Green, N. R.; Gebelin, J. C.
    The reliability of cast components is dependent on the quality of the casting process. During this highly transient filling phase the prevention of free surface turbulence and consequential oxide entrainment is critical to ensure the mechanical integrity of the component. Past research has highlighted a number of events that lead to entrainment of surface oxides. 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 and compared to experimental data from previously published work. A quantitative criterion is proposed to assess the damage of each type of event. Complete running systems have also been studied to understand how they could be assessed for quality of filling based on the flows within them.
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    Investigating surface entrainment events using CFD for the assessment of casting filling methods
    (Minerals, Metals & Materials Society, 2009) Jolly, Mark R.; Reilly, C.; Green, N. R.
    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.
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    The modelling of oxide film entrainment in casting systems using computational modelling
    (Elsevier, 2013-04-10) Reilly, C.; Green, N. R.; Jolly, Mark R.; Gebelin, J. C.
    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.
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    Oxide entrainment structures in horizontal running systems
    (Minerals, Metals & Materials Society, 2009) Jolly, Mark R.; Reilly, C.; Green, N. R.
    During the transient phase of filling a casting running system surface turbulence can cause the entrainment of oxide films into the bulk liquid. Research has shown that these are detrimental to the material’s integrity. Common mechanisms for this entrainment include returning waves, arising during filling of the runner bar, and plunging jets, found when pouring into a basin. One of these, the returning wave, has been studied in greater depth, using real-time X-ray and process modelling techniques alongside the application of physical principals. It has been concluded that when developed, returning waves cannot attain the more stable and less entraining tranquil flow regime desirable in the running system of castings.
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    The Present State of Modeling Entrainment Defects in the Shape Casting Process
    (Elsevier Science B.V., Amsterdam., 2013-02-28T00:00:00Z) Reilly, C.; Green, N. R.; Jolly, Mark R.
    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.
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    Surface oxide film entrainment mechanisms in shape casting running systems
    (Springer Verlag, 2009-12-31T00:00:00Z) Reilly, C.; Green, N. R.; Jolly, Mark R.
    During the transient phase of filling a casting running system, surface turbulence can cause the entrainment of oxide films into the bulk liquid. Research has shown that these are detrimental to the material’s integrity. Common mechanisms for this entrainment include returning waves, arising during filling of the runner bar, and plunging jets, found when pouring into a basin. One of these, the returning wave, has been studied in greater depth, using real- time X-ray and process modeling techniques alongside the application of physical principals. It has been concluded that when developed, returning waves cannot attain the more stable and less entraining tranquil flow regime desirable in the running system of casting
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    Using the calculated Froude number for quality assessment of casting filling methods
    (Minerals, Metals & Materials Society, 2009) Jolly, Mark R.; Reilly, C.; Green, N. R.; Gebelin, J. C.
    The reliability of cast components is dependent on the quality of the casting process. This can be characterised by the robustness (repeatability) and specific fluid flow characteristics within the running system. During this transient filling phase the prevention of free surface turbulence and thus oxide entrainment is critical to ensure the mechanical integrity of the component. Past research has highlighted that return waves are major causes of free surface entrainment. To reduce the entrainment occurring during the transitional filling of the runner a steady quiescent flow must be developed. Using FLOW-3D the Froude number has been extracted from simulated casting filling to allow the quantitative prediction of air entrainment for a number of different flow conditions. Different running system geometries have been simulated and the overall quality of the running system performance assessed using the Froude number entrainment criterion. The results have been compared to real-time X-ray imaging of transient aluminum alloy flow in running systems. The results show that, for the designs used, the correctly designed geometry is advantageous. An incorrect design may reduce the Froude number but can greatly increase the persistence of the return wave and entrainment and is therefore extremely detrimental to the cast component. The addition of a filter created a deeper quiescent incoming flow and greatly reduced the persistence giving a low total entrainment value. Additionally, the in-gate design is of utmost importance in controlling the back pressure and thus the persistence of the back wave between the in-gate and the downsprue exit. This has a direct effect on the level of oxide entrainment. The quantitative Froude number data obtained from the FLOW-3D model were seen to correlate well with the qualitative real time X-ray data, where as the lowest frequency of bubble occurrence and smallest size was observed in systems containing a filter.