Electromagnetic refining of aluminum alloys by the CREM process: Part II. Specific practical problems and their solution
- PDF / 1,340,069 Bytes
- 13 Pages / 614.28 x 794.28 pts Page_size
- 34 Downloads / 206 Views
I.
INTRODUCTION
THE
working principle and the main features of the CREM process have been described already, cl,21 In this new technology, the liquid metal is stirred using an inductor supplied with a low frequency current (50 or 60 Hz), and this vigorous forced convection in the melt leads to substantial grain refinement. An experimental study, I~1bearing on ingots of circular cross-sections, has shown that the characteristics of the as-cast products are dependent on two main parameters: the stirring intensity and the dome height, which influence the grain size and the thickness of the segregation zone, respectively. The rotational part of the electromagnetic body force is responsible for the intensity of the circulation of metal, while the dome height is nearly proportional to the magnitude of the potential forces. On account of the obvious symmetry of such a system, it was sufficient to take measurements of the electromagnetic and hydrodynamic parameters over any vertical and radial cross-section of the sump. The results reveal that in this case, the radial components of the electromagnetic forces are mainly irrotational, while the vertical components are primarily rotational. However, the production of ingots of rectangular cross-sections can be more delicate than the production of billets. Indeed, in the sump, the electromagnetic and velocity fields are 3-D and nonuniform, particularly in the corner regions. This situation may give rise to some defects concerning the grain homogeneity, as well as the shape and surface aspects of the slabs. Accordingly, a systematic and comprehensive study of electromagnetic and hydrodynamic phenomena is absolutely necessary to obtain a satisfactory knowledge of this technology. The approach was (1) to measure separately the electromagnetic parameters, namely, the magnetic field and current density components as well as the phase angle between these periodic vectors, and (2) to find the electromagnetic force field from these parts and to determine, most especially, its horizontal and ver-
C H A R L E S VIVI~S, Professor, is with the Laboratoire de Magn6tohydrodynamique, Facult6 des Sciences, 33, rue Louis Pasteur, 84000 Avignon, France. Manuscript submitted March 28, 1988. METALLURGICAL TRANSACTIONS B
tical components. As a first step, these findings were connected with the experimentally determined confining and stirring effects. Then it was possible to use our understanding of the behavior of this process to improve it, by modification of the force field distribution and of the ingot mold shape, for example. A similar procedure has been followed to investigate the role of the electrical conductivity of the ingot mold and the influence of the location of the inductor on the electromagnetic and velocity patterns. Obviously, the 3-D aspects of the problem require a great many measurements. Under these circumstances, a methodical experimentation on actual casters would be very expensive. This is due to both the cost of a casting and to the limited working time of the sensors
Data Loading...
