MXPA00001159A - Strip casting apparatus - Google Patents

Abstract

Twin roil strip caster comprising parallel casting rolls (16) one of which is mounted on moveable roil 5 supports (104) which allow it to move bodily toward and away from the other roll (16). A pair of roll biasing units (110) comprising compression act on roil supports (104) to bias the moving roil (16) toward the other roll. Biasing units (110) comprise compression springs (112) 10 acting on roll supports (104) through thrust transmission structures (122) and thrust reaction structures (121). T positions of thrust reaction structures (121) are set by hydraulic cylinder units (119) operable vary t position of each reaction structure (121) to replicate movements of 15 t respective thrust transmission structure 122 so as to maintain a constant compression of t biasing springs (112) regardless of lateral movements of the roll supports (104).

Description

APPARATUS FOR MELTING STRIPS FIELD OF THE ART This invention relates to the casting of metal strips. It has particular application to the casting of metal strips by continuous casting in a double roller casting machine. In a double roller casting machine the molten metal is inserted between a pair of horizontal, counter-rotating casting rollers that are cooled so that the metal molded parts solidify on the surfaces of the moving rollers and are brought together to the line of contact between the rollers to produce a solidified strip product that is sent down from the contact line between the rollers. The term "roller contact line" is used herein to indicate the general region in which the rollers are closer to each other. The molten metal can be emptied from a ladle to a smaller container or series of smaller containers from which it flows through a metal supply nozzle located on the line of contact between the rolls to direct it towards the line of contact between the rollers thus forming a pouring tank of the molten metal supported on the casting surfaces of the rollers immediately above the contact line and extending along the contact line between the rollers. This pouring tank is usually combined between side plates or checkers which are kept in sliding contact with the end surfaces of the rollers to make a dam at the two ends of the pouring tank against overflow, although alternative means have also been proposed as electromagnetic barriers. The arrangement and adjustment of the casting rolls in a double roller casting machine is a significant problem. The rollers must be precisely positioned to properly define a correct width for the line of contact between the rollers, generally of the order of a few millimeters or less, and there must also be some means to allow at least one of the rollers to move outwardly against a pushing force to accommodate fluctuations in the thickness of the belt particularly during start-up. Typically, one of the rollers is mounted on fixed journals or journals and the other is rotatably mounted on supports that can move against the action of the pushing means to allow the roller to move laterally to accommodate fluctuations in thickness of the strip. The thrust means may be in the form of helical compression springs or, otherwise, may consist of a pair of hydraulic pressure cylinder units. The roller squeeze die-casting machine with lateral movement is described in Australian Patent Application 85185/98. In this case, the push springs act between the roller supports and a pair of thrust reaction structures, the positions of which can be established by the operation of an energized mechanical link pair to allow the initial compression of the Springs are adjusted to establish the initial compression forces so that they are equal at both ends of the roller. The positions of the roller supports need to be established and subsequently adjusted after starting casting so that the space between the rollers is constant across the width of the contact line to produce a constant profile strip. However, as the casting continues the profile of the strip will inevitably vary due to eccentricities in the rollers and dynamic changes due to variable thermal expansion and other dynamic effects. Previously there was no means to offer dynamic support or profile control to suppress fluctuations of the profile of the strip during casting. By the present invention it is possible to offer a very efficient means for this dynamic profile control.DESCRIPTION OF THE INVENTION According to the invention there is provided the apparatus for continuously melting metal strips comprising a pair of parallel casting rollers forming a line of contact between them; the metal supply means for supplying molten metal to the nip between the rollers to form a casting tank of the molten metal supported on the surfaces of the casting rolls immediately above the nip; the confining means of the tank for confining the molten metal in the pouring tank against the overflow of the ends of the contact line; and means for driving the rollers in order to drive the casting rollers in counter rotating directions to produce a solidified strip of the metal that is sent down the contact line; wherein at least one of the casting rollers is mounted on a pair of movable roller carriers that allow one roller to move bodily towards and away from the other roller, where there are a pair of roller thrust units operating on each one of the pair of movable roller carriers for pushing one roller towards the other, and wherein each roller thrust unit consists of an impulse transmission structure connected to the respective roller carrier, a thrust reaction structure, the means of the compression spring acting between the splices of the spring on the reaction structure of the thrust and the transmission structure of the thrust to exert action on the structure of transmission of the thrust and the carrier of the respective rollers, the reaction structure to the thrust establishing the operable means for varying the position of the reaction structure of the thrust, and the control means for regulating the function of the arrangement means so that the movements of the thrust transmission structure are replicated as the movements of the thrust reaction structure whereby the movements of the thrust transmission structure do not significantly affect the thrust force imposed on the thrust transmission structure. the same by the compression spring. Preferably, the regulating means is a means that can act by hydraulic pressure acting between the thrust reaction structure and a fixed structure. The means that actuates by hydraulic pressure can be provided by a hydraulic cylinder and piston unit connected at one end to the fixed structure, the other end of this unit forming or being connected to the reaction structure to the thrust. The control means may consist of a first position detector for detecting the position of the thrust transmission structure, and means for operating the hydraulic pressure means so that a movement detected by the detector is replicated by a movement of the reaction structure of the push. The roller carriers may consist of a pair of support structures at the end of the rollers for each of the rollers generally positioned below the ends of the respective roller. Each pair of support structures at the ends of the rollers can carry plain bearings by mounting the ends of the respective rollers for rotation about a central axis of the roller. The casting rollers and roller carriers can be mounted on a roller module installed and removable from the casting machine as a unit. In this case, the thrust transmission structure of each thrust unit can be disengaged from the respective roller carrier to allow the module to be separated without removing or dismantling the thrust units from the rollers. In the apparatus according to the invention, the casting rolls can be pushed by the respective pairs of pushing units. Otherwise, one of the rollers may be limited in lateral body movement and the other may be left in lateral movement against the thrust forces of the spring according to the invention.

BRIEF DESCRIPTION OF THE DRAWING? For the invention to be fully explained a specific embodiment will be described in some detail with reference to the accompanying drawings, in which: Figure 1 is a vertical section through a strip casting machine constructed in accordance with the present invention. Figure 2 is an amplification of part of Figure 1 illustrating the important components of the casting machine. Figure 3 is a longitudinal section through the important parts of the casting machine. Figure 4 is an extreme elevation of the casting machine; Figures 5, 6 and 7 show the casting machine in different conditions during casting and during the separation of the roll module from the casting machine; Figure 8 is a vertical section through a roller thrust unit incorporating a roller thrust spring; and Figure 9 is a schematic representation of the essential components of the casting machine.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY The illustrated casting machine consists of a structure or main frame of the machine 11 that is raised from the floor of the factory (not shown) and supports a casting roller module in the form of a cassette 13 that can be moved to an operative position in the casting machine as a unit, but can be easily separated when the rollers are to be replaced. The cassette 13 carries a pair of parallel casting rolls 16 to which the molten metal is supplied during a casting operation from a pouring ladle (not shown) through a refractory tundish 17, the distributor 18 and a spray nozzle. supply 19 for creating a pouring tank 30. The casting rolls 16 are cooled with water so that the castings solidify on the surfaces of the moving roller and are brought to the line of contact between them to produce a product in strips solidified 20 at the exit of the rollers. This product can be fed to a standard winder. The casting rolls 16 are counter-rotating through the driving shafts 41 from an electric motor and the transmission mounted on the main structure of the machine. The drive shaft may be disconnected from the transmission when the cassette is to be removed. The rollers 16 have peripheral, copper walls formed with a series of cooling passages with water extending along and placed on the circumference provided with cooling water through the ends of the rollers from the water supply conduits in the drive shafts of the rollers 41 which are connected to the water supply hoses 42 via rotating sleeves 43. The roller can usually be about 500 mm in diameter and up to 2000 mm in length to produce the product of strips of the width of the rollers. The ladle is completely conventional construction and is supported on a rotating turret from where it can be brought to the position on the refractory trough 17 to fill the trough. The refractory tundish can be adjusted with a sliding gate valve 47 operable by a servo-cylinder to allow molten metal to flow from the refractory trough 17 through the valve 47 and the crankcase or peripheral refractory ring 48 to the distributor 18. The distributor 18 is formed as a wide plate made of refractory material such as magnesium oxide (? LgO). One side of the distributor 18 receives molten metal from the tundish 17 and the other side of the distributor 18 is provided with a series of longitudinally disposed metal discharge holes 52. The lower part of the distributor 18 carries mounting brackets 53 for the. distributor assembly on the main structure of the casting machine 11 when the cassette is installed in its operating position. The supply nozzle 19 is formed as an elongated body made of a refractory material such as graphite alumina. Its lower part has a decreasing section to converge inwards and downwards so that it can be projected onto the contact line between the casting rolls 16. Its upper part is formed with lateral tabs that extend outwards 55 which are located on a console of assembly 60 that forms part of the main structure 11. The nozzle 19 may have a series of hydraulic passages placed horizontally, extending in the generally vertical direction to produce a suitably low velocity discharge of the metal across the width of the rollers and to supply the molten metal in the nip between the rollers without the direct impact on the surfaces of the rollers in which occurs the initial solidification. Otherwise, the nozzle may have a single, slotted, continuous discharge outlet for supplying a low velocity curtain of the molten metal directly to the nip between the rollers and / or may be immersed in the molten metal reservoir. The reservoir is confined at the ends of the rollers by a pair of side closure plates 56 which are held against the staggered ends 57 of the rollers when the roller cassette is in its operative position. The side closure plates 56 are made of a strong refractory material, for example boron nitride, and have side edges festooned to match the curvature of the stepped ends of the rolls. The side plates may be mounted on plate supports 82 which are moved by activating a pair of hydraulic cylinder units 83 to bring the side plates into engagement with the stepped ends of the casting rolls to form extreme closures for the deposit of molten metal formed in the cast rolls during a melt operation. During a melt operation the slide gate valve 47 is operated to allow the molten metal to pour from the refractory tundish 17 to the distributor 18 and through the metal supply nozzle 19 by letting it flow over the cast rolls. The front end of the product strip 20 is guided by the activation of an articulated band table 96 to a guide cylinder station and thence to a winding station (not shown). The articulated band table 96 hangs from the pivot assemblies 97 on the main structure and can hang towards the guide cylinders by actuating a hydraulic cylinder unit (not shown) after the clean front end has been formed. The separable roller cassette 13 is constructed so that the casting rolls 16 can be positioned and the contact line between these adjusted before the cassette is installed in position in the casting machine. Further, when the cassette is installed two pairs of push units of the rollers 110, 111 mounted on the main structure of the machine 11 can be quickly connected to the roller supports on the cassette to provide pushing forces resisting the separation of the cassette. the rollers. The roller cassette 13 consists of a large structure 102 that carries the rollers 16 and the upper part 103 of the refractory casing to contain the molten strip below the nip. The rollers 16 are mounted on the supports of the rollers 104 which comprise support structures of the end of the roller 90 carrying the bearings at the end of the roller 100 by means of which the rollers are mounted for rotation about their longitudinal axis in parallel relation each. The two pairs of roller supports 104 are mounted on the frame for the roller cassette 102 by means of linear bearings 106 whereby they can slide laterally of the cassette structure to provide body movement of the towards and away from each other allowing thus the separation and closing movement between the two parallel rollers. The roller cassette structure 102 also carries two adjustable retainer means 107 positioned below the rollers about a central vertical plane between the rollers and located between the two pairs of roller supports 104 to serve as detents limiting inward movement of the rollers. two roller supports to thereby define the minimum width of the contact line between the rollers. As explained later, the units for pushing the rollers 110, 111 are operable to move the roller supports inwardly against these centrally adjustable detent means but to allow the movement of the spring out of one of the rollers against the pre-established thrust forces. Each adjustable retainer means 107 is in the form of a worm or helix-driven connection having a body 108 fixed relative to the central vertical plane of the casting machine and two ends 109 which can be moved with the activation of the connection equally in opposite directions to allow extension and contraction of the connection to adjust the. width of the contact line between the rollers and at the same time maintain the equidistant separation of the rollers from the central vertical plane of the casting machine. The casting machine is provided with two pairs of roller pushing units 110, 111 connected one pair to the brackets 104 of each roller 16. The pushing units of the rollers 110 on one side of the machine are constructed and operated from according to the present invention. These units are adapted with helical thrust springs 112 to provide thrust forces on the respective roller supports 104 while the thrust units 111 on the other side of the machine incorporate hydraulic actuators 113. These actuators are operable to maintain the thrust supports. respective rollers 104 of one roller firmly against the central detents and the other roller is free to move laterally against the action of the thrust springs 112 of the thrust units 110. The detailed construction of the thrust units 110 is illustrated in the Figure 8. As shown in this figure, the thrust unit consists of a spring barrel housing 114 positioned within an external housing 115 which is fixed to the main structure of the casting machine 116 by fixing screws 117. The housing of the spring 114 is formed with a piston 118 running inside the outer housing 115. The the spring housing 114 may alternatively be in an extended position as illustrated in Figure 8 and a retracted position by the flow of the hydraulic fluid to and from the cylinder 118. The outer end of the spring housing 114 bears a pressurized liquid operable medium. in the form of a hydraulic cylinder unit 119 which operates to establish the position of a spring reaction piston 121 connected to the piston of the unit 119 by a connecting rod 130. The inner end of the spring 112 acts on a transmission structure of the thrust 122 that is connected to the respective roller support 104 through a load cell 125. The thrust structure initially engages the firm coupling with the roller support via a connector 124 which may be extended by operation of the hydraulic cylinder 123 when the pushing unit is going to be disconnected. When the pushing unit 110 is connected to its respective roller support 104 when the spring housing 114 is set in its extended state as shown in Figure 8, the position of the spring housing 114 and the cylinder unit 119 is fixed in relation to the structure of the machine and the position of the spring reaction piston 121 can be established to adjust the effective space between the splices of the spring in the reaction piston and the thrust transmission structure 122. The compression of the spring 112 it can, therefore, be adjusted to vary the thrust force applied to the thrust transmission structure 122 and the respective roller support 104. With this arrangement the only relative movement during the casting operation is the roll support movement 104 and the push structure 122 as a unit against the thrust spring. Since the thrust unit acts to push the roller holder 104 inward against the retainer it can be adjusted to reload the roller holder with a necessary spring thrust force before the metal actually passes between the cast rolls and this Pushing force will be maintained during a subsequent casting operation. In accordance with the present invention, the dynamic wedge or profile control is achieved by the continuous operation of the hydraulic cylinder unit 119 to vary the position of the spring reaction piston to replicate the movements of the push transmission structure 122 due to lateral movements of the support of rollers 104. Any movement in or out of the roller holder 104 will make a corresponding inward or outward movement of the cylinder of the cylindrical unit 119 and thus of the spring reaction piston 121 to maintain a constant compression of the spring compression 112. Accordingly, it is possible to maintain a constant thrust force at each end of the roller regardless of the movements of the roller assemblies and whether control of the dynamic wedge can be achieved. It is not possible to achieve this result by trying to control the thrust forces generated by a pressurized fluid pushing system. This control would be dependent on the measured force signals that would necessarily have errors that would be fed back through the control system. The use of springs in combination with a continuous regulation means according to the present invention allows the very precise arrangement of the constant thrust forces that can be maintained during the casting operation. It is possible to use springs with very little rigidity and because the two compensation or control systems for the two roller ends operate completely independently there is no interference between the two. As illustrated in Figure 9, the control means may be composed of the position sensors 150, the position detector of the thrust transmission structures 122 and connected to a control circuit that regulates the operation of the cylinder unit 119 so that the movements of the thrust transmission structures 122 are replicated by the cylinders of the units 119. The control circuit may consist of the controllers 151 connected to the detectors 150 and the cylindrical units 119 for operating the cylinders 119 during the casting to replicate the movements of the thrust transmission structures 112. The controllers 151 can also receive input signals from a logic device 152 to allow the operation of the cylinders for the initial arrangement of the roller supports (entry point 153). ) before casting and after adjustment for the adjustment of the static wedge after the casting tion (entry point 154). The control means may also cause the cylindrical unit 119 to be operated to impose additional movements on the spring reaction piston 121 to produce variations in the thrust force to compensate for variations in the thickness of the strip across the width of the strip or on the corresponding edge of the strip due to variations in the deformation at the ends of the rolls during casting. Variations in the thickness of the strip can be detected by X-ray detectors scanning through the strip downstream of the casting machine and feeding signals to an entry point 155 of the logic device 152 of the control circuit as well as is indicated in Figure 9. Variations in thickness due to deformation of the rolls will generally be sinusoidal in the longitudinal direction of the strip to produce sinusoidal control signals that can be used to control the operation of the cylindrical units 119 to impose a corresponding and compensating sinusoidal movement in the spring reaction piston 121. In order to achieve adequate thickness control of the strips, the control signals must be applied to the cylindrical units 119 in proper phase relationship with the rotation of the rolls, that is, during each rotation the characteristic of the control signals must be coupled with the characteristic of the movements of the ends of the rollers caused by the deformations of the roller. The appropriate phase coupling is obtained by applying the signals in an initial phase relationship with a reference signal producing a pulse per revolution of the rolls and then varying the phase relationship to produce a minimization of the amplitude of the variations in the thickness. This can be achieved by tracing or plotting an amplitude error signal. The construction units of the push units 111 do not form part of the present invention. The full details of these units and the manner in which the cassette structure of the rollers 102 can move in and out of the casting machine are described in the specification of Australian Patent 85185/98.

Claims (10)

1. An apparatus for continuously melting metal strips consists of a pair of parallel casting rollers (16) forming a line of contact (16a) therebetween; the metal supply means (17, 18, 19) for supplying molten metal to the nip between the rollers (16) to form a casting tank (30) of the molten metal supported on the surfaces of the casting rolls immediately on the line of contact between the rollers (16A); the confining means of the tank (56) for confining the molten metal in the pouring tank (30) against overflow of the ends of the roller nip; and the driving means of the rollers (41) for driving the casting rolls (16) in counter rotating directions to produce a strip of solidified metal (20) sent down the line of contact between the rollers (16A); wherein at least one of the casting rollers is mounted on a pair of movable roller carriers (104) that allow one roller to move bodily toward and away from the other roller and there are a pair of roller thrust units (110 ) acting one on each of the pair of movable roller carriers (104) to push one roller bodily towards the other roller, characterized in that each roller thrust unit (110) consists of a thrust transmission structure (122) connected to the respective roller carrier (104), a thrust reaction structure (121), the compression spring means (112) acting between the splices of the spring in the thrust reaction structure (121) and the transmission structure of the pushing (122) to exert a thrust on the thrust transmission structure (122) and the respective roller carrier (104), the thrust reaction structure establishing operable means (119) to vary the thrust tion of the reaction structure to the thrust (121), and the control means (151) to regulate the operation of the regulating means (119) so that the movements of the thrust transmission structure (122) are replicated as movement of the thrust reaction structure (121) whereby the movements of the thrust transmission structure (122) does not significantly affect the thrust force imposed thereon by the compression spring means (112).

2. The apparatus as recited in claim 1 further characterized in that the regulating means (119) is a pressure-operable liquid medium acting between the thrust reaction structure (121) and a fixed structure (114).

3. The apparatus as recited in claim 2, further characterized in that the hydraulic action means (119) is provided by a piston and cylinder hydraulic unit connected at one end of the fixed structure (114), the other end of this unit forming or being connected to the thrust reaction structure (121).

4. The apparatus as recited in claim 2 or claim 3, further characterized in that the control means consists of a position detector (150) for detecting the position of the thrust transmission structure (122) and the means to operate the hydraulic pressure means so that a movement detected by the detector is replicated by a movement of the thrust reaction structure (121).

5. The apparatus as mentioned in any of claims 2 to 4, further characterized in that the hydraulic actuating means (119) is operable to impose additional movements on the thrust reaction structure (121) to produce variations in force of thrust to compensate for variations in the thickness of the strip during casting.

6. The apparatus as recited in claim 5, further characterized in that there is a thickness detecting means of the strips to produce signals indicative of the thickness of the strips and the control means (151) uses these signals to perform the operation of the hydraulic drive means for imposing (119) the additional movements on the thrust reaction structure (121).

7. The apparatus as mentioned in any of claims 1 to 6, further characterized in that the roller carriers (104) comprise a pair of supporting structures of the ends of the rollers (90) for each of the rollers, generally positioned down the ends of the respective roller.

8. The apparatus as recited in claim 7, further characterized in that each pair of supporting structures of the ends of the rollers (90) bears plain bearings (100) by mounting the ends of the respective rollers for rotation about an axis central roller.

9. The apparatus as recited in any of claims 1 to 8, further characterized in that the casting rolls (16) and the roller carriers (108) are mounted on a roller module (13) installed in and separable. of the casting machine as a unit.

10. The apparatus as recited in claim 9, further characterized in that the thrust transmission structure (122) of each thrust unit (110) is disconnectable from the respective roller carrier (104) to allow the module (13). ) is separated without separating or dismantling the pusher units from the rollers (110).