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

Abstract

A device (150) for applying a layer (10) to a flat steel product (100), - a zinc alloy molten bath (11) having an inlet side (E) and an outlet side (A), - a peeling nozzle device (14) provided with at least one nozzle lip gap and arranged in the region of the outlet side (A) such that a stationary liquid layer (10) on the flat steel product (100) can be blown off by a gas coming out through the nozzle lip gap and comprising The device (150) is configured to perform the following adjustments, namely, - increasing the bath temperature of the alloy molten bath when the current absolute local air humidity decreases and vice versa, and / or - decreasing the thickness of the nozzle lip gap when the current absolute local air humidity decreases and vice versa, and / or - decreasing the distance between the nozzle lip gap and the side of the flat steel product (100) when the current absolute local air humidity decreases and vice versa, and - automatically adjusting at least one of the gas flow rate so as to keep the target thickness of the layer to be applied essentially constant, a device (150) is provided.

Description

Technical Field

[0001] The present invention relates to a method that can be used when flat steel products are coated with a zinc-aluminum-magnesium (ZnAlMg)-based layer, for example as a protective coating. This also relates to a device configured to apply the method according to the present invention.

Background Art

[0002] It is well known that flat steel products 100, such as steel strips or steel plates, are coated with a ZnAlMg alloy to improve corrosion resistance. In practice, this is usually done by immersing the flat steel product 100 coming out of the furnace into the zinc alloy molten bath 11, as shown in FIG. 1 using an exemplary device 150. To protect the flat steel product 100 from oxidation, this is typically introduced into the bath 11 on the inlet side E through the trunk 12 using an inert atmosphere. In the bath 11, the flat steel product 100 is deflected by the (zinc bath) roller 13 and moved upward from the bath 11 on the outlet side A. When it comes out of this bath 11, the molten alloy film adhering to the front and rear sides of the flat steel product 100 is removed by a gas jet from the gas nozzle 15 of the stripping nozzle device to the target thickness (within the micrometer range) or until the target surface coating mass (unit is g / m 2 ), and then the flat steel product 100 is conveyed to the cooling area 16. This continuous method is generally referred to as hot dip galvanizing.

[0003] Details of suitable methods and particularly suitable alloy compositions are described, for example, in International Publication No. WO 2014 / 033153 A1 published by the applicant VOESTALPINE STAHL GMBH.

[0004] There is prior art that mentions water or water vapor in relation to hot dip galvanizing of flat steel products. The corresponding documents are listed below, and here the interesting points are briefly described.

[0005] The European Patent No. 0172682B1 of Armco Inc. filed in 1985 deals with the control of zinc vapor in relation to the hot-dip plating of iron-based metal strips. A low-oxygen atmosphere containing a small amount of water vapor is provided in a sealed area (corresponding to the trunk 12 in Figure 1) on the inlet side of the dipping tank. This small amount of water is intended to prevent the formation of zinc vapor on the surface of the dipping tank. The dew point of the gas used on the inlet side is set so that zinc vapor cannot form.

[0006] The object in Japanese Patent Application Laid-Open No. 2020100886A2 of a Japanese company is to produce a zinc-plated steel strip having a surface with an increased friction coefficient. To increase the friction coefficient, water is sprayed onto the surface of a flat steel product under pressure after gas blowing. The particle size of the water droplets should be at least 0.07 mm, preferably more than 1.5 mm. By spraying the water droplets, unevenness is intentionally formed on the surface of the steel strip. This document pursues different objectives, and the corresponding technical teachings proceed in a completely different direction from the present invention.

[0007] There are even more stringent requirements not only for protection against corrosion but also regarding the surface quality of hot-dip galvanized flat steel products. Especially in the automotive industry, products that meet the highest surface requirements are expected. However, providing a homogeneous surface is no small matter.

[0008] The main problem is often surface defects in the ZnAlMg layer. For example, defects in the form of marble patterns (marble effect), "toothpick" - like, or "beach pattern" - like can form on the ZnAlMg layer, or slag formation can occur. There are also patents (e.g., European Patent No. 20130826634, AM / J.M. Mataigne, Japanese Patent Application Laid-Open No. 20080256208, NSSMC / Ohashi et al.) that attempt to eliminate similar surface defects (luster effect or peeled oxide film) by other means (reduction of the O2 content around the wiper nozzle).

Prior Art Documents

Patent Documents

[0009] [Patent Document 1] International Publication No. 2014 / 033153 A1 [Patent Document 2] European Patent No. 0172682 B1 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2020-100886 A2 [Patent Document 4] European Patent No. 20130826634 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2008-0256208 [Non-Patent Document]

[0010] [Non-Patent Document 1] "Characteristic Features 095 - Melt-Dipped Coated Strip and Sheet", 2010 Edition, Steel Information Center 40039 Dusseldorf [Non-Patent Document 2] "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet", C.V. Tu et al., Experimental Thermal and Fluid Science, 1996, 16, pp. 364 - 373, Elsevier Science Inc. [Summary of the Invention] [Problems to be Solved by the Invention]

[0011] Therefore, the problem is to provide a method and a corresponding device for coating flat steel products that are particularly durable against corrosion and have a strong protective effect, and the surface of the protective coating should be particularly homogeneous, very smooth, free of marble patterns (no "marble effect") and / or free of toothpick defects (no "toothpick"). The aim is to achieve a surface quality that meets the highest customer requirements.

[0012] In addition, this method should be as energy efficient, cost-effective, simple, and reproducible as possible.

Means for Solving the Problem

[0013] According to the present invention, there are provided a continuous (hot dip coating) method and a corresponding device that enable a flat steel product to be provided with a metal layer that can function as, for example, a (protective) coating, and this layer protects the steel substrate of the flat steel product from external influences.

[0014] All embodiments include applying a (protective) layer to the flat steel product, and the thickness of this layer is intended to correspond to a target thickness (according to corresponding specifications). This layer is produced by passing the flat steel product through a zinc alloy molten bath and blowing and removing gas on the outlet side of the bath using a stripping nozzle device having at least one gas nozzle. The zinc alloy of the zinc alloy molten bath has the following composition, namely, - an aluminum content in the range of 1.0 wt% to 3.5 wt%, preferably in the range of 1.3 wt% to 2.8 wt%, and - a magnesium content in the range of 1.0 wt% to 3.0 wt%, preferably in the range of 1.2 wt% to 2.2 wt%, and - the remainder of the zinc alloy molten bath is zinc, and optionally contains one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, and the weight-related content of each additional element in the metal coating is less than 0.1%, including inevitable impurities.

[0015] This method is such that at least one of the following adjustable parameters is - increasing the bath temperature of the alloy molten bath when the current absolute local air humidity decreases, doing the reverse as well, and / or - When the current absolute local air humidity decreases, the thickness of the nozzle lip gap is decreased, and vice versa, and / or - When the current absolute local air humidity decreases, the distance between the nozzle lip gap and the side of the flat steel product is decreased, and vice versa is adjusted such that, additionally, the gas flow rate is adjusted to keep the target thickness of the layer to be applied essentially constant characterized in that.

[0016] A device configured to apply a coating to a flat steel product is - A zinc alloy molten bath having an inlet side, an outlet side, and a deflector for guiding the flat steel product coming from the inlet side through the zinc alloy molten bath at a strip speed to the outlet side, - A stripping nozzle device having at least one nozzle lip gap and arranged in the region of the outlet side such that a stationary liquid layer on the flat steel product can be blown off by a gas coming out through the nozzle lip gap and thereby blown off to the target thickness, comprising, The zinc alloy of the zinc alloy molten bath has the following composition, namely, - An aluminum content in the range of 1.0 wt% to 3.5 wt%, preferably in the range of 1.3 wt% to 2.8 wt%, - A magnesium content in the range of 1.0 wt% to 3.0 wt%, preferably in the range of 1.2 wt% to 2.2 wt%, having, - The remainder of the zinc alloy molten bath is zinc and optionally contains one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, and the weight content of each additional element in the metal coating is less than 0.1% and includes unavoidable impurities.

[0017] This device is manually or automatically adjusted as follows, namely, - When the current absolute local air humidity decreases, increase the bath temperature of the alloy melting bath, and vice versa, and / or - When the current absolute local air humidity decreases, decrease the thickness of the nozzle lip gap, and vice versa, and / or - When the current absolute local air humidity decreases, decrease the distance between the nozzle lip gap and the side of the flat steel product, and vice versa is adapted or configured to perform at least one of: In addition, the gas flow rate is automatically adjusted to keep the target thickness of the layer to be applied essentially constant.

[0018] In all embodiments or at least some of the embodiments, the metal bath has the following alloying concept, namely, - The aluminum content (weight percent) is in the range of 1.0 weight percent to 3.5 weight percent, preferably in the range of 1.3 weight percent to 2.8 weight percent, - The magnesium content (weight percent) is in the range of 1.0 weight percent to 3.0 weight percent, preferably in the range of 1.2 weight percent to 2.2 weight percent, - The remainder of the zinc alloy melting bath is zinc, and optionally contains one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, and the weight-related content of each additional element in the metal coating is less than 0.1%, including inevitable impurities to provide a ZnAlMg alloy having a composition according to.

[0019] In some embodiments, the aluminum content (weight percent) may be greater than or equal to the magnesium content (weight percent).

[0020] In all embodiments or at least some of the embodiments, the unavoidable impurities are in a range significantly less than 1 weight % (wt%), preferably the total of all unavoidable impurities is less than 0.5 weight %.

[0021] By combining an accurately defined ZnAlMg alloying concept, monitoring or observing the current absolute local air humidity, and target adjustment of the peeling process (or corresponding method and / or system parameters or peeling efficiency), a surface can be produced that shows no marble pattern or has a marble pattern to such an extent that it can be ignored.

[0022] In all embodiments, according to the present invention, the value of the absolute local air humidity, which should be present in the immediate vicinity of the flat steel product in the region between the outlet side and the cooling region (if present), is 1 g / m 3 to 300 g / m 3 in the range, preferably 1.08 g / m 3 to 51 g / m 3 in the range, that is, the method can be successfully carried out with the absolute local air humidity within the said range.

[0023] In all embodiments, after the peeling nozzle device, optionally, a strip stabilization device that functions to automatically stabilize the movement of the flat steel product may follow. In these embodiments, the value of the absolute local air humidity in the region between the peeling nozzle device and the strip stabilization device can be determined.

[0024] This method preferably operates the alloy molten bath at a bath temperature TB in the range of 3 - 400 < TB < 480 °C, preferably in the range of 409 < TB < 473 °C, particularly preferably in the range of 420 < TB < 460 °C, at an absolute local air humidity greater than 1 g / m - the step of operating the alloy molten bath at a bath temperature TB in the range of - the step of operating the peeling nozzle device at a nozzle distance from the flat steel product in the range of 2 to 15 mm, preferably 3 to 12 mm. - From 200 to 8000 Nm per hour 3 Blowing off the flat steel product on the outlet side of the alloy molten bath where the gas flows through the nozzle lip gap in the direction of the flat steel product using a gas flow rate within the range of 3 including.

[0025] The ZnAlMg alloying concept defined above is based on numerous investigations and calculations. Within the specified limits of the ZnAlMg alloying concept, the technical teachings presented here have been found to be particularly successful.

[0026] In at least some of the embodiments, the absolute local air humidity is measured permanently.

[0027] In at least some of the embodiments, the absolute local air humidity is measured from time to time.

[0028] In at least some of the embodiments, the method is interrupted to adjust one or more of the adjustable parameters if the absolute local air humidity is too low.

[0029] Preferably, the method is carried out in all embodiments with a low bath temperature TB red which is in the range of 420 < TB red < 460 °C. Within this range, slag formation can also be reduced.

[0030] In certain tests, it has been shown that the ZnAlMg alloying concept actually gives very good results. It has been shown that excellent results can be achieved especially by adjusting the peeling process (or the corresponding peeling efficiency).

[0031] The development of the new method, in particular the particularly suitable ZnAlMg alloying concept, and the targeted adjustment of the (method) parameters (or the corresponding peeling efficiency) is based on theoretical considerations, various simulations of the peeling process, and numerous experiments.

[0032] The process within the area of the peeling nozzle device and on flat steel products is very complex and depends on a number of (method) parameters and influencing variables (or the corresponding peeling efficiency). Therefore, the present method and device rely on some simplified assumptions and definitions in order to obtain reproducible results.

[0033] In all embodiments, the coated flat steel product can, as usual, undergo a dressing process or a re-rolling process, and / or a bending and stretching correction process after coating. Preferably, the overall degree of deformation for the coated flat steel product is between 0.5% and 2.5%, preferably between 0.7% and 1.7%. The dressing process or the re-rolling step (with the degree of deformation within the range of 0.7% to 1.7%) can further reduce the negative influence of the marble pattern.

[0034] In all embodiments, the coated flat steel product can be treated with normal transport protection means such as oil replenishment or other chemical treatment agents, as described in point 7 of the information sheet "Charakteristische Merkmale 095 - Schmelztauchveredeltes Band und Blech", 2010 edition, issued by the Steel Information Center 40039 Dusseldorf.

[0035] Further advantageous embodiments of the present invention are the subject of the dependent claims.

[0036] Embodiments of the present invention will be described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 7D

Figure 7E

Figure 7F

Figure 7G

Figure 8A

Figure 8B

Figure 9

[0038] The present invention relates to a method and a device 150 for applying a layer 10 to a strip-shaped flat steel product 100 (see FIG. 3A. Here, the layer 10 can be seen on the upper side of the strip). This layer 10 is produced by passing the flat steel product 100 from the inlet side E to the outlet side A through a zinc alloy molten bath 11 and blowing it off with a gas G on the outlet side A using a peeling nozzle device 14, as shown by way of example in FIGS. 2, 3A, 6, and 7. The purpose of the peeling nozzle device 14 is to strip off the excess (still liquid) ZnMgAl layer (layer 10) when it exits the bath 11.

[0039] In the context of the invention, on the one hand, it must be ensured that the layer 10 does not essentially change even when the absolute air humidity f of the environment changes, and on the other hand, that no marble pattern occurs. In other words, the aim is to avoid the occurrence of a marble pattern when the local absolute air humidity f changes, while at the same time substantially maintaining the target thickness of the layer 10.

[0040] In addition to the target thickness of the layer 10, the target (surface) coating mass of the layer 10 can also be specified in all embodiments. Typically, there is a narrowly specified tolerance range for the target thickness. As long as the layer 10 to be produced is within the tolerance range, the layer 10 essentially meets the specifications.

[0041] The process in the area of the peeling nozzle device 14 and on the flat steel product 100 is very complex and depends on a large number of parameters and influencing variables.

[0042] In all embodiments, the peeling nozzle device 14 comprises at least one gas nozzle 15 (if only one side of the strip is to be blown off), or two gas nozzles 15 facing each other (if both sides of the strip are to be blown off). FIGS. 2, 6, and 7 show embodiments with two nozzles 15, and FIG. 3A shows an embodiment with only one nozzle 15.

[0043] In at least some of the embodiments, the method is carried out and controlled such that each layer 10 of the strip side of the flat steel product 100 has a target thickness within an acceptable range. Preferably, in all embodiments, the target thickness of each layer 10 of the strip side is in the range of 3 to 30 μm, and particularly preferably in the range of 4.5 to 15 μm.

[0044] Preferably, in at least some of the embodiments, the target surface coating (coating mass per strip side, which is referred to as coating per side in FIGS. 8A and 8B) is in the range of 20 to 200 g / m 2 and particularly preferably in the range of 30 to 100 g / m 2 of the range.

[0045] In order to be able to reliably apply essentially the layer 10 corresponding to the target thickness, the zinc alloy of the zinc alloy melting bath 11 has, in all or at least some of the embodiments, the following composition, namely, - an aluminum content in the range of 1.0 weight percent to 3.5 weight percent, preferably in the range of 1.3 weight percent to 2.8 weight percent, and - a magnesium content in the range of 1.0 weight percent to 3.0 weight percent, preferably in the range of 1.2 weight percent to 2.2 weight percent and - The remaining part of the zinc alloy molten bath 11 is zinc and optionally contains one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, with the weight-related content of each additional element in the metal coating being less than 0.1% and including inevitable impurities. has a composition.

[0046] In all embodiments or at least some of the embodiments, the metal bath 11 has the following alloying concept, namely, - the aluminum content (in weight percent) is in the range of 2.09 weight percent to 2.66 weight percent, - the magnesium content (in weight percent) is in the range of 1.45 weight percent to 2.24 weight percent, - the remaining part of the zinc alloy molten bath 11 is zinc and optionally contains one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, with the weight-related content of each additional element in the metal coating being less than 0.1% and including inevitable impurities A particularly preferred AnAlMg alloy having a composition according to this is supplied.

[0047] In all embodiments, the aluminum content (in weight percent) may be greater than or equal to the magnesium content (in weight percent).

[0048] To prevent or significantly reduce the formation of marble patterns, the absolute local air humidity f is determined continuously or sometimes (e.g., by direct or indirect measurement). This description also applies to the prevention or reduction of whisker formation.

[0049] The absolute air humidity f is a physical quantity that can be expressed, for example, in units of g / m 3 and is, in other words, this is per 1 m 3It is the mass of gaseous water within a standardized volume body having a volume of . In other words, the absolute air humidity f indicates the water vapor content within the volume body. Here, f is used as the symbol for the formula for absolute air humidity. In all embodiments, the absolute air humidity f can be approximately estimated from the air temperature TL and the relative air humidity r, whereby the following formula applies.

[0050] [Number]

[0051] It is the relative air humidity in units of r %. It is the air temperature in units of TL °C.

[0052] The absolute local humidity f can be measured directly or indirectly in all embodiments. Indirect measurement is understood to mean, among other things, measuring the air temperature TL and the relative air humidity r and calculating / deriving the absolute local humidity f.

[0053] According to the present invention, the value of the absolute local air humidity, which should be present in the immediate vicinity of the flat steel product 100 in the region between the outlet side A and the cooling region 16 (if present), is within the range of 1 g / m 3 to less than 300 g / m 3 in all embodiments. Preferably, the absolute local air humidity is within the range of 1.08 g / m 3 to 51 g / m 3 in all embodiments.

[0054] When the local air absolute humidity f is greater than 1 g / m 3 and less than 300 g / m 3If it is smaller, this method enables the layer 10 to be applied while controlling it on at least one side of the flat steel product 100 by selectively adjusting adjustable parameters (method and system parameters). In all embodiments, care is taken to ensure that the adjustable parameters are adjusted such that the layer 10 to be applied still essentially corresponds to the target thickness. This means that care is taken to ensure that a layer that corresponds to the target thickness and at the same time shows no or only very little marble pattern is still applied (within the tolerance range).

[0055] The adjustable parameters (method and system parameters) in all embodiments - when the current absolute local air humidity f decreases, increase the bath temperature TB of the alloy melt bath, do the reverse as well, and / or - when the current absolute local air humidity f decreases, decrease the thickness d of the nozzle lip gap 17, do the reverse as well, and / or - when the current absolute local air humidity f decreases, decrease the distance Z between the nozzle lip gap 17 and the side of the flat steel product 100, do the reverse as well, can be adjusted as follows, In addition, the flow rate D of the gas G is adjusted (automatically, for example by control) so as to keep the target thickness of the layer 10 to be applied essentially constant.

[0056] In addition, in all embodiments, the strip speed v at which the flat steel product 100 is moved out of the zinc alloy melt bath 11 can also be changed, and care is also taken here to ensure that the target thickness of the layer 10 to be applied is kept essentially constant.

[0057] Preferably, in all embodiments, some of these adjustable parameters (method and system parameters) are changed in a coordinated manner to ensure that the layer 10 to be applied corresponds to the target thickness. The mathematical relationships applied here are described below.

[0058] The so-called target specifications for layer 10 to be applied, for all embodiments, - The coating layer of layer 10 for each side of the strip shall be within the range of 20 to 200 g / m 2 Preferably within the range of 30 to 100 g / m 2 And / or - The target thickness of layer (10) for each side of the strip shall be within the range of 3 to 30 μm, preferably within the range of 4.5 to 15 μm It can be stipulated that such specifications must be met.

[0059] The bath temperature TB of the alloy melting bath 11 affects the viscosity of the melt in the stripping process. As the bath temperature TB increases, the viscosity of the melt decreases. If the adjustable parameters (method parameters and system parameters) remain the same, more material than desired will be stripped. Therefore, when the bath temperature TB increases, other adjustable parameters (method parameters and system parameters) are changed so that layer 10 still has the target thickness. When the bath temperature TB is increased, for example, the flow rate D of gas G is reduced to reduce the stripping effect in order to still achieve the same target thickness.

[0060] In all embodiments, the bath temperature TB of the alloy melting bath 11 is preferably within the range of 400 < TB < 480 °C, preferably within the range of 409 < TB < 473 °C, particularly preferably within the range of 420 < TB < 460 °C. Within these range limits, the bath temperature TB can be adjusted to change the viscosity.

[0061] Regarding operating the alloy melting bath 11, the bath temperature TB within the specified temperature range is specified in all embodiments. It is important to maintain this temperature range (temperature range) because undesired slag can be formed on the flat steel product 100 when operating outside the specified range.

[0062] The bath temperature TB can be adjusted in all embodiments, for example, using the induction heating device 30 (see FIGS. 2 and 6) or a resistance heater.

[0063] To avoid slag formation, the bath temperature TB is preferably lowered in all embodiments. The lowered bath temperature TB red is preferably within the range 420 < TB red < 460 °C already mentioned.

[0064] When implementing this method, in all embodiments, preferably, - the thickness d of the nozzle lip gap 17 is in the range from 0.5 to 5 mm, preferably in the range from 0.6 to 2 mm, particularly preferably in the range from 0.8 to 1.5 mm, and / or - the flow rate D is in the range from 200 to 8000 Nm 3 per hour, and / or - the distance Z is in the range from 2 to 15 mm, preferably in the range from 3 to 12 mm, and / or - the strip speed (v) is in the range from 50 to 200 m / min, preferably in the range from 70 to 150 m / min should be noted.

[0065] This method functions with particularly high reliability within these ranges.

[0066] 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 an effective length corresponding to the strip width w of the strip-shaped flat steel product 100 (see also FIG. 5). The thickness d of the gas nozzle 15 is defined parallel to the x-axis.

[0067] The strip width w of the strip-shaped flat steel product 100 is preferably in the range of 500 mm to 2500 mm in all embodiments. Particularly preferably, the strip width w of the strip-shaped flat steel product is in the range of 800 mm to 1800 mm in all embodiments.

[0068] In at least some of the embodiments, the absolute local air humidity f is measured permanently or occasionally, and if the absolute local humidity f is too low, for example, the operation of applying the layer 10 is interrupted in order to adjust an adjustable parameter.

[0069] Since the thickness d of the nozzle lip gap 17 can only be adjusted manually in some of the devices 150, in at least some of the embodiments, the process is stopped before the nozzle lip gap 17 is adjusted manually.

[0070] In at least some of the embodiments, the absolute local air humidity f is measured directly or indirectly.

[0071] The measurement of the absolute local air humidity f is not carried out directly at the impact line where the gas G impinges on the layer 10 to be peeled off, because the mixed gas is relatively "dry" there (i.e., contains little air humidity). In all embodiments, the absolute local air humidity f is preferably measured directly or indirectly in a region at least perpendicular (right-angled) to the impact line or the flat steel product 100 at a distance of 20 cm.

[0072] Figures 2 and 7 show an approach 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 strip). In the schematic view, each of these sensors 51 has two contacts, which can be connected, for example, to the controller 250. The corresponding connections or lines V1, V2, V3, V4 are shown in Figures 2 and 6 by dashed lines.

[0073] In all embodiments, as the humidity sensor 51, a sensor of the following design or aspect, namely, - A measurement sensor that operates mechanically based on the expansion or contraction of a (usually organic) measurement element caused by humidity, - A measurement sensor that operates in a psychrometric manner, in which two identical very precise thermometers are used and the gas flow to be measured is induced at a defined speed, - A capacitance measurement sensor, for example, comprising a humidity-sensitive capacitor having two planar electrodes, - A dew point mirror hygrometer that determines the air humidity with a dew point mirror and evaluates the condensation of water vapor when the dew point becomes low, - A resistance measurement method, for example, in which the impedance of the AC resistance of a moisture-absorbing element is determined, - A spectroscopic measurement method, for example, that measures the gaseous water content in the near or mid-infrared (NIR or MIR) range without contact can be used.

[0074] All embodiments of the device 150 may include a controller 250. In all embodiments, this controller 250 may be designed as a computer-assisted automation and control unit and may include a human-machine interface, a computer, and a database.

[0075] In all embodiments, the controller 250 may be part of the overall system control of the device 150 or, in all embodiments, may be connected to the overall system control of the device 150.

[0076] In these embodiments, the adjustable parameters (system or method parameters), or the adjustment / change of the stripping efficiency AWZ, can then be carried out by the overall system controller and / or by the controller 250.

[0077] When indirectly measuring the absolute local air humidity, the air humidity is not measured in the device 150 (e.g., within the virtual cylinder vZK) or in its surrounding area, but the current air humidity is determined indirectly.

[0078] In all embodiments, the current air humidity can be measured indirectly, for example, by using a kind of optical barrier to determine the transmission rate of the optical path. The transmission rate is high in very dry air. On the other hand, the presence of water in the form of gas hinders the transmission of light through the optical path and the transmission rate becomes low.

[0079] In all embodiments, an indirect determination can be made by measuring the surface characteristics of the coated flat steel product 100 (three examples of the coated flat steel product 100 are shown in FIGS. 7A, 7B, and 7C). The corresponding measurement of the surface characteristics can be carried out optically, for example, before or after the cooling region 16 (e.g., by optically measuring the reflectivity of the surface of the layer 10). FIGS. 7D to 7G show exemplary photographs of the coated flat steel product 100.

[0080] Preferably, in all embodiments, an inert gas is used as the gas G. Nitrogen or a nitrogen-containing gas mixture has been demonstrated to be particularly effective.

[0081] FIG. 3A shows a highly schematic side view of another stripping nozzle device 14 that can more accurately define adjustable parameters (system and method parameters) or the stripping efficiency AWZ. The important adjustable parameters are - the thickness d of the nozzle lip gap 17, - the gas flow rate D, - the distance Z between the nozzle lip gap 17 and the (strip) side of the flat steel product 100, - the strip speed v at which the flat steel product 100 is moved out of the zinc alloy molten bath 11 (advancing parallel to the x-axis) are.

[0082] Figure 3A shows the nozzle distance Z between the nozzle 15 and the corresponding strip side (here the front side) of the flat steel product 100, and further shows the thickness d of the nozzle lip gap 17. The nozzle lip gap 17 serves as the gas outlet gap of the peeling nozzle device 14.

[0083] Figure 3B shows a schematic diagram of the gas pressure curve P generated along the front side of the flat steel product 100. The pressure P depends on the position on the x-axis. Ideally, the pressure curve P has the shape of a Gaussian curve as shown in Figure 3B. This Gaussian curve is often used to determine the half-width at P S / 2, where P S represents the maximum pressure. 2b represents the half-width in millimeters. A narrow gas jet is defined by a small half-width 2b. The larger the gas jet (wider in width), the larger the half-width 2b. More detailed information is described in the publication "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet", C.V. Tu et al., Experimental Thermal and Fluid Science 1996, 16, pages 364 - 373, Elsevier Science Inc.

[0084] The gas jet emerging from the nozzle 14, together with the force of gravity (for example, when the flat steel product 100 is pulled vertically upward from the bath 11 as shown in Figures 2, 6, and 7), exerts a shear force τ on the stationary liquid layer 10. Figure 3C represents the shear force τ with respect to the position on the x-axis (the shear force τ is determined by the negative first derivative of the pressure profile in Figure 3B). This is the shear force τ acting on the layer 10 to be peeled off. The course of the shear force curve τ is symmetric with respect to the point x = 0, τ = 0 as a first approximation (when the strip velocity v parallel to the x-axis is ignored). The nozzle 15 is arranged directly above the x = 0 position where Z > 0. τ max defines the maximum shear force occurring in the layer 10 to be peeled off.

[0085] Tests were conducted showing that adjustable system and / or method parameters, or the peeling efficiency AWZ, can be adjusted within a range without significantly changing the target thickness and / or surface weight (coating per strip side) of layer 10.

[0086] It has also been shown that two variables characterizing the shear force profile generated by the peeling nozzle 15 on the strip 100 (in addition to the absolute local air humidity f) are crucial for the formation of the marble pattern. One is the maximum shear force τ max and the other is the time t it takes for the flat steel product 100 in the strip shape to pass through the distance l between the maximum values of the shear force (see Figure 3C). This time t also depends here on the strip speed v.

[0087] There is a direct relationship between the time t, the strip speed v, and the half-width 2b as represented by Equation (1)

[0088]

Equation

[0089] as shown.

[0090] In all embodiments, the strip speed v is preferably in the range of 50 m / min to 200 m / min, particularly preferably in the range of 70 m / min to 150 m / min.

[0091] The equations describing the dynamic flow behavior of the gas G in the flat steel product 100 are very complex. This is due to the fact that regions with laminar and turbulent flow patterns are formed on the layer 10 of the flat steel product 100 in the gas jet exiting through the nozzle lip gap 17 of the nozzle 15. In addition, the gas jet draws in surrounding air, which swirls together with the gas G. Details are described, for example, in the already mentioned publication "Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet."

[0092] Statistical evaluation of the complex test and measurement results did not yield directly usable results regarding the correlation between stripping nozzle parameters and marbling due to the complex interrelationships. Only after additional systematic investigation of various internal and external influencing variables did a correlation emerge between the degree of marbling of layer 10, stripping nozzle parameters, and the environmental conditions of the test facility. Air humidity, in particular, has shown an influence on the marbling on layer 10.

[0093] Further targeted investigations and graphical processing of the results of these tests showed for the first time a correlation between air humidity, stripping nozzle parameters, and the tendency to marbleize. Figure 4 shows a summary graphical representation of a number of tests, with stripping efficiency AWZ (abbreviated as a summary or collective term for method and device parameters or stripping nozzle parameters) on the ordinate axis, g / m 3 Absolute air humidity f in units of is plotted on the abscissa axis.

[0094] Two variables τ max By weighting and adding t and t, the so-called stripping efficiency AWZ can be determined, which depends on the absolute local air humidity f as follows (inequality (2.1)):

[0095]

number

[0096] can be directly compared.

[0097] The right side of the inequality (2.1) corresponds to the peeling efficiency AWZ, that is, the relational expression (2.2) f > AWZ (2.2) holds.

[0098] The peeling efficiency AWZ is determined by the following methods and device parameters, namely, - The effective flow rate (quantity) D of the gas G over the strip width w for each strip side, - The proportionality coefficient k, - The strip width w of the flat steel product 100, - The thickness d of the nozzle lip gap 17, - The half-width 2b, - The speed v (strip speed) of the flat steel product 100, or the time t correlated with the speed v summarizes.

[0099] Further details regarding the peeling efficiency AWZ are also described in the inequality (3) to be explained later. The entire right side term of this inequality (3) can also be used as the definition of the peeling efficiency AWZ. Before explaining the inequality (3), we will further refer to Figure 4.

[0100] The symbols (squares, diamonds, triangles, or circles) filled in gray or black in Figure 4 represent the flat steel products 100 on which the marble pattern is clearly formed on the surface of layer 10. The marble pattern is particularly strong in the symbols filled in black. The symbols filled in gray represent a less prominent marble pattern. On the other hand, the unfilled symbols represent that there is no marble pattern or it is negligible. The circular symbols represent the tests conducted with a nozzle lip gap thickness of d = 0.8 mm, the square symbols represent the tests using a nozzle lip gap thickness of d = 0.9 mm, the diamond symbols represent 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.

[0101] The straight line Ge is inserted into the graph of FIG. 4 as a boundary line, and as a first approximation, those tests with distinct or medium marble patterns are distinguished from those tests that show no marble pattern or only a negligible degree of marble pattern. In the tests to the lower right of the straight line Ge, there is no marble pattern or only a negligible degree of marble pattern (a corresponding flat steel product 100 with a layer 10 without a marble pattern is shown in FIG. 7A). The straight line Ge may be understood as a function of the peeling efficiency AWZ (see also Inequalities (2.1) and (3)).

[0102] A detailed evaluation of the test results suggests that the above-mentioned peeling efficiency AWZ can be adjusted as a function of the local absolute air humidity f to avoid the occurrence of undesirable marble patterns. In all embodiments, this adjustment of the peeling efficiency AWZ is preferably carried out such that the target thickness of the layer 10 or the surface coating (mass) of this layer 10 does not change or hardly changes at all. This means that care is always taken to ensure that the layer 10 to be applied essentially has the target thickness when changing the peeling efficiency AWZ.

[0103] However, when adjusting the peeling efficiency AWZ, in addition to avoiding the occurrence of marble patterns, it is important to ensure that other defects such as toothpick defects and beach pattern defects are avoided or the formation of slag is reduced. For such reasons, a parameter range that has been proven to be particularly effective is specified here.

[0104] As described above, the straight line Ge shown in FIG. 4 is only a first approximation. The actual relationship is very complex. The following formula expression (Inequality (3)) shows a further mathematical explanation of the relationship between the absolute local air humidity f in g / m 3 units and the peeling efficiency AWZ. d Thickness of the nozzle lip gap [mm] D Gas flow rate per strip side [Nm 3 / h] w Width of the flat steel product 100 [mm] v Strip speed [m / min] 2b Half width [mm] k Proportionality coefficient

[0105] [Number]

[0106] Two exemplary approaches that serve to simplify inequality (3) are described below.

[0107] First approach: With the first approach, it is subdivided into three different curve regions (here referred to as cases 1.1 to 1.3). Such subdivision allows the right side of inequality (3) to be calculated in a simplified manner.

[0108] (Case 1.1) In the linear region, the assumption 2b / d = 1.9 or b = 1.9d / 2 applies. This simplification applies to the relational expression Z / d < 5.2 between the nozzle interval Z and the width d of the nozzle lip gap 17. Case 1.1

[0109] [Number]

[0110] (Case 1.2) In a further region starting approximately at Z / d = 5.2 and ending before Z / d = 10, the following relationship applies. Case 1.2

[0111] [Number]

[0112] (Case 1.3) In a further region starting approximately at Z / d = 10, the following relationship applies. Case 1.3

[0113] [Number]

[0114] To make the complex inequality (3) more practical to handle, a case distinction by three cases from Case 1.1 to 1.3 is recommended, and the ratio Z / d is used for the case distinction.

[0115] The distinction between the above three regions or cases still results in complex mathematical expressions, especially in the second region (Case 1.2).

[0116] Second approach: Therefore, a second approach is now described next, which makes the complex inequality (3) more practical to handle. In this second approach, a case distinction is made with only two cases (Case 2.1 and Case 2.2), and thereby the ratio Z / d is also used here for the case distinction. Case 2.1

[0117]

Number

[0118] Case 2.2

[0119]

Number

[0120] The second approach has the drawback that the separation between the plain steel product 100 without marble pattern and the plain steel product 100 with marble pattern is not completely clear or unambiguous in the boundary region. When the case distinction by the first approach using inequality (3) and / or inequality (2.1) is evaluated (e.g., numerically processed by the controller 250), the best results can be achieved.

[0121] In all embodiments or at least some of the embodiments, the adjustment of adjustable parameters (system and / or method parameters) or the peeling efficiency AWZ can currently be carried out using the first or second approach and using inequalities (2.1) and / or (3). Alternatively, as already stated, the numerical representations of inequalities (2.1) and / or (3) can also be used in the controller 250.

[0122] The adjustment of adjustable parameters (system and / or method parameters) or the peeling efficiency AWZ can be carried out in all embodiments or at least some of the embodiments such that the surface coating and / or (coating) mass of layer 10 and / or the target thickness of layer 10 remains constant or stays within a narrowly predefined tolerance, for example as defined by the target specifications.

[0123] In all embodiments, the target specifications can be predefined by the manufacturer and / or the customer or client.

[0124] Preferably, the inequalities (2.1) and / or (3) or the equations of the first approach or the second approach are implemented in the controller 250 by software, or the numerical values of the absolute local humidity f and the corresponding suitable adjustable parameters (system and / or method parameters) or the peeling efficiency AWZ are summarized in one or more tables. By using a "look-up" table, the controller 250 can then call the corresponding suitable adjustable parameters (system and / or method parameters) or the peeling efficiency AWZ for the currently effective absolute local humidity value f and can adjust the device 150 or provide the numerical values for adjusting the thickness d of the nozzle lip gap to the machine operator (for example, by displaying on a display).

[0125] In all embodiments, adjustable parameters (system and / or method parameters) or stripping efficiency AWZ within the numerical values or value ranges shown below are preferably used. The individual numerical values or value ranges in Table 1 are not correlated with each other or are correlated only in partial ranges because they are derived from tests with different maximum and minimum values. Only the respective maximum and minimum values are obtained from Table 2 (Figs. 8A, 8B) and summarized herein.

[0126] The nozzle height listed in Table 2 (Figs. 8A, 8B) is the vertical distance between the zinc bath level and the collision line of the gas jet on layer 10 to be stripped. The nozzle pressure in Table 2, Figs. 8A, 8B is defined in mbar as the (over)pressure of the stripping gas G in nozzle 15 (relative to ambient pressure).

[0127] The flow rate D of gas G per strip side is typically in the range of 200 to 8000 Nm per hour in all embodiments. 3 within the range.

[0128]

Table 1

[0129] Divided into two parts, Table 2 (see Figs. 8A and 8B) shows specific numerical values for the test results shown in Fig. 4. Table 2 in Fig. 8A shows tests in which a layer 10 without a (visible) marble pattern was produced by specifying suitable adjustable parameters (method and / or system parameters) or stripping efficiency AWZ (as exemplified in Fig. 7A). The values in Table 2 of Fig. 8A are sorted in ascending order of b.

[0130] On the other hand, Table 2 in Fig. 8B shows tests in which layer 10 having a medium marble pattern (as shown by way of example in Fig. 7B) or an even stronger marble pattern (as shown by way of example in Fig. 7C) was generated. The values in Table 2 of Fig. 8B were also sorted in ascending order of b.

[0131] From Table 2 in Fig. 8A, the following pairs of values for the absolute local air humidity f and the peeling efficiency AWZ can be extracted (sorted in ascending order of the peeling efficiency AWZ), whereby it can be seen that all layers 10 generated using these adjustable parameters (method and system parameters) or the peeling efficiency AWZ are below the straight line Ge in Fig. 4.

[0132] [Table 2]

[0133] The following pairs of values for the absolute air humidity f and the peeling efficiency AWZ can be extracted from Table 2 in Fig. 8B (sorted in ascending order of the peeling efficiency AWZ), whereby it can be seen that all layers 10 generated using these adjustable parameters (method and system parameters) or the peeling efficiency AWZ are above the straight line Ge in Fig. 4.

[0134] [Table 3]

[0135] If marble pattern defects occur under a given absolute local air humidity f and under given method conditions, in at least some of the embodiments for eliminating the occurrence of the marble pattern, the peeling efficiency AWZ (corresponding to the right side of inequalities (2.1) and (3)) is reduced until this inequality is satisfied again.

[0136] Generally, it is not allowed to change the coating layer of the produced flat steel product 100 because it is specified in the product specifications. Assuming that the thickness of the coating layer is kept constant, the reduction of the peeling coefficient AWZ can be achieved in various ways.

[0137] Using these specific examples, the possible ways to change the peeling coefficient AWZ will be illustrated below.

Example

[0138] Reduction of the peeling efficiency AWZ by reducing the nozzle interval Z (see Table 3 (Table 4)).

[0139] The following Table 3 (Table 4) shows two test examples 1.1 and 1.2 demonstrating the reduction of the peeling efficiency AWZ by reducing the nozzle interval Z from 10 mm to 8 mm.

[0140]

Table 4

[0141] 1691 Nm 3 For the initial state (Table 3 (Table 4) - Example 1.1) with a gas flow rate D of 1691 Nm / h, a stripe width w of 1315 mm, a nozzle lip gap d of 1.0 mm, a nozzle interval Z of 10 mm, and a strip speed v of 100 m / min, AWZ is calculated as 21.3 according to Inequality (3).

[0142] Based on Example 1.1, the nozzle interval Z was reduced from 10 mm to 8 mm to reduce the peeling efficiency AWZ, while keeping the strip width w, the nozzle lip gap d, the strip speed v, the bath temperature TB, and the layer coating per side constant. The changed nozzle distance Z shifted the ratio Z / d, which also changed the determined values for b and k. Table 3 (Table 4) shows that in order to keep the thickness of layer 10 essentially constant, as a result of the change in the nozzle interval Z, the nozzle pressure, and thus the gas flow rate D per side, was changed from 1691 to 1386 Nm 3It shows that it had to be reduced to / h.

[0143] Next, when calculating the peeling efficiency AWZ using these new process parameters (Table 3 (Table 4), Example 1.2), the result is a value of 13.5. By reducing the nozzle interval from 10 mm to 8 mm, the peeling efficiency AWZ can be reduced from 21.3 to 13.5 without changing the layer coating.

Example

[0144] Reduction of the peeling efficiency AWZ by reducing the nozzle lip gap d.

[0145] The following Table 4 (Table 5) shows two test examples 2.1 and 2.2 demonstrating the reduction of the peeling efficiency AWZ by reducing the nozzle interval Z from 1.2 mm to 1 mm.

[0146]

Table 5

[0147] Flow rate D = 1373 Nm 3 / h, strip width w = 1455 mm, nozzle lip gap d = 1.2 mm, nozzle interval Z = 7 mm, and for the initial state (Table 4 (Table 5), Example 2.1) with a strip speed v = 100 m / min, AWZ is calculated as 9.4 according to inequality (3).

[0148] Based on this, the nozzle lip gap d was reduced from 1.2 mm to 1.0 mm to reduce the peeling efficiency AWZ, while the other parameters remained essentially constant.

[0149] Table 4 (Table 5) shows that as a result of the change in the nozzle lip gap d, in order to keep the thickness of layer 10 constant, the nozzle pressure, and thus the gas flow rate D per side, had to be reduced from 1373 to 1166 Nm 3 / h by automatic support control. It shows that it had to be reduced.

[0150] With the changed nozzle lip gap d, the ratio Z / d is shifted, which also causes the determined values for b and k to change together. When these new process parameters (Table 4 (Table 5), Example 2.2) are then used to calculate the stripping efficiency AWZ, 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 be reduced from 9.4 to 4.9 without changing the layer coating.

Example

[0151] Reduction of the stripping efficiency AWZ by increasing the bath temperature TB.

[0152] The following Table 5 (Table 6) shows two test examples 3.1 and 3.2 demonstrating the reduction of the stripping efficiency by increasing the bath temperature TB from 439 °C to 455 °C.

[0153]

Table 6

[0154] Flow rate D = 1607 Nm 3 / h, strip width w = 1615 mm, nozzle lip gap d = 1.0 mm, nozzle spacing Z = 7 mm, and strip speed v = 100 m / min for the initial state (Table 5 (Table 6), Example 3.1), AWZ is calculated to be 12.4 according to inequality (3).

[0155] Based on this, the bath temperature TB was increased from 439 °C to 455 °C, thereby reducing the stripping efficiency AWZ while keeping the other parameters essentially constant. In this example, the ratio Z / d did not change, and the determined values for b and k here also remained unchanged when the bath temperature TB was increased.

[0156] Table 5 (Table 6) shows that, as a result of the change in the bath temperature TB, in order to keep the thickness constant, the nozzle pressure and thus the gas flow rate D per side of the strip had to be reduced from 1607 to 1339 Nm 3 / h by automatic support control. The reason for this is that when the bath temperature TB increases, the viscosity of the zinc melt decreases, which means that a lower peeling force is sufficient to strip the same amount of melt.

[0157] Next, when the peeling efficiency AWZ was calculated using these new method parameters (Table 5 (Table 6), Example 3.2), the result was a value of 5.8, i.e., the peeling efficiency AWZ can thus be reduced by increasing the bath temperature TB.

[0158] According to the present invention, the absolute local air humidity f is preferably defined as the absolute air humidity within a virtual cylinder vZK, as schematically shown in FIG. 5. In this virtual cylinder vZK, the regions extending left and right parallel to the strip-shaped flat steel product 100 are excluded.

[0159] The virtual cylinder vZK is composed of two virtual cylinder volume segments, which on the one hand are limited by a virtual cylinder surface concentrically or almost concentrically surrounding the gas nozzle 15. On the other hand, the cylinder volume segment is limited by two planes extending 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. When the two cylinder volume segments are combined, their volume is in the range from 1 m 3 to 10 m 3 and preferably less than 2 m 3 . The measurement of the absolute local humidity f is preferably carried out directly or indirectly within the cylinder volume segment in all embodiments.

[0160] In FIG. 5, a part of a further device 150 is shown, and two cylindrical volume segments of the virtual cylindrical body vZK are shown here. The bath 11 is shown here as a rectangular container that is open at the top. A liquid zinc alloy (abbreviated here as ZnAlMg) is contained within the bath 11. Only a short length of the flat steel product 100 having a strip shape is shown after being lifted out of the immersion in the bath 11. The flat steel product 100 is inducted vertically from the bath 11 in the x-axis direction between two opposing gas nozzles 15 of the stripping nozzle device 14. When the two gas nozzles 15 are arranged parallel to each other, a center line ML can be defined between these nozzles 15. This center line ML is shown as a dashed line in FIG. 5. The center line ML is placed within the nozzle plane DE (defined as the x-y plane).

[0161] The virtual cylindrical body vZK in the three-dimensional space is formed around the center line ML. The "outer shell" of the virtual cylindrical body vZK is concentric with the center line ML. All points of the "outer shell" are at an equal distance ra from the center line ML (ra is the radius of the virtual cylindrical body vZK).

[0162] The virtual cylindrical body vZK includes at least the nozzles 15 of the stripper nozzle device 14 and has a virtual cylindrical height vZH defined parallel to the y-axis. Preferably, in all embodiments, the virtual cylindrical height vZH corresponds to the strip width w of the flat steel product 100 and / or the length of the nozzles 15 (defined parallel to the y-axis).

[0163] A range of specified values for the absolute local air humidity f can be defined for all embodiments within this virtual cylindrical body vZK.

[0164] In all or at least some of the embodiments, the absolute local air humidity f is parallel to the flat steel product 100 and is measured along a y-line located inside the virtual cylindrical body vZK. This y-line runs parallel to the y-axis. The so-called nozzle plane (also called the stripping plane) is parallel to the y-z plane, and the center line ML is within the nozzle plane.

[0165] Preferably, the absolute local air humidity f is determined or measured at some points of this gamma ray in all or at least some of the embodiments, and the average of the determined or measured values is compared with the specified numerical range for the absolute local air humidity f.

[0166] Preferably, in all or at least some of the embodiments, the absolute local air humidity f inside the virtual cylinder vZK is 1 g / m 3 to 300 g / m 3 within the range, preferably 1.08 g / m 3 to 51 g / m 3 within the range, and this virtual cylinder vZK has a volume of 2 m 3 .

[0167] However, in all embodiments, the absolute local air humidity f is also defined within a volume range of 1 m 3 to 10 m 3 and may be measured directly or indirectly therein. The measurement is preferably performed not directly on the incident ray of the gas G but on a gamma ray running parallel to the y-axis above the incident ray.

[0168] In the embodiment of FIG. 2, the gamma ray described is in the region between the nozzle 15 of the peeling nozzle device 14 and the lower inlet side of the cooling region 16. In the embodiment of FIG. 6, the gamma ray described is above the incident ray and is at least 20 cm away from the center line ML of the virtual cylinder vZK, for example, shown on the flat steel product 100 with small white circles.

[0169] Figure 6 shows a further embodiment of device 150, by which an approach for directly measuring the absolute local air humidity is also used here. The equipment of device 150 is similar to that of device 150 shown in Figure 2, and thus the description of Figure 2 is also referred to. Only the area of the outlet side A of bath 11 is shown. Two gas nozzles 15 are arranged in parallel on the front and rear sides of the strip (the gas nozzles 15 penetrate into the plane of the drawing). As schematically shown, each of the nozzles 15 is supplied with an inert gas G using a pump P g Two pumps P g are connected to a controller 250 with respect to control technology (or regulation technology), and the controller 250 can control, for example, the gas flow rate D for each strip side. The corresponding connection lines or pipes are labeled V5, V6, V7, and V8 in Figure 6. An air supply unit equipped with a blower and a control valve is referred to here as pump P g .

[0170] Preferably, all embodiments of device 150 include control of the gas flow rate D of gas G (referred to as automatic layer control), which is designed such that a layer 10 with a substantially constant target thickness is always generated even when other adjustable parameters change. For this purpose, the control system includes at least one sensor (not shown) for measuring the actual thickness of layer 10 after spraying. If the actual thickness is smaller than the target thickness, the control system decreases the flow rate D, and vice versa.

[0171] Each of the nozzles 15 can be moved by a motor or actuator M parallel to the z-axis. The motor or actuator M is connected to the controller 250 as shown. The corresponding connection lines or cables are labeled V9, V10, V11, and V12 in FIG. 6. There is a sensor (not shown) to enable control of the nozzle distance Z. Thus, the nozzle spacing Z can be set and / or checked via the controller 250. Control of the nozzle distance Z can be laser-assisted in all embodiments.

[0172] In all embodiments, the controller 250 can also be connected to the induction heater 30 or the electrical resistance heater of the bath 11 to adjust the bath temperature TB. In the case where the coil 30 is the induction heater shown in FIG. 6, the controller 250 can set the operating frequency for driving the coil 30 via the frequency generator FG. Thus, the frequency generator FG is connected to the controller 250 for control purposes as shown. The corresponding connection lines or cables are labeled V13 and V14 in FIG. 6.

[0173] The virtual cylinder vZK is also shown in FIG. 6, and its center line ML intersects the drawing plane slightly above the nozzles 15. To not overly complicate the drawing, the position of the center line ML is indicated by small white circles on the strip-shaped flat steel product 100. Since the overall arrangement is limited on the bottom side by the bath 11 and on the top side by the optional cooling area 16, the virtual cylinder vZK is a virtual cylinder vZK cut off at the top and bottom.

[0174] Here too, for example, two humidity sensors 51 (one on each side of at least the strip) are used to enable determination of the absolute local air humidity. The humidity sensors 51 are connected to the controller 250. The corresponding connection lines or cables are labeled V1, V2, V3, and V4 in FIG. 6.

[0175] In device 150, as schematically and by way of example shown in FIG. 6, this method can be carried out particularly advantageously and can lead to reproducible results.

[0176] FIG. 9 shows, in the form of a flowchart, exemplary steps of the method described herein. Before the method for applying layer 10 to flat steel product 100 is carried out, the individual components and elements of device 150 are set (step S1). The device can be set, for example, based on the target specifications of layer 10 to be applied.

[0177] 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 satisfied (step S3). If f is greater than AWZ (YES in the flowchart), the method for applying layer 10 can be started (step S4). If the condition f>AWZ is not satisfied (NO in the flowchart), the method returns to step S1. After returning, the settings of the components and elements of device 150 can be adjusted with the aim of reducing AWZ so that the condition f>AWZ is satisfied. Note that when making the adjustment, care is taken to ensure that the target specifications of layer 10 to be applied are still met.

[0178] In a similar manner, the check of the condition f>AWZ can be repeated from time to time when applying layer 10, thereby being able to react to changes in the absolute local air humidity f. If f decreases, it is checked again (as in step S3) whether the condition f>AWZ is still satisfied. If yes, the application of layer 10 is continued. Otherwise, an adjustment (similar to step S1) can be made to the settings of the components and elements of device 150 with the aim of ensuring that the condition f>AWZ is satisfied or remains satisfied.

[0179] In all embodiments, the corresponding controller 250 is configured or programmed such that: - By increasing the bath temperature TB, a significant decrease in the peel efficiency AWZ is achieved and / or - By decreasing the thickness d of the nozzle lip gap 17, the peel efficiency AWZ can be reduced and / or - The peel efficiency AWZ can be reduced by decreasing the distance Z or programmed.

[0180] In all embodiments, the corresponding controller 250 is configured or programmed such that changes in the thickness d and / or the distance Z have little or no effect on the peel efficiency AWZ when the ratio Z / d is small.

[0181] If f drops significantly and reasonable adjustment within the target specifications is not possible, the method can be interrupted. As part of such an interruption, the width d of the nozzle lip gap 17 can then be adjusted, for example manually (this cannot be done automatically in most devices 150).

Description of the reference symbols

[0182]

Table 7A

[0183]

Table 7B

Claims

1. A method for applying a layer (10) having a target thickness to at least one side of a flat steel product (100) by passing the flat steel product (100) through a zinc alloy molten bath (11), and by passing gas (G) through the nozzle lip gap (17) of at least one gas nozzle (15) and releasing it toward the flat steel product (100) on its outlet side (A) to blow off the layer (10) to the target thickness, wherein the zinc alloy of the zinc alloy molten bath (11) has the following composition, namely: - Aluminum content in the range of 1.0 weight percent to 3.5 weight percent, preferably in the range of 1.3 weight percent to 2.8 weight percent, - A magnesium content in the range of 1.0 weight percent to 3.0 weight percent, preferably in the range of 1.2 weight percent to 2.2 weight percent, - Zinc, optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, with each additional element having a weight-related content of less than 0.1%, and the remainder including unavoidable impurities. It has, At least one of the following adjustable parameters: - When the current absolute local air humidity (f) decreases, increase the bath temperature (TB) of the alloy melting bath (11), and when the current absolute local air humidity (f) increases, decrease the bath temperature (TB) of the alloy melting bath (11), and / or - When the current absolute local air humidity (f) decreases, the thickness (d) of the nozzle lip gap (17) is reduced, and when the current absolute local air humidity (f) increases, the thickness (d) of the nozzle lip gap (17) is increased, and / or - When 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) is reduced, and when the current absolute local air humidity (f) increases, the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) is increased. It was adjusted to that extent. The flow rate (D) of the gas (G) is further adjusted to keep the target thickness of the layer (10) to be applied essentially constant. A method characterized by the following.

2. The aforementioned layer (10) is - The target coverage of the layer (10) on each side of the strip is 20 g / m². ２ From 200g / m ２ Within the range, preferably 30 g / m² ２ From 100g / m ２ Within the range, and / or - The target thickness of the layer (10) on each side of the strip is in the range of 3 μm to 30 μm, preferably in the range of 4.5 μm to 15 μm. The method according to claim 1, characterized in that it satisfies the requirement.

3. The adjustment of the aforementioned parameters is to prevent marble patterns and / or toothpick defects in the layer (10). - 1 g / m ３ From 300g / m ３ Preferably 1.08 g / m ３ From 51 g / m ３ Absolute local air humidity (f) within the range The method according to claim 1 or 2, characterized in that it is performed on.

4. The method according to claim 1, characterized in that the relationship between the current absolute local air humidity (f) and the adjustable parameter is specified using the peeling efficiency (AWZ), and the condition f > AWZ must be satisfied in order to avoid marble patterns and / or toothpick defects.

5. The aforementioned peeling efficiency (AWZ) is, [Math 1] It is defined as follows: Here, d is the thickness of the nozzle lip gap in millimeters. D is Nm ３ The effective flow rate D of the gas G for each strip side over the strip width (w) in units of / h, k is a dimensionless proportionality constant, w is the strip width of the flat steel product (100) in millimeters, 2b is the half-width of the pressure distribution of gas G in a strip measured in millimeters. v is the stripping speed in meters per minute. The method according to claim 4, characterized in that

6. The aforementioned peeling efficiency (AWZ) is, [Math 2] It is defined as follows: Here, d is the thickness of the nozzle lip gap in millimeters. D is Nm ３ This is the effective flow rate D of gas G at each side of the strip over the strip width (w) in units of / h. k is a dimensionless proportionality constant, w is the strip width of the flat steel product (100) in millimeters, 2b is the half-width of the pressure distribution of gas G in a strip measured in millimeters. v is the stripping speed in meters per minute. The method according to claim 4, characterized in that

7. When determining the values ​​for half of the half width (b) and the proportionality constant (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17), the following definitions apply: Case 1.1: [Math 3] Case 1.2: [Math 4] Case 1.3: [Math 5] The method according to claim 5 or 6, characterized in that the following is applied.

8. When determining the values ​​for half of the half width (b) and the proportionality constant (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: [Math 6] Case 2.2: [Number 7] The method according to claim 5 or 6, characterized in that the following is applied.

9. - The thickness (d) of the nozzle lip gap (17) is in the range of 0.5 mm to 5 mm, preferably in the range of 0.6 mm to 2 mm, particularly preferably in the range of 0.8 mm to 1.5 mm, and / or - The flow rate (D) is 200 Nm / hour. ３ From 8000 Nm per hour ３ Being within the range, and / or - The interval (Z) is in the range of 2 mm to 15 mm, preferably in the range of 3 mm to 12 mm, and / or - The stripping speed (v) is in the range of 50 m / min to 200 m / min, preferably in the range of 70 m / min to 150 m / min. The method according to claim 1, characterized by the above.

10. The method according to claim 1, characterized in that the bath temperature TB of the alloy melting bath (11) is in the range of 400°C < TB < 480°C, preferably in the range of 409°C < TB < 473°C, and particularly preferably in the range of 420°C < TB < 460°C.

11. The absolute local air humidity (f) is effective in two virtual cylindrical volume segments, one being limited by a virtual cylindrical surface concentrically or nearly concentrically surrounding the at least one gas nozzle (15), and the other being limited at a distance (s) from the flat steel product (100) by two planes running parallel to the flat steel product (100) on both sides of the flat steel product (100), with the cylindrical volume segments together comprising 1 m ３ 10m ３ Within the range, preferably 2m ３ The method according to claim 1, characterized in that it has a volume less than a certain amount, and the measurement of the absolute local air humidity (f) is performed directly or indirectly.

12. The method according to claim 11, characterized in that the absolute local humidity (f) is measured permanently or intermittently, 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 claim 1, characterized in that the step of applying the layer (10) is controlled using a controller (250) so that when the absolute local air humidity (f) changes, one or more of the adjustable parameters are automatically and / or manually adjusted in accordance with the current absolute local air humidity (f).

14. A device (150) for applying a layer (10) to a flat steel product (100), - A zinc alloy molten bath (11) having an input side (E), an outlet side (A), and a deflector (13) for passing the flat steel product (100) coming from the input side (E) through the zinc alloy molten bath (11) at a stripping speed (v) and guiding it to the outlet side (A), - A peeling nozzle device (14) is configured to have at least one nozzle lip gap (17), and to be able to blow away the stationary liquid layer (10) in the flat steel product (100) within the outlet side (A) region with gas (G) coming out through the nozzle lip gap (17), thereby blowing away the layer (10) to a target thickness. Equipped with, The zinc alloy in the zinc alloy molten bath (11) has the following composition, namely: - Aluminum content in the range of 1.0 weight percent to 3.5 weight percent, preferably in the range of 1.3 weight percent to 2.8 weight percent, - A magnesium content in the range of 1.0 weight percent to 3.0 weight percent, preferably in the range of 1.2 weight percent to 2.2 weight percent, - The remainder includes zinc, and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce, or Bi, with each additional element having a weight-related content of less than 0.1%, and unavoidable impurities. It has, The device (150) can be manually or automatically adjusted as follows: - When the current absolute local air humidity (f) decreases, increase the bath temperature (TB) of the alloy melting bath (11), and when the current absolute local air humidity (f) increases, decrease the bath temperature (TB) of the alloy melting bath (11), and / or - When the current absolute local air humidity (f) decreases, the thickness (d) of the nozzle lip gap (17) decreases, and when the current absolute local air humidity (f) increases, the thickness (d) of the nozzle lip gap (17) increases, and / or - When 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) is reduced, and when the current absolute local air humidity (f) increases, the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100) is increased. Adapted or configured to do at least one of the following: In addition, the flow rate (D) of the gas (G) is automatically adjusted to keep the target thickness of the layer (10) to be applied essentially constant. Device (150).

15. The layer (10) to be applied must meet the following requirements, namely: - The target coverage of the layer (10) on each side of the strip is 20 g / m². ２ From 200g / m ２ Within the range, preferably 30 g / m² ２ From 100g / m ２ Within the range, and / or - The target thickness of the layer (10) on each side of the strip is in the range of 3 μm to 30 μm, preferably in the range of 4.5 μm to 15 μm. The device (150) according to claim 14, characterized in that it satisfies the requirement.

16. To prevent marble patterns and / or toothpick defects in the aforementioned layer (10), the adjustment of adjustable parameters is performed. - 1 g / m ３ From 300g / m ３ Preferably 1.08 g / m ３ From 51 g / m ３ Absolute local air humidity (f) within the range The device (150) according to claim 14 or 15, characterized in that it is performed on.

17. - At least one humidity sensor (51) is configured to be positioned within the local peripheral area of ​​the peeling nozzle device (14), - A controller (250) that can be connected to the at least one humidity sensor (51) by communication in order to continuously or intermittently acquire measured values ​​or signals from which physical variables directly relating to the absolute local air humidity (f) within the vicinity of the local nozzle can be derived. It also includes, The controller (250) is used to keep the target thickness of the layer (10) to be applied essentially constant. - A step of changing the bath temperature (TB) of the alloy melting bath (11), and / or - A step of changing the thickness (d) of the nozzle lip gap (17), and / or - A step of changing the distance (Z) between the nozzle lip gap (17) and the side portion of the flat steel product (100), - Step of adjusting the flow rate (D) of the gas (G) It is configured to perform at least one of the following, or to trigger the performance of one of them. The device (150) according to claim 14, characterized in that

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

19. The device (150) according to claim 14, comprising a controller (250) configured to determine the peeling efficiency (AWZ), wherein the peeling efficiency (AWZ) defines the relationship between the current absolute local air humidity (f) and the adjustable parameter, and the condition f > AWZ must be satisfied in order to avoid marble pattern formation.

20. The device (150) according to claim 18 or 19, wherein the controller (250) is connected to a motor or actuator (M) for each gas nozzle (15) for control purposes, such that the controller (250) responds to a changing absolute local air humidity (f) by decreasing the distance (Z) when the current absolute local air humidity (f) decreases, and by increasing the distance (Z) when the current absolute local air humidity (f) increases.

21. Pumping device (P ｇ The device (150) according to claim 18 or 19, further comprising: a control loop for each gas nozzle (15) that automatically adjusts the flow rate (D) of the gas (G) in such a manner that the target thickness of the layer (10) remains essentially constant.

22. The device (150) according to claim 18 or 19, wherein the controller (250) comprises a bath heating device (30) connected to the controller (250) for control purposes in such a manner that it responds to a changing absolute local air humidity (f) by adjusting the bath temperature TB, and the bath temperature TB is in the range of 400°C < TB < 480°C, preferably in the range of 409°C < TB < 473°C, and particularly preferably in the range of 420°C < TB < 460°C.

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