Steady flow of liquid aluminum in a rectangular-vertical ingot mold, thermally or electromagnetically activated
- PDF / 639,698 Bytes
- 8 Pages / 603.28 x 783.28 pts Page_size
- 37 Downloads / 167 Views
I.
INTRODUCTION
ELECTROMAGNETIC stirring is currently applied in the metallurgical industry for various purposes. It is mainly used in the steel industry where it often occurs during the treatment of liquid steel in the ladle, before the casting stage. This treatment is used especially in vacuum degassing, for dissolving additives, or for decanting suspended particles. The electromagnetically induced movements result in an acceleration of the exchanges between the liquid and the external medium. ~-5 It is also used in continuous casting of steel. An electromagnetic stirrer operating just under the surface of the liquid metal is a convenient way to separate the suspended oxide particles and thus reduce the quantity of inclusions. If the electromagnetic stirrer is operating at the bottom of the liquid pool, it results in more uniform grain structure of the cast product and reduces segregation effect. 6 Therefore, electromagnetic stirring is shown to be an efficient method for improving the quality of metallurgical products when it is used in a manner appropriate to each individual effect. Forced flow of the liquid during solidification is known to play a major role in the formation of the grain structure of cast products. Although the mechanisms of grain refinement are not thoroughly understood, it is clear that the forced flow can act in several ways: for instance, by eliminating the initial superheat and by providing nuclei for equiaxed grains. Moreover, it is well established that the natural convection can also be very active in large castings 7"s and even in small laboratory ingots 9 and produces the same effects. In contrast, it has been shown that when the natural fluid flow is hindered in an ingot casting, it results in a full columnar grain structure. ~~ Another effect of forced molten metal flow during solidification is a reduction in macrosegregation. To obtain semi-quantitative information in the field of the metallurgical effects of fluid flow, there is an increasing trend to combine theoretical modeling with experimental measurements. Unfortunately, the latter are in most cases incomplete. ~2.J3 Most of the hydrodynamic measurements in liquid metals were made in liquid mercury. In industrial JEAN-LUC MEYER and FRANCIS DURAND, Professor, are with lnstitut National Polytechnique de Grenoble, L.T.P.C.M.-E.N.S.E.E.G., B.P. 75, 38402 Saint Martin D'Heres, France. RENt~ RICOU and CHARLES VIVES are with Facult6 des Sciences, Avignon, France. Manuscript submitted December 6, 1983, METALLURGICALTRANSACTIONS B
metallurgical melts, because of the temperature (about 660 ~ in aluminum melts and 1500 ~ in steels), measurements are rather scarce. ~4Consequently, even crude methods are not to be neglected. For instance, fluid flow at the free surface can be estimated from the movement of floating particles. ~s'~6 Chemical or radioactive tracer methods give some information on the general flow pattern. 7~ The dissolution rate of rods (carbon in steels, iron in aluminum) gives valuable information to the metallurgist,
Data Loading...
