Casting (1998) Part 14 pps

Fig. 11 Calculated and theoretical enthalpy versus temperature curves for cast iron of eutectic composition. Source: Ref 18 Fig. 12 Calculated and experimental cooling curves for eutectic gray iron poured in a 50 mm (2 in.) diam bar molded in resin bonded sand. Thermocouples were inserted in the middle of the casting. Source: Ref 34 Figure 13 gives theoretical predictions of the width of the mushy zone for the cast iron sample shown in Fig. 12. The data are in good agreement with the experimental values for the beginning and end of solidification for the thermocouple in the center of the sample. Fig. 13 Calculated beginning and end of solidification wave fronts for a 50 mm (2 in.) diam bar, and experimental points for a thermocouple placed at the center of the bar. Source: Ref 34 A macro-micro modeling approach can have many structure-related applications. For example, macro-micro modeling has been used to attempt to predict the gray/white structural transition in cast irons (Ref 35, 36). As previously discussed, applications of this method can also be extended to the primary phase. Typical calculated and experimental cooling curves for a hypoeutectic Al-8.5Si alloy are given in Fig. 14. Fig. 14 Experimental and simulated cooling curves and calculated fraction of solid for an Al-8.5Si alloy. Source: Ref 37 The microenthalpy scheme (Fig. 10b) has been incorporated into the 3-MOS program, an FEM code developed in Switzerland from the library Modulef (Ref 19, 38, 39). It is essentially based on an enthalpy method. Because the variation of enthalpy is independent of the solidification path once the heat flow is known, the macro- and microscopic calculations can be somehow decoupled. At the macro level, one can still solve the heat flow equation, as mentioned in the section "Macroscopic Modeling" in this article. Once the variations of enthalpy ∆{H} at all nodes are known, the solidification path can be computed. As shown in Fig. 10(b), the macroscopic time-step ∆t can be subdivided into many smaller time-steps δt to perform the microscopic calculations, assuming that heat removal is made at a constant rate during ∆t. The micro-macroscopic coupling scheme seems to give good convergence of the calculated values (undercooling or grain size) (Ref 19). The results (discussed below) illustrate the possibilities of integrating microscopic modeling of solidification into macroscopic heat flow calculations by using an enthalpy method. Figure 15 shows the recalescences of two Al-7Si specimens. The dotted curves have been measured at the center of two small volumes containing the alloy. The solid curves shown in Fig. 15 have been computed with the analytical model of solute diffusion and are based on the measured grain sizes. Fig. 15 Measured (dashed lines) and calculated (solid lines) recalescences for two Al- 7Si alloys. With 50 ppm Ti inoculant (curve A), the final grain radius was 0.5 mm (0.02 in.). Without inoculant (curve B), the final grain radius was 2 mm (0.08 in.). Source: Ref 32 The six cooling curves shown in Fig. 16 have been measured for a one-dimensional gray cast iron (3% C, 2.5% Si) casting poured in a ceramic mold over a copper chill plate (Ref 39). The effect of silicon on the mechanism of eutectic growth was taken into account by modifying the equilibrium eutectic temperature according to a Scheil model of silicon segregation. Although the agreement between modeling and experiment is poor in the liquid region (above 1160 °C, or 2120 °F), solidification is very well predicted with the macro-micro model. In particular, calculated recalescence undercooling and end of solidification are in good agreement with the experimental curves. However, the solidification of the primary phase close to 1190 °C (2175 °F) was not included in the modeling. Fig. 16 Measured (dashed lines) and calculated (solid lines) cooling curves for cast iron. Numbers on curves indicate locations of thermocouples in the casting. Height of castings: 120 mm (4.7 in.) ; number of meshes: 120. The parameters of nucleation deduced from separate microcasting experiments are the following: Gaussian distribution: center at 20 K undercooling, standard deviation: 4.75 K, and total density of sites: 1.2 × 10 11 /m 3 . Source: Ref 39 One of the primary applications of the macro-microscopic modeling of solidification is the prediction of microstructural features. Figure 17 compares the grain radii measured and calculated at the six locations of the thermocouples where the cooling curves shown in Fig. 16 are recorded. These radii are plotted as a function of the distance from the copper chill plate. The distribution of nucleation sites was a Gaussian line shape whose parameters were deduced from microcastings of the same alloy. Although the discrepancy between experiment and modeling may be substantial (especially for thermocouple No. 5), the trend of increasing the grain size with increasing distances from the chill (or decreasing cooling rates) is correctly predicted. Figure 18 shows a map of grain sizes, calculated with the same micro-macroscopic approach for a two-dimensional Al-7Si casting (Ref 19). As can be seen, the trend of larger grain size at the center of the casting is correctly predicted from the model. Fig. 17 Experimental and calculated grain radii at the locations of the thermocouples that recorded the cast iron cooling curves shown in Fig. 16. Source: Ref 39 Fig. 18 Map of calculated maximum undercooling ∆T max within a longitudinal section of an axisymmetric casting. Because undercooling can be directly related to the average grain size using the nucleation law, this figure also maps the average grain radius R within the casting. References cited in this section 18. C.S. Kanetkar, I.G. Chen, D.M. Stefanescu, and N. El-Kaddah, A Latent Heat Method for Macro- Micro Modeling of Eutectic Solidification, submitted to Trans. Iron Steel Inst. Jpn., 1987 19. Ph. Thévoz, J.L. Desbiolles, and M. Rappaz, Modeling of Equiaxed Microstructure Formation in Casting, submitted to Metall. Trans., 1988 20. M. Rappaz and D.M. Stefanescu, Modeling of Equiaxed Primary and Eutectic Solidification, in Solidification Processing of Eutectic Alloys, The Metallurgical Society, 1988 27. M. Rappaz, Ph. Thévoz, Zou Jie, J.P. Gabathuler, and H. Lindscheid, Micro- Macroscopic Modeling of Equiaxed Solidification, in State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 277-284 28. D. Turnbull, Kinetics of Heterogeneous Nucleation, J. Chem. Phys., Vol 18, 1950, p 198 29. D.M. Stefanescu and C. Kanetkar, Computer Modeling of the Solidification of Eutectic Alloys: Comparison of Various Models for Eutectic Growth of Cast Iron, in St ate of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 255-266 30. K.A. Jackson and J.D. Hunt, Lamellar and Rod Eutectic Growth, Trans. Metall. Soc. AIME, Vol 236, 1966, p 1129- 1142 31. H. Esaka and W. Kurz, Columnar Dendrite Growth: A Comparison of Theory, J. Cryst. Growth, Vol 69, 1984, p 362 32. M. Rappaz and Ph. Thévoz, Analytical Model of Equiaxed Dendritic Solidification, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 33. W.A. Johnson and R.F. Mehl, "Reaction Kinetics in Processes of Nucleation and Growth," AIME Technical Publication 1089, American Institute of Mining, Metallurgical, and Petroleum Engineers, 1939, p 5 34. C.S. Kanetkar, D.M. Stefanescu, N. El-Kaddah, and I.G. Chen, Macro- Microscopic Simulation of Equiaxed Solidification of Eutectic and Off-Eutectic Alloys, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 35. D.M. Stefanescu and C.S. Kanetkar, "Modeling of Microstructural Evolution of Cast Iron and Aluminum- Silicon Alloys," Paper 19, presented at the 54th International Foundry Congress, New Delhi, India, 1987 36. D.M. Stefanescu and C.S. Kanetkar, Modeling of Microstructural Evolution of Eutectic Cast Iron and of the Gray/White Transition, Paper 68, Trans. AFS, Vol 95, 1987 37. C.S. Kanetkar, Ph.D. dissertation, The University of Alabama, 1988 38. J.L. Desbiolles, M. Rappaz, J.J. Droux, and J. Rappaz, Simulation of Solidification of Alloys Using the FEM Code Modulef, in State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 49-55 39. Ph. Thévoz, Zou Jie, and M. Rappaz, Modeling of Equiaxed Dendritic and Eutectic Solidification in Castings, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 References 1. J.G. Henzel, Jr. and J. Keverian, Comparison of Calculated and Measured Solidification Patterns for a Variety of Steel Castings, Trans. AFS, Vol 73, 1965, p 661-672 2. R.D. Pehlke, R.E. Marrone, and J.O. Wilkes, Computer Simulation of Solidification, American Foundrymen's Society, 1976 3. H.D. Brody and D. Apelian, Ed., Modeling of Casting and Welding Processes, The Metallurgical Society, 1981 4. J.A. Dantzig and J.T. Berry, Ed., Modeling of Casting and Welding Processes, Vol II, The Metallurgical Society, 1984 5. H. Fredriksson, Ed., State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986 6. W. Oldfield, A Quantitative Approach to Casting Solidification: Freezing of Cast Iron, Trans. ASM, Vol 59, 1966, p 945-959 7. D.M. Stefanescu and S. Trufinescu, Zur Kristallisationskinetik von Grauguss, Z. Metallkd., Vol 65 (No. 9), 1974, p 610-666 8. O. Yanagisawa and M. Maruyama, "Silicon Inoculation Mechanism in Cast Iron," Paper 21, presented at the 46th International Foundry Congress, 1979 9. H. Fredriksson and I.L. Svensson, Computer Simulation of the Structure Formed During Solidification of Cast Iron, in The Physical Metallurgy of Cast Iron, H. Fredriksson and M. Hillert, Ed., North Holland, 1984, p 273-284 10. D.M. Stefanescu and C. Kanetkar, Computer Modeling of the Solidification of Eutectic Alloys: The Case of Cast Iron, in Computer Simulation of Microstructural Evolution, D.J. Srolovitz, Ed., The Metallurgical Society, 1985, p 171-188 11. K.C. Su, I. Ohnaka, I. Yaunauchi, and T. Fukusako, Computer Simulation of Solidification of Nodular Cast Iron, in The Physical Metallurgy of Cast Iron, H. Fredriksson and M. Hillert, Ed., North Holland, 1984, p 181-189 12. I. Dustin and W. Kurz, Modeling of Cooling Curves and Microstructures During Equiaxed Dendritic Solidification, Z. Metallkunde., Vol 77, 1986, p 265 13. S.C. Flood and J.D. Hunt, Columnar and Equiaxed Growth I and II, J. Cryst. Growth, Vol 82, 1987, p 543, 552 14. M. Rappaz and P. Thévoz, Solute Diffusion Model for Equiaxed Dendritic Growth, Acta Metall., Vol 353, 1987, p 1487 15. J.D. Hunt, Steady State Columnar and Equiaxed Growth of Dendrites and Eutectic, Mater. Sci. Eng., Vol 65 ( No. 1), 1984, p 75 16. W. Kurz and D.J. Fisher, Fundamentals of Solidification, Trans Tech, 1986 17. M.C. Flemings, Solidification Processing, McGraw-Hill, 1974 18. C.S. Kanetkar, I.G. Chen, D.M. Stefanescu, and N. El-Kaddah, A Latent Heat Method for Macro- Micro Modeling of Eutectic Solidification, submitted to Trans. Iron Steel Inst. Jpn., 1987 19. Ph. Thévoz, J.L. Desbiolles, and M. Rappaz, Modeling of Equiaxed Microstructure Formation in Casting, submitted to Metall. Trans., 1988 20. M. Rappaz and D.M. Stefanescu, Modeling of Equiaxed Primary and Eutectic Solidification, in Solidification Processing of Eutectic Alloys, The Metallurgical Society, 1988 21. M. Rappaz and E. Blank, Simulation of Oriented Dendritic Microstructures Using the Concept of Dendritic Lattice, J. Cryst. Growth, Vol 74, 1986, p 67 22. M. Rappaz, S.A. David, L.A. Boatner, and J.M. Vitek, Development of Microstructures in Fe-15Ni-15Cr Single- Crystal E-Beam Welds, Metall. Trans., to be published 23. T.W. Clyne, The Use of Heat Flow Modeling to Explore Solidification Phenomena, Metall. Trans. B, Vol 13B, 1982, p 471 24. T.W. Clyne, Numerical Treatment of Rapid Solidification, Metall. Trans. B, Vol 15B, 1984, p 369 25. B. Giovanola and W. Kurz, Modeling Dendritic Growth Under Rapid Solidification Conditions, in State of the Art of Computer Simulation of Solidification, H. Fredriksson, Ed., Proceedings of the E- MRS Conference, Strasbourg, Les Editions de Physique, 1986, p 129-135 26. M. Rappaz, B. Carrupt, M. Zimmermann, and W. Kurz , Numerical Simulation of Eutectic Solidification in the Laser Treatment of Materials, Helvet. Phys. Acta, Vol 60, 1987, p 924 27. M. Rappaz, Ph. Thévoz, Zou Jie, J.P. Gabathuler, and H. Lindscheid, Micro- Macroscopic Modeling of Equiaxed Solidification, in State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 277-284 28. D. Turnbull, Kinetics of Heterogeneous Nucleation, J. Chem. Phys., Vol 18, 1950, p 198 29. D.M. Stefanescu and C. Kanetkar, C omputer Modeling of the Solidification of Eutectic Alloys: Comparison of Various Models for Eutectic Growth of Cast Iron, in State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 255-266 30. K.A. Jackson and J.D. Hunt, Lamellar and Rod Eutectic Growth, Trans. Metall. Soc. AIME, Vol 236, 1966, p 1129- 1142 31. H. Esaka and W. Kurz, Columnar Dendrite Growth: A Comparison of Theory, J. Cryst. Growth, Vol 69, 1984, p 362 32. M. Rappaz and Ph. Thévoz, Analytical Model of Equiaxed Dendritic Solidification, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 33. W.A. Johnson and R.F. Mehl, "Reaction Kinetics in Processes of Nucleation and Growth," AIME Technical Publication 1089, American Institute of Mining, Metallurgical, and Petroleum Engineers, 1939, p 5 34. C.S. Kanetkar, D.M. Stefanescu, N. El-Kaddah, and I.G. Chen, Macro- Microscopic Simulation of Equiaxed Solidification of Eutectic and Off-Eutectic Alloys, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 35. D.M. Stefanescu and C.S. Kanetkar, "Modeling of Microstructural Evolution of Cast Iron and Aluminum- Silicon Alloys," Paper 19, presented at the 54th International Foundry Congress, New Delhi, India, 1987 36. D.M. Stefanescu and C.S. Kanetkar, Modeling of Microstructural Evolution of Eutectic Cast Iron and of the Gray/White Transition, Paper 68, Trans. AFS, Vol 95, 1987 37. C.S. Kanetkar, Ph.D. dissertation, The University of Alabama, 1988 38. J.L. D esbiolles, M. Rappaz, J.J. Droux, and J. Rappaz, Simulation of Solidification of Alloys Using the FEM Code Modulef, in State of the Art of Computer Simulation of Casting and Solidification Processes, Les Editions de Physique, 1986, p 49-55 39. Ph. Thévoz, Zou Jie, and M. Rappaz, Modeling of Equiaxed Dendritic and Eutectic Solidification in Castings, in Solidification Processing, H. Jones, Ed., Institute of Metals, 1987 Glossary of Terms o A • acid • A term applied to slags, refractories, and minerals containing a high percentage of silica. • acidity • The degree to which a material is acid. Furnace refractories are ranked by their acidity. • acid process • A steelmaking method using an acid refractory-lined furnace. Neither sulfur nor phosphorus is removed. • acid refractory • Siliceous ceramic materials of a high melting temperature, such as silica brick, used for metallurgical furnace linings. Compare with basic refractory . • addition agent • (1) Any material added to a charge of molten metal in a bath or ladle to bring the alloy to specifications. (2) Reagent added to plating bath. • additive • Any material added to molding sand for reasons other than bonding, for example, seacoal, pitch, graphite, cereals. • aerate • To fluff up molding sand to reduce its density. • airblasting • See blasting or blast cleaning . • air channel • A groove or hole that carries the vent from a core to the outside of a mold. • air dried • Refers to the air drying of a core or mold without the application of heat. • air-dried strength • Strength (compressive, shear, or tensile) of a refractory (sand) mixture after being air dried at room temperature. • air furnace • Reverberatory-type furnace in which metal is melted by heat from fuel burning at one end of the hearth, passing over the bath toward the stack at the other end. Heat is also reflected from the roof and sidewalls. See also reverberatory furnace . • air hole • A hole in a casting caused by air or gas trapped in the metal during solidification. • air setting • The characteristic of some materials, such as refractory cements, core pastes, binders, and plastics, to take permanent set at normal air temperatures. • allowance • In a foundry, the specified clearance. The difference in limiting sizes, such as minimum clearance or maximum interference between mating parts, as computed arithmetically. See also tolerance. • alpha process • A shell molding and coremaking method in which a thin resinbonded shell is baked with a less expensive, highly permeable material. • alumina • The mineral aluminum oxide (Al 2 O 3 ) with a high melting point (refractory) that is sometimes used as a molding sand. • angularity • The angular relationship of one surface to another. Specifically, the dimensional tolerance associated with such features on a casting. • arbitration bar • A test bar, cast with a heat of material, used to determine chemical composition, hardness, tensile strength, and deflection and strength under transverse loading in order to establish the state of acceptability of the casting. • arbor • A metal shape embedded in and used to support green or dry sand cores in the mold. • arc furnace • A furnace in which metal is melted either directly by an electric arc between an electrode and the work or indirectly by an arc between two electrodes adjacent to the metal. • arc melting • Melting metal in an electric arc furnace. • as-cast condition • Castings as removed from the mold without subsequent heat treatment. • atmospheric riser • A riser that uses atmospheric pressure to aid feeding. Essentially, a blind riser into which a small core or rod protrudes; the function of the core or rod is to provide an open passage so that the molten interior of the riser will not be under a partial vacuum when metal is withdrawn to feed the casting but will always be under atmospheric pressure. • austenite • A solid solution of one or more elements in face-centered cubic iron (gamma iron). Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon. • B • back draft • A reverse taper that prevents removal of a pattern from a mold or a core from a core box. • backing board (backing plate) • A second bottom board on which molds are opened. • backup coat • The ceramic slurry of dip coat that is applied in multiple layers to provide a ceramic shell of the desired thickness and strength for use as a mold. • bake • Heating in an oven to a low controlled temperature to remove gases or to harden a binder. • baked core • A core that has been heated through sufficient time and temperature to produce the desired physical properties attainable from its oxidizing or thermal-setting binders. • bank sand • Sedimentary deposits, usually containing less than 5% clay, occurring in banks or pits, used in coremaking and in synthetic molding sands. See sand. • basic refractory • A lime- or magnesia-base ceramic material of high melting temperature used for furnace linings. Compare with acid refractory . • batch • An amount of core or mold sand or other material prepared at one time. • bath • Molten metal on the hearth of a furnace, in a crucible, or in a ladle. • bead • (1) Half-round cavity in a mold, or half-round projection or molding on a casting. (2) A single deposit of weld metal produced by fusion. • bedding • Sinking a pattern down into the sand to the desired position and ramming the sand around it. • bedding a core • Placing an irregularly shaped core on a bed of sand for drying. • bench molding • Making sand molds by hand tamping loose or production patterns at a bench without the assistance of air or hydraulic action. • bentonite • A colloidal claylike substance derived from the decomposition of volcanic ash composed chiefly of the minerals of the montmorillonite family. It is used for bonding molding sand. • bimetal • A casting made of two different metals, usually produced by centrifugal casting . • binder [...]... the reduction in volume of metal from the solidus to room temperature casting stresses • Stresses set up in a casting because of geometry and casting shrinkage • casting thickness • casting volume • • • • See casting section thickness The total cubic units (mm3 or in.3) of cast metal in the casting casting yield • The weight of a casting( s) divided by the total weight of metal poured into the mold,... promote easy separation of cope and drag parting surfaces when the cope is lifted from the drag parting line • (1) The intersection of the parting plane of a casting mold or the parting plane between forging dies with the mold or die cavity (2) A raised line or projection on the surface of a casting or forging that corresponds to said intersection parting plane • (1) In casting, the dividing plane between... calcining, or drying a substance (1) Removal of sand cores from a casting (2) Jarring of an investment casting mold to remove the casting and investment from the flask (3) A mechanism for freeing formed parts from a die used for stamping, blanking, drawing, forging or heading operations (4) A partially pierced hole in a sheet metal part, where the slug remains in the hole and can be forced out by hand... into a mold to produce an object of desired shape casting defect • Any imperfection in a casting that does not satisfy one or more of the required design or quality specifications This term is often used in a limited sense for those flaws formed by improper casting solidification casting section thickness • The wall thickness of the casting Because the casting may not have a uniform thickness, the section... precision casting • A metal casting of reproducible, accurate dimensions, regardless of how it is made Often used interchangeably with investment casting preformed ceramic core • A preformed refractory aggregate inserted in a wax or plastic pattern to shape the interior of that part of a casting which cannot be shaped by the pattern The wax is sometimes injected around the preformed core pressure casting. .. cannot be shaped by the pattern The wax is sometimes injected around the preformed core pressure casting • (1) Making castings with pressure on the molten or plastic metal, as in injection molding , die casting , centrifugal casting , cold chamber pressure casting, and squeeze casting (2) A casting made with pressure applied to the molten or plastic metal primary alloy • Any alloy whose major constituent... furnace rheocasting • Casting of a continuously stirred semisolid metal slurry rigging • The engineering design, layout, and fabrication of pattern equipment for producing castings; including a study of the casting solidification program, feeding and gating, risering, skimmers, and fitting flasks riser • A reservoir of molten metal connected to a casting to provide additional metal to the casting, required... of sand, silt, and clay, used over brickwork or other structural backup material for making massive castings, usually of iron or steel locating boss • A boss -shaped feature on a casting to help locate the casting in an assembly or to locate the casting during secondary tooling operations lost foam casting (process) • An expendable pattern process in which an expandable polystyrene pattern surrounded... or particle size • • • • • • • • parting • (1) The zone of separation between cope and drag portions of the mold or flask in sand casting (2) In the recovery of precious metals, the separation of silver from gold (3) Cutting simultaneously along two parallel lines or along two lines that balance each other in side thrust (4) A shearing operation used to produce two or more parts from a stamping parting... piece (as on a casting or forging) or a separate piece made for test purposes (such as a test weldment) cover core • (1) A core set in place during the ramming of a mold to cover and complete a cavity partly formed by the withdrawal of a loose part of the pattern Also used to form part or all of the cope surface of the mold cavity (2) A core placed over another core to create a flat parting line critical . room temperature. • casting stresses • Stresses set up in a casting because of geometry and casting shrinkage. • casting thickness • See casting section thickness . • casting volume • The. limited sense for those flaws formed by improper casting solidification. • casting section thickness • The wall thickness of the casting. Because the casting may not have a uniform thickness, the. cavity partly formed by the withdrawal of a loose part of the pattern. Also used to form part or all of the cope surface of the mold cavity. (2) A core placed over another core to create a flat parting