Steel strip cooling methods and wet cooling galvanizing production lines

Abstract

The present invention relates to a method for cooling a steel strip (1) traveling in a continuous galvanizing production line (100), wherein the method includes the steps of checking the desired conditions defined by the temperature of the strip at the outlet of a wet chamber (4) relative to the Leiden Frost temperature, selecting the travel time of the strip through the wet chamber and the cumulative travel time of the strip through a drying chamber (7) and a downstream chamber under a drying and reducing atmosphere, wherein the liquid in the cooling device (5) may be an aqueous coolant with a formic acid mass concentration of 0.1% or higher, and the temperature of the strip at the outlet of the drying chamber may be 250°C or lower, and wherein the method may further include the step of adjusting the operating parameters of the production line to meet the desired conditions.

Description

Technical Field

[0001] This invention relates to a continuous galvanizing production line for metal strips, and more particularly to a galvanizing production line equipped with a wet cooling section.

[0002] Technical problem solved by the present invention

[0003] As is well known, wet cooling is performed on galvanizing production lines to produce third-generation steel, which requires a quenching rate of over 150°C / s after annealing to achieve the required metallurgical structure and mechanical properties.

[0004] For example, the applicant's patent FR3064279 describes a cooling section that uses an aqueous solution containing formic acid, enabling in-line galvanizing of these steels after quenching without the need for a pickling step before plating.

[0005] This solution was developed for third-generation steel for the following reasons:

[0006] • They are extremely sensitive to oxidation;

[0007] They need to be cooled very quickly;

[0008] • In some cases, it is necessary to achieve a cooling endpoint temperature below 200°C.

[0009] This may not apply to conventional steels (first and second generation) because these steels have different properties:

[0010] • They require a lower cooling rate;

[0011] • They are produced at cooling endpoint temperatures higher than those of third-generation steel (typically, the target is the temperature of the zinc bath), and therefore the oxidation conditions are different;

[0012] • Although they are not very sensitive to surface oxidation (because they contain less alloying elements), they still require careful atmosphere control to prevent any oxidation.

[0013] These differences necessitate adjustments to operating conditions to produce conventional steel on the same production line as third-generation steel, particularly in terms of cooling conditions, atmosphere management, and acid usage.

[0014] Finally, the presence of acid in the cooling solution may cause appearance defects, regardless of the type of steel involved.

[0015] Therefore, it is crucial to properly control and adjust atmosphere management according to cooling conditions.

[0016] Demand for third-generation steel remains low, making it impossible to utilize 100% capacity of production lines configured for galvanizing these steels. Therefore, it is essential to be able to produce all types of steel on production lines with rapid wet cooling to limit operating costs and avoid adversely impacting the plant's profitability.

[0017] The purpose of this invention is to enable third-generation steel and conventional steel to be galvanized without defects (uniform surface appearance, zinc coating, and no exposed spots) on the same production line, thereby achieving full-time operation of the production line. Therefore, steel manufacturers can recoup their investment more quickly, and the production cost of third-generation steel is significantly reduced. Background Technology

[0018] Wet cooling technology can achieve high cooling rates of up to 2000°C / s / mm. These technologies are primarily used on continuous annealing production lines. The strip must then pass through the pickling section before it can be plated on the galvanizing production line.

[0019] The most common cooling technique is water quenching via immersion in a tank. The principle involves passing the steel strip through a tank filled with water. This tank may include auxiliary equipment, such as additional water jet devices, whether or not the strip is submerged. The jet can be generated by nozzles, slits, or perforated plates.

[0020] For example, patent WO2020203261 describes a solution that uses an immersion turbulent jet device and a sliding plate to control the initiation of cooling, and uses an immersion-compatible stabilizing roller. Patent WO2021024096 describes a solution that uses an inclined immersion jet device to avoid non-planar free surfaces at the bath inlet, thereby improving control over homogeneity.

[0021] Spray quenching can also be used, but this will result in a significant reduction in the cooling rate. In this case, water mist is sprayed onto the strip.

[0022] Coolant or a gas / liquid mixture can also be sprayed onto the strip using single-fluid or dual-fluid nozzles. Spraying is performed under pressure, thus achieving cooling rates comparable to or even higher than immersion water quenching. Single-fluid or dual-fluid spraying offers greater control flexibility with its wide operating pressure range (typically between 1 bar and 12 bar).

[0023] Patent JP2019210549 describes a combination of two technologies: first, slow cooling via a spray bar, followed by rapid cooling via immersion water quenching.

[0024] Hot-dip galvanizing of steel strip was invented in the 1930s. Since its discovery, cooling equipment has developed significantly, but water has not been used because water cooling would cause excessive oxidation of the steel surface, thus hindering the wettability of zinc.

[0025] The applicant's patent FR3064279 describes a method for cooling third-generation steel strip in a wet cooling chamber of a galvanizing production line using an aqueous solution containing 0.5% to 6%, preferably 0.5% to 2% formic acid. By spraying the acidic solution onto the strip, a surface finish suitable for hot-dip galvanizing of these steel grades can be obtained through a combination of mechanical and chemical pickling effects associated with the spraying.

[0026] Therefore, the developments made by the applicant make it possible to implement wet cooling on galvanizing production lines, as these developments eliminate the pickling step.

[0027] In wet cooling, there are three different modes depending on the surface temperature of the strip, especially the so-called Leidenfrost temperature (i.e., the temperature that separates the stable vapor film cooling range from the unstable transition range). Depending on the cooling system used, the Leidenfrost temperature is typically between 250°C and 630°C.

[0028] The table below provides examples of Leidenfrost temperatures under different cooling conditions:

[0029]

[0030] The "System" column shows the data in the table corresponding to different spray systems; the "Nozzle Type" column specifies the type of nozzles used; the "X" column represents the distance between two nozzles across the strip width; the "Y" column represents the distance between two nozzles along the strip length; the "Z" column represents the distance from the nozzle to the strip; the "Water Temperature" column represents the temperature of the water spray; and the "G" column represents the distance per meter. 2 The flow rate of water sprayed onto the strip; and the "Leyton Frost temperature" column indicates the Leiden Frost temperature observed under these conditions.

[0031] At temperatures above the Leidenfrost temperature, the mode is film boiling. A vapor pad, tens of μm thick, separates the tape from the liquid water. The tape surface is unwetted. Since the thermal conductivity of vapor is approximately 1 / 27 that of liquid water, the wall is relatively thermally insulated from the water. The heat transfer coefficient is stable and low. Rapid cooling is difficult during this stage.

[0032] From the Leiden Frost temperature down to approximately 200°C, there exists a transitional range where the heat flux rapidly changes from a minimum to a maximum. The vapor layer tends to disappear, and liquid water begins to reach the strip surface at a few points before reaching its entire surface. During this phase, the cooling pattern is unstable, and large fluctuations in the heat transfer coefficient are observed. Cooling accelerates rapidly. Heat exchange becomes more intense; water vaporizes immediately upon contact with the wall.

[0033] At lower temperatures (typically below 150°C), nuclear boiling occurs. Initially, numerous continuous columns of vapor are observed in the liquid; then the bubbles begin to isolate, and the entire surface comes into contact with the liquid water. Cooling is quite rapid at the beginning of this stage, but it slows down as the surface temperature becomes too low.

[0034] The applicant’s patent WO2021116594 is an improvement on a previous patent, wherein the water-cooled zone is divided into two parts: the first part in which the strip is kept above the Leiden Frost temperature by water cooling (or water + air cooling); followed by the second part in which water + formic acid cooling is used.

[0035] Before reaching the Leidenfrost temperature, the vapor pad separates the strip from the liquid water, and the strip surface remains unwetted. Therefore, oxidation of the strip is limited during the first part of the cooling process.

[0036] This solution can reduce acid consumption and limit the amount of residues produced by acid decomposition, which are present on the strip surface at the outlet of the wet cooling chamber.

[0037] The applicant's patent WO2018172714 describes a dry cooling section and a wet cooling section arranged sequentially on a vertical pipe section. It specifically includes a three-roll lock between the two sections, which has an inert gas extraction zone and an inert gas injection zone, and a wet zone is dried by blowing nitrogen into the wet zone through heated walls and multiple injection points.

[0038] The aforementioned solutions are used for galvanizing third-generation steel, but they are not suitable for galvanizing conventional steel, especially because the surface of the strip will oxidize due to the humid atmosphere in the dehydration section and drying chamber after liquid cooling. Summary of the Invention

[0039] According to a first aspect of the invention, a method for cooling a steel strip traveling in a continuous galvanizing production line is provided, wherein:

[0040] • The steel strip passes through the upstream chamber and upstream atmosphere separation lock under a dry reducing atmosphere, and is subsequently cooled in a wet chamber containing a liquid cooling device.

[0041] • The method further includes passing a steel strip cooled in a wet chamber through a dry chamber, a downstream atmosphere separation lock, and at least one downstream chamber under a dry reducing atmosphere:

[0042] • A drying atmosphere is injected into the wet chamber and the dry chamber via an injection system.

[0043] • An extraction system draws in the atmosphere to continuously refresh the atmosphere in the wet chamber and create an atmosphere flow from the dry chamber to the wet chamber.

[0044] • Controlled via a control and command system:

[0045] • The travel time of the steel belt through the wet chamber,

[0046] • The cumulative travel time of the steel strip in the drying chamber and in at least one downstream chamber under a drying and reducing atmosphere.

[0047] • The temperature (Th) of the steel strip at the outlet of the wet chamber, and

[0048] • Temperature of the steel strip at the outlet of the drying chamber (Ts).

[0049] This method includes steps to verify the required conditions defined below:

[0050] • When the temperature (Th) of the steel strip at the outlet of the wet chamber is greater than or equal to the Leiden Frost temperature, the travel time of the steel strip through the wet chamber must be less than or equal to fifteen seconds, and the cumulative travel time through the dry chamber and through at least one downstream chamber under a dry reducing atmosphere must be greater than or equal to the residence time of the steel strip in the wet chamber.

[0051] • When the temperature (Th) of the steel strip at the outlet of the wet chamber is less than the Leiden Frost temperature, the liquid in the cooling device must be an aqueous coolant with a formic acid mass concentration of 0.1% or higher, and the temperature (Ts) of the steel strip at the outlet of the dry chamber must be 250°C or lower.

[0052] • When the temperature (Th) of the cooled steel strip at the outlet of the wet chamber is less than 110°C, at least a portion of the excess liquid carried by the cooled steel strip in the wet chamber is removed in the dehydration section, and the dehydrated steel strip is dried in the drying chamber.

[0053] If one of the required conditions is not met during the verification step, the method further includes adjusting at least one operating parameter of the production line so that the required conditions can be met during the verification step.

[0054] Adjustable operating parameters include, for example, strip travel speed, coolant flow rate, or coolant properties.

[0055] After adjusting the production line's operating parameters, repeat the verification process to ensure all required conditions are met. If this is still not the case, repeat the adjustment process for at least one operating parameter of the production line until the required conditions are met in the verification step.

[0056] Taking into account the inertia of the production line, new verification steps are only executed after a sufficiently long delay to ensure that the adjustments to the production line's operating parameters have taken effect.

[0057] The steps to verify the required conditions and to adjust at least one operating parameter of the production line are executed automatically by the production line's control and command system.

[0058] The system includes tables that allow selection of one or more operating parameters of the production line and the setpoints to be applied, especially based on the operating conditions of the production line and the composition of the strip.

[0059] When the strip leaves the wet chamber at a temperature greater than or equal to the Leiden Frost temperature, the coolant can be water, without the addition of acid. This avoids the presence of residues from acid decomposition on the strip, which are known to cause appearance defects such as coffee stains or streaks. Eliminating acid also reduces operating costs on the production line.

[0060] By limiting the residence time of the strip in the wet chamber to a maximum of 15 seconds, oxides are prevented from forming on the strip surface for conventional steel, or, in the case of third-generation steel, excessive oxides are prevented if any are present. For the latter, pre-oxidation (selective or complete oxidation) must be performed during the heating phase prior to rapid cooling.

[0061] Maintaining at least equal cumulative residence times for the strip in the drying chamber before plating and in the downstream chamber under a reducing atmosphere promotes the reduction of any oxides (primarily iron oxide) that may be present on the strip surface at the wet chamber exit. Therefore, when the strip is immersed in the plating bath, its surface no longer contains oxides, or if any remain, only in small amounts. These oxides do not adversely affect the coating quality.

[0062] If the atmosphere in the downstream chamber consists of a mixture of nitrogen and hydrogen, with hydrogen comprising at least 1% by volume and a dew point below -5°C, then the downstream chamber has a dry reducing atmosphere to prevent iron from being oxidized.

[0063] In the following text, HNx will represent a dry reducing atmosphere consisting of a mixture of nitrogen and hydrogen.

[0064] When the strip leaves the wet chamber at a temperature between 110°C (including the end value) and the Leiden Frost temperature (excluding the end value), partial contact has already occurred between the liquid and the strip, and this contact gradually increases as the cooling endpoint temperature decreases.

[0065] An acidic aqueous solution must be used to ensure that the amount of oxides present on the strip surface at the outlet of the wet chamber is not too high.

[0066] However, the solution can be used at a lower concentration, for example, a formic acid concentration of 0.2%.

[0067] Based on the chemical composition of steel and its manganese and silicon content, it can be determined from [ Figure 7 The formic acid concentration is determined in the diagram. The selected value is the higher of the value obtained from the manganese concentration and the value obtained from the silicon concentration. For example, for steel containing 3% manganese and 2% silicon, the acid concentration would be 0.5%.

[0068] As can be seen from the diagram, the required formic acid concentration remains low.

[0069] Within this acid concentration range, the pH changes only slightly. For example, the pH is 3.14 when the acid concentration is 0.3%, and 2.72 when the concentration is 2%.

[0070] When the strip exits the wet chamber at a temperature below 110°C, the liquid and strip have already reached complete contact during wet cooling. Therefore, an acidic aqueous solution must be used to prevent the formation of excessive oxides on the strip surface at the wet chamber outlet. The solution concentration is higher than when the strip exits at a temperature above 110°C, but it can still be kept at a relatively low concentration.

[0071] Based on the chemical composition of steel, it can be determined from [ Figure 8 The formic acid concentration is determined in the diagram. Similarly, the selected value is the higher of the value obtained from the manganese concentration and the value obtained from the silicon concentration. For example, for steel containing 4% manganese and 2% silicon, the acid concentration would be 0.7%.

[0072] As can be seen from the diagram, the required formic acid concentration remains low.

[0073] According to the present invention, when the temperature (Th) of the cooled steel strip at the outlet of the wet chamber is less than 110°C, at least a portion of the excess liquid carried by the cooled steel strip in the wet chamber is removed in the dehydration section, and the dehydrated steel strip is dried in the drying chamber.

[0074] Dehydrating the strip limits the amount of liquid carried into the drying chamber. Drying the strip prevents residual moisture from being carried into the downstream chamber.

[0075] These dehydration and drying operations are unnecessary when the temperature of the cooled steel strip at the outlet of the wet chamber is 110°C or higher.

[0076] According to the present invention, the pressure of the atmosphere in the upstream chamber and the pressure of the atmosphere in the downstream chamber are both greater than the pressure in the drying chamber, and the pressure of the atmosphere in the drying chamber is greater than the pressure in the wet chamber.

[0077] By ensuring that the pressure in the drying chamber is greater than the pressure in the cooling chamber, it is ensured that the atmosphere flows from the drying chamber to the cooling chamber without flowing in the opposite direction.

[0078] This prevents the atmosphere in the drying chamber from being contaminated by humid or acidic vapors from the cooling chamber.

[0079] By ensuring that the pressure in the downstream chamber is greater than the pressure in the drying chamber, it is ensured that even in the presence of an atmosphere separation lock, any atmosphere flow between the two chambers will flow from the downstream chamber to the drying chamber, rather than in the opposite direction.

[0080] Therefore, this avoids any risk of the atmosphere in the downstream chamber being contaminated by humid or acidic vapors from the drying chamber.

[0081] By ensuring that the pressure in the upstream chamber is greater than the pressure in the dry chamber, and not just greater than the pressure in the wet chamber, it is ensured that no atmosphere flow occurs from the wet chamber to the upstream chamber. Even with the atmosphere separation lock in place, any flow that may occur will be from the upstream chamber to the wet chamber, not the other way around.

[0082] This avoids any risk of the upstream chamber being contaminated by moisture or acidic vapors from the wet chamber.

[0083] It should be noted that the terms “upstream” and “downstream” used in this document are relative to the direction in which the strip travels in the production line.

[0084] Advantageously according to the invention, the method further includes the step of injecting an atmosphere consisting of a mixture of nitrogen and hydrogen into a wet chamber and a dry chamber, wherein the hydrogen content of the atmosphere is adjusted according to the chemical composition of the steel strip to be galvanized.

[0085] Injecting an atmosphere into the wet and dry chambers promotes the removal of steam from these chambers, thereby reducing the risk of strip surface oxidation, especially for conventional steels that are more sensitive to oxidation.

[0086] In the wet chamber, the injected atmosphere may be limited to nitrogen, with no hydrogen content. In the dry chamber, the atmosphere should contain hydrogen to reduce any oxides that may be present on the strip surface.

[0087] In the drying chamber, the hydrogen content can be adjusted according to the chemical composition of the steel. Therefore, for steel with a Mn content greater than 1.5% and a Si content greater than 0.5%, the hydrogen content should be greater than 1%.

[0088] Advantageously, according to the invention, with adjustable extraction flow rate Extracting atmosphere, the adjustable extraction flow rate makes the flow rate... Greater than the sum of flows The terms correspond to the flow rates of HNx injected into the wet chamber, the flow rates of HNx injected into the dehydration section, the flow rates injected into the drying chamber, the steam flow rates generated by the vaporization of coolant on the surface of the strip in the wet chamber, the steam flow rates generated by strip dehydration, and the steam flow rates generated by strip drying.

[0089] By increasing the extraction flow rate in the wet chamber The flow rate is greater than the air volume injected into the humidification chamber. Flow rate of the atmosphere injected into the dehydration system and the flow rate of the atmosphere injected into the drying chamber The sum of these, plus the flow rate generated by the evaporation of the cooling solution in the wet chamber. Flow rate generated by the evaporation of cooling solution in the dehydration system and the flow rate generated by the evaporation of the cooling solution in the drying chamber. The sum of these ensures that the atmosphere originating from the lock located upstream of the wet chamber enters the wet chamber, and the atmosphere originating from the lock located downstream of the dry chamber enters the dry chamber.

[0090] Advantageously according to the invention, the mass concentration of formic acid in the coolant is adjusted according to the chemical composition of the steel strip to be galvanized. Figure 7 and Figure 8 The formic acid concentration is determined from the schematic diagram.

[0091] According to a second aspect of the present invention, a continuous galvanizing production line is provided, which is capable of implementing the method for galvanizing steel strip according to the first aspect of the present invention, the production line comprising, in sequence, the following steps in the direction of movement of the steel strip to be galvanized:

[0092] • An upstream chamber under a dry reducing atmosphere, in which the steel strip is heated or cooled.

[0093] • Upstream atmosphere separation lock

[0094] • A wet chamber containing a liquid cooling system for cooling the steel strip.

[0095] • A dehydration section for cooling the steel strip, in which at least a portion of the excess liquid that can be carried by the cooled steel strip is removed.

[0096] • A drying chamber for dehydrating steel strips, in which the dehydrated steel strips are dried to evaporate the liquid still present on the dehydrated steel strips.

[0097] • Downstream atmosphere separation lock

[0098] • At least one downstream chamber under a dry reducing atmosphere.

[0099] The production line also includes:

[0100] • Atmosphere injection system, which can inject a drying and reducing atmosphere into the wet chamber and the dry chamber.

[0101] • An atmosphere extraction system that continuously replenishes the atmosphere in the wet chamber and generates an airflow from the dry chamber to the wet chamber.

[0102] • A control and command system capable of monitoring the travel time of the steel strip through the chamber, the cumulative travel time of the steel strip through the drying chamber and at least one downstream chamber under a drying and reducing atmosphere, the temperature (Th) of the cooled steel strip at the outlet of the wet chamber and the temperature (Ts) of the steel strip at the outlet of the dry chamber, and capable of implementing the verification and adjustment steps of the method.

[0103] Advantageously according to the invention, the wet chamber can be alternately supplied by at least two separate coolant supplies and recirculation loops.

[0104] For example, the first loop contains water but no acid, and the second loop contains a mixture of water and acid (e.g., formic acid) with a mass concentration of 1%.

[0105] According to another example, the first circuit contains water but no acid, the second circuit contains a first mixture of water and formic acid with a mass concentration of 0.5%, and the third circuit contains a second mixture of water and formic acid with a mass concentration of 1%.

[0106] Depending on the type of steel (e.g., whether it is a conventional steel or a third-generation steel) and the thermal cycle used, the wet chamber will be supplied by one or more loops in the circuit.

[0107] Advantageously, the wet chamber may be equipped with a device that allows for rapid evacuation of the cooling circuit in order to quickly switch the cooling circuit from a first acid concentration to a second acid concentration.

[0108] According to an alternative embodiment of the invention, the wet chamber includes a cooling device of the immersion water quenching type.

[0109] According to another alternative embodiment of the invention, the wet chamber includes a single-fluid and / or dual-fluid spray cooling device. Compared to immersion water quenching, spray cooling offers more possibilities in adjusting the cooling rate of the strip across its width and along its length. For example, the flow rate of the coolant can be varied across the width of the strip or along its length.

[0110] Advantageously, according to the invention, the dewatering system is arranged between the wet chamber and the dry chamber. This limits the amount of liquid carried by the strip into the dry chamber, thereby promoting the drying of the strip and reducing the amount of steam in the dry chamber. For example, it may include a water jet or dewatering rollers.

[0111] According to an advantage of the invention, the atmosphere separation lock includes two pairs of rollers and an atmosphere injection system located between the two pairs of rollers.

[0112] In combination with the atmosphere extraction system and the resulting flow phase, injecting atmosphere between the two pairs of rollers in the lock can create an atmosphere flow from the center of the lock towards the wet chamber (for the upstream lock) or towards the dry chamber (for the downstream lock). This forms a barrier to the atmosphere present in these chambers, preventing it from escaping through the lock into the upstream or downstream chambers and contaminating them. This prevents vapors from the wet or dry chambers from contaminating the reducing atmosphere in the upstream and downstream chambers.

[0113] Advantageously, the atmosphere extraction system includes atmosphere extraction from the wet chamber and atmosphere extraction from the dry chamber.

[0114] When the steam flow generated during strip drying and the flow rate injected into the drying chamber are too high to be extracted by the atmosphere in the wet cooling chamber alone, it is recommended to provide additional extraction in the drying chamber.

[0115] According to an exemplary embodiment of the invention, the production line further includes a strip oxidation system arranged in a preheating chamber or heating chamber upstream of the wet chamber.

[0116] For certain steel grades, such as those containing large amounts of alloying elements (such as manganese, silicon, or chromium), pre-oxidation or selective internal oxidation in the preheating or heating section is indeed advantageous in order to more easily reduce the oxides formed during the temperature holding phase.

[0117] This is achieved by combining oxygen atoms originating from the surface with certain alloying element atoms within the depth of the material, thereby forming oxide precipitates in an atmosphere with a dew point significantly higher than that in a wet cooling chamber without oxidizing the iron.

[0118] According to an exemplary embodiment of the invention, the drying chamber is combined with a downstream chamber or equipment component (such as an over-aging chamber or an induction heater). Attached Figure Description

[0119] Other features and advantages of the invention will become apparent as you read the following detailed description. To understand these features and advantages, reference will be made to the accompanying drawings, in which:

[0120] •[ Figure 1 [This is a schematic partial depiction of a portion of a horizontal production line employing spray cooling according to an exemplary embodiment of the present invention.]

[0121] •[ Figure 2 [This is a schematic partial depiction of a portion of a vertical production line employing spray cooling according to another exemplary embodiment of the present invention.]

[0122] •[ Figure 3 [This is a schematic partial depiction of a portion of a vertical production line employing immersion tank cooling according to another exemplary embodiment of the present invention.]

[0123] •[ Figure 4 [Illustrated partial view of a galvanizing production line according to an exemplary embodiment of the present invention]

[0124] •[ Figure 5 ]yes[ Figure 4 An enlarged view of the cooling area of ​​the production line.

[0125] •[ Figure 6 ] is similar to [ Figure 1 The illustrative depiction illustrates the airflow.

[0126] •[ Figure 7 [This is a schematic diagram showing the variation of the formic acid mass concentration in the cooling solution with respect to the steel composition when the strip temperature at the outlet of the wet chamber is below the Leiden Frost temperature but above 110°C.]

[0127] •[ Figure 8 [This is a schematic diagram showing how the mass concentration of formic acid in the cooling solution varies with the composition of the steel when the temperature at the outlet of the wet chamber is below 110°C.] Detailed Implementation

[0128] Since the embodiments described below are not intended to be limiting in any way, variations of the invention that specifically include only the series of features described below, isolated from the other features described, can be considered if such series of features is sufficient to provide a technical advantage or to distinguish the invention from the prior art. This series includes at least one feature, preferably functional, without structural details, or only a portion thereof, if this portion alone is sufficient to provide a technical advantage or to distinguish the invention from the prior art.

[0129] In the remainder of the specification, elements with the same structure or similar function will be indicated by the same reference numerals.

[0130] The liquid cooling section according to the invention comprises two chambers separated by a dehydration section, namely, a wet chamber for performing the water quenching process and a dry chamber immediately following the dehydration in the strip travel direction.

[0131] The two chambers are managed simultaneously in terms of airflow and pressure. The management of one chamber is carried out in accordance with the management of the other chamber.

[0132] The wet chamber has the following functions:

[0133] • Water-based technologies are used to quench steel, such as immersion water quenching, single-fluid spray quenching, two-fluid spray quenching, and atomization quenching.

[0134] • Inject HNx with a hydrogen concentration between 0% and 20%.

[0135] • Extract the atmosphere to continuously refresh the atmosphere in the humid chamber.

[0136] • Drain the liquid water from the chamber.

[0137] The wet chamber and dry chamber are separated by a strip dewatering system. The purpose of this system is to remove excess water present on the strip so that it can evaporate completely as the strip passes through the dry chamber.

[0138] The drying chamber, which begins immediately after the dehydration system, includes the following functionalities:

[0139] • Drying the strip. Various techniques can be used, such as convection with hot gas or radiation using, for example, an electric radiant heater.

[0140] • Inject HNx with a hydrogen concentration of up to 20%.

[0141] Finally, atmosphere separation locks are located upstream and downstream of the two chambers to prevent the upstream and downstream chambers from being contaminated by humid atmospheres.

[0142] However, the presence of these locks is insufficient to achieve this purpose. It is also necessary to manage the pressure and airflow within each chamber.

[0143] In industrial applications, there can be various configurations depending on whether the production line is vertical or horizontal, or depending on the cooling technology used.

[0144] Figures 1 to 3 Three examples of configurations are illustrated.

[0145] [ Figure 1 An example of a portion of a horizontal production line employing spray cooling (strip 1 travels horizontally in the direction indicated by the arrows in the figure) according to an exemplary embodiment of the present invention is shown. The diagram shows an upstream drying chamber 2 under a reducing atmosphere, an upstream atmosphere separation lock 31, a wet chamber 4 for quenching by sprayed liquid, a dehydration section 6, a drying chamber 7, a downstream atmosphere separation lock 32, and a downstream drying chamber 8 under a reducing atmosphere.

[0146] [ Figure 2 This image shows an example of a portion of a vertical production line (strip 1 traveling vertically) employing spray cooling according to another exemplary embodiment of the present invention. [The text appears to be incomplete and contains errors. A more accurate translation would require the full context.] Figure 1 The same rooms and sections in ]

[0147] [ Figure 3 This illustrates another example of a portion of a vertical production line according to another exemplary embodiment of the invention, but cooled by water quenching in an immersion tank. The presence of... Figure 1 and Figure 2 The same rooms and sections.

[0148] Especially in things like Figure 2 and Figure 3 In the case of the vertical configuration shown, it is advantageous to supplement the liquid knife and / or additional liquid removal system upstream of the dehydration section to limit liquid from entering the drying chamber.

[0149] The surface oxidation of the strip depends on:

[0150] • The chemical composition of steel

[0151] • The temperature of the strip, especially at the end of the wet cooling process and at the outlet of the drying chamber.

[0152] • The dew point of the area under discussion.

[0153] As explained in the section related to the prior art, the use of liquid cooling processes requires consideration of three different cooling modes, depending on the strip temperature at the end of the wet cooling process:

[0154] Mode 1: When the strip temperature is higher than the Leiden Frost temperature, a film boiling mode exists. In this case, there is no contact between the coolant and the steel strip.

[0155] Mode 2: When the temperature of the strip is between 100°C and the Leiden Frost temperature, transition boiling is achieved.

[0156] Mode 3: When the strip temperature is below 150°C, a "wet" cooling mode is achieved. In this mode, the liquid remains in constant contact with the steel strip.

[0157] The Leidenfrost temperature is particularly dependent on the temperature of the liquid. When cooling is achieved by spraying, it also depends on the surface area of ​​the sprayed liquid, the impact pressure on the strip, and the droplet size.

[0158] When cooling is performed by immersion in a tank, it also depends on the liquid circulation rate.

[0159] The Leidenfrost temperature can be considered to be between 250°C and 600°C.

[0160] Since adding acid to the cooling water only affects the surface condition of the strip when the water comes into contact with the strip, no acid is needed in Mode 1.

[0161] Conversely, using acid is appropriate in Mode 3.

[0162] If the final cooling temperature is 110°C or higher, the strip will not carry the water film into the drying chamber.

[0163] The atmosphere in the drying chamber will only be humid when the final cooling temperature is below 110°C.

[0164] The kinetics of iron oxidation are temperature-dependent. In an oxidizing atmosphere, iron is thought to begin oxidation only at temperatures above 250°C. Similarly, the reduction of iron oxide in a reducing atmosphere is generally considered to only truly begin at temperatures above 250°C.

[0165] Therefore, 250°C is such a temperature; above this temperature, oxidation of the strip must be avoided or the reduction of any existing iron oxide must be considered.

[0166] In the case of manganese, silicon, and chromium oxides, the oxidation onset temperature is significantly higher than that of iron. However, the dew point required to reduce these oxides is so low that they cannot be achieved in galvanizing production lines.

[0167] For steels containing large amounts of manganese, silicon, and chromium, it is important to manage the oxidation of these alloying elements by applying selective or complete oxidation during the heating phase.

[0168] When the cooling endpoint temperature is below the Leidenfrost temperature, the use of acid in the cooling water can eliminate these oxides, or at least limit their formation during the initial stage of cooling.

[0169] According to the present invention, three surface oxidation management ranges are defined based on the cooling endpoint temperature.

[0170] The table below summarizes these three ranges based on the cooling system, with key points highlighted:

[0171] • Is it necessary to use acid when water comes into contact with the strip?

[0172] • Is the atmosphere in the drying chamber humid or dry?

[0173]

[0174] Within the cooling range corresponding to Mode 1, the strip will oxidize during the cooling stage.

[0175] Acid is not required because there is almost no contact between the water and the strip.

[0176] However, the combination of the drying atmosphere in the drying chamber and HNx injection makes it possible to obtain a reducing atmosphere in the drying chamber.

[0177] Therefore, the operating conditions are as follows:

[0178] i. Pass through the wet chamber as quickly as possible, less than 15 seconds for conventional steel grades;

[0179] ii. Inject HNx into the drying chamber and downstream chamber. Adjust the hydrogen content (up to 20%) in these chambers according to the specific steel grade and the travel time through the wet chamber;

[0180] iii. To ensure sufficient time for the reduction of iron oxide, the cumulative travel time through the drying chamber and downstream chamber must be at least equal to the travel time through the wet chamber.

[0181] Within the cooling range corresponding to Mode 2, the strip will oxidize during the cooling phase.

[0182] Acid can be considered, and the drying chamber should have a dry atmosphere.

[0183] Therefore, the operating conditions are as follows:

[0184] i. Use low concentrations of acid;

[0185] ii. Inject HNx into the drying chamber and downstream chamber. Adjust the hydrogen content in the chamber downstream of the drying chamber (up to 20%), where the strip temperature again exceeds 250°C;

[0186] iii. A combination of a drying chamber and a downstream chamber equipped with heating equipment (e.g., an induction heater or an over-aging section);

[0187] iv. If the reducing capacity of the downstream chamber is sufficient, some steels may not require the use of acid.

[0188] Advantageously, in Mode 2, the strip does not leave the drying chamber at a temperature above 250°C (the strip must be dried before its temperature exceeds 250°C again), but it can exceed that temperature again in a downstream chamber. This is beneficial for reducing any oxides that may be present, as the downstream chamber is under a reducing atmosphere. If the reducing capacity of the downstream chamber is sufficient to reduce any additional oxides present at the outlet of the drying chamber due to the absence of acid, then acid may not be necessary.

[0189] Within the cooling range corresponding to Mode 3, the strip will oxidize during the cooling phase.

[0190] The use of acid is appropriate. However, the atmosphere in the drying chamber will be humid. Therefore, the aim is to ensure that all water has evaporated before the strip leaves the chamber and that the atmosphere is properly extracted.

[0191] Before the strip leaves the drying chamber, the temperature in the chamber must not exceed 250°C, otherwise the strip will oxidize again.

[0192] Therefore, the operating conditions are as follows:

[0193] i. Use a low concentration of acid in the cooling water.

[0194] ii. If the drying chamber is combined with a downstream chamber equipped with heating equipment, the outlet temperature shall not exceed 250°C.

[0195] In order to create an airflow into the humid chamber where air extraction is performed, the following must be present simultaneously:

[0196] • Pressure, such that the pressure Pam in the upstream chamber and the pressure Pav in the downstream chamber are greater than the pressure Ps in the drying chamber, and the pressure in the drying chamber is greater than the pressure Ph in the wet chamber:

[0197]

[0198] • Flow rate, resulting in the extraction flow rate from the wet chamber. The flow rate is greater than that of HNx injected into the wet chamber. The flow rate of HNx injected into the dehydration section Flow rate injected into the drying chamber Flow rate generated by coolant vaporization at the surface of the strip in the wet chamber Steam flow rate generated during strip dehydration and the steam flow rate generated during strip drying sum:

[0199]

[0200] The extraction flow rate must be strictly greater than the flow rate of the vaporized liquid. and the flow rate of HNx injected into the wet chamber The flow rate of HNx injected into the dehydration section The flow rate of HNx injected into the drying chamber Flow injected into the upstream lock HNx and the flow of HNx injected into the downstream lock In order to use traffic A small amount of atmosphere is extracted from the upstream chamber and at a flow rate of [missing information]. A small amount of atmosphere is extracted from the downstream chamber.

[0201] in this case:

[0202]

[0203] If the flow rate generated during strip drying and the flow rate injected into the drying chamber If the temperature is too high, an additional extraction can be performed into the drying chamber. ,in this case:

[0204]

[0205] Since the amount of coolant evaporated varies depending on the size and temperature of the strip, the extraction flow rate... It is adjustable; if an additional extraction is added in the drying chamber, It is also adjustable.

[0206] Refer to the attached diagram [ Figure 4 The schematic diagram shows a vertical furnace galvanizing production line 100 according to an exemplary embodiment of the present invention, schematically partially depicted in a longitudinal view.

[0207] The production line, in the direction of travel of strip 1, sequentially includes: a preheating chamber 101, a heating chamber 102, a holding chamber 103, a cooling section 104 including an air-cooled chamber 3, a wet liquid-cooled chamber 4, a dehydration and repositioning section 6, and a drying chamber 7, followed by an aging chamber 105, a furnace outlet section 106, and a hot-dip galvanizing section 107. A control and command system 11 ensures the correct operation of the production line and adjusts its operating parameters according to the characteristics of the strip at the inlet and the expected characteristics at the outlet.

[0208] Depending on the steel grade and the thermal cycle required to achieve the desired mechanical properties, the air-cooled chamber 3, for example, allows the strip to be slowly cooled from the annealing temperature (e.g., 900°C) to the quenching initiation temperature (e.g., 700°C). Faster cooling of the strip can also be achieved in chamber 3, but it will still be slower than cooling achieved in the wet liquid cooling chamber 4. In practice, air cooling, typically achieved by spraying a mixture of nitrogen and hydrogen, can achieve cooling rates on the order of 100°C / s to 200°C / s for a 1 mm thick steel strip.

[0209] Refer to the attached [ Figure 5 The diagram shows... Figure 1 The lower part of the cooling section 104 is partially depicted.

[0210] As the strip 1 travels downward in the direction indicated by arrow S, it leaves the air-cooled chamber 3.

[0211] The outlet of this chamber is an upstream lock 31, which ensures separation between the controlled reducing atmosphere, consisting of a mixture of nitrogen and hydrogen, present in the gas-cooled chamber 3, and the humid atmosphere in the liquid-cooled chamber 4 located downstream.

[0212] The lock described includes two pairs of rollers 30, with an air injection device 33 between the two pairs of rollers. It should be understood that other lock configurations are also possible.

[0213] The strip then passes through a liquid cooling chamber 4, in which a liquid cooling device 5 is arranged. The device includes nozzles 40 that spray coolant, such as an acidic solution containing water and 0.5% formic acid, onto the strip.

[0214] The liquid blade 41 formed by the flat nozzle 42 can remove most of the overflow liquid present on the strip. The jet is inclined at an acute angle relative to the strip in order to promote the removal of the water film present on the strip surface. The nozzle 42 is supplied with the same liquid as the coolant through a supply line (not shown).

[0215] The strip exits the wet chamber 4 through the reduced-size opening 43.

[0216] When the strip leaves the wet chamber at a temperature below 100°C to 110°C, the liquid film is mechanically carried away by the strip. The purpose of the dehydration section and the drying chamber is to remove the presence of liquid from the surface of the strip under a reducing atmosphere before it enters the downstream aging chamber. The dehydration process is beneficial to the drying of the strip.

[0217] Conversely, when the strip leaves the wet chamber at a higher temperature, there is no liquid film on it. To limit the energy consumption of the production line, the dehydration and drying equipment can be shut down.

[0218] After leaving the wet chamber, the strip passes through the dehydration section 6 equipped with air knives 60, which are designed to remove any liquid that may be present on the strip.

[0219] The air knife is formed by a flat nozzle 61 supplied through a supply line (not shown).

[0220] Liquid and air cutters extend across the entire width of the strip. On one side of the strip, liquid and air cutters can be obtained using a single nozzle with a length at least equal to the maximum width of the strip, or multiple nozzles arranged across the width of the strip.

[0221] The gas used for dehydration can be at ambient temperature or higher. These air knives have essentially the same tilt angle as the liquid knife 41.

[0222] The dehydration section 6 extends through a lower redirection section 62, in which two deflection rollers 63 and 44 and a nozzle 65 forming an additional air knife are arranged.

[0223] The strip 1 then passes through a drying chamber 7, which is equipped with heating pipes 70 designed to dry the strip by radiation. Drying can also be carried out by convection or by a combination of radiation and convection.

[0224] At the outlet 71 of the drying chamber 7, the strip passes through a downstream atmosphere separation lock 32 between the drying chamber and the over-aging chamber 105, which is located downstream in the direction of strip travel. The lock depicted includes two pairs of rollers 30 with an atmosphere injection device 31 between them, but other lock configurations are also possible.

[0225] According to the present invention, if the strip temperature Th at the outlet opening 43 of the wet chamber 4 At 250°C, the travel time of the strip through the wet chamber 4 must be less than or equal to 15 seconds, and the cumulative travel time through the drying chamber 7, the aging chamber 105 and the furnace outlet chamber 106 must be at least equal to the residence time in the wet chamber 4.

[0226] If the strip temperature Th at the outlet opening 43 of the wet chamber 4 is less than 110℃, then the strip temperature at the outlet 71 of the dry chamber 7 must be... 250℃.

[0227] The atmosphere injection system 9 can inject atmosphere into the wet chamber 4 via injection point 91 and into the dry chamber 7 via injection point 92, and the atmosphere extraction system 10 can continuously refresh the atmosphere in the wet chamber 4 and generate an atmosphere flow from the dry chamber 7 to the wet chamber 4.

[0228] When the sum of the steam flow rate generated during strip drying and the flow rate injected into the drying chamber is too high to allow for a single atmosphere extraction in the wet chamber, an additional atmosphere extraction 13 is added to the drying chamber in addition to the extraction 12 performed in the wet chamber.

[0229] The injection points 91 and 92 of the atmosphere injection system 9 and the extraction point 11 of the atmosphere extraction system 10 [ Figure 5 The locations shown do not represent their actual locations within the industrial facility. In such facilities, the locations of injection and extraction points are chosen to facilitate the renewal of the atmosphere in the wet chamber, dehydration section, and drying chamber.

[0230] The atmosphere injected by injection system 9 is a mixture of nitrogen and hydrogen, for example, with a hydrogen volume ratio of 5%. The hydrogen content can be adjusted according to the steel grade to be processed. Advantageously, the atmosphere injected by injection system 9 is the same as the atmosphere present in over-aging chamber 105.

[0231] [ Figure 6 The diagram schematically illustrates the gas flow in a wet cooling section according to an exemplary embodiment of the invention. For simplicity, the individual chambers are depicted horizontally.

[0232] The flow rate of the reducing atmosphere is Q31 ( The liquid is injected into the upstream lock 31 located between the air-cooled chamber 3 and the wet liquid-cooled chamber 4.

[0233] All flow rate Q31 injected into the lock is discharged into the wet chamber 4. The extraction performed in the wet chamber 4 results in the flow rate Q31b originating from the dry cooling chamber 3 being discharged into the wet chamber 4. The airflow passes through the upstream lock 31 and is added to the injection lock in the flow Q31, so that no airflow circulates from the wet chamber 4 toward the dry cooling chamber 3.

[0234] Therefore, the flow rate Q31a entering the wet chamber 4 from the lock 31 is equal to the sum of the flow rate Q31 injected into the lock and the flow rate Q31b originating from the dry cooling chamber 3.

[0235] The flow rate of the reducing atmosphere is Q32 ( It is injected into the downstream lock 32 located between the drying chamber 7 and the over-aging chamber 105.

[0236] All flow rate Q32 injected into the lock is discharged into the over-aging chamber. Extraction in wet chamber 4 and dehydration section 6 results in the flow rate Q32b originating from over-aging chamber 105 being discharged into the over-aging chamber. The flow rate Q32 passes through the downstream lock 32 and is added to the injection lock, so that no atmosphere flows from the drying chamber 7 to the aging chamber 105.

[0237] An atmosphere injection (not shown in the figure) is performed in chambers 3 and 105 to keep these chambers under pressure and compensate for the outflow rate Q31b. ) and Q32b ( ).

[0238] Therefore, the flow rate Q32a entering the drying chamber 7 from the lock 32 is equal to the sum of the flow rate Q32 injected into the lock and the flow rate Q32b originating from the over-aging chamber 105.

[0239] In wet chamber 4, a portion of the coolant Q40 ( It vaporizes upon contact with the tropical material. The remaining Q41 remains liquid and is discharged from the wet chamber 4 through outlet 44, and then recirculated to supply nozzle 40 again.

[0240] The amount of liquid to be evaporated, Q40, depends on:

[0241] The cooling process is less evaporative during immersion water quenching compared to spraying.

[0242] The dimensions of the strip (width and thickness) and its speed;

[0243] The inlet and outlet temperatures of the strip, i.e., the cooling rate.

[0244] The steam must be removed by atmospheric extraction.

[0245] The flow rate Q91 of the reducing atmosphere is delivered at injection point 91 via atmosphere injection system 9. Inject into the wet chamber 4.

[0246] The flow rate Q11 is extracted from the wet chamber 4 at the extraction point 11 by the atmosphere extraction system 10. ).

[0247] The extracted flow rate Q11 is greater than the sum of the flow rate Q31 originating from the upstream lock 31, the flow rate Q91 injected by the atmosphere injection system 9 at the injection point 91, and the flow rate Q40 generated by the vaporization of the coolant.

[0248] Therefore, the gas flow rate Q60 from the dehydration section 6 and the flow rate Q31b from the dry cooling chamber 3 enter the wet chamber 4.

[0249] Therefore: Q11 = Q31a + Q91 + Q40 + Q60.

[0250] In the dehydration section 6, the flow rate of the reducing atmosphere injected through nozzles 61 and 65 is Q6 ( This allows for the removal of any liquid film that may be present on the strip, depending on the strip's temperature.

[0251] A portion of the liquid vaporizes to form steam with a flow rate of Q62 ( The remaining liquid is discharged through outlet 61 and then circulated to supply nozzle 40 again.

[0252] The extraction flow rate Q11 in the wet chamber 4 makes the flow rate Q60 originating from the dehydration section 6 and entering the chamber 4 greater than the sum of the flow rate Q6 injected by nozzles 61 and 65 and the vaporization flow rate Q62 in the dehydration section 6.

[0253] Therefore, the gas flow rate Q71 originating from the drying chamber 7 enters the dehydration section 6.

[0254] Therefore: Q60 = Q6 + Q62 + Q71.

[0255] In the drying chamber 7, a reducing atmosphere is injected at injection point 92 via the atmosphere injection system 9 at a flow rate of Q92. Therefore, the gas flow rate Q71 from drying chamber 7 to dehydration section 6 is the flow rate Q92 injected at point 92 and the flow rate Q70 generated by the evaporation of liquid in chamber 7. The sum of the flow rate Q32a originating from the downstream lock 32 located between chamber 7 and over-aging chamber 105.

[0256] Therefore: Q71 = Q92 + Q70 + Q32a.

[0257] The control of the injected gas flow rate and the extracted gas flow rate makes the pressure P3 in the dry cooling chamber greater than the pressure P31 in the upstream lock 31, which in turn is higher than the pressure P4 in the wet chamber 4. Furthermore, it makes the pressure P105 in the over-aging chamber greater than the pressure P32 in the downstream lock 32, which in turn is greater than the pressure P7 in the drying chamber, which in turn is greater than the pressure P6 in the dehydration section, which in turn is greater than the pressure P4 in the wet chamber.

[0258] This ensures that the dry cooling chamber 3 and the over-aging chamber 105 are not contaminated by humid vapors, while providing sufficient atmosphere renewal in the drying chamber 7 and the dehydration section 6 so that the presence of humid vapors is zero or low enough to prevent excessive oxidation of the strip.

[0259] For steel grades that require wet cooling to temperatures above 110°C, the present invention can avoid the presence of a humid atmosphere in the dehydration zone 6 and the drying chamber 7 because the evaporation flow rates Q62 and Q70 of the liquid film are zero, which is due to the absence of such a film on the strip at the outlet of the wet chamber 4.

[0260] In an alternative embodiment, if the flow rate to the wet chamber is insufficient to allow for atmosphere renewal in the dry chamber, the dry chamber 7 may include an atmosphere extraction system 13.

[0261] Of course, the present invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. Furthermore, various features, forms, variations, and embodiments of the invention can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

1. A method for cooling a steel strip (1) traveling in a continuous galvanizing production line (100), wherein: • The steel strip (1) passes through the upstream chambers (2, 3, 103) and the upstream atmosphere separation lock (31) under a dry reducing atmosphere, and is then cooled in a wet chamber (4) containing a liquid cooling device (5). • The steel strip (1) cooled in the wet chamber (4) passes through the dry chamber (7), the downstream atmosphere separation lock (32), and at least one downstream chamber (8, 105, 106) under a dry reducing atmosphere. The method further includes: • A dry atmosphere is injected into the wet chamber (4) and the dry chamber (7) via the injection system (9). • An atmosphere is drawn in by an extraction system (10) to continuously refresh the atmosphere in the wet chamber (4) and generate an atmosphere flow from the dry chamber (7) to the wet chamber (4). • Controlled via the control and command system (11): • The travel time of the steel belt (1) through the wet chamber (4), • The cumulative travel time of the steel strip (1) through the drying chamber (7) and through at least one downstream chamber (8, 105, 106) under a drying and reducing atmosphere. • The temperature (Th) of the steel strip (1) at the outlet of the wet chamber (4), and • The temperature (Ts) of the steel strip (1) at the outlet of the drying chamber (7). The method is characterized by including the step of verifying the required conditions as defined below: • When the temperature (Th) of the steel strip (1) at the outlet of the wet chamber (4) is greater than or equal to the Leiden Frost temperature, the travel time of the steel strip (1) through the wet chamber (4) must be less than or equal to fifteen seconds, and the cumulative travel time through the dry chamber (7) and through at least one downstream chamber (8, 105, 106) under a dry reducing atmosphere must be greater than or equal to the residence time of the steel strip (1) in the wet chamber (4). • When the temperature (Th) of the steel strip (1) at the outlet of the wet chamber (4) is less than the Leiden Frost temperature, the liquid in the cooling device (5) must be an aqueous coolant with a formic acid mass concentration of 0.1% or higher, and the temperature (Ts) of the steel strip (1) at the outlet of the dry chamber (7) must be 250°C or lower. • When the temperature (Th) of the cooled steel strip (1) at the outlet of the wet chamber (4) is less than 110°C, at least a portion of the excess liquid carried by the cooled steel strip (1) in the wet chamber (4) is removed in the dehydration section (6), and the dehydrated steel strip (1) is dried in the drying chamber (7). If one of the required conditions is not met during the verification step, the method further includes the step of adjusting at least one operating parameter of the production line so that the required conditions can be met during the verification step.

2. The method according to the preceding claims, wherein the pressure of the atmosphere in the upstream chamber (2, 3, 103) and the pressure of the atmosphere in the downstream chamber (8, 105, 106) are both higher than the pressure of the drying chamber (7), and wherein the pressure of the atmosphere in the drying chamber (7) is higher than the pressure of the wet chamber (4).

3. The method according to any one of the preceding claims, the method further comprising the step of injecting an atmosphere consisting of a mixture of nitrogen and hydrogen into the wet chamber (4) and the dry chamber (7), the hydrogen content of the atmosphere being adjusted according to the chemical composition of the steel strip (1) to be galvanized.

4. The method according to any one of the preceding claims, wherein the adjustable flow rate is used. Perform atmosphere extraction to increase flow rate Greater than the sum of flows Each of these corresponds to the flow rate of HNx injected into the wet chamber, the flow rate of HNx injected into the dehydration section, the flow rate injected into the drying chamber, the steam flow rate generated by the vaporization of coolant on the surface of the strip in the wet chamber, the steam flow rate generated by the dehydration of the strip, and the steam flow rate generated by the drying of the strip.

5. The method according to claim 1, wherein the mass concentration of formic acid in the coolant is adjusted according to the chemical composition of the steel of the strip (1) to be galvanized.

6. A continuous galvanizing production line (100), the continuous galvanizing production line being capable of implementing the method for galvanizing a steel strip (1) according to any one of claims 1 to 5, the production line (100) comprising, in sequence, the following in the direction of movement of the steel strip (1) to be galvanized: • The upstream chamber (2, 3, 103) under a dry reducing atmosphere, in which the steel strip (1) is heated or cooled. • Upstream atmosphere separation lock (31). • A wet chamber (4) containing a liquid cooling device (5) for cooling the steel strip (1). • A dehydration section (6) for cooling the steel strip (1), in which at least a portion of the excess liquid that can be carried by the cooled steel strip (1) is removed. • A drying chamber (7) for dehydrating the steel strip (1), in which the dehydrated steel strip (1) is dried so as to evaporate the liquid still present on the dehydrated steel strip (1). • Downstream atmosphere separation lock (32). • At least one downstream chamber (8, 105, 106) under a dry reducing atmosphere. The production line also includes: • Atmosphere injection system (9), which is capable of injecting a drying and reducing atmosphere into the wet chamber (4) and the dry chamber (7). • Atmosphere extraction system (10), which is capable of continuously updating the atmosphere in the wet chamber (4) and generating an atmosphere flow from the dry chamber (7) to the wet chamber (4). • Control and command system (11), which is capable of monitoring the travel time of the steel strip (1) through the chamber (4), the cumulative travel time of the steel strip (1) through the drying chamber (7) and through at least one downstream chamber (8, 105, 106) under a drying and reducing atmosphere, the temperature (Th) of the cooled steel strip (1) at the outlet of the wet chamber (4) and the temperature (Ts) of the steel strip (1) at the outlet of the drying chamber (7), and is capable of implementing the verification and adjustment steps of the method.

7. The production line (1) according to the preceding claim, wherein the atmosphere extraction system (10) includes extracting (12) atmosphere from the wet chamber (4) and extracting (13) atmosphere from the dry chamber (7).

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