Method and apparatus for producing flat rolled products

Abstract

The invention relates to a method and an apparatus for producing flat rolled products in order to obtain a strip (S) with a multi-crown transverse profile, which strip must subsequently be longitudinally divided into strips of smaller width; the method provides for a rolling step carried out in a rolling mill comprising roughing stands (14a, 14b, 14c) and finishing stands (16a, 16b, 16c, 16d, 16e) equipped with corresponding working rolls (24a, 24b) for supplying strips (S) of determined width.

Description

Technical Field

[0001] The present invention relates to a method for producing a flat rolled product, such as a strip, and to a corresponding production plant. In particular, the invention relates to a method and a plant for obtaining a strip having a final transverse profile with multiple crowns and optimal geometrical characteristics with respect to the strip's profile and flatness, even when the strip is subsequently divided into a plurality of longitudinal portions.

[0002] The invention can be applied to hot and cold rolling processes for producing strips of any type of ferrous or non-ferrous material. Background Art

[0003] Rolling plants are known which comprise a multi-stand rolling mill which is usually divided into a first roughing stand and a second finishing stand. A temperature recovery system may be provided between the roughing stand and the finishing stand.

[0004] The rolling mill may or may not be located together with a continuous caster for producing thin slabs (a so-called "slab caster").

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

[0006] The process can be of the semi-headless type, arranged to cut the slab to form multiple coils, or of the reel-to-reel type, arranged to produce one coil for each cut performed on the slab.

[0007] It is known that the strips obtained in plants of this type generally have a width that can vary from 600 mm to 2500 mm, depending on the intended use of the rolled material.

[0008] However, in order to meet market requirements, it is often necessary to produce coils that are narrower than the roller body, which leads to a decrease in equipment productivity.

[0009] For example, if one wishes to obtain a strip width of 800 or 1000 mm on a strip rolling plant capable of producing strips up to a maximum width of 2000 mm, casting slabs of 800 or 1000 mm width, the productivity of the plant will essentially be reduced by half, a disadvantage that should be avoided.

[0010] Thus, for example, it is known from JPS 58-68405 or JP 57-175003 to process a strip of standard width (e.g. 1600 mm) and then cut it in the longitudinal direction along the space between the stands of the rolling mill to obtain two strip halves, e.g. 800 mm wide, which are then wound onto separate coils.

[0011] This solution, while effective in maintaining productivity, has some drawbacks. The first drawback relates to the crowns of the two strip halves.

[0012] The dimensional quality of the product emerging from the hot rolling process is primarily determined by the thickness distribution across the width of the rolled strip. The geometry of the thickness across the width of the rolled product is known as the profile. The primary parameter analyzed to assess the profile of a rolled product is the crown. The crown represents the difference between the thickness at the center of the rolled product and the average thickness at the edges.

[0013] It is generally preferred to obtain a rolled product that is thicker in the center than at the edges; thus, viewed in cross section, it presents a lens shape that is symmetrical about the center line, e.g. Figure 2 As shown in a.

[0014] Creating an accurate profile during hot rolling is extremely important because this profile cannot be modified in downstream processes, as any possible modification would result in defects in flatness and difficulties in executing subsequent steps in the production cycle.

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

[0016] During the rolling process, a defined crown is imparted to the strip over the entire width by the rollers, but if the strip thus conforming to the requirements is subsequently split into two halves, each half no longer has a symmetrical crown, e.g. Figure 2 b: In fact, the profile of half of the strip has a trapezoidal shape (wedge shape) with different edge thicknesses on both sides.

[0017] However, this asymmetric profile is not well suited to the subsequent processing of the strip halves, making their downstream handling unstable, with the possibility of drift and winding difficulties. Therefore, in order to obtain two finished strip halves, each with its own regular profile, JP'405 provides for another rolling step in another stand in order to restore the symmetry of the profile by tapering the cut edges.

[0018] Furthermore, in JP'405, due to the high speeds involved, longitudinal cutting in the space between the stands is problematic, and controlling the two strip halves is even more problematic, especially when dealing with thin thicknesses.

[0019] The solution of JP'405 does not allow, in practice, the control of the crowns of the two strip halves, since in a single rolling stand the profiles of the strip halves are restored to a more or less symmetrical state only by the Hertzian pressure at the edges.

[0020] It is therefore understandable that, in the current state of the art, there is no technical solution for precisely controlling the crown if the rolled strip subsequently has to be split longitudinally into two strip halves before, during or even after coiling.

[0021] In this context, 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 quality and in terms of dimensional quality.

[0022] Furthermore, equipment manufacturers and steel producers are constantly seeking to reduce conversion costs while maintaining, if not improving, the mechanical properties and subsequent processability of the hot rolled products.

[0023] The following aspects are associated with the importance of the dimensional quality of hot rolled strip:

[0024] - In the production of some products, hot-rolled strip is gradually replacing cold-rolled strip;

[0025] - Simplification of the production process for converting hot-rolled strip into finished products;

[0026] - Improvement of geometrical characteristics in terms of thickness, profile and flatness. In fact, better geometric conditions make downstream processes more reliable and automated, while also improving the quality of the final product.

[0027] The above points lead to the requirement for “extreme” geometric features, such as:

[0028] Depending on the type of product, the crown target for the strip can vary from 70μm to 10μm. For some products (especially thin and ultra-thin thicknesses), the crown must be contained within 1.0-1.2% of the nominal thickness of the strip. In other words, for a strip with a thickness of 1.0mm, a crown of 10μm is required;

[0029] The flatness of the strip is less than 12 and 30 IU (I-Unit) depending on the thickness and width of the strip.

[0030] • Reduction of the thickness drop at the edges of the strip (edge ​​thinning).

[0031] Therefore, in the production of hot rolled strip in thin and ultra-thin thicknesses, in endless or semi-endless mode as well as in roll-to-roll mode, rolling stands with sufficient capacity to control the profile and flatness of the strip throughout the production mix are required.

[0032] Thus, it is known to use work rolls having a certain shape, ie an outer shape or profile described by a mathematical function, so that the shape of the rolling gap can be varied by axial displacement of the rolls in opposite directions.

[0033] Regarding the crown, it must also be considered that the heating of the rolls is one of the fundamental issues faced in both hot and cold rolling. The direct contact between the rolled strip and the work rolls determines the heat flow, through the heat transfer to the rolls themselves and the subsequent heating of them; this requires changes in the size (diameter) and profile of the rolls themselves.

[0034] In order to limit the above-mentioned heating to values ​​adapted to the properties of the material constituting the roll and, for example, to contain the gradual deterioration of the roll surface to acceptable values, a cooling system is used.

[0035] A commonly used technical solution in hot rolling is to cool the work rolls externally using a series of nozzles mounted on ramps. In a conventional four-high-roll stand for hot strip mills, four cooling units are typically used: two in the exit area and two in the entry area. Each unit consists of one or more cooling ramps. To prevent heat transferred from the rolled material to the rolls from penetrating from the surface layer into the roll interior (making it difficult to subsequently extract the accumulated heat), it is preferable to increase the heat exchange between the rolls and the cooling water in the exit area of ​​the rolling gap, thereby increasing the flow rate and, potentially, the heat exchange efficiency.

[0036] The heat transferred to the roll creates a thermal crown; axial heat flow occurs in the roll, as heat flows from the center to the cooler sides, which are not exposed to the strip. The result is a differential expansion, which generally produces a quasi-parabolic roll profile in the center, while it decreases sharply at the edges of the strip and then remains at a lower value than in the center.

[0037] Variations in the “thermal profile” of the rolls obviously affect the rolling process and in particular the control of thickness, profile and flatness; therefore, the task of the system for cooling the rolls is to minimize the disturbances caused by variations in the thermal profile, without affecting the roll temperature, which must on average reach values ​​varying from 50 to 80°C (depending on the material constituting the roll jackets), in order to optimize the duration of operation and thus reduce surface wear caused by thermal fatigue and friction between the strip and the rolls.

[0038] These problems, already severe in the case of hot rolling using conventional processes, are even more severe with the headless production process, where rolling on the strip finishing mill can last for 10 hours uninterrupted, compared to 2-3 minutes in the conventional roll-to-roll process.

[0039] The thermal crown of the work rolls depends on the temperature distribution along the rolls; this distribution changes continuously during the rolling campaign, causing the thermal crown to increase or decrease as the working profile of the rolls changes. This phenomenon interferes with the control of the profile and flatness of the strip being rolled.

[0040] When the rolls are cold, for example after a roll change or a long production break, the thermal crown increases gradually; it takes 5 to 10 coils to reach a stable value.

[0041] When stable conditions are reached during the rolling mill cycle, the thermal crown will decrease during the waiting time between one coil and the next, returning to the average value of the thermal crown after a relatively short time from the start of rolling of the new coil.

[0042] In view of the above, one object of the present invention is to provide a method and a corresponding device for producing a finished thin or even ultra-thin strip which can subsequently be split longitudinally to obtain 2, 3, 4 or more different strip portions, each portion of the strip having optimal qualities in terms of cross-sectional profile, flatness and thickness.

[0043] The invention also aims to keep the productivity of the rolling mill constant, whether strips having a width equal to the maximum width or strips having a width less than said maximum width are to be produced.

[0044] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages. Summary of the Invention

[0045] The invention is set forth and characterized in the independent claims. The dependent claims describe variants or embodiments defining the main inventive idea.

[0046] According to one embodiment of the present invention, the slab is cast with a width determined by the design parameters of the equipment itself, such as the width of the mold, the scale of the production line, the required productivity, etc., and is sent to the hot strip rolling mill to obtain the final required thickness.

[0047] According to another embodiment of the present invention, the hot rolled strip is further rolled in a cold rolling mill to obtain a thinner thickness.

[0048] In both embodiments, the working rolls of the stands of the rolling mill are configured to impart to the strip a transverse profile having a number of crowns associated with the number of longitudinal portions into which the strip is subsequently divided.

[0049] In the following text we will use the following terms:

[0050] · A “positive” crown indicates a symmetrical lens-shaped profile that is thicker in the center, e.g. Figure 2 As shown in a;

[0051] A "negative" crown indicates a biconcave symmetrical profile that matches or complements the lenticular surface, being thinner in the center than at the edges.

[0052] According to the invention, the object is to produce two or more positive crowns on the rolled strip by using work rolls with profiled surfaces having two or more corresponding negative crowns.

[0053] The invention thus provides for the use of work rolls with a single crown when the finished strip is used in the width of the starting product fed to the rolling mill, and for the use of work rolls with a double crown, triple crown, quad crown or in any case a plurality of crowns when the rolled strip has to be subsequently split longitudinally into two, three, four or, in general, into a certain number of longitudinal portions of the strip.

[0054] The longitudinal splitting of the strip can be carried out along the entire length of the strip from beginning to end at a point between the exit of the last stand and the respective different winding units on which the respective coils of the strip portions are formed, or the longitudinal splitting of the strip can be carried out along the entire length of the strip except for the head and tail sections before winding into individual coils, or the longitudinal splitting of the strip can be carried out after the coil has been removed from the winding units, for example at the destination location of the coil itself.

[0055] According to the invention, at least the last stand of a rolling mill (for example the last stand of a finishing mill, or the last two or three stands of a finishing mill) comprises work rolls whose surfaces in contact with the strip have a shaped profile associated with and dependent on the portion of the strip subsequently obtained by longitudinal cutting.

[0056] In other words, if the strip is split longitudinally into two strip halves (double crown), the profile of the work roll will have a double negative crown, if the strip is split longitudinally into three strip parts (triple crown), it will have a triple negative crown, and so on.

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

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

[0059] D t (y) = D - C sin α / b (y - δ s -δ0)+a1(y-δ s -δ0)+a3(y-δ s -δ0) 3

[0060] D b (y) = D + Csinα / b(y + δ s +δ0)+a1(y+δ s +δ0)+a3(y+δ s +δ0) 3

[0061] in:

[0062] D t (y) is the diameter of the upper work roll;

[0063] D b (y) is the diameter of the lower work roll;

[0064] D is the nominal diameter of the work roll;

[0065] α is the angle of the modifiable shape of the curve of the gap between the rollers;

[0066] b is the barrel length of the working roll;

[0067] C is the amplitude of the sinusoid;

[0068] δ0 is the primary displacement value of the shaping curve of the roller;

[0069] δ s It refers to the relative movement value starting from the primary position;

[0070] a1 is the first coefficient;

[0071] a3 is the second coefficient;

[0072] In particular, amplitude "C" refers to the width of a single crown.

[0073] The value of the crown can also be modified by changing the value of the axial movement (displacement) of the working roll δ0. By changing the parameters α and C in the above formula, the crown function of the gap between the rolls will determine a set of different curves.

[0074] Thus, according to the invention, by assigning suitable values ​​to the coefficients α and C in the above formula, it is possible to obtain a "double crown" profile in the case of a strip produced divided into two halves, and even a triple crown profile or a quadruple crown profile, in general a multi-crown profile, in the case of a strip divided longitudinally into several parts.

[0075] As mentioned above, in the case of particularly thin thickness, a double crown (or triple crown, or quadruple crown . . . ) operation is performed on the strip at the last stand of the finishing mill (eg the last or last two or three stands).

[0076] It should be noted that in a finishing mill with five, six or seven finishing stands, the last three stands generally have work rolls of the same diameter and profile. Therefore, according to the present invention, it is convenient to produce multiple crowns on the last three stands of the finishing mill.

[0077] The invention thus provides for the production of a finished strip with multiple crowns, which is subsequently divided longitudinally in such a way as to obtain a plurality of distinct strip portions, each with its own crown, as if they were rolled individually.

[0078] In this way, each portion of the strip has the correct crown to obtain the required geometric and dimensional characteristics in terms of thickness, profile and flatness.

[0079] According to the invention, in order to control the multiple crowns more accurately, in addition to the mechanical crowns of the work rolls, intervention is also carried out on their thermal crowns using the cooling method described below.

[0080] According to the present invention, in the case of double-crown rolling, it is advantageous to have minimal cooling efficiency around the center area of ​​the work rolls, so that the thermal crown increases in this area where the strip will be subsequently split, and conversely, to have maximum cooling efficiency in the central portion corresponding to the two strip halves, so that the thermal crown decreases in the central area of ​​each strip half. In other words, the thermal crown of the work rolls is controlled so that it follows the trend of strengthening its mechanical crown. Similarly, for triple-crown, quad-crown, and so on, the crown cooling of the work rolls is similarly adjusted, with less cooling where the strip will be split and more cooling in the central area of ​​the corresponding multi-strip.

[0081] The control of the cooling system is generally achieved by means of an online model which processes a series of information about the process status (strip temperature, rolling force, thickness reduction, rolling speed, etc.) at time intervals to determine the thermal profile.

[0082] The possibility of varying the cooling efficiency over the width according to the invention allows, along a double crown or generally a multi-crown rolling cycle, to define an optimum hot crown in order to maximize the profile / flatness control capabilities on the portions of the strip subsequently divided. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] This and other features of the invention will now be described in detail with reference to some particular embodiments of the invention given as non-limiting examples with reference to the accompanying drawings, in which:

[0084] - Figure 1 An example of the layout of a hot strip rolling plant to which the production method according to the present invention is applicable is shown;

[0085] - Figure 2 a and Figure 2 b shows a cross section of a strip and two halves of a strip respectively obtained by longitudinal cutting through the strip according to the prior art;

[0086] - Figure 3 a and Figure 3 b shows cross sections of one strip and two halves of a strip obtained by longitudinal cutting of a strip according to an embodiment of the present invention;

[0087] - Figures 4 to 15 Graphs showing the profiles of the work rolls for a double crown profile, a triple crown profile and a quadruple crown profile for a strip width of 2000 mm and for a double crown profile for a strip width of 1600 mm, and graphs showing the resulting corresponding profiles of the strip;

[0088] - Figure 16 A diagram showing the variation trend of the angle α as a function of the width of the processed strip in the case of a double crown;

[0089] - Figure 17 An embodiment of a differential cooling system for work rolls used in the production method according to the present invention is shown;

[0090] - Figure 18 The positioning of the nozzles of the cooling system relative to the working rolls is shown schematically. DETAILED DESCRIPTION

[0091] Reference Figure 1 , shows an example of a co-rolling installation 10 for producing a strip S, in which a machine 11 for casting thin plates feeds a hot strip mill 12 .

[0092] It should be noted that the examples shown should not be considered as limiting in any way the applicability of the invention, since the presented concept can be applied to many other types of plants, with a different number of stands, with casting separated from the rolling mill, with slabs produced elsewhere, and in all cases where a metal strip having a determined nominal width at the end of rolling has to be longitudinally divided into several parts in order to obtain strip portions having a smaller width.

[0093] Although the embodiment disclosed in the figures represents a hot rolling mill in line with a casting mill, the invention is also applicable to cold rolling mills in which the strip obtained by a preceding hot working step is rolled.

[0094] In the case of a hot rolling process, as previously mentioned, the starting semi-finished product is represented by a slab which can be cast on-line on the same equipment (e.g. Figure 1 (disclosed in the embodiments of the present invention), can also be produced offline or on another device.

[0095] In the case of a cold rolling process, the starting semi-finished product is represented by a rolled strip coil previously produced in a hot rolling mill. According to the invention, during cold rolling, in order for the rolls to be able to apply multiple crowns to a previously hot-rolled strip with a single crown, the strip thickness is preferably at least 2.5 mm. Below this value, the strip to be cold-rolled preferably does not have a single crown profile, but rather already has the desired number of final crowns at the end of the cold rolling process. In this case, during the cold rolling process, the rolls are shaped to follow the multiple crown profile already applied to the strip during the previous hot rolling process.

[0096] Furthermore, the present invention may be used to produce both ferrous metal (eg, steel) and non-ferrous metal (eg, aluminum) strip.

[0097] exist Figure 1 In the particular example shown, the rolling mill 12 includes a roughing unit 13 (or roughing mill), and a finishing unit 15 (or finishing mill), the roughing unit 13 including in this case three stands 14a, 14b and 14c, and the finishing unit 15 including in this case five stands 16a, 16b, 16c, 16d and 16e.

[0098] A temperature recovery system, such as an induction furnace 20, is provided between the roughing unit 13 and the finishing unit 15, which recovers the slab coming out of the roughing unit 13 to the correct rolling temperature.

[0099] Between the casting machine 11 and the roughing unit 13 there is a tunnel furnace 17, which is long enough to accommodate a number of slabs between at least 2 and 5. This tunnel furnace 17 allows, in a known manner, to be used as a buffer area in the event of an interruption (even temporarily) of the rolling mill due to an accident or a planned change of work rolls, and also allows operation in semi-endless mode.

[0100] Upstream of the tunnel furnace 17 there is a first pendulum shear 18 which cuts the slabs to size when the plant 10 is operated in reel-to-reel or semi-endless mode.

[0101] Downstream of the finishing mill 15 there are a cooling device 22 and a second flying shear 19 which intervenes in the case of endless or semi-endless rolling to separate the strip caught on one of the two lower coilers 21 or on the reel.

[0102] According to one variant of the invention, the strip obtained is subsequently divided longitudinally (slit) in order to obtain portions of the strip having a width which is a factor of the width of the strand, or in any case smaller than the width of the strand.

[0103] In this way, strips with smaller widths can be obtained from individual rolled strips without in any way limiting the overall productivity of the plant, so that it is always possible to work with slabs and strips with a width close to the maximum width set for the plant itself.

[0104] The width division of the finished rolled strip can be carried out directly in the production line, at the exit of the rolling mill, or in a step after the coil has been removed, for example in a different end-of-line machine using the strip.

[0105] In the first case, the following can be considered when dividing the downstream of the finishing mill 15 into two parts, for example:

[0106] - Winding the two different halves S1, S2 of the strip onto respective reels 21 over the entire length of the strip S from beginning to end: in this way, two different coils are obtained;

[0107] - The entire length of the strip S except its head and tail portions to facilitate winding of the head into a single reel and the final tail-end turn: in this way there is a single coil divided into two parts for almost the entire length of the coil.

[0108] For this purpose, a special cutting device can be provided to longitudinally separate the strip S into two or more strip portions S1, S2 having the same or different widths. Advantageously, these devices can be inserted into or withdrawn from the production line as required.

[0109] Depending on the number of width sections into which the strip S is to be divided, the invention provides for profiling the work rolls 24a, 24b on at least some of the final finishing stands 16a-16e so as to define the correct crown on each section into which the strip is to be divided.

[0110] For example, Figure 3a and Figure 3 FIG. 2 b shows a cross section of the strip S downstream of the rolling mill 12 and a cross section of the two halves S1 and S2 obtained by longitudinally cutting the strip S along the center line. In this example, the strip S has a "double positive crown" that is approximately symmetrical with respect to a symmetry plane passing through the center line M, while the two halves S1 and S2 each have their own single positive crown.

[0111] Thus, if the strip is split in width into two strip halves, the profile of the work rolls 24a, 24b will show a double negative crown, one negative crown for each strip half obtained or obtainable downstream, and also in the case of a strip having three, four or more split strip portions.

[0112] The profile of each work roll 24a, 24b can be defined by a curve composed of an antisymmetric trigonometric function and a third-order polynomial function.

[0113] The curve equation of the profile is as follows:

[0114] D t (y) = D - C sin α / b (y - δ s -δ0)+a1(y-δ s -δ0)+a3(y-δ s -δ0) 3

[0115] D b (y) = D + Csinα / b(y + δ s +δ0)+a1(y+δ s +δ0)+a3(y+δ s +δ0) 3

[0116] in,

[0117] D t (y) is the diameter of the upper work roll 24a;

[0118] D b (y) is the diameter of the lower work roll 24b;

[0119] D is the nominal diameter of the work roll;

[0120] α is the angle of the modifiable shape of the curve of the gap between the rollers;

[0121] b is the barrel length of the working roll;

[0122] C is the amplitude of the sinusoid;

[0123] δ0 is the primary displacement value of the shaping curve of the roller;

[0124] δ s is the relative movement value from the primary position;

[0125] a1 is the first coefficient;

[0126] a3 is the second coefficient.

[0127] According to the invention, by assigning suitable values ​​to the coefficients α and C in the above formula, it is possible to obtain a "double crown" profile in the case of a strip produced that is split into two halves, or even a triple crown profile or a quadruple crown profile, in general a multi-crown profile, in the case of a strip split longitudinally into several parts.

[0128] Once the profile (mechanical crown) of the work rolls 24a, 24b has been determined, the extent of the crown on the strip can be modified by changing the value δs of the axial movement (displacement) of the work rolls 24a, 24b, as Figure 6 、 Figure 9 、 Figure 12 、 Figure 15 shown.

[0129] Reference Figure 4-Figure 6 , shows an example in which a strip S has a width of 2000 mm, corresponding to the width of the strand, and is rolled by work rolls 24a, 24b having a barrel length equal to 2450 mm through a double crown section in order to be subsequently split longitudinally into two strip halves of 1000 mm. It should be understood that these figures represent the case of splitting into two halves of equal width, as shown in FIG. Figure 3 As shown in b, we do not exclude that the two strip parts may have different widths.

[0130] As an example, the last finishing stand 16e (however, it may be the last two, three or more) is Figure 4 a and Figure 5 In a, it is shown as including upper and lower working rolls 24a and 24b, and upper and lower support rolls 25a and 25b.

[0131] Figure 4 b- Figure 4 c and Figure 5 b- Figure 5 C respectively represents the profiles of the upper working roll 24a and the lower working roll 24b under two different operating conditions.

[0132] exist Figure 4 b and Figure 4 In c, the profiles of the work rolls 24a and 24b are represented by line L(T) for the upper work roll 24a and line L(B) for the lower work roll 24b for the entire length of the roll barrel under non-axial movement conditions.

[0133] exist Figure 5 b and Figure 5 c, under the condition of axial movement, such as Figure 5 As indicated by the arrows F1 and F2 in a, the lines L(T) and L(B) indicated in dashed lines again represent the profile of the entire roll length of the work rolls 24a, 24b, while the solid lines L(Tu) and L(Bu) represent the useful part of the profile of the work rolls acting on the strip S.

[0134] at last, Figure 5 d shows the resultant profile P(S) of the strip S as the sum of the profiles L(Tu) and L(Bu). The vertical end lines indicate the lateral edges of the strip S, while the central vertical line 26 indicates the center point where the strip S will be divided.

[0135] As can be seen from the figure, the profile of the working rolls 24a, 24b and obviously the resulting profile P(S) of the strip has a "double crown" shape with two ridges and two corresponding grooves, which create the required crowns on the resulting profile of the two strip halves into which the strip S is to be divided in this particular case.

[0136] In particular, the crown on the working rolls 24a, 24b is "negative", ie has a concave shape, whereas on the rolled strip S a "positive" crown is obtained, ie has a convex shape.

[0137] In this way, the strip S can be divided longitudinally along its centre line and a small central strip can be removed so that the crowns of the two halves of the strip are "perfectly" symmetrical.

[0138] It should be considered that the crown extent of a single "bump" is a function of the axial displacement of the work rolls 24a, 24b.

[0139] This is advantageous because the adjustment of the profile is not static but can be dynamic and the displacement range of the work rolls 24a, 24b varies with the operating conditions of the work rolls 24a, 24b.

[0140] Furthermore, the same profile of the work rolls 24a, 24b can be applied to several stands, operating them in different displacement zones, in order to maintain the homogeneity of the cross section of the strip S in the final rolling stand. This is so as not to affect the flatness of the strip S itself.

[0141] Figure 6 The figures show how the crown of the strip S is modified by acting on the shift, ie the axial displacement of the two working rolls 24a, 24b, thereby modifying the surface portion of the corresponding roll acting directly on the strip S.

[0142] Due to the axial displacement of the work rolls 24 a and 24 b , the ridges and valleys of the profile of the strip S can be made protruding or flattened, which means that the crown of the strip S is increased or decreased.

[0143] The displacement of the working rolls 24a and 24b is symmetrical, that is, these rolls are translated by equal amounts in opposite directions relative to the center line M.

[0144] exist Figure 5 a- Figure 5 In the graph of d, a displacement equal to 50 mm is taken into account.

[0145] Figure 7 and Figure 8 Indicates the case where the strip S has to be divided longitudinally into three parts, in which case each part has a width equal to 1 / 3 of the width of the strip S.

[0146] Figure 7 a and Figure 8 a shows an upper working roll 24a and a lower working roll 24b, each of which has a profile with a triple negative crown.

[0147] Also in this case, Figure 7 b. Figure 7 c represents the profile of the entire roll length of the working rolls 24a, 24b under the reciprocating non-displacement condition, and Figure 8 b and Figure 8 c represents the profiles of the useful working portions L(Bu) and L(Tu) of the working rolls 24a and 24b under the condition that they reciprocate by 50 mm.

[0148] Figure 8 The number 26 in d indicates two sections which allow three parts to be obtained from the strip S produced.

[0149] It can be seen how the profiles of the working rolls 24a and 24b are formed to have a negative crown in order to obtain a profile of the strip with three ridges, as in Figure 8 d, the three ridges determine a resultant profile having three positive crowns which, in this case corresponding to the sectors 26, are substantially symmetrical with respect to the centre line of each of the (three) parts into which the strip S is divided.

[0150] Figure 9 In a corresponding manner, the Figure 7 b and Figure 7 c shows the range of crown control that can be achieved by axially shifting the work rolls 24a, 24b that determine the shape.

[0151] Finally, in a manner roughly equivalent to the above, Figure 10 and Figure 11This relates to the case where a produced strip S has to be divided into four parts, in this particular case all of the strips having approximately the same width.

[0152] Without repeating the concepts expressed above, we wish to point out how the profiles of the work rolls 24a, 24b are formed as four negative crowns and Figure 10 The middle is expressed in non-shifted condition. Figure 11 Represents the shifting conditions of the two working rolls 24a and 24b, and the useful profile L(Tu) of the upper working roll 24a ( Figure 11 b) and the useful profile L(Bu) of the lower working roll 24b ( Figure 11 c) are respectively represented by solid lines. In this case, the two working rollers 24a, 24b are displaced by 80 mm.

[0153] The composite profile of strip S ( Figure 11 d) Having four ridges or positive crowns in generally symmetrical positions so that after longitudinal separation of the four parts by section 26, each part has the correct pre-defined crown.

[0154] As in the previous case, the use of axial displacement allows control of the crown, e.g. Figure 12 shown.

[0155] Reference Figure 13-15 , shows the following example: the strip S is produced on the same rolling mill with a working roll barrel length of 2450 mm and is always rolled with a double crown so as to be subsequently split longitudinally into two 800 mm half-strips, said strip S having a width of 1600 mm corresponding to the width of the cast strand.

[0156] Figure 13 b and Figure 13 The working rolls 24a, 24b shown in c have in this exemplary case a shaped profile with a double negative crown having a straight end section (unshaped) since the strip to be rolled now has a smaller width than in the previous example.

[0157] Figure 13 b. Figure 13 c represents the overall profile of the working rolls 24a, 24b under the reciprocating non-displacement condition, and Figure 14 b and Figure 14 c represents the displacement condition of the two working rolls 24a and 24b, and the useful working profile L(Tu) of the upper working roll 24a ( Figure 14 b) and lower working roll 24b ( Figure 14 The useful working profile L(Bu) of c) is respectively indicated by a solid line. The working rolls 24a, 24b in this exemplary case are displaced by 50 mm.

[0158] The composite profile of strip S ( Figure 14 d) having two ridges or positive crowns in a generally symmetrical position, so that after longitudinal separation of the two parts by the section 26, each part has the correct crown pre-determined according to the required quality requirements.

[0159] As in the previous case, the use of axial displacement allows control of the crown, e.g. Figure 15 shown.

[0160] As mentioned above, for example, in the case of particularly thin thickness, a double crown (or triple crown, or quadruple crown . . . ) operation is performed on the strip at the last stand of the finishing mill 15 , for example, at the last or last two or three stands.

[0161] Figure 16 It is shown how the amplitude of the angle α varies as a function of the total width of the rolled strip S for width values ​​between 800 and 2000 mm, for example in the case of a strip S with a double crown.

[0162] As mentioned above, multi-crown rolling requires strict control of the cooling efficiency across the width of the work rolls so that it can be selectively varied from the center to the periphery.

[0163] According to the present invention, as shown by way of example only Figure 17 As shown in FIG, a cooling system 30 is provided which comprises one or more ramps 33 for delivering cooling fluid with respective main supply ducts 31 and delivery nozzles 32 distributed over the entire width of the working rolls 24a, 24b.

[0164] The delivery nozzles 32 are arranged adjacent to each other in double or triple rows with defined spacing and are connected to the pipes 31 in groups independently of each other in order to define independent and differentiated cooling zones across the width of the roll. Figure 17 In the example shown, the ramp is divided into 11 separate cooling zones.

[0165] Each supply line 31 is equipped with its own proportional valve, which regulates the flow rate to the respective group of nozzles 32 .

[0166] In this way, it is possible to have an individual management of the groups of nozzles 32 and thus to vary the cooling on the respective surface areas of the working rolls 24 a , 24 b .

[0167] According to the invention, each conveying ramp 33 can be divided into a plurality of independent zones, for example between 7 and 17, also based on the width fractions obtained starting from the width of a given strip. Thus, it is possible to define a suitable variation in the cooling efficiency along the axes of the working rolls 24 a, 24 b, in particular in order to individually control the cooling of the two halves of the strip into which the strip S is subsequently divided, or of three, four or more parts.

[0168] For example, in the case of double crown operation, it is advantageous to have the lowest cooling efficiency around the central zone of the work rolls 24a, 24b so that the thermal crown increases in this area, and conversely, to have the highest cooling efficiency in the area corresponding to the central portion of the rolls corresponding to the two halves of the strip so that the thermal crown decreases in this area. In this way, the thermal crown can be controlled so that it follows the trend of the mechanical crown.

[0169] For example, with work rolls 24a, 24b used 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.

[0170] According to, for example, Figure 18 In some described embodiments, the cooling system 30 may include four cooling ramps 33 for each of the multiple crown finishing stands 16a-16e arranged in pairs at the entrance and exit of the upper and lower work rolls 24a and 24b.

[0171] The cooling ramp 33 may advantageously be provided with a drive device 34 configured to move the cooling ramp 33 toward / away from the respective working rolls 24a, 24b or to rotate the cooling ramp 33 relative to the respective working rolls 24a, 24b to change the incident angle of the coolant on the working rolls 24a, 24b.

[0172] According to some embodiments, the strip S may be longitudinally cut in a process downstream of the rolling mill 12 and then fully wound into a coil having a multi-crown profile.

[0173] According to some variants, it can be provided that the strip S is wound for an initial head section with a multi-crown profile, and then a cutting disc located upstream of the reel 21 is driven to longitudinally split the strip S while the winding continues. In this case, the longitudinal cut can be interrupted before the final tail end, thus maintaining the entirety of the head section with a multi-crown profile.

[0174] Obviously, modifications and / or additions may be made to the above-described apparatus and method without departing from the field and scope of the present invention.

Claims

1. A method for producing flat rolled products to obtain a strip (S) with a multi-positive crown transverse profile, said method providing a rolling step carried out in a rolling mill (12) comprising finishing stands (16a, 16b, 16c, 16d, 16e) equipped with corresponding working rolls (24a, 24b) to supply a strip (S) of a determined width, wherein: The working rolls (24a, 24b) of at least the last finishing stand (16e) are arranged with a profile having multiple negative crowns, wherein the number of crowns present in the profile of the working rolls (24a, 24b) is correlated with the number of positive crowns on the strip (S) and the number of parts into which the produced rolled strip (S) is subsequently divided in the longitudinal direction, characterised in that the method provides for cooling the working rolls (24a, 24b) with a cooling intensity which is adjusted as a function of the profile of the working rolls (24a, 24b) with multiple negative crowns and therefore as a function of the profile of the strip (S) with multiple positive crowns, by a or a plurality of ramps (33) for delivering cooling fluid with corresponding main supply ducts (31) and delivery nozzles (32) distributed over the entire width of the working rolls (24a, 24b), wherein each supply duct (31) is equipped with its own proportional valve, which is configured to regulate the flow rate to each group of nozzles (32) so as to have individual management of the groups of nozzles (32), wherein the method provides for controlling the thermal crown of the working rolls (24a, 24b) so that the thermal crown follows and reinforces the tendency of the mechanical crown of the working rolls (24a, 24b), with less cooling where the strip (S) is to be split and more cooling in the central area of ​​the corresponding multi-strip.

2. The method according to claim 1, wherein The working rolls (24a, 24b) are arranged to have an axial displacement movement, and wherein the axial displacement movement allows modifying the position of the crowns of the working rolls (24a, 24b) relative to the position of the strip (S).

3. The method according to claim 1, wherein The last three finishing stands (16a-16e) have working rolls (24a, 24b) of the same diameter and the same profile, and wherein the profile of the working rolls (24a, 24b) with multiple negative crowns is applied to the last three finishing stands.

4. The method according to claim 1, wherein The curve equation of the shaped profile of the working rolls (24a, 24b) is as follows: D t (y)=DC sinα / b(y-δ s -δ0)+a1(y-δ s -δ0)+a3(y-δ s -δ0) 3 D b (y)=D+C sinα / b(y+δ s +δ0)+a1(y+δ s +δ0)+a3(y+δ s +δ0) 3 in, 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 working roll; α is the angle of the modifiable shape of the curve of the gap between the working rolls; b is the roller body length of the working roller; C is the amplitude of the sinusoid; δ0 is the primary displacement value of the shaping curve of the working roll; δ s is the relative movement value from the primary position; a1 is the first coefficient; a3 is the second coefficient; and wherein, by acting on parameters α and C, a multi-crown profile is determined in relation to the number of strip portions into which said strip (S) is divided.

5. A method according to any one of the preceding claims, wherein In the case of a double crown profile, differentiated cooling is provided, with minimum cooling intensity around the central area of ​​the working rolls (24a, 24b) and maximum cooling intensity in the areas corresponding to the central parts of the working rolls (24a, 24b) corresponding to the two halves of the rolled strip (S).

6. A finishing stand of a rolling mill (10) for strip (S), comprising work rolls (24a, 24b) with a multi-negative crown profile, wherein: The number of crowns present in the profile of the working rolls (24a, 24b) is correlated with the number of positive crowns on the strip (S) and the number of parts into which the produced strip (S) is intended to be divided longitudinally, characterised in that the finishing stand comprises a differential cooling system (30) for cooling the working rolls (24a, 24b) by means of a control device for adjusting the cooling intensity as a function of the multi-negative crown profile of the working rolls (24a, 24b) and therefore as a function of the multi-positive crown profile of the strip (S), wherein the differential cooling system (30) ) comprises one or more ramps (33) for delivering cooling fluid with corresponding main supply ducts (31) and delivery nozzles (32) distributed over the entire width of the working rolls (24a, 24b), wherein each supply duct (31) is equipped with its own proportional valve, which is configured to regulate the flow rate to each group of nozzles (32) so as to have individual management of the groups of nozzles (32) and thus vary the cooling on the corresponding surface areas of the working rolls (24a, 24b) so as to control the thermal crown of the working rolls (24a, 24b) so that the thermal crown follows and enhances the tendency of the mechanical crown of the working rolls (24a, 24b).

7. Plant for producing flat rolled products to obtain a strip (S) with a multi-positive crown transverse profile, said plant comprising a unit (15) of at least one finishing stand (16a-16e) with working rolls (24a, 24b), characterized in that In order to obtain a strip (S) which is longitudinally divided into a plurality of parts in a subsequent step and after the rolling is completed, at least the last finishing stand (16e) of the finishing unit (15) is a finishing stand according to claim 6.

8. The apparatus of claim 7, wherein: At least the last three stands (16a-16e) of the finishing unit (15) have working rolls (24a, 24b) with a multi-negative crown profile.

9. The apparatus of claim 7, wherein: At least the working rolls (24a, 24b) have an axial displacement movement, wherein the magnitude and direction of the axial displacement movement are correlated with obtaining a desired profile to be obtained on the strip (S).

10. The apparatus of claim 7, configured to operate in one and / or another of a headless mode, a semi-headless mode, or a roll-to-roll mode.

11. The device according to any one of claims 7 to 10, characterized in that The delivery nozzles (32) are arranged adjacent to each other in two or three rows at a defined distance from each other and are connected in groups independently of each other to corresponding supply pipes (31) in order to define independent and differentiated cooling zones across the width of the rolls (24a, 24b).

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