An experimental study on process variables in crystal growth by ohno continuous casting
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I.
INTRODUCTION
?~k continuous casting process has recently been developed ~y Ohno [1'2] using a heated, rather than cooled mold. The 3rocess is attractive because it can be used for directional ~olidification or crystal growth, and ingots or crystals of unJmited length can be produced. The usefulness of the process is based on the simple fact ~aat, if a mold is heated slightly above the melting point of :he metal to he solidified, no new grains can nucleate at the mold wall. Thus solidification is restricted to the contact ~rea between the melt and the dummy rod or single crystal seed, which is withdrawn from the melt. The process is _.~3] and b y similar to those previously proposed by StepanuvLaBelle.[41However, the mold is heated in the O.C.C. prozess, and it can be in any of the following three positions: vertically upward, vertically downward, and horizontal. The objective of the present paper is to understand better the new O.C.C. process, by studying its operating variables.
in order to maintain a constant melt level. The volume of the graphite rod fed into the melt per unit time was equal to the volume of the melt solidified per unit time. The aluminum dummy rod and the ingot connected to it were driven vertically upward by a pair of pinch rolls. The dummy rod had the same diameter as the mold cavity and a bell-shaped tip designed to attach firmly the ingot to it. A 76 mm long aluminum cooling jacket was used to provide cooling for the ingot. The cooling jacket was located between the graphite mold and the pinch rolls. Silicon O-rings were used to prevent leaking of water from the cooling jacket.
Pinch rolls II.
EXPERIMENTAL PROCEDURE
Figure 1 is a schematic sketch of the experimental setup for Ohno's continuous casting process. Essentially, it consists of a stainless steel crucible, a graphite mold, a cooling jacket, and a set of pinch rolls. The material was 99.9 pct Sn. The stainless steel crucible, about 110 mm diameter and 130 mm height, was heated by a Nichrome heating element which surrounded it. The graphite mold, about 6.4 mm inside diameter and 38 mm height, was heated by an embedded Nichrome heating element. A chromel-alumel thermocouple located about 1 mm below the top of the mold, and 0.5 mm from its inside surface was used to control the mold exit temperature during casting, i.e., the temperature of the inside surface of the mold at its exit. The mold exit temperature was set above the melting point of Sn to prevent heterogeneous nucleation at the inside surface of the mold. The melt temperature, i.e., the temperature of the bulk molten metal, was controlled with the help of a chromelalumel thermocouple placed in the bulk molten metal. A graphite rod with a diameter of 32 mm and driven by a stepping motor was lowered into the melt during casting Y.J. KIM, Graduate Student, and S. KOU, Professor, are with the Department of Metallurgical and Mineral Engineering, University of Wisconsin, Madison, WI 53706. Manuscript submitted May 12, 1987. METALLURGICALTRANSACTIONSA
dummy rod
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