Patent Application
20250129444
The present disclosure relates to a system and to a method for producing flat rolled products from thick-cast steel and/or non-iron metal slabs and, in a further aspect, to the use of at least one electric heating device, in particular an electric heating device for a direct hot charging process, arranged in front of a hot-rolling mill in the transport direction, for heating thick slabs having a thickness of at least 160 mm to a hot-rolling temperature.
In the prior art, systems and methods are known with which thick slabs are heated directly using the casting heat, or only after intermediate storage in a slab store, initially by means of gas-powered heating devices and subsequently fed to a hot-rolling mill. Heating the thick slabs in a gas-fired heating device requires high fuel quantities, in particular if the thick slabs coming from a slab store have to be heated from temperatures similar to room temperature to at least 1000° C., and also long heating times. The use of fossil fuels, such as natural gas in particular, also leads to high CO2 emissions.
Japanese patent JP 6562223 B2 describes a system by means of which thick slabs are fed directly to a hot-rolling mill using the casting heat. Thereby, the edges of the thick slabs are heated to a corresponding hot-rolling temperature by a series of inductive edge heaters arranged one behind the other. The targeted heating of the edges suppresses the cooling of the slab center section, but such a heating device does not enable the targeted heating of the entire thick slab.
The present disclosure provides an improved system along with an improved method for producing a flat rolled product from thick-cast steel and/or non-iron metal slabs.
The system for producing flat rolled products from thick-cast steel and/or non-iron metal slabs comprises a continuous casting device, by means of which a continually cast product with a thickness of at least 160 mm can be continually cast; a separating device arranged so as to adjoin the continuous casting device, by means of which the flat continually cast product can be separated into individual thick slabs; a hot-rolling mill, by means of which the thick slabs can be rolled into the flat rolled product, wherein the hot-rolling mill comprises a pre-rolling train and a finishing rolling train in each case with at least one rolling mill stand and is arranged in a common (first) transport line with the at least one continuous casting device; at least one thick slab supplying device arranged transversely to the transport line and positioned between the separating device and the rolling train; along with at least one electric heating device for a direct hot charging process arranged in the transport direction in front of the hot-rolling mill, in particular in the transport direction in front of the pre-rolling train, by means of which at least those thick slabs which come from the continuous casting device arranged in the common transport line can be heated over their entire surface to a hot-rolling temperature.
By means of the system, the thick slabs can be heated to the predetermined rolling temperature as required. The at least one electric heating device for a direct hot charging process arranged in the transport direction in front of the hot-rolling mill, in particular in the transport direction in front of the pre-rolling train, thus enables individual temperature control of the steel grade being cast.
Within the meaning of the present disclosure, the term “thick slab” is understood to mean a slab that has a minimum thickness of at least 160 mm, preferably a minimum thickness of at least 180 mm, more preferably a minimum thickness of at least 200 mm. Since the maximum thickness of the thick slabs is technologically limited due to the continuous casting devices currently available, the maximum thickness of the thick slabs is preferably 300 mm, more preferably 250 mm. Such thick slabs typically have widths in the range of 800 to 2500 mm, preferably widths in the range of 1000 to 2300 mm.
The production of thick slabs as opposed to thin slabs has several positive effects. On the one hand, the throughput alone can increase the output quantity, such that a higher degree of utilization can be achieved with the hot-rolling mill. Thick slabs also have a considerable advantage over thin slabs in terms of quality. Compared to thin slabs, thick slabs have a smaller surface area per cast ton of material. Temperature inhomogeneities of slabs transported in the transport line can be reduced. Due to the smaller surfaces in relation to each ton of cast material, the formation of scale is reduced, resulting in fewer casting residues and surface defects, as a result of which material losses due to their removal can be reduced.
The term “electric heating device,” which is also referred to in the present application as an electric heating device for a direct hot charging process, an electric thick slab preheating device, an electric thick slab reheating device, an electric pre-strip heating device or an electric supplementary thick slab heating device, is generally understood to mean an electrically operable device by means of which the thick slabs can be heated by means of electric current. The electric heating device can advantageously comprise inductive heating devices, conductive heating devices and/or electric heating devices with indirect resistance heating. It is particularly preferred that the electric heating device is an inductive heating device or a conductive heating device. Due to the thickness range of the thick slabs, an inductive heating device can be operated advantageously according to the longitudinal field principle and enables rapid heating due to the high energy density. With a conductive heating device, the respective thick slab forms part of the circuit and is therefore heated directly by the electric current passing through it, as a result of which a very high degree of efficiency (close to 1) and a particularly rapid heating is enabled.
An inductive and/or conductive electric heating device also has the advantage that it can be designed as a series connection of individual units for both the core and the regions close to the surface of the thick slabs.
Alternatively and/or additionally, an electric tunnel furnace operated via resistance heating can also be provided.
The system can be used to set a temperature profile in the respective thick slab, which is specifically adapted to the subsequent pre-rolling process, in particular the cooling that occurs during pre-rolling. If cold spots (so-called “skid marks”) are detected on the thick slab surface, for example upon the use of walking beam furnaces, they can be specifically removed by localized heating, as a result of which the quality of the flat rolled product that is then produced can be improved. The short heating times also reduce the formation of scale, as a result of which both the output quantity and the surface quality can be improved. In addition, the system enables the individual heating of each thick slab to the temperature level required for the respective technology without overheating or undercooling.
Within the meaning of the present disclosure, the term “entire surface” means that the thick slabs are heated to a predetermined nominal temperature over their entire surface and in a specific thickness upon passing through the electric heating device.
The nominal temperature of the thick slab is largely uniform and/or identical in three-dimensional extension, wherein permissible temperature differences amount to ≤±80° C., preferably ≤±50° C., particularly preferably ≤±20° C. of a target/nominal temperature.
The nominal temperature simplifies further processing of the thick slab. Non-uniformly heated thick slabs can lead to variable forming conditions during further processing, for example during rolling, such that no uniform forming takes place over the length and/or width of the thick slab, thus increasing the proportion of scrap in the necessary finishing cuts. Non-uniform temperatures can also cause non-uniform changes in the microstructure, along with as geometric defects such as, for example, flatness defects. By setting a uniform temperature level over the entire surface at an early stage, these problems and defects can be avoided or at least limited. Complex set-up and processes to compensate for such defects can be simplified or even eliminated. Interference between desired influences and reactions resulting from a non-uniform temperature level is also minimized.
Preferably, the electric heating device for a direct hot charging process is designed in such a manner that the thick slabs can be heated over their entire surface. In other words, such a heating device enables not only specific heating of the edges, but also heating of the central part of the thick slab located between the edges. A further advantage of such an electric heating device for a direct hot charging process arranged in the transport direction in front of the hot-rolling mill, in particular in the transport direction in front of the pre-rolling train, is that this enables maximum utilization of the casting heat, as a result of which energy savings of more than 70% are possible compared to conventional removal from a slab store.
The features listed individually in the dependent formulated claims can be combined with one another in a technologically useful manner and can define further embodiments of the invention. In addition, the features indicated in the claims are further specified and explained in the description, wherein further preferred embodiments are shown.
It should be noted that the present system is only suitable and intended for producing flat rolled products from thick-cast steel and/or non-iron metal slabs. With such systems, the thick slabs then produced can be stored temporarily without any problems or easily transported from a second transport line due to their typical dimensions, in contrast to systems intended for producing thin slabs. Thick slabs usually have a length of less than 12 meters, sometimes less than 10 meters, whereas thin slabs usually have lengths of at least 25 meters and are therefore more complex to transport and store. Furthermore, the flat rolled products of such systems also differ from systems intended for producing thin slabs. This means that specific steel grades, such as, for example, peritectic steel grades or steel grades with very high surface quality requirements, cannot be produced in the required quality on conventional thin slab systems.
The length of a particular thick slab, in particular for a direct hot charging process, can correspond not only to a single coil length but also to a multiple thereof, since transport across the transport line and further handling steps are not required.
Preferably, the continuous casting device is designed in such a manner that, by means of it, a continually cast product with a thickness of at least 160 mm can be continually cast. The continuous casting device can, for example, be designed as a single-strand or multi-strand continuous casting device.
In an advantageous embodiment, the system can comprise at least one electric pre-strip heating device arranged in the transport direction in front of the finishing rolling train, which is particularly preferably designed in such a manner that the rolled flat rolled pre-product can be heated over its entire surface. These can be used to heat the rolled flat rolled pre-products, which leave the pre-rolling train at a temperature of below 1000° C., for example, in a particularly energy-efficient manner to a temperature specifically predetermined for the finish rolling process, as a result of which the desired properties of the flat rolled product can be set. For example, effective compensation can be provided for temperature differences between the head and the end of a rolled flat rolled pre-product, as a result of which greater rolling stability and thus higher output are enabled. The resulting more homogeneous temperature distribution also enables lower final strip thicknesses and more homogeneous mechanical properties of the flat rolled product produced.
To the extent that absolute temperature values are stated in this application, they are exclusively average temperatures of the respective substrate.
The at least one thick slab supplying device is preferably designed as a transport and heating device, by means of which the transported and/or temporarily stored thick slabs can be heated to the hot-rolling temperature, if necessary over their entire surface. The transport and heating device can be designed in such a manner that, simultaneously or sequentially with the transport, a temperature increase or a holding of the temperature is enabled. Preferably, the thick slab supplying device is designed in the form of a walking beam furnace, which comprises at least one segment that comprises electrically operated heating elements and/or gas-powered burners.
A system designed in this manner thus comprises a first transport line, by means of which the thick slabs can be heated to the hot-rolling temperature for a short time using the casting heat by means of the electric heating device for a direct hot charging process and subsequently fed to the hot-rolling mill. Parallel to the first transport line, a second transport line can also be provided, by means of which thick slabs that have been temporarily stored and/or cooled to 400 to 800° C., which are usually stored in a slab store and/or a soaking pit, are heated directly to the hot-rolling temperature via the thick slab supplying device and then fed to the rolling process. Alternatively and/or additionally, thick slabs cast in a second continuous casting device can also be fed to the rolling process via the thick slab supplying device.
In an advantageous embodiment, the at least one, preferably two or a plurality of thick slab supplying devices are arranged between the electric heating device for the direct hot charging process and the pre-rolling train. In a further advantageous embodiment, the system can also comprise at least one, preferably two or a plurality of the thick slab supplying devices between the separating device and the electric heating device for the direct hot charging process.
In addition to the at least one thick slab supplying device, at least one electric thick slab preheating device can preferably be connected upstream on the inlet side, which is preferably designed in such a manner that the thick slabs can be heated over their entire surface. The electric thick slab preheating device is particularly suitable if higher temperatures are required for a short time to set the mechanical properties, such as, for example, the strength, of the flat rolled products to be produced and the thick slab supplying device that subsequently passes through can be operated at a lower temperature level required for the flat rolled products to be produced.
In a further advantageous embodiment, at least one electric thick slab reheating device can be connected downstream of the at least one thick slab supplying device on the outlet side, which is particularly preferably designed in such a manner that the thick slabs can be heated over their entire surface. In this connection, it is particularly preferably provided that the at least one electric thick slab reheating device is arranged between the at least one thick slab supplying device and the pre-rolling train. The electric thick-slab reheating device on the outlet side further increases the flexibility of the system in order to optimize energy production, on the one hand, and to meet the logistical and technological requirements of the rolling mill in the best possible manner, on the other hand.
In addition, the system can comprise at least one supplementary electric thick slab heating device, which is preferably connected upstream of the at least one electric thick slab reheating device.
In order to reduce production losses due to transition widths upon changing the casting width on the one hand and, on the other hand, to reduce the wear of the work rolls in the finishing train to a comparable level and to ensure an optimum result for a strip profile and/or strip flatness with the longest possible journey through the system, the rolling mill should enable specific rolling program profiles, since the availability in the hot-rolling mill is reduced by an increase in the number of necessary work roll changes upon the use of the same slab widths. Advantageously, the pre-rolling train therefore comprises at least one upsetting device in addition to a first and/or a second pre-rolling stand in the transport direction. Preferably, the upsetting device comprises at least one slab upsetting press and/or, if applicable, at least one, preferably a plurality of, upsetting presses. By using an upsetting device, such as the slab upsetting press, if applicable in combination with at least one upsetting press, a necessary width-related and profile-related optimized rolling program can be ensured, since larger and/or constant slab widths can be cast. Advantageously, the upsetting device is designed in such a manner that the slab width can be reduced by up to 450 mm, preferably up to 350 mm. In addition, the use of additional upsetting presses enables a further reduction in slab width of up to 100 mm per upsetting press.
Furthermore, in an advantageous embodiment, the system can comprise a control device with an associated calculation unit, wherein the control device is designed to control and/or regulate the system on the basis of a minimized energy consumption and/or a maximum throughput, and/or on the basis of product properties and/or product dimensions.
To set the system on the basis of minimized energy consumption, for example, the necessary temperature level, the possible heating steps, the possible heating devices, the possible temperature losses and/or the possible temperature inputs within the system can be optimized in such a manner that the system is set with minimized energy consumption. The calculation unit can preferably use a physical process model that maps the thermal conditions and determines suggestions for setting the system.
Alternatively or additionally, the control device can control the system in such a manner that maximum throughput is achieved. For this purpose, groups of batches in special thickness, width and/or length dimensions can be formed by optimizing the casting sequences, the insertion sequences, the transport device and/or by operating the rolling mill at the design limit, by means of which throughput can be increased. In particular, maintenance cycles such as roll change times, mold change times and/or mold changeover times can be taken into account. Grouping batches and/or sequences according to product dimensions has the advantage that material losses due to transition pieces in the event of width or thickness changes can be avoided as far as possible. The system can also be controlled by the calculation unit according to product properties. If, for example, a very high surface quality is required, the calculation unit can set a correspondingly slow casting speed, stronger descaling, corresponding temperature control, etc. Similarly, the setting of the system can be optimized to achieve optimum magnetic, mechanical and/or geometric properties.
In order to effectively reduce the energy and/or temperature losses of the thick slabs and/or the flat rolled pre-product in the pre-rolling train on the transport route, the system can also comprise a plurality of specifically arranged thermal insulation hoods. Thereby, the thermal insulation hoods can be designed as passive or active thermal insulation hoods. The active thermal insulation hoods are preferably operated with burners using hydrogen produced by “green” means as fuel, or electrically.
Thus, in an advantageous embodiment, the system can comprise a plurality of thermal insulation hoods between the separating device and the electric heating device for the direct hot charging process and, if applicable, between the electric heating device for the direct hot charging process and the hot-rolling mill, in particular the pre-rolling train.
In a further advantageous embodiment, the system can also comprise a plurality of thermal insulation hoods within the pre-rolling train. These can, for example, be arranged in the transport direction in front of and/or behind an upsetting device, and, if applicable, in front of and/or behind each pre-rolling stand.
In a further aspect, the present disclosure also relates to a method for producing flat rolled products from thick-cast steel and/or non-iron metal slabs, preferably by means of the system, comprising the following method steps:
Preferably, the thick slabs are fed to the first electric heating device for a direct hot charging process at a temperature of at least 500° C.
Furthermore, it is preferable for the pre-rolled flat rolled product to be heated to a temperature of at least 950° C. by means of an electric pre-strip heating device before it is finish-rolled into the flat rolled product.
In a further aspect, the present disclosure also relates to a use of at least one electric heating device for a direct hot charging process, in particular an inductive heating device, arranged in the transport direction in front of a hot-rolling mill, for heating thick slabs having a thickness of at least 160 mm to a hot-rolling temperature.
The invention and the technical environment are explained in more detail below with reference to the figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly shown otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description and/or figures. In particular, it should be noted that the figures and in particular the size relationships shown are only schematic. Identical reference signs designate identical objects, such that explanations from other figures can be used as a supplement if applicable.
For this purpose, the system 1 has a roller table 6 in the first transport line T, which extends through the system 1. The roller table 6 can be covered segment-by-segment with a plurality of active or passive thermal insulation hoods 22, two of which are shown purely by way of example in the present embodiment. In this manner, the energy and temperature losses of the thick slabs on the transport route to hot-rolling mill 5 can be kept to a minimum.
Despite the thermal shielding, the thick slabs usually cool down to an average temperature of 800 to 900° C. on the transport route to hot-rolling mill 5. It is therefore provided that the thick slabs are heated over their entire surface to a hot-rolling temperature of 1100 to 1300° C. in the transport direction in front of the hot-rolling mill 5 by means of an electric heating device for the direct hot charging process 7. The electric heating device 7 is designed as a longitudinal field inductor in the present exemplary embodiment and thus enables the cooled thick slab to be heated to the specific hot-rolling temperature for a short time.
Furthermore, the embodiment shown in
The thick slabs produced in this line can be temporarily stored and cooled in a slab store 13 arranged so as to directly adjoin the second separating device 12. Furthermore, the individual thick slabs can be temporarily stored in a soaking pit 14 with lower temperature losses.
As can also be seen from the representation in
In addition to the thick slab supplying device 15, the system 1 comprises two electric thick slab preheating devices 16.1, 16.2, which are connected upstream of the thick slab supplying device 15 on the inlet side. The two preheating devices 16.1, 16.2 are also designed as longitudinal field inductors/inductor combinations in such a manner that the thick slabs can be heated over their entire surface.
All heating devices 7, 10, 16.1, 16.2, 17, 18 of the exemplary embodiments are only shown schematically and usually comprise a number of individual inductors, which can be passed through sequentially. Individual switch-on and switch-off, along with an individual power setting, enable a very precise setting of the desired/necessary temperature increase. In addition to inductors designed exclusively as longitudinal field inductors, there are also combination sequences of longitudinal field and transverse field inductors that can be passed through sequentially.
In the embodiment according to
In the embodiment according to
The arrangement and number of thick slab supplying devices 15 can be varied as required. In a known design, the thick slab supplying device 15 can be an electrically and/or gas-powered continuous and/or walking beam furnace. Alternatively, a heating device belonging to the thick slab supplying device 15 can preheat the thick slab to a slightly higher temperature; the transport itself then takes place without active heat input via a preferably insulated transport aisle or walking beam.
The thick slab supplying device 15 can be used to heat the thick slabs temporarily stored and cooled in the slab store 13 or the thick slabs temporarily stored and slightly cooled to 200 to 800° C. in the soaking pit 14 to a hot-rolling temperature before they are then fed to the rolling process via the first roller table 6.1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 211 091.6 | Oct 2021 | DE | national |
| 10 2022 208 767.4 | Aug 2022 | DE | national |
This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application PCT/EP2022/077112, filed on Sep. 29, 2022, which claims the benefit of German Patent Applications DE 10 2021 211 091.6, filed on Oct. 1, 2021, and DE 10 2022 208 767.4, filed on Aug. 24, 2022.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/077112 | 9/29/2022 | WO |
