Method and computer program for adjusting the target thickness value for controlling the thickness of a strip to be rolled again for at least one roll stand

Abstract

The invention relates to a method and a computer program for adjusting the target thickness value for controlling the thickness of a strip to be newly rolled, in particular a metal strip, using at least one rolling stand. According to the method, the thickness profile of at least one previously rolled strip is first analyzed at a first width position with regard to the maximum and / or minimum value over at least one length section, and an average value is determined. To achieve a higher yield of 1A-quality strip after hot or cold rolling than in the prior art, a predicted thickness profile DP for the newly rolled strip is determined according to the invention, based on the analyzed and determined values.The system then checks whether the distance dAct between the predicted maximum value hpmx and the predicted minimum value hpmi for the predicted thickness profile DP is smaller than the distance dRef between a target upper limit Vo and a target lower limit Vu of a given tolerance band. If so, the mean value hp of the predicted thickness profile is either increased towards the target upper limit VO or decreased towards the target lower limit Vu, and the resulting mean value hpn is then set as the adjusted target thickness value for the new strip to be rolled over the length section l'.

Description

[0001] The invention relates to a method and a computer program product for adjusting the target thickness value for controlling the thickness of a strip to be newly rolled for at least one rolling stand. Stand der Technik

[0002] During hot and cold rolling of strip, the strip goes through various process situations with varying productivity and resulting strip quality. In process situations such as threading processes or product changeovers, good quality of the rolled strip can often not be guaranteed; the corresponding parts of the strip then have to be scrapped. However, once a hot or cold rolling mill has reached a steady state in which the so-called fillet area of ​​the strip is rolled, very good product quality can be achieved with the help of state-of-the-art actuators, sensors and control systems. In particular, the thickness of the strip can be very precisely controlled to predetermined target values ​​as a quality parameter. How precisely the strip thickness is achieved depends on various parameters, such as the control quality and the quality of the starting material.The exact thickness required for the strip is usually also known from specifications, typically provided by the end customer. During this phase, in which strip is rolled or produced with top-quality quality, Level 1 control and Level 2 setting operate with target thicknesses that usually correspond to the end customer's specifications. In the current state of the art, strip thickness control is usually performed at a thickness in the middle of the strip width.

[0003] This conventional operating procedure has the disadvantage that a relatively high proportion of the rolled strip does not meet the required quality criteria, and productivity is also low. This poor quality is sometimes reflected in strip thicknesses in the edge area that are outside the end customer's tolerance. However, significantly better qualities can also be achieved than the end customer demands; in this case, however, the cold or hot rolling mill is strategically not operated in a way that delivers maximum yield for the mill operator.

[0004] Chinese patent CN 102069094 B, which forms the basis for the preamble of claim 1, discloses a system for optimizing key process parameters for controlling the profile or contour of a cold-rolled strip based on data mining. The process parameters for profile or contour control are recorded during ongoing processes and, after preliminary processing, collected in a historical database. This historical data is then processed in further steps and, ultimately, is used to generate optimized process parameters for future newly rolled strips, taking into account known knowledge about cold and hot rolling of strips.

[0005] US patent US 2021 / 0178443 A1 discloses a rolling mill with multiple rolling stands for rolling flat rolled stock. In this case, both the actual values ​​of the rolled stock before rolling and the target values ​​of the rolled stock after rolling are fed to a control system before rolling. Based on the actual and target values ​​in combination with a description of the rolling line provided by a model of the rolling line, the control system determines values ​​for control or adjustment variables of the rolling stands.

[0006] The invention is based on the object of developing a known method and computer program for adjusting the target thickness value for controlling the thickness of a strip to be newly rolled in such a way that after hot or cold rolling of the strip, a higher yield rate with 1A quality results than in the prior art, which meets the tolerance requirements of the end customer.

[0007] This object is achieved by the method claimed in claim 1. It is characterized by: d) Generating a predicted thickness profile for the newly rolled strip, in each case at the same first width position over at least one length section of the newly rolled strip, based on the maximum value and / or minimum value determined in step b) and the mean value determined in step c), wherein the length section of the newly rolled strip is determined according to the same specification as the length section of the at least one previously rolled strip; e) Repeating steps b) and c) for the predicted thickness profile to determine a predicted maximum value and / or predicted minimum value and a predicted mean value;f) Check whether, for the predicted thickness profile of the newly rolled strip, the distance between the predicted maximum value and the predicted minimum value is smaller than the distance between a specified target upper limit and a specified target lower limit; if so: g1) Change the predicted mean value at the first width position such that the predicted maximum of the predicted thickness profile, at least over the length section of the newly rolled strip, corresponds to the target upper limit at least up to a specified maximum safety distance, whereby the thus modified predicted mean value is then set as the adjusted target thickness value for the newly rolled strip over the length section;or g2) changing the predicted mean value at the first width position such that the predicted minimum of the predicted thickness profile, at least over the length section of the strip to be newly rolled, corresponds to the target lower limit at least up to a predetermined minimum safety margin, wherein the predicted mean value thus changed is then determined as the adjusted target thickness value for the strip to be newly rolled over the length section.

[0008] The claimed alternative according to process step 1 g1) is recommended if the newly rolled strip is to be sold by tonnage or with a view to minimizing energy consumption. In contrast, the alternative according to claimed process step 1 g2) is recommended if the newly rolled strip is to be sold by product length.

[0009] The maximum safety distance and the minimum safety distance as well as the tolerance band can each be specified independently of each other, optionally also to zero.

[0010] The "predicted mean" of the predicted thickness profile of the newly rolled strip represents the intercept of the predicted thickness profile in a graph in which the thickness of the strip is plotted against its length.

[0011] The term "strip" refers specifically to a metal strip. However, the method according to the invention can also be applied to strips made of any material other than metal.

[0012] The claimed method ensures that, during strip rolling, the fillet length of the strip—i.e., the length or percentage of the rolled strip that meets the customer's tolerance requirements—is increased and, preferably, also qualitatively improved. The fillet area of ​​a strip is typically its middle section. This does not include the beginning and end of the strip. Optimizing the quality of the rolled strip is primarily in the interest of the end customer; increasing the high-quality, and thus saleable, portion of the strip after rolling is in the interest of the rolling mill operator because this results in less scrap and therefore lower costs.

[0013] According to the claimed method, the optimization is carried out by adapting the specified target thickness value for controlling the thickness of a strip to be newly rolled for a pass to be carried out on at least one rolling stand.

[0014] Advantageous embodiments of the method according to the invention are the subject of the dependent claims.

[0015] The above-mentioned problem is also solved by the claimed computer program product. The advantages of the computer program product correspond to those mentioned above with reference to the claimed method.

[0016] The description is accompanied by 15 figures, of which Fig. 0 shows a strip; Figures 1a) to 1g1) and 1g2) show the steps of the method according to the invention; Fig. 2a) to 2c) show the method steps according to a first embodiment of the method according to the invention; Fig. 3 shows an exemplary specification for defining the length section I'; and Figures 4a) and 4b) show the suitable adaptation of a hot strip target thickness value for thickness control of another strip to be newly rolled during hot rolling at at least one width position such that during subsequent cold rolling of the same strip, the predicted maximum value is below the specified target upper limit and the predicted minimum value is above the specified target lower limit; illustrated.

[0017] The invention is described in detail below with reference to the figures mentioned in the form of exemplary embodiments. In all figures, identical technical elements are designated by identical reference numerals.

[0018] Fig. 0 illustrates the reference numerals used below for specific parameters of a strip 20. Thus, the reference numerals B1, B2 denote various width positions on the strip. The reference numerals D, I denote the thickness or the thickness profile and the length of a length section of previously rolled strip, while the reference numerals DP, I' denote the thickness or the thickness profile and the length of a length section for newly rolled strip.

[0019] With the procedural steps a) Measuring the thickness profile D of at least one strip already rolled in the past, at at least one first width position B1 over at least one length section I; see Fig. 1a ); b) analyzing the recorded thickness profile D of the strip rolled in the past with regard to the maximum value hMax and / or the minimum value hMin over the length section I; see Fig. 1b ); and c) determining an average value hpa from the at least one recorded thickness profile D over the length section I or from target thickness specifications for the at least one strip already rolled in the past; see Fig. 1c ) according to the preamble of method claim 1, the present invention creates a database on which the method according to the invention is further built. This database is created by measuring and analyzing the thickness profiles of at least one, typically a plurality of, strips rolled in the past. In particular, the thickness profiles of these strips are recorded at at least one first width position over at least one length section I in the longitudinal direction of the strip and evaluated with regard to any deviations from the target strip thickness that have occurred. Specifically, the analysis of the recorded thickness profiles involves determining their maximum and / or minimum values ​​hMax, hMin over the length section I.Furthermore, the method according to the invention provides in step c) that the mean values ​​of the recorded thickness profiles are determined over the length section or from target thickness specifications for the at least one already rolled strip. In addition, further characteristic data of the strip can be stored, such as the tolerance range to be achieved for the strip thickness, the target strip thickness and / or the strip profile. A prerequisite for determining the characteristic data for the strip profile is the evaluation of the thickness profile of the strip at at least two, typically three different width positions (B1, B2), namely near the left and right edges and in the middle of the strip. All of this information is stored as mass data and, in the method according to the invention, serves as the basis for carrying out the characterizing method steps d) to at least g1) or g2), as cited above in the general part of the description as a solution to the inventive problem.

[0020] According to process step 1d), as in Fig. 1d ), a predicted thickness progression DP for the newly rolled strip, in each case at the same first width position B1 over a length l' of the newly rolled strip, based on the maximum value hMax and / or minimum value hMin determined in step b) and the mean value hpa determined in step c). The length l' of the newly rolled strip 20 is determined according to the same specification as the length l of the at least one previously rolled strip 20. The specification is described below with reference to Fig. 3 described in more detail.

[0021] Then, according to step 1e), as in Fig. 1e ) illustrates steps b) and c) for the predicted thickness progression DP over its length section I' repeatedly to determine a predicted maximum value hpmx and / or predicted minimum value hpmi and a predicted mean value hp.

[0022] The following is in accordance with Fig. 1f ) In step 1f), it is checked whether, for the predicted thickness profile DP of the newly rolled strip 20 over its length section I', the distance dAct between the predicted maximum value hpmx and the predicted minimum value hpmi is smaller than the distance dRef between a specified target upper limit Vo and a specified target lower limit Vu. The limits Vo and Vu define a tolerance band for the thickness of the strip specified by the end customer. Vo and Vu are usually Level 3 data.

[0023] According to the method according to the invention, the target thickness values ​​for the newly rolled strip for Level 1 and Level 2 are not determined according to the end customer's specifications as in the prior art, but rather, according to the invention, a target thickness value for the newly rolled strip is actively adjusted and specified in such a way that an improved operating point is achieved for the operator of a plant for implementing the method according to the invention. If the test in step f) is affirmed, this is subsequently carried out either according to step 1g1) or 1g2): For strips that are usually sold by the ton, this optimized operating point is determined according to method step 1g1) as follows, see also Fig. 1g1 ): Step 1g1): Changing the predicted mean value hp at the first width position B1 such that the predicted maximum hpmx of the predicted thickness profile DP at least over the length section I' of the strip 20 to be newly rolled corresponds to the target upper limit Vo at least up to a predetermined maximum safety distance dsmx, wherein the predicted mean value hpn thus changed is then determined as the adjusted target thickness value for the strip 20 to be newly rolled over the length section I'.

[0024] With the claimed shift of the forecast mean value towards the upper limit of the end customer's tolerance band, i.e. towards the target upper limit Vo, the new strip is rolled from the rolling stand to a mean value hpn that is somewhat higher than the mean value usual in the state of the art. Rolling can advantageously be carried out more quickly and with less roll abrasion or wear. This is accompanied by lower energy consumption and less maintenance. In this way, the rolling mill's output can be increased, and more tons can be processed in the same time. The subsequent processes can often treat the strip more quickly or earlier. For the operator of the rolling mill, this procedure is more efficient than the state-of-the-art procedure.

[0025] However, if the operator sells the tape, for example, depending on its length, the alternative process step 1g2) according to the method according to the invention is recommended, as in Fig. 1g2 ) illustrates: Step g2) is: Changing the predicted mean value hp at the first width position B1 such that the predicted minimum hpmi of the predicted thickness profile DP at least over the length section I' of the strip 20 to be newly rolled corresponds to the target lower limit Vu at least up to a predetermined minimum safety distance dsmi, wherein the predicted mean value hpn thus changed is then determined as the adjusted target thickness value for the strip 20 to be newly rolled over the length section.

[0026] The adjusted target thickness value hpn resulting from this process alternative is shifted to the target lower limit Vu of the thickness tolerance band specified by the end customer. This results in a longer coil per unit of time and thus a larger saleable output, i.e., increased productivity.

[0027] According to a first embodiment, the method according to the invention provides that, according to a first alternative, steps a) to g1) or, according to a second alternative, steps a) to f) and g2) are repeated for at least one further width position B2 of the strips. Both the first alternative and the second alternative then initially result in at least two different predicted thickness profiles DPB1, DPB2 at different width positions B1 and B2, each with individual thickness mean values ​​hpB1, hpB2; see Fig. 2a .

[0028] Continuing the method according to the first embodiment results in a modified predicted mean value hpn for the at least one further width position B2 in both the first and second alternatives. The determination of this modified predicted mean value for the width position B2 is carried out analogously to the determination at the width position B1. As a result, at least two modified predicted mean values ​​hpnB1, hpnB2 are then available for each band at the width positions B1 and B2; see the Figuren 2b ) and 2c ).

[0029] In the case of the first alternative, a minimum mean value hpn is then selected from the set of modified predicted mean values ​​at the first and at least one further width position B1, B2 and set as the adjusted target thickness value for rolling the new strip 20. This is done according to the following formula: hpn = Min hpnB 1 , hpnB 2

[0030] In the case of the second alternative, the maximum mean value hpn is selected from the set of modified predicted mean values ​​at the first and at least one further width position B2 and set as the adjusted target thickness value for rolling the new strip 20. This is done according to the following formula: hpn = Max hpnB 1 , hpnB 2

[0031] By repeating the process steps according to the invention at different width positions of the strip, either once or continuously, it can advantageously be achieved that the strip is kept within the tolerances required by the end customer across the entire strip width. This is achieved according to the invention through the aforementioned process adjustments, which are calculated individually for each strip. By repeating the process steps according to the invention at different width positions of the strip, the process carried out at a single width position can be further refined in order to optimize productivity and quality. In addition, taking the profiles at the different width positions into account offers the possibility of extending the maximum commitment of requested, tightest customer tolerances across the entire width of the strip and thus also being able to meet new and tighter tolerance requirements from, for example, automobile manufacturers.This will result in a larger market volume for a steel manufacturer and, depending on the capabilities of its competitors, in a higher margin.

[0032] Example 1: A strip must be cold-rolled to tight thickness tolerances; the crown, i.e. the cross-sectional profile, and the wedge portion of the strip in its cross-section are known. In the prior art, the strip thickness is controlled purely via the width position of the strip center. Since the relative strip profile hardly changes during cold rolling, the thickness difference between the strip center and the strip edge can be determined. Using this determined value, the target thickness value for the (width) center of the strip can be automatically specified using the method according to the invention such that both the thickness at the edge and the thickness in the (width) center of the strip are rolled within tolerance. If the required tolerances permit, productivity optimization according to the first embodiment of the invention is also possible.

[0033] Example 2: A strip is hot-rolled to tight thickness tolerances. Since the target thickness of the cold strip as well as the crown and wedge of the hot strip are known in the cold rolling process, the desired average target thickness can be adjusted in the cold rolling process so that the entire strip lies within the tolerance. In addition, the hot rolling data can be used before the cold rolling process to determine whether the target tolerances can be achieved at all. This can therefore be taken into account in production planning before rolling and thus represents additional added value, as such a hot strip can then be scheduled for another cold rolling order with lower quality requirements, where the tolerances are 100% met with the given hot strip profile. This represents significant added value. This is commonly referred to as "predictive quality."

[0034] Intelligent networking of various mill products to increase overall productivity, variant 3.

[0035] For example, the method according to the invention is carried out or calculated separately for processing the strip in a hot rolling mill and in a cold rolling mill. The savings potential for both processes, e.g., monetary, qualitative, and energy-related, is calculated online. The calculated process parameters that appear most favorable for the operator, taking into account the final thicknesses and tolerances, are selected and implemented. For example, both calculations recognize added value in the fact that the average strip thickness lies in the upper tolerance range. This means that the average target thickness in the hot strip mill is maintained, but with a simultaneous reduction of the maximum crown and the wedge to a certain value. In the simplest case, this means that the cold rolling mill only has to run to the original target value (state of the art).

[0036] Optionally, the cold rolling mill could also inform the hot rolling mill, beyond the state of the art, in which extended thickness ranges it can operate (for example, approval of a higher crown or wedge on the hot strip), which could result in planning optimisations in the hot strip area (change of rolls) or other energy savings). The reverse is of course also possible. For this purpose, the calculations for the hot rolling mill and the cold rolling mill can optionally exchange content, with the aim of allowing the prioritized system (e.g. the hot rolling mill) to operate even beyond its own tolerance limits, knowing and taking into account which deviations and to what extent these can be compensated in the downstream process, i.e. the downstream cold rolling process. The cold rolling mill and the downstream process continue to ensure that the end customer's target values ​​are reliably achieved, taking into account any possibledeviating main parameters from the hot strip mill. Expanding the exchange of process data beyond the cold rolling mill, for example in coating systems, would lead to further savings. This could be achieved, for example, by adjusting the zinc coatings (increasing or decreasing the coatings within the customer's final tolerance or to achieve the customer's final tolerance). Adjusting the skin-pass reduction in the skin-pass mill would also be conceivable, which is possible with regard to the tolerances of the mechanical values. This would allow strips that are slightly above or below the tolerance limit due to profile or thickness to still be brought within the permissible tolerance range.

[0037] Fig. 3 illustrates an example of a rule according to the invention for defining the length section I'. This rule comprises the following steps: Determining the profile of at least one of the following parameters for the at least one strip rolled in the past, such as material yield strength, strip dimension, rolling speed v and / or change in rolling speed; defining the length section I' for the newly rolled strip 20 as the length section in which the profile of the at least one parameter lies within a predetermined tolerance band Δ or undergoes a change that lies above or below at least one predetermined change threshold value.

[0038] Fig. 3 shows an example of a curve for the rolling speed parameter v. Only for the length sections I'2, I'7, and I'8 does the rolling speed v lie within the tolerance band Δ. According to the method according to the invention, only those length sections that, for example, fulfill this condition are defined as predicted length sections in method step 1d).

[0039] After determining the adjusted target thickness value according to the method according to the invention, the actual thickness of the new strip 20 over the length section I' is controlled to the adjusted target thickness value. Within the scope of this thickness control, the adjusted target thickness value acts as a reference variable, and the rolling stand serves as the actuator; in particular, the roll gap of the rolling stand is suitably varied during the thickness control.

[0040] The method according to the invention for determining the adjusted target thickness value can be carried out offline, prior to rolling the newly rolled strip, for at least one length section I' of the newly rolled strip. The term "offline" here means "not during an ongoing rolling process."

[0041] Alternatively, the method for determining the adjusted target thickness value can be performed during the rolling of a length of the strip. The resulting adjusted target thickness value can then be used as a reference variable for the thickness control system using the rolling stand during the rolling of the current length of the strip and / or for at least one later length of the same strip and / or for at least one additional new strip.

[0042] The method according to the invention for determining the adjusted target thickness values ​​for a thickness control can be used when the strip 20 to be newly rolled is hot rolled in a hot strip mill and / or cold rolled in a cold rolling mill.

[0043] If, when carrying out the method before or during the cold rolling of the length section I' of the newly rolled strip, it is determined that the test criterion according to step 1f) for the length section I' is met during cold rolling in a cold rolling mill, but the predicted maximum value hpmx is above the specified target upper limit Vo or the predicted minimum value hpmi is below the specified target lower limit Vu - the method provides the following procedure: For a length section of another new strip 20, which is to be first hot rolled in a hot strip mill and then cold rolled in a cold rolling mill, a hot strip target thickness value is adjusted at at least one width position as a reference variable for a thickness control using a rolling stand in the hot strip mill,that during the subsequent cold rolling of the additional new strip 20, the predicted maximum value hpmx* is below the specified upper limit Vo and the predicted minimum value hpmi* is above the specified lower limit Vu. This procedure is described in the , Figuren 4a) und 4b ) is illustrated.

[0044] In both Fig. 4a) und 4b ) the initial situation is the same, namely that the predicted thickness profile for another strip to be cold rolled again would have the predicted maximum value hpmx and the predicted minimum value hpmi.

[0045] Fig. 4a ) shows the undesirable situation that the forecast maximum value hpmx would exceed the target upper limit Vo typically specified by the end customer. To avoid this situation, the procedure in question provides for intervention in the hot rolling process of the additional strip prior to cold rolling in such a way that the final thickness of the additional new strip running out of the last rolling stand of the hot strip mill is suitably reduced. This is achieved specifically by lowering the hot strip target thickness value at at least one width position of the additional new strip as a reference variable for the thickness control of the strip using a rolling stand in the hot strip mill. This then automatically also reduces the inlet thickness of the additional new strip into the subsequent cold rolling stands, namely such that its forecast maximum value hpmx lies below the target upper limit Vo, namely at hpmx*.Accordingly, the predicted minimum value hpmi is reduced by the same amount to hpmi*. Care must be taken to ensure that the reduction is only as large as still allowing hpmi*>Vu. Based on the calculations described above with reference to . Fig. 1f ) defined condition d Act < d Ref this is possible.

[0046] Fig. 4b ) shows a similar undesirable situation in which the predicted minimum value hpmi would be below the target lower limit Vu typically specified by the end customer. To avoid this situation, the procedure in question provides for intervention in the hot rolling process of the additional strip prior to cold rolling in such a way that the final thickness of the additional new strip running out of the last rolling stand of the hot strip mill is appropriately increased. This is achieved specifically by raising the hot strip target thickness value at at least one width position of the additional new strip as a reference variable for the thickness control of the strip using a rolling stand in the hot strip mill. This then automatically increases the inlet thickness of the additional new strip into the subsequent cold rolling stands in such a way that its predicted minimum value hpmi is above the target lower limit Vu, namely at hpmi*.Accordingly, the predicted maximum value hpmx increases by the same amount to hpmx*. Care must be taken to ensure that the increase is only as large as to ensure that hpmx*1 still applies. <Vo. Aufgrund der oben unter Bezugnahme auf . Fig. 1f ) defined condition d Act < d Ref this is possible.

[0047] The abovementioned with reference to the Fig. 4a und 4b The procedure described is ideal in that the target thickness of the newly rolled metal strip is already changed in the hot rolling mill. However, if this is not possible, e.g., because the strip has already been hot-rolled or the customer exclusively operates a cold rolling mill, the target value for this length can also be changed exclusively in the cold rolling process.

[0048] Preferably, the hot strip target thickness values ​​are specified not just at one, but at two or more width positions, which, for example, describe a profile or a wedge shape. Process steps 1g1) or 1g2) can then be applied to the additional new strip. If step 1f) is not met, a message can be issued indicating that the target upper limit Vo and / or the target lower limit Vu of the new strip 20 is unlikely to be met.

[0049] The length section I' of the strip 20 to be newly rolled is, for example, a section at the strip beginning and / or a section at the strip end of the strip 20 to be newly rolled.

[0050] The thickness control claimed is one of the following controls known from the prior art: The control of the strip thickness to an absolute target value measured at at least one strip width position or the "elongation control", which sets a constant reduction for the strip to be newly rolled, wherein the amount of the reduction is modified based on the adjusted target thickness value for this strip to be newly rolled such that the predicted maximum value hpmx is below the specified target upper limit Vo and / or the predicted minimum value hpmi is above the specified target lower limit Vu.

Claims

1. Method of adapting the target thickness value for regulation of the thickness of a new strip (20), which is to be rolled, for at least one roll stand, comprising the following steps: a) detection by measurement technology of the thickness plot (D) of at least one strip, which is already rolled in the past, at a first width position (B1) over at least one length section (I); b) analysing the detected thickness plot (D) with respect to a maximum value (hMax) and / or a minimum value (hMin) over the length section (I); c) determining a mean value (hpa) from the at least one detected thickness plot over the length section (I) or from target thickness specifications for the at least one already rolled strip; characterised by d) generating a prognosticised thickness plot (DP) for the new strip, which is to be rolled, in each instance at the same first width position (B1) over at least one length section (I') of the new strip, which is to be rolled, on the basis of the maximum value (hMax) and / or minimum value (hMin) determined in step b) and of the mean value (hpa) determined in step c), wherein the length section (I') of the new strip (20), which is to be rolled, is fixed in accordance with the same specification as the length section (I) of the at least one strip (20) rolled in the past, wherein in accordance with the specification the length section (I') for the new strip (20) to be rolled is defined as that length section in which the determined plot of at least one parameter for the at least one strip rolled in the past lies in a predetermined tolerance band (Δ) or experiences a change which lies above or below at least one predetermined change threshold value; e) repeating the steps b) and c) for the prognosticised thickness plot (DP) for determining a prognosticised maximum value (hpmax) and / or prognosticised minimum value (hpmi) and a prognosticised mean value (hp); f) checking whether for the prognosticised thickness plot (DP) of the new strip (20) to be rolled a spacing (dAct) between the prognosticised maximum value (hpmx) and the prognosticised minimum value (hpmi) is less than a spacing (dRef) between a predetermined target upper limit (Vo) and a predetermined target lower limit (Vu); if yes: g1) changing the prognosticised mean value (hp) at the first width position (B1) so that the prognosticised maximum (hpmx) of the prognosticised thickness plot (DP) at least over the length section (I') of the new strip (20), which is to be rolled, corresponds with the target upper limit (Vo) at least up to predetermined maximum safety spacing (dsmx), wherein then a thus-changed prognosticised mean value (hpn) is fixed as the adapted target thickness value for the new strip (20), which is to be rolled, over the length section (I'); or g2) changing the prognosticised mean value (hp) at the first width position (B1) so that the prognosticised minimum (hpmi) of the prognosticised thickness plot (DP) at least over the length section (I') of the new strip (20), which is to be rolled, corresponds with the target lower limit (Vu) at least up to predetermined minimum safety spacing (dsmi), wherein then a thus-changed prognosticised mean value (hpn) is fixed as the adapted target thickness value for the new strip (20), which is to be rolled, over the length section (l').

2. Method according to claim 1, characterised in that in accordance with a first alternative the steps a) to g1) or in accordance with a second alternative the steps a) to f) and g2) are respectively repeated for at least one further width position (B2) of the strips; a changed prognosticised mean value (hpn') for the at least one further width position (B2) results from the first alternative or the second alternative; and in the case of the first alternative the minimum mean value is selected from the number of changed prognosticised mean values at the first width position (B1) and at the at least one further width position (B2) and is fixed as the adapted target thickness value for rolling the strip (20); or in the case of the second alternative the maximum mean value is selected from the number of changed prognosticised mean values at the first width position (B1) and at the at least one further width position (B2) and is fixed as the adapted target thickness value for rolling the new strip (20).

3. Method according to one of the preceding claims, characterised in that the at least one parameter for the at least one strip rolled in the past is, for example, material yield strength, strip dimension, rolling speed and / or change in rolling speed.

4. Method according to any one of the preceding claims, characterised by regulating the actual thickness of the new strip (20) over the length section (I') to the adapted target thickness value as guide variable, wherein the roll stand by its variably settable rolling gap serves as setting element.

5. Method according to claim 4, characterised in that the method is carried out off-line prior to rolling the new strip, which is to be rolled, for the at least one length section (I') of the new strip to be rolled.

6. Method according to claim 4, characterised in that the method is performed during rolling of a length section of the strip and the adapted target thickness value resulting therefrom is used as guide variable of a thickness regulation of the strip with the help of the roll stand still during rolling of the current length section of the strip and / or for at least one length section, which is to be rolled later, of the same strip and / or for at least one further new strip.

7. Method according to any one of the preceding claims, characterised in that the new strip (20) to be rolled is hot-rolled in a hot-strip train and / or in a cold-rolling mill and in that case is regulated in thickness by the adapted target thickness values determined in accordance with the invention.

8. Method according to claim 7, characterised in that if during performance of the method before or during cold-rolling of the length section (I') of the new strip to be rolled it is ascertained that the check criterion according to step 1f) for the length section (I') during cold-rolling in a cold-rolling mill is fulfilled, but the prognosticised maximum value (hpmx) lies above the predetermined target upper limit (Vo) or the prognosticised minimum value (hpmi) lies below the predetermined target lower limit value (Vu), the method provides the following procedure: for a length section of a further new strip (20), which is to be initially hot-rolled and subsequently cold-rolled, a hot-strip target thickness value at at least one width position as guide variable for thickness regulation with the help of a roll stand in a hot-strip train is so adapted that during subsequent cold-rolling of the further new strip (20) a prognosticised maximum value (hpmx*) lies below the predetermined target upper limit (Vo) and a prognosticised minimum value (hpmi*) lies above the predetermined target lower limit (Vu).

9. Method according to any one of the preceding claims, characterised in that in the case of the step 1f) not being fulfilled a report is lodged that the target upper limit (Vo) and / or the target lower limit (Vu) probably cannot be maintained by the new strip (20).

10. Method according to any one of the preceding claims, characterised in that the length section (I') of the new strip (20) to be rolled is a section at the strip start and / or a section at the strip end of the new strip (20) to be rolled.

11. Method according to any one of the preceding claims, characterised in that the thickness regulation is either a regulation of the strip thickness to an absolute target value measured at at least one strip width position or is an 'elongation regulation' which sets a constant reduction for the new strip to be rolled, wherein the degree of reduction based on the adapted target thickness value for this new strip to be rolled is so modified that the prognosticised maximum value (hpmx) lies below the predetermined target upper limit (Vo) and / or the prognosticised minimum value (hpmi) lies above the predetermined target lower limit (Vu).

12. Computer program product which can be downloaded into the internal memory of a digital computer and comprises software code sections by which: - the steps b) to g2) in accordance with the method according to claim 1 are carried out on the basis of a thickness plot, which is previously detected by measurement technology, of at least one strip already rolled in the past; - the steps in accordance with the method according to claim 2 and / or 3 are carried out; - the regulation step in accordance with the method according to claim 4 is carried out, wherein the roll stand serves by its variably settable rolling gap as setting element; - the steps in accordance with the method according to claim 5 or 6 are carried out; - the thickness regulation in accordance with the method according to claim 7 is carried out when the new strip (20), which is to be rolled, is hot-rolled in a hot-strip train and / or cold-rolled in a cold rolling mill; and / or - the steps according to any one of claims 8 to 11 are carried out when the computer program product is run on the computer.

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