EP1888804A1 - A device and a method for coating an elongated metallic element with a layer of metal - Google Patents

A device and a method for coating an elongated metallic element with a layer of metal

Info

Publication number
EP1888804A1
EP1888804A1 EP06747996A EP06747996A EP1888804A1 EP 1888804 A1 EP1888804 A1 EP 1888804A1 EP 06747996 A EP06747996 A EP 06747996A EP 06747996 A EP06747996 A EP 06747996A EP 1888804 A1 EP1888804 A1 EP 1888804A1
Authority
EP
European Patent Office
Prior art keywords
stabilizing
wiping
strip
coating
pole
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06747996A
Other languages
German (de)
French (fr)
Other versions
EP1888804A4 (en
Inventor
Jan-Erik Eriksson
Bengt Rydholm
Yujing Liu
Stefan Israelsson Tampe
Göte Tallbäck
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ABB AB
Original Assignee
ABB AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ABB AB filed Critical ABB AB
Publication of EP1888804A1 publication Critical patent/EP1888804A1/en
Publication of EP1888804A4 publication Critical patent/EP1888804A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
    • C23C2/18—Removing excess of molten coatings from elongated material
    • C23C2/20—Strips; Plates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0034—Details related to elements immersed in bath
    • C23C2/00342—Moving elements, e.g. pumps or mixers
    • C23C2/00344—Means for moving substrates, e.g. immersed rollers or immersed bearings
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0035—Means for continuously moving substrate through, into or out of the bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/24—Removing excess of molten coatings; Controlling or regulating the coating thickness using magnetic or electric fields
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/50—Controlling or regulating the coating processes
    • C23C2/51—Computer-controlled implementation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/50—Controlling or regulating the coating processes
    • C23C2/52—Controlling or regulating the coating processes with means for measuring or sensing
    • C23C2/524—Position of the substrate
    • C23C2/5245—Position of the substrate for reducing vibrations of the substrate

Definitions

  • the present invention relates to a device for controlling the thickness of a metallic coating on an elongated metallic element, wherein the coating is applied by continuous transport of the elongated metallic element through a bath of molten metal and the element is transported from the bath in a direction of transport along a predetermined transport path.
  • the invention also relates to a method for controlling the thickness of a metallic coating on an elongated metallic element.
  • the coating is applied by continuously transporting the element through a bath of molten metal.
  • Such a device and such a method are especially advantageous when continuously galvanizing a metallic strip.
  • the present invention will hereafter be described with reference to such an application.
  • the invention is also applicable to galvanization of other metal objects, such as wires, rods, pipes or other elongated ele- ments .
  • the invention is applicable to coating of an elongated metallic element with other coatings than zinc, for example tin or aluminium, or mixtures of these or other metals.
  • the steel strip continuously passes through a bath that contains molten metal, usually zinc.
  • the strip usually passes below a submerged roll and then moves upwards through stabilizing and correcting rolls.
  • the strip emerges from the bath and is transported through a wiper device, for example gas-knives or electromagnetic wipers.
  • An electromagnetic wiper generates a varying magnetic field that is used to control the thickness of the coating and to wipe off any excess zinc from the metal bath. The excess zinc is returned to the bath and may thus be reused.
  • the strip is then transported unsupported until the coating has cooled down 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 onto a roll. Normally, the strip moves in a vertical direction away from the submerged roll through the correcting and stabilizing rollers and the gas-knives to the upper roll.
  • WO 02/14574 discloses a device for controlling the thickness of a coating on a metal strip.
  • the device comprises an electromagnetic wiping member arranged on each side of the strip and comprising two wiping poles arranged one after the other in the transport direction of the strip. Excess molten metal is wiped off the object by the wiping member applying a magnetic force on the coating.
  • the device also comprises an electromagnetic stabilizing device ar- ranged on respective sides of the strip and comprising three stabilizing poles.
  • an electromagnetic stabilizing device ar- ranged on respective sides of the strip and comprising three stabilizing poles.
  • each electromagnetic wiping pole is disposed between two stabilizing poles in the transport direction of the strip.
  • the present invention aims to suggest an improved device for controlling the thickness of a metallic coating when coating a metallic strip, hence obtaining an improved quality of the coated strip.
  • the invention relates to a de- vice for controlling the thickness of a metallic coating on an elongated metallic element according to claim 1.
  • the elongated metallic element is preferably a metallic strip.
  • the coating is adapted to be applied by continuous transport of the strip through a bath of molten metal.
  • the strip is intended to be transported from the bath in a direction of transport along a predetermined transport path, and the device comprises at least one pair of electromagnetic wiping members, comprising one wiping member on each side of the strip for wiping off exces- sive molten metal from the strip by applying a travelling magnetic field to the strip, wherein each wiping member comprises a wiping pole.
  • the device comprises at least one pair of electromagnetic stabilizing members, comprising one stabilizing member on each side of the strip for stabilizing the position of the strip with respect to the predetermined transport path, whereby each stabilizing member comprises a stabilizing pole.
  • the wiping member and the stabilizing member on the same side of the strip are adapted such that the wiping pole and the stabilizing pole coincide. This causes the stabilizing magnetic force from the stabilizing member to act in_the same region as the disturbing force from the wiping member. Since the stabilizing force acts in the same region as the disturbance on the strip from the wiping mem- ber, the bending and the vibrations of the sheet are reduced. Another advantage is that the device provides a more compact design than prior art devices.
  • the wiping member and the stabilizing member preferably have a common magnetic core.
  • the common magnetic core comprises a rear and a front magnetic core part.
  • the wiping member and the stabilizing member form an integrated unit, which entails a compact design of the device.
  • the wiping member has two phase windings .
  • a wiping pole with two phase windings only, and not three phase windings as before, for wiping off excess metal, only one peak of the wiping force on the coat- ing is obtained, which has proved to be sufficient to achieve good wiping of excess coating.
  • This also implies that the disturbance from the wiping device only occurs in a region on the strip across the transport direction of the strip.
  • the stabilizing member comprises a stabilizing winding.
  • the stabilizing winding is ar- ranged between the strip and the phase windings. By arranging the stabilizing winding between the strip and the phase winding, the stabilizing member may act in the same region as the wiping member.
  • the magnetic core has an essentially T-shaped cross section and comprises a base and a roof.
  • the base substantially consists of the front magnetic- core part, which comprises the wiping pole and the stabili- zing pole, and the roof consists substantially of the rear magnetic-core part.
  • the roof is arranged in a direction essentially parallel to the transport direction, and the base extends from the roof in a direction towards the strip.
  • the stabilizing winding is arranged around the base and the phase windings are arranged around the roof on each side of the base. This provides a compact design and results in the stabilizing magnetic force from the stabilizing member acting in the same region on the strip as that where a disturbance from the wiping member occurs. Since the stabilizing force acts in the same region as the disturbance from the wiping member, the bending and vibrations of the sheet will be reduced, while at the same time the quality of the coating is maintained or improved.
  • the device comprises a second pair of wiping members arranged spaced from the first pair of wiping members in a direction across the transport direction. This results in further improved control of the thickness across the width of the strip, which entails an improved quality of the coated strip.
  • the device comprises a third pair of wiping members spaced from the first and second pairs of wiping members in a direction across the transport direction.
  • the control of the wiper forces and the stabilizing forces may be adjusted to the current need in the very region that is covered by the respective wiping member.
  • one wiping member is placed across the centre line of the strip and the other two on respective sides of the wiping member arranged across the centre line. This results in additionally improved control of the thickness across the width of the strip, which entails improved quality of the coated strip.
  • At least one sensor for sensing the position of the strip in relation to its predetermined transport path is arranged in close proximity to at least one of the wiping members.
  • improved sensing of the position of the strip is obtained. This in turn means that improved control of the stabilization of the strip may be achieved and hence improved quality of the coated strip.
  • the device comprises a stabilizing element adapted to control the permeability of that part of the stabilizing pole that lies nearest the strip.
  • the stabilizing element comprises, for example, an external coil arranged outside the stabilizing winding.
  • the permeability in said part of the stabilizing pole is determined on the basis of the distance of the strip to the respective stabilizing pole.
  • the device comprises an electric circuit that is adapted to apply a current to one edge of the strip for generating a supplementary wiping force.
  • the applied current at one edge of the strip is taken out at the other edge of the strip, for example through a closed circuit or by means of short-circuiting.
  • the supplementary wiping force is formed by a combination of the applied current and the magnetic field from the wiping pole, thus for- ming a supplementary wiping force directed downwardly towards the bath.
  • the circuit is adapted 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 with the desired value of the thick- ness of the coating along the width of the strip.
  • the actual thickness of the coating is measured, for example, at a control device arranged after the wiping member.
  • the supplementary wiping force is usually greatest at the edge of the strip and permits a more uniform wiping across the strip to be obtained where necessary.
  • the invention relates to a method for coating the thickness of a metallic coating on an elongated metallic element according to claim 17.
  • the elongated metallic element is a metallic strip.
  • the coating is applied by continuously transporting the strip through a bath of molten metal.
  • the strip is transported in a transport direction along a predetermined transport path, and excessive molten metal from the strip is wiped off by applying a travelling magnetic field to the still non-solidified metallic coating on the strip. Further, the position of the object is stabilized with respect to the predetermined transport path by applying a stabilizing magnetic force to the strip in the same region in which the travelling magnetic field acts on the strip.
  • the strip is stabilized in the same region as that in which the disturbance occurs, which reduces bending and vibrations in the strip and hence allows a higher force den- sity for the wiper, which in turn permits the speed of the strip to be increased and a faster process to be obtained with retained or improved quality of the strip.
  • the thickness of the coating is measured after wiping off excessive molten metal, and the measured thickness and a desired value of the thickness control the current that flows to two phase windings which generate the travelling magnetic field.
  • the position of the strip with respect to the transport path is determined by at least one sensor generating a value of a parameter, as for example the distance between the predetermined transport path and the actual position of the strip, which controls the magnitude of the stabilizing magnetic force. Said stabilizing magnetic force is then applied to the strip that responds to the position of the strip.
  • the strip is stabilized by controlling the permeability in at least that part of the stabilizing pole that lies nearest the strip.
  • the permeability of said part of the stabilizing pole is controlled by means of a stabilizing element comprising, for example, an exter- nal coil.
  • a current is applied to at least one of the edges of the metallic strip.
  • Figure 1 schematically shows a cross section through one embodiment of a device for controlling the thickness of a metallic coating on a metal strip, as viewed from the side.
  • Figure 2 schematically shows a first embodiment of the device in Figure 1, as viewed in a view from the front,
  • Figure 3 schematically shows a second embodiment of the device in Figure 1, as viewed in a view from the front,
  • Figure 4 schematically shows a third embodiment of the device in Figure 1, as viewed in a view from the front,
  • Figure 5 shows saturation of that end of a wiping pole that is arranged nearest the strip.
  • 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 transport direction 3 along a pre- determined transport path x.
  • the predetermined transport path x extends substantially between a roll submerged in the bath 2 and an upper roll arranged after a wiping and stabilizing unit 4a, 4b.
  • the wiping and stabilizing unit 4a, 4b is adapted to wipe off excessive molten metal from the strip 1 and to stabilize the strip 1.
  • the wiping and stabilizing unit 4a, 4b comprises a wiping member comprising a first phase winding 6a, ⁇ b for a first phase and a second phase winding 7a, 7b for a second phase, a stabilizing member comprising a stabilizing winding 8a, 8b, and a common magnetic core 12a, 12b, which comprises a wiping and stabilizing pole 5a, 5b.
  • the wiping and stabilizing unit 4a, 4b are arranged on opposite sides of the strip at essentially 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, where the cross section comprises a base and a roof.
  • the base is substantially constituted by the front magnetic core part, which comprises the wiping and stabilizing pole 5a, 5b, and the roof is substantially constituted by the rear magnetic core part 9a, 9b.
  • the roof is arranged in a direction essentially parallel to the transport direction 3, and the base extends from the roof in a direction towards the strip 1.
  • the stabilizing winding 8a, 8b is arranged around the base and the phase windings ⁇ a, 6b, 7a, 7b are arranged around the roof on each side of the base.
  • the phase windings 6a, 6b, 7a, 7b are fed with alternating current (not shown) and generate an alternating magnetic field, also called travelling magnetic field, on the strip 1. Said magnetic field induces current paths I in the coating (not shown) , and a force acts on the coating in a direction opposite to the transport direction of the strip.
  • the wiping member acts in accordance with the principle of a linear motor or an electromagnetic stirrer in order to achieve an electromagnetic field. In this way, excessive coating material is wiped off in a longitudinal direction of the strip.
  • the stabilizing winding 8a, 8b is fed with a direct current such that a stabilizing force acts perpendicular to the strip 1. Since the stabilizing pole 5a, 5b is adapted to coincide with the wiping pole 5a, 5b, the stabilizing force may act on the strip in the same region in which a disturbance from the wiping pole arises. Disturbances or vibra- tions may, of course, arise otherwise than from the wiping member, for example because of the free length of the strip 1, that is, the length over which the strip 1 is running unsupported. Also these disturbances or vibrations may be stabilized with said wiping member.
  • the wiping and stabili- zing pole 5a, 5b is arranged at a specified distance from the predetermined transport path x. The distance varies, of course, with the current thickness of the strip 1 and the thickness of the coating.
  • Figure 1 shows that a sensor 10a, 10b for sensing the position of the strip 1 in relation to its predetermined transport path x is arranged on each side of the strip 1.
  • the sensor 10a, 10b is arranged in close proximity of the wiping and stabilizing unit 4a, 4b.
  • the sensor 10a, 10b is adapted to detect the value of a parameter that depends on the position of the strip with respect to the predetermined transport path x, whereby the stabilizing member applies a force to the strip 1 that corresponds to the detected value .
  • the signal from the sensor 10a, 10b is processed in signal- processing equipment (not shown) , and a control program in a converter (not shown) controls the current that flows to the stabilizing winding 8a, 8b for stabilizing the strip 1.
  • a control device 11a, lib for measuring the thickness of the layer is arranged after the wiping and stabilizing unit 4a, 4b.
  • Figure 2 schematically shows how a first wiping and stabilizing unit 4a, 4b in a fist pair of wiping and stabilizing units according to Figure 1 is arranged along the width of the strip.
  • Figure 3 schematically shows how a second wiping and stabilizing unit 17a, 17b in a second pair of wiping and stabilizing units is arranged spaced from the first pair in a direction across the transport direction 3.
  • Figure 4 schematically shows how a third wiping and stabilizing unit 18a, 18b in a third pair of wiping and stabilizing units is arranged spaced from the second pair in a direction across the transport direction 3.
  • Figure 4 also shows how a circuit 16 is arranged to apply a current (I) at one edge
  • the wiping force is generated by the current (I) in combination with the electromagnetic force from the wiping member 4a, 4b, 4c.
  • the current (I) is taken out at the other edge of the strip 13b.
  • Figure 5 shows that the permeability in at least that part 15a, 15b of the stabilizing pole 5a, 5b that lies nearest the strip is controlled by means of a stabilizing element comprising, for example, an external coil.
  • the permeability in the respective part 15a, 15b is controlled based on where the metallic strip is located between the wiping poles 5a, 5b in a pair of wiping and stabilizing units.
  • the invention is not limited to the embodiments shown but a person skilled in the art may, of course, modify it in a plurality of ways within the scope of the invention as de- fined by the claims.
  • the outermost two wiping and stabilizing units 4a, 4b, 18a, 18b may be arranged in the same line along the strip and across the transport direction and the middle wiping and stabilizing unit 17a, 17b may be arranged before or after the two outermost wiping and stabilizing units.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Computer Hardware Design (AREA)
  • Coating With Molten Metal (AREA)

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

A device and a method for coating an elongated metallic element with a layer of metal
TECHNICAL FIELD
The present invention relates to a device for controlling the thickness of a metallic coating on an elongated metallic element, wherein the coating is applied by continuous transport of the elongated metallic element through a bath of molten metal and the element is transported from the bath in a direction of transport along a predetermined transport path.
The invention also relates to a method for controlling the thickness of a metallic coating on an elongated metallic element. The coating is applied by continuously transporting the element through a bath of molten metal.
Such a device and such a method are especially advantageous when continuously galvanizing a metallic strip. The present invention will hereafter be described with reference to such an application. However, it should be noted that the invention is also applicable to galvanization of other metal objects, such as wires, rods, pipes or other elongated ele- ments . It should also be noted that the invention is applicable to coating of an elongated metallic element with other coatings than zinc, for example tin or aluminium, or mixtures of these or other metals.
BACKGROUND ART
During continuous galvanization of a metallic strip, for example a steel strip, the steel strip continuously passes through a bath that contains molten metal, usually zinc. In the bath, the strip usually passes below a submerged roll and then moves upwards through stabilizing and correcting rolls. The strip emerges from the bath and is transported through a wiper device, for example gas-knives or electromagnetic wipers. An electromagnetic wiper generates a varying magnetic field that is used to control the thickness of the coating and to wipe off any excess zinc from the metal bath. The excess zinc is returned to the bath and may thus be reused. The strip is then transported unsupported until the coating has cooled down 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 onto a roll. Normally, the strip moves in a vertical direction away from the submerged roll through the correcting and stabilizing rollers and the gas-knives to the upper roll.
When steel strip is galvanized, an even and thin thickness of the coating is aimed at. One common method of controlling the thickness of the coating after excess molten metal has been wiped off the band, and the coating has solidified, is to measure the mass of the coating after the strip, for example, has passed through the upper roller. This reading is utilized for controlling the gas-knives and hence controlling the thickness of the coating. However, due to the geometry of the steel strip, the distance the strip has to run unsupported, its speed, and the influence from the electromagnetic wipers, the metal strip will move or vibrate in a direction essentially perpendicular to its direction of transport. Certain measures, such as the use of the correcting and stabilizing rolls, an adjustment of the speed of the steel strip and/or an adjustment of the distance over which the strip has to run unsupported, may be taken in order to reduce these transverse movements . If not reduced, these transverse movements will significantly disturb the precise wiping, resulting in an uneven coating thickness. Further disturbing forces on the strip may 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 wiping member arranged on each side of the strip and comprising two wiping poles arranged one after the other in the transport direction of the strip. Excess molten metal is wiped off the object by the wiping member applying a magnetic force on the coating. The device also comprises an electromagnetic stabilizing device ar- ranged on respective sides of the strip and comprising three stabilizing poles. To reduce the oscillations of the strip, which are caused by disturbing forces from the wiping member and by the free length of the strip, each electromagnetic wiping pole is disposed between two stabilizing poles in the transport direction of the strip.
The present invention aims to suggest an improved device for controlling the thickness of a metallic coating when coating a metallic strip, hence obtaining an improved quality of the coated strip.
SUMMARY OF THE INVENTION
According to a first aspect, the invention relates to a de- vice for controlling the thickness of a metallic coating on an elongated metallic element according to claim 1. The elongated 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 adapted to be applied by continuous transport of the strip through a bath of molten metal. The strip is intended to be transported from the bath in a direction of transport along a predetermined transport path, and the device comprises at least one pair of electromagnetic wiping members, comprising one wiping member on each side of the strip for wiping off exces- sive molten metal from the strip by applying a travelling magnetic field to the strip, wherein each wiping member comprises a wiping pole. The device comprises at least one pair of electromagnetic stabilizing members, comprising one stabilizing member on each side of the strip for stabilizing the position of the strip with respect to the predetermined transport path, whereby each stabilizing member comprises a stabilizing pole. The wiping member and the stabilizing member on the same side of the strip are adapted such that the wiping pole and the stabilizing pole coincide. This causes the stabilizing magnetic force from the stabilizing member to act in_the same region as the disturbing force from the wiping member. Since the stabilizing force acts in the same region as the disturbance on the strip from the wiping mem- ber, the bending and the vibrations of the sheet are reduced. Another advantage is that the device provides a more compact design than prior art devices. The wiping member and the stabilizing member preferably have a common magnetic core. The common magnetic core comprises a rear and a front magnetic core part.
According to one embodiment, the wiping member and the stabilizing member form an integrated unit, which entails a compact design of the device.
According to one embodiment, the wiping member has two phase windings . By arranging a wiping pole with two phase windings only, and not three phase windings as before, for wiping off excess metal, only one peak of the wiping force on the coat- ing is obtained, which has proved to be sufficient to achieve good wiping of excess coating. This also implies that the disturbance from the wiping device only occurs in a region on the strip across the transport direction of the strip.
According to one embodiment, the stabilizing member comprises a stabilizing winding. The stabilizing winding is ar- ranged between the strip and the phase windings. By arranging the stabilizing winding between the strip and the phase winding, the stabilizing member may act in the same region as the wiping member.
According to one embodiment, the magnetic core has an essentially T-shaped cross section and comprises a base and a roof. The base substantially consists of the front magnetic- core part, which comprises the wiping pole and the stabili- zing pole, and the roof consists substantially of the rear magnetic-core part. The roof is arranged in a direction essentially parallel to the transport direction, and the base extends from the roof in a direction towards the strip.
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 provides a compact design and results in the stabilizing magnetic force from the stabilizing member acting in the same region on the strip as that where a disturbance from the wiping member occurs. Since the stabilizing force acts in the same region as the disturbance from the wiping member, the bending and vibrations of the sheet will be reduced, while at the same time the quality of the coating is maintained or improved.
According to another embodiment, the device comprises a second pair of wiping members arranged spaced from the first pair of wiping members in a direction across the transport direction. This results in further improved control of the thickness across the width of the strip, which entails an improved quality of the coated strip.
According to one embodiment, the device comprises a third pair of wiping members spaced from the first and second pairs of wiping members in a direction across the transport direction. By arranging three wiping members across the transport direction and along the width of the strip, the control of the wiper forces and the stabilizing forces may be adjusted to the current need in the very region that is covered by the respective wiping member. For example, one wiping member is placed across the centre line of the strip and the other two on respective sides of the wiping member arranged across the centre line. This results in additionally improved control of the thickness across the width of the strip, which entails improved quality of the coated strip.
According to one embodiment, at least one sensor for sensing the position of the strip in relation to its predetermined transport path is arranged in close proximity to at least one of the wiping members. By arranging at least one sensor in close proximity to the point where a disturbing force is generated, for example the wiping member, improved sensing of the position of the strip is obtained. This in turn means that improved control of the stabilization of the strip may be achieved and hence improved quality of the coated strip.
According to one embodiment, the device comprises a stabilizing element adapted to control the permeability of that part of the stabilizing pole that lies nearest the strip. The stabilizing element comprises, for example, an external coil arranged outside the stabilizing winding. The permeability in said part of the stabilizing pole is determined on the basis of the distance of the strip to the respective stabilizing pole. By controlling the permeability in said part of the stabilizing pole, the position of the strip between the stabilizing poles is controlled.
According to one embodiment, the device comprises an electric circuit that is adapted to apply a current to one edge of the strip for generating a supplementary wiping force.
The applied current at one edge of the strip is taken out at the other edge of the strip, for example through a closed circuit or by means of short-circuiting. The supplementary wiping force is formed by a combination of the applied current and the magnetic field from the wiping pole, thus for- ming a supplementary wiping force directed downwardly towards the bath. The circuit is adapted 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 with the desired value of the thick- ness of the coating along the width of the strip. The actual thickness of the coating is measured, for example, at a control device arranged after the wiping member. The supplementary wiping force is usually greatest at the edge of the strip and permits a more uniform wiping across the strip to be obtained where necessary.
According to a second aspect, the invention relates to a method for coating the thickness of a metallic coating on an elongated metallic element according to claim 17. According to one embodiment, the elongated 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 strip is transported in a transport direction along a predetermined transport path, and excessive molten metal from the strip is wiped off by applying a travelling magnetic field to the still non-solidified metallic coating on the strip. Further, the position of the object is stabilized with respect to the predetermined transport path by applying a stabilizing magnetic force to the strip in the same region in which the travelling magnetic field acts on the strip. In this way, the strip is stabilized in the same region as that in which the disturbance occurs, which reduces bending and vibrations in the strip and hence allows a higher force den- sity for the wiper, which in turn permits the speed of the strip to be increased and a faster process to be obtained with retained or improved quality of the strip.
The thickness of the coating is measured after wiping off excessive molten metal, and the measured thickness and a desired value of the thickness control the current that flows to two phase windings which generate the travelling magnetic field.
According to one embodiment, the position of the strip with respect to the transport path is determined by at least one sensor generating a value of a parameter, as for example the distance between the predetermined transport path and the actual position of the strip, which controls the magnitude of the stabilizing magnetic force. Said stabilizing magnetic force is then applied to the strip that responds to the position of the strip.
According to one embodiment, the strip is stabilized by controlling the permeability in at least that part of the stabilizing pole that lies nearest the strip. The permeability of said part of the stabilizing pole is controlled by means of a stabilizing element comprising, for example, an exter- nal coil. By controlling the permeability on the basis of where the metallic strip is located between the wiping poles, the metallic strip is prevented to move, due to the magnetic forces, towards one of the poles and the strip remains centred between the wiping poles.
According to one embodiment of the invention, a current is applied to at least one of the edges of the metallic strip. By applying a current that is combined with the magnetic field from the wiping pole, a downward force is obtained that contributes to obtain a uniform wiping action. The downward force is greatest at the edges of the strip. BRIEF DESCRIPTION OP THE DRAWINGS
The invention will be explained in greater detail by description of embodiments with reference to the accompanying drawings, wherein
Figure 1 schematically shows a cross section through one embodiment of a device for controlling the thickness of a metallic coating on a metal strip, as viewed from the side.
Figure 2 schematically shows a first embodiment of the device in Figure 1, as viewed in a view from the front,
Figure 3 schematically shows a second embodiment of the device in Figure 1, as viewed in a view from the front,
Figure 4 schematically shows a third embodiment of the device in Figure 1, as viewed in a view from the front,
Figure 5 shows saturation of that end of a wiping pole that is arranged nearest the strip.
DESCRIPTION OF PREFERRED EMBODIMENTS
The following description relates both to 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 transport direction 3 along a pre- determined transport path x. The predetermined transport path x extends substantially between a roll submerged in the bath 2 and an upper roll arranged after a wiping and stabilizing unit 4a, 4b. The wiping and stabilizing unit 4a, 4b is adapted to wipe off excessive molten metal from the strip 1 and to stabilize the strip 1. The wiping and stabilizing unit 4a, 4b comprises a wiping member comprising a first phase winding 6a, βb for a first phase and a second phase winding 7a, 7b for a second phase, a stabilizing member comprising a stabilizing winding 8a, 8b, and a common magnetic core 12a, 12b, which comprises a wiping and stabilizing pole 5a, 5b. The wiping and stabilizing unit 4a, 4b are arranged on opposite sides of the strip at essentially 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, where the cross section comprises a base and a roof. The base is substantially constituted by the front magnetic core part, which comprises the wiping and stabilizing pole 5a, 5b, and the roof is substantially constituted by the rear magnetic core part 9a, 9b. The roof is arranged in a direction essentially parallel to the transport direction 3, and the base extends from the roof in a direction towards the strip 1. The stabilizing winding 8a, 8b is arranged around the base and the phase windings βa, 6b, 7a, 7b are arranged around the roof on each side of the base.
The phase windings 6a, 6b, 7a, 7b are fed with alternating current (not shown) and generate an alternating magnetic field, also called travelling magnetic field, on the strip 1. Said magnetic field induces current paths I in the coating (not shown) , and a force acts on the coating in a direction opposite to the transport direction of the strip. The wiping member acts in accordance with the principle of a linear motor or an electromagnetic stirrer in order to achieve an electromagnetic field. In this way, excessive coating material is wiped off in a longitudinal direction of the strip.
The stabilizing winding 8a, 8b is fed with a direct current such that a stabilizing force acts perpendicular to the strip 1. Since the stabilizing pole 5a, 5b is adapted to coincide with the wiping pole 5a, 5b, the stabilizing force may act on the strip in the same region in which a disturbance from the wiping pole arises. Disturbances or vibra- tions may, of course, arise otherwise than from the wiping member, for example because of the free length of the strip 1, that is, the length over which the strip 1 is running unsupported. Also these disturbances or vibrations may be stabilized with said wiping member. The wiping and stabili- zing pole 5a, 5b is arranged at a specified distance from the predetermined transport path x. The distance varies, of course, with the current thickness of the strip 1 and the thickness of the coating.
Figure 1 shows that a sensor 10a, 10b for sensing the position of the strip 1 in relation to its predetermined transport path x is arranged on each side of the strip 1. The sensor 10a, 10b is arranged in close proximity of the wiping and stabilizing unit 4a, 4b. The sensor 10a, 10b is adapted to detect the value of a parameter that depends on the position of the strip with respect to the predetermined transport path x, whereby the stabilizing member applies a force to the strip 1 that corresponds to the detected value . The signal from the sensor 10a, 10b is processed in signal- processing equipment (not shown) , and a control program in a converter (not shown) controls the current that flows to the stabilizing winding 8a, 8b for stabilizing the strip 1.
A control device 11a, lib for measuring the thickness of the layer is arranged after the wiping and stabilizing unit 4a, 4b. Figure 2 schematically shows how a first wiping and stabilizing unit 4a, 4b in a fist pair of wiping and stabilizing units according to Figure 1 is arranged along the width of the strip.
Figure 3 schematically shows how a second wiping and stabilizing unit 17a, 17b in a second pair of wiping and stabilizing units is arranged spaced from the first pair in a direction across the transport direction 3.
Figure 4 schematically shows how a third wiping and stabilizing unit 18a, 18b in a third pair of wiping and stabilizing units is arranged spaced from the second pair in a direction across 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 strip 1 for generating a further wiping force on the coating. The wiping force is generated by the current (I) in combination with the electromagnetic force from the wiping member 4a, 4b, 4c. The current (I) is taken out at the other edge of the strip 13b.
Figure 5 shows that the permeability in at least that part 15a, 15b of the stabilizing pole 5a, 5b that lies nearest the strip is controlled by means of a stabilizing element comprising, for example, an external coil. The permeability in the respective part 15a, 15b is controlled based on where the metallic strip is located between the wiping poles 5a, 5b in a pair of wiping and stabilizing units. By controlling the permeability, the metallic strip is prevented from mov- ing, due to magnetic forces, towards one of the poles, but the strip is instead kept centred between the wiping poles 5a, 5b.
The invention is not limited to the embodiments shown but a person skilled in the art may, of course, modify it in a plurality of ways within the scope of the invention as de- fined by the claims. For example, in the case where three pairs of wiping and stabilizing units 4a, 4b, 17a, 17b, 18a, 18b are arranged across the transport direction 3, the outermost two wiping and stabilizing units 4a, 4b, 18a, 18b may be arranged in the same line along the strip and across the transport direction and the middle wiping and stabilizing unit 17a, 17b may be arranged before or after the two outermost wiping and stabilizing units.

Claims

1. A device 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 (1) through a bath (2) of molten metal, and the element is adapted to be transported from the bath (2) in a transport direction (3) along a predetermined transport path (x) , and wherein the device comprises at least one pair of electromagnetic wiping members, comprising one wiping member on each side of the element for wiping off excessive molten metal from the element by applying a travelling magnetic field to the element, each wiping member comprising a wiping pole (5a, 5b) , and wherein the device comprises at least one pair of electromagnetic stabilizing members, comprising one stabilizing member on each side of the element for stabilizing the position of the element with respect to the predetermined transport path (x) , the stabilizing member comprising a stabilizing pole (5a, 5b ) , characterized in that the wiping member has a first and a second phase winding (6a, 6b, 7a, 7b), and that said wiping member and the stabilizing member on the same side of the element are arranged such that the wiping pole (5a, 5b) and the stabilizing pole (5a, 5b) coincide.
2. A device according to claim 1, wherein the elongated metallic element is a metallic strip (1) .
3. A device according to claim 1 or 2 , wherein the wiping member and the stabilizing member have a common magnetic core (12a, 12b) .
4. A device according to any of the preceding claims, wherein the wiping member and the stabilizing member form an integrated unit.
5. A device according to any of the preceding claims, wherein the stabilizing member comprises a stabilizing winding (8a, 8b).
6. A device according to any of claims 2-5, wherein the stabilizing winding (8a, 8b) is arranged between the strip (1) and the phase windings (6a, 6b, 7a, 7b) .
7. A device according to any of claims 2-6, 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 (ό) , and the base extends from the roof in a direction towards the strip (1) .
8. A device according to claim 7, wherein the stabilizing winding (8) is arranged around the base and the phase windings (6a, 6b, 7a, 7b) are arranged around the roof on each side of the base.
9. A device according to any of the preceding claims, wherein the device comprises a second pair of wiping members arranged spaced from the first pair of wiping members in a direction across the transport direction (3).
10. A device according to claim 9, wherein the device comprises a third pair of wiping members arranged spaced from the first and second pairs of wiping members in a direction across the transport direction (3).
11. A device according to any of claims 2-10, wherein at least one sensor (10a, 10b) for sensing the position of the strip (1) in relation to its predetermined transport path (x) is arranged in close proximity to at least one of the wiping members.
12. A device according to any of claims 3-11, wherein the device comprises a stabilizing element adapted to control the permeability in that part (15a, 15b) of the stabilizing pole (5a, 5b) that lies nearest the strip (1).
13. A device according to claim 12, wherein the stabilizing element comprises an external coil (14a, 14b) arranged outside the stabilizing winding (8a, 8b) .
14. A device according to any of claims 2-13, wherein the device comprises a circuit (16) adapted to apply a current (I) to at least one edge (13a, 13b) of the strip (1) for generating an additional wiping force.
15. A device according to claim 14, wherein the circuit (16) is adapted to control the current (I) based on the thickness of the coating as measured after the wiping off.
16. A method for controlling the thickness of a metallic coating on an elongated metallic element (1) , wherein the coating is applied by continuously transporting the element through a bath (2) of molten metal, wherein the method comprises :
- transporting the element (1) in a transport direction (3) along a predetermined transport path (x) ,
- wiping off excessive molten metal from the elongated metallic element (1) by applying a travelling magnetic field to the element (1) with the still non-solidified metallic coating, - measuring the thickness of the coating after wiping off excessive molten metal, whereby a difference between the measured thickness and a desired value of the thickness controls the current that passes to phase windings (6a, 6b, 7a, 7b) which generate the travelling magnetic field, - stabilizing the position of the object with respect to the predetermined transport path (x) by applying a stabilizing magnetic force to the elongated metallic element (1) in the same region as that in which the travelling magnetic field acts on the element .
17. A method according to claim 16, wherein the elongated metallic element is a metallic strip (1) .
18. A method according to claim 17, comprising
- determining the position of the strip (1) with respect to the transport path (x) by at least one sensor (10a, 10b) generating a value of a parameter that controls the magnitude of the stabilizing magnetic force, and
- applying said stabilizing magnetic force to the strip in response to the position of the strip (1) .
19. A method according to any of claims 17-18, wherein the strip (1) is stabilized by controlling the permeability in at least that part (15a, 15b) of the stabilizing pole (5) that is closest to the strip (1) .
20. A method according to claim 19, wherein the permeability in at least that part (15a, 15b) of the stabilizing pole (5) that is closest to the strip (1) is controlled by means of an external coil (14a, 14b) .
21. A method according to any of claims 17-20, wherein a current is applied to at least one edge (13a, 13b) of the strip (1) such that, together with the travelling magnetic field, a wiping force directed towards the bath (2) is created.
EP06747996A 2005-06-03 2006-05-24 A device and a method for coating an elongated metallic element with a layer of metal Withdrawn EP1888804A4 (en)

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SE0501338A SE528663C2 (en) 2005-06-03 2005-06-03 An apparatus and method for coating an elongated metallic element with a layer of metal
PCT/SE2006/050154 WO2006130102A1 (en) 2005-06-03 2006-05-24 A device and a method for coating an elongated metallic element with a layer of metal

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ITMI20071166A1 (en) * 2007-06-08 2008-12-09 Danieli Off Mecc METHOD AND DEVICE FOR THE CONTROL OF THE COATING THICKNESS OF A METAL METAL PRODUCT
ITMI20071164A1 (en) * 2007-06-08 2008-12-09 Danieli Off Mecc METHOD AND DEVICE FOR THE CONTROL OF THE COATING THICKNESS OF A METAL METAL PRODUCT
ITMI20071167A1 (en) * 2007-06-08 2008-12-09 Danieli Off Mecc METHOD AND DEVICE FOR THE CONTROL OF THE COATING THICKNESS OF A METAL METAL PRODUCT
BRPI0823127A2 (en) * 2008-09-23 2015-06-16 Siemens Vai Metals Tech Sas Method and apparatus for drying liquid coating metal at the outlet of a metal coating reservoir at tempering.
CN101665897B (en) * 2009-10-14 2011-01-05 天津市工大镀锌设备有限公司 Method and device for controlling thickness of steel wire hot-plating layer
ITMI20121533A1 (en) * 2012-09-14 2014-03-15 Danieli Off Mecc ELECTROMAGNETIC STABILIZER
EP3910089A1 (en) * 2020-05-12 2021-11-17 Clecim Sas Installation for coating a travelling metal product
CN111926278B (en) * 2020-09-24 2021-01-08 华中科技大学 Three-phase electromagnetic wiping device for strip-shaped workpiece and hot dip coating system

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CN101184861B (en) 2010-05-19
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SE528663C2 (en) 2007-01-16
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EP1888804A4 (en) 2011-03-16
KR20080027816A (en) 2008-03-28

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