additional benefit from this work would be the provision of interfacial heat transfer data for modeling of subsequent microgravity and space-based solidification processing ac- tivities.
Over the past two decades, many researchers have studied the interfacial heat transfer at the casting/mold interface and the mechanism of the heat transfer at a casting/mold inter- face.6-15
Experimental results would be better supported if an
analogue experiment could be devised to verify the method of collection of thermal data and the inverse modeling used to extract boundary conditions that rise to peak values and then decline, which is typical of results published in the lit- erature.5
It is quite possible that
peak may be an artifact of the experimental approach or the inverse technique adopted by many of the researchers.
This work is aimed at measur- ing the interfacial heat flux transients between a liquid metal and a solid metal chill under normal gravity condi- tions so that inaccuracies due to fluid flow can be avoided. An attempt has also been made to verify whether the peak in the heat flux transients during so- lidification experiments is an artifact of the experiment. The role of natural convection on the casting surface macro-pro- file is investigated.
experiment
Al-12% Si alloy (A413) was used for casting experiments involving downward solidifica- tion. Aluminum and graphite were used as chill materials. The chills were cylindrical in shape with a length of 100mm (10cm, 3.93 inches) and a di- ameter of 25mm (2.5cm, 0.98 inch). Chills were instrumented with K-type thermocouples. Three holes of diameter 1mm (0.1cm, 0.039 inch) were drilled on the interface of the chills at distances of 2mm (0.2cm, 0.079 inch), 14mm (1.4cm, 0.55 inch) and 26mm (2.6cm, 1.023 inch) from the interface to accom- modate thermocouples during solidification experiments.
64
About 500g of the alloy ingot is taken in a preheated fire- clay crucible and melted in an electric resistance furnace. The crucible containing the molten alloy at about 750C (1382F) was quickly transferred to the insulated base of the solidification experimental set-up and a twin-bore ce- ramic beaded K-type thermocouple was inserted into the melt. Temperature data from both casting and chill were recorded at 0.1 second interval using a computerized data acquisition system (NI PCI-6251). A schematic sketch of the experimental set-up is shown in Figure 1.
Heat flux transients are measured from temperature history and thermophysical properties of chill material by using the
Figure 1. Schematic sketch of the experimental set-up.
Figure 2. Thermal history inside the casting and the graphite chill.
Table 1. Thermophysical Properties of Chill Materials
International Journal of Metalcasting/Fall 2011
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