SE528663C2 - An apparatus and method for coating an elongated metallic element with a layer of metal - Google Patents

Abstract

A device and a method for controlling the thickness of a metallic coating on an elongated metallic element (1), wherein the coating is adapted to be applied by continuously transporting the element through a bath (2) of molten metal, and the element is transported from the bath in a transport direction (3) along a predetermined transport path (x). The device comprises at least one pair of electromagnetic wiping members, comprising one wiping member on each side of the element (1) for wiping off excessive molten metal from the element by applying a travelling magnetic field, and wherein each wiping member comprises a wiping pole (5). The device comprises at least one pair of electromagnetic stabilizing members, comprising one stabilizing member on each side of the element (1) for stabilizing the position of the element with respect to the predetermined transport path (x), the stabilizing member comprising a stabilizing pole (5). The wiping member and the stabilizing member on the same side of the element (1) are arranged such that the wiping pole (5) and the stabilizing pole (5) coincide.

Description

The bath usually passes below the belt a submerged roller and then moves upward through stabilizing and correcting rollers. The belt emerges from the bath and is transported by a wiper device, such as gas knives or electromagnetic wipers. An electromagnetic wiper generates a varying magnetic field which is used to control the thickness of the coating and to remove excess zinc from the metal strip. Excess zinc goes back to the bath and can thus be reused. The belt is then transported without support until the coating has cooled and solidified. The coated steel strip is then guided or directed via an upper roll to an arrangement for cutting the strip into separate strip elements or for winding the strip on a roll. Usually the belt moves in a vertical direction from the lowered roller through the correcting and stabilizing rollers and the wiper device to the upper roller.

When steel strips are galvanized, an even and thin coating thickness is sought. A common way to check the thickness of the coating after excess molten metal has been removed from the strip, and the coating has solidified, is to measure the mass of the coating after the strip has, for example, passed the upper roll. This reading is used to control the wiper device and thereby regulate the thickness of the coating. However, due to the geometry of the metal strip, the length of the strip having to run without support, its speed and the influence of the electromagnetic wipers, the metal strip will move or vibrate in a direction which is substantially perpendicular to its direction of transport. Certain measures, such as the use of corrective and stabilizing rollers, an adjustment of the speed of the steel strip and / or an adjustment of the distance over which the strip must run without support, may be taken in order to reduce these transverse movements. If the transverse movements are not reduced, they will significantly interfere with the exact wiping, resulting in an uneven coating thickness.

Additional disturbing forces on the belt can be caused by the wiper device. WO 02/14574 discloses a device for controlling the thickness of a coating on a metal strip.

The device comprises an electromagnetic wiper means arranged on each side of the belt, and comprising two wiper poles arranged one after the other in the conveying direction of the belt. Excess molten metal is wiped off the object by the wiper means applying a magnetic force to the coating. The device also comprises an electromagnetic stabilizing means arranged on each side of the belt, and comprising three stabilizing poles. In order to reduce the oscillations of the belt, which are caused partly by disturbing forces from the wiper means and partly by the free length of the belt, each electromagnetic wiper pole is arranged between two stabilizing poles in the conveying direction of the belt.

The present invention seeks to provide an improved device for controlling the thickness of a metallic coating when coating a metallic strip and thereby obtaining an improved quality of the coated strip.

DISCLOSURE OF THE INVENTION According to a first aspect, the invention relates to a device for controlling the thickness of a metallic coating on an elongate metallic element according to claim 1. The elongate metallic element is preferably a metallic strip.

In a device for controlling the thickness of a metallic coating on a metallic strip, the coating is arranged to be applied by continuous transport of the strip through a bath of molten metal. The belt is arranged to be transported from the bath in a transport direction along a predetermined transport path, and the device comprises at least a pair of electromagnetic wiper means, comprising a wiper means on each side of the belt for wiping excess molten metal from the belt by applying a traveling magnetic field. each wiper means comprises a wiper pole.

The device comprises at least a pair of electromagnetic stabilizing means, comprising a stabilizing means on each side of the belt for stabilizing the position of the belt with respect to the predetermined transport path, each stabilizing means comprising a stabilizing pole.

The wiper means and the stabilizing means on the same side of the belt are arranged so that the wiper pole and the stabilizing pole coincide. This causes the stabilizing magnetic force from the stabilizing means to act in the same range as the interfering force from the wiper means. Because the stabilizing force acts in the same area as the disturbance on the belt from the wiper member, reduced bending and vibrations of the plate occur. Another advantage is that the device provides a more compact design than previously known devices.

The wiper means and the stabilizing means preferably have a common magnetic core. The common magnetic core comprises a rear and a front magnetic core part.

According to one embodiment, the wiper means and the stabilizing means form an integrated unit, which results in a compact design of the device.

According to one embodiment, the wiper means has two phase windings. By arranging a wiper pole with only two phase windings, and not as before three phase windings, for ironing off excess metal, only a peak for the wiper force on the coating is obtained, which has proved to be sufficient to achieve good wiping of excess coating. This also means that the disturbance from the wiper device only occurs in an area on the belt across the conveying direction of the belt.

According to one embodiment, the stabilizing means comprise a stabilizing winding. The stabilizing winding is arranged between the strip and the phase windings. By arranging the stabilizing winding between the strip and the phase winding, the stabilizing means can act in the same area as the wiper means.

According to one embodiment, the magnetic core has a substantially T-shaped cross section and comprises a base and a roof. The base consists mainly of the front magnetic core part, which comprises the wiper pole and the stabilizing pole, and the roof consists mainly of the rear magnetic core part. The roof is arranged in a direction substantially parallel to the direction of transport, and the base extends from the roof in a direction towards the belt.

According to one embodiment, the stabilizing winding is arranged around the base and the phase windings are arranged around the roof on each side of the base. This gives a compact design and means that the stabilizing magnetic force from the stabilizing member acts in the same area on the belt as where a disturbance from the wiper member occurs. Because the stabilizing force acts in the same area as the disturbance from the wiper member, reduced bending and vibrations of the plate occur, while at the same time the quality of the coating is maintained or improved.

According to yet another embodiment, the device comprises a second pair of wiper means arranged at a distance from the first pair of wiper means in a direction transverse to the transport direction. Thereby a further improved control of the thickness over the width of the strip is obtained which results in an improved quality of the coated strip.

According to one embodiment, the device comprises a third pair of wiper means spaced from the first and second pairs of wiper means in a direction transverse to the direction of transport. By arranging three wiper means across the transport direction and along the bandwidth, the control of wiper forces and stabilizing forces can be adapted to the current need in the very area covered by the respective wiper means. For example, a wiper means is placed over the center line of the belt and the other two on each side of the wiper means arranged above the center line. This results in a further improved control of the thickness over the width of the strip, which results in an improved quality of the coated strip.

According to one embodiment, at least one sensor for sensing the position of the belt in relation to its predetermined transport path is arranged in close connection with at least one of the wiper means. By arranging at least one sensor in close proximity to the place where a disturbing force is generated, such as the wiper means, an improved sense of the position of the belt is obtained. This in turn means that an improved control of the stabilization of the belt can be achieved and thus an improved quality of the coated belt.

According to one embodiment, the device comprises a stabilizing element arranged to control the permeability in the part of the stabilizing pole which is closest to the belt.

The stabilizing element comprises, for example, an external coil arranged outside the stabilizing winding.

The permeability of said part of the stabilizing pole is determined from the distance of the belt to the respective stabilizing pole.

By controlling the permeability in said part of the stabilizing pole, the position of the belt between the stabilizing poles is regulated.

According to one embodiment, the device comprises a circuit which is arranged to apply a current to one edge of the belt to generate a supplementary wiping force. The applied current at one edge of the band is taken out at the other edge of the band, for example by a closed circuit or by means of a short circuit. The supplementary wiping force is formed by a combination of the applied current and the magnetic field from the wiper pole so that a complementary wiper force directed downwards towards the bath is formed. The circuit is arranged to control the current, which is applied to at least one edge of the strip, based on the actual thickness of the coating along the width of the strip compared to the setpoint of the coating thickness along the width of the strip.

The actual thickness of the coating is measured, for example, in a control device arranged after the wiper means. The supplementary wiper force is usually greatest at the edge of the belt and means that a smoother wiper across the belt can be obtained if necessary.

According to a second aspect, the invention relates to a method for controlling the thickness of a metallic coating on an elongate metallic element according to claim 17. According to one embodiment, the elongate metallic element is a metallic strip.

When controlling the thickness of a metallic coating on a metallic strip, the coating is applied by continuously transporting the strip through a bath of molten metal. The belt is transported in a conveying direction along a predetermined conveying path, excess molten metal from the belt is wiped off by applying a traveling magnetic field to the not yet solidified metallic coating 528 663 on the belt. Furthermore, the position of the object with respect to the predetermined transport path is stabilized by applying a stabilizing magnetic force to the belt in the same area as the traveling magnetic field acts on the belt. In this way, the belt is stabilized in the same area as the disturbance occurs, which reduces bending and vibrations in the belt and thus allows a higher force density for the wiper, which in turn means that the belt speed can be increased and that a faster process can be obtained while maintaining or improving quality. the band.

The thickness of the coating is measured after the scraping of excess molten metal, and the measured thickness and a setpoint of the thickness control the current that goes to two phase windings which generate the traveling magnetic field.

According to one embodiment, the position of the belt with respect to the conveyor path is determined by at least one sensor generating a value of a parameter, such as the distance between predetermined conveyor path and the actual position of the belt, which controls the magnitude of the stabilizing magnetic force. Said stabilizing magnetic force is then applied to the belt in response to the position of the belt.

According to one embodiment, the belt is stabilized by controlling the permeability of at least the part of the stabilizing pole closest to the belt.

The permeability in said part of the stabilizing coil is controlled by means of a stabilizing element comprising, for example, an external coil. By controlling the permeability based on where the metallic band is located between the wiper poles, the metallic band is prevented from moving towards one of the poles due to magnetic forces and the belt is centered between the wiper poles. According to an embodiment of the invention, a current is applied to at least one of the edges of the metallic strip.

By applying a current which is combined with the magnetic field from the wiper pole, a downward force is obtained and contributes to an even wiping. The downward force is greatest at the edges of the belt.

DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail by describing exemplary embodiments with reference to the accompanying drawings, in which Fig. 1 schematically shows a cross section through an embodiment of a device for controlling the thickness of a metallic coating on a metal strip, seen from the side, Fig. 2 schematically shows a first embodiment of the device in figure 1, seen in a front view, Fig. 3 schematically shows a second embodiment of the device in figure 1, seen in a front view, Fig. 4 schematically shows a third embodiment of the device in figure 1, seen in a view front view, and Fig. 5 shows saturation of the end of a wiper pole arranged closest to the belt.

DESCRIPTION OF EMBODIMENTS The following description relates to both a device and a method. Figure 1 shows a device for controlling the thickness of a metallic coating on a metallic strip 1. The strip 1 is coated with a layer of molten metal by continuously transporting the strip through a bath 2. The strip is transported from the bath in a conveying direction 3 along a predetermined conveying path x. The predetermined conveying path x extends mainly between a roller immersed in the bath 2 and an upper roller, arranged after a wiper and stabilizing unit 4a, 4b. The wiper and stabilizing unit 4a, 4b is arranged to wipe excess molten metal from the belt 1 and to stabilize the belt 1. The wiper and stabilizing unit 4a, 4b comprises a wiper means comprising a first phase winding 6a, 6b for a first phase and a second phase winding 7a , 7b for a second phase, and a stabilizing means comprising a stabilizing winding 8a, 8b, and a common magnetic core 12a, 12b which comprises a wiper and stabilizing pole 5a, 5b. The scraper and stabilization unit 4a, 4b are arranged on opposite sides of the belt at substantially the same level.

The magnetic core 12a, 12b comprises a rear 9a, 9b and a front magnetic core part, and has a substantially T-shaped cross-section, the cross-section comprising a base and a roof. The base consists mainly of the front magnetic core part, which comprises the wiper and stabilization pole 5a, 5b, and the roof consists mainly of the rear magnetic core part 9a, 9b. The roof is arranged in a direction substantially parallel to the transport direction 3; and the base extends from the roof in a direction towards the band l.

The stabilizing winding 8a, 8b is arranged around the base and the phase windings 6a, 6b, 7a, 7b are arranged around the roof on each side of the base.

The phase windings 6a, 6b, 7a, 7b are supplied with AC current (not shown) and generate an alternating magnetic field, also called traveling magnetic field, on the band 1. Said magnetic field induces current paths in the coating (not shown). ), and a force Appears on the coating in a direction opposite to the transport direction of the belt. The wiper means operates in accordance with the principle of a linear motor or an electromagnetic stirrer to provide an electromagnetic field. In this way, excess coating material is wiped off in a direction longitudinal in the strip.

The stabilizing winding 8a, 8b is supplied with a DC current so that a stabilizing force acts perpendicular to the band 1.

Because the stabilizing pole 5a, 5b is arranged to coincide with the wiper pole 5a, 5b, the stabilizing force can act on the belt in the same area as a disturbance from the wiper pole arises. Of course, disturbances or vibrations can also occur in other ways than from the wiper means, for example due to the free length of the belt 1, i.e. the length along which the belt 1 runs without support. These disturbances or vibrations can also be stabilized with said wiper means. The wiper and stabilization pole 5a, 5b are arranged at a certain distance from the predetermined transport path x. The distance of course varies with the actual thickness of the belt 1 and the thickness of the coating.

Figure 1 shows that on each side of the belt 1 a sensor 10a, 10b is arranged for sensing the position of the belt 1 in relation to its predetermined transport path x. The sensor 10a, 10b is arranged in close connection with the wiper and stabilization unit 4a, 4b. The sensor 10a, 10b is arranged to detect the value of a parameter which depends on the position of the belt with respect to the predetermined transport path x, the stabilizing means applying a force to the belt 1 corresponding to the detected value. The signal from the sensor 10a, 10b is processed in a signal processing equipment (not shown), and a control program in a converter (not shown) controls the current going to the stabilizing winding 8a, 8b for stabilizing the band 1.

A control device 11a, 11b for measuring the thickness of the layer is arranged after the wiper and stabilization unit 4a, 4b.

Figure 2 shows schematically how a first scraper and stabilization unit 4a, 4b in a first pair of scraper and stabilization units according to figure 1 is arranged along the width of the belt.

Figure 3 shows schematically how a second scraper and stabilization unit 17a, 17b in a second pair of scraper and stabilization units are arranged at a distance from the first pair in a direction transverse to the transport direction 3.

Figure 4 shows schematically how a third wiper and stabilization unit 18a, 18b in a third pair of wiper and stabilizer units are arranged at a distance from the second pair in a direction transverse to the transport direction 3. Figure 4 also shows how a circuit 16 is arranged to apply a current (I) at one edge 13a of the belt 1 to generate an additional wiping force on the coating. The wiping force is generated by the current (I) in combination with the electromagnetic force from the wiping means 4a, 4b, 4c. The current (I) is taken out at the other edge of the band 13b.

Figure 5 shows that the permeability of at least the part 15a, 15b of the stabilizing coil 5a, 5b which is closest to the belt is controlled by means of a stabilizing element comprising, for example, an external coil. The permeability of the respective parts 15a, 15b is controlled from where the metallic band is located between the wiper poles 5a, 5b in a pair of wiper and stabilization units. By controlling the permeability, the metallic band is prevented from moving towards one of the poles due to magnetic forces, the band instead stays centered between the wiper poles 5a, 5b.

The invention is not limited to the embodiments shown, but the person skilled in the art can of course modify it in a number of ways within the scope of the invention defined by the claims. For example, when three pairs of 4b, 17a, 17b, 18a, 18b are arranged across the conveying direction 3, the two outermost wiper and stabilizing units 4a, 4b, 18a, 18b may be arranged in the same line along the belt and across the conveying direction and the middle wiper and stabilizer 17a, wiper and stabilization units 4a, 17b are arranged before or after the two outermost wiper and stabilization units.

Claims (21)

10 15 20 25 30 35 528 663 14 PATENT REQUIREMENTS Device for controlling the thickness of a metallic coating on an elongate metallic element (1), wherein the coating is arranged to be applied by continuous transport of the element (1) through a bath (2) of molten metal, and the element is arranged to be transported from the bath (2) in a conveying direction (3) along a predetermined conveying path (x), and wherein the device comprises at least a pair of electromagnetic wiper means, comprising a wiper means on each side of the element for wiping excess molten metal from the element by applying a traveling magnetic field on the element, each wiper means comprising a wiper pole (5a, 5b), and wherein the device comprises at least a pair of electromagnetic stabilizing means, comprising a stabilizing means on each side of the element for stabilizing the position of the element with respect to the predetermined transport path (X), the stabilizing means comprises a stabilizing pole (5a, 5b ), characterized in that the wiper means has a first and a second phase winding (6a, 6b, 7a, 7b), and that said wiper means and the stabilizing means on the same side of the element are arranged so that the wiper pole (5a, 5b) and the stabilizing pole (5a, 5b ) coincides. Device according to claim 1, wherein the elongate metallic element is a metallic strip (1). Device according to claim 1 or 2, wherein the wiper means and the stabilizing means have a common magnetic core (12a, 12b). Device according to any one of the preceding claims, wherein the wiper means and the stabilizing means form an integrated unit. 10 15 20 25 30 35 528 663 15 Device according to any one of the preceding claims, wherein the stabilizing means comprises a stabilizing winding (8a, 8b). Device according to any one of claims 2-5, wherein the stabilizing winding (8a, 8b) is arranged between the strip (1) and the phase windings (6a, 6b, 7a, 7b). A device according to any one of claims 2-7, wherein the magnetic core (12) has a substantially T-shaped cross section, and comprises a base and a roof, and the roof is arranged in a direction substantially parallel to the transport direction (3), and the base extends from the roof in a direction towards the belt (1). Device according to claim 7, wherein the stabilizing winding (8a, 8b) is arranged around the base and the phase windings (6a, 6b, 7a, 7b) are arranged around the roof on each side of the base. Device according to any one of the preceding claims, wherein the device comprises a second pair of wiper means arranged at a distance from the first pair of wiper means in a direction transverse to the transport direction (3). 10. lO. Device according to claim 9, wherein the device comprises a third pair of wiper means arranged at a distance from the first and second pair of wiper means in a direction transverse to the transport direction (3). 11. ll. Device according to any one of claims 2-10, wherein at least one sensor (10a, 10b) for sensing the position of the belt (1) in relation to its predetermined transport path (x) is arranged in close connection with at least one of the wiper means. Device according to any one of claims 3-11, wherein the device comprises a stabilizing element arranged to control the permeability in the part (15a, 15b) of the stabilizing pole (5a, 5b) which is closest to the belt (1). ) - Device according to claim 12, wherein the stabilizing element comprises an external coil (14a, 14b) arranged outside the stabilizing winding (8a, 8b). Device according to any one of claims 2-13, wherein the device comprises a circuit (16) arranged to apply a current (I) to at least one edge (13a, 13b) of the belt (1) for generating an additional wiping force. Device according to claim 14, wherein the circuit (16) is arranged to control the current (I) based on the thickness of the coating measured after wiping. A method of controlling the thickness of a metallic coating on an elongate metallic element (1), the coating being applied by continuously transporting the element through a bath (2) of molten metal, the method comprising - transporting the element (1) in a conveying direction (3) along a predetermined conveying path (X), - wiping off excess molten metal from the elongated metallic element (1) by applying a traveling magnetic field to the element (1) with the not yet solidified metallic coating, characterized in that the method further comprising - measuring the thickness of the coating after scraping off excess molten metal, a difference between the measured thickness and a setpoint of the thickness controlling the current going to phase windings (6a, 6b, 7a, 7b) which generate the traveling magnetic field, - stabilizing the position of the object with respect to the predetermined transport path (x) by applying a 10 15 20 25 30 5 2528 663 17 stabilizing magnetic force on the elongated metallic element (1) in the same area as the traveling magnetic field acts on the element. A method according to claim 16, wherein the elongate metallic element is a metallic strip (1). A method according to claim 17, comprising - determining the position of the belt (1) with respect to the conveyor path (x) by at least one sensor (10a, 10b) generating a value of a parameter controlling the magnitude of the stabilizing magnetic force, and - applying said stabilizing magnetic force to the belt in response to the position of the belt (1). A method according to any one of claims 17-18, wherein the belt (1) is stabilized by controlling the permeability of at least the part (15a, 15b) of the stabilizing pole (5) closest to the belt (1). A method according to claim 19, wherein the permeability of at least the part (15a, 15b) of the stabilizing coil (5) closest to the belt (1) is checked by means of an external coil (14a, 14b). A method according to any one of claims 17-20, wherein a current is applied at at least one edge (13a, 13b) of the belt (1) so that together with the traveling magnetic field a wiper force directed towards the bath (2) is created.