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

Abstract

A device for applying a layer (to a front and/or rear side of a flat steel product includes a zinc alloy melt bath (11) (ZnAl; ZnAlMg) with an input side and an exit side, a stripping nozzle device with at least one gas nozzle for blowing off the front or rear side of the flat steel product with gas, the stripping nozzle device being arranged in the area of the exit side, and a water vapor device which is configured to emit gaseous water vapor and to provide a controlled water vapor atmosphere in the close range of the front and/or rear side of the flat steel product. The controlled water vapor atmosphere has an absolute local humidity which is greater than 1 g/m3 and less than 300 g/m3, the absolute local humidity preferably being in the range of 2.71 g/m3 to 50 g/m3.

1 . Device ( 150 ) for applying a layer ( 10 ) to a front and/or rear side of a flat steel product ( 100 ), comprising:
 a zinc alloy melt bath ( 11 ) (ZnAl; ZnAlMg) with an input side (E) and an exit side (A),   a stripping nozzle device ( 14 ) with at least one gas nozzle ( 15 ) for blowing off the front or rear side of the flat steel product ( 100 ) with gas (G), the stripping nozzle device ( 14 ) being arranged in the area of the exit side (A), and   
       a water vapor device ( 50 ) which is configured to emit gaseous water vapor and to provide a controlled water vapor atmosphere in the close range (NB) of the front and/or rear side of the flat steel product ( 100 ), the controlled water vapor atmosphere having an absolute local humidity (f) which is greater than 1 g/m 3  and less than 300 g/m 3 , the absolute local humidity (f) preferably being in the range of 2.71 g/m 3  to 50 g/m 3 . 
     
     
         2 . Device ( 150 ) according to  claim 1 , characterized in that, for applying the layer ( 10 ), system parameters and method parameters of the device ( 150 ) are set such that the layer ( 10 ) can be blown off with the stripping nozzle device ( 14 ) in accordance with a predetermined specification, the system parameters and method parameters defining a stripping efficiency (AWZ) which is essentially constant during the application of the layer ( 10 ). 
     
     
         3 . Device ( 150 ) according to  claim 2 , characterized in that the stripping efficiency (AWZ) is defined either as follows: 
       
         
           
             
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       or is defined as follows: 
       
         
           
             
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       where applies:
 d is the thickness (d) of a nozzle lip gap ( 17 ), in mm, of the at least one gas nozzle ( 15 ) of the stripping nozzle device ( 14 ) 
 D is the effective flow (quantity) (D) of the gas (G) per side of the flat steel product ( 100 ) over the strip width (w) in Nm 3 /h 
 k is a unitless proportionality factor 
 w is the strip width of the flat steel product ( 100 ) in mm 
 2b is the half-width of the pressure distribution of the gas (G) at the flat steel product ( 100 ) in mm 
 v is the strip speed in m/min at which the flat steel product ( 100 ) is moved along the stripping nozzle device ( 14 ) and through the close range (NB). 
 
     
     
         4 . Method according to  claim 1 , characterized in that the following definitions apply to the half half-width (b) and the proportionality factor (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap ( 17 ): 
       
         
           
             
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         5 . Method according to  claim 1 , characterized in that the following simplified definitions apply when determining the values for the half half-width (b) and the proportionality factor (k) using the ratio of the distance (Z) to the thickness (d) of the nozzle lip gap ( 17 ): 
       
         
           
             
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         6 . Device ( 150 ) according to  claim 3 , characterized in that
 the thickness (d) of the nozzle lip gap ( 17 ) is in a range between 0.5 mm and 10 mm, preferably between 0.8 mm and 2.0 mm, and/or   the flow rate (D) is in the range from 200 to 8000 Nm 3  per hour, and/or   the distance (Z) between the nozzle lip gap ( 17 ) and the front or rear side of the flat steel product ( 100 ) is in a range between 2 mm and 15 mm, preferably between 3 mm and 12 mm, and/or   the strip speed (v) is in a range between 50 m/min and 200 m/min, preferably between 70 m/min and 150 m/min, and/or   the close range (NB) has a volume in a range from 1 m 3  to 10 m 3  and preferably a volume of at least 2 m 3 .   
     
     
         7 . Device ( 150 ) according to  claim 1 , characterized in that the absolute local air humidity (f) is valid in a virtual cylinder volume which is limited on the one hand by a virtual cylinder surface and on the other hand by two virtual planes running parallel to the flat steel product ( 100 ) on both sides of the flat steel product ( 100 ), wherein the cylinder volume has a volume in a range from 1 m 3  to 10 m 3  and preferably a volume of at least 2 m 3 , wherein the measurement of the absolute local humidity (f) is carried out directly or indirectly. 
     
     
         8 . Device ( 150 ) according to  claim 2 , characterized in that it comprises a controller ( 250 ) which is adapted to regulate the controlled water vapor atmosphere to adjust the absolute humidity (f) such that the following inequality is satisfied during the application and blow-off of the layer ( 10 ):f>AWZ. 
     
     
         9 . Device ( 150 ) according to  claim 1 , characterized in that the water vapor device ( 50 ) encloses the front and/or rear side of the flat steel product ( 100 ) at least partially with a housing ( 52 ) in order to be able to define the controlled water vapor atmosphere as quasi-static surrounding condition in a close range (NB) inside the housing ( 52 ). 
     
     
         10 . Device ( 150 ) according to  claim 9 , characterized in that the absolute local air humidity (f) in the close range (NB) of the housing ( 52 ) is measurable, the measurement of the absolute local humidity (f) being carried out directly or indirectly. 
     
     
         11 . Device ( 150 ) according to  claim 9 , characterized in that the close range (NB) of the housing ( 52 ) has a volume in a range of 1 m 3  to 10 m 3  and preferably a volume of at least 2 m 3 . 
     
     
         12 . Device ( 150 ) according to  claim 2 , characterized in that the predetermined specification determines the coating of the layer ( 10 ) and/or the target thickness of the layer ( 10 ) and that the layer ( 10 ) to be applied meets the following specification:
 coating of the layer ( 10 ) per side of the flat steel product ( 100 ), which is in the range of 20 g/m 2  to 200 g/m 2 , preferably in the range of 30 g/m 2  to 100 g/m 2 , and/or   target thickness of the layer ( 10 ) per side of the flat steel product ( 100 ), which is in the range of 3 μm to 30 μm, preferably in the range of 4.5 μm to 15 μm.   
     
     
         13 . Device ( 150 ) according to  claim 1 , characterized in that a sufficiently high absolute local air humidity (f) in the close range (NB) is predetermined by the controlled water vapor atmosphere for a given stripping efficiency (AWZ) in order to prevent a marbling and/or the formation of toothpick defects at the layer ( 10 ). 
     
     
         14 . Device ( 150 ) according to  claim 1 , characterized in that
 at least one humidity sensor ( 51 ) is arranged in the close range (NB) of the water vapor device ( 50 ) in order to be able to directly measure the absolute local air humidity (f) in the close range (NB), and/or   at least one humidity sensor ( 56 ) is provided in order to be able to directly measure the absolute local air humidity (f UG ) in the surrounding of the device ( 150 ).   
     
     
         15 . Device ( 150 ) according to  claim 1 , characterized in that it comprises at least one steam generator (DG) to be able to automatically adjust the absolute local air humidity (f) so that the absolute local air humidity (f) is greater than the stripping efficiency (AWZ). 
     
     
         16 . Method for applying a layer ( 10 ) according to a target specification to at least one side of a flat steel product ( 100 ) by moving the flat steel product ( 100 ) through a zinc alloy melt bath ( 11 ) (ZnAl; ZnAlMg) and stripping gas (G) exiting on its exit side (A) through a nozzle lip gap ( 17 ) of at least one gas nozzle ( 15 ) in the direction of the flat steel product ( 100 ) in order to blow off the layer ( 10 ) in accordance with target specification, a stripping efficiency (AWZ) being defined by the following parameters:
 d thickness (d) of the nozzle lip gap ( 17 ) of the gas nozzle ( 15 ) of the stripping nozzle device ( 14 ),   D over the strip width (w) effective flow rate (quantity) (D) of the gas (G) per side of the flat steel product ( 100 ) in Nm 3 /h,   w strip width of the flat steel product ( 100 ) in mm,   2b half-width of the pressure distribution of the gas (G) at the flat steel product ( 100 ) in mm,   v strip speed in m/min, at which the flat steel product ( 100 ) is moved along the stripping nozzle device ( 14 ),   
       wherein the method comprises the following steps:
 determining the absolute local humidity (f) in a controlled water vapor atmosphere in a close range (NB) at the front and/or rear side of the flat steel product ( 100 ) and/or the surrounding air humidity (f UG ) before carrying out the method and/or during carrying out the method, 
 relating the determined humidity (f, f UG ) to the stripping efficiency (AWZ) to determine whether the condition f>AWZ or f UG >AWZ is fulfilled, 
 if the condition is fulfilled, initializing or continuing the method for applying the layer ( 10 ), or if the condition is not fulfilled, increasing the absolute local humidity (f) in the controlled water vapor atmosphere by using a water vapor device ( 50 ) adapted to emit gaseous water vapor so as to achieve the fulfilling of the condition f>AWZ, to then initialize or continue the method for applying the layer. 
 
     
     
         17 . Method according to  claim 16 , characterized in that the stripping efficiency (AWZ) is defined either as follows: 
       
         
           
             
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       or is defined as follows: 
       
         
           
             
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       wherein applies:
 d is the thickness (d) of a nozzle lip gap ( 17 ), in mm, of a gas nozzle ( 15 ) of the stripping nozzle device ( 14 ) 
 D is the effective flow rate (quantity) (D) of the gas (G) per side of the flat steel product ( 100 ) over the strip width (w) in Nm 3 /h 
 k is a unitless proportionality factor 
 w is the strip width of the flat steel product ( 100 ) in mm 
 2b is the half-width of the pressure distribution of the gas (G) at the flat steel product ( 100 ) in mm 
 v is the strip speed in m/min, at which the flat steel product ( 100 ) is moved along the stripping nozzle device ( 14 ) and through the close range (NB). 
 
     
     
         18 . Method according to  claim 16 , characterized in that the absolute local humidity (f) of the controlled water vapor atmosphere is determined at the front and/or rear side of the flat steel product ( 100 ) at a distance of more than 20 cm from the front and/or rear side. 
     
     
         19 . Method according to  claim 16 , characterized in that a controller ( 250 ) is used which is configured to regulate the controlled water vapor atmosphere in order to adjust the absolute humidity (f) such that the condition is fulfilled during the application and blowing off of the layer ( 10 ): f>AWZ.