Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Utility Patent
1998-09-16
2001-01-02
Lin, Kuang Y. (Department: 1722)
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
C164S480000
Utility Patent
active
06167942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the casting of metal strip. It has particular application to the casting of metal strip by continuous casting in a twin roll caster.
2. Description of Related Art
In a twin roll caster molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed.
The setting up and adjustment of the casting rolls in a twin roll caster is a significant problem. The rolls must be accurately set to properly define an appropriate width for the nip, generally the order of only a few millimetres, and there must also be some means for allowing at least one of the rolls to move outwardly against a biasing force to accommodate fluctuations in strip thickness particularly during start up. Previously proposed arrangements have employed roll mounting and biasing means in which require relative sliding movement between separate components at several locations, resulting in several sources of friction loading which interferes with accurate positioning of the rolls and accurate measurement of the roll biasing forces. Moreover, with the previous arrangements it has not been possible to provide preloading roll biasing forces which can be accurately set prior to casting and it has been necessary to wait for metal to pass through the rolls to develop reactive forces resisting roll separation in order to generate appropriate roll biasing forces. The present invention provides a novel roll biasing system which minimises the sources of friction during operation and which enables the preloading of the roll biasing forces prior to casting.
SUMMARY OF THE INVENTION
According to the invention there is provided apparatus for continuously casting metal strip comprising a pair of parallel casting rolls forming a nip between them; metal delivery means to deliver molten metal into the nip between the rolls to form a casting pool of molten metal supported on casting roll surfaces immediately above the nip; pool confining means to confine the molten metal in the casting pool against outflow from the ends of the nip; and roll drive means to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip; wherein at least one of the casting rolls is mounted on a pair of moveable roll carriers which allow that one roll to move bodily toward and away from the other roll, wherein there is an adjustable stop means to limit inward bodily movement of said one roll toward the other, wherein there is a pair of roll biasing units acting one on each of the pair of moveable roll carriers to bias said one roll bodily inwardly toward the other roll, and wherein each roll biasing unit comprises a thrust transmission structure connected to the respective roll carrier, a thrust reaction structure having a set position, thrust means acting between the thrust reaction structure and the thrust transmission structure to exert a thrust on the thrust transmission structure to bias the respective roll carrier inwardly against the limit imposed by the stop means.
Preferably the thrust transmission structure incorporates a load cell to monitor the thrust transmitted thereby without any friction generating movement within that structure.
The thrust means may comprise a spring acting between the thrust reaction structure and the thrust transmission structure.
Alternatively or in addition the thrust means may comprise a pressure fluid actuator means.
If the thrust means consists solely of a pressure fluid actuator means, the thrust reaction structure may be permanently fixed in said set position. However, in the case where the thrust means comprises a spring, the thrust reaction structure may be adjustable in position to vary said set position whereby to vary the biasing force generated by the spring.
The casting rolls may each be mounted on a pair of moveable roll carriers so as to be bodily moveable toward and away from the other roll and the adjustable stop means may then limit inward bodily movement of both of the rolls.
In that case the said pair of roll biasing units may be one of two such pairs acting on the pairs of roll carriers to bias both of the rolls inwardly against the limit established by the stop means.
The adjustable stop means may be disposed beneath the nip and between the roll carriers to serve as a spacer stop for engagement with the roll carriers to pre-set the minimum width of the nip between the rolls and adjustable in width to vary the minimum width of the nip.
The roll carriers may comprise a pair of roll end support structures for each of the rolls disposed generally beneath the ends of the respective roll. Each pair of roll end support structures may carry journal bearings mounting the respective roll ends for rotation about a central roll axis.
The adjustable stop means may comprise a pair of adjustable stops disposed one between each of the pairs of roll end support structures at the two ends of the roll assembly.
Each adjustable stop may serve as a centring stop disposed about a central vertical plane through the nip between the rolls and actuable such that it can be expanded and contracted by equal movements to either side of the central plane so as to maintain equal minimum spacing of the rolls from the central plane.
Each central stop may be comprised of an expansible and contractible mechanical jack. Each jack may, for example, be screw or worm driven for adjustment.
The casting rolls and roll carriers may be mounted on a roll module installed in and removable from the caster as a unit. In that case, the thrust transmission structure of each biasing unit may be disconnectable from the respective roll carrier to enable the module to be removed without removing or dismantling the roll biasing units.
In apparatus in accordance with the invention in which both of the casting rolls are biased by respective pairs of biasing units, the biasing units acting on one of the rolls may have thrust means in the form of springs whereas the biasing units acting on the other roll may have thrust means in the form of pressure fluid actuators whereby the apparatus can be operated in alternative modes in which one of the rolls is restrained against lateral bodily movement and the other is moveable laterally against either spring biasing forces or biasing forces generated by the pressure fluid actuators.
REFERENCES:
patent: 2796781 (1957-06-01), Mills
patent: 4702300 (1987-10-01), Nakanori et al.
patent: 5706882 (1998-01-01), Fellus et al.
patent: 62-6740 (1987-01-01), None
patent: 1380816 (1988-03-01), None
Fish John Andrew
Kato Heiji
Ishikawajima-Harima Heavy Industries Company Limited
Kerins John C.
Lin Kuang Y.
Miles & Stockbridge P.C.
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