Strip casting apparatus

Abstract

Twin roll strip caster comprising parallel casting rolls one of which is mounted on moveable roll supports which allow it to move bodily toward and away from the other roll. A pair of roll biasing units comprising compression act on roll supports to bias the moving roll toward the other roll. Biasing units comprise compression springs acting on roll supports through thrust transmission structures and thrust reaction structures. The positions of thrust reaction structures are set by hydraulic cylinder units operable to vary the position of each reaction structure to replicate movements of the respective thrust transmission structure so as to maintain a constant compression of the biasing springs regardless of lateral movements of the roll supports.

Description

RELATED PATENT APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 09/495,356, filed Feb. 1, 2000, 19 119 of the roll biasing units to vary the position of the spring reaction plunger to replicate movements of the thrust transmission structure 122 due to variations in strip thickness and resulting lateral movements of the roll carrier 104. Any inward or outward movement of roll carrier 104 will cause a corresponding inward or outward movement of the cylinder of cylinder unit 119 and spring reaction plunger 121 so as to maintain a constant compression of the compression spring 112.

Accordingly, it is possible to maintain profile control by a substantially constant biasing force of the carrier 104 and in turn the supported casting roll regardless of movements of the roll mountings. This result is not achieved by endeavoring to control these forces generated by any pressure fluid system that was previously available. Such pressure fluid systems are generally too slow in response time to track the profile in strip thickness variations. The use of compression springs or servo-mechanisms in combination with a continual control setting device as explained herein enables very accurate setting of controlled forces which can be maintained or varied throughout a casting operation. The compression springs of the carrier drive units may be very low stiffness springs, or, alternatively, sensitive servo-mechanisms may be used because the two roll carrier drive units of the carrier drive system at the two ends of the laterally moveable casting roll operate independently so that there is no cross-talk between them.

As illustrated diagrammatically in FIG. 9, the control system for the profile control can be comprised of position sensors 150, sensing the position of the thrust transmission structures 122 and connected into a control circuit which controls the operation of the cylinder unit 119 so that the movements of the thrust transmission structures 122 are replicated by the cylinders of units 119. The control system may comprise controllers 151 connected to the position sensors 150 and to the cylinder units 119 to operate the cylinders 119 during casting so as to replicate movements of the thrust transmission structures 122. Controllers 151 may also receive input signals from a logic device 152 to allow operation of the cylinders for initial setting of the roll supports (input point 153) prior to casting. Subsequent adjustment for static wedge adjustment during casting (input point 154) can also be provided as explained below.

For dynamic wedge control, variations in strip thickness can be sensed by X-ray sensors positioned at a plurality of locations across the strip downstream from the caster, and configured to feed electrical signals indicative of strip thickness at the positions of the sensors to an input point 155 of the logic device 152 of the control system as indicated in FIG. 9. The sensors may alternatively be optical, laser or other sensors capable of sensing the thickness of the steel strip and producing electrical signals indicative of the strip thickness sensed by the sensor.

The thickness variations of the strip due to roll eccentricity or other deformation will be generally sinusoidal in the longitudinal direction of the strip, so as to produce sinusoidal control signals which can be used to control operation of cylinder units 119 to impose a corresponding and compensating sinusoidal movement of the roll carriers 104 and supported casting rolls by the carrier drives. To achieve appropriate strip thickness control, the control signals must be applied to the carrier drive units 110 in proper phase relationship with the rotation of the rolls, i.e., during each rotation the pattern of the control signals are matched with the pattern of roll end movements caused by the roll deformations. Proper phase matching is achieved by applying the signals at an initial phase relationship with a reference signal producing one pulse per revolution of the rolls and then varying the phase relationship to produce a minimization of the amplitude of thickness variations. This may be achieved by tracking or plotting an amplitude error signal. Superimposed of the sinusoidal variations can also be thickness variations across the width of the strip, which is known as a dynamic wedge.

The control system for dynamic wedge control may cause cylinder unit 119 to be operated to impose additional movements on the spring reaction plunger 121 to produce variations in the force to compensate for variations in strip thickness across the width of the strip, or at the corresponding edge of the strip due to deformation variations at the ends of the rolls during casting.

The construction units of biasing units 111 forms no part of the present invention. Full details of these units and the manner in which the roll cassette frame 102 can be moved into and out of the casting machine are described in U.S. Pat. No. 6,167,943 to Fish et al.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

1. In an apparatus for continuously casting metal strip where a pair of positioned casting rolls form a nip therebetween, a metal delivery system delivers molten metal into the nip between the casting rolls to form a casting pool of molten metal supported on casting roll surfaces above the nip confined against outflow adjacent the ends of the casting rolls, and a casting roll drive system drives the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip, the improvement of controlling thickness of the strip against variation during casting comprising:

a. sensors positioned downstream of the nip capable of sensing the strip thickness at a plurality of locations along the strip width;

b. said sensors capable of producing electrical signals indicative of the strip thickness sensed at the sensor positions;

c. at least one of said casting rolls mounted on more than one roll carriers alone carrier along the strip width movable independently of another roll carrier and capable of allowing one of the casting rolls to move laterally toward and away from the other casting roll;

d. carrier drives capable of moving said roll carriers independently to enable the nip to be varied in a wedge-like shape and in turn varying the strip thickness across the strip width at the nip; and

e. a control system capable of controlling the carrier drives responsive to electrical signals from the sensors to vary the nip across the strip width to at least partially correct for variations in the strip thickness along the strip width sensed by the sensors.

2. Apparatus for continuously casting metal strip as claimed in claim 1, wherein the carrier drive system is drives are comprised of servo-mechanisms capable of independently moving the roll carriers so as to vary the strip thickness across the strip width at the nip.

3. Apparatus for continuously casting metal strip as claimed in claim 1, wherein the carrier drive system is comprised of roll biasing units each acting on a roll carrier to bias a casting roll bodily toward the other casting roll so as to vary the strip thickness across the strip width at the nip.

4. Apparatus for continuously casting metal strip as claim in claim 3,

wherein each roll biasing unit comprises thrust transmission structures connected to each roll carrier, compression springs acting against the thrust transmission structure to exert force on the thrust transmission structure and in turn the roll carrier, and a thrust reaction setting device operable to vary the lengths of the compression springs;

and wherein the control system controls operation of the thrust reaction setting device such that movement of the thrust transmission structure moves the roll carriers and in turn varies the strip thickness across the strip width at the nip.

5. Apparatus for continuously casting metal strip as claimed in claim 4, wherein each roll biasing unit further comprises a thrust reaction structure abutting the compression spring and moveable by the thrust reaction setting device such that the control system varies position of the thrust reaction structure to exert force through the compression spring on the thrust transmission structure and in turn vary the strip thickness across the strip width at the nip.

6. Apparatus as claimed in claim 1, wherein the carrier drives are disconnectable from the roll carriers to enable a module comprised of the casting roll and roll carrier to be removable without removing or dismantling the carrier drives.

7. In an apparatus for continuously casting metal strip where a pair of casting rolls form a nip between them, a metal delivery system delivers 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 confined against outflow adjacent the ends of the casting rolls, and a casting roll drive system drives the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip, the improvement of controlling thickness variation of the strip along the strip width during casting comprising:

a. at least one of said casting rolls mounted on roll carriers capable of allowing one of the casting rolls to move laterally toward and away from the other casting roll;

b. roll biasing units each acting on the roll carrier adjacent each end of the casting rolls to bias the casting roll bodily toward the other casting roll;

c. each roll biasing unit comprising thrust transmission structures connected to the roll carriers adjacent each end of the casting rolls, compression springs acting against the thrust transmission structure to exert force on the thrust transmission structure and in turn the roll carriers adjacent each end of the casting roll;

d. a thrust reaction structure capable of compressing the compression spring and moveable axially of the compression spring;

e. a thrust reaction structure setting device operable to vary the position of the thrust reaction structure relative to the compression spring; and

f. a control system capable of controlling operation of the thrust reaction structure setting device such that movements of the thrust reaction structure replicate movements of the thrust transmission structure such that movements of the thrust transmission structure do not significantly affect the biasing force imposed on the roll carrier and casting roll by the compression spring.

8. Apparatus as claimed in claim 7, wherein the setting device is a pressure fluid actuable drive acting between the thrust reaction structure and a fixed structure.

9. Apparatus as claimed in claim 8, wherein the fluid actuable drive comprises a fluid piston and cylinder unit connected at one end to the fixed structure, the other end of that unit either forming or being connected with the thrust reaction structure.

10. Apparatus as claimed in claim 7 claim 8, wherein the control system comprises a position sensor to sense the position of the thrust transmission structure, and operates the pressure fluid actuable device drive such that a movement sensed by the sensor is replicated by movement of the thrust reaction structure.

11. Apparatus as claimed in claim 6, wherein the roll carriers comprise a pair of roll end support structures for each of the casting rolls disposed generally beneath the ends of the respective roll.

12. Apparatus as claimed in claim 11, wherein each pair of roll and end support structures carries journal bearings mounting the respective roll ends for rotation about a central roll axis.

13. Apparatus as claimed in claim 7, wherein the casting rolls and the roll carriers are mounted on a roll module installed in and removable from the caster apparatus as a unit.

14. Apparatus as claimed in claim 13, wherein the thrust transmission structure of each biasing unit is disconnectable from the respective roll carrier to enable a module comprising the casting roll and roll carrier to be removable without removing or dismantling the roll biasing units.

15. In an apparatus for continuously casting metal strip where a pair of positioned casting rolls form a nip therebetween, a metal delivery system delivers molten metal into the nip between the casting rolls to form a casting pool of molten metal supported on casting roll surfaces above the nip confined against outflow adjacent the ends of the casting rolls, and a casting roll drive system drives the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip, the improvement of controlling thickness of the strip against variation during casting comprising:

a. sensors positioned downstream of the nip capable of sensing the strip thickness;

b. said sensors capable of producing electrical signals indicative of the strip thickness sensed at the sensor positions;

c. at least one of said casting rolls mounted on more than one roll carrier along the strip width movable independently of another roll carrier and capable of allowing one of the casting rolls to move laterally toward and away from the other casting roll;

d. carrier drives capable of moving said roll carriers independently to superimpose a compensating sinusoidal phase matched movement of the casting rolls corresponding to variations of the strip thickness at the nip; and

e. a control system capable of controlling the carrier drives responsive to the electrical signals from the sensors to cause variation of the nip to at least partially correct for variations in strip thickness along the strip length sensed by the sensors.

16. Apparatus as claimed in claim 15 where the casting roll drive system is capable of generating a reference signal indicating rotational position of the casting rolls, and the control system capable of controlling the carrier drives to cause variation of the nip to at least partially correct for variations in the strip thickness along the strip length sensed by the sensors to be applied based on the reference signal.

17. Apparatus as claimed in claim 16 where the control system capable of controlling the carrier drives is capable of varying a phase of said variation of the nip to reduce amplitude of strip thickness variations.

18. Apparatus as claimed in claim 15 where the carrier drives are capable of varying the nip in a wedge-like shape and in turn varying the strip thickness across the strip width at the nip and the control system capable of controlling the carrier drives is capable of varying the nip across the strip width to at least partially correct for variations in the strip thickness along the strip width.