Plant and method for producing rolled strip products

Abstract

A rolling plant (10) and method for producing a final strip (P) starting from a slab (50) having a predetermined initial thickness comprises at least one heating furnace (16) configured to heat at least one said slab (50) to a predetermined initial temperature, at least one reversible roughing stand (23) configured to subject said slab (50) to one or more rolling passes to obtain an intermediate rolled product (51), and a continuous rolling mill train (25) arranged in operative alignment with said at least one roughing stand (23) and configured to reduce the thickness of said intermediate rolled product (51) until said final strip (P) having a predetermined final thickness is obtained.

Description

[Technical Field]

[0001] The present invention relates to a plant and method for producing flat rolled products, such as, but not limited to, reeled or coiled steel strip. [Background technology]

[0002] It is known that rolling plants known as Hot Strip Mills, or more simply identified by the abbreviation "HSM", are designed for the hot production of metal strip from slabs typically having a thickness of from about 150 millimeters to about 350 millimeters.

[0003] Two examples of such plants are shown diagrammatically in Figures 1 and 2.

[0004] These plants include a "walking beam" gas-heated furnace 91 in which the slabs are heated, and one or two roughing stands 92, usually arranged reversibly. If they include a single roughing stand 92 (see Figure 1), this stand typically performs five to seven rolling passes, while if they include two roughing stands 92 (see Figure 2), the first typically performs three passes and the second a further three to five passes to obtain intermediate bars with thicknesses comprised between 35 and 45 millimeters.

[0005] Downstream of the reversible stands 92, there is provided a transfer table with, for example, a passive insulating hood 99 (see FIG. 2), i.e., without a heating burner, to limit heat loss from the intermediate bars, or a coil box 93 (see FIG. 1) in which the intermediate bars can be wound and unwound.

[0006] Downstream of the transfer table, or coil box 93, is a compact rolling or finishing train 94 having six or seven finishing stands, a cooling shower 96, and an exit table 95 (also called a run-out table) equipped with two or more take-up reels 98 (downcoilers) that take up the finished strip to form reels or coils.

[0007] To ensure that the rolling in the finisher train 94 occurs in the austenitic field, i.e., no phase transformation occurs in the structure of the steel, the strip must leave the last stand of the finisher train 94 at a temperature of no less than 830°C.

[0008] Therefore, the rolling mass flow in the finisher train 94 must be set to obtain said optimum temperature of at least 830°C at the exit of the final finishing stand.

[0009] It is also known that the rolling mass flow is calculated as the product of the thickness of the strip and its rolling speed. Thus, once a predetermined rolling mass flow is set, the rolling speed of the strip is determined solely by the final thickness of the strip.

[0010] A first drawback of known HSM plants is that the heating of thick or conventional slabs with an initial thickness comprised between 150 and 350 mm occurs in a heating furnace using gas burners that raise the temperature of the product up to about 1250°C. As we have said, this temperature is necessary so that the strip leaves the final rolling stand at a temperature of at least 830°C, taking into account all the temperature losses on said line.

[0011] However, the slab heating operation takes a long time, comprised between 4 and 7 hours for example, and requires very high gas consumption by the burners, which impacts environmental emissions and production costs.

[0012] Furthermore, when heating specific steels, the thermal targets can be even higher, further increasing both environmental emissions and production costs. It should also be noted that differentiating heating depending on the type of steel and the required final quality requires waiting for the furnace to heat correctly to the desired higher or lower temperature, limiting production flexibility given the need to organize production to heat thermally similar products to optimize the time required to reach the furnace target temperature. This leads to longer delivery times for finished products and increasingly demands for small batch production.

[0013] Another drawback of known HSM plants is the need to limit the maximum speed of the strip exiting the finishing train to prevent the head of the strip from dangerously rising due to aerodynamic effects of speed on its path from the last stand on the take-up reel 98. Typically, the maximum speed allowed for the head of the strip on the run-out table is about 11 to 12 meters / second, and this speed can be increased after winding on the take-up reel has begun.

[0014] By the head of the strip we normally mean the front end of the strip which, in the direction of travel, contacts the first stand of the finishing rolling line.

[0015] Similarly, by tail of the strip we mean the rear end of the strip which is the last to enter the first stand of the finishing rolling line in the direction of travel.

[0016] The portion of the strip contained between the head and tail is referred to as the body of the strip.

[0017] Due to such speed limitations, it may occur that the optimum temperature of at least 830°C cannot be reached at the exit of the finishing stand, particularly in the case of thin strips having a thickness of, for example, 1.2 millimeters or less.

[0018] To prevent this from happening, in known plants, a so-called "acceleration" of each stand of the finisher train 94 is carried out after the head enters the take-up reel 98, thereby making the strip travel faster and thus reducing losses in temperature, thereby allowing the body and tail of the strip leaving the finisher train 94 to be at an optimum temperature of no less than 830°C.

[0019] In practice, this "acceleration" consists in increasing the rotational speed of the rolls of each stand of the finisher train 94, so that, after the head of the strip has been wound onto the take-up reel 98, the rolling speed of the strip is increased to a speed at which a sufficient rolling mass flow can be obtained to obtain said optimum temperature at the exit of the finisher train 94. This speed increase is on average 40% / 50%, but in some cases can reach 100%.

[0020] Thus, performing acceleration means that the head portion of the strip is rolled at a first speed (e.g., 12 meters / second), while the body and tail portions of the strip are rolled at a second speed (e.g., 17 meters / second to 18 meters / second) that is higher than the first speed.

[0021] If this type of solution is applied, for example, to the production of rolled products with a final thickness of 1.2 mm, and the only active heat input coincides with the furnace upstream of the line, as shown diagrammatically in Figure 3, the speed of the tail section would need to be increased by approximately 40% to ensure a minimum temperature of 830°C at the exit from the last stand.

[0022] However, in conventional HSM plants, if you want to obtain a rolled product with a thickness of less than 1.2 mm, even if you increase the speed by 60% to the usual limit speed of 19 to 20 meters per second, it is still not possible to guarantee that the desired minimum temperature of 830°C will be maintained at the exit of the last stand, as the temperature loss in the rolled product will be too great, resulting in undesirable phase transformations in the steel and affecting the quality of the final product.

[0023] As shown schematically in the graph of Figure 4, with a conventional HSM plant and the acceleration limitations mentioned above, to produce a strip with a thickness of 1.0 millimeter, the exit temperature from the final rolling stand is approximately 780°C, which makes high-quality production of strip of such a limited thickness virtually impossible.

[0024] Another drawback of known HSM plants relates to the non-optimal arrangement of the head-tail trimming shears and descaling units, which are arranged upstream of the finisher train and which usually consist of six or seven compact stands.

[0025] In fact, the intermediate product leaving one or more reversing roughing stands is head-trimmed by shears to reduce entry problems, however the thickness of the intermediate product is still quite high, comprised between 35 and 45 millimeters, and therefore the trimming density is quite high, with a negative impact on the plant yield.

[0026] Furthermore, the shears must have large dimensions and capacity to allow accurate execution of the cuts and generally have a curved imprint with a convex shape in the feed direction to facilitate the subsequent entry of the head.

[0027] Once the cut is made, the head begins to undergo various rolling passes (typically seven finishing passes), gradually undergoing increasing deformation that can create irregularly shaped head "tongues" that can cause previous passes in the finishing machine or cause failed entries in the take-up reel, resulting in lumps and stalls in the rolling mill.

[0028] As the HSM plant operates in coil-to-coil mode, there are approximately 20 entries into each stand per hour, increasing head deformation and the likelihood of cobble formation, which can result in production stoppages and increased production costs.

[0029] Finally, in known HSM plants, a final step of descaling the intermediate product occurs before it enters the finisher train.

[0030] Considering that descaling results in a decrease in product temperature, performing it upstream in a compact multi-stand finishing train carries the risk that the desired minimum temperature of 830°C will not be met at the exit from the last rolling stand, especially at low thicknesses.

[0031] Therefore, to avoid this problem, it is known to provide an additional heat rise by means of an upstream gas-heated furnace, which further exacerbates the drawbacks already mentioned.

[0032] To overcome these limitations, a solution has been proposed in which induction heating is performed just before the compact finisher train so that the bar enters at a higher temperature; however, since this heating is performed before the first stand, which is the slowest, more scale is formed due to the higher temperature, whereas the bar rolled in the first stand is exposed to the atmosphere for a similar period of time.

[0033] One latter solution is known, for example, from EP 0 919 296 A1, in which a transfer table is produced which has an immersion furnace.

[0034] Furthermore, compact finisher trains in conventional HSM plants do not allow for additional high pressure descaling steps to be performed within the compact finisher train.

[0035] This means that, since it cannot be removed, scale formed by exposing the bar rolled in the first stand to the high temperature atmosphere will be imprinted into the strip in the final pass, resulting in a lower quality finished product.

[0036] Time-accurate heating solutions between successive finishing stands of a single compact rolling mill are also known, such as the examples described in DE 102011004245 A1 or WO 2012 / 080368.

[0037] However, these solutions, on the one hand, keep the rolling mill train compact in order to perform time-accurate operations between one rolling stand and its successor, and, on the other hand, apply to plants for thin slabs. In the latter plants, rolling starts immediately on the casting line, and the thermal and dimensional parameters include slabs with an initial thickness of about 110 mm to about 140 mm, a starting temperature of about 1130°C to about 1200°C, and a final temperature of 830°C, which is even lower.

[0038] Therefore, this technology does not appear to be applicable for effective application in plants designed to run coil-to-coil, starting from conventional slabs, as mentioned above, having thicknesses of about 150 millimeters to about 350 millimeters and starting temperatures between 1250°C and about 1200°C.

[0039] Therefore, one object of the present invention is to provide a hot rolling mill and a manufacturing method for flat rolled products that can produce high-quality strip with thicknesses of 1.8 mm or less, with minimum thicknesses ranging from 0.9 mm to 1.2 mm. Quality must be understood in terms of both the surface quality of the strip and the final mechanical properties required by the market.

[0040] Another object of the present invention is to produce thin gauge steel plates without adversely affecting the productivity of the plant, which may reach more than 6 million tons per year.

[0041] Another object of the invention is to provide a hot rolling mill plant which allows easy entry of the strip into the finishing stands and limits the risk of kobbles in the rolling stands and improper winding on the reels.

[0042] Another object of the present invention is to provide a hot rolling mill plant and a method for producing a rolled product in which the mechanical and geometrical properties are uniform throughout the length of the coil produced.

[0043] Another object of the present invention is to provide a plant for producing flat rolled products which has low manufacturing costs and is equipped with shears of small dimensions.

[0044] Applicant has invented, tested and embodied the present invention to overcome the shortcomings of the prior art and to obtain these and other objects and advantages. Summary of the Invention

[0045] The invention is set out and characterized in the independent claims, while the dependent claims describe other features of the invention or variations of the main inventive idea.

[0046] In accordance with the above-mentioned objects, the present invention provides a rolling plant for producing steel strip starting from slabs having a predetermined initial thickness, comprising at least one heating furnace configured to heat at least one of the slabs to a predetermined initial temperature, for example comprised between about 1100°C-1150°C and 1200°C, at least one reversible roughing stand configured to subject the slab to one or more rolling passes in order to obtain an intermediate rolled product having a thickness, for example comprised between about 45 millimeters and about 80 millimeters, and a rolling mill train arranged in operative alignment with the at least one roughing stand and configured to reduce the thickness of the intermediate rolled product until a final strip having a final thickness of less than 1.2 millimeters is obtained.

[0047] Said plant is therefore a new generation rolling plant operating in coil-to-coil mode, with all the operational, dimensional and production characteristics required for a plant of this type, said rolled product being obtained, for example, from a single slab with a thickness ranging from about 150 mm to about 350 mm.

[0048] According to one aspect of the invention, the finishing mill train is divided into at least one pre-finishing stand and a plurality of finishing stands.

[0049] In particular, the at least one pre-finishing stand is advantageously arranged at a minimum distance from the roughing stand so that the intermediate rolled product does not operatively abut both of the stands simultaneously, and the at least one pre-finishing stand is further capable of reducing the thickness of the intermediate rolled product to obtain a pre-finished rolled product having a thickness comprised between about 10 millimeters and about 50 millimeters, for example.

[0050] Meanwhile, the plurality of finishing stands are configured to reduce the thickness of the pre-finished rolled product so as to obtain the final strip having a thickness comprised between about 0.9 millimeters and about 26 millimeters, for example.

[0051] According to another aspect of the invention, a selectively activatable multi-element induction heating device is interposed between the at least one pre-finishing stand and the plurality of finishing stands to heat the pre-finished rolled product.

[0052] This heating is advantageously carried out until the outlet temperature from the induction heating device is comprised between about 1000°C and about 1100°C, or any time when, also as a function of the operating and product parameters, the temperature of the final strip at the outlet from the finishing stand exceeds at least 830°C.

[0053] The action of the induction heater therefore has a thermal capacity to bring the pre-finish rolled product to a temperature close to the starting temperature of the slab, i.e., a temperature rise of the order of several hundred degrees Celsius.

[0054] An advantageous aspect of the solution according to the invention allows the steel to remain substantially in the austenitic field and therefore undergo no phase transformation before leaving the final finishing stand.

[0055] The plant according to the invention is therefore of the hot rolling mill type, capable of producing high quality flat rolled products at thicknesses of less than 1.8 mm and down to minimum values ​​of 0.9 mm to 1.2 mm, reaching a maximum of 6 million tons / year, without adversely affecting the productivity of the plant.

[0056] According to another aspect of the invention, since the HSM plant does not provide an upstream connection to a succession of rolling mills, said plant comprises at least one warehouse configured to store slabs coming from other manufacturing plants or from other areas of the same plant.

[0057] According to another aspect of the invention, the continuous rolling mill train includes one to three pre-finishing stands and five to six finishing stands.

[0058] According to another aspect of the invention, the plant comprises at least a first descaling means interposed between the heating furnace and the at least one roughing roll stand, a second descaling means, advantageously of the reversible type, interposed between the reversible roughing roll stand and the first of the pre-finishing stands, and a third descaling means, advantageously interposed between the induction heating device and the first of the finishing stands.

[0059] According to another aspect of the invention, the at least one reversible roughing stand is equipped with descaling means located on both the inlet and outlet sides of the stand, the descaling means being mounted on boards and being an integral part of the stand itself.

[0060] According to another aspect of the invention, the plant includes a shearing machine interposed between the pre-finishing stand and the induction heating device for trimming the head and tail of the pre-finished rolled product. As previously mentioned, in this segment of the plant, the thickness of the pre-finished rolled product is already thin enough to be accommodated by a small shearing machine, such as a type known as a crop shear, which reduces production and management costs compared to a conventional shearing machine located upstream of the entire train of finisher rolls.

[0061] The invention also relates to a rolling method for producing a final strip in a rolling plant of the above-mentioned type, starting from a slab having a given initial thickness.

[0062] According to one aspect of the invention, the method provides for pre-finishing rolling of at least one of the intermediate rolled products by means of at least one advantageously reversible pre-finishing stand of the rolling mill train, arranged at a minimum distance from the roughing stand, to reduce the thickness of the intermediate rolled product and obtain a pre-finished rolled product.

[0063] Furthermore, also according to the invention, the method provides for finish rolling of at least one of the pre-finish rolled products by means of a plurality of finishing stands to reduce the thickness of the pre-finish rolled product and obtain the strip having the desired final thickness.

[0064] Furthermore, the method according to the invention provides at least one step of heating the pre-finish rolled product by means of an induction heating device consisting of a plurality of selectively activatable elements and interposed between the at least one pre-finishing stand and the plurality of finishing stands, so that the temperature of the final strip corresponding to the outlet of the final finishing stand is at least higher than 830°C, even in the case of thin thicknesses.

[0065] Advantageously, thanks to the presence of the induction heating device as described above, which allows additional active heat input to the pre-finished product, the slabs can be removed from the gas-heated furnace at a temperature below 1200°C, and therefore the residence time of the slabs in the gas-heated furnace is shorter than that provided in known plants. This advantageously reduces the occurrence of scale by 25% to 30%, thus reducing the loss of scale material by 25% to 30%, and improving the yield of the furnace itself.

[0066] The installation of the induction heater between the pre-finishing stand and the final stand also alleviates some of the heat imparted to the slab from the gas-fired furnace, thus making it possible to reduce gas consumption and emissions. Furthermore, the supplemental heat power of the induction heater is supplied only in the amount necessary and sufficient, closer to the final stand of the successive rolling mills, rather than being supplied too early to the gas furnace to compensate for temperature losses along the line, as occurs in conventional hot rolling mills.

[0067] Furthermore, the induction heating device allows the heating of the product to be completed to the optimum target value according to the type of steel within a short time, and therefore is not restricted by the thermal inertia of the gas furnace.

[0068] The induction heating device is, for example, an inductor with modular elements (or modules) that can be extracted completely or partially in several individual elements from the rolling line automatically or manually.

[0069] Each module can be activated or deactivated independently of the other modules, and each module can operate at a different power.

[0070] The number of modules of the inductor is comprised between 6 and 12, preferably between 8 and 10.

[0071] Each module has a rated power comprised between 3 and 7 megawatts, preferably comprised between 4 and 5 megawatts.

[0072] The total power rating of the inductor is comprised between 38 megawatts and 45 megawatts.

[0073] According to one exemplary embodiment, the number of modules is equal to 10, where each module has a rated power of 4.3 megawatts, and therefore the overall rated power of the inductor is 43 megawatts.

[0074] According to one aspect of the invention, the activation of the individual modules and the delivery of available power are managed by a control system as a function of the heat input required to ensure that the head and tail of each rolled product leaving the final finishing pass are at a temperature of at least 830°C for all workable thicknesses.

[0075] In particular, the power delivered depends primarily on the thickness and final width of the strip to be produced.

[0076] In some embodiments, temperature measurement, preferably an infrared system, is provided before the last two induction modules so that they can measure the temperature deficit of the pre-finished product, and therefore they are not manufactured to operate at full power like the previous modules, but are switched off or started at reduced power (they have a trimming function) so that there is enough headroom to integrate the heat deficit before the product enters the finishing stand.

[0077] An advantage of the solution according to the invention is that the number of rolling passes that a slab undergoes in a reversing rolling stand may not exceed five.

[0078] According to another aspect of the invention, a rolling plant is provided for producing strip wound on reels with a final thickness comprised between about 0.9 mm and about 26 mm for a production of up to 3 million tons per year without acceleration and up to 5 million tons per year with standard acceleration.

[0079] These and other aspects, features and advantages of the present invention will become apparent from the following description of some embodiments, given by way of non-limiting example with reference to the accompanying drawings. [Brief explanation of the drawings]

[0080] [Figure 1] 1 is a schematic diagram of an HSM plant of a type in accordance with the prior art for producing flat rolled products; [Figure 2] 1 is a schematic diagram of an HSM plant of a type in accordance with the prior art for producing flat rolled products; [Figure 3] FIG. 1 is a diagram illustrating the relationship between rolling speed and exit temperature for rolled products having different thicknesses according to the prior art. [Figure 4] FIG. 1 is a diagram showing the relationship between rolling speed and exit temperature for rolled products with different thicknesses according to the prior art. [Figure 5] FIG. 1 shows an embodiment of a new generation HSM plant for producing flat rolled products according to the present invention. [Figure 6] 1 is a diagram relating the final thickness of the flat rolled product and the required rolling speed for a defined mass flow. [Figure 7] FIG. 1 shows the relationship between rolling speed and exit temperature for rolled products of different thicknesses in a new generation HSM plant for producing flat rolled products according to the present invention. [Figure 8] FIG. 1 shows the relationship between rolling speed and exit temperature for rolled products of different thicknesses in a new generation HSM plant for producing flat rolled products according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0081] It must be made clear that the phraseology and terms used in this specification, as well as the symbols in the accompanying drawings, have the sole function of better illustrating and explaining the invention, the scope of protection of which is defined by the claims, and that their function is to provide a non-limiting example of the invention itself.

[0082] For ease of understanding, the same reference numerals have been used wherever possible to identify identical common elements in the drawings, it being understood that elements and features of one embodiment may be conveniently combined or incorporated in other embodiments without further description.

[0083] Referring to FIG. 5, this shows a plant 10 according to the invention for producing flat-rolled products, such as final strip P, starting from a slab 50 having an initial thickness comprised between about 150 mm and about 350 mm, which is wound to form a reel or coil and has a thickness comprised between about 0.9 mm and about 26 mm.

[0084] The plant 10 comprises one or more gas-heated furnaces 16, of the type known in the industry by the term "walking beam", configured to receive at least one slab 50, for example supplied at ambient temperature, and to heat it to a predetermined starting temperature T1. Advantageously, at the outlet from the gas-heated furnace 16, the slab 50 has a temperature comprised between about 1100°C-1150°C and about 1200°C.

[0085] A warehouse 40 is also part of the plant 10 and is located approximately in line with and upstream from the gas-fired furnace 16 and is configured to store slabs 50 coming from, for example, other production locations or other production areas within the same plant. The warehouse 40, which is only shown diagrammatically in Figure 3, allows the selective feeding of at least one slab 50 to the gas-fired furnace 16 according to a desired feeding sequence and timing.

[0086] Downstream of the gas-fired furnace 16 are arranged, in sequence, a first water scale remover 20, a vertical or edging stand 21, and a reversible roughing stand 23, which are configured to subject the slab 50 to a number of passes to reduce its thickness until an intermediate rolled product 51 is obtained. In a more advantageous embodiment, the intermediate rolled product 51 has a thickness comprised between about 45 millimeters and about 80 millimeters. By way of example only, at the end of the desired plurality of rough rolling passes, the intermediate rolled product 51 has a temperature having a range of about 1020°C to about 1120°C.

[0087] In other embodiments, it is not excluded that two roughing stands 23 each with a corresponding vertical stand 21 may be provided.

[0088] According to another aspect of the invention, at least one reversible roughing stand 23 is equipped with descaling means (not shown) mounted on a board and forming an integral part of the stand itself, the descaling means being located both on the inlet side and on the outlet side of the stand.

[0089] Downstream of the reversible roughing stand 23 there is arranged in sequence a second descaling unit 24 and a continuous rolling mill train 25 .

[0090] In particular, the continuous rolling mill train 25 consists of two macro rolling units, a pre-finishing unit including two pre-finishing stands 26, and a finishing unit including a number of finishing stands 31 (five in this particular case).

[0091] The continuous rolling mill train 25 is configured to gradually reduce the thickness of the intermediate rolled product 51 to obtain a final strip P having a minimum thickness of about 1 mm.

[0092] In some embodiments, although not shown, the plant 10 may also include vertical or edging stands 21 both downstream of the reversing roughing stands 23 and upstream of the continuous rolling mill train 25.

[0093] Generally, the number of pre-finishing stands 26 in the rolling mill train 25 is comprised between one and three, and the number of finishing stands 31 is comprised between five and six, and their number and arrangement are selected as a function of the steel grade, the application of the finished product, and the minimum and maximum thickness of the final strip P envisaged during rolling.

[0094] In the solution according to the invention, two pre-finishing stands 26 are provided that are spaced apart from the remaining finishing stands 31 of the rolling mill train 25 so that a pre-finished rolled product 52 leaves the pre-finishing stands 26 having a thickness comprised between approximately 10 millimeters and 50 millimeters.

[0095] Furthermore, the pre-finishing stands 26 are arranged at a predetermined distance D from the roughing stand 23 so that the intermediate rolled product 51 is never operatively brought into contact with two types of stands at the same time.

[0096] In the exemplary solution shown, downstream of the pre-finishing stand 26, a flying shear 27 of the crop shear type is arranged to trim the head and tail of the pre-finishing rolled product 52, making it easier to enter the finishing stand 31 and reducing the chance of kobble, especially for the production of final strip having a thickness of less than 3.0 millimeters.

[0097] Advantageously, because the pre-finished rolled product 52 has a smaller thickness than the associated intermediate product 51 of conventional HSM, the shear 27 can have smaller dimensions, resulting in benefits in terms of cost, overall size, and maintenance.

[0098] The plant 10 according to the invention may also include an induction heating device 28 interposed between the pre-finishing stand 26 and the finishing stand 31 of the continuous rolling mill train 25 .

[0099] Preferably, the induction heating device 28 comprises, for example, an induction furnace arranged downstream of the flying shear 27 and made up of elements that can be activated selectively or independently of each other.

[0100] The induction heating device 28 is configured to heat the pre-finished rolled product 52 in a selective and adjustable manner before it enters the finishing stand 31 .

[0101] The temperature to which the pre-finished rolled product 52 is heated is selected, among other parameters, as a function of at least its thickness and the final thickness of the final strip P, so that the final strip P reaches an optimum temperature of at least 830°C at the exit of the continuous rolling mill train 25, in particular at the exit of the final finishing stand.

[0102] By way of example only, the temperature to which the pre-finished rolled product 52 is heated, i.e. the temperature it has at the exit of the induction heating device 28, advantageously reaches a value comprised between approximately 1000°C and approximately 1100°C.

[0103] This is the rolling mass flow MF required to obtain the above-mentioned optimum temperature at the exit of the final finishing stand 31 of at least 830°C, for example comprised between 830°C and 900°C. L This allows the value of

[0104] Required rolling mass flow MF L This reduces the maximum rolling speed from the finisher train 25 as a whole to obtain the optimum temperature as described above. This makes it possible to avoid or at least reduce the so-called "accelerations" that occur during rolling, which occur in use.

[0105] Advantageously, downstream of the induction heating device 28 and upstream of the finishing stand 31, a third water descaling device 29 is also arranged, the function of which is to further clean scale from the surface of the pre-finished rolled product before it enters the finishing stand 31.

[0106] Therefore, the scale formed on the surface of the pre-finished rolled product 52 is effectively removed, thereby avoiding quality degradation on the rolled strip P, such as imprinted scale.

[0107] Downstream of the finishing stand 31 there is arranged a cooling device 33 comprising a number of showers 34 which can be activated selectively or independently of one another to cool the strip P.

[0108] Furthermore, at the outlet of the showers 34, two take-up reels 36, 38 are arranged which wind the strip P into a coil for subsequent storage and transport.

[0109] The solution according to the present invention allows the finishing stand 31 to carry out a larger thickness reduction compared to the prior art, thanks to the increase in temperature of the pre-finished rolled product 52 caused by the induction heating device 28, while ensuring that the temperature at the exit from the last finishing stand is at least 830°C.

[0110] The fact that large thickness reductions are possible in the continuous rolling mill train 25 makes it possible for the plant 10 to be equipped with a single reversing roughing stand 23, significantly reducing the overall plant costs.

[0111] Another advantage of using only one reversible stand 23, which provides an intermediate rolled product having a thickness comprised within the range of about 45 millimeters to about 80 millimeters, is that it makes it possible to limit the distance between the reversible stand 23 and the continuous rolling mill train 25, thus leading to reduced temperature losses, reduced surface scale formation, and a reduced overall length of the plant 10. In fact, a plant 10 according to the present invention can be 100 meters shorter than a prior art plant while still having the same annual output, for example, in the range of about 3 million to about 6 million tonnes per year (Mtpy).

[0112] Furthermore, thanks to the heating provided by the induction heating devices 28 associated with the continuous rolling mill train 25, it is possible to limit the heating of the starting slab 50 in the gas furnace 16 to only 1100 / 1150°C to 1200°C, which has the advantage of lower combustion gas consumption and limited emissions compared to known plants.

[0113] Furthermore, since the slab 50 is heated to a lower temperature compared to the prior art, the residence time in the gas furnace 16 is also shorter than that provided in known plants. This advantageously reduces the occurrence of scale by 25% to 30%, and therefore reduces the loss of scale material by 25% to 30%, and improves the yield of the furnace 16 itself.

[0114] The invention also relates to a method for manufacturing a strip P, starting from a slab 50 having an initial thickness comprised between about 150 millimeters and about 350 millimeters, which is wound to form a coil.

[0115] The method provides for heating at least one slab 50 in a gas-heated furnace 16 to a temperature of 1100 / 1150° C. to 1200° C. and feeding it towards a first descaling device 20 .

[0116] The slab 50 is then presented to the edging stand 21 and then to the reversing roughing stand 23, where it is subjected to several rolling passes to reduce its thickness, resulting in an intermediate rolled product 51 having a thickness comprised within the range of about 40 millimeters to about 80 millimeters. Preferably, the number of rolling passes performed by the reversing roughing stand 23 does not exceed five.

[0117] This reduces the temperature loss of the intermediate rolled product 51 between its head and tail while limiting its length.

[0118] The intermediate rolled product 51 is then conveyed to a second descaling unit 24 where surface descaling occurs and then provided to the continuous rolling mill train 25 .

[0119] The intermediate rolled product 51 enters the pre-finishing stand 26 where it is further reduced in thickness until a pre-finished rolled product 52 is defined, having a thickness comprised between about 10 millimeters and about 50 millimeters.

[0120] Having been dimensionally altered in this way, the pre-finished rolled product 52 is cut off at the head and tail by the shear 27 and enters the induction heating device 28, where it is heated to a temperature such that the temperature of the final strip P corresponding to the exit of the last finishing stand is an optimum temperature of at least 830°C, even in the case of thin strips having a thickness comprised between 0.9 and 1.2 millimeters.

[0121] In some embodiments, the heat provided by the induction heating device 28 is variable, heating the head portion of the pre-finished rolled product 52 to a predetermined temperature and then increasing the heat provided thereto in a substantially linear manner so that the body and tail portions of the final strip P can exit the last finishing stand 31 of the continuous rolling mill train 25 at an optimum temperature of at least 830°C.

[0122] Thanks to the heating provided by the induction heating unit, the rolling mass flow MF required to obtain an optimum temperature at the exit of the last finishing stand of at least 830 °C, for example comprised between 830 °C and 900 °C L It is possible to reduce the value of

[0123] As a purely limiting example, we plot the final thickness S of the final strip P on the horizontal axis. F , the vertical axis is the rolling speed V L 6, where the final thickness S is shown. Curve A is the thickness of the final thickness S without the heat input of the induction heater 28. F The required rolling mass flow MF is a function of L Curve B shows the trend of the final thickness S when there is heat input from the induction heater 28. F The required rolling mass flow MF is a function of L This shows the trend.

[0124] As can be seen, the mass flow associated with curve B is lower than the mass flow associated with curve A. In fact, the final thickness S of the final strip P F For the same rolling speed, V, the mass flow associated with curve B corresponds to a lower rolling speed V than that corresponding to the mass flow associated with curve A. L Corresponds to.

[0125] Rolling mass flow MF L The reduction of the rolling speed V is preferably lower than 12 m / s. LThis allows both the tail of the final strip P to reach an optimum temperature of at least 830°C at the exit of the continuous rolling mill train 25, eliminating the need for "acceleration" to be used as a tool to reach the target temperature. An example of this embodiment is shown diagrammatically in Figure 7.

[0126] Advantageously, in the absence of acceleration, the rolling speed V in the finishing stand 31 L is substantially constant, making it possible both to keep the temperature constant between the head and tail of the final strip P and to select an optimum temperature control (e.g., heat treatment) as a function of the steel grade and the use of the final strip P.

[0127] Another advantage of not accelerating is that it allows for a high degree of control over both the final shape of the final strip P, such as its crown and flatness, which are advantageously uniform along the entire length of the coil, and the mechanical properties of the final strip P, which are advantageously constant and uniform along the entire length of the coil.

[0128] This last advantage mentioned above, which is not obtainable with prior art plants, is particularly important for high quality products such as, for example, the final strip P for forming.

[0129] According to some embodiments, when producing products with very thin thicknesses or achieving very high productivity with other thicknesses, acceleration may be required to improve line productivity, an example of which is shown schematically in Figure 8.

[0130] Furthermore, according to other embodiments, the acceleration can be performed in combination with the induction heating device 28, for example to limit the power consumption of the latter.

[0131] For products with a relatively large final thickness, the acceleration can be carried out with the induction heater kept off to completely eliminate its power consumption.

[0132] It will be apparent that modifications and / or additions to components may be made to the plant 10 and the method for producing flat rolled products described above without departing from the field and scope of the present invention as defined in the claims.

[0133] Although the present invention has been described with reference to some particular examples, it is also clear to a person skilled in the art that many other equivalent forms of the method and plant 10 for producing flat rolled products can certainly be realised, which have the characteristics set out in the claims and therefore fall entirely within the field of protection defined by the claims.

[0134] In the following claims, references in parentheses have the sole purpose of improving readability and shall not be considered as limiting factors with regard to the field of protection defined by the same claims.

Claims

1. A rolling plant (10) for producing a final strip (P) starting from a slab (50) having a predetermined initial thickness, comprising: at least one furnace (16) configured to heat at least one said slab (50) to a predetermined initial temperature; at least one reversible roughing stand (23) configured to subject said slab (50) to one or more rolling passes to obtain an intermediate rolled product (51); a continuous rolling mill train (25) arranged in operative alignment with the at least one roughing stand (23) and configured to reduce the thickness of the intermediate rolled product (51) until the final strip (P) having a predetermined final thickness is obtained; Equipped with The rolling mill train (25) at least one pre-finishing stand (26) arranged at a minimum distance (D) from the roughing stand (23) so that the intermediate rolled product (51) does not operatively abut both stands (23, 26) simultaneously, and capable of reducing the thickness of the intermediate rolled product (51) to obtain a pre-finishing rolled product (52); a plurality of finishing stands (31) capable of reducing the thickness of the pre-finished rolled product (52) to obtain the final strip (P); Including, 1. A rolling plant (10) comprising: a selectively activatable multi-element induction heating device (28) interposed between the at least one pre-finishing stand (26) and the plurality of finishing stands (31) and configured to heat the pre-finish rolled product (52) in such a way that the temperature of the final strip (P) corresponding to the outlet of the final finishing stand (31) in the rolling mill train (25) is at least 830°C higher, even if the final thickness is less than 1.2 mm.

2. at least one warehouse (40) configured for storage of said slabs (50); 2. The rolling plant (10) according to claim 1, characterized in that the storehouse (40) is arranged substantially upstream of the heating furnace (16) and is capable of selectively supplying at least one of the slabs (50) to the heating furnace (16).

3. 3. The rolling plant (10) according to claim 1 or 2, characterized in that the rolling mill train (25) comprises one to three of the pre-finishing stands (26) and five to six finishing stands (31).

4. the at least one roughing stand (23) is configured to define the intermediate rolled product (51) having a thickness comprised between 45 millimeters and 80 millimeters; the at least one pre-finishing stand (26) is configured to define the pre-finished rolled product (52) having a thickness comprised between 10 millimeters and 50 millimeters; 4. The rolling plant (10) according to claim 1, wherein the plurality of finishing stands (31) are configured to define the final strip (P) having a thickness comprised between about 0.9 millimeters and about 26 millimeters.

5. a first descaling means (20) interposed between the heating furnace (16) and the at least one roughing rolling stand (23); a second descaling means (24) interposed between the roughing stand (23) and the first of the pre-finishing stands (26); a third descaling means (29) interposed between the induction heating device (28) and the first of the finishing stands (31); 5. A rolling plant (10) according to any one of claims 1 to 4, characterized in that it comprises at least

6. 6. A rolling plant (10) according to any one of claims 1 to 5, characterized in that it comprises a cutting machine (27) interposed between the pre-finishing stand (26) and the induction heating device (28).

7. A rolling method for producing a final strip (P) in a rolling plant (10) starting from a slab (50) having a predetermined initial thickness, comprising: The rolling plant (10) comprises: at least one furnace (16) configured to heat at least one said slab (50) to a predetermined initial temperature (T1); at least one reversible roughing stand (23) configured to subject said slab (50) to one or more rolling passes to obtain an intermediate rolled product (51); a continuous train of rolling mills (25) arranged in operative alignment with the at least one roughing stand (23) and configured to reduce the thickness of the intermediate rolled product (51) until the final strip (P) having a predetermined final thickness is obtained; Equipped with The rolling method comprises: at least one pre-finishing roll of the intermediate rolled product (51) by means of at least one pre-finishing stand (26) of the rolling mill train (25) arranged at a minimum distance (D) from the roughing stand (23) so that the intermediate rolled product (51) does not operatively abut both of the stands (23, 26) simultaneously and so as to reduce the thickness of the intermediate rolled product (51) to obtain a pre-finishing rolled product (52); at least one finish rolling of said pre-finished rolled product (52) to obtain said final strip (P) by means of a plurality of finishing stands (31) of said rolling mill train (25) capable of reducing said thickness of said pre-finished rolled product (52); at least one step of heating the pre-finish rolled product (52) by means of an induction heating device (28) consisting of a plurality of selectively activatable elements and interposed between the at least one pre-finishing stand (26) and the plurality of finishing stands (31) so that the temperature of the final strip (P) corresponding to the outlet of the final finishing stand (31) in the rolling mill train (25) is at least higher than 830°C, even if the final thickness is less than 1.2 mm; A rolling method comprising:

8. 8. The rolling method according to claim 7, characterized in that it includes at least one storing and feeding step, in which the slabs (50) are stored and selectively fed to the heated furnace (16) by means of a warehouse (40) located substantially upstream of the heated furnace (16).

9. 9. A rolling method according to claim 7 or 8, characterized in that the thickness of the intermediate rolled product (51) corresponding to the entrance of the rolling mill train (25) is comprised between 45 and 80 millimeters.

10. 10. The rolling method according to claim 7, wherein the predetermined initial temperature (T1) of the slab is 1200°C or less.

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