METHOD AND PLANT FOR PRODUCING FLAT ROLLED PRODUCTS

Abstract

The invention concerns a method and a plant for producing flat rolled products, in order to obtain strips having a multiple crown transverse profile that subsequently have to be divided in a longitudinal direction into strips of a smaller width; the method provides a rolling step carried out in a rolling mill comprising roughing stands and finishing stands equipped with respective work rolls, in order to supply a strip of a determinate width.

Claims

1. A method for producing flat rolled products, in order to obtain strips with a multiple positive crown transverse profile, which provides a rolling step carried out in a rolling mill comprising finishing stands equipped with respective work rolls, in order to supply a strip of a determinate width, wherein at least the work rolls of at least the last finishing stand are provided to have a profile with multiple negative crown, wherein the number of crowns present in the profile of the work rolls is correlated to the number of portions into which the rolled strip produced is subsequently divided in a longitudinal direction, wherein said method provides to cool the work rolls with cooling intensity which is adjusted as a function of the multiple negative crown shaped profile of the work rolls, delivering a cooling fluid by means of one or more ramps with respective main feed pipes and delivery nozzles distributed over the entire width of the work rolls, wherein each feed pipe is equipped with its own proportional valve which is configured to regulate the flow rate to a respective group of nozzles in order to have a separate management of the groups of nozzles, wherein said method provides to control a thermal crown of the work roll so that it follows the trend of the mechanical crown enhancing it, cooling less where the strip will be divided and cooling more in the central zones of the respective multi-strips.

2. The method as in claim 1, wherein the work rolls are provided to have an axial shifting movement, and wherein said axial shifting movement allows to modify the position of the crowns of the work rolls with respect to the position of the strip.

3. The method as in claim 1, wherein the last three finishing stands have work rolls with the same diameter and same profile, and wherein the profile of the work rolls with multiple negative crown is applied in said last three finishing stands.

4. The method as in claim 1, wherein equations of a curve of the shaped profile of the work rolls are as follows:
D.sub.t(y)=DC sin /b(y.sub.s.sub.0)+a.sub.1(y.sub.s.sub.0)+a.sub.3(y.sub.s.sub.0).sup.3
D.sub.b(y)D+C sin /b(y+.sub.s+.sub.0)+a.sub.1(y+.sub.s+.sub.0)+a.sub.3(y+.sub.s+.sub.0).sup.3 wherein Dt(y) is the diameter of the upper work roll; Db(y) is the diameter of the lower work roll; D is the nominal diameter of the work roll; 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 roll; C is the amplitude of sine curve; 0 is the value of the primary displacement of the shaped curve of the work roll; s is the value of the relative movement from the primary position; a.sub.1 is a first coefficient; a.sub.3 is a second coefficient; and wherein by acting on the parameters and C the multiple crown profile is determined in relation to the number of portions of strip into which the strip has to be divided.

5. The method as in claim 1, wherein in the case of a double crown profile, there is provided a differentiated cooling with minimum cooling intensity around the central zone of the work roll and maximum cooling intensity in correspondence with the zone of the work roll that operates in correspondence with the central part of the two halves of the rolled strip.

6. A plant for producing flat rolled products, in order to obtain strips with a multiple positive crown transverse profile, comprising at least one unit of finishing stands with work rolls, wherein in order to obtain a strip which, in a subsequent step and in a moment that follows the end of the rolling, will be longitudinally sectioned into multiple portions, at least the last finishing stand of the finishing unit comprises work rolls having a multiple negative crown profile, wherein the number of crowns present in the profile of the work rolls is correlated to the number of portions into which the strip will be divided, wherein said plant comprises a differentiated cooling system for cooling the work rolls with cooling intensity able to be adjusted as a function of the multiple negative crown shaped profile of the work rolls, wherein said cooling system comprises one or more ramps for delivering a cooling fluid with respective main feed pipes and delivery nozzles distributed over the entire width of the work rolls, wherein each feed pipe is equipped with its own proportional valve which is configured to regulate the flow rate to a respective group of nozzles in order to have a separate management of the groups of nozzles and therefore to vary the cooling on the corresponding surface zones of the work roll.

7. The plant as in claim 6, wherein at least the last three stands of the finishing unit have work rolls having a multiple negative crown profile.

8. The plant as in claim 6, wherein at least the work rolls are equipped with an axial shifting movement, wherein the magnitude and direction of the axial shifting movement is correlated to obtaining a desired profile to be obtained on the strip (S).

9. The plant as in claim 6, configured to operate in either one and/or the other of endless, semi-endless or coil-to-coil modes.

10. The plant as in claim 6, wherein said delivery nozzles are disposed adjacent to each other, with a determinate pitch, in double or triple rows and connected in groups to respective feed pipes, independent from each other, so as to define independent and differentiated cooling zones on the width of the rolls.

11. A finishing stand for a rolling plant for strips, comprising a work roll with a multiple negative crown profile, wherein the number of crowns present in the profile of said work roll is correlated to the number of portions into which the strip produced is intended to be divided longitudinally and a differentiated cooling system for cooling the work rolls with cooling intensity able to be adjusted as a function of the multiple negative crown shaped profile of the work rolls, wherein said cooling system comprises one or more ramps for delivering a cooling fluid with respective main feed pipes and delivery nozzles distributed over the entire width of the work rolls, wherein each feed pipe is equipped with its own proportional valve which is configured to regulate the flow rate to a respective group of nozzles in order to have a separate management of the groups of nozzles and therefore to vary the cooling on the corresponding surface zones of the work roll.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] We will now describe, in detail, this and other characteristics of the invention, with reference to some of its particular embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0082] FIG. 1 shows an example of a lay-out of a hot strip rolling plant on which the production method according to the invention is applicable;

[0083] FIG. 2, including FIGS. 2A and 2B, shows a section of one strip and of two half-strips obtained by means of a longitudinal cut of the strip according to the state of the art;

[0084] FIG. 3, including FIGS. 3A and 3B, shows a section of one strip and of two half-strips obtained by means of a longitudinal cut of the strip according to embodiments of the present invention;

[0085] FIGS. 4 to 15 (including FIGS. 4A-4C, FIGS. 5A-5D, FIG. 6, FIGS. 7A-7C, FIGS. 8A-8D, FIG. 9, FIG. 10, FIGS. 11A-11D, FIG. 12, FIGS. 13A-13C, and FIGS. 14A-14D) show graphs representative of the profiles of the work rolls, and of the resulting corresponding profiles of the strip, in the case, respectively, of a double, triple or quadruple crown profile for a strip width of 2000 mm and in the case of a double crown profile for a strip width of 1600 mm;

[0086] FIG. 16 shows a graph of the trend of the angle as a function of the width of the strip being worked in the case of a double crown;

[0087] FIG. 17 shows an embodiment of a differentiated cooling system of the work rolls used in the production method according to the present invention;

[0088] FIG. 18 schematically shows the positioning of the nozzles of the cooling system with respect to the work rolls.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

[0089] With reference to FIG. 1, an example is shown of a co-rolling plant 10 for producing strips S, in which a machine 11 for casting thin slabs feeds a hot strip rolling mill 12.

[0090] It should be noted that the example shown is not to be considered in any way as limiting the applicability of the present invention, since the concepts set forth find application in a number of other types of plant, with a different number of stands, with casting separated from the rolling mill, with slabs produced elsewhere and in any case in all situations in which a metal strip, having a determinate nominal width at the end of the rolling, has to be divided longitudinally into several portions in order to obtain strip portions with smaller widths.

[0091] While the embodiment disclosed in the figures represents a hot rolling mill provided in line with the casting machine, the present invention can be applied also to cold rolling mills in which a strip obtained by a previous step of the hot process is rolled.

[0092] In the case of hot rolling process, as mentioned, the starting semi-finished product is represented by a slab that can be cast in-line on the same plant (as disclosed in the embodiment of FIG. 1) or produced off-line or in another plant.

[0093] In the case of a cold rolling process, the starting semi-finished product is represented by a coil of rolled strip previously produced in a hot rolling mill According to the invention, in the cold rolling, in order that the rolling rolls are able to impart multiple crowns to a previously hot rolled strip having a single-crown, it is preferable that the thickness of the strip is at least 2.5 mm Below this value, it is preferable that the strip to be cold-rolled does not have a single crown profile, but has already the number of the final crowns to be obtained at the end of the cold rolling. In this case, in the cold process, the rolling rolls are shaped to follow the multicrown profile that has been already imparted to the strip in the previous hot rolling process.

[0094] Moreover, the present invention can be applied for the production of both ferrous, such as steel, and non-ferrous, such as aluminum, strips.

[0095] In this specific example shown in FIG. 1, the rolling mill 12 comprises a roughing unit 13 (or roughing mill), comprising in this case three stands 14A, 14B and 14C, and a finishing unit 15 (or finishing mill), comprising in this case five stands 16A, 16B, 16C, 16D and 16E.

[0096] Between the roughing unit 13 and the finishing unit 15 there is a temperature restoration system, for example an induction furnace 20, which takes the slab at exit from the roughing unit 13 back to the correct rolling temperature.

[0097] Between the casting machine 11 and the roughing unit 13 there is a tunnel furnace 17 having a length sufficient to contain at least a number of slabs comprised between 2 and 5. This tunnel furnace 17 allows, in a known manner, both to function as buffer in the event the rolling mill is interrupted, even temporarily, due to accidents or a planned change of the work rolls, and also to operate in semi-endless mode.

[0098] Upstream of the tunnel furnace 17 there is a first pendulum shears 18, which cuts the slab to size when the plant 10 operates in coil-to-coil or semi-endless mode.

[0099] Downstream of the finishing mill 15 there is a cooling unit 22 and a second flying shears 19, which intervenes in the case of endless or semi-endless rolling to separate the strip gripped on one of the two down-coilers 21, or reels.

[0100] In accordance with one aspect of the present invention, the strip obtained is subsequently divided longitudinally (slitting), so as to obtain portions of strip having a width that is a submultiple of, or in any case smaller than, the width of the cast slab.

[0101] In this way, it is possible to obtain strips with a smaller width from a single rolled strip without limiting in any way the overall productivity of the plant, which can always work with a width of the slab and of the strip close to the maximum one provided for the plant itself.

[0102] The division in width of the final rolled strip can take place directly in line, at exit from the rolling mill, or in a step following the removal of the coil, for example in a different destination plant where the strips are used.

[0103] In the first case, the division downstream of the finishing mill 15, for example into two parts, can concern: [0104] the entire length of the strip S, from head to tail, winding two different half-strips S1, S2 onto respective reels 21: in this way, two distinct coils will be obtained; [0105] the entire length of the strip S except a portion of the head and of the tail thereof, in order to facilitate the entry of the head into the single reel and the winding of the last tail-end turn: in this way, there will be a single coil sectioned into two parts for almost the totality of its length.

[0106] For this purpose, dedicated cutting devices can be provided which longitudinally separate the strip S into two or more strip portions S1, S2 having the same or different width. Advantageously, these devices can be inserted into and extracted from the production line based on requirements.

[0107] According to the number of portions in width into which the strip S will be divided, the present invention provides to make the profile of the work rolls 24a, 24b of at least some of the last finishing stands 16a-16e so as to determine the correct crown on each of the portions into which the strip will be divided.

[0108] By way of example, FIGS. 3A and 3B respectively show the cross-section of a strip S downstream of the rolling mill 12, and the sections of the two half-strips S1, S2 obtained by longitudinally cutting the strip S along the center line. In the example, the strip S has a double positive crown which is substantially symmetrical with respect to a plane of symmetry passing through the center line M, while the two half-strips S1, S2 each have their own single positive crown.

[0109] Therefore, in the event the strip is divided in width into two half-strips, the profile of the work rolls 24a, 24b will show a double negative crown, one for each half-strip obtained or obtainable downstream, the same is the case in the event of three, four or more divided portions of strip.

[0110] The profile of each work roll 24a, 24b can be defined by a curve consisting of an anti-symmetric trigonometric function and a 3rd order polynomial function.

[0111] The equations of the profile's curve are as follows:

D.sub.t(y)=DC sin /b(y.sub.s.sub.0)+a.sub.1(y.sub.s.sub.0)+a.sub.3(y.sub.s.sub.0).sup.3

D.sub.b(y)D+C sin /b(y+.sub.s+.sub.0)+a.sub.1(y+.sub.s+.sub.0)+a.sub.3(y+.sub.s+.sub.0).sup.3 [0112] wherein [0113] Dt(y) is the diameter of the upper work roll 24a; [0114] Db(y) is the diameter of the lower work roll 24b; [0115] D is the nominal diameter of the work roll; [0116] is the angle of the modifiable shape of the curve of the gap between the rolls; [0117] b is the barrel length of the work roll; [0118] C is the amplitude of sine curve; [0119] 0 is the value of the primary displacement of the shaped curve of the roll; [0120] s is the value of the relative movement from the primary position; [0121] a.sub.1 is a first coefficient; [0122] a.sub.3 is a second coefficient.

[0123] According to the present invention, by assigning suitable values to the coefficients and C of the formulas above, it is possible to obtain the double crown profiles, in the event the strip produced is divided into two half-strips, or even triple or quadruple crown, in general multiple crown profiles, in the event the strip is divided longitudinally into several portions.

[0124] Once the profile of the work rolls 24a, 24b has been determined (mechanical crown), the extent of the crown on the strip can be modified by varying the value s of the axial movement (shifting) of the work rolls 24a, 24b, as shown in FIGS. 6, 9, 12, 15.

[0125] With reference to FIGS. 4-6, an example is shown in which the strip S has a width of 2000 mm, corresponding to the width of the cast slab, and is rolled with a double crown by work rolls 24a, 24b having a barrel length equal to 2450 mm, in order to be subsequently divided longitudinally into two half-strips of 1000 mm. It should be understood that these drawings represent the case in which the division is into two halves of equal width, as shown for example in FIG. 3B, however we do not exclude that the two portions of strip can have different widths.

[0126] As an example, the last finishing stand 16e (however, it could be the last two, three or more), is represented in FIGS. 4A and 5A as comprising upper 24a and lower 24b work rolls, and upper 25a and lower 25b support rolls.

[0127] FIGS. 4B-4C and 5B-5C represent the profile, respectively, of the upper work roll 24a and of the lower work roll 24b, in two distinct operating conditions.

[0128] In FIGS. 4B and 4C the profile of the work rolls 24a and 24b is represented for the entire length of the barrel by lines L(T) for the upper work roll 24a and L(B) for the lower work roll 24b, in a non-axially shifted condition.

[0129] In FIGS. 5B and 5C the lines L(T) and L(B), indicated with a dashed line, again represent the profile of the entire length of the barrel 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 which works on the strip S, in an axially shifted condition, as represented by the arrows F1 and F2 in FIG. 5A.

[0130] Finally, FIG. 5D shows the resulting 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 central point in which the strip S will be divided.

[0131] As can be seen from the graphs, the profile of the work rolls 24a, 24b, and obviously the resulting profile of the strip P(S), has a double crown shape, with two humps and two corresponding troughs which create the desired crown on the resulting profile of the two half-strips into which, in this specific case, the strip S will be divided.

[0132] In particular, the crown on the work rolls 24a, 24b is negative, that is, it has a concave shape, while a positive crown, that is, having a convex shape, is obtained on the rolled strip S.

[0133] In this way, the strip S can be divided longitudinally in correspondence with its centerline, with the possible removal of a small central band in order to make the crown of the two half-strips perfectly symmetrical.

[0134] It should be considered that the extent of the crown of the single hump is a function of the axial shifting of the work rolls 24a, 24b.

[0135] This is an advantage because the adjustment of the profile is not static, but can be of a dynamic type and the extent of the shifting of the work rolls 24a, 24b will vary in relation to the operating conditions of the work rolls 24a, 24b.

[0136] In addition, a same profile of the work rolls 24a, 24b can be applied on several stands, making them operate in different shifting fields, in order to maintain the homothety of the section of the strip S in the last rolling stands. This is in order to not penalize the planarity of the strip S itself.

[0137] The graph of FIG. 6 shows how the crown of the strip S can be modified by acting on the shifting, that is, the axial displacement of the two work rolls 24a, 24b in order to vary the surface portions of the respective roll which work directly on the strip S.

[0138] Thanks to the axial shifting of the work rolls 24a and 24b it is possible to accentuate or flatten the ridges and valleys of the profile of the strip S, which means increasing or decreasing the crown of the S strip.

[0139] The shifting of the work rolls 24a and 24b is symmetrical, that is, the rolls are translated in the opposite direction with respect to the center line M by an equal value.

[0140] In the graphs of FIGS. 5A-5D, a shifting equal to 50 mm was considered.

[0141] FIGS. 7 and 8 represent the case in which the strip S has to be divided longitudinally into three portions, in this case, each having a width equal to of the width of the strip S.

[0142] FIGS. 7A and 8A show the upper 24a and lower 24b work rolls with respective profiles having a triple negative crown.

[0143] Also in this case, FIGS. 7B, 7C represent the profile of the entire barrel length of the work rolls 24a, 24b in a reciprocally non-shifted condition, while FIGS. 8B and 8C represent the useful work portion L(Bu), L(Tu) of the work rolls 24a and 24b in a condition in which they are reciprocally shifted by 50 mm.

[0144] Number 26 in FIG. 8D represents the two sections which allow to obtain the three portions from the strip S produced.

[0145] It can be seen how the profile of the work rolls 24a and 24b is shaped with a negative crown so as to obtain a profile of the strip with a triple hump which, as can be seen in FIG. 8D, determines a resulting profile with triple positive crown, in this case, substantially symmetrical with respect to the center line of each of the (three) portions into which the strip S is divided, in correspondence with the sections 26.

[0146] FIG. 9 shows, in a corresponding manner, the range of control of the crown that can be obtained by the axial shifting the work rolls 24a, 24b, which are shaped as shown in FIGS. 7B and 7C.

[0147] Finally, in a manner substantially equivalent to the cases described above, FIGS. 10 and 11 concern the case in which the strip S produced has to be divided into four portions, in this specific case, all with a substantially equal width.

[0148] Without repeating the concepts expressed above, we wish to point out how the profile of the work rolls 24a, 24b is shaped with a quadruple negative crown, and in FIG. 10 it is represented in a non-shifted condition. FIG. 11 represents the shifted condition of the two work rolls 24a, 24b with the useful profile L(Tu), L(Bu) respectively of the upper 24a (FIG. 11B) and lower 24b (FIG. 11C) work rolls shown with a solid line. In this case, the two work rolls 24a, 24b are shifted by 80 mm.

[0149] The resulting profile of the strip S (FIG. 11D) has the four humps or positive crowns in a substantially symmetrical position, so that, after the longitudinal separation of the four portions by means of the sections 26, each portion has the correct pre-established crown.

[0150] As in the previous cases, using the axial shifting allows to achieve control of the crown, as shown for example in FIG. 12.

[0151] With reference to FIGS. 13-15, an example is shown in which a strip S is produced, on the same rolling mill with a barrel length of the work rolls of 2450 mm, said strip S having a width of 1600 mm, corresponding to the width of the cast slab, and is rolled always with a double crown so as to be subsequently divided longitudinally into two half-strips of 800 mm.

[0152] The work rolls 24a, 24b shown in FIGS. 13B and 13C, in the example case have a shaped profile with a double negative crown with rectilinear end segments (not shaped) since the strip to be rolled now has a width smaller than the previous example.

[0153] FIGS. 13B, 13C represent the overall profile of the work rolls 24a, 24b in a reciprocally non-shifted condition, while FIGS. 14B and 14C represent the shifted condition of the two work rolls 24a, 24b with the useful work profile L(Tu), L(Bu) respectively of the upper 24a (FIG. 14B) and lower 24b (FIG. 14C) work rolls represented with a solid line. The work rolls 24a, 24b in the example case are shifted by 50 mm.

[0154] The resulting profile of the strip S (FIG. 14D) has the two humps or positive crowns in a substantially symmetrical position, so that, after the longitudinal separation of the two portions by means of the sections 26, each portion has the correct crown pre-established according to the qualitative requirements demanded.

[0155] As in the previous cases, using the axial shifting allows to achieve control of the crown, as shown for example in FIG. 15.

[0156] As mentioned, the operation of imparting to the strip a double (or triple, or quadruple, . . . ) crown is performed in the last stands of the finishing mill 15, for example in the last one or in the last two or three, in the case of particularly thin thicknesses.

[0157] FIG. 16 shows how the amplitude of the angle can vary as a function of the overall width of the rolled strip S, for example for width values comprised between 800 and 2000 mm in the case of a strip S having a double crown.

[0158] As mentioned above, multiple crown rolling requires strict control of the cooling efficiency on the width of the work roll, so that it can be selectively varied from the center to the periphery.

[0159] According to the invention, as shown by way of example only in FIG. 17, a cooling system 30 is provided comprising one or more ramps 33 for delivering a cooling fluid with respective main feed pipes 31 and delivery nozzles 32 distributed over the entire width of the work rolls 24a, 24b.

[0160] The delivery nozzles 32 are disposed adjacent to each other with a determinate pitch in a double or triple row and are connected, in groups, to the pipes 31, independent from each other, so as to define independent and differentiated cooling zones on the width of the rolls. In the example shown in FIG. 17, the ramp is divided into eleven independent cooling zones.

[0161] Each feed pipe 31 is equipped with its own proportional valve that regulates the flow rate to the respective group of nozzles 32.

[0162] In this way, it is possible to have a separate management of the groups of nozzles 32 and therefore to vary the cooling on the corresponding surface zones of the work roll 24a, 24b.

[0163] According to the invention, also on the basis of the portions in width to be obtained starting from a given width of strip, each delivery ramp 33 can be divided into a plurality of independent zones, for example between 7 and 17. It is therefore possible to define suitable variations of cooling efficiency, along the axis of the work roll 24a, 24b, in particular in order to separately control the cooling on the two halves of the strip, or on the three, four or more portions into which the strip S will be subsequently divided.

[0164] For example, in the case of double crown working, it is advantageous to have a minimum cooling efficiency around the central zone of the work roll 24a, 24b so that the thermal crown increases in this zone, and instead have maximum cooling efficiency in correspondence with the zone of the roll that operates in correspondence with the central part of the two halves of the strip, so that the thermal crown decreases in this zone. In this way, the thermal crown can be controlled so that it follows the trend of the mechanical crown.

[0165] For example, with a work roll 24a, 24b, for producing strips with a maximum width of 2000 mm, the width of each zone can vary from about 130 mm to about 220 mm.

[0166] According to some embodiments, for example described with reference to FIG. 18, the cooling system 30 can comprise four cooling ramps 33 for each of the multiple crown finishing stands 16a-16e, disposed in pairs at entry and at exit to the upper 24a and lower 24b work rolls.

[0167] The cooling ramps 33 can advantageously be provided with drive devices 34 configured to move them toward/away from the respective work roll 24a, 24b, or rotate them with respect thereto, in order to modify the angle of incidence of the cooling liquid on the work roll 24a, 24b.

[0168] According to some embodiments, the strip S can be cut longitudinally in the processes downstream of the rolling mill 12, and then be entirely wound into coils with multiple crown profile.

[0169] According to some variants, it can be provided that the strip S is wound for an initial head segment with a multiple crown profile, and subsequently a cutting disk located upstream of the reel 21 is driven in order to longitudinally divide the strip S while the winding continues. In this case, the longitudinal cutting can be interrupted before the final tail end, which therefore remains whole as the head, with a multiple crown profile.

[0170] It is clear that modifications and/or additions of parts may be made to the plant and to the method as described heretofore, without departing from the field and scope of the present invention.