Tundish positioning

Abstract

A tundish has an outlet and outlet shroud through which to deliver molten metal to a caster. The tundish is preheated at a heating station and moved to a casting station while supported on a moveable tundish car such that the tundish outlet is induced to a set position relative to the car and such that the tundish is located against horizontal movement at the position of a vertical central line of the tundish outlet but is free to move thermally about that position. Tundish is supported in a raised position on hoists during preheating and movement to the casting station and then lowered by actuation of the hoists to allow insertion of an outlet shroud into a metal distributor vessel of the caster.

Description

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/280,949, which was filed on Apr. 2, 2001.

BACKGROUND AND SUMMARY

[0002] This invention relates to the positioning of a tundish in a metal delivery system for delivering molten metal to a caster. It has particular but not exclusive application to a metal delivery system for a twin roll caster for direct continuous casting of thin metal strip.

[0003] In a twin roll caster, molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are internally chilled 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 a 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. This casting pool may be confined between side plates or dams held in sliding engagement with the ends of the rolls.

[0004] The molten metal delivery system for a twin roll caster will generally include a tundish to receive molten metal from a ladle and deliver it to the nozzle, either directly or via a small distributor vessel associated with and mounted directly above the nozzle. The various refractory components of the metal delivery system, including the nozzle, distributor vessel and the tundish must all be preheated to temperatures well in excess of 1000° C. to prevent premature cooling and freezing of the molten metal during start up and initiation of casting. In order to achieve this, the various refractory components are generally preheated at separated preheat stations from which they must be brought into an assembly over the casting rolls prior to casting. It then becomes a critical requirement of the start up for the strip casting process to move these components to position and assemble them rapidly so that molten metal can be poured through them before they suffer significant heat loss through radiation.

[0005] The tundish which receives metal from the ladle may typically have a capacity of 10-25 tons and it needs to be transported in a tundish car. It must be accurately positioned so that its outlet is properly aligned with the inlet for the next refractory component in the delivery system, whether that be the nozzle or a distributor vessel mounted above the nozzle. The tundish outlet may be provided with a downwardly depending outlet nozzle shroud which must be correctly aligned and inserted into the following component in the delivery system. This is a major contributor to the set up time and if performed under manual control introduces a non-defined time interval in the start up procedure. The present invention enables more accurate alignment to be achieved without manual intervention.

[0006] According to the present invention, there is provided a method of preheating a tundish at a preheat station and moving the preheated tundish into an operative position for delivery of molten metal from an outlet thereof to a caster, comprising the steps of:

[0007] supporting the tundish on a moveable tundish car such that the tundish outlet is indexed to a set position relative to the tundish car and such that the tundish is located against horizontal movement at the position of a vertical center line through the outlet, but is free to move thermally about that position;

[0008] preheating the tundish at the preheating station while supported on the tundish car; and

[0009] moving the tundish car with the preheated tundish supported thereon to a set position over the caster in which the center line of the tundish outlet is in a predetermined alignment relative to the caster.

[0010] The tundish outlet may be fitted with a downwardly depending outlet nozzle shroud and the method may comprise the further step of lowering the tundish so that the outlet nozzle shroud is inserted downwardly into a metal receiving component of the caster.

[0011] The invention also extends to a method of supporting in a support car a tundish having a metal flow outlet, said method comprising:

[0012] providing the tundish with a formation projecting laterally from the tundish in lateral alignment with a vertical center line through the tundish outlet and putting the tundish onto the car such that said formation is engaged with a guide on the tundish car so as to index the position of the tundish outlet relative to the car and to restrain the tundish against horizontal movement at the position of the center line of the outlet, but to permit tundish expansion and contraction movement about that center line.

[0013] The formation projecting from the tundish may be in the form of a boss or pin and the guide may be a vertical slot in the tundish car to receive the pin.

[0014] The invention further provides casting apparatus comprising:

[0015] a caster to receive molten metal;

[0016] a tundish through which to deliver molten metal to the caster via a tundish outlet;

[0017] a tundish car for transport of the tundish between a tundish preheating station and the caster;

[0018] locating means to locate the tundish on the tundish car such that the tundish outlet is indexed to a set position relative to the tundish car and the tundish is restrained against horizontal movement at the position of a center line through the tundish outlet, but is free to move thermally about that position; and

[0019] tundish car setting means to set the tundish car at a predetermined position at the casting station.

[0020] The invention further provides a refractory tundish and a moveable car to support the tundish, wherein the tundish is provided with a bottom outlet for flow of molten metal downwardly therefrom and with a lateral projection in lateral alignment with a vertical center line through the tundish outlet and the support car is provided with a guide to engage the tundish projection so as to index the position of the tundish outlet relative to the support car and to restrain the tundish against horizontal movement at the position of the center line of the tundish outlet while permitting expansion and contraction of the tundish about that location.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order that the invention may be more fully explained, one particular embodiment will be described in some detail with reference to the accompanying drawings in which:

[0022] FIG. 1 illustrates a continuous strip caster having a molten metal delivery system incorporating a tundish to receive molten metal from a ladle and to deliver that metal to the caster;

[0023] FIG. 2 illustrates a tundish car for moving the tundish between a preheating station and the caster;

[0024] FIG. 3 diagrammatically illustrates the location of the tundish on the tundish car;

[0025] FIG. 4 diagrammatically illustrates the positioning of the tundish over the caster; and

[0026] FIG. 5 illustrates a stop and buffer arrangement for accurately positioning the tundish car at the caster.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] The illustrated caster comprises a main machine frame, generally identified by the numeral 11, which stands up from the factory floor 12. Frame 11 supports a casting roll carriage 13 which is horizontally moveable between an assembly station and a casting station. Carriage 13 carries a pair of parallel casting rolls 16 which form a nip in which a casting pool 10 of molten metal is formed and retained between two side closure plates 30, or dams held in sliding engagement with the ends of the rolls.

[0028] Molten metal is supplied during a casting operation from a ladle 17 via a tundish 18, delivery distributor 19a and nozzle 19b into the casting pool. Before assembly above the carriage 13, tundish 18, distributor 19a, nozzle 19b and the side plates 30 are all preheated to temperatures in excess of 1000° C. in appropriate preheat facilities and moved into assembly prior to casting.

[0029] Casting rolls 16 are water cooled so that molten metal from the casting pool solidifies as shells on the moving roll surfaces and the shells are brought together at the nip between them to produce a solidified strip product 20 at the roll outlet. This product is fed to a run out table 21 and subsequently to a standard coiler. It will be appreciated that the rolls may be cooled by coolant other than water. A receptacle 23 is mounted on the machine frame adjacent the casting station and molten metal can be diverted into this receptacle via an overflow spout 25 on the distributor 19a if there is a severe malfunction during a casting operation.

[0030] Tundish 18 is fitted with a lid 32 and a flow outlet 40 is in the bottom of the tundish at its left-hand and as seen in FIG. 1. Molten metal is introduced into the right-hand end of the tundish from the ladle 17 via an outlet nozzle 37 and slide gate valve 38 and flows out through outlet 40 which is fitted with a slide gate valve 47 to selectively open and close the outlet and effectively control the flow of metal from the tundish 18. The slide gate valve 47 is fitted with a downwardly depending nozzle shroud 42 through which molten metal flows from the tundish outlet to the delivery distributor 19a and the nozzle 19b.

[0031] In operation of the illustrated apparatus, molten metal delivered from delivery nozzle 19b forms a pool 10 above the nip between the rollers, this pool being confined at the ends of the rollers by the side closure plates 30, which are held against stepped ends of the rollers by actuation of a pair of hydraulic cylinder units. The upper surface of pool 10, generally referred to as the “meniscus level” 14, rises above the lower end of the delivery nozzle. Accordingly, the lower end of the delivery nozzle 19a is immersed within the casting pool 10 and the nozzle outlet passage extends below the surface of the pool or meniscus level. The flow of metal is also such as to produce a head or pool of molten metal within the lower part of the delivery nozzle to a height above the meniscus level 14.

[0032] The slide gate valve 47 is actuated by a cylinder unit 48 to control the flow from the tundish 18 from complete shut off to full flow conditions.

[0033] When setting up the preheated refractory components of the metal delivery system prior to casting, the shroud 42 fitted to the slide gate valve 47 on the tundish outlet must be properly aligned with and inserted into a receiving shroud 50 located in the lid of the distributor 19a. This requirement is similar to insertion of an SEN (submerged entry nozzle) into a conventional casting mould but requires closer positioning. When strip casting ferrous metals, the start up process is time critical. The present invention enables appropriate alignment and setting of the tundish outlet and teleshroud to within the required tolerance without the need for manual intervention.

[0034] By the present invention, the alignment and setting of the tundish outlet and shroud can be achieved as follows:

[0035] 1. The alignment process begins with the setting of tight tolerances on the positioning of the flow control valve 47 to a known position on the tundish bottom.

[0036] 2. The tundish is then set into a tundish car, where the center line of the outlet shroud is fixed at a known position in the tundish car. All thermal movement is then allowed from this fixed position.

[0037] 3. The relative position of the tundish in the tundish car at the preheat position and after travelling to the casting position is maintained to a small tolerance (generally less than +/−2 mm).

[0038] 4. The positioning of the tundish car at the casting station is carried out using control and design of the tundish car drive. This may for example be to a tolerance of generally less than +/−2 mm.

[0039] The manner in which the above steps can be achieved is illustrated in FIGS. 2 to 4. FIG. 2 illustrates how the tundish 18 can be supported on a tundish car 60 having a body base 52 and a projecting beam 53 and fitted with wheels 57 by which it can be moved along rails 58 between a preheat station and the casting station. The tundish car is fitted with a pair of tundish support structures 72 extending along the sides of the base 52 between a pair of upstanding front and rear structures 73, 74 standing up from the base 52. Tundish support structures 72 can be raised and lowered by operation of hoists 75, the ends of the structures 72 being fitted with slides 76 to slide in tracks 77 in the upstanding structures 73, 74 during such raising and lowering movements. Hoists 75 may be in the form of vertical hydraulic or pneumatic cylinders or mechanical jack units.

[0040] Tundish support structures 72 have a series of vertical slots 78 to receive a set of tundish support bosses 79 projecting laterally from the tundish 18.

[0041] Tundish 18 is installed in the tundish car by lifting it into a position over the car 60 between the upstanding structures 73, 74 and setting it down onto the tundish support structures 72, the support bosses 79 entering the vertical slots 78 in the support structures and coming to rest on support pads 81 at the bottom of the slots 78.

[0042] The tundish may be set down onto the support structures 72 while those structures are in lowered positions and the hoists 75 then actuated to lift the tundish into a raised position in the tundish car. Alternatively, the tundish could be initially fitted to the support structures 72 with those structures raised on the hoists 75 to hold the tundish in the raised position from the outset. The tundish is subsequently held by the hoists 75 in the raised position in the car 60 during preheating at the preheat station and transport to the casting station. At the casting station the tundish is lowered within the car 60 by actuation of hoists 75 to cause insertion of the outlet shroud 42 into the receiving shroud 50 of the distributor 19a.

[0043] The engagement of the tundish support bosses 79 with the support pads 81 at the bottom of slots 78 is such as to allow some degree of horizontal movement of the support bosses on the support structures, regardless of whether the support structures are in their raised or lowered positions.

[0044] The tundish is fitted at one or each side with a laterally projecting pin 82 and when the tundish is set down on the support structures 72 this pin engages a vertical guideway 83 in one of the front upstanding structures 73. Pin 82 is laterally aligned with a vertical center line 56 through the tundish outlet 40 and nozzle shroud 42. The engagement of the pin 82 with guideway 83 accordingly fixes the center line of the outlet and the shroud 42 relative to the tundish car. Pin 82 remains in engagement with guideway 83 throughout raising and lowering movements of the tundish by actuation of hoists 75 so as to maintain the alignment of the tundish outlet shroud. In this way the tundish is fixed in relation to the tundish car at the location of the center line of the outlet 40 and shroud 42, but it is allowed to thermally expand about this center line during preheating and subsequent assembly and operation of the caster, the engagement of the tundish support bosses 79 with the pads 81 at the bottom ends of slots 78 in the support structures allowing sufficient horizontal movement to accommodate the thermal expansion and contraction.

[0045] Each guideway 83 is formed by a pair of spaced, vertical plates 84,85 and the plate 85 is extended upwardly to form an upstanding abutment 86 to engage the respective laterally projecting pin 82 so as to provide initial horizontal location of the tundish as it is being set onto the support structures 72 such that the pin 82 is positioned directly above the guideway 83.

[0046] After preheating, the tundish car is driven along the track rails 58 by an electric motor drive to the casting station and is stopped accurately at a preset position at the casting station in which the center line 56 of the tundish outlet and shroud 42 are accurately aligned for insertion into the shroud 50 as indicated in FIG. 4, prior to operation of hoists 75 to lower the tundish. The tundish car is stopped accurately at the preset position by the interaction of an adjustable stop 87 and buffer 88 as illustrated in FIG. 5. Adjustable stop 87 is mounted on the tundish car. It comprises a head 89 and screw thread stem 91 to enable the position of the head to be adjusted and set with a nut 92. Buffer 88 is a two stage (low force/high force) positioning buffer fixed in a position adjacent one of the track rails 58. It comprises a cylinder 93, fitted with a protruding striker plunger 94 which initially slides along the cylinder against a low force resistance until it strikes a buffer plate 95 within the cylinder movement which is resisted by a high force compression spring 96.

[0047] As the tundish car approaches the casting station it is driven by the electric motor drive at low speed and fixed torque until the adjustable stop 87 engages the two stage positioning buffer 88. The setting of the initial low force resistance of buffer 88 is less than the drive motor fixed torque value whereas the higher buffer force is set greater than the fixed torque value of the drive motor at low speed so that the drive motor stalls at the chosen preset position with the tundish outlet and shroud 42 accurately aligned for subsequent lowering movement. At that time the drive motor may be switched off and a brake engaged to hold the tundish car in the required preset position. Alternatively, the brake may be engaged when the drive motor senses a step change in current as a consequence of the tundish car engaging the high force buffer.

[0048] 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. A method of preheating a tundish at a preheat station and moving the preheated tundish into an operative position for delivery of molten metal from an outlet thereof to a caster, comprising the steps of:

supporting the tundish on a moveable tundish car such that the tundish outlet is indexed to a set position relative to the tundish car and such that the tundish is located against horizontal movement at the position of a vertical center line through the outlet, but is free to move thermally about that position;

preheating the tundish at the preheating station while supported on the tundish car; and

moving the tundish car with the preheated tundish supported thereon to a set position over the caster in which the center line of the tundish outlet is in a predetermined alignment relative to the caster.

2. A method as claimed in claim 1, wherein the tundish outlet is fitted with a downwardly depending outlet nozzle shroud and the method comprises the further step of lowering the tundish so that the outlet nozzle shroud is inserted downwardly into a metal receiving component of the caster.

3. A method as claimed in claim 1, wherein the tundish is located against horizontal movement at the position of said vertical center line through the outlet by the further steps of:

providing the tundish with a formation projecting laterally from the tundish in lateral alignment with said vertical center line; and

putting the tundish onto the car such that said formation is engaged with a guide on the tundish car so as to index the position of the tundish outlet relative to the car and to restrain the tundish against horizontal movement at the position of the center line of the outlet, but to permit tundish expansion and contraction movement about that center line.

4. A method as claimed in claim 3, wherein said guide is vertical.

5. A method as claimed in claim 4, wherein said laterally projecting formation is a generally horizontal pin formation.

6. A method as claimed in claim 1, wherein the tundish is supported by engagement with tundish supports on the tundish car such as to permit horizontal movement of the tundish on the supports to accommodate the thermal movement.

7. A method as claimed in claim 6, wherein the tundish is supported on the supports by providing the tundish with laterally projecting elements and engaging those elements with the supports.

8. A method as claimed in claim 2, wherein the tundish is supported on hoists on the tundish car during preheating and movement of the tundish car to the set position and the hoists are then actuated to lower the tundish so that the outlet nozzle shroud is inserted downwardly into the metal receiving component of the caster.

9. A method of supporting in a support car a tundish having a metal flow outlet, said method comprising:

providing the tundish with a formation projecting laterally from the tundish in lateral alignment with a vertical center line through the tundish outlet and putting the tundish onto the car such that said formation is engaged with a guide on the tundish car so as to index the position of the tundish outlet relative to the car and to restrain the tundish against horizontal movement at the position of the center line of the outlet, but to permit tundish expansion and contraction movement about that center line.

10. A method as claimed in claim 9, wherein the formation projecting from the tundish is in the form of a boss or pin.

11. A method as claimed in claim 9, wherein the tundish is supported by engagement with tundish supports on the tundish car such as to permit horizontal movement of the tundish on the supports to accommodate the thermal movement.

12. A method as claimed in claim 11, wherein the tundish is supported on the supports by providing the tundish with laterally projecting elements and engaging those elements with the supports.

13. A method as claimed in claim 11, wherein the tundish is initially supported by hoists on the tundish car and the hoists are then lowered to engage the tundish with the support structure on the tundish car.

14. Casting apparatus comprising:

a caster to receive molten metal;

a tundish through which to deliver molten metal to the caster via a tundish outlet;

a tundish car for transport of the tundish between a tundish preheating station and the caster;

locating means to locate the tundish on the tundish car such that the tundish outlet is indexed to a set position relative to the tundish car and the tundish is restrained against horizontal movement at the position of a center line through the tundish outlet, but is free to move thermally about that position; and

tundish car setting means to set the tundish car at a predetermined position at the casting station.

15. Casting apparatus as claimed in claim 14, wherein the locating means comprises a formation projecting laterally from the tundish in lateral alignment with said vertical center line and a guide on the tundish car engagable with said formation to index the tundish outlet to the set position.

16. Casting apparatus as claimed in claim 15, wherein said guide is vertical.

17. Casting apparatus as claimed in claim 14, wherein the locating means further comprises tundish supports on the tundish car engagable with the tundish in such manner as to support the tundish but permit horizontal movement of the tundish at the supports to accommodate thermal movement.

18. Casting apparatus as claimed in claim 17, wherein the supports are carried on hoists mounted on the tundish car and operable initially to support the tundish in a raised position in the tundish car and subsequently to lower the tundish.

19. Casting apparatus as claimed in claim 14, wherein the tundish car setting means comprises a track along which to move the tundish car to the casting station, and a buffer located along the track to stop the tundish car at said predetermined position.

20. A refractory tundish and a moveable car to support the tundish, wherein the tundish is provided with a bottom outlet for flow of molten metal downwardly therefrom and with a lateral projection in lateral alignment with a vertical center line through the tundish outlet and the support car is provided with a guide to engage the tundish projection so as to index the position of the tundish outlet relative to the support car and to restrain the tundish against horizontal movement at the position of the center line of the tundish outlet while permitting expansion and contraction of the tundish about that location.

21. The combination claimed in claim 20, wherein the car is provided with tundish supports engagable with the tundish in such manner as to support the tundish on the car but permit horizontal movement of the tundish at the supports to accommodate thermal movement.