Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1989-03-29
1990-01-30
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
B22D 1106
Patent
active
048967157
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to continuous direct casting of metal strip by a process employing a moving chill surface upon which molten metal is flowed for solidication beginning on the chill surface and progressing in a direction outwardly to the free top surface of the strip formed.
2. Prior Art
The advantages to be achieved in direct casting of molten metal into thin strip or sheet (hereinafter strip) on a continuous basis have long been recognized and numerous processes and apparatus have been proposed for the direct casting of metal strip. It is not believed, however, that any of these prior art processes or devices have been successfully used for use on a commercial basis, particularly for the production of a high quality strip suitable for use in the as-cast condition for the production of commercial products, or for further processing as by rolling or shaping by other means.
In the known prior art continuous or direct strip casting processes employing a continuously driven chill surface which contacts a melt of the metal to be cast, the melt is solidified by extracting heat through the chill surface so that a thin skin of the metal is solidified immediately upon contact with the chill. This skin grows in thickness as the chill moves progressively through or past the melt until the strip is completely formed. The thin skin initially formed is firmly adhered to the chill and this intimate bonded contact results in a maximum heat transfer from the melt to the chill.
As the solidifying skin progressively increases in thickness, the extraction of heat results in contraction of the solidifying strip at its bonded interface with the chill until the bond is broken, thereby resulting in a substantial reduction in the rate of heat extraction. The successful production of quality cast strip by such a process depends to a large degree upon the ability to extract heat at a uniform rate across the width of the strip to produce a uniform release of the cast product from the chill. One process for producing the uniform heat extraction through the chill surface is disclosed and claimed in copending U.S. patent application Ser. No. 885,718, assigned to the assignee of the present application, and involves establishing a natural oxide layer on the chill surface to provide an interface between the layer of molten metal and the chill surface and maintaining the natural oxide interface in a smooth layer of substantially uniform thickness.
In the production of directly cast strip on a chill, surface defects frequently occur in the top surface of the strip, i.e., the surface away from the chill. These defects may include surface cracks as well as variations in gauge or longitudinal shape of the strip and variations in transverse profile, making subsequent rolling or other processing of the cast strip difficult or impossible. Attempts have been made to control profile and gauge variations by contacting the top surface of the strip with a second chill roll prior to solidification of the top surface whereby the top roll cools and solidifies the top surface or skin of the strip and acts as a flow controller to limit the amount of molten metal deposited upon the chill. It is also known to contact the top surface with a pressure roll immediately after solidification of the strip in an attempt to control the strip gauge by a hot rolling action. Such pressure rolls have been internally cooled or otherwise configured to dissipate heat and provide a chilling effect on the strip.
U.S. Pat. No. 2,348,178 to J. M. Merle discloses, at FIGS. 1 and 4, means for flowing molten metal through a nozzle onto a continuous moving belt chill surface and a continuous cylindrical wheel chill surface, respectively. FIGS. 2, 8 and 9 of this patent disclose rolls 28 and 106 contacting the top surface of a stream of molten metal issuing from a nozzle in the bottom of a tundish, with the roll acting as a metering valve to control the size of the nozzle opening and hence the rate of flow of molten metal
Lin Kuang Y.
National Aluminum Corporation
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