METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE OF THIN CAST STRIP

BACKGROUND AND SUMMARY

This invention relates to the casting of metal strip, such as steel 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 roll surfaces and are brought together at a nip between them to produce a solidified strip product, delivered downwardly from the nip between the rolls. The term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip, so forming a casting pool of molten metal supported on the casting surfaces of the 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 rolls so as to dam the two ends of the casting pool against outflow.

Further, the twin roll caster may be capable of continuously producing cast strip from molten steel through a sequence of ladles. Pouring the molten metal from the ladle into smaller vessels before flowing through the metal delivery nozzle enables the exchange of an empty ladle with a full ladle without disrupting the production of cast strip.

When casting steel strip in a twin roll caster, the strip leaves the nip at temperatures of the order of 1400 ⁰ C and

greater, and must be cooled to lower temperatures for desired microstructure, desired properties, and subsequent handling and processing. In the past, various methods have been attempted to solve this cooling problem. Traditionally, hydraulic nozzles were used for spray cooling. U.S. Patent No. 5,816,311 illustrates the use of hydraulic nozzles for spraying coolant such as water onto the cast strip. In these hydraulic cooling systems, however, heat from the cast strip having temperatures greater than about 600 ⁰ C cause the water to boil, developing a vapor film over the hot surface. At these high surface temperatures, the vapor film caused by film boiling acts as a barrier to the spray of cooling water. This prevents the cooling water from the hydraulic nozzles from directly contacting the surface, resulting in a low rate of heat transfer. This phenomena is known as the Leidenfrost Effect, and additional water spray and cooling time was required to achieve desired cooling. The amount of water usage and cooling times to overcome the disadvantages in the prior processes have a deleterious effect on the strip.

The presently disclosed method provides improved control over temperatures of the cast strip after hot rolling, reduce scale build-up, provide for more uniform cooling of the strip, and reduce the amount of water used in the casting process.

A method of producing thin cast strip (such as thin cast steel strip) is disclosed comprising the steps of:

a. assembling a thin strip caster having a pair of casting rolls having a nip there between and casting strip downwardly from the nip;

b. assembling a metal delivery system and forming a casting pool supported on casting surfaces of

the casting rolls above the nip with side dams adjacent the ends of the nip to confine the casting pool;

c. assembling adjacent the thin strip caster a hot rolling mill having work rolls with work surfaces forming a gap between them through which hot strip delivered from the casting rolls is rolled, the work rolls having work surfaces relating to the desired strip profile across the work rolls; and

d. positioning misting jets in intervals along the path of the cast strip exiting from the hot rolling mill to form a cooling zone, and cooling the strip in the cooling zone by directing a mixture of gas and water via misting jets toward surfaces of the cast strip, the mixture of gas and water having a ratio of gas over water between 9 to 1 and 90 to 1 (both measured in liters) to cool the cast strip at more than 1.6 ⁰ C per liter of water used.

The mixture of gas and water may have a ratio of gas over water between 20 to 1 and 70 to 1 (both measured in liters) . The gas used to form the mixture of gas and water may be selected from the group consisting of nitrogen, inert gas, and air. In the disclosed method, the water may have a turn down ratio of at least 10 to 1 by volume.

The method may also include:

e. forming a shroud extending from adjacent the hot rolling mill to at least an end of the cooling zone through which the cast strip moves during cooling; and

f . generating steam from heating the mixture of gas and water by the strip to form a protective

atmosphere of less than 5% oxygen in the shrouded cooling zone such that the strip exiting the cooling zone has less than about 2 micrometer, or micron, scale.

Nitrogen may be introduced into the shroud for various reasons at various locations, such as adjacent instrumentation to inhibit steam from affecting measurements in the protective atmosphere. The cooling zone may extend to pinch rolls positioned in the path of the cast strip.

The temperature of the strip at entry to the cooling zone may be greater than 75O ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C. More particularly, the temperature of the strip at entry to the cooling zone may be greater than 850 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C. Alternately, the temperature of the strip at entry to the cooling zone may be between 750 and 850 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C.

The cast strip exiting the cooling zone may have less than 20 ⁰ C in temperature variation across the width thereof. The cast strip is between about 0.3 and 2.0 millimeters in thickness .

Alternately, the method of producing thin cast strip with controlled cooling may include steps of assembling a thin strip caster having a pair of casting rolls having a nip there between and casting strip, such as cast steel strip, downwardly from the nip, assembling a metal delivery system and forming a casting pool supported on casting surfaces of the casting rolls above the nip with side dams adjacent the ends of the nip to confine the casting pool, and positioning misting jets in intervals along the path of the cast strip downstream of the casting rolls to form

a cooling zone, and cooling the strip in the cooling zone by the directing toward surfaces of the cast strip, the mixture of gas and water having a ratio of gas over water between 9 to 1 and 90 to 1 (both measured in liters) to cool the cast strip at more than 1.6 ⁰ C per liter of water used.

Additionally an apparatus is disclosed for casting thin cast strip (such as thin cast steel strip) , comprising

a. a thin strip caster having a pair of casting rolls having a nip there between capable of delivering cast strip downwardly from the nip;

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

c. a hot rolling mill positioned adjacent the thin strip caster having work rolls with work surfaces forming a gap capable of rolling hot strip delivered from the casting rolls, with work surfaces of the work rolls relating to the desired strip profile across the work rolls; and

d. misting jets positioned in intervals along the path of the cast strip exiting from the hot rolling mill to form a cooling zone, the misting jets capable of directing toward surfaces of the cast strip a mixture of gas and water having a ratio of gas over water between 9 to 1 and 90 to 1 (both measured in liters) to cool the cast strip at more than 1.6 ⁰ C per liter of water used.

The mixture of gas and water may have a ratio of gas over water between 20 to 1 and 70 to 1 (both measured in liters) . The gas used to form the mixture of gas and

water may be selected from the group consisting of nitrogen, inert gas, and air. In the apparatus for casting thin cast strip, the water may have a turn down ratio of at least 10 to 1 by volume.

The apparatus for casting thin cast strip may include:

e. a shroud extending from adjacent the hot rolling mill to at least end of the cooling zone through which the cast strip moves during cooling,

f . a protective atmosphere of less than 5% oxygen in the shrouded cooling zone comprising steam generated from heating the mixture of gas and water such that the strip exiting the cooling zone has less than 2 μm scale.

The apparatus for casting thin cast strip may be capable of introducing nitrogen into the shroud adjacent instrumentation to inhibit steam from affecting measurements in the protective atmosphere. The cooling zone may extend to pinch rolls positioned in the path of the cast strip.

The temperature of the strip at entry to the cooling zone may be greater than 750 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C. More particularly, the temperature of the strip at entry to the cooling zone may be greater than 85O ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C. Alternately, the temperature of the strip at entry to the cooling zone may be between 750 and 850 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C.

The cast strip at exit from the cooling zone may have less than about 80 ⁰ C in temperature variation across the width

thereof. Alternately, the cast strip at exit from the cooling zone may have less than 2O ⁰ C in temperature variation across the width thereof. The cast strip may be between about 0.3 and 2.0 millimeters in thickness.

Alternately, the apparatus for casting thin cast strip (such as cast steel strip) may include a thin strip caster having a pair of casting rolls having a nip there between capable of delivering cast strip downwardly from the nip, a metal delivery system capable of forming a casting pool supported on casting surfaces of the casting rolls above the nip with side dams adjacent the ends of the nip to confine the casting pool, and misting jets positioned in intervals along the path of the cast strip downstream of the casting rolls to form a cooling zone, the misting jets capable of directing toward surfaces of the cast strip a mixture of gas and water having a ratio of gas over water between 9 to 1 and 90 to 1 (both measured in liters) to cool the cast strip at more than 0.3 ⁰ C per second per liter of water used.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 is a partial sectional view through a pair of casting rolls mounted in the roll cassette of the caster shown in FIG. 1;

FIG. 3 is a partial sectional view of the enclosure of the twin roll caster of FIG. 1;

FIG. 4 is a diagrammatical plan view of the roll cassette of FIG. 3 removed from the caster;

FIG. 5 is a diagrammatical side view of the roll cassette of FIG. 3 removed from the caster; and

FIG. 6 is a partial diagrammatical side view of the twin roll caster of FIG. 1 including the enclosed cooling zone following the hot rolling mill of the caster.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIGS. 1 through 6, a twin roll caster for casting thin strip is illustrated that comprises a main machine frame 10 that stands up from the factory floor and supports a pair of 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 facilitates rapid movement of the casting rolls ready for casting from a setup position into an operative casting position in the caster as a unit, and ready removal of the casting rolls from the casting position when the casting rolls are to be replaced. There is no particular configuration of the roll cassette that is desired, so long as it performs that function of facilitating movement and positioning of the casting rolls as described herein. The following description is in the context of casting thin steel strip.

The twin roll caster for continuously casting thin strip includes the pair of counter-rotatable casting rolls 12 having casting surfaces 12A laterally positioned to form a nip 18 there between. Molten steel is supplied from a ladle 13 through a metal delivery system to a metal delivery nozzle 17, or core nozzle, positioned between the casting rolls 12 above the nip 18. Molten steel thus delivered forms a casting pool 19 of molten steel above the nip 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 closures or side dam plates 20 (shown in dotted line in FIG. 3) . 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 is immersed within the casting pool . 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 with molten metal.

The movable tundish 14 may be positioned on a tundish car 66 capable of transferring the tundish from a heating station (not shown) , where the tundish is heated to near a casting temperature, to the casting position. A tundish guide, such as rails, are 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 steel flows to the delivery nozzle 17 positioned between the casting rolls 12 above the nip 18.

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

At the start of the casting operation, a short length of imperfect steel strip is typically produced as casting conditions stabilize. After continuous casting is established, the casting rolls are moved apart slightly and then brought together again to cause this leading end of the strip to break away forming a clean head end of the following cast strip. 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 strip 21 onto the guide table 30 that feeds it to the pinch roll stand 31. The apron 28 is then retracted back to its hanging position to allow the cast strip 21 to hang in a loop beneath the casting rolls 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 steel that may spill from the tundish. As shown in FIGS. 1 and 2, 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 overflow container may be provided for the distributor 16 adjacent the distributor (not shown) .

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. Additionally, the scrap receptacle 26 may be capable of attaching with the enclosure 27 so that the enclosure 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, 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 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, 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 engages the scrap receptacle, and a clearance position in which the rim portion 45 is disengaged from the scrap receptacle. Alternately, the caster or the scrap receptacle may include a lifting mechanism to raise the scrap receptacle into sealing engagement with the rim portion 45 of the enclosure, and then lower the scrap receptacle 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 and provide a protective atmosphere for the cast strip.

As shown in FIG. 3, a lower plate 46 may be operatively positioned within or adjacent the lower enclosure portion 44 to permit further control of the atmosphere within the enclosure when the scrap receptacle 26 is moved from the scrap receiving position and provide an opportunity to continue casting while the scrap receptacle is being changed for another. The lower plate 46 may be operatively positioned within the enclosure 27 capable of closing the opening of the lower portion of the enclosure, or lower enclosure portion 44, when the rim portion 45 is disengaged from the scrap receptacle. Then, the lower plate 46 may be retracted when the rim portion 45 sealingly engages the scrap receptacle to enable scrap

material to pass downwardly through the enclosure 27 into the scrap receptacle 26.

The enclosure 27 may include an upper collar portion 43 supporting a protective atmosphere immediately beneath the casting rolls in the casting position. The upper collar portion 43 may be moved between an extended position capable of supporting the protective atmosphere immediately beneath the casting rolls and an open position enabling an upper cover 42 to cover the upper portion of the enclosure 27. The upper cover 42 may be movable along guide 64 by cover actuator 59, as shown on FIGS. 2 and 3. When the roll cassette 11 is in the casting position, the upper cover 42 is moved uncovering the upper portion of the enclosure 27, and the upper collar portion 43 is moved to the extended position closing the space between a housing portion 53 adjacent the casting rolls 12 and the enclosure 27, as shown in FIG. 2. The upper collar portion 43 may be provided within or adjacent the enclosure 27 and adjacent the casting rolls, and may be moved by a plurality of actuators (not shown) such as servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators. The twin roll caster illustratively may be of the kind described in U.S. Patent Application Serial No. 12/050,987, and reference may be made to that for appropriate constructional details. The disclosure in the US application is incorporated herein by cross-reference.

The roll cassette 11 with casting rolls may be assembled in a module for rapid installation in the caster in preparation for casting strip, and for rapid set up of the casting rolls 12 for installation. The roll cassette 11 comprises a cassette frame 52, roll chocks 49 capable of supporting the casting rolls 12 and moving the casting rolls on the cassette frame, and the housing portion 53 positioned beneath the casting rolls capable of supporting

a protective atmosphere in the enclosure 27 immediately beneath the casting rolls during casting. The housing portion 53 is positioned corresponding to and sealingly engaging an upper portion of the enclosure 27 for enclosing the cast strip below the nip.

A roll chock positioning system is provided on the main machine frame 10 having two pairs of positioning assemblies 50, 51 that can be rapidly connected to the roll cassette adapted to enable movement of the casting rolls on the cassette frame 52, and provide forces resisting separation of the casting rolls during casting. The positioning assemblies 50, 51 may include actuators such as mechanical roll biasing units or servo-mechanisms, hydraulic or pneumatic cylinders or mechanisms, linear actuators, rotating actuators, magnetostrictive actuators or other devices for enabling movement of the casting rolls and resisting separation of the casting rolls during casting.

The casting rolls 12 have copper peripheral walls formed with an internal series of longitudinally extending and circumferentially spaced water cooling passages, supplied with cooling water through the roll ends from water supply ducts in shaft portions 22, which are connected to water supply hoses 24 through rotary joints (not shown) . The casting rolls 12 may be about 500 millimeters in diameter, or may be up to 1200 millimeters or more in diameter. The length of the casting rolls 12 may be up to about 2000 millimeters, or longer, in order to enable production of strip product of about 2000 millimeters width, or wider, as desired in order to produce strip product approximately the width of the rolls. Additionally, the casting surfaces may be textured with a distribution of discrete projections, for example, as random discrete projections as described and claimed in U.S. Patent No. 7,073,565.

The casting surface may be coated with chrome, nickel, or other coating material to protect the texture.

As shown in FIG. 3, cleaning brushes 36 are disposed adjacent the pair of casting rolls, such that the periphery of the cleaning brushes 36 may be brought into contact with the casting surfaces 12A of the casting rolls 12 to clean oxides from the casting surfaces during casting. The cleaning brushes 36 are positioned at opposite sides of the casting area adjacent the casting rolls, between the nip 18 and the casting area where the casting rolls enter the protective atmosphere in contact with the molten metal casting pool 19. Optionally, a separate sweeper brush 37 may be provided for further cleaning the casting surfaces 12A of the casting rolls 12, for example at the beginning and end of a casting campaign as desired.

Once in operating position, the casting rolls are secured with the positioning assemblies 50, 51 connected to the roll cassette 11, drive shafts connected to the end couplings 23, and a supply of cooling water coupled to water supply hoses 24. A plurality of jacks 57 may be used to further place the casting rolls in operating position. The jacks 57 may raise the roll cassette 11 in the casting position, as shown in FIG. 2. Alternately, the roll cassette may be lowered or laterally moved in the casting position to place the casting rolls in operating position. The positioning assemblies 50, 51 may move at least one of the casting rolls 12 to provide a desired nip, or gap between the rolls in the casting position.

Each casting roll 12 is mounted in the roll cassette 11 to be capable of moving toward and away from the nip for controlling the casting of the steel strip product. The positioning assemblies 50, 51 include actuators capable of moving each casting roll toward and away from the nip as

desired. Position sensors are provided capable of sensing the location of the casting rolls and producing electrical signals indicative of each casting roll's position. A control system is provided capable of receiving the electrical signals indicating the casting roll's position and causing the actuators to move the casting rolls into desired position for casting metal strip. The apparatus for continuously casting strip may have separate actuators capable of moving each casting roll independently.

In operation, the cast steel strip leaves the nip at temperatures of the order of 1400 ⁰ C and greater. To prevent oxidation and scaling of the strip, the steel 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 steel strip until the first pinch roll stand 31, and may extend further along the path of the cast strip until the hot rolling mill 32 to reduce oxidation and scaling. After the hot rolling mill 32, the rolled steel strip then passes onto the runout table 33 where the strip is cooled by the spray misting jets 90.

The spray misting jets 90 are water spray misting jets capable of delivering a mixture of gas and water to the strip surface. The spray misting jets 90 provide small droplets of water at a sufficient velocity to penetrate a vapor film of steam caused by water boiling. By penetrating the vapor film, the droplets contact the surface of the strip and enable more effective heat transfer from the strip.

The spray misting jets 90 are in communication with a cooling header pipe (not shown) and one or more outlet valves capable of controlling the flow of coolant to the spray misting jets 90 as desired. Additionally, the spray

misting jets 90 are in communication with a supply of pressurized gas, such as nitrogen, inert gas, air, or a combination thereof. The pressure of the gas may be variable as desired. The turn down ratio of spray misting jets 90 may be about 10 to 1 at an approximately constant gas pressure. The turn down ratio is the ratio of the upper to lower water flow rates of the operating water flow rate range for a desired water pressure of a spray nozzle. The turn down ratio may be greater than about 10 to 1 at an approximately constant gas pressure, or alternately, may be less than 10 to 1.

The spray misting jets 90 are positioned in intervals along at least a portion of the path of the strip in a cooling zone 97, the misting jets directing toward surfaces of the strip a mixture of gas and water having a ratio of gas over water between 9 to 1 and 90 to 1 (both measured in liters) to cool the strip at more than 1.6 ⁰ C per liter of water used. Alternately, the mixture of gas and water may have a ratio of gas over water between about 20 to 1 and 70 to 1 (both measured in liters) .

The cooling zone 97 extends along the path of the strip exiting from the hot rolling mill 32, extending along the path of the strip between the hot rolling mill 32 and a second pinch roll stand 91. Alternately or in addition, the cooling zone 97 extends from the hot rolling mill 32 along the path of the strip to where the strip reaches a desired temperature. The strip exits the cooling zone 97 at temperature between about 300 ⁰ C and 700 ⁰ C as desired to provide a desired coiling temperature. Optionally, the hot rolling mill 32 may be omitted, and the cooling zone 97 extends along at least a portion of the path of the strip from adjacent the pair of casting rolls 12 to the second pinch roll stand 91. Alternately or in addition, the cooling zone 97 extends along at least a portion of

the path of the strip to where the strip reaches a desired temperature .

The temperature of the strip at entry to the cooling zone 97 may be greater than 750 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C as desired. More particularly, the temperature of the strip at entry to the cooling zone 97 may be greater than 850 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C as desired.

Alternately, the temperature of the strip at entry to the cooling zone 97 may be between 750 and 850 ⁰ C and the temperature of the strip at exit from the cooling zone may be greater than 300 ⁰ C as desired.

The spray misting jets 90 reduce the amount of cooling water used over previous hydraulic nozzles, and improved the evenness, or uniformity, in cooling of the strip. Using spray mist jets 90 in the cooling zone of FIG. 1, it was found that cast steel strip temperature dropped about 600 ⁰ C in about 5.25 seconds using about 380 liters of water, or 1.6 ⁰ C per liter of water used. In this test configuration, about 72 liters/second of water was delivered through the spray misting jets 90. Hydraulic nozzles used about 60% more water than the spray misting jets to achieve the same temperature reduction in this test configuration.

A venting hood may be provided over at least a portion of the cooling zone 97 to remove steam and water vapor generated by the cooling water on the hot strip. The steam may then be directed from the venting hood to a reclamation device capable of returning the coolant to the cooling system, delivering the coolant to a waste management system, or other disposition.

A shroud 99 may be provided extending from adjacent the hot rolling mill 32 to at least end of the cooling zone 97 through which the cast strip moves during cooling. A protective atmosphere of less than 5% oxygen may be provided in the shrouded cooling zone comprising steam generated from heating the mixture of gas and water such that the strip exiting the cooling zone has less than 2 μm scale. The shroud may be positioned to maintain a protective atmosphere of less than 5% oxygen until the strip reaches a desired temperature at the end of the cooling zone. Optionally, the hot rolling mill 32 may be omitted, and the shroud 99, with the enclosure 27, may extend from adjacent the pair of casting rolls 12 to at least the end of the cooling zone.

Nitrogen or other inert gas may be provided in the shroud 99 to inhibit oxidation of the strip. In addition, steam and water vapor generated by the cooling water boiling adjacent the surface of the strip may be retained in the shroud 99. The generated steam and vapor in the nitrogen or other inert gas atmosphere further inhibits oxidation by inhibiting the inflow of air containing reactive oxygen. By retaining steam and water vapor in the shroud 99, less nitrogen may be used to inhibit oxidation, further reducing cost of operation. The steam, water vapor, and excess cooling water may then be directed from the shroud to a reclamation device capable of returning the coolant to the cooling system, delivering the coolant to a waste management system, or other disposition.

Sensors such as x-ray gauges or other instrumentation may be provided above the run-out table 33 in advance the cooling water sprays 90, or following at least a portion of the cooling water sprays, to monitor thickness variations in the strip, surface quality, or other strip attributes . Nitrogen may be introduced into the shroud adjacent the instrumentation to inhibit water spray and

steam from affecting measurements in the protective atmosphere .

The cast strip having less than 2 μm scale exiting the cooling zone may be further processed, such as by cold rolling. The cast strip having less than 2 μm scale may be cold rolled without pickling.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.