Estimation of multiple heat-flux components at the metal/mold interface in bar and plate aluminum alloy castings
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4/27/04
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Estimation of Multiple Heat-Flux Components at the Metal/Mold Interface in Bar and Plate Aluminum Alloy Castings T.S. PRASANNA KUMAR and H.C. KAMATH In the present investigation, a serial solution of the inverse heat-conduction problem (IHCP) is extended for Al-3 pct Cu-4.5 pct Si alloy square bars and rectangular plates cast in metal molds. The metal/mold interface was divided into three segments, viz., the half face, the quarter face, and the corner. The heatflux transients during casting solidification were then estimated at these segments. Three configurations were considered, viz., (1) one boundary segment for the whole length on the interface, (2) two boundary segments delineating two heat-flux components, and (3) three boundary segments leading to three heat-flux components. In order to identify the most acceptable spatial distribution of interface heat flux, two types of analyses were performed on the results of the IHCP, viz., convergence of absolute error in the computed and the measured temperatures at the sensor locations and total heat energy transferred across the boundary from the casting to the mold. The error convergence at the thermocouple locations was more or less identical for all the three cases in both bars and plates. However, the total heat absorbed by the mold, in the case of the one-segment model in bars and the three-segment model in plates, was found to be a minimum. This indicated that the interface heat flux did not show any spatial distribution in the case of bars, while a distinct spatial distribution could be identified in the case of plates. The individual heat fluxes at the different interface segments for the plate casting showed a peak within 3 to 3.5 seconds of pouring, after which it reduced and reached stable values in about 200 seconds. The maximum heat flux occurred at the corner segment. The analysis of heat-flux gradients showed that the air gap initiated at the corner and spread toward the center.
I.
INTRODUCTION
MODELING of solidification simulation of a casting process close to reality depends on the accuracy of heattransfer modeling. One of the difficult tasks in solidification simulation is finding the heat transfer at the casting/ mold interface, influenced by the formation of the air gap. The air gap varies both spatially and with time. It has an important effect on redistribution of heat within the castings. The thermal resistance offered by the air gap is difficult or even impossible to measure. In such cases, a mathematical model of the interface heat transfer will have to be developed for use as a boundary condition for the casting. Mathematical modeling of interface heat transfer during casting is a well-researched subject.[1–20] Essentially, their studies involved unidirectional solidification of cylindrical castings cast in various mold materials as well as chills, under various processing conditions and alloys. The methods adopted by the various researchers for the assessment of interface heat transfer were mostly based on the
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