Abstract:
The invention relates to a method for reducing the edge drop of a rolled strip in a roll train having one or more roll stands, at least one roll stand having actuators for reducing the edge drop, which are set as a function of the edge drop of the rolled strip running out of the roll stand and, if appropriate, of the edge drop of the rolled strip running into the roll stand, the edge drop being measured with at least one edge drop measuring device, and the values of the edge drop of the rolled strip being determined using a roll gap model, in order to set the actuators for reducing the edge drop at those points on the rolled strip at which the edge drop is not measured.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and device for reducing the edge drop of a rolled strip in a roll train. 
     BACKGROUND INFORMATION 
     During the rolling of metal strips, because of the mechanical properties of roll stands and the flow properties of the rolled metal, so-called edge drop occurs, i.e., a flattening of the rolled strip at the edges. It is known e.g., from Japanese Patent Application No. 08 155 517 and from article “development of accurate control techniques of strip shop and edge-drop in cold rolling,” Journal of the Iron and Steel Industry of Japan, Vol. 79, No. 3, 1993, pp. 388-94, to counteract the edge drop by means of so-called tapered rolls. To this end, the working rolls are curved in a suitable way. For a particularly precise driving of the so-called tapered rolls, the edge drop is measured upstream and downstream of the appropriate roll stand. However, these measurements are expensive, in particular when they have to be carried out for a plurality of roll stands. A further problem in the known method for reducing the edge drop is that the measures for reducing the edge drop must not lead to an impermissibly high tension in the edge region of the rolled strip nor to wavy edges. If the permissible tension in the edge region of the rolled strip is exceeded, then this can lead to an impermissible reduction in the quality of the rolled strip. In order to avoid this, in the case of the conventional method for reducing the edge drop, according to Japanese Patent Application No. 62 192 205, provision is made to measure the strip tension in the edge region of the rolled strip. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide method and device for circumventing the abovementioned disadvantages. 
     According to the present invention, measuring device for measuring the edge drop is dispensed with. Furthermore, using the roll gap model it is possible to calculate the tension relationships in the roll strip, that an expensive measurement of the tension relationships for monitoring is not necessary. In addition, the method according to the present invention can advantageously be combined with flatness regulation or flatness control. The roll gap model moreover permits the edge drop to be calculated in advance, so that if appropriate necessary presettings can be made. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a cross-section of a rolled strip. 
     FIG. 2 shows a block diagram of a method for reducing an edge drop of a rolled strip according to the present invention. 
     FIG. 3 shows another block diagram of the method according to the present invention for reducing the edge drop of the rolled strip. 
     FIG. 4 shows a model of the method according to the present invention for reducing the edge drop of the rolled strip. 
     FIG. 5 shows a part of a device for reducing the edge drop of the rolled strip. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the cross-section of a rolled strip with edge drop. In this case, b designates the width of rolled strip b 1  the region of the rolled strip which is free of edge drop and b G,L  and b G,R  the edge region of the rolled strip having edge drop. 
     Furthermore, d 5 , designates the thickness of the rolled strip at a distance of 5 mm from the edge of the rolled strip, and d 100  the thickness of the rolled strip at a distance of 100 mm from the edge of the rolled strip. These two values are included in one possible definition for edge drop P, if this is expressed by a numerical value. This possible definition is:        p   =             d   100     -     d   5         d   100       ·   100        %                            
     However, the edge drop can also be represented as a contour, i.e., as a function over the strip width. This representation advantageously forms the basis of the method according to the present invention for reducing the edge drop of a rolled strip. 
     FIG. 2 shows an exemplary application of the method according to the present invention for reducing the edge drop of a rolled strip  11 . Rolled strip  11  is rolled by means of five roll stands, a first roll stand indicated by rolls  1  and  2 , a second roll stand indicated by rolls  3  and  4 , a third roll stand indicated by rolls  5  and  6 , a fourth roll stand indicated by rolls  7  and  8  and a fifth roll stand indicated by rolls  9  and  10 . The five roll-stands are part of a five-stand or multi-stand roll train. The first, second and third roll stand have actuators  12 ,  13 ,  14 , with which the edge drop of rolled strip  11  can be influenced. Input variables for actuators  12 ,  13  and  14  are the values for edge drop P 1 , P 2  and P 3 . Since the system has only two items of measuring device  21  and  22  for measuring the edge drop upstream of the first and downstream of the fifth roll stand, the edge drops downstream of first roll stand P 1 , downstream of second roll stand P 2  and downstream of third roll stand P 3  are determined using a roll gap model. This model has five partial models  15 ,  16 ,  17 ,  18 ,  19 , which are each assigned to one roll stand. Partial model  15  is assigned to the first roll stand, partial model  16  to the second roll stand, partial model  17  to the third roll stand, partial model  18  to the fourth roll stand and partial model  19  to the fifth roll stand. Output variables of partial model  15  are edge drop P 1 , and tension relationships σ 1 , in or downstream of the first roll stand, which are in turn input variables of partial model  16 . Output variables of partial model  16  are edge drop P 2  and tension relationships σ 2  in or downstream of the second roll stand, which are in turn input variables of partial model  17 . Output variables of partial model  17  are edge drop P 3  and tension relationships σ 3  in or downstream of the third roll stand, which are in turn input variables of partial model  18 . Output variables of partial model  18  are edge drop P 4  and tension relationships σ 4  in or downstream of the fourth roll stand, which are in turn input variables of partial model  19 . output variables of partial model  19  are edge drop P 5  and tension relationships σ 5  in or downstream of the fifth roll stand. Tension relationships σ 1 , σ 2 , σ 3 , σ 4 , and σ 5  are to be understood as the web tension (flatness) and/or the tension of the rolled strip directly before entering the roll gap or directly after exiting from the roll gap. 
     Input variables of first partial model  15  are edge drop P 0  upstream of the first roll stand and, if appropriate, tension relationships σ 0  upstream of the first roll stand. Tension relationships σ 0  upstream of the first roll stand are then included in partial model  15  when the rolled strip is, for example, uncoiled from a coil. Further input variables of partial models  15 ,  16 ,  17 ,  18 ,  19  are the roll contours for the individual roll stands. These input variables are not shown in FIG.  1 . The roll contour is advantageously calculated in a roll contour model which, inter alia, comprises a temperature model, a wear model and a bending model. in this case there is advantageously an individual roll contour model for each roll stand. 
     During the rolling of rolled strip  11 , partial models  15 ,  16 ,  17 ,  18 ,  19  are continuously adapted to the actual relationships in the roll stands using an adaptation  20 , which determines appropriate parameters π 1 , π 2 , π 3 , π 4  and π 5 , for corresponding partial models  15 ,  16 ,  17 ,  18 ,  19  from the edge drop upstream of first roll stand P 0, ist , from edge drop P 5  determined by partial model  19  downstream of the fifth roll stand, and from the actual value of edge drop P 5, ist  downstream of the fifth roll stand. 
     FIG. 3 shows an exemplary application of the method according to the present invention for reducing the edge drop of a rolled strip  11 . Rolled strip  11  is rolled using five roll stands, a first roll stand indicated by rolls  1  and  2 , a second roll stand indicated by rolls  3  and  4 , a third roll stand indicated by rolls  5  and  6 , a fourth roll stand indicated by rolls  7  and  8  and a fifth roll stand indicated by rolls  9  and  10 . The five roll stands are part of a five-stand or multi-stand roll train. The first, second and third roll stands have actuators  30 ,  31 ,  32  with which the edge drop of rolled strip  11  can be influenced. input variables of actuators  30 ,  31  and  32  are the values for edge drop P 1 , P 2  and P 3, ist . Since the system has only two items of measuring device  40  and  41  for measuring the edge drop upstream of the first and downstream of the third roll stand, the edge drops downstream of first roll stand P 1 , downstream of second roll stand P 2  and downstream of third roll stand P 3  are determined by means of a roll gap model. This model has three partial models  33 ,  34  and  35 , each of which is assigned to one roll stand. Partial model  33  is assigned to the first roll stand, partial model  34  to the second roll stand and partial model  35  to the third roll stand. output variables of partial model  33  are edge drop P 1 , and tension relationships σ 1 , in or downstream of the first roll stand, which are in turn input variables of partial model  34 . output variables of partial model  34  are edge drop P 2  and tension relationships σ 2  in or downstream of the second roll stand, which are in turn input variables of partial model  35 . output variables of partial model  35  are edge drop P 3  and , if appropriate, tension relationships σ 3  in or downstream of the third roll stand. 
     Input variables of first partial model  33  are edge drop P 0, ist  upstream of the first roll stand and, if appropriate, tension relationships σ 0  upstream of the first roll stand. Tension relationships σ 0  upstream of the first roll stand are then included in partial model  35  when the rolled strip is, for example, uncoiled from a coil. Further input variables of partial models  33 ,  34  and  35  are the roll contours for the individual roll stands. These input variables are not shown in FIG.  3 . The roll contour is advantageously calculated in a roll contour model which, inter alia, comprises a temperature model, a wear model and a bending model in this case there is advantageously an individual roll contour model for each roll stand. 
     During the rolling of rolled strip  11 , partial models  33 ,  34  and  35  are continuously adapted to the actual relationships in the roll stands by means of an adaptation  36 , which determines appropriate parameters π 1 , π 2 , and π 3  for corresponding partial models  33 ,  34  and  35  from the edge drop upstream of first roll stand P 0, ist , from edge drop P 3  determined by partial model  35  downstream of the third roll stand and the actual value of edge drop P 3, ist  downstream of the third roll stand. 
     FIG. 4 illustrates the interaction of roll contour model  60 , roll gap model  61  and an actuator  62 . On the basis of process state information X i  and output U i  of actuator  62 , roll contour model  60  calculates roll contour W i  which is in turn an input variable into roll gap model  61 . Further input variables into the roll gap model are edge drop P i−1 , and tension relationships σ i−1  upstream of the roll stand. Output variables of roll gap model  61  are edge drop P i . and tension relationships σ 1  downstream of the roll stand. On the basis of edge drop P i  downstream of the roll stand, actuator  62  determines manipulated variable U i . 
     FIG. 5 shows a possible roll configuration for implementing manipulated variable U i  from FIG.  4 . Steel strip  56  is rolled between two operating rolls  57  and  58 . Supporting and intermediate rolls are not shown in FIG.  5 . In order to reduce the roll diameter at the end region of the rolled strip, which counteracts the edge drop, the system has two cooling devices  54  and  55 , from which coolant  50 ,  51 ,  52 ,  53 , advantageously water, emerges and is applied to working rolls  54  and  58 . The necessary coolant quantity corresponds, for example, to variable U 1  of FIGS. 1 to  4 .