Method and device for rapidly cooling a metal strip and continuous production line for metal strips

Abstract

A device and method for rapidly cooling metal strips on a continuous production line, the device being arranged so as to cool the strip as it travels by spraying a liquid, or a mixture of a gas and a liquid, thereon by nozzles arranged on spraying units, wherein the cooling device includes spraying units that are rotatable on a plane perpendicular to the strip and perpendicular to the direction of travel of the strip, thereby making it possible to adjust a spraying angle of the spraying units that are movable relative to the strip.

Description

TECHNICAL FIELD

[0001] The invention relates to lines for processing metal strips equipped with a section for rapid cooling by spraying liquid or a mixture of liquid and gas, such as nitrogen or a mixture of nitrogen and hydrogen.

[0002] More particularly, the invention relates to the production of steels with very high yield strengths, typically in excess of 500 MPa, which require heat treatments with high rates of cooling, typically in excess of 200° C. / s, in order to establish complex structures with a variable distribution of different metallurgical phases, including austenitic, ferritic, pearlitic, bainitic and martensitic phases.

[0003] In particular, AHSS and UHSS very-high-yield-strength steels can be produced by controlling rates of cooling, from a fully austenitic or mixed ferritic and austenitic metallurgical structure.

[0004] The heat treatment to be applied to the strip depends on the chemical composition of the steel, its initial state, in particular its metallurgical structure and mechanical properties, and the metallurgical characteristics and mechanical properties expected at the end of the treatment. It includes, for example, a step of heating to a temperature of between 750° C. and 950° C., a holding time at this temperature followed by slow cooling, e.g. to 650° C., then ultra-fast quenching to room temperature or an intermediate temperature, e.g. 300° C., with a specific rate of cooling for each metallurgical grade.

[0005] For example, obtaining a given steel may require an annealing temperature higher than its austenitizing temperature, then a holding time at this temperature, followed by slow cooling for partial transformation of austenite into ferrite, and finally rapid cooling for transformation of austenite into martensite.TECHNICAL PROBLEMS ADDRESSED BY THE INVENTION

[0006] The quality of the products at the end of treatment, including their metallurgical characteristics, flatness and homogeneity of mechanical properties, depends on the thermal homogeneity of the products during the various heat treatment operations, consisting of a series of heating, temperature-holding and cooling steps.

[0007] In particular, the homogeneity of the metallurgical structure and mechanical properties at the end of treatment depends on the similarity of the thermal histories for all points across the width of the product.

[0008] Flatness depends on differences in expansion or contraction during heat treatment, observed in the length, width and thickness of the products, which cause internal stresses in the strip.

[0009] Stresses depend on:

[0010] The geometry of the product, i.e. the width, thickness and unevenness of the initial product,

[0011] The temperature distribution in the product, in the direction of travel and widthwise, and also in the thickness of the product for thick strips,

[0012] Variations in the thermo-physical properties of the product with variation in temperature during heat treatment.

[0013] Defects vary in type and extent depending on the cooling method applied and the type of steel in question.

[0014] Common flatness defects encountered during the heat treatment of metal strips of common low-yield-strength steels, for moderate rates of cooling below 200° C. / s, are typically transverse corrugations in response to interruptions in cooling slopes in the direction of travel of the product.

[0015] Common flatness defects encountered during the heat treatment of metal strips of high-yield-strength steels with complex metallurgical structures, for rapid cooling by spraying liquid, or by spraying a mixture of gas and liquid, and for rates of cooling in the range of 200° C. / s to 1000° C. / s, are typically longitudinal corrugations, e.g. long edges or a long center in response to thermal deviation between center and edges of the products.

[0016] Scattered blister defects may be observed when cooling is locally very heterogeneous, e.g. during immersion or spray cooling at low pressures.TECHNICAL BACKGROUND

[0017] According to the prior art, various technologies can be used to rapidly cool steel strips on a continuous line.

[0018] Liquid contact cooling allows slopes in excess of 200° C. / s to be obtained using three types of technology:

[0019] cooling by spraying a mixture of gas and liquid using dual-fluid nozzles,

[0020] cooling by spraying a liquid using single-fluid nozzles,

[0021] quenching by immersion in a liquid, optionally combined with liquid spraying.

[0022] According to the prior art, liquid contact rapid cooling technologies give rise to thermal heterogeneity as a result of a number of physical effects and technical constraints.

[0023] The first physical effect to consider is the Leidenfrost effect, which consists of a sudden increase in the convective heat transfer coefficient during the transition between the vapor-phase cooling regime and the liquid-phase cooling regime.

[0024] When cooling a high-temperature surface by liquid contact, immersion or spraying, all points on the surface follow a non-linear thermal path depending on the change in the heat transfer coefficient according to the four consecutive cooling regimes representative of liquid contact cooling:

[0025] For high temperatures of the cooled surface, typically above around 600° C., there is vapor film cooling. A layer of vapor completely isolates the strip from contact with the liquid, resulting in a stable, low heat transfer coefficient.

[0026] For intermediate temperatures defining a transition range, typically between around 600° C. and 200° C., the cooling regime is unstable and a sharp variation in the heat transfer coefficient is observed.

[0027] At lower temperatures, typically between around 200° C. and 100° C., there is nucleate boiling regime cooling, with a rapid decrease in the heat transfer coefficient as the surface temperature falls.

[0028] For low temperatures, typically below 100° C., the cooling regime is a convection regime.

[0029] Local thermal instability in the transition zone between vapor-phase cooling and liquid-phase cooling, usually observed between 600° C. and 200° C., can cause flatness defects in response to local thermal heterogeneity.

[0030] The second effect to consider is the discontinuity in the physical and mechanical properties of products observed during metallurgical phase transformations associated with rapid cooling methods, for example at 500° C. for a typical bainitic transformation temperature and at 350° C. for a typical martensitic transformation onset temperature.

[0031] In addition to the thermal stresses resulting from differences in expansion in the direction of travel of the product and across the width of the product, there are metallurgical phase transformation stresses, leading to a highly heterogeneous distribution of internal stresses, with alternating tensile and compressive stresses at different points in the product.

[0032] A first technical constraint lies in controlling the rate of cooling and final temperature for specific thermal cycles to obtain steels with complex structures such as TRIP, Q&P or CP steels.

[0033] Another technical constraint lies in controlling the difference in thermal efficiency across the width of the product, whatever the fluid used, resulting from the preferred flow paths of the fluid between the center and edges of the product in relation with nozzle arrangement, gas or liquid distribution heterogeneity related to feed geometry, initial unevenness or vibration of the strip.

[0034] Another technical constraint lies in controlling the discontinuity in cooling efficiency in the direction of travel of the product, created by equipment ancillary to cooling such as stabilizing rollers, water cutters or air cutters placed between the various spray sections to interrupt water runoff which disrupts product transverse homogeneity.

[0035] The constraints of controlling transverse thermal homogeneity, controlling cooling continuity in the direction of travel and controlling the precision of the final temperature cannot be effectively met with current immersion cooling methods according to the prior art.

[0036] Spray cooling methods allow adjustment of cooling in the direction of travel, for example by adjusting the longitudinal pitch between the rows of nozzles, adjusting the geometry of flat-jet or conical-jet nozzles and adjusting the characteristics of the cooling liquid.

[0037] FR2940978 from the applicant describes a method for controlling the homogeneity of cooling by spraying a liquid or a mixture of gas and liquid along the width and / or length of a metal strip by determining the region in which the vapor film disappears and adapting cooling parameters such as liquid temperature, speed, flow rate or droplet size and gas flow rate for cooling by spraying a mixture of gas and liquid in order to maintain the vapor phase at all points.

[0038] The invention does not allow thermal homogeneity control for thermal cycles with a final temperature below the Leidenfrost temperature (between 300° C. and 500° C.).

[0039] In addition, this method, which keeps spray cooling in the vapor film phase inefficient in terms of heat exchange, does not allow the cooling slopes required for the production of very-high-yield strength steels to be achieved.

[0040] FR 16 62421 from the applicant describes a cooling device with a variation in nozzle geometry in the direction of travel of the product in order to adjust heat transfer coefficients and maintain a constant rate of cooling for all cooling regimes.

[0041] This invention allows continuity of cooling to be controlled in the direction of travel of the product only.

[0042] FR 1911391 from the applicant describes a method for reducing flatness defects by adjusting the thermal path in the direction of travel of the product according to changes in metallurgical phase proportions, in particular for complex dual-phase steels, TRIP steels or martensitic steels.

[0043] The improvement in flatness results from the reduction in internal stresses in the strip by compensating for thermal stresses and microstructure change stresses.

[0044] The solutions described in the prior art generally improve product flatness by controlling cooling efficiency only in the direction of travel of the product, and sometimes also in the direction of width of the product.

[0045] According to the prior art, a common solution for adjusting cooling capacity across the width of the product is to split the cooling device into a plurality of cooling units arranged transversely and controlled independently in terms of cooling fluid flow rate.

[0046] The number of independent units is restricted by the constraints of industrial operation, typically five units equipped with fluid control valves, leading to discontinuous transverse control.

[0047] These solutions do not allow precise adjustment of cooling efficiency to the variable width of the product.

[0048] They do not allow cooling to be adjusted for the application of a variable thermal profile, e.g. convex or concave or more complex, wave shapes, for example to compensate for the effects of runoff along a preferred path related to an initial shape defect in the product.

[0049] They cannot correct an initial thermal profile that is not uniform across the width of the product.

[0050] The object of the invention is to provide a method for cooling a steel strip that improves upon the performance of the methods according to the prior art, in particular by allowing gradual and continuous adjustment of cooling efficiency in the direction of travel and in the transverse direction of the product, and which is adaptable according to the initial geometric and thermal state of the strip and its particular thermomechanical behavior as a result of its composition and the change in proportions of metallurgical phases.SUMMARY OF THE INVENTION

[0051] The invention provides improved control in the intensity of the cooling of the product according to the width and length thereof, in the method of rapid cooling by spraying liquid, or gas and liquid, in order to improve the homogeneity of metallurgical characteristics and mechanical properties and also improve the flatness of the steel strips at the end of the heat treatment.

[0052] According to a first aspect, the invention provides a cooling device for rapidly cooling metal strips on a continuous production line, the device being arranged so as to cool the strip as it travels by spraying a liquid, or a mixture of a gas and a liquid, thereon by means of nozzles arranged on spraying units, the invention being characterized in that the cooling device comprises spraying units that are rotatable on a plane perpendicular to the strip and perpendicular to the direction of travel of the strip, thereby making it possible to individually and multidirectionally adjust the spraying angle of said spraying units that are movable with respect to the strip.

[0053] With cooling by spraying liquid, or a mixture of gas and liquid, cooling efficiency depends mainly on the surface flow of liquid over the surface to be cooled.

[0054] The principle of the invention is based on a combination of, on the one hand, varying the area of impact of the jet from a nozzle on the strip, which depends on the distance of the nozzle from the cooled surface, the angle of inclination of the jet and the distance of the nozzles from one another and, on the other hand, simultaneously varying the lateral flow of liquid over the surface of the product from adjacent nozzles.

[0055] The invention is also based on controlling the location of the area of impact of the jets along the direction of travel of the product.

[0056] The device according to the invention allows gradual and continuous control of cooling efficiency by locally adjusting the total surface flow of liquid over each portion of the strip and controlling the location of the area of impact of the jets on the strip.

[0057] In particular, multidirectional adjustment of independent cooling units allows differentiated adjustment according to the thermal and geometric profile of the strip at the inlet to the cooling section and during cooling.

[0058] At a point on the strip, the total surface flow corresponds to the sum of the flow sprayed at this point by one nozzle, or at least two nozzles in the case of overlapping jets at this point, and the runoff flow over the strip resulting from other jets not impacting the strip at this point.

[0059] Runoff flows partly downward due to gravity but also in other directions due to the speed of a jet in these directions.

[0060] The movement of a rotatable spraying unit in a plane perpendicular to the strip and perpendicular to the direction of travel of the strip makes it easy to adjust a spraying angle of said movable spraying unit with respect to the strip for all of the nozzles that this spraying unit comprises. This rotation makes it possible to modify the location of the area of impact of the jets, as well as the size and shape of the area of impact of the jets produced by these nozzles.

[0061] According to one embodiment of the invention, the rotational movement of a movable spraying unit is obtained by means of a pivot element arranged on a first side of the movable spraying unit and a sliding element arranged on a second side of the movable spraying unit, opposite the first.

[0062] The pivot element is advantageously arranged on the side of the spraying unit closest to the center of the strip. Thus, the effect on cooling of the strip of the rotation of a spraying unit is more pronounced toward the edge of the strip.

[0063] According to one exemplary embodiment of the invention, two rotatable spraying units are arranged side by side in a direction defined by the strip width, the two rotatable spraying units covering the entire width of the strip, the pivot elements thereof being arranged in the vicinity of the center of the strip.

[0064] The two rotatable spraying units can be the same width, according to the strip width, each covering half the strip width. They can also be of different widths.

[0065] According to one exemplary embodiment of the invention, two rotatable spraying units are arranged on either side of a central spraying unit in a direction defined by the strip width, the three spraying units, covering the entire width of the strip, the pivot elements of the rotatable spraying units being proximal to the central spraying unit.

[0066] It is possible for the central spraying unit arranged between the two side units not to be rotatable.

[0067] Transverse division into three units allows constant cooling conditions to be maintained in the central portion while varying those at the edges of the strip by rotating the side units.

[0068] The length of the units, according to strip width, is determined in particular by the maximum width of the strip and by the size of the strip surface on the edges where cooling adjustment must be possible. Thus, the rotatable side portions may be longer or shorter than the central portion. The side portions may, for example, be twice as long as the central portion.

[0069] The side spraying units may be in one piece, or they may comprise at least two portions that are movable with respect to one another.

[0070] For example, if they comprise two rotatable portions, the portion farthest from the center of the strip can be rotatable with respect to the second portion about an axis of rotation located between the two portions.

[0071] In this configuration, a first rotation of the spraying unit can move the nozzles of both portions together away from the strip by the same angle, and a second rotation restricted to the portion farthest from the center of the strip can move the nozzles of this portion farther away still. Conversely, the nozzles of both portions together can be moved away from the strip by the same angle, and then those of the portion farthest from the center of the strip can be moved closer.

[0072] Similarly, a first rotation of the spraying unit can move the nozzles of both portions closer to the strip by the same angle, and a second rotation restricted to the portion farthest from the center of the strip can move the nozzles of this portion closer still. Conversely, the nozzles of both portions together can be moved closer to the strip by the same angle, and then those of the portion farthest from the center of the strip can be farther away.

[0073] According to another example, if spraying unit comprises two rotatable portions, the portion farthest from the center of the strip can be rotatable with respect to the second portion about an axis of rotation located in the vicinity of the end of the spraying unit farthest from the center of the strip.

[0074] The rotation of a first portion of a movable spraying unit with respect to a second portion of this movable unit can be obtained by means of a pivot element arranged on a first side of the first portion and a sliding element arranged on a second side of said first portion, opposite the first.

[0075] A sliding element may comprise a roller that rotates about its longitudinal axis.

[0076] The sliding element facilitates the rotation of the movable unit, or a portion thereof, by providing a mechanical support that reduces the weight to be borne by the pivot element.

[0077] According to the invention, the angle of rotation of a movable spraying unit is between −30° and +30° with respect to a plane parallel to the strip passing through the axis (61) of rotation of the movable unit. The angle of rotation of a first portion of a movable spraying unit with respect to a second portion of this movable unit may also be between −30° and +30°.

[0078] These large angular apertures allow a wide range of adjustment of the area of impact of the jets on the strip, in terms of position, shape and extent, particularly across the width of the strip.

[0079] A movable spraying unit comprises at least one row of nozzles in a direction parallel to the strip width. Advantageously, it comprises a plurality of rows of nozzles, for example five or ten rows.

[0080] A row of nozzles of a movable spraying unit forms a longitudinal axis parallel to the direction defined by the strip width. In one embodiment of the invention, a row of nozzles is rotatable about this longitudinal axis. Advantageously, at least two rows of nozzles of a movable spraying unit are rotatable about their respective longitudinal axes.

[0081] Advantageously, non-rotatable spraying units also have one or more rows of nozzles that are rotatable about their longitudinal axes.

[0082] The inclination of one or more rows of nozzles allows the location of the area of impact of said nozzles to be adjusted according to the length of the strip. It also makes it possible to influence the shape and extent of the area of impact of the jets on the strip. Modifying the inclination of the rows of nozzles thus allows the cooling profile of the strip to be controlled according to the length of the cooling section.

[0083] Nozzles are advantageously inclined along their longitudinal axis at critical points on the cooling profile of the strip, e.g. in the vicinity of the Leidenfrost point, where metallurgical transformations take place, or where equipment that introduces cooling discontinuities, such as stabilizing rollers, are located.

[0084] The angle of rotation of a row of nozzles of a movable spraying unit about its longitudinal axis is between −30° and +30° with respect to a plane perpendicular to the strip and perpendicular to the direction of travel of the strip comprising this longitudinal axis. This large angular aperture allows a wide range of adjustment of the area of impact of the jets on the strip, in terms of position, shape and extent, along the length of the strip.

[0085] According to one embodiment of the invention, the movable spraying units are translationally movable in a plane perpendicular to the strip and perpendicular to the direction of travel of the strip in order to adjust the spraying distance of said movable spraying units with respect to the strip.

[0086] Advantageously, any non-rotatable spraying units arranged in the center of the strip are also translationally movable in the same direction as the rotatable units.

[0087] All of the spraying units arranged across the same strip width can be arranged on a common frame so that they can be moved in translation simultaneously along the same length. Alternatively, each unit can be moved in translation independently of the others, allowing different distances with respect to the strip depending on the spraying unit.

[0088] Translational movement of the spraying units provides an additional means for acting on the shape and extent of the area of impact of the jets, and therefore the intensity of the cooling.

[0089] Advantageously, the translation of a movable spraying unit is possible over a distance with respect to the strip of between 50 and 500 mm, thereby providing a wide range of adjustment of the area of impact of the jets on the strip.

[0090] Translational movement of the movable spraying units can be achieved via a sliding element that slides in the plane perpendicular to the strip and perpendicular to the direction of travel. This sliding element reduces the force required to move the spraying units. The sliding element may comprise a slide or one or more rollers rotating about a longitudinal axis.

[0091] The two degrees of freedom of the movable spraying units, which result from a combination of rotational and translational movement, allow great freedom of adjustment and thus precise control of the intensity and distribution of the cooling of the strip. They allow a wide range of simultaneous adjustments in the distance and angle from which the cooling fluid is sprayed onto the moving strip.

[0092] The rapid cooling device according to the invention comprises all or some of the following features:

[0093] nozzles for spraying a liquid, or a mixture of gas and liquid, arranged on either side of the strip with respect to its plane of travel,

[0094] means for adjusting the area of impact of the jets of liquid, or a mixture of gas and liquid, on the product,

[0095] means for adjusting the flow rate of the cooling fluids,

[0096] means for measuring the temperature across the width of the product before spray cooling and after spray cooling,

[0097] means for measuring the flatness of the strip before spray cooling and after spray cooling,

[0098] means for calculating the metallurgical transformation temperatures of the strip according to its chemical composition and expected thermal cycles,

[0099] means for calculating the Leidenfrost temperature according to the characteristics of the spray nozzles installed in the cooling device, and the fluid flow rates applied to achieve the expected thermal cycles,

[0100] means for calculating the optimum temperature distribution across the width and in the direction of travel of the strip in the cooling zone,

[0101] means for controlling the cooling device, in particular adjusting the area of impact and flow rate of the cooling fluid.

[0102] According to the invention, the intensity of cooling of the strip can be controlled by adjusting the surface flow in the direction of travel and in the transverse direction of the strip.

[0103] Surface flow adjustment can be achieved by adjusting the amount of liquid, or mixture of gas and liquid, sprayed onto the strip. Cooling zones bounded by a transverse subdivision and a longitudinal subdivision can comprise elements for adjusting the amount of liquid, or mixture of gas and liquid, sprayed onto the strip. Thus, adjustment means can be used to adjust the feed rate of the nozzles along the length and / or across the width of the strip.

[0104] Surface flow adjustment can be achieved by adjusting the angle of rotatable spraying units. It can also be achieved by moving movable spraying units in translation without inclining the spraying units or in addition to inclining the spraying units.

[0105] Inclining jets toward the edges of the strip leads to an increase in the area of impact of these jets and to an increase in the degree of overlap of these contiguous jets at the edges of the strip.

[0106] The lateral flow of the liquid along the surface toward the edges of the strip compensates for the reduction in surface flow resulting from the increase in the area of impact with constant feed rate for a jet.

[0107] The combination of the redistribution of the overlap of the areas of impact and the flow of the liquid on the surface of the strip leads to an increase in the total flow rate received by the edges of the strip.

[0108] Similarly, inclining the jet toward the center of the strip leads to a decrease in the area of impact of the jet and to an increase in the degree of overlap of the contiguous jets in the center of the strip.

[0109] The combination of the redistribution of the overlap of the areas of impact and the flow of the liquid on the surface of the strip toward the center leads to an increase in the total flow rate received by the center of the strip.

[0110] According to one possibility afforded by the invention, the liquid, or the mixture of a gas and a liquid, may be non-oxidizing for the strip. The liquid is, for example, an aqueous solution comprising between 0.1% and 6% by weight formic acid. The gas is, for example, nitrogen, or a mixture of nitrogen and hydrogen.

[0111] Advantageously, the spray nozzles are staggered in rows of nozzles. For example, the nozzles of a second row are offset with respect to those of a first row, depending on the width of the strip, by half the distance between two nozzles. The nozzles arranged on either side of the strip are also staggered such that there are no opposing nozzles on either side of the strip.

[0112] The intensity of the cooling can also be regulated by adjusting the temperature of the cooling fluid in the direction of travel and in the transverse direction of the strip.

[0113] According to one embodiment of the invention, the rapid cooling device comprises at least three spraying units which are movable in the direction of travel of the strip and three spraying units which are movable across the strip width, each unit comprising at least two rows of nozzles that are rotatable about their longitudinal axes.

[0114] According to a second aspect, the invention provides a continuous production line for metal strips, characterized in that it comprises a cooling device according to the first aspect of the invention, the line further comprising means for determining the geometric transverse profile of the strip and means for determining the transverse temperature profile of the strip at the inlet to the cooling section.

[0115] The means for determining the geometric transverse profile of the strip is, for example, a laser or an optical camera.

[0116] The means for determining the transverse temperature profile of the strip is a pyrometer, for example.

[0117] Knowledge of the geometric transverse profile and of the temperature transverse profile of the strip at the inlet to the cooling section is used to adjust the intensity of the cooling across the width of the strip, depending on the nature of these profiles.

[0118] According to a third aspect, the invention provides method for rapidly cooling a moving strip on a continuous production line for metal strips by spraying a liquid, or a mixture of a gas and a liquid, thereon by means of a rapid cooling device according to the first aspect of the invention, characterized in that the intensity of the cooling is locally adjusted in a portion of strip by modifying the amount of surface flow of liquid over said portion by acting on the spraying angle of a movable spraying unit arranged in the vicinity of said portion.

[0119] Advantageously, the intensity of the cooling of a movable spraying unit can be refined by moving it toward or away from the strip by moving it in translation in a direction parallel to the plane perpendicular to the strip and perpendicular to the direction of travel.

[0120] According to the invention, the intensity of the cooling of a movable spraying unit is adjusted by acting on its spraying angle, and optionally on its distance from the strip, in order to minimize internal stresses that result from differences in temperatures of the strip in the direction of travel and in the transverse direction of the strip.

[0121] Advantageously, according to the invention, the method comprises a step of determining the geometric transverse profile and the temperature transverse profile of the strip at the inlet to the cooling section, and the intensity of the cooling in a portion of strip is locally adjusted by modifying the amount of surface flow of liquid over said portion according to said transverse profiles of the strip.

[0122] Modifying the amount of surface flow of liquid is advantageously obtained by adjusting the spraying angle of the nozzles.

[0123] Advantageously, the adjustment of the spraying angle, and optionally the spraying distance, is determined for each spraying unit according to the target temperature distribution over the length and across the width of the strip along the cooling section and the initial shape of the strip at the inlet to the cooling section and its change during cooling.

[0124] Advantageously, the method according to the invention further comprises a step of determining the thermomechanical behavior of the strip according to the composition thereof and the change in the proportions of metallurgical phases during the cooling thereof, and in that the intensity of the cooling is locally adjusted in a portion of strip by modifying the amount of surface flow of liquid over said portion according to said behavior.

[0125] Control parameters for the movable spraying units are adjusted to minimize internal stresses resulting from temperature differences in the direction of travel and in the transverse direction of the strip.

[0126] The method for determining the control parameters for the rapid cooling device to improve the thermal homogeneity of the strip in the direction of travel and in the transverse direction can be described as comprising three steps.

[0127] The first step is to assess the characteristic parameters of the products to be cooled.

[0128] The first characteristic parameter is the metallurgical transformation temperature. This is accompanied by a sharp variation in the mechanical and thermo-physical properties of the strip, in particular a sharp variation in the coefficient of thermal expansion.

[0129] Specifically, the transformations from the austenitic to the ferritic, pearlitic, bainitic or martensitic phases are accompanied by a change in crystallographic structure and an increase in volume, resulting in a lower coefficient of thermal expansion.

[0130] This interruption observed in the thermal expansion curve during the cooling method causes internal stresses that result from the changes in volume that accompany the phase changes.

[0131] The combination of this metallurgical effect with the thermal heterogeneity resulting from the cooling method according to the prior art leads to a heterogeneous distribution of stresses, with alternating tensile and compressive stresses at different points on the strip.

[0132] The metallurgical transformation temperatures and the change in the expansion coefficient depend mainly on the composition of the strip and the annealing thermal cycle, which determines the percentage of austenite likely to transform during cooling, and the rate of cooling.

[0133] The metallurgical transformation temperatures and the curves for the change in thermo-physical properties during rapid cooling can be precisely determined by the usual laws available according to the prior art, based on working data such as the chemical composition of the strip and the associated thermal cycles. Typical values for the bainitic transformation temperature are between 600° C. and 400° C. Typical values for the onset of martensitic transformation are between 450° C. and 250° C.

[0134] The second characteristic parameter is the minimum rate of cooling required to achieve the one or more desired metallurgical transformations.

[0135] If only austenite-to-martensite transformation is sought, the minimum rate of cooling is calculated so as to avoid transformation into another phase, such as bainite.

[0136] The rates of cooling required to obtain the required metallurgical microstructures depend on the composition of the steel, the annealing temperature and the holding time at the annealing temperature.

[0137] The type of metallurgical transformation observed from a totally or partially austenitic structure obtained at the end of the holding zone depends on the rate of cooling applied.

[0138] At slow rates of cooling of less than 1° C. / s, a transformation from austenitic to ferritic and pearlitic structures is observed. At medium rates of cooling, below 25° C. / s, the austenitic structure is transformed into the ferritic and bainitic structures. For rapid rates of cooling in excess of 100° C. / s, the transformation from austenitic to martensitic structure is mainly observed when the end-of-cooling temperature is lower than that of the onset of martensitic transformation. The content of alloying elements, such as manganese, chromium or molybdenum, has an impact on these cooling rate thresholds.

[0139] The second step is to determine the optimum temperature distribution along the length and across the width of the product, using predictive models to obtain the expected product quality, i.e. homogeneity of metallurgical characteristics, homogeneity of mechanical properties and flatness.

[0140] These three characteristics, which determine the quality of the final product, depend on thermal homogeneity during the cooling stage.

[0141] The thermal predictive model is based on the change curve of the heat transfer coefficient between the strip and the fluid depending on cooling regime.

[0142] For rapid cooling methods using liquid sprays, the Leidenfrost effect generates a sharp increase in the transfer coefficient in the transition zone between the vapor and liquid phases, which implies a sharp variation in internal stresses in the strip.

[0143] The Leidenfrost temperature is dependent on many parameters, in particular spray characteristics such as droplet speed and diameter, nozzle mesh size, nozzle distance from the strip, fluid type and temperature.

[0144] These parameters can be determined experimentally for different types of spray nozzles, to create tables that can be applied to industrial production.

[0145] Typical Leidenfrost temperature values range from 200° C., for the lowest spray speeds, to 1000° C. for the highest speeds.

[0146] The thermal predictive model makes it possible to determine the temperature distribution in the direction of travel and across the width of the product, by integrating the characteristic parameters of the product identified in step 1, i.e. the minimum rate of cooling, the temperatures characteristic of the metallurgical transformations and the temperature characteristic of the change in the heat transfer coefficient, i.e. the Leidenfrost temperature.

[0147] The thermomechanical predictive model makes it possible to evaluate the internal stresses and flatness defects resulting from the temperature distribution evaluated by the thermal predictive model.

[0148] The combination of the two, thermal and thermomechanical, predictive models makes it possible to determine the optimum temperature distribution to achieve the expected flatness and reduce local temperature variations and the overall variation in temperature between the center and edges of the product to achieve the expected quality, including homogeneity of metallurgical characteristics, homogeneity of mechanical properties and flatness.

[0149] The third step is to determine the control parameters to be applied to the cooling device according to the invention in order to obtain the temperature distribution calculated in step 2.

[0150] The line according to the invention may comprise means for measuring the temperature across the width of the products and means for measuring flatness, before spray cooling and after spray cooling.

[0151] According to one aspect of the invention, the predictive models described in step 2 can be used to produce a table of cooling device control parameters to obtain the optimum temperature distribution for each production case.

[0152] Advantageously, the line equipped with the cooling device according to the invention may comprise artificial intelligence means for linking the data collected by the temperature and flatness sensors to the temperature distribution objectives determined by the predictive models and finally to the control parameters for the cooling device according to the invention to achieve these objectives.

[0153] The line comprises a monitoring and control system able to determine and apply the operating parameters for the cooling section according to the characteristics of the strip at the inlet to the cooling section and the change therein along the cooling section.

[0154] The monitoring and control system comprises computing means for determining the operating parameters of the cooling section, in particular for implementing thermal and metallurgical models and artificial intelligence algorithms.

[0155] Advantageously, the monitoring and control system of the line may determine and apply the operating parameters for the cooling section autonomously, without requiring operator intervention.

[0156] Apart from the arrangements set out above, the invention consists of a certain number of other provisions that will be more explicitly discussed below with regard to exemplary embodiments described with reference to the accompanying drawings, but which are in no way limiting.BRIEF DESCRIPTION OF THE FIGURES

[0157] Other features and advantages of the invention will become apparent from reading the detailed description that follows, for the understanding of which reference will be made to the accompanying drawings, in which::

[0158] FIG. 1 is a schematic and partial longitudinal view of a vertical-furnace continuous processing line comprising a rapid cooling section 1, equipped with cooling units 2 for cooling by spraying a cooling fluid, according to one exemplary embodiment of the invention;

[0159] FIG. 2 is a schematic and partial front view of a cooling unit 2 of the rapid cooling section 1 from FIG. 1 comprising two rotatable side spraying units 3 and a translatable central spraying unit 4;

[0160] FIG. 3 is a schematic and partial top view of a cooling unit 2 from FIG. 2, in a position where the central spraying unit 4 and the side spraying units 3 are aligned in a direction parallel to the width of the strip, producing a jet perpendicular to the strip 8;

[0161] FIG. 4 is a schematic and partial top view of the cooling unit 2 from FIG. 3, in a position where the side units 3 are inclined by 10°, leading to an increase in the spraying distance;

[0162] FIG. 5 is a schematic and partial top view of the cooling unit 2 from FIG. 3, in a position where the side units 3 are inclined by −10°, leading to a decrease in the spraying distance;

[0163] FIG. 6 adds to FIG. 3 a schematic view of the area of impact of the jets for this arrangement of side units 3;

[0164] FIG. 7 adds to FIG. 4 a schematic view of the area of impact of the jets for this arrangement of side units 3;

[0165] FIG. 8 is a graph illustrating the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets for the cases shown in FIGS. 6 and 7;

[0166] FIG. 9 adds to FIG. 5 a schematic view of the area of impact of the jets for this arrangement of side units 3;

[0167] FIG. 10 is a graph illustrating the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets in the cases of FIGS. 6 and 9;

[0168] FIG. 11 is a schematic view of the area of impact of the jets for the case of a jet perpendicular to the strip as shown in FIG. 3, but with a decrease in flow at the edges of the strip;

[0169] FIG. 12 is a graph illustrating the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets in the case of FIG. 13;

[0170] FIG. 13a is a schematic and partial top view of a cooling unit 2 from FIG. 2, in a position where the central spraying unit 4 and the side spraying units 3 are aligned in a direction parallel to the width of the strip, the strip 8 having an initially concave geometric profile in the plane perpendicular to the plane of the strip and perpendicular to the direction of travel;

[0171] FIG. 13b is a schematic view of the combination of the areas of impact of the jets for the two faces of the strip for the arrangement of side units 3 of FIG. 13a;

[0172] FIG. 14a is a schematic and partial top view of a cooling unit 2 from FIG. 2, in a position where the side spraying units 3 are inclined, the strip 8 having an initially concave geometric profile in the plane perpendicular to the plane of the strip and perpendicular to the direction of travel;

[0173] FIG. 14b is a schematic view of the combination of the areas of impact of the jets for the two faces of the strip for the arrangement of side units 3 of FIG. 14a;

[0174] FIG. 15 is a schematic and partial side view of two spraying units 3 from FIG. 2 arranged opposite one another on either side of the strip, each unit comprising six spraying bars 11 and 12 perpendicular to the plane of the strip 8, the spraying bars 11 on one side being offset from the spraying bars 12 on the other side in the plane perpendicular to the strip and parallel to the travel of the strip;

[0175] FIG. 16 is a view similar to that of FIG. 15, with the first row of nozzles inclined by 10° in the plane perpendicular to the plane of the strip 8 and parallel to the travel of the strip, in the opposite direction to the travel of the strip, this being downward;

[0176] FIG. 17 is a view similar to that of FIG. 16, with the first row of nozzles being inclined by 10° in the plane perpendicular to the plane of the strip 8 and parallel to the travel of the strip, in the direction of travel of the strip;

[0177] FIG. 18 comprises, on its left-hand side, a schematic and partial side view of two consecutive spraying units 3 according to FIG. 15 and, on its right-hand side, a curve 20 illustrating the change in the temperature of the strip on which discontinuities 15, 16, 17, 18 can be seen in the direction of travel of the strip which are obtained when the jets are perpendicular to the strip;

[0178] FIG. 19 is a view similar to that of FIG. 18, with jets inclined in the direction of travel of the strip in order to adjust cooling efficiency through the discontinuity points observed in FIG. 18;

[0179] FIG. 20 is a graph illustrating the change in the thermal profile across the width of the strip obtained after cooling with and without inclination of the jets in the plane perpendicular to the strip and perpendicular to the direction of travel, starting from a concave initial transverse thermal profile.DETAILED DESCRIPTION OF THE INVENTION

[0180] In one exemplary embodiment of the invention, cooling units 2 according to FIG. 2 are integrated into a rapid cooling section 1 of a vertical processing line according to FIG. 1. They comprise a transverse division into three spraying units 3, 4, which are translatable in the horizontal plane perpendicular to the strip according to FIG. 3. The side units 3 are also rotatable in a plane perpendicular to the strip and to the direction of travel of the strip.

[0181] The rotatable spraying units 3 comprise a pivot element 6 arranged in the vicinity of their end 31 located toward the center of the strip, and a sliding element 5 arranged in the vicinity of their end 32 located toward an edge of the strip. A complementary sliding element 7 contributes to the translational movement of the spraying units 3, 4. In the example shown in FIG. 2, the three units 3, 4 are mechanically linked. They move in translation in a single movement, moving the same distance toward or away from the strip.

[0182] In this exemplary embodiment, each unit 3, 4 of the transverse subdivision of a cooling unit comprises six rows of spray nozzles in the direction of travel of the strip. Each spray row is equipped with twenty spray nozzles 21 spaced 80 mm apart in the horizontal plane perpendicular to the plane of the strip. The rows of nozzles are spaced 150 mm apart in the direction of travel of the strip. The distance between the strip and the nozzles is, in this example, equal to 300 mm for all of the nozzles when the transverse subdivision units 3, 4 are all parallel to the strip.

[0183] The angle of rotation of the side spraying units 3 for inclining the jets of cooling fluid is between −30° and +30° in the plane perpendicular to the strip and perpendicular to the direction of travel. This angle is zero when the nozzles are parallel to the strip, −30° when the nozzles are moved closer to the strip, and +30° when the nozzles are moved away from the strip.

[0184] The translation distance of the spraying units 3, 4 for increasing or decreasing the length of the spray jet is between 50 and 500 mm in the plane perpendicular to the strip and perpendicular to the direction of travel.

[0185] Rotating a side unit away from the strip increases the distance between its nozzles and the strip. Conversely, rotating a side unit closer to the strip decreases the distance between its nozzles and the strip. This increase or decrease in distance resulting from the rotation of the side units is dependent on the position of the nozzle on the spraying unit. The greater the distance between the nozzle and the axis of rotation of the unit, the greater this increase or decrease. As a result, nozzles located toward one edge of the strip move farther away or closer to the strip than nozzles located toward the center of the strip when the axis of rotation of the spraying unit is on the side of the unit closest to the center of the strip.

[0186] FIGS. 6 to 12 illustrate the distribution of surface flow over the width of an initially flat strip from a row of nozzles in the direction of the width of the strip, for different inclination configurations of the side spraying units 3.

[0187] FIG. 6 illustrates the distribution of surface flow for jets perpendicular to the strip. In this configuration the area of impact 9 of the jets on the strip is circular and the overlap of the jets is such that it leads to a substantially uniform distribution of the water flow along a median axis 10 of impact of the jets from a row of nozzles.

[0188] FIG. 7 illustrates the distribution of surface flow when the side spraying units are inclined by an angle of +10°, away from the strip. This inclination leads to an increase in the spraying distance in the plane perpendicular to the strip and perpendicular to the direction of travel. This increase in spraying distance differs from nozzle to nozzle. It is greatest for those nozzles farthest from the center of the strip, in this exemplary embodiment where the axis of rotation of the spraying unit is on the side of the unit closest to the center of the strip. The central spraying unit 4 remains parallel to the strip. The distance between its nozzles and the strip is constant.

[0189] In this configuration, the area of impact 9 of the jets from the side unit is elliptical with its main axis in the direction of width of the strip.

[0190] On the surface of the strip affected by the side spraying units 3, the combination of the increase in area of impact, the resulting overlap of the jets and the effect of water discharge toward the edges of the strip leads to an increase in the surface flow received by the edge of the strip, along the median axis 10 of impact of the jets. As the central spraying unit 4 remains parallel to the strip, the central portion of the strip receiving the jets is not affected by the inclination of the side units 3. Strip distance and overlap between jets remain constant.

[0191] Advantageously, the effect resulting from the inclination of the side spraying units 3 compensates for an initial transverse thermal profile characterized by strip edges that are hotter than the middle of the strip.

[0192] FIG. 8 illustrates the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets for the two configurations illustrated in FIGS. 3 and 4:

[0193] solid line, in the case of a jet perpendicular to the strip;

[0194] dashed line, in the case of a jet inclined by an angle of +10° for the side units 3.

[0195] FIG. 9 illustrates the distribution of surface flow for the case when the side spraying units 3 are inclined by an angle of −10°, closer to the strip. The result is a decrease in the spraying distance in the plane perpendicular to the strip and perpendicular to the direction of travel for these units.

[0196] In this configuration, the area of impact 9 of the jets is elliptical with its main axis in the direction of width of the product. For the nozzles of the spraying units 3, arranged toward the center of the strip, inclination of the units increases the area of impact and the overlap of the jets. Conversely, for the nozzles arranged toward the edges of the strip, inclination of the units decreases the area of impact and the overlap of the jets. Combined with the effect of water discharge toward the center of the strip, this leads to a decrease in the surface flow received by the edge of the strip and an increase in the surface flow received by the center of the strip, along a median axis 10 of impact of the jets.

[0197] Advantageously, this effect compensates for an initial transverse thermal profile characterized by strip edges that are cooler than the middle of the strip.

[0198] FIG. 10 illustrates the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets for the two configurations illustrated in FIGS. 6 and 9:

[0199] solid line, in the case of a jet perpendicular to the strip,

[0200] dashed line, in the case of a jet inclined by an angle of −10° for the side units 3, with the decrease in the spraying distance in the plane perpendicular to the strip and perpendicular to the direction of travel that results from this inclination.

[0201] Simultaneous adjustment of the inclination of the side spraying units and the resulting spraying distance also allows precise adjustment of cooling efficiency to the variable width of the products.

[0202] FIG. 11 illustrates the distribution of surface flow for the case of a jet perpendicular to the strip, with a decrease in the flow of cooling liquid at the edges of the strip.

[0203] The area of impact 9 of the jets is circular and the overlap of the jets results in a uniform distribution of water flow along the median axis 10 of impact of the jets in the central portion of the strip and a gradual decrease in surface flow toward the edges of the strip.

[0204] This adjustment results in a discontinuous surface flow distribution profile, characterized by a uniform distribution in the central portion of the strip and a linear decrease in surface flow at the edge of the strip.

[0205] The strip width affected by the flow adjustment depends on the feed to the nozzles. These can be fitted with means for individually adjusting the flow rate from each nozzle. According to another example, adjustment is carried out collectively for a row of nozzles arranged vertically over the same strip width, or for two or more vertical rows of nozzles. Other combinations are possible. The feed to groups of nozzles can also differ along the length of the cooling section, in the direction of travel of the strip.

[0206] For example, for a feed subdivided into five transverse sections, the strip width affected by a flow adjustment is at least equal to the width of one section.

[0207] FIG. 12 illustrates the change in the distribution of surface flow of cooling fluid across the width of the strip along the median axis of the impact of the jets for the two configurations illustrated in FIGS. 6 and 11:

[0208] solid line, in the case of a jet perpendicular to the strip, applied uniformly across the entire width of the strip,

[0209] dashed line, in the case of a uniform distribution in the central portion of the strip and a gradual decrease in flow toward the edge of the strip.

[0210] The discontinuity in the application of the flow of cooling fluid leads to a discontinuity in the transverse thermal profile and an increase in the internal stresses that cause flatness defects.

[0211] By adjusting the inclination of the orientable side spraying units and the resulting spraying distance, it is possible to modify the distribution of surface flow of cooling fluid on the surface of the strip in order to adjust cooling efficiency in the transverse direction of the products and to compensate for the effects of runoff along a preferred path due to an initial shape defect, or to correct an initial thermal profile that is not uniform across the width of the products.

[0212] According to another exemplary embodiment of the invention, the strip is not flat before cooling, for example characterized by a concave initial shape defect associated with a concave thermal profile resulting in edges of the strip that are hotter than the center.

[0213] FIG. 13a illustrates the variation in spraying distance and spraying angle with spraying bars aligned in the plane perpendicular to the plane of the strip and perpendicular to the direction of travel. The result is asymmetrical spraying on the two sides of the strip.

[0214] FIG. 13b illustrates the overlap in areas of impact of the jets on the two sides of the strip. It can be seen that if opposite areas of impact on the two sides of the strip are superimposed, then a compensating effect is obtained, with an overall area of impact that is substantially constant across the width of the strip.

[0215] For this configuration, the effect of compensating for the opposing effects on the two sides with respect to the spraying distances and spraying angles does not allow the initial thermal profile to be modified, in particular to reduce the difference in temperature between the center and edges of the product and to reduce the difference in rate of cooling between the center and edges of the product.

[0216] The different inclinations of the cooling units on either side of the strip, as illustrated in FIG. 14a, enhances cooling at the center of the strip by combining the effect of concentrating water runoff on the convex side of the strip with the effect of reducing the spraying distance from the center on the concave side of the strip.

[0217] FIG. 14b illustrates the overlap in the areas of impact of the jets for the two sides of the strip and the effect of accentuating the surface flow obtained by superimposing the opposite areas.

[0218] In contrast to FIG. 13b, it can be seen that if opposite areas of impact on the two sides of the strip are superimposed, then an overall area of impact that is substantially different across the width of the strip is obtained. According to one embodiment of the invention, the cooling unit according to FIG. 2 integrated into a vertical processing line according to FIG. 1 also comprises means for adjusting the cooling efficiency in the direction of travel of the product.

[0219] For example, in FIG. 15, each row 210 of nozzles of the cooling device forms a longitudinal axis 62 and comprises a device 13 for rotating about this longitudinal axis 62.

[0220] These means of adjusting the cooling efficiency in the direction of travel of the products complement all or some of the means of adjusting cooling efficiency described in the preceding exemplary embodiments, in particular when combined with an offsetting of the jets in the plane perpendicular to the strip and parallel to the travel of the strip.

[0221] FIG. 15 illustrates the distribution of surface flow for six spraying bars 11, 12 aligned in the plane perpendicular to the plane of the strip 8 and parallel to the travel of the strip.

[0222] In this configuration, the area of impact of the jets is circular and the overlap of the areas leads to a uniform distribution of the water flow along a median axis of impact of the jets.

[0223] FIG. 16 illustrates the distribution of surface flow for the case where the first pair of bars in the direction of travel of the strip produces a jet inclined in the plane perpendicular to the strip and parallel to the direction of travel of the strip, in the opposite direction to the direction of travel of the strip.

[0224] In this configuration, by modifying the overlap of the areas of impact of the jets, the intensity of the cooling in the impact zone of the first two bars is decreased, resulting in slower cooling at the start of the spraying unit.

[0225] FIG. 17 illustrates the distribution of surface flow for the case where the first pair of bars produces a jet inclined in the plane perpendicular to the strip and parallel to the direction of travel of the strip, in the direction of travel of the strip.

[0226] In this configuration, by modifying the overlap of the areas of impact of the jets, the intensity of the cooling in the impact zone of the first two bars is increased, resulting in faster cooling at the start of the spraying unit.

[0227] According to another exemplary embodiment, inclining the spray jet in the plane perpendicular to the strip and parallel to the direction of travel of the product compensates for the discontinuity in cooling efficiency resulting from the discontinuity in the heat transfer coefficient depending on the consecutive vapor film, transition boiling, nucleate boiling or forced convection cooling regimes observed during spray or liquid immersion cooling of a hot sheet.

[0228] It also compensates for the discontinuity in cooling at metallurgical transformation points.

[0229] In addition, it compensates for the discontinuity in the heat transfer coefficient caused by ancillary equipment such as stabilizing rollers, water cutters or air cutters.

[0230] The case is considered of a carbon steel composed of 0.1% carbon, 1% manganese and 1% silicon, annealed at a temperature above 850° C. for complete austenitization, cooled from 850° C. to 650° C. in a slow cooling section and then from 650° C. to 150° C. in a rapid cooling section by spraying comprising two cooling units according to the invention, each composed of six pairs of bars equipped with conical-jet nozzles.

[0231] The average cooling slope required in the rapid cooling section to achieve complete martensitic transformation can be determined from the metallurgical transformation curves established for the steel composition, i.e. 200° C. / s for the example under consideration.

[0232] For this example, four discontinuities in the cooling slope can be observed in the thermal profile 14 of the strip in the direction of travel of the product.

[0233] FIG. 18 shows, on its left-hand side, the distribution of surface flow on one side of the strip for the exemplary embodiment comprising two cooling units and a total of twelve spraying bars perpendicular to the strip, and on the right-hand side, the thermal profile 20 of the strip in the direction of travel corresponding to the associated uniform surface flow distribution.

[0234] A first discontinuity 15 is observed at the inlet to the rapid cooling section, resulting from the increase in rate of cooling between the upstream slow cooling section and the rapid cooling section.

[0235] A second discontinuity 16 is observed when the temperature of the strip reaches the Leidenfrost temperature at 550° C.

[0236] A third discontinuity 17 is observed at the transition between the two rapid cooling sections.

[0237] A fourth discontinuity 18 is observed when the temperature of the strip reaches the martensitic transformation temperature at 300° C.

[0238] FIG. 19 illustrates the application of all of the provisions described in the first exemplary embodiments, allowing the cooling efficiency to be adjusted in the direction of travel of the product in order to reduce the internal stresses that cause flatness defects.

[0239] For example, inclining the spray jet in the plane perpendicular to the strip and parallel to the direction of travel of the strip, in the opposite direction to the travel of the strip at the inlet to the rapid cooling section, smooths the interruption in the slope at the transition between slow cooling and rapid cooling.

[0240] By inclining the spray jet in the opposite direction to the travel before the strip reaches Leidenfrost temperature, the effect of the sudden increase in the heat transfer coefficient during the transition between vapor film cooling regime and transition regime to nucleate boiling is mitigated.

[0241] Inclining the spray jet in the direction of travel at the outlet of the first cooling device compensates for the discontinuity in the heat transfer coefficient caused by ancillary equipment such as stabilizing rollers, water cutters or air cutters.

[0242] Inclining the spray jet in the direction of travel before the strip reaches martensitic transformation temperature compensates for the internal stresses caused by austenitic-to-martensitic phase transformations.

[0243] Implementation of the provisions of the invention described in the first exemplary embodiments allows the cooling efficiency to be adjusted across the width of the product to compensate for an initial transverse thermal profile characterized by product edges that are cooler than the middle of the product.

[0244] Inclination of the jets by an angle of −10° and the resulting decrease in spraying distance in the plane perpendicular to the strip and perpendicular to the direction of travel increases thermal efficiency in the center of the strip.

[0245] The graph in FIG. 20 illustrates this result for transverse thermal profiles:

[0246] solid line, before rapid cooling,

[0247] dashed line, after rapid cooling in the case of a jet applied uniformly across the entire width of the strip,

[0248] dotted line, after rapid cooling in the case of a jet inclined by −10° with the resulting decrease in spraying distance in the plane perpendicular to the strip and perpendicular to the direction of travel.

[0249] According to another exemplary embodiment of the invention, the cooling device according to FIG. 2 integrated into a vertical processing line according to FIG. 1 and comprising means for adjusting the cooling efficiency across the width of the product and in the direction of travel of the product as described in the first exemplary embodiments is equipped with flat-jet spray nozzles or a combination of conical-jet and flat-jet spray nozzles.

Claims

1. A cooling device for rapidly cooling metal strips on a continuous production line, the device being arranged so as to cool the strip as it travels by spraying a liquid, or a mixture of a gas and a liquid, thereon by means of nozzles arranged on spraying units, wherein the cooling device comprises spraying units that are rotatable on a plane perpendicular to the strip and perpendicular to the direction of travel of the strip, thereby making it possible to individually and multidirectionally adjust a spraying angle of said spraying units that are movable with respect to the strip, and wherein two rotatable spraying units are arranged on either side of a central spraying unit in a direction defined by the strip width, the three spraying units covering the entire width of the strip, the pivot elements of the movable spraying units being proximal to the central spraying unit.

2. The cooling device as claimed in claim 1, wherein the rotational movement of a movable spraying unit is obtained by means of a pivot element arranged on a first side of the movable spraying unit and a sliding element arranged on a second side of the movable spraying unit, opposite the first.

3. The cooling device as claimed in claim 1, wherein the angle of rotation of a rotatable spraying unit is between −30° and +30° with respect to a plane parallel to the strip passing through the axis of rotation of the movable unit.

4. (canceled)5. (canceled)6. The cooling device as claimed in claim 1, wherein a row of nozzles of a movable spraying unit forms a longitudinal axis parallel to the direction defined by the strip width, and in that this row of nozzles is rotatable about this longitudinal axis.

7. The cooling device as claimed in claim 6 wherein the angle of rotation of a row of nozzles about its longitudinal axis is between −30° and +30° with respect to a plane perpendicular to the strip and perpendicular to the direction of travel passing through the longitudinal axis.

8. The cooling device as claimed in claim 1, wherein the spraying units are translationally movable in a direction parallel to the plane perpendicular to the strip and perpendicular to the direction of travel in order to adjust the spraying distance of said spraying units with respect to the strip.

9. The cooling device as claimed in claim 8 wherein the translation of a movable spraying unit is possible over a distance with respect to the strip of between 50 and 500 mm.

10. A continuous production line for metal strips, comprising the cooling device recited in claim 1, the production line further comprising means for determining the geometric transverse profile of the strip and means for determining the temperature profile of the strip at the inlet to the cooling section.

11. A method for rapidly cooling a moving strip on a continuous production line for metal strips by spraying a liquid, or a mixture of a gas and a liquid, thereon by means of a rapid cooling device as claimed in claim 1, wherein the intensity of the cooling is locally adjusted in a portion of strip by modifying the amount of surface flow of liquid over said portion by acting on the spraying angle of a movable spraying unit arranged in the vicinity of said portion.

12. The method as claimed in claim 11, wherein the local adjustment of the intensity of the cooling in the portion of strip is refined by acting on the distance with respect to the strip of the movable spraying unit arranged in the vicinity of said portion via translational movement thereof in a direction parallel to the plane perpendicular to the strip and perpendicular to the direction of travel.

13. The method as claimed in claim 11, further comprising a step of determining the geometric transverse profile and the temperature transverse profile of the strip at the inlet to the cooling section, and in that the intensity of the cooling in a portion of strip is locally adjusted by modifying the amount of surface flow of liquid over said portion according to said transverse profiles of the strip.

14. The method as claimed in claim 11, wherein it further comprises a step of determining the thermomechanical behavior of the strip according to the composition thereof and the change in the proportions of metallurgical phases during the cooling thereof, and in that the intensity of the cooling is locally adjusted in a portion of strip by modifying the amount of surface flow of liquid over said portion according to said behavior.

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