Sponsored by: Jt. EPD/MDMD Synthesis, Control, and Analysis in Materials Processing Committee, EPD Process Fundamentals, Aqueous Processing, Copper, Nickel-Cobalt, Pyrometallurgy, Lead, Zinc, Tin Committees, MSD Thermodynamic & Phase Equilibria Committee
Program Organizers: R. G. Reddy, Department of Chemical and Metallurgical Engineering, University of Nevada, Reno NV 89557; S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; J.C. Malas, Wright-Patterson AFB, OH 45433-6533
Tuesday, PM Room: A16-17
February 6, 1995 Location: Anaheim Convention Center
Session Chairpersons: S. Viswanathan, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6083; J.C. Malas, Wright-Patterson AFB, OH 45433-6533
A 3D NUMERICAL MODEL FOR REMOVAL OF INCLUSIONS TO GAS BUBBLES: B.J. Hoo, S.T. Johansen, SINTEF Materials Technology, N-7034 Trondheim-NTH, Norway, and B. Rasch, Hydro Aluminium, Metallurgical R&D Centre, N-6601 Sunndalsora, Norway
The flow field set up by the standard Hydro gas purging unit has been predicted by a numerical model. In addition, turbulent trajectories of gas bubbles released from the rotor are predicted. The deposition rate of inclusions on the bubble surface is allowed to depend on local conditions. Bubbles passing regions with strong pressure gradients, such as close to the rotor, will experience large slip velocities and large deposition rates. This model can deal with any distribution of bubble sizes and inclusions. The results found from the multidimensional flow predictions are compared to the predictions due to a much simpler metallurgical engineering approach. The differences between these two approaches to predict the same process will be discussed. The model predictions are compared to experimental results for removal of SiC-particles from aluminium.
EQUILIBRIUM PARTITION RATIOS IN MULTICOMPONENT STEELS: M.S. Bhat, D.R. Poirier, P.M.N. Ocansey, Department of Materials Science and Engineering, The University of Arizona, Tucson, AZ 85721
The equilibrium partition ratios of alloy elements in two multicomponent steels were determined. The ratios can be used in models to simulate dendritic solidification. In one system, the equilibrium partition ratios of Mn, Si and C were determined to cover a scope of concentrations pertaining to the solidification path of a high carbon steel (91125). In the second, the equilibrium partition ratios of C and Cr were measured for concentrations relevant to the solidification of a bearing steel (52100). The experimental method employed and the effect of sample preparation on the quantitative analyses are also discussed.
MODELLING OF LEDGES AND SKULLS: Vaughan R. Voller, Department of Civil Engineering, 500 Pilsbury Drive, University of Minnesota, Minneapolis, MN 55455-0220
In many high temperature processes involving liquid melts the common practice is to solidify a fraction of the melt adjacent to the containment walls; a practice that can provide protection of the structural components of the process. The position, shape and transient behavior of these so called "skulls" and/or "ledges" are directly dependent on the thermal process conditions. This paper presents a model of a generic ledge process that can predict both the steady shape of the ledge and its transient behavior driven by time dependent process conditions. Two numerical implementations of the model are presented and compared: (1) based on a space grid of continuously deforming control volume finite elements, and (2) based on a conjugate grid of fixed control volumes and deforming boundary elements.
3:15 pm BREAK
MODELING THE COLUMNAR-EQUIAXED TRANSITION IN CASTINGS: S. Sundarraj, G. Upadhya, U. Chandra, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
The morphological transition between columnar and equiaxed structures is an important solidification phenomenon frequently observed in castings, especially complex parts with varying cross-section. The mechanical properties and the occurrence of defects such as hot tears are strongly dependent on the structure formed in the casting. Hence, it is important to understand the conditions leading to columnar or equiaxed structures. Extensive work has been done in modeling solidification systems. Almost all of these models are based on the assumption that the structure formed in the casting is either purely columnar or purely equiaxed. The prediction of the Columnar-Equiaxed Transition (CET), however, requires a solidification model which accounts for the formation of both columnar and equiaxed structures, along with related microscopic and macroscopic solidification phenomena. Such a model is presented which: (i) takes account of both columnar and equiaxed structures; (ii) accounts for microscopic phenomena, such as solidification kinetics and microsegregation, coupled with macroscopic heat transfer; (iii) satisfies solute conservation; and (iv) is easy to implement in commercial finite element and finite difference software. The proposed model has been validated with available experimental results. A sensitivity analysis has also been carried out to determine the effects of the model parameters on predicting the CET position. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation under contract to the U. S. Navy, as part of the U. S. Navy Manufacturing Science and Technology Program.
A MONTE CARLO SIMULATION OF THE DEVELOPMENT OF MICROSTRUCTURE IN AN ALLOY SOLIDIFYING WHILE FLOWING OVER A CHILL: R.A. Stoehr, Materials Science and Engineering, 848 Benedum Hall, University of Pittsburgh, Pittsburgh, PA 15261
A Monte Carlo simulation of solidification of a metal alloy flowing over a chill has been developed. Velocity, temperature, and solute concentration profiles in the bulk flow regime are calculated on a fairly coarse grid by macroscopic techniques. Bulk flow conditions are presumed to be externally determined (i.e., quasi-forced convection), and a given distribution of nuclei is carried with the entering fluid. In the interface region, Monte Carlo simulation is used to model solidification on a much finer scale. Microscopic longitudinal and transverse velocity fluctuations are addressed by a shuffling routine. Growth, shrinkage, and possible annihilation of solid regions are modeled based on probability factors related to the local supersaturation. Capillarity and crystallographic considerations can be included in the supersaturation. The model has been related to the type and orientation of microstructures observed in aluminum-copper alloys solidified during flow over a water cooled chill.
NEW DIMENSIONLESS HEAT TRANSFER CORRELATIONS FOR LIQUID METALS: Stavros A. Argyropoulos, Department of Metallurgy and Materials Science, University of Toronto, Toronto,Ontario, Canada M5S 1A4; Anthony C. Mikrovas, Cominco Ltd., Trail, British Columbia, P.O. Box 2000, Canada V1R 4S4; Don. A. Doutre, Alcan International Ltd. Kingston Research and Development Centre, PO Box 8400, Kingston, Ontario, Canada K7L 5L9
This paper presents a method for deducing dimensionless heat transfer
correlations in liquid metals for natural and forced convection conditions.
This method was applied to liquid metals with different Prandtl numbers,
namely, aluminum and steel. Solid spheres of aluminum and steel, initially at
room temperature, were immersed into liquids of aluminum and steel,
respectively. In the first set of tests the spheres were immersed under natural
convection conditions, and in the second, under forced convection conditions.
The melting time of the spheres was carefully monitored and it was related to
the average heat flux from the metal bath to the immersed sphere. New
dimensionless heat transfer correlations will be presented for natural and
forced convective heat transfer in liquid metals. The validity of these new
dimensionless heat transfer correlations was examined with a different set of
experiments in an independent setting. This validation work will be shown.
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