Method and device for applying a layer to a flat steel product

Abstract

A device (150) for applying a layer (10) to a front and / or rear side of a flat steel product (100), the device (150) comprising a zinc alloy melting tank (11) with an input side (E) and an outlet side (A), a stripping nozzle device (14) with at least one gas nozzle (15) for stripping the front or rear side of the flat steel product (100) using a gas (G), the stripping nozzle device (14) is arranged in the region of the outlet side (A), a water vapor device (50) configured to emit gaseous water vapor and to provide a controlled water vapor environment in a close distance (NB) of the front and / or rear side of the flat steel product (100), the controlled water vapor environment having an absolute local humidity greater than 1 g / m3 and less than 300 g / m3.

Description

[0001] The invention relates to a device by means of which flat steel products can be coated with a zinc (Zn) or zinc-aluminum-magnesium (ZnAlMg) base layer, for example as a protective coating, and also to a corresponding method.

[0002] As is known, a flat steel product 100 such as a steel strip or steel sheet is coated with zinc (Zn) or a ZnAlMg alloy to improve its corrosion resistance. Figure 1 In the illustrated example device 150, a flat steel product 100 is introduced from a furnace into a zinc alloy molten bath 11. To protect the flat steel product 100 from oxidation, it is usually introduced into the bath 11 at the inlet side E through a trunk 12 with an inert atmosphere. In the bath 11, the flat steel product 100 is deflected by (zinc bath) rollers 13 and moves upward out of the bath 11 at the outlet side A. When it emerges from the bath 11, the molten alloy film adhering to the front and rear sides of the flat steel product 100 is stripped off by gas jets from gas nozzles 15 of a stripping nozzle device to a target thickness (in the micrometer range) or to a target surface coating (in g / m 2 ), and the flat steel product 100 is then transferred to a cooling zone 16. This continuous process is generally referred to as hot dip coating.

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

[0004] There is prior art that mentions water or water vapor in connection with hot dip coating of flat steel products. The relevant documents are listed below and their contents of interest are briefly described here.

[0005] Patent EP0172682B1 filed by Armco in 1985 relates to zinc vapor control in connection with hot dip coating of iron-based metal strip. Figure 1 In the trunk 12) in the immersion tank, a reduced oxygen environment containing a small amount of water vapor is provided. This small amount of water is to prevent the formation of zinc vapor on the surface of the immersion tank. The dew point of the gas used on the inlet side is set so that zinc vapor will not form.

[0006] In the published patent application JP2020100886A2 of the company Nippon, the aim is to produce a galvanized steel strip whose surface has an increased coefficient of friction. To increase the coefficient of friction, water is sprayed under pressure onto the surface of the flat steel product after the air blowing. The particle size of the water droplets should be at least 0.07 mm and preferably greater than 1.5 mm. The spraying of water droplets deliberately creates irregularities on the surface of the steel strip. This document pursues different objectives and therefore the corresponding technical teaching is completely different from the direction of the present invention.

[0007] In addition to pure corrosion protection, the requirements on the surface quality of zinc-coated flat steel products are even more stringent. The automotive industry in particular expects products to meet the highest surface requirements. However, providing a homogeneous surface is not an easy task.

[0008] The main problem here is often surface defects in the ZnAlMg layer. For example, marbling (marble effect), "toothpick" or "beach pattern" defects may form on the ZnAlMg layer, or slag formation may occur. Some patents (such as EP20130826634AM / JMMataigne; JP20080256208NSSMC / Oohashi et al.) try to eliminate similar surface defects (glossy effect or displaced oxide scale) by other means (reducing the O2 content around the stripping nozzle).

[0009] In some cases, zinc coatings containing a small amount of aluminum (usually less than 1 wt.%) can also exhibit similar surface defects. These coatings are referred to herein as ZnAl coatings.

[0010] The object is therefore to provide a device for coating flat steel products with a ZnAlMg layer or a ZnAl layer which has a particularly durable and strong protection against corrosion, wherein the surface of the protective coating should be particularly homogeneous and free of marbling (no "marble effect") and / or toothpick-like defects (no "toothpick"). The aim is to achieve a surface quality that meets the highest customer requirements.

[0011] Furthermore, the device should consume as little energy as possible, be cost-effective to operate and be robust in use. Summary of the invention

[0012] According to the invention, a corresponding device is provided which uses a continuous (hot-dip) process and which can provide a flat steel product with a metallic ZnAlMg layer or ZnAl layer, which can be used, for example, as a (protective) coating. This layer is intended to protect the steel substrate of the flat steel product from external influences. In the following, the corresponding immersion bath is referred to as a zinc bath, wherein the term zinc alloy bath is intended to include baths containing mainly zinc (Zn) and small amounts of aluminum (Al) admixtures (usually less than 1% by weight), as well as baths containing a ZnAlMg alloy. The layer to be applied is also referred to here as a zinc-containing (protective) layer.

[0013] A device for applying a ZnAlMg layer or a ZnAl layer to a flat steel product is proposed. In all embodiments, the device comprises: - a zinc alloy melting pool with an input side and an output side, a stripping nozzle device with at least one gas nozzle for blowing off the front or rear side of the flat steel product with gas, the stripping nozzle device being arranged in the region of the outlet side, - a water vapor device arranged and configured so that it can emit gaseous water vapor in the region of the front and / or rear side of the flat steel product and provide a controlled water vapor environment with an absolute local humidity of more than 1 g / m 3 And less than 300g / m 3 The absolute local humidity is preferably 2.71 g / m 3 Up to 50g / m 3 within the range.

[0014] All embodiments relate to applying a Zn-containing (protective) layer to a flat steel product, the thickness of which corresponds to a target thickness (according to the respective specification). The layer is produced by passing the flat steel product through a zinc alloy melting bath and blowing it off with gas on the outlet side of the bath by means of a stripping nozzle arrangement comprising at least one gas nozzle.

[0015] In all embodiments, the zinc alloy of the zinc alloy molten pool may preferably have the following composition: - an aluminum content in the range between 1.0 and 3.0 weight percent, and preferably in the range between 1.3 and 2.8 weight percent, a magnesium content in the range between 1.0 and 2.5 weight percent, and preferably in the range between 1.2 and 2.2 weight percent, and - the remainder of the zinc alloy molten pool is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-related content of each additional element in the metallic coating being less than 0.1%, and unavoidable impurities.

[0016] In all embodiments, the zinc alloy of the zinc alloy molten pool may preferably have the following composition: - an aluminum content of less than 1.0 weight percent, and preferably in the range between 0.1 and 0.5 weight percent, and -The remainder of the zinc alloy molten pool is zinc and unavoidable impurities.

[0017] In all or at least some embodiments, the device is characterized in that it can be set up or prepared before the layer is applied and blown off to produce and coat flat steel products with a ZnAlMg layer or a ZnAl layer according to specifications.

[0018] When setting up / preparing the device, one or more of the following system parameters and / or method parameters are determined: - the bath temperature of the alloy melt bath, and / or - the thickness of the nozzle lip gap, and / or - the distance between the nozzle lip gap and the front or rear side of the flat steel product, - strip width of the flat steel product, - belt speed of the flat steel product as it moves along the stripping nozzle arrangement, - The flow rate of the gas emitted through the nozzle lip gap in the front or rear direction.

[0019] Preferably, the following definitions apply to system parameters and / or method parameters in all embodiments: - the thickness of the nozzle lip gap is in the range between 0.5 and 5 mm, preferably between 0.6 and 2 mm, particularly preferably between 0.8 and 1.5 mm, and / or - Effective flow rate (D) over the belt width between 200 and 8000 Nm per hour 3 and / or - the distance between the nozzle lip gap and the front or rear side of the flat steel product is in the range between 2 and 15 mm, preferably between 3 and 12 mm, and / or The belt speed is in the range between 50 and 200 m / min, preferably between 70 and 150 m / min.

[0020] The system parameters and the method parameters define the so-called stripping efficiency AWZ, which is essentially constant during the application of the layer (as long as the corresponding parameters do not change). However, the stripping efficiency AWZ may vary slightly.

[0021] All embodiments can have one of the following sensor layouts: - at least one sensor for determining the absolute local humidity within a short distance of the device, or - at least one sensor for determining the absolute local humidity around the device, or - at least one sensor for determining the absolute local humidity in the close proximity of the device and at least one sensor for determining the absolute local humidity in the surroundings of the device.

[0022] In all or at least some embodiments, the method is characterized in that a ZnAlMg layer or a ZnAl layer according to a target specification is applied to at least one side of the flat steel product, which is achieved by moving the flat steel product through a molten zinc alloy bath (ZnAl; ZnAlMg) and, on its outlet side, stripping gas exits through the nozzle lip gap of at least one gas nozzle in the direction of the flat steel product to blow off the coating according to the target specification, wherein the stripping efficiency AWZ is defined by the following parameters, which stripping efficiency AWZ remains essentially constant during the application of the coating: d The thickness of the nozzle lip gap of the gas nozzle of the stripping nozzle device, D is the effective flow rate (volume) of gas on each side of the flat steel product over the strip width, in Nm 3 / h, w is the strip width of the flat steel product, in mm, 2b Half width of the gas pressure distribution at the flat steel product, in mm, v The belt speed of the flat steel product when it moves along the stripping nozzle device, in m / min, The method comprises the following steps: - before and / or during the method, determining the absolute local humidity in a controlled water vapor atmosphere and / or the ambient air humidity f in the immediate vicinity of the front and / or rear side of the flat steel product UG , - Relating the determined humidity (e.g. determined as absolute humidity) to the stripping efficiency AWZ to determine whether the condition f>AWZ or f UG >AWZ, - if this condition is met, then starting or continuing the method of applying a layer; or if this condition is not met, then increasing the absolute local air humidity in the controlled water vapor environment at close range by using a water vapor device suitable for emitting gaseous water vapor to achieve the condition f>AWZ at close range, and then starting or continuing the method of applying a layer.

[0023] In some embodiments, the stripping efficiency is defined as follows:

[0024] In some embodiments, the stripping efficiency is defined as follows:

[0025] The following applies in each case: d is the thickness of the nozzle lip gap of the gas nozzle of the stripping nozzle device D is the effective flow rate (volume) of gas on each side of the flat steel product over the strip width k is the unitless scaling factor w is the strip width of the flat steel product 2b is the half width of the gas pressure distribution at the flat steel product v is the belt speed of the flat steel product as it moves along the stripping nozzle arrangement.

[0026] When determining the value of the half width and the value of the proportionality factor for the ratio of the use distance to the thickness of the nozzle lip gap, the following definitions apply: Situation 1.1: And k = 1 Case 1.2: Case 1.3: and

[0027] In order to prevent marbling and / or the formation of toothpick-like defects in the ZnAlMg layer or ZnAl layer to be produced, in at least some embodiments the absolute local humidity f is determined in the immediate vicinity of a controlled water vapor environment. Preferably, in all embodiments, the absolute local humidity f of the controlled water vapor environment is determined within a predefined virtual cylinder volume which surrounds or encloses the flat steel product in the region of at least one gas nozzle. In this case, the predefined virtual cylinder volume defines the immediate vicinity. Since the mixing of the gases takes place in front of and behind the flat steel product, regions parallel to the front and rear sides of the flat steel product are excluded when defining the virtual cylinder volume. Preferably, the virtual cylinder volume is limited by two planes for this purpose, each at a distance s / 2 from the flat steel product.

[0028] If the determined ambient humidity f UG is greater than the stripping efficiency (i.e. if f UG > AWZ), the layer can be produced without marbling or the formation of toothpick-like defects. If the determined ambient humidity f UG is currently below the stripping efficiency (i.e. if f UG < AWZ), the absolute local humidity f within the controlled water vapor environment is deliberately increased until the absolute local humidity f in the immediate vicinity is greater than the stripping efficiency (f > f UG and f > AWZ). Only then will the produced coating be free of marbling or the formation of toothpick-like defects.

[0029] In at least some embodiments, the absolute local humidity f of the controlled water vapor environment is generated by means of a water vapor device. That is to say, the water vapor device is configured to selectively increase the absolute local humidity f within the controlled water vapor environment (i.e. in the immediate vicinity).

[0030] In all embodiments, the controlled water vapor environment is defined in the immediate vicinity of the water vapor device, or a controlled water vapor environment is provided in the immediate vicinity of the water vapor device. In all embodiments, this immediate vicinity can be defined by a predefined virtual cylinder volume which extends on both sides of the flat steel product and which also surrounds or encloses at least one gas nozzle. However, in all embodiments, this volume can also optionally be defined by a housing or periphery surrounding the two sides of the flat steel product. If a housing or periphery is used, the internal region defined in this way is referred to as the immediate vicinity.

[0031] In at least some embodiments, the immediate vicinity of the water vapor device comprises between 1 m 3 and 10 m 3range, and preferably at least 2m 3 volume, wherein, when determining the absolute local humidity in the short distance (by direct or indirect measurement), it must be taken into account that, due to the mixing of gaseous water vapor with the stripping gas, the area directly adjacent to the flat steel product may be drier than areas further away from the flat steel product.

[0032] In all embodiments, it is preferred to selectively increase the absolute local humidity in the close proximity of the water vapor device (if the ambient humidity f UG Should be less than AWZ), where the current absolute local humidity is monitored or controlled by means of direct or indirect measurement at a distance of more than 20 cm from the flat steel product to avoid significantly drier areas.

[0033] In all embodiments, the apparatus or stripping nozzle system may include an automatic coating control configured to automatically adjust the flow rate of the (stripping) gas to keep the target thickness of the coating to be applied substantially constant. The automatic coating control is preferably configured to be able to compensate for fluctuations in one or more system parameters and method parameters.

[0034] In all embodiments using a molten pool of ZnAlMg alloy, the aluminum content (in weight percent) may be equal to or greater than the magnesium content (in weight percent).

[0035] In all or at least some embodiments, the range of unavoidable impurities is significantly lower than 1 weight percent (wt. %), preferably the sum of all unavoidable impurity contents is lower than 0.5 weight percent.

[0036] To precisely define the pool composition, monitor or observe the surrounding humidity UG In combination with optionally also monitoring or observing the current absolute local humidity f in the close proximity of the water vapor device and targeted regulation of the absolute local air humidity f in the close proximity of the water vapor device, a surface with no or negligible marbling and no or negligible toothpick defects can be produced. During the production of the respective coating, the stripping efficiency AWZ remains essentially constant in order to obtain a consistent coating that is within predetermined specifications.

[0037] In all the exemplary embodiments, the absolute local humidity f which should occur in the close proximity of the flat steel product according to the invention should be within a value of 1 g / Nm 3 Up to 300g / Nm 3 In the range of 2.71 g / Nm 3 Up to 50g / Nm 3 This means that the device can operate reliably at an absolute local humidity f within the above range.

[0038] In all embodiments, the stripping nozzle device can optionally be usefully followed by a strip stabilizer device that automatically stabilizes the movement of the flat steel product.

[0039] In all embodiments, the device is preferably operated within the following ranges: - The bath temperature TB of the alloy melting bath is in the range of 400 < TB < 480 °C, preferably in the range of 409 < TB < 473 °C, and particularly preferably in the range of 420 < TB < 460 °C, - The nozzle distance from the flat steel product, which is between 2 and 15 mm, preferably between 3 and 12 mm, - Using (stripping) gas to blow off the flat steel product on the outlet side of the alloy melting bath, and the gas flows through the nozzle lip gap in the direction of the flat steel product at a gas flow rate in the range of 200 to 8000 Nm per hour per meter of strip width. 3

[0040] The specifications of the ZnAl and ZnAlMg alloy concepts defined as above are the result of extensive research and calculations. Within the specific ranges of the alloy concepts defined herein, the technical teachings presented herein have proven to be particularly successful.

[0041] In at least some embodiments, the ambient humidity f is permanently measured. UG .

[0042] In at least some embodiments, the ambient humidity f is measured from time to time. UG .

[0043] In at least some embodiments, the absolute local humidity f is permanently measured at close range.

[0044] In at least some embodiments, the absolute local humidity f in the close range is measured from time to time.

[0045] Preferably, in all embodiments, the device operates at a bath temperature TB in the range of 420 < TB red < 460 °C. Within this range, the formation of slag is also reduced. red

[0046] Specific tests have shown that the method described herein does achieve very good results. It has been shown that excellent results can be obtained by making a targeted (pre) adjustment to the stripping process (or the corresponding stripping efficiency AWZ) as long as the absolute local air humidity f is set or specified to be higher than the stripping efficiency AWZ at close range.

[0047] The development of the new method and the targeted adjustment of the absolute air humidity f at close range for (method and system) parameters (or for the corresponding stripping efficiency AWZ) are based on theoretical considerations, various simulations of the stripping process, and extensive tests.

[0048] The processes in the area of ​​the stripping nozzle arrangement and at the flat steel product are very complex and depend on a large number of (process and system) parameters and influencing variables (or respectively the stripping efficiency). Therefore, the arrangement relies on some simplifying assumptions and specifications in order to obtain reproducible results.

[0049] By specifically increasing the absolute local humidity f within a controlled water vapor environment (referred to as "close proximity"), additional degrees of freedom can be gained for the definition or specification of method and system parameters.

[0050] Further advantageous embodiments of the invention form the subject matter of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Figure 1 A highly schematic diagram of a known device for dipping and stripping flat steel products is shown (prior art); Figure 2A shows a highly schematic diagram of a first example apparatus in which the method of the present invention is used; Figure 2B A schematic diagram of the height used to define the volume of the virtual cylinder is shown; Figure 3A shows a highly schematic side view of a stripping nozzle arrangement with only one nozzle to enable definition of certain method and system parameters associated therewith (the figure is not drawn to scale); Figure 3B A schematic diagram showing a pressure curve P at the surface of the coating as a function of the position on the x-axis; Figure 3C A schematic diagram showing a shear force curve τ at the surface of the coating as a function of the position on the x-axis; Figure 4 A summary diagram of a large number of example tests is shown, with the stripping efficiency AWZ plotted on the horizontal axis and the absolute air humidity f on the vertical axis; Figure 5 shows a highly schematic cross-sectional view of a further apparatus according to the invention in which the method according to the invention is used; Fig. 6A A schematic elevation view of the strip side of a flat steel product without marbling is shown; Figure 6B A highly schematic diagram showing the strip side of a flat steel product with medium marbling; Figure 6C A highly schematic view showing the strip side of a flat steel product with intense marbling; Figure 7 shows a table with example test results of the methods described herein; Figure 8 Example steps of the methods described herein are shown. DETAILED DESCRIPTION

[0052] The invention relates to a method for applying a layer 10 to a strip-shaped flat steel product 100 (see Figure 2B , in which layer 10 is vaguely recognizable on both sides) (see e.g. Figure 2A The layer 10 is produced by conveying the flat steel product 100 from the input side E through the zinc alloy melting bath 11 to the outlet side A and stripping it on the outlet side A by means of a stripping nozzle device 14 using a (stripping) gas G. The purpose of the stripping nozzle device 14 is to strip off the excess (still liquid) ZnMgAl layer or ZnAl layer (layer 10) on the flat steel product 100 after leaving the bath 11.

[0053] In the context of the present invention, care should be taken to ensure that the layer 10 is produced according to (predetermined) specifications (which define, for example, a target thickness) and that no marbling and / or toothpick defects appear / occur. More precisely, it is important to avoid these "defects" when ambient conditions vary in the production area (such as in a production hall). Even if the ambient air humidity f UG Should changes be made around the device 150, the device 150 according to the invention can also ensure that no marbling and / or toothpick defects occur and that the layer 10 continues to be produced according to specification.

[0054] In all embodiments, the specification may, for example, specify a target thickness of the layer 10 and / or a target (surface) coating of the layer 10. Typically, the tolerance range specified for the target thickness is narrow. As long as the layer 10 to be produced is within the tolerance range, the layer 10 substantially meets the requirements of the specification.

[0055] In at least some embodiments, the device 150 is operated and controlled so that the target thickness of the layer 10 on each strip side of the flat steel product 100 is within the tolerance window of the specification. Preferably, in all embodiments, the target thickness of the layer 10 on each strip side is in the range of 3 to 30 μm, and particularly preferably in the range of 4.5 to 15 μm.

[0056] Preferably, in at least some embodiments, the target surface coating (coating on each side of the belt) is between 20 and 200 g / m 2 In the range of 30 to 100 g / m 2 within the range.

[0057] The processes in the region of the stripping nozzle arrangement 14 and at the flat steel product 100 are very complex and depend on a large number of parameters and influencing variables.

[0058] In all embodiments, the stripping nozzle arrangement 14 comprises at least one gas nozzle 15 (if only one side of the tape is to be blown off), or two gas nozzles 15 facing each other (if both sides of the tape are to be blown off). Figure 2A and Figure 5 An embodiment with two nozzles 15 is shown, and Figure 3A An embodiment with only one nozzle 15 is shown. The flow rate D of the (stripping) gas G released along the front or rear side through the nozzle lip gap 17 is expressed in Nm here. 3 Indicates. (Nm 3 Stands for standard cubic meter). A standard cubic meter is the amount of gas G contained in a volume of one cubic meter. This applies at a temperature of 0 degrees Celsius and a pressure of 1.01325 bar.

[0059] In order to be able to reliably apply such a ZnAlMg based layer 10 which substantially corresponds to the target thickness, the zinc alloy of the zinc alloy molten pool 11 has the following composition in all or at least some embodiments: - an aluminum content in the range between 1.0 and 3.0 weight percent, and preferably in the range between 1.3 and 2.8 weight percent, a magnesium content in the range between 1.0 and 2.5 weight percent, and preferably in the range between 1.2 and 2.2 weight percent, and - The remainder of the zinc alloy molten pool 11 is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-related content of each additional element in the metallic coating (i.e. in the layer 10) being less than 0.1%, and unavoidable impurities.

[0060] In all or at least some of the embodiments relating to the ZnAlMg based layer 10, a metal pool with a particularly preferred ZnAlMg alloy is provided as the alloy melt pool 11, which is composed according to the following alloy concept: - an aluminum content (in weight percent) in the range between 2.09 and 2.66 weight percent; - a magnesium content (in weight percent) in the range between 1.45 and 2.24 weight percent; - The remainder is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-related content of each additional element in the metallic coating (i.e. in layer 10) being less than 0.1%, and unavoidable impurities.

[0061] In order to be able to reliably apply a ZnAl-based layer 10 that substantially corresponds to the target thickness, the zinc alloy of the zinc alloy molten pool 11 has the following composition in all or at least some embodiments: - an aluminum content of less than 1.0 weight percent, and preferably in the range between 0.1 and 0.5 weight percent, and -The remainder of the zinc alloy molten pool is zinc and unavoidable impurities.

[0062] In order to prevent the formation of marbling and / or toothpick defects, or to significantly reduce marbling and toothpick defects, in all embodiments, the absolute local air humidity f and / or the ambient air humidity f in the close distance NB is preferably determined continuously or from time to time (e.g. by direct or indirect measurement). UG .

[0063] In all embodiments, the device 150 includes a water vapor device 50 (see Figure 2A and Figure 5 ), which will be described in more detail. In all embodiments, the water vapor device 50 is preferably located in the region of the outlet side A of the pool 11.

[0064] In at least some embodiments, the short distance NB (see Figure 2A , 5 ) in the absolute local air humidity f. Figure 2A and 5 In the embodiment, the corresponding device 150 comprises a humidity sensor 51 arranged in the close range NB or protruding into the close range NB, so as to be able to continuously or from time to time control the absolute local air humidity f in the close range NB. The control of the absolute local air humidity f in the close range NB can control the air humidity f in the close range NB in ​​a targeted manner.

[0065] In all exemplary embodiments, however, the humidity sensor 51 for determining the absolute local air humidity f can also be arranged at a different location of the device 150 .

[0066] In all embodiments, the device 150 may include a device for determining the ambient air humidity f UG At least one humidity sensor 56, such as Figure 2A and Figure 5 Shown above right.

[0067] Absolute air humidity f is a physical quantity, for example, it can be expressed in units of g / m 3 In other words, it is expressed in a volume of 1m 3 The mass ratio of gaseous water WG in a standard volume. In other words, the absolute air humidity f represents the content of gaseous water vapor in a volume. Here, f and f are used UGAs the formula symbol of absolute air humidity. In all embodiments, the absolute air humidity f and f can be roughly estimated from the air temperature TL and the relative air humidity r UG , whereby the following applies: rRelative air humidity, in % TL: air temperature, in °C.

[0068] In all embodiments, the measurement / monitoring of the absolute local air humidity f can be carried out directly or indirectly (preferably within a short distance NB). Indirect measurement here is mainly understood to mean measuring the air temperature TL and the relative air humidity r and calculating / deriving the absolute local humidity f. Correspondingly, the ambient air humidity f can also be determined in all embodiments by measuring the air temperature TL and the relative air humidity r of the ambient air and calculating / deriving the absolute ambient air humidity. UG .

[0069] The absolute local air humidity f which should be present according to the invention in the short distance NB near the flat steel product 100 between the outlet side A and the cooling zone 16 (if any) has a value of 1 g / m 3 and less than 300g / m 3 Preferably, in all embodiments, the absolute local air humidity f is within the range of 2.71 g / m 3 Up to 50g / m 3 within the range.

[0070] The device 150 is capable of measuring the absolute local air humidity f at a close distance NB at 1 g / m 3 Up to 300g / m 3 Targeted adaptation / regulation within a range of values.

[0071] To this end, in all embodiments, the device 150 may comprise at least one steam generator DG in or at a close distance NB. Figure 2A An embodiment with two steam generators DG is shown, which are placed at the upper edge at a close distance NB close to the front and rear sides of the flat steel product 100 . Figure 5 An embodiment is shown with four steam generators DG, which are arranged outside the close distance IB and introduce gaseous water vapor WG into the close distance NB via gas lines 54 and inlet bridges 53 near the front and rear sides of the flat steel product 100 .

[0072] Preferably, in all embodiments, one or more steam generators DG are used which are converted as high-purity steam generators which generate gaseous water vapor WG from pure or highly pure water.

[0073] Before applying the layer 10 to the flat steel product 100 and blowing off the layer 10, the device 150 is set or prepared. During the setting / preparation process, one or more of the following system parameters and / or method parameters can be set in all embodiments: - the bath temperature TB of the molten bath 11, and / or - the thickness d of the nozzle lip gap 17, and / or - nozzle distance Z between nozzle lip gap 17 and the front or rear side of the flat steel product 100, - strip width w of the flat steel product 100, - the strip speed v of the flat steel product 100 as it moves through the stripping nozzle arrangement 14, - The flow rate D of the (stripping) gas G emitted through the nozzle lip gap 17 in the front or rear side direction.

[0074] In all embodiments, care is taken to ensure that the system parameters and / or method parameters are specified so that the layer 10 to be applied substantially complies with the specifications. This means that care is taken to apply and blow off a layer 10 which, for example, complies with the target thickness (within tolerances) and which at the same time exhibits no or only very slight marbling and no or only very slight toothpick defects.

[0075] In all embodiments, the current flow rate D of the gas G can be automatically adjusted in a known manner (e.g. controlled by an automatic coating control) to keep the target thickness of the layer 10 to be applied substantially constant if one or more of the system parameters and / or method parameters should be changed.

[0076] In the following, a mathematical relationship which can be used here during the setup / preparation will be described. It will also be described how the so-called stripping efficiency AWZ can be defined by means of the method and system parameters.

[0077] Figure 3A Also shown are the nozzle distance Z between the nozzle 15 and the respective strip side (here the front side) of the flat steel product 100 , as well as the thickness d of the nozzle lip gap 17 . The nozzle lip gap 17 serves as an exhaust gap for the stripping nozzle arrangement 14 .

[0078] Figure 3A Additionally, the supply of gaseous water vapor WG according to the invention is shown in purely schematic form (by means of two block arrows to the left and right of the nozzle 15 ).

[0079] Available Figure 3A To define the adjustable parameters (system and method parameters) or the stripping efficiency AWZ. The important adjustable method and system parameters are - the thickness d of the nozzle lip gap 17, - flow rate D of gas G, - distance Z between the nozzle lip gap 17 and the (strip) side of the flat steel product 100, The strip speed v (parallel to the x-axis) at which the flat steel product 100 is removed from the zinc alloy molten bath 11 .

[0080] Figure 3B A schematic diagram of a gas pressure curve P along the front side of a flat steel product 100 is shown. The pressure P depends on the position on the x-axis. Ideally, the pressure curve P has a Gaussian shape, such as Figure 3B The Gaussian curve can be used to determine the pressure P S / 2, as shown, where P S Represents the maximum pressure. 2b is the half width in millimeters. A narrow gas jet is defined by a small half width 2b. The larger (wider) the gas jet becomes, the larger the half width 2b becomes. For more details, see the publication "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet", CVTu et al., Experimental Thermal and Fluid Science, 1996, Vol. 16, pages 364-373, Elsevier Science Inc.

[0081] The gas jets exiting the nozzles 14 and the force of gravity (if the flat steel product 100 is pulled vertically upwards out of the tank 11, as for example Figure 2A and Figure 5 Together with the shear force τ, the layer 10, which is still liquid, is exerted. Figure 3C A graph showing the shear force τ versus position on the x-axis (shear force τ is given by Figure 3B = τ = 0. This is the shear force τ acting on the layer 10 to be peeled off. To a first approximation, the shear force curve τ runs symmetrically about the point x = 0, τ = 0 (if the belt speed v parallel to the x axis is neglected). The nozzle 15 is located at a distance Z>0 directly above the position x = 0. τ max The maximum shear force occurring at the layer 10 to be peeled is defined.

[0082] The strip-shaped flat steel product 100 passes through the distance between the maximum shear forces / (see Figure 3C There is a direct relationship between the time t, the tape velocity v and the half-width 2b, as expressed in equation (1):

[0083] In all exemplary embodiments, the belt speed v is preferably in the range of 50 m / min to 200 m / min and particularly preferably between 70 and 150 m / min.

[0084] The equations describing the dynamic flow behavior of the gas G at the flat steel product 100 are very complex. This is mainly due to the fact that in the gas jet leaving through the nozzle lip gap 17 of the nozzle 15, a region with laminar and turbulent flow patterns is formed on the layer 10 of the flat steel product 100. In addition, the gas jet sucks in the surrounding air, which swirls with the gas G. For details, see, for example, the publication "Measurement of wall pressure and shear stress under an impinging jet" already mentioned. In addition to the surrounding air, the gas jet also sucks in gaseous water vapor WG.

[0085] Due to the complex interrelationships, complex tests and statistical evaluation of the measurement results do not provide any directly usable results on the correlation between the stripping nozzle parameters, air humidity and marbling. Only after a systematic investigation of various internal and external influencing variables did a correlation emerge between the degree of marbling on the layer 10 and the ambient conditions of the test setting. Air humidity in particular showed an influence on the marbling.

[0086] Further targeted investigations and graphical processing of these test results showed for the first time a correlation between (ambient) air humidity and marbling. Figure 4 A graphical summary of a large number of tests is shown in g / m 3 The absolute air humidity f is plotted on the vertical axis and the stripping efficiency AWZ (as a summary or general term for process and apparatus parameters) is plotted on the horizontal axis.

[0087] By max and t are weighted and added together (see also Figure 3C and equation (1)), can be compared with the absolute ambient air humidity f UG The directly comparable stripping efficiency AWZ can be determined as follows (inequality (2.1)):

[0088] The right-hand side of inequality (2.1) corresponds to the stripping efficiency AWZ, that is, the following relationship (2.2) applies: f UG >AWZ (2.2)

[0089] In at least some embodiments, the stripping efficiency is defined as follows:

[0090] In at least some embodiments, the stripping efficiency is defined as follows:

[0091] The following applies in each case: d is the thickness of the nozzle lip gap of the gas nozzle of the peeling nozzle device 14 D is the effective flow rate (volume) of gas G on each side of the flat steel product 100 over the strip width w k is the unitless scaling factor w is the strip width of the flat steel product 100 2b is the half width of the pressure distribution of the gas G at the flat steel product 100 v is the strip speed of the flat steel product 100 as it moves along the stripping nozzle arrangement 14 .

[0092] When determining the value of the half width b and the value of the proportionality factor k for the ratio of the nozzle distance Z to the thickness d of the nozzle lip gap 17, the following definitions apply (thereby distinguishing between the three cases 1.1, 1.2 and 1.3): Situation 1.1: And k = 1 Case 1.2: Case 1.3: and

[0093] Reference below Figure 4 . Figure 4 The black filled circles in the figure represent flat steel products 100 with a clear marbleization on the surface of the layer 10, and the grey filled circles represent flat steel products 100 with a moderate marbleization. On the other hand, the unfilled circles indicate no or negligible marbleization. All the tests shown were conducted with a nozzle lip gap thickness of d = 1.0 mm.

[0094] Figure 4 A total of five test pairs are shown (Examples 1-5). The corresponding method and system parameters are listed in Table 1 as well as the stripping efficiency AWZ and the absolute air humidity f measured in the close distance NB. Figure 7 The third column from the bottom of Table 1 indicates whether the water vapor device 50 is turned on to increase the local air humidity. The black circles, gray circles and white circles used in Table 1 are Figure 4 The penultimate column indicates in words whether there is strong marbling, moderate marbling, or no marbling, and the last column on the far right of Table 1 indicates whether the condition of the inequality f>AWZ is satisfied.

[0095] exist Figure 4A straight line Ge is inserted as a demarcation line to, as a first approximation, separate those tests with marbling from those tests without or with negligible marbling. In the tests above the straight line Ge, no or negligible marbling appears ( Fig. 6A and a corresponding flat steel product 100 with no marbling in its layer 10 is shown). The straight line Ge can be understood as a function of the stripping efficiency AWZ and is defined as follows: f = AWZ

[0096] A detailed evaluation of the test results shows that for a given stripping efficiency AWZ, it is possible to ensure that the inequality (2.2) is always satisfied during production by specifically increasing the absolute local air humidity f in the close proximity NB.

[0097] In all embodiments, the bath temperature TB of the alloy melting bath 11 is preferably in the range of 400 < TB < 480 degrees Celsius, preferably in the range of 409 < TB < 473 degrees Celsius, and particularly preferably in the range of 420 < TB < 460 degrees Celsius.

[0098] In all embodiments, the bath temperature TB is specified within the specified temperature range to operate the melting bath 11. It is very important to maintain this temperature window (temperature range) because when operating outside the specified range, more undesired slag will form at the flat steel product 100.

[0099] In all embodiments, the bath temperature TB can be predetermined, for example, by means of an induction heating device 30 (see Figure 2A and 5 ) or a resistance heater.

[0100] To avoid slag formation, in all embodiments, the alloy melting bath 11 is preferably operated at a reduced bath temperature TB red The reduced bath temperature TB red is preferably in the range already mentioned of 420 < TB red < 460 degrees Celsius.

[0101] The bath temperature TB is an important parameter and can preferably be set / preset relatively freely within the above temperature range in all embodiments, provided that the AWZ is kept substantially constant if other method and system parameters are adjusted, and the condition f > AWZ is still satisfied if the air humidity in the close proximity NB is adjusted.

[0102] When operating the device 150, it is preferably noted in all embodiments that - the thickness d of the nozzle lip clearance 17 is in the range between 0.5 and 5 mm, preferably between 0.6 and 2 mm, and particularly preferably between 0.8 and 1.5 mm, and / or - Flow rate D between 200 and 8000 Nm per hour 3 within the scope of, and / or - the distance Z is in the range between 2 and 15 mm, preferably between 3 and 12 mm, and / or - the belt speed v is in the range between 50 and 200 m / min, preferably between 70 and 150 m / min.

[0103] Device 150 operates particularly reliably within these (value) ranges.

[0104] In all embodiments, the corresponding gas nozzle 15 has a longitudinal extension parallel to the y-axis. Preferably, in all embodiments, the effective length (active length) of the nozzle 15 ) (referred to as nozzle length DL) corresponds to the strip width w of the strip-shaped flat steel product 100 (see Figures 6A-6C ). The thickness d of the gas nozzle 15 is defined as parallel to the x-axis (see Figure 3A ).

[0105] In all exemplary embodiments, the strip width w of the strip-shaped flat steel product 100 is in the range of 500 mm to 2500 mm and particularly preferably in the range of 1159 mm to 1614 mm.

[0106] In at least some embodiments, the absolute local air humidity f in the close distance NB is measured permanently or from time to time, and if the absolute local humidity f in the close distance NB "has the potential (droht)" to fall below a threshold value defined by the AWZ, the air humidity is increased by using the water vapor device 50. To this end, the steam generator DG can increase the output of gaseous water vapor, or the steam generator DG can be switched on to produce gaseous water vapor.

[0107] In at least some embodiments, the steam generator DG preferably includes a steam generator and, for example, a valve 55 that can control the flow of gas through the pipeline 54 (see Figure 5 To this end, in all embodiments, the steam generator and / or the valve 55 may be connected to a controller 250 (not shown).

[0108] The absolute local air humidity f is preferably not measured directly at the impact line where the gas G hits the layer 10 to be stripped, since the gas mixture there is relatively "dry" (i.e., low in air humidity). Instead, in all exemplary embodiments, the absolute local air humidity f is measured directly or indirectly in a region at a distance of at least 20 cm s / 2 from the impact line. Figure 2A In the embodiment shown, the humidity sensor 51 is accordingly positioned a short distance above the nozzle 15 and the impingement line. Figure 5 In the embodiment of FIG. 5 , the humidity sensor 51 is located a short distance below the nozzle 15 and the impingement line.

[0109] exist Figure 2B In the embodiment, the virtual cylindrical volume vZV is shown as an example in the form of a schematic diagram. The predefined virtual cylindrical volume vZV is at least one gas nozzle 15 ( Figure 2B The predefined virtual cylindrical volume vZV defines the close distance NB in ​​this case. Since the mixing of the gases WG and G occurs close to the front and rear sides of the flat steel product 100, the definition of the virtual cylindrical volume vZV excludes the areas parallel to the front and rear sides of the flat steel product 100, such as Figure 2B Preferably, the virtual cylindrical volume vZV is bounded for this purpose by two planes, each of which is at a distance s / 2 from the flat steel product 100 .

[0110] Figure 2A and Figure 5 Display for direct measurement of absolute local air humidity f and ambient air humidity f UG The device 150 comprises, for example, two humidity sensors 51 (at least one on each side of the belt) and a humidity sensor 56. In the schematic diagram, each of the sensors 51 and 56 has two contacts, which can be connected to, for example, the controller 250. The corresponding connections or lines V1, V2, V3, V4, V5, V6 are Figure 2A and Figure 5 Shown with dotted lines.

[0111] In all embodiments, sensors of the following designs or modes of operation can be used as humidity sensors 51 and 56: - Mechanically operated measuring sensors, based on the humidity-induced expansion or contraction of the (usually organic) measuring element; - hygrometric measuring sensors, in which two identical, very precise thermometers are used, along which the gas flow to be measured is guided at a defined speed; - capacitive measuring sensors, such as humidity-sensitive capacitors comprising two flat electrodes; - Dew point hygrometers, which determine the air humidity with a dew point mirror, wherein the condensation of water vapor is evaluated when the dew point is below; - resistance measurement, in which, for example, the impedance of the alternating current resistance of the hygroscopic element is determined; Spectroscopic measurements, for example contactless measurement of the gaseous water content in the near-infrared or mid-infrared (NIR or MIR) range.

[0112] Indirect measurement of absolute local air humidity f or ambient air humidity f UG When measuring the air humidity directly, the current air humidity is not determined directly, but indirectly (eg optically).

[0113] In all exemplary embodiments, the surface properties of the coated flat steel product 100 can be measured (three examples of coated flat steel products 100 are shown in FIG. Fig. 6A , 6B 6C ). For example, the surface properties can be measured optically before the optional cooling zone 16 or after the optional cooling zone 16 (for example, by optically measuring the reflectivity of the surface of the layer 10). If there is little or no marbling, the reflectivity is above a predetermined limit value. If the reflectivity should be reduced (for example, it is below the tolerance limit), the air humidity in the close distance NB can be adjusted so that the inequality f>AWZ is satisfied again.

[0114] All embodiments of the apparatus 150 may include a controller 250. In all embodiments, the controller 250 may be configured as a computer-supported automation and control unit and include a human-machine interface, a computer, and a database.

[0115] In all embodiments, controller 250 may be part of an overall system controller of device 150 or, in all embodiments, may be connected to an overall system controller.

[0116] The setting / preparation of the device 150 by adjusting parameters (system or method parameters) can then be performed by the overall system controller in these embodiments and / or by the controller 250 .

[0117] In all embodiments, the above-mentioned stripping efficiency AWZ can be calculated by the controller 250 and / or by the overall system controller. The corresponding formula is as follows. However, in all embodiments, the stripping efficiency AWZ can also be determined by an external method (such as with the help of a workstation computer).

[0118] In all exemplary embodiments, an inert gas is preferably used as the (stripping) gas G. Nitrogen or a nitrogen-containing gas mixture has proven to be particularly effective.

[0119] To ensure that the target thickness of layer 10, or the coating on each side of the tape, does not vary or barely varies, care should be taken to ensure that the system and method parameters or stripping efficiency AWZ remain substantially constant. In Examples 1 and 2, AWZ is kept constant (see Figure 7 In Examples 3, 4 and 5, AWZ remains substantially constant (see Table 1). Figure 7 Table 1 in the table).

[0120] However, when specifically increasing the absolute local air humidity f in the close distance NB, it is important to take care to ensure that defects other than marbling, such as the formation of toothpick defects, slag etc., are also avoided.

[0121] If, for example, the humidity of the surrounding air is f UGVery low, inhalation of dry ambient air can lead to marbling on layer 10 (if f UG The invention is effective in automatically increasing the absolute local air humidity f in the controlled water vapor environment in the close distance NB of the flat steel product 100, while the AWZ remains substantially constant.

[0122] Preferably, the inequality (2.2) is implemented by software in the controller 250, or the stripping efficiency AWZ to be specified and the corresponding minimum humidity f min The digital pairs are stored in one or more tables. Using the "lookup" table, the controller 250 can then determine the minimum value f of the absolute local air humidity f for the currently applied stripping efficiency AWZ. min , and transmits it to the water vapor device 50. Then, the water vapor device 50 generates a current greater than f in the close distance NB. min In these embodiments, f min More or less corresponds to Figure 4 The straight lines in the.

[0123] In all embodiments, the following parameters (system and / or method parameters) are preferably used within the numerical or value ranges. The individual numerical or value ranges in Table 2 are not related to each other, or are only not related in part, because the corresponding maximum and minimum values ​​are derived from different test examples. Figure 7 ) Select the corresponding maximum and minimum values ​​and summarize them here.

[0124] Table 1 (see Figure 7 ) shows Figure 4 Specific numerical values ​​of the test results shown. Figure 7 Table 1 in FIG. 1 shows five test examples, in which the stripping efficiency AWZ is increased by specifying suitable method and / or system parameters and by increasing the absolute local humidity value f in the close distance NB (e.g. Fig. 6A ), a layer 10 without (visible) marbling is produced. In the first two columns of Table 1, the coating on each side and the strip width w of the flat steel product 100 are given according to the specifications.

[0125] exist Figure 4 The graphs shown in Figure 1 and Table 1 ( Figure 7 In the test example shown in ), the following applies. If the ambient air humidity f UGIf marbling defects occur under given method and system conditions, then at least in the close distance NB, the absolute local air humidity f (corresponding to the left-hand side of inequality (2.2)) in the close distance NB can be increased according to the present invention until inequality (2.2) is satisfied to eliminate the marbling.

[0126] Apart from the usual changes in production, the method and system conditions, i.e. the process and stripping nozzle parameters, can remain unchanged as shown in Table 1 ( Figure 7 )

[0127] Table 1 illustrates five examples 1-5 of using the water vapor device 50 to increase the absolute local humidity f in a close distance NB.

[0128] In specific examples 1-5, the nozzle spacing Z, the nozzle lip gap d and the belt speed v were kept constant, and the coating, the belt width w, the nozzle pressure, the flow rate D and the pool temperature TB were not deliberately changed and were only affected by the usual variations in production. This means that in each example, the stripping efficiency AWZ calculated therefrom remained essentially unchanged (±10%). Preferably, in all embodiments, the device 150 is operated so that when the absolute local air humidity f in the close distance NB is increased and the method and system parameters are adjusted, the calculated stripping efficiency AWZ varies by a maximum of ±5%.

[0129] The initial situation of Example 1 is shown in Table 1, 1.1 (Table 1, row 1.1): For the given method and stripping nozzle parameters, at the existing absolute ambient air humidity f UG 3.8g / m 3 When , the stripping efficiency AWZ is 9.6 according to inequality (2.2). Therefore, the condition for production without marbling in inequality (2.2), i.e. f>AWZ, is not satisfied. In fact, strong marbling defects also appear in the production under these conditions. Figure 4 It shows that at AWZ = 9.6 and f = 3.8 g / m 3 The corresponding black circle.

[0130] On this basis, the water vapor device 50 is used to increase the local absolute air humidity f in the close distance NB from 3.8 to 20.6 g / m 3 , where the method and stripping nozzle parameters remain within the usual process dispersion range (Table 1, row 1.2). After a targeted increase in the air humidity f, the condition for marbling-free production in inequality (2.2) is met, i.e. f>AWZ. In fact, under these conditions, marbling defects no longer occur on layer 10. Figure 4 It shows that at AWZ = 9.6 and f = 20.6 g / m 3The block arrows marked 1.1→1.2 mark this first example.

[0131] Examples 2-5 should be understood to be similar to Example 1. The block arrows labeled 2.1 → 2.2 represent the second example, and the block arrows labeled 3.1 → 3.2 represent the third example. Figure 4 Examples 4 and 5 are also marked accordingly.

[0132] from Figure 7 From Table 1 in the following pairs of values ​​of stripping efficiency AWZ and absolute local air humidity f can be extracted (sorted from smallest to largest stripping efficiency AWZ). All values ​​of absolute local air humidity f are greater than the corresponding AWZ (in Figure 4 , the corresponding white filled circle is above the line Ge).

[0133] from Figure 7 From Table 1 in the figure, the following pairs of values ​​of stripping efficiency AWZ and absolute air humidity f can also be extracted (sorted from small to large by stripping efficiency AWZ). All values ​​of absolute local air humidity f are less than the corresponding AWZ (in Figure 4 , the corresponding black or gray filled circle is below the straight line Ge).

[0134] Figure 5 A further embodiment of a device 150 is shown, wherein here also a method for directly measuring the absolute local air humidity f in the close distance NB and the ambient air humidity f in the vicinity of the device 150 is used. UG The setting of the device 150 is Figure 2A The device 150 shown in FIG. 1 is similar to that shown in FIG. 1 , and therefore may also be referred to as Figure 2A However, with Figure 2A The difference is, Figure 5 The device 150 in the embodiment has a housing 52. Such a housing 52 is optional, since it is sufficient for the present invention if the water vapor device 50 generates a sufficiently high absolute local air humidity f in the close distance NB.

[0135] The liquid ZnAlMg alloy or ZnAl alloy is located in a bath 11 , which is shown here as a rectangular container open at the top. Figure 5 Only a short length of the strip-shaped flat steel product 100 is shown after it has been leached out of the tank 11. The flat steel product 100 is guided vertically out of the tank 11 at a strip speed v in the x-axis direction between two opposing gas nozzles 15 of the stripping nozzle arrangement.

[0136] The water vapor device 50 here comprises the above-mentioned housing 52, which here, for example, is defined by an approximately cylindrical shape in three-dimensional space. Figure 5 In FIG. 5 , a substantially cylindrical housing 52 of a water vapor device 50 is schematically shown. The housing 52 here consists of two housing halves arranged symmetrically about the x-axis. The close distance NB defined in this way is almost between the two halves of the housing.

[0137] The shell 52 of the water steam device 50 can be divided into four quadrants in the schematic cross-sectional view. Here, the water steam device 50 includes a steam generator DG in each quadrant (i.e., two steam generators DG in each shell half). Each steam generator DG is arranged outside the close distance NB (or outside the shell 52). As shown in the figure, each steam generator DG can introduce gaseous water vapor WG into the close distance NB via a corresponding gas pipeline 54, a valve 55 and an inlet bridge 53. Figure 5 As can be seen in the cross-sectional view of FIG, each inlet bridge 53 is fluidly connected to the close distance NB via at least one channel opening in the shell 52. In this way, gas can flow from the corresponding steam generator DG into the close distance NB through the pipeline 54, the valve 55 and the inlet bridge 53. The shell 52 can optionally have a series of such channel openings parallel to the y-axis so that the gas WG can be evenly distributed in the close distance NB.

[0138] In this embodiment, the housing 52 of the water vapor device 50 is located directly at the nozzle 15 of the stripping nozzle device, and its housing height is defined parallel to the x-axis. Preferably, the housing length defined parallel to the y-axis corresponds in all embodiments at least to the strip width w of the flat steel product 100 and / or the length DL of the nozzle 15 (also defined parallel to the y-axis).

[0139] In all embodiments, the housing 52 of the water vapor device 50 may also have different shapes.

[0140] As shown in the figure, with the help of pump P G An inert (stripping) gas G is supplied to each nozzle 15. Two pumps P G In terms of control (or regulation), it is connected to the controller 250, and thus the controller 250 can, for example, control the gas flow D on each belt side. The corresponding connecting lines or pipelines are Figure 5 The pumps are marked as V7, V8, V9 and V10. G This refers to, for example, a blower with a control valve.

[0141] Preferably, all embodiments of the apparatus 150 include control of the flow rate D of the gas G (referred to as automatic coating control), which is configured to always produce a layer 10 with a substantially constant target thickness regardless of changes in other method and system parameters. To this end, the control includes at least one sensor (not shown) that measures the actual thickness of the layer 10 after blowing off the excess molten zinc. If the actual thickness is less than the target thickness, the control reduces the flow rate D, and vice versa.

[0142] In all or at least some embodiments, the absolute local air humidity f in the close range NB can be measured along a horizontal y-line parallel to the flat steel product 100 and parallel to the y-axis (which is, for example, at least s / 2 = 20 cm from the flat steel product 100). In Figure 2A the embodiment, this horizontal y-line is generally in the region between the nozzle 15 of the stripping nozzle device 14 and the two steam generators DG. In Figure 5 the embodiment, the described y-line is between the outlet side A of the bath 11 and the nozzle 15 (a short distance below the nozzle 15 here).

[0143] Each nozzle 15 can be moved parallel to the z-axis by an engine or actuator (not shown). The engine or actuator can be connected to the controller 250. There are sensors (not shown) to enable control of the nozzle spacing Z. Thus, the nozzle distance Z can be set and / or controlled via the controller 250. In all embodiments, the control of the nozzle distance Z can be laser-supported. If the housing halves of the housing 52 are mechanically connected to the nozzle 15, the housing halves can move together with the nozzle.

[0144] In all embodiments, the controller 250 can also be connected to the induction heater 30 or the resistance heater of the bath 11 to adjust the bath temperature TB. In the case of the induction heater, its coil 30 is as Figure 5 shown, and the controller 250 can set the operating frequency for driving the coil 30 via the frequency generator FG. Therefore, as shown, the frequency generator FG is connected to the controller 250 for control purposes. The corresponding connection lines or pipes are labeled V11 and V12 in Figure 5 A.

[0145] Preferably, in all or at least some embodiments, the water vapor device 50 is configured to specify an absolute local air humidity f in the local range NB within the range of 1 g / m 3 to 300 g / m 3 preferably within the range of 2.71 g / m 3 to 50 g / m 3 wherein, preferably, the water vapor device 50 is only turned on or switched on when f UG <AWZ.

[0146] In all embodiments, the volume of the water vapor device 50 (eg, defined by the virtual cylinder volume vZV or by the housing 52) at a close distance NB may be within 1 m 3 and 10m 3 between.

[0147] Figure 8 Exemplary steps of a method that may be performed in the apparatus 150 are shown. Figure 8 These steps are shown in the form of a flow chart. Before the method for applying a layer 10 to a flat steel product 100 is carried out, the individual components and elements of the device 150 are set or prepared (step S1). For example, the device 150 can be set or prepared based on the target specifications of the layer 10 to be applied. Setting or preparing includes defining and (pre-)setting method and system parameters.

[0148] Before, during or after setting S1, the corresponding stripping efficiency AWZ is determined (step S2). It is then determined using one of the inequalities or the "lookup" table whether the condition f>AWZ is satisfied (step S3). If f is greater than AWZ ("yes" in the flow chart), the method for applying the layer 10 can be started (step S4). If the condition f>AWZ is not satisfied ("no" in the flow chart), the method branches to step S5. In step S5, the air humidity f in the close distance NB is increased by the water vapor device 50. It is then checked again in step S3 whether the condition f>AWZ is now satisfied.

[0149] Optionally, method and / or system parameters can also be slightly adjusted in intermediate steps, wherein in all exemplary embodiments such adjustments are preferably made in such a way that AWZ remains essentially constant.

[0150] Similarly, during the application of the layer 10, the condition f>AWZ can be repeatedly checked from time to time to be able to react to changing ambient conditions. If f in the surroundings or in the close distance NB of the device 150 drops, it should be checked again (as in step S3) whether the condition f>AWZ is still met. If so, the application of the layer 10 is continued. If not, the air humidity f in the close distance NB can be increased (similar to step S5).

[0151] If f near the device 150 UG If the target specification cannot be reached, the process may be interrupted.

[0152] Reference numerals

Claims

1. A device (150) for applying a layer (10) to the front and / or rear side of a flat steel product (100), the device (150) comprising: - a zinc alloy molten pool (11) (ZnAl; ZnAlMg) with an input side (E) and an outlet side (A), a stripping nozzle device (14) with at least one gas nozzle (15) for blowing off the front or rear side of the flat steel product (100) with gas (G), the stripping nozzle device (14) being arranged in the region of the outlet side (A), A water vapor device (50) configured to emit gaseous water vapor and provide a controlled water vapor environment in a close distance (NB) to the front and / or rear side of the flat steel product (100), the absolute local humidity (f) of the controlled water vapor environment being greater than 1 g / m 3 And less than 300g / m 3 The absolute local humidity (f) is preferably 2.71 g / m 3 Up to 50g / m 3 within the range.

2. The device (150) according to claim 1, characterized in that In order to apply the layer (10), system parameters and method parameters of the device (150) are set so that the layer (10) can be blown off according to predetermined specifications using the stripping nozzle device (14), and the system parameters and method parameters define a stripping efficiency (AWZ), which is essentially constant during the application of the layer (10).

3. The device (150) according to claim 2, characterized in that The stripping efficiency (AWZ) is defined as follows: Or defined as follows: in Applicable: d is the thickness (d) of the nozzle lip gap (17) of the at least one gas nozzle (15) of the stripping nozzle device (14), in mm D is the effective flow (D) of the gas (G) on each side of the flat steel product (100) over the strip width (w), in Nm 3 / h k is a unitless proportionality factor w is the strip width of the flat steel product (100) in mm 2b is the half width of the pressure distribution of the gas (G) at the flat steel product (100), in mm v is the belt speed of the flat steel product (100) when it moves along the stripping nozzle device (14) and through the close distance (NB), and the unit is m / min.

4. The method according to any one of claims 1 to 3, characterized in that The following definition applies to the ratio of the half width (b) and the proportionality factor (k) of the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17): Situation 1.1: And k = 1 Case 1.2: Case 1.3: and 5. The method according to any one of claims 1 to 3, characterized in that When determining the value of the half width (b) and the value of the proportionality factor (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17), the following simplified definitions apply: Case 2.1: And k = 1 Case 2.2: and 6. The device (150) according to claim 3, characterized in that: - the thickness (d) of the nozzle lip gap (17) is in the range between 0.5 mm and 10 mm, preferably between 0.8 mm and 2.0 mm, and / or - The flow rate (D) is between 200 and 8000 Nm per hour 3 within the scope of, and / or - the distance (Z) between the nozzle lip gap (17) and the front or rear side of the flat steel product (100) is in the range between 2 mm and 15 mm, preferably between 3 mm and 12 mm, and / or - the belt speed (v) is in the range between 50 m / min and 200 m / min, preferably between 70 m / min and 150 m / min, and / or - The volume of the near distance (NB) is 1m 3 Up to 10m 3 and preferably has a volume of at least 2m 3 .

7. The device (150) according to any one of claims 1 to 5, characterized in that The absolute local air humidity (f) is applied within a virtual cylindrical volume which is limited on the one hand by the virtual cylindrical surface and on the other hand by two virtual planes parallel to the flat steel product (100) on both sides of the flat steel product (100), wherein the volume of the cylindrical volume is 1 m 3 Up to 10m 3 and preferably has a volume of at least 2m 3 , wherein the measurement of the absolute local humidity (f) is performed directly or indirectly.

8. The device (150) according to any one of claims 2 to 7, characterized in that The device (150) comprises a controller (250) adapted to regulate the controlled water vapor environment to adjust the absolute humidity (f) such that the following inequality is satisfied during application and stripping of the layer (10): f>AWZ.

9. The device (150) according to any one of claims 1 to 7, characterized in that The water vapor device (50) at least partially surrounds the front and / or rear side of the flat steel product (100) with a housing (52) to define the controlled water vapor environment as a quasi-static ambient condition in a close distance (NB) within the housing (52).

10. The device (150) according to claim 9, characterized in that The absolute local air humidity (f) is measurable in the close distance (NB) of the housing (52), the measurement of the absolute local air humidity (f) being carried out directly or indirectly.

11. The device (150) according to claim 9 or 10, characterized in that The volume of the near distance (NB) of the housing (52) is 1m 3 Up to 10m 3 and preferably has a volume of at least 2m 3 .

12. The device (150) according to any one of claims 2 to 11, characterized in that The predetermined specifications determine the coating of the layer (10) and / or the target thickness of the layer (10), and the layer (10) to be applied complies with the following specifications: - a coating of the layer (10) on each side of the flat steel product (100) at 20 g / m 2 Up to 200g / m 2 In the range of 30 g / m 2 Up to 100g / m 2 within the scope of, and / or A target thickness (10) of the layer (10) on each side of the flat steel product (100) is in the range of 3 μm to 30 μm, preferably in the range of 4.5 μm to 15 μm.

13. The device (150) according to any one of claims 1 to 12, characterized in that For a given stripping efficiency (AWZ), a sufficiently high absolute local air humidity (f) in the close distance (NB) is predetermined by the controlled water vapor environment to prevent marbling and / or the formation of toothpick-shaped defects at the layer (10).

14. The device (150) according to any one of claims 1 to 12, characterized in that: - at least one humidity sensor (51) is arranged in the close distance (NB) of the water vapor device (50) to be able to directly measure the absolute local air humidity (f) in the close distance (NB), and / or - providing at least one humidity sensor (56) to be able to directly measure the absolute local air humidity (f UG ).

15. The device (150) according to any one of claims 1 to 14, characterized in that The device (150) comprises at least one steam generator (DG) capable of automatically adjusting the absolute local air humidity (f) so that the absolute local air humidity (f) is greater than the stripping efficiency (AWZ).

16. A method for applying a layer (10) to at least one side of a flat steel product (100) in accordance with target specifications, wherein the flat steel product (100) is moved through a zinc alloy molten bath (11) (ZnAl; ZnAlMg), and a stripping gas (G) exits at its outlet side (A) through a nozzle lip gap (17) of at least one gas nozzle (15) in the direction of the flat steel product (100) to blow off the layer (10) in accordance with the target specifications, the stripping efficiency (AWZ) being defined by the following parameters: d is the thickness (d) of the nozzle lip gap (17) of the gas nozzle (15) of the stripping nozzle device (14), D is the effective flow rate (amount) (D) of the gas (G) on each side of the flat steel product (100) over the strip width (w), in Nm 3 / h, w is the strip width of the flat steel product (100), in mm, 2b half width of the pressure distribution of the gas (G) at the flat steel product (100), in mm, v belt speed of the flat steel product (100) when it moves along the stripping nozzle device (14), in m / min, wherein the method comprises the following steps: - before and / or during the method, determining the absolute local humidity (f) and / or the ambient air humidity (f) in a controlled water vapor environment in a close distance (NB) to the front and / or rear side of the flat steel product (100); UG ), - The determined humidity (f,f UG ) is linked to the stripping efficiency (AWZ) to determine whether the condition f>AWZ or f UG >AWZ, - if said condition is met, starting or continuing said method for applying said layer (10); or if said condition is not met, increasing said absolute local humidity (f) in a controlled water vapor environment by using a water vapor device (50) suitable for emitting gaseous water vapor to achieve the condition f>AWZ, and then starting or continuing said method for applying said layer.

17. The method according to claim 16, characterized in that The stripping efficiency (AWZ) is defined as follows: Or defined as follows: in Applicable: d is the thickness (d) of the nozzle lip gap (17) of the gas nozzle (15) of the stripping nozzle device (14), in mm D is the effective flow rate (volume) (D) of the gas (G) on each side of the flat steel product (100) over the strip width (w), in Nm 3 / h k is the unitless scaling factor w is the strip width of the flat steel product (100), in mm 2b is the half width of the pressure distribution of the gas (G) at the flat steel product (100), in mm v is the belt speed of the flat steel product (100) as it moves along the stripping nozzle device (14) and through the close distance (NB), in m / min.

18. The method according to any one of claims 16 or 17, characterized in that The absolute local humidity (f) of the controlled water vapor environment is determined at the front and / or rear side of the flat steel product (100) at a distance of more than 20 cm from the front and / or rear side.

19. The method according to any one of claims 16 to 18, characterized in that A controller (250) is used, which is configured to regulate the controlled water vapor environment to adjust the absolute humidity (f) so that the condition f>AWZ is met during application and blow-off of the layer (10).

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