Method of controlling the strip shape and apparatus therefor

Abstract: The present invention relates to a method of controlling for obtaining the aimed strip shape using a rolling mill pro­ vided with rolls, which are variable in amount of crown by feeding a pressurized oil in the inside thereof, and an ap­ paratus therefor. According to the present invention, the strip shape is detected, the detected strip shape being approxi­ mated by a function including a term of the second power of a variable, which is a position or a distance in the direction of width of the strip, and the amount of crown being adjusted to coincide the term of the second power with the aimed value thereof. In addition, the rolling mill is provided with right and left pressing-down balancers and roll benders. The strip shape in the width direction of the strip is detected, the detected shape being approximated by a function including terms of the first, second, fourth, sixth or eighth power of a variable, which is a position or a distance in the width direc­ tion of the strip, the amount of pressing-down of the right and left pressing-down balancers being adjusted to coincide the term of the first power with the aimed value thereof, the amount of crown of the roll being adjusted to coincide the term of the second power with the aimed value thereof, and a roll bending force being adjusted to coincide the term of the fourth, sixth or eighth power with the aimed value thereof.

Description: Background of the invention Field of the invention The present invention relates to a method of controlling the shape i.e. flatness of iron or nonferrous metals strip and an apparatus therefor. Herein, the strip shape designates a surface shape of strip such as a center buckle (the state where the central portion of the strip in the width direction thereof is stretched longer than the side edge portion thereof) and a wary edge (the state wherein the side edge portion of the plate in the width direction thereof is stretched longer than the central portion thereof), in particular a strip shape appearing in the width direction of the strip. Since the strip is subjected to a tension by means of a rolling-mill and pinch-rolls in the rolling process, the strip shape corresponds to a tensile stress given to each portion of the strip in the width direction thereof in the rolling process. That is to say, the portion, on which a larger tensile stress occurs, corresponds to the portion of which elongation has been small, and vice-versa, and the shape is determined depending on such an elongation. Accordingly, means for measuring the shape, in the form of a shape or flatness meter is constructed to measure a tensile stress at a large number of points of the strip being rolled in the width direction thereof. Prior art The shape is remarkably important for the evaluation of the quality of the strip. A rolling mill, which is capable of controlling the strip shape, is disclosed in US―A―4,269,051 (Clark et al.). This rolling mill is provided with a detector for detecting the tension, in short, abovementioned tensile stress downstream thereof and a signal obtained by the detector is used for controlling the strip shape. Summarizing Clark et al.'s invention in order to make the comparison of the invention with the present invention easy, the shape is approximated by a+bx+cx 2 on the basis of an output signal from the detector, wherein x is a variable designating a distance from the center of the strip in the width direction thereof; a, b and c is a constant, respectively. Although ideally the strip shape should be flat, the aimed strip shape which is desired in the rolling process is not flat, in short, it is not expressed only by the constant a but also by bx and cx 2 in the above described formula. It is the reason of the above described that an influence of heat is given to the strip in the rolling process, the strip shape being detected by the tensile stress, and the tensile stress being different at end portions and the central portion of the strip in the width direction thereof even though the strip shape is identical. So, the shape aimed in the rolling process is expressed by a parabolical equation of x, and right and left pressing-down balancers for adjusting the leveling of roll gap, a roll-bender and a roll-cooling apparatus are controlled to coincide a quadratic equation (a+bx+cx 2 ) of the measured shape with the parabolical equation of the aimed shape. That is to say, according to Clark et al.'s invention, a term of the first power of x is controlled by the right and left pressing-down balancer and a quadratic term of x is controlled by the roll-bender and the roll-cooling apparatus. In short, a rolling mill according to Clark et al.'s invention is ineffective for a complex shape defect appearing by compounding various forms of stretch at all. It is perhaps the reason of the above described that a parabolic equation approximating the strip shape is insufficient, the control of the strip shape by the roll-cooling apparatus being slow in response, whereby being ineffective for the control of the complex shape defect, and the like. In addition, since the strip shape is greatly dependent upon the control by said roll-cooling apparatus and the control of the shape by the roll-cooling apparatus is slow in response, it can not be said that the controlling accuracy is high even for a simple stretch. Furthermore, since it is necessary to stabilize a temperature of mill rolls to some extent, such disadvantages as the necessity of a warming up rolling are found. Object of the invention It is the first object of the present invention to provide a method of controlling the strip shape and an apparatus therefor in which the dependency of the shape control upon the control by cooling a roll can be reduced, the response of control being heightened, and the aimed at shape being obtained in high accuracy, whereby the quality of produced strip being able to be heightened. It is a further object of the present invention to provide a method of controlling the strip shape and an apparatus therfor in which the response can be heightened and the warming up rolling is unnecessary by carrying out the main control by the use of a variable crown roll and a roll-bender, and the fine control by a roll-cooling apparatus, and in which the shape control can be simply carried out by controlling means having a relation well corresponding to each term of a function including power terms of the above described variable for approximating the strip shape. Brief Summary of the Invention A method of controlling the strip shape of the present invention consists in controlling the shape of a strip rolled by means of a rolling mill provided with rolls, including work rolls and back-up rolls, the amount of the crown of the back-up rolls being variable by expanding or shrinking their shells radially using the pressure of a liquid fed into the inside thereof, right and left pressing-down balancers, roll benders, a cooling apparatus for cooling the work rolls and a shape meter for detecting variations in the strip shape, comprising the steps of: detecting the strip shape at the outlet side of said rolling mill; obtaining a power function approximating the detected strip shape, said power function depending on a variable which is a distance in the direction of width from a given position across the strip and including the terms of the first, second and fourth, sixth or eighth power of said variable and a constant term; adjusting the amount of right and left pressing down by means of said right and left pressing-down balancers to coincide said term of the first power with an aimed first power value for the strip shape; adjusting the amount of the crown of said back-up rolls to coincide said term of the second power with an aimed second power value for the strip shape; adjusting the roll bending force by means of said roll benders to coincide said term of the fourth, sixth or eighth power with an aimed power value for the strip shape; and cooling said work rolls by means of said roll--cooling apparatus to eliminate the deviation of the strip shape detected by said shape meter from the strip shape expressed by said approximated power function. Apparatus corresponding to this method is claimed in Claim 2. Brief description of the drawings Figures 1 to 3 is a graph showing a characteristic of elongation change of right and left pressing-down balancer, a variable crown roll and a roll-bender, respectively. Figure 4 is a diagram showing an elongation change. Figure 5 is a schematic view showing a controlling apparatus of the present invention. Figure 6 is a general view showing a controlling method of the present invention. Figure 7 is a graph showing an elongation change of a variable crown roll and a roll-bender used in the test. Figure 8 is a graph showing a transition of elongation of a strip used in the test. Figure 9 is a time chart showing a pressure being given to a variable crown roll in the test, a roll bending force and a rolling speed. A method of controlling the strip shape and an apparatus for carrying out same will be concretely described below. Detailed description of the invention According to the present inventors' experiments, an elongation change of right and left pressing-down balancers which adjust the levelling of roll gap for controlling the strip shape, that of variable crown sleeve rolls expanding and shrinking a sleeve thereof by a pressurized oil (hereinafter referred to as VC roll) and that of roll benders are shown in Figures 1, 2 and 3, respectively. Figures 1(a), 2(a) and 3(a) and Figures 1(b), 2(b) and 3(b) show an elongation change when the right and left pressing-down balancers, the VC roll and the roll bender are independently applied to a narrow strip having a width of 1150 mm or less and a wide strip having a width of 1150 mm or more respectively. An axis of abscissas designates a distance x from the center of strip width (both side edge portions are designated as +1, -1) and an axis of ordinate designates an elongation change. As obvious from these graphs, the controlling characteristic of the right and left pressing-down balancers are expressed by an equation of the first power of x regardless of the strip width, the controlling characteristic of the VC roll being expressed by an equation of the second power of x, and the controlling characteristic of the roll bender being expressed by an equation of the fourth power of x for the narrow strip and an equation of the sixth power or eighth power of x for the wide strip. The elongation change is given by a difference between an elongation E i prior to the control and an elongation ε i after the control of the right and left pressing-down balancers, the VC roll and the roll bender. Figures 4(a), 4(b) show the strip shape prior to and after the rolling. Each elongation E i , ε i is given by the following equations (1), (2): E i = L-L i L ε i = l-l i l wherein L, l are the length of base position, for example, strip width center, and L i , l i are a length of another optional position. Provided that the strip shape detected by a shape meter is expressed by g(x), a power function f i (x) as described by the following equation (3) is obtained by making g(x) correspond to an elongation change expressed by an equation of the first power of x, an equation of the second power of x and an equation of the fourth, sixth or eighth power of x designating the controlling characteristic of the pressing-down balancer, the VC roll and the roll bender, respectively. f i (x)=A i +B i x+C i |x| m +Di|x| n wherein m, n are selected depending upon the milling condition and the materials of strip but m is 2 and n is 4, 6 or 8. In addition, the aimed shape is determined and expressed by a power function f o (x) as described by the following equation (4) similarly to the above described: f o (x)=A o +B o x+C o |x| m +D o |x| n The right and left pressing-down balancers are adjusted in pressing-down quantity to coincide B i of the term of the first power with the aimed value B o , the pressurized oil of the VC roll being adjusted to coincide C i of the aimed of the second power with the target value C o , and a force of the roll bender being adjusted to coincide D i of the term of the fourth, sixth or eighth power with the aimed value D o independently, respectively. In addition, an ON-OFF control of each nozzle of a roll cooling apparatus is carried out to be obtained an elongation change corresponding to a difference between the g(x) and the f i (x). The preferred embodiment of the present invention will be concretely described below with reference to the drawings. Referring to Figure 5, which is a schematic view showing the state in which a method of controlling the strip shape of the present invention is carried out by the use of an apparatus for controlling the strip shape of the present invention, 1, 1 designate work rolls, 2, 2 designating back-up rolls using variable crown sleeve rolls, in short, a VC roll therein, and 3 designating a strip to be rolled such as steel strip or nonferrous metal strip. The strip to be rolled is passed through the work rolls 1,1 of a rolling mill from the direction shown by the white arrow and wound around a reel 5 via a guide roll 4. The back-up rolls 2, 2 are adapted to expand or shrink the sleeve as a shell thereof by feeding a pressurized oil in the space between an axis portion of roll and the sleeve of roll concentrically arranged outside the axis portion of roll through the inside of the axis portion of roll so that an amount of the crown of a roll may be set and adjusted. Independently driven and controlled pressing-down apparatus 6l, 6r, which adjust the levelling of roll gap between the work roll 1 and 1, are provided at both ends (only one side end is shown in the drawing) of an axis 2a of the back-up roll 2 positioned below a pass line, independently driven and controlled roll benders 7, 8u, 8d being provided between axes 1a, 1a of the work rolls 1, 1 as well as between each of the work rolls 1, 1 and axes 2a of the back-up rolls, 2, 2, respectively, and a plurality of nozzles 9u, 9u..., 9d, 9d... of the roll cooling apparatus capable of separately injecting and stopping a coolant, for example water or the like, being arranged in parallel in the axial direction of the work rolls, 1, 1 in an opposite relation to the circumference of the work rolls 1, 1. The pressing-down apparatus 6l, 6r are adapted to change a roll gap in the axial direction of the work rolls 1, 1 to adjust an elongation in the width direction of the strip 3 to be rolled by adjusting the pressing-down quantity of both end portions -the right end portion and the left end portion-of the back-up roll 2, whereby correcting the strip shape. In addition, the roll benders 7, 8u, 8d are adapted to change the shape of work rolls 1, 1 to adjust an elongation at each portion in the width direction of the strip 3 to be rolled by making the axes 1a, 1a of the work rolls 1, 1 or the axes 1a, 2a of the work rolls 1, 1 and the back-up rolls 2, 2 approach to each other (in the decrease direction) or apart from each other (in the increase direction) operating a hydraulic cylinder, whereby correcting the strip shape. 10 designates a calculation unit for control and is adapted to read-in a signal detected by a shape meter 11, for example, manufactured by Davy Mckee Ltd. disposed at the outlet side of a rolling mill at the predetermined timing through a signal processing unit 12, approximating the strip shape by a power function f i (x) including a term of the first power, a term of the second power and a term of the fourth, sixth or eighth power as shown by the equation (3) on the basis of the detected signal, expressing also the predetermined aimed shape by a power function f o (x) including a term of the first power, a term of the second power and a term of the fourth, sixth or eighth power likewise, calculating a pressing-down quantity of each pressing-down balancer 6l, 6r, an oil-pressure of VC roll 2, 2 and an oil-pressure of roll benders 7, 8d, 8u necessary for making both power functions coincide with each other, that is to say, making B i coincide with B o , C i with C o and D i with D o , calculating the opening and closing or the opening degree of each nozzle 9u, 9u... and 9d, 9d... of the roll cooling apparatus necessary for elimination of the difference between g(x) and f i (x), and putting out a controlling signal to each of control units 21, 22, 23, 24. Figure 6 is a general view showing a shape-controlling process of the method of the present invention as described above. At first, provided that the strip shape in the width direction detected by the shape meter 11 has such a form as shown in Figure 6(a) (expressed by g(x)), it is approximated by a function f i (x) as shown in Figure 6(b) similarly taking a strip width on an axis of abscissas and an elongation on an axis of ordinate. This function f i (x) is expressed by a power function obtained by summing up a component of the first power f 1 (x)=B i x, a component of the second power f 2 (x)=C i x 2 and a component of the fourth, sixth or eighth power, for example, f 4(6, 8) =D i x 4(6, 8) alike to a graph shown in Figures 6(c), 6(d) and 6(e) taking the position in the direction of width from the strip width on an axis of abscissas and an elongation on an axis of ordinate, comparing the function f i (x) with the power function f o (x) such as the equation (4) expressing the predetermined aimed shape, putting out a controlling signal to each of the control units 21, 22, 23 of the pressing-down balancers 6l, 6r, the VC rolls 2, 2 and the roll benders 7, 8d, 8u to coincide the term of the first power B i with B o , the term of the second power C i with C o , and the term of the fourth, sixth or eighth power D i with D o , calculating the difference between f 1 (x) and g(x) as shown by a graph drawn separately in Figure 6(f) taking the strip width on an axis of abscissas and an elongation on an axis of ordinate, and putting out a signal to the roll coolant control unit 24 of the roll cooling apparatus to eliminate the difference between f 1 (x) and g(x), whereby carrying out the control. Then, the control for the complex shape defect carried out by the combined adjustment of the VC rolls used as back-up rolls 2, 2 and roll benders 7, 8d, 8u will be described with giving concrete numerical values. An elongation change characteristic of the VC roll and the roll bender used is shown in Figure 7(a) and Figure 7(b), respectively. Figure 7(a) shows the results obtained in the process of rolling a pure aluminum strip having a width of 1150 mm and a thickness of 1.90 mm at the inlet side to a thickness of 0.095 mm at the outlet side while Figure 7(b) shows the results obtained in the process of rolling a pure aluminium strip having a width of 1510 mm and a thickness of 1.90 mm at the inlet side to a thickness of 0.095 mm at the outlet side. In both cases, a distance from center of strip width is shown on an axis of abscissas and an elongation change (x10 -5 ) is shown on an axis of ordinate. The results of the VC roll are shown by ○ marks and those of the roll bender are shown by  marks in the graph. The shape control was applied to a strip having an elongation as shown in Figure 8(a) by the use of VC rolls and roll benders having an elongation change as described above. In Figure 8(a), the strip width from the strip width center is shown on an axis of abscissas and an elongation E i (see Figure 4) is shown on an axis of ordinate. As obvious from Figure 8(a), a general complex shape defect is produced in the strip. That is to say, an elongation is increased toward both side portions in the direction of width from the strip width center reaching the maximum value at both quarter portions and slightly reduced at both side edge portions in comparison with the maximum value. An oil pressure of the VC roll, a roll bending force of the roll bender and a rolling speed were controlled for such a strip under the controlling condition as shown in Figures 9(a), 9(b) and 9(c). The oil pressure of the VC roll, the oil pressure of the roll bender (that in the direction of increase the gap between work rolls, that is to say, in the increase direction in the upper side and that in the direction of decrease the gap between work rolls, that is to say, in the decrease direction in the lower side) and the rolling speed is shown on an axis of ordinate in Figure 9(a), 9(b) and 9(c), respectively, and time is shown on an axis of abscissas in all Figures 9(a), 9(b) and 9(c). As obvious from Figures 9(a), 9(b) and 9(c), the component of the second power of the elongation and the component of the fourth power of the elongation as shown in Figure 8(a) was independently controlled by means of the VC roll and the roll bender, respectively, to coincide the component of the second power and the fourth power of the elongation with the target value, respectively, by slightly increasing the oil pressure of the VC roll from that in the stationary condition and then gradually reducing it taking the thermal expansion due to the contact with the strip into consideration and gradually reducing the oil pressure of the roll bender from that in the initial condition where the maximum oil pressure was given in the increasing direction. In addition, the rolling speed is stepwise increased and then kept constant. The results of the above described shape control are shown in Figures 8(b) and 8(c). Figure 8(b) and Figure 8(c) show an elongation at the position shown by the line I-I and the line II-II in Figure 9, respectively. In both Figure 8(b) and Figure 8(c), the position of strip width is shown on an axis of abscissas and an elongation is shown on an axis of ordinate. As obvious from Figures 8(b) and 8(c), as a result of increasing elongation at the position shown by the line I-I in comparison with the strip width center an elongation at the central portion and both the edge portions are reduced until such an extent that it hardly changes and only both the quarter portions are still under the condition that an elongation is slightly large. Furthermore, at the position shown by the line II-II also an elongation of both the quarter portions were remarkably reduced and an elongation of the portion nearly both the edge portions become slightly larger than that of the strip width center, whereby the shape was controlled to an almost aimed strip shape. Furthermore, although the construction, in which a variable crown roll, that is to say, a VC roll was used as the upper and lower back-up rolls, was disclosed in the above described preferred embodiment, the construction, in which the VC roll is used as only one of the upper and lower back-up rolls, may be adopted. The present embodiment is illustrative and not restrictive, since the extent of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the scope of the claims are therefore comprised within the present invention.

Claims: A method of controlling the shape of a strip rolled by means of a rolling mill provided with rolls, including work rolls and back-up rolls, the amount of the crown of the back-up rolls being variable by expanding or shrinking their shells radially using the pressure of a liquid fed into the inside thereof, right and left pressing-down balancers, roll benders, a cooling apparatus for cooling the work rolls and a shape meter for detecting variations in the strip shape, comprising the steps of: detecting the strip shape at the outlet side of said rolling mill; obtaining a power function approximating the detected strip shape, said power function depending on a variable which is a distance in the direction of width from a given position across the strip and including the terms of the first, second and fourth, sixth or eighth power of said variable and a constant term; adjusting the amount of right and left pressing down by means of said right and left pressing-down balancers to coincide said term of the first power with an aimed first power value for the strip shape; adjusting the amount of the crown of said back-up rolls to coincide said term of the second power with an aimed second power value for the strip shape; adjusting the roll bending force by means of said roll benders to coincide said term of the fourth, sixth or eighth power with an aimed power value for the strip shape; and cooling said work rolls by means of said roll--cooling apparatus to eliminate the deviation of the strip shape detected by said shape meter from the strip shape expressed by said approximated power function. An apparatus for controlling the shape of a strip rolled by means of a rolling mill having work rolls (1) and back-up rolls (2), and being provided with: roll benders (7, 8u, 8d); right and left pressing-down balancers (6ℓ, 6r); a roll cooling apparatus; the back-up rolls (2) comprising a roll whose amount of crown is variable by expanding or shrinking its shell radially using the pressure of a liquid fed into the inside thereof; a shape meter (11) disposed at the outlet side of said rolling mill for detecting the strip shape; and a calculation and control unit (10, 21, 22, 23) for obtaining a power function approximating the strip shape detected by said shape meter (11), said power function depending on a variable which is a distance in the direction of width-from a given position across the strip and including terms of the first, second, and fourth, sixth or eighth power of said variable and a constant term, for calculating the amount necessary to adjust the setting of said right and left pressing-down balancers (6ℓ, 6r) to coincide said term of the first power with an aimed first power value for the strip shape, the amount necessary to adjust the roll crown of said back-up rolls (2) to coincide said term of the second power with an aimed second power value for the strip shape, the amount necessary to adjust the roll benders (7, 8u, 8d)to coincide said term of the fourth, sixth or eighth power with an aimed fourth, sixth or eighth power value for the strip shape and the amount necessary to adjust said roll cooling apparatus to eliminate the deviation of the strip shape detected by said shape meter (11) from the strip shape expressed by said approximated power function, and for controlling the pressing-down balancers (6ℓ, 6r)the crown of the back-up rolls (2) and the roll benders (7, 8u, 8d) by the amount determined from the first, second and fourth, sixth or eighth power term respectively.

Inventors: KONDO KATSUYA, TAHARA AKIHIRO, KONDO, KATSUYA, TAHARA, AKIHIRO, KONDO, KATSUYA C/O CENTRAL RESEARCH LABORATORY
Applicants: SUMITOMO METAL IND, SUMITOMO METAL INDUSTRIES, LTD.
Application year: 1985
Main classification: B21B37
IPC codes: B21B37, B21B27