Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
Search Results
Item Heat transfer at the casting/chill interface during solidification of Al-11 % Si eutectic alloy (LM 6) was investigated. Experiments were carried out for various combinations of chill thickness, casting height and chill material. The thermal history at nodal locations in the chill was used to estimate the interfacial heat flux by inverse modelling. A new parameter called the heat flux penetration time was proposed to model the transformation of the interfacial condition from a perfect contact to a nonconforming contact. The heat transfer coefficient was modelled as a function of the chill thickness, casting height and the thermal diffusivity of the chill material. Real time x-ray imaging technique was adopted to observe the casting/chill interface during solidification of the alloy. The video pictures indicate that a gas gap forms in the case of thin chills. The formation of the gap in thick chills could not be detected. The widths of the gap formed at the interface were measured by an image analyser which revealed that the width of the gap not only varies with time but also with position along the chill surface.(Maney Publishing michael.wagreich@univie.ac.at, Investigation of casting/chill interfacial heat transfer during solidification of Al-11% Si alloy by inverse modelling and real-time x-ray imaging) Prabhu, K.; Campbell, J.1999Item Item Heat transfer at the metal/chill interface during solidification of commercially pure aluminium square bar castings with cast iron chill at one end was investigated. Experiments were carried out for different chill thicknesses and superheats. The inner surface temperature of the chill initially was found to increase at a faster rate for higher superheats. The effect of chill thickness on the inner surface temperature of the chill was observed only after the heat from the solidifying casting had sufficient time to diffuse to the interior of the chill material. Inverse analysis of the non-linear one-dimensional Fourier heat conduction equation indicated the occurrence of peak heat flux at the end of filling of the mould. The effect of superheat on heat flux was minimal after filling. However, the effect of chill thickness had a significant effect on the heat flux after the occurrence of peak heat flux. Higher heat flux transients were estimated for castings poured at higher superheats. The corresponding heat transfer coefficients were also estimated and reported. The heat flux model presented in this work can be used for determination of casting/chill interfacial heat flux as a function of chill thickness and superheat. These heat flux transients could be used as boundary conditions during numerical simulation of solidification of the casting. © 2002 Elsevier Science B.V. All rights reserved.(Effect of chill thickness and superheat on casting/chill interfacial heat transfer during solidification of commercially pure aluminium) Gafur, M.A.; Haque, M.N.; Prabhu, K.2003Item For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al-13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing. © 2003 Elsevier B.V. All rights reserved.(Elsevier BV, Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al-13% Si alloy) Prabhu, K.; Ravishankar, B.N.2003Item The microstructure of a solidifying lead free Sn-3.5Ag solder alloy is found to be highly sensitive to the surface condition of the copper substrate. A transition from lamellar to fine fibrous eutectic structure is observed as the surface condition of the substrate is altered by increasing the surface roughness and application of flux. This is attributed to lowering of interfacial tension and improved wetting of the solidifying solder on the substrate material leading to a better contact at the metal/substrate interface. The results also indicated the importance of surface texture of the substrate and the application of the flux to the quality of the solder/substrate joint. © 2003 Elsevier Ltd. All rights reserved.(Elsevier Ltd, Effect of substrate surface texture and flux coating on the evolution of microstructure during solidification of lead free Sn-3.5Ag solder alloy) Prabhu, K.; Bali, R.; Ranjan, R.2004Item Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell, which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall thickness and increase in the casting thickness. © ASM International.(Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds) Prabhu, K.; Chowdary, B.; Venkataraman, N.2005