Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1998-04-14
1999-09-21
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164476, 164480, B22D 1106, B22D 1107, B21B 146
Patent
active
059541172
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing metal sheet by a casting process. More particularly, this invention pertains to a process for producing roll cast aluminum sheet products on a twin roll caster at higher than conventional casting speeds.
DESCRIPTION OF THE ART/TECHNOLOGY REVIEW
Metal sheet, plate and foil products have been made by a variety of processes. One process for producing aluminum and aluminum alloy sheet is the roll casting process. The present invention is particularly directed to the process of roll casting using twin casting rolls. In this preferred process, molten metal, which is typically filtered and may be alloyed and refined, is fed between mating casting rolls. Such rolls may be of various widths and diameters, with 600 to 1,000 mm roll diameters being common, as are strip product widths on the order of 1 to 2 meter. The rolls are cooled, such as by internal liquid cooling, to cause the exterior surface of the roll shell to be maintained at a temperature sufficient to cause progressive solidification of the molten metal as the metal passes through the bite of the rolls, undergoes reduction and forward extrusion due to high applied load, and exits at a gauge of typically 2 to 8 mm. The metal sheet exiting the caster is coiled for subsequent hot rolling, cold rolling, homogenization and annealing.
In roll casting there are a number of factors that affect productivity and product quality. These factors include, but are not limited to, metal preparation, metal transfer, gauge control, solidification behavior such as centerline segregation, constituent distribution, and thermal management, surface uniformity, flatness and appearance and sheet-to-roll adherence (sticking) during casting.
Solidification is, of course, a limiting factor in attaining increased productivity in casting, particularly in roll casting. The casting speed must be controlled at a rate that insures that the outside walls of the sheet are adequately and progressively solidified. Also, casting speed must insure that the entire sheet is solidified prior to hot reduction of the sheet. Solidification must be uniform to insure that internal voids are not present. A surface void condition, called a bleed-out, must be avoided. As casting speed is increased, it has been found that the casting roll surface temperature increases. Likewise, the temperature of the outside surface of the cast product increases. As the temperatures of the aluminum sheet being cast and the outside shell of the steel casting roll rise, the surfaces experience a surface welding which tends to cause sticking of the sheet to the roll. When such sticking occurs, the casting speed must be reduced.
One approach to alleviating the sticking condition is to provide an agent on the roll surface. Such agents include release agents which act to prevent sticking between the sheet and the outside shell of the casting roll. Typical agents that have been used in roll casting are graphite and magnesium oxide.
However, the application of a thermal barrier may impede the cooling efficiency in the casting process since the thermal barrier serves as an insulative layer between the sheet and roll shell. So, when using a release agent with the intent of being able to maintain the casting speed to avoid a sticking situation, the thermal efficiency is reduced thereby requiring a reduction in the casting speed to avoid a melt-through or a bleed-through condition.
It has also been found to be difficult to apply a uniform coating of a release agent onto the surface of a roll shell. Areas not covered by the release agent tend to cause microwelding to occur between the cast strip and the roll shell.
The prior art discloses various casting surface treatments for various purposes. For example, Hazelett Strip Casting Corporation discloses in a number of U.S. patents, including U.S. Pat. No. 4,487,157, U.S. Pat. No. 4,487,790, U.S. Pat. No. 4,588,021, U.S. Pat. No. 4,749,027, U.S. Pat. No. 4,915,158, and U.S. Pat. No. 5,086,827, the imp
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Alcoa Aluminio Do Nordeste S.A.
Handelman Joseph H.
Lin Kuang Y.
Topolosky Gary P.
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