Annealing device for metal strip coating system

Abstract

An annealing device for a metal strip (9) advancing in a longitudinal direction into a coating system for coating the metal strip with a layer of molten metal, the device comprising, in sequence:-at least one longitudinal flow inductive heating device (10); -at least one transverse flow inductive heating device (12); -at least one cooling zone.

Description

Technical Field

[0001] The invention relates to the field of systems for coating flat bodies made of ferromagnetic material, such as metal strips, in particular strips made of steel. More specifically, the invention relates to an annealing device and the associated process for heating and annealing a moving strip made of ferromagnetic material before coating it with molten metal, such as zinc. The invention also relates to a system for coating a metal strip with molten metal, comprising the annealing device. Background Art

[0002] It is known to coat strips made of ferromagnetic materials externally by various coating processes, for example by galvanizing.

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

[0004] Cold rolled pickled strip or hot rolled pickled strip is processed in a hot dip galvanizing system through a continuous heating and annealing unit. Depending on the product and quality of the input material and the expected quality of the output material, the heating cycle is determined by the maximum temperature of the material in the unit, the temperature holding time and the strip processing speed.

[0005] Depending on the construction, annealing devices, or more simply furnaces, can be divided into horizontal furnaces, vertical furnaces or mixed furnaces with horizontal and vertical extension.

[0006] The part of the plant dedicated to reheating usually consists of the following modules:

[0007] - Preheating module;

[0008] - Open flame heating module by burner;

[0009] - Radiant tube heating module by burners.

[0010] A known example of a system for coating metal strips is Figure 1 Such a system comprises an annealing device arranged upstream of a tank 8 containing a molten metal bath, the annealing device being provided with:

[0011] - Preheating zone 1;

[0012] - an open flame heating device 2, arranged immediately downstream of the preheating zone 1 and connected to the preheating zone 1, so that the flue gas generated by the open flame heating device 2 is directly used for preheating in the preheating zone 1;

[0013] - a radiant tube heating device 4, arranged immediately downstream of the open flame heating device 2;

[0014] - Cooling zone 6,

[0015] an area 7 provided with at least one tensioning roller which changes the direction of the path of advancement of the metal strip 9 coming out of the annealing device and applies tension to the strip, and a connecting duct 26 between the annealing device and the tank 8 .

[0016] The preheating zone 1 is provided with an extractor 3 for extracting the flue gas produced by the burner of the open flame heating device 2, while the radiant tube heating device 4 is provided with another extractor 5 for extracting the flue gas produced by the corresponding burner of the radiant tube heating device.

[0017] Some devices only include a heating section with radiant tubes. In this case, since the open-fire heating device lacks cleaning capabilities, a cleaning section must be provided upstream of the device.

[0018] The most commonly used technology uses gaseous fossil fuels, mainly natural gas. As a result, annealing units emit carbon dioxide into the atmosphere due to the combustion effect. The emphasis on reducing direct greenhouse gas emissions from the combustion process has prompted a rethinking of the technology used.

[0019] Heating by burners requires temperature ramps ranging from 10°C / s up to 100°C / s.

[0020] Furthermore, when the processing speed or the cross-section of the sheet to be processed changes, existing devices require a response time of tens of seconds to reach the new process parameter setting conditions.

[0021] This leads to increased uncertainty in maintaining the desired mechanical properties during the transient steps of the process, resulting in increased scatter and, therefore, higher costs due to wasted mass or increased energy consumption.

[0022] The heating rate and thermal inertia of burner-based systems also determine the metalworking process of the product, and the choices related to the analysis of the alloying elements present in the steel, for example, have a direct impact on production costs.

[0023] In view of the above, it is obvious that there is a need for innovative improvements to the heating and annealing devices of thermal coating production lines to eliminate the above-mentioned defects. Summary of the invention

[0024] One object of the present invention is to create a continuous annealing device for a metal strip that advances into a coating system that is able to reduce as much as possible or even virtually eliminate the direct emission of carbon dioxide into the environment.

[0025] Another object of the invention is to create an annealing device which allows a high degree of production flexibility and / or a significant increase in the hourly production capacity.

[0026] Another object of the present invention is to implement a relatively efficient annealing process with low environmental impact.

[0027] The present invention therefore aims to achieve the above-mentioned objects by means of an annealing device for a metal strip, the metal strip advancing in a longitudinal direction into a coating system for coating the metal strip with a layer of molten metal, the device comprising in sequence:

[0028] - at least one longitudinal flow induction heating device;

[0029] - at least one transverse flow induction heating device;

[0030] - at least one cooling zone;

[0031] Therein, at least one preheating zone is arranged upstream of the longitudinal flow induction heating device.

[0032] Another aspect of the present invention relates to a system for coating a metal strip with a layer of molten metal, the system comprising the aforementioned annealing apparatus.

[0033] Another aspect of the present invention relates to an annealing process for annealing a cold rolled metal strip, the cold rolled metal strip being advanced in a longitudinal direction into a coating system, the coating system being used to coat the metal strip with a layer of molten metal, the process being performed by the aforementioned apparatus and comprising the following steps:

[0034] a) heating the metal strip at a temperature below the Curie temperature of the metal strip material by at least one longitudinal flow induction heating device;

[0035] b) heating the metal strip at a temperature above the Curie temperature of the metal strip material by at least one transverse flow induction heating device;

[0036] c) cooling the metal strip by at least one cooling zone;

[0037] Therein, the metal strip is preheated in at least one preheating zone arranged upstream of the longitudinal flow induction heating device.

[0038] Other advantages of some embodiments of the present invention include:

[0039] High production flexibility, whether the annealing unit is configured horizontally or vertically;

[0040] - Significantly increase hourly production capacity, especially when using induction and gas burners in combination;

[0041] - The realization of a heating ramp (which is not possible with gas burners alone) allows the production of steels with the same mechanical characteristics, while simplifying the chemical composition and significantly reducing production costs;

[0042] The combined use of different types of inductors, or different types of inductors and burners, allows to eliminate the position difference between the center and the edge of the strip;

[0043] The combined use of an open flame and an induction allows to obtain a clean surface without adding a cleaning section upstream of the annealing device.

[0044] The dependent claims describe preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further features and advantages of the invention will become more apparent from the detailed description of a preferred but non-exclusive embodiment of the device shown by way of non-limiting example, with the aid of the accompanying drawings, in which:

[0046] Figure 1 shows a schematic diagram of a strip coating system with an annealing device according to the prior art;

[0047] Figure 2 A schematic diagram of a strip coating system with a first embodiment of an annealing device according to the present invention is shown;

[0048] Figure 3 Shows Figure 2 A schematic diagram of a first component of the annealing device;

[0049] Figure 4 Shows Figure 2 A schematic diagram of a second part of the annealing device;

[0050] Figure 5 A schematic diagram of a strip coating system according to a second embodiment of the present invention with an annealing device is shown;

[0051] Figure 5a Shows Figure 5 A first variation of the second embodiment;

[0052] Figure 5b Shows Figure 5 A second variation of the second embodiment;

[0053] Figure 5c Shows Figure 5 A third variation of the second embodiment;

[0054] Figure 6 A schematic diagram of a strip coating system with a third embodiment of an annealing device according to the present invention is shown;

[0055] Figure 6a Shows Figure 6 A first variation of the third embodiment;

[0056] Figure 6b Shows Figure 6 A second variation of the third embodiment;

[0057] Figure 6c Shows Figure 6 A third variation of the third embodiment.

[0058] The same reference numerals in the drawings represent the same elements or components. DETAILED DESCRIPTION

[0059] Reference Figures 2 to 6 , shows some exemplary embodiments of parts of a system for coating a metal strip 9 with a layer of molten metal, the system comprising an annealing device according to the invention. As is known, a metal strip is a product in which one dimension, namely thickness, is significantly smaller than the other two dimensions, namely length and width.

[0060] In all embodiments of the invention, the annealing device for the metal strip 9 (which is advanced into the coating system in the longitudinal direction) comprises, in sequence:

[0061] - at least one longitudinal flow induction heating device 10;

[0062] - at least one transverse flow induction heating device 12;

[0063] - and at least one cooling zone 6.

[0064] Advantageously, for ferromagnetic materials, longitudinal flow induction is applied below the Curie temperature. Above the Curie temperature, the material becomes non-magnetic, at which point transverse flow induction is preferably used.

[0065] Doing the opposite will result in a poor energy output, with very low energy delivered to the strip. In addition, applying a transverse flow to a ferromagnetic material will cause the strip to be attracted, risking contact with the induction coil.

[0066] Advantageously, at least one preheating zone 1, 27, 32, 33 is provided and arranged upstream of the longitudinal flow induction heating device for preheating the substrate, preferably by means of a heat transfer fluid by recovering heat from the same annealing device or from other production devices cooperating with the annealing device.

[0067] In some variants of the device, only one longitudinal flow induction heating device 10 and one transverse flow induction heating device 12 are provided.

[0068] Coating systems are, for example, hot-dip galvanizing lines for treating pickled steel strip or cold-rolled steel strip, such as:

[0069] - Strip made of low carbon steel, medium carbon steel or high carbon steel;

[0070] - strips made of microalloyed steel;

[0071] - Strips made of interstitial free high strength steel (IFHSS);

[0072] - Strip made of Advanced High Strength Steel (AHSS);

[0073] - Strip made of ferritic stainless steel.

[0074] Advantageously, a first embodiment of the device according to the invention comprises an induction heating system used in combination with a heating system, preferably provided with a burner, supplied with a combustible gas.

[0075] In this case, the strip is heated and annealed by combining the thermal energy applied by an induction system (using the Joule effect produced by eddy currents induced by a magnetic field) with the thermal energy produced by combustion.

[0076] The first embodiment of the device of the present invention comprises or consists of the following parts in sequence: Figure 2 ):

[0077] - a preheating zone 1, preferably a preheating tunnel;

[0078] - at least one longitudinal flow induction heating device 10;

[0079] - Open flame heating device 2;

[0080] - At least one transverse flow induction heating device 12, heating the strip to a target temperature or final annealing temperature.

[0081] The open flame heating device 2 is provided with a plurality of burners, preferably supplied with natural gas, whose flames directly contact the strip, making the strip temperature uniform, also in the transverse direction.

[0082] The ratio between air and combustible gas can be adjusted so as to have an excess of combustible gas (overstoichiometric combustion), producing reducing fumes containing carbon monoxide, which improves the surface cleanliness of the strip, eliminating oily residues, iron powder, and oxides.

[0083] Advantageously, the combined use of the longitudinal flow induction heating device 10 and the open flame heating device 2, and adjusting the power to the lowest level that can achieve a surface cleaning effect, can significantly reduce the direct emissions of carbon dioxide, for example, by -30% to -50% compared to the solutions of the prior art while maintaining the same production capacity.

[0084] Preferably, the radiant tube heating device 4 is arranged downstream of the at least one transverse flow induction heating device 12 for effectively completing the annealing cycle and also ensuring the temperature holding time so that the crystallization cycle of the strip material can be completed.

[0085] The radiant tube heating device 4 may also be provided with a burner, preferably supplied with natural gas.

[0086] The flue gases generated by the burners of the radiant tube heating device 4 are preferably conveyed via a dedicated extraction duct 5 to an exhaust chimney.

[0087] Advantageously, the combined use of longitudinal flow induction heating systems and transverse flow induction heating systems, and the reduction of the use of open flame heating devices and gas-supplied radiant tube heating devices, can significantly reduce direct carbon dioxide emissions, for example, by -60% to -80% compared to prior art solutions while maintaining the same production capacity.

[0088] Downstream of at least one transverse flow induction heating device 12 or downstream of the radiant tube heating device 4, if present, there is a cooling zone 6, followed by an area 7 in which at least one tensioning roller is arranged, which changes the direction of the forward path of the metal strip 9 coming out of the annealing device and applies tension to the strip, and a connecting duct 26 is arranged between the annealing device and the tank 8.

[0089] Preferably, a duct 11 is provided for conveying the flue gas generated by the open flame heating device 2 to the preheating zone 1, and the duct 11 bypasses the longitudinal flow induction heating device 10. In the preheating zone 1, the flue gas passes countercurrently with respect to the advancing direction of the strip.

[0090] Only when both the longitudinal flow induction heating device 10 and the open flame heating device 2 are in operation, the bypass conduit 11 starts to operate.

[0091] The flue gases generated by the burners of the open flame heating device 2 are preferably conveyed to the exhaust chimney through a dedicated extraction duct 3 arranged in the preheating zone 1 , which is preferably located at the far end of the preheating zone 1 away from the longitudinal flow induction heating device 10 .

[0092] Advantageously, this first embodiment allows:

[0093] - Modernization of existing installations without completely remodeling the annealing furnace, thus controlling the part that produces the largest CO2 emissions;

[0094] - Reduce capital expenditure and downtime for retrofitting units;

[0095] - Reduce energy consumption by recovering the heat of flue gases produced by open-fire heating devices;

[0096] - Clean the strip surface with an open flame.

[0097] Furthermore, constant power combustion and variable power inductors can be combined in transient conditions to improve product characteristics by taking advantage of the shorter response time of the inductor.

[0098] A second embodiment of the device of the invention advantageously comprises the sole use of the induction heating system, and therefore the sole use of the thermal energy applied by the induction system, instead of the thermal combustion energy.

[0099] In this case, the heating and annealing of the strip is carried out entirely by the Joule effect using eddy currents induced by the magnetic field. Advantageously, therefore, CO2 emissions can be completely eliminated.

[0100] The second embodiment of the device of the present invention comprises or consists of the following parts in sequence: Figure 5 ):

[0101] - at least one longitudinal flow induction heating device 10,

[0102] - a compensation zone 23 for making the temperature of the strip coming out of at least one longitudinal flow induction heating device 10 uniform both in the longitudinal direction and in the transverse direction;

[0103] - at least one transverse flow induction heating device 12, heating the strip to a target temperature or final annealing temperature;

[0104] - and a holding zone 24 for keeping the strip at the target temperature.

[0105] The compensation zone 23 may be passive, not providing thermal energy to the strip, or active, providing thermal energy to the strip.

[0106] In contrast, holding zone 24 is an active zone providing thermal energy to the strip which allows the final annealing temperature to be maintained for the dwell time required by the metalworking recipe.

[0107] Preferably, the holding zone 24 and the optional compensation zone 23 are each provided with an electric radiating element.

[0108] For example, these electric radiating elements may be resistive spark plugs or tubes.

[0109] Downstream of the holding zone 24, a cooling zone 6 is arranged, followed by an area 7 provided with at least one tensioning roller which changes the direction of the forward path of the metal strip 9 coming out of the annealing device and applies tension to the strip, and a connecting duct 26 is provided between the annealing device and the tank 8.

[0110] At least one cross-flow induction heating device 12, the holding zone 24 and the cooling zone 6 can be kept pressurized by a technical gas flow, which is preferably a single technical gas flow, such as nitrogen and / or hydrogen, to ensure oxidation prevention (e.g. with nitrogen) and cleaning / reduction (e.g. with hydrogen). After the technical gas is heated in the holding zone 24, it is used at a low temperature in the cooling zone.

[0111] The first variation of the second embodiment is as follows Figure 5a Advantageously, the preheating zone 27 is arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0112] The conduit 28 connects the cooling zone 6 to the preheating zone 27. The conduit 28 is used to convey part of the industrial gas (for example, at a temperature of 150°C-180°C) to the preheating zone 27 to preheat the strip entering at room temperature.

[0113] The second modification of the second embodiment is as follows Figure 5b Advantageously, the preheating zone 27 is arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0114] The conduit 30 passes through the preheating zone 27 to preheat the strip by means of a heat transfer fluid carried by the conduit 30 .

[0115] For example, a heat exchanger 29 is provided outside the preheating zone through which a conduit 30 passes in order to heat the heat transfer fluid in turn by recovering heat from other heat transfer fluids of any other production units carried by a discharge conduit 31. The discharge conduit 31 may also pass through the heat exchanger 29.

[0116] As a non-limiting example, the heat transfer fluid may be steam from a water exchanger in which it recovers heat from other heat transfer fluids, which may include, for example, flue gases from an arc furnace or a heating furnace, etc. In this case, the temperature of the strip may reach about 90°C from room temperature, and even about 200°C if the steam is pressurized.

[0117] The third variation of the second embodiment is as follows Figure 5c Advantageously, the two preheating zones 32 , 33 are arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0118] The conduit 34 connects the cooling zone 6 to the first preheating zone 32 for introducing a portion of the industrial gas (for example, at a temperature of 150° C.-180° C.) into the first preheating zone 32 to preheat the strip entering at room temperature.

[0119] Preferably, the conduit 34 passes through the first preheating zone 32 and returns to the cooling zone 6 .

[0120] For example, the industrial gas reaches the first preheating zone 32 with the spray cooler system at a temperature of 150-180°C and exchanges heat with the incoming strip by convection effect. The strip can be heated from room temperature to a temperature in the range of 100-120°C.

[0121] The second preheating zone 33 is arranged downstream of the first preheating zone 32 , preferably immediately downstream of the first preheating zone 32 .

[0122] The conduit 35 passes through the second preheating zone 33 , and the strip is further preheated by the heat transfer fluid carried by the conduit 35 .

[0123] For example, a heat exchanger 36 is provided outside the preheating zone through which the conduit 35 passes in order to heat the heat transfer fluid in turn by recovering heat from other heat transfer fluids of any other production units carried by the discharge conduit 37. The discharge conduit 37 may also pass through the heat exchanger 36.

[0124] As non-limiting examples, the heat transfer fluid may include molten salt or supercritical carbon dioxide, which is heated, preferably at a temperature greater than or equal to 600° C., by a heat exchanger or thermal energy storage (TES) 36 (i.e., a component responsible for storing excess thermal energy generated by the generator, even discontinuously, and being able to return it to the user when needed).

[0125] Alternatively, the heat transfer fluid may be of any type suitable for preheating the substrate, while molten salt or supercritical carbon dioxide is used in the thermal energy store 36 .

[0126] The thermoelectric generator is outside the annealing device, and includes, for example, an electric arc furnace (EAF), solar parabolas, and the like.

[0127] Other heat transfer fluids may include, for example, flue gases from an arc furnace or a heating furnace, or steam.

[0128] For example, a thermal energy storage or TES 36 may be provided between the external EAF-TES loop and the TES annealer loop.

[0129] In this second preheating zone 33 the strip may be heated from the temperature in the range 100-120° C. reached in the first preheating zone 32 to a temperature in the range 450-500° C., for example by radiation or convection.

[0130] use Figure 5a , Figure 5b ,and Figure 5cThe three variants in the present invention can save energy and reduce the size of the subsequent parts of the annealing system by facilitating the action of the subsequent parts of the annealing system.

[0131] The third embodiment of the device of the present invention uses an induction heating system as in the second embodiment, and the device comprises or consists of the following parts in sequence: Figure 6 ):

[0132] - at least one longitudinal flow induction heating device 10,

[0133] at least one first transverse flow induction heating device 12,

[0134] - a compensation zone 23 for homogenizing the temperature in the longitudinal and transverse directions,

[0135] - at least one second transverse flow induction heating device 12 ′ for heating the strip to a target temperature or final annealing temperature;

[0136] - and a holding zone 24 for keeping the strip at the target temperature.

[0137] The compensation zone 23 can be passive, not providing heat to the strip, or active, providing heat to the strip. The purpose of the compensation zone is to make the temperature uniform, especially in the transverse direction, since the at least one first transverse flow induction heating device 12 can generate overheating at the edges of the strip.

[0138] In contrast, holding zone 24 is an active zone that provides thermal energy to the strip to maintain the final annealing temperature for the dwell time required by the metalworking recipe to achieve the desired grain size.

[0139] Preferably, the holding zone 24 and possibly the compensation zone 23 are each provided with an electric radiating element.

[0140] For example, these electric radiating elements may be resistive spark plugs or tubes.

[0141] Downstream of the holding zone 24, a cooling zone 6 is arranged, followed by an area 7 provided with at least one tensioning roller which changes the direction of the forward path of the metal strip 9 coming out of the annealing device and applies tension to the strip, and a connecting duct 26 is provided between the annealing device and the tank 8.

[0142] At least one first transverse flow induction heating device 12, the compensation zone 23, at least one second transverse flow induction heating device 12', the holding zone 24, and the cooling zone 6 can be kept pressurized by an industrial gas flow, which is preferably a single industrial gas flow, such as nitrogen and / or hydrogen, to ensure (e.g. with nitrogen) oxidation prevention and (e.g. with hydrogen) cleaning / reduction. After the industrial gas is heated in the holding zone 24, it is used at a low temperature in the cooling zone.

[0143] The first modification of the third embodiment is as follows Figure 6a Advantageously, the preheating zone 27 is arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0144] The conduit 28 connects the cooling zone 6 to the preheating zone 27. The conduit 28 is used to introduce a portion of industrial gas (for example, at a temperature of 150°C-180°C) into the preheating zone 27 to preheat the strip entering at room temperature.

[0145] The second modification of the third embodiment is as follows Figure 6b Advantageously, the preheating zone 27 is arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0146] The conduit 30 passes through the preheating zone 27 to preheat the strip by means of a heat transfer fluid carried by the conduit 30 .

[0147] For example, a heat exchanger 29 is provided outside the preheating zone through which a conduit 30 passes in order to heat the heat transfer fluid in turn by recovering heat from other heat transfer fluids of any other production units carried by a discharge conduit 31. The discharge conduit 31 may also pass through the heat exchanger 29.

[0148] As a non-limiting example, the heat transfer fluid may be steam from a water exchanger in which it recovers heat from other heat transfer fluids, which may include, for example, flue gases from an arc furnace or a heating furnace, etc. In this case, the temperature of the strip may reach about 90°C from room temperature, and even about 200°C if the steam is pressurized.

[0149] The third modification of the third embodiment is as follows Figure 6c Advantageously, the two preheating zones 32 , 33 are arranged upstream of the at least one longitudinal flow induction heating device 10 .

[0150] The conduit 34 connects the cooling zone 6 to the first preheating zone 32. The conduit 28 is used to introduce part of the industrial gas (for example, at a temperature of 150°C-180°C) into the first preheating zone 32 to preheat the strip entering at room temperature.

[0151] Preferably, the conduit 34 passes through the first preheating zone 32 and returns to the cooling zone 6 .

[0152] For example, the industrial gas reaches the first preheating zone 32 with the spray cooler system at a temperature of 150-180°C and exchanges heat with the incoming strip by convection effect. The strip can be heated from room temperature to a temperature in the range of 100-120°C.

[0153] The second preheating zone 33 is arranged downstream of the first preheating zone 32 , preferably immediately downstream of the first preheating zone 32 .

[0154] The conduit 35 passes through the second preheating zone 33 , and the strip is further preheated by the heat transfer fluid carried by the conduit 35 .

[0155] For example, a heat exchanger 36 is provided outside the preheating zone through which the conduit 35 passes in order to heat the heat transfer fluid in turn by recovering heat from other heat transfer fluids of any other production units carried by the discharge conduit 37. The discharge conduit 37 may also pass through the heat exchanger 36.

[0156] As non-limiting examples, the heat transfer fluid may include molten salt or supercritical carbon dioxide, which is heated, preferably at a temperature greater than or equal to 600° C., by a heat exchanger or a thermal energy storage (TES) 36 (i.e., a component outside the annealing device responsible for storing excess thermal energy generated by the generator, even thermal energy generated discontinuously).

[0157] Alternatively, the heat transfer fluid may be of any type suitable for preheating the substrate, while molten salt or supercritical carbon dioxide is used in the thermal energy store 36 .

[0158] The thermoelectric generator is external to the annealing device, and the thermoelectric generator includes, for example, an electric arc furnace (EAF) or a solar parabola.

[0159] Other heat transfer fluids may include, for example, flue gases from an arc furnace or a heating furnace, or steam.

[0160] For example, a thermal energy storage or TES 36 may be provided between the external EAF-TES loop and the TES annealer loop.

[0161] In this second preheating zone 33 the strip may be heated from the temperature in the range 100-120° C. reached in the first preheating zone 32 to a temperature in the range 450-500° C., for example by radiation or convection.

[0162] use Figure 6a , Figure 6b ,and Figure 6c The three variants in the present invention can save energy and reduce the size of the subsequent parts of the annealing system by facilitating the action of the subsequent parts of the annealing system.

[0163] In the second and third embodiments of the invention, a cleaning zone, such as an alkaline cleaning zone, for cleaning the strip surface is provided upstream of at least one longitudinal flow induction heating device 10, possibly in the absence of one or more preheating zones, whereas in the first embodiment the cleaning is performed by an open flame heating device.

[0164] Advantageously, the combined use of a longitudinal flow induction system and a transverse flow induction system, together with the aforementioned compensation zone and holding zone, allows avoiding direct emission of carbon dioxide into the environment while maintaining production capacity.

[0165] In the second and third embodiments, the device can also be completely pressurized with industrial gases, such as nitrogen, hydrogen or mixtures thereof, to ensure protection against oxidation and cleaning / reduction effects.

[0166] In all embodiments of the annealing device of the invention, at least one longitudinal flow induction heating device 10 may comprise at least one induction coil 14, for example only one induction coil, which is transversely wound around the advancing plane of the strip, i.e. transversely wound around part of the advancing path of the strip.

[0167] Upstream and downstream of the at least one induction coil 14, a pair of guide rollers 13, preferably coated with a ceramic material, are provided respectively for guiding and supporting the strip.

[0168] Two pairs of guide rollers 13 isolate the longitudinal flow induction heating device 10 from other adjacent parts of the annealing device.

[0169] Preferably, the longitudinal flow induction heating apparatus 10 is pressurized using a nitrogen supply line 25 to prevent oxidation of the strip due to the temperature in the presence of oxygen.

[0170] Optionally, a plurality of temperature sensors 17 are provided for detecting the temperature of the strip entering and leaving the longitudinal flow induction heating device 10 .

[0171] Preferably, at least one induction coil 14 is connected to a capacitor bank 15 and a high-frequency converter 16 .

[0172] exist Figure 3 In the example, the longitudinal flow induction heating device 10 includes two induction heating modules, or is composed of two induction heating modules.

[0173] Each induction heating module comprises or consists of at least one induction coil 14, for example, only one induction coil is wound around the corresponding portion of the strip advancement path.

[0174] Each induction heating module is delimited by two pairs of guide rollers 13 , one pair upstream of the respective induction coil 14 and the other pair downstream.

[0175] The first temperature sensor 17 is arranged upstream of the first pair of rollers 13 , while the second temperature sensor 17 is arranged between the induction coil 14 and the second pair of rollers 13 .

[0176] The second temperature sensor 17 of the first induction heating module corresponds to the first temperature sensor 17 of the second induction heating module.

[0177] Therefore, in this example, three pairs of guide rollers 13 are provided, the middle pair of guide rollers is shared by two induction heating modules, and the two pairs of end guide rollers isolate the longitudinal flow induction heating device 10 from other adjacent parts of the annealing device.

[0178] Each induction coil 14 is connected to a respective capacitor bank 15 and a respective high-frequency converter 16 .

[0179] Alternatively, the transverse flow induction heating device 12, 12' comprises at least one pair of induction coils 18, 19, for example, only one pair of induction coils consisting of a first induction coil 18 arranged on a first side of the strip advancing plane and a second induction coil 19 arranged on a second side of the strip advancing plane opposite to the first side.

[0180] Preferably, the cross flow induction heating apparatus 12 is pressurized using nitrogen and oxygen supply lines to prevent oxidation of the strip due to high temperatures in the presence of oxygen.

[0181] The same nitrogen and hydrogen atmospheres may be used in any of the radiant tube heating devices 4 of the first embodiment.

[0182] Preferably, a position sensor 21, such as an optical sensor or an inductive sensor, is provided for detecting the position of the strip edge relative to the center line of the strip advancement path.

[0183] Optionally, the position of the induction coil relative to the strip edge may be controlled to better orient the magnetic field. For example, at least one movement 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 advancement direction.

[0184] Optionally, the first induction coil 18 and the second induction coil 19 remain fixed and, in order to better orient the magnetic field, at least one moving actuator 22 is adapted to move a screen made of copper or another 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.

[0185] For example, two movement actuators 22 are provided, each of which is configured to move a respective induction coil 18 or 19, or a respective shield (not shown), in a direction transverse to the longitudinal advancement path of the strip.

[0186] Adjusting the position of the induction coils 18, 19 or the position of the shield may be useful in situations where the strip temperature distribution is uneven, or where the strip is laterally offset relative to the centre line of the plane of advancement, or where the strip width varies.

[0187] Pairs of guide rollers 13 ′ may also be provided in the transverse flow induction heating device 12 , which guide rollers are 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 .

[0188] Preferably, temperature sensors 17 ′, 20 are provided for detecting the temperature of the strip entering and leaving the transverse flow induction heating device 12 .

[0189] The first induction coil 18 and the second induction coil 19 may be connected to respective capacitor banks 15 ′ and respective high frequency converters 16 ′, respectively.

[0190] Preferably, the two capacitor bank-converter assemblies are arranged on either side of the forward planar path, ie one assembly on each side.

[0191] exist Figure 4 In the example shown in FIG. 4 , the transverse flow induction heating device 12 includes or consists of a single induction heating module, which consists of only a pair of induction coils 18 , 19 .

[0192] The induction heating module is defined by two pairs of guide rollers 13', one upstream and the other downstream of the induction coils 18, 19. A first temperature sensor 17' is arranged upstream of the first pair of rollers 13', while a second temperature sensor 20 is arranged between the induction coils 18, 19 and the second pair of rollers 13'.

[0193] In various embodiments, all temperature sensors 17 , 17 ′, 20 may be pyrometers, such as scanning pyrometers for measuring the thermal profile of the strip.

[0194] In addition to the temperature sensor, one or more of the following sensors may be provided in different devices of the system of the present invention:

[0195] -Sensors for detecting atmosphere composition (O2, N2, H2, dew point, CO2, CO, etc.);

[0196] -Sensors for detecting the flow rate of combustion air, combustion flue gases, N2, H2 and their mixtures;

[0197] -Sensors to detect gas and electricity consumption.

[0198] Some examples of annealing processes performed using the above-described apparatus embodiments are described below.

[0199] In all embodiments of the apparatus of the invention, the process for annealing a pickled metal strip 9 or a cold rolled metal strip 9 advancing in the longitudinal direction into a coating system for coating the metal strip with a layer of molten metal comprises the following steps:

[0200] a) heating the metal strip by means of at least one longitudinal flow induction heating device 10 at a temperature below the Curie temperature of the metal strip material;

[0201] b) heating the metal strip by means of at least one transverse flow induction heating device 12, 12' at a temperature above the Curie temperature of the metal strip material;

[0202] c) Cooling the metal strip by means of at least one cooling zone 6 .

[0203] Advantageously, at least one preheating zone 1 , 27 , 32 , 33 for preheating the metal strip is arranged upstream of the longitudinal flow induction heating device 10 .

[0204] In step a) and step b), the heating gradient may vary within 50°C / s-500°C / s, preferably 100°C / s-500°C / s, even more preferably 110°C / s-450°C / s.

[0205] Preferably, at least one longitudinal flow induction heating device 10 is kept pressurized by a nitrogen flow supplied by nitrogen supply line 25; while at least one cross-flow induction heating device 12, 12' is kept pressurized by a mixed flow of nitrogen and hydrogen supplied by respective supply lines.

[0206] When using Figure 2 In the first embodiment of the heating and annealing device shown, the flue gas generated by the open flame heating device 2 is directly conveyed into the preheating tunnel 1 through the bypass duct 11 to preheat the pickled strip or the cold-rolled strip from room temperature to a temperature in the range of 50° C. to 200° C., preferably 100° C. to 200° C., even more preferably 150° C. to 200° C. Then, the flue gas is extracted from the preheating tunnel 1 through the extraction duct 3.

[0207] Downstream of the preheating tunnel 1 , preferably immediately downstream of the preheating tunnel 1 , the strip is heated by means of a longitudinal flow induction heating device 10 at a temperature below the Curie temperature of the strip material.

[0208] For example, a strip preferably made of low carbon steel or ferritic stainless steel is heated to a temperature in the range of 500-650°C, preferably 550-600°C, with a heating gradient of 50-500°C / s, preferably 100-500°C / s.

[0209] Downstream of the longitudinal flow induction heating device 10, preferably immediately downstream of the device 10, the strip is heated to a temperature in the range of 650°C-750°C, preferably 670°C-730°C, for example up to 700°C, by means of an open flame heating device 2, preferably supplied with natural gas, with a heating gradient of 30°C / s-100°C / s.

[0210] Downstream of the open flame heating device 2, preferably directly downstream of the device 2, the strip is heated by a cross-flow induction heating device 12 at a temperature above the Curie temperature of the strip material.

[0211] For example, the strip is heated to a temperature in the range of 740-950°C, preferably 750-950°C, even more preferably 800-900°C, with a heating gradient of 50-500°C / s, preferably 100-500°C / s.

[0212] Preferably, when the temperature of the strip coming out of the open flame heating device 2 is close to the Curie temperature, the transverse flow induction heating device 12 is activated.

[0213] Optionally, downstream of the transverse flow induction heating device 12, preferably immediately downstream of the device 12, by means of a radiant tube heating device 4, preferably supplied with natural gas, the strip is heated to maintain a temperature within the range of 750°C-950°C, preferably 780°C-920°C, so as to make the temperature uniform in the transverse direction of the strip and to complete the annealing of the strip to obtain the desired mechanical properties.

[0214] In a special variant of the process, the strip is heated by:

[0215] - by means of longitudinal flow induction heating device 10, in a temperature range of 550°C-600°C,

[0216] - by means of open flame heating device 2, in the temperature range of 670°C-730°C,

[0217] - by means of a transverse flow induction heating device 12, in a temperature range of 750°C to 950°C,

[0218] - Preferably, the temperature is maintained in the range of 780°C - 920°C by means of the radiant tube heating device 4 .

[0219] The cross-flow induction heating device 12 is kept pressurized by a flow of a mixture of nitrogen and hydrogen, which is preferably the same mixture as that which prevents oxidation in the region of the radiant tube heating device 4 .

[0220] Downstream of the cross-flow induction heating device 12, or downstream of the radiant tube heating device 4, if present, the strip is cooled in a cooling zone 6 to a suitable temperature for immersion in a tank 8 containing a molten metal bath for coating the strip.

[0221] When using Figure 5 , Figure 5a , Figure 5b and Figure 5cIn the second embodiment of the heating and annealing device shown, the pickled strip or the cold-rolled strip is heated from room temperature to a temperature below the Curie temperature of the strip material by means of a longitudinal flow induction heating device 10 .

[0222] For example, a strip preferably made of low carbon steel or ferritic stainless steel is heated to a temperature in the range of 680-740°C, preferably 700-730°C, with a heating gradient of 50-500°C / s, preferably 80-400°C / s.

[0223] Downstream of the longitudinal flow induction heating device 10, preferably immediately downstream of the device 10, the strip passes through a compensation zone 23 in order to make its temperature uniform, in particular in the transverse direction, for example to about 700-730°C.

[0224] Downstream of the compensation zone 23 , preferably immediately downstream of the compensation zone 23 , the strip is heated by means of a transverse flow induction heating device 12 at a temperature above the Curie temperature of the strip material.

[0225] For example, the strip is heated to a target temperature or final annealing temperature, preferably in the temperature range of 750-950°C, preferably 850-950°C, optionally with a heating gradient of 50-500°C / s, preferably 80-400°C / s.

[0226] Preferably, when the temperature of the strip coming out of the longitudinal flow induction heating device 10 is close to the Curie temperature, the transverse flow induction heating device 12 is activated.

[0227] Downstream of the transverse flow induction heating device 12, preferably immediately downstream of this device 12, the strip passes through a holding zone 24 to keep the strip at the target temperature, preferably for a period of 5 to 60 seconds, and to allow the material to fully recrystallize to a grain size desired for the quality of steel to be produced.

[0228] Downstream of the holding zone 24, preferably immediately downstream of the holding zone 24, the strip is cooled in a cooling zone 6 to a suitable temperature, for example in the range of 420-480°C, for immersion in a tank 8 containing a molten metal bath for coating the strip.

[0229] In a special variant of the process, the strip:

[0230] - heating to a temperature in the range of 700°C to 730°C by means of a longitudinal flow induction heating device 10,

[0231] - passing through a compensation zone 23 in order to make the strip temperature uniform, especially in the transverse direction,

[0232] - heating to a target temperature in the range of 850° C. to 950° C. by means of a transverse flow induction heating device 12,

[0233] - Passing through a holding zone 24 to keep the strip at the target temperature.

[0234] When using the second embodiment Figure 5a In the variation, relative to Figure 5 The difference of the process shown in the schematic diagram in is indicated by the fact that the pickled strip or the cold-rolled strip is preheated, for example from room temperature to a temperature within the range of 70° C. to 90° C., by means of a preheating zone 27. In particular, part of the industrial gas present in the cooling zone 6 is conveyed to the preheating zone 27 via a conduit 28 connecting the cooling zone 6 and the preheating zone 27.

[0235] Similarly, when using the second embodiment Figure 5b In the variation, relative to Figure 5 The difference of the process shown in the schematic diagram in FIG. 1 is indicated by the fact that the pickled strip or the cold-rolled strip is preheated, for example from room temperature to a temperature within the range of 70° C. to 90° C., by means of the preheating zone 27. In particular, a heat transfer fluid carried by a conduit 30 passes through the preheating zone 27 for preheating the strip. In the case of using steam or other pressurized heat transfer fluids, the strip can also reach a temperature of about 180° C. to 220° C. in the preheating zone 27.

[0236] exist Figure 5a-Figure 5b In both variants, downstream of the preheating zone 27, the strip directly enters the longitudinal flow induction heating device 10, in which the strip is heated from a temperature of 70°C-90°C or 180°C-220°C to a temperature below the Curie temperature of the strip material, for example a temperature in the range of 680°C-740°C, preferably 700°C-730°C.

[0237] When using the second embodiment Figure 5c In the variation, relative to Figure 5 The difference in the process shown in the schematic diagram in is indicated by the fact that the pickled strip or the cold-rolled strip is preheated from room temperature to a temperature in the range of 100° C.-120° C. by the first preheating zone 32, and is heated to a temperature in the range of 450° C.-500° C. by the next second preheating zone 33. Specifically, part of the industrial gas present in the cooling zone 6 is conveyed to the first preheating zone 32 through a first conduit 34 connecting the cooling zone 6 and the first preheating zone 32; and a heat transfer fluid carried by a second conduit 35 passes through the second preheating zone 33 to further preheat the strip.

[0238] Downstream of the second preheating zone 33, the strip directly enters the longitudinal flow induction heating device 10, where the strip is heated from a temperature of 450°C to 500°C to a temperature below the Curie temperature of the strip material, for example a temperature in the range of 680°C to 740°C, preferably 700°C to 730°C.

[0239] When using Figure 6 , Figure 6a , Figure 6b and Figure 6c In the third embodiment of the heating and annealing device shown, the pickled strip or the cold-rolled strip is heated from room temperature to a temperature below the Curie temperature of the strip material by means of a longitudinal flow induction heating device 10 .

[0240] For example, a strip preferably made of low carbon steel or ferritic stainless steel is heated to a temperature in the range of 680-740°C, preferably 700-730°C, with a heating gradient of 50-500°C / s, preferably 80-400°C / s.

[0241] Downstream of the longitudinal flow induction heating device 10 , preferably immediately downstream of this device 10 , the strip is heated by a first transverse flow induction heating device 12 to a temperature above the Curie temperature of the strip material.

[0242] For example, the strip is heated to a temperature in the range of 750-850°C, preferably 750-800°C, optionally with a heating gradient of 50-500°C / s, preferably 80-400°C / s.

[0243] Preferably, when the temperature of the strip coming out of the longitudinal flow induction heating device 10 is close to the Curie temperature, the first transverse flow induction heating device 12 is activated.

[0244] Downstream of the first transverse flow induction heating device 12, preferably immediately downstream of this device 12, the strip passes through a compensation zone 23 in order to make its temperature uniform, in particular in the transverse direction, for example to about 700-780°C.

[0245] Downstream of the compensation zone 23, preferably immediately downstream of the compensation zone 23, the strip is heated by a second transverse flow induction heating device 12' to a target or final annealing temperature, preferably a temperature in the range of 800-950°C, preferably 810-900°C.

[0246] Downstream of the second transverse flow induction heating device 12', preferably immediately downstream of this device 12', the strip passes through a holding zone 24, which holds the strip at the target temperature, preferably for 5 to 60 seconds, and allows the material to fully recrystallize to the grain size desired for the quality of steel to be produced.

[0247] Downstream of the holding zone 24, preferably immediately downstream of the holding zone 24, the strip is cooled in a cooling zone 6 to a suitable temperature, for example in the range of 420-480°C, for immersion in a tank 8 containing a molten metal bath for coating the strip.

[0248] In a special variant of the process, the strip:

[0249] - heating to a temperature in the range of 700°C to 730°C by means of a longitudinal flow induction heating device 10,

[0250] - heating to a target temperature in the range of 750° C. to 800° C. by means of a first transverse flow induction heating device 12,

[0251] - passing through a compensation zone 23 in order to make the strip temperature uniform, especially in the transverse direction,

[0252] - heating to a target temperature in the range of 810° C. to 900° C. by a second transverse flow induction heating device 12 ′,

[0253] - Passing through a holding zone 24 to keep the strip at the target temperature.

[0254] When using the third embodiment Figure 6a In the variation, relative to Figure 6 The difference in the process shown in the schematic diagram in is indicated by the fact that the pickled strip or the cold-rolled strip is preheated from room temperature to a temperature, for example, in the range of 70° C. to 90° C. by means of a preheating zone 27. In particular, part of the industrial gas present in the cooling zone 6 is conveyed to the preheating zone 27 via a conduit 28 connecting the cooling zone 6 and the preheating zone 27.

[0255] Similarly, when using the third embodiment Figure 6b In the variation, relative to Figure 6 The difference in the process shown in the schematic diagram in is indicated by the fact that the pickled or cold rolled strip is preheated from room temperature to a temperature, for example, within 70° C.-90° C. by means of a preheating zone 27. Specifically, a heat transfer fluid carried by a conduit 30 passes through the preheating zone 27 for preheating the strip.

[0256] The strip may also reach a temperature of about 180° C. to 220° C. in the preheating zone 27 using steam or other pressurized heat transfer fluid.

[0257] exist Figure 6a-Figure 6b In both variants, downstream of the preheating zone 27, the strip directly enters the longitudinal flow induction heating device 10, in which the strip is heated from a temperature of 70°C-90°C or 180°C-220°C to a temperature below the Curie temperature of the strip material, for example a temperature in the range of 680°C-740°C, preferably 700°C-730°C.

[0258] When using the third embodiment Figure 6c In the variation, relative to Figure 6 The difference in the process shown in the schematic diagram in is indicated by the fact that the pickled strip or the cold-rolled strip is preheated from room temperature to a temperature in the range of 100° C.-120° C. by the first preheating zone 32, and is heated to a temperature in the range of 450° C.-500° C. by the next second preheating zone 33. Specifically, part of the industrial gas present in the cooling zone 6 is conveyed to the first preheating zone 32 through a first conduit 34 connecting the cooling zone 6 and the first preheating zone 32; and a heat transfer fluid carried by a second conduit 35 passes through the second preheating zone 33 to further preheat the strip.

[0259] Downstream of the second preheating zone 33, the strip directly enters the longitudinal flow induction heating device 10, in which the strip is heated from a temperature of 450°C-500°C to a temperature below the Curie temperature of the strip material, for example a temperature in the range of 680°C-740°C, preferably 700°C-730°C.

[0260] In the second and third embodiments, surface cleaning of the strip is provided upstream of the at least one longitudinal flow induction heating device 10, for example by means of an alkaline cleaning section, possibly in the absence of one or more preheating zones.

[0261] Furthermore, the annealing unit can be fully pressurized with industrial gases, such as nitrogen, hydrogen or mixtures thereof, to ensure protection against oxidation and cleaning / reducing effects.

Claims

1. An annealing device for a metal strip (9), the metal strip (9) advancing in a longitudinal direction into a coating system, the coating system being used to coat the metal strip with a layer of molten metal, the annealing device comprising in sequence: - at least one longitudinal flow induction heating device (10); - at least one transverse flow induction heating device (12); - at least one cooling zone (6); Wherein, at least one preheating zone (1, 27, 32, 33) is arranged upstream of the longitudinal flow induction heating device (10).

2. The device according to claim 1, wherein: Only one longitudinal flow induction heating device (10) and one transverse flow induction heating device (12) are provided.

3. The device according to claim 1 or 2, wherein: Set up - an open flame heating device (2) arranged between the longitudinal flow induction heating device (10) and the transverse flow induction heating device (12); - Preferably, a radiant tube heating device (4) is arranged downstream of said cross-flow induction heating device (12).

4. The device according to claim 3, wherein: A duct (11) is provided for conveying the flue gas generated by the open flame heating device (2) to the preheating zone (1), and the duct (11) bypasses the longitudinal flow induction heating device (10).

5. The device according to claim 1 or 2, wherein: Set up - a holding zone (24), arranged downstream of the cross-flow induction heating device (12), for maintaining a predetermined temperature; - and a compensation zone (23), which is arranged between the longitudinal flow induction heating device (10) and the transverse flow induction heating device (12) and is used to make the temperature of the strip coming out of the longitudinal flow induction heating device (10) uniform.

6. The device according to claim 1, wherein: Set up - a first transverse flow induction heating device (12) arranged downstream of the longitudinal flow induction heating device (10); - a compensation zone (23), arranged downstream of the first transverse flow induction heating device (12), for making the strip temperature uniform; - a second transverse flow induction heating device (12') arranged downstream of said compensation zone (23); A holding zone (24) arranged downstream of said second cross-flow induction heating device (12').

7. The device according to claim 5 or 6, wherein: The holding area (24) is provided with a first electric radiating element; wherein the compensation area (23) is preferably provided with a second electric radiating element; preferably, wherein the electric radiating element is a resistance spark plug or a tube.

8. The device according to claim 5 or 6, wherein: a conduit (28) connecting the at least one cooling zone (6) and the preheating zone (27) for conveying part of the industrial gas present in the cooling zone (6) to the preheating zone (27), or wherein the conduit (30) is adapted to convey a heat transfer fluid through the preheating zone (27) for preheating the wood.

9. The device according to claim 5 or 6, wherein: The first preheating zone (32) and the second preheating zone (33) are arranged upstream of the longitudinal flow induction heating device (10); preferably, a first conduit (34) connecting the at least one cooling zone (6) and the first preheating zone (32) is used to transport part of the industrial gas present in the cooling zone (6) toward the first preheating zone (32), and wherein the second conduit (35) is adapted to transport a heat transfer fluid through the second preheating zone (33) to further preheat the wood material.

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

11. The device according to any one of the preceding claims, wherein: The transverse flow induction heating device (12) comprises at least one pair of induction coils (18, 19), the at least one pair of induction coils (18, 19) consisting of a first induction coil (18) arranged on a first side of a strip advancing plane and a second induction coil (19) arranged on a second side of the strip advancing plane opposite to the first side; preferably, at least one moving actuator (22) is provided therein 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, wherein the first induction coil (18) and the second induction coil (19) are fixed, and at least one moving actuator (22) is provided therein for moving a plurality of movable shields, the plurality of movable shields being preferably arranged above the first induction coil (18) and below the second induction coil (19), respectively; preferably, a position sensor (21) is provided therein for detecting the position of the strip edge relative to the center line of the strip advancing plane.

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

13. A process for annealing a pickled metal strip (9) or a cold rolled metal strip (9) which is advanced in a longitudinal direction into a coating system for coating the metal strip with a layer of molten metal, the process being performed by a device according to any one of the preceding claims and comprising the steps of: a) heating the metal strip at a temperature below the Curie temperature of the metal strip material by means of the at least one longitudinal flow induction heating device (10); b) heating the metal strip at a temperature above the Curie temperature of the metal strip material by means of the at least one transverse flow induction heating device (12); c) cooling the metal strip by passing through the at least one cooling zone; The metal strip is preheated in at least one preheating zone (1, 27, 32, 33) arranged upstream of the longitudinal flow induction heating device (10).

14. The method according to claim 13, wherein: When setting - an open flame heating device (2), arranged between the longitudinal flow induction heating device (10) and the transverse flow induction heating device (12), preferably supplied with natural gas, for further heating the strip; - preferably, a radiant tube heating device (4), preferably supplied with natural gas, is arranged downstream of said cross-flow induction heating device (12) for maintaining the temperature achieved in said cross-flow induction heating device (12); The flue gas generated by the open flame heating device (2) is directly conveyed to the preheating zone (1) through a duct (11) to preheat the wood, preferably to a temperature in the range of 50°C-200°C, and the duct (11) bypasses the longitudinal flow induction heating device (10).

15. The method according to claim 13, wherein: 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) in order to make the strip temperature uniform, in particular in the transverse direction; And wherein, downstream of the transverse flow induction heating device (12), the strip enters a holding zone (24) for holding the strip at the target temperature reached by the transverse flow induction heating device (12) until the strip is completely recrystallized.

16. The method according to claim 13, wherein: Step b) comprises: - heating the strip to a temperature above the Curie temperature of the strip by means of a first transverse flow induction heating device (12); - homogenizing the temperature of the strip, in particular in the transverse direction, by passing the strip through a compensation zone (23); - further heating the strip to a target temperature by a second transverse flow induction heating device (12'); - The strip is held at the target temperature by passing the strip through a holding zone (24) until the strip is fully recrystallized.

17. The method according to claim 15 or 16, wherein: part of the industrial gas present in the cooling zone (6) is conveyed to the preheating zone (27) via a conduit (28) connecting the at least one cooling zone (6) and the preheating zone (27); or wherein a heat transfer fluid carried by the conduit (30) passes through a preheating zone (27) to preheat the material; Alternatively, when the first preheating zone (32) and the second preheating zone (33) are arranged upstream of the longitudinal flow induction heating device (10), part of the industrial gas present in the cooling zone (6) is transported toward the first preheating zone (32) through a first conduit (34) connecting the at least one cooling zone (6) and the first preheating zone (32); and the heat transfer fluid transported by the second conduit (35) passes through the second preheating zone (33) to further preheat the wood material.

18. A system for coating a metal strip (9) with a layer of molten metal, comprising an annealing device according to any one of claims 1 to 12.

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