Annealing Device for Metal Strip Coating System

Abstract

An annealing device for coating a metal strip (9) traveling longitudinally within a coating system with a layer of molten metal. The device comprises, in order, at least one longitudinally flowing induction heating device (10), at least one transversely flowing induction heating device (12), and at least one cooling zone.

Description

Technical Field

[0001] The present invention relates to the field of systems for coating a strip made of a flat object (e.g., a metal strip, particularly steel) made of a ferromagnetic material. More specifically, the present invention relates to an annealing apparatus and related processes for heating and annealing a moving strip made of a ferromagnetic material prior to coating with a molten metal (e.g., zinc). The present invention further relates to a system for coating a metal strip with a molten metal, including such an annealing apparatus.

Background Art

[0002] As is well known, strips made of ferromagnetic materials are externally coated by a plurality of coating processes (e.g., zinc coating).

[0003] The zone of a tank containing a molten metal bath (e.g., zinc) is central to the coating process and affects the operation of the system, the productivity of the process, the quality of the product, and the consumption of zinc.

[0004] Cold-rolled strips or hot-rolled and pickled strips are processed in a hot-dip zinc coating system of a continuous heating and annealing apparatus. Depending on the product and quality of the incoming material and the expected quality of the outgoing material, the heating cycle is defined by the maximum temperature of the material in the apparatus, the temperature holding time, and the strip processing speed.

[0005] An annealing apparatus, or more simply a furnace, can be classified into a horizontal furnace, a vertical furnace, or a hybrid furnace with horizontal and vertical extensions depending on its configuration.

[0006] The device part dedicated to reheating usually · Preheating, · Direct firing by burners, · Radiant tube heating by burners It is composed of modules for

[0007] A known example of a system for coating a metal strip is shown in FIG. 1. Such a system includes an annealing device, which is arranged upstream of a tank 8 containing a molten metal bath, · A preheating zone 1, · Arranged immediately downstream of the preheating zone 1, communicating with the preheating zone 1, and an open-flame heating device 2 in which the smoke generated by the open-flame heating device 2 is directly used to perform preheating in the zone 1, · A radiant-tube heating device 4 arranged immediately downstream of the open-flame heating device 2, · A cooling zone 6, · A zone 7 comprising at least one bridle roller for changing the direction of the traveling path of the metal strip 9 coming out of the annealing device and applying tension to the strip, and a connecting conduit 26 between the annealing device and the tank 8 is provided.

[0008] The preheating zone 1 is provided with an exhaust device 3 for exhausting the smoke generated by the burner of the open-flame heating device 2, while the radiant-tube heating device 4 is provided with a further exhaust device 5 for exhausting the smoke generated by each burner of the radiant-tube heating device.

[0009] Some devices only include a heating section with radiant tubes. In this case, it is essential to provide a cleaning section upstream of the device due to the insufficient cleaning ability of the open-flame heating device.

[0010] The most commonly used technology is the technology that uses gaseous fossil fuels (mainly natural gas). Therefore, as a result of the combustion effect, the annealing device emits carbon dioxide into the atmosphere. With the emphasis on reducing greenhouse gas emissions directly discharged by the combustion process, the technology used will be reexamined.

[0011] Heating by a burner requires a temperature increase gradient in the range of 10 °C / s to a maximum of 100 °C / s.

[0012] Furthermore, when changing the processing speed or the cross-section of the sheet to be processed, existing devices require a response time on the order of several tens of seconds to reach the new process parameter setting conditions.

[0013] As a result, the uncertainty in maintaining the mechanical properties expected in the transient stage of the process increases, the variation increases, leading to an increase in cost due to an increase in qualitative waste or energy consumption.

[0014] The heating rate and thermal inertia of the burner-based system also define the metal processing of the product, for example, require a selection related to the analysis of alloy elements present in the steel material, and directly affect the production cost.

[0015] Considering the above, it is clear that in order to eliminate the aforementioned drawbacks, an innovative improvement of the heating and annealing device of the hot coating line is necessary. Summary of the Invention Problems to be Solved by the Invention

[0016] An object of the present invention is to manufacture a continuous annealing apparatus in which a metal strip advances in a coating system, which can reduce and almost eliminate the direct emission of carbon dioxide into the environment as much as possible.

[0017] Another object of the present invention is to manufacture an annealing apparatus that enables high production flexibility and / or a significant increase in production capacity per unit time.

[0018] Another object of the present invention is to execute an annealing process with less environmental impact and high efficiency. Means for Solving the Problems

[0019] Accordingly, the present invention is an annealing apparatus for coating a metal strip traveling longitudinally within a coating system with a layer of molten metal, the apparatus comprising, in order: · at least one longitudinal-flow induction heating device; · at least one transverse-flow induction heating device; · at least one cooling zone and is provided with at least one preheating zone arranged upstream of the longitudinal-flow induction heating device, and aims to achieve the above object by the annealing apparatus. It is an object of the present invention to achieve the above object by an annealing apparatus provided with at least one preheating zone arranged upstream of the longitudinal-flow induction heating device.

[0020] A further aspect of the present invention relates to a system for coating a metal strip with a layer of molten metal, comprising the above-described annealing apparatus.

[0021] A further aspect of the present invention is a method for annealing a cold-rolled metal strip traveling longitudinally within a coating system, the coating system being for coating the metal strip with a layer of molten metal, the method being carried out by the above-described apparatus, a) heating the metal strip by the at least one longitudinal-flow induction heating device to a temperature lower than the Curie temperature of the material of the metal strip; b) heating the metal strip by the at least one transverse-flow induction heating device to a temperature higher than the Curie temperature of the material of the metal strip; c) cooling the metal strip by the at least one cooling zone and including preheating of the metal strip is provided by the at least one preheating zone upstream of the longitudinal-flow induction heating device.

[0022] Other advantages of some embodiments of the present invention include the following. · High production flexibility regardless of the horizontal or vertical configuration of the annealing apparatus. · Especially when used in combination with an inductor and a gas burner, the production capacity per hour is significantly improved. · It is possible to have a heating ramp (tilt) that cannot be achieved by using only a gas burner, enabling the production of high-quality steel with the same mechanical properties, simplified chemicals, and obvious advantages in production costs. · By using different types of inductors, or a combination of different types of inductors and burners, the potential difference between the center and the edge of the strip can be eliminated. · By using an inductor and direct firing together, surface cleaning can be performed without the need to add a cleaning section upstream of the annealing apparatus.

[0023] The dependent claims describe preferred embodiments of the present invention.

[0024] Further configurations and advantages of the present invention will become more apparent when considering the detailed description of the preferred embodiments (but not exclusive) of the apparatus shown by way of non-limiting example with reference to the accompanying drawings.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 5a

Figure 5b

Figure 5c

Figure 6

Figure 6a

Figure 6b

Figure 6c

[0026] The same reference numerals in the figures are regarded as the same elements or components.

Embodiments for Carrying Out the Invention

[0027] With reference to FIGS. 2 to 6, some exemplary embodiments of a system for coating a metal strip 9 with a molten metal layer, which is part of a system comprising an annealing apparatus according to the present invention, will be described. As is well known, a metal strip is a product having a dimension, i.e., thickness, that is significantly smaller than the other two dimensions, i.e., length and width.

[0028] In all embodiments of the present invention, the annealing apparatus for the metal strip 9 that travels longitudinally within the coating system sequentially comprises: · At least one longitudinal flow induction heating device 10; · At least one transverse flow induction heating device 12; · At least one cooling zone 6 and is provided with.

[0029] Advantageously, the longitudinal flow induction is applied to ferromagnetic materials and thus below the Curie temperature. Above the Curie temperature, the material becomes non-magnetic and transverse flow induction is preferably used.

[0030] Instead, in the reverse case, the energy transfer to the strip becomes very low, and the energy output deteriorates. Furthermore, the transverse flow applied to the ferromagnetic material attracts the strip and there is a risk of contact with the induction coil.

[0031] Advantageously, at least one preheating zone 1, 27, 32, 33 is provided upstream of the longitudinal flow induction heating device for preheating the strip, preferably by recovering heat from the same annealing device or from a further manufacturing device cooperating with the annealing device by means of a heat transfer fluid.

[0032] In some variants of the device, only one longitudinal flow induction heating device 10 is provided and only one transverse flow induction heating device 12 is provided.

[0033] For example, the coating system is · a strip made of low carbon steel, medium carbon steel, or high carbon steel, · a strip made of microalloyed steel, · a strip made of Interstitial Free High Strength Steel (IFHSS), · a strip made of Advanced High Strength Steel (AHSS), · a strip made of ferritic stainless steel and is a hot dip galvanizing line for treating pickled or cold rolled steel strips such as these.

[0034] Advantageously, the first embodiment of the device of the present invention includes the combined use of an induction heating system and a heating system (preferably equipped with a burner and supplied with a combustible gas).

[0035] In this case, the heating and annealing of the strip are carried out by combining the thermal energy applied through the induction system by the Joule effect of the eddy currents induced by the magnetic field and the thermal energy by combustion.

[0036] This first embodiment of the device of the present invention comprises, in order: · A preheating zone 1 (preferably a preheating tunnel); · At least one longitudinal flow induction heating device 10; · A direct-fired heating device 2; · At least one transverse flow induction heating device 12 for bringing the strip to the target temperature or the final annealing temperature and is provided with or consists of them (Figure 2).

[0037] The direct-fired heating device 2 is preferably provided with a burner to which natural gas is supplied, and the flame thereof directly contacts the strip to make the temperature of the strip uniform in the transverse direction.

[0038] By controlling the ratio of air to the combustible gas to make the combustible gas excessive (above stoichiometric combustion) and generating reducing smoke by carbon monoxide, the surface cleaning of the strip can be improved, and it is possible to remove oily residues, iron powder, and oxides.

[0039] Advantageously, by using the longitudinal flow induction heating device 10 and the direct-fired heating device 2 in combination at a minimum power level to obtain a surface cleaning effect, the production capacity remains the same, and the direct carbon dioxide emissions can be significantly reduced (for example, the carbon dioxide emissions are reduced by -30% to -50% compared with the prior art solutions).

[0040] Preferably, the radiant tube heating device 4 is arranged downstream of the at least one transverse flow induction heating device 12 to efficiently complete the annealing cycle, ensure the temperature holding time, and complete the crystallization cycle of the strip material.

[0041] The radiant tube heating device 4 can also be provided with a burner to which natural gas is preferably supplied.

[0042] The smoke generated by the burner of the radiant tube heating equipment 4 is preferably conveyed to the exhaust chimney through a special exhaust duct 5.

[0043] Advantageously, by combining the use of a longitudinal flow induction heating system and a transverse flow induction heating system and reducing the use of direct-fired heating equipment and radiant tube heating equipment supplied with gas, the production capacity remains the same while significantly reducing the direct carbon dioxide emissions (for example, reducing the carbon dioxide emissions by -60% to -80% compared to the prior art solutions).

[0044] Downstream of at least one transverse flow induction heating equipment 12 or downstream of the radiant tube heating equipment 4 (if present), a cooling zone 6 is arranged, followed by a zone 7 provided with at least one bridle roller. This bridle roller changes the direction of the traveling path of the metal strip 9 coming out of the annealing device, applies tension to the strip, and is provided with a connecting duct 26 between the annealing device and the tank 8.

[0045] Preferably, a duct 11 is provided for conveying the smoke generated by the direct-fired heating equipment 2 to the preheating zone 1. This duct 11 bypasses the longitudinal flow induction heating equipment 10. In the preheating zone 1, the smoke passes through in a countercurrent direction with respect to the traveling direction of the strip.

[0046] The bypass duct 11 operates only when both the longitudinal flow induction heating equipment 10 and the direct-fired heating equipment 2 are operating.

[0047] The smoke generated by the burner of the direct-fired heating equipment 2 is preferably conveyed to the exhaust chimney through a special exhaust duct 3 arranged at its distal end, preferably within the preheating zone 1 and preferably from the longitudinal flow induction heating equipment 10.

[0048] Advantageously, this first embodiment · enables the modernization of existing equipment, except for including the part that results in the maximum carbon dioxide emissions without completely modifying the annealing furnace. ·Interruptions for equipment investment and equipment modification can be reduced, ·Energy consumption can be reduced by recovering the heat of the smoke generated by the direct-fired heating equipment, ·The surface of the strip can be cleaned by the direct fire.

[0049] Furthermore, by taking advantage of the short response time of the inductor, it is also possible to improve the product characteristics during transient periods using constant power combustion and a variable power inductor.

[0050] The second embodiment of the device of the present invention advantageously includes the use of only an induction heating system, and thus the use of only the thermal energy applied through the induction system as an alternative to thermal combustion energy.

[0051] In this case, the heating and annealing of the strip are carried out only by the Joule effect of the eddy current induced by the magnetic field. Therefore, advantageously, complete elimination of carbon dioxide emissions is obtained.

[0052] The second embodiment of the device of the present invention comprises, in order, ·At least one longitudinal flow induction heating device 10, ·A compensation zone 23 for making the temperature of the strip discharged from the at least one longitudinal flow induction heating device 10 uniform in both the longitudinal and transverse directions, ·At least one transverse flow induction heating device 12 for bringing the strip to the target temperature or the final annealing temperature, ·A maintenance zone 24 for maintaining the strip at the target temperature and is provided with or composed of them (Figure 5).

[0053] The compensation zone 23 can be passive without the supply of thermal energy to the strip or active with the supply of thermal energy to the strip.

[0054] The holding zone 24 is, instead, an active zone that enables the maintenance of the final annealing temperature over the residence time required by the metalworking recipe, with the supply of thermal energy to the strip.

[0055] Preferably, the holding zone 24 and optionally also the compensation zone 23 are each provided with an electric radiant element.

[0056] These electric radiant elements can be, for example, resistor spark plugs or tubes.

[0057] Downstream of the holding zone 24, a cooling zone 6 is arranged, followed by a zone 7 with at least one bridle roller. The bridle roller changes the direction of travel of the metal strip 9 coming out of the annealing apparatus, applies tension to the strip, and there is a connecting conduit 26 between the annealing apparatus and the tank 8.

[0058] At least one lateral flow induction heating device 12, the holding zone 24, and the cooling zone 6 can be maintained under pressure by a technical gas flow, preferably a single flow of technical gas such as nitrogen and / or hydrogen. Thereby, protection from oxidation, for example by nitrogen, and a cleaning / reduction action, for example by hydrogen, are ensured. The technical gas is heated up to the holding zone 24 and then used at a low temperature in the cooling zone.

[0059] A first variant of this second embodiment is shown in Fig. 5a. Advantageously, a preheating zone 27 is provided upstream of at least one longitudinal flow induction heating device 10.

[0060] One conduit 28 connects the cooling zone 6 to the preheating zone 27 and conveys a part of the technical gas at a temperature of, for example, 150 to 180 °C to the preheating zone 27 for preheating the strip entering at room temperature.

[0061] A second modification of this second embodiment is shown in Fig. 5b. Advantageously, a preheating zone 27 is provided upstream of at least one longitudinal flow induction heating device 10.

[0062] The conduit 30 crosses the preheating zone 27 and preheats the strip with the heat transfer fluid carried by the conduit 30.

[0063] For example, a heat exchanger 29 is provided outside the preheating zone, and the conduit 30 crosses the heat exchanger 29 to heat the heat transfer fluid by recovering heat from another heat transfer fluid carried by the discharge conduit 31 of another manufacturing apparatus. The discharge conduit 31 can also cross the heat exchanger 29.

[0064] As a non-limiting example, the heat transfer fluid may be steam coming from a water exchanger, and in the water exchanger, heat is recovered from another heat transfer fluid that can be composed of, for example, smoke from an electric arc furnace or a heating furnace. In this case, the strip can be heated from room temperature to a temperature of about 90°, or up to a temperature of about 200°C if the steam is pressurized.

[0065] A third modification of this second embodiment is shown in Fig. 5c. Advantageously, two preheating zones 32, 33 are provided upstream of at least one longitudinal flow induction heating device 10.

[0066] The conduit 34 connects the cooling zone 6 to the first preheating zone 32 and conveys a part of the technical gas at a temperature of, for example, 150 - 180°C to the first preheating zone 32 for preheating the strip entering at room temperature.

[0067] Preferably, the conduit 34 crosses the first preheating zone 32 and returns to the cooling zone 6.

[0068] For example, the technical gas reaches the first preheating zone 32 equipped with a jet cooling system at a temperature of 150 - 180°C and exchanges heat with the incoming strip by the convection effect. The strip can be heated to a temperature in the range of 100 - 120°C from room temperature.

[0069] The second preheating zone 33 is arranged downstream of the first preheating zone 32, preferably immediately downstream.

[0070] The conduit 35 traverses the second preheating zone 33 and further preheats the strip with the heat transfer fluid carried by the conduit 35.

[0071] For example, a heat exchanger 36 is provided outside the preheating zone, the conduit 35 traverses this heat exchanger 36, and the heat transfer fluid is heated by recovering heat from another heat transfer fluid carried by the discharge conduit 37 of another manufacturing apparatus. Also, the discharge conduit 37 can traverse the heat exchanger 36.

[0072] As a non-limiting example, the heat transfer fluid can include molten salt or supercritical carbon dioxide, and has a role of storing the heat energy that is discontinuous or excessively generated by a heat exchanger or a thermal energy storage device (TES) 36, i.e., a generator, and can return it to the user when necessary, and is preferably heated to a temperature of 600 °C or higher by a component.

[0073] Alternatively, the heat transfer fluid can be of any type suitable for the purpose of preheating the strip, while molten salt or supercritical carbon dioxide is used in the thermal energy storage device 36.

[0074] The heat energy generator is outside the annealing apparatus and includes, for example, an electric arc furnace (EAF), a solar parabola, etc.

[0075] The other heat transfer fluid can be composed of, for example, the flue gas or steam of an electric arc furnace or a heating furnace.

[0076] The thermal energy storage device or TES 36 can be provided, for example, between the outer EAF-TES loop and the TES-annealing apparatus loop.

[0077] In this second preheating zone 33, the strip can be heated, for example, by radiation or convection, from a temperature in the range of 100 to 120 °C reached in the first preheating zone 32 to a temperature in the range of 450 to 500 °C.

[0078] Using the three variants of FIGS. 5a, 5b, and 5c makes it possible to save energy by facilitating the operation of the next section of the annealing system and, in some cases, to reduce its size.

[0079] The third embodiment of the device of the present invention uses an induction heating system as in the second embodiment and, in order, · at least one longitudinal flow induction heating device 10, · at least one first transverse flow induction heating device 12, · a compensation zone 23 for equalizing the temperature in both the longitudinal and transverse directions, · at least one second transverse flow induction heating device 12' for bringing the strip to the target temperature or the final annealing temperature, · a maintenance zone 24 for maintaining the strip at the target temperature and is provided with or consists of these (FIG. 6).

[0080] The compensation zone 23 can be passive without supplying thermal energy to the strip or active with supplying thermal energy to the strip. It is particularly aimed at equalizing the temperature in the transverse direction because at least one first transverse flow induction heating device 12 generates overheating at the edges of the strip.

[0081] The maintenance zone 24, instead, is an active zone with supplying thermal energy to the strip, maintaining the final annealing temperature over the residence time required in the metalworking recipe, and obtaining the desired particle size.

[0082] Preferably, electric radiation elements are also provided in the maintenance zone 24 and, in some cases, in the compensation zone 23, respectively.

[0083] These electrical radiation elements can be, for example, resistor spark plugs or tubes.

[0084] Downstream of the maintenance zone 24, a cooling zone 6 is arranged, followed by a zone 7 with at least one bridle roller, which changes the direction of travel of the metal strip 9 coming out of the annealing device, applies tension to the strip, and there is a connecting conduit 26 between the annealing device and the tank 8.

[0085] At least one first laterally flowing induction heating device 12, a compensation zone 23, at least one second laterally flowing induction heating device 12', a maintenance zone 24, and a cooling zone 6 can be maintained under pressure by a single flow of technical gas, preferably a technical gas such as nitrogen and / or hydrogen, thereby ensuring protection from oxidation, for example by nitrogen, and a cleaning / reduction action, for example by hydrogen. The technical gas is heated up to the maintenance zone 24 and then used at a low temperature in the cooling zone.

[0086] A first variant of this third embodiment is shown in Figure 6a. Advantageously, a preheating zone 27 is provided upstream of at least one longitudinally flowing induction heating device 10.

[0087] One conduit 28 connects the cooling zone 6 to the preheating zone 27 and conveys a part of the technical gas at a temperature of, for example, 150 to 180 °C into the preheating zone 27 for preheating the strip entering at room temperature.

[0088] A second variant of this third embodiment is shown in Figure 6b. Advantageously, a preheating zone 27 is provided upstream of at least one longitudinally flowing induction heating device 10.

[0089] The conduit 30 crosses the preheating zone 27 and preheats the strip by means of the heat transfer fluid conveyed by the conduit 30.

[0090] For example, a heat exchanger 29 is provided outside the preheating zone, and the heat transfer fluid is heated by the conduit 30 crossing the heat exchanger 29 and recovering heat from another heat transfer fluid carried by the discharge conduit 31 of another manufacturing apparatus. Further, the discharge conduit 31 can also cross the heat exchanger 29.

[0091] As a non-limiting example, the heat transfer fluid may be steam coming from a water exchanger, where the water exchanger recovers heat from another heat transfer fluid that can be composed of, for example, smoke from an electric arc furnace or a heating furnace. In this case, the strip can be raised in temperature from room temperature to about 90°, or up to about 200 °C if the steam is pressurized.

[0092] A third modification of this third embodiment is shown in FIG. 6c. Advantageously, two preheating zones 32, 33 are provided upstream of at least one longitudinal flow induction heating device 10.

[0093] The conduit 34 connects the cooling zone 6 to the first preheating zone 32 and conveys a part of the technical gas at a temperature of, for example, 150 to 180 °C to the preheating zone 32 for preheating the strip entering at room temperature.

[0094] Preferably, the conduit 34 crosses the first preheating zone 32 and returns to the cooling zone 6.

[0095] For example, the technical gas reaches the first preheating zone 32 equipped with a jet cooling system at a temperature of 150 to 180 °C and exchanges heat with the incoming strip by the convection effect. The strip can be heated to a temperature in the range of 100 to 120 °C from room temperature.

[0096] The second preheating zone 33 is arranged downstream of the first preheating zone 32, preferably immediately downstream.

[0097] The conduit 35 crosses the second preheating zone 33 and further preheats the strip with the heat transfer fluid carried by the conduit 35.

[0098] For example, a heat exchanger 36 is provided outside the preheating zone, and the heat transfer fluid is heated by the conduit 35 crossing the heat exchanger 36 and recovering heat from another heat transfer fluid carried by the discharge conduit 37 of another manufacturing apparatus. Further, the discharge conduit 37 can also cross the heat exchanger 36.

[0099] As a non-limiting example, the heat transfer fluid can include molten salt or supercritical carbon dioxide and is preferably heated to a temperature of 600 °C or higher by a component having a role of storing heat energy that is generated discontinuously or excessively by a generator outside the heat exchanger or the thermal energy storage device (TES) 36, that is, outside the annealing apparatus.

[0100] Alternatively, the heat transfer fluid can be of any type suitable for the purpose of preheating the strip, while molten salt or supercritical carbon dioxide is used in the thermal energy storage device 36.

[0101] The heat energy generator outside the annealing apparatus includes, for example, an electric arc furnace (EAF) or a solar parabola.

[0102] The other heat transfer fluid can be composed of, for example, the flue gas or steam of an electric arc furnace or a heating furnace.

[0103] The thermal energy storage device or TES 36 can be provided, for example, between the outer EAF-TES loop and the TES-annealing apparatus loop.

[0104] In this second preheating zone 33, the strip can be heated from a temperature in the range of 100 to 120 °C reached in the first preheating zone 32 to a temperature in the range of 450 to 500 °C, for example, by radiation or convection.

[0105] Using the three modifications of FIGS. 6a, 6b, and 6c can save energy by facilitating the operation of the next section of the annealing system and, in some cases, can reduce its size.

[0106] In both the second and third embodiments of the present invention, when there may be no one or more preheating zones, a cleaning section for surface cleaning of the strip, for example an alkaline cleaning section, is provided upstream of at least one longitudinal flow induction heating device 10 instead of the direct-fired heating device of the first embodiment.

[0107] Advantageously, by using the longitudinal flow induction system and the transverse flow induction system in combination with the aforementioned compensation zone and maintenance zone, the production capacity remains the same, and direct carbon dioxide emissions to the environment can be eliminated.

[0108] In both the second and third embodiments, the apparatus can be fully pressurized with a technical gas such as nitrogen, hydrogen, or a mixture thereof, ensuring protection from oxidation and cleaning / reduction action.

[0109] In all embodiments of the annealing apparatus of the present invention, at least one longitudinal flow induction heating device 10 can include at least one induction coil 14 wound transversely around the advancing surface of the strip, i.e., transversely around a part of the advancing path of the strip, for example, only one induction coil.

[0110] On both the upstream and downstream sides of the at least one induction coil 14, respective guide roller pairs 13, preferably coated with a ceramic material for guiding and supporting the strip, are provided.

[0111] The two guide roller pairs 13 isolate the longitudinal flow induction heating device 10 from other sections of the annealing apparatus adjacent thereto.

[0112] Preferably, the longitudinal flow induction heating device 10 is pressurized with a nitrogen supply line 25 to prevent the strip from oxidizing in the presence of oxygen due to temperature.

[0113] Optionally, a temperature sensor 17 is provided for detecting the temperature of the strip entering and exiting the longitudinal flow induction heating device 10.

[0114] Preferably, at least one induction coil 14 is connected to a capacitor bank 15 and a high-frequency converter 16.

[0115] In the example of FIG. 3, the longitudinal flow induction heating device 10 comprises or is composed of two induction heating modules.

[0116] Each induction heating module comprises or is composed of at least one induction coil 14, for example, only one induction coil wound around each part of the strip travel path.

[0117] Each induction heating module is delimited by two pairs of guide rollers 13, one pair each upstream and downstream of the respective induction coil 14.

[0118] The first temperature sensor 17 is arranged upstream of the first pair of rollers 13, and the second temperature sensor 17 is arranged between the induction coil 14 and the second pair of rollers 13.

[0119] The second temperature sensor 17 of the first induction heating module corresponds to the first temperature sensor 17 of the second induction heating module.

[0120] Thus, in this example, three pairs of guide rollers 13 are provided, the central pair of rollers being common to the two induction heating modules, and the two end pairs of rollers isolating the longitudinal flow induction heating device 10 from other sections of the adjacent annealing device.

[0121] Each induction coil 14 is connected to a respective capacitor bank 15 and a respective high-frequency converter 16.

[0122] The cross-flow induction heating devices 12, 12' can instead comprise only one pair of induction coils 18, 19, for example, a first induction coil 18 arranged on the first side of the strip advancing surface and a second induction coil 19 arranged on the second side opposite to the first side of the strip advancing surface.

[0123] Preferably, the cross-flow induction heating device 12 is pressurized with a nitrogen and hydrogen supply line to prevent the strip from oxidizing in the presence of oxygen due to high temperature.

[0124] In any of the radiant tube heating devices 4 of the first embodiment, the same nitrogen atmosphere and hydrogen atmosphere can be used.

[0125] Preferably, a position sensor 21, for example, an optical or inductive one, is provided to detect the position of the edge of the strip with respect to the center line of the advancing path of the strip.

[0126] Optionally, in order to more appropriately direct the magnetic field, it is also possible to control the position of the induction coil with respect to the edge of the strip. For example, at least one moving actuator 22 is provided for moving at least one of the first induction coil 18 and the second induction coil 19 in a direction transverse to the longitudinal advancing direction.

[0127] Alternatively, the first induction coil 18 and the second induction coil 19 remain fixed, and at least one moving actuator 22 is adapted to move a screen made of copper or other suitable material, preferably arranged above the first induction coil 18 and below the second induction coil 19 respectively, so as to follow the position of the edge of the strip.

[0128] For example, two moving actuators 22 are provided, and each actuator is configured to move its respective induction coil 18 or 19, or its respective screen (not shown), in a direction transverse to the longitudinal path of travel of the strip.

[0129] This adjustment of the position of the induction coils 18, 19, or the position of the screen, is useful when the temperature profile of the strip is non-uniform, or when the strip is displaced laterally with respect to the centerline of the travel plane path, or when the width of the strip varies.

[0130] The transverse flow induction heating apparatus 12 can also be provided with a pair of guide rollers 13', preferably coated with a ceramic material, for guiding and supporting the strip upstream and downstream of the at least one pair of induction coils 18, 19.

[0131] Preferably, temperature sensors 17', 20 are provided for detecting the temperature of the strip entering and exiting the transverse flow induction heating apparatus 12.

[0132] Both the first induction coil 18 and the second induction coil 19 can be individually connected to their respective capacitor banks 15' and their respective high-frequency converters 16'.

[0133] Preferably, the two capacitor bank converter assemblies are arranged on both sides of the travel plane path (i.e., one assembly on each side).

[0134] In the example of FIG. 4, the transverse flow induction heating apparatus 12 comprises or consists of a single induction heating module composed of only one pair of induction coils 18, 19.

[0135] This induction heating module is delimited by two pairs of guide rollers 13', one upstream and the other downstream of the induction coils 18, 19. The first temperature sensor 17' is arranged upstream of the first roller pair 13', and the second temperature sensor 20 is arranged between the induction coil pair 18, 19 and the second roller pair 13'.

[0136] In various embodiments, all of the temperature sensors 17, 17', 20 can be pyrometers (e.g., a scanning type pyrometer for measuring the thermal profile of a strip).

[0137] In addition to the temperature sensors, one or more of the following sensors may be present along various devices of the system of the present invention. · A sensor for detecting the composition of the atmosphere (O 2 , N 2 , H 2 , dew point, CO 2 , CO, etc.). · A sensor for detecting the flow rate of combustion air, combustion smoke, N 2 , H 2 , and their mixtures. · A sensor for detecting the consumption of natural gas and electricity.

[0138] Some examples of the annealing process performed using the above-described embodiments of the apparatus will be described below.

[0139] In all embodiments of the apparatus of the present invention, an annealing method for coating a pickled or cold-rolled metal strip 9 that travels longitudinally within a coating system with a layer of molten metal is a) heating the metal strip at a temperature lower than the Curie temperature of the material of the metal strip by at least one longitudinal flow induction heating device 10; b) heating the metal strip at a temperature higher than the Curie temperature of the material of the metal strip by at least one transverse flow induction heating device 12, 12'; c) cooling the metal strip by at least one cooling zone includes

[0140] Advantageously, the preheating of the metal strip is provided in at least one preheating zone 1, 27, 32, 33 upstream of the longitudinal flow induction heating device 10.

[0141] In both step a) and step b), the heating gradient can vary in the range of 50 - 500 °C / s, preferably can vary in the range of 100 - 500 °C / s, and more preferably can vary in the range of 110 - 450 °C / s.

[0142] Preferably, at least one longitudinal flow induction heating device 10 is kept under pressure by a nitrogen flow supplied by a nitrogen supply line 25, while at least one transverse flow induction heating device 12, 12' is kept under pressure by a flow of a mixture of nitrogen and hydrogen supplied by their respective supply lines.

[0143] When using the first embodiment of the heating and annealing apparatus shown in FIG. 2, the smoke generated by the direct - fired heating device 2 is directly conveyed through the bypass conduit 11 to the preheating tunnel 1 to preheat the pickled or cold - rolled strip from room temperature to a temperature in the range of 50 - 200 °C, preferably 100 - 200 °C, and more preferably 150 - 200 °C. Then, the smoke is exhausted from the preheating tunnel 1 by the exhaust conduit 3.

[0144] Downstream of the preheating tunnel 1, preferably immediately downstream of the preheating tunnel 1, the strip is heated by the longitudinal flow induction heating device 10 at a temperature lower than the Curie temperature of the material of the strip.

[0145] For example, a strip made of preferably low - carbon steel or ferritic stainless steel is heated at a temperature in the range of 500 - 650 °C, preferably 550 - 600 °C, with a heating gradient of 50 - 500 °C / second, preferably 100 - 500 °C / second.

[0146] Downstream of the longitudinal flow induction heating device 10, preferably immediately downstream of the device 10, the strip is heated by the direct-fired heating device 2, preferably supplied with natural gas, at a heating gradient of 30 to 100 °C / s to a temperature of 650 to 750 °C, preferably 670 to 730 °C, for example up to 700 °C.

[0147] Downstream of the direct-fired heating device 2, preferably immediately downstream of the device 2, the strip is heated by the transverse flow induction heating device 12 at a temperature higher than the Curie temperature of the strip material.

[0148] For example, the strip is heated at a temperature in the range of 740 to 950 °C, preferably 750 to 950 °C, more preferably 800 to 900 °C, at a heating gradient of 50 to 500 °C / second, preferably 100 to 500 °C / second.

[0149] Preferably, the transverse flow induction heating device 12 is operated when the temperature of the strip emerging from the direct-fired heating device 2 is close to the Curie temperature.

[0150] Optionally, downstream of the transverse flow induction heating device 12, preferably immediately downstream of the device 12, the strip is heated by the radiant tube heating device 4, preferably supplied with natural gas, maintaining a temperature in the range of 750 to 950 °C, preferably 780 to 920 °C, equalizing the transverse temperature of the strip to complete the annealing of the strip and obtaining the required mechanical properties.

[0151] In a specific variant of this process, the strip is · Using the longitudinal flow induction heating device 10 at a temperature in the range of 550 to 600 °C, · Using the direct-fired heating device 2 at a temperature in the range of 670 to 730 °C, · Using the transverse flow induction heating device 12 at a temperature in the range of 750 to 950 °C, · Preferably, using the radiant tube heating device 4 to maintain the temperature in the range of 780 to 920 °C Heated.

[0152] The transverse flow induction heating device 12 is kept under pressure by the flow of a mixture of nitrogen and hydrogen, and this mixture is preferably the same mixture as that which prevents oxidation in the zone of the radiant tube heating device 4.

[0153] Downstream of the transverse flow induction heating device 12, or downstream of the radiant tube heating device 4 if it exists, the strip is cooled in the cooling zone 6 to a temperature suitable for immersion in a tank 8 containing a molten metal bath for coating the strip.

[0154] When using the second embodiment of the heating and annealing apparatus shown in FIGS. 5, 5a, 5b, and 5c, the pickled or cold-rolled strip is heated by the longitudinal flow induction heating device 10 from room temperature to a temperature lower than the Curie temperature of the strip material.

[0155] For example, a strip preferably made of low-carbon steel or ferritic stainless steel is heated at a temperature in the range of 680 - 740 °C, preferably 700 - 730 °C, and optionally at a heating rate of 50 - 500 °C / second, preferably 80 - 400 °C / second.

[0156] Downstream of the longitudinal flow induction heating device 10, preferably immediately downstream of the device 10, the strip passes through the compensation zone 23 to make its temperature (especially the transverse temperature) uniform (for example, about 700 - 730 °C).

[0157] Downstream of the compensation zone 23, preferably immediately downstream of the compensation zone 23, the strip is heated by the transverse flow induction heating device 12 to a temperature higher than the Curie temperature of the strip material.

[0158] For example, the strip is heated to a target temperature or final annealing temperature preferably in the range of 750 - 950 °C, preferably 850 - 950 °C, and optionally at a heating rate of 50 - 500 °C / second, preferably 80 - 400 °C / second.

[0159] Preferably, the transverse flow induction heating device 12 is activated when the temperature of the strip exiting the longitudinal flow induction heating device 10 is close to the Curie temperature.

[0160] Downstream of the transverse flow induction heating device 12, preferably immediately downstream of the device 12, the strip passes through the holding zone 24, preferably for 5 to 60 seconds, maintaining the strip at the target temperature to obtain complete recrystallization of the material reaching the dimensions of the particles expected for the quality of the steel to be produced.

[0161] Downstream of the holding zone 24, preferably immediately downstream of the holding zone 24, the strip is cooled to an appropriate temperature (for example, in the range of 420 - 480 °C) in the cooling zone 6 and immersed in a tank 8 containing a molten metal bath for coating the strip.

[0162] In a particular variation of this process, the strip is · heated by the longitudinal flow induction heating device 10 to a temperature in the range of 700 - 730 °C, · passed through the compensation zone 23 to equalize its temperature (especially the transverse temperature), · heated by the transverse flow induction heating device 12 to a target temperature in the range of 850 - 950 °C, · passed through the holding zone 24 to maintain the strip at the target temperature.

[0163] When using the variation of Figure 5a of the second embodiment, the difference from the process carried out using the figure of Figure 5 is represented by the fact that the pickled or cold - rolled strip is pre - heated from room temperature to a temperature of, for example, 70 - 90 °C by the pre - heating zone 27. In particular, a part of the technical gas present in the cooling zone 6 is conveyed towards the pre - heating zone 27 by a conduit 28 connecting the cooling zone 6 and the pre - heating zone 27.

[0164] Similarly, when using the variant of FIG. 5b of the second embodiment, the difference from the process executed in the figures of FIG. 5 is represented by the fact that the pickled or cold-rolled strip is preheated from room temperature to a temperature in the range of, for example, 70 to 90 °C by the preheating zone 27. In particular, the heat transfer fluid conveyed by the conduit 30 crosses the preheating zone 27 to preheat the strip. When using steam or other pressurized heat transfer fluid, the strip can also reach a temperature of about 180 to 220 °C in the preheating zone 27.

[0165] In both variants of FIGS. 5a - 5b, downstream of the preheating zone 27, the strip enters directly into the longitudinal flow induction heating device 10, where it is heated from a temperature of 70 to 90 °C, or 180 to 220 °C, to a temperature lower than the Curie temperature of the strip material (for example, a temperature in the range of 680 to 740 °C, preferably 700 to 730 °C).

[0166] When using the variant of FIG. 5c of the second embodiment, the difference from the process executed in the figures of FIG. 5 is represented by the fact that the pickled or cold-rolled strip is preheated from room temperature to a temperature in the range of 100 to 120 °C by the first preheating zone 32 and then to a temperature in the range of 450 to 500 °C by the next second preheating zone 33. In particular, a part of the technical gas present in the cooling zone 6 is conveyed towards the first preheating zone 32 by the first conduit 34 connecting the cooling zone 6 to the first preheating zone 32, and the heat transfer fluid conveyed by the second conduit 35 crosses the second preheating zone 33 to further preheat the strip.

[0167] Downstream of the second preheating zone 33, the strip enters directly into the longitudinal flow induction heating device 10, where it is heated from a temperature of 450 to 500 °C to a temperature lower than the Curie temperature of the strip material (for example, a temperature of 680 to 740 °C, preferably 700 to 730 °C).

[0168] When using the third embodiment of the heating and annealing apparatus shown in FIGS. 6, 6a, 6b, and 6c, the pickled or cold-rolled strip is heated by the longitudinal flow induction heating device 10 from room temperature to a temperature lower than the Curie temperature of the strip material.

[0169] For example, a strip preferably made of low-carbon steel or ferritic stainless steel is heated at a temperature in the range of 680 to 740 °C, preferably 700 to 730 °C, and optionally at a heating gradient of 50 to 500 °C / sec, preferably 80 to 400 °C / sec.

[0170] Downstream of the longitudinal flow induction heating device 10, preferably immediately downstream of the device 10, the strip is heated by the first transverse flow induction heating device 12 to a temperature higher than the Curie temperature of the strip material.

[0171] For example, the strip is heated at a temperature in the range of 750 to 850 °C, preferably 750 to 800 °C, and optionally at a heating gradient of 50 to 500 °C / sec, preferably 80 to 400 °C / sec.

[0172] Preferably, the first transverse flow induction heating device 12 is activated when the temperature of the strip exiting the longitudinal flow induction heating device 10 is close to the Curie temperature.

[0173] Downstream of the first transverse flow induction heating device 12, preferably immediately downstream of the device 12, the strip passes through the compensation zone 23 to make its temperature (especially the transverse temperature) uniform (e.g., about 750 to 780 °C).

[0174] Downstream of the compensation zone 23, preferably immediately downstream of the compensation zone 23, the strip is heated by the second transverse flow induction heating device 12' to a target temperature or final annealing temperature preferably in the range of 800 to 950 °C, preferably 810 to 900 °C.

[0175] Downstream of the second transverse flow induction heating device 12’, preferably immediately downstream of said device 12’, the strip passes through the holding zone 24 and preferably maintains the strip at said target temperature for 5 to 60 seconds to obtain complete recrystallization of the material reaching the dimensions of the particles expected for the quality of the steel to be produced.

[0176] Downstream of the holding zone 24, preferably immediately downstream of the holding zone 24, the strip is cooled to a suitable temperature (for example, in the range of 420 - 480 °C) in the cooling zone 6 and immersed in a tank 8 containing a molten metal bath for coating the strip.

[0177] In a particular variant of this process, the strip · is heated by the longitudinal flow induction heating device 10 to a temperature in the range of 700 - 730 °C, · is heated by the first transverse flow induction heating device 12 to a target temperature in the range of 750 - 800 °C, · is passed through the compensation zone 23 to equalize its temperature (especially the transverse temperature), · is heated by the second transverse flow induction heating device 12’ to a target temperature in the range of 810 - 900 °C, · is passed through the holding zone 24 to maintain the strip at said target temperature.

[0178] When using the variant of Figure 6a of the third embodiment, the difference from the process carried out in the figure of Figure 6 is represented by the fact that the pickled or cold-rolled strip is preheated by the preheating zone 27 from room temperature to a temperature of, for example, 70 - 90 °C. In particular, a part of the technical gas present in the cooling zone 6 is conveyed towards the preheating zone 27 by a conduit 28 connecting the cooling zone 6 to said preheating zone 27.

[0179] Similarly, when using the variant of FIG. 6b of the third embodiment, the difference from the process executed in the figures of FIG. 6 is represented by the fact that the pickled or cold-rolled strip is preheated by the preheating zone 27 from room temperature to a temperature of, for example, 70 to 90 °C. In particular, the heat transfer fluid conveyed by the conduit 30 crosses the preheating zone 27 to preheat the strip.

[0180] When using steam or other pressurized heat transfer fluid, the strip can also reach a temperature of about 180 to 220 °C in the preheating zone 27.

[0181] In both variants of FIGS. 6a - 6b, downstream of the preheating zone 27, the strip directly enters the longitudinal flow induction heating device 10, where it is heated from a temperature of 70 to 90 °C, or 180 to 220 °C, to a temperature lower than the Curie temperature of the strip material (for example, in the range of 680 to 740 °C, preferably 700 to 730 °C).

[0182] When using the variant of FIG. 6c of the third embodiment, the difference from the process executed in the figures of FIG. 6 is represented by the fact that the pickled or cold-rolled strip is preheated by the first preheating zone 32 from room temperature to a temperature in the range of 100 to 120 °C, and then by the next second preheating zone 33 to a temperature in the range of 450 to 500 °C. In particular, a part of the technical gas present in the cooling zone 6 is conveyed towards the first preheating zone 32 by the first conduit 34 connecting the cooling zone 6 to the first preheating zone 32, and the heat transfer fluid conveyed by the second conduit 35 crosses the second preheating zone 33 to further preheat the strip.

[0183] Downstream of the second preheating zone 33, the strip directly enters the longitudinal flow induction heating device 10, where it is heated from a temperature of 450 to 500 °C to a temperature lower than the Curie temperature of the strip material (for example, a temperature in the range of 680 to 740 °C, preferably 700 to 730 °C).

[0184] In both the second and third embodiments, if there may be no one or more preheating zones, surface cleaning of the strip is provided upstream of at least one longitudinal flow induction heating device 10, for example by an alkaline cleaning section.

[0185] Furthermore, the annealing apparatus can be fully pressurized with a technical gas such as nitrogen, hydrogen, or a mixture thereof, thereby ensuring protection from oxidation and a cleaning / reducing action.

Claims

1. An annealing apparatus for coating a metal strip (9) advancing longitudinally in a coating system with a layer of molten metal, said apparatus comprising, in sequence, at least one longitudinally flowing induction heating device (10), at least one transversely flowing induction heating device (12), at least one cooling zone (6) and at least one preheating zone (1, 27, 32, 33) provided upstream of said longitudinally flowing induction heating device (10).

2. The apparatus according to claim 1, wherein said longitudinally flowing induction heating device (10) and said transversely flowing induction heating device (12) are each provided singly.

3. A direct-fired heating device (2) disposed between said longitudinally flowing induction heating device (10) and said transversely flowing induction heating device (12), and preferably a radiant tube heating device (4) disposed downstream of said transversely flowing induction heating device (12) are provided, in the apparatus according to claim 1 or 2.

4. A conduit (11) for conveying the smoke generated by said direct-fired heating device (2) to said preheating zone (1) is provided, said conduit (11) bypassing said longitudinally flowing induction heating device (10), in the apparatus according to claim 3.

5. A maintenance zone (24) disposed downstream of said transversely flowing induction heating device (12) for maintaining a predetermined temperature, and a compensation zone (23) disposed between said longitudinally flowing induction heating device (10) and said transversely flowing induction heating device (12) for equalizing the temperature of said strip exiting said longitudinally flowing induction heating device (10) are provided, in the apparatus according to claim 1 or 2.

6. A first transversely flowing induction heating device (12) disposed downstream of said longitudinally flowing induction heating device (10), a compensation zone (23) disposed downstream of said first transversely flowing induction heating device (12) for equalizing the temperature of said strip, a second transversely flowing induction heating device (12') disposed downstream of said compensation zone (23), and a maintenance zone (24) disposed downstream of said second transversely flowing induction heating device (12') are provided, in the apparatus according to claim 1.

7. Said maintenance zone (24) is provided with a first electrical radiation element, and said compensation zone (23) is preferably provided with a second electrical radiation element. The device according to claim 5 or 6, wherein preferably, the electric radiation element is a resistive spark plug or a tube.

8. A conduit (28) connects the at least one cooling zone (6) to the preheating zone (27) and conveys a part of the technical gas present in the cooling zone (6) towards the preheating zone (27), or A conduit (30) adapted to convey a heat transfer fluid crosses the preheating zone (27) to preheat the strip, the device according to claim 5 or 6.

9. A first preheating zone (32) and a second preheating zone (33) are provided upstream of the longitudinal flow induction heating device (10), Preferably, a first conduit (34) connects the at least one cooling zone (6) to the first preheating zone (32) and conveys a part of the technical gas present in the cooling zone (6) towards the first preheating zone (32), A second conduit (35) adapted to convey a heat transfer fluid crosses the second preheating zone (33) to further preheat the strip, the device according to claim 5 or 6.

10. The longitudinal flow induction heating device (10) comprises at least one induction coil (14) wound laterally around the strip advancing surface, Preferably, a pair of guide rollers (13), preferably coated with a ceramic material, for guiding and supporting the strip is provided upstream and downstream of the at least one induction coil (14), Preferably, a temperature sensor (17) for detecting the temperature of the strip entering and leaving the longitudinal flow induction heating device (10) is provided, Preferably, the at least one induction coil (14) is connected to a capacitor bank (15) and a high-frequency converter (16), the device according to any one of claims 1 to 9.

11. The transverse flow induction heating device (12) comprises at least one pair of induction coils (18, 19) consisting of a first induction coil (18) arranged on a first side of the strip advancing surface and a second induction coil (19) arranged on a second side of the strip advancing surface opposite to the first side, Preferably, at least one moving actuator (22) is provided for moving at least one of the first induction coil (18) and the second induction coil (19) in a direction transverse to the longitudinal direction, or the first induction coil (18) and the second induction coil (19) are fixed, and preferably, at least one moving actuator (22) is provided for moving a movable screen, which is preferably disposed above the first induction coil (18) and below the second induction coil (19), respectively. The apparatus according to any one of claims 1 to 10, preferably provided with a position sensor (21) for detecting the position of the edge of the strip with respect to the center line of the strip advancing surface.

12. A pair of guide rollers (13') is provided for guiding and supporting the strip upstream and downstream of the at least one induction coil pair (18, 19), preferably coated with a ceramic material. Preferably, temperature sensors (17', 20) are provided for detecting the temperature of the strip entering and leaving the transverse flow induction heating device (12). The apparatus according to claim 10 or 11, wherein the first induction coil (18) and the second induction coil (19) are respectively connected to their respective capacitor banks (15') and their respective high-frequency converters (16').

13. A method for annealing a pickled or cold-rolled metal strip (9) advancing longitudinally in a coating system, the coating system being for coating the metal strip with a layer of molten metal, the method being carried out by the apparatus according to any one of claims 1 to 12, a) heating the metal strip at a temperature lower than the Curie temperature of the material of the metal strip by the at least one longitudinal flow induction heating device (10); b) heating the metal strip at a temperature higher than the Curie temperature of the material of the metal strip by the at least one transverse flow induction heating device (12); c) cooling the metal strip by the at least one cooling zone and including The preheating of the metal strip is carried out in at least one of the preheating zones (1, 27, 32, 33) upstream of the longitudinal flow induction heating device (10), method.

14. A direct-fired heating device (2) arranged between the longitudinal flow induction heating device (10) and the transverse flow induction heating device (12) for further heating the strip, preferably supplied with natural gas, and Preferably, a radiant tube heating device (4) arranged downstream of the transverse flow induction heating device (12) for maintaining the temperature reached by the transverse flow induction heating device (12), preferably supplied with natural gas, and When provided, The smoke generated by the direct-fired heating device (2) is directly conveyed to the preheating zone (1) via a conduit (11), preferably preheating the strip at a temperature in the range of 50 to 200 °C, and the conduit (11) bypasses the longitudinal flow induction heating device (10), the method according to claim 13.

15. Between the at least one longitudinal flow induction heating device (10) and the at least one transverse flow induction heating device (12), the strip passes through a compensation zone (23) for equalizing the temperature of the strip, especially in the transverse direction, Downstream of the transverse flow induction heating device (12), the strip enters a maintenance zone (24) for maintaining the strip at the target temperature reached by the transverse flow induction heating device (12) until complete recrystallization of the strip material is obtained, the method according to claim 13.

16. Step b) is Heating the strip by a first transverse flow induction heating device (12) to a temperature higher than the Curie temperature of the strip material; The strip passing through a compensation zone (23) for equalizing the strip temperature, especially in the transverse direction; Further heating the strip to the target temperature by a second transverse flow induction heating device (12'); The strip passing through a maintenance zone (24) for maintaining the strip at the target temperature until complete recrystallization of the strip material is obtained. Including the method according to claim 13.

17. A part of the technical gas present in the cooling zone (6) is conveyed towards the preheating zone (27) by a conduit (28) connecting the at least one cooling zone (6) to the preheating zone (27), or or the heat transfer fluid conveyed by a conduit (30) crosses the preheating zone (27) for preheating the strip, or or, when a first preheating zone (32) and a second preheating zone (33) are provided upstream of the longitudinal flow induction heating device (10), a part of the technical gas present in the cooling zone (6) is conveyed towards the first preheating zone (32) by a first conduit (34) connecting the at least one cooling zone (6) to the first preheating zone (32), and the heat transfer fluid conveyed by a second conduit (35) crosses the second preheating zone (33) to further preheat the strip, the method according to claim 15 or 16. **Claim 18** A system for coating a metal strip (9) with a molten metal layer, comprising the annealing apparatus according to any one of claims 1 to 12.

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