Plant and method for producing flat rolled products

Abstract

A rolling plant (10) and method for producing a strip (P) from a slab (50) having a predetermined starting thickness, comprising: at least one walking beam furnace (16) configured to heat at least the slab (50) to a starting temperature; a finishing mill (25) operatively arranged in series with at least one roughing stand (23) and configured to reduce the thickness of an intermediate rolled product (51) until a final strip (P) is obtained at the outlet from the roughing stand (23), the finishing mill (25) including at least one pre-finishing stand (26) for obtaining a pre-finished rolled product (52); and a finishing mill (25) for producing the final strip (P). and a plurality of finishing stands (31) capable of obtaining a rolling force of the pre-finishing rolled product (52), the plant (10) comprising: load cells (40) directly associated with the pre-finishing stands (26) for detecting a rolling force applied to the pre-finishing rolled product (52); rapid heating devices (28) disposed between the pre-finishing stands (26) and the finishing stands (31) for heating the pre-finishing rolled product (52); and a command and control unit (44) connected to both the load cells (40) and the rapid heating devices (28) and configured to selectively activate the rapid heating devices (28) in response to at least the rolling force detected by the load cells (40).

Description

[Technical Field]

[0001] The present invention relates to a plant and method for producing flat rolled products, such as, for example and without loss of generality, coiled steel strip. [Background technology]

[0002] Rolling plants known as hot strip mills (HSM) are designed to produce hot metal strip from slabs, typically with thicknesses of about 150 mm to about 350 mm.

[0003] HSM typically consists of a "walking beam" gas-fired furnace in which the slab is heated to rolling temperature, after which it is subjected to 3 to 8 rough rolling passes in one or more reversing stands to obtain an intermediate bar that is significantly thinner than the starting thickness, typically 35 to 80 mm. The intermediate bar then undergoes a number of finish rolling steps to obtain the final strip thickness.

[0004] In all plants using slab heating with "walking beam" furnaces, a common problem is the formation of cold impressions or skid marks corresponding to the contact surfaces of the slab on the fixed longitudinally extending members (hereinafter referred to as "strings") inside the furnace. In practice, the strings are usually water-cooled so that they can maintain their mechanical properties even at temperatures above 1000°C. The contact area where part of the underside of the (hot) slab is in contact with the (cold) strings will be at a lower temperature than the rest of the underside that is not in contact with the strings, and this temperature difference will persist even outside the oven.

[0005] As an example, a "skid mark" extending across the full width of the slab may be approximately 200 mm long, resulting in a local temperature difference of approximately 100°C lower than the rest of the surface, with the average temperature difference in the section concerned ranging from approximately 15°C to approximately 30°C.

[0006] These cold impressions in the slab adversely affect thickness control during the rolling step, compromising the quality of the finished product in terms of both dimensional uniformity and microstructural uniformity. This last requirement is of fundamental importance in some types of steel applications, especially in deep drawing and electrical steel applications.

[0007] In the prior art, some solutions have been proposed in which a radiation thermometer is installed downstream of the last reversing stand to detect skid marks, and one or more heating inductors are installed upstream of the finishing mill to provide additional heating based on the temperature detected by the radiation thermometer in order to compensate for the low thermal energy of the skid marks and to try to make the temperature of the bar uniform.

[0008] However, since the radiation thermometer usually measures the surface temperature of the top surface of the bar, and the skid marks are particularly present on the underside of the bar, the temperature measured by the radiation thermometer is hardly affected by large fluctuations. Therefore, such temperature measurements made according to the prior art may not be able to accurately identify the actual temperature fluctuations along the length of the bar, which may result in partial inefficiency or inaccuracy of the inductor's operation.

[0009] Furthermore, measurements using a radiation thermometer can be affected by the presence of moisture or scale on the surface of the bar, which further impairs the accuracy of the measurement and thus the effectiveness of the subsequent thermal recovery treatment.

[0010] In any case, by its very nature, measurements using a radiation thermometer only measure surface temperature and do not represent the average temperature of the cross section.

[0011] Therefore, to determine the degree of additional heating, it is necessary to estimate the average temperature of the cross section from the surface temperature using a thermal model, but this estimation is not always accurate.

[0012] Therefore, since the rolling force varies depending on the average temperature of the bar, it is clear that this existing technology cannot provide any reliable guarantees as to the magnitude of the average temperature and the behavior of the finishing roll and therefore the thickness control of the final product.

[0013] It is therefore an object of the present invention to provide a hot strip mill plant and to develop a method for producing flat rolled products, which makes it possible to reduce or even eliminate the quality problems caused by skid marks and to effectively equalize the average temperature at the entrance of the bar to the finishing mill.

[0014] Another object of the present invention is to produce thin gauge plates in plants up to 6 million tons per year without adversely affecting production capacity.

[0015] Another object of the present invention is to provide a plant and develop a method for the production of rolled products that allows the mechanical and geometrical properties to be kept uniform over the entire length of the coil produced.

[0016] Applicant has invented, tested and embodied the present invention to overcome the shortcomings of the prior art and to achieve these and other objects and advantages. Summary of the Invention

[0017] The invention is set out and characterized in the independent claims. The dependent claims describe aspects which represent developments and improvements to the independent claims.

[0018] To achieve the above object, the rolling plant according to the invention is adapted to produce steel strip from a slab having a predetermined starting thickness.

[0019] In particular, the plant according to the invention comprises at least one heating furnace, for example a gas-fired furnace, commonly known as a "walking beam", in which the slab rests on fixed uprights and is advanced through the furnace by movable uprights, so that the slab is heated to a predetermined starting temperature, for example in the range of approximately 1150°C to 1280°C.

[0020] Typically, the plant according to the present invention comprises at least one reversing roughing rolling stand configured to perform one or more rolling passes on the heated slab to obtain an intermediate rolled product having a thickness of about 35 mm to about 80 mm.

[0021] According to the invention, the plant also comprises a finishing mill operatively arranged in series with the roughing stand, the finishing mill being configured to reduce the thickness of the intermediate rolled product until a strip having a final thickness of not more than 1.2 mm, or even 0.9 mm, is obtained.

[0022] This plant is therefore configured as a new generation rolling plant compared to conventional hot strip mills, which operate in coil-to-coil mode and obtain the rolled product from a single slab with a thickness of about 150 mm to about 350 mm, and which has all the operational, dimensional and production characteristics required for this type of plant.

[0023] According to the invention, the finishing mill is preferably divided into a pre-finishing machine consisting of at least one pre-finishing stand and a finishing machine consisting of several finishing stands, the pre-finishing machine and the finishing machine always operating in tandem and therefore synchronized with each other.

[0024] The at least one pre-finishing stand is suitable for reducing the thickness of the intermediate rolled product, for example to obtain a pre-finished rolled product having a thickness of between about 10 mm and about 50 mm.

[0025] The finishing stand, on the other hand, is configured to reduce the thickness of the unfinished rolled product to obtain the final strip, for example, with a thickness ranging from approximately 0.9 mm to about 26 mm.

[0026] According to one aspect of the invention, the plant comprises mechanical deformation detection means directly associated with at least the last of said at least one pre-finishing stand and capable of detecting the rolling force exerted on said pre-finish rolled product.

[0027] In accordance with another aspect of the invention, the plant includes a rapid heating device comprising selectively operable elements or modules, the rapid heating device being interposed between the last prefinishing stand and a plurality of finishing stands and configured to heat the prefinish rolled product.

[0028] This heating can be carried out to an exit temperature of the rapid heating device in the range of approximately 1000°C to 1150°C, or in any case, depending on the operating conditions and product parameters, until the temperature of the final strip at the exit of the last finishing stand exceeds at least 830°C, and in some cases even exceeds 900°C.

[0029] Furthermore, in the solution according to the present invention, the plant comprises a command and control unit, which is connected to both the mechanical deformation detection means and the rapid heating device of the final pre-finishing stand, and is configured to selectively operate the rapid heating device in response to at least the rolling force detected by the mechanical deformation detection means to provide localized over-supply or over-heating of heat, thereby increasing the temperature at the skid marks and making the temperature uniform over the entire length of the bar.

[0030] In fact, skid marks are created on the resting surface of the slab on the fixed longitudinal members in the furnace, at geometrically defined intervals, where increasing areas have a lower temperature than the rest of the slab, which increases the deformation resistance of the material and leads to an increase in the rolling force corresponding to the lower temperature areas.

[0031] The value of this load increase is detected by the mechanical deformation detection means and sent to the command control unit, which commands the rapid heating device to locally overheat the aforementioned area, which has a high resistance to deformation (and therefore a low temperature), detected by the mechanical deformation detection means of the last pre-finishing stand, depending on the rolling speed at the exit of the pre-finishing rolled product and taking into account its thickness.

[0032] Applicant has determined that there is a correlation between the average temperature of the bar and the rolling force, and that from measurements of the rolling force, i.e., changes in the applied force, it is possible to derive the average temperature change in a particular portion of the bar.

[0033] An example of this relationship is that an increase in rolling force of approximately 4% compared to the nominal load results in a change in the average temperature of the bar of approximately 20°C.

[0034] From this, knowing the thickness of the prefinished product at the exit from the last prefinishing stand, it is possible to establish the local superheat value that must be actuated by the rapid heating device to homogenize the temperature of the cold impression.

[0035] The solution according to the invention therefore makes it possible to produce flat rolled products by effectively equalizing the average temperature of the bar at the inlet to the finisher, which is beneficial to the dimensional and microstructural quality of the finished rolled product.

[0036] Because the bar exits the pre-finisher at a relatively slow speed of around 0.6-1.5 m / s, accurate and precise tracking of the skid marks along the bar itself is possible through changes in the rolling force of the final pre-finishing stand. The rapid response time of the rapid heating device makes it possible to perform closed-loop adjustments of the inductor to thermally compensate for the cold bands caused by the skid marks, "leveling" the temperature profile and delivering a bar to the finisher at a uniform temperature along its entire length.

[0037] According to a preferred embodiment, the rapid heating device includes both a first heat induction module that can be selectively activated and controlled by the command and control unit in response to the rolling force detected by the mechanical deformation detection means, and a second heat induction module that can be selectively activated and controlled by the command and control unit.

[0038] In particular, the rapid heating device can use the first two or three modules to perform the task of equalizing the temperature delta of the skid marks, while subsequent modules can be dedicated to heating the head of the bar, gradually increasing the power to also heat the body and tail of the bar, so that the bar can exit the final finishing step at a predefined target temperature depending on the rolled product.

[0039] Each module can be enabled or disabled independently of the other modules, and each module can operate at a different power.

[0040] The number of modules in the inductor is 6 to 12, preferably 8 to 10, of which two are first modules and the rest are second modules.

[0041] The nominal power of each module ranges from 3MW to 7MW, but preferably from 4MW to 5MW.

[0042] The overall nominal power of the inductor may be in the range of, for example, 38 MW to 45 MW.

[0043] For example, there are 10 modules, each with a nominal power of 4.3 MW, so the nominal power of the entire inductor is 43 MW.

[0044] Preferably, a heat scanner is provided at least at the exit of the rapid heating device to ensure that the result of the skid mark thermal repair is indeed successful, which also serves to control the cross-sectional thermal profile of the product and the relative overheating of the edges. Overall, heating is preferably carried out to an exit temperature from the rapid heating device of about 1000°C to about 1150°C, or in any case advantageously to a temperature such that the temperature of the final strip leaving the last finishing stand is at least above 830°C, and in some cases above 900°C, depending on the operating and product parameters.

[0045] Due to this preferred embodiment of the solution according to the invention, the steel remains substantially within a single phase field before leaving the final finishing stand and therefore does not undergo phase transformations.

[0046] According to another aspect of the present invention, the continuous finishing mill includes 1 to 3 pre-finishing stands and 5 to 6 finishing stands.

[0047] The invention also relates to a rolling method for producing a final strip in a rolling plant of the type described above, starting from a slab having a specific starting thickness.

[0048] According to one aspect of the invention, the method comprises: at least one detection step of constantly detecting the rolling force applied to the intermediate rolled product by means of a mechanical deformation detection means; At least one heating step of heating the pre-finished rolled product by a rapid heating device; a command step of selectively activating, by a command and control unit, the rapid heating devices in response at least to the rolling force detected by the mechanical deformation detection means to thermally compensate the cooled areas and achieve a uniform temperature along the entire length of the bar; Equipped with.

[0049] According to another aspect of the invention, the rolling plant makes it possible to produce strip with a final thickness of about 0.9 mm to about 26 mm, which strip can be wound onto reels without increasing speed for production up to 3 million tons per year and with moderate increasing speed for production up to 6 million tons per year.

[0050] These and other aspects, features and advantages of the present invention will become apparent from the following description of some embodiments thereof, given by way of non-limiting example with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 1 is a schematic diagram of an embodiment of a new generation HSM plant for producing flat rolled products according to the present invention. [Figure 2] FIG. 2 shows a graph correlating the variation in rolling force used in a particular time segment for a defined segment of pre-finished rolled product. [Figure 3] FIG. 3 is a graph showing the temperature trend and resulting thickness change of a bar affected by skid marks in a known type of HSM. [Figure 4] FIG. 4 is a graph showing trends corresponding to FIG. 3 for a new generation HSM plant for producing flat rolled products according to the present invention. [Figure 5] FIG. 5 is a graph showing the relationship between rolling speed and exit temperature when the same final rolled product is rolled at different tail speeds in a new generation HSM plant for manufacturing flat rolled products according to the present invention, where the rolling speeds of the head, body, and tail are the same. [Figure 6] FIG. 6 is a graph showing the relationship between rolling speed and exit temperature when the same final rolled product is rolled at different tail speeds in a new generation HSM plant for producing flat rolled products according to the present invention. In FIG. 6, the tail is rolled at a slightly faster speed. DETAILED DESCRIPTION OF THE INVENTION

[0052] It must be made clear that the phraseology and terminology used in this specification, as well as the figures of the accompanying drawings, however they may be described, have the sole function of better illustrating and explaining the invention, the scope of protection being defined by the claims, and their purpose is to provide a non-limiting example of the invention itself.

[0053] To facilitate understanding, the figures use the same reference numerals to indicate identical common elements whenever possible, and it will be understood that elements and features of one embodiment may be combined or incorporated into other embodiments as appropriate without further description.

[0054] Referring to Figure 1, this shows a plant 10 according to the invention for producing flat rolled products such as final strip P having a thickness of about 0.9 mm to about 26 mm, which is wound to form a coil starting from a slab 50 having a starting thickness of about 150 mm to about 350 mm.

[0055] The plant 10 includes one or more gas-heated furnaces 16, for example of the type known in the art as "walking beam" furnaces, configured to receive at least one slab 50 (which may be at room temperature) and heat it to a predetermined starting temperature T1. Preferably, the temperature of the slab 50 at the outlet from the gas-heated furnace 16 is in the range of about 1150°C to about 1280°C.

[0056] As is known, in this type of furnace 16, the slab 50 rests on fixed uprights and is moved by movable uprights, not shown in the accompanying drawings, which are water-cooled to prevent deformation or structural failure due to the weight of the slab at heating temperatures.

[0057] As shown diagrammatically in FIG. 2, the underside of the slab 50 has several transverse impressions 50a, called "skid marks," which correspond to the areas where the slab 50 rests on the cooled stringers.

[0058] These impressions 50a are approximately 200 mm long, and their surface temperature is approximately 100°C lower than that of surfaces not in contact with the longitudinal members, and this temperature difference persists outside the furnace. Considering the average temperature of the cross section of the slab 50, the temperature corresponding to the impressions 50a is approximately 15°C to 30°C lower than in areas not affected by skid marks.

[0059] During rolling, this average temperature difference decays and the impact of crushing depending on the slab thickness / bar thickness ratio lengthens the corresponding area affected by skid marks.

[0060] For example, if the initial slab thickness is 200 mm and the thickness when it leaves the final pre-finishing stand is 15 mm, the length of the bar affected by skid marks will be 200 x 200 / 15 = 2667 mm, and the average temperature difference will be reduced to 10-20°C.

[0061] As an example, a warehouse 40 is also part of the plant 10 and is arranged substantially in series upstream of the heated gas furnace 16 and is configured to store slabs 50, for example, delivered from other production sites or other production areas within the same facility. This warehouse 40, which is only shown diagrammatically in Figure 1, allows at least one slab 50 to be selectively fed to the gas furnace 16 according to a desired feeding sequence and timing.

[0062] Arranged downstream of the gas heating furnace 16 are a first water scale remover 20, a vertical or edging pass stand 21, and a reversible roughing mill stand 23, in that order. The reversible roughing mill stand 23 is configured to reduce the thickness of the slab 50 by passing it through the stand a predetermined number of times to obtain an intermediate rolled product 51. In a preferred embodiment, the intermediate rolled product 51 has a thickness of approximately 35 mm to 80 mm. As a guideline, at the end of the desired roughing passes, the average temperature of the intermediate rolled product 51 in areas not affected by the impression 50a is approximately 1000°C to approximately 1150°C.

[0063] In other embodiments, it is not excluded that two roughing stands 23 are provided with corresponding vertical stands 21 .

[0064] According to a further aspect of the invention, at least one reversible roughing stand 23 is equipped with on-board descaling means forming an integral part of the stand itself, said descaling means being located on both the inlet and outlet sides of the stand (not shown).

[0065] Downstream of the reversible roughing stand 23, a second descaling device 24 and a continuous finishing mill 25 are arranged in this order.

[0066] In particular, the continuous finishing mill 25 is composed of two macro rolling units, one pre-finishing unit including two pre-finishing stands 26, and one finishing unit including a number of finishing stands 31 (five in this particular case).

[0067] The continuous finishing mill 25 is configured to reduce the thickness of the intermediate rolled product 51 in stages to obtain a final strip P having a minimum thickness of about 1 mm.

[0068] Although not shown in the drawings, in some embodiments, the plant 10 may also include vertical or edging pass stands 21 both downstream of the reversing roughing mill stands 23 and upstream of the continuous finishing mill 25.

[0069] Typically, the number of pre-finishing stands 26 in the finishing mill 25 will be between 1 and 3, and the number of finishing stands 31 will be between 5 and 6, their number and arrangement being selected depending on the steel grade, the intended use of the finished product, and the minimum and maximum thickness that the final strip P will assume during rolling.

[0070] In the solution according to the invention, two pre-finishing stands 26 are provided apart from the remaining finishing stands 31 of the finishing mill 25, so that a pre-finished rolled product 52 having a thickness of about 10 mm to about 50 mm is discharged from the pre-finishing stands 26.

[0071] Furthermore, the pre-finishing stand 26 is positioned a fixed distance D from the roughing stand 23 so that the intermediate rolled product 51 is not operatively engaged with both types of stand simultaneously.

[0072] In the solution according to the invention, at least one load cell 40, shown only diagrammatically in the accompanying drawings, is associated with the last pre-finishing stand 26, which detects the increase in rolling force caused by the greater resistance to compression of the "colder" impression 50a compared to the rest of the pre-finished rolled product 52.

[0073] It is not excluded to use, instead of the load cell 40, another mechanical deformation detection device suitable for the purpose of continuously detecting the rolling load applied to obtain the pre-finished rolled product 52.

[0074] As illustrated in FIG. 2, each impression 50a corresponds to a corresponding peak "A" in rolling force, which at a temperature approximately 20°C lower corresponds to an approximately 4% increase in the force required to roll compared to the bar section between two consecutive skid marks.

[0075] In the exemplary solution shown in the drawings, a "crop shear" type flying shear 27 is arranged downstream of the pre-finishing stand 26 to trim the head and tail of the pre-finished rolled product 52 to facilitate its entry into the finishing stand 31 and reduce the possibility of failure, especially when producing final strip with a thickness of less than 3.0 mm.

[0076] The plant 10 according to the invention further comprises a rapid heating device 28 arranged between the pre-finishing stand 26 and the finishing stand 31 of the continuous rolling mill 25 .

[0077] The rapid heating device 28 is configured to selectively and adjustably heat the pre-finished rolled product 52 before it enters the finishing stand 31 .

[0078] Preferably, rapid heating device 28 comprises an induction furnace, for example, made up of heat induction modules that can be selectively activated independently of each other.

[0079] In particular, the rapid heating device 28 comprises two first heat induction modules 41 arranged immediately downstream of the flying shear 27 and, in this particular case, five second heat induction modules 42. The first and second heat induction modules 41 and 42 are preferably of the cross-flow type, so as to act on the entire cross section of the pre-finished rolled product 52.

[0080] Furthermore, the plant 10 according to the present invention is provided with a command and control unit 44 connected to both the load cell 40 associated with the last stand 26 of the pre-finishing unit and the rapid heating device 28, which allows selective and individual control of both the driving force and the heating intensity applied to the cold impression 50a.

[0081] Because the bar exiting the pre-finishing machine travels at a relatively slow speed of 0.6 to 1.5 m / s, it is possible to accurately and precisely track the bar's own skid marks through changes in the rolling force of the final pre-finishing stand. The rapid response time (reactivity) of the rapid heating device 28 allows for closed-loop adjustment of the inductor to thermally compensate for the cold bands caused by the skid marks, uniformizing the temperature profile and supplying a pre-finished rolled product 52 with a uniform temperature throughout its entire length to the finishing stand 31.

[0082] In particular, the first heat induction module 41 is selectively controlled to provide localized heating corresponding to the impression 50a, substantially "leveling out" the surface temperature of the impression 50a, while the second heat induction module 42 is selectively controlled to raise the overall temperature of the pre-finished rolled product 52, distinguishing between the head, body, and tail, to achieve a consistent target temperature along the entire length of the product 52 at the exit from the rapid heating device 28.

[0083] Preferably, to ensure that the results of the skid mark thermal repair are indeed successful, a heat scanner 45 is provided at the exit of the rapid heating device 28, which also serves to control the lateral heat profile of the product 52 and the relative overheating of the edges.

[0084] By way of example, the temperature to which the pre-finished rolled product 52 is heated, ie, the temperature it will assume upon exiting the rapid heating device 28, preferably reaches a value in the range of about 1000°C to about 1150°C.

[0085] As a result, the rolling mass flow rate MF required to obtain the aforementioned optimum temperature of at least 830°C (for example, 830°C to 920°C) at the exit of the final finishing stand 31 is L The value of can be reduced.

[0086] Preferably, a third water descaling device 29 is also located downstream of the rapid heating device 28 and upstream of the finishing stand 31, and has the function of further removing scale from the surface of the pre-finished rolled product before it enters the finishing stand 31.

[0087] Therefore, scale formed on the surface of the pre-finished rolled product 52 is effectively removed, and quality defects of the rolled strip P, such as scale inclusion, are prevented.

[0088] For purposes of example only, in the illustrated embodiment of the plant 10, downstream of the finishing stand 31 is located a cooling device 33 including a plurality of showers 34 that can be selectively activated independently of one another to cool the strip P.

[0089] Furthermore, two take-up reels 36, 38 are arranged at the exit of the shower 34 for coiling the strip P for subsequent storage and shipping.

[0090] The solution of the present invention allows optimal control of thickness during finish rolling by selectively overheating the cold band of the intermediate bar detected through the change in rolling force in the final pre-finishing stand, by homogenizing the average temperature of the pre-finishing rolled product 52, and by closed-loop adjustment of modules 41 and 42 of the rapid heating device 28, which increases the overall temperature of the pre-finishing rolled product 52, and ensures that the exit temperature from the last finishing stand is at least 830°C.

[0091] The present invention also relates to a method for producing a strip P that is wound to form a coil, starting from a slab 50 having a starting thickness in the range of about 150 mm to about 350 mm.

[0092] The method provides for heating at least one slab 50 to a temperature of 1150 to 1280° C. in a gas-heated furnace 16 and then feeding the slab 50 toward a first descaling device 20 .

[0093] The slab 50 is then conveyed to the edging pass stand 21 and then to the reversing roughing stand 23 where it is reduced in thickness through multiple rolling passes to obtain an intermediate rolled product 51 having a thickness in the range of about 35 mm to about 80 mm. Preferably, the number of rolling passes performed in the reversing roughing stand 23 is five or less.

[0094] Next, the intermediate rolled product 51 is transported to the second descaling device 24 where surface scales are removed, and then moved towards the continuous rolling mill 25.

[0095] Next, the intermediate rolled product 51 enters the pre-finishing stand 26, where the thickness of the intermediate rolled product 51 is further reduced to define a pre-finishing rolled product 52 having a thickness of about 10 mm to about 50 mm.

[0096] In this step, the load cell 40 associated with the last pre-finishing stand 26 detects the change in rolling force applied by the pre-finishing stand 26 to the pre-finished rolled product 52 due to the cold impression 50a created upstream by the slab 50 contacting the longitudinal members of the gas furnace 16, as described above.

[0097] Measurements made by the load cell 40 of the last pre-finishing stand 26 accurately detect the trend in the rolling force and thereby the position of skid marks along the pre-finished rolled product 52, and this measurement is sent to a command control unit 44 which commands a constant superheat to the first module 41 in response to the detected impressions 50a, thereby equalizing the temperature difference and equalizing the average temperature of the pre-finished rolled product 52 fed to the finishing stand 31.

[0098] Upstream of the rapid heating device 28 , the pre-finished rolled product 52 is subjected to a thermal scan by a thermal scanner 43 suitable for performing a complete thermal scan of the section of the pre-finished rolled product 52 entering the device 28 .

[0099] This scanning allows the temperature of the pre-finished rolled product 52 to be determined over substantially its entire length, taking into account its complete cross section, and transmits the actual temperature conditions of the product 52 itself to the command and control unit 44, which in turn commands the second module 42 to define the extent of heating to be applied over the entire pre-finished rolled product 52 and to make its temperature uniform.

[0100] Downstream of the rapid heating device 28, the pre-finished rolled product 52 is again thermally scanned by the thermal scanner 45 to inspect the longitudinal and transverse temperature profiles at the exit. The transverse temperature profile can be altered by adjusting the position of the individual rapid heating modules 28.

[0101] The thermal uniformity achieved by the rapid heating device 28 allows a thermally uniform product 52 to be supplied to the finishing stand 31, preferably at a value of about 1000°C to about 1150°C, while at the same time maintaining the rolling mass flow MF required to obtain the aforementioned optimum temperature of at least 830°C (e.g., 830°C to 920°C) at the exit of the final finishing stand. L The value of can be reduced.

[0102] To better clarify the product characteristics and advantages resulting from the solution of the present invention, attention is drawn to a comparison of the graphical representations in FIGS.

[0103] FIG. 3 shows a conventional HSM plant having a roughing stand 92 and a finishing mill 94 with finishing stands substantially adjacent to one another, downstream of which is a cooling system 96 for producing the final strip P.

[0104] As disclosed in the prior art, in conventional HSM plants, temperature control of the bar leaving the roughing stand 92 is performed by a high temperature detector 93, all of whose drawbacks have already been explained.

[0105] When a control scan of the final strip P leaving the finishing mill 94 is carried out, a temperature-related curve B1 and a thickness-related curve C1 associated with a segment of the strip P are obtained.

[0106] As can be seen, despite several thermal measurements being taken by the high temperature detector 93, there are peaks and valleys with significant differences in both the temperature trend and the thickness trend over the length of the finished strip P, particularly corresponding to the impressions 50a caused by the skid marks, which ultimately impairs the quality of the produced strip P.

[0107] Instead, in the solution of the plant 10 according to the invention, the same control scan of the final strip P at the exit of the finishing mill 25 results in a curve B for temperature and a curve C for thickness relating to the same segment of the strip P.

[0108] For the sake of clarity, the curves B and C drawn by scanning a strip P produced in a plant 10 according to the invention are shown superimposed on the respective curves B1 and C1 obtained in the conventional plant described above.

[0109] It can be seen that the trends of the curves are more consistent, both in terms of temperature and thickness, which has the advantage of improving the thermal and dimensional uniformity of the final strip P. This uniformity improves the quality of the final strip P obtained with the plant 10 according to the invention.

[0110] Rolling mass flow rate MF L By reducing the rolling speed V, preferably less than 12 m / s L At the same time, the tail of the final strip P can also reach an optimum temperature of at least 830°C at the exit of the continuous rolling mill 25, eliminating the need for "speed-up" as a tool to reach the target temperature. An example of such an embodiment is shown in Figure 5.

[0111] In some embodiments, increased speed may be required to improve line productivity when producing films of very thin thickness, or to achieve very high productivity when producing films of other thicknesses, an example of such an embodiment is shown schematically in Figure 6.

[0112] It will be apparent that modifications and / or additions of components or steps may be made to the plant 10 and method for producing flat rolled products described above without departing from the field and scope of the present invention as defined in the claims.

[0113] Although the present invention has been described with reference to some particular examples, it is clear to those skilled in the art that other equivalent methods and plants 10 for producing flat rolled products can be realized which have the characteristics set out in the claims and which therefore all fall within the field of protection defined by the claims.

[0114] In the following claims, references in parentheses are for the purpose of readability only and should not be considered as limiting factors with regard to the field of protection defined by the claims.

Claims

1. A rolling plant (10) for producing a final strip (P) from a slab (50) having a predetermined starting thickness, comprising: at least one walking beam furnace (16) configured to heat at least said slab (50) to a predetermined temperature; a finishing mill (25) operatively arranged in series with at least one roughing stand (23) and configured to reduce the thickness of the intermediate rolled product (51) until the final strip (P) is obtained at the outlet from the roughing stand (23), the finishing mill (25) including at least one pre-finishing stand (26) capable of further reducing the thickness of the intermediate rolled product (51) to obtain a pre-finished rolled product (52); a plurality of finishing stands (31) capable of further reducing the thickness of said pre-finished rolled product (52) to obtain said final strip (P); A plant (10) comprising: The plant (10) further comprises: a mechanical deformation detection means (40) directly associated with at least the last of said at least one pre-finishing stand (26) and capable of detecting the rolling force applied to said pre-finish rolled product (52); a rapid heating device (28) interposed between the at least one pre-finishing stand (26) and the plurality of finishing stands (31) for heating the pre-finished rolled product (52); a command and control unit (44) connected to both the mechanical deformation detection means (40) and the rapid heating device (28), and configured to selectively activate the rapid heating device (28) in response at least to the rolling force detected by the mechanical deformation detection means (40) to thermally compensate the cooled area and achieve a uniform temperature along the entire length of the bar; A plant (10) comprising:

2. The rapid heating device (28) comprises a first heat induction module (41) that can be selectively activated and controlled by the command and control unit (44) in response to the rolling force detected by the mechanical deformation detection means (40).

2. The plant (10) according to claim 1 .

3. The rapid heating device (28) comprises a second heat induction module (42) selectively operable and controllable by the command and control unit (44) according to a predetermined target temperature of the intermediate rolled product (52) to be obtained at the outlet from the rapid heating device (28).

3. A plant (10) according to claim 1 or 2.

4. The first heat induction module (41) and the second heat induction module (42) are of a cross-flow type. A plant (10) according to any one of claims 1 to 3.

5. and a thermal scanning means (45) arranged at the outlet from said rapid heating device (28) and configured for transverse thermal detection of said pre-finished rolled product (52). A plant (10) according to any one of claims 1 to 4.

6. a first thermal scanning means (43) arranged upstream of the rapid heating device (28) and configured to thermally scan the pre-finished rolled product (52); A plant (10) according to any one of claims 1 to 5.

7. A rolling method for producing a final strip (P) from a slab (50) having a predetermined starting thickness in a rolling plant (10), comprising: The rolling plant (10) comprises: at least one walking beam furnace (16) configured to heat at least said slab (50) to a predetermined starting temperature; a finishing mill (25) operatively arranged in series with at least one roughing stand (23) and configured to reduce the thickness of the intermediate rolled product (51) until the final strip (P) is obtained at the outlet from the roughing stand (23), the finishing mill (25) including at least one pre-finishing stand (26) capable of further reducing the thickness of the intermediate rolled product (51) to obtain a pre-finished rolled product (52); a plurality of finishing stands (31) capable of further reducing the thickness of said pre-finished rolled product (52) to obtain said final strip (P); Equipped with The method comprises: at least one detection step in which a rolling force applied to said pre-finishing rolled product (52) is detected by a mechanical deformation detection means (40) directly associated with the last stand of said at least one pre-finishing stand (26); at least one heating step in which the pre-finish rolled product (52) is heated by a rapid heating device (28) disposed between the at least one pre-finishing stand (26) and the plurality of finishing stands (31); a command step of selectively operating the rapid heating device (28) by a command and control unit (44) connected to both the mechanical deformation detection means (40) and the rapid heating device (28) in response to at least the rolling force detected by the mechanical deformation detection means (40) to thermally compensate the cooled area and achieve a uniform temperature over the entire length of the bar; A method comprising:

8. The mechanical deformation detection means (40) detects one or more impressions (50a) of the pre-finish rolled product (52), and in response to the one or more impressions (50a), the material's resistance to deformation increases, and the rolling force applied by the pre-finishing stand (26) increases.

8. The method of claim 7.

9. In the rapid heating step, The first heat induction module (41) of the rapid heating device (28) is selectively activated by the command and control unit (44) in response to at least an increase in the material's resistance to deformation with increasing rolling force to increase the temperature of the impression (50a) and to uniform the temperature over the entire length of the pre-finished rolled product (52).

9. The method of claim 8.

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