Method and Device For Hot-Dip Coating a Metal Strip
The invention relates to a method for hot-dip coating a metal strip ( 1 ), particularly a steel strip, in which the metal strip ( 1 ) is fed to a receptacle ( 5 ) accommodating the melted coating metal ( 4 ) through a hole ( 6 ) in the bottom area of the receptacle ( 5 ) after passing through a furnace ( 2 ) and a roll chamber ( 3 ) that adjoins the furnace ( 2 ) in the direction of travel (F) of the metal strip ( 1 ). An electromagnetic field is generated in the bottom area of the receptacle ( 5 ) so as to retain the coating metal ( 4 ) in the receptacle ( 5 ). In order to obtain more advantageous operating conditions especially in case the performance of the hot-dip coating system drops, different gas atmospheres are maintained in at least two separate spaces ( 7, 8 ) of the roll chamber ( 3 ). The invention further relates to a hot-dip coating device.
1 . A method for hot dip coating a metal strip ( 1 ), especially a steel strip, in which the metal strip ( 1 ) is fed through a furnace ( 2 ) and a roller chamber ( 3 ), which follows the furnace ( 2 ) in the direction of conveyance (F) of the metal strip ( 1 ), and into a tank ( 5 ) that holds the molten coating metal ( 4 ) through an opening ( 6 ) in the bottom of the tank ( 5 ), where an electromagnetic field is generated near the bottom of the tank ( 5 ) to retain the coating metal ( 4 ) in the tank ( 5 ), wherein different gas atmospheres are maintained in at least two separated spaces ( 7 , 8 ) of the roller chamber ( 3 ).
2 . A method in accordance with claim 1 , wherein the gas atmosphere of a space ( 8 ) of the roller chamber ( 3 ) that is downstream in the direction of conveyance (F) of the metal strip ( 1 ) has a lower hydrogen concentration than the gas atmosphere of another space ( 7 ) of the roller chamber ( 3 ) that is upstream of this space ( 8 ).
3 . A method in accordance with claim 1 or claim 2 , wherein the first space ( 7 ) of the roller chamber ( 3 ) in the direction of conveyance (F) of the metal strip ( 1 ) has a gas atmosphere with a hydrogen concentration of greater than 5 vol. %.
4 . A method in accordance with any of claims 1 to 3 , wherein the last space ( 8 ) of the roller chamber ( 3 ) in the direction of conveyance (F) of the metal strip ( 1 ) has a gas atmosphere with a hydrogen concentration of less than 5 vol. %.
5 . A method in accordance with any of claims 1 to 4 , wherein, besides hydrogen, the gas atmospheres in the spaces ( 7 , 8 ) of the roller chamber ( 3 ) contain essentially only nitrogen.
6 . A method in accordance with any of claims 1 to 5 , wherein the desired compositions of the gas atmospheres in the spaces ( 7 , 8 ) of the roller chamber ( 3 ) are maintained by a closed-loop control system.
7 . A device for hot dip coating a metal strip ( 1 ), especially a steel strip, with a furnace ( 2 ), a roller chamber ( 3 ) downstream of the furnace ( 2 ) in the direction of conveyance (F) of the metal strip ( 1 ), and a tank ( 5 ) for holding the molten coating metal ( 4 ), where the bottom of the tank ( 5 ) has an opening ( 6 ), through which the metal strip ( 1 ) is fed into the tank ( 5 ), and where an electromagnetic inductor ( 9 ) for retaining the coating metal ( 4 ) in the tank ( 5 ) is located near the bottom of the tank ( 5 ), especially for carrying out the method in accordance with any of claims 1 to 6 , wherein at least one partition ( 10 ) is present in the roller chamber ( 3 ), so that the roller chamber ( 3 ) is divided into at least two spaces ( 7 , 8 ).
8 . A device in accordance with claim 7 , wherein each space ( 7 , 8 ) of the roller chamber ( 3 ) has at least one gas supply line ( 11 , 12 ), through which gas of a well-defined type and/or composition can be introduced into the space ( 7 , 8 ).
9 . A device in accordance with claim 7 or claim 8 , wherein each space ( 7 , 8 ) of the roller chamber ( 3 ) has at least one gas sensor ( 13 , 14 ), with which the type and/or composition and/or concentration of a gas in the space ( 7 , 8 ) can be determined.
10 . A device in accordance with any of claims 7 to 9 , wherein an automatic control unit ( 15 ) is present, with which the gas composition and/or the concentration of a gas can be maintained at the desired values in at least one of the spaces ( 7 , 8 ) and preferably in all of the spaces ( 7 , 8 ).
11 . A device in accordance with any of claims 7 to 10 , wherein the roller chamber ( 3 ) is provided with a ceramic inner lining.
12 . A device in accordance with any of claims 7 to 11 , wherein the roller chamber ( 3 ) has a steel housing.
13 . A device in accordance with any of claims 7 to 12 , wherein means are provided for heating the gas introduced into a space ( 7 , 8 ) of the roller chamber ( 3 ) to a desired temperature.
14 . A device in accordance with any of claims 7 to 13 , wherein the roller chamber ( 3 ) has an essentially rectangular cross-sectional contour, and a guide channel ( 16 ) for the metal strip ( 1 ) is joined with the first space ( 7 ) in the direction of conveyance (F) of the metal strip ( 1 ).
15 . A device in accordance with any of claims 7 to 13 , wherein the roller chamber ( 3 ) has an essentially rectangular cross-sectional contour, which forms one of the spaces ( 8 ), which is joined with a second space ( 7 ) that is formed by a guide channel ( 16 ) for the metal strip ( 1 ).