EP4299784A1 - Method and device for applying a film to a flat steel product - Google Patents

Abstract

Device (150) for applying a layer to a flat steel product (100), comprising
- a zinc alloy melt pool (11) with an input side (E), an output side (A) and a deflection (13) to move the flat steel product (100) from the input side (E) through the zinc alloy melt pool (11) at a belt speed ) to lead through to the exit side (A),
- a stripping nozzle device (14), which comprises at least one nozzle lip gap, and which is arranged in the area of the output side (A) in such a way that the still liquid layer on the flat steel product (100) can be blown off with gas that exits through the nozzle lip gap in order to form the layer to blow off to a target thickness,

wherein the zinc alloy of the zinc alloy melt pool (11) has the following composition:
- an aluminum content that lies in the range between 1.0 and 3.5 percent by weight,
- a magnesium content that is in the range between 1.0 and 3.0 percent by weight, and
- the remainder of the zinc alloy melt pool (11) is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1%, and unavoidable impurities,

characterized in that the device (150) is set up or designed to carry out at least one of the following adjustments manually or automatically:
- Increasing the bath temperature of the alloy melt pool (11) if the current absolute local air humidity is reduced and vice versa, and/or
- Reducing the thickness of the nozzle lip gap if the current absolute local humidity is reduced and vice versa, 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,

In addition, the flow rate of the gas is automatically adjusted in order to keep the target thickness of the layer to be applied essentially constant.

Description

The present invention relates to a method with which flat steel products can be coated with a layer based on zinc-aluminum-magnesium (ZnAlMg), for example as a protective coating. This is also about a device that is designed to use the method according to the invention.

It is well known that flat steel products 100, such as steel strips or steel sheets, are coated with a ZnAlMg alloy to improve corrosion resistance. In practice, this usually happens by introducing the flat steel product 100 from a furnace into a zinc alloy melt pool 11, as in Fig. 1 indicated using an exemplary device 150. In order to protect the flat steel product 100 from oxidation, it is typically introduced into the bath 11 on the input side E through a trunk 12 with an inert atmosphere. In the bath 11, the flat steel product 100 is deflected by a (zinc bath) roller 13 and moved upwards out of the bath 11 on the exit side A. When emerging from this bath 11, the alloy melt film adhering to the front and back of the flat steel product 100 is stripped with a gas jet from the gas nozzles 15 of a stripping nozzle device to the target thickness (in the micrometer range) or to the target surface coating mass (in g/m ² ) and the flat steel product 100 then transferred to a cooling area 16. This continuous process is generally called hot-dip coating.

Details of a suitable process and particularly suitable alloy compositions can be found, for example, in the published application WO 2014/033153 A1 from the applicant VOESTALPINE STAHL GMBH.

There is prior art that mentions water or steam in connection with hot-dip coating of flat steel products. The relevant documents are listed below and their content, where relevant here, is briefly described.

In the patent EP0172682B1 from Armco Inc., filed in 1985, involves the control of zinc vapor associated with hot-dip coating of an iron-based metal strip. On the entry side of the immersion bath there is an enclosed area (comparable to the trunk 12 in Fig. 1 ) an oxygen-reduced atmosphere is provided that contains a small proportion of water vapor. This small proportion of water is intended to prevent the formation of zinc vapor on the surface of the immersion bath. The dew point of the gas used on the inlet side is adjusted so that the zinc vapor cannot form.

In the published patent application JP2020100886 A2 The Nippon company's goal is to produce a galvanized steel strip that has a surface with an increased coefficient of friction. In order to increase the coefficient of friction, water is sprayed onto the surface of the flat steel product under pressure after the gas has been blown off. The particle size of the water drops should be at least 0.07mm and preferably more than 1.5mm. By spraying water drops, irregularities are deliberately created on the surface of the steel strip. This document pursues a different objective and the corresponding technical teaching therefore goes in a completely different direction than the present invention.

In addition to pure protection against corrosion, there are increasingly more stringent requirements regarding the surface quality of zinc-coated flat steel products. The automotive industry in particular expects products that meet the highest surface requirements. However, providing homogeneous surfaces is not trivial.

The main problems here are often surface defects in the ZnAlMg layer. For example, a marble effect, the “toothpick” or “beach pattern” defect can develop on the ZnAlMg layer slag formation may occur. There are patents (e.g EP20130826634 AM/JMMaigne; JP20080256208 NSSMC/ Oohashi et al.), who try to eliminate similar surface defects (gloss effects or displaced oxide skins) with other means (reducing the O ₂ content in the area around the wiper nozzle).

The task is therefore to provide a method and a corresponding device in order to be able to coat flat steel products which have a particularly long-lasting and robust protective effect in terms of corrosion, whereby the surface of the protective coating is particularly homogeneous, very smooth and without marbling (without "marbel Effect") and/or toothpick error (without "toothpick"). The aim is to achieve a surface quality that meets the highest customer requirements.

In addition, this process should be as energy-intensive as possible, cost-effective, simple and reproducible.

Summary of the invention

According to the invention, a continuous (hot-dipping) process and a corresponding device are provided, which make it possible to provide a flat steel product with a metallic layer, which can serve, for example, as a (protective) coating, this layer protecting the steel substrate of the flat steel product from the outside protects against influences.

• einen Aluminium-Anteil, der im Bereich zwischen 1,0 und 3,5 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,3 und 2,8 Gewichtsprozent liegt,
• einen Magnesium-Anteil, der im Bereich zwischen 1,0 und 3,0 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,2 und 2,2 Gewichtsprozent liegt, und
• der Rest des Zink-Legierungsschmelzbads sind Zink und optional einem oder mehreren aus Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce oder Bi ausgewählten zusätzlichen Elementen, wobei der gewichtsbezogene Gehalt jedes zusätzlichen Elementes in der metallischen Beschichtung weniger als 0,1 % beträgt, und unvermeidbare Verunreinigungen.

All embodiments involve applying a (protective) layer to a flat steel product, whereby the layer thickness of this layer should correspond to a target thickness (according to a corresponding specification). This layer is produced by passing the flat steel product through a zinc alloy melting bath and blowing off gas on the exit side of the bath using a stripping nozzle device which comprises at least one gas nozzle. The zinc alloy of the zinc alloy molten pool has the following composition:

• an aluminum content which is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight,
• a magnesium content which is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight, and
• the remainder of the zinc alloy molten pool is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1% and unavoidable contamination.

• Erhöhen der Badtemperatur des Legierungsschmelzbades, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa, und/oder
• Reduzieren der Dicke des Düsenlippenspalts, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa, und/oder
• Reduzieren des Abstands zwischen dem Düsenlippenspalt und der Seite des Stahlflachprodukts, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa,

wobei zusätzlich die Durchflussmenge des Gases, angepasst wird, um die Solldicke der aufzubringenden Schicht im Wesentlichen konstant zu halten.The method is characterized by the fact that at least one of the following adjustable parameters is adjusted as follows:

• Increasing the bath temperature of the alloy melt pool if the current absolute local humidity is reduced and vice versa, and/or
• Reducing the thickness of the nozzle lip gap if the current absolute local humidity is reduced 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 humidity is reduced and vice versa,

wherein the flow rate of the gas is additionally adjusted in order to keep the target thickness of the layer to be applied essentially constant.

• ein Zink-Legierungsschmelzbad mit einer Eingangsseite, einer Ausgangsseite und einer Umlenkung, um das Stahlflachprodukt von der Eingangsseite kommend mit einer Bandgeschwindigkeit durch das Zink-Legierungsschmelzbad hindurch zur Ausgangsseite zu führen,
• eine Abstreifdüsenvorrichtung, die mindestens einen Düsenlippenspalt umfasst, und die im Bereich der Ausgangsseite so angeordnet ist, dass die noch flüssige Schicht am Stahlflachprodukt mit Gas abblasbar ist, das durch den Düsenlippenspalt austritt, um die Schicht auf eine Solldicke abzublasen,

wobei die Zink-Legierung des Zink-Legierungsschmelzbads die folgende Zusammensetzung aufweist:

• einen Aluminium-Anteil, der im Bereich zwischen 1,0 und 3,5 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,3 und 2,8 Gewichtsprozent liegt,
• einen Magnesium-Anteil, der im Bereich zwischen 1,0 und 3,0 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,2 und 2,2 Gewichtsprozent liegt, und
• der Rest des Zink-Legierungsschmelzbads sind Zink und optional einem oder mehreren aus Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce oder Bi ausgewählten zusätzlichen Elementen, wobei der gewichtsbezogene Gehalt jedes zusätzlichen Elementes in der metallischen Beschichtung weniger als 0,1 % beträgt, und unvermeidbare Verunreinigungen.

A device designed to apply a layer to a flat steel product includes

• a zinc alloy melt pool with an input side, an output side and a deflection to remove the flat steel product from the input side coming at a belt speed through the zinc alloy melt pool to the output side,
• a stripping nozzle device which comprises at least one nozzle lip gap and which is arranged in the area of the output side in such a way that the still liquid layer on the flat steel product can be blown off with gas which emerges through the nozzle lip gap in order to blow off the layer to a target thickness,

wherein the zinc alloy of the zinc alloy melt pool has the following composition:

• an aluminum content which is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight,
• a magnesium content which is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight, and
• the remainder of the zinc alloy molten pool is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1% and unavoidable contamination.

• Erhöhen der Badtemperatur des Legierungsschmelzbades, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa, und/oder
• Reduzieren der Dicke des Düsenlippenspalts, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa, und/oder
• Reduzieren des Abstands zwischen dem Düsenlippenspalt und der Seite des Stahlflachprodukt, falls sich die momentane absolute lokale Luftfeuchtigkeit reduziert und vice versa,

wobei zusätzlich die Durchflussmenge des Gases automatisch angepasst wird, um die Solldicke der aufzubringenden Schicht im Wesentlichen konstant zu halten.This device is set up or designed to make at least one of the following adjustments manually or automatically:

• Increasing the bath temperature of the alloy melt pool if the current absolute local humidity is reduced and vice versa, and/or
• Reducing the thickness of the nozzle lip gap if the current absolute local humidity is reduced 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 humidity is reduced and vice versa,

In addition, the flow rate of the gas is automatically adjusted in order to keep the target thickness of the layer to be applied essentially constant.

• der Aluminium-Anteil (in Gewichtsprozent) liegt im Bereich zwischen 1,0 und 3,5 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,3 und 2,8 Gewichtsprozent;
• der Magnesium-Anteil (in Gewichtsprozent) liegt im Bereich zwischen 1,0 und 3,0 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,2 und 2,2 Gewichtsprozent;
• der Rest des Zink-Legierungsschmelzbads sind Zink und optional einem oder mehreren aus Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce oder Bi ausgewählten zusätzlichen Elementen, wobei der gewichtsbezogene Gehalt jedes zusätzlichen Elementes in der metallischen Beschichtung weniger als 0,1 % beträgt, und unvermeidbare Verunreinigungen.

In all embodiments or at least some of the embodiments, a metallic bath is presented with a ZnAlMg alloy, which is composed according to the following alloy concept:

• the aluminum content (in percent by weight) is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight;
• the magnesium content (in percent by weight) is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight;
• the remainder of the zinc alloy molten pool is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1% and unavoidable contamination.

In some of the embodiments, the aluminum content (in percent by weight) can be greater than or equal to the magnesium content (in percent by weight).

In all embodiments or at least some of the embodiments, the unavoidable impurities are in a range that is significantly smaller than 1 percent by weight (wt.%), preferably the sum of all unavoidable impurities is less than 0.5 percent by weight.

The combination of a precisely defined ZnAlMg alloy concept, monitoring or observation of the current absolute local air humidity and a targeted adjustment of the stripping process (or the corresponding process and/or system parameters or the stripping effectiveness factor) can create a surface that does not or shows negligible marbling.

The values of the absolute local air humidity, which according to the invention should be present in the immediate vicinity of the flat steel product in an area between the output side and the cooling area (if present), are in the range from 1 g/m ³ to 300 g/m ³ in all embodiments. preferably in the range from 1.08 g/m ³ to 51 g/m ³ , ie the process can be carried out at an absolute local air humidity that lies within the specified range can be carried out successfully.

In all embodiments, the stripping nozzle device can optionally be followed by a belt stabilization device, which serves to automatically stabilize the movement of the flat steel product. In these embodiments, the values of the absolute local air humidity can be determined in the area between the stripping nozzle device and the belt stabilization device.

• Betreiben des Legierungsschmelzbades mit einer Badtemperatur TB im Bereich 400 < TB < 480 Grad Celsius, vorzugsweise im Bereich 409 < TB < 473 Grad Celsius, und besonders vorzugsweise im Bereich 420 < TB < 460 Grad Celsius,
• Betreiben der Abstreifdüsenvorrichtung mit einen Düsenabstand gegenüber dem Stahlflachprodukt, der zwischen 2 und 15 mm, vorzugsweise zwischen 3 und 12 mm, beträgt,
• Abblasen des Stahlflachproduktes auf der Ausgangsseite des Legierungsschmelzbades mit dem Gas, das durch den Düsenlippenspalt in Richtung des Stahlflachproduktes mit einer Gas-Durchflussmenge strömt, die im Bereich von 200 bis 8000 Nm³ pro Stunde beträgt.

The method preferably comprises the following steps at an absolute local air humidity that is greater than 1 g/m ³ :

• Operating the alloy melt pool with a bath temperature TB in the range 400 <TB <480 degrees Celsius, preferably in the range 409 <TB <473 degrees Celsius, and particularly preferably in the range 420 <TB <460 degrees Celsius,
• Operating the stripping nozzle device with a nozzle distance from the flat steel product that is between 2 and 15 mm, preferably between 3 and 12 mm,
• Blowing off the flat steel product on the exit side of the alloy melt pool with the gas that flows through the nozzle lip gap in the direction of the flat steel product with a gas flow rate that is in the range of 200 to 8000 Nm ³ per hour.

The determination of the ZnAlMg alloy concept defined above results from numerous investigations and calculations. Within the stated limits of the ZnAlMg alloy concept, the technical teaching presented here has proven particularly useful.

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

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

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

In all embodiments, the method is preferably carried out with a reduced bath temperature TB _red , which is in the range 420 <TB _red <460 degrees Celsius. In this area, the formation of slag can also be reduced.

Concrete tests have shown that the ZnAlMg alloy concept actually leads to very good results. It has been shown that excellent results can be achieved by specifically adapting the stripping process (or the corresponding stripping effectiveness number).

The development of the new process, the particularly suitable ZnAlMg alloy concept and the targeted adjustment of the (process) parameters (or the corresponding stripping effectiveness number) is based on theoretical considerations, various simulations of stripping processes and numerous tests.

The processes in the area of the stripping nozzle device and on the flat steel product are highly complex and depend on numerous (process) parameters and influencing variables (or the corresponding stripping effectiveness). Therefore, the present method and apparatus rely on some simplified assumptions and specifications to obtain reproducible results.

In all embodiments, the coated flat steel product can, as usual, be subjected to a temper-rolling or temper-rolling process and/or a bending-stretching process after coating. The total degree of deformation for the coated flat steel product is preferably between 0.5% and 2.5%, preferably between 0.7% and 1.7%. Through the dressing or The negative influence of marbling can be further reduced in the re-rolling step (with a deformation in the range of 0.7 - 1.7%).

Furthermore, in all embodiments, the coated flat steel product can be treated with the usual transport protection measures such as oiling or other chemical treatment agents, as in point 7 of the leaflet "Characteristic features 095 - hot-dip coated strip and sheet", edition 2010, published by the Steel Information Center Center 40039 Düsseldorf.

Further advantageous embodiments of the invention form the subject matter of the dependent claims.

DRAWINGS

FIG. 1

zeigt eine stark schematisierte Darstellung einer bekannten Vorrichtung zum Tauchbeschichten und Abstreifen von Stahlflachprodukten (Stand der Technik);

FIG. 2

zeigt eine stark schematisierte Darstellung einer ersten beispielhaften Vorrichtung, in der das Verfahren der Erfindung zum Einsatz kommt;

FIG. 3A

zeigt eine stark schematisierte Seitenansicht einer Abstreifdüsenvorrichtung mit nur einer Düse, um einige der hier relevanten Verfahrens- und Anlagenparameter definieren zu können (diese Darstellung ist nicht maßstabsgetreu);

FIG. 3B

zeigt eine schematische Darstellung des Druckverlaufs P an der Oberfläche der Beschichtung bezogen auf eine Position auf der x-Achse;

FIG. 3C

zeigt eine schematische Darstellung des Scherkraftverlaufs τ an der Oberfläche der Beschichtung bezogen auf eine Position auf der x-Achse;

FIG. 4

zeigt eine zusammenfassende grafische Darstellung zahlreicher beispielhafter Versuche, wobei auf der Ordinatenachse die Abstreifwirkzahl AWZ und auf der Abszisse die absolute Luftfeuchtigkeit f aufgetragen sind;

FIG. 5

zeigt eine stark schematisierte Darstellung einer Vorrichtung, in der das Verfahren der Erfindung zum Einsatz kommt, wobei zwei virtuelle Zylindervolumensegmente gezeigt sind;

FIG. 6

zeigt eine stark schematisierte Darstellung einer weiteren Vorrichtung der Erfindung, in der das Verfahren der Erfindung zum Einsatz kommt;

FIG. 7A

zeigt eine stark schematisierte Darstellung einer Bandseite eines Stahlflachprodukts, das keine Marmorierung aufweist;

FIG. 7B

zeigt eine stark schematisierte Darstellung einer Bandseite eines Stahlflachprodukts, das eine mittlere Marmorierung aufweist;

FIG. 7C

zeigt eine stark schematisierte Darstellung einer Bandseite eines Stahlflachprodukts, das eine starke Marmorierung aufweist;

FIG. 7D

zeigt ein Foto eines beschichteten Stahlflachprodukts ohne Marmorierung;

FIG. 7E

zeigt ein Foto eines beschichteten Stahlflachprodukts mit starker Marmorierung inklusive Zahnstocher-Fehler;

FIG. 7F

zeigt ein Foto eines beschichteten Stahlflachprodukts ohne Marmorierung nach dem Dressieren;

FIG. 7G

zeigt ein Foto eines beschichteten Stahlflachprodukts mit Marmorierung inklusive Zahnstocher-Fehler nach dem Dressieren;

FIG. 8A

zeigt Details der Tabelle 2 mit Versuchsergebnissen;

FIG. 8B

zeigt Details der Tabelle 2 mit weiteren Versuchsergebnissen;

FIG. 9

zeigt beispielhafte Schritte des hier beschriebenen Verfahrens.

Embodiments of the invention are described in more detail below with reference to the drawings.

FIG. 1

shows a highly schematic representation of a known device for dip-coating and stripping flat steel products (prior art);

FIG. 2

shows a highly schematic representation of a first exemplary device in which the method of the invention is used;

FIG. 3A

shows a highly schematic side view of a stripping nozzle device with only one nozzle in order to be able to define some of the process and system parameters relevant here (this representation is not to scale);

FIG. 3B

shows a schematic representation of the pressure curve P on the surface of the coating based on a position on the x-axis;

FIG. 3C

shows a schematic representation of the shear force curve τ on the surface of the coating based on a position on the x-axis;

FIG. 4

shows a summarized graphical representation of numerous exemplary tests, with the ordinate axis showing the The stripping effectiveness number AWZ and the absolute humidity f are plotted on the abscissa;

FIG. 5

shows a highly schematic representation of an apparatus in which the method of the invention is used, with two virtual cylinder volume segments shown;

FIG. 6

shows a highly schematic representation of a further device of the invention in which the method of the invention is used;

FIG. 7A

shows a highly schematic representation of a strip side of a flat steel product that has no marbling;

FIG. 7B

shows a highly schematic representation of a band side of a flat steel product that has medium marbling;

FIG. 7C

shows a highly schematic representation of a strip side of a flat steel product that has strong marbling;

FIG. 7D

shows a photo of a coated flat steel product without marbling;

FIG. 7E

shows a photo of a coated flat steel product with heavy marbling including a toothpick defect;

FIG. 7F

shows a photo of a coated flat steel product without marbling after tempering;

FIG. 7G

shows a photo of a coated flat steel product with marbling including toothpick defects after tempering;

FIG. 8A

shows details of Table 2 with experimental results;

FIG. 8B

shows details of Table 2 with further test results;

FIG. 9

shows example steps of the process described here.

Detailed description

This is about a method and a device 150 for applying a layer 10 to a strip-shaped flat steel product 100 (see Fig. 3A , where layer 10 can be seen on the upper side of the band). This layer 10 is produced by passing the flat steel product 100 from an input side E to an output side A through a zinc alloy melt pool 11 and on the output side A is blown off with gas G by means of a stripping nozzle device 14, as exemplified in the Figures 2 , 3A , 6 and 7 shown. The purpose of the stripping nozzle device 14 is to strip off the excess (still liquid) ZnMgAl layer (layer 10) as it exits the bath 11.

Within the scope of the invention, care must be taken to ensure that, on the one hand, the layer 10 essentially does not change, even if the absolute humidity f of the environment changes, and, on the other hand, that no marbling occurs. In other words, it is about avoiding marbling when the absolute local humidity f changes, while at the same time the target thickness of the layer 10 is essentially maintained.

In addition to the target thickness of the layer 10, the target (area) coating mass of the layer 10 can also be specified in all embodiments. Typically there is a narrow tolerance range for the target thickness. As long as the layer 10 to be created lies within the tolerance range(s), the layer 10 essentially meets the specifications.

The processes in the area of the stripping nozzle device 14 and on the flat steel product 100 are highly complex and depend on numerous parameters and influencing variables.

In all embodiments, the stripping nozzle device 14 comprises at least one gas nozzle 15 (if only one side of the band is to be blown off), or two gas nozzles 15, which are opposite one another (if both sides of the band are to be blown off). In the Figures 2 , 6 and 7 are embodiments with two nozzles 15 and in Fig. 3A an embodiment with only one nozzle 15 is shown.

In at least some of the embodiments, the method is carried out and controlled in such a way that the layer 10 per band side of the flat steel product 100 has a target thickness that lies within the tolerance window. Preferably, the target thickness of the layer 10 is the same for each band side Embodiments in the range 3 to 30 µm, and particularly preferably in the range 4.5 to 15 µm.

Preferably, in at least some of the embodiments, the target surface layer (layer mass per band side; referred to as layer per side in Tables 8A and 8B) is in the range from 20 to 200 g/m ² and particularly preferably in the range from 30 to 100 g/m ² .

• einen Aluminium-Anteil, der im Bereich zwischen 1,0 und 3,5 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,3 und 2,8 Gewichtsprozent liegt,
• einen Magnesium-Anteil, der im Bereich zwischen 1,0 und 3,0 Gewichtsprozent und vorzugsweise im Bereich zwischen 1,2 und 2,2 Gewichtsprozent liegt, und
• der Rest des Zink-Legierungsschmelzbads 11 sind Zink und optional einem oder mehreren aus Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce oder Bi ausgewählten zusätzlichen Elementen, wobei der gewichtsbezogene Gehalt jedes zusätzlichen Elementes in der metallischen Beschichtung weniger als 0,1 % beträgt, und unvermeidbare Verunreinigungen.

In order to be able to reliably apply such a layer 10, which essentially corresponds to the target thickness, the zinc alloy of the zinc alloy melt pool 11 has the following composition in all or at least some of the embodiments:

• an aluminum content which is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight,
• a magnesium content which is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight, and
• the remainder of the zinc alloy molten pool 11 is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element being in of the metallic coating is less than 0.1% and unavoidable contamination.

• der Aluminium-Anteil (in Gewichtsprozent) liegt im Bereich zwischen 2,09 und 2,66 Gewichtsprozent;
• der Magnesium-Anteil (in Gewichtsprozent) liegt im Bereich zwischen 1,45 und 2,24 Gewichtsprozent;
• der Rest des Zink-Legierungsschmelzbads 11 sind Zink und optional einem oder mehreren aus Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce oder Bi ausgewählten zusätzlichen Elementen, wobei der gewichtsbezogene Gehalt jedes zusätzlichen Elementes in der metallischen Beschichtung weniger als 0,1 % beträgt, und unvermeidbare Verunreinigungen.

In all embodiments or at least some of the embodiments, a metallic bath 11 is presented with a particularly preferred ZnAlMg alloy, which is composed according to the following alloy concept:

• the aluminum content (in percent by weight) is in the range between 2.09 and 2.66 percent by weight;
• the magnesium content (in percent by weight) is in the range between 1.45 and 2.24 percent by weight;
• the remainder of the zinc alloy molten pool 11 is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element being in of the metallic coating is less than 0.1% and unavoidable contamination.

In all embodiments, the aluminum content (in percent by weight) can be equal to or greater than the magnesium content (in percent by weight).

In order to prevent the formation of marbling or to significantly reduce marbling, the absolute local air humidity f is determined continuously or from time to time (e.g. by direct or indirect measurement). This statement also applies to preventing or reducing toothpick formation.

r

relative Luftfeuchtigkeit in %

TL

Lufttemperatur in °C

Absolute humidity f is a physical quantity that can be expressed, for example, in the unit g/m ³ . Ie, it is the mass of the gaseous water in a standardized volume body that has a volume of 1 m ³ . In other words, the absolute humidity f indicates the water vapor content in a volume. f is used here as a symbol for the absolute humidity. Approximately, the absolute air humidity f can be estimated in all embodiments from the air temperature TL and the relative air humidity r, where the following applies: $$f=\frac{\mathrm{13,235}\cdot r}{\mathit{TL}+273.15}{.10}^{\frac{7.5\cdot \mathit{TL}}{\mathit{TL}+237.3}}$$

r

relative humidity in %

TL

Air temperature in °C

The absolute local humidity f can be measured directly or indirectly in all embodiments. Indirect measurement here includes, among other things, measuring the air temperature TL and the relative humidity r and calculating/deriving the absolute local humidity f .

The values of the absolute local air humidity f, which according to the invention in the immediate vicinity of the flat steel product 100 in a range between The output side A and the cooling area 16 (if present) should be present are in the range 1 g/m ³ and less than 300 g/m ³ in all embodiments. Preferably, the absolute local air humidity is in the range 1.08 g/m ³ to 51 g/m ³ in all embodiments.

The method enables the controlled application of the layer 10 to at least one at an absolute local humidity f that is greater than 1 g/m ³ and less than 300 g/m ³ by specifically adjusting adjustable parameters (process and system parameters). Side of the flat steel product 100. In all embodiments, care is taken to ensure that the adjustable parameters are adjusted in such a way that the layer 10 to be applied (continues to) essentially correspond to the target thickness. This means that care is taken to ensure that a layer is applied that corresponds to the target thickness (within tolerances) and that at the same time shows no or only very little marbling.

• Erhöhen der Badtemperatur TB des Legierungsschmelzbades 11 falls sich die momentane absolute lokale Luftfeuchtigkeit f reduziert und vice versa, und/oder
• Reduzieren der Dicke d des Düsenlippenspalts 17, falls sich die momentane absolute lokale Luftfeuchtigkeit f reduziert und vice versa, und/oder
• Reduzieren des Abstands Z zwischen dem Düsenlippenspalt 17 und der Seite des Stahlflachprodukts 100, falls sich die momentane absolute lokale Luftfeuchtigkeit f reduziert und vice versa,

wobei zusätzlich die Durchflussmenge D des Gases G, (automatisch, zum Beispiel regelungstechnisch) angepasst wird, um die Solldicke der aufzubringende Schicht 10 im Wesentlichen konstant zu halten.The adjustable parameters (process and system parameters) can be adjusted in all embodiments as follows:

• Increasing the bath temperature TB of the alloy melt pool 11 if the current absolute local air humidity f is reduced and vice versa, and/or
• Reducing the thickness d of the nozzle lip gap 17 if the current absolute local air humidity f is reduced and vice versa, 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 is reduced and vice versa,

wherein the flow rate D of the gas G is additionally adjusted (automatically, for example through control technology) in order to keep the target thickness of the layer 10 to be applied essentially constant.

In addition, in all embodiments, the belt speed v with which the flat steel product 100 is moved out of the zinc alloy melt pool 11 can also be changed, here too It is ensured that the target thickness of the layer 10 to be applied remains essentially constant.

In all embodiments, several of these adjustable parameters (process and system parameters) are preferably changed in coordination with one another in order to ensure that the layer 10 that is applied corresponds to the target thickness. The mathematical relationships that apply here will be described later.

• Beschichtungsauflage der Schicht 10 je Bandseite soll im Bereich 20 bis 200 g/m², vorzugsweise Bereich 30 bis 100 g/m², liegen, und/oder
• Solldicke der Schicht (10) je Bandseite, die im Bereich 3 bis 30 µm, vorzugsweise Bereich 4,5 bis 15 µm liegt.

A so-called target specification of the layer 10 to be applied can specify for all embodiments that the following specification(s) must be met:

• Coating layer 10 per band side should be in the range 20 to 200 g/m ² , preferably in the range 30 to 100 g/m ² , and/or
• Target thickness of the layer (10) per strip side, which is in the range 3 to 30 µm, preferably in the range 4.5 to 15 µm.

The bath temperature TB of the alloy melt pool 11 has an influence on the viscosity of the melt during the stripping process. An increased bath temperature TB leads to a reduced viscosity of the melt. If the adjustable parameters (process and system parameters) remained the same, more material would be stripped off than desired. Therefore, when the bath temperature TB is increased, the other adjustable parameters (process and system parameters) are changed so that the layer 10 continues to have the target thickness. For example, when increasing the bath temperature TB, the flow rate D of the gas G is reduced to reduce the stripping effect in order to continue to achieve the same target thickness.

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

For operating the alloy melt pool 11, a bath temperature TB in the specified temperature range is specified in all embodiments. Maintaining this temperature window (temperature range) is important because unwanted slag can increasingly form on the flat steel product 100 if you work above the specified range.

In all embodiments, the bath temperature TB can be adjusted, for example, by means of an inductive heating device 30 (see Fig. 2 and 6 ) or a resistance heater.

To avoid slag formation, the bath temperature TB is preferably reduced in all embodiments. The reduced bath temperature TB _red is preferably in the already mentioned range 420 < TB _red < 460 degrees Celsius.

• die Dicke d des Düsenlippenspalts 17 in einem Bereich zwischen 0,5 und 5 mm, vorzugsweise zwischen 0,6 und 2 mm, besonders vorzugsweise zwischen 0,8 und 1,5 mm, und/oder
• die Durchflussmenge D im Bereich von 200 bis 8000 Nm³ pro Stunde beträgt, und/oder
• der Abstand Z in einem Bereich zwischen 2 und 15 mm, vorzugsweise zwischen 3 und 12 mm liegt, und/oder
• die Bandgeschwindigkeit (v) in einem Bereich zwischen 50 und 200 m/min, vorzugsweise zwischen 70 und 150 m/min beträgt.

When carrying out the method, care is preferably taken in all embodiments that

• the thickness d of the nozzle lip gap 17 in a 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
• the flow rate D is in the range from 200 to 8000 Nm ³ per hour, and/or
• the distance Z is in a range between 2 and 15 mm, preferably between 3 and 12 mm, and / or
• the belt speed (v) is in a range between 50 and 200 m/min, preferably between 70 and 150 m/min.

The process works particularly reliably within these areas.

In all embodiments, a corresponding gas nozzle 15 has a length parallel to the y-axis. Preferably the nozzle has 15 at all Embodiments have an active length that corresponds to the bandwidth 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.

The bandwidth w of the strip-shaped flat steel product 100 is preferably in the range from 500 mm to 2500 mm in all embodiments. The bandwidth w of the strip-shaped flat steel product is particularly preferably in the range from 800 mm to 1800 mm in all embodiments.

In at least some of the embodiments, the absolute local humidity f is measured permanently or from time to time and if the absolute local humidity f is too low, the application of the layer 10 is interrupted, for example to make adjustments to the adjustable parameters.

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.

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

The measurement of the absolute local air humidity f is not carried out directly at the line of impact at which the gas G hits the layer 10 to be stripped off, since the gas mixture there is relatively “dry” (i.e. contains little air humidity). In all embodiments, the measurement of the absolute local air humidity f is preferably carried out directly or indirectly in an area that has at least a normal (at a right angle) distance of 20 cm from the line of impact or from the flat steel product 100.

In Fig. 2 and 7 An approach for directly measuring absolute local humidity is shown. The device 150 includes, for example, two Moisture sensors 51 (at least one per hinge side). Each of these sensors 51 has two contacts in the schematic representation, which can be connected to a controller 250, for example. The corresponding connections or lines V1, V2, V3, V4 are in Fig. 2 and 6 shown by dashed lines.

• mechanisch arbeitende Messsensoren, die auf der feuchtebedingten Ausdehnung bzw. dem Zusammenziehen von (meist organischen) Messelementen basieren;
• psychrometrisch arbeitende Messsensoren, wobei zwei identische, sehr genaue Thermometern zum Einsatz kommen, an denen die zu messende Gasströmung in definierter Geschwindigkeit entlanggeführt wird;
• kapazitive Messsensoren, die z.B. einen feuchteempfindlichen Kondensator mit zwei flachen Elektroden umfassen;
• Tauspiegelhygrometer, das die Luftfeuchtigkeit mit Taupunktspiegeln ermittelt, bei denen die Kondensation von Wasserdampf bei einer Taupunktunterschreitung ausgewertet wird;
• Resistives Messverfahren, bei dem z.B. die Impedanz des Wechselstromwiderstandes eines hygroskopischen Elementes ermittelt wird;
• Spektrometrische Messverfahren, die beispielsweise im nahen oder mittleren Infrarotbereich (NIR oder MIR) den gasförmigen Wassergehalt berührungslos messen.

Sensors of the following type or mode of operation can be used as moisture sensors 51 in all embodiments:

• mechanically operating measuring sensors that are based on the moisture-related expansion or contraction of (mostly organic) measuring elements;
• psychrometric measuring sensors, whereby two identical, very precise thermometers are used, along which the gas flow to be measured is guided at a defined speed;
• capacitive measurement sensors, which include, for example, a moisture-sensitive capacitor with two flat electrodes;
• Dew mirror hygrometer, which determines the air humidity using dew point mirrors, in which the condensation of water vapor is evaluated when the dew point falls below;
• Resistive measuring method in which, for example, the impedance of the alternating current resistance of a hygroscopic element is determined;
• Spectrometric measurement methods that, for example, measure the gaseous water content without contact in the near or mid-infrared range (NIR or MIR).

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

The controller 250 can be part of the overall system control of the device 150 in all embodiments, or it can be connected to the overall system control in all embodiments.

The adjustment/adjustment of the adjustable parameters (system or process parameters), or the stripping effectiveness AWZ, can then be carried out in these embodiments by the overall system control and/or by the controller 250.

When indirectly measuring the absolute local air humidity, the air humidity is not measured at or in the surrounding area of the device 150 (e.g. within a virtual cylinder body vZK), but rather the current air humidity is determined indirectly.

In all embodiments, the current humidity can be measured indirectly, for example, by using a type of light barrier to determine the transmission rate of an optical path. When the air is very dry, the transmission rate is high. The presence of gaseous water, on the other hand, hinders the transmission of light through the optical path and the transmission rate is lower.

In all embodiments, the indirect determination can be made by measuring the surface property(s) of the coated flat steel product 100 (three examples of a coated flat steel product 100 are shown in FIGS Figures 7A, 7B and 7C shown). A corresponding measurement of the surface property(s) can be carried out optically, for example, before the cooling region 16 or after the cooling region 16 (for example by optically measuring the reflectivity of the surface of the layer 10). In the Figures 7D to 7G Example photos of coated flat steel products 100 are shown.

An inert gas is preferably used as gas G in all embodiments. Nitrogen or a gas mixture containing nitrogen has proven particularly useful.

• die Dicke d des Düsenlippenspalt 17,
• die Durchflussmenge D des Gases G,
• der Abstand Z zwischen dem Düsenlippenspalt 17 und der (Band-)Seite des Stahlflachprodukt 100,
• die Bandgeschwindigkeit v (parallel zur x-Achse verlaufend) mit der das Stahlflachprodukt 100 aus dem Zink-Legierungsschmelzbad 11 herausbewegt wird.

Fig. 3A shows a highly schematic side view of another stripping nozzle device 14 in order to be able to define the adjustable parameters (system and process parameters), or the stripping effectiveness AWZ, more precisely. Important customizable parameters are

• the thickness d of the nozzle lip gap 17,
• the flow rate D of the gas G,
• the distance Z between the nozzle lip gap 17 and the (strip) side of the flat steel product 100,
• the belt speed v (running parallel to the x-axis) with which the flat steel product 100 is moved out of the zinc alloy melt pool 11.

Fig. 3A shows the nozzle distance Z between the nozzle 15 and the corresponding strip side (here the front) of the flat steel product 100, as well as the thickness d of the nozzle lip gap 17. The nozzle lip gap 17 serves as a gas outlet gap of the stripping nozzle device 14.

Fig. 3B shows a schematic representation of the gas pressure curve P, which results along the front of the flat steel product 100. The pressure P depends on the position on the x-axis. The pressure curve P ideally has the shape of a Gaussian curve, as in Fig. 3B indicated. The half-width at the pressure P _S /2 can be determined from this Gaussian curve, as shown, where P _S represents the maximum pressure. 2b is the half width in millimeters. A narrow gas jet is defined by a small half-width 2b. The larger (further) the gas jet becomes, the larger the half-width 2b becomes. Further details can be found in the publication “Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet”, CV Tu et al., Experimental Thermal and Fluid Science 1996, 16, pages 364 - 373, Elsevier Science Inc. , can be removed.

The gas jet emerging from the nozzle 14 acts together with gravity (if the flat steel product 100 is pulled vertically upwards from the bath 11, as for example in Fig. 2 , 6 and 7 shown) a shear force τ on the still liquid layer 10. Fig. 3C shows a representation of the shear force τ relative to a position on the x-axis (the shear force τ was given by the negative first derivative of the pressure profile of Fig. 3B determined). This is the shear force τ, which acts on the layer 10 to be stripped off. In a first approximation, the course of the shear force curve τ is symmetrical to the point x=0, τ=0 (if you neglect the belt speed v parallel to the x-axis). Exactly Above the x=0 position, the nozzle 15 is at a distance Z > 0. τ _max defines the maximum shear force occurring on the layer 10 to be stripped off.

Tests have shown that the adjustable system and/or process parameters, or the stripping effectiveness AWZ, can be adjusted within certain limits without significantly changing the target thickness and/or the basis weight (coverage per strip side) of the layer 10.

It has also been shown that (in addition to the absolute local humidity f) two variables that characterize the shear force profile that the stripping nozzle 15 generates on the belt 100 are crucial for the formation of marbling. On the one hand it is the maximum shear force τ _max and on the other hand it is the time t in which the strip-shaped flat steel product 100 passes through the distance l between the shear force maxima (see Fig. 3C ). The time t in turn depends on the belt speed v.

There is a direct relationship between the time t, the belt speed v and the half-width 2b, as expressed in equation (1): $$t=\frac{120}{v}\cdot \sqrt{\frac{-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{2\cdot \ln \left(0.5\right)}}$$

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

The equations that describe the dynamic flow behavior of the gas G on the flat steel product 100 are very complex. This is due, among other things, to the fact that in the gas jet that emerges through the nozzle lip gap 17 of the nozzle 15, areas with laminar and turbulent flow patterns form on the layer 10 of the flat steel product 100. In addition, the gas jet sucks in ambient air, which is swirled with the gas G. Details can be found, for example, in the aforementioned publication “Wall Pressure and Shear Stress Measurements Beneath an Impinging Jet”.

Due to the complex relationships, complex tests and statistical evaluations of the measured results have not provided any immediately usable results with regard to a connection between the wiper nozzle parameters and the marbling. Only after various internal and external influencing variables were additionally systematically examined did a connection become apparent between the degree of marbling on layer 10, the wiper nozzle parameters and the environmental conditions of the test setup. The humidity in particular has an influence on the marbling on layer 10.

Further targeted investigations and the graphical processing of the results of these tests showed for the first time a correlation between air humidity, the wiper nozzle parameters and the tendency to marbling. Fig. 4 shows a summarized graphical representation of numerous tests, with the stripping effectiveness AWZ (as a summary or generic term for the process and device parameters or, for short, stripping nozzle parameters) being plotted on the ordinate axis and the absolute air humidity f in g/m ³ being plotted on the abscissa.

By weighting and adding the two variables τ _max and t, a so-called stripping effectiveness AWZ can be determined, which can be compared directly with the absolute local air humidity f , as follows (inequality (2.1)): $$f>\frac{{\tau }_{\mathit{Max}}+500\cdot t-636}{14}$$

The right-hand side of inequality (2.1) corresponds to the stripping effectiveness AWZ, ie the following relationship (2.2) applies: $$f>\mathit{EEZ}$$

• die über die Bandbreite w wirksame Durchfluss(menge) D des Gases G pro Bandseite,
• den Proportionalitätsfaktor k,
• die Bandbreite w des Stahlflachproduktes 100,
• die Dicke d des Düsenlippenspalts 17,
• die Halbwertsbreite 2b,
• die Geschwindigkeit v (Bandgeschwindigkeit) des Stahlflachproduktes 100, respektive die Zeit t, die mit der Geschwindigkeit v korreliert ist.

Stripping effectiveness AWZ summarizes the following process and device parameters:

• the flow rate (quantity) D of the gas G effective over the band width w per band side,
• the proportionality factor k,
• the bandwidth w of the flat steel product 100,
• the thickness d of the nozzle lip gap 17,
• the half-width 2b,
• the speed v (belt speed) of the flat steel product 100, or the time t, which is correlated with the speed v.

Further details on the stripping effectiveness AWZ can also be found in inequality (3), which will be discussed later. The entire term on the right-hand side of this inequality (3) can also be used as a definition of the stripping efficiency AWZ. Before describing inequality (3), let us further refer to the Fig. 4 .

The gray or black filled symbols (squares, diamonds, triangles or circles) of the Fig. 4 represent flat steel products 100 in which marbling has clearly visibly formed on the surface of layer 10. The marbling is particularly strong in the black-filled symbols. The gray filled symbols represent less severe marbling. The unfilled symbols, on the other hand, represent no or negligible marbling. Circular symbols represent tests that were carried out with a nozzle lip gap thickness of d=0.8 mm, square symbols represent tests with a nozzle lip gap thickness of d=0.9 mm, diamond-shaped symbols represent a nozzle lip gap thickness of d=1 mm and triangular symbols represent d=1.2 mm and upside down triangular symbols represent d=1.4 mm.

It was included in the graphic Fig. 4 A straight line Ge is inserted as a dividing line in order to separate, as a first approximation, those tests with clear or moderate marbling from those that show no or only negligible marbling. In the tests that lie to the right below the line Ge, there is no or only negligible marbling (a corresponding flat steel product 100 with a Layer 10 without marbling is in Fig. 7A shown). The straight line Ge can be understood as a function of the stripping effectiveness AWZ (see also inequalities (2.1) and (3)).

A detailed evaluation of the test results suggests that the above-mentioned stripping effectiveness AWZ can be adjusted depending on the absolute local air humidity f in order to avoid the occurrence of undesirable marbling. This adjustment of the stripping effectiveness AWZ is preferably carried out in all embodiments in such a way that the target thickness of the layer 10, or the surface support (mass) of this layer 10, does not change or hardly changes. This means that when changing the stripping effectiveness AWZ, care is always taken to ensure that the layer 10 to be applied essentially has the desired thickness.

However, it is important that when adjusting the wiping effectiveness AWZ, care is taken to ensure that, in addition to avoiding marbling, other errors such as toothpick errors, beach pattern errors and so on are avoided or the formation of slag is reduced . Therefore, parameter ranges that have proven particularly effective are specified here.

In the Fig. 4 As mentioned, the straight line Ge shown is only a first approximation. The actual connections are very complex. The following formula representation (inequality (3)) shows a further mathematical description of the relationship between the absolute local air humidity f in g/m ³ and the stripping effectiveness AWZ: d Thickness of the nozzle lip gap [mm] D Gas flow per belt side [Nm ³ /h] w Width of steel flat product 100 [mm] v Belt speed [m/min] 2 B half-width [mm] k proportionality factor $$f>\frac{1}{14}\cdot \left(\frac{{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">D</figure-callout>}}^2\cdot k\cdot e^{-0.5}\cdot \mathrm{1,251}\cdot {10}^4}{{\mathrm{<figure-callout\; id="2"\; label="w"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">w</figure-callout>}}^2\cdot {\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}^2\cdot 25.92}\cdot \sqrt{\frac{-2\cdot \ln \left(0.5\right)}{b^2}}+\frac{6\cdot {10}^4}{v}\cdot \sqrt{\frac{-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">b</figure-callout>}}^2}{2\cdot \ln \left(0.5\right)}}-636\right)$$

1. 1. Ansatz: Es wird gemäß einem 1. Ansatz eine Unterteilung in drei verschiedene Kurvenbereiche vorgenommen (hier als Fälle 1.1 bis 1.3 bezeichnet). Mit einer solchen Unterteilung kann die rechte Seite der Ungleichung (3) vereinfacht berechnet werden.

Two exemplary approaches that serve to simplify inequality (3) are described below:

1. 1st approach: According to a 1st approach, a division into three different curve areas is made (referred to here as cases 1.1 to 1.3). With such a division, the right-hand side of inequality (3) can be calculated in a simplified manner.

und k = 1 (Case 1.1). In a linear area the assumption applies: 2b/d=1.9 or b = 1.9d/2. This simplification applies to the following relationship between the nozzle distance Z and the width d of the nozzle lip gap 17: Z/d<5.2. Case 1.1 $$\frac{Z}{d}<5.2\to b=1.9\cdot \frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}$$

and k = 1

$$\begin{array}{l}\to b=\left[-{\left(\frac{Z}{d}\right)}^4\cdot \mathrm{3,22}\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot \mathrm{9,78}\cdot {10}^{-3}-{\left(\frac{Z}{d}\right)}^2\cdot \mathrm{8,39}\cdot {10}^{-2}+\left(\frac{Z}{d}\right)\cdot \mathrm{2,72}\cdot {10}^{-1}+\mathrm{1,62}\right]\cdot \frac{d}{2}\\ \to k=-{\left(\frac{Z}{d}\right)}^4\cdot \mathrm{6,05}\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot \mathrm{2,2}\cdot {10}^{-2}-{\left(\frac{Z}{d}\right)}^2\cdot \mathrm{2,89}\cdot {10}^{-1}+\left(\frac{Z}{d}\right)\cdot \mathrm{1,55}-\mathrm{1,9}\end{array}$$

(Case 1.2) In another area that begins at approximately Z/d=5.2 and ends before Z/d=10, the following relationships apply: Case 1.2 $$5.2\le \frac{Z}{d}<10$$

$$\begin{array}{l}\to b=\left[-{\left(\frac{Z}{d}\right)}^4\cdot 3.22\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot 9.78\cdot {10}^{-3}-{\left(\frac{\mathrm{<figure-callout\; id="2"\; label="Z\; d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">Z</figure-callout>}}{d}\right)}^2\cdot 8.39\cdot {10}^{-2}+\left(\frac{Z}{d}\right)\cdot 2.72\cdot {10}^{-1}+1.62\right]\cdot \frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}\\ \to k=-{\left(\frac{Z}{d}\right)}^4\cdot 6.05\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot 2.2\cdot {10}^{-2}-{\left(\frac{\mathrm{<figure-callout\; id="2"\; label="Z\; d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">Z</figure-callout>}}{d}\right)}^2\cdot 2.89\cdot {10}^{-1}+\left(\frac{Z}{d}\right)\cdot 1.55-1.9\end{array}$$

(Case 1.3) In a further area that starts at approx. Z/d=10, the following relationships apply: Case 1.3 $$\frac{Z}{d}\ge 10\to b=0.125\cdot Z\mathit{and}k=6.5\cdot \frac{d}{Z}$$

In order to make the complicated inequality (3) manageable in practice, a case distinction with the three cases 1.1 to 1.3 is recommended, whereby the ratio Z/d is used to differentiate the cases.

The distinction between the three areas or cases mentioned still leads to complicated mathematical formulas, especially in the second area (case 1.2).

Fall 2.2 $$\frac{Z}{d}\ge \mathrm{7,6}\to b=\mathrm{0,125}\cdot Z\mathit{und}k=\mathrm{6,5}\cdot \frac{d}{Z}$$

2nd approach: A second approach is therefore described here, which serves to make the complicated inequality (3) easier to handle in practice. In this second approach, a case distinction is made with only two cases (cases 2.1 and 2.2), whereby the ratio Z/d is also used to differentiate between cases. Case 2.1 $$\frac{Z}{d}<7.6\to b=1.9\cdot \frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}\mathit{and}k=1$$

Case 2.2 $$\frac{Z}{d}\ge 7.6\to b=0.125\cdot Z\mathit{and}k=6.5\cdot \frac{d}{Z}$$

The second approach has the disadvantage that in the border area the separation between flat steel products 100 without marbling and flat steel products 100 with marbling is not entirely clear or unambiguous. The best results can be achieved if a case distinction is evaluated according to the first approach using inequality (3) and/or inequality (2.1) (e.g. processed numerically by the controller 250).

The adjustment/adjustment of the adjustable parameters (system and/or process parameters), or the stripping effectiveness AWZ, can now be done in all embodiments or in at least some of the embodiments either using the inequality(s) (2.1) and/or (3). be made using the 1st or 2nd approach. Or, as already mentioned, a numerical representation of the inequality(s) (2.1) and/or (3) can also be used in the controller 250.

The adaptation/adjustment of the adjustable parameters (system and/or process parameters), or the stripping effectiveness AWZ, can now be carried out in all embodiments or in at least some of the embodiments in such a way that the surface support of the layer 10 and/or the (support) ) Mass of the layer 10, and / or the target thickness of the layer 10 remains constant or within narrowly specified tolerance limits, such as defined by a target specification.

For all embodiments, the target specification can be specified by the manufacturer and/or the customer or client.

Preferably, either inequality(s) (2.1) and/or (3) or the formulas of the 1st approach or the formulas of the 2nd approach are implemented in the controller 250 by software, or they are in one or more tables Numerical values for the absolute local humidity f and correspondingly suitable adjustable parameters (system and/or process parameters), or the stripping effective numbers AWZ, are stored. Using a lookup table, the controller 250 can then retrieve the correspondingly suitable adjustable parameters (system and/or process parameters), or stripping effective numbers AWZ, for a currently valid absolute local moisture value f and adjust the device 150, or give the machine operator a numerical value, for example for adjusting the thickness d of the nozzle lip gap (e.g. show on a display).

In all embodiments, adjustable parameters (system and/or process parameters), or stripping effective numbers AWZ in the following number or value ranges are preferably used. The individual number or value ranges in Table 1 are not correlated with each other, or only in some areas, because the respective maximum and minimum values come from different experiments. There were only those respective maximum and minimum values from Table 2 ( Fig. 8A , 8B ) and summarized here.

The table 2 ( Fig. 8A , 8B ) mentioned nozzle height is the vertical distance between the zinc bath level and the impact line of the gas jet on the layer 10 to be stripped off. The nozzle pressure in Table 2, Fig. 8A , 8B is defined as the (over)pressure (based on the ambient pressure) of the stripping gas G in the nozzle 15 in mbar.

The flow rate D of the gas G per band side is typically in the range between 200 and 8000 Nm ³ per hour in all embodiments. Table 1 parameter lower limit Upper limit TB [ ⁰ C] 409 473 Z [mm] 2.5 14.1 d [mm] 0.8 1.2 D [Nm ³ /h] 410 1775 k 0.55 1.0 w [mm] 1159 1614 b [mm] 0.76 1.76 v [m/min] 70 150

From Table 2, which is divided into two parts (see Figures 8A and 8B ), are concrete numerical values for the in Fig. 4 shown experimental results shown. The table 2 of the Fig. 8A shows experiments in which layers 10 without (visible) marbling were produced by specifying suitable adjustable parameters (process and/or system parameters), or stripping effectiveness numbers AWZ (as exemplified in Fig. 7A shown). The values of Table 2 of the Fig. 8A were sorted by ascending b.

The table 2 of the Fig. 8B On the other hand, shows experiments in which layers 10 with medium (as exemplified in Fig. 7B shown) or even stronger Marbling (as exemplified in Fig. 7C shown) were generated. The values of Table 2 of the Fig. 8B were also sorted by ascending b.

From table 2 of Fig. 8A you can extract the following pairs of values for the absolute local humidity f and the stripping effectiveness AWZ (sorted according to ascending stripping effectiveness AWZ), with all layers 10 that were created with these adjustable parameters (process and system parameters), or stripping effectiveness AWZ, below the straight line Ge in Fig. 4 lay. Excerpt from Table 2 ( Fig. 8A ) absolute humidity (n) Stripping effectiveness (AWZ) Assessment of layer 10 g/ ^m3 3.33 -8.59 no marbling 4.2 -6.27 no marbling 3.13 -5.68 no marbling 3.33 -4.16 no marbling 4.52 -3.76 no marbling 2.93 -2.25 no marbling 2.93 -0.60 no marbling 13,14 -0.46 no marbling 13.22 2.23 no marbling 5.99 2.53 no marbling 6.93 3.10 no marbling 15.54 3.81 no marbling 9.29 4.43 no marbling 5.22 4.70 no marbling 6.86 4.89 no marbling 9.13 5.71 no marbling 11.08 5.87 no marbling 13.47 6.48 no marbling 6.97 6.89 no marbling 17.67 8.22 no marbling 9.52 8.30 no marbling 15.34 9.26 no marbling 11.99 9.26 no marbling 20.4 10.81 no marbling 13.47 12.03 no marbling

From table 2 of Fig. 8B you can extract the following pairs of values for the absolute humidity f and the stripping effectiveness AWZ (sorted by increasing stripping effective number AWZ), with all layers 10 that were generated with these adjustable parameters (process and system parameters), or stripping effective numbers AWZ, above the straight line Ge in Fig. 4 lay. Excerpt from Table 2 ( Fig. 8B ) absolute humidity (n) Stripping effectiveness (AWZ) Assessment of layer 10 g/ ^m3 3.17 3.80 medium marbling 3.76 6.43 medium marbling 2.71 7.21 medium marbling 5.95 8.14 medium marbling 5.14 8.26 strong marbling 3.76 9.10 strong marbling 3.13 9.24 strong marbling 5.99 9.56 strong marbling 7.83 10.02 strong marbling 8.96 10.25 medium marbling 4.09 12.15 strong marbling 7.83 12.51 strong marbling 5.99 13.28 strong marbling 11.47 13.36 medium marbling 8.36 13.50 strong marbling 3.87 14.58 strong marbling 9.12 15.19 medium marbling 4.21 16.43 strong marbling 3.17 17.98 strong marbling 3.17 20.02 strong marbling 13.67 21.25 medium marbling

If marbling errors occur under a given absolute local humidity f and under given process conditions, then in at least some of the embodiments to eliminate the marbling, the stripping effectiveness AWZ (corresponds to the right-hand side of inequality (2.1) and (3)) is reduced until this Inequality is fulfilled again.

As a rule, it is not permitted to change the coating layer of the flat steel product 100 produced, as this is stipulated in the product specification. Under the condition of keeping the thickness of the layer constant, the reduction in the stripping effectiveness AWZ can be brought about in different ways.

Using three concrete examples, options for changing the AWZ stripping index are presented as examples.

Example 1: Reduction of the stripping effectiveness AWZ by reducing the nozzle distance Z (see Table 3).

The following Table 3 shows two test examples 1.1 and 1.2, which demonstrate a reduction in the stripping effectiveness AWZ by reducing the nozzle distance Z from 10 mm to 8 mm.

For the initial state (Table 3 - Example 1.1) with a gas flow D of 1691 Nm ³ /h, the belt width w of 1315 mm, a nozzle lip gap d of 1.0 mm, the nozzle distance Z of 10 mm and the belt speed v of 100 m /min, the EEZ is calculated according to inequality (3) to a value of 21.3.

Based on example 1.1, in order to reduce the stripping effectiveness AWZ, the nozzle distance Z was reduced from 10 mm to 8 mm, whereby the bandwidth w, the nozzle lip gap d, the belt speed v, the bath temperature TB and the layer coverage per side were left constant. Due to the changed nozzle distance Z, the ratio Z/d is shifted, which also changes the values determined for b and k. From Table 3 it can be seen that here as As a result of the change in the nozzle distance Z, the nozzle pressure and thus the gas flow per side D had to be reduced from 1691 to 1386 Nm ³ /h by an automatic control of the stripping nozzle system in order to keep the thickness of the layer 10 essentially constant.

If you now calculate the stripping effectiveness AWZ 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 effectiveness AWZ could be reduced from 21.3 to 13.5 with an unchanged layer thickness.

Example 2: Reduction of the stripping effectiveness AWZ by reducing the nozzle lip gap d.

The following Table 4 shows two test examples 2.1 and 2.2, which demonstrate a reduction in the stripping effectiveness AWZ by reducing the thickness d from 1.2 mm to 1 mm.

For the initial state (Table 4, Example 2.1) with a flow D = 1373 Nm ³ /h, the bandwidth w = 1455 mm, a nozzle lip gap d = 1.2 mm, the nozzle distance Z = 7 mm and the belt speed v = 100 m/min, the AWZ is calculated according to inequality (3) to a value of 9.4.

Based on this, in order to reduce the stripping effectiveness AWZ, the nozzle lip gap d was reduced from 1.2 mm to 1.0 mm, with the other parameters remaining essentially constant.

From Table 4 it can be seen that as a result of the change in the nozzle lip gap d, the nozzle pressure and thus the gas flow per side D had to be reduced by the automatic circulation control from 1373 to 1166 Nm ³ /h in order to keep the thickness of the layer 10 constant.

Due to the changed nozzle lip gap d, the ratio Z/d is shifted, which also changes the values determined for b and k. If you now calculate the stripping effectiveness AWZ using these new process 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 effectiveness AWZ could be reduced from 9.4 to 4.9 with an unchanged layer layer.

Example 3: Reduction of the stripping effectiveness AWZ by increasing the bath temperature TB.

The following Table 5 shows two test examples 3.1 and 3.2, which demonstrate a reduction in the stripping effectiveness AWZ by increasing the bath temperature TB from 439 ° C to 455 ° C.

For the initial state (Table 5, Example 3.1) with a flow rate D = 1607 Nm ³ /h, the bandwidth w = 1615 mm, a nozzle lip gap d = 1.0 mm, the nozzle distance Z = 7 mm and the belt speed v = 100 m /min, the EEZ is calculated according to inequality (3) to a value of 12.4.

Based on this, in order to reduce the stripping effectiveness AWZ, the bath temperature TB was increased from 439 ° C to 455 ° C mm, with the other parameters remaining essentially constant. In this example, the ratio Z/d remains unchanged, so the values determined for b and k remain constant when the bath temperature TB increases.

From Table 5 it can be seen that as a result of the change in the bath temperature TB, the nozzle pressure and thus the gas flow D per strip side had to be reduced by the automatic circulation control from 1607 to 1339 Nm ³ /h in order to keep the thickness constant. The reason for this is that as the bath temperature TB increases, the viscosity of the zinc melt decreases, meaning that lower stripping forces are required to strip off the same amount of melt.

If you now calculate the stripping effectiveness AWZ using these new process parameters (Table 5, Example 3.2), the result is a value of 5.8. Ie, by increasing the bath temperature TB, the stripping effectiveness AWZ could be reduced.

According to the present invention, the absolute local humidity f is preferably defined as the absolute humidity within a virtual cylinder body vZK, as in Fig. 5 shown schematically. In this virtual cylinder body vZK, an area that extends to the right and left parallel to the band-shaped flat steel product 100 is excluded.

The virtual cylinder body vZK is composed of two virtual cylinder volume segments, which are delimited on the one hand by a virtual cylinder surface which encloses the gas nozzles 15 concentrically or almost concentrically. On the other hand, the cylinder volume segments will be delimited by two planes running parallel to the flat steel product 100 on both sides of the flat steel product 100, each with a distance of, for example, s = 20 cm from the flat steel product 100. The two cylinder volume segments together have a volume in a range of 1m ³ to 10m ³ and preferably a volume of less than 2 m ³ . In all embodiments, the measurement of the absolute local humidity f is preferably carried out directly or indirectly within the cylinder volume segments.

In Fig. 5 a part of a further device 150 is shown, the two cylinder volume segments of the virtual cylinder body vZK being shown here. The bath 11 is shown here as a rectangular container that is open at the top. The liquid zinc alloy (abbreviated here as ZnAIMg) is located in the bath 11. Only a short length section of the flat steel product 100, which has a strip shape, is shown after emerging from the bath 11. The flat steel product 100 is passed vertically out of the bath 11 in the direction of the x-axis between two opposing gas nozzles 15 of the stripping nozzle device 14. If the two gas nozzles 15 are arranged parallel to one another, then a center line ML can be defined between these nozzles 15. This center line ML is in Fig. 5 shown in dashed lines. The center line ML lies in a nozzle plane DE (which is defined as the xy plane).

The virtual cylindrical body vZK results in 3-dimensional space around the center line ML. The “outer shell” of the virtual Cylinder body vZK runs concentric to the center line ML. All points of the “outer shell” have an equidistant distance ra from the center line ML (ra is the radius of the virtual cylinder body vZK).

The virtual cylinder body vZK includes at least the nozzles 15 of the stripping nozzle device 14 and has a virtual cylinder height vZH, which is defined parallel to the y-axis. In all embodiments, the virtual cylinder height vZH preferably corresponds to the bandwidth w of the flat steel product 100 and/or the length of the nozzle 15 (defined parallel to the y-axis).

The specified value ranges for the absolute local air humidity f can be defined for all embodiments within this virtual cylinder body vZK.

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

Preferably, the absolute local humidity f is determined or measured in all or at least some of the embodiments at several points on this y-line and an average of the determined or measured values is compared with the numerical range specified for the absolute local humidity f .

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

However, in all embodiments, the absolute local air humidity f can also be defined in a volume range of 1m ³ to 10m ³ and can be measured there directly or indirectly, the measurement preferably not being carried out directly on the impingement line of the gas G but on a y-line , which runs parallel to the y-axis above the impact line.

The y-line described is in the embodiment of Fig. 2 in the area between the nozzles 15 of the stripping nozzle device 14 and the lower entrance side of the cooling area 16. The y-line described is in the embodiment of Fig. 6 above the impact line and is, for example, at least 20 cm away from the center line ML of the virtual cylinder body vZK, which is marked on the flat steel product 100 by a small white circle.

In Fig. 6 A further embodiment of a device 150 is shown, whereby an approach for directly measuring the absolute local air humidity is also used here. The structure of the device 150 is similar to that in Fig. 2 Device 150 shown, therefore the description of the Fig. 2 referred. Of the bath 11, only the area of the exit side A 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). Each of the nozzles 15 is, as indicated schematically, fed with the inert gas G by means of pumps P _g . The two pumps P _g are connected to the controller 250 in terms of control technology (or regulation technology) and the controller 250 can, for example, control the gas flow rate D per band side. The corresponding connecting lines or lines are in Fig. 6 designated V5, V6, V7 and V8. An air supply unit with blower(s) and control valves is referred to here as pump P _g .

Preferably, all embodiments of the device 150 include a control of the flow rate D of the gas G (called automatic circulation control), which is designed so that despite a change in the other adjustable parameters, a layer 10 with a substantially constant target thickness is always produced. For this purpose, the regulation includes at least one Sensor (not shown) that measures the actual thickness of the layer 10 after blowing off. If the actual thickness is smaller than the target thickness, the control reduces the flow rate D and vice versa.

Each of the nozzles 15 can be moved parallel to the z-axis by a motor or actuator M. The motors or actuators M are connected to the controller 250 as shown. The corresponding connecting lines or lines are in Fig. 6 labeled V9, V10, V11 and V12. There are sensors (not shown) to be able to control the nozzle distance Z. This allows the nozzle distance Z to be adjusted and/or controlled via the control 250. The control of the nozzle distance Z can be laser-assisted in all embodiments.

In all embodiments, the controller 250 can also be connected to an inductive heater 30 or to an electrical resistance heater of the bath 11 in order to adjust the bath temperature TB. For an inductive heater whose coil is 30 in Fig. 6 is indicated, the controller 250 can set the operating frequency for driving the coil(s) 30 via a frequency generator FG. Therefore, the frequency generator FG is connected to the controller 250 in terms of control technology, as indicated. The corresponding connecting lines or lines are in Fig. 6 designated V13 and V14.

It's also in Fig. 6 a virtual cylinder body vZK is indicated, the center line ML of which cuts through the drawing plane slightly above the nozzles 15. In order not to overload the drawing, the location of the center line ML is shown by a small white circle on the strip-shaped flat steel product 100. Since the overall constellation is limited on the bottom by the bath 11 and on the top by the optional cooling area 16, the virtual cylinder body vZK is a virtual cylinder body vZK cut at the top and bottom.

Here too, for example, two moisture sensors 51 (at least one per hinge side) are used in order to be able to determine the absolute local humidity. The humidity sensors 51 are with the Control 250 connected. The corresponding connecting lines or lines are in Fig. 6 labeled V1, V2, V3 and V4.

In such a device 150, as shown in Fig. 6 is shown as an example and schematically, the method can be carried out particularly advantageously and with reproducible results.

Fig. 9 shows exemplary steps of the method described here in the form of a flowchart. 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). The device can be set up, for example, based on a target specification of the layer 10 to be applied.

Before, during or after setting up S1, the current absolute local humidity f is measured (directly or indirectly) (step S2). Then, using one of the inequalities or using a “lookup” table, it is determined whether the condition f > AWZ is met (step S3). If f should be greater than AWZ (YES in the flowchart), the method for applying a layer 10 can start (step S4). If the condition f > AWZ is not met (NO in the flowchart), the method branches back to step S1. After branching back, adjustments may be made to the setup of the components and elements of the device 150, aiming to reduce AWZ to satisfy the condition f > AWZ. When adjusting, care is taken to ensure that the target specification of the layer 10 to be applied continues to be met.

In a similar manner, checking the condition f > AWZ can be repeated from time to time during the application of the layer 10 in order to be able to react to changing absolute local air humidity f . If f has been reduced, it is checked again (as in step S3) whether the condition f > AWZ is still met. If yes, then the application of layer 10 continues. If not, then (analogous to step S1) adjustments can be made to the setup of the components and elements of the device 150 the aim is that the condition f > AWZ is or remains fulfilled.

• durch ein Erhöhen der Badtemperatur TB ein deutliches Verkleinern der Abstreifwirkzahl AWZ erzielt wird, und/oder
• durch ein Verkleinern der Dicke d des Düsenlippenspalts 17 die Abstreifwirkzahl AWZ verkleinert werden kann, und/oder
• durch ein Verkleinern des Abstandes Z die Abstreifwirkzahl AWZ verkleinert werden kann.

A corresponding controller 250 can be designed or programmed in all embodiments so that

• By increasing the bath temperature TB, a significant reduction in the stripping effectiveness AWZ is achieved, and / or
• by reducing the thickness d of the nozzle lip gap 17, the stripping effectiveness AWZ can be reduced, and/or
• By reducing the distance Z, the stripping effectiveness AWZ can be reduced.

A corresponding controller 250 can be designed or programmed in all embodiments in such a way that it is taken into account that a change in the thickness d and/or the distance Z has little or no influence on the stripping effectiveness AWZ if the ratio Z/d is small .

If f drops significantly and no meaningful adjustment is possible within the target specification, the process can be interrupted. As part of such an interruption, the width d of the nozzle lip gap 17 can then be adjusted manually, for example (which is not possible automatically in most devices 150). Reference symbol: (Protective) layer / (protective) coating 10 Zinc alloy molten pool/bath 11 trunk 12 role 13 Nozzles/wiper nozzle device 14 Gas nozzle / scraper nozzle 15 Cooling area 16 (Gas) nozzle lip gap 17 Inductive heating device 30 Humidity sensor 51 Steel flat product / steel strips / steel sheets / strip 100 Coated steel flat product / steel strip / steel sheet 100, 10 contraption 150 steering 250 Home page A Stripping effectiveness factor EEZ half-width 2 B Thickness of the nozzle lip gap d effective gas flow rate per belt side across the bandwidth D Nozzle level / wiper level EN Entrance page E absolute humidity f Frequency generator FG gas G Straight Ge Proportionality factor k Curve K1 Distance between the two shear force maxima / Motor/actuator M Centerline ML Pressure P Pressure history P(x) pump _Pg Maximum pressure Ps Distance/radius ra relative humidity in % r steps S1, S2, ... temperature T Bath temperature TB reduced bath temperature TBred Air temperature in °C TL shear force τ Maximum shear force occurring Tmax Belt speed v virtual cylinder height vZH virtual cylinder body vZK Connections/lines V1, V2, V3, ... Bandwidth w axis x axis y axis e.g Nozzle spacing Z

Claims (22)

Method for applying a layer (10) with a target thickness to at least one side of a flat steel product (100) by moving the flat steel product (100) through a zinc alloy melt pool (11) and gas (G) on its output side (A) through a nozzle lip gap (17) at least one gas nozzle (15) emerges in the direction of the flat steel product (100) in order to blow off the layer (10) to the desired thickness, the zinc alloy of the zinc alloy melt pool (11) having the following composition: - an aluminum content which is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight, - a magnesium content which is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight, and - the remainder of the zinc alloy melt pool (11) is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1%, and unavoidable impurities, characterized in that at least one of the following adjustable parameters is adjusted as follows: - Increasing the bath temperature (TB) of the alloy melt pool (11) if the current absolute local humidity (f) is reduced and vice versa, and/or - Reducing the thickness (d) of the nozzle lip gap (17) if the current absolute local humidity (f) is reduced and vice versa, 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 humidity (f) is reduced and vice versa, wherein the flow rate (D) of the gas (G) is additionally adjusted in order to keep the target thickness of the layer (10) to be applied essentially constant. Method according to claim 1, characterized in that the layer (10) to be applied fulfills the following requirement(s): - Target surface area of the layer (10) per band side, which is in the range 20 to 200 g/m ² , preferably in the range 30 to 100 g/m ² , and/or - Target thickness of the layer (10) per band side, which is in the range 3 to 30 µm, preferably in the range 4.5 to 15 µm Method according to claim 1 or 2, characterized in that the adjustment of said parameters is carried out for the following range in order to prevent marbling and/or toothpick defects on the layer (10): - absolute local air humidity (f) in the range from 1 g/m ³ to 300 g/m ³ , preferably in the range from 1.08 g/m ³ to 51 g/m ³ . Method according to one of claims 1 to 3, characterized in that a connection between the current absolute local air humidity (f) and the adjustable parameters is specified on the basis of a stripping effectiveness number (AWZ), the following condition being met to avoid marbling and/or toothpick errors must be fulfilled: f > AWZ. Method according to claim 4, characterized in that the stripping effectiveness number (AWZ) is defined as follows: $$\mathit{EEZ}=24.61\cdot \frac{D^2\cdot k}{w^2\cdot d^2\cdot b}+3639\cdot \frac{b}{v}-45.42$$

where: d is the thickness of the nozzle lip gap in mm D is the effective flow rate (quantity) D of the gas G per band side in Nm ³ /h over the band width (w). k is a unitless proportionality factor w is the width of the steel specialist product (100) in mm 2b is the half-width of the pressure distribution of the gas G on the strip in mm v is the belt speed in m/min. Method according to claim 4, characterized in that the stripping effectiveness number (AWZ) is defined as follows: $$\mathit{EEZ}=\frac{1}{14}\cdot \left(\frac{D^2\cdot k\cdot e^{-0.5}\cdot \mathrm{1,251}\cdot {10}^4}{w^2\cdot d^2\cdot 25.92}\cdot \sqrt{\frac{-2\cdot \ln \left(0.5\right)}{b^2}}+\frac{6\cdot {10}^4}{v}\cdot \sqrt{\frac{-b^2}{2\cdot \ln \left(0.5\right)}}-636\right)$$

where: d is the thickness of the nozzle lip gap in mm D is the effective flow rate (quantity) D of the gas G per band side in Nm ³ /h over the band width (w). k is a unitless proportionality factor w is the width of the steel specialist product 100 in mm 2b is the half-width of the pressure distribution of the gas G on the strip in mm v is the belt speed in m/min. Method according to claim 5 or 6, characterized in that when determining the values for the half width at half maximum (b) and the proportionality factor (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17) the following Definitions apply: $$\frac{\mathrm{e.g}}{d}<5.2\to b=1.9\cdot \frac{d}{2}\mathit{and}k=1$$

$$\begin{array}{l}5.2\le \frac{Z}{d}<10\\ \to b=\left[-{\left(\frac{Z}{d}\right)}^4\cdot 3.22\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot 9.78\cdot {10}^{-3}-{\left(\frac{Z}{d}\right)}^2\cdot 8.39\cdot {10}^{-2}+\left(\frac{Z}{d}\right)\cdot 2.72\cdot {10}^{-1}+1.62\right]\cdot \frac{d}{2}\\ \to k=-{\left(\frac{Z}{d}\right)}^4\cdot 6.05\cdot {10}^{-4}+{\left(\frac{Z}{d}\right)}^3\cdot 2.2\cdot {10}^{-2}-{\left(\frac{Z}{d}\right)}^2\cdot 2.89\cdot {10}^{-1}+\left(\frac{Z}{d}\right)\cdot 1.55-1.9\end{array}$$

$$\frac{Z}{d}\ge 10\to b=0.125\cdot Z\mathit{and}k=6.5\cdot \frac{d}{Z}$$

Method according to claim 5 or 6, characterized in that when determining the values for the half width at half maximum (b) and the proportionality factor (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap (17) the following simplified definitions apply: $$\frac{Z}{d}<7.6\to b=1.9\cdot \frac{d}{2}\mathit{and}k=1$$

$$\frac{Z}{d}\ge 7.6\to b=0.125\cdot Z\mathit{and}k=6.5\cdot \frac{d}{Z}$$

Method according to one of claims 1 to 8, characterized in that - The thickness (d) of the nozzle lip gap (17) in a 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 - the flow rate (D) is in the range from 200 to 8000 Nm ³ per hour, and/or - the distance (Z) is in a range between 2 and 15 mm, preferably between 3 and 12 mm, and/or - The belt speed (v) is in a range between 50 and 200 m/min, preferably between 70 and 150 m/min. Method according to one of claims 1 to 9, characterized in that the bath temperature TB of the alloy melt pool (11) is in the range 400 <TB <480 degrees Celsius, preferably in the range 409 <TB <473 degrees Celsius, and particularly preferably in the range 420 <TB < 460 degrees Celsius. Method according to one of claims 1 to 10, characterized in that the absolute local air humidity (f) applies in two virtual cylinder volume segments, which are defined on the one hand by a virtual cylinder surface which concentrically or almost concentrically encloses the at least one gas nozzle (15) and on the other hand by two on both sides of the flat steel product, planes running parallel to the flat steel product (100) are delimited at a distance (s) from the flat steel product (100), the cylinder volume segments together having a volume in a range of 1m ³ to 10 m ³ and preferably a volume of less than 2 m ³ , with the absolute local humidity (f) being measured directly or indirectly. Method according to claim 11, characterized in that the absolute local air humidity (f) is measured permanently or from time to time and at a low absolute local humidity (f) the process is interrupted to adjust one or more of the adjustable parameters. Method according to one of claims 1 to 12, characterized in that the application of the layer (10) is controlled by means of a controller (250) in such a way that when the absolute local humidity (f) changes, one or more of the adjustable parameters depend on the current absolute local air humidity (f) can be adjusted automatically and/or manually. Device (150) for applying a layer (10) to a flat steel product (100), comprising - a zinc alloy melt pool (11) with an input side (E), an output side (A) and a deflection (13) to move the flat steel product (100) from the input side (E) through the zinc at a belt speed (v). to guide the alloy melt pool (11) through to the output side (A), - a stripping nozzle device (14), which comprises at least one nozzle lip gap (17), and which is arranged in the area of the output side (A) in such a way that the still liquid layer (10) on the flat steel product (100) can be blown off with gas (G), which emerges through the nozzle lip gap (17) in order to blow off the layer (10) to a target thickness, wherein the zinc alloy of the zinc alloy melt pool (11) has the following composition: - an aluminum content which is in the range between 1.0 and 3.5 percent by weight and preferably in the range between 1.3 and 2.8 percent by weight, - a magnesium content which is in the range between 1.0 and 3.0 percent by weight and preferably in the range between 1.2 and 2.2 percent by weight, and - the remainder of the zinc alloy melt pool (11) is zinc and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, Zr, Sr, La, Ce or Bi, the weight-based content of each additional element in the metallic coating is less than 0.1%, and unavoidable impurities, characterized in that the device (150) is set up or designed to carry out at least one of the following adjustments manually or automatically: - Increasing the bath temperature (TB) of the alloy melt pool (11) if the current absolute local humidity (f) is reduced and vice versa, and/or - Reducing the thickness (d) of the nozzle lip gap (17) if the current absolute local humidity (f) is reduced and vice versa, 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 humidity (f) is reduced and vice versa, wherein, in addition, the flow rate (D) of the gas (G) is automatically adjusted in order to keep the target thickness of the layer (10) to be applied essentially constant. Device (150) according to claim 14, characterized in that the layer (10) to be applied fulfills the following requirement: - Target surface area of the layer (10) per band side, which is in the range 20 to 200 g/m ² , preferably in the range 30 to 100 g/m ² , and/or - Target thickness of the layer (10) per band side, which is in the range 3 to 30 µm, preferably in the range 4.5 to 15 µm. Device (150) according to claim 14 or 15, characterized in that the adjustment of the adjustable parameters can be carried out for the following range in order to prevent marbling and / or toothpick defects on the layer (10): - absolute local air humidity (f) in the range from 1 g/m ³ to 300 g/m ³ , preferably in the range from 1.08 g/m ³ to 51 g/m ³ . Device (150) according to one of claims 14 to 16, characterized in that it additionally comprises: - at least one moisture sensor (51), which is arranged in the local area of the wiper nozzle device (14), - a controller (250), which can be connected to the at least one moisture sensor (51) in order to continuously or from time to time receive a measured value or signal from which a physical quantity is obtained can be derived, which is directly related to the absolute local air humidity (f) in a local nozzle environment, wherein the controller (250) is designed to carry out or trigger the implementation of at least one of the following steps: - Changing the bath temperature (TB) of the alloy melt pool (11), and/or - Changing the thickness (d) of the nozzle lip gap (17), and/or - changing the distance (Z) between the nozzle lip gap (17) and the side of the flat steel product (100), - Adjusting the flow rate (D) of the gas (G) in order to keep the target thickness of the layer (10) to be applied essentially constant. Device (150) according to one of claims 14 to 16 , characterized in that it comprises a controller (250) which is designed to adapt one or more of the adjustable parameters depending on the current absolute local air humidity (f) or to trigger their adaptation. Device (150) according to one of claims 14 to 16 , characterized in that it comprises a control (250) which is designed to determine a wiping effectiveness number (AWZ), the wiping effectiveness number (AWZ) having a relationship between the current absolute local air humidity ( f) and the adjustable parameters and where the following condition must be fulfilled to avoid marble formation: f > AWZ. Device according to claim 18 or 19, characterized in that it comprises a motor or actuator (M) for each gas nozzle (15), which is connected to the controller (250) in terms of control technology in such a way that the controller (250) responds to a changing absolute local Humidity (f) reacts with a reduction in the distance (Z) if the current absolute local humidity (f) is reduced and vice versa. Device according to claim 18 or 19, characterized in that it comprises a pump device (P _g ) and a control loop for each gas nozzle (15). Flow rate (D) of the gas (G) is adjusted automatically so that the target thickness of the layer (10) remains essentially constant. Device according to claim 18 or 19, characterized in that it comprises a bath heater (30) which is connected to the controller (250) in terms of control technology in such a way that the controller (250) with an adjustment in the event of a changing absolute local air humidity (f). the bath temperature TB reacts, the bath temperature TB being in the range 400 <TB <480 degrees Celsius, preferably in the range 409 <TB <473 degrees Celsius, and particularly preferably in the range 420 <TB <460 degrees Celsius.

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