Plant and process for the multiple-mode production of steel strips

Abstract

A plant for the continuous or batch production of hot-rolled steel strips with a thickness of up to 0.6 mm comprises a continuous caster (1) followed by an inlet roller conveyor (2), a first shear (3), a roughing mill (4), a second shear (5), an induction furnace (6), a finisher (7), a third shear (8), and finally a multiple coiler (9). Production can be carried out either from thin slabs coming from the caster (1) or from 200-300 mm thick slabs of external origin introduced via an offline slab loading unit, including a reversible rougher (10) that receives the slabs loaded into a heating furnace (11) via a connecting roller conveyor (13), as well as a translating tunnel furnace (12) comprising at least two parallel sections (12a, 12b), a first section (12a) of which is movable between a position aligned with the reversible rougher (10) and an offline rest position, and a second section (12b) of which is movable between a position aligned with the reversible rougher (10) and a position aligned with the inlet roller conveyor (2).

Description

[0001] PLANT AND PROCESS FOR THE MULTIPLE-MODE PRODUCTION OF STEEL STRIPS

[0002] The present invention relates to a plant and a process for the continuous, batch or combined production of hot-rolled steel strips in a wide range of sizes with high productivity and cost-effectiveness of the plant and high product quality. In particular, the present invention allows the rolling of thin slabs (typically 90-140 mm thick) from a continuous casting device to be combined with the rolling of thicker slabs (typically OOSOO mm thick) purchased on the market.

[0003] It is well known that in the steel industry, given the increases in the costs of raw materials and energy used, as well as the greater competitiveness required by the global market, as well as increasingly restrictive regulations in terms of pollution, there is a particularly strong need for a method of manufacturing high-quality hot-rolled steel strips that requires lower investment and production costs and offers greater production flexibility. This means that the end product manufacturing industry can also be made more competitive with lower energy consumption, thereby minimizing the negative impact on the environment.

[0004] The state of the art is essentially that described by the inventor himself in his previous patents, in particular EP 1558408 and EP 3606681, to which reference is made for further details. EP 1558408 uses so-called ‘cast rolling’ technology, which combines continuous casting of a thin slab with liquid core reduction (LCR) with an initial roughing stage using a roughing mill (HRM=High Reduction Mill), which produces an intermediate product that, after a heating phase in an induction furnace and subsequent descaling, is further processed in a second finishing rolling phase. This type of rolling is defined as continuous or “endless” because, once started, it does not require repeated feeding of the slabs into the roughing mill and finishing mill, as is the case in batch mode, where the slabs are separated.

[0005] To improve productivity and production flexibility, EP 3606681 introduced the possibility of batch or combined production with an interruption of the cast slab between the casting device (caster) and the rolling mill, in which the possible difficulties of feeding are offset by advantages such as: - if the casting rate (so-called “mass flow” = slab thickness x casting speed) of the caster is lower than that of the rolling mill, e.g. due to the reduced casting speed required by the type of steel, batch mode allows for a reduction in energy consumption, particularly in the induction furnace, thanks to the higher rolling speed and the consequent reduction in heat losses;

[0006] - in the manufacture of coils with a significant difference in thickness between two adjacent coils, which requires a change in the setting of the rolling stand openings when no material is passing through them, a combined mode allows the first coil to be produced mainly in endless mode, but the last portion of the strip is produced in batch mode by cutting the slab so that it can be accelerated and rolled faster to create the time interval required for resetting the empty rolling mill for the production of the second coil of different thickness.

[0007] In addition, to increase the profitability of the plant, the possibility of rolling external slabs has been introduced, which are loaded into the production cycle in the event of unavailability of the caster arranged in line with the rolling mill. For this purpose, after the continuous casting exit, there is an interconnection furnace with rollers or movable beams that makes it possible to choose between three operating modes: endless, combined, and batch. It is also possible to start the production cycle from slabs introduced into the furnace at room temperature via a loading station, and to evacuate slabs, in case of unavailability of the rolling mill, which can then be recovered for production.

[0008] A similar solution is also described in WO 93 / 23182, which provides for a caster for thin slabs 90-140 mm thick followed by a shear to cut the slabs arriving on a conveyor from where they can be loaded into a roller or mobile beam interconnection furnace or transferred to a storage area. At the furnace outlet, the slabs are fed into a reversible rolling mill consisting of a rolling stand preceded and followed by a coder and heater. The slabs collected in the storage area can then be fed into the furnace to be sent to the rolling mill, and slabs from outside the plant can also be loaded through the storage area, so the furnace must be able to heat to rolling temperature slabs loaded into it at room temperature.

[0009] The current scenario of particular uncertainty regarding the cost of electricity and raw materials, in particular scrap and DRI (Direct Reduced Iron) or HBI (Hot Briquetted Iron), has made it necessary to consider new plant and process solutions for endless or batch modes, and also to consider a mixed solution so that thick slabs purchased on the market can also be used in the production of steel strips as an alternative to thin slabs cast on site with the caster. In other words, it is useful to have an alternative to continuous casting in line with the rolling mill, so that the latter can be used even if technical problems occur on the caster or if the cost of energy and raw materials to obtain liquid steel for casting is such that it is more convenient to buy slabs elsewhere where costs are lower.

[0010] However, slabs sourced externally must have a minimum standard weight in order to obtain coils of adequate weight, and if the external slabs are already as thin as if they came out of the continuous casting machine, they become too cumbersome to transport. For example, if I use a thin slab from the caster, which typically has a thickness of 100 mm and a length of 30 m, as the starting material to obtain a desired coil, transporting a similar external slab of the same length would be very complicated and expensive, whereas a 200 mm thick slab is half as long and therefore much easier to transport. On the other hand, a rolling mill in line with the caster as described in EP 3606681 would not be able to achieve the required strip thickness starting from a slab with a thickness of 200 mm, because it would require a greater number of rolling stands.

[0011] Even in the case of the plant described in WO 93 / 23182, where it is possible to increase the number of passes in the reversible rolling mill, there would be similar problems due to the excessive thickness of the starting slab. In fact, it would first be necessary to pass the flat slab through the reversible rolling mill several times before it could be wound onto the heating coils, since even in the examples given in WO 93 / 23182, at least three passes are required starting from a slab approximately 100 mm thick. Furthermore, numerous passes would also be necessary to achieve a strip thickness of 0.6 mm as envisaged in EP 3606681, given that in the above examples nine passes are required to go from 100 mm to approximately 2.5 mm. Therefore, the processing times would be unacceptably long, given that in the examples cited, it takes approximately 10 minutes to go from 100 mm to 2.5 mm (reduction factor 40), so that to obtain a reduction factor of approximately 330 (from 200 mm to 0.6 mm), the times are incompatible with adequate productivity. WO 2013 / 046348 describes a plant according to the preamble of claim 1, in which the translating furnace can move towards a homogenization furnace of the rolling line, and therefore does not arrive in line with the roller conveyor at the exit of the caster, or towards a thick plate treatment line if it is not necessary to roll the slab rough-rolled by the reversible rougher into a strip. In both cases, when the translating furnace is not in line with the reversible rougher, it is not possible to proceed with the roughing of another slab loaded from the external furnace.

[0012] EP 2667983 describes a slab transport system between two rolling lines, using two shuttles with the rough-rolled slab passing from one shuttle to the other at an intermediate position, so that neither shuttle travels the entire distance between the two rolling lines. In this case too, when the first shuttle is not in line with the reversible rougher of the first rolling line, it is not possible to proceed with the roughing of another slab.

[0013] The technical problem is thus to provide the possibility of using externally sourced slabs in a more convenient and quick way, for a seamless integration with the cast slabs and shorter cycle times.

[0014] The purpose of this invention is therefore to provide a solution for the production of hot-rolled strips with a thickness of up to 0.6 mm with greater productivity and flexibility than in the aforementioned prior art. This purpose is achieved by using an offline slab loading unit, consisting essentially of a reversible rougher arranged between a heating furnace through which the slabs are loaded, typically a moving beam furnace long enough to contain multiple slabs, and a translating tunnel furnace comprising at least two parallel sections, one of which is movable between a position aligned with the reversible rougher and a position aligned with the casting and rolling line, and the other movable between a position aligned with the reversible rougher and an offline rest position.

[0015] The fundamental advantage of this configuration is that of increasing the productivity of the plant thanks to the ability of roughing the slabs offline even while the previously rough-rolled slab is transferred to the rolling line by the translating tunnel furnace, significantly reducing cycle times.

[0016] A second embodiment also includes a joining unit located upstream of the rolling mill to join the slabs in order to create an “artificial” endless mode, with the additional advantage of avoiding slab feeding problems despite the slabs being fed into the plant separately.

[0017] In a third embodiment, a shear and an insulated roller conveyor are arranged between the exit of the continuous casting machine and the translating tunnel furnace, obtaining the further advantage of a more increased productivity thanks to the alternation of external slabs and thin slabs cast in line in the feeding of the rolling mill, preferably through the aforementioned joining unit.

[0018] Further advantages and features of the plant and process according to the present invention will be apparent to those skilled in the art from the following detailed and nonlimiting description of some of its embodiments with reference to the accompanying drawings, in which:

[0019] Fig.lA is a schematic view of the plant in its simplest embodiment, with the translating tunnel furnace positioned offline with respect to the rolling mill;

[0020] Fig, IB is a schematic view of the plant of Fig. lA, with the translating tunnel furnace positioned in line with the rolling mill;

[0021] Fig,2A is a schematic view of the plant in a second embodiment similar to the previous one but also including a joining unit, with the translating tunnel furnace positioned offline with respect to the rolling mill;

[0022] Fig,2B is a schematic view of the plant of Fig.2A, with the translating tunnel furnace positioned in line with the rolling mill;

[0023] Fig,3A is a schematic view of the plant in its most complete embodiment, with the translating tunnel furnace equipped with three sections and positioned so that one of its side sections is aligned with the rolling mill;

[0024] Fig,3B is a schematic view of the plant shown in Fig.3 A, with the translating tunnel furnace positioned so that its central section is aligned with the rolling mill.

[0025] Note that in the above schematic figures, for ease of understanding, both the casting and rolling line and the offline slab loading unit are shown in side view with the latter depicted above the former, but in reality the latter unit is located alongside the line on the same horizontal plane. In other words, the translating tunnel furnace does not move vertically but horizontally, i.e., perpendicular to the plane of the sheet. Furthermore, even though the rolling mill is shown in the figures as being divided into a rougher and a finisher with an induction furnace between them, what is said below obviously also applies in the case of an undivided rolling mill without an induction furnace between the stands, as in EP 3606681. Similarly, the number of stands forming the rougher, finisher or undivided rolling mill can vary freely depending on production requirements.

[0026] Referring to Figs.lA-lB, it can be seen that a plant according to the present invention traditionally comprises a continuous caster 1 followed by a preferably insulated inlet roller conveyor 2, a first shear 3, a rougher 4 (e.g., with three stands), a second shear 5, an induction furnace 6, a finisher 7 (e.g., with five cages), a third shear 8, preferably a flying shear, and finally a multiple coiler 9 (e.g., with three coilers). Since these are traditional elements, a person skilled in the art does not need further details on their structure and operation, and the presence of other components (e.g., control unit, cooling system, exit roller conveyor, sensors, etc.) is taken for granted.

[0027] An offline slab loading unit essentially consists of a reversible rougher 10 located between a heating furnace 11, through which the external slabs are loaded and heated, and a translating tunnel furnace 12. As mentioned above, a first innovative aspect of the present invention lies in the fact that furnace 12 comprises at least two parallel sections 12a, 12b having a pitch P equal to the distance D between the reversible rougher 10 and the casting and rolling line. More specifically, each section 12a, 12b comprises a motorized and insulated roller conveyor, as well as heating means such as gas heating nozzles or electric heating resistors.

[0028] Starting from the position shown in Fig.1 A, a plurality of external slabs S, typically 200 to 300 mm thick, are loaded into furnace 11, preferably a moving beam furnace, to increase and homogenize their temperature to a value between 1150°C and 1300°C. When a slab S has been sufficiently heated, it is then transferred via a connecting roller conveyor 13 to the reversible rougher 10, where its thickness is reduced by a plurality of passes, always in odd numbers, until a so-called “transfer bar” with a thickness typically between 60 and 140 mm is obtained.

[0029] Note that when slab S passes through the reversible rougher 10, it is housed in the translating tunnel furnace 12, specifically in the second section 12b in Fig.1 A, while when it returns towards furnace 11, it is supported by the roller conveyor 13. Therefore, both the latter and furnace 12 must be long enough to accommodate the transfer bar resulting from roughing, approximately 30-35 m. It is preferable to limit the length of furnace 12 and, consequently, the distance between caster 1 and rougher 4, which must be as short as possible in endless rolling, when the thin slab is cast directly, in order to limit the cooling of the slab before rolling.

[0030] In the last roughing pass, the transfer bar is positioned in the second section 12b, then furnace 12 moves towards the rolling line and this section 12b, as shown in Fig. IB, is positioned in line with the roller conveyor 2, while the first section 12a is positioned in line with rougher 10 to receive the next slab S' while it is being processed in the reversible rougher 10. The roller conveyor of section 12b, preferably controlled by a variable frequency converter, accelerates so that the transfer bar is loaded onto the insulated roller conveyor 2 and enters rougher 4.

[0031] Once the transfer bar has left section 12b, furnace 12 can return to the position shown in Fig. lA, and the transfer takes place while the next external slab S' is on the roller conveyor 13. If this slab S' has already been thinned sufficiently and only needs to make a final pass through the reversible rougher 10 to be loaded as a transfer bar into section 12b, furnace 12 can then immediately return to the position shown in Fig. IB. Otherwise, the additional passes necessary to achieve the thickness required for the transfer bar are performed in the position shown in Fig. lA, while the other slabs are heated in furnace 11.

[0032] Note that the thickness of the transfer bar is generally less than that of the thin slab cast by caster 1 to avoid problems with feeding into rougher 4, problems that do not exist when the line operates in endless mode with the continuous slab coming from caster 1. For example, if caster 1 is set to produce a 100 mm thick slab, reversible rougher 10 produces an 80 mm thick transfer bar (the thinning limit of an external slab being given by the length of furnace 12 and roller conveyor 13).

[0033] The rolling mill feeding process implemented by the first embodiment of this plant can therefore be summarized in the following steps: a) loading a plurality of external slabs into the heating furnace 11 designed to increase and homogenize their temperature, preferably to a value between 1150°C and 1300°C; b) transferring a heated slab from furnace 11 via the connecting roller conveyor 13 to the reversible rougher 10, where it is thinned to obtain a transfer bar preferably between 60 and 140 mm thick; c) loading the transfer bar into the second section 12b of the translating tunnel furnace 12 and moving said second section 12b to the position aligned with the inlet roller conveyor 2, while the first section 12a is moved to the position aligned with the reversible rougher 10; d) transferring the transfer bar from the second section 12b to the inlet roller conveyor 2 and the next slab heated by the furnace 11 to the reversible rougher 10, where it is thinned at least partially or almost completely; e) moving the first section 12a to its rest position and the second section 12b to the position aligned with the reversible rougher 10, while the next slab is on the connecting roller conveyor 13; f) completing the thickness reduction of the next slab until a transfer bar is obtained; g) cyclical repetition of steps c)-f).

[0034] A second innovative aspect of the present invention, illustrated in Figs.2A-2B, lies in the addition of a joining unit located between the roller conveyor 2 and the first shear 3. As mentioned above, the presence of this unit allows the tail of each slab to be joined to the head of the next slab in order to reproduce the effect of continuous casting, so that endless rolling can be carried out even using the external slabs loaded separately into furnace 11. Although the joining unit itself is already known in the art, its application to a plant of this type is new and inventive, and for the sake of completeness, its structure and operation are described below.

[0035] The unit includes a trimming shear 14, which serves to even out the tail of the transfer bar already engaged by rougher 4 and the head of the next transfer bar coming from the roller conveyor 2, followed by a welding station 15 comprising an induction welder, or a welder based on other technologies such as flash welding or laser, and then followed by a deburring station 16 with the task of removing the excess steel that forms around the joint during the welding phase.

[0036] As an example, the operation of the joining unit can be described as follows: from the position shown in Fig.2B, the transfer bar in section 12b of the tunnel furnace 12 is transferred to the roller conveyor 2 at a speed preferably between 4 and 12 m / min. The trimming shear 14 cuts the tail of the previous transfer bar and the head of the transfer bar loaded onto the roller conveyor 2, which is divided into two sections controlled by two variable frequency inverters to enable the transfer bar to accelerate so that its head reaches the tail of the previous transfer bar.

[0037] When the two transfer bars are adjacent, a device locks their ends (head and tail) leaving a small space, and the two ends are partially fused until the desired amount of molten steel is obtained, for example by flowing an intense current, typically for no more than 5 seconds. Subsequently, the two fused ends of the transfer bars are pressed together by a hydraulic mechanism until a complete joint is obtained, and once the joint is made, the device locks open and the joined transfer bar advances towards rougher 4. However, since the pressure applied causes a small amount of molten steel to leak around the joint, which cools quickly and creates a thickness that would interfere with rolling, before entering rougher 4, the transfer bar is processed in the deburring station 16, which preferably uses rotating cutting discs equipped with special tips and positioned on adjustable hydraulic arms.

[0038] In a preferred embodiment, the welding station is positioned on a carriage that travels synchronized with the rolling speed of the first roughing stand, and the aforementioned welding phases (locking, melting, pressing) are performed during a forward stroke of the carriage. When the joining process is complete, the carriage returns to its initial position, ready for the next joining process, and during the return stroke an automatic cleaning cycle is performed to remove steel splashes.

[0039] Note that the deburring station 16 operates independently of the welding station 15, thus without lengthening the overall cycle time. Furthermore, when the joining unit is not in use, it is preferably moved out of line by means of carriages operated by hydraulic cylinders and replaced by a roller conveyor, to allow endless rolling of the slab coming from continuous casting. In this second embodiment, the rolling mill feeding process therefore includes an additional phase d') of transferring the transfer bar from the roller conveyor 2 to the joining unit, where it is joined to the previous transfer bar. This phase d') takes place after phase d) and substantially simultaneously with phase e) and possibly also with phase f).

[0040] A third innovative aspect of the present invention, in the most complete configuration of Figs.3A-3B, lies in the further addition, between caster 1 and the translating furnace 12, of a fourth shear 17 followed by a second insulated roller conveyor 18. In addition, the translating furnace 12 is equipped with a third section 12c with the same pitch P as the second section 12b, so as to be aligned with the first roller conveyor 2 when section 12b is aligned with the reversible rougher 10 (Fig.3A). In this way, the plant can operate with a “mixed” feed of thin slabs and transfer bars, coming alternately from caster 1 and the translating furnace 12, respectively, to achieve significantly higher productivity.

[0041] Essentially, the configuration of this third embodiment is a combination of batch cast rolling technology with the second embodiment of Figs. 2A-2B. In fact, shear 17 cuts the slab coming out of caster 1, which is loaded onto the roller conveyor 18 and arrives at the roller conveyor 2 via the third section 12c of the translating furnace 12. Meanwhile, an external slab is reduced in thickness in the reversible rougher 10 by passing it between the second section 12b and the connecting roller conveyor 13 (Fig.3A).

[0042] When the transfer bar is ready and positioned in section 12b, furnace 12 moves and section 12b is positioned in line with the roller conveyor 2, while section 12a is positioned in line with the roughing mill 10 to receive the next slab and section 12c is located on the opposite side of the casting and rolling line in a waiting position, as shown in Fig.3B. The roller conveyor of section 12b advances the transfer bar onto the roller conveyor 2 while the roller conveyor 18 receives a new slab from caster 1. After the transfer bar has been unloaded onto the roller conveyor 2, the translating furnace 12 returns to the position shown in Fig.3 A so that section 12c can receive the slab from the roller conveyor 18, which has meanwhile been cut to size by shear 17, to then be unloaded onto the roller conveyor 2 where its head approaches the tail of the previous transfer bar that is already advancing and whose head is undergoing the process of joining with the tail of the previous slab coming from the roller conveyor 18. Through the joining process, in which slabs from continuous casting and transfer bars from the reversible rougher 10 are alternately welded, a continuous transfer bar is created, which is rolled in endless mode in rougher 4 and then in finisher 7 at significantly higher speeds and consequently with higher productivity. For example, the transfer bar can enter rougher 4 at a speed of approximately 12 m / min and finisher 7 at a speed of approximately 80 m / min, with a productivity of approximately 6 million tons / year, which is impossible to achieve in an endless plant with a single continuous casting line.

[0043] Please note that in order to achieve this level of productivity with this “mixed” feed, the cycle time of the joining unit must be reduced to approximately half that achievable with the configuration shown in Figs.2A-2B. Therefore, a faster welding station is required, preferably using so-called “flash welding,” where the heads and tails are fused using an electric arc with a higher current intensity.

[0044] In addition, a sophisticated automation system is required to precisely coordinate the operation of the reversible rougher 10, translating furnace 12, roller conveyors 2 and 18, caster 1 and the joining unit, synchronizing them with rougher 4. In this regard, although the three sections 12a, 12b, and 12c of the translating tunnel furnace 12 are illustrated in an “integrated monolithic” configuration where they perform the same stroke moving synchronously under the action of a single actuator, depending on the layout of the plant (in particular the distance D), the three sections could be independent to make different strokes and / or with different timings to comply with the cycle time necessary for proper plant management. For example, the third section 12c could move separately from the other two sections, making a much shorter stroke between the position in Fig.3A and the position in Fig.3B, since it only needs to make room for section 12b to come into alignment with the roller conveyor 2.

[0045] Similarly, section 12c could return in line with the roller conveyor 18 before section 12b has returned in line with the reversible rougher 10, so that it is ready in advance to receive the slab cast by caster 1. The same applies to the first section 12a, which in the position shown in Fig.3A could be closer to the reversible rougher 10 in order to travel a shorter distance and come in line with the latter before section 12b comes in line with the roller conveyor 2 in the transition to the position shown in Fig.3B. The same automation system, through sophisticated thickness controls, must also ensure that the thickness of the transfer bar coming from the translating furnace 12 is substantially the same as that of the slab coming from the roller conveyor 18, so as to obtain a joined transfer bar of practically uniform thickness.

[0046] In this third embodiment, the rolling mill feeding process can therefore be summarized in the following steps: a) loading a plurality of external slabs into the heating furnace 11 to increase and homogenize their temperature, preferably to a value between 1150°C and 1300°C, and in the meantime a thin slab is cast from caster 1 onto the roller conveyor 18 and cut to size by the fourth shear 17; b) transferring a heated slab from furnace 11 via the connecting roller conveyor 13 to the reversible rougher 10, where it is thinned to obtain a transfer bar preferably between 60 and 140 mm thick, while the thin slab is transferred from the roller conveyor 18 to the inlet roller conveyor 2 through the third section 12c of the tunnel furnace 12, which is aligned with said roller conveyors 18 and 2; c) loading the transfer bar into the second section 12b of the translating tunnel furnace 12 and moving said second section 12b to the position aligned with the inlet roller conveyor 2, and in the meantime, the first section 12a is moved to the position aligned with the reversible rougher 10 and the third section 12c is moved to the rest position, while the thin slab is transferred from the roller conveyor 2 to the joining unit, where it is joined to the previous transfer bar; d) transferring the transfer bar from the second section 12b to the inlet roller conveyor 2 and the next slab heated by furnace 11 to the reversible rougher 10, where it is thinned at least partially or almost completely, and in the meantime a subsequent slab is cast from caster 1 onto the roller conveyor 18 with cutting to size by means of shear 17; e) moving the first section 12a to its rest position and the second section 12b to the position aligned with the reversible rougher 10, while the next slab is on the connecting roller conveyor 13, and moving the third section 12c to the position aligned with roller conveyors 18 and 2; f) completing the thickness reduction of the next slab until a transfer bar is obtained and transferring the next thin slab from the roller conveyor 18 to the inlet roller conveyor 2 through the third section 12c; g) cyclical repetition of steps c)-f).

[0047] The plant described above according to the present invention is therefore suitable for producing high-quality strips with thicknesses of up to 0.6 mm, starting either from thin slabs 90-140 mm thick coming from a continuous caster aligned with the rolling mill or from slabs 200-300 mm thick coming from an external source. Furthermore, this plant can operate both in endless mode, without interruption of the slab between caster 1 and the rolling mill, and in batch mode and even, in the second and third embodiments, in “artificial” endless mode by joining the slabs and / or transfer bars separately before they enter the rolling mill.

[0048] It is clear that the embodiments of the plant according to the invention described and illustrated above are only examples that are subject to numerous variations. In particular, other embodiments not illustrated in the drawings are clearly possible combinations of these three embodiments. For example, the translating furnace 12 could include the third section 12c also in the first and second embodiments, so as not to have an interruption on the casting and rolling line in the positions of Figs.1 A and 2A, or the joining unit could be absent in the third embodiment, which would therefore be more compact but could not operate in the “artificial” endless mode.

Claims

CLAIMS1. A plant for the in-line continuous, batch or combined production of hot-rolled steel strips down to 0.6 mm of thickness, comprising a device (1) for continuous casting of thin slabs with liquid core reduction, followed by an infeed roller conveyor (2), a first shear (3), a rolling mill preferably divided into a rougher (4) and a finisher (7) with a second shear (5) and an induction furnace (6) between them, followed by an exit roller conveyor with a cooling device and then a third shear (8) and a plurality of coders (9), said plant further comprising an offline slab loading unit arranged in the same horizontal plane and comprising a reversible rougher (10) receiving by means of a connecting roller conveyor (13) slabs loaded in a heating furnace (11), as well as a translating tunnel furnace (12) positioned to accommodate the slabs processed in said reversible rougher (10), characterized in that said translating tunnel furnace (12) comprises at least two parallel sections (12a, 12b) of which a first section (12a) movable between a position of alignment with the reversible rougher (10) and an offline rest position, and a second section (12b) movable between a position of alignment with the reversible rougher (10) and a position of alignment with said infeed roller conveyor (2).

2. A plant according to claim 1, characterized in that it further comprises, between the infeed roller conveyor (2) and the first shear (3), a joining unit comprising sequentially a trim shear (14), a welding station (15) and a deburring station (16), and in that the infeed roller conveyor (2) is divided into two sections having independent feed speeds, preferably controlled by two variable frequency inverters.

3. A plant according to claim 1 or 2, characterized in that it further comprises, between the continuous casting device (1) and the translating furnace (12), a fourth shear (17) followed by an insulated roller conveyor (18), and in that the translating tunnel furnace (12) comprises a third section (12c) movable between an alignment position between said insulated roller conveyor (18) and the infeed roller conveyor (2) and an offline rest position.

4. A plant according to claims 2 and 3, characterized in that the welding station (15) uses the flash welding technique.

5. A plant according to any of claims 2 to 4, characterized in that the welding station (15) is positioned on a carriage that travels synchronized with the rolling speed ofthe first rolling stand and welding is performed during a forward stroke of the carriage, while a cleaning cycle is preferably performed during the return stroke.

6. A plant according to any of claims 2 to 5, characterized in that the j oining unit can be moved offline and replaced by a roller conveyor.

7. A plant according to any of the preceding claims, characterized in that at least some of the sections (12a, 12b, 12c) of the translating tunnel furnace (12) perform the same stroke by moving synchronously under the action of a single actuator.

8. A process for feeding the rolling mill of a plant according to claim 1, comprising the steps of a) loading a plurality of external slabs into the heating furnace (11) suitable for increasing and homogenizing their temperature, preferably to a value between 1150°C and 1300°C; b) transfer of a heated slab from the heating furnace (11) by means of the connecting roller conveyor (13) to the reversible rougher (10), where it is thinned to a transfer bar preferably between 60 and 140 mm thick; c) loading of the transfer bar into the second section (12b) of the translating tunnel furnace (12) and moving said second section (12b) to the position in alignment with the infeed roller conveyor (2), while the first section (12a) is moved to the position in alignment with the reversible rougher (10); d) transfer of the transfer bar from the second section (12b) to the infeed roller conveyor (2) and of a subsequent heated slab from the heating furnace (11) to the reversible rougher (10), where it is thinned at least partially or almost completely; e) moving the first section (12a) to its rest position and the second section (12b) to the position in alignment with the reversible rougher (10), while the subsequent slab is on the connecting roller conveyor (13); f) completion of the thickness reduction of the subsequent slab to a transfer bar; g) cyclic repetition of steps (c)-(f).

9. A process for feeding the rolling mill of a plant according to claim 2, comprising in addition to the steps of claim 8 also an additional step d') of transferring the transfer bar from the infeed roller conveyor (2) to the joining unit, wherein it is joined to the previous transfer bar, said step d') taking place after step d) and substantiallysimultaneously with step e) and possibly also with step f).

10. A process for feeding the rolling mill of a plant according to claim 3, comprising the steps of: a) loading a plurality of external slabs into the heating furnace (11) suitable for increasing and homogenizing their temperature, preferably to a value between 1150°C and 1300°C, and meanwhile a thin slab is cast from the continuous casting device (1) onto the insulated roller conveyor (18) and cut to size by the fourth shear (17); b) transfer of a heated slab from the heating furnace (11) via the connecting roller conveyor (13) to the reversible rougher (10), where it is thinned to a transfer bar preferably between 60 and 140 mm thick, while the thin slab is transferred from the insulated roller conveyor (18) to the infeed roller conveyor (2) via the third section (12c) of the tunnel furnace (12), which is in alignment with said roller conveyors (18, 2); c) loading of the transfer bar into the second section (12b) of the tunnel furnace (12) and moving said second section (12b) to the position in alignment with the infeed roller conveyor (2), and meanwhile the first section (12a) is moved to the position in alignment with the reversible rougher (10) and the third section (12c) is moved to the rest position, while the thin slab is transferred from the infeed roller conveyor (2) to the joining unit, where it is joined to the previous transfer bar; d) transfer of the transfer bar from the second section (12b) to the infeed roller conveyor (2) and of a subsequent heated slab from the heating furnace (11) to the reversible rougher (10), where it is thinned at least partially or almost completely, and meanwhile a subsequent slab is cast from the continuous casting device (1) onto the insulated roller conveyor (18) and cut to size by the fourth shear (17); e) moving the first section (12a) to its rest position and the second section (12b) to the position in alignment with the reversible rougher (10), while the subsequent slab is on the connecting roller conveyor (13), and moving the third section (12c) to the position in alignment with the roller conveyors (18, 2); f) completion of the thickness reduction of the subsequent slab until a transfer bar is obtained and transfer of the subsequent thin slab from the insulated roller conveyor (18) to the infeed roller conveyor (2) via the third section (12c); g) cyclic repetition of steps (c)-(f).

Images