Method and Device for the Hot Dip Coating of a Metal Strip
The invention relates to a method for the hot dip coating of a metal strip ( 1 ), in particular a steel strip, according to which the metal strip ( 1 ) is fed vertically through a container ( 3 ) that holds the molten coating metal ( 2 ) and a guide channel ( 4 ) that is connected upstream. According to the invention, to retain the coating metal ( 2 ) in the container ( 3 ) in the vicinity of the guide channel ( 4 ), an electromagnetic field is generated by means of at least two inductors ( 5 ) that are situated on either side of the metal strip ( 1 ) and to stabilise the metal strip ( 1 ) in a central position in the guide channel ( 4 ), the electromagnetic excitation of the inductors ( 5 ) is modified and/or an electromagnetic field that overlaps the electromagnetic field of the inductors ( 5 ) is generated by means of at least two correction coils ( 6 ) that are situated on either side of the metal strip ( 1 ). The aim of the invention is to control the centring of the metal strip in a manner that is not susceptible to interference. To achieve this, the stabilisation of the central position of the metal strip ( 1 ) in the guide channel ( 4 ) takes place in a closed-loop control circuit by the sequence of the following steps: a) measurement of the force (F H ) that acts in a horizontal direction and that the metal strip ( 1 ) exerts on a force measuring element ( 7 ) when it leaves the central position; b) the induction current (I I ) in the inductors ( 5 ) and/or on the induction current (I I ) in the correction coils ( 6 ) is influenced in accordance with the measured force (F H ), in order to hold the metal strip ( 1 ) in a central position in the guide channel ( 4 ). The invention also relates to a device for the hot dip coating of a metal strip.
1 . A method for hot dip coating a metal strip ( 1 ), especially a steel strip, in which the metal strip ( 1 ) is passed vertically through a tank ( 3 ) that contains the molten coating metal ( 2 ) and through a guide channel ( 4 ) upstream of the tank ( 3 ), where an electromagnetic field is generated in the area of the guide channel ( 4 ) by means of at least two inductors ( 5 ) installed on both sides of the metal strip ( 1 ) in order to keep the coating metal ( 2 ) in the tank ( 3 ), and where, in order to stabilize the metal strip ( 1 ) in a center position in the guide channel ( 4 ), the electromagnetic excitation of the inductors ( 5 ) is varied and/or an electromagnetic field superimposed on the electromagnetic field of the inductors ( 5 ) is generated by means of at least two correction coils ( 6 ) installed on both sides of the metal strip ( 1 ), wherein the center position of the metal strip ( 1 ) in the guide channel ( 4 ) is stabilized by the following sequence of steps in a closed-loop control system:
(a) measurement of the horizontally acting force (F H ) that the metal strip ( 1 ) exerts on a force-measuring element ( 7 ) when it deviates from the center position;
(b) action to control the induction current (I I ) in the inductors ( 5 ) and/or the induction current (I K ) in the correction coils. ( 6 ) as a function of the measured force (F H ) to keep the metal strip ( 1 ) in the center position in the guide channel ( 4 ).
2 . A method in accordance with claim 1 , wherein the horizontally acting force (F H ) is measured below the guide channel ( 4 ).
3 . A method in accordance with claim 1 , wherein the electromagnetic field is a polyphase traveling field generated by applying an alternating current with a frequency of 2 Hz to 2 kHz.
4 . A method in accordance with claim 1 , wherein the electromagnetic field is a single-phase alternating field generated by applying an alternating current with a frequency of 2 kHz to 10 kHz.
5 . A device for hot dip coating a metal strip ( 1 ), especially a steel strip, in which the metal strip ( 1 ) is passed vertically through a tank ( 3 ) that contains the molten coating metal ( 2 ) and through a guide channel ( 4 ) upstream of the tank ( 3 ), with at least two inductors ( 5 , 6 ) installed on both sides of the metal strip ( 1 ) in the area of the guide channel ( 4 ) for generating an electromagnetic field for retaining the coating metal ( 2 ) in the tank ( 3 ), wherein at least one force-measuring element ( 7 ) for measuring the horizontally acting force (F H ) that the metal strip ( 1 ) exerts on a force-measuring element ( 7 ) when it deviates from the center position in the guide channel ( 4 ) and by an automatic control system ( 8 ) that is suitable for controlling the induction current (I I , I K ) in the one or more inductors ( 5 , 6 ) as a function of the measured force (F H ).
6 . A device in accordance with claim 5 , wherein, besides the inductors ( 5 ), two correction coils ( 6 ) are installed on both sides of the metal strip ( 1 ), where the automatic control system ( 8 ) is suitable for controlling their induction current (I K ).
7 . A device in accordance with claim 5 , wherein the force-measuring element ( 7 ) is designed as a strip guide roller equipped with a load cell ( 9 ).
8 . A device in accordance with claim 7 , wherein the load cell ( 9 ) is designed as a strain gauge.
9 . A device in accordance with claim 5 , wherein the force-measuring element ( 7 ) is installed below the guide channel ( 4 ).
10 . A device in accordance with claim 5 , wherein a force-measuring element ( 7 ) is installed on each side of the metal strip ( 1 ).