Modeling of continuous strip production by rheocasting
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FROMthe viewpoints of energy, labor and ease of manufacturing, continuous and direct production of metal sheet and rod from the molten state is an attractive and pivotal technology, t Aluminum, copper, and zinc are currently cast into sheet by processes such as the Hazlett twin belt caster, 2 Hunter process, 3 or rod, such as in the Properzi process 4 and the SCR system? In the case of steel production, steel rods of small diameter are produced directly in several proprietary processes and caster and casting roll designs exist in the patent literature for direct rolling of steel s h e e t y but actual production of sheet steel in this way has not yet become a commercial reality. Steel strip casting is considerably more difficult than aluminum, copper, or zinc because of 1) the much higher temperature of molten steel, 2) greater cracking tendency of steel, and 3) a greater surface problem due to inclusions, and so forth. Since Rheocasting was first discovered, s die casting of semisolid aluminum alloys, 9 copper alloys ~~ and ferrous alloys ~z,'3has been extensively studied with fractions solid between 0.40 and 0.60. These studies were mainly concerned with "Thixocasting", i.e., reheating a solidified Rheocast slurry up to the semisolid temperature region and then die casting it. In these studies, advantages were demonstrated of the use of Rheocast semisolid over liquid with respect to die life, casting soundness and surface quality. The current work was undertaken to extend these studies to strip casting. The ultimate aim of the work is to develop a method to utilize the fluid-like behavior of Rheocast semisolid metal to produce homogeneous and sound sheet of commercially useful materials, (e.g., steel). As a first T. MATSUMIYA, formerlywith Massachusetts Institute of Technology, Cambridge, MA, is now with the Fundamental Research Laboratories,Nippon Steel Corporation,Kawasaki, Japan. M. C. FLEM1NGS is Ford Professorof Engineering,Department of Materials Scienceand Engineering,Massachusetts Institute of Technology,Cambridge, MA. Manuscript submitted December3, 1979. METALLURGICALTRANSACTIONSB
step, work reported herein comprises: 1) design and construction of a model process employing Sn-15 pct Pb, 2) experimental demonstration of feasibility of strip production using Rheocast semisolid alloy, 3) establishment of mathematical models of heat flow, solidification and deformation in the strip production, and 4) comparison of results of the experimental and mathematical modeling studies.
EXPERIMENTAL APPARATUS AND PROCEDURE Sn-15 pct Pb alloy was used as the modeling alloy, since its rheology has been studied extensively. '4,15The alloy was prepared from commercially pure tin and pure lead, with a total impurity content under about 0.05 pct. The semisolid alloy was produced from the molten alloy in a continuous Rheocaster, which is shown in Fig. 1. The Rheocaster mainly consists of a reservoir, a mixing chamber, and a rotor, which are all made of stainless steel. The mixing chamber is a cylinder with 33.5 mm inner di
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