Дисертації з теми "Remelting process"

The electroslag remelting process combines both a chemical refining ability and a better control on solidification which produces materials of more uniform properties. In spite of the advantages of this process, segregation-prone alloys are still difficult to produce via ESR, particularly when large ingot diameters are involved. In this context the study of externally applied electromagnetic fields is of great interest. An AC operated stirring device was designed and laboratory-scale experiments were conducted. The solidification structures resulting from the stirring as well as the mixing conditions prevailing in the liquid pool were investigated. Also, modelling studies on the electromagnetic body force produced by the stirrer and the resulting thermal field were conducted. The start of stirring results in a clearly defined band in both steady- and unsteady-state regimes. The microstructure was not significantly modified in the center of the ingot but a loss in directionality was found at the mould wall. It seems apparent that the stirred liquid does not penetrate significantly inside the interdendritic region. Mixing studies revealed that the degree of mixing in the pool is enhanced by the stirring. The theoretical calculations show that most of the electromagnetic body force is confined to the magnetic skin depth at the mould wall and the metal-slag interface. Using a previously developed two-dimensional heat transfer model it was not possible to reproduce the experimental pool profiles obtained when stirring was applied.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Le procédé Plasma Arc Melting Cold Hearth Refining (PAMCHR) permet de recycler des chutes de titane afin d’élaborer des alliages de titane de qualité aéronautique. Les travaux de thèse présentés dans ce manuscrit se concentrent sur l’étape d’affinage du procédé. Elle correspond, après fusion de la matière et avant coulée en lingotière, au transport du métal liquide dans un creuset à fond plat en cuivre refroidi à l’eau. L’apport de chaleur du procédé se fait par des torches à plasma, dans un environnement de gaz inerte. Une modélisation tridimensionnelle de l’écoulement thermo-hydrodynamique de l’alliage de titane, a été développée avec pour base le logiciel CFD Ansys-Fluent. L’objectif de cet outil, nommé PAM3D, est d’améliorer notre compréhension du comportement du titane liquide au sein du creuset d’affinage. Un grand nombre de fonctions ont été intégrées au modèle pour décrire, entre autres, les transferts thermique et dynamique entre le jet de plasma et la surface du bain liquide. La compréhension de ces transferts est primordiale à la modélisation du procédé : ils ont pu être obtenus à l’aide d’une série d’essais, réalisés sur un four pilote PAMCHR, et de simulations obtenues par le développement de deux modèles numériques simples. Des résultats de simulations obtenues par cette première version de PAM3D sont confrontés à des mesures prises à partir de fusions expérimentales, et la comparaison est jugée satisfaisante. Cependant, la valeur maximale implémentée dans le modèle de la contrainte pariétale, dû à l’impact de la torche à la surface du bain, semble être sous-estimée. Des simulations complémentaires mettent d’ailleurs en avant le rôle important des forces hydrodynamiques sur le comportement thermique du bain, et en particulier de cette contrainte pariétale
The recycling of titanium scraps can be achieved using the Plasma Arc Melting Cold Hearth Refining (PAMCHR) process with the aim of producing aeronautical titanium alloy ingots. In this manuscript, the research work focuses on the refining stage of the process where the liquid is transported in a horizontal copper water-cooled crucible. This important step takes place downstream the melting of the charge and upstream the casting of liquid titanium into the ingot mold crucible. Plasma torches are used as heat source of PAMCHR process, which is conducted under an atmosphere of inert gas. A three-dimensional modeling of the thermo-hydrodynamic flow of the titanium alloy has been set up based on Ansys-Fluent CFD software. The purpose of this tool, named PAM3D, is to improve our understanding of the liquid titanium behavior within the refining crucible. A large number of user functions have been integrated into the model to describe, among other mechanisms, the thermal and momentum transferred from the plasma plume to the surface of the liquid bath. The analysis of these transfers is essential for modeling the process. They are obtained by a study coupling melting tests, carried out in a pilot PAMCHR furnace, and numerical modeling. Numerical results, obtained by this first version of PAM3D are compared to experimental measurements, and the agreement is satisfactory. However, the maximum value of the shear stress, due to the impact of the plasma plume on the bath surface, implemented in the model seems to be underestimated. Moreover, complementary simulations highlight the important role of hydrodynamic forces on the thermal behavior of the bath, and in particular of this shear stress

A soldagem tem grande importância no setor metroferroviário, pois é empregada na fabricação de componentes estruturais e no acabamento de vagões de passageiros, que em sua maior parte são de aço inoxidável. As juntas soldadas podem apresentar descontinuidades que são interrupções que afetam as propriedades mecânicas e metalúrgicas da junta soldada. A presença destas descontinuidades, dependendo do seu tamanho, natureza ou efeito combinado, pode ocasionar a reprovação da junta soldada, quer pela redução de propriedades mecânicas ou pela não aceitação, segundo critérios estabelecidos em normas. Uma estrutura que tenha uma solda reprovada durante sua qualificação ou inspeção, pela presença de descontinuidades pode ser recuperada, por meio de um retrabalho a ser realizado nesta junta. A refusão do cordão de solda por meio do processo TIG (Tungsten Inert Gas), sem a utilização do material de adição, é uma técnica de retrabalho que pode ser empregada, em especial pela viabilidade técnica e econômica do processo. Neste estudo analisou-se a influência que o processo de reparo por soldagem TIG exerceu no comportamento mecânico e microestrutural das juntas soldadas pelo processo MIG, por meio de: ensaios mecânicos (tração, fadiga e microdureza Vickers), ensaios não destrutivos (inspeção visual e líquidos penetrantes) e caracterização microestrutural do cordão de solda. Resultados das amostras de ensaio de tração e fadiga indicaram que o reparo dos cordões de solda não alterou o comportamento mecânico das juntas. As juntas submetidas ao reparo nas quais foram retirados os reforços dos cordões apresentaram modificações nas propriedades mecânicas, mas também apresentaram resultados satisfatórios.
The welding has great importance in manufacture of subway cars because it is used in the manufacture of structural components and finishing in passenger cars which are mostly stainless steel. Joints may show the presence of discontinuities. The discontinuities are interruptions that affect the mechanical and metallurgical properties of the weld. The presence of these discontinuities, depending on their size, nature or the combined effect may lead to failure of the weld either by reduction of mechanical properties or non-acceptance criteria established in standards. A structure that has a weld failed during its qualification or inspection by the presence of discontinuities can be retrieved through a rework to be done in this joint. The remelting of the weld using the TIG process without the use of additional material, rework is a technique that can be employed in particular the technical and economic feasibility of the process. This study analyzes the influence that the process of TIG welding rework has on mechanical behavior and microstructure of welded joints by means of: mechanical tests (tensile and Vickers hardness), non-destructive testing (visual inspection and liquid penetrant) and characterization microstructure of the weld. Results of tensile test specimens and fatigue indicated that the repair of the weld beads did not change the mechanical behavior of joints. The joints subjected to repair in which they were removed the ribs of the beads showed changes in the mechanical properties, but also had satisfactory results.

Thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application and typically consisting of ceramic top coat and CoNiCrAlY bond coat (BC), both thermally sprayed. Nanostructured CoNiCrAlY bond coatings were deposited onto Ni-based alloy (Inconel 718) by both HVOF and CGDS spraying techniques. Subsequently the deposits were remelted by electron beam up to depth of about 100 m which resulted in removal of defects on the substrate to the bond coat interface. The primary objective of this thesis was to investigation of the influence of parameters used for EB remelting, including multiple remelting on the microstructural changes, phase modification and final state of the coatings. The amount of porosity in the coatings and surface roughness has been evaluated. Scanning electron microscopy and X-Ray diffraction were performed in order to characterize the phase modification before and after the applied treatment. The results indicated that multiple remelting process improved the coating properties in terms of porosity, smooth surface, strength and chemical homogeneity and at last but not least this study demonstrate that low-temperature processing of CoNiCrAlY bond coat represents an interesting and promising alternative for their manufacturing.

碩士
國立中央大學
機械工程學系在職專班
107
High pressure die-casting is one of the most widely used and important manufacturing method in modern industry, but the working environment is often dangerous, hard and dirty due to its high temperature and high noise. This is the reason why fewer people are willing to devote themselves to the job, and furthermore, most of researches about high pressure die-casting is academic study. One of the most important problem in the die-casting process is die service life improvement, and the problem affects not only capacity of production but also quality. In this paper, die- casting die service life improvement by laser-remelting process is investigated. In the view of microstructure, the main cause of thermal fatigue crack of die-casting die and inhibiting the propagation of the crack is discussed. Finally, finding the high-risk region where thermal fatigue crack occurs is worked out by the application of CAE(Computer Aided Engineering) technology.

Vacuum Arc Remelting (VAR) is a secondary process used for homogenization of high-melting-point and oxygen-sensitive materials such as superalloys and titanium alloys. The VAR process is carried out with the aim of melting a large consumable electrode in such a way that the resulting ingot has improved homogeneity. The Specialty Metals Processing Consortium (SMPC) has spent the past 20 years developing technology to improve control over the final ingot remelting and solidification processes to alleviate conditions that lead to the formation of inclusions and segregation. Channel segregates are concentration defects arising during the solidification of large-diameter solute-rich alloys. As manufacturers for turbine engines and generators call for larger ingots, it becomes more difficult to produce them without these defects. If, however, liquid pool depth can be controlled precisely to stabilize the solidification zone in the ingot, we could, in principle, produce larger ingots that are defect free. A problem arises because measurements obtained from the VAR furnace do not give enough information to accurately estimate the liquid pool shape in dynamic melting situations. Also, the solidification process in VAR is extremely complex due to the multiple physical domains present and a high-fidelity model is required to give an accurate description of the dynamic process. The Basic Axisymmetric Remelting (BAR) code was initially developed by Lee Bertram at Sandia National Laboratories as a high-fidelity multi-energy model to describe ingot casting in this system. In this work we present a new strategy to improve the accuracy of the estimates used in the control system. This strategy consists of implementing BAR as a new set of measurements to be used by the estimator. This new strategy was used in tests jointly sponsored by SMPC and Los Alamos National Laboratory (LANL) in February 2011 using a laboratory-scale furnace and alloy 718 electrodes.
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碩士
國立高雄應用科技大學
化學工程與材料工程系
98
Fly ashes with high contents of N element (4.9%) collected from the flue gas for the waste aluminum remelting process are usually treated by landfill. In this study, a hydrolysis reaction using a high-temperature oven reactor for the denitrification of fly ashes was proposed. The effects of experimental parameters, including reaction temperature, the addition of water, and reaction time, on the denitrification efficiency and the N contents of fly ashes, were discussed. The content of N element was measured by an N, O-element analyzer. The results showed that at a high reaction temperature, a long reaction time, and the addition of much water condition, a higher denitrification efficiency could be achieved, while mixing strong acid or alkali at the room temperature, it was hard to remove N atoms. At a high temperature of 1400℃, the N contents could be reduced to 0.02%, however, the high-temperature process is difficult to be proceeded. A better operating condition is to remove N atoms of fly ash by wet pretreatment at final reaction temperature of 850℃ keeping 60 mins and passing through air and steam, the contents of N atoms in fly ashes was decreased to 0.11% with a denitrification efficiency of 97.8%. The removal of N atoms can avoid to the formation of odor NH3 when AlN in fly ash reacts with water. Moreover, from the XRD patterns, very weak intensity of AlN crystal phase with strong Al2O3 peaks were identified.

Vacuum arc remelting is a secondary melting process used to produce a variety of segregation sensitive and reactive metal alloys. The present day VAR practice for superalloys involves, typically, melting electrodes of 17'' into ingots of 20'' in diameter. Even larger diameter forging stock is desirable. However, beyond 20'' ingots of superalloys are increasingly prone to segregation defects if solidification is not adequately controlled. In the past years a new generation of model-based controllers was developed to prevent segregation in VAR by controlling melt rate, or the total amount of power flowing into the liquid pool. These controllers were seen as significant improvements in the industry of remelting processes, but these controllers were still focusing on the melting sub-process and ignoring ingot solidification. Accurate control of the liquid pool profile is expected to result in segregation-free ingots, but unfortunately a controller capable of stabilizing the solidification front in VAR is currently not available. The goal of the proposed research is to develop a cyber-enabled controller for VAR pool depth control that will enhance the capabilities of current technologies. More specifically, the objectives of this research are threefold. Firstly, a control-friendly model is proposed based on a high-fidelity ingot solidification model and is coupled to a thermal model of electrode melting. Secondly, sequential Monte Carlo estimators are proposed to replace the traditional Kalman filter, used in the previous VAR controllers. And finally, a model predictive controller (MPC) is designed based on the proposed reduced-order model. The time-critical characteristics of these methods are studied, and the feasibility of their real-time implementation is reported.
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碩士
國立高雄應用科技大學
化學工程與材料工程系
98
Fly ashes collected from the flue gas for the waste aluminum remelting process adsorbed toxic dioxins (1.675 ng I-TEQ/g) and usually treated by landfill. It will be far-reaching affect to the environment. In this study, a high-temperature oven reactor was used to remove dioxins by thermal desorption principle. The effects of different experimental parameters, including: wet pre-treatment, purge air, purge air/saturated water vapor, desorption temperature, and holding time after reaching the desorption temperature, on the removal efficiency of dioxin were discussed. The results showed that at without wet pre-treatment, without carrier gas (air and steam), and without holding time conditions, a higher removal efficiency of dioxins could be achieved. A better case was at desorption temperature = 400 ℃, the dioxin removal efficiency reached 99.95% (Total I-TEQ) or 99.17% (Total PCDD/Fs), much higher than that at 300 ℃ with a dioxin removal efficiency of 69.49% for Total I-TEQ or 78.81% for Total PCDD/Fs.

碩士
國立高雄應用科技大學
化學工程與材料工程系
98
High concentration of fluorine-containing waste water is usually treated by adding excessive calcium-containing coagulants for removing fluorine ions. On the other hand, a large amount of heavy metals in the fly ashes produced form the waste aluminum remelting process need to be treated by solidification method. Both the two process will spend a lot of money. Hence, in this study, by adding fly ashes to react with fluorine ions for forming metal fluoride for reducing the cost was carried out. The effects of experimental parameters, including the waste water/fly ash weight ratio (LSR) and reaction time, on the removal efficiency of fluoride ions and the final concentration of fluoride ions were discussed. Moreover, the addition of anion polymer coagulants and the retention time for reducing the turbidity were also studied. The results showed that at LSR = 17 and reaction time = 30 mins, the concentration of fluoride ions was decreased from 6800 mg/L to 13 mg/L with a removal efficiency of 99.8%. In addition, after 10 mins when the polymer coagulants (0.1%, 1 ml) were added into the waste water, the turbidity was significant reduced from > 1000 NTU to 47 NTU with a concentration of suspended solid of only 3.2 mg/L. Finally, the contents of metals, such as Ca, Fe, Mn, Na, P, and Zn, in the solids collected by filtration decreased, as well as the concentration of metals in the liquid increased, indicating the metals were released from the fly ashes to the liquid (metal ions or nano metal fluoride).

Melt convection and solid phase movement play an important role in solidification processes, which significantly influence the formation of grain structures and solute segregations. In general, the melt convection and grain movement are a result of buoyancy forces. The densities within melt are different due to the variation of temperature and concentration, leading to thermally and solutally driven melt convection. Similarly, the density differences between the grains and the bulk melt cause the grain movement, leading to solid sedimentation or grain floating, as the case may be. Free, unattached solid grains are produced by partial remelting and fragmentation of dendrites, by mechanical disturbances such as stirring or vibration and by heterogeneous nucleation of grains in solidification of grain-refined alloys. In this way, movement of solid crystals during solidification can be ascertained in the following two cases. In the first case, during columnar solidification of non-grain-refined alloys, solid movement is possible in the form of dendrite fragments detached from the columnar stalks by the process of remelting and fragmentation. Movement of grains during columnar solidification gives rise to altogether different microstructure from columnar to equiaxed. In the second case, during equiaxed solidification of grain-refined alloys, the movement of solid crystals is possible in the form of equiaxed dendrite crystals nucleated due to presence of grain refiners. The rate and manner by which the free solids settle (or float) will influence macrosegregation in metal castings. Control of the solidification process is possible through an understanding of the solid movement and its effect on macrosegregation and microstructure. With this viewpoint, the overall objective of the present thesis is to study, experimentally and numerically, the phenomenon of solid phase movement during solidification. Through this study, deeper insights of the role of solid phase movement in solidification are developed which can be used for possible control of quality in castings. Both columnar and equiaxed solidification are considered. Models for transport phenomena associated with columnar solidification with solid phase movement are rarely found in the literature, because of inherent difficulty associated with consideration of microscopic features such as remelting and fragmentation. To tackle this problem, solidification modules for remelting and fragmentation are developed first, followed by integration of these molecules in a macroscopic solidification model. A Rayleigh number based fragmentation criterion is developed for detachment of dendrite fragments from the developing mushy zone, which determines the conditions favorable for fragmentation of dendrites. The criterion developed is a function of net concentration difference, liquid fraction, permeability, growth rate of mushy layer, and thermophysical properties of the material. The effect of various solidification parameters on fragmentation is highlighted. The integrated continuum model developed is applied to stimulate the solidification of aqua-ammonia system in a side-cooled rectangular cavity. The numerical results are in good qualitative agreement with those of experiments reported in literature. A gentle ramp of the mushy zone due to settling of solid crystals, as also noticed in experimental literature, is observed towards the bottom of the cavity. The influence of various modeling parameters on solid phase movement and resulting macrosegregation is investigated through a parametric study. Movement of grains during columnar solidification gives rise to altogether different microstructure and sometimes may initiate a morphological transition of the microstructure from columnar to equiaxed if the number and size of equiaxed grains ahead of the columnar front become sufficient to arrest the columnar growth. The generalised model developed, considering solid phase movement during columnar solidification is used to predict columnar-to-equiaxed transition (CET) based on a prescribed cooling rate criterion. It is found that presence of convection significantly affects the solidification behaviour. Moreover, the movement of dendrite fragments and their accumulation at the columnar front further trigger the occurrence of CET. Cooling configuration, too significantly affects the nature of CET. In unidirectional solidification cases, the locations of CET are found to be in a plane parallel to the chill face. However, for the case of the non-unidirectional solidification (as in side-cooled cavity), the locations of CET need not be in a plane parallel to the chill face. In contrast to fixed columnar solidification, equiaxed solidification is poorly understood; in particular, the phenomena associated with solid crystal movement. Movement of unattached solid crystals, formed due to heterogeneous nucleation on grain-refiners, is induced by the convective currents as well as by buoyancy effects, causing the solid to sediment or to float, depending on density of solid compared to that of the bulk melt. While moving in the bulk melt these crystals can also remelt or grow. A series of casting experiments with AI-based alloys are performed to investigate the role and influence of movement of solid crystals on macrosegregation and microstructure evolution during equiaxed solidification. Controlled experiments are designed for studying, separately, settling and floatation of equiaxed crystals for different cooling conditions and configurations. Further, these experiments are carried out in convective and non-convective cases to understand the effect of convection on solid phase movement. Temperature measurements are performed at various locations in the mould during the experiments. After the cavity is solidified, microstructural and chemical analyses of the experimental samples are carried out, several notable features are observed in temperature histories, macrosegregation pattern, and microstructures due to settling/flotation phenomenon of solid crystals. It is found that the flow behavior of solid grains has a profound influence on the progress of solidification (in terms of grain size distribution and fraction eutectic) and macrosegregation distribution. In some cases, the induced flow due to solid phase movement can cause a flow reversal. The observations and quantitative data obtained from experiments, with the help of detailed solidification conditions provided, can be used for future validations of models for equiaxed solidification. Subsequently, numerical studies are carried out, using a modified version of the macroscopic model developed for columnar solidification with motion of solid crystals, to predict the transport phenomena during equiaxed solidification. The model is applied to simulate the solidification processes corresponding to each of the experimental cases performed in this study. For a better understanding of the phenomenon of movement of solid crystals, the following two special cases of solidification are also presented: 1) without movement of solid crystals and 2) movement of solid crystals without any relative velocity between solid and liquid phases. The numerical predictions showing nature of flow field and progress of solidification are substantiated by the experimental data for the thermal analysis, qualitative microstructural Images and quantitative microstructural analysis. It is concluded, with the help of various experiments and simulations, that movement of solid crystals influences the casting quality appreciably, in terms of macrosegregation and microstructures. It is expected that the improved understanding of the role and influence of solid phase movement during solidification processes (both columnar and equiaxed) obtained through this thesis will be useful for possible control of quality of as-cast products.

Melt convection and solid phase movement play an important role in solidification processes, which significantly influence the formation of grain structures and solute segregations. In general, the melt convection and grain movement are a result of buoyancy forces. The densities within melt are different due to the variation of temperature and concentration, leading to thermally and solutally driven melt convection. Similarly, the density differences between the grains and the bulk melt cause the grain movement, leading to solid sedimentation or grain floating, as the case may be. Free, unattached solid grains are produced by partial remelting and fragmentation of dendrites, by mechanical disturbances such as stirring or vibration and by heterogeneous nucleation of grains in solidification of grain-refined alloys. In this way, movement of solid crystals during solidification can be ascertained in the following two cases. In the first case, during columnar solidification of non-grain-refined alloys, solid movement is possible in the form of dendrite fragments detached from the columnar stalks by the process of remelting and fragmentation. Movement of grains during columnar solidification gives rise to altogether different microstructure from columnar to equiaxed. In the second case, during equiaxed solidification of grain-refined alloys, the movement of solid crystals is possible in the form of equiaxed dendrite crystals nucleated due to presence of grain refiners. The rate and manner by which the free solids settle (or float) will influence macrosegregation in metal castings. Control of the solidification process is possible through an understanding of the solid movement and its effect on macrosegregation and microstructure. With this viewpoint, the overall objective of the present thesis is to study, experimentally and numerically, the phenomenon of solid phase movement during solidification. Through this study, deeper insights of the role of solid phase movement in solidification are developed which can be used for possible control of quality in castings. Both columnar and equiaxed solidification are considered. Models for transport phenomena associated with columnar solidification with solid phase movement are rarely found in the literature, because of inherent difficulty associated with consideration of microscopic features such as remelting and fragmentation. To tackle this problem, solidification modules for remelting and fragmentation are developed first, followed by integration of these molecules in a macroscopic solidification model. A Rayleigh number based fragmentation criterion is developed for detachment of dendrite fragments from the developing mushy zone, which determines the conditions favorable for fragmentation of dendrites. The criterion developed is a function of net concentration difference, liquid fraction, permeability, growth rate of mushy layer, and thermophysical properties of the material. The effect of various solidification parameters on fragmentation is highlighted. The integrated continuum model developed is applied to stimulate the solidification of aqua-ammonia system in a side-cooled rectangular cavity. The numerical results are in good qualitative agreement with those of experiments reported in literature. A gentle ramp of the mushy zone due to settling of solid crystals, as also noticed in experimental literature, is observed towards the bottom of the cavity. The influence of various modeling parameters on solid phase movement and resulting macrosegregation is investigated through a parametric study. Movement of grains during columnar solidification gives rise to altogether different microstructure and sometimes may initiate a morphological transition of the microstructure from columnar to equiaxed if the number and size of equiaxed grains ahead of the columnar front become sufficient to arrest the columnar growth. The generalised model developed, considering solid phase movement during columnar solidification is used to predict columnar-to-equiaxed transition (CET) based on a prescribed cooling rate criterion. It is found that presence of convection significantly affects the solidification behaviour. Moreover, the movement of dendrite fragments and their accumulation at the columnar front further trigger the occurrence of CET. Cooling configuration, too significantly affects the nature of CET. In unidirectional solidification cases, the locations of CET are found to be in a plane parallel to the chill face. However, for the case of the non-unidirectional solidification (as in side-cooled cavity), the locations of CET need not be in a plane parallel to the chill face. In contrast to fixed columnar solidification, equiaxed solidification is poorly understood; in particular, the phenomena associated with solid crystal movement. Movement of unattached solid crystals, formed due to heterogeneous nucleation on grain-refiners, is induced by the convective currents as well as by buoyancy effects, causing the solid to sediment or to float, depending on density of solid compared to that of the bulk melt. While moving in the bulk melt these crystals can also remelt or grow. A series of casting experiments with AI-based alloys are performed to investigate the role and influence of movement of solid crystals on macrosegregation and microstructure evolution during equiaxed solidification. Controlled experiments are designed for studying, separately, settling and floatation of equiaxed crystals for different cooling conditions and configurations. Further, these experiments are carried out in convective and non-convective cases to understand the effect of convection on solid phase movement. Temperature measurements are performed at various locations in the mould during the experiments. After the cavity is solidified, microstructural and chemical analyses of the experimental samples are carried out, several notable features are observed in temperature histories, macrosegregation pattern, and microstructures due to settling/flotation phenomenon of solid crystals. It is found that the flow behavior of solid grains has a profound influence on the progress of solidification (in terms of grain size distribution and fraction eutectic) and macrosegregation distribution. In some cases, the induced flow due to solid phase movement can cause a flow reversal. The observations and quantitative data obtained from experiments, with the help of detailed solidification conditions provided, can be used for future validations of models for equiaxed solidification. Subsequently, numerical studies are carried out, using a modified version of the macroscopic model developed for columnar solidification with motion of solid crystals, to predict the transport phenomena during equiaxed solidification. The model is applied to simulate the solidification processes corresponding to each of the experimental cases performed in this study. For a better understanding of the phenomenon of movement of solid crystals, the following two special cases of solidification are also presented: 1) without movement of solid crystals and 2) movement of solid crystals without any relative velocity between solid and liquid phases. The numerical predictions showing nature of flow field and progress of solidification are substantiated by the experimental data for the thermal analysis, qualitative microstructural Images and quantitative microstructural analysis. It is concluded, with the help of various experiments and simulations, that movement of solid crystals influences the casting quality appreciably, in terms of macrosegregation and microstructures. It is expected that the improved understanding of the role and influence of solid phase movement during solidification processes (both columnar and equiaxed) obtained through this thesis will be useful for possible control of quality of as-cast products.