Device and method for humidity-controlled blowdown after application of layer on flat steel product

Abstract

The invention relates to a device (150) and a method for applying a ZnAlMg layer or a ZnAl layer to a front side (V) and a rear side (R) of a flat steel product (100), comprising the following steps:-moving the flat steel product (100) from an input side to an outlet side (A) of a zinc alloy melt bath,-providing a drying gas stream (TG),-providing water vapor (WG),-combining the drying gas stream (TG) and the water vapor (WG) to obtain a desorbed gas (AG) mixture,-removing the desorbed gas (AG) mixture from the front side (V) and the rear side (R) of the flat steel product (100). Determining a gas humidity of the removal gas (AG), discharging the removal gas (AG) via at least one gas nozzle (15) for removing the front side (V) and at least one gas nozzle (15) for removing the rear side (R), thereby removing the front side (V) and the rear side (R) of the flat steel product (100) with the removal gas (AG), wherein the discharged removal gas stream (AG) satisfies at least one of the following two conditions (B1, B2): B1: the moisture content of the removal gas (AG), the ratio of the moisture content to the gaseous water vapor (WG), is greater than 200 ppm and less than 43700 ppm, the moisture content preferably being between 500 ppm and 9980 ppm; b2: the dew point (TP) of the desorbed gas (AG) is higher than-39 DEG C and lower than + 30 DEG C, wherein the dew point (TP) is preferably between-29 DEG C and + 7 DEG C.

Description

[0001] The invention relates to a device by means of which a flat steel product can be coated with a layer based on zinc (Zn) or zinc-aluminum-magnesium (ZnAlMg) in a molten bath, for example as a protective layer, and the flat steel product can be blown off in a controlled manner at the outlet of the molten bath. The invention also relates to a corresponding method.

[0002] As is known to all, the surface of the flat steel product 100 (such as steel strip or steel plate) is coated with zinc (Zn) or ZnAlMg alloy to improve its corrosion resistance. In actual operation, the flat steel product 100 taken out of the furnace is usually placed in a zinc alloy molten bath 11, such as Figure 1 An exemplary device 150 is shown in the figure. In order to protect the flat steel product 100 from oxidation, it is usually introduced into the molten bath 11 from the input side E through a trunk 12 with an inert atmosphere. In the bath 11, the flat steel product 100 is deflected by a (zinc bath) roller 13 and moves upward from the outlet side A of the bath 11. After coming out of the molten bath 11, the molten alloy film attached to the front and rear sides of the flat steel product 100 is stripped by the gas jet ejected from the gas nozzle 15 of the stripping nozzle device to the target thickness (micrometer range) or the target surface coating rate (unit: g / m 2 ), and then the flat steel product 100 is transferred to the cooling zone 16. This continuous process is generally referred to as hot dip galvanizing.

[0003] Details of suitable methods and particularly suitable alloy compositions can be found, for example, in the published application WO 2014 / 033153 A1 of the applicant voestalpine Stahl AG.

[0004] The flat steel product 100 can then be rolled by a temper rolling process and / or a bending and stretching process. The flat steel product 100 can also be chemically post-treated. For example, a flat steel product 100 for the automotive industry (e.g., in the form of a steel strip) can be further processed by oiling. For example, an oiling machine can be used for the oiling.

[0005] It has been shown that the new hot-dip galvanized flat steel product 100 may have surface defects or errors, depending on the alloy composition and the specific process control. On the one hand, in the zinc molten bath, zinc vapor is formed above the bath 11, which has a negative impact on the surface of the hot-dip galvanized flat steel product 100. On the other hand, the blowing process on the outlet side A of the molten bath 11 also has an impact on the surface quality.

[0006] Patent EP0172682B1 filed by Armco in 1985 relates to the reduction or elimination of oxygen in the area around the stripping nozzle and in the strip leaving the zinc bath, and the control of zinc vapor in connection with hot dip galvanizing of ferrous metal strip. On the exit side of the bath, a reduced oxygen atmosphere is provided instead of the ambient air normally present in the enclosed area where the stripping nozzle is located. Since zinc evaporates strongly in this atmosphere, a small amount of water vapor must be added to the reduced oxygen atmosphere. The enclosed area is located just above the surface of the molten bath, thus forming a sealed space. The reduced oxygen atmosphere in this space is to improve the stripping process, while the small proportion of water is to prevent the formation of zinc vapor on the surface of the bath. The moisture content in the enclosed space is adjusted so that zinc vapor does not form.

[0007] From the published application DE 2033847 a device is known which is suitable for adjusting the coating thickness when a steel strip is galvanized. Air, gas or steam is blown onto the galvanized steel strip using a wide slit nozzle for the purpose of stripping. Taking into account the possible curved shape of the steel strip on the outlet side of the bath, the nozzle slit is larger in the edge region of the steel strip than in the center region of the steel strip.

[0008] More than 50 years ago, National Steel proposed a device for removing wet steam in the form of a steam jet in the published patent application DE1521405A1. Wet steam is used to quickly cool the steel strip after hot-dip galvanizing, wherein the blown wet steam causes the coating to solidify in a short time. It is recommended to use a condenser device suitable for supplying wet steam at the required temperature and the required pressure.

[0009] In the published patent application JP2020100886A2 of the Nippon Steel Corporation, the aim is to produce a galvanized steel strip with an increased coefficient of surface friction. In order to increase the coefficient of friction, water is sprayed under pressure onto the surface of the flat steel product after blowing. The particle size of the water droplets is at least 0.07 mm, preferably greater than 1.5 mm. By spraying the water droplets, irregularities are intentionally created on the surface of the steel strip. The goal pursued by this document is different from that of the present invention, and therefore the direction of the corresponding technical teaching is completely different from that of the present invention.

[0010] In addition to avoiding surface defects and inaccuracies and pure corrosion protection, the requirements for the surface quality of Zn-coated flat steel products, especially ZnAlMg-coated flat steel products, are becoming increasingly stringent. The automotive industry in particular expects products to meet the highest surface requirements. However, providing a homogeneous surface is not easy.

[0011] The main problem here is usually surface defects of the ZnAlMg layer. For example, marbling (marble effect), "toothpick" or "beach pattern" defects may form on the ZnAlMg layer, or slag formation may occur. There are some patents (e.g. EP20130826634AM / JMMataigne; JP20080256208 NSSMC / Oohashi et al.) that try to eliminate similar surface defects (gloss effect or displaced oxide skin) by other means than the present invention (reducing the O2 content around the stripping nozzle).

[0012] In some cases, a Zn layer containing a certain proportion of aluminum (for example, the proportion of aluminum may be less than 1 wt %) may also exhibit similar surface defects.

[0013] The object is therefore to provide a device and a method for coating flat steel products with ZnAlMg or ZnAl layers which provide particularly durable and robust protection against corrosion, wherein the surface of the protective layer should be particularly uniform and free of marbling (no “marble effect”) and / or toothpick defects (no “toothpick”). The aim is to achieve a surface quality that meets the highest customer requirements.

[0014] Furthermore, the device and method should consume as little energy as possible, be cost-effective and robust. Summary of the invention

[0015] According to the invention, a corresponding device is provided, which uses a continuous (hot-dip) process to provide a flat steel product with a metallic ZnAlMg layer or ZnAl layer, which can be used as a (protective) coating, for example. The function of this layer is to protect both sides of the steel substrate of the flat steel product from external influences. In the following, the corresponding dipping bath is referred to as a zinc alloy molten bath (or short zinc melt bath), wherein the term zinc alloy molten bath includes both a molten bath mainly containing zinc (Zn) and a small amount of aluminum (Al) (for example less than 1% by weight) added, and a molten bath containing a ZnAlMg alloy. The layer applied on both sides is also referred to as a Zn-containing (protective) layer.

[0016] A device for applying a ZnAlMg layer or a ZnAl layer to a flat steel product is proposed. In all embodiments, the device comprises: - a zinc alloy molten bath having an input side and an output side, - a gas supply device configured to provide a drying gas, - a water vapor device configured to provide water vapor, - a device (such as an apparatus) for determining the humidity (or moisture content) of a gas, a stripping nozzle device fluidly connected to the gas supply device and the water vapor device so as to supply the stripping nozzle device with a stripping gas, the stripping gas being a mixture of a dry gas and gaseous water vapor, wherein the stripping nozzle arrangement comprises at least one gas nozzle for blowing the front side of the flat steel product with stripping gas, and at least one gas nozzle for blowing the rear side of the flat steel product with stripping gas, ○The gas nozzle is arranged in the area on the outlet side of the zinc alloy molten bath, a device for determining the humidity (or moisture content) of the gas is arranged in or at the stripping nozzle arrangement, so that the moisture content of the stripping gas is determined (e.g. by measurement) before or during the stripping gas outflow in the direction of the front side or the rear side of the flat steel product, and ○ At least one of the following two conditions B1 and B2 is met: B1: The moisture content of the removed gas (AG) or the proportion of gaseous water vapor (WG) is greater than 200 ppm and less than 43700 ppm, and the moisture content is preferably between 500 ppm and 9980 ppm, B2: The dew point (TP) of the degassed gas (AG) is higher than -39°C and lower than +30°C, the dew point (TP) is preferably between -29°C and +7°C.

[0017] For at least some embodiments of the apparatus and corresponding methods, the moisture content of the degassing gas can be defined by a volume fraction (referred to herein as condition B1) ranging from 200 ppm to 43700 ppm. Preferably, for at least some embodiments, the volume fraction is between 500 ppm and 9980 ppm.

[0018] For at least some embodiments of the apparatus and corresponding methods, the moisture content of the stripped gas can be defined by a dew point (referred to herein as condition B2) that is above -39°C and below +30°C. Preferably, for at least some embodiments, the dew point of the stripped gas is within the parameter range of -29°C to +7°C.

[0019] It is important to note that the B1 and B2 conditions define a large overlapping region. Only the boundary values ​​may be biased due to rounding.

[0020] Alternatively, for at least some embodiments of the apparatus and the corresponding method, the moisture content of the degassing gas can be defined by using a mixture of dry gas and gaseous water vapor, which mixture is controlled and adjusted so that it is always unsaturated (in this alternative method, conditions B1 and / or B2 are also met). Unsaturated degassing gas always contains only water in the gas phase. In other words, the proportion of gaseous water vapor (moisture content) in the degassing gas used is kept at a low level, so that the degassing gas is unsaturated with respect to the water vapor content. This means that the current dew point of the degassing gas is always lower than the current temperature of the degassing gas. This statement about the unsaturated state also applies to changing the gas pressure and / or changing the temperature of the degassing gas.

[0021] For all embodiments, unsaturated degassing can also be defined as follows: as long as it contains only superheated water vapor, it is considered unsaturated. In the unsaturated state, the degassing is a homogeneous single-phase mixture containing only a gas phase (no solids or liquids). In the unsaturated state, the relative humidity of the degassing is less than 100%.

[0022] In order to avoid water condensation when the stripping gas ejected from the stripping nozzle mixes with the surrounding gas (or surrounding air) in the area around the stripping nozzle, the dew point upper limit for the moisture content of the stripping gas is limited to +30°C, which is equivalent to a water volume fraction of 43700 ppm in the stripping gas.

[0023] The corresponding method and device are based on the control specification of the required moisture content of the flat steel product at the impact point of the stripping jet in order to avoid the formation of marbling and / or toothpick defects. In other words, there must always be a sufficiently high moisture content in the stripping gas to allow stripping without the formation of marbling and / or toothpick defects. At the same time, however, as mentioned above, the formation of condensed water must be avoided. In addition to conditions B1 and / or B2, these two boundary conditions or boundary conditions create a parameter window that is preferably observed in all embodiments.

[0024] Preferably, in the device and the corresponding method, the moisture content, i.e. the water vapor content, is controlled by monitoring the current dew point of the stripping gas and keeping it within an appropriate predetermined parameter window (condition B2). This prevents the formation of condensed water and allows stripping to be performed without the above-mentioned drawbacks. Condensed water can have a negative impact on the stripping process and the surface quality of the galvanized steel strip.

[0025] In all embodiments, the control or control unit of the device can execute a humidity regulation protocol in order to be able to react in an appropriate form to changes in the current moisture content and to ensure compliance with conditions B1 and / or B2.

[0026] In all embodiments, the respective required moisture content is provided directly by the stripping gas. In other words, the stripping gas acts as a carrier or transport medium for the very small amount of water vapor required here.

[0027] In all embodiments, it is preferred that a water vapor gas stream is introduced into the dry stripping gas (referred to herein as a dry gas stream) in the gas supply line leading to the stripping nozzle to mix the dry gas and water vapor gas streams.

[0028] Preferably, in all embodiments, the drying gas stream comprises nitrogen or consists of nitrogen.In all embodiments, the drying gas stream may also contain other inert gases instead of nitrogen.

[0029] In all embodiments, the moisture content of the stripping gas can be measured, for example using a humidity sensor (e.g. a thermal or capacitive dew point sensor) which is arranged between the feed point of the gaseous water vapor and the nozzle opening of the stripping nozzle and can also be adjusted in further possible embodiments.

[0030] The advantage of the method or the corresponding device is that marbling and / or toothpick errors can be effectively avoided without the need to build or install additional destructive devices (e.g., housings or shells according to the applicant's European patent application EP22182309.9 (V08-0015P-EP / P219205 / VA23004)) directly above the zinc bath area or in the vicinity of the stripping nozzle and above the zinc bath. It is possible to access the stripping nozzle and the zinc bath surface for regular cleaning work, which is necessary for correct process management.

[0031] Furthermore, compared to the method that is the subject of the above-mentioned European patent application EP22182309.9, this method is very efficient in terms of medium consumption, since only a small fraction of the water vapor is consumed to avoid marbling and / or toothpick defects.

[0032] All embodiments relate to applying a zinc-containing (protective) layer on the flat steel product, the thickness of which corresponds to the target thickness (according to the corresponding specification). This layer is produced by passing the flat steel product through a molten zinc alloy bath and blowing it with a controlled "moistened" stripping gas on the outlet side of the molten bath through a stripping nozzle arrangement, which comprises at least one gas nozzle on each side of the flat steel product.

[0033] In all embodiments, the zinc alloy in the zinc alloy molten bath may preferably have the following compositions, but is not limited to these compositions: - an aluminum content between 1.0 and 3.0% by weight, preferably between 1.3 and 2.8% by weight, - a magnesium content between 1.0 and 2.5% by weight, preferably between 1.2 and 2.2% by weight, and - the remainder of the zinc alloy molten bath is zinc, and one or more optional additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the content of each additional element in the metal coating being less than 0.1% by weight, and unavoidable impurities.

[0034] In all embodiments, the zinc alloy in the zinc alloy molten bath may preferably have the following compositions, but is not limited to these compositions: - an aluminum content of less than 1.0% by weight, preferably between 0.1 and 0.5% by weight, and -The remainder of the zinc alloy molten bath is zinc and unavoidable impurities.

[0035] Preferably, the following definitions apply to system parameters and / or method parameters in all embodiments: - the thickness of the nozzle lip gap between the two nozzles (referred to as nozzle opening height) is between 0.5 and 5 mm, preferably between 0.6 and 2 mm, particularly preferably between 0.8 and 1.5 mm, and / or - The effective flow rate (D) of the stripping gas over the strip width is between 200 and 8000 Nm per hour 3 between, and / or - the distance between the nozzle lip gap and the front or rear side of the flat steel product is between 2 and 15 mm, preferably between 3 and 12 mm, and / or The steel belt speed is between 50 and 200 m / min, preferably between 70 and 150 m / min.

[0036] It should be noted that under certain ambient conditions, marbling and / or toothpick defects do not occur. This occurs, for example, if the ambient air is sufficiently humid (e.g. high humidity in the summer). This is because the ambient air is sucked in by the stripping gas ejected from the nozzle and rotates together with the stripping gas. However, the occurrence of such surface defects also depends on many other parameters (e.g. bath temperature). At low bath temperatures, the likelihood of the formation of surface defects also increases if the ambient air humidity is high. According to the invention, hot-dip galvanizing and blowing are largely unaffected by the currently existing, uncontrollable ambient conditions if it can be ensured that the stripping gas itself has an appropriate moisture content. In other words, hot-dip galvanizing and blowing can be more robustly protected against external influences.

[0037] All embodiments may have one or more of the following sensor arrays: - at least one sensor for determining the humidity of the surrounding air in the close proximity of the device, and / or - At least one sensor for determining the ambient air humidity in the area surrounding the device, such as a factory floor.

[0038] In addition, all embodiments include at least one device (for example, implemented as a hardware device) for determining the humidity or moisture content of the gas in or at the stripping nozzle device, so as to determine (for example, measure) the humidity of the gas in front of or at the stripping gas outlet (in the direction of the front side or rear side of the flat steel product).

[0039] Preferably, the means for determining the humidity or moisture content of the gas or sensors for these means are located in the gas supply line at a point in the flow direction after the dry gas flow and the water vapor gas flow are combined / mixed.

[0040] Alternatively, the means for determining the humidity or moisture content of the gas or a sensor of the device may be located in or at the gas nozzle.

[0041] In all embodiments, the means for determining the humidity or moisture content of the gas or the sensors of the device may be located in the gas supply line and in the gas nozzle.

[0042] In all or at least some embodiments, the method is characterized in that the ZnAlMg layer or the ZnAl layer is applied to both sides of the flat steel product by blowing according to target specifications by moving the flat steel product through a molten bath of a zinc alloy (ZnAl; ZnAlMg) and then, on its output side, discharging a stripping gas through the nozzle lip gap of at least one gas nozzle in the direction of the front side of the flat steel product and through the lip gap of at least one gas nozzle in the direction of the rear side of the flat steel product, thereby blowing off the layers on both sides according to target specifications.

[0043] The method for applying a ZnAlMg layer or a ZnAl layer to the front and rear sides of a flat steel product comprises the following steps: - moving the flat steel products from the input side to the output side of the zinc alloy molten bath, - Provide dry air flow, - Provides water vapor airflow, - combining the dry gas stream and the water vapor gas stream to obtain the stripping gas as a mixture, - determine the gas humidity or moisture content of the degassing gas, - discharge of the stripping gas through at least one gas nozzle for blowing off the front side and at least one gas nozzle for blowing off the rear side, so that the front side and the rear side of the flat steel product are blown off with the stripping gas, ○At least one of the following two conditions B1 and B2 is met: B1: The moisture content of the stripping gas (AG) or the proportion of gaseous water vapor (WG) is greater than 200 ppm and less than 43700 ppm, and the moisture content is preferably between 500 ppm and 9980 ppm, B2: The dew point (TP) of the stripped gas (AG) is higher than -39°C and lower than +30°C, wherein the dew point (TP) is preferably between -29°C and +7°C.

[0044] In order to prevent the occurrence of marbling and / or the formation of toothpick defects in the ZnAlMg layer or ZnAl layer to be produced, at least in some embodiments, the ambient air humidity in the area of ​​the device can also be optionally determined. Since the device or method draws in ambient air during the blowing process (as described above), the gas humidity (moisture content) of the stripping gas can be taken into account and the gas humidity (moisture content) of the stripping gas can be adjusted more accurately. For example, if the ambient air humidity is currently particularly low, the humidity of the stripping gas is generally very important in order to reliably prevent surface defects. Under "humid" ambient conditions, it is not always absolutely necessary to add water vapor to the stripping gas in order to reliably prevent the formation of marbling and / or toothpick defects.

[0045] At least in some embodiments, a water vapor device is used to provide a large flow of water vapor gas corresponding to the actual flow of the provided dry gas flow, and combine / mix it with the dry gas flow, thereby setting / adjusting the gas humidity (moisture content) of the removed gas. That is, in these embodiments, the flow of the water vapor gas flow is actively adjusted according to the actual flow of the provided dry gas flow (referred to as control or adjustment of the water vapor gas flow source).

[0046] In all embodiments, it can be assumed in a first approximation that the water vapor flow is negligibly small relative to the dry gas flow. Therefore, the dry gas flow rate does not actually change when water vapor is added. Therefore, adjustment of the dry gas flow rate is not absolutely necessary. However, in all embodiments, if the water vapor flow rate is increased, the dry gas flow rate can be reduced (and vice versa).

[0047] In another part of the embodiment, the humidity (moisture content) of the removed gas is set / adjusted by adjusting the flow rate of the dry gas flow and the flow rate of the water vapor gas flow. For example, this can be achieved by using adjustable gas valves in the dry gas supply device and the water vapor gas supply device. Alternatively, the output of the dry gas flow source and the water vapor gas flow source is controlled or adjusted.

[0048] In some embodiments, the gas humidity (moisture content) of the purge gas may be set / adjusted by a mixing valve that adjusts the flow of one or both gas streams in the region where the two gas streams are combined.

[0049] In at least some embodiments, the close range of the device is defined as 1 m 3 Up to 10m 3 The volume between.

[0050] In at least some embodiments, the perimeter of the device is defined as a volume greater than 10 m 3 .

[0051] In all embodiments, the device or the stripping nozzle system may include an automatic deposition control device that is adapted to automatically adjust the flow rate of the (stripping) gas to keep the target thickness of the layer to be deposited substantially constant. The automatic coating control device is preferably adapted to be able to compensate for fluctuations in one or more system parameters and method parameters.

[0052] In all embodiments or at least some embodiments, the range of inevitable impurities in the alloy is significantly less than 1 wt% (wt%), preferably the sum of all inevitable impurities is less than 0.5 wt%.

[0053] By combining a precisely defined bath composition with the monitoring and / or adjustment of the gas humidity (moisture content) of the stripping gas, a surface can be produced that is free of marbling or has negligible marbling and is free of toothpick defects or has negligible toothpick defects. During the production of each layer, the humidity (moisture content) of the stripping gas can be kept substantially constant or adjusted (e.g., when the humidity in the vicinity or perimeter of the device changes) to obtain a consistent layer (within a predetermined specification).

[0054] In all embodiments, a steel strip stabilizing device may optionally be provided after the stripping nozzle device for automatically stabilizing the movement of the flat steel product.

[0055] In all embodiments, the device preferably operates within the following ranges: - The melting bath temperature TB of the alloy melting bath is in the range of 400 < TB < 480 °C, preferably in the range of 409 < TB < 472 °C, and particularly preferably in the range of 410 < TB < 460 °C, - The distance between the nozzle and the flat steel product is between 2 and 15 mm, preferably between 3 and 12 mm, - The flat steel product on the outlet side of the alloy melting bath is purged with the (stripping) gas, and the gas flows through the nozzle lip gap and towards the flat steel product, and the gas flow rate ranges from 200 to 8000 Nm per hour per meter of the steel strip width 3 .

[0056] The technological process in the area of the stripping nozzle device and the flat steel product is very complex and depends on numerous (method and system) parameters and influencing variables. Therefore, the control or regulation of the device can be based on some simplified assumptions and specifications.

[0057] The preferred specifications of the ZnAl and ZnAlMg alloy concepts defined above, as well as the preferred specifications of the moisture content of the removed gas (for example, defined by a dew point between -39°C and +30°C, or a specification in ppm (such as between 200ppm and 43700ppm)) are derived after extensive research. Within the specified limits of the alloy concepts and moisture content according to conditions B1 and / or B2 as exemplarily defined herein, the technical teachings proposed herein have proven to be particularly successful.

[0058] In addition to the devices and methods described herein for controlling and regulating the moisture content of water vapor in the stripping gas, a cooling surface or cooling area may optionally be provided on or in the stripping nozzle device to provide a controlled area for condensation of excess water vapor in the event that condensation of excess water vapor still occurs after all measures have been taken. A water outlet may also be provided in this area to allow condensed water to be discharged from time to time. The temperature of the cooling surface or cooling area should always be below the current dew point temperature of the stripping gas.

[0059] However, means for condensing excess water vapor may also be used in the water vapor supply line.

[0060] In all embodiments, the flat steel product may be subjected to an annealing or tempering step at a temperature of about 765° C. (or lower or higher) prior to hot-dip galvanizing in a molten zinc alloy bath.

[0061] In all embodiments, the flat steel product may be cold rolled (eg, using smooth cold rolling rolls and / or using skin-pass rolls having a particular roughness) after hot-dip galvanizing.

[0062] In addition, in order to improve the flatness of the steel strip, the steel strip can be subjected to a flat rolling process or a separate online bending and stretching process.

[0063] In all embodiments, strip flat steel products, such as deep drawing steel, low carbon steel, structural steel, high strength steel grade steel, in each case in strip form, can be cleaned of rolling oil and rolling wear by a so-called pretreatment or pre-cleaning in a continuous hot dip galvanizing device by combined immersion / brushing / electrolytic cleaning, rinsing with water and drying. The cleaned and dried strip flat steel products then enter the annealing furnace of the continuous hot dip galvanizing line, where they are preheated, heated and brought to annealing temperature under an inert gas atmosphere. At the end of the annealing furnace, the strip flat steel products are cooled to the strip immersion temperature and immersed in a molten bath of zinc-magnesium-aluminum alloy. After leaving the molten bath, the strip flat steel products are adjusted to the target coating thickness at the stripping nozzle using a stripping gas according to the embodiments described herein and claimed for protection. In the subsequent cooling tower, the molten zinc alloy on the steel strip solidifies.

[0064] After the cooling tower, the strip flat product can be further rolled in-line in a skin pass mill (on a continuous hot dip galvanizing line) and a predetermined roughness is applied.

[0065] After an online inspection for surface defects (e.g., detection of surface defects such as marble or toothpick defects), the flat steel product can be coated with anticorrosion oil and forming oil in an oiler and finally wound onto a reel. After being wound onto a reel, the steel product in the form of a wound steel strip can be coated with a lacquer in a steel strip coating machine. Alternatively, after finishing by bending-stretching-straightening and / or chemical post-treatment, an organic / inorganic passivation layer is applied to the strip-shaped flat steel product by a coating machine (coating device) and then dried. The flat steel product 100 is then inspected for surface defects and, if no marble or toothpick defects are found, is wound onto a reel.

[0066] All embodiments may include a PC or other computer for automatically controlling or adjusting the moisture content of the purge gas and / or manually operating the purge gas to be within the dew point window.

[0067] Further advantageous embodiments of the invention form the subject matter of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Figure 1 A highly schematic diagram of a known device for coating and stripping flat steel products is shown (prior art); Figure 2 A highly schematic diagram of a first exemplary device for using the method according to the invention is shown, the stripping nozzle device comprising only one nozzle for blowing off the front side of a flat steel product; Figure 3 A highly schematic diagram of a second exemplary apparatus for using the method of the present invention is shown, the stripping nozzle apparatus comprising two nozzles, one for blowing off the front side and the other for blowing off the rear side of the flat steel product; Figure 4 A highly schematic diagram showing two gas nozzles facing each other; Figure 5 Contains tables with numerous examples. DETAILED DESCRIPTION

[0069] The moisture content of a gas can be described in different ways. Usually the dew point is specified in °C and the moisture content in g / m 3The mass fraction of water per volume of gas (also called absolute humidity) is specified in units of ppm (parts per million, also called ppmV), and the volume fraction is specified in units of ppm (parts per million, also called ppmV). The dew point describes the temperature at which water vapor begins to condense in a gas (here, the strip gas AG). When the dew point temperature is reached, the gas can no longer absorb any additional water vapor, i.e. the gas is saturated with water vapor. The term frost point can be used for temperatures below 0°C. However, we always use the term dew point (even at negative temperatures). The temperature of pure nitrogen used as strip gas AG for purging is usually 10 to 30°C. However, the nitrogen can also be heated before purging (for example, to a temperature in the range of 50 to 200°C). The heated strip gas AG can absorb more water vapor and therefore the dew point will be higher. The opposite is true for cold strip gas AG. In addition, the strip gas AG absorbs less water vapor at high pressure than at lower gas pressure. It should also be noted that condensation of water vapor usually occurs in pipelines and components of the gas delivery system (such as nozzles 15).

[0070] In the present invention, the moisture content of the removed gas AG is preferably determined by setting the minimum dew point TP min In all embodiments that rely on the addition of a small amount of water vapor WG to the stripping gas AG, the minimum dew point TP min The lowest dew point TP is -39℃. min = -29°C. In all embodiments, a maximum dew point TP can also be set max , i.e. +30°C (equivalent to about 43700 ppm of H2O in the degas AG). In order to avoid surface defects, the moisture content of the degas AG is adjusted in all these embodiments so that the dew point TP of the degas AG is always higher than TP min =-39°C or preferably TP min =-29°C. This means that the formula TP>TP min Applicable. In these embodiments, this specification means that we are not affected by ambient conditions (on a factory floor where device 150 is running, the temperature and humidity of the ambient air can fluctuate significantly depending on the climate and time of year).

[0071] In all embodiments, in order to prevent water from condensing in the removal nozzle device 14, in all embodiments, the formula TP = T AG -ΔT, specifies the temperature difference ΔT. The temperature difference ΔT is preferably at least 5° C., particularly preferably at least 10° C. In the formula, TP defines the current dew point in the purge gas stream AG and TAG defines the current temperature of the purge gas stream AG.

[0072] For example, by specifying a temperature difference ΔT, the following fact can be considered: when the pressure of the stripping gas AG increases, the condensation tendency of the water vapor component also increases. By specifying the temperature difference ΔT (which can be understood as a safety margin), it can be ensured that even if the pressure of the stripping gas AG increases slightly, no condensed water will be produced. The safety margin can also prevent condensation from occurring in the stripping gas AG due to fluctuations in the regulation of the metered water vapor gas.

[0073] In addition, in all embodiments, the maximum dew point of the stripping gas AG, i.e., TP, is specified. max = +30 °C (corresponding to approximately 43700 ppm H2O in the stripping gas AG). Preferably, the maximum dew point is TP max = +7 °C (sample number 74 in Table 1). For example, if the temperature T of the stripping gas AG is 18 °C, then the dew point TP value of the stripping gas AG should be set between -39 °C < TP < 18 °C, or preferably between -29 °C < TP < +7 °C.

[0074] If the optional safety margin ΔT of 10 °C described above is now additionally applied, then, for example, when the gas temperature T AG is 18 °C, the dew point TP of the stripping gas AG will be set to a value within the following range: -39 °C < TP < T AG - ΔT (T AG - ΔT = 18 °C - 10 °C = 8 °C) → -39 °C < TP < +8 °C, or preferably within the range of -29 °C < TP < +7 °C.

[0075] In addition to this, there is also a device 150 (for example, see Figure 2 ), which is suitable for applying a layer 10 (see Figure 4 ) to the front side V and the rear side R of the strip flat steel product 100. The components of the immersion bath 11 are not shown here (refer to Figure 1 , Figure 1 which shows exemplary components). The outlet side of the immersion bath 11 is identified by the letter A in Figure 2 . The flat steel product 100 moves vertically upward in the direction of arrow B. The stripping nozzle device 14 includes at least one gas nozzle 15 for blowing the front side V of the flat steel product 100 and at least one gas nozzle 15 for blowing the rear side R of the flat steel product 100. In Figure 2 , due to the relatively simple representation, the stripping nozzle device 14 only includes one gas nozzle 15 for blowing the front side V. The gas nozzle 15 for blowing the rear side R is correspondingly applicable. In the embodiment shown in Figure 3 , two stripping nozzle devices 14 are provided, which include nozzles 15 facing each other.

[0076] The flat steel product 100 is passed from the input side E through the zinc bath 11 to the output side A (see Figure 1 ) and blow it with (stripping) gas AG at the outlet side A via a stripping nozzle device 14, thereby producing a layer 10 on both sides V, R. The purpose of the stripping nozzle device 14 is to remove the excess (still liquid) zinc-magnesium-aluminum layer or zinc-aluminum layer (layer 10) on the flat steel product 100 with (stripping) gas AG in a controlled manner after the flat steel product 100 emerges from the molten bath 11.

[0077] Care must be taken to ensure that the layer 10 is produced to (predetermined) specifications (e.g., specifications defining target thickness or coating per side V, R), and that marbling and / or toothpick defects do not appear / occur. For example, some embodiments may be concerned with avoiding these "errors" when ambient conditions in the production area (e.g., a factory floor) change. Even if the ambient air humidity f UG Apparatus 150 and methods according to the present invention can also ensure that marbling and / or toothpick defects do not occur / appear and that layer 10 can continue to be produced according to specifications despite changes within the larger environment of apparatus 150 (e.g., a factory floor) or in close proximity.

[0078] In some embodiments, for example, the method and device 150 can also be used in the following manner: only when the ambient air humidity f UG When the temperature is too low, water vapor WG is added to the dry gas TG.

[0079] In at least some embodiments, the target surface coating (coating on each side of the steel strip) can be between 20 and 200 g / m 2 In the range of 30 to 160 g / m 2 within the range.

[0080] In all embodiments, the removal nozzle arrangement 14 comprises at least one gas nozzle 15 on each side V, R (e.g. two gas nozzles 15 facing each other, such as Figure 3 and Figure 4 shown).

[0081] The flow rate of the (removal) gas AG ejected through the nozzle lip gap 17 toward the front side V or the rear side R is expressed in Nm in this article. 3 Indicates (Nm 3 Stands for standard cubic meter). A standard cubic meter is the amount of degassing gas AG contained in a volume of one cubic meter. This applies to a temperature of 0 degrees Celsius and a pressure of 1.01325 bar.

[0082] The dry gas TG referred to herein is an inert gas having a dew point of approximately -70°C and below. This corresponds to a water vapor content of approximately 5 ppm and below. Therefore, the residual moisture content (also referred to as trace moisture) of the dry gas TG is very low and is within the range commonly found in industrial gases. In all embodiments, the dry gas TG used herein meets the requirements of the "Industrial Nitrogen Specification" (e.g. British Standard BS4366:1993). According to this standard, the moisture content of the gaseous nitrogen dry gas TG (see paragraph 8) is a maximum of 10 / 10 6 , which is equivalent to 10 ppm. Therefore, in all embodiments, the residual moisture content of the drying gas TG should be less than 10 ppm, preferably less than 5 ppm.

[0083] In all embodiments, the apparatus 150 includes a dry gas supply or dry gas source 18 (see Figure 2 ). For example, a gas tank, a gas cylinder or a gas pipeline (eg directly from a gas supplier or from an air separation unit operated according to the Linde process) can serve as gas source 18 .

[0084] In all embodiments, the device 150 may also include, for example, two drying gas supply devices or drying gas sources 18 (see Figure 3 ), wherein one drying gas source 18 is associated with each removal nozzle device 14. In all embodiments, the device 150 may also include a drying gas supply device or a drying gas source 18, for example, for supplying gas to two removal nozzle devices 14.

[0085] In all embodiments, the device 150 includes at least one water vapor device or water vapor source 50 (see Figure 2 ). For example, an evaporator or a gas humidifier (e.g., by ultrasonic atomization) can be used as the water vapor source 50. In all embodiments, the water vapor device or source 50 is fluidly connected to the gas nozzle 15, such as Figure 2 As shown. Figure 2 In the embodiment of the present invention, the water vapor source 50 is connected to the drying gas supply (pipeline) 21 via the water vapor supply (pipeline) 22. The two gas supply lines 21, 22 are fluidly connected to each other in the T-shaped area 19. The drying gas flow is indicated by arrows TG and the water vapor gas flow is indicated by arrows WG.

[0086] Preferably, in all embodiments, one or more steam generators are used as steam means or steam sources 50, which are high-purity steam generators adapted to generate gaseous steam WG or a water vapor gas stream WG from purified water or highly purified water.

[0087] In all embodiments, the water vapor device 50 preferably comprises a pure steam generator and, for example, a valve capable of regulating the water vapor gas flow WG through the conduit 22. For this purpose, in all embodiments, the high-purity steam generator and / or the valve can be connected to the controller of the device 150 and / or the device 20 or 26 for determining the humidity of the gas (not shown). In all embodiments, the water vapor gas flow WG can also come from a condensate recovery system.

[0088] In all embodiments, the device 150 may also include, for example, two water vapor devices or water vapor sources 50 (see Figure 3 ), wherein each water vapor source 50 is associated with a respective removal nozzle device 14.

[0089] In region 19 (see Figure 2 and Figure 3 ), the gas streams TG and WG converge and mix. The resulting mixed gas is referred to herein as stripping gas AG. The stripping gas AG flows from the region 19 through the gas nozzles 14 in the direction of the front side V or rear side R of the flat steel product 100. The stripping gas AG is discharged through the (gas) nozzle lip gap 17 of the respective gas nozzle 14, as in Figure 2 and Figure 3 It is represented by three parallel arrows.

[0090] In all embodiments, for example, in area 19 (see Figure 2 and Figure 3 ) is provided with a mixing chamber to mix the gases TG and WG.

[0091] In order to prevent the formation of marbling and / or toothpick defects, or to significantly reduce marbling and toothpick defects, in all embodiments, the air humidity f in the vicinity of the device 150 and / or in the surroundings may be continuously or occasionally measured. UG (eg by direct or indirect measurement), so that when the ambient conditions change, the moisture content of the degassing gas AG can be adjusted accordingly. However, such adjustment of the ambient conditions is optional.

[0092] Optionally, in all embodiments, a water vapor flow WG is provided to the purge gas AG only if the ambient conditions themselves are not sufficient (eg the ambient air is too dry) in order to avoid these errors.

[0093] In all embodiments, the device 150 may include at least one device 20 configured to determine the moisture content in the stripping nozzle device 14 and arranged accordingly. The device 20 is configured to determine the current moisture content of the stripping gas AG (e.g. in the form of a signal or measurement containing the current dew point TP and / or moisture content in ppm or absolute or relative humidity information). Figure 2In the embodiment shown, the device 20 comprises two sensors 23 and 24, both of which extend into the gas line 25. Figure 3 In the embodiment shown, the device 20 comprises a combined or integrated sensor 23 / 24 , each extending into a respective gas line 25 .

[0094] In all embodiments, additionally or alternatively, the moisture content of the exhaust gas AG can be determined before or during its outflow in the direction of the front side V and / or the rear side R of the flat steel product 100 .

[0095] For example, the sensor 23 may be a humidity sensor and the sensor 24 may be a temperature sensor. Both sensors 23, 24 are communicatively connected to a module 26 of the device 20 via lines KV3, KV4.

[0096] In all embodiments, a combined or integrated sensor may also be used to measure the moisture content and temperature T of the AG. AG . Figure 3 An embodiment is shown in which a combined or integrated sensor 23 / 24 is provided for each stripping nozzle arrangement 14. The corresponding communication line is referenced KV5.

[0097] In all embodiments, sensors can also be used to measure, for example, the pressure dew point, the absolute moisture content f and the temperature T of the gas AG AG .

[0098] Digital and / or analog sensors may be used in all embodiments.

[0099] In all embodiments, a dew point measuring device can also be used as device 20 .

[0100] Suitable humidity sensors include, for example, sensors based on the absorption of electromagnetic waves (microwave absorption sensors) or sensors that determine changes in the dielectric constant (capacitive sensors). One example is a polymer sensor, which is suitable for measuring the humidity of gases in the temperature range of interest here.

[0101] In all embodiments, sensors of the following designs or modes of operation can be used as humidity sensors: - Mechanical measuring sensors based on the expansion or contraction of a measuring element (usually an organic element) under the influence of humidity; - psychrometric measuring sensor, using two identical, very accurate thermometers, along which the airflow to be measured is directed at a defined speed; - a capacitive measuring sensor, for example comprising a humidity-sensitive capacitor with two flat electrodes; - resistance measurement, in which, for example, the alternating current resistance impedance of a hygroscopic element is determined; - Spectroscopic measurement methods that measure the gaseous water content in the near-infrared or mid-infrared (NIR or MIR) range, e.g. contact-free.

[0102] Instead of determining and regulating the water vapor content in the stripped gas AG by means of the dew point TP, in all embodiments, the moisture content in the stripped gas AG can also be determined and processed by measuring the volume fraction in ppm (also ppmV). For this purpose, a measuring cell with a humidity sensor (e.g., a sensor that absorbs moisture in the gas AG and then decomposes it electrolytically) can be used as part of the device 20. It should be noted that the relationship between the dew point temperature (° C.) and the volume fraction (ppm) is not linear, but exponential (see also equation (1)).

[0103] As shown in Table 1, the context of this article is based on the following estimates / approximations. Relative air humidity r can be used to express the ratio of the water content in a gas to the highest saturation the gas can reach. r = 100% humidity means that the gas can no longer absorb water vapor. When r = 100%, the gas is saturated with water vapor. If the temperature of the gas increases, the gas can absorb more water and the saturated vapor pressure of the gas increases. If the amount of water in the gas remains unchanged when the temperature increases, the value of relative humidity r decreases. The absolute humidity f of the gas (in g / m 3 ) and the absolute humidity of the surrounding air f UG It is also temperature-dependent. On the other hand, the dew point in ° C and the H2O volume fraction in ppm are independent of temperature and are applicable regardless of the gas type. Therefore, it is preferred to use the dew point in ° C and the H2O volume fraction in ppm to specify the moisture content of the degassing gas AG.

[0104] Table 1 (see Figure 5 ) are specifically applicable to the alloy compositions and process conditions specified in each case. Figure 5 ) contains the following columns from left to right: sample number; dew point TP of the removed gas AG, in °C (wherein the examples in Table 1 are sorted from low to high by dew point); volume fraction of water vapor H2O in the removed gas AG, in ppm; coating on each side (layer 10 of V and R on each side), in g / m 2; steel strip speed of the flat steel product 100 (parallel to the movement arrow B), in m / min; thickness of the nozzle lip gap 17, in mm (called nozzle opening height); horizontal distance between the nozzle and the steel strip (flat steel product 100), in mm; nozzle height, the vertical distance from the nozzle to the zinc bath surface, in mm; nozzle pressure, in mbar; bath temperature of the zinc bath 11, in ° C; zinc bath composition, specifying the ratio of aluminum and magnesium, in weight %; absolute humidity of the surrounding air f UG , unit is g / m 3 The two rightmost columns contain marbling information, where - Black dots indicate alloys / process examples where strong marbling was detected, - Grey dots represent alloy / process examples where mild to moderate marbling was observed, - White dots represent alloy / process examples where no marbling was detected.

[0105] From Table 1 (see Figure 5 ) can be seen that in many alloy / process examples, dry nitrogen is used as the degassing gas, resulting in sometimes severe marbling defects (specifically in the examples with sample numbers 1 to 43). If one looks at the second and third columns (from left to right) of the examples with sample numbers 1 to 43, the degassing gas AG is dry nitrogen with a dew point TP between -77°C and -72°C and a moisture content between 1.8 ppm and 3.8 ppm. Such nitrogen meets the requirements of the aforementioned British Standard with a residual moisture content of less than 10 ppm. As can be seen from the two rightmost columns, using such dry nitrogen as the degassing gas AG does not reliably and repeatably avoid marbling.

[0106] Strong marbling no longer occurs only in the examples with sample numbers 53 to 74. A significant reduction in strong marbling is achieved by adding a small proportion of water vapor WG of at least 208 ppm (sample number 53) and at most 9978 ppm (sample number 74) to the dry nitrogen TG. The dew point of the stripping gas AG of sample numbers 53 to 74 is between -390°C (sample number 53) and +70°C (sample number 74).

[0107] This leads to the following condition B1: The moisture content of the stripping gas AG or the proportion of gaseous water vapor WG should always be greater than 200 ppm and less than 43700 ppm. The lower limit of 200 ppm is based on the test results in Table 1 (208 ppm is rounded down to 200 ppm), and the upper limit of 43700 ppm is to ensure that there is no condensation of water around the stripping nozzle as mentioned above.

[0108] The following condition B2 can also be derived from this: the dew point TP of the degassing gas AG should always be higher than -39°C and lower than +30°C. The lower limit of -39°C comes from the test results shown in Table 1, and the upper limit of +30°C ensures that there is no condensation of water around the degassing nozzle.

[0109] Only in the examples with sample numbers 58 to 74 does marbling no longer occur at all (except sample number 59). A significant reduction in the strong marbling is achieved by adding a small proportion of water vapor WG of at least 552 ppm (sample number 58) and at most 9978 ppm (sample number 74) to the dry nitrogen TG. The dew point of the stripping gas AG of sample numbers 58 to 74 is between -29°C (sample number 58) and +7°C (sample number 74).

[0110] This leads to the following more preferred condition B1: The moisture content of the stripped gas AG, correspondingly the proportion of gaseous water vapor WG, should always be in the range from 500 ppm to 9980 ppm, wherein these ppm specification values ​​are rounded up or down.

[0111] This also leads to the following preferred condition B2: the dew point TP of the degassing gas AG should always be between -29°C and +7°C.

[0112] The specification values ​​of these conditions B1 and B2 are related to the temperature T of nitrogen as the drying gas TG and the degassing gas AG. AG It is related to temperature, which ranges from 10℃ to 30℃.

[0113] Therefore, for the conditions specified under B2, the respective dew point TP of the purge gas AG is lower than the current temperature T of the purge gas AG. AG This condition (TP <T AG ) is referred to as condition B2.1. The application advantage of condition B2.1 is that it is consistent with the temperature T of the removal gas AG. AG No. For example, if the temperature TAG of the purge gas AG is 27°C, the dew point TP of the purge gas AG must be lower than +27°C to satisfy condition B2.1.

[0114] The preferred condition B2.1 can also be defined as follows: the temperature T of the removal gas AG AG There should always be an optional safety margin ΔT between the dew point TP of the stripped gas AG as shown below: TP <T AG -ΔT. In all embodiments, the optional safety margin ΔT may be ΔT=10°C. In order to satisfy the preferred condition B2.1, if the temperature T of the stripping gas AG AG If the temperature is 27℃, the dew point TP of the removed gas AG should be lower than +17℃.

[0115] Changing the gas pressure and / or changing the temperature T of the removal gas AG AG , Condition B2.1 also applies.

[0116] An additional condition B3 may be defined, stipulating that the removed gas AG is a gas in an unsaturated state.

[0117] Changing the gas pressure and / or changing the temperature T of the removal gas AG AG , condition B3 also applies.

[0118] If conditions B1 and / or B2 and / or B2.1 regarding the removal of gas AG are met, then one is on the safe side with regard to marbling. Condition B3 is an additional condition that can be met in all embodiments in addition to conditions B1 and / or B2 and / or B2.1.

[0119] By complying with these conditions, the hot-dip galvanizing and blowing processes are stabilized. That is, the processes become more robust to ambient disturbance conditions, some of which cannot be influenced. In addition, the parameter window within which the method operates reliably is expanded.

[0120] In a series of tests and evaluation of process data, it has been shown that the humidity of the air around or in the immediate vicinity of the stripping nozzle has a significant influence on the occurrence of marbling defects. UG Here, the absolute air humidity f is used as a formula symbol for the absolute air humidity in the vicinity or in the immediate vicinity of the removal nozzle (also referred to as the ambient air humidity). UG It can be based on the surrounding or close air temperature T L And the relative air humidity r of the surrounding or close distance is estimated. The formula used here is as follows: rRelative humidity or air humidity in % f UG The humidity of the surrounding or nearby air T L The ambient or close air temperature in °C.

[0121] As mentioned above, the ambient or close air humidity f UG and / or air temperature T L The determination / measurement / monitoring of can be carried out directly or indirectly in all embodiments. The indirect measurement here mainly refers to the measurement of the air temperature T L and relative air humidity r, and from this calculate / derive the absolute local air humidity f UG .

[0122] In all embodiments, the current flow rate of the stripping gas AG can be automatically adjusted in a known manner (for example, by the automatic coating control of the device 150) so as to keep the target thickness or coating on each side of the layer 10 to be applied substantially constant when one or more system parameters and / or process parameters change. The supply of the water vapor flow WG must be adjusted accordingly to ensure that the stripping gas AG complies with the conditions B1, B2, B2.1, B3 of the invention with respect to the moisture content.

[0123] Figure 4 Also shown are the nozzle spacing (defined parallel to the y-axis) between the nozzle 15 and the respective strip side (front side V, rear side R) of the flat steel product 100, as well as the thickness (defined parallel to the x-axis) of the nozzle lip gap 17 (referred to as the nozzle opening height). The nozzle lip gap 17 is the gas outlet gap of the stripping nozzle arrangement 14. Figure 4 In FIG. 1 , the thickness of the flat steel product 100 and of the two layers 10 are exaggerated, so that in the spatial region X it is possible to schematically show the reduction in thickness of the steel layer 10 due to the blowing with the stripping gas AG.

[0124] The gas ejected from the nozzle 14 and the gravity (if the flat steel product 100 is pulled vertically upward out of the molten bath 11, such as Figure 2 and Figure 3 The liquid layer 10 is blown away by the removal gas AG, and the shear force reduces the thickness of the liquid layer 10.

[0125] The equations describing the dynamic flow behavior of the gas AG over the flat steel product 100 are very complex. This is due in particular to the fact that in the gas jet that flows out through the nozzle lip 17 of the nozzle 15, regions of laminar and turbulent flow form over the layer 10 of the flat steel product 100. In addition, the gas jet draws in ambient air, which rotates with the stripping gas AG (so if the ambient air humidity f UG(If the pressure drop is high, it may not be necessary to add the water vapor gas WG to the dry gas TG). For details, see the following publications: "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet", CV Tu, DH Wood, Experimental Thermal and Fluid Science, Vol. 13, No. 4, November 1996, pp. 364-373, and "Minimization of the N2 Dilution When Wiping in Air", M. Dubois, AISTech 2019-Proceedings of the Iron & Steel Conference, May 6-9, Association for Iron & Steel Technology, Warrendale, Pennsylvania, 2019, Pittsburgh, USA.

[0126] It is important that by combining the drying gas TG and the water vapor gas stream WG, the resulting purge gas stream AG contains a very small but sufficiently high amount of water vapor to avoid the formation of surface defects and errors in the layer 10. Furthermore, the water vapor in the purge gas stream AG must not be too high to prevent condensation and the formation of water droplets.

[0127] Further detailed investigations have shown that there is a correlation between the moisture content of the degassing gas AG and the occurrence of such surface defects and errors, where the (surrounding) air humidity f UG can also have an effect (if the surrounding air humidity is high enough, surface defects and errors may not appear in some cases). Figure 5 ), a summary of all parameter ranges or sample numbers that enable immersion and controlled blowing off of layer 10 without severe surface defects and errors is highlighted in light grey (sample numbers 53 to 74). Figure 5 ), a summary of all parameter ranges or sample numbers are highlighted in dark grey (sample numbers 58 to 74), which enable immersion coating and controlled blowing off of the layer 10 without surface defects and errors.

[0128] When operating the device 150, it is preferred in all embodiments to pay attention to the following points: the thickness of the nozzle lip gap 17 (referred to as the height of the nozzle opening) is between 0.5 and 5 mm, preferably between 0.6 and 2 mm, particularly preferably between 0.8 and 1.4 mm, and / or - Exhaust gas flow AG flow rate range from 200 to 8000 Nm per hour 3 , and / or - the nozzle distance of the nozzle 15 from the side V or R (nozzle-strip distance) is between 2 and 15 mm, preferably between 2.5 and 14.1 mm, and / or The strip speed of the steel strip 100 is between 50 and 200 m / min, preferably between 70 and 150 m / min.

[0129] Within these (value) ranges, the device 150 and the method operate particularly reliably.

[0130] In all embodiments, the corresponding gas nozzle 15 has a vertical Figure 2 , Figure 3 and Figure 4 The drawing plane (parallel to Figure 4 The effective nozzle width of the nozzle 15 preferably corresponds in all embodiments to at least the width of the strip-shaped flat steel product 100. In all embodiments, the width of the strip-shaped flat steel product 100 can be, for example, between 500 and 2500 mm, preferably between 800 and 1800 mm, and particularly preferably between 1159 mm and 1614 mm. For wider strip-shaped flat steel products 100, the effective nozzle width increases accordingly.

[0131] The vertical distance between the nozzle and the zinc bath surface can be varied. This distance is usually referred to as the nozzle height. The setting of this distance depends mainly on the speed of the steel strip and / or the zinc coating to be set. For example, in all embodiments, the nozzle height can be between 230 and 500 mm.

[0132] All embodiments of the apparatus 150 may include an optional controller 250, such as Figure 3 In all embodiments, the controller 250 may be adapted as a computerized automation and control unit and may include a human-machine interface, a computer and a database.

[0133] In all embodiments, the controller 250 , if present, can be connected to the means or device 20 for determining the humidity of the gas via communication links KV1 , KV2 .

[0134] In all embodiments, controller 250 may be part of an overall system controller for device 150 or may be connected to an overall system controller in all embodiments.

[0135] In all embodiments, the controller 250 (if present) may have one or more analog and / or digital inputs to obtain information about currently existing ambient conditions (e.g., current air temperature TL and / or the (absolute) air humidity f in the surrounding or near area UG ). Based on this information, the controller 250 can reduce or increase (or even shut down) the metering of the water vapor gas flow WG, so as to continue to produce a layer 10 with surface defects in the device 150.

[0136] In all embodiments, the controller 250 (if present) may include a communication link, allowing the controller 250 to reduce or increase the flow rate of the water vapor gas flow WG, and / or reduce or increase the flow rate of the dry gas flow TG. Alternatively, the controller 250 may also adjust the mixing valve of the confluence area 19 of the two gas flows TG and WG through the communication link according to the situation.

[0137] For example, if the ambient air humidity f UG Very low, the inhalation of dry ambient air can lead to marbling in the layer 10. At this point, the present invention can function by turning on or automatically increasing the moisture content in the purge gas AG.

[0138] First embodiment: In at least some embodiments, in the pretreatment of the continuous hot-dip galvanizing system, the rolling oil and rolling wear of the strip cold-rolled flat steel product 100 (i.e., the strip cold-rolled deep-drawing steel) are removed by immersion / brushing / electrolytic combined cleaning, and then rinsed and dried with water. The cleaned and dried strip flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, where it is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 820°C in a radiant tube furnace under a protective gas with a dew point of -40°C. At the end of the annealing furnace, the strip flat steel product 100 is cooled to a steel strip immersion temperature of 450°C, and immersed in a warm ZnMgAl alloy molten bath 11 of 430°C for 3 seconds. After leaving the molten bath 11 at the outlet side A, the strip flat steel product 100 is adjusted to a predetermined target layer thickness of ZM90 (V, R per side 45 g / m2) at the stripping nozzle 15 of the stripping nozzle device 14 using dry stripping gas AG with a dew point of minus 73°C or a H2O content of 3 ppm. 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (called the nozzle opening height) and is located at a horizontal distance of 6 mm from both sides of the strip flat steel 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. Then, the strip flat steel product 100 is rolled in a skin pass mill and embossed with a roughness of 1.4 μm. The surface defects are inspected, and after the surface defects (such as marble and toothpick defects) are determined, 1.0 g / m2 of V and R are applied to each side of the strip flat steel product 100 in an oiling machine. 2The strip is then coated with corrosion protection oil and forming oil and finally wound on a reel. In a further step, for example in a so-called inspection line, the strip-shaped flat steel product 100 can be unwound, defective areas can be separated, and the steel strip can then be wound again.

[0139] Second embodiment: As part of the online pretreatment of the continuous hot-dip galvanizing system, the rolling oil and rolling wear of the strip cold-rolled flat steel product 100 (i.e., the strip cold-rolled deep-drawing steel) are removed by immersion / brushing / electrolytic combined cleaning, and then rinsed and dried with water. The cleaned and dried strip flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, where it is preheated and heated by a direct-fired furnace (DFF) and reaches an annealing temperature of 820°C in a radiant tube furnace under a protective gas with a dew point of -40°C. At the end of the annealing furnace, the strip flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 450°C, and immersed in the warm ZnMgAl alloy bath 11 of 430°C for 3 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to a target layer thickness of ZM90 (45 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture with gaseous H2O vapor as described and claimed herein to a dew point of 310 ppm or -35°C). 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (nozzle opening height) and is located at a horizontal distance of 6 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. Then, the flat steel product 100 is rolled in a skin pass mill and embossed with a roughness Ra of 1.4 μm. After inspecting the surface defects and determining whether there is marble pattern, the flat steel product 100 is coated with an oiler at a temperature of 1.0 g / m per side. 2 Anticorrosion oil and forming oil are applied online (in a continuous hot-dip galvanizing system) and finally wound on a reel. In a further step, for example in a so-called inspection line, the strip-shaped flat steel product 100 can be unwound, defective areas separated, and the steel strip rewound.

[0140] Third embodiment: In the pretreatment process of the continuous hot-dip galvanizing system, the strip cold-rolled deep-drawing steel is cleaned online to remove rolling oil and rolling wear by immersion / brushing / electrolytic combined cleaning, and then rinsed with water and dried. The cleaned and dried strip flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 820°C in a radiation tube furnace under a protective gas with a dew point of -40°C. At the end of the annealing furnace, the strip flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 450°C, and is immersed in the ZnMgAl alloy bath 11 of 430°C for 3 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to a target layer thickness of ZM90 (45 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture with gaseous H2O vapor, to a dew point of 552 ppm or -29°C). 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (nozzle opening height) and is located at a horizontal distance of 6 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. Then, the flat steel product 100 is rolled in a skin pass mill and embossed with a roughness of 1.4 μm. After the surface defects are inspected (no marble or toothpick defects are found during the inspection), the flat steel product 100 is coated with an oiler at a temperature of 1.0 g / m per side. 2 The wire is coated with anti-corrosion oil and molding oil and finally wound on a reel.

[0141] Fourth embodiment: In the pretreatment process of the continuous hot-dip galvanizing system, the rolling oil and rolling wear of the strip-shaped high-strength cold-rolled flat steel product 100 are cleaned by immersion / brushing / electrolytic combined cleaning, and then rinsed with water and dried. The flat steel product 100 after cleaning and drying enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 800°C in a radiant tube furnace under a protective gas with a dew point of -50°C. At the end of the annealing furnace, the strip-shaped flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 490°C, and is immersed in the warm ZnMgAl alloy bath 11 of 430°C for 5 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to a target layer thickness of ZM90 (45 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture with gaseous H2O vapor, to a dew point of 3065 ppm or -9°C). 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (nozzle opening height) and is located at a horizontal distance of 7.6 mm on both sides of the flat steel product 100 (parallel to Figure 4At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. Then, the flat steel product 100 is rolled in a skin pass mill and embossed with a roughness of 1.3 μm. After the surface defects are inspected (no marble or toothpick defects are found during the inspection), the flat steel product 100 is coated with an oiler at 0.8 g / m per side. 2 The wire is coated with anti-corrosion oil and molding oil and finally wound on a reel.

[0142] Fifth embodiment Example: During the pretreatment process of the continuous hot-dip galvanizing system, the structural steel as the strip-shaped cold-rolled flat steel product 100 is cleaned by immersion / brushing / electrolytic combined cleaning to remove rolling oil and rolling wear, and then rinsed with water and dried. The cleaned and dried flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 730° C. in a radiant tube furnace under a protective gas with a dew point of -45° C. At the end of the annealing furnace, the strip-shaped flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 465° C., and is immersed in the warm ZnMgAl alloy bath 11 of 455° C. for 4 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to the target layer thickness of ZM120 (60 g / m per side) at the stripping nozzle 15 using dry nitrogen (without admixture of gaseous H2O vapor; 3 ppm or -75°C dew point). 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (referred to as the nozzle opening height) and is located at a horizontal distance of 7.7 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. The flat steel product 100 is then flattened in a bending-stretching-straightening machine, then rolled in a skin-pass mill and embossed with a roughness of 1.4 μm. After inspection for surface defects (no marbling or toothpick defects were found during the inspection), the flat steel product 100 is wound on a reel. The steel strip 100 is then painted in a continuous strip coating system.

[0143] Sixth embodiment example: During the pretreatment process of the continuous hot-dip galvanizing system, the structural steel as the strip-shaped cold-rolled flat steel product 100 is cleaned by immersion / brushing / electrolytic combined cleaning to remove rolling oil and rolling wear, and then rinsed with water and dried. The cleaned and dried strip flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, where it is preheated and heated by a direct-fired furnace (DFF) and reaches an annealing temperature of 730° C. in a radiant tube furnace under a protective gas with a dew point of -45° C. At the end of the annealing furnace, the strip flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 465° C., and is immersed in the warm ZnMgAl alloy bath 11 of 455° C. for 4 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to the target layer thickness of ZM120 (60 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture with gaseous H2O vapor, to a dew point of 1470 ppm or -18°C). 2 The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (referred to as the nozzle opening height) and is located at a horizontal distance of 7.7 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. The flat steel product 100 is then flattened in a bending-stretching-straightening machine, then re-rolled in a skin-passing mill and embossed with a roughness of 1.4 μm. After inspection for surface defects (no marbling or toothpick defects were found during the inspection), the flat steel product 100 is wound on a reel. The steel strip 100 is then painted in a continuous strip coating system.

[0144] Seventh embodiment: During the pretreatment process of the continuous hot-dip galvanizing system, the structural steel as the strip-shaped cold-rolled flat steel product 100 is cleaned by immersion / brushing / electrolytic combined cleaning to remove rolling oil and rolling wear, and then rinsed with water and dried. The cleaned and dried flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 730°C in a radiant tube furnace under a protective gas with a dew point of -45°C. At the end of the annealing furnace, the strip-shaped flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 465°C, and is immersed in the warm ZnMgAl alloy bath 11 of 455°C for 4 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to the target layer thickness of ZM120 (60 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture with gaseous H2O vapor, to a dew point of 5230 ppm or -2°C). 2The nozzle lip gap of the stripping nozzle 15 is 1.0 mm (nozzle opening height) and is located at a horizontal distance of 7.7 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. The flat steel product 100 is then flattened in a bending-stretching-straightening machine, then rolled in a skin-passing mill and embossed with a roughness of 1.4 μm. After inspection for surface defects (no marbling or toothpick defects were found during the inspection), the steel strip 100 is wound on a reel. The steel strip 100 is then painted in a continuous steel strip coating system.

[0145] Eighth embodiment example: During the pretreatment process of the continuous hot-dip galvanizing system, the low-carbon steel as the strip-shaped cold-rolled flat steel product 100 is cleaned by immersion / brushing / electrolytic combined cleaning to remove rolling oil and rolling wear, and then rinsed with water and dried. The cleaned and dried strip flat steel product 100 enters the annealing furnace of the continuous hot-dip galvanizing system, where it is preheated and heated by a direct-fired furnace (DFF) and reaches an annealing temperature of 720° C. in a radiant tube furnace under a protective gas with a dew point of -50° C. At the end of the annealing furnace, the strip flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 460° C., and immersed in the warm ZnMgAl alloy bath 11 of 455° C. for 3 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to a target layer thickness of ZM90 (45 g / m per side) at the stripping nozzle 15 using dry nitrogen (without admixture of gaseous H2O vapor; 3 ppm or -74°C dew point). 2 The nozzle lip gap of the stripping nozzle 15 is 1.2 mm (referred to as the nozzle opening height) and is located at a horizontal distance of 10 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. The flat steel product 100 is then flattened in a bending-stretching-straightening machine, then rolled in a skin-passing mill and embossed with a roughness of 1.0 μm. As part of an inline chemical post-treatment, a coater (coating device) applies an organic / inorganic passivation layer and dries. After an inspection for surface defects (marbling or toothpick defects are found during the inspection), the steel strip 100 is wound on a reel. In a further step, for example in a so-called inspection line, the strip-shaped flat steel product 100 can be unwound, defective areas separated, and the steel strip wound again.

[0146] Ninth embodiment example: During the pretreatment process of the continuous hot-dip galvanizing system, the low-carbon steel as the strip-shaped cold-rolled flat steel product 100 is cleaned by immersion / brushing / electrolytic combined cleaning to remove rolling oil and rolling wear, and then rinsed with water and dried. The flat steel product 100 after cleaning and drying enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated and heated by a direct-fired furnace (DFF), and reaches an annealing temperature of 760° C. in a radiant tube furnace under a protective gas with a dew point of -50° C. At the end of the annealing furnace, the strip-shaped flat steel product 100 is cooled to the steel strip immersion temperature of the ZnMgAl alloy molten bath 11 of 460° C., and is immersed in the warm ZnMgAl alloy bath 11 of 455° C. for 4 seconds. After leaving the molten bath in the outlet zone A, the strip flat steel product 100 is adjusted to the target layer thickness of ZM120 (60 g / m per side) at the stripping nozzle 15 using humidified nitrogen (after admixture of gaseous H2O vapor to 9980 ppm or a dew point of +7°C). 2 The nozzle lip gap of the stripping nozzle 15 is 1.2 mm (referred to as the nozzle opening height) and is located at a horizontal distance of 10 mm on both sides of the flat steel product 100 (parallel to Figure 4 At the connected cooling tower 16 (see Figure 1 ), the zinc alloy melt solidifies on the flat steel product 100. The flat steel product 100 is then flattened in a bending-stretching-straightening machine. After inspection for surface defects (no marbling or toothpick defects were found during the inspection), the steel strip 100 is wound on a reel. The steel strip 100 is then painted in a continuous steel strip coating system.

[0147] Reference numerals:

Claims

1. A device (150) for applying a ZnAlMg layer or a ZnAl layer (10) to a flat steel product (100), the device comprising: - a zinc alloy molten bath (11) having an input side (E) and an outlet side (A), - a drying gas supply device (18) configured to provide a drying gas flow (TG), - a water vapor device (50) configured to provide water vapor (WG), - a device (20) for determining the humidity and / or water content of a gas, a stripping nozzle device (14) fluidly connected to a gas supply device (18) and a water vapor device (50) so as to supply a stripping gas (AG) to the stripping nozzle device (14), the stripping gas (AG) being a mixture of a dry gas stream (TG) and gaseous water vapor (WG), wherein the stripping nozzle arrangement (14) comprising at least one gas nozzle (15) for blowing the front side (V) of the flat steel product (100) with stripping gas (AG), and at least one gas nozzle (15) for blowing the rear side (R) of the flat steel product (100) with stripping gas (AG), The gas nozzle (15) is arranged in the area of ​​the outlet side (A) of the zinc alloy molten bath (11), The device (20) for determining the gas humidity and / or moisture content is arranged in or at the stripping nozzle device (14) so ​​that the gas humidity is determined before or during the outflow of the stripping gas (AG) in the direction of the front side (V) or the rear side (R) of the flat steel product (100), and at least one of the following two conditions B1, B2 is met: B1: The moisture content of the removed gas (AG) or the proportion of gaseous water vapor (WG) is greater than 200 ppm and less than 43700 ppm, wherein the moisture content is preferably between 500 ppm and 9980 ppm, B2: The dew point (TP) of the stripped gas (AG) is higher than -39°C and lower than +30°C, wherein the dew point (TP) is preferably between -29°C and +7°C.

2. The device (150) according to claim 1, wherein the ratio of the dry gas flow (TG) and the water vapor (WG) used to mix the stripping gas (AG) is adjusted so that the current dew point (TP) obtained in the stripping gas (AG) is lower than the temperature (T AG ) to avoid water condensation in the removal nozzle device (14).

3. The device (150) as claimed in claim 1 or 2, wherein according to the formula TP <T AG -ΔT, providing a temperature difference ΔT of at least 5°C, preferably at least 10°C, where TP defines the current dew point in the stripping gas stream (AG), T AG Defines the current temperature of the aeration gas stream (AG).

4. The device (150) according to claim 1 or 2, characterized in that The dew point (TP) defined by the degassing gas (AG) is higher than -39°C and lower than +30°C, wherein if the temperature T of the degassing gas stream (AG) AG Between 10 and 30°C, the dew point (TP) is preferably within the parameter range of -29°C to +7°C.

5. The device (150) according to any one of claims 1 to 3, comprising: - a temperature sensor (24) for measuring the current temperature (TAG) of the stripping gas flow (AG), a controller for the dry gas flow (18) and / or the water vapor flow (WG) to control the ratio of the dry gas flow (TG) and the water vapor (WG) for mixing the stripped gas (AG) so that the dew point (TP) in the stripped gas flow (AG) is lower than the current temperature (T AG ) to avoid condensation of water in the stripping nozzle device (14).

6. The device (150) according to any one of claims 1 to 5, wherein it is specified that even if the temperature of the removed gas exceeds 30°C, the maximum dew point of the removed gas flow can only be +30°C.

7. The device (150) according to any one of claims 1 to 6, wherein the drying gas (TG) is nitrogen, the volume fraction of water vapor (WG) of which is less than 5 ppm, or the dew point (TP) is lower than -70°C.

8. A method for applying a ZnAlMg layer or a ZnAl layer (10) to the front side (V) and the rear side (R) of a flat steel product (100), the method comprising the following steps: - moving the flat steel product (100) from the input side (E) to the output side (A) of the zinc alloy molten bath (11), - provide a dry air flow (TG), - Provide water vapor (WG), - combining the dry gas stream (TG) and the water vapour (WG) to obtain the stripping gas (AG) as a mixture, - determination of the gas humidity of the absorptive gas (AG), - discharging a stripping gas (AG) through at least one gas nozzle (15) for blowing off the front side (V) and at least one gas nozzle (15) for blowing off the rear side (R), thereby blowing off the front side (V) and the rear side (R) of the flat steel product (100) with the stripping gas (AG), ○ The discharged stripping gas flow (AG) satisfies at least one of the following two conditions B1 and B2: B1: The moisture content of the removed gas (AG) or the proportion of gaseous water vapor (WG) is greater than 200 ppm and less than 43700 ppm, wherein the moisture content is preferably between 500 ppm and 9980 ppm, B2: The dew point (TP) of the stripped gas (AG) is higher than -39°C and lower than +30°C, wherein the dew point (TP) is preferably between -29°C and +7°C.

9. The method according to claim 8, wherein the ratio of the dry gas flow (TG) and the water vapor (WG) in the stripped gas (AG) is adjusted so that the current dew point (TP) obtained in the stripped gas (AG) is lower than the temperature (T AG ) to avoid water condensation in the removal nozzle device (14).

10. The method according to claim 8 or 9, characterized in that The moisture content of the stripping gas stream (AG) is defined by a dew point (TP) above -39°C and below +30°C, wherein if the temperature T of the stripping gas stream (AG) is AG Between 10 and 30°C, the dew point (TP) is preferably in the range of -29°C to +7°C.

11. The method according to any one of claims 8 to 10, characterized in that Only around the outlet side (A) of the zinc alloy molten bath (11) or in the close distance, the absolute humidity (f UG ) is lower than the predetermined limit, the addition of gaseous water vapor (WG) is carried out.

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