Patent Description:
This invention relates to the casting of metal strip by continuous casting in a twin roll caster.

In a twin roll caster, molten metal is introduced between a pair of counter-rotated horizontal casting rolls that are cooled so that metal shells solidify on the moving casting roll surfaces and are brought together at a nip between them to produce a solidified strip product delivered downwardly from the nip between the casting rolls. The term "nip" is used herein to refer to the general region at which the casting rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle and nozzles located above the nip forming a casting pool of molten metal supported on the casting surfaces of the casting rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the casting rolls so as to restrict the two ends of the casting pool against outflow.

The twin roll caster is capable of continuously producing cast strip from molten steel through a sequence of ladles positioned on a turret. The molten metal is poured from each ladle in turn into a tundish and then into a moveable tundish before flowing through the metal delivery nozzle into the casting pool. The tundish enables the exchange of an empty ladle for a full ladle on the turret without disrupting the production of the cast strip. In casting thin strip by a twin roll caster, the casting rolls generally made of copper or copper alloy, usually coated with chromium or nickel, are cooled internally with cooling water enabling high heat fluxes and in turn rapid solidification of strip during casting, where the casting rolls undergo substantial thermal deformation from exposure to the molten metal. The crown of the casting surfaces of the casting rolls varies during a casting campaign. The crown of the casting surfaces of the casting rolls, in turn, determines the strip thickness profile, i.e., cross-sectional shape, of the thin cast strip produced by the twin roll caster. Casting rolls with convex (i.e., positive crown) casting surfaces produce cast strip with a negative (i.e. center thermal fatigue from the cyclic heat flux experienced during twin roll casting on larger cylinder masses), and are much less responsive due to their large thermal mass.

It has also been proposed to position expansion rings directly on a cylindrical tube, for example, of <NUM> millimeters thickness of copper and copper alloy, optionally with a coating of chromium or chromium alloy thereon, and having a plurality of longitudinal water flow passages extending through the tube to form casting rolls. This proposal was tried and failed. The heat provided to the expansion rings transferred into the cylindrical tube so the rings were not effectively responsive to the heat to expand the cylindrical tube to commercially control the shape of the crown of the casting surfaces of the casting rolls. Accordingly, there remains a need for a reliable and effective way to directly and closely control the shape of the crown of the casting surfaces of the casting rolls during casting, and in turn, the cross-sectional thickness profile of the thin cast strip produced by the twin roll caster.

<CIT>, which is considered to represent the closest prior art, discloses a method of continuously casting thin strip in which a thin portion is formed close to an outer circumferential portion of each opposite end portion of a pair of water cooling drums, and a thin annular member having a hot water flow passage therein is formed in between the thin portion and a shaft, each thin annular member being expanded when hot water is supplied to the hot water flow passages so as to deform the thin ends of the water cooling drums.

Other prior art systems are disclosed in <CIT> and <CIT>. Disclosed is a reliable and effective method of controlling casting roll crown and, in turn, the cross-sectional strip thickness profile, by controlling the crown of the casting surfaces of the casting rolls by expansion rings positioned within and adjacent cylindrical tubes forming the casting rolls. Accordingly, the present invention provides a method of continuously casting thin strip by controlling roll crown according to claim <NUM>. The at least two expansion rings are preferably spaced within <NUM> of edge portions of the cast strip.

The amount of power applied to the expansion rings may be varied based on the feedback from the at least one sensor, said sensor or sensors capable of sensing at least one of the following properties:.

and capable of generating digital or analogous (typically electrical) signals indicative of at least one of the above mentioned properties of the cast strip.

The insulating coating on each expansion ring is sufficiently thick to control or eliminate heat transfer from the expansion rings to the casting rolls. The insulating coating of at least <NUM> (<NUM>) inch in thickness according to the invention (in one embodiment <NUM> (<NUM> inch)) is necessary to have an effective control of heat transfer from the expansion ring to the casting roll. The insulating coating on each expansion ring may be plasma sprayed on the expansion rings. The insulating coating may be plasma sprayed with zirconia spray such as <NUM>% Yttria stabilized zirconia spray. Note that the insulating coating may additionally be applied to the cylindrical tube, but for economy and effectiveness the insulating coating should be applied to the expansion rings directly.

The at least one heating element of each expansion ring may be made of stainless steel, nickel or nickel alloy. The heating element or elements may be located as desired in each expansion ring. Each expansion ring may provide a heating input of up to <NUM> kW; preferably, of at least <NUM> kW.

Water flowing through the expansion rings may be regulated to expand or contract the expansion rings in radial dimension and, in turn, to increase or decrease the diameter of the cylindrical tube as desired to control the crown shape of the casting surfaces of the casting rolls during a campaign.

Moreover, the method of continuously casting thin strip by controlling roll crown may further comprise the step of controlling casting roll drive to vary the speed of rotation of the casting rolls while varying the radial dimension of the expansion rings responsive to at least one of the digital or analogous signals received from the at least one sensor and control roll crown of the casting surfaces of the casting rolls during the casting campaign.

Additionally, the method of continuously casting thin strip by controlling roll crown may comprise the step of positioning at least up to <NUM> expansion rings. Furthermore, the method of continuously casting thin strip by controlling roll crown may include the step of controlling casting roll drive to vary the speed of rotation of the casting rolls, while varying the radial dimension of the expansion rings with insulating coating spaced from the edge portions of the cast strip and the radial dimension of the expansion ring or rings with insulating coating corresponding to center portions of the cast strip responsive to electrical signals received from a sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign.

In each embodiment, the expansion rings may be made of an austenitic stainless steel such as <NUM>/<NUM> austenitic stainless steel. Each expansion ring may have an annular dimension between <NUM> to <NUM> millimeters; preferably, <NUM> millimeters. Each expansion ring may have a width of up to <NUM> millimeters; preferably up to <NUM>, more preferably <NUM> millimeters.

In each embodiment of the method, the crown of the casting surfaces of the casting rolls can readily be varied to achieve a desired thickness profile of the cast strip. Each expansion ring with an insulating coating thereon is adapted to increase or decrease in radial dimension and cause the cylindrical tube to expand changing crown of the casting surfaces of the casting rolls and the thickness profile of the cast strip. The thickness of the cylindrical tube may range between <NUM> and <NUM> millimeters in thickness or between <NUM> and <NUM> millimeters in thickness.

In each embodiment of the method, at least one sensor may be positioned downstream adapted to sense the thickness profile of the cast strip and generate electrical signals indicative of the thickness profile of the cast strip. The sensor may be located adjacent to pinch rolls through which the strip passes after casting. Crown control of the casting surfaces of the casting rolls may be achieved by controlling the radial dimension of each expansion ring responsive to electrical signals received from said sensor. Furthermore, crown control of the casting surfaces of the casting rolls may be achieved by controlling the casting roll drive to vary the speed of rotation of the casting rolls while also varying the radial dimension of each expansion ring responsive to the electrical signals received from the sensor.

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 expansion rings adjacent the strip edges on the casting surfaces of the casting rolls may be controlled independently from each other. Additionally, the radial dimension of the expansion rings adjacent the strip edges on the casting surfaces of the casting rolls may be controlled independently from the expansion ring or rings corresponding to the center portions of the cast strip.

The present invention further provides an apparatus for continuously casting thin strip for controlling roll crown according to claim <NUM>.

The at least one sensor may be located adjacent to pinch rolls through which the strip passes after casting.

The at least one sensor is preferably positioned downstream of the nip capable of sensing the thickness profile of the cast strip and generating electrical signals indicative of the thickness profile of the cast strip to control radial dimension of the expansion rings responsive to the electrical signals received from the sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign.

Furthermore, the apparatus for continuously casting thin strip by controlling roll crown may comprise a control system capable of controlling casting roll drive and varying the speed of rotation of the casting rolls, while varying the radial dimension of the expansion rings with an insulating coating thereon responsive to electrical signals received from the sensor to control the roll crown of the casting surfaces of the casting rolls during the casting campaign.

Moreover, the apparatus for continuously casting thin strip for controlling roll crown may further comprise a control system capable of controlling casting roll drive and varying the speed of rotation of the casting rolls, while varying the radial dimension of the expansion rings spaced from the edge portions of the cast strip and the radial dimension of the expansion ring or rings corresponding to center portions of the cast strip responsive to electrical signals received from the at least one sensor and control the roll crown of the casting surfaces of the casting rolls during the casting campaign.

In each embodiment of the apparatus, the expansion rings may be made of an austenitic stainless steel such as <NUM>/<NUM> austenitic stainless steel. Each expansion ring may have an annular dimension between <NUM> to <NUM> millimeters; (e.g., <NUM> millimeters). Each expansion ring may have a width of up to <NUM> millimeters; (e.g., <NUM> millimeters).

In each embodiment of the apparatus, each expansion ring with an insulating coating thereon is adapted to increase in radial dimension causing the cylindrical tube to expand and change crown of the casting surfaces of the casting rolls and the thickness profile of the cast strip during casting. Each expansion ring has at least one heating element that may be made of stainless steel, nickel or nickel alloy. The heating element or elements may be located around each expansion ring as desired. Each expansion ring may provide a heating input of up to <NUM> kW; preferably, of at least <NUM> kW.

Crown control of the casting surfaces of the casting rolls may be achieved by controlling the radial dimension of each expansion ring responsive to the electrical signals received from a sensor. Furthermore, crown control of the casting surfaces of the casting rolls may be achieved by controlling the casting roll drive to vary the speed of rotation of the casting rolls, while also varying the radial dimension of each expansion ring with an insulating coating thereon responsive to the electrical signals received from the sensor.

The radial dimension of the expansion rings adjacent the strip edges formed on the casting surfaces of the casting rolls may be controlled independently from each other. Additionally, the radial dimension of the expansion rings adjacent the strip edges formed on the casting surfaces of the casting rolls may be controlled independently from the expansion ring or rings corresponding to the center portions of the cast strip.

Again, in each of the embodiments of the method and the apparatus, the insulating coating of the expansion rings is sufficiently thick that the expansion ring can be heated to expand the expansion rings and control the crown shape of the casting rolls as desired during the casting campaign with a small amount of heat being conducted to the cylindrical tubing. An insulating coating of at least <NUM> (<NUM> inch) in thickness (e.g. <NUM> (<NUM> inch)) is effective. Note that the insulating coating may additionally be applied to the cylindrical tube, but for economy and effectiveness the insulating coating should be applied to the expansion rings directly during assembly for the expansion rings and casting rolls.

In each of these latest embodiments of the method and apparatus, the expansion rings may also have water passages there through to permit the flow of water through the passages in the rings, and regulate the water flow through those passages. The water flowing through the expansion rings may be regulated to expand or contract the expansion rings in radial dimension and, in turn, to increase or decrease the diameter of the cylindrical tube as desired to control the crown shape of the casting surfaces of the casting rolls during a campaign.

Various aspects of the invention will become apparent to those skilled in the art from the following detailed description, drawings and claims.

In order that the invention may be well understood, there will now be described embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:.

Referring now to <FIG>, <FIG>, and <FIG>, a twin roll caster is illustrated that comprises a main machine frame <NUM> that stands up from the factory floor and supports a pair of counter-rotatable casting rolls <NUM> mounted in a module in a roll cassette <NUM>. The casting rolls <NUM> are mounted in the roll cassette <NUM> for ease of operation and movement as described below. The roll cassette <NUM> facilitates rapid movement of the casting rolls <NUM> 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 <NUM> from the casting position when the casting rolls <NUM> are to be replaced. There is no particular configuration of the roll cassette <NUM> that is desired, so long as it performs that function of facilitating movement and positioning of the casting rolls <NUM> as described herein.

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

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

The movable tundish <NUM> may be fitted with a slide gate <NUM>, actuable by a servo mechanism, to allow molten metal to flow from the tundish <NUM> through the slide gate <NUM>, and then through a refractory outlet shroud <NUM> to a transition piece or distributor <NUM> in the casting position. From the distributor <NUM>, the molten metal flows to the delivery nozzle <NUM> positioned between the casting rolls <NUM> above the nip <NUM>.

The side dams <NUM> 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 <NUM> have a face surface capable of physical contact with the casting rolls <NUM> and molten metal in the casting pool <NUM>. The side dams <NUM> are mounted in side dam holders (not shown), which are movable by side dam actuators (not shown), such as a hydraulic or pneumatic cylinder, servo mechanism, or other actuator to bring the side dams <NUM> into engagement with the ends of the casting rolls <NUM>. Additionally, the side dam actuators are capable of positioning the side dams <NUM> during casting. The side dams <NUM> form end closures for the molten pool of metal on the casting rolls <NUM> during the casting operation.

<FIG> shows the twin roll caster producing the cast strip <NUM>, which passes across a guide table <NUM> to a pinch roll stand <NUM>, comprising pinch rolls 31A. Upon exiting the pinch roll stand <NUM>, the thin cast strip <NUM> may pass through a hot rolling mill <NUM>, comprising a pair of work rolls 32A, and backup rolls 32B, forming a gap capable of hot rolling the cast strip <NUM> delivered from the casting rolls <NUM>, where the cast strip <NUM> 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 <NUM> then passes onto a run-out table <NUM>, where it may be cooled by contact with a coolant, such as water, supplied via water jets <NUM> or other suitable means, and by convection and radiation. In any event, the hot rolled cast strip <NUM> may then pass through a second pinch roll stand <NUM> to provide tension of the cast strip <NUM>, and then to a coiler <NUM>. The cast strip <NUM> may be between about <NUM> and <NUM> millimeters in thickness before hot rolling.

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 <NUM> are moved apart slightly and then brought together again to cause this leading end of the cast strip <NUM> to break away forming a clean head end of the following cast strip <NUM>. The imperfect material drops into a scrap receptacle <NUM>, which is movable on a scrap receptacle guide. The scrap receptacle <NUM> is located in a scrap receiving position beneath the caster and forms part of a sealed enclosure <NUM> as described below. The enclosure <NUM> is typically water cooled. At this time, a water-cooled apron <NUM> that normally hangs downwardly from a pivot <NUM> to one side in the enclosure <NUM> is swung into position to guide the clean end of the cast strip <NUM> onto the guide table <NUM> that feeds it to the pinch roll stand <NUM>. The apron <NUM> is then retracted back to its hanging position to allow the cast strip <NUM> to hang in a loop beneath the casting rolls <NUM> in enclosure <NUM> before it passes to the guide table <NUM> where it engages a succession of guide rollers.

An overflow container <NUM> may be provided beneath the movable tundish <NUM> to receive molten material that may spill from the tundish <NUM>. As shown in <FIG>, the overflow container <NUM> may be movable on rails <NUM> or another guide such that the overflow container <NUM> may be placed beneath the movable tundish <NUM> as desired in casting locations. Additionally, an optional overflow container (not shown) may be provided for the distributor <NUM> adjacent the distributor <NUM>.

The sealed enclosure <NUM> is formed by a number of separate wall sections that fit together at various seal connections to form a continuous enclosure wall that permits control of the atmosphere within the enclosure <NUM>. Additionally, the scrap receptacle <NUM> may be capable of attaching with the enclosure <NUM> so that the enclosure <NUM> is capable of supporting a protective atmosphere immediately beneath the casting rolls <NUM> in the casting position. The enclosure <NUM> includes an opening in the lower portion of the enclosure <NUM>, lower enclosure portion <NUM>, providing an outlet for scrap to pass from the enclosure <NUM> into the scrap receptacle <NUM> in the scrap receiving position. The lower enclosure portion <NUM> may extend downwardly as a part of the enclosure <NUM>, the opening being positioned above the scrap receptacle <NUM> in the scrap receiving position. As used in the specification and claims herein, "seal," "sealed," "sealing," and "sealingly" in reference to the scrap receptacle <NUM>, enclosure <NUM>, 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 <NUM> as desired with some tolerable leakage.

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

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

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

Referring now to <FIG>, each casting roll <NUM> includes a cylindrical tube <NUM> 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 <NUM> may be mounted between a pair of stub shaft assemblies <NUM> and <NUM>. The stub shaft assemblies <NUM> and <NUM> have end portions <NUM> and <NUM>, respectively (shown in <FIG>),which fit snugly within the ends of cylindrical tube <NUM> to form the casting roll <NUM>. The cylindrical tube <NUM> is thus supported by end portions <NUM> and <NUM> having flange portions <NUM> and <NUM>, respectively, to form internal cavity <NUM> therein, and support the assembled casting roll between the stub shaft assemblies <NUM> and <NUM>.

The outer cylindrical surface of each cylindrical tube <NUM> is a roll casting surface 12A. The radial thickness of the cylindrical tube <NUM> may be no more than <NUM> millimeters thick. The thickness of the tube <NUM> may range between <NUM> and <NUM> millimeters in thickness or between <NUM> and <NUM> millimeters in thickness.

Each cylindrical tube <NUM> is provided with a series of longitudinal water flow passages <NUM>, which may be formed by drilling long holes through the circumferential thickness of the cylindrical tube <NUM> from one end to the other. The ends of the holes are subsequently closed by end plugs <NUM> attached to the end portions <NUM> and <NUM> of stub shaft assemblies <NUM> and <NUM> by fasteners <NUM>. The water flow passages <NUM> are formed through the thickness of the cylindrical tube <NUM> with end plugs <NUM>. The number of stub shaft fasteners <NUM> and end plugs <NUM> may be selected as desired. End plugs <NUM> 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 <NUM>, or alternatively, to provide multi-pass cooling where, for example, the flow passages <NUM> are connected to provide three passes of cooling water through adjacent flow passages <NUM> before returning the water to the water supply directly or through the cavity <NUM>.

The water flow passages <NUM> through the thickness of the cylindrical tube <NUM> may be connected to water supply in series with cavity <NUM>. The water passages <NUM> may be connected to the water supply so that the cooling water first passes through cavity <NUM> and then the water supply passages <NUM> to the return lines, or first through the water supply passages <NUM> and then through cavity <NUM> to the return lines.

The cylindrical tube <NUM> may be provided with circumferential steps <NUM> at end to form shoulders <NUM> with the working portion of the roll casting surface 12A of the casting roll <NUM> there between. The shoulders <NUM> are arranged to engage the side dams <NUM> and confine the casting pool <NUM> as described above during the casting operation.

End portions <NUM> and <NUM> of stub shaft assemblies <NUM> and <NUM>, respectively, typically sealingly engage the ends of cylindrical tube <NUM> and have radially extending water passages <NUM> and <NUM> shown in <FIG> to deliver water to the water flow passages <NUM> extending through the cylindrical tube <NUM>. The radial flow passages <NUM> and <NUM> are connected to the ends of at least some of the water flow passages <NUM>, 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 <NUM> may be closed by, for example, threaded end plugs <NUM> as described where the water cooling is a multi-pass system.

As shown in detail by <FIG>, cylindrical tube <NUM> may be positioned in annular arrays in the thickness of cylindrical tube <NUM> either in single pass or multi-pass arrays of water flow passages <NUM> as desired. The water flow passages <NUM> are connected at one end of the casting roll <NUM> by radial ports <NUM> to the annular gallery <NUM> and in turn radially flow passages <NUM> of end portion <NUM> in stub shaft assembly <NUM>, and are connected at the other end of the casting roll <NUM> by radial ports <NUM> to annular gallery <NUM> and in turn radial flow passages <NUM> of end portions <NUM> in stub shaft assembly <NUM>. Water supplied through one annular gallery, <NUM> or <NUM>, at one end of the roll <NUM> can flow in parallel through all of the water flow passages <NUM> in a single pass to the other end of the roll <NUM> and out through the radial passages, <NUM> or <NUM>, and the other annular gallery, <NUM> or <NUM>, at that other end of the cylindrical tube <NUM>. 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 <NUM> may be optionally connected or blocked from the radial passages <NUM> and <NUM> to provide a multi pass arrangement, such as a three pass.

The stub shaft assembly <NUM> may be longer than the stub shaft assembly <NUM>. As illustrated in <FIG>, the stub shaft assembly <NUM> may be provided with two sets of water flow ports <NUM> and <NUM>. Water flow ports <NUM> and <NUM> are capable of connection with rotary water flow couplings <NUM> and <NUM> by which water is delivered to and from the casting roll <NUM> axially through stub shaft assembly <NUM>. In operation, cooling water passes to and from the water flow passages <NUM> in the cylindrical tube <NUM> through radial passages <NUM> and <NUM> extending through end portions <NUM> and <NUM> of the stub shaft assemblies <NUM> and <NUM>, respectively. The stub shaft assembly <NUM> is fitted with axial tube <NUM> to provide fluid communication between the radial passages <NUM> in end portions <NUM> and the central cavity within the casting roll <NUM>. The stub shaft assembly <NUM> is fitted with an axial space tube, to separate a central water duct <NUM>, in fluid communication with the central cavity <NUM>, and from annular water flow duct <NUM> in fluid communication with radial passages <NUM> in end portion <NUM> of stub shaft assembly <NUM>. Central water duct <NUM> and annular water duct <NUM> are capable of providing inflow and outflow of cooling water to and from the casting roll <NUM>.

In operation, incoming cooling water may be supplied through supply line <NUM> to annular duct <NUM> through ports <NUM>, which is in turn in fluid communication with the radial passages <NUM>, gallery <NUM> and water flow passages <NUM>, and then returned through the gallery <NUM>, the radial passages <NUM>, axial tube <NUM>, central cavity <NUM>, and central water duct <NUM> to outflow line <NUM> through water flow ports <NUM>. Alternatively, the water flow to, from and through the casting roll <NUM> may be in the reverse direction as desired. The water flow ports <NUM> and <NUM> may be connected to water supply and return lines so that water may flow to and from water flow passages <NUM> in the cylindrical tube <NUM> of the casting roll <NUM> in either direction, as desired. Depending on the direction of flow, the cooling water flows through the cavity <NUM> either before or after flow through the water flow passages <NUM>.

Each cylindrical tube <NUM> may be provided with at least one expansion ring with insulating coating thereon. As illustrated in <FIG>, cylindrical tube <NUM> may be provided with at least two expansion rings <NUM> each with an insulating coating <NUM> thereon spaced on opposite end portions of the cylindrical tube <NUM> inward within <NUM> of edge portions of the cast strip formed during the casting campaign. <FIG> shows a cross sectional view longitudinally through a portion of a casting roll with expansion ring <NUM> with insulating coating <NUM> thereon spaced from the edge portions of the cast strip and having heating elements <NUM>.

Alternatively, as illustrated in <FIG>, at least two expansion rings <NUM> with insulating coating <NUM> thereon are spaced on opposite end portions of the cylindrical tube <NUM> within <NUM> of edge portions of the cast strip on opposite end portions of the casting rolls during the casting campaign, and an additional expansion ring <NUM> with insulating coating <NUM> thereon is positioned within cylindrical tube <NUM> at a position corresponding to center portions of the cast strip formed on the casting surfaces during casting.

In another alternative, as illustrated back in <FIG>, expansion ring <NUM> with insulating coating <NUM> thereon may be positioned within the cylindrical tube <NUM>, at a position corresponding to center portions of the cast strip formed on the casting surfaces of the casting rolls during casting.

As illustrated in <FIG>, expansion rings with an insulating coating thereon may be position within and adjacent the cylindrical tube and spaced from the edge portions of the cast strip. Each expansion ring may have an annular dimension between <NUM> and <NUM>; (e.g. <NUM>). 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 <NUM> and <NUM>; (e.g. <NUM>).

Each expansion ring with an insulating coating spaced from the edge portions of the cast strip may have a width of up to <NUM> (e.g., <NUM>). Similarly, the expansion ring or rings with an insulating coating thereon positioned in the center portions of the cast strip during casting may have a width of up to <NUM> (e.g., <NUM>).

Deformation of the crown of the casting surfaces of the casting rolls may be controlled by regulating the radial dimension of the at least one expansion ring located inside the cylindrical tube. The radial dimension of the at least one expansion ring with an insulating coating thereon may be controlled by regulating the temperature of the expansion ring. In turn, the thickness profile of the cast strip may be controlled with the radius of the expansion ring and in turn the crown of the casting surfaces of the casting rolls. Since the circumferential thickness of the cylindrical tube is made to a thickness of no more than <NUM>, the crown of the casting surfaces may be deformed responsive to changes in the radial dimension of the expansion ring.

Each expansion ring with an insulating coating thereon is adapted to increase in radial dimension causing the cylindrical tube to expand changing the crown of the casting surfaces and the thickness profile of the cast strip during casting. Power wire <NUM> and control wire <NUM> extend from slip ring <NUM> to each expansion ring. Power wire <NUM> supplies electrical power to the expansion ring. Control wire <NUM> provides the temperature feedback that is then used to control the power of the expansion ring.

As shown in <FIG>, each expansion ring may have water passages <NUM> therein wherein water can flow through. The water flow may be controlled to regulate the expansion of the expansion rings.

Each expansion ring may be electrically heated increasing in radial dimension. As illustrated in <FIG>, each expansion ring may have at least one heating element positioned as desired to effectively heat the ring. Expansion ring <NUM> has heating element <NUM> on the right side and heating element <NUM> on the left side for that purpose. Each expansion ring may provide a heating input of up to <NUM> kW; preferably, of at least <NUM> 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. 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 <NUM> may be positioned downstream to detect the thickness profile of the cast strip <NUM> as shown in <FIG> and <FIG>. The strip thickness sensor <NUM> is provided typically between the nip <NUM> and the pinch rolls 31A to provide for direct control of the casting roll <NUM>. 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. Alternatively, a plurality of non-contact type sensors are arranged across the cast strip <NUM> at the roller table <NUM> and the combination of thickness measurements from the plurality of positions across the cast strip <NUM> are processed by a controller <NUM> to determine the thickness profile of the strip periodically or continuously. The thickness profile of the cast strip <NUM> may be determined from this data periodically or continuously as desired.

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 <NUM> 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.

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 <NUM> controlling in turn the roll crown of the casting surfaces of the casting rolls during the casting campaign.

It was found that an insulating coating is necessary to control heat transfer from the expansion ring to the casting roll. Conducted tests showed that the heat transfer from the expansion rings to the casting rolls during casting is minimal with the insulating coating thereon and the expansion rings can reach the desired temperature and expansion and, in turn, the desired cross-sectional strip thickness profile to commercially control the crown of the casting surfaces.

To illustrate, <FIG> shows tests conducted with and without the insulating coating on the expansion rings. An insulating coating of <NUM>% Yttria stabilized zirconia was plasma sprayed onto the outside of the expansion ring obtaining an insulating coating of thickness of <NUM> (<NUM> inch). Each expansion ring had a section of casting roll of approximately <NUM> in width shrink fitted on to the expansion ring. Each casting roll section had water passages there through. Water was supplied at approximately <NUM> bar (<NUM> psi) and the water flow varied between <NUM> and <NUM> gpm. The inlet water temperature was <NUM> (<NUM> °F). Separate tests were conducted at <NUM> % power and at <NUM> % power. As illustrated in <FIG>, when tested at <NUM> % power, the expansion ring resulted in a peak delta temperature of <NUM>. While the expansion ring with the insulating coating thereon resulted in a peak delta temperature of <NUM>, namely an increase of <NUM> % in the peak delta temperature. As illustrated in <FIG>, during the testing, heating of the uncoated expansion ring at <NUM> % power failed; whereas, the testing of the expansion ring with the insulating coating thereon at <NUM> % power resulted in a peak delta temperature of approximately <NUM>.

<FIG> shows a graph of the average expansion ring temperature versus the edge drop. The edge drop correlates to the thickness of the cast strip. As illustrated in <FIG>, the edge drop appears to respond each time to the changes in the heated expansion ring temperatures. As the temperature increases, the expansion ring expands; the cast trip thickness at the edge of the casting roll decreases and the edge drop increases.

<FIG> shows a graph of heated ring expansion versus temperature for expansion rings coated with an insulating coating. The expansion rings were located adjacent and within casting rolls provided with water passages there through and water flowing there through in normal casting operations. The coated expansion rings were heated from <NUM> to <NUM> (<NUM> °F to <NUM> °F). After holding briefly at <NUM> (<NUM> °F), the expansion rings with the insulating coating were heated to <NUM> (<NUM> °F) and <NUM> (<NUM> °F). As evidenced, over <NUM> of dimensional expansion was achieved when the coated expansion rings were heated by <NUM> (<NUM> °F). As illustrated, these results would have not been possible with uncoated expansion rings because of the heat transfer to the casting rolls. The expansion of the expansion ring is directly correlated to the temperature to which the expansion ring can be heated. As illustrated expansion rings coated with an insulating coating may be heated rapidly and achieve high effective temperature. As such, an insulating coating of at least. <NUM> (<NUM> inch) in thickness (e.g. <NUM> (<NUM> inch)) is essential to control or eliminate heat transfer from the expansion ring to the casting roll.

Claim 1:
A method of continuously casting thin strip by controlling roll crown comprising the steps of:
a. assembling a caster having a pair of counter rotating casting rolls (<NUM>) with a nip (<NUM>) there between capable of delivering cast strip downwardly from the nip (<NUM>), each casting roll (<NUM>) having a casting surface (12A) formed by a cylindrical tube (<NUM>) having thickness of no more than <NUM> millimeters of a material selected from the group consisting of copper and copper alloy, optionally with a metal or metal alloy coating thereon, and having a plurality of longitudinal water flow passages (<NUM>) extending through the cylindrical tube (<NUM>);
b. positioning at least two expansion rings (<NUM>) within and adjacent the cylindrical tube (<NUM>) and spaced within <NUM> of edge portions of the cast strip formed on opposite end portions of the casting rolls (<NUM>) during a casting campaign, and/or positioning at least one expansion ring (<NUM>) within the cylindrical tube (<NUM>) corresponding to center portions of the cast strip formed on the casting rolls (<NUM>) during casting, each expansion ring (<NUM>) having at least one heating element (<NUM>) and an insulating coating (<NUM>) of at least <NUM> (<NUM> inches), with the insulating coating (<NUM>) being such that when the cylindrical tube (<NUM>) is cooled with the longitudinal water flow passages (<NUM>) and the heating element (<NUM>) operated, one said expansion ring (<NUM>) with an insulating coating of <NUM> (<NUM> inches) is capable of achieving a temperature difference relative to the cylindrical tube (<NUM>) at least <NUM>% greater than a temperature difference that a similar but uncoated expansion ring could achieve under similar operating conditions;
c. assembling a metal delivery system capable of forming a casting pool (<NUM>) supported on the casting surfaces (12A) of the casting rolls (<NUM>) above the nip (<NUM>) with side dams (<NUM>) adjacent to the ends of the nip (<NUM>) to confine the casting pool (<NUM>); and
d. controlling the radial dimension of the expansion rings (<NUM>) responsive to at least one of digital or analogous signal received from at least one sensor (<NUM>) to control the roll crown of the casting surfaces (12A) of the casting rolls (<NUM>) during the casting campaign.