Apparatus and method for continuous production of hot-rolled ultra-thin steel strip

Abstract

Apparatus and method for the continuous production of hot rolled steel strip with a minimum thickness of 0.3 mm, comprising a continuous casting device (1) for thin or medium slabs with a thickness between 40 and 150 mm and a maximum width of at least 2100 mm, followed by a roughing mill (2), a first induction furnace, a water descaling machine, a second induction furnace, a finishing mill, a cooling station, a cutting station and a coiling station, a system arranged to feed a protective atmosphere containing ≤3% by volume of oxygen from at least the inlet of the second induction furnace to the third stand of the finishing mill, and also comprising an initial heat conditioning and descaling section (4) between the continuous casting device (1) and the roughing mill (2), the initial heat conditioning and descaling section (4) comprising, in sequence, an induction edge heater (4.1), an induction heater (4.2) for the rest of the slab surface and a water descaling machine (5).

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for the continuous production of hot rolled ultra-thin steel strip having a thickness down to 0.3 mm and having a limited amount of scale, so that it is suitable for direct coating for corrosion protection without undergoing a specific preliminary surface conditioning treatment. Background Art

[0002] As is well known, in the steel industry, given the increasing costs of both raw materials and energy consumption, the increasing competitiveness required by global markets, and increasingly stringent regulations regarding pollution, there is a particular need for methods to produce high-quality hot-rolled steel strip that require lower investment and production costs, leading to increasingly thinner strip thicknesses. As a result, the end-product processing industry can also become more competitive through lower energy consumption, thereby minimizing negative environmental impacts.

[0003] This state of the art is essentially as described in previous patents by the same inventor, such as EP 1558408, EP 1868748, and EP 1909979, to which reference is made for further details. In practice, the so-called ESP (Endless Strip Production) technology is used, which is based on "cast rolling" and combines continuous casting of thin slabs with liquid core reduction (LCR) with a first roughing stage, which produces an intermediate product, the so-called "transfer bar," by a roughing mill (HRM). Casting is carried out from an ingot mold system, also by the same inventor, based on patents EP 0946316, EP 1011896, and EP 3154726. Reference is made to these patents for further details regarding the geometric profiles of both the horizontal and vertical sections of the ingot mold, as well as the special geometry of the nozzles designed for high mass flow rates of up to 7 to 8 tons / minute of material.

[0004] The above-mentioned patent EP 1558408 also envisages the possibility of extracting rough plates after the first roughing stage as an emergency system in the event of problems in the part of the equipment downstream of the roughing mill, in order to avoid interruptions in the continuous casting and therefore in the production of the production line, rather than for the programmed production of plates, since the first part of the equipment does not have the controlled cooling system necessary for the production of high-quality plates.

[0005] After a stage of heating in an induction furnace and subsequent descaling, the intermediate strand is further processed in a second stage of finishing rolling in order to transform it into a strip by controlling its temperature so that it still has a temperature at the exit of the finishing mill above about 820 to 850°C, which corresponds to the lower limit of the austenitic temperature range of most steels.

[0006] However, the results so far, although optimal in terms of strip quality, have proven to be improvable in terms of plant compactness, energy savings, and the current minimum strip thickness value of 0.6 mm. Furthermore, although the formation of oxides (scale) on the strip surface can be reduced due to the minimum residence time of the material at temperature, this reduction in formation has not yet proven to be sufficient to avoid a pickling stage before applying the anti-corrosion coating due to the aforementioned inductive heating of the intermediate roll between the roughing and finishing stages.

[0007] In order to ensure that the required final rolling is carried out in the austenitic field with greater production flexibility and to further reduce the formation of scale, a plant of the above-mentioned type is known from US Pat. No. 9,108,234, which also includes a second induction furnace between the descaling mill and the finishing mill, the heating in this second furnace being carried out in a protective atmosphere which prevents oxidation of the intermediate rolling mill and which consists essentially of an inert gas (nitrogen) with a minimum presence of oxygen (about 5% or less). Other examples of induction heating in a protective atmosphere before final rolling can be found in US 8479550, US 2012 / 043049 and DE 19936010, however, US 8479550 only provides an induction furnace after the descaler, US 2012 / 043049 also provides a reducing atmosphere using hydrogen but without roughing, however, DE 19936010 does not include an induction furnace after the descaler, and for the protective atmosphere, the patent teaches the use of combustion gas generated by the equipment itself instead of inert gas to reduce costs, and this gas can also be distributed in different parts of the equipment before and after the induction furnace (for example, induction edge heater, descaler, finishing mill, exit roller conveyor, winder).

[0008] However, none of these prior art documents envisages achieving strip thicknesses below the current limit of 0.6 mm, nor do they take into account the specific problems that arise below this limit. In fact, none of the equipment described in these documents is suitable for this purpose due to the conflicting requirements: maintaining a high temperature of the intermediate bar at the entrance to the finishing mill to ensure complete austenitic rolling of such thin strips, thus undergoing greater cooling, and limiting the formation of scale despite the intense heating, both in terms of time and temperature. Summary of the Invention

[0009] The object of the present invention is therefore to provide a solution for the continuous production of hot rolled strip with a thickness down to 0.3 mm and a maximum width of at least 2100 mm, or the maximum width of any provided ingot mould, starting from slabs with a cast thickness between 40 and 150 mm, without passing through intermediate equipment for pickling, cold rolling and annealing, and with a limited amount of scale, making these strips suitable for direct coating to protect against corrosion, in particular in galvanizing lines, without undergoing specific preliminary surface conditioning treatments, in particular in pickling lines.

[0010] This result was obtained by using a continuous production technology (so-called endless) which minimizes production time and consumption, thus reducing production costs, in particular by taking the following measures to control the temperature of the material and limit its reduction, while avoiding excessive surface oxidation of the material:

[0011] a) in order to remove scale from the slab before entering the roughing mill (HRM) and to allow a roughing pass count of from a minimum of 3 to a maximum of 5, there is an initial heat conditioning and descaling section at the exit of the continuous casting (casting machine), which comprises, in sequence in the advancing direction of the slab, an induction edge heater, an induction heater for the rest of the slab surface and a water descaling machine;

[0012] b) In order to prevent the jets of water and steam from the descaler from damaging the induction coils of the surface heater, the descaler is provided at the inlet with transversely movable shutters, which are placed directly on the edges of the slab, while the closure on the upper and lower sides of the slab is provided by small drive racks (so-called pinch rollers) which are placed adjacent to the shutters on the inlet side of the descaler facing the surface heater;

[0013] c) Since the slab has a low speed at the exit of the casting mill, less than 10 m / min, in order to minimize the time it takes for the slab to be transferred from the casting mill to the entrance of the roughing mill in order to minimize scale formation and temperature drop, the initial section must be as compact as possible so that the edge heaters, surface heaters and descaler (the latter including pinch rolls and shielding shutters) occupy a space of approximately 3 to 5 meters in length;

[0014] d) the edge heater is equipped with a handling system that allows the efficiency of the heating system to remain constant as the slab width varies, to set the optimal width of the area to be heated at the edge and to remove / lift the induction coils in case of “waves” on the slab due to pebbles in the roughing mill;

[0015] e) edge heaters capable of heating the right and left edges of the slab differently to ensure an optimal and uniform profile of the slab entering the roughing mill, even if the slab leaving the casting mill exhibits temperature inhomogeneities between the two edges;

[0016] f) The descaler is designed with a cooling water nozzle diameter and a delivery pressure such that the temperature drop at the outlet of the descaler is limited to less than 10° C. between when the descaler is in operation and when it is not in operation.

[0017] Other advantageous arrangements which are preferably employed in the present invention to improve the present apparatus and method are:

[0018] g) building a second water descaling machine before the finishing mill, located between the two induction furnaces, with a structure similar to the first descaling machine mentioned above and including pinch rollers at the inlet and outlet to protect the two induction furnaces from water and steam jets;

[0019] h) the nozzles for feeding the protective atmosphere into the finishing mill are mounted on a mobile structure called a "looper" arranged between the stands of the mill, i.e. a roller equipped with a tension sensor, which can be moved vertically and allows the material to be arranged in a suitable loop between the stands, so that the speed control system varies the reciprocating speed of the stands, thus maintaining a constant tension on the strip;

[0020] i) providing a mechanical scale breaking device, located immediately before the second water descaling machine, consisting of at least three rollers, which are alternately arranged above and below the feed line of the intermediate rolling mill and are at a height sufficient to cause plastic stretching of its surface, which plastic stretching causes the rigid scale layer to break and facilitates its removal in the subsequent water descaling machine;

[0021] j) in order to allow high temperatures for coiling ultra-thin strips up to 750° C. and in any case above the transformation point, a winding coiler is also provided close to the last rolling mill stand, either above (“upper coiler”) or below (“lower coiler”) the surface of the exit roller conveyor and preceded by a short cooling line and a high-speed shear (in addition to a similar final coiler conventionally provided after the normal cooling line and the opposing shear);

[0022] k) providing first and second mechanical descaling machines, located between the cooling line and the shears of the adjacent coiler and final coiler, respectively, using counter-rotating brushes or abrasive slurry jets;

[0023] 1) providing an anti-corrosion coating line directly after the final coiler so that the coating can be applied without having to previously wind the steel strip onto a coiler to form a coil;

[0024] m) Provide a cooling tank in which the coils removed from the coiler can be immersed in water or a slightly oxidizing aqueous solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Further advantages and features of the device and method according to the invention will become apparent to those skilled in the art from the following detailed and non-limiting description of some embodiments thereof with reference to the accompanying drawings, in which:

[0026] Figure 1a 、 1b 、1c A schematic diagram of the apparatus in the embodiment is shown, which includes all optional components except the anti-corrosion coating line;

[0027] Figure 2 is only shown with Figures 1a to 1c Schematic diagram of the anti-corrosion coating line connected to the end of the equipment;

[0028] Figure 3 is a side view of the initial thermal conditioning and descaling section;

[0029] Figure 4 yes Figure 3 A schematic diagram of a vertical cross section of a descaling machine;

[0030] Figure 5 It shows Figure 3 A transparent front view of some components of the descaling machine;

[0031] Figure 6 is a schematic diagram of a vertical section of a second descaling machine;

[0032] Figure 7 is a schematic diagram of a vertical section of some components of the second induction furnace preceding the finishing mill;

[0033] Figure 8 is a schematic diagram of a vertical section of a first embodiment of a protective atmosphere distribution device placed between two stands of a finishing mill;

[0034] Figure 9 It is along Figure 8 Schematic diagram of a vertical section of a detail of the spreading device along line AA;

[0035] Figure 10 The second embodiment of the protective atmosphere dispersing device is Figure 8 Similar views;

[0036] Figure 11 It is along Figure 10 Schematic diagram of a vertical section of a detail of the spreading device along line BB;

[0037] Figure 12 The third embodiment of the protective atmosphere dispersing device is Figure 8 Similar views; and

[0038] Figure 13 It is along Figure 12 Schematic diagram of a vertical section of a detail of the spreading device along the line CC. DETAILED DESCRIPTION

[0039] refer to Figures 1a to 1cAs can be seen, the plant according to the invention conventionally comprises a casting mill 1 for continuously casting thin or medium slabs with a thickness of 40 to 150 mm, followed by a roughing mill (HRM) 2. In the illustrated example, the HRM 2 comprises four stands 2.1 to 2.4, but could also comprise three or five stands. The HRM 2 transforms the slab into an intermediate strand with a thickness of ≤8 mm. Experimental tests have shown how a limited thickness reduction (≤20%) in the first roughing stand 2.1 can keep surface stresses within the strength limit of the coarse austenite that will form the slab into the casting. This almost static recrystallization of the surface during the first roughing step, particularly for microalloyed steels, allows for a subsequent, substantial thickness reduction without defects or cracks, which is essential for obtaining intermediate strands suitable for the production of ultra-thin strip.

[0040] After the HRM 2, an emergency system for producing and removing rough slabs in the event of problems in the equipment section downstream of the HRM is arranged. Such a system includes a pendulum shear 15, a stacker 16 for extracting the slabs, a rotary shear 17 and a ring former 18. The purpose of the latter two devices is to free the pipeline from the material between the pendulum shear 15 and the subsequent first induction furnace 6.1 during the initial cobblestone stage.

[0041] The first induction furnace 6.1 is the first component of the central heat conditioning and descaling section 6, which also includes, in sequence, a mechanical device 7 (optional) for breaking up scales of the type described above, a water descaling machine 8, and a second induction furnace 6.2, in the direction of advance of the intermediate strand. The mechanical device 7, in this case, consists of five rollers. Thus, the intermediate strand undergoes further heating before entering the adjacent finishing mill 3, which, in the illustrated example, consists of seven stands 3.1 to 3.7, but could also consist of five or six. Finally, the strip is cooled in a controlled manner by a cooling roller conveyor 12, followed by a final coiling station comprising a flying shear 10 and at least one pair of single coilers 11.

[0042] In order to allow high coiling temperatures for ultra-thin strips, as described above, the plant preferably also includes a close winding coiler, i.e., before the above-mentioned elements 10 to 12, in the form of a pair of "carousel" coilers 9, arranged close to the last rolling mill stand 3.7 and preceded by a short cooling roller conveyor 12' and a high-speed shear 10' similar to the elements 10, 12, although the roller conveyor 12' can preferably be made to perform ultra-rapid cooling in order to obtain scales that are easier to remove in the subsequent process of applying the protective coating.

[0043] Between each pair of elements 10, 12 and 10', 12', there is preferably also arranged a respective mechanical descaler 14, 14' of known type, which will therefore not be described further, and which uses counter-rotating brushes or jets of abrasive slurry to give the strip a final surface treatment before it is wound onto the reel 9 or 11.

[0044] As mentioned above, Figures 1a to 1c The plant depicted in FIG. 1 also includes a system for distributing a protective atmosphere in certain areas thereof, schematically indicated by a thick-lined box. In the illustrated example, this system extends at least from the inlet of the second induction furnace 6.2 to the third stand 3.3 of the finishing mill 3, preferably up to the last stand, and even more preferably also in the subsequent cooling and coiling stations. It is obviously also conceivable to extend this system to other components of the plant as described in the above-mentioned prior art.

[0045] As mentioned above, the first innovative aspect of the present invention is the presence of an initial heat conditioning and descaling section 4, which is arranged between the outlet of the casting machine 1 and the HRM 2 and is designed to be only slightly longer than 3 meters in order to minimize the transit time between the two components. The section 4 comprises an induction edge heater 4.1, an induction heater 4.2 and a water descaling machine 5. Figures 3 to 5 More detailed and better illustrated in the figure.

[0046] More specifically, edge heater 4.1 is preferably designed to operate with transverse magnetic flux, using side coils 4.1a in a "channel" configuration with magnetic flux concentrators. This serves the dual purpose of increasing the efficiency of the heating system and concentrating the magnetic flux on selected areas of the slab to be heated. Furthermore, the presence of two frequency converters, one for each coil 4.1a, rather than a single converter for the entire arrangement as is typically the case, allows for differential heating of the right and left edges of the slab. Experimental tests conducted by the applicant indicate that the width of the strip to be heated should preferably be up to 150 mm from the edge, and that the optimal temperature rise of the strip is no more than 120°C to avoid melting of the scales.

[0047] The edge heater 4.1 is provided with a handling system which performs a transverse movement to adapt the device to the width of the slab, to set the width of the edge zone to be heated and to move the coil 4.1a away from the edge of the slab (if necessary, by rotating it to lift it) in the event of "waves" on the slab due to pebbles in the roughing mill. For example, such a handling system can be implemented by placing each coil 4.1a on a slide which can be moved along transverse guides under the action of an actuator (such as an electric motor driving a screw jack).

[0048] The induction heater 4.2 comprises a surface heating coil, designed to be integrated with the edge heater 4.1, and can be controlled in such a way that the temperature of the slab is raised to a maximum value of at most 150°C, thereby preventing the slab from melting.

[0049] The subsequent descaler 5 consists of pinch rollers 5.1 on the side facing the induction heater 4.2 and the actual descaler 5.2 on the side facing the HRM 2. Figures 4 and 5 As shown, in order to prevent the jets of water and steam from the descaling machine 5.2 from damaging the induction coil of the heater 4.2, the descaling machine 5.2 is provided with a transversely movable shutter 20 at the inlet, which directly rests on the edge of the slab, while the clamping rollers 5.1 provide closure on the upper and lower sides of the slab.

[0050] More specifically, in Figure 5 In the embodiment illustrated in FIG, each shutter 20 is mounted on a parallelogram support formed by a pair of parallel arms 21 pivoting between the shutter 20 and the structure of the descaler 5.2 and moved by an actuator 22. It should be noted that Figure 5 The shutter 20 is shown in the open position and also partially in the closed position 20 ′ abutting the edge of the slab.

[0051] Water descaling is carried out by upper and lower rows of nozzles 23, 24 arranged transversely to the slab, with the nozzles tilted to deliver the jets in the opposite direction of the slab's movement. Upper and lower reels 25, 26, arranged mirror-image upstream of the nozzles with their openings facing the nozzles, collect most of the water through their lips in contact with the slab and convey it to their ends where it is discharged.

[0052] Furthermore, the upper and lower rows of nozzles 27 and 28 are arranged transversely to the slab, upstream of the reel, and the nozzles are tilted to deliver jets of air in the direction of motion of the slab, thereby eliminating residual water. The combination of components 5.1, 20, 25, 26, 27, and 28 ensures that the induction coils of heater 4.2 are not damaged by the water used in descaler 5.

[0053] As mentioned above, the descaling agent 5.2 is designed to limit the temperature drop between its operation and its non-operation to less than 10°C, for which the cooling water pressure is less than 150 bar and the nozzle diameter is less than 3 mm. Figure 5The water nozzle rows 23, 24 shown in (with the scrolls 25, 26 and the air nozzle rows 27, 28 omitted) are wider than the slab because they are dimensioned for the maximum width of the slab. The nozzles outside the slab being processed can be closed with plugs or the jets from them can be "cancelled" by collision, in which case the upper and lower nozzles must be arranged in opposite positions, vertically aligned and with the same inclination angle (e.g. 5°).

[0054] exist Figure 6 The second water descaler 8 shown in the figure has a similar structure to the first water descaler 5, but it is essentially doubled, as it is arranged between the two induction furnaces 6.1 and 6.2 and must prevent water and steam from escaping both upstream and downstream. Therefore, it comprises a first inlet pinch roller 8.1 on the side facing the first induction furnace 6.1, the actual descaler 8.2, and a second outlet pinch roller 8.1' on the side facing the second induction furnace 6.2. It should be noted that in this case, transverse shutters similar to the shutters 20 of the first descaler 5 can be omitted, as the latter must close lateral passages with a height equal to the thickness of the slab coming from the casting machine 1, i.e., 40 to 150 mm. The intermediate slab entering the second descaler 8 is approximately 5 to 20 mm thick, so the potential for lateral water leakage is much smaller.

[0055] Furthermore, since the second descaler 8 is followed by a second induction furnace 6.2, which significantly increases the temperature of the intermediate strand before final rolling, descaling can be more robust, even at the expense of a greater temperature drop. Therefore, a first upper nozzle row 33 and a corresponding lower nozzle row 34, as well as an identical second upper nozzle row 33' and a corresponding lower nozzle row 34', are provided. The nozzle rows 33, 34 are also arranged transversely to the intermediate strand, and the nozzles are tilted so as to deliver the jets in a direction opposite to the direction of motion of the strand. Preferably, the second rows 33', 34' are transversely staggered relative to the first rows 33, 34 by half a pitch, where the pitch is the distance between two nozzles in a row, so that two consecutive rows 33, 33' and 34, 34' completely cover the upper and lower surfaces of the strand, respectively, thereby improving the efficiency of the hydraulic descaling process by eliminating the inefficiencies associated with overlapping strips of adjacent nozzles in each row.

[0056] Similarly, the two upper nozzle rows 33, 33' are preceded by upper reels 35, 35' which, however, in this case are separated from the lips 32, 32' which contact the upper surface of the intermediate strand and can be opened as shown. Figure 635 '. Similarly, the first lip 32 is preceded by a first upper row of nozzles 37 arranged transversely to the intermediate billet to deliver air jets, in this case substantially perpendicular to the upper surface of the billet, while an identical second upper row of air nozzles 37' is arranged downstream of the second upper row of water nozzles 33'.

[0057] Since descaler 8 does not need to be as compact as descaler 5, the intermediate strand can be supported from below by conventional transport rollers 36, 36', which perform a similar closing function on the lower side as lower reel 26. For this reason, descaler 8 does not include a lower assembly corresponding to upper assemblies 32, 32', 37, 37', but only lower water nozzles 34, 34'. However, the combination of assemblies 8.1, 8.1', 32, 32', 35, 35', 36, 36', 37, and 37' ensures that the induction coils of furnaces 6.1 and 6.2 are not damaged by the water used in descaler 8.

[0058] As already mentioned, since the descaling machine 8 is designed for more severe descaling, the cooling water pressure can be up to 380 bar, also using nozzles with a diameter of less than 3 mm, even though this may result in a temperature drop of the intermediate strand by up to 150 to 200° C. Obviously, even in the descaling machine 8, the water nozzle rows 33, 34 and 33 ′, 34 ′ are dimensioned for the maximum width of the strand, the nozzles outside the processed strand being closed with plugs or the jets being “cancelled” by collision, in which case the upper and lower nozzles must be aligned vertically and have the same inclination angle (e.g. 5°).

[0059] Now refer to Figure 7 , Figure 7 The four inductors 40 of the second induction furnace 6.2 are shown, and it can be seen that the intermediate strand is supported by lower rollers 41 arranged in the space between the inductors 40, said space being closed at the bottom by the support structure of said rollers 41 and at the top by a removable cover 42. It is therefore advantageous to mount a transverse row of nozzles 43 on said cover 42 so as to obtain a series of chambers into which a protective atmosphere can be injected through said nozzles 43.

[0060] This protective atmosphere can be of various types, as long as it has a very low or zero oxygen content to limit or prevent surface oxidation of the material. Typically, oxygen is reduced by continuously delivering nitrogen from the nozzle 43 until a low-oxidizing atmosphere with a maximum oxygen content of 3% by volume is obtained. Other possibilities are to use an atmosphere consisting entirely of inert gases (nitrogen, argon, etc.) or to add hydrogen to the inert gas up to a maximum content of 5% by volume to obtain a weakly reducing atmosphere.

[0061] As described above, a similar solution for obtaining a chamber between the stands of the finishing mill 3 can be envisaged by mounting the nozzles on a ring-top structure arranged in the space between the two stands. A first embodiment of this solution is Figure 8 and Figure 9 In the figure, Figure 8 and Figure 9 Shows how the protective atmosphere feed system is related to Figure 8 The cross section AA shown in FIG (ie, the upstream and downstream sides relative to the ring top 51) and the cross section AA shown in FIG Figure 9 In the example illustrated in the figures, the system is arranged between the first two stands 3.1 and 3.2 of the finishing mill 3, but it is obvious that the same system can be arranged between any pair of stands of this mill.

[0062] The system comprises a pair of vertical feed pipes 52, 52' mounted on the structure of the ring top 51 on each side of the belt, upstream and downstream thereof, respectively, and from each of said pipes 52, 52' branches two substantially horizontal rows of nozzles arranged longitudinally above and below the belt and parallel to its edge. More specifically, each of the two upper rows of nozzles 53, 53' extends towards both frames 3.1, 3.2, almost to the plane of the section AA passing through the center of the ring top 51, while each of the two lower rows of nozzles 54, 54' extends only towards the adjacent frame 3.1, 3.2, respectively. In addition, as Figure 9 As shown in the detail of , the nozzles are inclined in a vertical plane, towards the surface of the belt.

[0063] In order to limit the diffusion of the protective atmosphere, the nozzle row is preferably enclosed in a chamber formed by an upper pair of flaps 55, 55' and a lower pair of flaps 56, 56', which are obviously shaped to allow the belt to pass through the chamber. More specifically, each of the flaps is pivoted at one of its outer ends to allow the closed chamber to be opened by a 90° rotation, as shown. Figure 8 , wherein the closed chamber is depicted with a thicker line, while reference numerals 55 , 55 ′, 56 and 56 ′ denote flaps rotated in the open position.

[0064] exist Figure 10 and Figure 11 A second embodiment of a system similar to the previous one is illustrated in FIG. Figure 10 and Figure 11 Shown Figure 8 and 9The same elements as those of the present invention are not repeated in the same way, and their reference numerals are omitted, except that at least two parallel transverse rows of nozzles 57, 57', 58, 58' are added on the outer face of each flap. The protective atmosphere is supplied to each pair of rows via corresponding feed pipes 50, 50', 59, 59', and the nozzles are oriented substantially perpendicularly to the upper and lower surfaces of the strip.

[0065] Finally, in Figure 12 and Figure 13 The third embodiment of the system is shown in FIG. 3 , which is actually achieved by removing Figure 8 and Figure 9 and retain only at least two transverse parallel rows 63, 63', 64, 64' arranged on the respective flaps 65, 65', 66, 66' and fed through the respective tubes 61, 61', 62, 62' obtained from the previous embodiment. Figure 10 、 Figure 11 The differences between similar elements shown in FIG. 1 are as follows:

[0066] - replacing the plurality of nozzles 57, 57', 58, 58' with a single nozzle, i.e. a slit, of substantially the same width as the strip;

[0067] - the nozzles are not oriented in a direction substantially perpendicular to the upper and lower surfaces of the strip, but are oriented obliquely towards the adjacent rolling stands 3.1 and 3.2, respectively;

[0068] - The protective atmosphere is not passed through a single central tube as in the second embodiment but rather through Figure 8 and Figure 9 The first embodiment is fed to each pair of transverse rows 63 , 63 ′, 64 , 64 ′ by two lateral tubes 61 , 61 ′, 62 , 62 ′.

[0069] As mentioned above, the above-mentioned equipment can be integrated with a production line 13 for applying a protective coating (typically a galvanizing line), such as Figure 2 As shown, the production line 13 is connected directly downstream of the final coiler 11. In this way, the apparatus can produce both coils of uncoated tape wound on the coilers 9 or 11 and coils of coated tape wound in a further winding station at the end of the production line 13.

[0070] Another possible alternative is to liquid cool the coil wound on the coiler 9 or 11 in a tank (not shown) containing water or a weakly oxidizing aqueous solution. This allows obtaining scales that are more easily removed in the subsequent process of applying the protective coating.

[0071] Furthermore, thermal scanners (not shown) are preferably positioned at the exits of the casting machine 1, HRM 2, first induction furnace 6.1, descaling mill 8, second induction furnace 6.2, finishing mill 3, and cooling roller conveyors 12 and 12'. These thermal scanners are operatively connected to a temperature control and management system that also influences the temperature distribution of the steel in the mold, thanks to thermocouples (not shown) inserted in the copper plates of the ingot mold, and through electromagnetic brakes (EMBRs) (also not shown) inserted in the mold. In effect, the thermal scanners and thermocouples provide an image of the temperature distribution in the slab, enabling the control system to take corrective action on the operating parameters of the EMBRs and the slab cooling system. This control system also obviously acts on all other components that actively influence the temperature of the processed material during heating (4.1, 4.2, 6.1, 6.2) and cooling (5.2, 7, 8.2, 12, 12', 14, 14').

[0072] By way of example, the following table shows possible rolled sheets for producing ultra-thin strip with a thickness of 0.4 mm at a coiling temperature of 680° C. on the final coiler:

[0073]

[0074] Therefore, in its most complete embodiment, the corresponding production method using the above-described device comprises the following sequence of steps:

[0075] (a) Continuous casting of thin slabs or medium slabs (1);

[0076] (b) Induction heating of the slab edge (4.1);

[0077] (c) Induction heating of the rest of the slab surface (4.2)

[0078] (d) First water descaling (5.2);

[0079] (e) performing rough rolling (2) for 3 to 5 passes to obtain an intermediate slab;

[0080] (f) First induction heating of the intermediate slab (6.1)

[0081] (g) mechanical rupture of scales (7);

[0082] (h) Second water descaling (8.2);

[0083] (i) Second induction heating of the intermediate slab (6.2);

[0084] (j) finishing rolling (3) 5 to 7 passes to obtain a strip;

[0085] (k) controlled cooling of the strip (12; 12');

[0086] (1) Mechanical descaling (14; 14');

[0087] (m) cutting the strip (10; 10') and winding it on a reel (9; 11); or

[0088] (n) passing the tape directly to step (13): application of a protective coating, with final winding;

[0089] At least stages (i) and (j) (at least up to the third pass), and preferably also stages (k) and (m) (in the winding section) are carried out in a weakly oxidizing, inert or weakly reducing protective atmosphere as described above.

[0090] It is obvious that the embodiments of the apparatus and method according to the present invention described and illustrated above are merely examples susceptible to numerous variations. Figures 4 to 6 and Figures 8 to 11 All nozzle rows shown in the drawings are formed by a plurality of nozzles arranged at a constant pitch, but nozzles with different pitches may also be provided according to the region and / or by using a nozzle arrangement such as Figure 13 The continuously extending slits shown replace all or part of the nozzles. Similarly, both the approaching reel and the final reel can be implemented as carousel reels 9 or single reels 11, whereby the apparatus can comprise any combination thereof.

[0091] Furthermore, it is obvious that for reasons of space and / or cost, the system may not have Figures 8 to 13 Although this would make it more difficult to control the composition of the atmosphere in the space between the mill stands, Figures 10 to 13 The lateral nozzle row shown in is to be mounted on a simple rotating support which does not form a closed chamber.

Claims

1. An apparatus for continuously producing hot-rolled steel strip having a minimum thickness of 0.3 mm, comprising, in order along the direction of movement of the processed material: - a continuous casting device (1) for continuously casting thin or medium slabs having a thickness between 40 and 150 mm and a maximum width of 2100 mm, - a roughing mill (2) comprising at least three stands for obtaining intermediate billets, - First Induction Furnace (6.1), - Second water descaling machine (8), - Second induction furnace (6.2), - a finishing mill (3), said finishing mill (3) comprising 5 to 7 stands, - Cooling station (12), - a cutting station (10), and - a winding station having at least a pair of carousel coilers (9) or a single coiler (11), and a system for feeding a protective atmosphere containing ≤3% by volume of oxygen at least from the inlet of the second induction furnace (6.2) to the third stand of the finishing mill (3), Characterized in that the device also includes an initial section (4) of thermal conditioning and descaling between the continuous casting device (1) and the roughing mill (2), and the initial section (4) of thermal conditioning and descaling includes, in sequence, an induction edge heater (4.1), an induction heater (4.2) for the rest of the slab surface and a first water descaling machine (5).

2. The device according to claim 1, characterized in that The first water descaling machine (5) comprises a pinch roller (5.1) on the side facing the induction heater (4.2), followed by an actual descaling machine (5.2) provided with a pair of transversely movable shutters (20) at the inlet, the shutters (20) being directly adjacent to the edge of the slab.

3. The device according to claim 1, characterized in that The initial section (4) of thermal conditioning and descaling has a length of 3 to 5 meters.

4. The device according to any one of claims 1 to 3, characterized in that The edge heater (4.1) is designed to operate in transverse flux using side coils (4.1a) in a "channel" configuration with flux concentrators.

5. The device according to any one of claims 1 to 3, characterized in that The edge heater (4.1) is dimensioned to heat the edge strips of the slab up to 150 mm from each edge and / or to achieve a temperature increase of up to 120°C in the edge strips.

6. The device according to claim 5, characterized in that The edge heater (4.1) is equipped with a handling system that performs transverse movements to adapt the edge heater (4.1) to the slab width, to set the width of the webbing to be heated and to move the induction coil away from the edge of the slab.

7. The device according to any one of claims 1 to 3, characterized in that The first water descaling machine (5) comprises: - an upper row (23) of water nozzles and a lower row (24) of water nozzles, said upper row (23) of water nozzles and said lower row (24) of water nozzles being arranged transversely to the slab and with the nozzles being inclined so as to deliver the jets in a direction opposite to the direction of movement of the slab, - an upper reel (25) and a lower reel (26), said upper reel (25) and lower reel (26) being arranged in a mirror image, upstream of said upper water nozzle row (23) and said lower water nozzle row (24), respectively, and with openings of said upper reel (25) and said lower reel (26) facing said upper water nozzle row (23) and said lower water nozzle row (24), respectively, each of said upper reel (25) and said lower reel (26) being provided with an end drain for removing water collected by the lip in contact with said slab, - an upper row (27) of air nozzles and a lower row (28) of air nozzles, said upper row (27) of air nozzles and said lower row (28) of air nozzles being arranged upstream of said upper reel (25) and said lower reel (26) respectively, transversely to said slab, and said nozzles being inclined so as to deliver the jets in the direction of movement of said slab.

8. The device according to any one of claims 1 to 3, characterized in that The second water descaling machine (8) placed between the first induction furnace (6.1) and the second induction furnace (6.2) comprises a first pinch roller (8.1) on the side facing the first induction furnace (6.1), the actual descaling machine (8.2) and a second pinch roller (8.1') on the side facing the second induction furnace (6.2).

9. The device according to claim 8, characterized in that The second water descaling machine (8) comprises: - a first upper row (33) and a second upper row (33') of water nozzles and a first lower row (34) and a second lower row (34') of water nozzles, all of said rows being arranged transversely to said intermediate billet and with nozzles inclined so as to deliver jets in a direction opposite to the direction of movement of said billet, said second upper row (33') of water nozzles being transversely staggered at half a pitch relative to said first upper row (33) of water nozzles and said second lower row (34') of water nozzles being transversely staggered at half a pitch relative to said first lower row (34), - each of the two upper water nozzle rows (33, 33') is preceded by an upper reel (35, 35') and a movable lip (32, 32'), said movable lip (32, 32') being in contact with the upper surface of the intermediate billet in the operating position and being aligned with the corresponding upper reel (35, 35'), - a first upper row of air nozzles (37) and a second upper row of air nozzles (37'), the first upper row of air nozzles (37) and the second upper row of air nozzles (37') being arranged transversely to the intermediate billet and with the nozzles perpendicular to the upper surface of the billet, the first upper row of air nozzles (37) being placed upstream of the movable lips (32, 32') and the second upper row of air nozzles (37') being placed downstream of the second upper row of water nozzles (33').

10. The device according to claim 1, characterized in that The system for feeding the protective atmosphere from at least the inlet of the second induction furnace (6.2) to the third stand of the finishing mill (3) comprises a pair of feed pipes (52, 52') on each side of the strip and in the space between two finishing stands (3.1, 3.2, ..., 3.7), the feed pipes (52, 52') being mounted on the structure of the ring top (51), respectively on its upstream and downstream sides, and from each of these feed pipes (52, 52') branching off two essentially horizontal rows of nozzles, two upper rows of nozzles (53, 53') and two lower rows of nozzles (54, 54') being arranged longitudinally above and below the strip, respectively, and parallel to its edge.

11. The device according to claim 10, characterized in that The system for feeding the protective atmosphere from at least the inlet of the second induction furnace (6.2) to the third stand of the finishing mill (3) also includes at least two pairs of parallel horizontal nozzle rows, two upper nozzle rows (57, 57') and two lower nozzle rows (58, 58') arranged transversely above and below the strip at each of the two longitudinally arranged upper nozzle rows (53, 53') and the two lower nozzle rows (54, 54'), the protective atmosphere reaching each of the two transversely arranged upper nozzle rows (57, 57') and the two lower nozzle rows (58, 58') through corresponding feed pipes (50, 50', 59, 59').

12. The device according to any one of claims 1 to 3, characterized in that The system for feeding the protective atmosphere from at least the inlet of the second induction furnace (6.2) to the third stand of the finishing mill (3) comprises at least two pairs of parallel horizontal nozzle rows in the space between two finishing stands (3.1, 3.2, ..., 3.7), two upper nozzle rows (63, 63') and two lower nozzle rows (64, 64') being arranged transversely above and below the strip upstream and downstream of the ring top (51), respectively, the protective atmosphere reaching each of the two upper nozzle rows (63, 63') and the two lower nozzle rows (64, 64') arranged transversely through a corresponding pair of feed pipes (61, 61', 62, 62').

13. The device according to claim 11, characterized in that The two upper nozzle rows (53, 53') and the two lower nozzle rows (54, 54') arranged longitudinally and the two upper nozzle rows (57, 57') and the two lower nozzle rows (58, 58') arranged transversely are enclosed in a chamber formed by an upper flap pair (55, 55') and a lower flap pair (56, 56'), which are shaped to allow the belt to pass through the chamber and can be rotated about an end pin to allow the chamber to be opened.

14. The device according to claim 13, characterized in that The two upper nozzle rows (57, 57') and the two lower nozzle rows (58, 58') arranged transversely are mounted on the upper flap pair (55, 55') and the lower flap pair (56, 56'), respectively.

15. The device according to any one of claims 1 to 3, characterized in that The first stand (2.1) of the roughing mill (2) is a stand designed for a slab thickness reduction of ≤20%.

16. The device according to any one of claims 1 to 3, characterized in that The plant also includes an emergency system for producing and removing rough plates after the roughing mill (2), which includes, in sequence, a swing shear (15), a stacker (16) for extracting metal plates, a rotary shear (17) and a ring former (18).

17. The device according to any one of claims 1 to 3, characterized in that The apparatus further comprises a mechanical scale breaking device (7) between the first induction furnace (6.1) and the second water descaling machine (8), wherein the mechanical scale breaking device (7) is formed by at least three rollers alternately arranged above and below the intermediate rolling mill feed line, and the height of the mechanical scale breaking device (7) causes plastic stretching on its surface, thereby causing the rigid scale layer to rupture.

18. The device according to any one of claims 1 to 3, characterized in that The plant further comprises, in sequence, a further cooling station (12'), a further cutting station (10') and a further winding station between the finishing mill (3) and the cooling station (12).

19. The device according to claim 18, characterized in that The apparatus also comprises a mechanical descaling machine (14; 14') using counter-rotating brushes or abrasive slurry jets between each cooling station (12; 12') and each cutting station (10; 10').

20. The device according to any one of claims 1 to 3, characterized in that The plant also comprises a line (13) for an anti-corrosion coating located directly after the final winding station, so that the coating can be applied to the strip without first having to be wound into a coil.

21. The device according to any one of claims 1 to 3, characterized in that The apparatus further comprises a control system for controlling and managing the temperature of the material being processed, the control system being operatively connected to an electromagnetic brake inserted into an ingot mould forming part of the continuous casting device (1), to thermocouples connected to a copper plate inserted into the mould, and to thermal scanners arranged along the apparatus, the control system also being operatively connected to all other components of the apparatus that actively influence the temperature of the material being processed during heating and during cooling.

22. The device according to claim 2, characterized in that Each of the shutters (20) is mounted on a parallelogram support formed by a pair of parallel arms (21) that pivot between the shutter (20) and the structure of the descaler (5.2) and are moved by an actuator (22).

23. The device according to claim 4, characterized in that Each of the side coils (4.1a) is equipped with its own frequency converter, enabling the edge heater (4.1) to heat the right and left edges of the slab differently.

24. The device according to claim 6, characterized in that The handling system is implemented by placing each induction coil on a slide movable along a transverse guide by an actuator.

25. The apparatus according to claim 7, wherein The upper water nozzle row (23) and the lower water nozzle row (24) are arranged in opposing positions, wherein the nozzles are vertically aligned and at the same inclination angle.

26. The apparatus according to claim 9, wherein The first upper water nozzle row (33) is arranged opposite the first lower water nozzle row (34), and the second upper water nozzle row (33') is arranged opposite the second lower water nozzle row (34'), with the nozzles being vertically aligned and at the same inclination angle.

27. The apparatus according to claim 10, wherein Each of the two upper nozzle rows (53, 53') extends towards the two finishing stands (3.1, 3.2, ..., 3.7) almost to a vertical plane transverse to the strip and passing through the center of the ring top (51), while each of the two lower nozzle rows (54, 54') extends only towards the adjacent finishing stand (3.1, 3.2, ..., 3.7).

28. The apparatus according to claim 12, wherein The two upper nozzle rows (63, 63') and the two lower nozzle rows (64, 64') arranged transversely are enclosed in a chamber formed by an upper flap pair (65, 65') and a lower flap pair (66, 66'), which are shaped to allow the belt to pass through the chamber and can be rotated about an end pin to allow the chamber to be opened.

29. The device according to claim 28, characterized in that The two upper nozzle rows (63, 63') and the two lower nozzle rows (64, 64') arranged transversely are mounted on the upper flap pair (65, 65') and the lower flap pair (66, 66'), respectively.

30. The apparatus according to claim 21, wherein The thermal scanner is located at the outlets of the continuous casting device (1), the roughing mill (2), the first induction furnace (6.1), the second water descaling machine (8), the second induction furnace (6.2), the finishing mill (3) and the cooling station (12, 12').

31. A method for continuously producing a hot rolled steel strip having a minimum thickness of 0.3 mm by means of an apparatus according to any one of claims 1 to 30, comprising the following steps in sequence: (a) Continuous casting of thin slabs or medium slabs with a thickness of 40 to 150 mm; (b) performing rough rolling in 3 to 5 passes to obtain an intermediate slab; (c) first induction heating of the intermediate slab; (d) water descaling; (e) a second induction heating of the intermediate slab; (f) finishing rolling for 5 to 7 passes to obtain the strip; (g) controlled cooling of the strip; and (h) cutting the strip and winding it into coils, wherein at least step (e) and at least up to the third step (f) are carried out in a weakly oxidizing, inert or weakly reducing protective atmosphere, It is characterized by: Between steps (a) and (b) there is provided an additional step: (a') induction heating of the edges of the slab; (a") induction heating of the remaining portion of the slab surface; (a'") Water descaling.

32. The method according to claim 31, characterized in that Step (h) is replaced by the strip being passed directly to the step of applying a protective coating with subsequent final winding.

33. The method according to claim 31 or 32, characterized in that In step (b), the first pass of the rough rolling results in a thickness reduction of the slab of ≤ 20%.

34. The method according to claim 31 or 32, characterized in that Between steps (c) and (d) a further step (c') of mechanical disruption of the scales is provided.

35. The method according to claim 31 or 32, characterized in that Between steps (g) and (h) a further step (g') of mechanical descaling is provided.

36. The method according to claim 31 or 32, characterized in that Between steps (b) and (c) there is provided a further step of producing and removing the rough plate in the event of problems in parts of the equipment downstream of the roughing rolling.

37. The method according to claim 31 or 32, characterized in that Step (a'") is performed at a water pressure of less than 150 bar and / or step (d) is performed at a water pressure of at most 380 bar.

38. The method according to claim 31 or 32, characterized in that Step (e) is performed at the final temperature to ensure that step (f) is fully performed in the austenite field.

39. The method according to claim 31 or 32, wherein Step (a') is performed on the strip at most 150 mm from each edge of the slab and / or results in a temperature increase in the strip of at most 120°C.

40. The method according to claim 31 or 32, characterized in that Step (h) is followed by step (i) of liquid cooling the coil in a tank containing water or a weakly oxidizing aqueous solution.

41. The method according to claim 31 or 32, characterized in that Step (g) and step (h) in the winding section are also carried out in a weakly oxidizing, inert or weakly reducing protective atmosphere.

Images