Method for operating a coating device for coating a metal strip, and coating device

Abstract

A method for operating a coating device for coating a metal strip. The corresponding coating device has an electromagnetic strip-stabilizing device having a plurality of electromagnetic actuators or coils for applying forces to the metal strip. In order to ensure that the strip-stabilizing device is operated only within the operating limits thereof, the magnitudes of the set currents for the actuators or the coils are compared with a specified current threshold value or the forces applied to the metal strip by the actuators are compared with a specified force threshold value and the correction roller is moved into such an adjustment position that the magnitudes of the set currents are below the current threshold value or the magnitudes of the forces are below the force threshold value.

Claims

1. A method for operating a coating device for coating a metal strip, wherein the coating device has a container for a liquid coating medium, a pot roller arranged in the container for deflecting the metal strip, a correction roller for adjustment against the metal strip after passing the pot roller, a stripping device having nozzles for blowing excess coating medium off the metal strip after the metal strip exits from the container, distance sensors for measuring the actual position of the metal strip after leaving the container and a strip stabilizing device arranged downstream of the stripping device in a transport direction of the metal strip, having a plurality of electromagnetic actuators for applying forces to the metal strip, wherein the method comprises the steps of: controlling a position of the metal strip to a predefined target position in a slot of the stripping device by way of correspondingly suitable setting of currents of the plurality of electromagnetic actuators; predefining a force threshold value to represent an operating limit of the strip stabilizing device; comparing magnitudes of the forces exerted on the metal strip by the plurality of electromagnetic actuators with the predefined force threshold value to prevent the forces exerted on the metal strip from exceeding the operating limit of the strip stabilizing device; moving the correction roller to an adjustment position so that the magnitudes of the forces lie below the force threshold value; and converting the actual position of the metal strip measured by the distance sensors, which are arranged between the stripping device and the strip stabilizing device and/or within the strip stabilizing device, to the actual position of the metal strip within the slot of the stripping device.

2. The method according to claim 1, wherein the step of controlling the position of the metal strip includes: measuring the actual position of the metal strip using the distance sensors, comparing the actual position of the metal strip with the predefined target position of the metal strip for determining a possible position control deviation as a difference between the target position and the actual position; and setting currents of the plurality of electromagnetic actuators so that the position control deviation comes as close as possible to zero and therefore the target position is as far as possible achieved.

3. The method according to claim 1, further including storing the set currents of the plurality of electromagnetic actuators in the adjustment position of the correction roller, the forces on the metal strip in the adjustment position of the correction roller and/or the adjustment position of the correction roller.

4. The method according to claim 3, wherein the storing strep includes classifying in accordance with steel grade of the metal strip, temperature of the coating medium in the container, temperature of the metal strip, thickness of the metal strip, width of the metal strip and/or yield strength of the material of the metal strip.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Appended to the description is a FIGURE which illustrates the structure of the coating device according to the invention. The invention will be described in detail below with reference to this FIGURE in the form of exemplary embodiments.

DETAILED DESCRIPTION OF THE INVENTION

(2) The FIGURE shows a coating device 100 for coating a metal strip 200 with an initially still liquid coating medium 300. The coating device 100 can be, for example, a hot-dip galvanizing device for coating the metal strip 200 with zinc. The coating device 100 has a container 110 which, during operation, is filled with the liquid coating medium 300. Arranged in the container 110 is a pot roller 120, i.e. a deflection roller, for deflecting the metal strip 200 into a typically vertical exit direction. The transport direction of the metal strip is designated by the designation R. Following its exit from the container 110, the metal strip 200 with the adhering initially still liquid coating medium passes through a stripping device 140 having nozzles 142 for blowing excess coating medium off the metal strip. To stabilize the metal strip, the metal strip passes through an electromagnetic strip stabilizing device 160 having a plurality of electromagnetic actuators 162, typically coils. The coils are arranged on both sides of the metal strip to apply forces to the metal strip 200. In the FIGURE, by way of example the strip stabilizing device 160 is arranged downstream of the stripping device 140 in the transport direction R of the metal strip 200. The coating device 100 also has distance sensors 150 for the direct or indirect measurement of the actual position of the metal strip 200 within the stripping device 140. A control device 170 is provided to receive the position signals generated by the distance sensors 150, which represent the position of the metal strip at the location of the measurement, and the currents of the coils 162 within the strip stabilizing device 160, measured with the aid of an ammeter 180. The control system 170 is also designed to emit output signals to the strip stabilizing device 160 for the individual adjustment of the currents of the coils, and to emit an output signal to an actuator 132 to adjust or move the correction roller 130.

(3) According to the invention, the said coating device 100 is operated as follows:

(4) Firstly, the actual position of the metal strip 200 in the slot of the stripping device 140 is measured directly or indirectly with the aid of the distance sensors 150. The term “direct measurement” assumes that the distance sensors 150 are actually arranged within the stripping device 140 and monitor the slot there. Typically, the measurement of the actual position of the metal strip in the slot of the stripping device 140 is carried out indirectly, however, in that the actual position of the metal strip 200 is measured outside the stripping device 140 with the aid of the distance sensors and then, with the aid of a conversion device 152, is converted to the actual position within the stripping device 140. If only coarse measurement of the actual position of the metal strip in the slot of the stripping device 140 is required, and in particular if the distance sensors 150 are not arranged within the stripping device 140 but very closely adjacent to the latter, it is also possible to dispense with the aforesaid conversion device.

(5) The method according to the invention then further provides for the measured actual position of the metal strip to be compared with a predefined target position in the slot of the stripping device 140 for the purpose of determining a possible position control deviation. The metal strip is then positioned within the slot of the strip stabilizing device by adjusting suitable currents of the actuators such that the position control deviation comes as close as possible to zero. It may be necessary for considerable forces to be applied to the metal strip, which require correspondingly high currents in the actuators or coils 162 of the strip stabilizing device 160.

(6) In order to prevent these forces and currents exceeding the operating limits of the strip stabilizing device 160, the invention provides for the magnitudes of the set currents to be compared with a predefined current threshold value, or for the forces exerted on the metal strip by the actuators 162 to be compared with a predefined force threshold value, and for the correction roller 130 to be moved with the aid of the control system 170 to such an adjustment position that the magnitudes of the set currents lie below the current threshold value or the magnitudes of the forces lie below the force threshold value. In this way, it is ensured that the operating limits of the strip stabilizing device 160 are not exceeded.

LIST OF DESIGNATIONS

(7) 100 Coating device 110 Container 120 Pot roller 130 Correction roller 132 Actuator for correction roller 140 Stripping device 142 Nozzle 150 Distance sensors 152 Conversion device 160 Strip stabilizing device 162 Actuators or coils of the strip stabilizing device 170 Control system 180 Current measuring device or ammeter 200 Metal strip 300 Coating medium R Transport direction of the metal strip