Method for operating a rolling line, and computer program product for carrying out the method

Abstract

The invention relates to a method and a computer program product for operating a rolling line having a total number of N roll stands for the rolling of rolling material, more particularly metal strip, from a previous final rolling dimension to a changed new final rolling dimension, said roll stands being disposed one behind the other in a rolling direction. According to the method, the rolling is carried out in two temporal phases I and II. In the first temporal phase, the rolling is carried out in accordance with a first load redistribution in accordance with known wedge-on-wedge rolling, the first load redistribution taking into account that the last roll stand maintains its previously set nip unchanged. In order that the desired change in the dimension of the rolling material to the new final rolling dimension can be limited in the manner of a shorter transition time and on a shortest possible portion of the rolling material, in the method according to the invention the roll stands drive pass changes in accordance with a second load redistribution, the second load redistribution taking into account that, differently than in the first temporal phase I, the last roll stand is dynamically driven to the new final rolling dimension.

Description

[0001] The invention relates to a method and a computer program product for operating a rolling mill with a total number of M rolling stands arranged one behind the other in the rolling direction for rolling rolling stock, in particular a metal strip, from a previous final rolling dimension to a changed new final rolling dimension.

[0002] If a final rolling dimension of the rolled stock is to be changed, optimal wear distribution of the individual rolling stands and optimal quality of the rolled stock can only be ensured with a suitable, newly calculated load redistribution at the individual rolling stands in a rolling mill and with correspondingly readjusted roll gaps. Typically, the transition to the new final rolling dimension takes place in a fixed section of the rolled stock, i.e. a so-called virtual strip section. This strip section is tracked through the entire rolling mill, and each rolling stand changes the size of its roll gap in exactly this same strip section in accordance with the aforementioned load redistribution. During rolling, wedges then form in the rolled stock. These are transition areas in which the thickness or width of the rolled stock changes from a previous final rolling dimension to a new final rolling dimension.

[0003] If all rolling stands in the rolling mill simultaneously implement the pass changes required for their load redistribution, i.e., the new roll gap sizes, this can lead to mass flow problems. To minimize such mass flow problems, the desired change in the final rolling dimension is traditionally carried out as follows: Each rolling stand in the rolling mill rolls a wedge into the rolling stock or strip section in such a way that this wedge begins in the rolling stock where the preceding rolling stand began rolling it (wedge-on-wedge). This process is described, for example, in European patent EP 3 346 625 B1.

[0004] This so-called "wedge-on-wedge rolling" has a disadvantage when used with endless rolled stock, via which a casting machine, in which the rolled stock is cast, and the rolling mill, in which the rolled stock is subsequently rolled, are coupled. This disadvantage is that, due to the aforementioned coupling to the casting machine, not only is the transport speed of the rolled stock through the rolling stands favored. In addition, the adjusting cylinder travel speed, particularly of the first rolling stands in the rolling mill, must also be artificially limited. The reason for this necessary limitation lies in the following fact: The higher the adjusting cylinder travel speed, i.e., in particular, the speed at which the roll gap is closed, for example, the greater the exit speed and the acceleration of the rolled stock from the rolling stand, because the mass flow must remain constant.The higher the exit speed, the higher the entry speed of the rolled stock into the subsequent rolling stand. This means that the work rolls of the subsequent rolling stand would then have to be able to accelerate accordingly to cope with the higher entry speed of the rolled stock. However, because the acceleration capacity of the work rolls of a rolling stand is limited, loopers are typically used in the intermediate rolling stand areas of a finishing mill. These loopers temporarily store or buffer the rolled stock exiting faster from a previous rolling stand until the work rolls of the subsequent rolling stand have accelerated sufficiently to roll the faster incoming rolled stock at the required rolling speed.However, if the adjusting cylinder travel speed of the preceding rolling stand is too high, it may happen that both the acceleration capacity of the work rolls of the subsequent rolling stand and the looper's intake capacity are no longer sufficient to process the rapidly incoming rolled stock. This inevitably leads to compression or "rising" of the rolled stock in the rolling mill. To prevent such a situation, the adjusting cylinder travel speed must be sufficiently limited, i.e., it is usually significantly lower than the maximum technically possible adjustment cylinder travel speed for the rolling stand.

[0005] The artificially reduced travel speed of the adjusting cylinder results – again due to the necessarily constant mass flow – in a very long wedge in the rolled stock, especially at the exit of the last rolling stand, even though this last rolling stand could certainly open or close more quickly due to its technology. This long wedge means a long transition time and a long strip section in which the transition to the new desired final dimension takes place. The wedge in the rolled stock is usually scrap or waste material.

[0006] The long wedge and the long transition time result from the current state of the art approach, which involves achieving the desired final dimension in a single phase by pure wedge-on-wedge rolling. The underlying load redistribution also includes a pass change for the last rolling stand.

[0007] In order to increase production throughput and reduce material loss, it is advisable to implement a planned change in the final rolling dimension within a shorter transition period and on the shortest possible strip section of the rolled material.

[0008] Based on this prior art, the invention is based on the object of further developing a known method and a known computer program for operating a rolling mill such that a change in the final rolling dimension of the rolled stock is carried out within a shorter transition time and limited to the shortest possible section of the rolled stock. This object is achieved by the method claimed in claim 1. It is characterized in that no pass change is provided for the last of the M rolling stands in the first load redistribution; and it is further characterized by the following steps: Determining a second load redistribution for a second temporal phase in the form of second pass changes for at least the last rolling stand with regard to the new final rolling dimension; and in the second temporal phase (II), viewed in the rolling direction: rolling the rolled stock to the new final rolling dimension by sequentially carrying out the pass changes in the rolling stands as provided for by the second load redistribution.

[0009] The feature that "... no change in the pass is provided for the last rolling stand" means that the size of the roll gap of the last rolling stand remains unchanged in the first time phase compared to its size at the beginning of the first time phase due to its last adjustment during the previous rolling.

[0010] The term "final rolling dimension" means the final rolling thickness or final rolling width of the rolled stock at the exit of the last rolling stand of the rolling mill.

[0011] The term "roll stand" in the sense of the invention means an active roll stand that actively changes the dimensions, i.e. the thickness or width, of the rolled stock through the application of force. Two variants of the term "active" must be distinguished. An active roll stand can change its roll gap dynamically, i.e. over a time interval with a setting cylinder traversing speed, or its roll gap is statically fixed. In the first case, we will refer to a "dynamic roll stand" and in the second case, we will refer to a "static roll stand". In both cases, the dimensions, i.e. the thickness or width, of the outgoing rolled stock change compared to the dimensions of the incoming rolled stock. In this respect, in the present invention only active roll stands of the rolling train are involved in processing the rolled stock with regard to the desired new final dimension. I.e.Unless a specific statement is made about a rolling stand, it is an active rolling stand.

[0012] This does not preclude the possibility of additional inactive rolling stands following or being located in the rolling mill, which, however, no longer influence the (final) dimensions of the rolled stock, in particular, they do not exert any force on the rolled stock. The inactive rolling stands can be located upstream, intermediate, or downstream of the active rolling stands in the rolling mill. The method according to the invention only begins with the first active rolling stand in the rolling mill.

[0013] The term "rolling mill" may mean a plurality of roughing stands or a finishing mill with a plurality of finishing stands or a combination of both.

[0014] The term "wedge" refers to a thickness or width change rolled by a rolling stand over a limited (strip) section of the rolled stock. A wedge is created because the rolled stock is moved through the roll gap at a specific transport speed during a pass change. The wedge can have a positive or negative gradient, viewed in the direction of mass flow. This means that a wedge is understood to mean a wedge that moves from a smaller run-out thickness to a larger run-out thickness, or vice versa. The wedge can be physically moved and designed in a linear or non-linear manner; this depends on the temporal progression of the adjustment cylinder travel speed of the roll stand's adjustment cylinders for changing the roll gap and the simultaneous transport speed of the rolled stock through the roll gap.

[0015] The term "pass change" can mean a pass reduction or a pass increase, i.e. a reduction or enlargement of the roll gap and, consequently, a decrease or increase in the thickness or width of the rolled stock.

[0016] The term "sequential process" also includes leaving the roll gaps of static rolling stands at their previous roll gap sizes if the new roll gap sizes of these stands remain unchanged according to the load redistribution. The roll gap settings of these stands are then static. However, these rolling stands are still active because they also contribute to the target of the new final rolling dimension through the static change in the rolled stock dimensions they cause, even if they do not generate a wedge in the rolled stock due to the purely static adjustment of their roll gap.

[0017] The process feature, according to which "up to M-1" wedges are formed in the first phase, is explained by the fact that during this phase, at least the last roll stand remains unchanged in its roll gap size, i.e., it does not form a wedge. This is mandatory for the last roll stand. Furthermore, the load distribution for the first phase can also stipulate that other of the M roll stands do not undergo a pass change and thus do not form wedges.

[0018] The method according to the invention typically takes place as part of or within the framework of an ongoing rolling process. During the ongoing rolling process, the instruction is given that the currently (previously) used final rolling dimension is to be changed to a new final rolling dimension. Then, according to the invention, the said first and second load redistributions are determined. Both load redistributions are designed with regard to the desired final dimension and with regard to the most uniform loading possible on the rolling stands involved. The most uniform loading possible means the most uniform wear possible on the rolls in the rolling stands. At an initial time t 0 , the first load redistribution is then implemented during the ongoing rolling process according to the method according to the invention. The starting point for the method according to the invention is therefore the static settings of the roll gaps in the rolling mill at time t 0 .

[0019] In the first phase, according to the invention, traditional wedge-on-wedge rolling takes place, but with the special feature that the previous final rolled dimension remains unchanged in the last roll stand during this first phase. The claimed sequential operation of the pass changes in the roll stands, except for the last roll stand, to intermediate roll gap sizes according to the first load redistribution serves to achieve intermediate dimensions in the rolled stock. In this respect, the first phase forms an intermediate stage on the way to a roll gap and dimension distribution such as will be required to achieve the final dimension at the exit of the last roll stand. The claimed pass changes in the first phase are typically smaller than in the prior art, where, as mentioned above, no second phase is provided, but the desired new final dimension is generated in only a single phase by wedge-on-wedge rolling.The load redistribution for the first phase is carried out in such a way that the load and thus the wear on the rolls in all active rolling stands involved is evened out and minimized. This also applies to the load redistribution for the second phase.

[0020] The pass changes carried out in the rolling stands result in the formation of wedges in the rolled stock. Due to the wedge-on-wedge rolling, the wedges generated by the individual dynamically operated rolling stands lie on top of one another. They can be of different lengths. Advantageously, however, the wedges generated in the first time phase are smoothed out again at the end of the first phase by the last static rolling stand because the last static rolling stand does not carry out any pass changes, i.e. its roll gap size remains statically set. This results in the major advantage that no wedge-shaped rolled stock is generated at the end of the first phase. The rolling stock leaving the mill has at least one changed intermediate dimension compared to the previous final dimension. The changed intermediate dimensions are generated in the rolled stock by the rolling stands in the rolling mill, except for the last rolling stand, which remains at its previous setting.Because the last rolling stand remains at its previous setting, the dimensions of the rolled stock remain constant. Therefore, the portion of the strip processed during the first phase is generally usable and does not need to be discarded as scrap.

[0021] Furthermore, mass flow or process disturbances advantageously occur comparatively rarely during the initial phase, and—if at all—only to a moderate extent. This is due to the following: The approached intermediate roll gap sizes and the resulting intermediate dimensions are smaller in this rolling stock than in the state-of-the-art technology. The wedge can also be longer, thus reducing the process disturbance.

[0022] During the time intervals in which the rolling stands carry out the specified dynamic pass changes, wedges form in the rolled stock and the exit speed of the rolled stock from the rolling stands changes. When the rolling stands approach, they decelerate; when they close, they accelerate due to the constant mass flow. At the end of the respective travel time intervals, i.e. after deceleration or acceleration, the exit speed remains constant. This generally applies to any dynamic movement of pass changes, both in the first and second time phases. For this reason, the speed of the strip section is also constant at the beginning of the second time phase if the second time phase follows the first phase.

[0023] In the second phase of the rolling process according to the invention, the roll gap of at least the last roll stand of the rolling mill is moved to the new final rolling dimension by a second pass change. This and optionally further pass changes are carried out according to a previously defined second load redistribution, which again aims to ensure the most even loading possible on all roll stands involved. Unlike the first load redistribution, however, the second load redistribution takes into account the dynamic movement of the pass change at the last roll stand to the new final dimension for the rolled stock. A large part of the necessary changes to the dimensions of the rolled stock with regard to the new final dimension have already been implemented in the first phase, so that in the second phase only a comparatively small remaining change in the dimension or pass change needs to be made to achieve the new final dimension.The remaining small change in dimension can therefore be made on a relatively short wedge-shaped strip section compared to the state of the art. This strip section is also comparatively short because the travel speed of the adjusting cylinders of the last rolling stand can be selected to a maximum, resulting in a maximum change in the exit speed of the rolled stock from the last rolling stand in the second phase. The travel speed is not limited by the limited acceleration capability of the subsequent rolling stand; typically, there is simply no such subsequent rolling stand. Only the coiler would be a limiting element here. The shorter wedge-shaped strip section for the transition to the new final dimension advantageously means a reduction in scrap material.Secondly, the time required to complete the final pass reduction in the second phase is also comparatively short due to the high possible travel speed of the adjusting cylinder. This advantageously results in an increase in production throughput. The remaining, small and short-term dimensional change – due to a brief change in the exit speed of the rolled stock – also advantageously leads to a temporary reduction in disruptions in the cooling section downstream of the last rolling stand, and thus to a reduction in disruptions in the quality or material properties of the rolled stock.

[0024] In the first and second phases, typically different rolling stands from the set of all rolling stands in the rolling mill are operated dynamically. However, some of the same rolling stands can also be operated dynamically. According to the invention, the last rolling stand is actively involved in both phases; it is operated statically in the first phase and dynamically in the last phase.

[0025] According to a first embodiment, the first and / or second load redistribution does not necessarily require a pass change for each roll stand of the rolling mill. Rather, no pass schedule change may be required for individual roll stands. These roll stands are then operated statically; that is, their roll gaps remain unchanged.

[0026] According to a further embodiment, the rolling stock rolled using the method according to the invention is an "endless" cast strand, through which the rolling mill is coupled to a casting machine upstream in the rolling direction. The term "endless" means that the rolling stock is cast in the casting machine in the form of an endless cast strand, without subsequent transverse cutting.

[0027] Alternatively, the rolled stock can also be a slab produced by portioning, i.e., at least a simple transverse division of the continuously cast strand. Due to the transverse division, the casting machine and the rolling mill are then no longer coupled. This results in the advantage that the rolled stock can be rolled in the rolling mill at a higher speed than the casting machine would allow due to its comparatively low casting speed.

[0028] The continuous cast strand or the slab separated from the continuous cast strand can contain one or more strip sections, on which the method according to the invention is carried out separately, with the first and second time phases. If the slab contains several strip sections, it is also referred to as "semi-continuous" rolling. A strip section preferably corresponds to a coil length that will later be wound onto a reel. If, however, the slab comprises only one strip section, which typically also corresponds to only one coil length, it is referred to as batch rolling.

[0029] According to a further embodiment of the method according to the invention, the roll gaps are gradually increased if the new final dimension is larger than the previous final dimension. This, of course, assumes that the dimensions of the rolled stock were correspondingly larger. Alternatively, the roll gaps are closed to reduce the final rolled dimension of the rolled stock.

[0030] It is generally advantageous if the adjusting cylinders in the rolling stands for opening or closing the roll gap for wedge formation in the rolled stock are moved at a constant travel speed - apart from an initial acceleration and deceleration. In conjunction with an exit speed proportional to the thickness at which the rolled stock exits a rolling stand, this advantageously results in an approximately linear wedge in the rolled stock. If the travel speeds of the adjusting cylinders are not constant and / or in conjunction with non-constant exit speeds of the rolled stock for the same rolling stand, the wedges resulting in the rolled stock may also be non-linear, i.e. they may then have an uneven, e.g. curved, surface.

[0031] Typically, the first and second phases follow one another with a pause. Alternatively, however, the pause can be omitted, so that the first and second phases follow one another immediately. Furthermore, it is alternatively possible for the first and second phases to overlap such that the second phase begins before the first phase is completed. The last two alternatives advantageously lead to a shortening of the implementation time for the method according to the invention and to a shortening of the length of the transition strip section required for changing the final dimension.

[0032] The method according to the invention is advantageously applied in a hot rolling mill and with hot strip as the rolling stock, because the high temperature allows changes in the roll gap size or the dimensions of the rolling stock to be carried out relatively easily, i.e., without excessive force. However, this does not preclude the application of the method according to the invention for cold rolling of rolling stock.

[0033] Further advantageous embodiments of the method according to the invention are the subject of the dependent method claims.

[0034] The above-mentioned object is further achieved by a computer program product according to patent claim 15. The advantages of this computer program product correspond to those mentioned above with reference to the claimed method. The term "computer program product" also includes software burned into memory chips and software in specially manufactured ICs (integrated circuits). The memory chips and / or ICs are then the "memory of a digital computer" within the meaning of the claim.

[0035] The description includes 5 figures, where Figure 1 shows the method according to the invention according to a first embodiment; Figure 2 shows a wedge with a negative pitch in the rolling direction for increasing the dimension of the rolling stock being rolled out; Figures 3a and 3b show a second embodiment of the method according to the invention; Figure 4 shows a wedge shape with a positive pitch in the rolling direction, as it is when carrying out the method according toFigure 3 a +b; and Figure 5 shows a comparison of wedge lengths in different operating modes of rolling stands shows.

[0036] In all figures, identical elements are designated by identical reference numerals.

[0037] Figure 1 illustrates the sequence of the individual steps of the method according to the invention at the individual rolling stands of a rolling mill. The rolling stands of the rolling mill are designated F1 to F6, whereby the rolling stands F1 and F2, ie the first two rolling stands of the rolling mill, are not actively involved in the implementation of the method according to the invention according to the example in Figure 1 are involved and therefore in the Figure 1 are not mentioned. In the Figure 1 The rolling direction, ie, the direction of movement of the rolled material through the rolling stands F1 to F6, runs from left to right. In contrast, the time axis runs in the opposite direction, from right to left.

[0038] The implementation of the method according to the invention relates to a single (virtual) tape section 10, which is defined at least in terms of software, in which Figure 1 marked with the black horizontal double arrow. This strip section is created by virtual or later real transverse division of a cast endless strand at two different times, as shown in Figure 1 marked. The two cuts not only create the strip section in question, but also simultaneously separate the rolling mill from an upstream casting machine that produces the endless cast strand.

[0039] With respect to one (virtual) strip section, the method according to the invention is carried out in two separate phases, a first temporal phase I and a second temporal phase II, which here, for example, follow one another in time with a pause P. The total number of M active rolling stands in the case of the Figure 1shown embodiment 4; it comprises the rolling stands F3, F4, F5 and F6 of a rolling mill. Of these, the rolling stands F3, F4 and F5, but not the rolling stand F6, are active in the first temporal phase I. The rolling stand F6 is only active in the second temporal phase II. These rolling stands are all operated dynamically here, for example. In accordance with the method according to the invention, they are not moved simultaneously, but sequentially from their initial roll gap sizes to new roll gap sizes. The pass changes (ordinate hx ) carried out for this purpose take place in the first temporal phase I according to a previously determined first load redistribution and in the second temporal phase II according to a previously determined second load redistribution. Both load redistributions are determined by a process model with regard to a desired new final dimension of the rolled stock and with regard to the most even possible wear of the rolls of the rolling stands.The pass changes occur during rolling of the rolled stock. These pass changes cause wedges to form in the rolled stock.

[0040] In the Figure 1 In the embodiment shown, the desired new final rolling dimension, here, for example, the new desired final rolling thickness, for the strip section 10 of the rolled stock considered here is greater than the final rolling thickness of previously rolled strip sections. Therefore, the roll gaps of the rolling stands involved are each increased.

[0041] In Figure 1 It can be seen that during the first temporal phase I, the rolling stand F3, as the first active rolling stand of the rolling mill, opens its roll gap for a pass change over the time interval Δt 3 , starting from the time t 1 ; see the ramp-like increase in Fig. 1. By widening the roll gap, the intermediate dimension of the rolling stock increases as desired from an initial thickness D3E at the inlet of the rolling stand F3 to a thickness D3A at the outlet of the rolling stand F3. This exit intermediate thickness D3A corresponds to the inlet thickness D4E at the inlet of the rolling stand F4. The roll gap of the rolling stand F4 is also widened further during the time Δt 4 for a pass change, with the result that the thickness of the rolling stock at the outlet of the rolling stand F4 increases to the new intermediate thickness D4A. According to wedge-on-wedge rolling, the rolling stand F4 advantageously begins to widen its roll gap when the beginning of the first wedge produced by the previous rolling stand F3 arrives at its inlet, i.e., at the inlet of the rolling stand F4. This is typically the case with a time interval Δk 1. In Figure 1It can also be seen that the opening of the roll gap of the rolling stand F3 is not yet completely completed when the rolling stand F4 already starts opening its roll gap; therefore, Δk 1 < Δt 3 applies.

[0042] The approach to new intermediate sizes for the roll gaps according to the previously calculated first load redistribution for the first time phase is then repeated on the rolling stand F5.

[0043] In all three rolling stands F3, F4 and F5, the roll gap is Figure 1In the embodiment shown, the rolled stock is continually increased so that the resulting intermediate rolling dimensions of the rolled stock at the exits of the rolling stands increase successively. This is by no means always the case, as described in the introduction. In concrete terms, however, it has already been stated that the input thickness at rolling stand F4 increases from thickness D4E = D3A to D4A > D4E. Analogously, the final rolling thickness of the rolled stock increases again when passing through rolling stand F5, even if its roll gap is further increased during a time interval Δt 5; then the final dimension of the rolled stock increases from D5E = D4A to D5A > D5E. The adjustment time that rolling stands F4 and F5 require to respectively increase their roll gaps is Δt 4 and Δt 5 . In this way, the individual rolling stands F3 to F5 each generate wedges that overlap in the rolled material (wedge-on-wedge).This allows the desired transition from the previous final rolling dimension of the rolled stock to the new final rolling dimension to be realized in a comparatively short section of the strip section.

[0044] The intermediate thickness D5A enters the rolling stand F6 as the input intermediate roll dimension D6E. The rolling stand is operated statically during the first time phase I, i.e., its roll gap remains unchanged. However, because the size of the roll gap at F6 is typically different than D5A, the rolled stock also experiences a change in its dimensions in the first time phase in the rolling stand F6. However, this change in dimension is not associated with wedge formation because the roll gap of F6 is not changed over a time interval. The exit speed of the rolled stock and its intermediate dimension at the end of the first time phase are constant over time. Regarding the associated advantages, reference is made to the general part of the description above.

[0045] Because the rolled stock has not yet reached its desired new final dimension at the end of the first phase, a second phase II follows. In this phase, the Fig.1In the example shown, only the rolling stand F6 is actively involved. This is by no means always the case. Rather, other rolling stands can also be involved in the second time phase, which can be operated statically or dynamically. The last rolling stand F6 is now operated dynamically according to the method according to the invention - unlike in the first time phase. This means that it undergoes a pass change during a time interval Δt6. Specifically, the roll gap of F6 is moved from its initial opening D6E to the new final dimension D6A in this example due to the pass change specified by the second load redistribution. The resulting wedge is very short compared to the prior art. In addition, the adjusting cylinders of F6 can be moved very quickly, as shown in the upper line of Fig. 1This allows the time interval Δt 6 to be kept very short. Regarding the associated advantages, please also refer to the general part of the description.

[0046] Finally, Figure 1 Below the strip diagram, the speed profile of the rolled stock at the exit of the last rolling stand F6 is shown. In the first phase I, the exit speed is lower because the stands F3 - F5 are moving up during their pass changes and the mass flow must be maintained. The rolling stand F6 performs Figure 1 in the first temporal phase does not contribute to a change in the dimensions of the rolled stock or to a change in its exit speed.

[0047] In the second phase II, only F6 is driven. Again, due to the conservation of mass flow, its exit velocity decreases during the time interval Δt 6 . Afterward, the exit velocity of the rolled material at the exit of F6 remains constant.

[0048] Figure 2 illustrates a roll wedge with a negative pitch, as it is produced by driving the rolling stands according to Figure 1 can arise.

[0049] The Figure 3a and 3billustrate a second exemplary embodiment of the method according to the invention, in which the roll gaps of the rolling stands involved are not opened but closed in order to reduce the thickness of the rolled stock. In this example, the rolling stands F1 to F5 are involved in rolling the rolled stock, both during the first time phase I and during the subsequent second time phase II. The stands F1 to F4 are operated dynamically in the first time phase I, i.e. they carry out the pass changes assigned to them by a first load redistribution in the time intervals Δt 1 I, Δt 2 I, Δt 3 I and Δt 4 I. In contrast, the fifth rolling stand F5 is operated statically in the first time phase I, i.e. its roll gap remains fixedly set to the position that the roll gap already had before the start of the first time phase.At the end of the first temporal phase I, no wedge is produced in the rolling stock by the rolling stand F5 and all wedges generated by the previous rolling stands, as shown in . Figure 3a are flat-rolled by stand F5. Therefore, the exit thickness of the rolled stock at the exit of roll stand F5 is constant during the first phase I.

[0050] The first temporal phase is followed by the second temporal phase II, here with a short pause P. In this second temporal phase II, all rolling stands F1 to F5 are operated dynamically, i.e. they roll one wedge each in the time intervals Δt 1 II, Δt 2 II, Δt 3 II, Δt 4 II and Δt 5 II, whereby the wedges overlap in the rolling stock (wedge-on-wedge rolling), see Figure 3a and enlarged in Figure 3b. Roll stand F5 is now also operated dynamically, unlike in the first temporal phase I. Specifically, the second load redistribution provides for roll stand F5 to undergo a pass change, with its roll gap being moved from its static setting in the first temporal phase I to the new, smaller final rolling thickness. Due to this dynamic mode of operation of roll stand F5, a short wedge-shaped transition to the new final rolling thickness is created in the rolled stock. However, this wedge-shaped part of the strip section 10 changed overall by the method according to the invention is significantly shorter compared to the prior art. This means less scrap material, and the transition to the new final rolling thickness takes place in a shorter time.

[0051] Figure 4 illustrates the formation of a wedge with a positive pitch in the rolling direction, as used in the second embodiment according to the Figure 3a and 3bgenerated by the rolling stands F1 to F5, particularly in the second temporal phase II.

[0052] The Figure 2 and 4 Each shows linear wedges. Alternatively, the wedge surface could also be curved, depending on the temporal progression of the adjusting cylinder travel speeds and the temporal progression of the rolling stock exit speeds from the rolling stands.

[0053] Figure 5shows a comparison of wedge lengths as they run out at the last stand F5 of a rolling mill when the rolling stands F1 to F5 of the rolling mill are operated in different operating modes. In addition to the same rolling mill with the same rolling stands F1 to F5, the same presetting of the rolling stands is assumed in all three embodiments. In concrete terms: The rolling stand F1 is preset to a roll gap size of 16 mm, the rolling stand F2 to a roll gap size of 8 mm, the rolling stand F3 to a roll gap size of 4 mm, the rolling stand F4 to a roll gap size of 2 mm and the rolling stand F5 is each preset to a roll gap size of 1 mm (run-out thicknesses initial state). The stands F1 to F5 are thus preset in such a way that a reduction in the thickness of the rolled stock of 50% occurs at each stand.In addition to this initial state, all three examples also specify that the initial thickness of the rolled stock should be reduced from 16 mm to 0.8 mm at the exit of the last rolling stand F5. This is the initial situation.

[0054] The first example according to Figure 5 This concerns the wedge-on-wedge rolling process known from the prior art. Starting from their initial states, the stands are each closed by the amount specified in the "Delta" line. The resulting initial thickness can be seen in the penultimate line.

[0055] The table for the prior art embodiment shows that, with the aforementioned thickness reduction, the rolled stock exits the last roll stand F5 with a wedge length of 16 m. This large exit wedge length is unfavorable because, in case of doubt, it must be discarded as scrap. The present invention, as is known, aims at reducing this wedge length, which is illustrated by the two examples, extreme cases 1 and 2.

[0056] In contrast to the prior art, the two exemplary embodiments distinguish between a first temporal phase I and a second temporal phase II. For these two phases, the run-out thicknesses at the respective stands and the respective thickness reduction in the individual phases are specified, each designated by a delta in the two tables for the exemplary embodiments. The essential method step in the two exemplary embodiments according to the invention, in contrast to the prior art, is that the rolling stand F5 remains in its initial state, here 1 mm, during phase I. Accordingly, the delta in phase I is 0 mm in each case. Only at the end of the second temporal phase II is the last rolling stand dynamically moved from its initial position to the desired new final dimension, here 0.8 mm.The corresponding delta for the F5 framework in temporal phase II is therefore, as stated, 0.2 mm in both extreme cases.

[0057] Extreme case 1 is extreme in that stands F1 to F4 are operated analogously to the state of the art, but stand F5, as mentioned above, remains in its initial state. In the second phase, stands F1 to F4 remain at their settings according to the first phase I, and only stand F5 operates as described above. The result is an ultra-short wedge length in the run-out of stand F5 of only 0.5 m, compared to the state of the art, where the run-out length is 16 m.

[0058] Extreme case 2 involves successive closing of each of the stands F1 to F5, with the result that the run-out length at the end of the second phase at the exit of the last rolling stand F5 is 8 m.

[0059] Both extreme cases illustrate that the object of the invention, namely to shorten the run-out wedge lengths on the last rolling stand, can be effectively achieved with the method according to the invention; the run-out wedge lengths are shortened by a considerable factor compared to the prior art: in extreme case 1, the factor is 16 : 0.5 = 32, and in extreme case 2, it is 16 : 8 = 2. List of reference symbols

[0060] Ifirst temporal phase IIsecond temporal phase 10Strip section PPause hx Thickness of the rolled stock or approach path of a rolling stand or pass size

Claims

1. Method of operating a rolling train with a total number of M roll stands, which are arranged in succession in rolling direction, for the rolling of rolling material, particularly a metal strip, from a previous end rolling dimension to a changed new end rolling dimension, comprising the following steps: - determining a first load redistribution for a first time phase (I) in the form of first pass changes for at least individual ones of the M roll stands with respect to the new end rolling dimension and - in the first time phase (I) as seen in rolling direction: sequential execution of the pass changes in the roll stands in correspondence with the first load redistribution during rolling of the rolling material with formation of up to M-1 wedges in the rolling material, wherein each of the wedge-rolling roll stands - apart from the first roll stand - begins to roll the wedge, which is caused by it due to the pass change, in the rolling material where also the preceding roll stand has begun to roll it so that the wedges, which are rolled in the first time phase, in the rolling material are superimposed; characterised in that no pass change is provided in the first load redistribution for the last one of the M roll stands; and the method comprises the following further steps: - determining a second load redistribution for a second time phase (II) in the form of second pass changes for at least the last roll stand with respect to the new end rolling dimension; and - in the second time phase (II) as seen in rolling direction: rolling the rolling material to the new end rolling dimension by sequential execution of the pass changes at the roll stands to the extent provided by the second load redistribution.

2. Method according to claim 1, characterised in that the first and / or second load redistribution provides or provide no pass change for individual ones of the roll stands.

3. Method according to claim 1, characterised int hat the first and / or the second load redistribution provides or provide a pass decrease for individual ones of the roll stands and no pass increase for other roll stands.

4. Method according to any one of the preceding claims, characterised in that the rolling material is an 'endless' cast strip by which the rolling train is coupled with a casting machine upstream in rolling direction.

5. Method according to any one of claims 1 to 3, characterised in that an endless cast strip which has been cast is transversely divided after leaving a casting machine so that a slab as rolling material arises and so that the rolling train is decoupled from a casting machine upstream thereof in rolling direction.

6. Method according to any one of the preceding claims, characterised in that the rolling material comprises at least one strip section in which the method is separately carried out with the first and second time phases so that the strip section represents a transition region in which the dimension of the rolling material transtions from the previous end rolling dimension to the new end rolling dimension.

7. Method according to any one of the preceding claims, characterised in that the execution of the pass changes is an opening movement of the rolling gaps for increasing the dimension of the rolling material or is a closing movement of the rolling gaps for decreasing the dimension of the rolling material.

8. Method according to any one of the preceding claims, characterised in that the adjusting cylinders in the roll stands for execution of the pass changes, for example for opening movement or closing movement of the roll gaps for wedge formation in a rolling material, are operated at a constant or non-constant adjusting cylinder operating speed apart from an initial acceleration and a slowing down.

9. Method according to any one of the preceding claims, characterised in that the first and second time phases (I, II) follow one another in time with or without a pause, preferably directly follow one another.

10. Method according to any one of claims 1 to 8, characterised in that the first and second time phases overlap in time in such a manner that the second phase (II) begins before the first phase (I) has ended.

11. Method according to any one of the preceding claims, characterised in that the roll stands are hot-rolling stands for hot-rolling of the rolling material.

12. Method according to any one of the preceding claims, characterised in that the end rolling dimension is the end rolling thickness and the roll stands are thickness reduction roll stands.

13. Method according to any one of claims 1 to 11, characterised in that the roll stands are respectively an upsetting press or an upsetting roll stand and the rolling is an upsetting for reduction of the end rolling width as the end rolling dimension of the rolling material.

14. Method according to any one of the preceding claims, characterised in that the rolling train is formed by a plurality of roughing stands or by a finishing rolling train with a plurality of finishing rolling stands or that the rolling train apart from the roll stands of a finishing rolling train also includes roughing stands.

15. Computer program product which can be directly downloaded into the preferably internal memory of a digital computer and comprises software code sections by which the steps in accordance with the method according to any one of the preceding claims 1 to 3 and 6 to 10 are performed when product runs on the computer.

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