RU2552802C2 - Rolling mill for production of pipe steel and thin strip - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to strip rolling mill. Fast heater and at least one roller-type straightening unit are arranged at rolling mill between finishing stands. Spacing between finishing stands where between fast heater and roller-type straightener are located makes 5-25 m. Besides, rolling mill is equipped with adjustment element to affect strip convexity and/or strip start flexure.

EFFECT: higher efficiency of rolling mill.

17 cl, 5 dwg

Description

The invention relates to a rolling mill, in particular a CSP installation, for manufacturing a strip, in particular tubular steel, and / or a thin strip containing a casting device for creating a thin workpiece, and also a rolling mill for rolling a thin workpiece into a strip or thin strip.

The manufacture of a steel strip or steel sheet by hot rolling is sufficiently described in the prior art. Relevant disclosures are found, for example, in P. Uranga et al. “Improvement of Microstructural Homogenity in Thermomechanical Processed Nb Steels by Thin Slab Casting”, 43 ^rd Mechanical Working and Steel Processing Conference, Charlotte, ISS, Vol. 39, pages 511-529; in L. Klinkenberg et al., Processing of Niobium Microalloyed API Grade Steel on a Thin Slab Plant, Material Science Forum, vols. 500-501, 2005, pages 253-260, and in an article by SV Subramanian et al., “Process modeling of microalloyed sreel for near net shane casting”, Proc. Of the int. Conf. On Thermomechanical Processing: “Mechanics, Microstructure,” EJ Palmiere et al., The University of Sheffield, Sheffield, 2003, pages 148-156.

The prior art installation of the prior art is disclosed in EP 0 721 813 A1. Similar solutions are disclosed in EP 2258491 A1, WO 2007/073841 A1 and DE 102008029581 A1.

CSP (Compact Strip Production) plants are continuous rolling units in which two separately working process steps for the manufacture of steel strips are closely connected to each other, namely, casting molten steel into thin billets (thin slabs) and rolling thin billets into steel strips in a rolling mill. become. In this case, rolling of the pre-cast billet before this is usually carried out directly using foundry heat or by setting the desired rolling temperature using a leveling furnace or a heating device between the casting unit and the rolling mill.

Conventional rolling mill plants with thick billets have at least one preliminary stand, respectively a plate stand, and a finishing rolling mill located at a distance after this preliminary stand, respectively a plate stand. While in the preliminary stand, or the plate stand, the thin billet is rolled with reversal into an intermediate strip with a predetermined thickness, rolling in the finishing rolling mill is carried out in a continuous mode, for which the finishing rolling mill is made in the form of a continuous rolling mill. While the distance between the individual rolling stands of such finishing rolling mills is usually approximately 5.5 m, the distance between the preliminary stand, respectively the plate stand, and the first stand of the finishing rolling mill is usually many times greater, in order to provide reversible rolling mode in the preliminary stand, respectively plate stand. In this regard, the distances between the preliminary stand, respectively the plate stand, and the finishing rolling mill are often about 50 m or more.

Conventional rolling mills have a large length based on the usually coaxial arrangement of the roll of delivery of thick billets, a preliminary stand, respectively a plate stand, and a finishing rolling mill, and many powerful rolling stands are required, thereby increasing investment costs. Energetically conventional rolling mills are less efficient than CSP plants. Especially in the manufacture of a thin strip, the input temperature in the finishing mill is very low, which makes it difficult to roll a thin strip. The manufacture of pipe steel in a conventional strip hot rolling mill is also time-consuming due to the required temperature conditions and reduces the performance of a conventional strip hot rolling mill.

Therefore, the objective of the invention is the creation of a rolling mill specified at the beginning of the form, with which at least the above disadvantages are reduced. This problem is solved, according to the invention, using a rolling mill containing the characteristics of paragraph 1 of the claims. Preferred embodiments of the invention are given in the dependent claims.

The rolling mill according to the invention, in particular the CSP installation, preferably consists of a compact rolling mill for the manufacture of metal strips, mainly pipe steel and / or a thin strip, in which between two successive finishing stands Fi and Fi + 1 it is possible effects on temperature using a quick heating device, in particular induction heating. In addition to the quick heating device, a correct unit, preferably a roller leveling device, is provided between two successive finishing stands Fi and Fi + 1. In addition, scissors and / or optionally a scale descaler or other means for cooling the strip may be located between stands Fi and Fi + 1. All devices are so compact that they enter a distance between the stands between 5 and 25 m. In addition, the Fi stand before the quick heating device is preferably equipped with adjusting elements to influence the bulge of the strip and / or bending up the end of the strip.

Thus, by using the correct assembly, preferably the roller alignment device and / or scissors and the above adjusting elements, it is possible to ensure reliable passage through the device of rapid heating, in particular induction heating, with a minimum passage size in the thickness direction in a limited structural space. According to the method, it is possible to use a quick-heating device, scissors and / or a device for descaling, depending on the product to be rolled, or in the transverse direction from the rolling line, or, as an alternative solution, place a roller table there with or without thermal insulation or table. For rolling the thin strip, scissors between the stands can also be provided for use at the beginning and / or end and providing the most direct start and end of the deformable strip.

Due to the additional devices between the stands, the normal distance between the stands increases, which is, for example, ≥5.5 m. To eliminate the possible additional formation of secondary scale, a single-row scale descaling device is preferably provided, which is compact and preferably located in front of the stand Fi + 1 and after the quick heating device. When rolling strips with high surface requirements (for example, when rolling a thin strip), you can turn on the device for descaling in front of the stand Fi + 1. In the manufacture of pipes, the descaling apparatus can optionally be turned off or pushed out of the rolling line.

To save structural space, you can optionally abandon the loop former, instead of which regulation of the minimum tension can be provided with or without a roller for measuring tension.

Compared to a conventional rolling mill with induction heaters between the preliminary and finishing rolling mills, by using the rolling mill according to the invention, preferably the rolling mill of the CSP unit with the corresponding additional units, the overall structural space of the rolling mill is significantly reduced. The use of additional units selectively introduced into the rolling line inside the rolling mill has a generally beneficial effect on the rolling process both from the point of view of the method and from the point of view of regulating the structure in the rolled product. These additional units, according to the invention, require a little constructive space and are located between two finishing stands, the distance between which is 5-25 m. In other words, the need for space between two stands with additional units is much less than the length of the intermediate strip rolled there.

Preferably, the thin preform, preferably produced in a CSP casting device, has a thickness of ≤120 mm. Due to this, the CSP installation is obtained, which is reliable, without using a reverse preliminary rolling stand, and preferably only through the use of several finishing rolling stands as a rolling mill, is capable of providing the production of the desired product range from a thick tube strip to a thin strip.

As an example and a preferred embodiment, a description can be made of a method for manufacturing a tube strip in a CSP installation. The TM method (thermomechanical method) in a CSP installation usually consists of one or more deformations of the austenitic initial structure in the range of recrystallization temperatures to create a uniform, thin, recrystallized austenitic structure and a subsequent stage of one or more deformations of the recrystallized austenitic structure flat stretched, with many displacements, unrecrystallized austenitic structure (the so-called pancake structure (Pan-Cake)). These stages are also called austenite conditioning.

Finally, in the next step, the austenitic structure, conditioned by the first step, is cooled to create a fine-grained structure in the finished hot rolled strip or hot rolled sheet during phase transformation. In this case, the structure of the hot-rolled strip, respectively, of the hot-rolled sheet, consists of a combination of ferrite, perlite, bainite and martensite, while the content of these four components of the structure can be between 0% and 100%.

In accordance with the above description of the TM method, it is also possible to abandon the above stage of deformation in the temperature range without recrystallization of austenite. In this case, the conditioning of austenite occurs completely in the temperature range of austenite recrystallization.

However, the difficulty of thermomechanical hot rolling is that in order to create a uniform finely crystallized austenitic grain in the recrystallization range, it is necessary to deform as large as possible. A finely crystallized structure is characterized by the fact that both the old, uneven cast structure, and individual coarse grains or zones of the structure are completely converted into a uniform, finely crystallized structure with a small scatter around the average grain size. Often these conditions are not met or are not fully met, which leads to insufficiently conditioned austenitic structure.

If the stage of hot rolling in the recrystallization temperature range of austenite is followed by the stage in the non-crystallization temperature range, then with a relatively large ratio of the thickness of the finished hot-rolled strip, respectively, of the hot-rolled sheet, and the thickness of the billet or intermediate strip, only a small residual deformation remains for the subsequent stages of deformation in thermomechanical processing. Even when disconnecting individual rolling stands, this is sometimes not enough to transfer the possibly still remaining remains of the casting structure, as well as individual coarse grains or zones of the structure, into a uniform, flat pancake structure from unrecrystallized austenitic grains. In this case, insufficiently conditioned austenite also occurs.

However, insufficiently conditioned austenite leads in the finished hot-rolled strip, respectively hot-rolled sheet, to individual coarser grains outside the normal distribution around the average grain size and / or to zones of the structure, the substructure of which is characterized by small-angle grain boundaries. However, such zones of the structure lead to poor mechanical properties of the finished strip or the finished sheet, in particular, reduced viscosity.

In accordance with the above description of the TM method, deformation in the recrystallization range of austenite is crucial for the properties of the finished steel strip or sheet. Although the degree of deformation required in the first stage of thermomechanical processing can be partially replaced by an increased inlet temperature, this possibility is limited by the maximum temperature of the furnace, as well as by cooling during contact with the rolls during rolling and by thermal radiation between stands, when several stands are involved in this stage.

A CSP installation is preferred in which the heating device is located between at least two stands Fi and Fi + 1 of the rolling mill, in particular between the first stand F1 and the second stand F2. If necessary, this heating device can be made with the possibility of extension from the rolling mill and insertion into it again. Particularly preferred is an induction heating device, in particular with 1-4 inductor elements. In general, the goal is to obtain the most compact design of such a heating device with a high power density. This power density is preferably in the range of at least 1,500 MW per square meter, preferably about 4,000 MW per square meter, which is actually introduced into the strip or induced in the strip. In this case, an inductor element is a structural element through which power is introduced into the strip. Thus, one or more inductor elements can form an induction heater.

The rolling installation is preferably used in the form of a continuous rolling mill, inside of which the above-mentioned deformation stages are used at a high temperature and, if necessary, with the support of a heating device between the finishing rolling stands and optional cooling of the rolling at low temperatures. In this case, a preliminary rolling stand, respectively a plate stand, is not used, as is customary in an installation with thick blanks.

Preferably, the deformation steps are interconnected, i.e. all participating stands after the entry of a thin blank, respectively, of an intermediate strip, are simultaneously engaged. In this case, the rolling stands operate in a continuous mode, i.e. in the mode in which thin billets or an intermediate strip simultaneously pass through all rolling stands. However, in this case, individual stands can be raised and thereby not participate in the work of deformation.

In the endless mode, a method can be applied in which the cast billet should not be separated into flat billets by means of transverse separation, but fed to the hot rolling mill continuously, preferably through a tunnel furnace, and subjected to rolling into a finished hot rolled strip, cooled and only transversely divided before the coiler and wound up in rolls. This method of operation reduces the amount of waste, since there are no beginning and end parts of the strip. In addition to this, thinner strips can also be created, preferably with a thickness of less than 1 mm, since the danger of a shortage in the form of "accordions" (cobbles) when entering thin strips in the last stands of the hot rolling mill is present only at start-up. In endless rolling, the retraction speed of the first active stand is reduced to the casting speed, which can lead to increased temperature loss before and / or during hot rolling. Therefore, rolling requires higher rolling temperatures and thereby heating the strip to prevent rolling temperatures in the ferrite phase and / or in the region of the two phases, austenite plus ferrite.

This method and the device explained allow, in principle, to produce steel grades with a reduced region of the austenite phase, for example, with a silicon content of more than 1%. Moreover, higher rolling temperatures are required for rolling in order to reliably prevent the final rolling temperatures in the ferrite phase and / or in the region of the two phases austenite plus ferrite. Steel of this quality can be manufactured in a CSP unit according to the invention.

In the manufacture of a strip or thin strip, as indicated above, an induction heater is preferably installed between the front rolling stands or is introduced at least into the area between the front stands. Preferably, an induction heater is used between the first and second and / or second and third stands of the finishing mill.

However, induction heating is characterized by a relatively small passage size in the thickness direction and is a sensitive structural part. When rolling in a finishing mill, especially in the first stands, especially at the beginning often bends up or down (the so-called skis) or other bends of the strip or irregularities occur, which are dangerous for reliable passage of the tube strip or thin strip through an induction heater or other units (scissors, descaling device) between two finishing rolling stands. In addition, the aforementioned bending up or down can greatly complicate the introduction of a pre-rolled intermediate strip into the next stand. In the worst case, the intermediate strip damages the aggregates between the two finishing rolling stands.

Minimizing or eliminating bending can be accomplished, for example, using suitable pressure rollers or using a properly bending device. However, it is particularly preferred that, inside the apparatus according to the invention, the beginning of the pre-rolled intermediate strip is cut off with suitable scissors. Optionally, with the help of such scissors, it is possible to trim the pre-rolled intermediate strip at the beginning and at the end, when thin finished strips are to be manufactured in a batch operation mode.

In another preferred embodiment of the installation according to the invention, it may be possible, depending on the material being rolled, to provide descaling in the rolling direction after heating the intermediate strip, possibly after passing the strip through the heating device and the pair of drive rollers located after it, before the intermediate strip enters one or several other finishing rolling stands. This ensures that it is possible to roll the finished thin strip or tube strip with almost no pollution, without damaging the scale surface of the strip or thin strip.

To ensure reliable passage of the intermediate strip through the devices between the two finishing rolling stands in accordance with the invention, a number of adjusting elements are preferably provided that can be used individually or in any combination.

As a measure in the rolling mill itself, it is possible to install a dual drive, as well as various adjustments to the rotation speed of the upper and lower rolls depending, for example, on the initial thickness, reduction in thickness, material or temperature, as well as various diameters of the upper and lower work rolls.

To influence the temperature distribution of the rolled product in the thickness direction, it is possible to regulate the cooling of the flat billet, or strip, in front of the rolling stand Fi so that a possibly more symmetrical temperature profile occurs along the thickness of the rolled product, or the bending is influenced by targeted temperature control. As an alternative solution, also for this purpose, it is possible to control the temperature of the flat billet on the upper and lower sides in front of the cage using a heating device.

In addition, it is contemplated that the table height is adjusted in front of the finishing rolling stand Fi, so that a certain input position of the workpiece or strip in the deformation zone is provided (for example, the middle of the rolled product corresponds to the middle of the deformation zone).

Installing the correct unit can also exclude the indirect passage of the strip (bending, bending, curvature) using simple means. This device for correcting or preventing the bending, respectively bending of the strip, in the form of a correct unit, can be, along with the roller leveling device, also a pressure roller, pressure plate, pressure spacers, a correctly bending device or device for pressing the beginning of the strip.

As already mentioned above, bending can be cut out of the rolled product using scissors.

Finally, it is possible, with the aid of suitable distance sensors to the surface, to detect irregularities in the intermediate strip, in particular before entering the heating device. Suitable sensors are mechanical, optical or other sensors known to those skilled in the art. Based on the alarm signal of the control unit connected to the sensors, appropriate measures can be initiated to eliminate or reduce the detected indirect passage of the strip or the deviation of the intermediate strip or workpiece.

The heating device can be protected from damage due to curvature of the strip not only in the manner described above; also damage, in particular of induction heaters, due to the cooling water remaining on the strip or a thin strip, can be prevented by the use of blowing devices, which are also particularly preferably located between the rolling stands of the finishing rolling mill according to the invention, or can be moved into this place.

The above additional units and anti-bending measures can preferably be used in the CSP finishing mill for various application examples. However, it is also possible and intended to use between the finishing rolling stands of a conventional rolling mill.

Induction heating and additional units can be located motionless or with the possibility of pushing in, respectively extending, in the lateral direction into the rolling line.

The following is a more detailed explanation of the invention based on several examples of the installation of the CSP according to the invention, with reference to the accompanying drawings, which depict:

figure 1 is a first exemplary embodiment of the invention, in which an induction heater and a pair of drive rollers are located between two stands of a schematically depicted strip hot rolling mill;

figure 2 is a second exemplary embodiment of the invention with a device for correction / prevention of bending at the beginning of the intermediate strip located in the rolling direction in front of the heating device;

figure 3 is a third exemplary embodiment of a rolling mill according to the invention, located between the device for correcting / preventing bending at the beginning of the intermediate strip and the device for descaling the heating device, which are all located between two rolling stands of the hot strip rolling mill;

4 is a fourth embodiment of a strip hot rolling mill according to the invention, with scissors arranged one after another in the rolling direction, a high-speed heater, a pair of drive rollers, as well as a device for descaling; and

5 is a fifth exemplary embodiment of a strip hot rolling mill according to the invention.

1 shows a portion of a hot rolling mill 2 according to a first embodiment of the invention, in which the metal strip 1 passes through the first depicted rolling stand indicated by Fi and the second depicted rolling stand indicated by Fi + 1. The distance between stands Fi and Fi + 1 is between 5 and 25 m. Immediately after leaving the finishing stand Fi, strip 1 enters the induction heater 8, and then into a pair of 12 drive rollers. Using this pair of 12 drive rollers in the strip 1, the strip tension can be created (also before the start of the strip enters the next stand), and in addition, the remaining water 1. is squeezed out slightly on the strip 1. Between the stands Fi and Fi + 1, the minimum tension can be adjusted . At the same time, a pair of 12 drive rollers helps to establish the exact speed of the stand Fi + 1. As an alternative solution, a tension measuring roller or looper (not shown) is located between the stands, in order to ensure a mass flow. Finally, in the rolling direction W after the rolling stand Fi + 1, for one application example, there is a cooling section 11, by means of which the strip 1, heated in the heating device 8 to a temperature above the recrystallization temperature, is cooled to a temperature outside the recrystallization range. Both devices 8 and 12 can also be located on the contrary. It is also possible the location of a pair of 12 drive rollers before or after the heating device 8.

Figure 2 shows another embodiment of the hot rolling mill 2 according to the invention, from which only the finishing mill stand Fi and the finishing mill stand Fi + 1 are shown. Between the rolling stands Fi, Fi + 1, a heating device 8 is again arranged for quickly heating the metal strip 1 by induction heating. In the rolling direction W, between the finishing rolling stand Fi and the heating device 8, there is arranged a device 14 for correcting / preventing bending in the intermediate strip that leaves the finishing rolling stand Fi. Such a device 14 for correcting / preventing bending up or down can be, for example, a correct bending device or a pressure roller. Such devices 14 should correct the phenomenon, for example, of raising up the beginning of the strip after leaving the rolling stand (the so-called folding up), i.e. eliminate or at least reduce to an acceptable minimum. This serves primarily to prevent downtime due to an inaccurate or unrealized input of the beginning of the intermediate strip into subsequent units, for example, into a quick heating device 8, other units (scissors, a descaling device) or every other rolling stand Fi + 1. To prevent the bending phenomenon, the hot rolling mill 2, respectively, has at least one rolling stand, preferably a first rolling stand, separate and unconnected drives for the upper work roll Fia and the lower work roll Fib. Due to this, with suitable control of the drives, it is possible to limit the bending up or bending down to the minimum values already during rolling.

Figure 3 shows a third embodiment of a hot rolling mill 2 according to the invention, in which, between the first depicted rolling stand Fi and the second depicted rolling stand Fi + 1, there is a device 14 for correcting the bending at the beginning of the intermediate strip with a quick heating device 8 located behind it . Between the quick heating device 8 and the rolling mill Fi + 1, there is again a scale descaling device 15, with which it is possible to reliably remove the scale located on the surface of the strip 1 before the strip 1 enters the Fi + 1 rolling mill. Optionally, this embodiment of the invention may also have a pair of drive rollers (not shown) and / or cooling (not shown).

Fig. 4 shows a fourth embodiment of a hot rolling mill 2 according to the invention, in which there are scissors 13, a quick heating device 8, a pair of drive 12 located between the first depicted rolling stand Fi and the second depicted rolling stand Fi + 1 in the direction W of rolling strip 1 rollers, as well as a device 15 for descaling. While the quick heating device 8, the pair of drive rollers 12, as well as the descaling device 15 work, as in the embodiment shown in FIGS. 2-4, the scissors 13 are primarily used to cut off the beginning of the strip, as well as perhaps the end of the strip on which rolling tongues or bends can form (the so-called skis). Thus, the scissors 13 replace, on the one hand, the devices for correcting / preventing bending, shown in the previous embodiments, in addition to this, the scissors 13 preferably support the further rolling process by cutting off the tongues, which in the subsequent rolling process can have an adverse effect on the passage of the strip 1, as well as on the work rolls of subsequent stands.

FIG. 5 shows a fifth embodiment of a hot rolling mill 2 according to the invention, in which a finishing rolling stand Fi, an adjustment device 14 for correcting / preventing folding upward, scissors 13, and a quick heating device 8 are arranged in the rolling direction W of the strip 1. After exiting the quick heating device, the metal strip 1 enters a pair of 12 drive rollers, with the help of which the residual water located on the strip 1 is squeezed out. After leaving the pair 12 of drive rollers, the metal strip 1 enters the scale descaling device 15, in which the residual scale that has formed on the surface of strip 1 is reliably removed before the strip 1 enters the finishing rolling stand Fi + 1. Finally, depending on the application, the hot strip 1 heated in the quick heating device 8 is again cooled in the cooling device 11 and rolled to a final strip thickness.

As an alternative solution, the quick heating device 8 and the scissors 13 can also be located opposite in the direction of passage of the strip.

If it is necessary to further reduce the distance between the stands, the quick heating device 8 and the scale descaling device 15 can be located in the same place in the direction of the strip or alternatively move into the rolling line from the side, so that either a device 15 for hydroscale descaling, or a device 8 for quick heating.

Claims (17)

1. Rolling mill for the manufacture of metal strips, preferably a tubular steel strip or a thin steel strip, in which between two successive finishing rolling stands (Fi, Fi + 1) there is a quick heating device (8) and at least one other additional unit, characterized in that the distance between the stands (Fi, Fi + 1), between which there is a quick heating device (8) and at least one other additional unit, is 5-25 m, and at least one other additional aggregate al represents the correct assembly, preferably a roller straightening device (14). 2. A rolling mill according to claim 1, characterized in that the stand (Fi) in front of the quick heating device and / or zone (8) before and after this rolling stand (Fi) is equipped with adjusting elements to influence the convexity of the strip and / or bending at the beginning of the strip. 3. The rolling mill according to claim 1, characterized in that the rolling stands (Fi, Fi + 1) are finishing rolling stands of a preferably compact continuous rolling mill. 4. The rolling mill according to claim 1, characterized in that it is preferably a rolling mill in a CSP installation in which thin blanks with a thickness of ≤120 mm are made. 5. The rolling mill according to any one of paragraphs. 1-4, characterized in that the quick heating device (8) is made in the form of an induction heating device, preferably with 1-4 induction elements, located between the first and second stands (F1, F2) and / or between the second and third stands (F2 , F3), or designed to be pushed between them. 6. Rolling mill according to any one of paragraphs. 1-4, characterized in that at least one pair of drive rollers is located between one stand (Fi) and the next stand (Fi + 1) or is designed to slide in between. 7. Rolling mill according to any one of paragraphs. 1-4, characterized in that the device for correcting or preventing the bending on the strip is located between the stand (Fi) and the next stand (Fi + 1), preferably in front of the device (8) for quick heating, or is intended to be inserted between them. 8. The rolling mill according to claim 7, characterized in that the device for correcting or preventing bending is a pressure roller, a pressure plate, a pressure spacer, a correct bending device, a correct channel for starting a strip or a device for pressing the beginning of a strip. 9. The rolling mill according to any one of paragraphs. 1-4, characterized in that at least one rolling stand (Fi) has separate drives for the upper and lower work rolls (Fia, Fib). 10. The rolling mill according to any one of paragraphs. 1-4, characterized in that in front of the rolling stand (Fi) there is a device for cooling or heating the strip, with which a temperature distribution is established over the thickness of the workpiece, or strip, to affect the bending and bending of the strip. 11. Rolling mill according to any one of paragraphs. 1-4, characterized in that the rolling stand (Fi) contains on the entrance side a guide table for the strip and a device for adjusting the height of the guide table, with which it is possible to adjust the position of the strip. 12. The rolling mill according to any one of paragraphs. 1-4, characterized in that at least between two rolling stands (Fi, Fi + 1) the scissors are located or designed to be moved in between. 13. Rolling mill according to any one of paragraphs. 1-4, characterized in that the device for hydroscale descaling is located between at least two rolling stands (Fi, Fi + 1) or is intended to be moved in between. 14. The rolling mill according to any one of paragraphs. 1-4, characterized in that the distance between two successive stands (Fi, Fi + 1) is less than the length of the intermediate strip rolled between the stands. 15. Rolling mill according to any one of paragraphs. 1-4, characterized in that at least between the two rolling stands (Fi, Fi + 1) are insulating casings, in particular, as a replacement for the units previously removed between the rolling stands (Fi, Fi + 1), or are intended for pushing in between. 16. Rolling mill according to any one of paragraphs. 1-4, characterized in that it has a process model, with which it is possible to control and regulate the process of folding the strip. 17. Rolling mill according to any one of paragraphs. 1-4, characterized in that the power density that is induced in the strip is at least 1500 MW per square meter, preferably about 4000 MW (+/- 18%) per square meter.

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