Device and method and device for moisture-controlled blow-off after the application of a layer onto a flat steel product

Abstract

A device and method for applying ZnAlMg layers or ZnAl layers to the front and rear side of a flat steel product, includes moving the flat steel product from an input side to an exit side of a zinc alloy melt bath, providing a dry gas stream, providing a water vapor gas, combining the dry gas stream and the water vapor gas to obtain a stripping gas as a mixture, determining the gas humidity of the stripping gas, discharging the stripping gas through at least one gas nozzle which serves to blow off the front side and through at least one gas nozzle which serves to blow off the back side in order to blow off the front side and rear side of the flat steel product with the stripping gas.

1 . Device ( 150 ) for applying a ZnAlMg layer or a ZnAl layer ( 10 ) to a flat steel product ( 100 ), comprising:
 a zinc alloy melt bath ( 11 ) with an input side (E) and an exit side (A),   a dry gas supply ( 18 ) configured to provide a dry gas stream (TG),   a water vapor device ( 50 ) configured to provide water vapor gas (WG),   means ( 20 ) for determining gas humidity and/or moisture content,   a stripping nozzle device ( 14 ) which is fluidically connected to the gas supply ( 18 ) and to the water vapor device ( 50 ) in order to supply the stripping nozzle device ( 14 ) with a stripping gas (AG) as a mixture of the dry gas stream (TG) and the gaseous water vapor (WG), wherein
 the stripping nozzle device ( 14 ) comprises at least one gas nozzle ( 15 ) for blowing off the front side (V) and at least one gas nozzle ( 15 ) for blowing off the back side (R) of the flat steel product ( 100 ) with the stripping gas (AG), 
 the gas nozzles ( 15 ) are arranged in the region of the exit side (A) of the zinc alloy melt bath ( 11 ), 
 the means ( 20 ) for determining gas humidity and/or moisture content are arranged in or at the stripping nozzle device ( 14 ) in order to determine the gas humidity before or when the stripping gas (AG) exits in direction of the front side (V) or back side (R) of the flat steel product ( 100 ), and wherein at least one of the following two conditions B1, B2 is met: 
 B1: the stripping gas (AG) has a moisture content, or a proportion of the gaseous water vapor gas (WG), that is greater than 200 ppm and less than 43700 ppm, with the moisture content preferably being in the range 500 ppm to 9980 ppm, 
 B2: the stripping gas (AG) has a dew point (TP) that is greater than −39° C. and less than +30° C., with the dew point (TP) preferably being in the range between −29° C. and +7° C. 
   
     
     
         2 . Device ( 150 ) according to  claim 1 , wherein the proportions of the dry gas stream (TG) and the water vapor gas (WG) for mixing the stripping gas (AG) are regulated such that a current dew point (TP) is obtained in the stripping gas (AG) that is lower than the temperature (T AG ) of the stripping gas stream (AG) in order to avoid condensation of water in the stripping nozzle device ( 14 ). 
     
     
         3 . Device ( 150 ) according to  claim 1 , wherein according to the formula TP<T AG −ΔT a temperature difference ΔT is specified that is at least 5° C. and preferably at least 10° C., wherein TP defines the current dew point in the stripping gas stream (AG) and T AG  defines the current temperature of the stripping gas stream (AG). 
     
     
         4 . Device ( 150 ) according to  claim 1 , characterized in that the stripping gas stream (AG) is defined by a dew point (TP) which is greater than −39° C. and less than +30° C., wherein the dew point (TP) is preferably in the parameter range −29° C. to +7° C. if the temperature T AG  of the stripping gas stream (AG) is in the range 10 to 30° C. 
     
     
         5 . Device ( 150 ) according to  claim 1 , comprising:
 a temperature sensor ( 24 ) to measure the current temperature (T AG ) of the stripping gas stream (AG),   a control of the dry gas stream ( 18 ) and/or the water vapor gas stream (WG) to control the proportions of the dry gas stream (TG) and the water vapor gas (WG) for mixing the stripping gas (AG) such that a dew point (TP) results in the stripping gas stream (AG) which is lower by a temperature difference (ΔT) than the current temperature (T AG ) of the stripping gas stream (AG) in order to avoid condensation of water in the stripping nozzle device ( 14 ).   
     
     
         6 . Device ( 150 ) according to  claim 1 , wherein a maximum dew point of +30° C. is specified in the stripping gas stream, even if the temperature of the stripping gas is more than 30° C. 
     
     
         7 . Device ( 150 ) according to  claim 1 , wherein the dry gas (TG) is nitrogen gas which has a volume fraction of the water vapor gas (WG) of less than 5 ppm, or a dew point (TP) of less than −70° C. 
     
     
         8 . Method for applying ZnAlMg layers or ZnAl layers ( 10 ) to the front (V) and rear side (R) of a flat steel product ( 100 ), comprising the steps:
 moving the flat steel product ( 100 ) from an input side (E) to an exit side (A) of a zinc alloy melt bath ( 11 ),   providing a dry gas stream (TG),   providing a water vapor gas (WG),   combining the dry gas stream (TG) and the water vapor gas (WG) to obtain a stripping gas (AG) as a mixture,   determining the gas humidity of the stripping gas (AG),   discharging the stripping gas (AG) through at least one gas nozzle ( 15 ) which serves to blow off the front side (V) and through at least one gas nozzle ( 15 ) which serves to blow off the back side (R) in order to blow off the front side (V) and rear side (R) of the steel flat product ( 100 ) with the stripping gas (AG),
 wherein a stripping gas stream (AG) is discharged which satisfies at least one of the following two conditions B1, B2:
 B1: the stripping gas (AG) has a moisture content, or a proportion of the gaseous water vapor gas (WG), which is greater than 200 ppm and less than 43700 ppm, wherein the moisture content is preferably in the range 500 ppm to 9980 ppm, 
 B2: the stripping gas (AG) has a dew point (TP) which is greater than −39° C. and less than +30° C., wherein the dew point (TP) is preferably in the range between −29° C. and +7° C. 
 
   
     
     
         9 . Method according to  claim 8 , wherein the proportions of the dry gas stream (TG) and the water vapor gas (WG) in the stripping gas (AG) are regulated such that a current dew point (TP) results in the stripping gas (AG) that is lower than the temperature (T AG ) of the stripping gas stream (AG) in order to avoid condensation of water in the stripping nozzle device ( 14 ). 
     
     
         10 . Method according to  claim 8 , characterized in that the moisture content of the stripping gas stream (AG) is defined by a dew point (TP) that is greater than −39° C. and less than +30° C., and wherein the dew point (TP) is preferably in the range −29° C. to +7° C. if the temperature T AG  of the stripping gas stream (AG) is in the range 10 to 30° C. 
     
     
         11 . Method according to  claim 8 , characterized in that an admixture of the gaseous water vapor gas (WG) is only carried out if in the surrounding or in the close range of the exit side (A) of the zinc alloy melt bath ( 11 ) there is an absolute surrounding air humidity (f UG ) which is lower than a predetermined limit value.