MX2008005516A - Method and finishing train for hot-rolling starting material - Google Patents

Abstract

The invention relates to a method and a finishing train for hot-rolling starting material. Starting material is finished in several successive roll stands (110 n) in the finishing train, the material cooling off because of heat loss. The material has to be reheated in order for the temperature of the material not to drop below the predefined lower threshold temperature value at low speeds within and at the discharge end of the finishing train. In order to use as little energy as possible for said reheating process, the reheating process within the finishing train is carried out for the first time only when the temperature of the material risks falling below the lower threshold temperature value for the first time relative to the direction of flow of the material because of heat loss. Furthermore, the temperature of the material during the reheating process is increased only to the point where the temperature of the material will not drop below the lower threshold temperature value (TU) while the material is conveyed on to a next heating device that is mounted downstream in the direction of flow of the material and until the material is discharged from the mill train.

Description

PROCEDURE AND TRAIN OF FINISHING LAMINATION FOR HOT LAMINATE ENTRY MATERIAL FIELD OF THE INVENTION. The invention relates to a process and to a finishing rolling mill for hot-rolling input material, especially thin slabs or pre-blanks.

BRIEF DESCRIPTION OF THE INVENTION Such a process and a corresponding finishing rolling mill are known in the prior art, for example from European patent EP 0 415 987 B2. It describes a finishing rolling mill comprising a plurality of successive rolling boxes. Roll stands serve to hot-roll input material to obtain web material which, initially, is heated to an inlet temperature that is higher than a desired final rolling temperature at the end of the finishing roll mill. During the passage through the finishing rolling mill the material undergoes a cooling due to heat losses. Inductive heating devices are provided within the finishing rolling mill to compensate for heat losses by overheating the material to the extent that the The desired final rolling temperature of the web material does not exceed a predetermined lower threshold value upon exiting the rolling mill. The aforesaid European patent does not give more detailed information on the criteria according to which the reheating of the material inside the finishing train is carried out by means of the inductive heating device. From an energetic point of view, the procedure described in it is not optimal. From this state of the art it is therefore the object of the invention to improve a known method for the hot rolling of finishing of input material and a corresponding known finishing rolling mill, in such a way as to reduce to a minimum the energy supplied to the material within the finishing mill to obtain a desired final rolling temperature upon leaving the finishing mill. This object is solved by the process claimed in patent claim 1. This method is characterized in that, firstly, said heating device is determined, seen in the direction of the material flow, at whose height or behind which the temperature of the material runs the risk for the first time of descending below the temperature of the material. lower temperature threshold value, due to heat loss, and because the reheating of the material is done by increasing the temperature of the material by the heating device determined only to the extent that, during the movement of the material to the next heating device connected downstream, seen in the direction of the material, or when in the direction of the flow of material is no longer connected downstream any additional heating device until the exit of the finishing rolling mill, the temperature only drops to the lower threshold value of temperature due to corresponding local heat losses in the finishing mill, and because the reheating of the material is repeated by each additional heating device connected downstream in the direction of material flow within the finishing mill. Advantageously, in the claimed procedure, the temperature level and the temperature fluctuations of the material inside the finishing rolling mill are kept low and, thus, the thermal energy necessary inside the finishing rolling mill for the overheating of the material and the necessary costs for it are reduced to a minimum. The claimed type of reheating leads only to increases moderate temperatures and at relatively low temperatures in total on the entire finished rolling mill, which is also advantageous with respect to the quality of the surface. Compared to a heating of the input material before entering the finishing rolling mill at an inlet temperature that is so high that the temperature of the material, even as it passes through the entire finishing rolling mill with its heat losses , does not fall below the desired final rolling temperature, the necessary heat input is fundamentally lower in the claimed process. According to one embodiment of the invention, during reheating, the material is not heated above a pre-established upper temperature threshold value, so that its temperature remains, after the first reheating inside the finishing rolling mill until the exit of the finishing rolling mill, at least essentially always within a target temperature range which is limited by the lower and upper temperature threshold value. In this target temperature range, a practically isothermal lamination with a periodic overheating of the material takes place. The target temperature range is selects for a particular material used [eg ULC steel (Ultra Low Carbon, ultra low carbon) or steel IF (interstitial free, interstitial free)] in such a way that the development of average resistance to the hot creep of the material used with respect to the temperature, it has a local minimum in the target temperature range. Advantageously, the material used can then be deformed particularly well in the target temperature range, which can be used to reduce the stress on the rolling mill (boxes, motors, etc.) as well as to reduce the minimum final thickness. In this respect it is ferritic cylinders. With respect to a good rolling result, especially good material properties and a good surface quality, it is advantageous to preset the lower threshold value of temperature as a function of the material. In certain slab or strip installations it may be necessary for the input material to be heated, before being introduced into the finishing rolling mill, by means of an additional preheating device at an inlet temperature above the lower temperature threshold value . This may be necessary when the material temperatures, when leaving the kiln or from a casting installation, are especially low or when the casting speed and / or the distance between a bar guiding device and the finishing rolling mill is especially large and the material would then be cooled to the entrance in the finishing rolling mill at an inlet temperature below of the lower temperature threshold value. In these cases, the preheating device serves to at least partially compensate for these heat losses before entering the finishing rolling mill. Alternatively or additionally, the preheating device can also be used to prevent a decrease in the temperature of the material below the lower threshold value in the entrance area of the finishing rolling mill when it is provided therein, with respect to a desired good quality of the surface, dehulling devices or cooling devices between boxes, which cause a particularly intense cooling of the material. Advantageously, the amounts of heat that must be transmitted by the individual heating devices between the rolling stands of the finishing rolling mill and the material being passed are previously calculated by means of a calculation model individually for each of the heating devices. The previous calculation is done taking into it accounts for known heat losses, such as appear especially in the transport of the material between successive rolling stands or between successive heating devices and during passage through individual rolling stands. The calculation model advantageously takes into account pre-established limitations on the part of the manufacturer, conditioned by the material, mechanical or electronic for the rolling stands of the finishing line, for the heating devices as well as admissible intervals for the rolling process. To meet these pre-established limitations, the calculation model evaluates numerous process parameters. The calculation model can be configured to iteratively calculate the heat quantities that must be transmitted from the individual heating devices in each case to the material either based on a direct calculation in the material flow direction or in a reverse calculation , starting from the desired final rolling temperature of the web material at the exit of the finishing rolling mill, against the direction of material flow. The calculation of the heat quantities that must be generated or transmitted to the material is basically done before a finishing rolling process. Advantageously, the calculation model is however, it is also configured to take into account variations in the process parameters that are detected during a finishing lamination process by means of its own adaptation. The lateral edges of the input material are normally exposed from an outlet of the material of a casting mold and function in this respect as the heat irradiation surface. Furthermore, in the edges all the cooling water that is applied, for example during a descaling of the input material, runs downwards on its surface on the wide side, so that they are cooled very much additionally. Therefore, as a result, the input material is usually cooler at its edges than at its center before it enters the finishing rolling mill. However, it is desired that the material be uniformly heated at the latest on leaving the finishing rolling mill, preferably everywhere, also transversely to the direction of material flow. To achieve this, the present invention proposes placing the heating devices for reheating the material inside the finishing rolling mill in a manner oriented to the band edges and activating them through the calculation model in such a way that the edges of the material chilled in excess at the entrance are heated more than the center of the material, so that the material is uniformly heated at the very latest when leaving the finishing rolling mill also in the transverse direction. In practice, it has been successful to carry out overheating with inductive heating devices, because these enable, for example, unlike burners, a greater heating of the material in a short path and at the same time also a homogeneous or directed distribution of the introduced heat in the material.

DESCRIPTION OF THE FIGURES. In the description there are in total 7 attached figures, which illustrate Figure 1, an overview of a slab installation with a finishing rolling mill according to the present invention with the components of the control unit (calculation model); Figure 2, the method according to the invention; 3 shows the efficiency of the method according to the invention against a method known from the prior art; Figure 4, a variant of the method according to the invention; Figure 5, the development of resistance medium to hot fluence for different steels as a function of temperature; Figure 6, an example of embodiment of a heating device placed on the band edges to reheat the material; and Figure 7, different temperature developments with respect to the width of the material with a different temperature of the band edges, these temperature developments representing the heat distribution that must be transmitted from a heating device to the material.

DETAILED DESCRIPTION. The invention is described in detail below in the form of exemplary embodiments with reference to the figures mentioned. Figure 1 shows a slab installation which in the direction of the material flow (direction of the arrow) comprises: a casting machine 300 for casting a pouring bar, a device 320 for guiding bars to guide the pouring bar, cast from vertical to horizontal, a finishing mill 100 for finishing lamination of the pouring rod in the form of input material to obtain a web material, a cooling path 400 to cool the material of finished sheet web, a shear 500 for dividing the normally continuous web material and finally one of several winding devices 600 for winding the web material adjusted by the shear 160. The finishing mill 100 basically consists of boxes 110. - laminating n arranged one behind the other in the material flow direction, with n = 1 - N, and heating devices 120 - k disposed between the individual rolling boxes 110 - n, with k = 1 - K. In specific cases upstream of the finishing rolling train 100 a device can be connected 120 - 0 of previous heating. Normally, this is the case, for example, when low pouring machine outlet temperatures are to be expected or when cooling devices 140 between boxes are provided between the first rolling stands of the finishing rolling mill. Furthermore, it can be observed in FIG. 1 that a control device 130 is associated to the finishing rolling train 100 for activating the heating devices 120-k and the cooling devices 140 between boxes. According to the present invention, the control device 130 is not only configured to turn on or off the aforementioned devices but also to individually adjust the cooling devices between boxes the individual cooling intensity by regulating the amount of water emitted or, in 120-k heating devices, the amount of heat that must be transmitted from them to the material. The decisions on switching on and off the aforementioned devices as well as on the cooling and heating capacities that must be adjusted are taken by the control device 130 by means of a calculation model 132 which, for decision making, takes into account especially the Heat losses inside the finished rolling mill. In the case of these heat losses, it is basically the heat losses that appear in the transport of the material 200 between successive boxes 110-n or between successive heating devices 120-k and during the passage through the boxes 110-n of lamination. The calculation model 132 also takes into account, in order to establish the pass planning as well as the activation of the aforementioned devices, the pre-established, mechanical limitation, conditioned by the material or electronics for the rolling boxes 110-n, the devices 120 - k for heating as well as pre-established limitations for the rolling process. Specifically, the calculation model 132 calculates the heat losses based on a plurality of pre-established process parameters, for example the type of the input material used, that is to say, for example of the type of steel used or of the type of aluminum used, the thickness of the input material 200, the casting speed VG, the temperature TG behind the rod guiding device 320, the number N of rolling stands in the finishing rolling mill 100, the distance of the boxes or the distance of the heating devices 120 from each other, the temperature TA of the strip material at the exit of the finishing rolling mill, the maximum cooling capacity of the cooling devices 140 between enclosures, pre-established increased temperature specifications for the edges of the material and optionally also taking into account in each case temperature values currently measured between the enclosures 110-n. The limitations mentioned above considered by the calculation model 132 for the rolling stands, the heating devices and the inter-box cooling devices are symbolized in figure 1 with the reference symbol 133, while the process-dependent parameters for the The type of material used or the thickness of the input material, the casting speed, etc., are symbolized by reference symbol 134. Figure 2 illustrates the procedure according to invention for the hot rolling of the input material for the finishing mill 100 that has just been described. The process is especially suitable for input material 200 in the form of thin slabs with a thickness of 120 to 50 mm or pre-bands. These are, when transported to the finishing rolling mill 100, of course according to the invention, heated to an input temperature TE above a value ?? lower threshold of pre-set temperature. The value Ty lower temperature threshold is preset according to the material. Thus, for example, it is adjusted for austenitic rolled steel at approximately 900 ° C and for ferritic rolled steel at approximately 800 ° C. The input material 200 is then just rolled in the various successive lamination boxes 110-1 ... - 7 to obtain web material, cooling due to heat losses inside the finishing mill with respect to the TE temperature of entry. The development of the mean temperature T of the material during the passage through the finishing rolling mill 100 is shown in FIG. 2 in a graphic manner. In this respect, the heat losses of the material are represented basically through the sections of the development with a negative slope, while a contribution of temperature by means of one of The heating devices are represented through sections of the development with a positive slope. The sections Al, A2 and A3 which decrease drastically within the path sections XI, X2 and X3 are due to an activation of the descaling device 142 or of the cooling device 140 between boxes which, advantageously, are ignited for obtain an especially good surface quality in the laminate. Furthermore, it can be observed in FIG. 2 that the heat losses, that is to say, the decrease in temperature of the material during the passage through the rolling boxes 110, is especially great, which is represented in each case by a discontinuity in the temperature development. according to figure 2. The cause of these drastic temperature discontinuities is the fact that the material releases a lot of heat during the passage through the rolling boxes to the corresponding work cylinders. The dotted line shown in FIG. 2 represents the temperature development of the material in the direction of the material flow within the finishing rolling mill without the activation of one of the heating devices 120-k between the rolling stands. say, also without application of process according to the invention. The final lamination temperature that appears in this respect is too low for austenitic lamination and is below the Threshold temperature value. In contrast, the continuous black curve shows the temperature development of the material using the method according to the invention. This provides that, in the first place, that heating device, seen in the direction of the material flow, at which height or behind which the temperature of the material 200 runs the risk of descending for the first time below the threshold value T0, is determined. lower temperature due to heat losses. This value Your lower temperature threshold is indicated in figure 2 by a horizontal dashed line and is set by way of example at 900 ° C. In Figure 2, the black curve runs the risk of descending for the first time below this value T0 lower temperature threshold between boxes 110-3 and 110-4, that is, in the X4 interval, if this is not compensated imminent decrease. Precisely such compensation is provided by the method according to the invention by increasing the temperature of the material by the heating device 120-3 arranged in this position interval X4 to prevent a temperature drop below the lower threshold temperature value. However the increase in temperature in the The same is not done arbitrarily, but with respect to a minimization of the energy supplied only to the extent necessary, that is, only until the temperature of the material falls, during the movement of the material inside the finishing rolling mill to the next heating device connected downstream, seen in the direction of the material flow, in this case the heating device 120-4, only up to the lower temperature threshold value T0, but not below it, due to the corresponding local heat losses in the finishing rolling mill. In the heating device 120 - 4 connected downstream as well as in all other heating devices 120 - 5, 120 - 6 connected downstream inside the finishing rolling mill 100, the heating of the material according to the invention is then repeated in each case. described invention, so that the finished sheet material 200 has at the outlet of the finishing rolling mill 100 a temperature in the order of the desired final rolling temperature TA, ie, approximately in the order of the value of the lower threshold of pre-set temperature. Unlike heating devices 120-3, 120-4 and 120-5 within the finishing mill 100, the amount of heat that must be provided by the last heating device 120-6 of the finishing rolling mill can be adjusted slightly less, since this heating device must no longer compensate for heat losses between the last rolling box 110-7 and a heating device ( non-existent) connected downstream of it. In the exemplary embodiment shown in FIG. 2, the heating devices 120-1 and 120 2 are turned off inside the finishing rolling mill because there between-box cooling is performed in favor of an improved surface of the material. The method according to the invention for activating the heating devices can therefore be applied only to the heating devices 120-3 ... 6 in FIG. 2. The preheating device 120-0 serves to heat the material 200 to a temperature such that the temperature of the material does not fall below the value of the lower temperature threshold during the passage through the peeling device 142 and the cooling device 140 between boxes, that is, during the passage through the intervals XI, X2 and X3 of position. The most favorable operation mode from the energy point of view of the method according to the invention is illustrated in FIG. 3 against a method known from the prior art. He The process known from the prior art is represented in the upper half in FIG. 3 and provides that the material, starting from a temperature TG of 1150 ° C at the outlet of the casting machine 300 or of the rod guiding device 320 , is heated in a preheating device 120 - 0 to the extent that, during the subsequent passage through the entire finishing rolling mill 100, it does not cool at the exit of the finishing rolling mill 100 below a temperature of final rolling of 850 ° C without overheating inside the finishing rolling mill. For the described heating of the material inside the pre-heating device 120-0, a power of 14700 kW is needed in the example. On the other hand, in the lower half of FIG. 3, the temperature development according to the method according to the invention is represented. With the same marginal conditions and starting from the same temperature TG at the outlet of the pouring machine 300 or the bar guiding device 320 of 1150 ° C, it also results in the desired final rolling temperature of 850 ° C in the output of the same finishing mill 100. Unlike the illustration above, in the lower representation there is no pre-heating of the material before entering the train. finishing lamination, but a repeated reheating of the material according to the process according to the invention by the heating devices 120-k between the rolling boxes 110-n. As shown in the illustration below, in order to obtain the same final rolling temperature at the outlet of the rolling mill, in the process according to the invention, only a heat input of the order of 8000 kW is required, which is equivalent only to 55% of the thermal energy that must be used in the process described above in the state of the art. Figure 4 shows a rolling train consisting of a pre-deformation group 90 and finishing boxes 110-n. Inductive heating devices 120-0, 120-k are arranged between the pre-deformation group and the finishing train as well as within the finishing train. The 120-0 inductive heating device before the finishing train serves to preset the inlet temperature in order to be able to react to different variations of the marginal conditions (casting temperature or speed) and thus be able to maintain constant the temperature of entrance to the interior of the 110-n finishing train, which supports the procedure in question. Figure 4 also shows a variant of the The method according to the invention, which consists in the fact that the temperature during the reheating of the material by means of the heating devices 120-k is limited by a value T0, absolute upper threshold of pre-established temperature. In this variant of the process according to the invention, the temperature of the material then oscillates, within the finishing train 100 during the repeated reheating according to the invention, only in a range? T of target temperature formed by the difference between the upper and lower threshold value of temperature. Then a practically isothermal lamination of the material takes place; A target temperature range of this type is represented illustratively in Figure 4. The interval? The target temperature T is preferably also selected in such a way that the material used in each case has good material properties and / or malleability as well as possible in this target temperature range. A material exhibits an especially good malleability of this type, for example where the development of its average hot flow velocity with respect to temperature presents, said mathematically, a local minimum. Figure 5 shows the developments of the average resistance to hot creep with respect to the temperature for two different steel types, the dot curve representing the hot creep resistance for a normal type C steel (carbon steel) and the curve the hot creep resistance for a ULC steel. It can be seen that the continuous curve presents for the ULC steel in the range of approximately 820 to 860 ° C a local minimum that can be exploited in the ferritic lamination with this method in a positive manner. Figure 6 shows an exemplary embodiment for an inductive heating device 120-k. The heating device is constructed in two parts with an inductor 120-k-1 on the operator side and an inductor 120-k-2 on one side of the motor. The two inductors are displaced if necessary from the right or from the left towards the line of the finishing rolling mill so that they overlap, so that finally the induction coils I are finally arranged above the wide sides of the material 200. The inductor heads of the inductors are adjusted in a direction oriented to the band edges and are arranged one behind the other in pairs. In this respect, the orientation oriented to the band edges means that the inductor heads are adjusted beyond the width of the material, for example remote with a distance A from the edge of the material. According to the invention, the 120-k devices of The heating is then activated by the control device 130 in such a way that, for example, a distribution of the temperature contribution, shown in FIG. 7, is achieved by the width of the material, that is to say, transversely to the direction of material flow. . In figure 7 it can be observed that in the edges of the material 200, due to the proper activation of the heating devices and their positioning oriented to the band edges, a cross-field heating is achieved with the particularity that the edges of the material 200, as shown in Figure 7, are heated relatively more intensively with respect to the center of the material; see the reference symbol H in figure 7. Taking into account a particularly intense cooling of the edges of the material before entering the finishing rolling mill, a relatively uniform heat distribution is obtained by the width of the material when leaving of the finishing rolling mill. In contrast, the development of the curve W in FIG. 7 represents a relatively uniform heating of the material by the width. In Figure 7, the effect or relationship of the temperature of the band edges with respect to the temperature of the band center is plotted by the width of the material 200 transversely to the material flow direction for different positions A of the inductor heads. The controlled inductive adjustment of the temperature of the band edges within the finishing train can be used additionally or alternatively to influence the flatness of the band and the profile of the band. Especially in the case of austenitic honed steel, the influence is largely influenced by the temperature of the band edges and thus in the band form. The influences are described in a profile, contour and flatness model and the position of the inductive heating is established in a controlled manner according to the specifications of the model.

Claims (16)

NOVELTY OF THE INVENTION Having described the invention as antecedent, property is claimed as contained in the following: CLAIMS

1. Method for hot rolling (200) input material for a finishing rolling mill (100), especially for thin slabs or pre-blanks, which comprises the following steps: introducing the input material (200), heated to an input temperature (TE) above a preset temperature lower threshold value (Tu) in the finishing rolling mill; laminating the input material (200) heated in several successive lamination boxes (110-n) of the finishing rolling mill to obtain strip material, especially to obtain steel strip, cooling the material due to heat losses in the train (100) finishing lamination with respect to input temperature (TE); and compensating for heat losses by reheating the material at least between successive individual lamination boxes (110-n) by heating devices (120-k) to the extent that the temperature inside the rolling mill and the temperature (TA) of final rolling of the web material does not fall below the value (Tu) lower temperature threshold preset upon leaving the finishing lamination train (100); characterized in that first said heating device (120-k) is determined, seen in the direction of the material flow, at whose height or behind which the temperature of the material runs the risk of descending for the first time below the value ( Tu) lower temperature threshold due to heat losses; and because the reheating of the material is carried out by increasing the temperature of the material by the heating device (120-k) determined only to the extent that the temperature, during the movement of the material to the next device (120 - [k + 1] ) of heating connected downstream, seen in the direction of material flow, or when in the direction of material flow is no longer connected downstream no heating device until the exit of the finishing rolling mill (100), only descends up to the value (Tu) lower temperature threshold due to the corresponding local heat losses in the finishing train; and because the reheating of the material is repeated by each heating device connected downstream in the direction of the material flow within the finishing rolling mill.

2. Method according to one of the preceding claims, characterized in that the temperature of the material during reheating inside the rolling train does not rise beyond a pre-established upper temperature threshold value (T0) which is above the lower threshold value (Tu) of temperature, and in this way is maintained in a range (? T) of target temperature between the lower and upper temperature threshold value. Method according to claim 2, characterized in that the target temperature range (? T) is selected according to the type of material used in such a way that the development of the average resistance to the hot creep with respect to the temperature for the The material used presents, mathematically speaking, a local minimum in the target temperature range. Method according to one of the preceding claims, characterized in that the lower temperature threshold value (Tu) is preset as a function of the material and is adjusted, for example, for austene low-carbon rolled steels at approximately 900 ° C and for rolled steels in a ferritic manner at approximately 800 ° C. Method according to one of the preceding claims, characterized in that the input material (200) is heated if necessary by a heating device (120-0) prior to the input temperature (TE) above the value (Tu) lower temperature threshold before entering the train (100) of finishing lamination. 6. Method according to claim 5, characterized in that, when between the first boxes (110-1, 110-2, 110-3) of rolling of the finishing rolling mill, seen in the direction of material flow, an intermediate cooling (140) of the material takes place. (200), the input material, before being introduced into the finishing rolling mill, is heated by the heating device (120-0) prior to an input temperature (TE) such that the material, during its transport by the zone of cooling (140) between boxes until reaching a next heating device (120-3) connected downstream in the direction of material flow behind the zone of cooling between boxes, does not cool below the value ( Your) lower temperature threshold. Method according to one of the preceding claims, characterized in that the determination of the heating level and of the heating device at which height or behind which the temperature of the material runs the risk of descending by first time below the value (Tu) lower temperature threshold due to heat losses, it is calculated by a calculation model (132) and / or due to temperature measurement values of the interior of the finishing mill. Method according to one of the preceding claims, characterized in that the amount of heat that must be transmitted for a reheating process by one of the heating devices (120-k) individually in each case to the material being passed, is calculated previously before the start of the rolling operation by means of a calculation model (132), taking into account the heat losses, such as those that appear especially in the transport of the material between successive lamination boxes (110-n) or between devices (120-k) of successive heating and during the passage through the rolling boxes. Method according to claim 8, characterized in that the calculation model (132) calculates the heat losses taking into account pre-established limitations (133) for the rolling stands of the finishing rolling mill, for the heating devices as well as for the rolling process based on pre-established process parameters, such as the type of input material used, for example the type of steel used or the type of aluminum used, the thickness of the input material, the casting speed, the number of rolling stands in the finishing rolling mill, the distance of the boxes or the heating devices between them, the measured temperature of the input material at the output of a bar guiding device (320) and the web material at the exit of the finishing rolling mill, if applicable, the cooling power of the devices ( 140) between boxes, temperature values optionally mediated between the boxes and / or pre-set temperature specifications for the edges of the material, etc. Method according to claim 7, 8 or 9, characterized in that the calculation model (132) calculates iteratively the first heating device or the amount of heat that must be transmitted from the individual heating devices (120-k) in each case to the material (200) either based on a direct calculation in the direction of material flow or in a reverse calculation starting with the final rolling temperature (TA) of the web material at the output of the train (100) of Finishing lamination against the direction of material flow. 11. Procedure according to one of the previous claims 7 to 10, characterized in that the calculation model (132) and thus the determination of the first heating device and the individually preset heat quantities for the individual heating devices (120-k) are adapted during a lamination process to modified process parameters, such as for example a modified temperature determined between two rolling stands. Method according to one of the preceding claims 8 to 11, characterized in that the heating devices (120-k) are positioned in a direction oriented to the band edges and activated by the calculation model (132) in such a way that , viewed transversally with respect to the direction of material flow, a greater contribution of heat than in the center of the material is made in the chords of the material cooled with an intensity greater than the average. Method according to claim 12, characterized in that the inductive adjustment of the strip temperature inside the finishing train is used to influence the flatness of the strip and the profile of the strip and the influences are described in the profile model , contour and flatness as well as the position of the inductive heating is preset. 14. Procedure according to one of the previous claims, characterized in that the reheating is carried out inductively by the heating devices (120-k). 15. Finishing lamination train (100) comprising: a plurality of successive lamination boxes (110-n) in the material flow direction for hot rolling input material (200) to obtain web material, undergoing input material (200) heated to an input temperature (TE) above a value (Tu) lower temperature threshold a cooling due to heat losses in the finishing lamination train (100); heating devices (120 - k) disposed at least between individual lamination boxes (110 - n); and a control device (130) for activating the heating devices (120-k), so that the heat losses are compensated for by an overheating of the material (200) insofar as the temperature (TA) of Final lamination of the web material does not fall below the value (T0) lower threshold of pre-set temperature after the exit of the finishing rolling mill; characterized in that the device (130) of control is configured to a) determine that heating device (120-k) at which height or behind which, seen in the direction of material flow, the temperature of the material runs the risk of descending for the first time below the value ( T0) lower temperature threshold due to heat losses in the finishing train; and b) activating the heating device (120-k) determined in this way and, if necessary, the additional heating devices connected downstream in the direction of the material flow within the finishing rolling mill, in such a way that the material is only reheated in each case to the extent that its temperature, during travel to the next device (120 - [k + 1]) of heating in each case connected downstream, seen in the direction of material flow, or after passing through the last heating device until the exit of the last of the lamination boxes (110-n), it only descends to the value (Tu) lower temperature threshold due to heat losses. 16. Finishing lamination train (100) according to claim 15, characterized in that the control device (130) is further configured to perform the method according to one of claims 2 to 14. SUMMARY OF THE INVENTION The invention relates to a process and to a finishing rolling mill for hot rolling input material. In the finishing rolling mill, the input material is finished in several successive lamination boxes (110-n), cooling the material due to heat losses. In order that the temperature of the material inside and at the exit of the finishing rolling mill does not fall below the lower threshold value of the preset temperature at low speeds, the material must be reheated within the finishing rolling mill. In order to keep the energy for this reheating as small as possible, it is proposed according to the invention to reheat for the first time in the finishing rolling mill only where the temperature of the material runs the risk of falling below the threshold value for the first time. lower temperature, seen in the direction of material flow, due to heat losses. It is also proposed to increase the temperature of the material during reheating only to the extent that the temperature, during the movement of the material to a subsequent heating device connected downstream, seen in the direction of material flow, as well as to the output of the rolling mill, it only goes down to the value (Tu) lower threshold of temperature, but not below it.