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

Abstract

An apparatus (150) for applying a layer to a flat steel article (100), comprising: a molten zinc alloy bath (11) having an input side (E), an outlet side (A); comprising at least one nozzle lip gap, and which is arranged in the region of the outlet side (A) such that a still liquid layer on the flat steel product (100) can be blown off by means of gas discharged through the nozzle lip gap, wherein the device (150) is configured to make at least one of the following adjustments: increase the bath temperature of the molten alloy bath (11) if the current absolute local air humidity decreases, and vice versa, and / or decrease the thickness of the nozzle lip gap if the current absolute local air humidity decreases, and vice versa, and increase the bath temperature of the molten alloy bath (11) if the current absolute local air humidity decreases. And / or reducing the distance between the nozzle lip gap and the side of the flat steel product (100) if the current absolute local air humidity is reduced, and vice versa, and automatically adjusting the flow rate of the gas to keep the target thickness of the layer to be applied substantially constant.

Description

[0001] The invention relates to a method by which a flat steel product can be coated with a zinc-aluminum-magnesium (ZnAlMg) base layer, for example as a protective coating. The invention also relates to an apparatus which is configured to apply the method according to the invention.

[0002] As is known, flat steel products 100 such as steel strips or sheets are coated with ZnAlMg alloys to improve their corrosion resistance. In practice, this is usually done by Figure 1 This is achieved by placing a flat steel product 100 from a furnace into a zinc alloy bath 11 using an exemplary device 150. To protect the flat steel product 100 from oxidation, it is generally 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 a (zinc bath) roller 13 and moves upward out of the bath 11 at the outlet side A. When it is discharged from the bath 11, the molten alloy film attached to the front and rear sides of the flat steel product 100 is stripped to a target thickness (in the micrometer range) or to a target surface coating mass (in g / m 2 ), 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] Detailed information on 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] Water or water vapor is mentioned in the prior art in connection with hot dip coating of flat steel products. The relevant documents are listed below and their contents are briefly described here insofar as they are of interest.

[0005] Patent EP0172682B1 filed by Armco in 1985 relates to the control of zinc vapor in connection with hot dip coating of iron-based metal strip. Figure 1 A reduced oxygen atmosphere containing a small amount of water vapor is provided in the main trunk 12). 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 patent application JP2020100886A2 published by Nippon, the aim is to produce a galvanized steel strip with a surface having an increased coefficient of friction. In order to increase the coefficient of friction, water is sprayed under pressure onto the surface of the flat steel product after blowing. The particle size of the water droplets should be at least 0.07 mm and preferably greater than 1.5 mm. The spraying of water droplets intentionally creates irregularities on the surface of the steel strip. This document pursues different objectives and the corresponding technical teaching is therefore 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 easy.

[0008] The main problem here is usually the surface defects of the ZnAlMg layer. For example, marble (marbling effect), "toothpick" or "beach texture" defects may form on the ZnAlMg layer, or slag may appear. These patents (e.g. EP20130826634AM / JMMataigne; JP20080256208NSSMC / Oohashi, etc.) try to eliminate similar surface defects (gloss effect or oxide skin displacement) by other means (reducing the O2 content around the stripping nozzle).

[0009] The object is therefore to provide a method and a corresponding device for coating flat steel products with a particularly durable and powerful protective effect against corrosion, wherein the surface of the protective coating should be particularly uniform, very smooth and free of marbling (no "marbling effect") and / or toothpick-like defects (no "toothpicks"). The goal is to achieve a surface quality that meets the highest customer requirements.

[0010] Furthermore, the method should be as energy-efficient, economical, simple and reproducible as possible. Summary of the invention

[0011] According to the invention, a continuous (hot-dip) method and a corresponding device are provided which allow flat steel products to be provided with a metal layer which can be used, for example, as a (protective) coating which protects the steel substrate of the flat steel product from external influences.

[0012] All embodiments relate to applying a (protective) layer to a flat steel product, the layer thickness of which is intended to correspond to a target thickness (according to the respective specification). The layer is produced by passing the flat steel product through a zinc alloy bath and stripping it with gas at the outlet side of the bath by means of a stripping nozzle arrangement comprising at least one gas nozzle. The zinc alloy of the zinc alloy bath has the following composition: - an aluminum content in the range between 1.0 and 3.5 weight percent, and preferably in the range between 1.3 and 2.8 weight percent, a magnesium content ranging between 1.0 and 3.0 weight percent, and preferably ranging between 1.2 and 2.2 weight percent, and - the remainder of the zinc alloy bath 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.

[0013] The method is characterized in that at least one of the following adjustable parameters is adjusted as follows: - increasing the pool temperature of the alloy bath if the current absolute local air humidity decreases, and vice versa, and / or - reducing the thickness of the nozzle lip gap if the current absolute local air humidity decreases, and vice versa, and / or - if the current absolute local air humidity decreases, the distance between the nozzle lip gap and the side of the flat steel product is reduced, and vice versa, Therein, the flow rate of the gas is additionally adjusted in order to keep the target thickness of the layer to be applied substantially constant.

[0014] An apparatus configured to apply a coating to a flat steel product comprises: - a zinc alloy bath having an inlet side, an outlet side and a deflector for guiding the flat steel product at a strip speed from the inlet side through the zinc alloy bath to the outlet side, - a stripping nozzle arrangement comprising at least one nozzle lip gap and arranged in the region of the outlet side so that a layer still liquid on the flat steel product can be blown off with gas discharged through the nozzle lip gap to blow off the layer to a target thickness, wherein the zinc alloy of the zinc alloy bath has the following composition: an aluminum content ranging between 1.0 and 3.5 weight percent, and preferably ranging between 1.3 and 2.8 weight percent, a magnesium content ranging between 1.0 and 3.0 weight percent, and preferably ranging between 1.2 and 2.2 weight percent, and - the remainder of the zinc alloy bath 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.

[0015] The device is adapted or configured to manually or automatically make at least one of the following adjustments: - increasing the pool temperature of the alloy bath if the current absolute local air humidity decreases, and vice versa, and / or - reducing the thickness of the nozzle lip gap if the current absolute local air humidity decreases, and vice versa, and / or - reducing the distance between the nozzle lip gap and the side of the flat steel product if the current absolute local air humidity decreases, and vice versa, wherein, in addition, the flow rate of the gas is automatically adjusted in order to keep the target thickness of the layer to be applied substantially constant.

[0016] In all or at least some embodiments, the metal bath comprises a ZnAlMg alloy formed according to the following alloying concept: - an aluminum content (in weight percent) in the range between 1.0 and 3.5 weight percent, and preferably in the range between 1.3 and 2.8 weight percent; - a magnesium content (in weight percent) in the range between 1.0 and 3.0 weight percent, and preferably in the range between 1.2 and 2.2 weight percent; and - the remainder of the zinc alloy bath 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.

[0017] In some embodiments, the aluminum content (by weight percent) may be greater than or equal to the magnesium content (by weight percent).

[0018] In all or at least some embodiments, unavoidable impurities are in the range significantly below 1 weight percent (wt %), preferably the sum of all unavoidable impurities is below 0.5 wt %.

[0019] By combining a precisely defined ZnAlMg alloying concept, monitoring or observation of the current absolute local air humidity and targeted adjustment of the stripping process (or the corresponding method and / or system parameters or the stripping efficiency), surfaces with no or negligible marbling can be produced.

[0020] In all exemplary embodiments, the absolute local air humidity which should be present in the vicinity of the flat steel product in the region between the outlet side and the cooling region (if any) should be within a value of 1 g / m 3 Up to 300g / m 3 In the range of 1.08 g / m 3 Up to 51g / m 3 range, i.e. the method can be successfully carried out at an absolute local air humidity within the range.

[0021] In all embodiments, the stripping nozzle device can optionally be followed by a belt stabilization device for automatically stabilizing the movement of the flat steel product. In these embodiments, the value of the absolute local air humidity in the area between the stripping nozzle device and the belt stabilization device can be determined.

[0022] The absolute local air humidity is greater than 1g / m 3 In this case, the method preferably comprises the following steps: - operating the alloy bath at a bath temperature TB 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, - operating the stripping nozzle device at a nozzle distance of between 2 and 15 mm, preferably between 3 and 12 mm, from the flat steel product; - blowing off the flat steel product at the outlet side of the alloy bath with gas at a rate of 200 to 8000 Nm / h; 3 The gas flow rate within the range flows through the nozzle lips in the direction of the flat steel product.

[0023] The ZnAlMg alloying concept defined above is based on extensive studies and calculations. Within the specified limits of the ZnAlMg alloying concept, the technical teaching presented here has proven to be particularly successful.

[0024] In at least some embodiments, the absolute local air humidity is permanently measured.

[0025] In at least some embodiments, the absolute local air humidity is measured from time to time.

[0026] In at least some embodiments, if the absolute local humidity is too low, the method is interrupted to adjust one or more adjustable parameters.

[0027] Preferably, in all embodiments, the red Reduced bath temperature TB in the range of <460 degrees Celsius red The method is carried out within this range, and slag formation can also be reduced.

[0028] Detailed tests have shown that the ZnAlMg alloying concept indeed leads to very good results. This shows that very good results can be achieved by specifically adjusting the stripping process (or respectively the stripping efficiency).

[0029] The development of the new method, of a particularly suitable ZnAlMg alloying concept and of a targeted adjustment of the (process) parameters (or respectively the stripping efficiency) was based on theoretical considerations, various simulations of the stripping process and extensive experiments.

[0030] The processes in the area of ​​the stripping nozzle device and at the flat steel product are very complex and depend on a large number of (process) parameters and influencing variables (or respectively the stripping efficiency). Therefore, the method and device rely on some simplifying assumptions and definitions to obtain reproducible results.

[0031] In all embodiments, the coated flat steel product can be subjected to a trimming process or a re-rolling process and / or a bending-stretching-straightening process as usual after coating. Preferably, the overall deformation degree of the coated flat steel product is between 0.5% and 2.5%, preferably between 0.7% and 1.7%. The trimming process or re-rolling step (with a deformation in the range of 0.7-1.7%) can further reduce the negative effects of marbling.

[0032] In all embodiments, the coated flat steel products can be treated with customary transport protection measures, such as oiling or other chemical treatments as described in point 7 of the information sheet ("Charakteristische Merkmale 095-Schmelztauchveredeltes Band und Blech", 2010 edition, published by the Steel Information Center, 40039 Düsseldorf).

[0033] Further advantageous embodiments of the invention form the object of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. Figure 1 A highly schematic diagram of a known device for dip coating and stripping of flat steel products is shown (prior art); Figure 2 A highly schematic diagram showing a first exemplary apparatus for using the method of the present invention; Figure 3A shows a highly schematic side view of a stripping nozzle arrangement having only one nozzle, to enable definition of some of the method and system parameters relevant herein (the illustration is not drawn to scale); Figure 3B A schematic diagram showing a pressure curve P at a coating surface as a function of the position on the x-axis; Figure 3C A schematic diagram showing a shear force curve τ at a coating surface as a function of the position on the x-axis; Figure 4 shows a summary diagram of a number of exemplary tests, with the stripping efficiency AWZ plotted on the ordinate and the absolute air humidity f on the abscissa; Figure 5 A highly schematic diagram of an apparatus for using the method of the present invention is shown, whereby two virtual cylindrical volume segments are shown; Figure 6 A highly schematic diagram showing a further apparatus of the invention for use with the method of the invention; Fig. 7A A schematic elevation view of the strip side of a flat steel product without marbling is shown; Figure 7BA schematic elevation view of the strip side of a medium marbling flat steel product is shown; Figure 7C A highly schematic view showing the strip side of a strongly marbled flat steel product; Fig.7D A photograph showing a coated flat steel product without marbling; Fig. 7E A photograph showing a coated flat steel product with intense marbling including toothpick-shaped defects; Figure 7F A photograph showing a coated flat steel product without marbling after flattening; Figure 7G A photograph showing a coated flat steel product having marbled texture including toothpick-shaped defects after flattening; FIG8A shows detailed information of the test results of Table 2; FIG8B shows detailed information of further test results of Table 2; Fig. 9 Exemplary steps of the methods described herein are shown. DETAILED DESCRIPTION

[0035] The invention relates to a method for applying a layer 10 to a strip-shaped flat steel product 100 (see Figure 3A , wherein the layer 10 is visible on the upper side of the strip). The layer 10 is produced by passing the flat steel product 100 from the input side E through a zinc alloy bath 11 to the outlet side A and blowing it off at the outlet side A by means of a stripping nozzle device 14 using a gas G, such as Figure 2 , 3A , 6 and 7. The purpose of the stripping nozzle device 14 is to strip off the excess (still liquid) ZnMgAl layer (layer 10) as it leaves the bath 11.

[0036] In the context of the present invention, care must be taken to ensure that, on the one hand, the layer 10 does not substantially change even if the absolute air humidity f of the environment changes, and, on the other hand, no marbling occurs. In other words, the goal is to avoid marbling when the absolute local air humidity f changes, while at the same time substantially maintaining the target thickness of the layer 10.

[0037] In addition to the target thickness of the layer 10, in all embodiments, a target (surface) coating quality of the layer 10 can also be specified. Usually, there is a narrow specified tolerance range for the target thickness. As long as the layer 10 to be produced is within the tolerance range, the layer 10 substantially meets the specifications.

[0038] 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.

[0039] In all embodiments, the stripping nozzle arrangement 14 comprises at least one gas nozzle 15 (if only one side of the strip is blown off), or two gas nozzles 15 facing each other (if both sides of the strip are blown off). Figure 2 , 6 7 and 7 show an embodiment with two nozzles 15, and Figure 3A An embodiment with only one nozzle 15 is shown.

[0040] In at least some embodiments, the method is performed and controlled so that the layer 10 on each strip side of the flat steel product 100 has a target thickness within a tolerance window. 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.

[0041] Preferably, in at least some embodiments, the target surface coating (mass of coating per belt side; referred to as coating per side in Tables 8A and 8B) is between 20 and 200 g / m 2 In the range of 30 to 100 g / m 2 within the range.

[0042] In order to be able to reliably apply such a layer 10 which corresponds substantially to the target thickness, in all or at least some embodiments the zinc alloy of the zinc alloy bath 11 has the following composition: an aluminum content ranging between 1.0 and 3.5 weight percent, and preferably ranging between 1.3 and 2.8 weight percent, a magnesium content ranging between 1.0 and 3.0 weight percent, and preferably ranging between 1.2 and 2.2 weight percent, and - The remainder of the zinc alloy bath 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 being less than 0.1%, and unavoidable impurities.

[0043] In all or at least some of the embodiments, the metal pool 11 comprises a particularly preferred ZnAlMg alloy formed according to the following alloying 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 of the zinc alloy bath 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 being less than 0.1%, and unavoidable impurities.

[0044] In all embodiments, the aluminum content (by weight percent) may be equal to or greater than the magnesium content (by weight percent).

[0045] In order to prevent the formation of marbling or to significantly reduce it, the absolute local air humidity f is determined continuously or from time to time (for example by direct or indirect measurement). This also applies to preventing or reducing the formation of toothpicks.

[0046] The absolute air humidity f can be expressed, for example, in g / m 3 In other words, it is the volume of 1m 3 The mass of gaseous water in a standard volume of a volume. In other words, the absolute air humidity f represents the water vapor content in a volume. f is used here as the formula symbol for absolute air humidity. In all embodiments, the absolute air humidity f can be roughly estimated based on the air temperature TL and the relative air humidity r. The following applies: rRelative air humidity, in % TL air temperature, in °C

[0047] In all exemplary embodiments, the absolute local humidity f can be measured directly or indirectly. Indirect measurement is here primarily understood to mean measuring the air temperature TL and the relative air humidity r and calculating / deriving the absolute local humidity f.

[0048] In all exemplary embodiments, the absolute local air humidity f which should be present according to the invention in the vicinity of the flat steel product 100 in the region between the outlet side A and the cooling zone 16 (if present) has a value of 1 g / m 3 Less than 300g / m 3 Preferably, in all embodiments, the absolute local air humidity is within the range of 1.08 g / m 3 Up to 51g / m 3 within the range.

[0049] When the absolute local air humidity f is greater than 1g / m 3 And less than 300g / m 3In the case of the method, the layer 10 can be controlled to be applied to at least one side of the flat steel product 100 by selectively adjusting the adjustable parameters (method and system parameters). In all embodiments, care is taken to ensure that the adjustable parameters are adjusted so that the layer 10 to be applied (still) substantially corresponds to the target thickness. This means that care is taken to ensure that a layer corresponding to the target thickness (within tolerance) is still applied and which at the same time exhibits no or only very slight marbling.

[0050] In all embodiments, the adjustable parameters (method and system parameters) can be adjusted as follows: - increasing the bath temperature TB of the alloy bath 11 if the current absolute local air humidity f decreases, and vice versa, and / or - reducing the thickness d of the nozzle lip gap 17 if the current absolute local air humidity f decreases, and vice versa, and / or - if the current absolute local air humidity f decreases, the distance Z between the nozzle lip gap 17 and the side of the flat steel product 100 decreases, and vice versa, Therein, the flow rate D of the gas G is additionally adjusted (for example automatically by a control) in order to keep the target thickness of the layer 10 to be applied substantially constant.

[0051] Furthermore, in all exemplary embodiments, the strip speed v at which the flat steel product 100 is removed from the zinc alloy bath 11 can also be varied, wherein care must also be taken here to ensure that the target thickness of the layer 10 to be applied remains substantially constant.

[0052] Preferably, in all embodiments, several of these adjustable parameters (process and system parameters) are varied in a coordinated manner to ensure that the applied layer 10 corresponds to a target thickness. The mathematical relationships applicable here will be described below.

[0053] So-called target specifications for the layer 10 to be applied may dictate that all embodiments must meet the following specifications: - The coating of layer 10 on each belt side should be between 20 and 200 g / m 2 In the range of 30 to 100 g / m 2 and / or - the target thickness of the layer (10) per belt side falls within the range of 3 to 30 μm, preferably within the range of 4.5 to 15 μm.

[0054] The pool temperature TB of the alloy molten pool 11 has an effect on the viscosity of the melt during the stripping process. An increase in the pool temperature TB results in a decrease in the viscosity of the melt. If the adjustable parameters (method and system parameters) remain unchanged, more material will be stripped than expected. Therefore, when the pool temperature TB increases, other adjustable parameters (method and system parameters) are changed so that the layer 10 still has the target thickness. For example, when the pool temperature TB is increased, the flow rate D of the gas G is reduced to reduce the stripping effect, so that the same target thickness is still achieved.

[0055] In all embodiments, the pool temperature TB of the alloy pool 11 is preferably in the range of 400 < TB < 480 degrees C, preferably in the range of 409 < TB < 473 degrees C, and particularly preferably in the range of 420 < TB < 460 degrees C. Within these range limits, the pool temperature TB can be adjusted to change the viscosity.

[0056] For the operation of the alloy bath 11, a bath temperature TB within a specified temperature range is specified in all embodiments. Maintaining this temperature window (temperature range) is important because more undesirable slag will form on the flat steel product 100 when operating outside the specified range.

[0057] In all embodiments, the heating can be carried out, for example, by means of an induction heating device 30 (see Figure 2 and Figure 6 ) or resistance heater to adjust the pool temperature TB.

[0058] In order to avoid slag formation, in all embodiments, the bath temperature TB is preferably reduced. red Preferably, the above mentioned 420 < TB red In the range of <460 degrees Celsius.

[0059] In carrying out the method, in all embodiments, it is preferably noted that the thickness d of the nozzle lip gap 17 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 - 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.

[0060] The method operates particularly reliably within these ranges.

[0061] In all embodiments, the corresponding gas nozzle 15 has a longitudinal extension parallel to the y-axis. Preferably, in all embodiments, the nozzle 15 has a strip width w corresponding to the strip-shaped flat steel product 100 (see also Figure 5 The thickness d of the gas nozzle 15 is defined as being parallel to the x-axis.

[0062] In all exemplary embodiments, the strip width w of the strip-shaped flat steel product 100 is preferably in the range of 500 mm to 2500 mm. Particularly preferably, in all exemplary embodiments, the strip width w of the strip-shaped flat steel product is in the range of 800 mm to 1800 mm.

[0063] In at least some embodiments, the absolute local air humidity f is measured permanently or from time to time, and if the absolute local air humidity f is too low, the application of the layer 10 is interrupted, for example to adjust an adjustable parameter.

[0064] Since the thickness d of the nozzle lip gap 17 can only be adjusted manually in some devices 150 , in at least some embodiments, the process stops before the nozzle lip gap 17 is manually adjusted.

[0065] In at least some embodiments, the absolute local air humidity f is measured directly or indirectly.

[0066] The absolute local humidity f is not measured directly at the impact line of the gas G on the layer 10 to be stripped, since the gas mixture there is relatively "dry" (i.e. contains very low humidity). In all embodiments, the absolute local humidity f is preferably measured directly or indirectly in a region at a normal (perpendicular) distance of at least 20 cm from the impact line or from the flat steel product 100.

[0067] Figure 2 7 shows a method for directly measuring the absolute local air humidity. The device 150 comprises, for example, two humidity sensors 51 (at least one on each side of the belt). In the schematic diagram, each of these sensors 51 has two contacts that can be connected to the controller 250, for example. Figure 2 and Figure 6 The corresponding connections or lines V1 , V2 , V3 , V4 are shown with dashed lines in FIG.

[0068] In all embodiments, sensors of the following design or operating mode can be used as humidity sensor 51: - Mechanically operated measuring sensors, based on the expansion or contraction of a (usually organic) measuring element caused by humidity; - a hygrometrically operated measuring sensor, whereby two identical, very precise thermometers are used, along which the gas flow to be measured is guided at a defined speed; - a capacitive measuring sensor, for example comprising a humidity-sensitive capacitor having two planar electrodes; - dew point mirror hygrometers, which determine the air humidity using a dew point mirror, where the condensation of water vapor is evaluated if it falls below the dew point; - resistive measurement methods, in which, for example, the impedance of the alternating current resistance of the hygroscopic element is determined; - Spectroscopic measurement methods, for example, contactless measurement of the gaseous water content in the near-infrared or mid-infrared range (NIR or MIR).

[0069] All embodiments of the apparatus 150 may include a controller 250. In all embodiments, the controller 250 may be designed as a computer-supported automation and control unit and may include a human-machine interface, a computer and a database.

[0070] In all embodiments, controller 250 may be part of an overall system controller of device 150 , or in all embodiments, it may be coupled to an overall system controller of device 150 .

[0071] In these embodiments, adjustment / variation of the adjustable parameters (system or process parameters) or the stripping efficiency AWZ can be performed by the overall system controller and / or by the controller 250 .

[0072] In the case of an indirect measurement of the absolute local air humidity, the air humidity is not measured at or in the surrounding area of ​​device 150 (for example within a virtual cylinder v ZK ), but rather the current air humidity is determined indirectly.

[0073] In all embodiments, the current air humidity can be measured indirectly, for example by using a grating to determine the transmission rate of the light path. In very dry air the transmission rate is high. On the other hand, the presence of gaseous water impedes the transmission of light through the light path and the transmission rate is lower.

[0074] In all embodiments, the determination can be made indirectly by measuring the surface properties of the coated flat steel product 100 ( Fig. 7A , 7B Three examples of coated flat steel products 100 are shown in 7C . For example, a corresponding measurement of the surface properties can be performed optically before or after the cooling zone 16 (eg by optically measuring the reflectivity of the surface of the layer 10 ). Figures 7D to 7G An exemplary photograph of a coated flat steel product 100 is shown.

[0075] Preferably, in all embodiments, an inert gas is used as gas G. Nitrogen or nitrogen-containing gas mixtures have proven to be particularly effective.

[0076] Figure 3AA highly schematic side view of another stripping nozzle arrangement 14 is shown in order to be able to define the adjustable parameters (system and method parameters) or stripping efficiency AWZ more precisely. The important adjustable 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) when the flat steel product 100 is removed from the zinc alloy bath 11 .

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

[0078] Figure 3B Schematic diagram of the gas pressure curve P along the front side of the flat steel product 100 is shown. The pressure P depends on the position on the x-axis. Ideally, Figure 3B As shown, the pressure curve P has the shape of a Gaussian curve. As shown, the Gaussian curve can be used to determine the pressure P S / 2, where P S Indicates 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, the larger the half width 2b. For more details, see the publication "Wall Pressure and Shear Stress Measurements Beneathan Impinging Jet", CVTu et al., Experimental Thermal and Fluid Science, 1996, vol. 16, pages 364-373, Elsevier Science Inc.

[0079] The gas jet discharged from the nozzle 14 and the gravity (if the flat steel product 100 is pulled vertically upward from the pool 11, such as Figure 2 , 6 7 ) exerts a shear force τ on the still liquid layer 10 . Figure 3C A schematic diagram showing the shear force τ related to the position on the x-axis (shear force τ is represented by Figure 3Bτ = 0. The negative first derivative of the pressure profile in the pressure curve is determined). This is the shear force τ acting on the layer 10 to be peeled off. In 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 off is defined.

[0080] Testing has shown that adjustable system and / or process parameters, or stripping efficiency AWZ, can be adjusted within certain limits without significantly changing the target thickness and / or surface weight (coating per belt side) of layer 10 .

[0081] It has also been shown that (in addition to the absolute local air humidity f) two variables characterizing the shear force profile generated by the stripping nozzle 15 on the strip 100 have a decisive effect on the formation of the marbling. One is the maximum shear force τ max , and the other is the time t for the strip-shaped flat steel product 100 to pass through the distance l between the maximum values ​​of the shear force (see Figure 3C ). The time t in turn depends on the belt speed v.

[0082] There is a direct relationship between time t, tape velocity v and half-width 2b, as expressed in equation (1):

[0083] In all 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 exiting 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 draws in ambient air that swirls together with the gas G. For details, see, for example, the already mentioned publication "Measurement of wall pressure and shear stress below the impinging jet".

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

[0086] Further targeted investigations and graphical processing of these test results showed for the first time a correlation between air humidity, stripping nozzle parameters and marbling trends. Figure 4 A summary diagram of a large number of tests is shown, with the stripping efficiency AWZ (as a summary or general term for method and device parameters or abbreviation for stripping nozzle parameters) plotted on the vertical axis and the unit g / m 3 The absolute air humidity f is on the abscissa.

[0087] By changing the two variables τ max By weighting and adding t, the so-called stripping efficiency AWZ can be determined as follows (inequality (2.1)), which can be directly compared with the absolute local air humidity f:

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

[0089] Stripping efficiency AWZ summarizes the following method and device parameters: - effective flow rate (volume) D of the gas G over the belt width w on each belt side, - proportionality factor k, - strip width w of the flat steel product 100, - the thickness d of the nozzle lip gap 17, - half width 2b, The speed v of the flat steel product 100 (strip speed), or the time t dependent on the speed v.

[0090] Further details about the stripping efficiency AWZ can also be found in inequality (3), which will be discussed later. The entire term on the right-hand side of inequality (3) can also be used as the definition of the stripping efficiency AWZ. Before describing inequality (3), we further refer to Figure 4 .

[0091] Figure 4 The grey or black filled symbols (squares, diamonds, triangles or circles) in the figure represent flat steel products 100 with clearly formed marble on the surface of the layer 10. The marble is particularly strong in the case of the black filled symbols. The grey filled symbols represent less pronounced marble. On the other hand, the unfilled symbols represent no or negligible marble. The circular symbols represent tests with a nozzle lip gap thickness of d=0.8 mm, the square symbols represent tests with a nozzle lip gap thickness of d=0.9 mm, the diamond symbols represent tests with a nozzle lip gap thickness of d=1 mm, the triangular symbols represent d=1.2 mm and the inverted triangular symbols represent d=1.4 mm.

[0092] exist Figure 4A straight line Ge is inserted in the graph of , as a dividing line, to separate, as a first approximation, those tests with clear or moderate marbling from those with no or negligible marbling. In the tests below the straight line Ge, there is no or negligible marbling ( Fig. 7A A corresponding flat steel product 100 is shown, the layer 10 of which is free of marbling.) The straight line Ge can be understood as a function of the stripping efficiency AWZ (see also inequalities (2.1) and (3)).

[0093] A detailed evaluation of the test results shows that the above-mentioned stripping efficiency AWZ can be adjusted as a function of the absolute local air humidity f in order to avoid the appearance of undesired marbling. In all embodiments, this adjustment of the stripping efficiency AWZ is preferably carried out so that the target thickness of the layer 10 or the surface coating (mass) of the layer 10 is not changed or hardly changed. This means that when changing the stripping efficiency AWZ, care must always be taken to ensure that the layer 10 to be applied has substantially the target thickness.

[0094] However, it is important to ensure that when adjusting the stripping efficiency AWZ, in addition to avoiding marbling, other defects such as toothpick defects, beach pattern defects or reducing slag formation are also avoided. For this reason, the parameter range specified here has proven to be particularly effective.

[0095] As mentioned earlier, Figure 4 The straight line Ge shown is only a first-order approximation. The actual relationship is much more complicated. The following formula (inequality (3)) shows the absolute local air humidity f (in g / m 3 ) and the stripping efficiency AWZ:

[0096] Two exemplary methods are described below to simplify inequality (3):

[0097] First method: According to the first method, it is subdivided into three different curve regions (herein referred to as cases 1.1 to 1.3). With such a subdivision, the right-hand side of inequality (3) can be calculated in a simplified manner.

[0098] (Case 1.1) In the linear region, the assumption applies: 2b / d=1.9 or b=1.9d / 2. This simplification applies to the following relationship between the nozzle spacing Z and the width d of the nozzle lip gap 17: Z / d<5.2.

[0099] (Case 1.2) In another region starting from about Z / d=5.2 and ending before Z / d=10, the following relationship applies:

[0100] (Case 1.3) In another region starting from about Z / d=10, the following relationship applies:

[0101] In order to make the complex inequality (3) manageable in practice, it is suggested to differentiate between the three cases 1.1 to 1.3, whereby the ratio Z / d is used for the differentiation.

[0102] The distinction between the three regions or cases still leads to complex mathematical formulae, especially in the second region (case 1.2).

[0103] Second method: Therefore, a second approach is described here, which is used to make the complex inequality (3) easier to handle in practice. In this second method, only two cases (cases 2.1 and 2.2) are used for case differentiation, whereby the ratio Z / d is also used for case differentiation.

[0104] The disadvantage of the second method is that the separation in the boundary region between the flat steel product 100 without marble and the flat steel product 100 with marble is not completely clear or unambiguous. The best results can be achieved if the case differentiation according to the first method using inequality (3) and / or inequality (2.1) is evaluated (e.g., numerically processed by the controller 250).

[0105] In all embodiments or in at least some embodiments, the first or second method can now be used to adjust / adapt the adjustable parameters (system and / or method parameters) or the stripping efficiency AWZ using inequalities (2.1) and / or (3). Alternatively, as already mentioned, numerical representations of inequalities (2.1) and / or (3) can also be used in the controller 250.

[0106] An adjustment / adaptation of adjustable parameters (system and / or method parameters) or the stripping efficiency AWZ can now be performed in all embodiments or in at least some embodiments so that the surface coating of layer 10 and / or the (coating) quality of layer 10 and / or the target thickness of layer 10 remain constant or within narrow predetermined tolerance limits, for example defined by target specifications.

[0107] In all embodiments, the target specifications may be predetermined by the manufacturer and / or the consumer or customer.

[0108] Preferably, the inequality (2.1) and / or (3) or the formula of the first method or the formula of the second method is implemented by software in the controller 250, or the values ​​of the absolute local humidity f and the corresponding suitable adjustable parameters (system and / or method parameters) or the stripping efficiency AWZ are provided in one or more tables. Using the "lookup" table, the controller 250 can call up the corresponding suitable adjustable parameters (system and / or method parameters) or the stripping efficiency AWZ for the currently applied absolute local humidity value f and adjust the device 150, or provide the machine operator with a value for adjusting the nozzle lip gap thickness d (for example, displayed on a display).

[0109] In all embodiments, preferably the following numbers or value ranges of adjustable parameters (system and / or method parameters) or stripping efficiency AWZ are used. The individual numbers or value ranges in Table 1 are not related to each other, or are only not related in part, because the respective maximum and minimum values ​​are derived from different tests. Only the respective maximum and minimum values ​​are selected from Table 2 (Figures 8A, 8B) and summarized here.

[0110] The nozzle heights listed in Table 2 (FIGS. 8A, 8B) are the vertical distances between the zinc bath level and the impact line of the gas jet on the layer to be stripped 10. The nozzle pressure in Table 2, FIGS. 8A, 8B is defined as the (over) pressure of the stripping gas G in the nozzle 15 (relative to the ambient pressure) in mbar.

[0111] In all embodiments, the flow rate D of the gas G per belt side is typically between 200 and 8000 Nm per hour. 3 in the range between.

[0112] Table 2, divided into two parts (see Figures 8A and 8B), shows Figure 4 Table 2 of FIG. 8A shows the results of tests (e.g., Fig. 7A example shown). Figure 8A Table 2 The values ​​in b are sorted in ascending order.

[0113] On the other hand, Table 2 of FIG. 8B shows that the Figure 7B ) or even strongly marbled (as in the examples in Figure 7C ) for layer 10 testing. Figure 8B Table 2 The values ​​in are also sorted in ascending order by b.

[0114] From Table 2 of FIG. 8A , the following pairs of values ​​for absolute local air humidity f and stripping efficiency AWZ can be extracted (sorted in ascending order of stripping efficiency AWZ), whereby all layers 10 produced with these adjustable parameters (process and system parameters) or stripping efficiency AWZ are in Figure 4 Below the straight line.

[0115] The following pairs of values ​​for absolute air humidity f and stripping efficiency AWZ can be extracted from Table 2 of FIG. 8B (sorted in ascending order of stripping efficiency AWZ), whereby all layers 10 produced with these adjustable parameters (process and system parameters) or stripping efficiency AWZ are in the range Figure 4 Above the straight lines.

[0116] If marbling defects occur at a given absolute local air humidity f and given process conditions, then in at least some embodiments, in order to eliminate the marbling, the stripping efficiency AWZ is reduced (corresponding to the right-hand side of inequalities (2.1) and (3)) until the inequality is satisfied again.

[0117] Usually, it is not permitted to change the coating of the produced flat steel product 100, because this is stipulated in the product specifications. As long as the thickness of the coating remains constant, the stripping efficiency AWZ can be reduced in various ways.

[0118] Three specific examples are used below to illustrate possible ways of changing the peeling factor AWZ.

[0119] Example 1: The stripping efficiency AWZ is reduced by reducing the nozzle spacing Z (see Table 3).

[0120] Table 3 below shows two test examples 1.1 and 1.2, which demonstrate that by reducing the nozzle spacing Z from 10 mm to 8 mm, the stripping efficiency AWZ decreases.

[0121] For gas flow rate D is 1691Nm 3 / h, belt width w is 1315mm, nozzle lip gap d is 1.0mm, nozzle spacing Z is 10mm and belt speed v is 100m / min (Table 3-Example 1.1), AWZ is calculated according to inequality (3) to be 21.3.

[0122] Based on Example 1.1, the nozzle spacing Z is reduced from 10 mm to 8 mm to reduce the stripping efficiency AWZ, keeping the tape width w, nozzle lip gap d, tape speed v, pool temperature TB and coating per side constant. The changed nozzle distance Z changes the ratio Z / d and also changes the determined values ​​of b and k. Table 3 shows that due to the change in nozzle spacing Z, the nozzle pressure and thus the gas flow rate D per side must be reduced from 1691 to 1386 Nm 3 / h to keep the thickness of the layer 10 substantially constant.

[0123] If the stripping efficiency AWZ is now calculated using these new process parameters (Table 3, Example 1.2), the result is a value of 13.5. By reducing the nozzle spacing from 10 mm to 8 mm, the stripping efficiency AWZ can thus be reduced from 21.3 to 13.5 with unchanged coating.

[0124] Example 2: Reduce the stripping efficiency AWZ by reducing the nozzle lip gap d.

[0125] Table 4 below shows two test examples 2.1 and 2.2 which show that by reducing the thickness d from 1.2 mm to 1 mm, the peeling efficiency AWZ decreases.

[0126] For flow rate D = 1373Nm 3 / h, belt width w = 1455mm, nozzle lip gap d = 1.2mm, nozzle spacing Z = 7mm and belt speed v = 100m / min (Table 4, Example 2.1), AWZ is calculated according to inequality (3) to be 9.4.

[0127] On this basis, the nozzle lip gap d was reduced from 1.2 mm to 1.0 mm to reduce the stripping efficiency AWZ, so that the other parameters remained substantially constant.

[0128] Table 4 shows that due to the change in the nozzle lip gap d, the nozzle pressure and thus the gas flow rate D on each side must be reduced from 1373 to 1166 Nm by automatic support control. 3 / h to keep the thickness of the layer 10 constant.

[0129] By changing the nozzle lip gap d, the ratio Z / d changes, which also changes the values ​​of b and k determined accordingly. If the stripping efficiency AWZ is now calculated using these new method parameters (Table 4, Example 2.2), the result is a value of 4.9. By reducing the nozzle lip gap from 1.2 mm to 1.0 mm, the stripping efficiency AWZ can thus be reduced from 9.4 to 4.9 with unchanged coating. Example 3: Reducing the stripping efficiency AWZ by increasing the bath temperature TB.

[0130] Table 5 below shows two test examples 3.1 and 3.2 which show that by increasing the bath temperature TB from 439°C to 455°C the stripping efficiency decreases.

[0131] For flow rate D = 1607Nm 3 / h, belt width w = 1615mm, nozzle lip gap d = 1.0mm, nozzle spacing Z = 7mm and belt speed v = 100m / min (Table 5, Example 3.1), AWZ is calculated according to inequality (3) to be 12.4.

[0132] On this basis, the cell temperature TB was increased from 439°C to 455°C mm to reduce the stripping efficiency AWZ, keeping the other parameters substantially constant. In this example, the ratio Z / d remained constant, and the values ​​of b and k determined accordingly also remained constant when the cell temperature TB was increased.

[0133] Table 5 shows that due to the change in the bath temperature TB, the nozzle pressure and thus the gas flow rate D per belt side must be reduced from 1607 to 1339 Nm by automatic support control. 3 / h to keep the thickness constant. The reason is that the viscosity of the zinc melt decreases with increasing bath temperature TB, which means that a lower peeling force is required to peel the same amount of melt.

[0134] If the stripping efficiency AWZ is now calculated using these new method parameters (Table 5, Example 3.2), the result is a value of 5.8, ie the stripping efficiency AWZ can therefore be reduced by increasing the bath temperature TB.

[0135] According to the present invention, Figure 5 As shown schematically, the absolute local air humidity f is preferably defined as the absolute air humidity within a virtual cylinder vZK. In this virtual cylinder vZK, regions extending parallel to the strip-shaped flat steel product 100 to the right and to the left are excluded.

[0136] The virtual cylinder vZK consists of two virtual cylindrical volume segments, which are limited on the one hand by a virtual cylindrical surface which concentrically or almost concentrically surrounds the gas nozzle 15. On the other hand, the cylindrical volume segment is limited by two planes parallel to the flat steel product 100 on both sides of the flat steel product 100, each at a distance of, for example, s=20 cm from the flat steel product 100. The common volume of the two cylindrical volume segments is 1 m 3 Up to 10m 3 The volume is preferably less than 2m 3 In all embodiments, the measurement of the absolute local humidity f is preferably carried out directly or indirectly within the cylindrical volume segment.

[0137] exist Figure 5 , a part of a further device 150 is shown, wherein two cylindrical volume segments of a virtual cylinder vZK are shown here. The tank 11 is shown here as a rectangular container with an open top. The tank 11 contains a liquid zinc alloy (abbreviated here as ZnAlMg). Only a short length of the flat steel product 100 in strip form is shown after leaching out of the tank 11. The flat steel product 100 is guided vertically out of the tank 11 in the x-axis direction between two opposing gas nozzles 15 of the stripping nozzle device 14. If the two gas nozzles 15 are arranged parallel to each other, a center line ML can be defined between these nozzles 15. The center line ML is at Figure 5 The center line ML is located in the nozzle plane DE (which is defined as the xy plane).

[0138] A virtual cylinder vZK in three-dimensional space is formed around the center line ML. The "shell" of the virtual cylinder vZK is concentric with the center line ML. All points of the "shell" have the same distance ra to the center line ML (ra is the radius of the virtual cylinder vZK).

[0139] The virtual cylinder vZK comprises at least the nozzle 15 of the stripping nozzle arrangement 14 and has a virtual cylinder height vZH defined parallel to the y-axis. Preferably, in all embodiments, the virtual cylinder height vZH corresponds to the strip width w of the flat steel product 100 and / or the length of the nozzle 15 (defined parallel to the y-axis).

[0140] A specified value range for the absolute local air humidity f within this virtual cylinder vZK can be defined for all exemplary embodiments.

[0141] In all or at least some embodiments, the absolute local humidity f is measured along a y-line parallel to the flat steel product 100 and located in the virtual cylinder vZK. The y-line is parallel to the y-axis. The so-called nozzle plane (also called peeling plane) lies parallel to the yz plane and the center line ML lies in the nozzle plane.

[0142] Preferably, in all or at least some embodiments, the absolute local air humidity f is determined or measured at several points of the y-line and the average of the determined or measured values ​​is compared with a value range specified for the absolute local air humidity f.

[0143] Preferably, in all or at least some embodiments, the absolute local air humidity f in the virtual cylinder vZK is between 1 g / m 3 Up to 300g / m 3 In the range of 1.08 g / m 3 Up to 51g / m 3 Within the range, the volume of the virtual cylinder vZK is 2m 3 .

[0144] However, in all embodiments, the absolute local air humidity f can also be defined as 3 Up to 10m 3 The measurement is preferably performed not directly at the incident line of the gas G, but at a y-line above the incident line and parallel to the y-axis, within a volume range and directly or indirectly measured within this range.

[0145] exist Figure 2 In the embodiment of the embodiment of the present invention, the y-line is described in the region between the nozzle 15 of the stripping nozzle arrangement 14 and the lower inlet side of the cooling zone 16. Figure 6 In the exemplary embodiment of FIG. 1 , the described y-line is located above the incident line and, for example, at least 20 cm from the center line ML of the virtual cylinder vZK, which is marked on the flat steel product 100 by a small white circle.

[0146] Figure 6 A further embodiment of a device 150 is shown, whereby here also a method of directly measuring the absolute local air humidity is used. The arrangement of the device 150 is similar to Figure 2 The device 150 shown in FIG. Figure 2 Only the area of ​​the outlet side A of the pool 11 is shown. Two gas nozzles 15 are arranged parallel to the front and rear sides of the belt (the gas nozzles 15 extend into the plane of the drawing). As shown in the schematic diagram, by means of a pump P g The inert gas G is supplied to each nozzle 15. Two pumps P g In terms of control technology (or regulation technology), it is connected to a controller 250, and the controller 250 can, for example, control the gas flow D on each belt side. The corresponding connecting lines or pipelines are Figure 6 The air supply unit with blower and control valve is referred to here as pump P g .

[0147] Preferably, all embodiments of the device 150 include a control of the flow rate D of the gas G (called automatic layer control) designed so that, despite variations in other adjustable parameters, a layer 10 with a substantially constant target thickness is always produced. To this end, the control system includes at least one sensor (not shown) that measures the actual thickness of the layer 10 after the stripping. If the actual thickness is less than the target thickness, the control system reduces the flow rate D, and vice versa.

[0148] Each nozzle 15 can be moved parallel to the z-axis by a motor or actuator M. As shown, the motor or actuator M is connected to the controller 250. The corresponding connecting wires or cables are connected at Figure 62 are marked as V9, V10, V11 and V12. A sensor (not shown) is present to enable control of the nozzle distance Z. This allows the nozzle spacing Z to be set and / or checked via the controller 250. In all embodiments, the control of the nozzle distance Z may be laser supported.

[0149] In all embodiments, the controller 250 may also be connected to an induction heater 30 or to a resistance heater to the pool 11 to adjust the pool temperature TB. In the case of an induction heater, its coil 30 is Figure 6 As shown, 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 connecting wires or cables are Figure 6 are marked as V13 and V14.

[0150] Figure 6 Also shown in the figure is a virtual cylinder vZK, whose center line ML intersects the drawing plane slightly above the nozzle 15. In order not to overload the drawing, the position of the center line ML is indicated by a small white circle on the strip-shaped flat steel product 100. Since the overall layout is limited on the bottom side by the tank 11 and on the top side by the optional cooling zone 16, the virtual cylinder vZK here is a virtual cylinder vZK that is cut at the top and bottom.

[0151] For example, two humidity sensors 51 are also used here (at least one on each side of the belt) in order to be able to determine the absolute local air humidity. The humidity sensors 51 are connected to the controller 250. The corresponding connecting wires or cables are connected at Figure 6 are labeled V1, V2, V3, and V4.

[0152] In such an apparatus 150, if Figure 6 As shown schematically and by way of example in FIG. , the method can be carried out particularly advantageously and with reproducible results.

[0153] Fig. 9 Exemplary steps of the method described here 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 up (step S1). For example, the device can be set up based on the target specifications of the layer 10 to be applied.

[0154] Before, during or after setting S1, the current absolute local air humidity f is measured (directly or indirectly) (step S2). Then, one of the inequalities or a "look-up" table is used to determine whether the condition f>AWZ is met (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 met ("no" in the flow chart), the method branches back to step S1. After branching back, the settings of the components and elements of the device 150 can be adjusted with the aim of reducing the AWZ so that the condition f>AWZ is met. When making adjustments, care is taken to ensure that the target specifications for the layer 10 to be applied remain met.

[0155] In a similar manner, during the application of the layer 10, the condition f>AWZ can be repeatedly checked from time to time in order to be able to react to a changing absolute local air humidity f. If f has fallen, it is checked again (as in step S3) whether the condition f>AWZ is still satisfied. If so, the application of the layer 10 continues. If not, (analogously to step S1) the settings of the components and elements of the device 150 can be adjusted in order to ensure that the condition f>AWZ is satisfied or maintained.

[0156] In all embodiments, the corresponding controller 250 can be configured or programmed so that - Achieving a significant reduction in the stripping efficiency AWZ by increasing the bath temperature TB, and / or - by reducing the thickness d of the nozzle lip gap 17, the stripping efficiency AWZ can be reduced, and / or - By reducing the distance Z, the stripping efficiency AWZ can be reduced.

[0157] In all embodiments, the respective controller 250 may be configured or programmed such that it is taken into account that if the ratio Z / d is small, a change in the thickness d and / or the distance Z has no or only a small effect on the peeling efficiency AWZ.

[0158] If f drops significantly, and if reasonable adjustment cannot be made within the target specification, the method can be interrupted. As part of this interruption, the width d of the nozzle lip gap 17 can be adjusted manually, for example (this cannot be adjusted automatically in most devices 150).

[0159] Reference numerals:

Claims

1. A method for applying a layer (10) having a target thickness to at least one side of a flat steel product (100), wherein the flat steel product (100) is moved through a zinc alloy bath (11) and gas (G) is discharged at its outlet side (A) toward the flat steel product (100) through a nozzle lip gap (17) of at least one gas nozzle (15) to blow off the layer (10) to the target thickness, wherein the zinc alloy bath (11) has the following composition: an aluminum content ranging between 1.0 and 3.5 weight percent, and preferably ranging between 1.3 and 2.8 weight percent, a magnesium content in the range between 1.0 and 3.0 weight percent, and preferably in the range between 1.2 and 2.2 weight percent, and the remainder, which comprises zinc, one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, each of which has a weight-related content of less than 0.1%, and unavoidable impurities, It is characterized in that At least one of the following tunable parameters is adjusted as follows: - increasing the pool temperature (TB) of the alloy pool (11) if the current absolute local air humidity (f) decreases, and decreasing the pool temperature (TB) of the alloy pool (11) if the current absolute local air humidity (f) increases, and / or - reducing the thickness (d) of the nozzle lip gap (17) if the current absolute local air humidity (f) decreases, and increasing the thickness (d) of the nozzle lip gap (17) if the current absolute local air humidity (f) increases, and / or - reducing the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) if the current absolute local air humidity (f) decreases, and increasing the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) if the current absolute local air humidity (f) increases, Therein, the flow rate (D) of the gas (G) is additionally adjusted to keep the target thickness of the layer (10) to be applied substantially constant.

2. The method according to claim 1, characterized in that The layer (10) meets the following requirements: - The target surface coating of the layer (10) per belt side is 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 - the target thickness of said layer (10) per belt side is in the range of 3 μm to 30 μm, preferably in the range of 4.5 μm to 15 μm 3. The method according to claim 1 or 2, characterized in that: The adjustment of the parameters is carried out in the following ranges to prevent marbling and / or toothpick defects in the layer (10): - Absolute local air humidity (f) at 1g / m 3 Up to 300g / m 3 In the range of 1.08 g / m 3 Up to 51g / m 3 within the range.

4. The method according to any one of claims 1 to 3, characterized in that The relationship between the current absolute local air humidity (f) and the adjustable parameter is specified by the stripping efficiency (AWZ), the following condition having to be met to avoid marbling and / or toothpick defects: f>AWZ.

5. The method according to claim 4, characterized in that The stripping efficiency (AWZ) is defined as follows: in Applicable: d is the thickness of the nozzle lip gap, in mm, D is the effective flow rate (velocity) of gas G per belt side over the belt 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 strip, in mm, v is the strip speed, in m / min.

6. The method according to claim 4, characterized in that The stripping efficiency (AWZ) is defined as follows: where Applicable: d is the thickness of the nozzle lip gap, in mm, D is the effective flow rate (velocity) of gas G per belt side over the belt width (w), in Nm 3 / h, k is a dimensionless proportionality coefficient, 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 strip, in mm, v is the strip speed, in m / min.

7. The method according to claim 5 or 6, characterized in that: When determining the value of the half-half width (b) and the value of the proportionality coefficient (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17), the following definitions apply: Situation 1.1: And k = 1 Case 1.2: Case 1.3: and 8. The method according to claim 5 or 6, characterized in that: When determining the value of the half-half width (b) and the value of the proportionality coefficient (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 9. The method according to any one of claims 1 to 8, characterized in that: - the thickness (d) of the nozzle lip gap (17) is in the range between 0.5 mm and 5 mm, preferably between 0.6 mm and 2 mm, particularly preferably between 0.8 mm and 1.5 mm, and / or - The flow rate (D) is 200 Nm per hour 3 Up to 8000Nm per hour 3 within the scope of, and / or - the spacing (Z) is in the range between 2 mm and 15 mm, preferably between 3 mm and 12 mm, and / or - the strip speed (v) is in the range between 50 m / min and 200 m / min, preferably between 70 m / min and 150 m / min.

10. The method according to any one of claims 1 to 9, characterized in that The bath temperature TB of the alloy bath (11) is in the range of 400 degrees Celsius < TB < 480 degrees Celsius, preferably in the range of 409 degrees Celsius < TB < 473 degrees Celsius, and particularly preferably in the range of 420 degrees Celsius < TB < 460 degrees Celsius.

11. The method according to any one of claims 1 to 10, characterized in that The absolute local air humidity (f) is applied in two virtual cylindrical volume segments which are limited on the one hand by a virtual cylindrical surface which concentrically or almost concentrically surrounds the at least one gas nozzle (15) and on the other hand by two planes which are parallel to the flat steel product (100) and at a distance (s) from the flat steel product (100) on both sides of the flat steel product, wherein the common volume of the cylindrical volume segments is 1 m 3 Up to 10m 3 within the range and preferably less than 2m 3 , wherein the measurement of the absolute local air humidity (f) is carried out directly or indirectly.

12. The method according to claim 11, characterized in that The absolute local air humidity (f) is measured permanently or from time to time and, if the absolute local humidity (f) is too low, the method is interrupted to adjust one or more of the adjustable parameters.

13. The method according to any one of claims 1 to 12, characterized in that The application of the layer (10) is controlled by a controller (250) such that when the absolute local air humidity (f) changes, one or more of the adjustable parameters are automatically and / or manually adjusted according to the current absolute local air humidity (f).

14. An apparatus (150) for applying a layer (10) to a flat steel product (100), comprising: - a zinc alloy bath (11) having an input side (E), an output side (A) and a deflector (13) for guiding the flat steel product (100) at a strip speed (v) from the input side (E) through the zinc alloy bath (11) to the output side (A), - a stripping nozzle device (14) comprising at least one nozzle lip gap (17), and the stripping nozzle device (14) is arranged in the region of the output side (A) such that the gas (G) discharged through the nozzle lip gap (17) can blow off the still liquid layer (10) at the flat steel product (100) to blow off the layer (10) to the target thickness, The zinc alloy in the zinc alloy molten pool (11) has the following composition: an aluminum content ranging between 1.0 and 3.5 weight percent, and preferably ranging between 1.3 and 2.8 weight percent, a magnesium content in the range between 1.0 and 3.0 weight percent, and preferably in the range between 1.2 and 2.2 weight percent, and the remainder, which comprises zinc, one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, each of which has a weight-related content of less than 0.1%, and unavoidable impurities, Characterized in that the device (150) is adapted or configured to manually or automatically make at least one of the following adjustments: - increasing the pool temperature (TB) of the alloy pool (11) if the current absolute local air humidity (f) decreases, and decreasing the pool temperature (TB) of the alloy pool (11) if the current absolute local air humidity (f) increases, and / or - reducing the thickness (d) of the nozzle lip gap (17) if the current absolute local air humidity (f) decreases, and increasing the thickness (d) of the nozzle lip gap (17) if the current absolute local air humidity (f) increases, and / or - reducing the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) if the current absolute local air humidity (f) decreases, and increasing the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) if the current absolute local air humidity (f) increases, Therein, additionally, the flow rate (D) of the gas (G) is automatically adjusted to keep the target thickness of the layer (10) to be applied substantially constant.

15. The device (150) according to claim 14, characterized in that The layer (10) to be applied meets the following requirements: - The target surface coating of the layer (10) per belt side is 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 - The target thickness of said layer (10) per belt side is in the range of 3 to 30 μm, preferably in the range of 4.5 to 15 μm.

16. The device (150) according to claim 14 or 15, characterized in that The adjustable parameters are adjusted within the following ranges to prevent marbling and / or toothpick defects at the layer (10): - Absolute local air humidity (f) at 1g / m 3 Up to 300g / m 3 In the range of 1.08 g / m 3 Up to 51g / m 3 within the range.

17. The device (150) according to any one of claims 14 to 16, characterized in that The device (150) additionally comprises: - at least one moisture sensor (51) arranged around a portion of the stripping nozzle arrangement (14), a controller (250) which can be connected by communication to said at least one humidity sensor (51) to continuously or from time to time obtain measurement values ​​or signals from which a physical variable directly related to said absolute local air humidity (f) around the local nozzle can be derived, The controller (250) is configured to execute or trigger the execution of at least one of the following steps: - changing the bath temperature (TB) of the alloy bath (11), and / or - changing the thickness (d) of the nozzle lip gap (17), and / or - Change the distance (Z) between the spray lip gap (17) and the side of the flat steel product (100), - Adjust the flow rate (D) of the gas (G), to keep the target thickness of the layer (10) to be applied substantially constant.

18. The device (150) according to any one of claims 14 to 16, characterized in that The device (150) includes a controller (250) configured to adjust or trigger the adjustment of one or more of the adjustable parameters according to the current absolute local air humidity (f).

19. The device (150) according to any one of claims 14 to 16, characterized in that The device (150) includes a controller (250) configured to determine the stripping efficiency (AWZ), where the stripping efficiency (AWZ) defines the relationship between the current absolute local air humidity (f) and the adjustable parameters and where the following condition must be met to avoid marbling formation: f > AWZ.

20. The device according to claim 18 or 19, characterized in that The device includes an engine or actuator (M) for each gas nozzle (15), the engine or actuator (M) being connected to the controller (250) for control purposes such that if the current absolute local air humidity (f) decreases, the controller (250) reacts to the changing absolute local air humidity (f) by reducing the distance (Z), and if the current absolute local air humidity (f) increases, the controller (250) reacts by increasing the distance (Z).

21. The device according to claim 18 or 19, characterized in that The device comprises a pumping device (P) for each gas nozzle (15) g ) and a control loop to automatically adjust the flow rate (D) of the gas (G) so that the target thickness of the layer (10) remains substantially constant.

22. The device according to claim 18 or 19, characterized in that The device includes a bath heater (30), the bath heater (30) being connected to the controller (250) for control purposes such that the controller (250) reacts to the changing absolute local air humidity (f) by adjusting the bath temperature TB, the bath temperature TB being in the range of 400 degrees Celsius < TB < 480 degrees Celsius, preferably in the range of 409 degrees Celsius < TB < 473 degrees Celsius, and particularly preferably in the range of 420 degrees Celsius < TB < 460 degrees Celsius.

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