System and method for producing a metal strip in continuous or batch operation

Abstract

The present invention relates to combined casting and rolling processes that can be operated in both continuous and batch modes. The object of the present invention is to provide a compact system for producing a metal strip that can be operated in both continuous and batch modes. This object is achieved, on the one hand, by a system in which a first inductive heating furnace (25) is arranged between the last strand guide roll and the first cutting device (3). Downstream of the first cutting device (3), at least one slab handling device (25a) for feeding and removing cut slabs is arranged. Parallel to a first casting system (1), a second continuous casting system (2) with a second cutting device (4) for separating a strand into second slabs (42) is arranged.A second inductive heating furnace (28) is arranged in front of the second separating device (4), and a transport device (18) is arranged after the second separating device (4).

Description

field of technology

[0001] The present invention relates to combined casting and rolling processes, which can be operated in both continuous and batch operation.

[0002] On the one hand, the invention relates to a system for producing a metal strip, comprising the following system components a first continuous casting plant, wherein the end of the casting plant is determined by a strand guide roller arranged as the last, a first cutting device downstream of the first casting plant for separating a strand into first slabs, a rolling mill downstream of the first cutting device, wherein a beginning of the rolling mill is determined by a rolling stand arranged as the first, a shear downstream of the rolling mill, a reeling device downstream of the shear, an automation device which can control the plant in such a way that it can be operated in continuous or batch operation.

[0003] On the other hand, the invention relates to a method for producing a metal strip using the system. State of the art

[0004] Combined casting and rolling processes are currently replacing the conventional methods of thick slab casting and hot strip milling.

[0005] The most important advantages of combining casting and rolling processes in continuous operation: Minimal energy consumption Reduced or no CO2 emissions; production of ultra-thin strips; highest consistent quality in continuous operation; lower investment costs; lower operating costs

[0006] Since the mass flow through the entire system is essentially constant in continuous operation and no phased acceleration to bridge longer distances is possible, many advantages of continuous operation are linked to the short overall length of the system.

[0007] However, in many cases a single-strand casting and rolling mill is insufficient to completely replace an existing hot strip mill and all its products due to the mass flow limitations of today's casting process.

[0008] The maximum mass flow rate that a continuous casting plant can currently deliver is in the range of 7 to 8 tons per minute. This results in a maximum annual production of approximately 3 million tons per year. High-performance hot rolling mills, on the other hand, have a production volume between 4 and 6 million tons per year (Mt / J), which can easily be double that of a continuous casting plant.

[0009] Therefore, steel producers try to combine two continuous casting plants with one rolling mill to achieve the same capacity, e.g.: 2.5 Mt / J with casting plant 1 + 2.5 Mt / J with casting plant 2 = 5 Mt / J for one rolling mill

[0010] By definition, this means that continuous operation is not possible when producing two casting strands.

[0011] Since many demanding grades (ultra-thin and high-quality) can only be produced in continuous operation, steel manufacturers want a plant that meets both requirements: Continuous line for the production of ultra-thin, high-quality grades; high-capacity line for combining two casting lines with a rolling mill

[0012] A system should meet the following requirements: Flat sheet production in the dimension range of: thickness 0.6 to 32 mm, preferably: 0.8 to 25.4 mm; width 600 to 2600 mm, preferably 900 to 2134 mm. All steel grades with a carbon content of 0.001% to 1%, preferably 0.005% to 0.5%. Standard grades requiring high productivity are produced by fast casting. Special grades requiring slow solidification are produced by slow casting. Productivity: 3 to 8 Mt / year (preferably 4 to 6 Mt / year).

[0013] Due to the demand for continuous production, there have recently been developments to also use continuous operation on combined twin-strand slab casting and rolling mills.

[0014] These solutions are currently characterized by large distances between the casting and rolling sections, which are necessary to link the production of the two strands.

[0015] To overcome heat losses during the transport of the slabs from the casting machines to the rolling mill, tunnel kilns with a length of 150 to 250 m are currently being proposed.

[0016] While these furnaces effectively prevent temperature losses, they are very energy-intensive and require a lot of maintenance. Furthermore, the furnace is always in operation in the line with the rolling mill, even during continuous production.

[0017] However, concepts based on twin-strand casting and rolling processes have emerged that also offer the possibility of continuous single-strand production. These concepts all feature a long tunnel furnace and a heated ferry upstream of the rolling mill, which performs the buffering and merging functions during batch operation.

[0018] Batch operation requires two ovens, each up to 250 m long, to be heated continuously, resulting in high energy consumption.

[0019] A plant with a tunnel kiln and heating conveyor must also be bridged during continuous operation. At a casting speed of 4 m / min and a kiln length of 160 m, this takes approximately 40 minutes. This leads not only to high oxidation but also to significant energy losses during this time. Any advantage gained from utilizing the hot core of the strand coming from the casting machine is thus lost after transport through the tunnel kiln. Overall, this setup is not advantageous for continuous operation, as the distance between the casting machine and the rolling mill must be significantly increased.

[0020] Many advantages typically associated with continuous operation, such as low energy consumption, no CO2 emissions, low yield losses, maximum initial frame reductions and thus minimal thicknesses, cannot be fully achieved with this type of plant design.

[0021] Furthermore, the tunnel kiln requires a lot of maintenance, and during maintenance periods neither the continuous casting plant nor the rolling mill can be operated. Summary of the invention

[0022] The object of the present invention is to create a compact system for producing a metal strip, which can be operated both in continuous operation and in batch operation.

[0023] The task is further solved by a system.

[0024] In the system, a first induction heating furnace is arranged between the last strand guide roller and the first cutting device. Downstream of the first cutting device, at least one slab handling device, preferably two slab handling devices, is arranged for feeding and removing cut slabs. The slab handling device can feed or remove the cut slabs transversely to the casting direction and transport them in the casting direction. Parallel to the first casting system, a second continuous casting system with a second cutting device is arranged for separating a strand into two slabs. A second induction heating furnace is arranged upstream of the second cutting device, and a transport device is arranged downstream of the second cutting device.A slab transport device is arranged in such a way that second slabs can be fed to the slab manipulation device and / or first slabs can be removed from the slab manipulation device.

[0025] This arrangement according to the invention makes it possible to avoid CO2 emissions and achieves a compact design.

[0026] The placement of the induction heating furnace immediately after the first and second casting plants and before each cutting device has proven particularly advantageous. This arrangement counteracts temperature differences between the slab head and slab foot of the first and second slabs, ensuring a consistent temperature profile along the entire length of the first slab as it arrives at the rolling mill. These temperature differences arise, for example, because the slab head remains in the area after the cutting device for a longer period due to the casting velocity before reaching the subsequent rolling mill. The slab is usually accelerated after being cut by the cutting device—that is, transported at a higher speed than the casting velocity—to the subsequent rolling mill.In the area upstream of the cutting device, the speed of the strand is lower because the transport speed only increases after the strand has been cut into the first and second slabs. Therefore, due to the longer residence time in the induction heating furnace, less power is required for heating, and the furnace can be smaller because the mass flow is even lower than after the cutting device. By pre-calculating the heating power of the induction heating furnace, taking into account the casting speed and the transport speed after cutting, a homogeneous temperature can be achieved along the entire length of the slabs for an optimal subsequent rolling process. The slab head area requires a higher heating power than the area around the slab foot because the slab head remains in the area downstream of the cutting device for a longer time than the slab foot.Without the additional heating power of the induction heating furnace, the area around the slab head would have a lower temperature than the slab foot due to the longer residence time. Another advantage is that the core of the strand is still hot immediately after casting and before cutting, and the heating of the strand can be limited to the outer layer of the slab to a depth of 30–45 mm from the surface. The penetration depth for induction heating can be calculated using the following formula: δ = 1 π ∗ f ∗ μ ∗ κ δ ... Penetration depth f... Operating frequency of inductive heating oven µ... Permeability κ... Electrical conductivity

[0027] By selecting a suitable operating frequency, the penetration depth can be limited to the required range, ensuring effective heating with minimal power consumption. In the context of this invention, a second casting system is understood to mean a system that produces a second casting strand. It is therefore also conceivable that a first casting system could produce a first casting strand and simultaneously produce a second casting strand. The second casting strand would then be the one produced by the second casting system in this invention.

[0028] A preferred embodiment provides for a buffer storage tank – with an enclosure featuring thermal insulation, a heat-reflecting surface, and / or a heating element – ​​to be arranged between the slab handling device and the rolling mill. This arrangement allows sufficient time for the heat introduced into the surface of the slabs to penetrate and ensure thorough heating. The enclosure effectively encloses the respective plant section, and the slabs must be fed in through openings, which may also be closable. The enclosure is designed to minimize heat loss. When heat is supplied, the enclosure ensures that it is used as completely as possible to heat the slab and is not lost to the environment. The heat-reflecting surface radiates the heat back onto the slab.

[0029] An advantageous embodiment provides that the transport device, the slab manipulation device and / or the slab transport device has an enclosure with thermal insulation, an enclosure with a heat-reflecting surface and / or an enclosure with a heating device.

[0030] This ensures that the heat loss from the slabs is kept as low as possible for the subsequent rolling process.

[0031] A suitable design provides that the transport device is downstream of at least a buffer storage tank with an enclosure with thermal insulation, an enclosure with a heat-reflecting surface and / or an enclosure with a heating device.

[0032] Another advantageous embodiment provides that at least two buffer storage tanks with an insulated enclosure, an enclosure with a heat-reflecting surface, and / or an enclosure with a heating device are arranged downstream of the transport device, with a slab ferry for transverse transport being arranged between two buffer storage tanks. In the event of an upcoming roll change in the rolling mill or another problem in the plant, the slabs can be kept at the desired temperature or the temperature loss can be minimized.

[0033] Another advantageous embodiment provides that the distance between the end of the first casting plant and the beginning of the rolling mill is less than 150m, preferably less than 130m, and particularly preferably less than 110m.

[0034] A preferred embodiment provides that the automation device can control the slab manipulation device in such a way that a first slab cut at the first cutting device can be transported to the rolling mill at a transport speed greater than a casting speed of the first casting plant.

[0035] A suitable embodiment provides that the first casting plant produces first slabs with a thickness of 100 to 200 mm, preferably 120 to 160 mm.

[0036] An advantageous embodiment provides that the second continuous casting plant produces second slabs with a thickness range that essentially corresponds to that of the first slab, or produces second slabs with a maximum thickness of 250 mm; preferably, these can be reduced in thickness by means of a pre-frame.

[0037] The problem is further solved by a method for producing a metal strip with a system according to claims 1-6. Depending on a final thickness, a desired CO2 footprint, a predetermined low energy consumption, a predetermined casting speed, and / or a mechanical property of the metal strip to be produced, the system is operated by an automation device in continuous or batch operation.

[0038] The system is operated continuously for grades with a final thickness of less than 1.5 mm. For grades from 1.5 to 2.5 mm, the system is operated continuously or in batch mode, depending on the desired mechanical properties, such as strength.

[0039] If low CO2 emissions and / or low energy consumption are required, the plant is operated in continuous operation whenever possible.

[0040] If a quality of metal strip is to be produced which requires slow casting by the casting plant, the plant is operated in batch mode. Brief description of the drawings

[0041] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of an exemplary embodiment, which is explained in more detail in conjunction with the drawings. These drawings show: Fig. 1-3 a schematic representation of a first casting plant with subsequent rolling mill and with a parallel second casting plant with an induction heating furnace Description of the embodiments

[0042] In the Fig. 1 Figure 1 shows a system with a first induction heating furnace 25 upstream of the first cutting device 3. In this embodiment, a first strand 1a, produced by the first casting plant 1, is heated in the first induction heating furnace 25. Downstream of the first induction heating furnace 25, a first cutting device 3 is arranged, which separates a first slab 40 from the heated strand 1a. Downstream of the first cutting device 3, a slab handling device 25a is arranged for feeding and unloading slabs. Slabs are transported either to or away from the slab handling device 25a – for example, to a slab storage area 50 – by a slab transport device 16.The slab transport device 16 can, for example, be guided via rails mounted on the ground and a cable, chain, or wheel drive as a slab ferry, or on rails located at a certain height – overhead – as a slab manipulator or crane. Cold slabs 43 stored in the slab storage area 50 can be heated with a third induction heating furnace 27 and then fed to the rolling mill 8 via the slab transport device 16.

[0043] The slab handling device 25a is followed by a buffer storage unit 26, a first intensive heating device 6, and a first descaling device and / or intensive cooling device 7. A rolling mill 8 is arranged downstream. The beginning of the rolling mill 8 is defined by a first rolling stand 8a. The distance L between the end of the casting plant 1 and the beginning of the rolling mill 8 should be as small as possible to minimize potential heat losses from the cast first strand 1a and thus enable continuous operation. The distance L should be less than 150 m, preferably less than 130 m, and particularly preferably less than 110 m. Downstream of the rolling mill 8, a third cutting device 9, a second intensive heating device 10, and a second descaling device and / or an intensive cooling device 11 can be arranged. A further rolling mill 12 can then be arranged.Following this are a cooling device 13, a shear 14, and a reeling device 15 for winding a rolled metal strip. The system has an automation unit 45 which controls all system components in such a way that the system can be operated either in batch mode or in continuous mode.

[0044] In the Fig. 2 is compared to Fig. 1 A further slab manipulation device 25a is arranged between the slab manipulation device 25a and a buffer storage tank 26.

[0045] In the Fig. 3A pre-frame 20 is provided upstream of the second induction heating furnace 28 to reduce the thickness of the second strand 2a. The transport device 18 is equipped with thermal insulation 18a, followed by buffer storage tanks 26 and a slab ferry 19. The slab ferry 19 is subsequently connected to further buffer storage tanks 26. After the buffer storage tanks 26, the slabs are fed to the slab manipulation devices 25a by means of the slab transport device 16.

[0046] Although the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention. Reference symbol list

[0047] 1 First casting plant 1 First strand 2 Second casting plant 2 Second strand 3 First cutting device 4 Second cutting device 6 Intensive heating device 7 Descaling device and / or intensive cooling device 8 Rolling mill 8 First rolling stand 9 Third cutting device 10 Second intensive heating device 11 Descaling device and / or an intensive cooling device 12 Further rolling mill 13 Cooling device 14 Shear 15 Reel device 16 Slab transport device 18 Transport device 18a Thermal insulation 19 Slab ferry 20 Pre-stand 25 First inductive heating furnace 25a Slab handling device 26 Buffer tank 27 Third inductive heating furnace 28 Second inductive heating furnace 30 Strand guide segment 31 Strand guide roller 40 First slab 41 Slabs 42 Second Slab 43 Cold slab 45 Automation device 50 Slab storage Casting direction L Distance

Claims

1. Plant for producing a metal strip, comprising the following plant components: - a first continuous casting plant (1), wherein the end of the casting plant (1) is defined by a strand guide roller (31) arranged as the last, - a first cutting device (3) downstream of the first casting plant (1) for cutting a first strand (1a) into first slabs (40), - a rolling mill (8) downstream of the first cutting device (3), wherein a beginning of the rolling mill is defined by a rolling stand (8a) arranged as the first, - a shear (14) downstream of the rolling mill (8), - a reeling device (15) downstream of the shear (14), - an automation device (45) which can control the plant in such a way that it can be operated in continuous or batch operation. characterized by the fact thatbetween the last strand guide roller (31) and the first cutting device (3) ∘ a first inductive heating furnace (25) is arranged, ∘ downstream of the first cutting device (3) at least one slab handling device (25a), preferably two slab handling devices (25a), for feeding and removing cut slabs, is arranged, wherein the slab handling device (25a) can feed or remove the cut slabs transversely to the casting direction (G) and can transport them in the casting direction, wherein ∘ parallel to the first casting plant (1) a second continuous casting plant (2) with a second cutting device (4) for separating a cast second strand (2a) into second slabs (40) is arranged, wherein a second inductive heating furnace (28) is arranged upstream of the second cutting device (4), and wherein a transport device (18) is arranged downstream of the second cutting device (4).• A slab transport device (16) is arranged such that second slabs (42) can be fed to the slab manipulation device (25a) and / or first slabs (40) can be removed from the slab manipulation device (25a).

2. Apparatus for producing a metal strip according to claim 1, characterized by the fact that A buffer storage unit (26) is arranged between the slab manipulation device (25a) and the rolling mill. The buffer storage unit has an enclosure with thermal insulation (18a), an enclosure with a heat-reflecting surface and / or an enclosure with a heating device.

3. Apparatus for producing a metal strip according to one of claims 1 or 2, characterized by the fact thatthe transport device (18), the slab handling device (25a) and / or the slab transport device (16) shall have an enclosure with thermal insulation (18a), an enclosure with a heat-reflecting surface and / or an enclosure with a heating device.

4. Apparatus for producing a metal strip according to one of claims 1-3, characterized by the fact that the transport device (18) is downstream of at least a buffer storage tank (26) with an enclosure with thermal insulation, an enclosure with a heat-reflecting surface and / or an enclosure with a heating device.

5. Apparatus for producing a metal strip according to one of claims 1 - 4, characterized by the fact thatThe transport device (18) is followed by at least two buffer storage tanks (26) with an enclosure with thermal insulation, an enclosure with a heat-reflecting surface and / or an enclosure with a heating device, wherein a slab ferry for transverse transport is arranged between two buffer storage tanks.

6. Apparatus for producing a metal strip according to one of claims 1 - 5, characterized by the fact that the distance (L) between the end of the first casting plant (1) and the beginning of the rolling mill (8) is less than 150m, preferably less than 130m, particularly preferably less than 110m.

7. Apparatus for producing a metal strip according to one of claims 1 - 6, characterized by the fact thatthe automation device (45) can control the slab manipulation device (25a) in such a way that a first slab (40) cut at the first cutting device (3) can be transported to the rolling mill (8) at a transport speed greater than a casting speed of the first casting plant (1).

8. Plant for producing a metal strip according to claims 1-7, characterized by the fact that by the first casting plant (1) first slabs (40) with a thickness of 100 to 200 mm, preferably of 120 to 160 mm, are produced.

9. Apparatus for producing a metal strip according to any one of claims 1 - 8, characterized by the fact that the second continuous casting plant (2) produces second slabs with a thickness range which essentially corresponds to that of the first slab or second slabs (42) with a maximum thickness of 250mm, preferably these can be reduced in thickness by means of a pre-frame (20).

10. Method for producing a metal strip with a system according to claims 1-6, characterized by the fact that that the system can be operated in continuous or batch operation using an automation device (45), depending on the thickness, CO2 footprint, casting speed and / or mechanical strength of the metal strip to be produced.

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