Abstract:
The invention relates to a method for rolling a product in a rolling train comprising at least two roll stands having a roll gap, the product to be rolled comprising a transition region. If a critical transition region crosses the rolling train, the roll gaps of the roll stands are successively opened and closed according to the position of the transition region moving at speed through the rolling train, in the direction of the direction of travel of the conveyor. The opening of the roll gaps occurs parallel to the position of the critical transition region when the product is displaced. A transition region is critical when the structure requires the roll gaps to be opened. The inventive opening of the roll gaps, when the device is moving, enables the controlled transition of a product to be rolled with extreme variations in dimensions and/or hardness, for a shorter length.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is the US National Stage of International Application No. PCT/EP2005/051943, filed Apr. 28, 2005 and claims the benefits of German Patent application No. 10 2004 022 334.3 filed May 6, 2004. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION  
       [0002]     The invention relates to a method for rolling rolling stock in a mill train that has at least two roll stands each having one roll gap, with the rolling stock requiring to be rolled having at least one transitional region. The invention relates further to a computing device for appropriately regulating a mill train.  
       BACKGROUND OF THE INVENTION  
       [0003]     Particularly in the case of a continuously operated mill train the rolling stock has a plurality of partial areas that can differ in terms of their dimensions and/or material properties (also temperatures). Two successive partial areas of the rolling stock are joined by means of a transitional region. The plurality of partial areas of rolling stock are a result of, for example, supplying metal coils singly and welding them together prior to rolling. The partial areas of the rolling stock correspond in this case to individual coils. The rolling stock is as a rule separated again into single coils after being rolled.  
         [0004]     DE 101 59 608 A1 describes a rolling method for a strip having one seam weld in a mill train having a plurality of roll stands and at least one draw tension measuring element. According to DE 101 59 608 A1, setting variables for the rolling speed and for screwing down the roll stands are determined as a function of the position of the seam weld within the mill train.  
         [0005]     Known methods for rolling rolling stock having a transitional region operate reliably only when the physical characteristics of said transitional region are such that the change in the at least one dimension and/or at least one material property between the partial area of the rolling stock in front of the transitional region and the partial area behind the transitional region is relatively slight. When, according to known methods, partial areas having extremely different properties and/or dimensions are rolled in direct succession, that will as a rule be associated with substantial disruptions to the process variables. In extreme cases said disruptions can cause the rolling stock to split.  
       SUMMARY OF INVENTION  
       [0006]     The object of the invention is to avoid the disadvantages known from the prior art and provide a method with the aid of which rolling stock having at least one transitional region can be reliably rolled, even in the possible presence of in part substantial differences in terms of the dimensions and/or properties of the rolling stock between partial areas of the rolling stock joined by means of a transitional region.  
         [0007]     Said object is achieved by means of a method of the type described in the introduction, with the roll gap of at least one roll stand being opened, when the transitional region&#39;s physical characteristics so require, as a function of the position of the transitional region of the rolling stock moving at a speed through the mill train. Said object is further achieved by means of a corresponding computing device for regulating the mill train.  
         [0008]     The invention enables rolling stock to be rolled reliably even when successive partial areas thereof differ substantially in terms of, for instance, strip thickness, strip hardness, and/or alloying. According to the invention it is no longer imperative for rolling stock to be assembled in a lengthy planning process from partial areas, which is to say single coils or, as the case may be, single strips, in such a way that the differences between successive strips are relatively only slight. Thus, for example, it is possible according to the invention when production schedules are tight to assemble rolling stock from coils or, as the case may be, strips without taking the individual coils&#39; or, as the case may be, strips&#39; properties or, as the case may be, dimensions into account, and to reliably roll the rolling stock continuously. That will result in a substantial increase in the operating plant&#39;s flexibility and reliability.  
         [0009]     The roll gap of at least one roll stand will be opened only in the case of a critical transitional region, which is to say when the physical characteristics of the transitional region so require. Critical transitional regions are transitional regions that join partial areas of rolling stock having properties or, as the case may be, dimensions differing in such a way that their transit through a roll stand having a closed roll gap would entail substantial disruptions to the process variables. If a transitional region is critical, its physical characteristics will require a roll gap to be opened. That applies also to the following developments of the invention. Stopping of the operating plant before a critical transitional region enters it is inventively avoided, resulting in an increase in throughput rate.  
         [0010]     It is expedient for a roll stand&#39;s roll gap to be opened no later than when the critical transitional region of the rolling stock has reached said roll stand.  
         [0011]     In each case no more than one of the roll gaps of the mill train&#39;s roll stands is advantageously open at any instant within the method&#39;s application. According to said development of the invention and that described in the preceding, as much of the rolling stock as possible will be rolled in accordance with the required product properties and the portion of spoilage thus significantly reduced.  
         [0012]     It is furthermore expedient for said roll stand&#39;s roll gap to be closed when the critical transitional region has traversed said roll stand.  
         [0013]     The front tension in the rolling stock in front of and behind a roll stand is advantageously equalized before the roll gap of said roll stand is opened so as to minimize the adverse impact on the rolling process taking place on the roll stands involved, which is to say particularly on said roll stand and those surrounding it.  
         [0014]     The rotating speed of at least one of the rolls, in particular the work rolls, of the roll stand is advantageously matched to the speed of the rolling stock when the roll gap is closed. Controlled closing of the roll gap in this manner using speed synchronizing will largely prevent undesired roll-surface damage.  
         [0015]     The speed of the rolling stock is therein advantageously measured. The accuracy of synchronizing will be enhanced thereby.  
         [0016]     The speed of the rolling stock is advantageously determined with the aid of at least one model. A particularly efficient method of speed determining will be provided thereby.  
         [0017]     The reduction in a roll stand is advantageously regulated in a time-optimized manner with regard to the position of the transitional region in the mill train. The reduction in a roll stand is diminished when the transitional region is approached, with compensatory adjusting of the change in peripheral precession to the speed of the roll stand&#39;s rolls.  
         [0018]     Before a transitional region&#39;s transit, the roll gap is advantageously eased through controlled opening of the screw-down device. The relational speeds of the mill train&#39;s other drives are preferably additionally adjusted accordingly. Disrupting of the process variables will in this way be prevented.  
         [0019]     The front tension in the rolling stock in front of a roll stand is advantageously regulated by way of the other roll drives&#39; rotating speed as long as the reduction in said roll stand has been reduced around the critical transitional region. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     Further advantages and details will emerge from the following description of exemplary embodiments in conjunction with the drawings, in which:  
         [0021]      FIG. 1  shows a mill train having computing equipment,  
         [0022]      FIGS. 2 and 3  show examples of rolling stock having a seam weld,  
         [0023]      FIG. 4  shows examples of rolling stock having a wedge,  
         [0024]      FIG. 5  shows rolling stock having a transitional region between two roll stands,  
         [0025]      FIG. 6  is a schematic of the curve of the front tension with roll gaps closed,  
         [0026]      FIG. 7  shows-an example of front-tension regulating in the rolling stock. 
     
    
     DETAILED DESCRIPTION OF INVENTION  
       [0027]      FIG. 1  shows a mill train  10  for rolling rolling stock  1  that moves through the mill train  10  at a speed v. The mill train  10  has at least two roll stands  2  which rolling stock  1  traverses. Rolling stock  1  traverses the mill train  10  in the direction of strip travel x. Rolling stock  1 , preferably a metal strip, is continuously rolled in the mill train  10 . The mill train  10  is preferably a cold-rolling mill train for steel having as a rule more than three roll stands  2 . Located downstream of the roll stands  2  is a coiling device  3  on which the rolled rolling stock  1  is coiled.  
         [0028]     The mill train  10 , in particular the stands  2  of the mill train  10 , is/are coupled to a computing device  4 . Located in the mill train  10  are generators, not shown further in the drawing, which convey, for example, measuring signals to the computing device  4 . The computing device  4  conveys preferably control signals to actuators in the mill train  10 .  
         [0029]     The computing device  4  preferably has a model  12  that models processes in the mill train  10  with the aid of data relating to, for example, rolling stock  1 .  
         [0030]     The directions indicated in  FIG. 1 , namely the direction of strip travel x, the direction of strip thickness y, and the direction of strip width z, principally relate only to the position of the rolling stock  1  and the position of the roll stands  2 , not, though, to the arrangement of the computing device  4  in relation to the mill train  10 . The roll stands  2  each have a roll gap  11 , only intimated in  FIG. 1 . A roll stand  2  has at least two work rolls of which at least one is arranged in the direction of strip thickness y above the rolling stock  1  and at least one in the direction of strip thickness y below the rolling stock  1 . The roll gap  11  is located between said work rolls. Back-up rolls, likewise not shown further in the drawing, are as a rule provided in addition to the work rolls.  
         [0031]     In particular in the case of cold rolling, rolling stock  1 , for example sheet metal, is increasingly produced in continuous mill trains  10 , with the coils that are as a rule supplied singly being welded together in the run-in of the production plant, of which the mill train  10  is also a constituent part. The mill train  10  rolls the rolling stock  1 , consisting of a plurality of coils welded together, continuously, which is to say without stopping. In the production plant&#39;s run-out the rolling stock is separated again into single coils. That is done by, for example, shearing or cutting. Particularly when production schedules are tight, rolling stock  1  is rolled in a continuous mill train  10  without taking account of the properties of the individual coils forming the rolling stock  1 . The individual coils differ in terms of, for example, thickness and/or width in the direction of strip thickness y or, as the case may be, the direction of strip width z and/or with respect to their alloying and/or hardness.  
         [0032]      FIG. 2  shows a section of rolling stock  1  having two partial areas  1   a,    1   b  that correspond to two different coils and differ in thickness. The two partial areas  1   a,    1   b  of the rolling stock  1  are joined by a transitional region  9 , with the transitional region  9  having a seam weld  5 .  
         [0033]      FIG. 3  shows a section of rolling stock  1  having two partial areas  1   a,    1   b  each corresponding to different coils. The two partial areas  1   a,    1   b  are joined by a transitional region  9 , with the transitional region  9  having a seam weld  5 . The seam weld  5  is only intimated in both  FIG. 3  and  FIG. 2 . The partial areas  1   a,    1   b  or, as the case may be, coils shown in  FIG. 3  differ in width.  
         [0034]      FIG. 4  shows a section of rolling stock  1 , with two partial areas  1   a,    1   b  being in this case joined by a transitional region  9  between the two partial areas  1   a,    1   b  corresponding preferably to two coils. The transitional region  9  is in  FIG. 4  shown by way of example only as being almost wedge-shaped. The transitional region  9  has in many cases a thickness curve differing from that shown. Thus the thickness of the rolling stock  1  in the transitional region  9  can initially also increase then decrease. What was said previously applies analogously to the width of the rolling stock  1 .  
         [0035]     Properties such as strip thickness, strip width, strip hardness, and/or alloying change at the transitional region  9 . If the rolling stock is assembled with no account taken of the properties of the coils or, as the case may be, subsequent partial areas, then properties of the rolling stock  1  can change abruptly particularly at the seam welds  5 .  
         [0036]      FIG. 5  shows by way of example a transitional region  9  embodied as a wedge  6  between two roll stands  2 ′ and  2 ″, with the roll stand  2 ′ being arranged in front of the roll stand  2 ″. The roll stand  2 ′ has a top work roll  7 ′ and a bottom work roll  8 ′. The roll stand  2 ″ likewise has a top work roll  7 ″ and a bottom work roll  8 ″. Located between the top work roll  7 ′ or, as the case may be,  7 ″ and the bottom work roll  8 ′ or, as the case may be,  8 ″ of a roll stand  2 ′ or, as the case may be,  2 ″ is the roll gap  11 ′ or, as the case may be,  11 ″.  
         [0037]     The partial areas  1   a,    1   b  of the rolling stock  1  have on the one hand a difference in strip thickness already present prior to run-in into the first roll stand  2 . On the other hand, the strip thickness of the rolling stock  1  also changes during traversing of the roll stand  2 ′,  2 ″ with a closed roll gap  11 ′,  11 ″. Thus before entering the roll stand  2 ′ the partial area  1   b  of the rolling stock  1  has a strip thickness h 1  that is greater than its strip thickness h 2  on exiting the roll stand  2 ′. Likewise, the strip thickness h 3  before entering the roll stand  2 ″ is greater than the strip thickness h 4  on exiting the roll stand  2 ″. The difference between the strip thicknesses h 1  and h 2  or, as the case may be, h 3  and h 4  is due to the reduction in the roll stands  2 ′,  2 ″.  
         [0038]     The reduction occurring in a roll stand  2 ,  2 ′,  2 ″ is due to the rolling force exerted by the work rolls  7 ′,  7 ″,  8 ′,  8 ″ on the rolling stock  1 . The roll gap  11 ,  11 ′,  11 ′″ is said to be closed when both the at least one top and the at least one bottom work roll  7 ′,  7 ″ or, as the case may be,  8 ′,  8 ″ of a roll stand  2 , 2 ′,  2 ″ are in contact with the rolling stock  1  or, as the case may be, exert a rolling force on the rolling stock  1 . The roll gap  11 ,  11 ′,  11 ″ of a roll stand  2 ,  2 ′,  2 ″ is open when in a roll stand  2 ,  2 ′,  2 ″ the rolling stock  1  is not in contact with the at least one work roll  7 ′,  7 ″ or  8 ′,  8 ″, in particular the at least one top work roll  7 ′,  7 ″, at least on one side of the rolling stock  1  in the direction of strip thickness y, in particular on the top side of the rolling stock  1 .  
         [0039]     As already described in the foregoing, the rolling stock  1  sometimes has one or more transitional regions  9  due to whose physical characteristics a traversing by a transitional region  9  of said type of a roll stand  2  having a closed roll gap  11  would lead to substantial disruptions in the process variables. The transitional region  9  will exhibit said type of critical physical characteristics when the partial areas  1   a,    1   b,  joined by the transitional region  9 , of rolling stock  1  differ substantially in at least one of their properties and/or at least one dimension. A considerable risk associated with a transitional region  9  that is critical in this way is that the rolling stock  1  will split when traversing a closed roll gap  11 . The roll gap  11  of a roll stand  2  is therefore opened as a function of the position of said type of transitional region  9 . If a transitional region  9  of a rolling stock  1  is moving at a speed v through the mill train  10 , then the roll gap  11  of a roll stand  2  will be opened if the physical characteristics of said transitional region  9  so require.  
         [0040]     During continuous rolling operations a critical transitional region  9  traverses the roll stands  2  of the mill train  10  successively. The computing device  4  therein drives the mill train  10  in such a way that the roll gaps  11  of the roll stands  2  will be opened stand by stand and in parallel with the critical transitional region&#39;s position as the rolling stock  1  moves. A roll gap  11 ″ of a roll stand  2 ′″ will therein be opened no later than when the critical transitional region  9  reaches said roll stand  2 ″. The roll gap  11  of a roll stand  2  will preferably not be opened until shortly before a critical transitional region  9  runs into said roll stand  2 , and it will be closed when the critical transitional region  9  has traversed the roll stand  2 . Preferably at most one roll gap  11  of the roll stands  2  is open or, as the case may be, in particular fully open at a specific instant while the rolling stock  1  is being moved through the mill train. As a consequence of the roll gaps  11  of individual roll stands  2  being opened only as briefly as possible, the portion of spoilage will be very small and an extremely large portion of the rolling stock  1  can be rolled in a controlled manner. Alongside the saving in time, this is a major advantage compared to what are termed “open-gap” processes according to which a mill train  10  is stopped before a critical transitional region  9  is run in, all the roll gaps  11 ,  11 ′,  11 ″ are then opened, the critical transitional region  9  is driven through the entire mill train  10  with the roll gaps  11 ,  11 ′,  11 ″ open, and further according to which all the roll gaps  11 ,  11 ′,  11 ′″ are thereafter closed again and the rolling process is then resumed.  
         [0041]      FIG. 6  is a schematic of the curve of the front tension T over the direction of strip travel x in a mill train  10 . Located at the positions x 1 , x 2 , x 3 , x 4  are stands  2  of the mill train. A coiling device  3  is arranged at the position x 5 . During regular rolling operations the front tension T in the rolling stock  1  reduces behind the first roll stand  2  at the position x 1  at each roll stand  2  up to the coiling device  3 . To prevent the rolling stock  1  from impacting or, as the case may be, splitting when a roll gap  11  is opened, the front tension T in the rolling stock  1  in front of and behind the roll stand  2  is equalized before the roll gap  11  of a roll stand  2  is opened. This means that if the roll gap  11  of a roll stand  2  is being opened, the front tension T in the environs of said roll stand  2  will ideally be constant shortly before the roll gap  11  is opened, while it is being opened, and briefly thereafter.  
         [0042]     It is furthermore advantageous for the reduction in a roll stand  2  to be diminished in a time-optimized manner with compensatory adjusting of the change in peripheral precession to the roll speed. The roll gap  11  is preferably eased through controlled opening of the screw-down device in the roll stand  2  depending on the transition to a position-regulated or rolling-force-regulated operating mode, with the relational speed of the drives of the other roll stands  2  of the mill train  10  then being adjusted accordingly. Disrupting of the process variables is in this way prevented. The relational speed is the speed in a roll stand  2  relative to the other roll stands  2  of the mill train  10 .  
         [0043]     Should it not be possible to reliably roll a transitional region  9  through controlled opening of the screw-down device with the roll gap  11  closed, then—as described previously—the roll gap  11  will be opened. If a roll gap  11  has been opened owing to a critical transitional region  9 , it will be closed in a controlled manner when the critical transitional region  9  has passed through until contact is made with the strip. The roll speed is therein synchronized with the measured and/or modeled speed v of the rolling stock  1 .  
         [0044]      FIG. 7  shows two roll stands  2 ′ and  2 ″, with the roll stand  2 ″ being located downstream of the roll stand  2 ′. Both roll stands  2 ′ and  2 ″ have a roll-stand screw-down device  2   a ′ or, as the case may be,  2   a ″ and a roll-stand drive  2   b ′ or, as the case may be,  2   b ″. A front-tension regulator  13  is provided. Measurement variables and/or values, determined with the aid of models, for the front tension T in the rolling stock  1  between the two roll stands  2 ′ and  2 ″ are advantageously conveyed to the front-tension regulator  13 . Described below is an advantageous variant of inventive front-tension regulating in the rolling stock  1  in front of the roll stand  2 ″. During standard rolling operations the front tension T is regulated via the backward slip of the roll stand  2 ″ by means of the roll-stand screw-down device  2   a ″ of the roll stand  2 ″. So long as the reduction in the roll stand  2 ″ is being diminished around the critical transitional region  9 , the front-tension regulator  13  will adjust the front tension T by means of the rotating speed of the roll-stand drive  2   b ′ of the roll stand  2 ′.  
         [0045]     The idea underlying the invention can be summarized substantially as follows:  
         [0046]     The invention relates to a method for rolling rolling stock  1  in a mill train  10  having at least two roll stands  2 , with each roll stand  2  having a roll gap  11  and with the rolling stock  1  requiring to be rolled having at least one transitional region  9 . When a critical transitional region  9  traverses the mill train  10 , the roll gaps  11  of the at least two roll stands  2  will be closed and opened successively in the direction of strip travel x as a function of the position of the transitional region  9  moving at a speed v through the mill train  10 . The roll gaps  11  are opened in parallel with the position of the critical transitional region  9  with the rolling stock  1  being moved. A transitional region  9  is critical if its physical characteristics require roll gaps  11  to be opened. The changes in at least one of the dimensions or, as the case may be, properties such as the hardness or alloying of the rolling stock  1  around the transitional region  9  could, with the roll gap  11  closed, lead to substantial disruptions in the process variables or, as the case may be, cause the rolling stock  1  to split. Inventive stand-by-stand opening of the roll gaps  11  with the plant running will also enable controlled transiting by a rolling stock  1  exhibiting extreme changes in dimension and/or hardness with an ensuing deviation length that is slight.  
         [0047]     Equalizing of the tensile force will prevent slipping of the rolls, in particular of the work rolls  7 ′,  7 ″,  8 ′,  8 ″ of the roll stands  2 . Nor will any equalizing operations then be performed on the front tension T in the adjacent stands when the roll gap  11  is opened in a roll stand  2 . The speed v of the rolling stock  1  is measured and/or determined with the aid of at least one model  12  implemented in the computing device  4 . Placing the work rolls  7 ′,  7 ″,  8 ′,  8 ″ onto the rolling stock  1  with a synchronized roll speed will prevent damage to the rolls. Time-optimized opening and closing of the roll gap  11  will minimize the length of deviation.  
         [0048]     The position of the transitional region  9  in the mill train  10  is tracked from a synchronizing point  8 , sited preferably at the entrance of mill train  10 , by means of differential speed monitoring.