Experimental Determination of Heat Transfer Within the Metal/Mold Gap in a DC Casting Mold: Part II. Effect of Casting M
- PDF / 886,668 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 38 Downloads / 159 Views
d wall heat transfer is critical in semi-continuous DC casting of aluminum and other light metals. Figure 1 shows the steady-state phase of DC casting (adapted from Reference 1). The heat from the hot metal is transferred to the water-cooled mold across the metal-mold gap filled with gas (or a combination of different gases). While the mechanism of surface defect formation in DC casting differs in the work reported in the literature,[2–7] the role of mold wall heat transfer in defect formation is universally accepted. The heat extracted by the mold must be optimum and a deviation from this optimum will result in surface defect formation in the casting. Bi and Pe numbers can be used to assess the importance of heat extraction from the casting surface.[8] The much higher thermal conductivity of Al results in lower Bi and Pe numbers.[9] This in turn renders the convective heat transfer from the metal surface to be more critical in DC castings, valid for both ARVIND PRASAD, Research Fellow, is with the CAST CRC, Division of Materials, School of Mechanical & Mining Engineering, University of Queensland, Brisbane, QLD, 4072 Australia. Contact e-mail: [email protected] IAN F. BAINBRIDGE, Senior Research Consultant (Retd.), formerly with the CAST CRC, Division of Materials, School of Mechanical & Mining Engineering, University of Queensland, and is now retired. Manuscript submitted September 9, 2011. Article published online February 13, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
within-mold and sub-mold cooling.[1] A prior publication[1] provides a detailed review of the research done to estimate the metal-mold heat transfer from the casting surface within the mold wall region of a DC casting, with an aspect of this work shown to be lacking in several respects. Table I in Reference 1, duplicated here for convenience, shows the values that are often used in describing the heat transfer coefficient in DC castings. As can be seen from the table, a wide range of values is used and it is clear that there is no agreement between the values to be used. Published work carried out on the continuous casting process used in the steel industry, including modeling of the process, has also identified the influence of mold wall heat flow on the formation of surface defects on the solidifying product.[10–20] This work has therefore been reviewed to assess the applicability of the methods used and the results obtained to the aluminum DC casting process and hence to the present work. The mold wall heat transfer coefficient (HTC) for the steel continuous casting process has been determined by a number of methods including the inverse method.[10,13] A popular version of the inverse method uses thermocouples embedded at known positions within the mold wall in a similar manner to that used for aluminum.[21] Other versions rely on the determination of the longitudinal temperature difference (DT) present in the mold wall from the point of metal entry to the point of water cooling exit from the mold, or a measurement of the increase in DT of the cooli
Data Loading...
