CROSS-STRIP TEMPERATURE VARIATION CONTROL

Abstract

To achieve a substantially uniform microstructure across a continuously cast thin metal strip, it is beneficial to cool a width of the strip to a substantially constant temperature before further cooling the strip to reach any desired phase transformation temperature. Accordingly, methods of continuously casting a thin metal strip may include moving the thin strip to a cooling section, the cooling section having a plurality of coolant discharge ports configured to discharge a flow of coolant along the thin strip; initially sensing the temperature of the thin strip to determine a temperature distribution across the width of the thin strip, and producing a sensor signal corresponding to a sensed temperature at each of the first plurality of locations; and individually controlling the cooling across a width of the thin strip by way of the plurality coolant discharge ports in each zone of a first row using the determined temperature distribution.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S. provisional patent application No. 62/334,763, filed May 11, 2016 with the U.S. Patent and Trademark Office, which is also incorporated by reference.

BACKGROUND AND SUMMARY

This invention relates to the making of thin strip and more particularly to casting of thin strip by a twin roll caster. In a twin roll caster, molten metal is delivered from a delivery system to a casting pool supported on casting surfaces of a pair of counter-rotated horizontal casting rolls, which are internally water cooled so that solidified metal shells form on the moving casting roll surfaces. The metal shells 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 or nozzles located above the nip, to form the casting pool of molten metal supported on the casting surfaces of the casting rolls above the nip and extending the length of the nip. The casting pool is usually confined between side plates or side dams held in sliding engagement with end portions of the casting rolls to restrict the casting pool against outflow. The upper surface of the casting pool (generally referred to as the “meniscus” level) is usually above the lower end of the delivery nozzle so that the lower end of the delivery nozzle is immersed within the casting pool.

When casting steel strip by a twin roll caster, the thin strip exits the nip, passes across a guide table, through a pinch roll stand and then through a hot rolling mill, where the thin strip is reduced to a desired thickness. As the thin strip exits the hot rolling mill, the temperature distribution across the width of the thin strip is generally at variance. Thus, spray cooling the entire width of the thin strip with a constant flow may result in diverse microstructures and/or strip properties through the thin strip. As such, there is a need for a method to control the cross-strip temperature variation and provide more uniform temperature distribution across the width of the thin strip, as well as controlling the cooling rate of the thin strip to produce a final, cooled thin strip product having a desired microstructure and/or one or more desired material properties.

The presently disclosed method provides for selective control of temperatures across the width of the thin strip and provides for more uniform control of microstructure and properties of the strip. In certain embodiments, a method of continuously casting metal strip includes: assembling a pair of counter-rotatable casting rolls having casting surfaces laterally positioned to form a gap at a nip between the casting rolls through which thin strip less than 3 mm in thickness can be cast; assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent the ends of the nip to confine the casting pool; and counter rotating the casting rolls to form metal shells on the casting surfaces of the casting rolls that are brought together at the nip to deliver thin strip downwardly. In certain embodiments, such methods may include: moving the thin strip from the casting rolls through a hot rolling mill to reduce the thickness of the thin strip to a desired thickness and then to a cooling section, the cooling section having a plurality of coolant discharge ports configured to discharge a flow of coolant along the thin strip. It is appreciated that the coolant discharge ports may comprise any structure or mechanism configured to discharge coolant, such as a spray nozzle, tube, or orifice, for example. It is noted that in any embodiment discussed herein, any coolant discharge port may be employed as a substitute there for unless specifically noted otherwise. The plurality of coolant discharge ports are arranged into a plurality of rows each configured to substantially cool a full width of the thin strip. Because each coolant discharge port may discharge coolant in a pattern wider than the port itself, greater coverage may be attained, such as when the port is a spray nozzle, where the spray may discharge outwardly to form a pattern of spray wider than the nozzle itself. Accordingly, any row of discharge ports may be configured to discharge coolant across a full width of the strip without the row fully extending across the strip width. Each coolant discharge port is adapted to independently cool a portion of the thin strip across the width of the thin strip, where a first row of the plurality of rows is divided into three or more zones, each of the three or more zones including at least one of the plurality of coolant discharge ports.

Such methods may further include initially sensing the temperature of the thin strip at a first plurality of locations across the width of the thin strip prior to the first row to determine a temperature distribution across the width of the thin strip, and producing a sensor signal corresponding to a sensed temperature at each of the first plurality of locations, and individually controlling the cooling across the thin strip by way of the plurality coolant discharge ports in each zone of the first row using the temperature distribution determined in the step of initially sensing for the purpose of achieving a substantially uniform temperature across the width of the thin strip. After achieving a substantially uniform temperature substantially across the width of the thin strip, the methods further include substantially cooling the width having a substantially uniform temperature to achieve a desired microstructure extending substantially across the width of the thin strip.

After initially sensing an initial temperature distribution and initially cooling the thin strip using the initial temperature distribution, such methods may optionally include subsequently sensing a temperature of the thin strip at any of one or more locations along the thin strip or cooling section, that is, subsequent to sensing the temperature distribution at the first plurality of locations. For example, such methods described above may include subsequently sensing a temperature of the thin strip at a second plurality of locations across the thin strip to determine a temperature distribution across the width of the thin strip subsequent to the first plurality of locations and after individually controlling the cooling across the thin strip along the first row, and producing a sensor signal corresponding to a sensed temperature at each of the second plurality of locations. The subsequently sensed temperatures or temperature distributions may be employed any of a variety of ways to control the cooling of the thin strip.

These subsequently determined temperatures may be used to further control the cooling to achieve a substantially uniform temperature across the width of the thin strip, and/or may be used to determine that a substantially uniform temperature distribution has been achieved so thereafter the substantially full width of the strip may be together cooled to or below a desired phase transformation temperature and/or cooled by a particular cooling rate to achieve any desired cooling effects. In certain examples, the methods include subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of a second row of the plurality of rows using the temperature distribution determined in the step of subsequently sensing, to assist in achieving the substantially uniform temperature across the width of the thin strip and/or to achieve the particular microstructure in the thin strip at the end of the cooling section. In certain instances, the second row is located along the cooling section between the first row and the second plurality of locations across the thin strip or the end of the cooling section, or anywhere after the first row and the end of the cooling section.

It is appreciated that the second plurality of locations, when present, may be located anywhere along the cooling section, from the beginning to the end of the cooling section. In certain instances, where the first plurality of locations determines a temperature distribution at the beginning of the cooling section, the second plurality of locations is located between the beginning and the end, or at the end, of the cooling section. In other instances, the second plurality of locations is configured to determine a final temperature distribution across the thin strip, which may or may not be located at an end of the cooling section. It is also appreciated that the subsequently determined temperature distribution at the second plurality of locations may be used to control the first row of coolant discharge ports, in addition to, or without, using said subsequent temperature distribution to control any second row of coolant discharge ports, if present. It is also contemplated that additional cooling may be performed, which may be controlled. Accordingly, additional steps may include subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of any one or more additional rows of the plurality of rows, to assist in achieving the substantially uniform temperature across the width of the thin strip and/or to achieve the particular microstructure in the thin strip at the end of the cooling section.

Ultimately, as these methods are being performed, and as a result thereof, a thin strip is formed at the end of the cooling section having a particular microstructure and/or any desired material property extending substantially across the width of the thin strip. These methods perform this by cooling a width of the strip to achieve a substantially constant temperature, and in certain instances before reaching any phase transformation temperature, and then cooling the substantially constant temperature strip width to a desired temperature at any desired rate to achieve the substantially uniform microstructure and/or material property across the strip width.

“Substantially”, as used herein, represents that minor imperfections and/or variations may exist due to the imperfections in performing any process, whereby, even though minor imperfections may exist, an overwhelming majority is characterized as achieving the intended purpose or characterization, such as in cooling a full width of the thin strip or in forming a uniform microstructure across the full width of the thin strip.

As each of the plurality of rows are configured to substantially cool a full width of the thin strip, it is appreciated that for any row, the plurality of coolant discharge ports, each of which may comprise any structure or mechanism for discharging coolant, such as tubes, spray nozzles, or orifices, for example, may be arranged to extend partially or fully across the width of the cooling section or thin strip. It is appreciated that for any such row, the plurality of spray nozzles arranged in the row may also be arranged in a linear arrangement extending purely in the widthwise direction of the thin strip or cooling section, meaning, that the nozzles are arranged along a linear path extending in a direction normal to the direction of thin strip travel. In other variations, the row is across the width in a non-normal direction, that is, any direction biased to the normal direction, so long as the row extends substantially (that is, greater than 45 degrees from the direction of strip travel) in the widthwise direction of the thin strip or cooling section.

It is appreciated that, for any row of coolant discharge ports, the coolant discharge ports may be arranged along one or more headers, each header comprising a conduit, such as a tube or pipe, having a length extending at least partially across a width of the thin strip. The plurality of headers may comprise at least two headers. Alternatively, the plurality of headers may comprise at least three headers. The headers in the cooling section may have at least three or five zones, each zone having one or more coolant discharge ports adapted to independently cool the thin strip in each zone across the width with a coolant flow. Further, the zones in each header in the cooling section can be independently adjusted so that the temperature distribution across the strip after each header in the cooling section may be more uniform. It is also appreciated that in certain embodiments of the methods, the plurality of coolant discharge ports include coolant discharge ports spaced apart in a lengthwise direction of the thin strip as arranged in the multiple rows to continue to cool the thin strip as the thin strip translates along a length of the cooling section.

In controlling the cooling of the thin strip, such methods may utilize any known parameter. In certain exemplary embodiments of such methods, individually controlling the cooling of the thin strip in each zone of the first row is performed by controlling the discharge flow rate of any one or more of the plurality of the coolant discharge ports. This controlling may be achieved by controlling any available parameter. For example, in certain instances, individually controlling the cooling of the thin strip is performed by adjusting the discharge flow rate of one or more of the plurality of coolant discharge ports. Accordingly, any sensor configured to measure or monitor any desired parameter may be employed by a user or a controller for the purpose of controlling the cooling rate of the thin strip. For example, x-ray gauges may be employed to measure the thickness of the thin strip at any desired location.

The method of continuously casting metal strip may further comprise a controller. The controller may be adapted to control the coolant flow from the spray nozzles in each zone in the headers in the cooling zone to provide temperature regulation across the width of the thin strip at each header along the length of the cooling section.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be described in more detail, some illustrative examples will be given with reference to the accompanying drawings in which:

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

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;

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

FIG. 3 is a partial diagrammatical side view of the twin roll caster of FIG. 1 including a cooling section following a hot rolling mill;

FIG. 4 is a graphical representation of the cast thin strip temperature as the strip exits the hot rolling mill; and

FIG. 5 is an enlarged partial top view of another variation of the cooling section of FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description of the embodiments is in the context of high strength cast thin strip with microalloy additions made by continuous casting steel strip using a twin roll caster.

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.

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 rolls 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 end 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.

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 heated to near a casting temperature, to the casting position. A tundish guide (not shown) may be positioned beneath the tundish car 66 to enable moving the movable tundish 14 from the heating station to the casting position.

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 15 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.

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 shown), such as 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.

FIG. 1 shows the twin roll caster producing the cast thin 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 cast thin strip 21 may pass through a hot rolling mill 32, comprising a pair of work rolls 32A, and backup rolls 32B, forming a gap capable of hot rolling the cast thin strip 21 delivered from the casting rolls 12, where the cast thin 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 thin strip 21 then passes onto a run-out table 33 within cooling section 97, where it may be cooled by contact with a coolant, such as water, supplied via spray nozzles 90 or other suitable means, and by convection and radiation. In any event, the hot rolled cast thin strip 21 may then pass through a second pinch roll stand 91 having a pair of rollers 91A to provide tension of the cast thin strip 21, and then to a coiler 92.

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 thin strip 21 to break away forming a clean head end of the following cast thin 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 sealed 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 thin 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 thin strip 21 to hang in a loop beneath the casting rolls 12 in enclosure 27 before it passes to the guide table 30 where it engages a succession of guide rollers.

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.

The sealed enclosure 27 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 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

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 sealing 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 thin strip 21.

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.

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 cast thin strip product 21 delivered downwardly from the nip 18. The cast thin strip product 21 is formed from the shells at the nip 18 between the casting rolls 12 and delivered downwardly and moved downstream as described above.

A strip thickness profile sensor 71 may be positioned downstream to detect the thickness profile of the cast thin strip 21 as shown in FIGS. 2 and 2A. The strip thickness sensor 71 may be provided 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. Alternatively, a plurality of non-contact type sensors may be arranged across the cast thin strip 21 at the roller table 30 and the combination of thickness measurements from the plurality of positions across the cast thin strip 21 are processed by a controller 72 to determine the thickness profile of the strip periodically or continuously. The thickness profile of the cast thin strip 21 may be determined from this data periodically or continuously as desired.

In operation, the strip leaves the nip at temperatures of the order of 1400° C. and greater. To prevent oxidation and scaling of the strip, the metal strip is cast downwardly into the enclosure 27 supporting a protective atmosphere immediately beneath the casting rolls in the casting position. The enclosure 27 may extend along the path of the cast thin strip until the first pinch roll stand 31, and may extend along the path of the cast thin strip until the hot rolling mill 32 to reduce oxidation and scaling.

After the hot rolling mill 32, the rolled thin strip then passes into cooling section 97 via the run-out table 33 where the strip may be cooled by spray nozzles 90, or more generally coolant discharge ports. While spray nozzles atomize coolant to generate a spray, any coolant discharge port may be employed in any embodiment in lieu of spray nozzles. In addition to generating a spray, other types of coolant discharge ports may discharge a non-atomized flow of coolant. In the exemplary embodiment shown in FIG. 3, cooling section 97 extends along the path 99 of the strip between the hot rolling mill 32 and the second pinch roll stand 91 with multiple spray nozzles 90 arranged there between. Temperature sensors 100 are also provided to measure the temperature of the thin strip across its width as the strip exits the hot rolling mill and enters the cooling section 97 for final cooling prior to entering the coilers 92. Although it is not discernable in the view depicted in FIG. 3, a plurality of spray nozzles 90 are arranged to extend substantially across the strip width or the cooling section width in a widthwise arrangement forming a row. Each temperature sensor 100 is arranged in communication with a controller 110 to measure and monitor the temperature of the thin strip across its width. As shown in FIG. 3, this may be done at the beginning and end of the cooling section 97. Additionally, or alternatively, in other embodiments, the temperature of the thin strip may be measured across its width at any one or more locations between the beginning and end of the cooling section, such as to monitor the thin strip temperatures as it translates through the cooling section. This is shown in one exemplary embodiment in FIG. 5, which is discussed further below, where an intermediate sensor 100 is arranged between the beginning and end of the cooling section 97. Temperature sensors may each comprise any desired sensor, such as a pyrometer, for example. By measuring the temperature across the thin strip width at or near the beginning of the cooling section 97, any deviation in temperature across the strip width may be determined so cooling may be implemented to minimize or eliminate the temperature variation across the strip width. In doing so, the strip having a generally uniform temperature across its width may then be further cooled as needed to achieve a desired microstructure or material property at the end of the cooling section 97 or prior to entering the coilers 92.

At least knowing the discharge flow rate(s) of the spray nozzles (which may be variable), the location of the spray nozzles across the strip width, and the temperature distribution across the thin strip, individualized cooling may be accomplished to provide a generally uniform temperature across the strip width. Subsequently, the thin strip having a generally uniform (constant) temperature across its width is further cooled as desired to achieve a uniform microstructure and/or material property across the strip width. In certain examples, the thin strip exits the hot rolling mill within the austenitic temperature range and enters the coilers in the range of 200 to 700° C. with a martensitic or bainitic microstructure. Of course any desired microstructure or material property may be achieved as desired. It is appreciated that while spray nozzles are shown arranged along a top side of the thin strip within the cooling section, additional spray nozzles may be arranged along the bottom side of the thin strip.

As noted previously, as the thin strip exits the rolling mill, the temperature of the strip may be at variance across the width of the strip. This is illustrated in FIG. 4 according to one example, where the temperature across the center of a thin strip is much lower than the temperature adjacent the edges of the strip. Of course, other temperature variations may be present in other instances. As such, cooling the entire width of the strip with all coolant discharge ports at constant flow would produce strip cooling differently across the width of the strip. Stated differently, by applying coolant consistently across the width of a strip characterized as having a variable temperature distribution, cooler portions of the strip width are similarly cooled concurrently with warmer portions of the strip width. As a result, this approach does not facilitate the achievement of a uniform temperature across the strip width along the cooling section, but rather achieves the undesirable formation of different microstructures and/or material properties across the width of the thin strip. To avoid this result, the improved methods disclosed herein strategically cool warmer portions of the thin strip separately from, or different from, cooler portions of the strip width to more quickly achieve a generally uniform temperature across the width of the thin strip. Thereafter, the strip width is further cooled uniformly to a final temperature at any particular cooling rate to achieve a desired microstructure and/or material property across the strip width. This improves product quality and eliminates scrap.

By spacing the plurality of coolant discharge ports across the strip width in a widthwise arrangement, temperature variants across the width of the thin strip may be better controlled and generally eliminated. While each coolant discharge ports may operate independent of the other ports in each widthwise arrangement, in certain instances, the coolant discharge ports along each widthwise arrangement are arranged into one of a plurality of zones, where each zone within the widthwise arrangement is configured to discharge coolant along a particular portion of the strip width. In this way, each zone and each coolant discharge port contained therein may operate independent of other zones to independently cool particular widthwise portions of the strip as desired. In arranging the coolant discharge ports in a widthwise arrangement across the strip width or cooling section width, the ports are commonly arranged in a row. When in this row, commonly the coolant discharge ports are arranged along a common pipe or conduit, which is referred to as a header. This header is fluidly connected to a common coolant source, such as a reservoir. In other variations, while arranged in a row, the coolant discharge ports may be individually arranged separate from any common pipe or conduit, whether or not each is fluidly connected to a common coolant source.

It is also noted that coolant discharge ports are also spaced along the length of the cooling section, so to continue to cool the thin strip as it translates along the cooling section. This continued cooling may further to eliminate any temperature variation across the strip width, as necessary, and to cool the strip to achieve the desired microstructure and/or material property. In certain instances, the coolant discharge ports arranged along the cooling section length form multiple widthwise arrangements of coolant discharge ports spaced along the length of the cooling section. In certain instances, these widthwise arrangements of coolant discharge ports form a row. As noted previously, each row of coolant discharge ports may be arranged along a header or otherwise.

In an exemplary embodiment illustrated in FIG. 5, cooling section 97 includes a plurality of coolant discharge ports forming spray nozzles 90 arranged into two pluralities forming rows, each extending across the width, and in a widthwise direction, of each of the cooling section and the thin strip. Of particular note, each row of spray nozzles 90 is arranged along a header 120, which may be a pipe or other conduit fluidly connected to a coolant source. In particular, the spray nozzles 90 in each header 120 is arranged into one of three zones. Specifically, a first plurality P1 of nozzles 90 is divided into three zones (zones 1-3) and a second plurality P2 of nozzles 90 is divided into three zones (zones 4-6). While each zone in the first plurality P1 of spray nozzles 90 spans a width synonymous with a width of a zone in the second plurality P2 of spray nozzles 90, it is appreciated that the widthwise span of each zone may vary between pluralities of nozzles. And while each zone within each plurality P1, P2 spans an equal width, the widthwise span of each zone within any widthwise arrangement of nozzles may vary as desired in other embodiments.

With reference to FIG. 5, each zone has spray nozzles 90 adapted to independently cool the thin strip in each corresponding zone with a coolant flow. Each spray nozzle 90 is arranged such that the spray from each nozzle is closely arranged to spray from an adjacent nozzle or substantially abuts or overlaps spray from an adjacent nozzle across the width. Each zone may be independently controlled to regulate the coolant flow (i.e., flow rate) from any corresponding spray nozzle 90 to provide a desired temperature distribution across the width of the thin strip leaving each zone of each header.

As noted previously, the cooling section may also include temperature sensors for measuring the temperature distribution across the thin strip at any location along the cooling section as the thin strip translates. In this way, the temperature of the thin strip may be sensed at a plurality of locations across the width of the thin strip to determine a temperature distribution across the width of the thin strip. With reference to the exemplary embodiment shown in FIG. 5, sensors 100 measure the temperature distribution across the width of the thin strip entering and/or leaving each zone and produce a sensor signal corresponding to a sensed temperature at each of a plurality of locations across the strip width. In this instance, the widthwise temperature distribution is measured at different locations along the length of the strip using multiple sensors 100, one arranged at the beginning of the cooling section 97, one between the two rows P1, P2 of spray nozzles 90, and another at the end of cooling section 97. Each sensor 100 may comprise single sensor or a plurality of sensors arranged partially or fully across the width of the thin strip and/or of the cooling section 97. In this scenario, where the first sensor 100 measures the temperature distribution at the beginning of the cooling section, the second sensor 100 measures the temperature distribution between the beginning and the end of the cooling section, and the third sensor 100 measures the temperature distribution at the end of the cooling section so to control the cooling rate of the thin strip using coolant discharged from the plurality of spray nozzles 90 as the thin strip translates through the cooling section 97.

It is appreciated that by measuring the temperatures of the thin strip, tailored cooling of the thin strip may be achieved to obtain a desired microstructure and/or material property. To achieve this tailored cooling, for any known thin strip being made of a particular material and having a particular thickness, knowledge of other parameters may be helpful in addition to knowing the temperatures of the thin strip across its width. For example, knowing the length of the cooling section, the translation speed of the thin strip through the cooling section, the rate of coolant discharge from each coolant discharge port, and the distance between spray nozzles along the length of the cooling section. For example, for any given thin strip, at any given location along the thin strip width, if a variable temperature distribution is identified, cooling is controlled across the strip width to eliminate the temperature variation. This may be achieved by selectively discharging coolant from particular coolant discharge ports or zones, and/or controlling the discharge rate of coolant from any such port. Thereafter, the strip width now having a substantially uniform temperature is further cooled as desired to obtain a desired microstructure and/or particular material properties. It is desirable to eliminate any temperature variations as quickly as possible and well before the strip temperatures reach phase transformation temperatures to achieve substantially uniform mechanical properties across the strip width. In these instances, the port discharge rates may be increased or decreased as desired to achieve the desired cooling rates and the desired final temperature at the end of the cooling section. If at the end of the cooling section, or at any point along the length of the cooling section, it is determined that any target strip temperature is not being achieved, adjustments may be made, manually or automatically using any of the controllers, to the nozzle discharge rates across the cooling section width and/or length to better obtain the desired strip temperatures.

While it has been noted that any or all of the parameters may be altered manually, any or all may also be automatically controlled, which includes controlling the coolant flow from the spray nozzles in each zone. This automatic control may be achieved, by a controller, such as any controller 110 in FIGS. 3 and 5, to provide temperature regulation across the width of the thin strip. With specific reference to the embodiment shown in FIG. 3, sensors 100 are arranged at the beginning and at end of a cooling section 97, where the first measures the temperature at the beginning of the cooling section and the second sensor 100 measures the temperature distribution at the end of the cooling section so to control the cooling rate of the thin strip using coolant discharged from the plurality of spray nozzles 90 arranged along the thin strip as the thin strip translates through the cooling section 97. In this way, the thin strip moves from a pair of casting rolls through a hot rolling mill to reduce the thickness of the thin strip and then to a cooling section 97. As the thin strip approaches and/or departs each zone of each header, a controller is adapted to control the coolant flow from the coolant discharge port in each zone to provide temperature regulation across the width and/or length of the thin strip. Furthermore, the temperature of the thin strip approaching and/or departing each zone of the headers 120 in the cooling section 97 is measured and a sensor signal produced corresponding to the measured temperature in each zone along each header 120. Each zone is individually controlled by regulating the coolant flow from the coolant discharge ports in each zone along each header in the cooling zone to provide a desired temperature distribution across the width of the thin strip. Note that the desired temperature distribution across the strip is expected to be more uniform with each header 120 as the strip moves through the cooling section 97.

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

Claims

1. A method of continuously casting metal strip comprising:

assembling a pair of counter-rotatable casting rolls having casting surfaces laterally positioned to form a gap at a nip between the casting rolls through which thin strip less than 3 mm in thickness can be cast;

assembling a metal delivery system capable of forming a casting pool supported on the casting surfaces of the casting rolls above the nip with side dams adjacent the ends of the nip to confine the casting pool;

counter rotating the casting rolls to form metal shells on the casting surfaces of the casting rolls that are brought together at the nip to deliver thin strip downwardly;

moving the thin strip from the casting rolls through a hot rolling mill to reduce the thickness of the thin strip to a desired thickness and then to a cooling section, the cooling section having a plurality of coolant discharge ports configured to discharge a flow of coolant along the thin strip, the plurality of coolant discharge ports being arranged into a plurality of rows each extending at least partially across a width of the cooling section and configured to substantially cool a full width of the thin strip, where each coolant discharge port is adapted to independently cool a portion of the thin strip across the width of the thin strip, where a first row of the plurality of rows is divided into three or more zones, each of the three or more zones including at least one of the plurality of coolant discharge ports;

initially sensing the temperature of the thin strip at a first plurality of locations across the width of the thin strip prior to the first row to determine a temperature distribution across the width of the thin strip, and producing a sensor signal corresponding to a sensed temperature at each of the first plurality of locations;

individually controlling the cooling across the thin strip by way of the plurality coolant discharge ports in each zone of the first row using the temperature distribution determined in the step of initially sensing for the purpose of achieving a substantially uniform temperature substantially across the width of the thin strip;

after achieving a substantially uniform temperature substantially across the width of the thin strip, substantially cooling the width having a substantially uniform temperature to achieve a desired microstructure extending substantially across the width of the thin strip.

2. The method of claim 1 further comprising:

subsequently sensing a temperature of the thin strip at a second plurality of locations across the thin strip to determine a temperature distribution across the width of the thin strip subsequent to the first plurality of locations and after individually controlling the cooling across the thin strip along the first row, and producing a sensor signal corresponding to a sensed temperature at each of the second plurality of locations;

and,

subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of a second row of the plurality of rows using the temperature distribution determined in the step of subsequently sensing, to assist in achieving the substantially uniform temperature across the width of the thin strip and/or to achieve the particular microstructure in the thin strip at the end of the cooling section.

3. The method of claim 2, where the second row is located along the cooling section between the first row and the second plurality of locations across the thin strip.

4. The method of claim 3, where the temperature distribution determined in the step of subsequently sensing is a final temperature distribution sensed along the cooling section.

5. The method of claim 4, where the second plurality of locations are located at an end of the cooling section.

6. The method of claim 2, where the second plurality of locations are located after the beginning and up to the end of the cooling section.

7. The method of claim 2 further comprising:

subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of the first row using the temperature distribution determined in the step of subsequently sensing, to assist in achieving the substantially uniform temperature across the width of the thin strip.

8. The method of claim 1 further comprising:

subsequently sensing a temperature of the thin strip at a second plurality of locations across the thin strip to determine a temperature distribution across the width of the thin strip subsequent to the first plurality of locations and after individually controlling the cooling across the thin strip along the first row, and producing a sensor signal corresponding to a sensed temperature at each of the second plurality of locations; and,

subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of the first row using the temperature distribution determined in the step of subsequently sensing, to assist in achieving the substantially uniform temperature across the width of the thin strip.

9. The method of claim 8, where the temperature distribution determined in the step of subsequently sensing is a final temperature distribution sensed along the cooling section.

10. The method of claim 1, where individually controlling the cooling of the thin strip in each zone of the first row is performed by controlling the discharge flow rate of any one or more of the plurality of the coolant discharge ports.

11. The method of claim 10, where in individually controlling the cooling of the thin strip, is performed by adjusting the discharge flow rate of one or more of the plurality of coolant discharge ports.

12. The method of continuously casting metal strip as recited in claim 1, wherein the first row is divided into at least five zones.

13. The method of continuously casting metal strip as recited in claim 1 further comprising:

a controller adapted to control the coolant flow from the plurality of coolant discharge ports in each zone to provide temperature regulation across the width of the thin strip.

14. The method of claim 2 further comprising:

subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of any one or more additional rows of the plurality of rows, to assist in achieving the substantially uniform temperature across the width of the thin strip and/or to achieve the particular microstructure in the thin strip at the end of the cooling section.

15. The method of claim 14, where subsequently controlling the cooling across the thin strip by way of the coolant discharge ports in each zone of any one or more additional rows of the plurality of rows is performed using any temperature distribution determined in any one or more additional steps of subsequently sensing a temperature of the thin strip at any further plurality of locations across the thin strip to determine any further temperature distribution across the width of the thin strip subsequent to the first and second plurality of locations and after individually controlling the cooling across the thin strip along the one row and along the second row, and producing a sensor signal corresponding to a sensed temperature at each of the further plurality of locations.

16. The method of claim 1, where the plurality of coolant discharge ports are a plurality of spray nozzles.

17. The method of claim 2, where the temperature distribution determined in the step of subsequently sensing is a final temperature distribution sensed along the cooling section.

18. The method of claim 2, where the plurality of coolant discharge ports are a plurality of spray nozzles.

19. The method of claim 14, where the plurality of coolant discharge ports are a plurality of spray nozzles.