Apparatus, method, and apparatus for moisture-controlled blow-off after application of a layer to a flat steel product

Abstract

An apparatus (150) and method for applying a ZnAlMg layer or a ZnAl layer to the front side (V) and the back side (R) of a flat steel product (100), - moving the flat steel product (100) from the inlet side (E) to the outlet side (A) of a zinc alloy melting bath (11); - providing a dry gas stream (TG); - providing a water vapor gas (WG); - mixing the dry gas stream (TG) and the water vapor gas (WG) to obtain a stripping gas (AG) as a mixture; - determining the gas humidity of the stripping gas (AG); - discharging the stripping gas (AG) through at least one gas nozzle (15) provided to blow off the front side (V) and at least one gas nozzle (15) provided to blow off the back side (R) to blow off the front side (V) and the back side (R) of the flat steel product (100); comprising · the following two conditions B1, B2, namely, B1: the stripping gas (AG) has a moisture content greater than 200 ppm and less than 43700 ppm, or a proportion of gaseous water vapor gas (WG), preferably the moisture content is in the range from 500 ppm to 9980 ppm; B2: the stripping gas (AG) has a dew point (TP) higher than -39 °C and lower than +30 °C, preferably the dew point (TP) is in the range between -29 °C and +7 °C An apparatus (150) and method in which a stripping gas stream (AG) satisfying at least one of the above is discharged.

Description

Technical Field

[0001] The present invention relates to an apparatus in which flat steel products can be coated in a melting bath, for example as a protective coating, with a layer based on zinc (Zn) or zinc - aluminum - magnesium (ZnAlMg) and can be blown off in a controlled manner on the outlet side of the melting bath. The present invention also relates to a corresponding method.

Background Art

[0002] It is well known that flat steel products 100 such as steel strips or steel plates are coated with zinc (Zn) or a ZnAlMg alloy in order to improve their corrosion resistance. In fact, this is usually done by introducing the flat steel product 100 coming from a furnace into a zinc alloy melting bath 11 using an exemplary apparatus 150 as shown in FIG. 1. To protect the flat steel product 100 from oxidation, the flat steel product 100 is typically introduced into the bath 11 through a trunk 12 with an inert atmosphere at the input side E. In the bath 11, the flat steel product 100 is deflected by a (zinc bath) roller 13 and is moved upward out of the bath 11 at the outlet side A. When the flat steel product 100 emerges from this bath 11, the molten alloy film adhering to the front and back sides of the flat steel product 100 is stripped by a gas jet from a gas nozzle 15 of a peeling nozzle device to the desired thickness (in the micron range) or to the desired surface coating (in g / m 2 ), and then the flat steel product 100 is transferred to a cooling area 16. This continuous method is generally referred to as hot - dip galvanizing.

[0003] Details of suitable methods and in particular of suitable alloy compositions can be found, for example, in the published application WO2014 / 033153A1 of the applicant VOESTALPINE STAHL GMBH.

[0004] The flat steel product 100 can subsequently be rolled by undergoing a quenching and tempering rolling process step and / or a bending - stretching process. The flat steel product 100 may be chemically post - treated. The flat steel product 100 (for example, in the form of a steel strip) for the automotive industry can be further processed, for example, by oil treatment. The oil treatment can be carried out, for example, using an oil treatment machine.

[0005] The just - hot - dip - galvanized flat steel product 100 may exhibit surface defects or malfunctions depending on the alloy composition and specific process control. On the other hand, zinc vapor may occur above the immersion bath 11 in the zinc melting bath, which may have an adverse effect on the surface of the hot - dip - galvanized flat steel product 100. On the other hand, the blowing - off process at the outlet side A of the melting bath 11 also affects the surface quality.

[0006] The patent EP0172682B1 of Armco Inc. filed in 1985 addresses the reduction or elimination of oxygen and the control of zinc vapor associated with the hot - dip galvanizing of an iron - based metal strip around the peeling nozzle and in the area of the steel strip exiting the zinc bath. Instead of the ambient air that normally exists in the enclosed area where the peeling nozzle is also positioned at the outlet side of the immersion bath, a reduced - oxygen atmosphere is provided. Since zinc evaporates violently in this atmosphere, a small amount of water vapor must be added to the reduced - oxygen atmosphere. The enclosed area is positioned immediately above the surface of the melting bath, thus forming a sealed and enclosed space. The reduced - oxygen atmosphere in this space is intended to improve the peeling process, and a small proportion of water is intended to prevent the formation of zinc vapor at the surface of the immersion bath. The moisture content in the sealed and enclosed space is adjusted so that zinc vapor cannot occur.

[0007] An apparatus adapted to adjust the layer thickness when galvanizing a steel strip is known from the published application DE2033847. A nozzle with a wide slot is used to blow air, gas, or steam onto the zinc-coated strip for the purpose of peeling. The nozzle slot is larger in the edge region of the strip compared to the central region of the strip to account for the fact that the strip may have a curved shape at the exit side of the bath.

[0008] An apparatus using wet steam in the form of steam jets for peeling has been known for over 50 years from the published application DE1521405A1 from National Steel. The use of wet steam results in rapid cooling of the steel strip after hot-dip galvanizing, and the blown wet steam solidifies the coating within a short period of time. It has been proposed to use a condensation device adapted to supply wet steam at a desired temperature and a desired pressure.

[0009] In Japanese Patent Application Laid-Open No. 2020100886, a published patent application of Nippon Steel Corporation, the object is to produce a galvanized steel strip having a surface with an increased coefficient of friction. To increase the coefficient of friction, water is sprayed onto the surface of the flat steel material under pressure after gas spraying. The particle size of the water droplets should be at least 0.07 mm and preferably larger than 1.5 mm. By spraying the water droplets, irregularities are intentionally created on the surface of the steel strip. Since this document pursues different objectives, the corresponding technical teachings are moving in a completely different direction from the present invention.

[0010] In addition to avoiding surface defects and malfunctions and protecting against corrosion, there are always stricter requirements in terms of the surface quality of flat steel materials generally coated with Zn, specifically flat steel materials coated with ZnAlMg. Specifically, the automotive industry expects products that meet the highest surface requirements. However, providing a homogeneous surface is no small matter.

[0011] Here, the main problem is often surface defects in the ZnAlMg layer. For example, defects such as marbling, "toothpick" or "beach pattern" may occur in the ZnAlMg layer, or slag formation may occur. There are patents (e.g., EP20130826634 AM / J.M.Mataigne; JP20080256208 NSSMC / Oohashi et al.) that attempt to eliminate similar surface defects (gross effect or displaced oxide film) by means other than the present invention (reduction of the O2 content around the peeling nozzle).

[0012] Similar surface defects can also occur under certain circumstances with a Zn layer containing a certain proportion of Al (for example, a proportion of Al that can be less than 1 wt.%).

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Non-Patent Documents

[0014]

Non-Patent Document 1

[0015] Therefore, the problem is to provide an apparatus and a method for coating flat steel materials with a ZnAlMg layer or a ZnAl layer that has particularly high durability and a robust protective effect from the perspective of corrosion, and the surface of the protective coating should be particularly homogeneous, without marbling (without the "marble effect") and / or without toothpick defects (without "toothpick"). The aim is to achieve a surface quality that meets the highest customer requirements.

[0016] In addition, the apparatus and method should consume as little energy as possible, be cost - effective to operate, and be robust in use. [Means for Solving the Problems]

[0017] According to the present invention, there is provided a corresponding apparatus for providing a ZnAlMg layer or a ZnAl layer of a metal, which can be used, for example, as a (protective) coating, on a flat steel material using a continuous (melting) process. This layer is intended to protect both sides of the steel substrate of the flat steel material from external influences. In the following, the corresponding immersion bath is referred to as a zinc alloy melting bath (or a short-time zinc melting bath), and the term zinc alloy melting bath is intended to include both a melting bath mainly containing a mixture of zinc (Zn) and a little aluminum (Al) (for example, less than 1% by weight) and a melting bath containing a ZnAlMg alloy. The layer applied on both sides is also referred to herein as a Zn-containing (protective) layer.

[0018] An apparatus for applying a ZnAlMg layer or a ZnAl layer to a flat steel material has been proposed. In all embodiments, this apparatus - comprises a zinc alloy melting bath having an inlet side and an outlet side, - a gas supply unit configured to provide a drying gas, - a steam device configured to provide gaseous steam, - means (for example, an apparatus) for determining the gas humidity (or moisture content), - a stripping nozzle device fluidly connected to the gas supply unit and the steam device so that a stripping gas as a mixture of the drying gas and the gaseous steam is supplied, and · The stripping nozzle device comprises at least one gas nozzle for blowing off the front side of the flat steel material with the stripping gas and at least one gas nozzle for blowing off the back side of the flat steel material with the stripping gas, · The gas nozzle is arranged in the region of the outlet side of the zinc alloy melting bath, · The means for determining the gas humidity (or moisture content) is arranged in the stripping nozzle device to determine the moisture content of the stripping gas (for example, by measurement) before or when the stripping gas exits in the direction of the front side or the back side of the flat steel material, · The following two conditions B1, B2, namely, B1: The stripping gas (AG) has a water content greater than 200 ppm and less than 43700 ppm, or a proportion of gaseous water vapor (WG), and preferably, the water content is in the range from 500 ppm to 9980 ppm. B2: The stripping gas (AG) has a dew point (TP) higher than -39°C and lower than +30°C, and preferably, the dew point (TP) is in the range between -29°C and +7°C. At least one of the above is satisfied.

[0019] The water content of the stripping gas for at least some of the embodiments of the device and the corresponding method can be determined by a volume fraction in the range from 200 ppm to 43700 ppm (referred to herein as condition B1). Preferably, the volume fraction for at least some of the embodiments is in the range from 500 ppm to 9980 ppm.

[0020] The water content of the stripping gas for at least some of the embodiments of the device and the corresponding method can be determined by a dew point greater than -39°C and less than +30°C (referred to herein as condition B2). Preferably, the dew point of the stripping gas is in the parameter range from -29°C to +7°C for at least some of the embodiments.

[0021] It should be noted that a largely overlapping region is defined by the conditions of B1 and B2. Only the boundary values may deviate due to rounding.

[0022] Alternatively, for at least some of the embodiments of the apparatus and corresponding method, the moisture content of the stripping gas may be defined using a mixture of a dry gas and gaseous water vapor that is always controlled and modified to be unsaturated (thereby also satisfying condition B1 and / or B with this alternative approach). The unsaturated stripping gas always contains water only in the gas phase. In other words, a stripping gas is used in which the proportion (moisture content) of gaseous water vapor is kept low so that the stripping gas is unsaturated with respect to its water vapor content. This means that the current dew point of the stripping gas is always lower than the current temperature of the stripping gas. This description of the unsaturated state also applies at varying gas pressures and / or varying temperatures of the stripping gas.

[0023] The unsaturated stripping gas can be defined for all embodiments by the fact that it is considered unsaturated as long as it contains only superheated water vapor. In the unsaturated state, the stripping gas is a homogeneous single-phase mixture containing only the gas phase (no solids or liquids). In the unsaturated state, the stripping gas has a relative humidity of less than 100%.

[0024] When the stripping gas released by the stripping nozzle mixes with the ambient gas (or ambient air) in the region around the stripping nozzle, a dew point upper limit of +30 °C is defined for the moisture content of the stripping gas to avoid condensation of water, which corresponds to a volume fraction of water of 43700 ppm in the stripping gas.

[0025] The corresponding method and apparatus are based on a controlled specification of the water content required at the point of impact of the peeling jet in the flat steel, in such a way that marbling and / or toothpick defects are avoided. In other words, there must always be enough water content in the peeling gas to enable peeling to take place without the formation of marbling and / or toothpick defects. However, at the same time, as described above, the formation of condensed water must be avoided. These two boundary conditions or configuration conditions, in addition to conditions B1 and / or B2, result in a parameter window that is preferably adhered to in all embodiments.

[0026] Preferably, in the apparatus and the corresponding method, the water content, i.e., the water vapor content, is controlled by monitoring the current dew point of the peeling gas and maintaining it within a suitably pre-defined parameter window (condition B2). In this way, the formation of condensed water can be prevented and peeling can be carried out without touching on defects. Condensed water can have an adverse effect on the peeling process and the surface quality of the zinc-plated strip.

[0027] In all embodiments, the control or control device of the apparatus can implement a moisture adjustment protocol in order to be able to react in a suitable manner to changes in the current water content and to ensure compliance with conditions B1 and / or B2.

[0028] In all embodiments, the required water content is provided directly via the peeling gas. In other words, the peeling gas serves herein as a carrier or transport medium for the very small amount of water vapor required.

[0029] In all embodiments, preferably a water vapor gas stream is introduced into the dry peeling gas, herein referred to as the dry gas stream, in order to mix the dry gas and the water vapor gas stream from the gas supply pipe to the peeling nozzle.

[0030] Preferably, in all embodiments, the dry gas stream comprises or consists of nitrogen. In all embodiments, the dry gas stream may comprise other inert gases instead of nitrogen.

[0031] In all embodiments, the moisture content of the stripping gas can be measured, and in further possible embodiments also adjusted, by a humidity sensor (e.g., a thermal or capacitive dew point sensor) arranged between the feed position for the gaseous water vapor and the nozzle opening of the stripping nozzle.

[0032] It is an advantage of this method or the corresponding apparatus that marbling and / or toothpick defects can be effectively avoided without constructing or installing additional and destructive devices immediately above the zinc bath or in the region above the zinc bath in the immediate vicinity of the stripping nozzle (e.g., the housing or enclosure (V08-0015P-EP / P219205 / VA23004) according to the applicant's European patent application EP22182309.9). Access to the stripping nozzle and the zinc bath surface for regular cleaning operations, which is necessary for precise process control, remains possible.

[0033] Furthermore, the process is very efficient in terms of media consumption compared to the process which is the subject of the aforementioned European patent application EP22182309.9, since only a part of the amount of water vapor is consumed to avoid marbling and / or toothpick defects.

[0034] All embodiments involve the application of a Zn-containing (protective) layer to flat steel, and the thickness of this layer is intended to correspond to the target thickness (in accordance with the corresponding specifications). This layer is produced by passing the flat steel through a zinc alloy melting bath and blowing off the flat steel on the outlet side of the bath with a controlled "wet" stripping gas using a stripping nozzle device with at least one gas nozzle for each side of the flat steel.

[0035] In all embodiments, the zinc alloy of the zinc alloy melting bath has the following composition, namely, - An aluminum content in the range of from 1.0 percent to 3.0 percent by weight, preferably in the range of from 1.3 percent to 2.8 percent by weight, - A magnesium content in the range of from 1.0 percent to 2.5 percent by weight, preferably in the range of from 1.2 percent to 2.2 percent by weight, and, - Zinc of the remainder of the zinc alloy plating bath and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, wherein the content regarding the weight of each additional element in the metal coating is less than 0.1% and unavoidable impurities can preferably be had, but is not limited to those compositions.

[0036] In all embodiments, the zinc alloy of the zinc alloy plating bath can preferably have the following composition, i.e., but is not limited to those compositions. - An aluminum content of less than 1.0 percent by weight, preferably in the range of from 0.1 percent to 0.5 percent by weight, and, - Zinc of the remainder of the zinc alloy plating bath and unavoidable impurities can preferably be had, but is not limited to those compositions.

[0037] Preferably, the following definitions, i.e., - The thickness of the nozzle lip gap (referred to as the height of the nozzle opening) of both nozzles is in the range of from 0.5 mm to 5 mm, preferably in the range of from 0.6 mm to 2 mm, particularly preferably in the range of from 0.8 mm to 1.5 mm, - The effective flow rate (D) of the peeling gas across the width of the strip is in the range of from 200 Nm 3 per hour to 8000 Nm 3 per hour, - The distance between the nozzle lip gap and the front or back side of the flat steel material is in the range of 2 mm to 15 mm, preferably in the range of 3 mm to 12 mm, and / or - The strip speed is in the range of 50 m / min to 200 m / min, preferably in the range of 70 m / min to 150 m / min applies to system parameters and / or method parameters in all embodiments.

[0038] It should be noted that marbling and / or toothpick defects do not occur under certain ambient conditions. This can be the case, for example, when the ambient air is sufficiently humid (e.g., high air humidity in summer). This is because the ambient air is attracted by the peeling gas coming out of the nozzle and is swirled around the peeling gas. However, the occurrence of such surface defects also depends on many other parameters (e.g., bath temperature, etc.). At low bath temperatures, the tendency to form surface defects increases as the humidity in the ambient air increases. According to the present invention, when an appropriate moisture content of the peeling gas itself is ensured, hot-dip galvanizing and blowing are almost independent of the currently prevalent uncontrollable ambient conditions. This means that hot-dip galvanizing and blowing become more robust against external influences.

[0039] All embodiments may have one or more of the following sets of sensors, namely - at least one sensor for determining the humidity of the ambient air in the immediate vicinity of the device, and / or - at least one sensor for determining the humidity of the ambient air in the surrounding area of the device (e.g., factory space) of the collection.

[0040] Also, all embodiments include at least one means (e.g., implemented as a hardware device) for determining (e.g., measuring) the gas humidity or moisture content in the stripping nozzle device in order to determine the gas humidity at the outlet of the stripping gas or prior thereto (in the direction of the front or back side of the flat steel).

[0041] Preferably, this means for determining the gas humidity or moisture content, or the sensor of these means, is positioned in the gas supply pipe at a location positioned in the direction of the flow at a location where the dry gas stream and the water vapor gas stream merge / mix after merging / mixing.

[0042] Alternatively, this means for determining the gas humidity or moisture content, or the sensor of this device, may be positioned in the gas nozzle.

[0043] In all embodiments, this means for determining the gas humidity or moisture content, or the sensor of this device, can be positioned in the gas supply pipe and the gas nozzle.

[0044] In all or at least some of the embodiments, the method is characterized in that the flat steel is moved through a zinc alloy melting bath (ZnAl; ZnAlMg) so that a ZnAlMg layer or a ZnAl layer is applied to both sides of the flat steel according to the desired specifications, and at the output side of the zinc alloy melting bath, the stripping gas exits through the nozzle lip gap of at least one gas nozzle in the direction of the front side of the flat steel and through the nozzle lip gap of at least one gas nozzle in the direction of the back side of the flat steel in order to blow off the layer on both sides according to the desired specifications.

[0045] A method for applying a ZnAlMg layer or a ZnAl layer to the front and back sides of a flat steel is - moving the flat steel from the inlet side to the outlet side of the zinc alloy melting bath; - providing a dry gas stream; - providing a water vapor gas stream; - To obtain the stripping gas as a mixture, steps of mixing a dry gas stream and a water vapor gas stream; - Determining the gas moisture or moisture content of the stripping gas; - Discharging the stripping gas through at least one gas nozzle used to blow off the front side and at least one gas nozzle provided to blow off the back side to blow off the front and back sides of the flat steel material; including; · The following two conditions B1 and B2, namely, B1: The stripping gas (AG) has a moisture content or a proportion of gaseous water vapor (WG) of more than 200 ppm and less than 43700 ppm, preferably, the moisture content is in the range of 500 ppm to 9980 ppm; B2: The stripping gas (AG) has a dew point (TP) higher than -39°C and lower than +30°C, preferably, the dew point (TP) is in the range between -29°C and +7°C; at least one of which is satisfied.

[0046] To prevent defects in the marbling and / or toothpick formation of the ZnAlMg layer or ZnAl layer to be formed, in at least some of the embodiments, the ambient air humidity in the region of the device can also be optionally determined. Since the device or method draws in the ambient air during blowing (as already described), more accurate adjustment can be made to the gas humidity (moisture content) of the stripping gas in consideration of the currently existing ambient air humidity. When the current ambient air humidity is particularly low, for example, the gas humidity of the stripping gas is usually very important to reliably prevent surface defects. Under "humid" ambient conditions, it is not always absolutely necessary to add water vapor to the stripping gas to reliably prevent the formation of marbling and / or toothpick defects.

[0047] In at least some of the embodiments, the gas humidity (moisture content) of the stripping gas is set / regulated by using a water vapor device by providing a water vapor gas flow at a corresponding large flow rate to the actual flow rate of the drying gas flow provided and mixing / mixing the water vapor gas flow with the drying gas flow. That is, in these embodiments, the flow rate of the water vapor gas flow is actively adjusted with respect to the actual flow rate of the drying gas flow provided (referred to as the control or regulation of the water vapor gas flow source).

[0048] In all embodiments, it can be assumed in a first approximation that the water vapor gas flow is negligibly small relative to the drying gas flow. Therefore, when water vapor is added, the drying gas flow is not actually changed. Therefore, it is not absolutely necessary to adjust the drying gas flow. However, in all embodiments, the drying gas flow can be decreased when the water vapor gas flow is increased and can be increased when the water vapor gas flow is decreased.

[0049] In some other parts of the embodiments, the gas humidity (moisture content) of the stripping gas is set / regulated by adjusting both the flow rate of the drying gas flow and the flow rate of the water vapor gas flow. This can be done, for example, by using adjustable gas valves in the drying gas supply section and the water vapor gas supply section. Alternatively, the output quality of the drying gas flow source and the water vapor gas flow source is controlled or regulated.

[0050] In some of the embodiments, the gas humidity (moisture content) of the stripping gas can be set / regulated by a mixing valve that adjusts the flow rate of one or both in the region where the two gas flows are mixed.

[0051] In at least some of the embodiments, the short distance of the device is defined as a volume in the range from 1 m 3 to 10 m 3 up to.

[0052] In at least some of the embodiments, the surroundings of the apparatus are defined as having a volume greater than 10 m 3 than.

[0053] In all embodiments, the apparatus or the peeling nozzle system may be provided with an automatic deposition control adapted to automatically adjust the flow rate of the (peeling) gas in order to maintain a target thickness of the layer to be deposited substantially constant. The automatic deposition control is preferably adapted to compensate for variations in one or more system parameters and method parameters.

[0054] In all embodiments, or at least some of the embodiments, the inevitable impurities of the alloy are in a range significantly less than 1% by weight (wt%), preferably the total of all inevitable impurities is less than 0.5% by weight.

[0055] By combining a well-defined bath composition with monitoring and / or adjusting the gas humidity (moisture content) of the peeling gas, a surface can be produced that exhibits no or negligible marbling defects and no or negligible toothpick defects. During the production of each layer, the gas humidity (moisture content) of the peeling gas can be maintained substantially constant or adjusted (e.g., when the humidity changes in the vicinity or surroundings of the apparatus) in order to obtain a consistent layer (a layer within predetermined specifications).

[0056] In all embodiments, the peeling nozzle apparatus may optionally be followed by a strip stabilizing device used to automatically stabilize the movement of the flat steel.

[0057] In all embodiments, the apparatus has the following ranges, namely - A molten metal bath with a bath temperature TB in the range of 400 °C < TB < 480 °C, preferably in the range of 409 °C < TB < 472 °C, particularly preferably in the range of 410 °C < TB < 460 °C, - The nozzle distance from the flat steel material is between 2 mm and 15 mm, preferably between 3 mm and 12 mm. - For the blowing-off of the flat steel material on the outlet side of the molten metal bath by the (peeling) gas flowing through the nozzle lip gap in the direction of the flat steel material, 200 Nm per hour for a strip width of 1 meter 3 to 8000 Nm 3 within the range of the gas flow rate. is preferably operated.

[0058] The processes in the area of the peeling nozzle device and the processes on the flat steel material are complex and depend on numerous (method and system) parameters and influencing variables. Therefore, the control or adjustment of the device can be based on some simplified assumptions and specifications.

[0059] The preferred specifications for the previously defined alloying concepts of ZnAl and ZnAlMg, and the preferred specifications for the moisture content of the peeling gas determined, for example, by the dew point in the range between -39 °C and +30 °C or by the ppm specifications (for example, between 200 ppm and 43700 ppm), etc., are derived from numerous studies. Using the moisture content according to Example and Conditions B1 and / or B2, it has been proven that the technical teachings presented herein have been specifically successful within the defined limits of the alloying concepts defined herein.

[0060] In addition to the means and methods described herein for controlling and regulating the moisture content of the water vapor in the peeling gas, a cooling surface or cooling area may optionally be provided in the peeling nozzle device to provide a controlled area for the condensation of excess water vapor that may occur despite all measures. An outlet for draining the condensed water from time to time may be provided in this area. The cooling surface or cooling area must always be colder than the current dew point temperature of the peeling gas.

[0061] However, a device for condensing excess water vapor may be used in the supply pipe for the water vapor gas.

[0062] In all embodiments, the flat steel may undergo an annealing or tempering step at a temperature of about 765 °C (or a lower or higher temperature) before hot-dip galvanizing in a zinc alloy melting bath.

[0063] In all embodiments, the flat steel may be cold-rolled after hot-dip galvanizing (e.g., using smooth cold rolls and / or skin pass rolls with a special roughness).

[0064] Furthermore, the steel strip may additionally undergo a temper rolling process or a single in-line bending-stretching process to increase the flatness of the steel strip.

[0065] In all embodiments, the flat steel in strip form can be cleaned of rolling oil and rolling wear, rinsed with water, and dried in a so-called pretreatment or pre-washing in a continuous hot-dip galvanizing plant using combined immersion / brushing / electrolytic cleaning, for example, in each case in the form of strip, as deep drawing steel, mild steel, structural steel, or steel of a higher strength steel grade. The flat steel in strip form that has been cleaned and dried then enters the tempering furnace of the continuous hot-dip galvanizing line, where it is preheated, heated, and brought to the tempering temperature under an inert gas. At the end of the tempering furnace, the flat steel in strip form is cooled to the strip immersion temperature and immersed in a ZnMgAl alloy melting bath. After emerging from the bath, the flat steel in strip form is adjusted to the desired coating thickness by stripping gas at the stripping nozzle according to the embodiments described above and claimed in this application. In the subsequent cooling tower, the molten zinc alloy on the steel strip is solidified.

[0066] Following the cooling tower, the flat steel in strip form may be re-rolled in-line (continuous hot-dip galvanizing line) in a skin pass rolling mill, and a predefined roughness may be applied.

[0067] For example, after inline inspection for surface defects where surface defects such as marbling or toothpick are detected, flat steel in strip form can be coated with corrosion protection forming oil in an oiling machine and finally wound onto a reel. The steel material in the form of a coiled steel strip can be coated with lacquer in a strip coating machine after being wound onto a reel. Alternatively, flat steel in strip form can be coated with an organic / inorganic passivation layer using a coating machine (coating device) after bending-stretching-strain removal and / or after finishing and subsequent drying in a chemical post-treatment. Next, the flat steel 100 is inspected for surface defects and wound onto a reel if no marbling or toothpick defects are detected.

[0068] All embodiments may include a PC or other computer to automatically control or regulate the moisture content of the stripping gas and / or to manually operate the stripping gas within the dew point window.

[0069] Further embodiments of the present invention form the subject of the dependent claims.

[0070] Embodiments of the present invention are described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0071]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5-1

Figure 5-2

Figure 5-3

Figure 5-4

[0072] The moisture content of the gas can be described in different ways. It is common to define the dew point in °C, the mass fraction of water per unit volume of gas (also known as absolute humidity) in g / m 3 and the volume fraction in ppm (parts per million, also known as ppmV). The dew point represents the temperature at which water vapor begins to condense in the gas (here, in the stripping gas AG). When the dew point temperature is reached, the gas can no longer absorb 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, the term dew point is used throughout (even for negative temperatures). The pure nitrogen gas used as the stripping gas AG for blowing typically has a temperature between 10 °C and 30 °C. However, the nitrogen gas may be heated (e.g., to temperatures in the range from 50 °C to 200 °C or higher) before blowing. The warmer stripping gas AG can absorb more water vapor, so the dew point can be higher. The opposite is true for a cold stripping gas AG. Also, the stripping gas AG can absorb less water vapor under higher pressure than under lower gas pressure. It should also be noted that condensation of water vapor usually occurs in the pipes and components of the gas transport system (e.g., nozzle 15).

[0073] In the context of the present invention, the moisture content of the stripping gas AG is preferably at a minimum dew point TP minIs determined by setting. In all embodiments that rely on adding a small percentage of water vapor WG to the stripping gas AG, the minimum dew point TP min Is -39 °C, and preferably, the minimum dew point is TP min = -29 °C. In all embodiments, the maximum dew point TP which is +30 °C max (corresponding to approximately 43700 ppm of H2O in the stripping gas AG) can also be set. To avoid the occurrence of surface defects, the moisture content of the stripping gas AG is such that the dew point TP of the stripping gas AG is always TP min Higher than -39 °C, and preferably TP min Higher than -29 °C, and is adjusted in all these embodiments. In these embodiments, this specification means that it is independent of the ambient conditions (in the factory space where the device 150 operates, the temperature and humidity of the ambient air can vary significantly depending on the climate and time).

[0074] To avoid condensation of water in the stripping nozzle device 14 in all embodiments, the temperature difference ΔT can be defined in all embodiments according to the formula TP = T AG - ΔT. The temperature difference ΔT can preferably be at least 5 °C, and particularly preferably at least 10 °C. In this formula, TP defines the current dew point in the stripping gas flow AG, and T AG Defines the current temperature of the stripping gas flow AG.

[0075] By defining the temperature difference ΔT, for example, the fact that the tendency of condensation of the water vapor component increases when the pressure of the stripping gas AG is increased can be considered. By defining the temperature difference ΔT, which is understood as a kind of safety margin, it can be ensured that no condensed water is formed even when the pressure of the stripping gas AG increases slightly. The safety margin also prevents condensation in the stripping gas AG due to fluctuations in the regulation of the measured water vapor gas.

[0076] Also, in all embodiments, TP maxThe maximum dew point of the release gas AG at = +30 °C (corresponding to approximately 43700 ppm of H2O in the release gas AG) is defined. Preferably, the maximum dew point is TP max at = +7 °C (sample number 74 in Table 1). For example, the temperature T AG of the release gas is 18 °C, the dew point TP of the release gas AG is set to a value in the range of -39 °C < TP < 18 °C, and preferably, to a value in the range of -29 °C < TP < +7 °C.

[0077] If the previously described optional safety margin ΔT of 10 °C is additionally applied here, for example, for a gas temperature T AG of 18 °C, the dew point TP of the release gas AG is -39 °C < TP < T AG - ΔT (where T AG - ΔT = 18 °C - 10 °C = 8 °C) → -39 °C < TP < +8 °C, or preferably, to a value in the range of -29 °C < TP < +7 °C.

[0078] In particular, this relates to an apparatus 150 (e.g., FIG. 2) adapted to apply the layer 10 (see FIG. 4) to the front side V and the back side R of a flat steel sheet 100 in the form of a strip. The components of the immersion bath 11 are not shown here (see FIG. 1 showing exemplary components). The outlet side of the immersion bath 11 is identified by the letter A in FIG. 2. The flat steel sheet 100 is moved vertically upward in the direction of arrow B. The release nozzle device 14 comprises at least one gas nozzle 15 for blowing off the front side V of the flat steel sheet 100 and at least one gas nozzle 15 for blowing off the back side R of the flat steel sheet 100. In FIG. 2, for simplicity of depiction, the release nozzle device 14 comprises only one gas nozzle 15 for blowing off the front side V. The gas nozzle 15 for blowing off the back side R is adapted accordingly. In the embodiment shown in FIG. 3, two release nozzle devices 14 with opposing nozzles 15 are provided.

[0079] The layer 10 on both sides V and R is produced by passing the flat steel material 100 from the input side E through a zinc melting bath 11 (see, for example, FIG. 1) to the outlet side A, and by blowing off the flat steel material 100 with a (stripping) gas AG using a stripping nozzle device 14 at the outlet side A. The purpose of the stripping nozzle device 14 is to strip off the excessive (still liquid) ZnMgAl layer or ZnAl layer (layer 10) on the flat steel material 100 by a controlled method using the (stripping) gas AG after the flat steel material 100 emerges from the bath 11.

[0080] Attention must be paid to ensure that the layer 10 is produced according to a (predetermined) specification (the specification defines, for example, the target thickness or the coating for each side V, R), and that no marbling and / or toothpick defects occur. Some of the embodiments may be related to avoiding these "problems" in the case of changing ambient conditions in the production area (e.g., factory space). The ambient air humidity f UG Even if it changes in the wider surroundings (e.g., factory space) of the device 150 or at a short distance nearby, the device 150 and method according to the invention can ensure that no marbling and / or toothpick defects occur and that the layer 10 can continue to be produced according to the specification.

[0081] In some of the embodiments, for example, when the ambient air humidity f UG is too low, it may also be a problem to use the method and device 150 in such a way that only the water vapor gas WG is added to the dry gas TG.

[0082] In at least some of the embodiments, the target surface coating (coating for each side of the strip) can range from 20 g / m 2 to 200 g / m 2 and particularly preferably from 30 g / m 2 to 160 g / m 2 can be achieved.

[0083] In all embodiments, the peeling nozzle device 14 includes at least one gas nozzle 15 for each of the side surfaces V and R (for example, two gas nozzles 15 facing each other as indicated in FIGS. 3 and 4).

[0084] The flow rate of the (peeling) gas AG discharged through the nozzle lip gap 17 in the direction of the front surface V or the back surface R is Nm in this specification. 3 as indicated (Nm 3 represents standard cubic meters). A standard cubic meter is the amount of peeling gas AG contained in a volume of 1 cubic meter. This is applied at a temperature of 0°C and a pressure of 1.01325 bar.

[0085] The term dry gas TG refers herein to an inert gas having a dew point of approximately -70°C or lower. This corresponds to a water vapor content of approximately 5 ppm or less. Therefore, the dry gas TG has a very low residual moisture content (also referred to as trace moisture) within the range that is standard for industrial gases. In all embodiments, the dry gas TG used herein can meet, for example, the requirements of "Specification for Industrial nitrogen", British Standard BS 4366:1993. According to this standard, the water content of the gaseous nitrogen dry gas TG (see paragraph 8) is set to a maximum of 10 ppm corresponding to 10 / 10 6 . Therefore, in all embodiments, the dry gas TG should have a residual moisture content of less than 10 ppm, preferably less than 5 ppm.

[0086] In all embodiments, the device 150 includes a dry gas supply or a dry gas source 18 (see FIG. 2). For example, a gas tank, a gas cylinder, or a gas pipe (for example, coming directly from a gas supply device or an air separation device operating according to the Linde process) can be used as the source 18.

[0087] In all embodiments, the apparatus 150 may include, for example, two dry gas supply units or dry gas sources 18 (see FIG. 3), with one of the sources 18 associated with each of the peeling nozzle devices 14. In all embodiments, the apparatus 150 may include, for example, a dry gas supply unit or dry gas source 18 that feeds both of the peeling nozzle devices 14.

[0088] In all embodiments, the apparatus 150 includes at least one water vapor device or source 50 (see FIG. 2). For example, an evaporator or gas humidifier using ultrasonic spraying or the like can be used as the source 50. In all embodiments, the water vapor device or source 50 is fluidly connected to the gas nozzle 15 as indicated in FIG. 2. In the embodiment of FIG. 2, the source 50 is connected to the dry gas supply unit (pipe) 21 via a water vapor gas supply unit (pipe) 22. The two gas supply pipes 21, 22 are fluidly connected to each other in the T-shaped region 19. The dry gas flow is represented by the arrow TG, and the water vapor gas flow is represented by the arrow WG.

[0089] Preferably, in all embodiments, one or more steam generators are used as the water vapor device or source 50 adapted as a high-purity steam generator that generates gaseous steam WG or water vapor gas flow WG from purified water or highly purified water.

[0090] In all embodiments, the water vapor device 50 may preferably include a pure steam generator and a valve or the like that can regulate the steam of the water vapor gas WG through the conduit 22. For this purpose, in all embodiments, the high-purity steam generator and / or the valve may be connected to the control device of the apparatus 150 and / or to a device (not shown) for determining the gas humidity 20 or 26. In all embodiments, the water vapor gas flow WG may result from a condensate recovery system.

[0091] In all embodiments, the apparatus 150 may comprise, for example, two steam apparatuses or sources 50 (see FIG. 3), with one of the sources 50 being associated with each peeling nozzle apparatus 14.

[0092] In region 19 (see FIGS. 2 and 3), the gas flows TG and WG are combined and mixed. The resulting gas mixture is herein referred to as the peeling gas AG. The peeling gas AG flows from region 19 through the gas nozzle 14 in the direction of the front side V or the back side R of the flat steel material 100. The peeling gas AG exiting through the (gas) nozzle lip gap 17 of each gas nozzle 14 is symbolized in FIGS. 2 and 3 by three parallel arrows.

[0093] In all embodiments, for example, a mixing chamber may be provided in region 19 (see FIGS. 2 and 3) for mixing the gases TG, WG.

[0094] In order to prevent the formation of marbling and / or toothpick defects, or to considerably reduce marbling and toothpick defects, the air humidity f UG in the vicinity and / or surroundings of the apparatus 150 can be determined continuously or intermittently in all embodiments (e.g., by direct or indirect measurement) in order to be able to adjust the moisture content of the peeling gas AG accordingly when the ambient conditions change. However, this adjustment to the ambient conditions is optional.

[0095] Optionally, in all embodiments, the water vapor gas flow WG may be supplied to the peeling gas AG only if the ambient conditions themselves are not sufficient to avoid these problems (e.g., if the ambient air is too dry).

[0096] In all embodiments, the apparatus 150 may comprise at least one apparatus 20 configured and arranged accordingly to determine the moisture content in the peeling nozzle apparatus 14. The apparatus 20 is configured to determine the current moisture content of the peeling gas AG (in the form of a signal or measurement value containing information about the current dew point TP and / or moisture content in ppm, or absolute or relative humidity). In the embodiment shown in FIG. 2, the apparatus 20 comprises two sensors 23, 24 both protruding into the gas pipe 25. In the embodiment shown in FIG. 3, the apparatus 20 comprises a combined or integral sensor 23 / 24 protruding into the gas pipe 25 respectively.

[0097] In all embodiments, the moisture content of the peeling gas AG may be determined additionally or alternatively before or when the peeling gas AG exits in the direction of the front side V and / or the back side R of the flat steel material 100.

[0098] For example, the sensor 23 can be a humidity sensor and the sensor 24 can be a temperature sensor. Both sensors 23, 24 are connected via the wiring KV3, KV4 to the module 26 of the apparatus 20 for means of communication.

[0099] In all embodiments, a combined or integral sensor for measuring the moisture content and temperature T of AG AG may be used. FIG. 3 shows an embodiment in which one combined or integral sensor 23 / 24 is provided for each peeling nozzle apparatus 14. The corresponding communication wiring is labeled KV5.

[0100] In all embodiments, sensors for measuring, for example, the pressure dew point, the absolute moisture content f, and the temperature T of the gas AG AG may be used.

[0101] Digital sensors and / or analog sensors may be used in all embodiments.

[0102] In all embodiments, a dew point meter may be provided as the apparatus 20.

[0103] Suitable moisture sensors include, for example, sensors based on the principle of electromagnetic wave absorption (microwave absorption sensors) or sensors that determine changes in permittivity (capacitively operating sensors). An example of this is a polymer sensor adapted to measure the humidity of a gas in the temperature range of interest.

[0104] In all embodiments, sensors of the following designs or modes of operation can be used as humidity sensors. - Mechanically operating measurement sensors based on the expansion or contraction of a (usually organic) measurement element caused by humidity. - A moist air measurement sensor in which two identical and very accurate thermometers are used where the gas flow to be measured is guided at a predetermined velocity. - A capacitive measurement sensor comprising, for example, a humidity sensing capacitor with two flat electrodes. - A resistance measurement method in which, for example, the impedance of the alternating current resistance of a moisture-absorbing element is determined. - A spectroscopic measurement method in which, for example, the gaseous water content is measured in the near-infrared or mid-infrared region (NIR or MIR) without contact.

[0105] Instead of determining and regulating the water vapor content in the stripping gas AG using the dew point TP, the moisture content of the stripping gas AG may be determined and processed in all embodiments by measuring the volume fraction in ppm (also ppmV). For this purpose, for example, a measurement cell with a humidity sensor (e.g., a sensor that adsorbs moisture in the gas AG and then electrolyzes that moisture) may be used as part of the device 20. It should be noted that the relationship between the dew point temperature in °C and the volume fraction in ppm is not linear but exponential (see also Equation (1)).

[0106] This context is based on the following assumptions / approximations, as shown in Table 1. The relative air humidity r can be used to indicate the proportion of moisture in the gas with respect to the highest possible saturation of the gas. A humidity of r = 100% means that no more water vapor can be absorbed by the gas. At r = 100%, the gas is saturated with water vapor. When the temperature of the gas is increased, the gas can absorb a large amount of water, and the saturation vapor pressure of the gas increases. If the amount of water in the gas remains constant when the temperature is increased, the value of the relative humidity r decreases. The absolute humidity f of the gas (g / m 3 ), and by extension, the absolute humidity f of the ambient air used in this specification UG is also temperature-dependent. On the other hand, the dew point in °C and the volume fraction of H2O in ppm are independent of temperature and apply regardless of the type of gas. Therefore, the dew point in °C and the volume fraction of H2O in ppm are preferably used in this specification to define the moisture content of the stripping gas AG.

[0107] The examples shown in Table 1 (see Figure 5) clearly apply to the composition of the alloy and the conditions of the method indicated in each case. Table 1 (see Figure 5) has the following columns from left to right, namely, sample number, dew point TP of the stripping gas AG in °C (whereby the examples in Table 1 are classified from the lowest dew point to the highest dew point), volume fraction of water vapor H2O in the stripping gas AG in ppm, coating per side in g / m 2 , strip speed of the flat steel 100 in m / min (parallel to the moving arrow B), thickness of the nozzle lip gap 17 in mm (referred to as the height of the nozzle opening), horizontal distance between the nozzle and the strip (flat steel 100) in mm, nozzle height, vertical distance of the nozzle to the zinc bath surface in mm, nozzle pressure in mbar, bath temperature of the bath 11 in °C, composition of the bath by defining the proportions of Al and Mg in wt.%, absolute ambient air humidity f in g / m3 UG . The two rightmost columns contain information about marbling, - The black dots symbolize examples of alloys / methods where strong marbling was detected, - The grey dots symbolize examples of alloys / methods in which moderate marbling was found, - The white dots symbolize examples of alloys / methods in which no marbling was detected.

[0108] From Table 1 (see Figure 5), it can be seen that the use of dry nitrogen as the stripping gas in many examples of alloys / methods sometimes results in the occurrence of serious marbling defects (specifically, examples with sample numbers 1 - 43). Looking at the second and third columns (from the left) for the examples involving sample numbers 1 - 43, the stripping gas AG is dry nitrogen gas 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 gas meets the aforementioned British Standard requirements as the residual moisture is less than 10 ppm. Marbling, as can be seen from the rightmost two columns, cannot be reliably and reproducibly avoided with such dry nitrogen gas as the stripping gas AG.

[0109] For only the examples with sample numbers 53 - 74, intense marbling no longer occurs. This distinct reduction in intense marbling is achieved by adding a small percentage of water vapor gas WG, with at least 208 ppm (sample number 53) and up to 9978 ppm (sample number 74), to the dry nitrogen gas TG. The dew point of the stripping gas AG for sample numbers 53 - 74 is between -39°C (sample number 53) and +7°C (sample number 74).

[0110] From this, condition B1 can be derived as follows. The stripping gas AG must always have a moisture content or percentage of gaseous water vapor WG that is more than 200 ppm and less than 43700 ppm. The lower limit of 200 ppm is derived from the test results shown in Table 1 (208 ppm is rounded down to 200 ppm), and the upper limit of 43700 ppm ensures that there is no condensation of water around the stripping nozzle, as previously described.

[0111] Next, condition B2 can also be derived as follows. The peeling gas AG must always have a dew point TP greater than -39°C and less than +30°C. The lower limit of -39°C is derived from the test results shown in Table 1, and the upper limit of +30°C ensures no condensation of water around the peeling nozzle.

[0112] For only the examples with sample numbers 58 - 74, marbling no longer occurs at all (sample number 59 is an exception). This considerable reduction in marbling is achieved by adding a small percentage of water vapor gas WG, which ranges from at least 552 ppm (sample number 58) to a maximum of 9978 ppm (sample number 74), to the dry nitrogen gas TG. The dew point of the peeling gas AG for sample numbers 58 - 74 is between -29°C (sample number 58) and +7°C (sample number 74).

[0113] Next, a more preferable condition B1 can be derived as follows. The peeling gas AG must always have a proportion of gaseous water vapor WG with a moisture content in the range of 500 ppm to 9980 ppm, whereby these ppm specifications are rounded down or up.

[0114] Next, condition B2 can also be derived as follows. The peeling gas AG must always have a dew point TP in the range of -29°C to +7°C.

[0115] These specifications regarding conditions B1 and B2 relate to nitrogen as the dry gas TG and the temperature T of the peeling gas AG in the range of 10°C to 30°C AG and.

[0116] For the conditions defined under B2, the dew point TP of the peeling gas AG is less than the current temperature T of the peeling gas AG AG This condition (TP < T AG ) is referred to in this specification as condition B2.1. The application of condition B2.1 is for the temperature T of the peeling gas AG AGhas the advantage of being independent thereof. For example, when the stripping gas AG has a temperature T of 27 °C AG the dew point TP of the stripping gas AG must be less than +27 °C in order to meet condition B2.1.

[0117] The preferred condition B2.1 can also be defined as follows, i.e., TP < T AG like - ΔT, there should always be an optional safety margin ΔT between the temperature T of the stripping gas AG AG and the dew point TP of the stripping gas AG. This optional safety margin ΔT can be ΔT = 10 °C in all embodiments. In order to meet this preferred condition B2.1, the dew point TP of the stripping gas AG should be less than +17 °C when the temperature T of the stripping gas AG AG is, for example, 27 °C.

[0118] This condition B2.1 also applies to the changing gas pressure and / or changing temperature of the stripping gas AG.

[0119] An additional condition B3 can be defined which specifies that the stripping gas AG is a gas in an unsaturated state.

[0120] This condition B3 also applies to the changing gas pressure and / or changing temperature of the stripping gas AG.

[0121] Condition B1 and / or B2 and / or B2.1, when followed with respect to the stripping gas AG, is on the safe side from the perspective of marbling. Condition B3 is an additional condition that can be followed in all embodiments in addition to condition B1 and / or B2 and / or B2.1.

[0122] By following these conditions, the processes of hot dip galvanizing and spraying can be stabilized. That is, these processes become more robust against disturbing ambient conditions (some of which may not be affected). Also, the parameter window within which the method functions reliably is expanded.

[0123] In a series of tests and in the evaluation of process data, it has been shown that the air humidity in the ambient or close vicinity around the peeling nozzle has a significant influence on the occurrence of marbling defects. f UG UG is used herein as a mathematical symbol for the absolute air humidity (also called ambient air humidity) in the ambient or close vicinity around the peeling nozzle. In all embodiments, the absolute air humidity f UG is dependent on the ambient or close vicinity air temperature T L and the relative air humidity r in the ambient or close vicinity and can be estimated accordingly. The following formula is used here.

[0124]

Equation

[0125] Relative humidity or air humidity at r % f UG Ambient or close vicinity air humidity T L Ambient or close vicinity air temperature in °C

[0126] Ambient or close vicinity air humidity f UG or air temperature T L The determination / measurement / monitoring of can be carried out directly or indirectly in all embodiments, as already described. Indirect measurement means, among other things, in this document, measuring the air temperature T L and the relative air humidity r and then calculating / deriving the absolute local air humidity f UG from this.

[0127] In all embodiments, the current flow rate of the stripping gas AG is maintained by known techniques (e.g., using the adjustment by the automatic coating control of the apparatus 150) to be automatically adjusted so that when one or more of the system parameters and / or method parameters change, the desired thickness or coating per side of the layer 10 is applied essentially uniformly. Therefore, the supply quality of the water vapor gas flow WG must be adjusted accordingly to ensure that the stripping gas AG complies with the conditions B1, B2, B2.1, B3 of the present invention regarding the moisture content.

[0128] FIG. 4 shows not only the nozzle spacing (defined parallel to the y-axis) between the respective stripping sides (front side V, back side R) of the nozzle 15 and the flat steel material 100, but also the thickness of the nozzle lip gap 17 (referred to as the height of the nozzle opening, defined parallel to the x-axis). The nozzle lip gap 17 serves as the gas outlet gap of the stripping nozzle device 14. In FIG. 4, the thickness of the flat steel material 100 and the two layers 10 are exaggerated in order to be able to schematically show in the spatial region X that the thickness of the layer 10 is reduced by the blowing-off by the stripping gas AG.

[0129] The gas jet emerging from the nozzle 14, together with the force of gravity, still exerts a shear force on the liquid layer 10 (for example, as shown in FIGS. 2 and 3 when the flat steel material 100 is pulled vertically upward from the bath 11). The shear force reduces the thickness of the layer 10 by blowing off the layer 10 with the stripping gas AG.

[0130] The equation representing the dynamic flow behavior of the gas AG in the flat steel material 100 is very complex. This is because, among other things, regions with laminar and turbulent flow patterns occur in the gas jet emerging through the nozzle lip gap 17 of the nozzle 15 on the layer 10 of the flat steel material 100. Also, the gas jet draws in the ambient air, and the ambient air is swirled by the stripping gas AG (for this reason, the ambient air humidity f UGWhen it is high, it may not be necessary to add the water vapor gas WG to the dry gas TG). For details, see, for example, "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet", C.V. Tu, D.H. Wood, Experimental Thermal and Fluid Science Volume 13, Issue 4, November 1996, pages 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, PA, 2019, Pittsburgh, USA.

[0131] By mixing the dry gas TG and the water vapor gas flow WG, it is important that a stripping gas flow AG containing a very small but sufficient amount of water vapor is generated to avoid the formation of defects and malfunctions on the surface of the layer 10. Also, there should not be excessive water vapor in the stripping gas flow AG to prevent condensation and the formation of water droplets.

[0132] Further specific investigations have shown the correlation between the moisture content of the stripping gas AG and the occurrence of such surface defects and malfunctions, (ambient) air humidity f UGIt may also have an impact (when the ambient air humidity is sufficiently high, surface defects and malfunctions may not occur under certain circumstances). In Table 1 (see FIG. 5), all parameter ranges or sample numbers that enable dip coating and controlled blowing of layer 10 without serious surface defects and malfunctions are highlighted in light gray (sample numbers 53 - 57). In Table 1 (see FIG. 5), all parameter ranges or sample numbers that enable dip coating and controlled blowing of layer 10 without surface defects and malfunctions are highlighted in dark gray (sample numbers 58 - 74).

[0133] When operating the apparatus 150, - the thickness of the nozzle lip gap 17 (referred to as the height of the nozzle opening) is in the range from 0.5 mm to 5 mm, preferably in the range between 0.6 mm and 2 mm, and particularly preferably in the range between 0.8 mm and 1.4 mm, - the flow rate of the exhaust gas stream AG is in the range from 200 Nm 3 per hour to 8000 Nm 3 per hour, - the nozzle distance from the nozzle 15 to the side V or R (nozzle - strip distance) is in the range between 2 mm and 15 mm, preferably in the range between 2.5 mm and 14.1 mm, and / or, - the strip speed of the steel strip 100 is in the range between 50 m / min and 200 m / min, preferably in the range between 70 m / min and 150 m / min are preferably paid attention to in all embodiments.

[0134] The apparatus 150 and the method operate particularly reliably within these (value) ranges.

[0135] In all embodiments, the corresponding gas nozzle 15 has an extension in length (referred to as nozzle width) perpendicular to the plane of the drawings of FIGS. 2, 3, and 4 (parallel to the z-axis in FIG. 4). Preferably, in all embodiments, the nozzle 15 has an effective nozzle width that at least corresponds to the strip width of the flat steel strip 100 shaped like a strip. In all embodiments, the strip width of the flat steel strip 100 shaped like a strip can be in the range of, for example, 500 mm to 2500 mm, preferably in the range between 800 mm and 1800 mm, and particularly preferably in the range between 1159 mm and 1614 mm. In the case of a wider strip-shaped flat steel strip 100, the effective nozzle width also increases accordingly.

[0136] The nozzle is positioned at a variable vertical distance from the surface of the zinc bath. This distance is generally referred to as the nozzle height. This distance is mainly set as a function of the speed of the passing strip and / or the set zinc coating layer. In all embodiments, the nozzle height can be, for example, between 230 mm and 500 mm.

[0137] All embodiments of the device 150 can include an optional control device 250, as schematically and illustratively indicated in FIG. 3. In all embodiments, the control device 250 can be adapted as a computerized automatic control unit and can include a human-machine interface, a computer, and a database.

[0138] In all embodiments, the control device 250 can be connected, when present, via communication wiring KV1, KV2, to means or devices for determining the gas humidity 20.

[0139] In all embodiments, the control device 250 can be part of the overall system control device of the device 150 or can be connected to the overall system control device in all embodiments.

[0140] In all embodiments, the control device 250 may have one or more analog inputs and / or digital inputs to obtain information about the ambient conditions that are currently prevalent, if any (e.g., the current air temperature T L , and / or the ambient or near - distance (absolute) air humidity f UG ). Based on this information, the control device 250 can, for example, reduce or increase (or even switch off) the metering of the water vapor gas flow WG in order to continue to produce layer 10 with a defect - free surface in device 150.

[0141] In all embodiments, the control device 250 may, if present, be provided with a communication link that enables the control device 250 to reduce or increase the flow of the water vapor gas flow WG and / or to reduce or increase the flow of the dry gas flow TG. Alternatively, the control device 250 can, for example, adjust a mixing valve in the region where the two gas flows TG, WG merge 19 via the communication link according to the situation.

[0142] For example, when the air humidity of the ambient air f UG is very low, the intake of dry ambient air may cause the formation of marbling in layer 10. Here, the present invention can start to act by switching on or by automatically increasing the moisture content in the stripping gas AG.

[0143] Example of the First Embodiment: The cold-rolled flat steel material 100 in strip form, i.e., the cold-rolled deep-drawing steel sheet in strip form, is, in at least some of the embodiments, pre-treated in a continuous hot-dip galvanizing system using a combined immersion / brushing / electrolytic cleaning to wash away rolling oil and rolling wear, be rinsed with water, and be dried. The flat steel material 100 in strip form that has been washed and dried enters the annealing furnace of the continuous hot-dip galvanizing system, where it is preheated, heated using a direct-fired furnace (DFF), and brought to an annealing temperature of 820 °C in a radiant tube furnace under a protective gas at a dew point of -40 °C. At the end of the annealing furnace, the flat steel material 100 in strip form is cooled to a strip immersion temperature of 450 °C and immersed in a warm ZnMgAl alloy melting bath 11 at 430 °C for 3 seconds. After leaving the bath 11 at the outlet side A, the flat steel material 100 in strip form is adjusted to a predetermined target layer thickness of ZM90 (45 g / m for each side V, R) at the stripping nozzle 15 of the stripping nozzle device 14 using a dry stripping gas AG with a dew point of -73 °C or an H2O content of 3 ppm. The stripping nozzle 15 has a nozzle lip gap of 1.0 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 6 mm on both sides (parallel to the y-axis in Figure 4) up to the flat steel material 100 in strip form. The zinc alloy melting solidifies on the flat steel material 100 in the connected cooling tower 16 (see Figure 1). Next, the flat steel material 100 in strip form is rolled in a skin pass rolling mill, and a roughness of 1.4 μm is pressed. After inspection for surface defects such as marbling or toothpick defects being identified, the flat steel material 100 in strip form is coated with a corrosion protection forming oil of 1.0 g / m for each side V, R in an oiling machine and finally wound onto a reel. In a further step, for example, on a so-called inspection line, the flat steel material 100 in strip form can be unwound, defective areas can be separated, and then the strip can be wound again. 2 ) 2 and is finally wound onto a reel. In a further step, for example, on a so-called inspection line, the flat steel material 100 in strip form can be unwound, defective areas can be separated, and then the strip can be wound again.

[0144] Example of the Second Embodiment: A cold-rolled flat steel material 100 in strip form, i.e., a cold-rolled deep-drawing steel sheet in strip form, is washed of rolling oil and rolling wear, rinsed with water, and dried as part of the in-line pretreatment of a continuous hot-dip galvanizing system using a combined immersion / brushing / electrolytic cleaning. The flat steel material 100 in strip form that has been washed and dried enters a tempering furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and brought to a tempering temperature of 820°C in a radiant tube furnace under a protective gas at a dew point of -40°C. At the end of the tempering furnace, the flat steel material 100 in strip form is cooled to a strip immersion temperature of a ZnMgAl alloy melting bath 11 at 450°C and immersed in the warm ZnMgAl alloy melting bath 11 at 430°C for 3 seconds. After leaving the bath in the exit region A, the flat steel material 100 in strip form is brought to a target layer thickness of ZM90 (45 g / m per side) at the peeling nozzle 15 by humidified nitrogen (after mixing of gaseous H2O, to 310 ppm or a dew point of -35°C as described and claimed herein). The peeling nozzle 15 has a nozzle lip gap (height of the nozzle opening) of 1.0 mm and is positioned at a horizontal distance of 6 mm (parallel to the y-axis in FIG. 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see FIG. 1), the zinc alloy melt solidifies on the flat steel material 100. Next, the flat steel material 100 is rolled in a skin pass rolling mill and a roughness Ra of 1.4 μm is pressed. After inspection for surface defects, where the presence of marbling is determined, the flat steel material 100 is coated in-line (in the continuous hot-dip galvanizing system) with 1.0 g / m per side by a corrosion protection forming oil and finally wound onto a reel. In a further step, for example on a so-called inspection line, the flat steel material 100 can be unwound in strip form, defective areas can be separated, and then the strip can be rewound. 2 ) is set. The peeling nozzle 15 has a nozzle lip gap (height of the nozzle opening) of 1.0 mm and is positioned at a horizontal distance of 6 mm (parallel to the y-axis in FIG. 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see FIG. 1), the zinc alloy melt solidifies on the flat steel material 100. Next, the flat steel material 100 is rolled in a skin pass rolling mill and a roughness Ra of 1.4 μm is pressed. After inspection for surface defects, where the presence of marbling is determined, the flat steel material 100 is coated in-line (in the continuous hot-dip galvanizing system) with 1.0 g / m per side by a corrosion protection forming oil and finally wound onto a reel. 2 per side by an oiling machine and finally wound onto a reel. In a further step, for example on a so-called inspection line, the flat steel material 100 can be unwound in strip form, defective areas can be separated, and then the strip can be rewound.

[0145] Example of the Third Embodiment: A cold-rolled deep-drawing steel sheet in strip form is in-line cleaned in a pretreatment of a continuous hot-dip galvanizing system using a combination of rolling oil and immersion / brushing / electrolytic cleaning of rolling wear, rinsed with water, and dried. The flat steel material 100 in strip form that has been cleaned and dried enters a tempering furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and brought to a tempering temperature of 820°C in a radiant tube furnace under a protective gas at a dew point of -40°C. At the end of the tempering furnace, the flat steel material 100 in strip form is cooled to a strip immersion temperature of 450°C in a ZnMgAl alloy melting bath 11 and immersed in the ZnMgAl alloy melting bath 11 at 430°C for 3 seconds. After leaving the bath in the exit region A, the flat steel material 100 in strip form is set to a target layer thickness of ZM90 (45 g / m2 per side) at a peeling nozzle 15 by humidified nitrogen (after mixing gaseous H2O, up to 5522 ppm or a dew point of -29°C). The peeling nozzle 15 has a nozzle lip gap of 1.0 mm (height of the nozzle opening) and is positioned at a horizontal distance of 6 mm (parallel to the y-axis in FIG. 4) on both sides of the flat steel material 100. The zinc alloy melting solidifies on the flat steel material 100 in a connected cooling tower 16 (see FIG. 1). Next, the flat steel material 100 is rolled in a skin pass rolling mill, and a roughness of 1.4 μm is pressed. After inspection for surface defects where no mottling defects or toothpick defects are found, the flat steel material 100 is in-line coated on each side with a corrosion protection forming oil at 1.0 g / m 2 and finally wound onto a reel by an oiling machine.

[0146] Example of the 4th Embodiment: The high-strength cold-rolled flat steel material 100 in strip form is subjected to combined immersion / brushing / electrolytic cleaning to wash away rolling oil and rolling wear in the pretreatment of a continuous hot-dip galvanizing system, rinsed with water, and dried. The washed and dried flat steel material 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and brought to 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 flat steel material 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 490 °C and immersed in the warm ZnMgAl alloy melting bath 11 at 430 °C for 5 seconds. After leaving the bath in the exit region A, the flat steel material 100 in strip form is adjusted to a target layer thickness of ZM90 (45 g / m2 per side) at the peeling nozzle 15 by humidified nitrogen (after mixing with gaseous H2O, up to 3065 ppm or a dew point of -9 °C). The peeling nozzle 15 has a nozzle lip gap of 1.0 mm (height of the nozzle opening) and is positioned at a horizontal distance of 7.6 mm (parallel to the y-axis in Fig. 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see Fig. 1), the zinc alloy melting solidifies on the flat steel material 100. Next, the flat steel material 100 is rolled in a skin pass rolling mill, and a roughness of 1.3 μm is pressed. After inspection for surface defects where no marbling defects or toothpick defects are found, the flat steel material 100 is inline coated by an oiling machine at 0.8 g / m per side with corrosion protection forming oil and finally wound onto a reel. 2 and is inline coated by an oiling machine and finally wound onto a reel.

[0147] Example of the Fifth Embodiment: Structural steel is cleaned, rinsed with water, and dried as cold-rolled flat steel 100 in strip form in the pretreatment of a continuous hot-dip galvanizing system using a combination of rolling oil and immersion / brushing / electrolytic cleaning with rolling wear. The cleaned and dried flat steel 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and brought to an annealing temperature of 730 °C in a radiant tube furnace under a protective gas at a dew point of -45 °C. At the end of the annealing furnace, the flat steel 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 465 °C and immersed in the warm ZnMgAl alloy melting bath 11 at 455 °C for 4 seconds. After leaving the bath in the exit region A, the flat steel 100 in strip form is set to a target layer thickness of ZM120 (60 g / m 2 per side) at the peeling nozzle 15 by dry nitrogen (without mixing of gaseous H2O, 3 ppm or a dew point of -75 °C). The peeling nozzle 15 has a nozzle lip gap of 1.0 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 7.7 mm from both sides of the flat steel 100 (parallel to the y-axis in Fig. 4). The zinc alloy melting is solidified on the flat steel 100 in the connected cooling tower 16 (see Fig. 1). The flat steel 100 is then flattened by a bending-stretching-strain removing machine, then rolled in a skin pass rolling mill, and a roughness of 1.4 μm is pressed. After inspection for surface defects where no marbling defects or toothpick defects are found, the flat steel 100 is wound onto a reel. Next, the steel strip 100 is coated with lacquer in a continuous peeling and coating system.

[0148] Example of the 6th Embodiment: Structural steel is washed, rinsed with water, and dried as cold-rolled flat steel material 100 in strip form in the pretreatment of a continuous hot-dip galvanizing system using a combination of rolling oil and rolling wear, dipping / brushing / electrolytic cleaning. The flat steel material 100 in washed and dried strip form enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and brought to an annealing temperature of 730 °C in a radiant tube furnace under a protective gas at a dew point of -45 °C. At the end of the annealing furnace, the flat steel material 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 465 °C and immersed in the warm ZnMgAl alloy melting bath 11 at 455 °C for 4 seconds. After exiting the bath in the exit region A, the flat steel material 100 in strip form is set to the target layer thickness of ZM120 (60 g / m per side) at the peeling nozzle 15 by humidified nitrogen (after mixing gaseous H2O to 1470 ppm or a dew point of -18 °C). The peeling nozzle 15 has a nozzle lip gap of 1.0 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 7.7 mm (parallel to the y-axis in Fig. 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see Fig. 1), the zinc alloy melting solidifies on the flat steel material 100. The flat steel material 100 is then flattened by a bending-stretching-strain removing machine, re-rolled in a skin pass rolling mill, and a roughness of 1.4 μm is pressed. After inspection for surface defects where no mottling defects or toothpick defects are found, the flat steel material 100 is wound onto a reel. Next, the steel strip 100 is coated with lacquer in a continuous peeling coating system. 2 )

[0149] 7th Embodiment: The structural steel is pre-treated in a continuous hot-dip galvanizing system using immersion / brushing / electrolytic cleaning combined with rolling oil and rolling wear, and is cleaned, rinsed with water, and dried as cold-rolled flat steel 100 in strip form. The cleaned and dried flat steel 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is pre-heated, heated using a direct-fired furnace (DFF), and is brought to 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 flat steel 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 465 °C and is immersed in the warm ZnMgAl alloy melting bath 11 at 455 °C for 4 seconds. After exiting the bath in the exit area A, the flat steel 100 in strip form is set to a target layer thickness of ZM120 (60 g / m per side) at the peeling nozzle 15 using humidified nitrogen (after mixing gaseous H2O to 5230 ppm or a dew point of -2 °C). The peeling nozzle 15 has a nozzle lip gap (height of the nozzle opening) of 1.0 mm and is positioned at a horizontal distance of 7.7 mm (parallel to the y-axis in Figure 4) on both sides of the flat steel 100. In the connected cooling tower 16 (see Figure 1), the zinc alloy melting solidifies on the flat steel 100. The flat steel 100 is then flattened by a bending-stretching-strain removing machine, rolled in a skin pass rolling mill, and a roughness of 1.4 μm is pressed. After inspection for surface defects where no mottling defects or toothpick defects are found, the steel strip 100 is wound onto a reel. Next, the steel strip 100 is coated with lacquer in a continuous peeling and coating system. 2 )

[0150] Example of the 8th Embodiment: Mild steel is cleaned as cold-rolled flat steel material 100 in strip form in the pretreatment of a continuous hot-dip galvanizing system using a combination of rolling oil and immersion / brushing / electrolytic cleaning with rolling wear, rinsed with water, and dried. The flat steel material 100 in the washed and dried strip form enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and annealed at an annealing temperature of 720°C in a radiant tube furnace under a protective gas at a dew point of -50°C. At the end of the annealing furnace, the flat steel material 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 460°C and immersed in the warm ZnMgAl alloy melting bath 11 at 455°C for 3 seconds. After exiting the bath in the exit region A, the flat steel material 100 in strip form is set to the target layer thickness of ZM90 (45 g / m per side) at the peeling nozzle 15 by dry nitrogen (without mixing of gaseous H2O, 3 ppm or dew point of -74°C). The peeling nozzle 15 has a nozzle lip gap of 1.2 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 10 mm (parallel to the y-axis in FIG. 4) on both sides of the flat steel material 100. The zinc alloy melting solidifies on the flat steel material 100 in the connected cooling tower 16 (see FIG. 1). The flat steel material 100 is then flattened by a bending-stretching-strain removal machine, rolled in a skin pass rolling mill, and a roughness of 1.0 μm is pressed. As part of the in-line chemical post-treatment, an organic / inorganic passivation layer is applied and dried using a coater (coating device). After inspection for surface defects where marbling and toothpick defects are identified, the steel strip 100 is wound onto a reel. In a further step, for example, on a so-called inspection line, the flat steel material 100 can be unwound in strip form, defective areas can be separated, and then the strip can be wound again. 2 )

[0151] Example of the 9th Embodiment: Mild steel is washed, rinsed with water, and dried as cold-rolled flat steel material 100 in strip form in the pretreatment of a continuous hot-dip galvanizing system using a combination of rolling oil and immersion / brushing / electrolytic cleaning of rolling wear. The washed and dried flat steel material 100 enters the annealing furnace of the continuous hot-dip galvanizing system, is preheated, heated using a direct-fired furnace (DFF), and is brought to 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 flat steel material 100 in strip form is cooled to the strip immersion temperature of the ZnMgAl alloy melting bath 11 at 460°C and immersed in the warm ZnMgAl alloy melting bath 11 at 455°C for 4 seconds. After exiting the bath in the exit region A, the flat steel material 100 in strip form is set to a target layer thickness such as ZM120 (60 g / m per side) at the peeling nozzle 15 by humidified nitrogen (after mixing gaseous H2O, up to 9980 ppm or a dew point of +7°C). The peeling nozzle 15 has a nozzle lip gap of 1.2 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 10 mm (parallel to the y-axis in Figure 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see Figure 1), the zinc alloy melting solidifies on the flat steel material 100. Next, the flat steel material 100 is flattened in a bending-stretching-strain removal machine. After inspection for surface defects where no marbling defects or toothpick defects are found, the steel strip 100 is wound onto a reel. Next, the steel strip 100 is coated with lacquer in a continuous peeling and coating system. 2 ) etc. The peeling nozzle 15 has a nozzle lip gap of 1.2 mm (referred to as the height of the nozzle opening) and is positioned at a horizontal distance of 10 mm (parallel to the y-axis in Figure 4) on both sides of the flat steel material 100. In the connected cooling tower 16 (see Figure 1), the zinc alloy melting solidifies on the flat steel material 100. Next, the flat steel material 100 is flattened in a bending-stretching-strain removal machine. After inspection for surface defects where no marbling defects or toothpick defects are found, the steel strip 100 is wound onto a reel. Next, the steel strip 100 is coated with lacquer in a continuous peeling and coating system.

Description of Reference Numerals

[0152]

Table 1A

[0153]

Table 1B

Claims

1. An apparatus (150) for applying a ZnAlMg layer or a ZnAl layer (10) to a flat steel material (100), comprising: A zinc alloy melting bath (11) with an inlet side (E) and an outlet side (A); A dry gas supply unit (18) configured to provide a dry gas flow (TG); A steam device (50) configured to provide a steam gas (WG); Means (20) for determining the gas humidity and / or moisture content; A peeling nozzle device (14) fluidly connected to the gas supply unit (18) and the steam device (50) such that a peeling gas (AG), which is a mixture of the dry gas flow (TG) and the gaseous steam (WG), is supplied; And The peeling nozzle device (14) includes at least one gas nozzle (15) for blowing off the front side (V) of the flat steel material (100) with the peeling gas (AG), and at least one gas nozzle (15) for blowing off the back side (R) of the flat steel material (100); The gas nozzle (15) is arranged in the region of the outlet side (A) of the zinc alloy melting bath (11); The means (20) for determining the gas humidity and / or moisture content is arranged in the peeling nozzle device (14) to determine the gas humidity before or when the peeling gas (AG) exits in the direction of the front side (V) or the back side (R) of the flat steel material (100), and satisfies at least one of the following two conditions B1, B2, that is: B1: The peeling gas (AG) has a moisture content greater than 200 ppm and less than 43700 ppm, or a proportion of the gaseous steam gas (WG), preferably, the moisture content is in the range of 500 ppm to 9980 ppm; B2: The peeling gas (AG) has a dew point (TP) higher than -39 °C and lower than +30 °C, preferably, the dew point (TP) is in the range between -29 °C and +7 °C The apparatus (150) in which at least one of the above is satisfied.

2. The ratio of the dry gas stream (TG) and the water vapor gas (WG) for mixing the stripping gas (AG) is such that the current dew point (TP) lower than the temperature (T ＡＧ ) of the stripping gas stream (AG) is obtained in the stripping gas (AG) in order to avoid condensation of water in the stripping nozzle device (14). The apparatus (150) according to claim 1, wherein the apparatus is adjusted.

3. The mathematical formula TP < T ＡＧ - According to ΔT, a temperature difference ΔT of at least 5°C, preferably at least 10°C, is defined, TP determines the current dew point in the stripping gas stream (AG), and T ＡＧ determines the current temperature of the stripping gas stream (AG). The apparatus (150) according to claim 1 or 2

4. The stripping gas stream (AG) is defined by a dew point (TP) that is greater than -39°C and less than +30°C, and the dew point (TP) is the temperature T of the stripping gas stream (AG). ＡＧ The apparatus (150) according to claim 1 or 2, characterized in that when T is in the range from 10°C to 30°C, preferably in the parameter range from -29°C to +7°C.

5. A temperature sensor (24) for measuring the current temperature (T ＡＧ ) of the peeling gas flow (AG); In order to avoid condensation of water in the peeling nozzle device (14), the dew point (TP) is such that the peeling gas stream (AG) is lower than the current temperature (T ＡＧ ) of the peeling gas stream (AG) by a temperature difference (ΔT). A control unit for the dry gas stream (18) and / or the water vapor gas stream (WG) for controlling the ratio of the dry gas stream (TG) and the water vapor gas (WG) for mixing the peeling gas (AG). The apparatus (150) according to any one of claims 1 to 3, comprising

6. The apparatus (150) according to any one of claims 1 to 5, wherein even when the temperature of the peeling gas exceeds 30 °C, a maximum dew point of +30 °C is defined in the peeling gas flow.

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

8. A method for applying a ZnAlMg layer or a ZnAl layer (10) to the front side (V) and the back side (R) of a flat steel material (100), moving the flat steel material (100) from the inlet side (E) to the outlet side (A) of a zinc alloy melting bath (11); providing a drying gas stream (TG); providing a water vapor gas (WG); mixing the drying gas stream (TG) and the water vapor gas (WG) to obtain a stripping gas (AG) as a mixture; determining the gas humidity of the stripping gas (AG); discharging the stripping gas (AG) through at least one gas nozzle (15) provided to blow off the front side (V) and at least one gas nozzle (15) provided to blow off the back side (R) to blow off the front side (V) and the back side (R) of the flat steel material (100); comprising the following two conditions B1, B2, namely, B1: the stripping gas (AG) has a moisture content of more than 200 ppm and less than 43700 ppm, or a proportion of the gaseous water vapor gas (WG), preferably the moisture content is in the range from 500 ppm to 9980 ppm; B2: the stripping gas (AG) has a dew point (TP) higher than -39°C and lower than +30°C, preferably the dew point (TP) is in the range between -29°C and +7°C; A method in which a stripping gas stream (AG) satisfying at least one of them is discharged.

9. The ratio of the dry gas stream (TG) and the water vapor gas (WG) in the stripping gas (AG) is such that a current dew point (TP) lower than the temperature (T ＡＧ ) of the stripping gas stream (AG) results in the stripping gas (AG) to avoid condensation of water in the stripping nozzle device (14), the method according to claim 8.

10. The water content of the stripping gas stream (AG) is defined by a dew point (TP) greater than -39°C and less than +30°C, and the dew point (TP) is the temperature T of the stripping gas stream (AG) ＡＧ The method according to claim 8 or 9, characterized in that when ＡＧ is in the range from 10°C to 30°C, preferably in the range from -29°C to +7°C.

11. In the vicinity or in the immediate vicinity of the outlet side (A) of the zinc alloy melting solution (11), when there is an absolute ambient air humidity (f ＵＧ ) lower than a predetermined limit value, the method according to any one of claims 8 to 10, characterized in that only the mixing of the gaseous water vapor gas (WG) is carried out.

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