Continuous casting and rolling plant for the production of metallic bands and related procedure in case of stoppage of the metallic band

Abstract

A continuous casting and rolling plant for producing strips, the plant comprising, along a processing line - a continuous casting machine (1) adapted to cast a flat product along a casting curve (7); - at least two horizontal containment segments (3) for containing the advancement of the flat product downstream of said casting curve (7); - a first cutting device (4) arranged downstream of said at least two horizontal containment segments (3); - a rolling mill (35, 39) comprising a roughing train (35), including at least one roughing stand provided with respective working rolls, and a finishing train (39) including at least one finishing stand provided with respective working rolls and arranged downstream of said roughing train (35); wherein there is provided at least one second cutting device (2) arranged downstream of the casting curve (7) and upstream of the first cutting device (4).

Description

[0001] CONTINUOUS CASTING AND ROLLING PLANT FOR THE PRODUCTION OF METALLIC BANDS AND RELATED PROCEDURE IN CASE OF STOPPAGE OF THE METALLIC BAND

[0002] ***********

[0003] Field of the invention

[0004] The present invention relates to a continuous casting and rolling plant for producing metal strips starting from a cast flat product, such as a slab, and a related method in the event of the stop of the rolling train, whether the stop is scheduled, e.g. for the replacement of worn-out working rolls, a change of production or other scheduled maintenance work, or accidental, e.g. due to cobbles or accidents.

[0005] Background art

[0006] Conventional continuous casting and rolling plants, used for producing metal strips, for example made of steel, provide for the machinery forming the casting line not to be arranged in line with the rolling mill.

[0007] Indeed, in standard plants, the casting line is disconnected from the rolling line, whereby the cast products, e.g. slabs, are cut and stored in special storages. The slabs are sent from such storages to a heating furnace, conventionally using gas, which brings them to an adequate temperature to be rolled in the rolling line, which usually is positioned downstream of the heating furnace. The casting line and rolling mill often are arranged in different areas of the plant.

[0008] Therefore, there are significant limitations to the efficiency and productivity of the plant associated with the fact that the continuous casting machine and the rolling mill in any case work partially disconnected, without continuity, and the need remains to provide an intermediate storage which can deal with the different operating needs of these components.

[0009] A second generation of plants has overcome these limitations by arranging the plant machines, comprising also the machines forming the casting line and the rolling mill, along a same production line.

[0010] In particular, in such a second generation of plants, a single product advancement line is defined, without intermediate storage and material being taken again.

[0011] Thus, a continuous casting and rolling process in coil-to-coil (also called ‘batch’) mode or in semi-endless mode, more generally in discontinuous mode, is allowed, in which the slab, upstream of the rolling mill, is cut to size in segments or portions having the length generally corresponding to the weight of a finished rolled coil or a multiple thereof.

[0012] A continuous casting and rolling process in endless mode, i.e. , seamlessly, is also possible, in which the casting machine and the rolling mill are directly connected and in direct contact with each other, and the rolled strip is cut to size only downstream of the rolling mill prior to winding onto the downcoilers.

[0013] In any case, the plants of this second generation have a considerably more flexible production and can also be more compact with respect to the previous type of plants.

[0014] Although it is particularly advantageous, this second generation of plants can be further improved, both in terms of plant sizes - which have a significant effect on the cost of making the plant itself - and in terms of energy efficiency.

[0015] In the endless operating mode, the rolling and casting processes are closely connected, therefore any need to stop the rolling mill, for example, for a scheduled replacement of the working rolls, to carry out checks, or due to incidents, sudden interruptions or small breakdowns, can force the continuous casting process to be stopped, and potentially also the one of the steel mill upstream, with a loss in production and complications associated with the possible solidification of the liquid steel. All this occurs in the absence of storage devices or buffers arranged downstream of the casting, such as mid-line heating furnaces. If said mid-line heating furnaces were instead provided, in order to be able to suitably also perform this function, they must have an adequate length, greater than 80 m, thus affecting CAPEX, OPEX and space requirements of the plant.

[0016] Therefore, in endless operation and in the absence of buffers, a stop of the rolling mill results in a reduction of productivity and usage factor of the plant, an increase in management costs, and it is the main reason for an increase in the energy required by the process.

[0017] Therefore, the need is felt to make a continuous casting and rolling plant for producing metal strips and a related method, in the event of a stop of the rolling mill, whether it is scheduled or accidental, which overcomes the aforesaid drawbacks.

[0018] Summary of the invention

[0019] It is an object of the present invention to make a continuous casting and rolling plant (co-rolling) for producing metal strips, in endless mode or discontinuous mode, and a related process, which allow managing the stops of the rolling mill, for example due to the scheduled replacement of the working rolls or other maintenance intervention, or due to incidents such as cobbles, not only without interrupting the casting, and therefore without loss of production and without penalizing the steel mill upstream, but also without interrupting the production of rolled strip downstream, in particular in the absence of a specific buffer device downstream of the casting.

[0020] It is another object of the invention to significantly reduce the length of any buffer devices downstream of the casting in the plants providing them.

[0021] It is another object of the invention to install a cutting system at the exit from the casting curve which allows the horizontal part of the casting machine itself, substantially from the end of the curve up to the casting machine output, to be used as buffer for the co-rolling line, without lengthening the layout.

[0022] The present invention achieves at least one of such objects, and other objects which will be apparent in light of the present description, by means of a continuous casting and rolling plant for producing metal strips, the plant comprising, along a processing line

[0023] - a continuous casting machine adapted to cast a flat product along a casting curve and comprising at least two horizontal containment segments for containing the flat product downstream of said casting curve;

[0024] - a rolling mill comprising a roughing train, including at least one roughing stand provided with respective working rolls, and a finishing train including at least one finishing stand provided with respective working rolls and arranged downstream of said roughing train; wherein there is provided a first cutting device arranged downstream of said at least two horizontal containment segments; wherein there is provided at least one second cutting device arranged downstream of the casting curve and upstream of the first cutting device; and wherein the distance between the first cutting device and the second cutting device is comprised in a range between 18 m and 40 m, preferably between 20 m and 35 m, even more preferably between 20 m and 30 m.

[0025] A further aspect of the invention relates to a method for performing an operation in a rolling mill of the aforesaid continuous casting and rolling plant, switching from an endless mode to a discontinuous mode and without interrupting the casting, wherein the continuous casting machine is adapted to cast flat products at least at a first speed vi and at a second speed V2 greater than the first speed vi ; wherein the method comprises the following steps: a) cutting the flat product by means of the first cutting device to release the continuous casting machine from at least one part of the rolling mill, and reducing the casting speed of the continuous casting machine from the second speed V2 to the first speed vi so that the closing point of the liquid cone of the flat product can retract; b) cutting the flat product by means of the first cutting device, thus obtaining first portions of flat product that advance towards at least one rolling stand belonging to the rolling mill; c) once the closing point of the liquid cone retracts upstream of the second cutting device, cutting the flat product by means of said second cutting device, thus obtaining a second portion of flat product which advances towards the rolling mill; wherein the first portions and the second portion advance at a respective third speed greater at least than the first speed vi to obtain a time range usable to perform an operation in at least one part of the rolling mill, whereby a space at least at said at least two horizontal containment segments, downstream of the second cutting device, is used as buffer for the part of flat product upstream of said second portion.

[0026] In particular, due to the aforesaid management of the first cutting device and second cutting device, of the casting speed and advancement speed of said first portions and said second portion (acceleration of said first portions and said second portion up to reaching the aforesaid third speed), it is possible to determine a buffer within the footprint of the casting machine allowing a sufficient time range to be obtained to perform the necessary operations in the rolling mill, such as, for example, a scheduled replacement of the working rolls, which lasts about 10 minutes. Such a buffer is created by slowing down the casting machine to a first casting speed vi up to obtaining the retraction of the liquid cone upstream of the second cutting device which is more proximal to the casting curve and, by maintaining said first casting speed vi, cutting, with said second cutting device, a slab, the cut portions of which are advanced from the casting machine towards the rolling mill so as to be rolled, accelerating them up to said third speed greater than the first casting speed vi. Thereby, a space is made available at at least two horizontal containment segments in which the head of the new slab being formed advances at reduced speed vi. Such space therefore constitutes an alternative or additional buffer to the possible heating furnace, which can therefore be made with smaller dimensions, with subsequent advantages in terms of CAPEX, OPEX and of the environment.

[0027] The operation in the rolling mill, such as changing the working rolls or maintenance intervention, is therefore performed after the rolling of the first portions and the second portion of the flat product and prior to the arrival of the head of the new flat product at the rolling mill.

[0028] The possibility of being able to suitably change working cylinders or rolls as needed and without stopping the rolled strip production enables the plant of the present invention to produce several types of steel, such as peritectic steel, silicon grades, interstitial free grades.

[0029] Further features and advantages of the invention will become more apparent in light of the detailed description of exemplary but not exclusive embodiments.

[0030] The dependent claims describe particular embodiments of the invention. Brief description of the drawings

[0031] The description of the invention refers to the accompanying drawings, which are provided by way of non-limiting example, in which:

[0032] Figure 1 is a side view of three embodiments of a plant according to the invention; Figure 2 is a perspective view of a first variant of a cutting device of the plant according to the invention;

[0033] Figure 3 is a side view of a second variant of said cutting device;

[0034] Figure 4 is a side view of a third variant of said cutting device; Figure 5 is a further side view of said cutting device of the second and third variants;

[0035] Figure 6 diagrammatically shows the movement of said cutting device to cut the slab.

[0036] The same reference numerals and letters in the drawings identify the same elements or components.

[0037] Description of exemplary embodiments of the invention

[0038] Figure 1 shows some layout examples of a continuous casting and rolling plant for continuously producing strips, according to the present invention.

[0039] In all the embodiments of the invention, the plant comprises, along a processing line

[0040] - a continuous casting machine 1 adapted to cast a flat product, such as a slab, along a casting curve 7 and comprising at least two horizontal containment segments 3 for containing the advancement of the flat product downstream of the casting curve 7;

[0041] - a rolling mill 35, 39 comprising a roughing train 35, including at least one roughing stand provided with respective working rolls, and a finishing train 39 including at least one finishing stand provided with respective working rolls and arranged downstream of the roughing train 35;

[0042] - preferably a cooling device 40, preferably a laminar cooling device;

[0043] - winding reels or downcoilers 42.

[0044] The continuous casting machine 1 is adapted to cast flat products at least at a first speed vi and at a second speed V2 greater than the first speed vi.

[0045] It is worth noting that the second speed V2 is the speed at full capacity at which the plant operates in endless mode and can be, by way of example, equal to 6 m / min.

[0046] A first cutting device 4 is arranged downstream of said at least two horizontal containment segments 3 and can be positioned upstream or downstream of the roughing train 35, but in any case, upstream of the finishing train 39.

[0047] Advantageously, there is provided at least one second cutting device 2, arranged downstream of the casting curve 7 and upstream of the first cutting device 4, and which is used to cut the cast product after the casting speed is reduced from the second speed V2 to the first speed vi and after the closing point of the liquid cone b of the cast product has retracted upstream of said second cutting device 2. By way of example, the first speed vi can be comprised between 2 and 3 m / min.

[0048] The cast product preferably is a slab, for example having a thickness at the exit from crystallizer comprised between 150 and 170 mm, preferably 160 mm, said slab, after a reduction of thickness through soft reduction, exiting the containment segments 3 with a thickness of about 140 mm.

[0049] Preferably, in all layout variants of the plant, the hot-rolling mill comprises (Figure 1 ):

[0050] - a roughing train or first rolling train 35, preferably comprising from two to four roughing stands, for performing a hot roughing of the slab and obtaining a blank, called transfer bar;

[0051] - and a finishing train or second rolling train 39, preferably comprising from four to seven finishing stands, for performing a hot finishing of the transfer bar and obtaining a strip.

[0052] The plant of the present invention, in a first embodiment thereof, can comprise, in sequence (Figure 1a):

[0053] - the casting curve 7;

[0054] - the cutting device 2;

[0055] - at least two horizontal containment segments 3, 3’;

[0056] - the cutting device 4;

[0057] - a heating furnace 5, 6, also serving the function of buffer, preferably comprising a tunnel furnace 5 provided with heating elements, which can be of any type known in the prior art (e.g. gas or hydromethane burners, electric resistors, etc.), also in combination with each other, and possibly provided with an end section comprising an induction heater 6 for maintaining or equalizing or increasing the temperature of the slab;

[0058] - a possible vertical rolling stand 33 (edger), for reducing the width of the slab and bringing it closer to that of the desired strip, so as to reduce the waste and improve the yield;

[0059] - a possible first descaler 34, immediately upstream of the roughing train 35;

[0060] - the roughing train 35;

[0061] - possible shears 36 for cutting the transfer bar in the case of an emergency or for eliminating the ends that may have an irregular shape, avoiding damaging the working rolls of the finishing train 39 and reducing the probability of cobbles with the consequent generation of waste;

[0062] - a heating device, preferably a rapid induction heating device 37, the power of which can be modulated and opportunely activated to restore the temperature that the product loses with roughing and to succeed in exiting the finishing train while remaining in the austenitic field;

[0063] - a possible second descaler 38, immediately upstream of the finishing train 39;

[0064] - the finishing train 39;

[0065] - a laminar cooling device 40, for example, in the shape of a roller table, positioned downstream of the second rolling train 39 and immediately upstream of cutting means 41 , said roller table being provided with laminar cooling systems for cooling the upper and lower surfaces of the rolled strip;

[0066] - at least two winding systems 42, arranged downstream of the cutting means 41 , defining a winding station 9 and preferably comprising, for example, gripping and deflector rollers, winding reels, winding rollers and coil unloading system.

[0067] Said heating furnace 5, 6 preferably has a length not greater than 80 meters, more preferably not greater than 60 meters, even more preferably not greater than 40 meters, for example comprised between 20 and 40 meters.

[0068] Preferably, the length that from the upper end of the crystallizer reaches the output section of the at least two horizontal containment segments 3 does not exceed 60 meters, preferably varies between 40 and 50 meters. Such a length is measured along the casting curve and along an initial horizontal stretch of the plant.

[0069] A second embodiment of the plant of the invention (Figure 1b) is different from the first embodiment, in particular in that it has:

[0070] - a tunnel furnace 5 arranged between the cutting device 4 and the roughing train 35, said furnace being similar to or shorter than the heating furnace of said first embodiment;

[0071] - and a further tunnel furnace 5’, replacing the quick induction heating device 37 present in the first embodiment, arranged between the roughing train 35 and the finishing train 39.

[0072] The tunnel furnace 5 can be provided with at least one section comprising an a induction heater.

[0073] Said tunnel furnace 5 preferably has a length not greater than 60 meters, even more preferably not greater than 40 meters, for example comprised between 20 and 40 meters.

[0074] In a third embodiment of the plant, shown in Figure 1c, no heating furnace is provided between the casting machine and the roughing train 35, which stands are therefore subsequent to the casting machine without any significant intermediate space where a buffer can be inserted, and the following is provided in sequence:

[0075] - the casting curve 7;

[0076] - the cutting device 2;

[0077] - at least two horizontal containment segments 3;

[0078] - a possible vertical rolling stand 33 (edger);

[0079] - the possible first descaler 34, immediately upstream of the roughing train 35;

[0080] - the roughing train 35;

[0081] - the cutting device 4;

[0082] - the quick induction heating device 37, for increasing the temperature of the transfer bar;

[0083] - the possible second descaler 38, immediately upstream of the finishing train 39;

[0084] - the finishing train 39;

[0085] - the laminar cooling device 40;

[0086] - the cutting means 41 ;

[0087] - the at least two winding systems 42, defining the aforesaid winding station 9.

[0088] In all embodiments of the plant of the invention, the distance between the cutting device 2 and the cutting device 4 can be in a range from 18 to 40 meters, preferably from 20 to 35 meters. An advantageous variant provides the distance between the cutting device 2 and the cutting device 4 to be in a range from 20 to 30 meters, preferably from 20 to 25 meters.

[0089] The cutting device 4 is, for example, a pendulum shear for cutting the slab.

[0090] Preferably, the cutting device 2 can comprise one or more hydraulic shears, one or more oxy-acetylene torches, one or more rotary disc shears, one or more milling cutters with a rotating tool, or other suitable cutting tools.

[0091] Further, in all the embodiments of the plant, each containment segment 3, 3’ comprises an upper part 10 provided with upper containment rolls 11 and a lower part 12 provided with lower containment rolls 13.

[0092] A preferred variant, which can be implemented in all the above-described embodiments of the plant, provides for said at least one cutting device 2 to be arranged, in a resting position, alongside a containment segment 3’ of said at least two horizontal containment segments 3, and to be translatable from said resting position to a cutting position, and vice versa. This preferred variant allows the length of the plant layout to be further compacted.

[0093] The containment segment 3’, to which the cutting device 2 is alongside, can be the containment segment closest to the casting curve 7, as shown in Figure 1 , or an intermediate containment segment within the group of containment segments 3, as shown in Figure 2.

[0094] A first embodiment of said preferred variant, shown in Figure 2, has both the cutting device 2 and the containment segment 3’, alongside each other transversely to the processing line, i.e., transversely to the advancement line of the cast flat product 14 (slab), being displaceable transversely to said processing line so that only one of said cutting device 2 and said containment segment 3’ is arranged along the processing line.

[0095] The example in Figure 2 in particular shows an intermediate containment segment 3’, translated in a first direction laterally outside the processing line, while the cutting device 2 is about to translate in said first direction from the resting position to the cutting position. Preferably, the cutting device 2 is also adapted to translate parallel to the advancement direction of the flat product 14 and at the same advancement speed as said flat product, during the translation of the same cutting device 2 towards the cutting position, so as to perform a complete cut along the width of the flat product 14.

[0096] Optionally, the upper part 10 of said intermediate containment segment 3’ can be advantageously rotated by about 90° up to reaching a substantially vertical position, so as not to risk contact with the product during the translation.

[0097] In this example in Figure 2, the cutting device 2 comprises, by way of example only, a plurality of oxy-acetylene torches, adapted in turn to translate parallel to the advancement direction of the cast product 14 and at the same advancement iu speed as said cast product, during the translation of the cutting device 2 towards the cutting position, so as to perform a complete cut along the width of the flat product 14. Alternatively, any cutting tool allowing the cutting of the cast flat product during the advancement thereof can be used.

[0098] Other embodiments instead provide for at least one of the upper part 10 and the lower part 12 of the containment segment 3’, to which the at least one cutting device 2 is alongside, to be configured for being displaced to clear a space adapted for the passage of said at least one cutting device 2 from the resting position to the cutting position, and vice versa.

[0099] In particular, a second embodiment provides for both the upper part 10 and the lower part 12 of the containment segment 3’, to which the at least one cutting device 2 is alongside, to be configured for being moved so as to clear said space.

[0100] Figure 3, for example, shows a solution in which both the upper part 10 and the lower part 12 of the containment segment 3’ are rotated by about 90° up to reaching a substantially vertical position to clear said space.

[0101] Alternatively, a third embodiment provides that only the lower part 12 is configured to be moved, preferably rotated, to clear said space.

[0102] Figure 4, for example, shows a solution in which the lower part 12 of the containment segment 3’ is divided into two portions 12’, 12” hinged to an outer end thereof to be respectively rotated to clear said space.

[0103] In these examples of Figures 3 and 4, the cutting device 2 comprises, by way of example only, rotary disc shears 15, shown in Figure 5.

[0104] Such rotary disc shears 15 are fastened on a support structure 16.

[0105] In particular, the shears 15 can slide on a guide 17 provided on said support structure 16 to be displaced from the resting position 18 to the cutting position 19, and vice versa.

[0106] Further, the support structure 16 in turn can slide, for example inside a frame 20, parallel to the advancement direction of the cast product 14 and at the same advancement speed as said cast product, during the translation of the shears 15 towards the cutting position, so as to perform a complete cut along the width of product 14, as diagrammatically shown in Figure 6 where there are visible different positions of shears 15, which translate, performing the cut transversely to the advancement direction A of the flat product 14, moving simultaneously parallel to said advancement direction A of the flat product. Arrows B and C indicate the two components of the movement of shears 15 during the cutting.

[0107] Alternatively, any cutting tool allowing the cutting of the cast flat product during the advancement thereof can be used.

[0108] Both in the second and third embodiment, it is possible to provide two cutting devices 2 arranged alongside the containment segment 3’, in the respective resting position thereof, on opposite sides with respect to the processing line (solution not shown).

[0109] Below is a description of the method for performing an operation in the rolling mill 35, 39 according to any of the embodiments described above of the continuous casting and rolling plant, passing from an endless mode to a discontinuous mode and advantageously without interrupting the casting and production of rolled strip. The continuous casting machine 1 is adapted to cast a slab at least at a first speed vi and at a second speed V2 greater than the first speed vi.

[0110] The method, in all the variants thereof, comprises the following steps: a) cutting the slab by means of the first cutting device 4 to separate the material and release the continuous casting machine 1 from at least one part of the rolling mill 35, 39, and reducing the casting speed of the continuous casting machine 1 from the second speed V2 to the first speed vi so that the closing point of the liquid cone of the cast slab can retract; b) cutting the cast slab by means of the cutting device 4, thus obtaining first portions of slab advancing towards at least one rolling stand belonging to the rolling mill 35, 39, each first portion preferably having a length corresponding to the weight of a single coil of rolled product formed on a winding system 42; c) once the closing point of the liquid cone retracts upstream of the cutting device 2, cutting the cast slab by means of said cutting device 2, thus obtaining a second portion of slab advancing towards the rolling mill 35, 39, said second portion preferably having a length corresponding to the weight of a single coil of rolled product or a multiple thereof.

[0111] Advantageously, the first portions and the second portion of slab advance towards at least one rolling stand belonging to the rolling mill 35, 39, at a respective third speed greater than at least the first speed vi to obtain a time range usable to perform an operation in at least one part of the rolling mill 35, 39, whereby a space at least at the at least two horizontal containment segments 3, downstream of the cutting device 2, is used as buffer for the part of slab upstream of said second portion.

[0112] For example, this third speed can be greater than, equal to or less than the second speed V2.

[0113] The operation in the rolling mill, as the change of the working rolls or a maintenance intervention, is therefore performed in said time range between the end of the rolling of the first portions and the second portion of the cast slab and the beginning of the rolling of the part of slab upstream of said second portion.

[0114] Preferably, a motorized roller table is provided for the advancement of the slab, or of the portions thereof, towards said at least one rolling stand belonging to the rolling mill 35, 39.

[0115] In particular, said roller table comprises at least:

[0116] - a first part 43 arranged between the cutting device 2 and the cutting device 4;

[0117] - and a second part 44 arranged immediately downstream of the cutting device 4. Both the first part 43 and the second part 44 of said motorized roller table are controlled independently of each other by a respective control system, or by a single control system, which allows to adjust the advancement speed of the second portion of slab, cut by means of the cutting device 2, and of the first portions of slab, cut by means of the cutting device 4, respectively.

[0118] The first part of said motorized roller table comprises at least the lower containment rolls 13 of the containment segments 3 arranged downstream of the cutting device 2 (Figures 1 and 2).

[0119] In a first variant of the method of the invention, performed using the embodiments of the plant shown in Figures 1a and 1 b having a heating furnace 5, 6 between the cutting device 4 and the roughing train 35, after step c), it is provided to cut the cast slab by means of said cutting device 2, thus obtaining at least one third portion of slab, with length preferably corresponding to the weight of a coil of rolled product, said at least one third portion being kept in the heating furnace 5, 6, so as to obtain said time range between the end of the rolling of said second portion and the beginning of the rolling of said at least one third portion.

[0120] In this case, the space used as buffer comprises both the space at the at least two horizontal containment segments 3 and the space of the heating furnace 5, 6.

[0121] Preferably, the at least one third portion of slab advances in the heating furnace 5, 6 at a fourth speed less than said third speed, and preferably greater than at least the first speed vi. The aforesaid control systems, or the single control system, controlling the first part and the second part of said motorized roller table, also allow the advancement speed of said at least one third slab portion to be regulated.

[0122] Also the fourth speed, in any case less than the third speed, can be greater than, equal to or less than the second speed V2.

[0123] In a second variant of the method of the invention, performed using the embodiment of the plant shown in Figure 1c, no heating furnace serving as buffer between the casting machine and the roughing train 35 is provided.

[0124] In this case, the space used as buffer comprises only the space at the at least two horizontal containment segments 3.

[0125] In all the variants of the method of the invention, after the operation in the rolling mill 35, 39 has been performed during the aforesaid time range, the casting speed of the continuous casting machine 1 can be increased from the first speed vi to the second speed V2, the plant resuming operation from a discontinuous mode to an endless mode.

[0126] Preferably, said operation in the rolling mill 35, 39 can comprise a replacement of working rolls or a scheduled maintenance intervention or an accidental maintenance intervention in the event of cobbles or breakdowns.

Claims

CLAIMS1. A method for performing an operation in a rolling mill (35, 39) of a continuous casting and rolling plant for producing strips, switching from an endless mode to a discontinuous mode and without interrupting the casting, wherein said plant comprises, along a processing line- a continuous casting machine (1 ) adapted to cast a flat product along a casting curve (7) and comprising at least two horizontal containment segments (3) for containing the flat product downstream of said casting curve (7);- the rolling mill (35, 39) comprising a roughing train (35) including at least one roughing stand provided with respective working rolls, and a finishing train (39) including at least one finishing stand provided with respective working rolls and arranged downstream of said roughing train (35);- a first cutting device (4) arranged downstream of said at least two horizontal containment segments (3);- at least one second cutting device (2) arranged downstream of the casting curve (7) and upstream of the first cutting device (4); wherein the continuous casting machine (1 ) is adapted to cast flat products at least at a first speed vi and at a second speed V2 greater than the first speed vi ; wherein the method comprises the following steps: a) cutting the flat product by means of the first cutting device (4) to release the continuous casting machine (1 ) from at least one part of the rolling mill (35, 39), and reducing the casting speed of the continuous casting machine (1 ) from the second speed V2 to the first speed vi so that the closing point of the liquid cone of the flat product can retract; b) cutting the flat product by means of the first cutting device (4), thus obtaining first portions of flat product that advance towards at least one rolling stand belonging to the rolling mill (35, 39); c) once the closing point of the liquid cone retracts upstream of the second cutting device (2), cutting the flat product by means of said second cutting device (2), thus obtaining a second portion of flat product which advances towards the rolling mill (35, 39);wherein the first portions and the second portion advance at a respective third speed greater at least than the first speed vi so as to obtain a time range usable to perform an operation in at least one part of the rolling mill (35, 39), whereby a space at least at said at least two horizontal containment segments (3), downstream of the second cutting device (2), is used as buffer for the part of flat product upstream of said second portion.

2. A method according to claim 1 , wherein, the first cutting device (4) being arranged between said at least two horizontal containment segments (3) and said roughing train (35), and a heating furnace (5, 6) being provided between the first cutting device (4) and the roughing train (35), after step c) the cutting of the flat product is provided by means of said second cutting device (2), thus obtaining at least one third portion of flat product, preferably said at least one third portion having a length corresponding to the weight of a coil of rolled product, said at least one third portion being kept in the heating furnace (5, 6), used as additional buffer, so as to obtain said time range between the end of the rolling of said second portion and the beginning of the rolling of said at least one third portion; preferably wherein the at least one third portion of flat product advances in the at least one heating furnace (5, 6) at a fourth speed less than said third speed, and preferably greater than at least the first speed vi.

3. A method according to claim 1 or 2, wherein, after the operation in at least one part of the rolling mill (35, 39) has been performed, the casting speed of the continuous casting machine (1 ) can be increased from the first speed vi to the second speed V2, the plant resuming operation from a discontinuous mode to an endless mode; preferably wherein said operation can comprise a change of working rolls or a maintenance intervention.

4. A method according to any one of the preceding claims, wherein in step b), each first portion has a length corresponding to the weight of a single coil of rolled product; and wherein in step c), said second portion has a length corresponding to the weight of a single coil of rolled product or a multiple thereof.

5. A method according to any one of the preceding claims, wherein there is provided a motorized roller table for advancing the flat product, or portions thereof, towards said at least one rolling stand belonging to the rolling mill (35, 39); wherein said motorized roller table comprises at least- a first part (43) arranged between the at least one second cutting device (2) and the first cutting device (4);- and a second part (44) arranged immediately downstream of the first cutting device (4); and wherein both the first part and the second part of said motorized roller table are controlled independently of each other by a respective control system, or by a single control system, which regulates the advancement speed of the second portion of flat product, cut by means of the second cutting device (2), and of the first portions of flat product, cut by means of the first cutting device (4), respectively.

6. A continuous casting and rolling plant for producing strips, adapted to perform a process according to any one of the preceding claims, the plant comprising, along a processing line- a continuous casting machine (1 ) adapted to cast a flat product along a casting curve (7) and comprising at least two horizontal containment segments (3) for containing the flat product downstream of said casting curve (7);- a rolling mill (35, 39) comprising a roughing train (35) including at least one roughing stand provided with respective working rolls, and a finishing train (39) including at least one finishing stand provided with respective working rolls and arranged downstream of said roughing train (35); wherein there is provided a first cutting device (4) arranged downstream of said at least two horizontal containment segments (3); wherein there is provided at least one second cutting device (2) arranged downstream of the casting curve (7) and upstream of the first cutting device (4); and wherein the distance between the first cutting device (4) and the second cutting device (2) is comprised in a range between 18 m and 40 m, preferably between 20 m and 35 m, even more preferably between 20 m and 30 m.

7. A plant according to claim 6, wherein said at least one second cutting device (2) is arranged, in a resting position, alongside a containment segment (3’) of said at least two horizontal containment segments (3) and is translatable from said resting position to a cutting position, and vice versa.

8. A plant according to claim 7, wherein both the second cutting device (2) and said containment segment (3’) are displaceable transversely to the processing line so that only one of said second cutting device (2) and said containment segment (3’) is arranged along the processing line.

9. A plant according to claim 8, wherein said containment segment (3’) of said at least two horizontal containment segments (3) is the containment segment closest to the casting curve (7) or an intermediate containment segment within at least three containment segments.

10. A plant according to claim 7, wherein said containment segment (3’) comprises an upper part (10) provided with upper containment rolls (11 ) and a lower part (12) provided with lower containment rolls (13); wherein at least one of said upper part (10) and said lower part (12) is configured to be displaced to clear a space adapted for the passage of said at least one second cutting device (2) from the resting position to the cutting position, and vice versa.

11. A plant according to claim 10, wherein both said upper part (10) and said lower part (12) are configured to be moved so as to clear said space; or wherein said lower part (12) is divided into two portions (12’, 12”) hinged at an outer end thereof to be respectively moved so as to clear said space.

12. A plant according to claim 10 or 11 , wherein there are provided two second cutting devices (2) arranged alongside said containment segment (3’), in the respective resting position thereof, on opposite sides with respect to the processing line.

13. A plant according to any one of claims 6 to 12, wherein said at least one second cutting device (2) can be one or more hydraulic shears, one or more oxyacetylene torches, one or more rotary disc shears, one or more milling cutters with a rotating tool.

14. A plant according to any one of claims 6 to 13, wherein the first cutting device (4) is arranged between said at least two horizontal containment segments (3) and i tssaid roughing train (35), and wherein between the first cutting device (4) and the roughing train (35) there is at least one heating furnace (5, 6) having a length not greater than 80 meters, more preferably not greater than 60 meters, even more preferably not greater than 40 meters.

15. A plant according to claim 14, wherein said at least one heating furnace (5, 6) comprises a tunnel furnace (5) provided with heating elements, preferably provided with at least one section comprising an induction heater (6).

16. A plant according to any one of claims 6 to 15, wherein at least one quick induction heating device (37) or a tunnel furnace (5’) is provided downstream of the roughing train (35) and upstream of the finishing train (39).

17. A plant according to any one of claims 6 to 13, wherein the first cutting device (4) is arranged between said roughing train (35) and said finishing train (39), preferably between said roughing train (35) and a quick induction heating device (37), arranged downstream of the roughing train (35) and upstream of the finishing train (39).

18. A plant according to any one of claims 6 to 17, wherein there is provided a motorized roller table for advancing the flat product, or portions thereof cut by means of the first cutting device (4) or the second cutting device (2), towards at least one rolling stand belonging to the rolling mill (35, 39); wherein said motorized roller table comprises at least- a first part (43) arranged between the at least a second cutting device (2) and the first cutting device (4);- and a second part (44) arranged immediately downstream of the first cutting device (4); and wherein both the first part and the second part of said motorized roller table are configured to be controlled independently of each other by a respective control system, or by a single control system, to regulate the advancement speed of said portions of flat product.

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