Comparisons of the Effects of Air and Helium on Heat Transfer at the Metal-Mold Interface
- PDF / 1,044,887 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 35 Downloads / 207 Views
CTION
THE importance of HTC at the metal-mold interface in predicting solidification rate and grain structure of the cast metal is well known. The controlling factors of HTC have been outlined in a recent publication.[1] Helium gas is nontoxic and nonflammable and is widely available at relatively low cost.[2] In addition, for a range of temperatures from 25 C to 500 C, helium’s thermal conductivity is at least 5 times higher than that of air.[2,3] As such, it holds great promise of increasing the heat transfer. All these attributes make helium a promising alternative to air at the metal-mold interface. Doutre has reported that the injection of helium at the metal-mold interface can increase the solidification rate in permanent mold castings.[2] In that publication, cooling curves were presented under different experimental conditions, indicating faster cooling rates under helium injection than under air injection. A purely theoretical estimation of the helium effect on HTC was given by Wan et al. using elementary heat-transfer calculations.[3] This article has two aims. First, experimental work will be reported, where the casting solidified under helium injection at the metal-mold interface was compared against casting solidified using air at the metal-mold STAVROS A. ARGYROPOULOS, Professor, is with the Department of Materials Science and Engineering, University of Toronto. Contact email: [email protected] HORAZIO CARLETTI, formerly Graduate Student, Department of Materials Science and Engineering, University of Toronto, Toronto, ON, Canada M5S 3E4, is Metallurgical Engineer, Arise Technologies Corporation, Waterloo, ON, Canada N2V 1Y8. Manuscript submitted September 4, 2007. Article published online June 6, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
interface. Heat-transfer coefficients, as well as the onset of the metal-mold gap formation, were compared under these two types of solidification. An inverse heat conduction procedure (IHCP) was applied to deduce the heat-transfer coefficient. Second, the size of the gap at the metal-mold interface was measured. Equations correlating the HTC and gap size at the metal-mold interface were also deduced.
II.
EXPERIMENTAL
The casting apparatus is shown schematically in Figure 1. The apparatus is composed of an outer-facing steel shell, which contained a cylindrical refractory tube. This tube was connected to a pouring cup, as can be seen on the left-hand side of Figure 1, into which the liquid metal was poured. On the right-hand side of the ceramic tube, the metal mold was connected to the steel shell and ceramic tube. This forms a seal that prevents metal from leaking into the mold section. Figure 1 also shows the location of the linear variable differential transformer (LVDT) and thermocouples (TC). In order to record the temperature history inside the metal mold, two thermocouples were strategically placed at locations (TC1 and TC2 in Figure 1). Thermocouples TC1 and TC2 were spring loaded so that any movement of the mold would maintain the tip of the sen
Data Loading...
