Method and coating device for coating a metal strip

Abstract

The invention relates to a method for coating a metal strip with the aid of a coating device. Within the coating device, the strip first runs through a coating container with a liquid coating agent and then a stripping nozzle device for stripping off excess coating agent from the surface of the strip. After the stripping nozzle device, the strip typically runs through a strip stabilizing device with a plurality of magnets on both broad sides of the strip. A form control deviation is determined as the difference between a determined actual form of the strip and a specified desired form of the strip and this form control deviation is used for activating the magnets of the strip stabilizing device in order to transform the actual form of the strip into the desired form. As an alternative possibility for producing a moment, in particular a bending moment, in the strip, on the basis of the form control deviation the magnets of the strip stabilizing device 130 are moved in the widthwise direction R of the strip 200 into a traversing position in relation to the magnets on the respectively opposite broad side of the strip.

Claims

1. A method for coating a metal strip with the help of a coating device, in which the metal strip is led through a coating container with a liquid coating medium, subsequently through a slot of a stripping nozzle device and further subsequently through a slot of a strip stabilizing device with a plurality of magnets on both wide sides of the strip, comprising the following steps: determining an actual shape of the metal strip within the stripping nozzle device over a width of the metal strip; determining a shape regulation difference as a difference between the actual shape of the metal strip and a predetermined target shape of the metal strip in a region of the stripping nozzle device; and controlling the plurality of magnets of the strip stabilizing device as setting elements so that the actual shape of the metal strip is converted into the target shape of the strip, wherein controlling the plurality of magnets of the strip stabilizing device is carried in that at least one of the magnets, in dependence on the shape regulation difference, is displaced in a width direction (R) of the metal strip to be offset relative to all of the magnets on the opposite wide side of the metal strip and displaced into a moved position where it is at least approximately opposite a trough in the actual shape of the metal strip, and wherein the plurality of magnets on both wide sides of the strip are arranged in a plane perpendicular to a traveling direction of the metal strip.

2. The method according to claim 1, wherein in addition to the actual shape, an actual position of the metal strip within the stripping nozzle device is determined; in addition to the shape regulation difference, a position regulation difference as difference between the actual position of the strip and a predetermined target position of the metal strip in the region of the stripping nozzle device is determined; and the displacement of the at least one of the magnets in the width direction (R) of the metal strip relative the at least one magnet on the opposite wide side of the metal strip is also carried out in dependence on the position regulation difference so that the strip is transferred from its actual position to the predetermined target position.

3. The method according to claim 1, wherein, as seen in width direction, a stationary magnet pair or a plurality of stationary magnet pairs is arranged in a stationary position symmetrically with respect to a center of the slot of the strip stabilizing device or a center of the metal strip, wherein two magnets of the stationary magnet pair or each of the stationary magnet pairs are arranged to be opposite at the two wide sides of the metal strip; and wherein at least individual ones of magnets adjacent to the at least one stationary magnet pair are so displaced relative to the stationary magnet pair in width direction (R) of the metal strip that in their moved position they are at least approximately opposite a trough in the actual shape of the strip.

4. The method according to claim 1, wherein the displacement of the at least one magnet in width direction (R) is carried out symmetrically with respect to a strip center.

5. The method according to claim 1, wherein two further magnets form a left-hand magnet pair which is so displaced in a region of a left-hand edge of the metal strip that that magnet of the left-hand magnet pair having a greater spacing (d.sub.I1) from the edge of the metal strip is displaced with its center at the level of the left-hand edge and that magnet of the left-hand magnet pair having a smaller spacing (d.sub.I2) from the left-hand edge of the metal strip is arranged to be so offset as seen in width direction towards the center of the metal strip that it is at least approximately opposite a trough in the actual shape of the strip; and/or wherein two further magnets form a right-hand magnet pair which is so displaced in a region of a right-hand edge of the metal strip that that magnet of the right-hand magnet pair having a greater spacing (d.sub.r1) from the edge of the metal strip is displaced with its center at the level of the right-hand edge and that magnet of the right-hand magnet pair having a smaller spacing (d.sub.r2) from the right-hand edge of the strip is arranged to be so offset as seen in width direction towards the center of the metal strip that it is at least approximately opposite a trough in the actual shape of the strip.

6. The method according to claim 5, wherein remaining magnets not belonging to the right-hand, left-hand or middle magnet pair are so moved in width direction (R) of the metal strip that they are each at least approximately opposite a trough in the actual shape of the strip.

7. The method according to claim 1, wherein determination of the actual position and/or the actual shape of the metal strip within the stripping nozzle device is carried out by measuring the position and/or shape of the strip either between the stripping nozzle device and the strip stabilizing device or within the strip stabilizing device or downstream of the strip stabilizing device and by determining the actual position and/or the actual shape of the strip within the stripping nozzle device from the measured position and/or shape of the strip.

8. The method according to claim 7, wherein determination of the actual position and/or the actual shape of the strip within the strip stabilizing device is carried out by measuring a spacing of the strip from the magnets of the strip stabilizing device over the width of the strip.

9. The method according to claim 1, wherein the displacement of the magnets in the width direction (R) is additionally carried out in dependence on an available number of magnets at each of the wide sides of the metal strip.

10. The method according to claim 1, wherein the displacement of the magnets in width direction (R) is carried out in dependence on a force (F), which can be generated by individual magnets, on the metal strip.

11. The method according to claim 1, wherein the magnets are electromagnetic coils.

12. The method according to claim 11, wherein at least one of the coils is supplied with such a current that the metal strip by reason of a force (F) acting through the electromagnetic coil on the metal strip is transferred to its target position in the center of the stripping nozzle device and stabilized thereat and/or the actual shape of the strip is adapted as best possible to the target shape.

13. The method according to claim 1, wherein a correction roller is so positioned and adjusted upstream of the stripping nozzle device that the strip stabilizing device and the magnets thereof can be operated within their operating limits.

14. The method according to claim 1, wherein the actual shape of the metal strip has an S-shaped or U-shaped or W-shaped cross-section of the metal strip.

15. The method according to claim 1, wherein the target shape of the metal strip has a rectangular cross-section or planarity of the metal strip.

16. The method according to claim 1, wherein the actual position of the metal strip is an inclined setting (I1) or a parallel displacement (I2) or an offset (I3) of the metal strip relative to the target position (SL) in the slot of the stripping nozzle device.

17. The method according to claim 1, wherein the target position (SL) of the strip is a center position in the slot of the stripping nozzle device.

18. The method according to claim 1, wherein moved positions of the magnets in width direction (R), currents acting on electromagnetic coils and/or a position and adjustment of a correction roller are stored in a database.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Four figures accompany the description, wherein:

(2) FIG. 1 illustrates a coating device;

(3) FIG. 2 illustrates known actual shapes and a known target shape of the strip;

(4) FIG. 3 illustrates known actual and target positions of the strip; and

(5) FIG. 4 illustrates movement in accordance with the invention of magnets in width direction of the strip.

DETAILED DESCRIPTION

(6) The coating device according to the invention and the method according to the invention are described in detail in the following in the form of embodiments with reference to the stated figures. In all figures the same technical elements are denoted by the same reference numerals.

(7) FIG. 1 shows a coating device 100 for coating a metal strip 200. The coating device 100 includes a coating container 110 filled with liquid coating medium 112, for example zinc. The metal strip 200 dips into the coating container and is there deflected in the liquid coating medium with the help of a pot roller 150. The metal strip 200 is then led past a correction roller 140 and subsequently through the slot of a stripping nozzle device 120 and further subsequently through the slot of a strip stabilizing device 130. Within the stripping nozzle device 120 the strip is acted on preferably at both sides with an air flow so as to strip off excess liquid coating medium.

(8) The strip stabilizing device 130 includes of a plurality of magnets 132 arranged at the two wide sides of the strip or strip stabilizing device. These magnets 132 are typically constructed in the form of electromagnetic coils. The coating device 100 additionally comprises a control device 160 for controlling an actuator 136 for displacing or moving the magnets 132 in accordance with the invention in width direction R of the strip and for setting the current I fed to the individual magnets. In addition, the control device can have an output for controlling an actuator 146 for positioning and adjusting the correction roller 140. The control of the actuators 136, 146 as well as the setting of the current for the magnets take place in dependence on measurement signals of a distance sensor preferably traversing in width direction of the strip. The distance sensor detects the distribution of the spacing of the metal strip in width direction with respect to a reference position, for example the gap or slot of the strip stabilizing device. In this way, there is detection of the actual shape and/or the actual position of the metal strip. Alternatively, a separate shape sensor 170 for detecting the actual shape of the strip and a separate position sensor 180 for detecting the actual position of the metal strip can be provided.

(9) Determination of the actual position and/or actual shape of the metal strip within the stripping nozzle device 120 is carried out by measuring the position and/or shape of the strip either between the stripping nozzle device 120 and the strip stabilizing device 130 or within the strip stabilizing device 130 or upstream of the strip stabilizing device 130 and by subsequently drawing a conclusion about the actual position and/or the actual shape of the strip within the stripping nozzle device from the respectively measured position and/or shape of the strip. In that case, determination of the actual position and/or actual shape of the strip within the strip stabilizing device 130 is carried out by measuring the spacing of the strip from the magnets of the strip stabilizing device over the width of the strip.

(10) FIG. 2 shows different examples for possible undesired actual shapes of the metal strip 200, in concrete terms a metal strip wavy in U-shape, S-shaped and W-shape. By contrast, in the lower region FIG. 2 shows the desired target shape of the metal strip 200. Accordingly, the metal strip in its target shape is formed to be straight or planar.

(11) FIG. 3 shows different undesired actual positions of the metal strip 200 in the slot 122 of the stripping nozzle device 120. The different actual positions are illustrated in dashed lines, whereas the target position SL is illustrated by a continuous dash. In concrete terms, the target position is distinguished by the fact that the metal strip 200 has a uniform spacing from the sides of the slot 122. By contrast, in a first undesired actual position I1 relative to the target position SL the metal strip can be twisted or swiveled through an angle α. A second undesired actual position I2 of the metal strip consists of the metal strip being displaced parallelly relative to the target position SL so that the metal strip no longer has equal spacings from the wide sides of the slot. Finally, a third typical undesired actual position for the metal strip consists in that the metal strip in accordance with the position I3 is displaced in longitudinal direction relative to the target position SL so that its spacings from the narrow sides of the slot 122 of the stripping device are no longer equal.

(12) FIG. 4 illustrates the method according to the invention. After determination of the actual shape of the strip 200 within the stripping nozzle device 120 over the width of the strip, for example in the form of the types shown in FIG. 2 at the top, the actual shape is compared with a predetermined target shape of the strip, typically as shown in FIG. 2 at the bottom. The departures in shape form a shape regulation difference and the magnets 132 of the strip stabilizing device 130 are so controlled in dependence on the shape regulation difference that the actual shape of the strip is converted into the target shape of the strip. In that case, according to the invention at least individual ones of the magnets 132 are displaced in width direction R of the strip 200 relative to the magnets on the respective opposite wide side of the strip into a moved position. These moved positions are illustrated by way of example in FIG. 4.

(13) In addition to the actual shape, the actual position of the strip 200 within the stripping nozzle device 120 can also be determined. Undesired manifestations of this actual position were already presented above with reference to FIG. 3. In addition to the shape regulation difference, analogously also a position regulation difference as a difference between the actual position of the strip and a predetermined target position SL in the region of the stripping nozzle device 120 can be determined. The displacement of the at least one magnet 132-A in width direction R of the strip 200 relative to the magnets 132-B on the opposite wide side of the strip 200 can accordingly also be carried out in such a way in dependence on the position regulating difference that the strip is transferred from its actual position to the predetermined target position SL.

(14) In general, it is feasible that at least individual ones of the current-conducting, i.e. active, magnets 132 are so moved in width direction R of the strip 200 that in their moved position, also called end position, they are at least approximately opposite a trough in the actual shape of the strip 200, as illustrated in FIG. 4. The advantage of this procedure is that the forces, which act in different directions, of the individual coils act at a spacing from one another and thus a torque or bending moment on the strip 200 can be generated to provide compensation for, in particular, transverse curvatures or undesired wave shapes. The bending moments generated by the forces F of the coils are denoted in FIG. 4 by the reference sign M.

(15) FIG. 4 shows a special embodiment for possible moved positions. In concrete terms, in this embodiment a magnet pair 132-3-A, 132-3-B is arranged in stationary position in the center of the strip 200 as seen in width direction R. The two magnets of this magnet pair are mutually opposite at the two wide sides A, B of the strip 200. By contrast, the remaining coils or magnets are not arranged in the form of magnet pairs of which the individual magnets 132-1, 132-2, 132-4 and 132-5 are directly opposite. These remaining magnets are arranged to be displaced or offset in width direction R of the strip relative to the magnets on the other strip side.

(16) In concrete terms, two further magnets 132-1-A and 132-1-B form a left-hand magnet pair which is displaced in the region of the left-hand edge of the strip 200 in such a way that that magnet 132-1-B of the left-hand magnet pair having the greater spacing d.sub.l1 from the edge of the strip is displaced with its center at the level of the left-hand edge and that magnet 132-1-A of the left-hand magnet pair having the smaller spacing d.sub.l2 from the left-hand edge of the strip is arranged to be displaced—relative to the magnet 132-1-B with the greater spacing d.sub.l1 from the edge of the strip—some distance towards the stationary magnet pair 132-3-A, 132-3-B, i.e. towards the strip center. Through the offset arrangement of the two part coils 132-1-A and 132-1-B of the left-hand coil pair the torque shown in FIG. 4 is exerted on the left-hand edge region of the strip 200 in anticlockwise sense, whereby the transverse curvature thereof at that place can be eliminated.

(17) Alternatively or additionally a right-hand magnet pair 132-5-A, 132-5-B can be provided, which is displaced in such a way in the region of the right-hand edge of the strip 200 that its part magnet 132-5-B having the greater spacing d.sub.r1 from the right-hand edge of the strip 200 is displaced with its center at the level of the right-hand edge. In addition, then that part magnet 132-5-A of the right-hand magnet pair having the smaller spacing d.sub.r2 from the right-hand edge of the strip is offset—relative to the magnet with the greater spacing from the edge of the strip—some distance towards the center of the strip 200. In this case, the tension forces F which are generated in FIG. 4 by the part coils and which act at a spacing from one another on the strip 200 produce a bending moment M in clockwise sense on the strip 200. As a result, compensation can be provided for the wave shape, which is additionally shown in FIG. 4, at the right-hand edge.

(18) The remaining magnets 132-2-A, 132-2-B, 132-4-A and 132-4-B, which do not belong to the right-hand, left-hand or middle magnet pair, are preferably so moved in width direction R of the strip 200 that they are each at least approximately opposite a trough in the actual shape of the strip, as is illustrated in FIG. 4, whereby the above-described advantageous effect by generation of the bending moments is achieved.

(19) As can be similarly seen in FIG. 4, particularly in the case of a symmetrical undesired actual shape of the strip, when the said displacement of the magnets in width direction takes place the symmetrical arrangement of the magnets shown in FIG. 4 is created, particularly the symmetrical arrangement with respect to the stationary magnet pair 132-3-A, 132-3-B.

REFERENCE NUMERAL LIST

(20) 100 coating device 110 coating container 112 coating medium 120 stripping nozzle device 122 slot of the stripping nozzle device 130 strip stabilizing device 132 magnet 136 actuator 140 correction roller 150 pot roller 160 control device 170 shape sensor 180 position sensor 200 metal strip d.sub.l1 spacing d.sub.l2 spacing d.sub.r1 spacing d.sub.r2 spacing F force l1 inclined setting l2 parallel displacement l3 offset M bending moment R width direction SL target position α angle