Method and plant for manufacturing flat rolled products

Abstract

The present invention relates to a method and a plant for manufacturing flat rolled products to obtain a strip (S) having a multi-crown transverse profile and subsequently divided longitudinally into a plurality of strips of smaller width, said method comprising a rolling step carried out in a rolling mill comprising roughing stands (14a, 14b, 14c) and a plurality of finishing stands (16a, 16b, 16c, 16d, 16e) each equipped with work rolls (24a, 24b) to obtain a strip (S) having a predetermined width.

Description

[Technical field]

[0001] The present invention relates to a method for producing flat rolled products such as strip and to a corresponding production plant, in particular to a method and a plant for obtaining a strip having a final transverse profile with multiple crowns and having optimal geometrical characteristics in terms of strip profile and planarity, even if the strip is subsequently divided into longitudinal sections.

[0002] The present invention can be applied to both hot and cold rolling processes to produce strip of any type of ferrous or non-ferrous material. [Background technology]

[0003] It is known that rolling plants comprise a multi-stand mill, which is usually divided into a first roughing stand and a second finishing stand. There may be a temperature recovery system between the roughing stand and the finishing stand.

[0004] The rolling mill may or may not be located in-line with a continuous caster producing thin slabs, a so-called "thin slab caster".

[0005] These plants can be designed and configured for a substantially continuous rolling process, a so-called "endless" process, where the cast product is rolled in a rolling mill that is directly engaged with and located downstream of the continuous caster.

[0006] The process may be of the semi-endless type, in which the cast slab is cut to form multiple coils, or of the coil-to-coil type, in which one coil is produced at a time per cut of the slab.

[0007] It is known that the width of the strip obtained in this type of plant can usually vary within the range of 600 mm to 2500 mm, depending on the application of the rolled material.

[0008] However, to meet market demand, there is a constant need to produce coils with a width narrower than the barrel of the rolling rolls, resulting in reduced plant productivity.

[0009] For example, if a rolling plant capable of producing strip up to a maximum width of 2000 mm and capable of casting slabs of width 800 or 1000 mm wishes to obtain a strip width of 800 or 1000 mm, the productivity of the plant will be effectively halved, a drawback to be avoided.

[0010] Thus, for example, according to the examples of JP-A-58-68405 and JP-A-57-175003, it is known to process a strip of standard width, for example 1600 mm, and then cut it longitudinally in the interstand space along the rolling mill, thereby obtaining, for example, two half strips of width 800 mm which are then wound onto corresponding respective coils.

[0011] Although this solution is effective in terms of maintaining productivity, it has some drawbacks. The first drawback is related to the crowning or crown of the two half strips. In the following, the terms "crowning" and "crown" are used interchangeably to mean the same thing, as explained below.

[0012] The dimensional quality of the product coming out of the hot rolling process focuses on controlling the thickness distribution along the width of the rolled strip. The shape of the thickness of the rolled product across its width is called the profile. The main parameter analyzed to evaluate the profile of the rolled product is the crown. Crown describes the difference between the thickness at the center of the product and the average thickness at the edges.

[0013] In general, it is desirable to obtain a rolled product that is thicker in the center than at the edges, and therefore assumes the shape of a convex lens, when viewed in cross section, symmetrical about a centerline, as shown in Figure 2a.

[0014] Producing an accurate profile during hot rolling is very important because possible variations would result in defects in planarity and difficulties in carrying out subsequent steps in the production cycle, and because the profile cannot be altered in downstream processes.

[0015] Conversely, the planarity of a rolled product is defined as its ability to follow a theoretical plane, and the non-planarity is the difference between the theoretical plane and the rolled product.

[0016] During rolling, the rolling rolls impart a certain crown over the entire width of the strip, but if such a fitted strip is subsequently divided in half, each half strip will not have a symmetrical crown, as shown in Figure 2b: in fact, the profile of the half strip is trapezoidal (wedge-shaped) with different thicknesses at both edges.

[0017] However, this asymmetric profile is less suitable for further processing of the half strip, which may lead to instabilities in downstream processing, drift, winding difficulties, etc. Therefore, in order to obtain two finished half strips each with a normal profile, JP 58-68405 A proposes to perform an additional rolling step in an additional stand to restore the symmetry of the profile by tapering the cut edges.

[0018] Furthermore, in JP 58-68405 A, there are problems with making the longitudinal cuts in the inter-stand space and, especially when dealing with thin thicknesses, there are further problems with controlling the two half strips due to the high speeds involved.

[0019] The solution described in JP 58-68405 does not in practice allow to control the crown of the two half strips, since in a single rolling stand the profile of the half strips is returned to approximately symmetry only by the Hertzian pressure occurring at the edges.

[0020] GB 2 114 034 A1 describes a process for cold finishing and / or straightening a hot rolled pickled strip using work rolls with a double central raised crown to obtain a strip narrowed in the middle and having a central crown on both corresponding lateral sides. However, in the strip obtained with this shape of work roll, the width of the central narrowing zone is very limited and very precise positioning of the shearing means is required to obtain two substantially symmetrical half strips.

[0021] JP 51-094453 describes a rolling method for forming a strip with a central constriction and two rounded zones on either side of the constriction. The work rolls used have two recesses and a substantially pointed central protruding zone so that a substantially accurate constriction can be defined. Again, precise positioning of the shearing means is required to accurately divide the strip into two parts of the same shape.

[0022] It can therefore be seen that if the rolled strip then has to be split longitudinally into two half strips either before, during or even after winding, there is no solution in the prior art for precise control of the crown.

[0023] Conventional solutions such as those described above not only do not guarantee that two half-strips with the desired crown characteristics and symmetry are obtained, but also do not allow the crown profile to be dynamically changed or adapted as needed.

[0024] In this connection it should be noted that in recent years the market requirements for flat products, in particular hot rolled strip, have become increasingly stringent both in terms of metallurgical and dimensional quality.

[0025] Furthermore, plant manufacturers and steelmakers are constantly seeking to reduce conversion costs while maintaining, if not improving, the mechanical properties and subsequent workability of the hot rolled product.

[0026] The following points correlate with the importance of the dimensional quality of hot rolled strip: The gradual replacement of cold-rolled strip with hot-rolled strip in the manufacture of some products. Simplifying the manufacturing process of converting hot rolled strip into finished products. Improve the geometrical properties in terms of thickness, profile and planarity. Indeed, improved geometrical conditions not only improve the quality of the final product, but also the reliability and automation of downstream processes.

[0027] The above points lead to some "extreme" geometric property requirements, e.g.: Depending on the type of product, the crown target for strip can vary from 70µm down to 10µm. For some products (especially thin and extra thin thicknesses), the crown must be within 1.0-1.2% of the nominal thickness of the strip. In other words, for a 1.0mm thick strip, a crown of 10µm is required. Strip flatness of less than 12 and 30 I-Units depending on strip thickness and width. Reduced thickness loss at the strip edges (edge ​​drop).

[0028] Therefore, in production processes supplying hot rolled strip of thin and very thin gauge, both in endless or semi-endless mode and in coil-to-coil mode, the rolling stands need to have sufficient capability to control the profile and planarity of the strip throughout the entire production mix.

[0029] Thus, by using work rolls having a molded shape, i.e., a contour or profile described by a mathematical function, the shape of the roll gap can be changed by axial shifting of the rolls in opposite directions.

[0030] With regard to crown, it must also be considered that heating of the rolling rolls is one of the fundamental problems faced in both hot and cold rolling. The direct contact of the strip being rolled against the work rolls determines the heat flow, the heat transfer to the roll itself and the heating of the roll. These involve variations in both the dimensions (diameter) and the profile of the roll itself.

[0031] In order to limit said heating to values ​​compatible with the properties of the material from which the roll is made and to keep the progressive deterioration of the roll surface within acceptable limits, it is essential to use a cooling system.

[0032] A commonly adopted solution in hot rolling is to cool the work rolls from the outside by a series of nozzles mounted on several ramps. In a conventional 4-high rolling stand for a hot strip rolling mill, four cooling units are usually used, two in the exit zone and two in the entry zone. Each cooling unit consists of one or more cooling ramps. To prevent the heat transferred from the rolled material to the rolls from penetrating the rolls from the surface layer into the roll interior, which makes it difficult to remove the accumulated heat inside the rolls, it is preferable to increase the heat exchange between the rolls and the cooling water from the roll gap in the exit zone. This increases the flow rate and, in some cases, the heat exchange efficiency.

[0033] Thermal crown is created by heat transfer to the roll. Axial flow occurs within the roll as heat flows from the center zone to the cooler sides that are not affected by the strip contact. The result is differential expansion, which typically produces a parabolic roll profile in the center zone, while the edges of the strip experience a rapid decrease in expansion and remain at a lower value than the center zone.

[0034] Variations in the "thermal profile" of the rolls clearly affect the rolling process, especially the control of thickness, profile and flatness. The role of the roll cooling system is therefore to minimize disturbances due to thermal profile variations, although the roll temperature must reach a value on average between 50 and 80°C (depending on the material that constitutes the jacket of the rolls) so as to optimize the duration and reduce thermal fatigue and surface wear caused by friction between the strip and the rolls.

[0035] These challenges, already considerable in the case of hot rolling by conventional processes, become even more acute, especially in endless production processes where rolling in the strip finishing mill can last up to 10 hours without interruption, compared to 2-3 minutes in a conventional coil-to-coil process.

[0036] The thermal crown of the work rolls depends on the temperature distribution along the axis of the roll. This distribution changes continuously during rolling, causing both an increase and a decrease in the thermal crown depending on the changes in the work profile of the roll. This phenomenon causes disturbances in the control of the profile and flatness of the rolled strip: When the roll is cold, e.g. after a roll change or a long production stop, the thermal crown increases gradually and requires 5-10 coils to reach a stable value. When steady conditions are reached during rolling, the thermal crown decreases during the waiting time between one coil and the next, returning to its average value relatively quickly after the start of rolling the new coil.

[0037] Taking all the above into consideration, one object of the present invention is to provide a method and a corresponding plant for producing finished thin and even ultra-thin strips, which are subsequently divided longitudinally in such a way as to obtain two, three, four and more strips having optimal quality in terms of profile, planarity and thickness of each cross section.

[0038] The object of the invention is to keep the productivity of the rolling mill unchanged whether a strip of width equal to the maximum width is produced or a strip of width less than said maximum width is produced.

[0039] Applicant has conceived, tested and embodied the present invention to overcome the shortcomings of the prior art and to obtain these and other objects and advantages. Summary of the Invention

[0040] The invention is set forth and characterized in the independent claims. The dependent claims describe variants or define embodiments of the main inventive idea.

[0041] According to one embodiment of the present invention, slabs are cast in a width defined by the design parameters of the plant itself, such as the width of the mould, the dimensions of the line and the required productivity, and are then fed into a hot strip rolling mill to obtain the final required thickness.

[0042] According to another embodiment of the invention, the hot rolled strip is further rolled in a cold rolling mill to obtain a thinner gauge.

[0043] In both of these embodiments, the work rolls of the rolling mill stands are configured to impart a transverse profile to the strip having a number of positive crowns that correlates to the number of longitudinal portions into which the strip must subsequently be divided.

[0044] In the following description, the following terms are used: · A “positive” crown exhibits a symmetrical convex lens-shaped profile that is thicker in the middle, such as the example shown in Figure 2a. "Negative" crowns exhibit a biconcave symmetrical profile, mating or complementary to the convex lens shaped profile described above, and being thinner in the center than at the edges.

[0045] According to the invention, the object is to use work rolls with a profile shaped to produce two or more positive crowns on the rolled strip and two or more corresponding negative crowns.

[0046] In accordance with another aspect of the invention, the work roll is provided with a profile having alternating negative crowns and connecting segments formed in an arched shape having a positive curvature.

[0047] Correspondingly, the resulting rolled strip also has alternating positive crowns and intermediate portions formed into an arcuate shape having a negative curvature.

[0048] In the following description, the term "positive curvature" means a convex profile that is thicker in the middle and thinner at the sides, and the term "negative curvature" means a concave profile that is thinner in the middle than at the sides.

[0049] The invention thus provides a method for using work rolls with a single negative crown when the finished strip is used at the width of the initial product fed into the rolling mill, whereas work rolls with double, triple, quadruple or any number of multiple negative crowns are used when the rolled strip is to be subsequently divided longitudinally into two, three, four or generally any number of longitudinal portions of the strip.

[0050] The longitudinal division of the strip can occur along the entire length of the strip from head to tail, at a location between the exit from the last stand and each corresponding winding unit where the individual coils of each portion of the strip are formed, or along the entire length, except for the head and tail portions of the strip just prior to winding into a single coil, or even after the coils have been removed from the winding units, for example at their destination.

[0051] According to the invention, at least the last stand of the rolling mill, for example the last stand of the finishing mill, or the last two or three stands of the finishing mill, are equipped with work rolls whose contact surface with the strip has a profile which correlates and depends on the respective portion of the strip to be subsequently obtained by the longitudinal cut.

[0052] According to some embodiments, the work rolls have multiple negative crown profiles in a number that correlates with the number of portions into which the produced rolled strip will subsequently be longitudinally divided.

[0053] In other words, the profile of the work roll has a double negative crown (double crown) if the strip is divided longitudinally into two half strips, a triple negative crown (triple crown) if the strip is divided longitudinally into three parts, and so on.

[0054] Consistently, in the case of double negative crowns there is only one connecting segment with positive curvature, in the case of triple negative crowns there are two connecting segments with positive curvature, and similarly for the following cases.

[0055] According to some embodiments, in the profile of the work roll, the negative crown and the connecting segment having the positive curvature have widths that are substantially equal to each other, in other words, the width of the negative crown is substantially equal to the width of the connecting segment, so that on the strip, between the corresponding positive crown portions, an intermediate portion of negative curvature is defined having a width and depth that correlates to the crown width and height of the positive crown portion.

[0056] This allows for a larger operating space for positioning the longitudinal cutting means and further allows for minimal deviations from the longitudinal centre line to be negligible.

[0057] It is known from the literature that the profile of a work roll can be defined by a curve consisting of antisymmetric trigonometric functions and third order polynomial functions.

[0058] The equation of the profile curve is given as follows:

number

[0059] The value of crown can be modified by changing the value of the axial shift of the work rolls δ0. Also, by changing the parameters α and C in the above formula, the crown function of the gap between the rolls determines a family of different curves.

[0060] In other words, the axial translation motion of the work rolls is performed to modify the position of the negative crown of the work rolls relative to the position of the strip, thereby dynamically modifying the extent of the crown on the strip, i.e., accentuating or flattening the peaks and valleys of the strip profile.

[0061] Therefore, according to the invention, by assigning appropriate values ​​to the parameters α and C in the above formula, if the manufactured strip is divided into two half-strips, a "double crown" profile can be obtained. Moreover, if the strip is divided into several parts in the longitudinal direction, general multiple crown profiles such as triple or quadruple crown can be obtained.

[0062] As mentioned above, especially when the strip thickness is small, the operation of giving the strip a double (or triple, or quadruple, ...) crown is carried out in the last stand of the finishing mill, for example the last or last two or three stands.

[0063] It should be noted that in a finishing mill with five, six or seven finishing stands, the last three stands usually have work rolls of the same diameter and the same profile. Therefore, according to the present invention, it is convenient to form a multiple crown in the last three stands of the finishing mill.

[0064] The present invention thus provides for producing a finished strip having multiple crowns which is then longitudinally divided in a manner to obtain a plurality of separate strip portions, each having its own crown, as if each strip portion had been rolled individually.

[0065] In this manner, each portion of the strip has an appropriate crown that provides the desired geometric and dimensional characteristics in terms of thickness, profile, and flatness.

[0066] According to the invention, in addition to the mechanical crown of the work rolls, intervention is also performed on the thermal crown of these work rolls using the cooling method described below, in order to more accurately control the multiple crowns.

[0067] According to the invention, in the case of double crown rolling, it is advantageous to have a minimum cooling efficiency around the central zone of the work rolls, so that the thermal crown in this zone where the strip is to be divided increases, while in the central zone of the strip halves, the thermal crown decreases, with a maximum cooling efficiency corresponding to the center of the two strip halves. In other words, the thermal crown of the work rolls is controlled to follow and improve the mechanical crown trend. In the case of other numbers of crowns, such as triple, quadruple, etc., the cooling of the work rolls is adjusted in a similar way, with less cooling in the part where the strip is to be divided and more cooling in the central zone of each multi-strip.

[0068] Essentially, the control of the cooling system is realized through an online model that processes a set of information about the process states (strip temperature, rolling force, thickness reduction, rolling speed, etc.) in time intervals to determine the thermal profile.

[0069] The present invention allows for varying the cooling efficiency across the width, thereby making it possible to define an optimum thermal crown in a double or generally multiple crown rolling campaign to maximize the control capacity over the profile / flatness of each portion of the strip that will subsequently be divided.

[0070] The features of the present invention will now be described in detail with reference to some specific embodiments, given by way of non-limiting examples with reference to the accompanying drawings in which: [Brief description of the drawings]

[0071] [Figure 1] FIG. 1 is a diagram showing an example of the layout of a hot rolling plant to which the manufacturing method according to the present invention is applied. [Diagram 2] 2a and 2b show respectively a cross section of one strip and of two half-strips obtained by longitudinal cutting of the strip according to the prior art. [Diagram 3]3a and 3b respectively show a cross-section of one strip and of two half-strips obtained by longitudinal cutting of the strip according to one embodiment of the invention. [Figure 4] When applying a double crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition of no axial shift. [Diagram 5] When applying a double crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition with axial shift. [Figure 6] The relationship between the shift amount of the work roll and the crown of the work roll when a double crown profile is applied to a 2000 mm wide strip is shown. [Figure 7] When applying a triple crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition of no axial shift. [Figure 8] When applying a triple crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition with axial shift. [Figure 9] The relationship between the shift amount of the work roll and the crown of the work roll when a triple crown profile is applied to a strip having a width of 2000 mm is shown. [Figure 10] When applying a quadruple crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition of no axial shift. [Figure 11] When applying a quadruple crown profile to a 2000 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition with axial shift. [Figure 12]The relationship between the shift amount of the work roll and the crown of the work roll when a quadruple crown profile is applied to a 2000 mm wide strip is shown. [Figure 13] When applying a double crown profile to a 1600 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition of no axial shift. [Figure 14] When applying a double crown profile to a 1600 mm wide strip, the work roll profile and the corresponding strip profile are shown under the condition with axial shift. [Figure 15] The relationship between the shift amount of the work roll and the crown of the work roll when a double crown profile is applied to a 1600 mm wide strip is shown. [Figure 16] FIG. 13 is a graph showing the trend of change in angle α as a function of strip width when processed into a double crown. [Figure 17] FIG. 2 illustrates one embodiment of a differential cooling system for work rolls used in a manufacturing method according to the present invention. [Figure 18] FIG. 4 is a schematic diagram showing the location of nozzles of a cooling system relative to a work roll. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072] With reference to FIG. 1, an example of a co-rolling plant 10 for producing strip S is shown, in which a machine 11 for casting thin slabs feeds a hot strip rolling mill 12 .

[0073] It should be noted that the examples shown here should in no way be considered as limiting the applicability of the invention, since the concepts shown here can be applied to many other types of plants, for example those with a different number of stands, those having a caster separated from the rolling mill, those in which the slabs are produced elsewhere, and all those cases in which a metal strip having a given nominal width at the end of rolling needs to be divided longitudinally into several parts to obtain strip parts having smaller widths.

[0074] Although the illustrated embodiment shows a hot rolling mill in the same production line as a caster, the invention is also applicable to a cold rolling mill which rolls the strip obtained prior to hot processing.

[0075] In the case of a hot rolling process, as previously mentioned, the starting semi-finished product is represented by a slab that can be cast in-line in the same plant (as disclosed in the embodiment of FIG. 1) or produced offline or in a separate plant.

[0076] In the case of a cold rolling process, the starting semi-finished product is represented by a coil of rolled strip previously produced in the hot rolling mill.

[0077] According to the invention, in cold rolling, the thickness of the strip is preferably at least 2.5 mm, in order to be able to form a multiple crown on the previously hot rolled strip with a single crown. Below this value, it is preferred that the strip to be cold rolled does not have a single crown profile, but already has the final number of crowns obtained at the end of the cold rolling. In this case, in the cold process, the rolling rolls are shaped to follow the multiple crown profile already imparted to the strip in the previous hot rolling process.

[0078] Furthermore, the present invention is applicable to the production of both ferrous strip products, such as steel, and non-ferrous strip products, such as aluminum.

[0079] In the particular example shown in FIG. 1, the rolling mill 12 comprises a roughing unit 13 (or referred to as a roughing mill), in this case comprising three stands 14a, 14b and 14c, and a finishing unit 15 (or referred to as a finishing mill), in this case comprising five stands 16a, 16b, 16c, 16d and 16e.

[0080] Between the roughing unit 13 and the finishing unit 15 there is a temperature recovery system, for example an induction furnace 20, which returns the exit slabs from the roughing unit 13 to the correct rolling temperature.

[0081] Between the caster 11 and the roughing unit 13 there is a tunnel furnace 17, the length of which is sufficient to accommodate at least 2-5 slabs. This tunnel furnace 17 allows, in a known manner, both to act as a buffer in case the rolling mill is interrupted, even temporarily, due to an accident or a work roll replacement schedule, and to operate in a semi-endless mode.

[0082] Upstream of the tunnel furnace 17 is a first pendulum shear 18 which cuts the slabs to size when the plant 10 operates in coil-to-coil or semi-endless mode.

[0083] Downstream of the finishing mill 15 there is a cooling unit 22 and a second flying shear 19 which, in the case of endless or semi-endless rolling, intervenes to separate the strip gripped by one of the two down coilers 21 or reels.

[0084] According to one aspect of the invention, the strip obtained is subsequently divided longitudinally (slitting) so as to obtain strip portions having a width which is a submultiple of the width of the cast slab or in any case smaller than the width of the cast slab.

[0085] In this way narrower width strips can be obtained from a single rolled strip, without in any case limiting the overall productivity of the plant, which can always work on slabs and strips having widths close to the maximum width offered by the plant itself.

[0086] The division of the finished rolled strip to width can take place either in-line directly at the exit of the rolling mill or in a step subsequent to decoiling, for example in another destination plant where the strip is used.

[0087] In the first case, downstream of the finishing mill 15, the following can be considered for splitting, for example into two parts:

[0088] Two different half strips S1, S2 are wound on respective reels 21 and then split along the entire length from head to tail of the strip S. In this way, two separate coils are obtained.

[0089] To facilitate the insertion of the head portion onto the single reel and the winding of the final tail end turn, the strip S is split along its entire length, excluding the head and tail portions of the strip S. By this method, a single coil is split into two portions along nearly its entire length.

[0090] For this purpose, dedicated cutting devices can be provided which longitudinally separate the strip S into two or more strip portions S1, S2 of the same or different widths. Advantageously, these devices can be inserted into or removed from the production line according to demand.

[0091] According to the present invention, a method is provided for profiling at least some of the work rolls 24a, 24b of the final finishing stands 16a-16e in a manner that determines the exact crown at each portion into which the strip S is divided according to the number of width portions into which the strip S is divided.

[0092] 3a and 3b show, by way of example, a cross section of the strip S downstream of the rolling mill 12 and of two half strips S1, S2 obtained by cutting the strip S longitudinally along its centre line, respectively. In this example, the strip S has a "double positive crown" PC that is substantially symmetrical about a plane of symmetry through the centre line M, while each of the two half strips S1, S2 has its own single positive crown PC.

[0093] As can be seen in the figure, strip S has an intermediate portion 40 connecting between two positive crown PC zones, intermediate portion 40 having a negative curvature and having a width and depth that correspond to the width and height, respectively, of the positive crown PC zones.

[0094] Thus, if the strip is split widthwise into two half strips, the profile of the work rolls 24a, 24b will be shown as a double negative crown NC, one for each half strip obtained or that can be obtained downstream, as well as if the strip is split into three, four or more.

[0095] In particular, each of the work rolls 24a, 24b has multiple negative crowns NC, the number of negative crowns NC corresponding to the number of portions into which the strip S is to be divided.

[0096] Advantageously, the negative crowns NC alternate with connecting segments 50 having a positive curvature.

[0097] Preferably, as can be observed by comparing the curves shown above and below the abscissa in Figures 4-5, 7-8, 10-11 and 13-14, the negative crown NC and the connecting segment 50 having positive curvature have corresponding widths and depths / heights that are substantially equal to each other.

[0098] The profile of each of the work rolls 24a, 24b can be defined by a curve consisting of an antisymmetric trigonometric function and a third order polynomial function.

[0099] The equation of the profile curve is given as follows:

number

[0100] According to the invention, by assigning appropriate values ​​to the parameters α and C in the above equation, it is possible to obtain a "double crown" profile if the manufactured strip is divided into two half strips. Moreover, it is also possible to obtain triple, quadruple and generally multiple crown profiles if the strip is divided into several parts in the longitudinal direction.

[0101] Once the profile (mechanical crown) of the work rolls 24a, 24b is determined, as shown in Figures 6, 9, 12, and 15, the extent of the crown on the strip is determined by the value of the axial movement (shift) δ of the work rolls 24a, 24b. s can be modified by changing

[0102] This is made possible because of the inherent consistency in the profiles of the work rolls 24a, 24b.

[0103] With reference to the example shown in figures 4 to 6, a strip S having a width of 2000 mm, corresponding to the width of the cast slab, is rolled to a double crown by work rolls 24a, 24b having a barrel length equal to 2450 mm, so as to be subsequently split longitudinally into two half strips of 1000 mm. It should be understood that these figures represent the case where the strip is split into two half strips of the same width, as shown in figure 3b, but do not exclude the possibility that the two parts of the strip have different widths.

[0104] As an example, the final finishing stand 16e (but could be the last two, three or more) comprises upper and lower work rolls 24a, 24b and upper and lower support rolls 25a, 25b, as shown in Figures 4a and 5a.

[0105] 4b-c and 5b-c show profiles of the upper work roll 24a and lower work roll 24b, respectively, at two different operating conditions.

[0106] In Figures 4b and 4c, the profile of the upper work roll 24a over the length of the barrel and the profile of the lower work roll 24b over the length of the barrel, in the absence of axial shift, are shown by lines L(T) and L(B), respectively.

[0107] In Figures 5b and 5c, dashed lines L(T) and L(B) show the profiles of the work rolls 24a, 24b over the entire length of the barrel, while solid lines L(Tu) and L(Bu) show the useful parts of the profiles of the work rolls acting on the strip S with axial shift as indicated by arrows F1 and F2 in Figure 5a.

[0108] Finally, Fig. 5d shows the resulting profile P(S) of the strip S as the sum of the profile L(Tu) and the profile L(Bu). The vertical edge lines indicate the lateral edges of the strip, while the central vertical line 26 indicates the centre point along which the strip S will subsequently be divided.

[0109] As can be observed from the graph, the profiles of the work rolls 24a, 24b, and the resulting profile P(S) of the strip, clearly comprise two humps and two corresponding valleys, in this particular example, a "double crown shape" NC which forms the desired crown in the resulting profiles of the two half strips into which the strip S is divided.

[0110] In particular, the crown on the work rolls 24a, 24b is "negative", i.e. has a concave shape, while a "positive" crown on the rolled strip S is obtained, i.e. has a convex shape.

[0111] Similarly, the connection segment 50 between the negative crowns NC on the work rolls 24a, 24b has a positive curvature, while the corresponding intermediate portion 40 obtained on the rolled strip S has a negative curvature corresponding to the central vertical line 26 along which the strip S is divided.

[0112] As can also be observed by comparing the curves above and below the horizontal axis in Figures 5d, 8d, 11d, and 14d, the positive crown PC and the intermediate portion 40 having negative curvature on the strip S have widths and depths / heights, respectively, that are substantially equal to each other.

[0113] In this way, the strip S can be divided longitudinally, corresponding to its centerline, and it is also possible to remove a small central band in order to make the crowns of the two half-strips "perfectly" symmetrical.

[0114] It should be considered that the extent of the crown of a single "hump" is a function of the axial shift of the work rolls 24a, 24b.

[0115] This has the advantage that the profile adjustment can be of dynamic rather than static type and the degree of shifting of the work rolls 24a, 24b varies in relation to the operating conditions of the work rolls 24a, 24b.

[0116] Furthermore, in order to maintain the uniformity of the cross section of the strip S in the last rolling stand, the same profile of the work rolls 24a, 24b can be applied to several stands and operated in different shift fields, without compromising the planarity of the strip S itself.

[0117] The graph of FIG. 6 shows how the crown of the strip S can be modified by affecting the shift, i.e. the axial displacement, of the two work rolls 24a, 24b in order to vary the surface portion of each roll that directly acts on the strip S.

[0118] Thanks to the axial shift of the work rolls 24a, 24b it is possible to accentuate or flatten the peaks and valleys of the profile of the strip S, which means increasing or decreasing the crown of the S strip.

[0119] The shifting of the work rolls 24a, 24b is symmetric, that is, the rolls are translated by equal amounts in opposite directions about the centerline M.

[0120] In the graphs of Figures 5a to 5d a shift equal to 50 mm was considered.

[0121] 7 and 8 represent the case where the strip S needs to be divided lengthwise into three parts, each of which has a width equal to 1 / 3 of the width of the strip S.

[0122] 7a and 8a show upper and lower work rolls 24a and 24b, respectively, having a triple negative crown profile.

[0123] Again, Figures 7b and 7c show the profile of the work rolls 24a, 24b over the entire barrel length in a reciprocating, non-shifting condition. Figures 8b and 8c show the effective working sections L(Bu), L(Tu) when the work rolls 24a, 24b are reciprocated 50 mm.

[0124] The reference number 26 in FIG. 8d represents two sections from which three parts can be obtained from the produced strip S.

[0125] As can be seen from FIG. 8d, it can be seen how the profiles of the work rolls 24a, 24b are formed with a negative crown NC so as to obtain a strip profile with a triple hump, in this case corresponding to section 26, to determine a resultant profile with a triple positive crown PC that is substantially symmetrical about the centerline of each of the (three) parts into which the strip S is divided.

[0126] FIG. 9 correspondingly illustrates the range of crown control obtainable by axially shifting the work rolls 24a, 24b which are formed to the shapes shown in FIGS. 7b and 7c.

[0127] Finally, in a manner substantially equivalent to the case described above, Figures 10 to 11 consider the case where the manufactured strip S needs to be divided into four parts, in this particular case all parts having substantially equal width.

[0128] It should be noted how the profiles of the work rolls 24a, 24b are formed into a quadruple negative crown, which is represented in the non-shifted condition in Fig. 10. Fig. 11 shows the shifted condition of the two work rolls 24a, 24b with the effective profiles L(Tu) and L(Bu) corresponding to the upper work roll 24a (Fig. 11b) and the lower work roll 24b (Fig. 11c) respectively shown in solid lines. In this case, the two work rolls 24a, 24b are shifted by 80 mm.

[0129] The resulting profile of the strip S (FIG. 11d) has four humps or positive crowns PC in substantially symmetrical positions, so that after separation in the longitudinal direction into four parts by means of sections 26, each part has the correct pre-established crown.

[0130] As in each of the above cases, crown control can be achieved by using axial shifting, for example as shown in FIG.

[0131] 13 to 15, in the same rolling mill with a work roll barrel length of 2450 mm, An example is shown in which a strip S is produced, said strip S having a width of 1600 mm corresponding to the width of the cast slab, which is then longitudinally divided into two half strips of 800 mm, always by rolling with a double crown.

[0132] In the example shown in Figures 13b and 13c, the work rolls 24a, 24b have a formed profile with a double negative crown with straight edge segments (not formed) since the width of the strip to be rolled is smaller than in the above-mentioned examples.

[0133] Figures 13b and 13c show the overall profiles of the work rolls 24a, 24b in a reciprocating, non-shifted condition, while Figures 14b and 14c show the overall profiles of the two work rolls 24a, 24b in a shifted condition. The effective profiles L(Tu) and L(Bu) corresponding to the upper work roll 24a (Figure 14b) and the lower work roll 24b (Figure 14c), respectively, are shown in solid lines. In this case, the work rolls 24a, 24b have been shifted by 50 mm.

[0134] The resulting profile of strip S (FIG. 14d) has two humps or positive crowns in substantially symmetrical positions, such that after separation longitudinally into two parts by means of sections 26, each part has a correct crown pre-established in accordance with the required quality requirements.

[0135] As in the previous case, crown control can be achieved by using axial shifting, as shown in the example of FIG.

[0136] As mentioned above, the operation of imparting a double (or triple, or quadruple, ...) crown to the strip is carried out in the last stand of the finishing mill 15, for example the last stand or the last two or three stands, especially in the case of low thicknesses.

[0137] Figure 16 shows how the amplitude of the angle α varies as a function of the total width of the rolled strip S, for example for a strip S with a double crown PC, including width values ​​between 800 and 2000 mm.

[0138] As mentioned above, multiple crown rolling can be selectively varied from center to periphery by requiring tight control over the cooling efficiency across the width of the work roll.

[0139] According to the present invention, as shown in FIG. 17 by way of example only, a cooling system 30 includes respective main feed pipes 31 and delivery nozzles 32 arranged across the entire width of the work rolls 24a, 24b, and one or more lamps 33 for delivering cooling fluid.

[0140] The delivery nozzles 32 are arranged adjacent to each other in two or three rows at a fixed pitch and are connected to the pipes 31 in independent groups so as to define independent differentiated cooling zones in the width direction of the roll. In the example shown in Figure 17, the ramp is divided into eleven independent cooling zones.

[0141] Each feed pipe 31 is equipped with its own proportional valve to regulate the flow to a corresponding group of nozzles 32 .

[0142] In this manner, groups of nozzles 32 can be individually controlled, thus varying the cooling of corresponding surface zones of the work rolls 24a, 24b.

[0143] According to the invention, each delivery ramp 33 can be divided into several, for example between 7 and 17, independent zones, also based on the width portion obtained starting from a given width of the strip. It thus becomes possible to define an appropriate variation of the cooling efficiency along the axis of the work rolls 24a, 24b, in order to individually control the cooling, in particular, of the two halves of the strip, or of the three, four and even more parts into which the strip S is subsequently divided.

[0144] For example, in the case of double crown machining, it is advantageous to have a minimum cooling efficiency around the central zone of the work rolls 24a, 24b, in which the thermal crown increases, while having a maximum cooling efficiency in the zone of the rolls operating corresponding to the central portions of the two halves of the strip, in which the thermal crown decreases. In this way, the thermal crown can be controlled to follow the trend of the mechanical crown.

[0145] For example, for work rolls 24a, 24b intended to produce a strip having a maximum width of 2000 mm, the width of each zone may vary from about 130 mm to about 220 mm.

[0146] According to some embodiments, for example, as illustrated in the example described with reference to FIG. 18, the cooling system 30 may include four cooling lamps 33 arranged in pairs at the inlet and outlet to the upper work roll 24a and lower work roll 24b for each of the multi-crown finishing stands 16a-16e.

[0147] The cooling ramps 33 are advantageously provided with drives 34 configured to move the cooling ramps 33 toward or away from the respective work rolls 24a, 24b and / or rotate the cooling ramps 33 to vary the angle of incidence of the coolant on the work rolls 24a, 24b.

[0148] According to some embodiments, the strip S may be cut longitudinally in a process downstream of the rolling mill 12 and then wound into a coil having an overall multiple crown profile.

[0149] According to some variants, the strip S is wound onto an initial head segment with a multiple crown shape, after which a cutting disk located upstream of the reel 21 can be driven to split the strip S longitudinally during winding. In this case, the longitudinal cut can be interrupted before the final tail end, so that this tail end remains intact as a head with a multiple crown profile.

[0150] It will be apparent that modifications and / or additions to components may be made to the plants and methods described hereinabove without departing from the field and scope of the present invention.

Claims

1. 1. A method for producing a flat rolled product to obtain a strip (S) having a multiple positive crown transverse profile, comprising: The method comprises a rolling step carried out in a rolling mill (12) including a number of finishing stands (16a, 16b, 16c, 16d, 16e) each equipped with a work roll (24a, 24b) so as to provide a strip (S) having a predetermined width, the work rolls (24a, 24b) of at least the last finishing stand (16e) have a multiple negative crown profile; a number of negative crowns (NC) in the profile of the work rolls (24a, 24b) is related to the number of portions into which the strip (S) to be rolled is longitudinally divided downstream of the plurality of finishing stands (16a, 16b, 16c, 16d, 16e); The negative crowns (NC) and connecting segments (50) having a positive curvature are alternately arranged, the work rolls (24a, 24b) are configured to have axial movement, the axial movement being performed to modify the position of the negative crown (NC) of the work rolls (24a, 24b) relative to the position of the strip (S) and the extent of the positive crown (PC) in the strip (S); providing differentiated cooling to the work rolls (24a, 24b) with a maximum cooling intensity corresponding to the negative crown (NC) and a minimum cooling intensity corresponding to the connection segment (50) having the positive curvature, to control thermal crown to follow a trend of mechanical crown of the work rolls (24a, 24b).

2. The method of claim 1, wherein widths of the connection segments (50) having the negative crown (NC) and the positive curvature in the work rolls (24a, 24b) are substantially equal to one another.

3. The last three of the finishing stands (16a, 16b, 16c, 16d, 16e) have work rolls (24a, 24b) having the same diameter and the same profile, The method of claim 1 or 2, wherein the profile of the work rolls (24a, 24b) having multiple negative crowns is applied to the last three of the finishing stands.

4. The equation of the curve of the forming profile of the work rolls (24a, 24b) is as follows: [0010] Here, D ｔ (y) is the diameter of the upper work roll, D ｂ (y) is the diameter of the lower work roll, D is the nominal diameter of the work roll, α is the angle of the modifiable shape of the curve of the gap between the work rolls, b is the barrel length of the work rolls, C is the amplitude of the sine curve, δ ０ is the value of the primary displacement of the formed curve of the work roll, and δ ｓ is the value of the relative movement from the first position, and a １ is the first coefficient, a ３ is the second coefficient, 4. The method according to claim 1, wherein by determining the parameters α and C, a profile of the multiple positive crowns is determined which is related to the number of portions into which the strip (S) is divided.

5. 5. The method according to claim 1, further comprising providing a differential cooling with a maximum cooling intensity around a central zone of the work rolls and a maximum cooling intensity in zones of the work rolls acting corresponding to the central portions of the two halves of the rolled strip, for a strip (S) having a double positive crown profile.

6. A plant for producing flat rolled products in order to obtain a strip (S) having a transverse profile of multiple positive crowns, comprising: The plant comprises at least one unit (15) comprising a finishing stand (16a-16e) having work rolls (24a, 24b), at least the last finishing stand (16e) of said finishing unit (15) has said work rolls (24a, 24b) with a multiple negative crown profile, in order to obtain a strip (S) which is divided longitudinally into a plurality of parts at the end of rolling and in the next step, the number of negative crowns (NC) in the profile of the work rolls (24a, 24b) is related to the number of portions into which the strip (S) to be rolled will subsequently be longitudinally divided; The negative crowns (NC) and connecting segments (50) having a positive curvature are alternately arranged, at least the work rolls (24a, 24b) are configured to have an axial movement, the magnitude and direction of the axial movement being related to a desired profile to be obtained in the strip (S); The plant further comprises a differentiated cooling system (30) for the work rolls (24a, 24b) having a cooling intensity adjustable as a function of the profile of the shaped multiple negative crowns of the work rolls (24a, 24b), The cooling system (30) includes a plurality of cooling ramps (33) each having a plurality of delivery nozzles (32) so as to define cooling zones that are independently differentiated in the width direction of the work rolls (24a, 24b), the plurality of delivery nozzles (32) being arranged adjacent to each other in two or three rows at a constant pitch, and each group of the delivery nozzles being connected to a corresponding plurality of feed pipes (31) that are independent of each other; each feed pipe (31) is provided with a proportional valve for adjusting the flow rate of the corresponding nozzle (32) by providing differentiated cooling to the work rolls (24a, 24b) including a minimum cooling intensity corresponding to the negative crown (NC) and a maximum cooling intensity corresponding to the connection segment (50) having the positive curvature, in order to control a thermal crown to follow a trend of the mechanical crown of the work rolls (24a, 24b).

7. 7. The plant of claim 6, wherein at least the last three stands (16a-16e) of the finishing unit (15) are equipped with work rolls (24a, 24b) having a multiple negative crown profile.

8. 8. A plant as claimed in claim 6 or claim 7, configured to operate in one of an endless mode, a semi-endless mode and a coil-to-coil mode.

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