Method and coating device for coating a metal strip

Abstract

Within a coating device, a metal 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 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 an actual form of the strip and a desired form of the strip and this form control deviation is used for activating the magnets in order to transform the actual form of the strip into the desired form. The magnets of the strip stabilizing device may be moved in the widthwise direction of the strip into a traversing position in relation to the magnets on the respectively opposite broad side of the strip.

Claims

1. A coating device for coating a metal strip with a liquid coating medium, comprising: a coating container filled with the liquid coating medium; a stripping nozzle device; a strip stabilizing device with a plurality of magnets on the two wide sides of a slot of the strip stabilizing device; at least one sensor for detecting the actual shape and/or or the actual position of the metal strip in the slot of the stripping nozzle device; and a control device for 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 for controlling the magnets by way of a magnet actuator, wherein the control device and the magnet actuator are further constructed to offset at least one of the magnets in dependence on the shape regulation difference in width direction of the metal strip relative to at least one of the magnets on an opposite wide side of the metal strip and displace it into a moved position where it is at least approximately opposite a trough in the actual shape of the strip.

2. The coating device according to claim 1, wherein the control device and the magnet actuator are further constructed to displace the at least one magnet also in dependence on a position regulation deviation of the metal strip in width direction.

3. The coating device according to claim 1, wherein the control device is further constructed to also control an actuator of a correction roller in such a way that the strip stabilizing device is operable within its operating limits.

4. The coating device according to claim 1, wherein the control device is further constructed to also set a current (l) through the at least one magnet in such a way in dependence on the actual shape and/or the actual position of the metal strip that the target shape and the target position is or are achieved as far as possible.

5. The coating device according to claim 1, wherein a number of magnets per wide side is uneven.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Four figures accompany the description, wherein:

[0027] FIG. 1 illustrates a coating device;

[0028] FIG. 2 illustrates known actual shapes and a known target shape of the strip;

[0029] FIG. 3 illustrates known actual and target positions of the strip; and

[0030] FIG. 4 illustrates movement in accordance with the invention of magnets in width direction of the strip.

DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 die 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.

[0042] 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.

[0043] 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.

[0044] 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

[0045] 100 coating device [0046] 110 coating container [0047] 112 coating medium [0048] 120 stripping nozzle device [0049] 122 slot of the stripping nozzle device [0050] 130 strip stabilizing device [0051] 132 magnet [0052] 136 actuator [0053] 140 correction roller [0054] 150 pot roller [0055] 160 control device [0056] 170 shape sensor [0057] 180 position sensor [0058] 200 metal strip [0059] d.sub.l1 spacing [0060] d.sub.l2 spacing [0061] d.sub.r1 spacing [0062] d.sub.r2 spacing [0063] F force [0064] l1 inclined setting [0065] l2 parallel displacement [0066] l3 offset [0067] M bending moment [0068] R width direction [0069] SL target position [0070] α angle