METHOD FOR CASTING METAL STRIP WITH EDGE CONTROL

Abstract

This disclosure concerns methods and apparatus for continuously casting thin strip where one or more expansion rings are positioned within at least one of a pair of casting rolls, and automatically measuring a thickness of the cast strip close to the first side edge of the strip using at least one sensor, and if the thickness measured is too thin, automatically decreasing the radial dimension of the expansion ring arranged in close proximity to the first side edge to cause the cylindrical tube to contract and increase the thickness of the cast strip during casting, and if the thickness measured indicates that the thickness of the cast strip is too thick, automatically increasing the radial dimension of the expansion ring arranged in close proximity to the first side edge to cause the cylindrical tube to expand and reduce the thickness of the cast strip during casting.

Claims

1. A casting roll control system with adjustable circumference control for use in a twin roll caster for producing cast strip metal, comprising: a casting roll including a casting surface formed by a cylindrical tube; a logic controller; a first expansion ring disposed within the cylindrical tube within 450 mm of an edge of the casting surface, the first expansion ring having at least one heating element and at least one temperature sensor adapted to provide signals indicative of expansion ring temperature, the temperature sensor being coupled to the logic controller, the first expansion ring being formed of a material that expands an outer diameter of the expansion ring when heated by the at least one heating element, thereby expanding an outer diameter of the casting surface corresponding to a location of the expansion ring; and a plurality of strip thickness sensors adapted to provide output signals indicative of a thickness of a cast strip capable of being arranged to make thickness measurements across a width of a cast strip in a line substantially perpendicular to the casting direction including an edge thickness and being coupled to the logic controller; wherein the logic controller is configured with instructions stored in nonvolatile memory to receive thickness measurements from the strip thickness sensors and temperature measurements from the at least one temperature sensor, fit a curve to the thickness measurements, determine a target edge thickness of the cast strip based on the curve, determine a delta thickness as a difference between the measured edge thickness and the target edge thickness and cause an amount of power applied to the at least one heating element to be adjusted to reduce the delta thickness.

2. The casting roll control system of claim 1, wherein the curve fitted to the thickness measurements is a polynomial function defining a parabola.

3. The casting roll control system of claim 1, wherein the target edge thickness is determined as an extrapolation of the curve fitted to the thickness measurements.

4. The casting roll control system of claim 1, wherein the target edge thickness is determined as an extrapolation of the curve fitted to the thickness measurements with a positive or negative offset added.

5. (canceled)

6. The casting roll control system of claim 1, further comprising a power controller coupled between the logic controller and the at least one heating element, wherein the power controller increases and decreases an amount of power being applied to the at least one heating element in response to a signal from the logic controller.

7. The casting roll control system of claim 1, wherein the logic controller is configured to periodically update the curve fitted to the thickness measurements based on new measurements, and periodically update the target edge thickness based on the updated curve.

8. The casting roll control system of claim 1, wherein the logic controller is configured to continuously update the curve fitted to the thickness measurements based on new measurements, and continuously update the target edge thickness based on the updated curve.

9. (canceled)

10. The casting roll control system of claim 1, wherein the logic controller is configured with instructions stored in non-volatile memory to cause an amount of power applied to the at least one heating element to be adjusted by determining a target temperature of the first expansion ring based on the delta thickness, measuring the temperature of the first expansion ring, determining a delta temperature as a difference between the measured temperature with the target temperature, and causing an amount of power applied to the at least one heating element to be adjusted to reduce the delta temperature.

11. The casting roll control system of claim 1, further comprising a second expansion ring disposed within 450 mm of an edge of the casting surface opposite the first expansion ring and controlled in a likewise manner.

12-18. (canceled)

19. The casting roll control system of claim 1, wherein the expansion ring is disposed inwardly from the edge of the casting surface.

20. A casting roll control system with adjustable circumference control for use in a twin roll caster for producing cast strip metal, comprising: a casting roll including a casting surface formed by a cylindrical tube; a logic controller; a first expansion ring disposed within the cylindrical tube and under a step which forms a shoulder of the casting surface, the first expansion ring having at least one heating element and at least one temperature sensor adapted to provide signals indicative of expansion ring temperature, the temperature sensor being coupled to the logic controller, the first expansion ring being formed of a material that expands an outer diameter of the expansion ring when heated by the at least one heating element, thereby expanding an outer diameter of the casting surface corresponding to a location of the expansion ring; and a plurality of strip thickness sensors adapted to provide output signals indicative of a thickness of a cast strip capable of being arranged to make thickness measurements across a width of a cast strip in a line substantially perpendicular to the casting direction including an edge thickness and being coupled to the logic controller; wherein the logic controller is configured with instructions stored in non-volatile memory to receive thickness measurements from the strip thickness sensors and temperature measurements from the at least one temperature sensor, fit a curve to the thickness measurements, determine a target edge thickness of the cast strip based on the curve, determine a delta thickness as a difference between the measured edge thickness and the target edge thickness and cause an amount of power applied to the at least one heating element to be adjusted to reduce the delta thickness.

21. The casting roll control system of claim 20, wherein the curve fitted to the thickness measurements is a polynomial function defining a parabola.

22. The casting roll control system of claim 20, wherein the target edge thickness is determined as an extrapolation of the curve fitted to the thickness measurements.

23. The casting roll control system of claim 20, wherein the target edge thickness is determined as an extrapolation of the curve fitted to the thickness measurements with a positive or negative offset added.

24. The casting roll control system of claim 20, further comprising a power controller coupled between the logic controller and the at least one heating element, wherein the power controller increases and decreases an amount of power being applied to the at least one hearing element in response to a signal from the logic controller.

25. The casting roll control system of claim 20, wherein the logic controller is configured to periodically update the curve fitted to the thickness measurements based on new measurements, and periodically update the target edge thickness based on the updated curve.

26. The casting roll control system of claim 20, wherein the logic controller is configured to continuously update the curve fitted to the thickness measurements based on new measurements, and continuously update the target edge thickness based on the updated curve.

27. The casting roll control system of claim 20, wherein the logic controller is configured with instructions stored in non-volatile memory to cause an amount of power applied to the at least one heating element to be adjusted by determining a target temperature of the first expansion ring based on the delta thickness, measuring the temperature of the first expansion ring, determining a delta temperature as a difference between the measured temperature with the target temperature, and causing an amount of power applied to the at least one heating element to be adjusted to reduce the delta temperature.

28. The casting roll control system of claim 20, further comprising a second expansion ring disposed under a step opposite the first expansion ring and controlled in a likewise manner.

29. The casting roll control system of claim 20, wherein the first expansion ring is aligned with an edge of the casting surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The invention is described in more detail in reference to the accompanying drawings in which:

[0064] FIG. 1 is a diagrammatical side view of a twin roll caster of the present disclosure;

[0065] FIG. 2 is an enlarged partial sectional view of a portion of the twin roll caster of FIG. 1 including a strip inspection device for measuring strip profile;

[0066] FIG. 2A is a schematic view of a portion of twin roll caster of FIG. 2;

[0067] FIG. 3A is a cross sectional view longitudinally through a portion of one of the casting rolls of FIG. 2 with two expansion rings spaced from the edge portions of the cast strip;

[0068] FIG. 3B is a cross sectional view longitudinally through the remaining portion of the casting roll of FIG. 3A joined on line A-A;

[0069] FIG. 4 is an end view of the casting roll of FIG. 3A on line 4-4 shown in partial interior detail in phantom;

[0070] FIG. 5 is a cross sectional view of the casting roll of FIG. 3A on line 5-5;

[0071] FIG. 6 is a cross sectional view of the casting roll of FIG. 3A on line 6-6;

[0072] FIG. 7 is a cross sectional view of the casting roll of FIG. 3A on line 7-7;

[0073] FIG. 8 is across sectional view longitudinally through a portion of a casting roll with an expansion ring spaced from the edge portions of the cast strip:

[0074] FIG. 9 is a cross sectional view longitudinally through a portion of a casting roll with an expansion ring spaced from the edge portions of the cast strip, the expansion ring being shifted relative to the expansion ring shown in the embodiment of FIG. 8;

[0075] FIG. 10 is a cross sectional view longitudinally through a portion of one of the casting rolls of FIG. 2 with two expansion rings spaced from the edge portions of the cast strip and an expansion ring corresponding to center portions of the cast strip;

[0076] FIG. 11 is a top view of a cast strip showing locations for measuring the cast strip thickness according to particular embodiments of the invention;

[0077] FIG. 12 is a cross sectional view of an expansion ring with water passages;

[0078] FIG. 13 is a side and cross sectional view of an expansion ring with heating elements;

[0079] FIG. 14 is a top view of a pair of casting rolls showing in each a pair of expansion rings where each ring is arranged in close proximity to both a side edge of the casting surface and a side edge of the cast strip, w here the expansion rings of one casting roll are offset relative to a corresponding expansion ring in the other casting roll;

[0080] FIG. 15 is a block diagram of a control system and casting roll;

[0081] FIG. 16 is a plot showing a plurality of thickness measurements taken along the width of a cast strip, where a polynomial curve has been fit to the plurality of thickness measurements in accordance with particular embodiments of the invention; and

[0082] FIG. 17 is a flow chart of a control process.

DETAILED DESCRIPTION OF THE DRAWINGS

[0083] Referring now to FIGS. 1, 2, and 2A, a twin roll caster is illustrated that comprises a main machine frame 10 that stands up from the factory floor and supports a pair of counter-rotatable casting rolls 12 mounted in a module in a roll cassette 11. The casting rolls 12 are mounted in the roll cassette 11 for ease of operation and movement as described below. The roll cassette 11 facilitates rapid movement of the casting rolls 12 ready for casting from a setup position into an operative casting position as a unit in the caster, and ready removal of the casting rolls 12 from the casting position when the casting rolls 12 are to be replaced. There is no particular configuration of the roll cassette 11 that is desired, so long as it performs that function of facilitating movement and positioning of the casting rolls 12 as described herein.

[0084] The casting apparatus for continuously casting thin steel strip includes the pair of counter-rotatable casting rolls 12 having casting surfaces 12A laterally positioned to form a nip 18 there between. Molten metal is supplied from a ladle 13 through a metal delivery system to a metal delivery nozzle 17 (core nozzle) positioned between the casting mils 12 above the nip 18. Molten metal thus delivered forms a casting pool 19 of molten metal above the nip 18 supported on the casting surfaces 12A of the casting rolls 12. This casting pool 19 is confined in the casting area at the ends of the casting rolls 12 by a pair of side closure plates, or side dams 20 (shown in dotted line in FIG. 2A). The upper surface of the casting pool 19 (generally referred to as the meniscus level) may rise above the lower one of the delivery nozzle 17 so that the lower end of the delivery nozzle 17 is immersed within the casting pool 19. The casting area includes the addition of a protective atmosphere above the casting pool 19 to inhibit oxidation of the molten metal in the casting area.

[0085] The ladle 13 typically is of a conventional construction supported on a rotating turret 40. For metal delivery, the ladle 13 is positioned over a movable tundish 14 in the casting position to fill the tundish 14 with molten metal. The movable tundish 14 may be positioned on a tundish car 66 capable of transferring the tundish 14 from a heating station (not shown), where the tundish 14 is healed to near a casting temperature, to the casting position. A tundish guide, such as rails 39, may be positioned beneath the tundish car 66 to enable moving the movable tundish 14 from the heating station to the casting position.

[0086] The movable tundish 14 may be fitted with a slide gate 25, actuable by a servo mechanism, to allow molten metal to flow from the tundish 14 through the slide gate 25, and then through a refractory outlet shroud 13 to a transition piece or distributor 16 in the casting position. From the distributor 16, the molten metal flows to the delivery nozzle 17 positioned between the casting rolls 12 above the nip 18.

[0087] The side dams 20 may be made from a refractory material such as zirconia graphite, graphite alumina, boron nitride, boron nitride-zirconia, or other suitable composites. The side dams 20 have a face surface capable of physical contact with the casting rolls 12 and molten metal in the casting pool 19. The side dams 20 are mounted in side dam holders (not shown), which are movable by side dam actuators (not show n), such us a hydraulic or pneumatic cylinder, servo mechanism, or other actuator to bring the side dams 20 into engagement with the ends of the casting rolls 12. Additionally, the side dam actuators are capable of positioning the side dams 20 during casting. The side dams 20 form end closures for the molten pool of metal on the casting rolls 12 during the casting operation.

[0088] FIG. 1 shows the twin roll caster producing the cast strip 21, which passes across a guide table 30 to a pinch roll stand 31, comprising pinch rolls 31A. Upon exiting the pinch roll stand 31, the thin cast strip 21 may pass through a hot rolling mill 32, comprising a pair of work mils 32A, and backup rolls 32B, forming a gap capable of hot rolling the cast strip 21 delivered from the casting rolls 12, where the cast strip 21 is hot rolled to reduce the strip to a desired thickness, improve the strip surface, and improve the strip flatness. The work rolls 32A have work surfaces relating to the desired strip profile across the work rolls 32A. The hot rolled cast strip 21 then passes onto a run-out table 33, where it may be cooled by contact with a coolant, such as water, supplied via water jets 90 or other suitable means, and by convection and radiation. In any event, the hot rolled cast strip 21 may then pass through a second pinch roll stand 91 to provide tension of the cast strip 21, and then to a coiler 92. The cast strip 21 may be between about 0.3 and 2.0 millimeters in thickness before hot rolling.

[0089] At the start of the casting operation, a short length of imperfect strip is typically produced as casting conditions stabilize. After continuous casting is established, the casting rolls 12 are moved apart slightly and then brought together again to cause this leading end of the cast strip 21 to break away forming a clean head end of the following cast strip 21. The imperfect material drops into a scrap receptacle 26, which is movable on a scrap receptacle guide. The scrap receptacle 26 is located in a scrap receiving position beneath the caster and forms part of a scaled enclosure 27 as described below. The enclosure 27 is typically water cooled. At this time, a water-cooled apron 28 that normally hangs downwardly from a pivot 29 to one side in the enclosure 27 is swung into position to guide the clean end of the cast strip 21 onto the guide table 30 that feeds it to the pinch roll stand 31. The apron 28 is then retracted back to its hanging position to allow the cast strip 21 to hang in a bop beneath the casting rolls 12 in enclosure 27 before it passes to the guide table 30 where it engages a succession of guide rollers.

[0090] An overflow container 38 may be provided beneath the movable tundish 14 to receive molten material that may spill from the tundish 14. As shown in FIG. 1, the overflow container 38 may be movable on rails 39 or another guide such that the overflow container 38 may be placed beneath the movable tundish 14 as desired in casting locations. Additionally, an optional overflow container (not shown) may be provided for the distributor 16 adjacent the distributor 16.

[0091] The scaled enclosure 27 is formed by a number of separate wall sections that lit together at various seal connections to form a continuous enclosure wall that permits control of the atmosphere within the enclosure 27. Additionally, the scrap receptacle 26 may be capable of attaching with the enclosure 27 so that the enclosure 27 is capable of supporting a protective atmosphere immediately beneath the casting rolls 12 in the casting position. The enclosure 27 includes an opening in the lower portion of the enclosure 27, lower enclosure portion 44, providing an outlet for scrap to pass from the enclosure 27 into the scrap receptacle 26 in the scrap receiving position. The lower enclosure portion 44 may extend downwardly as a part of the enclosure 27, the opening being positioned above the scrap receptacle 26 in the scrap receiving position. As used in the specification and claims herein, seal, sealed. sealing. and sealingly in reference to the scrap receptacle 26, enclosure 27, and related features may not be a complete seal so as to prevent leakage, but rather is usually less than a perfect seal as appropriate to allow control and support of the atmosphere within the enclosure 27 as desired with some tolerable leakage.

[0092] A rim portion 45 may surround the opening of the lower enclosure portion 44 and may be movably positioned above the scrap receptacle 26, capable of sealingly engaging and/or attaching to the scrap receptacle 26 in the scrap receiving position. The rim portion 45 may be movable between a sealing position in which the rim portion 45 engages the scrap receptacle 26, and a clearance position in which the rim portion 45 is disengaged from the scrap receptacle 26. Alternately, the caster or the scrap receptacle 26 may include a lifting mechanism to raise the scrap receptacle 26 into scaling engagement with the rim portion 45 of the enclosure 27, and then lower the scrap receptacle 26 into the clearance position. When sealed, the enclosure 27 and scrap receptacle 26 are filled with a desired gas, such as nitrogen, to reduce the amount of oxygen in the enclosure 27 and provide a protective atmosphere for the cast strip 21.

[0093] The enclosure 27 may include an upper collar portion 43 supporting a protective atmosphere immediately beneath the casting rolls 12 in the casting position. When the casting rolls 12 are in the casting position, the upper collar portion 43 is moved to the extended position closing the space between a housing portion 53 adjacent the casting rolls 12, as shown in FIG. 2, and the enclosure 27. The upper collar portion 43 may be provided within or adjacent the enclosure 27 and adjacent the casting rolls 12, and may be moved by a plurality of actuators (not shown) such as servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators.

[0094] The casting rolls 12 are internally water cooled as described below so that as the casting rolls 12 are counter-rotated, shells solidify on the casting surfaces 12A, as the casting surfaces 12A move into contact with and through the casting pool 19 with each revolution of the casting rolls 12. The shells are brought close together at the nip 18 between the casting rolls 12 to produce a thin cast strip product 21 delivered downwardly from the nip 18. The thin cast strip product 21 is formed from the shells at the nip IS between the casting rolls 12 and delivered downwardly and moved downstream as described above.

[0095] Referring now to FIGS. 3A-10, each carting roll 12 includes ft cylindrical tube 120 of a metal selected from the group consisting of copper and copper alloy, optionally with a metal or metal alloy coating thereon, e.g., chromium or nickel, to form the casting surfaces 12A. Each cylindrical tube 120 may be mounted between a pair of stub shaft assemblies 121 and 122. The stub shaft assemblies 121 and 122 have end portions 127 and 128, respectively (shown in FIGS. 4-6), which fit snugly within the ends of cylindrical tube 120 to form the casting roll 12. The cylindrical tube 120 is thus supported by end portions 127 and 128 having flange portions 129 and 130, respectively, to form internal cavity 163 therein, and support the assembled casting roll between the stub shaft assemblies 121 and 122.

[0096] The outer cylindrical surface of each cylindrical tube 120 is a roll casting surface 12A. The radial thickness of the cylindrical tube 120 may be no more than 80 millimeters thick. The thickness of the tube 120 may range between 40 and 80 millimeters in thickness or between 60 and 80 millimeters in thickness.

[0097] Each cylindrical tube 120 is provided with a series of longitudinal water flow passages 126, which may be formed by drilling long holes through the circumferential thickness of the cylindrical tube 120 from one end to the other. The ends of the holes are subsequently closed by end plugs 141 attached to the end portions 127 and 128 of stub shaft assemblies 121 and 122 by fasteners 171. The water flow passages 126 are formed through the thickness of the cylindrical tube 120 with end plugs 141. The number of stub shaft fasteners 171 and end plugs 141 may be selected as desired. End plugs 141 may be arranged to provide, with water passage in the stub shaft assemblies described below, in single pass cooling from one end to the other of the casting roll 12, or alternatively, to provide multi-pass cooling where, for example, the flow passages 126 are connected to provide three passes of cooling water through adjacent flow passages 126 before returning the water to the water supply directly or through the cavity 163.

[0098] The water flow passages 126 through the thickness of the cylindrical tube 120 may be connected to water supply in series with cavity 163. The water passages 126 may be connected to the water supply so that the cooling water first passes through cavity 163 and then the water supply passages 126 to the return lines, or first through the water supply passages 126 and then through cavity 163 to the return lines.

[0099] The cylindrical tube 120 may be provided with circumferential steps 123 at end to form shoulders 124 with the working portion of the roll casting surface 12A of the casting roll 12 there between. The shoulders 124 are arranged to engage the side dams 20 and confine the casting pool 19 as described above during the casting operation.

[0100] End portions 127 and 128 of stub shaft assemblies 121 and 122, respectively, typically sealingly engage the aids of cylindrical tube 120 and have radially extending water passages 135 and 136 shown in FIGS. 4-6 to deliver water to the water flow passages 126 extending through the cylindrical tube 120. The radial flow passages 135 and 136 are connected to the ends of at least some of the water flow passages 126, for example, in threaded arrangement, depending on whether the cooling is a single pass or multi-pass cooling system. The remaining ends of the water flow passages 126 may be closed by for example, threaded end plugs 141 as described where the water cooling is a multi-pass system.

[0101] As shown in detail by FIG. 7, water flow passages 126 may be positioned in annular arrays in the thickness of cylindrical tube 120 either in single pass or multi-pass arrays of water flow passages 126 as desired. The water flow passages 126 are connected at one end of the casting roll 12 by radial ports 160 to the annular gallery 140 and in turn radially flow passages 135 of end portion 127 in stub shaft assembly 121, and are connected at the other end of the casting roll 12 by radial ports 161 to annular gallery 150 and in turn radial flow passages 136 of end portions 128 in stub shaft assembly 121. Water supplied through one annular gallery, 140 or 150, at one end of the roll 12 can flow in parallel through all of the water flow passages 126 in a single pass to the other end of the roll 12 and out through the radial passages, 135 or 136, and the other annular gallery 150 or 140, at that other end of the cylindrical tube 120. The directional flow may be reversed by appropriate connections of the supply and return line(s) as desired. Alternatively or additionally, selective ones of the water flow passages 126 may be optionally connected or blocked from the radial passages 135 and 136 to provide a multi pass arrangement, such as a three pass arrangement.

[0102] The stub shaft assembly 122 may be longer than the stub shaft assembly 121. As illustrated in FIG. 3B, the stub shaft assembly 122 may be provided with two sets of water How ports 133 and 134. Water flow ports 133 and 134 are capable of connection with rotary water flow couplings 131 and 132 by which water is delivered to and from the casting roll 12 axially through stub shaft assembly 122. In operation, cooling water passes to and from the water flow passages 126 in the cylindrical tube 120 through radial passages 135 and 136 extending through end portions 127 and 128 of the stub shaft assemblies 121 and 122, respectively. The stub shaft assembly 121 is fitted with axial tube 137 to provide fluid communication between the radial passages 135 in end portions 127 and the central cavity within the casting roll 12. The stub shaft assembly 122 is fitted with an axial space tube, to separate a central water duct 138, in fluid communication with the central cavity 163, and from annular water flow duct 139 in fluid communication with radial passages 136 in end portion 128 of stub shaft assembly 122. Central water duct 138 and annular water duct 139 are capable of providing inflow and outflow of cooling water to and from the casting roll 12.

[0103] In operation, incoming cooling water may be supplied through supply line 131 to annular duct 139 through ports 133, which is in turn in fluid communication with the radial passages 136, gallery 150 and water flow passages 126, and then returned through the gallery 140, the radial passages 135, axial tube 137, central cavity 163, and central water duct 138 to outflow-line 132 through water flow ports 134. Alternatively, the water flow to, from and through the casting roll 12 may be in the reverse direction as desired. The water flow ports 133 and 134 may be connected to water supply and return lines so that water may flow to and from water How passages 126 in the cylindrical tube 120 of the casting roll 12 in either direction, as desired. Depending on the direction of flow, the cooling water flows through the cavity 163 either before or after flow through the water flow passages 126. It is appreciated that any other cooling variations may be employed as desired, such as single-pass cooling, by example.

[0104] As noted previously, each cylindrical tube may include two or more expansion rings. In an exemplary embodiment illustrated in FIG. 3A, each cylindrical tube 120 is provided with two expansion rings 210, each including an insulating coating 350 thereon. The two expansion rings are spaced apart and located on opposite end portions of the cylindrical tube 120 inward within 450 mm of edge portions of the cast strip formed during the casting campaign. These edge portions are also referred to herein as side edge portions of the strip, where the strip includes a pair of opposing side edges forming the strip width. FIG. 8 shows a cross sectional view longitudinally through a portion of a casting roll with expansion ring 210 with insulating coating 350 thereon spaced from the edge portions of the cast strip and having heating elements 370. In this embodiment, an expansion ring 210 is arranged in close proximity to both a side edge 125 of the casting surface CS and a side edge of a cast strip (when cast on the casting surface). Particularly, expansion ring 210 is arranged such that one side extent (an inner side) of the expansion ring width W.sub.210 is aligned with the casting surface CS side edge 125 (as well as being substantially aligned with shoulder 124 formed by side edge 125), where the width Who extends outwardly away from the center of the casting roll 12A and cylindrical tube 120. In appreciating that expansion rings may be arranged at other locations within cylindrical tube 120, with reference to an exemplary embodiment in FIG. 9, the inner side of expansion ring 210 is now offset towards the center of the casting roll 12A or cylindrical tube 120 from casting surface side edge 125 by an offset distance of .sub.125. By example, the expansion ring width is 67 mm and the offset distance Acs is 7 mm, although other distances may be employed as desired to achieve proper cast strip thicknesses.

[0105] Alternatively, as illustrated in FIG. 10, at least two expansion rings 210 with insulating coating 350 thereon are spaced on opposite end portions of the cylindrical tube 120 within 450 mm of edge portions of the east strip on opposite end portions of the casting rolls during the casting campaign, and an additional expansion ring 220 with insulating coating 330 thereon is positioned within cylindrical tube 120 at a position corresponding to center portions of the cast strip formed on the casting surfaces during casting.

[0106] In any embodiment, each expansion ring may have an annular dimension between 50 and 150 mm; (e.g. 70 mm). Similarly, the expansion ring or rings with an insulating coating thereon positioned at corresponding to center portions of the cast strip formed during casting may have an annular dimension between 50 and 150 mm; (e.g. 70 mm). Each expansion ring may have a width of up to 200 mm (e.g., 83.5 mm).

[0107] Deformation of the crown of the casting surfaces of the casting rolls may be automatically controlled, thereby automatically controlling the thickness near the side edge of the cast strip. This is achieved by automatically regulating the radial dimension of the at least one expansion ring located inside the cylindrical tube. While the expansion ring may expand in any desired manner, in particular instances the radial dimension of any expansion ring may be controlled by automatically regulating the temperature of the expansion ring. In turn, the thickness profile near each side edge of the cast strip may be controlled with by maintaining or altering the radius of the expansion ring and h turn the crown of the casting surfaces of the casting rolls. This thickness profile is also referred to as an edge drop. A minimum edge drop is often targeted, so that the thickness of the strip nearest a width wise side edge of the strip is not too thin. This thickness is also referred to as a side edge thickness. In addition to generating a side edge thickness that is under a desired thickness, a side edge thickness that is too thin will generate waves along the side edge (where the side edge thickness undulates), Edge drop may be determined by measuring the thickness at two or more widthwise locations relative a side edge, where the measured values are compared to any representation of a target thickness profile to determine if any adjustment to the cylinder diameter is required to achieve the desired strip thicknesses. In particular embodiments, two measurements of the strip thickness are taken near a side edge, the first measurement location being located furthest from the corresponding side edge while the second measurement location is located closer to the corresponding side edge. It is appreciated that each first and second location may be located at any desired locution. For example, with reference to FIG. 11 and cast strip 21, in certain embodiments the first location P1 is arranged a distance D.sub.P1 of 75 to 125 mm from a corresponding side edge 22 and the second location P2 is arranged a distance D.sub.P2 of 0 to 50 mm from the same side edge 22 in the direction of the cast strip width W.sub.21. The edge drop is determined by subtracting the thickness T2 measured at the second location P2 from the thickness T1 measured at the first location P1, which can be expressed as: T1T2=edge drop. It is appreciated that the target edge drop may be zero (0) (where T1=T2) or may be positive (that is, where T1>T2). For example, where a positive edge drop is targeted, the positive edge drop is 50 to 100 microns (m); however, other values are contemplated above or below this stated example.

[0108] Because the circumferential thickness of the cylindrical tube is made sufficiently thin, such as to a thickness of no more than 80 mm, for example, the crown of the casting surfaces may be deformed responsive to changes in the radial dimension of the expansion rings. To achieve this deformation, each expansion ring is adapted to change in radial dimension causing the cylindrical tube to expand or contract, and thereby change the crown of the casting surfaces and the thickness profile of the cast strip during casting. In the exemplary embodiment shown in FIG. 10, this is achieved by controlling the temperature of the expansion ring, where a power wire 222 and control wire 224 each extend from slip ring 240 to each expansion ring. Power wire 222 supplies electrical power to the expansion ring. Control wire 224 provides the temperature feedback that is then used to control the power of the expansion ring. As shown in FIG. 12, each expansion ring 210 may have water passages 340 therein wherein water can flow through. The water flow may be controlled by logic controller 72 to regulate the expansion of the expansion rings.

[0109] As previously noted, each expansion ring may be electrically heated to increase its radial dimension. Referring to die exemplary embodiment illustrated in FIG. 13, each expansion ring has at least one heating element positioned as desired to effectively heat the ring. Expansion ring 300 has heating element 310 on the right side and heating element 320 on the left side for that purpose. Each expansion ring may provide a heating input of up to 30 kW; preferably, of at least 3 kW. The force generated from the increase in radial dimension will be applied on the cylindrical tube causing the cylindrical tube to expand changing the crown of the casting surfaces and the thickness profile of the cast strip.

[0110] To achieve a desired thickness profile by control of the radial dimension of the expansion rings and control of the casting speed, a strip thickness profile sensor 71 may be positioned downstream to detect the thickness profile of the cast strip 21 as show n in FIGS. 2 and 2A. The strip thickness sensor 71 is provided typically between the nip 18 and the pinch rolls 31A to provide for direct control of the casting roll 12. The sensor may be an x-ray gauge or other suitable device capable of directly measuring the thickness profile across the width of the strip periodically or continuously. It is appreciated that in lieu of having one profile sensor, multiple sensors may be employed to measure the strip thickness at different corresponding locations across the strip width. For example, in particular instances, a plurality of non-contact type sensors are arranged across the cast strip 21 at the guide table 30 and the combination of thickness measurements from the plurality of positions across the cast strip 21 are processed by a logic controller 72 to determine the thickness profile of the strip periodically or continuously. The thickness profile of the cast strip 21 may be determined front this data periodically or continuously as desired. Logic controller 72 may be a dedicated logic controller or a general purpose computer with appropriate programming.

[0111] The radial dimension of each expansion ring may be controlled independently from the radial dimension of the other expansion ring or rings. The radial dimension of the each expansion ring with an insulating coating thereon within and adjacent the strip edges of the casting rolls may be controlled independently from each other. Additionally, the radial dimension of the expansion rings within and adjacent the strip edges of the casting rolls may be controlled independently from the expansion ring or rings with insulating coating thereon corresponding to the center portions of the cast strip. The sensor 71 generates signals indicative of the thickness profile of the cast strip. The radial dimension of each expansion ring with an insulating coating thereon is controlled according to the signals generated by the sensor, which in turns control roll crown of the casting surfaces of the casting rolls during the casting campaign.

[0112] Furthermore, the casting roll drive may be controlled to vary the speed of rotation of the casting rolls, while also varying the radial dimension of the expansion ring responsive to the electrical signals received from the sensor 71 controlling in turn the roll crown of the casting surfaces of the casting rolls during the casting campaign.

[0113] The use of an insulating coating is helpful to control beat transfer from the expansion ring to the casting roll. In particular, heat transferred from the expansion rings to the casting rolls during casting is minimal with the insulating coating arranged thereon. Additionally, expansion rings including the insulating coating may be heated more rapidly than those without any such coating, which also allows an expansion ring to achieve a high effective temperature. In certain instances, an insulating coating of at least 0.010 inch in thickness (e.g. 0.025 mm) is desired to control or eliminate heat transfer from the expansion ring to the casting roll. While any insulating material suitable for its intended purpose for use on the expansion rings may be employed, in certain instances, the insulating coating comprises 8% Yttria stabilized zirconia, which may or may not be plasma sprayed onto the outside of an expansion ring. It is appreciated that five insulating coating may have a minimum thickness of at least 0.010 inch oral least 0.025 mm.

[0114] In each of these embodiments of the method and apparatus, the expansion rings may also have water passages there through to permit the flow of w ater through the passages in the rings, and regulate the water flow through those passages. The water flow is regulated by logic controller 72 to increase or decrease the diameter of the expansion rings and in turn cylindrical tube as desired, and control the shape of the casting rolls during a campaign.

[0115] With reference to an exemplary embodiment in FIG. 14, two expansion rings 210 are arranged in each cylindrical tube for each of the pair of casting rolls arranged in close proximity to a side edge 125 of each casting roll casting surface CS, although additional expansion rings could be employed at other locations in other variations. As noted previously, while each expansion ring in one casting roll may be arranged at a substantially identical axial location relative to a corresponding expansion ring in the other casting roll of a pair of casting rolls with regard to expansion rings arranged in close proximity to side edges of a cast strip or of a casting surface, in the instance shown, the pair of casting rings in one casting roll are arranged at a different axial location relative to a corresponding expansion ring in the other casting roll to offer more flexibility in controlling the cast strip thickness. This difference between corresponding expansion rings 210 in different casting rolls 12 is designated offset distance 210a. In this specific instance, two expansion rings arranged in one casting roll 12 (or cylindrical tube 120) closer to a center (or centerline) of the roll or tube than the two expansion rings arranged in the oilier roll or tube. While the expansion rings 210 in each casting toll 12 are symmetrically arranged within each corresponding casting roll 12, in other variations, asymmetrical arrangements may be employed within each casting roll, which may or may not provide a difference between offsets (210a) between corresponding side edges (125).

[0116] Edge thickness control relative to cast strip thickness may be achieved according to one aspect of the present invention. With reference to FIGS. 15-17, thickness measurements M.sub.T are taken substantially along a line extending directly across the cast strip width W.sub.21 in a direction perpendicular to the casting direction (that is, measurements are made in a line perpendicular to a lengthwise direction of the strip) in step 402 and provided to the logic controller 72. In the embodiment shown, the thickness measurements M.sub.T extend across the substantial width W.sub.21 of the strip. In accordance with certain embodiments of the methods described herein, a plurality of thickness measurements M.sub.T may be represented as a plot of thickness versus width in association with each widthwise location at which the measurement was taken across the strip width W.sub.21, as in FIG. 16. As noted elsewhere herein, one or more thickness measurements may only be taken in close proximity to the strip edge or along a greater portion than at the strip edge, such as along a half of the width W.sub.21, that is, up to a widthwise centerline CL of the strip width W.sub.21 or for the substantial full width W.sub.21 as exemplarily shown. It is appreciated that the measurements may be taken at constant or random intervals (spacings). For any series of thickness measurements taken across the cast strip width, the logic controller 72 performs a polynomial curve fit in step 404, such as by way of regression, to arrive at a polynomial curve P that best fits the plurality of measurements M.sub.T. The measurements may be updated periodically or continuously and logic controller 72 configured to fit a new curve to updated measurements. In the embodiment shown, the polynomial curve is a parabola and describes a cast strip having a convex thickness, where the center thickness is greatest and whereby the thickness gradually decreases towards the side edges 22. For a constant thickness strip, the measured thicknesses and curve fit would be linear.

[0117] Once a curve has been fit to the measured thicknesses and their locations along the strip width, a target edge thickness is computed based on the curve in step 406. The target edge thickness may comprise an extrapolation of the polynomial curve, or an extrapolation of the polynomial curve with a positive or negative offset added. The measured thickness of each edge is compared to the target edge thickness for each edge (which may be the same), anti a delta thickness is determined as a difference between the measured edge thickness and the target edge thickness in step 408. The measurements may be updated periodically or continuously, and delta thickness recalculated accordingly. In this way, edge thickness may be dynamically controlled relative to an overall profile of strip of metal as it is being cast, rather than having a static target thickness.

[0118] The above process may also be performed for each of one or more measured thicknesses capable of being altered by way of an expansion ring. These widthwise locations that may be affected by an expansion ring are at least located at or in close proximity to any widthwise location of an expansion ring, where such location may be any location of an expansion ring contemplated herein, including without limitation the widthwise location of any expansion ring shown in FIGS. 3A, 8, 9. It may be that a measured thickness arranged between a pair of expansion rings may be affected by expansion or contraction of the pair of expansion rings, so it is the effect of one or more (multiple) expansion rings that should be considered. Should the measured thickness deviate from the curve fit thickness at the same widthwise location, a corresponding expansion ring is expanded or contracted as needed to alter the measured thickness to correspond to the curve fit thickness. With reference to FIG. 16, measured thickness M.sub.T* is located along the strip width W.sub.21 at a location that was at or near a corresponding expansion ring 210 (shown in dashed imaginary lines) during its formation, and upon comparison with the fit curve P, a deviation A (variation) is determined. Thereafter, the outer diameter of the corresponding expansion ring is changed to reduce or eliminate the deviation A for subsequent strip formation. A corresponding expansion ring is one that is located at or sufficiently near or in close proximity to the measured location along the width of the strip as it corresponds to its location along the casting roll. This correction of a measured thickness may be performed in relation to a measured thickness closely associated with any expansion ringwhether or not such expansion ring is located at or near a side edge of the strip or more centrally across the width of the strip. Of course, other variations may be performed in accordance with this disclosure.

[0119] The diameters of the expansion rings are controlled by controlling a temperature of each expansion ring. Temperature control may be achieved with electric heating and water cooling. For example, for edge thickness control, the delta thickness may be used to determine a target temperature for the corresponding expansion ring in step 410. For example, the delta thickness may be integrated overtime to generate a target temperature. The temperature sensors of the expansion ring measure the temperature of the expansion ring in step 412 and provide signals indicative of that temperature to the logic controller 72. The logic controller 72 determines a delta temperature between the target temperature and the measured temperature in step 414, and causes power to the heating element 370 of the expansion ring to be increased or decreased to reduce the delta temperature in step 416. For example, logic controller 72 may be coupled to a power controller 73, which regulates power to the heating element 370. The power controller 73 may comprise one or more silicon controlled rectifiers (SCR). As the expansion ring expands (narrowing thickness) or contracts (increasing thickness), the logic controller 72 updates the delta thickness computations and target temperature computations. This process may be performed continuously or periodically on an iterative basis.

[0120] While principles and modes of operation have been explained and illustrated with regard to particular embodiments, it must be understood, however, that the invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.