EP2681348B1 - Method for refining a metallic coating on a steel strip - Google Patents

Method for refining a metallic coating on a steel strip Download PDF

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Publication number
EP2681348B1
EP2681348B1 EP12700622.9A EP12700622A EP2681348B1 EP 2681348 B1 EP2681348 B1 EP 2681348B1 EP 12700622 A EP12700622 A EP 12700622A EP 2681348 B1 EP2681348 B1 EP 2681348B1
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EP
European Patent Office
Prior art keywords
coating
steel strip
electromagnetic radiation
irradiation
strip
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.)
Not-in-force
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EP12700622.9A
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German (de)
French (fr)
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EP2681348A1 (en
Inventor
Winfried Höhn
Helmut Oberhoffer
Benjamin Johannes LIEBSCHER
Reiner Sauer
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ThyssenKrupp Rasselstein GmbH
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ThyssenKrupp Rasselstein GmbH
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Publication of EP2681348A1 publication Critical patent/EP2681348A1/en
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Publication of EP2681348B1 publication Critical patent/EP2681348B1/en
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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
    • C23C26/00—Coating not provided for in groups C23C2/00 - C23C24/00
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
    • 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
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/08—Tin or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C25D5/50—After-treatment of electroplated surfaces by heat-treatment
    • C25D5/505—After-treatment of electroplated surfaces by heat-treatment of electroplated tin coatings, e.g. by melting
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12708—Sn-base component
    • Y10T428/12722—Next to Group VIII metal-base component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12785—Group IIB metal-base component
    • Y10T428/12792—Zn-base component
    • Y10T428/12799—Next to Fe-base component [e.g., galvanized]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12861—Group VIII or IB metal-base component
    • Y10T428/12937—Co- or Ni-base component next to Fe-base component

Definitions

  • the invention relates to a method for refining a metallic coating on a steel strip or steel sheet according to the preamble of claim 1.
  • the melting of the coating can be done for example by inductive heating of the coated steel strip or by electrical resistance heating.
  • a method for increasing the corrosion protection of metallized iron strips or sheets is known in which the metallic coating is melted by increasing to a temperature above the melting temperature of the coating material and exposed to higher frequency vibrations during the crystallization process in the range between melting temperature and recrystallization temperature.
  • an arrangement for inductive heating of metallic strips for the melting of particular electrolytically applied coatings on steel strips is known.
  • the DE 196 11 929 C1 and the DE 42 33 516 A1 disclose methods in which metallic coatings of layered composites are melted by means of high-energy radiation, in particular laser beams.
  • the DE 199 49 972 C1 relates to a method for the production of moldings or for applying coatings to workpieces, wherein layers are formed by means of plasma build-up welding.
  • the WO 97/19816 -A describes a method for producing a metallic printing form for gravure printing, wherein a coating is applied to the surface of the printing form and this is removed directly by means of a focused beam, in particular a laser beam, in desired areas of the surface and in the areas freed from the coating the surface of the printing plate by etching or electrolysis made a metal removal for the production of gravure dot filter cups and the remaining parts of the coating are removed by means of a removal process from the surface of the printing plate.
  • a focused beam in particular a laser beam
  • the present invention seeks to provide a method for finishing a metallic coating on a steel strip or sheet, which is much more energy efficient compared to the known methods.
  • the method should also achieve a high corrosion stability of the treated according to the method coating even with thin coating runs.
  • the metallic coating is melted at least on its surface and over a portion of its thickness by heating to a temperature above the melting temperature of the coating material, wherein the heating by irradiation of the surface of the coating with a high power density electromagnetic radiation over a limited irradiation time of at most 10 ⁇ s.
  • the energy requirement is independent of the sheet thickness. It has surprisingly been found that compared to a mean standard thickness of tinplate of 0.2 mm, for example, in a two-sided melting within an irradiation time of at most 10 microseconds about 90% less heat energy in the band is needed. For the total energy requirement, the degree of absorption - depending on the wavelength of the radiation, the surface quality of the coating, etc. - and the efficiency of the radiation source must be taken into account.
  • the limited irradiation time can be achieved either by using a pulsed radiation source, which emits the electromagnetic radiation in short pulses with a maximum pulse duration of 10 microseconds.
  • the irradiation time can also be limited to the maximum value of 10 ⁇ s by using a radiation source emitting continuous electromagnetic radiation, which is moved at high speed with respect to the coated steel strip.
  • This embodiment of the invention is particularly suitable in strip coating systems in which a steel strip to be coated passes through a coating system in the strip longitudinal direction at high speed.
  • tinplate in a strip-tinning plant for example, in the electrolytic tinning of Steel belt achieves belt speeds of up to 700 m / min. At such high belt speeds, the irradiation times of at most 10 ⁇ s to be observed according to the invention can be maintained by focusing the electromagnetic radiation on the surface of the coating, without pulsed irradiation of the electromagnetic radiation being necessary.
  • irradiate the coated surface of the steel strip or sheet by means of a laser beam of high power density.
  • Short-pulse lasers which emit high-power laser beams with pulse durations in the nanosecond (ns) range are known in the prior art. With such short-pulse lasers, the irradiation time in the method according to the invention can also be reduced to values of less than 100 ns. It is also conceivable to reach these irradiation times with a cw laser.
  • the electromagnetic radiation radiated onto the surface of the coating merely heats the surface and a partial area or the entire thickness of the coating to temperatures above the melting temperature of the coating material.
  • the underlying steel strip or sheet is heated only slightly.
  • a significant energy input by the irradiation of the coated surface takes place in the inventive method at best in the uppermost layers of the steel surface.
  • the heat introduced into the coating can be dissipated through the still cool steel strip or sheet.
  • the temperature compensation after the melting of the coating is thus carried out automatically in the inventive method by the dissipation of heat in the coating by the still cool steel strip or sheet.
  • a radiation source which emits electromagnetic radiation is moved in order to heat the coating in the transverse direction of a steel belt moving at a belt speed.
  • the radiation is guided on the surface of the coating, that the entire surface of the coating is irradiated.
  • the rays of the individual radiation sources are expediently placed next to one another and overlapping on the surface of the coating in subregions.
  • the various radiation sources can also be moved relative to the coated steel strip, which moves itself away with a predetermined tape speed in the tape longitudinal direction.
  • the electromagnetic radiation emitted by the radiation source or radiation sources is thereby focused onto the surface of the coating by means of a deflecting and focusing device.
  • the diameter or the extent of the or each focus is expediently adapted to the speed of the moving steel belt (belt speed) so that a predetermined point on the surface of the coating passes through the extent of the focus in the direction of belt travel within the predetermined irradiation time of a maximum of 10 ⁇ s , This can ensure that any point on the surface of the coating is not irradiated with the electromagnetic radiation for more than the maximum irradiation time.
  • the radiation source or the radiation sources are expediently arranged so that the entire surface of the coating is irradiated as uniformly as possible and at most over an irradiation time which is lower than the maximum irradiation time of 10 ⁇ s.
  • an area of more than 1 m 2 per second is treated by irradiation with the coating surface with the electromagnetic radiation.
  • the energy density, which is introduced by the electromagnetic radiation in the coating, and the predetermined irradiation time is selected and matched so that the coating melts completely over its entire thickness to the boundary layer to the steel strip.
  • an alloy layer which is thin (compared to the thickness of the coating) and which consists of iron atoms and atoms of the coating material is formed at the boundary layer between the coating and the steel strip or steel sheet.
  • the energy density is preferably chosen so that only a part of the coating with the steel strip or Steel sheet alloyed and therefore still unalloyed coating after melting is present.
  • a very thin iron-tin alloy layer is formed at the boundary layer of the tin coating to the steel.
  • the thickness of the alloy layer corresponds approximately to a basis weight of only 0.05 to 0.3 g / m 2 . This ensures that a very good corrosion-resistant alloy layer with a visually appealing surface is achieved even with thin total tin deposits of, for example, 2.0 g / m 2 .
  • This very thin alloy layer leads to increased corrosion resistance of the coated steel and improved adhesion of the coating on the steel strip or sheet.
  • the exemplary embodiments relate to the finishing of a tinned steel sheet or a steel strip coated in a strip tin plating plant by electrodeposition of a tin layer.
  • the method according to the invention can be used not only for the finishing of tin-plated steel strips but in general for the finishing of metallic coatings on steel strips or steel sheets.
  • the metallic coatings may, for example, also be coatings of zinc or nickel.
  • FIG. 1 1 schematically shows a device for carrying out the method according to the invention for finishing a metallic coating on a steel sheet, the refinement of a tinned steel sheet being shown here by way of example.
  • the steel sheet is designated by reference numeral 1 and the tin coating is indicated by reference numeral 2.
  • the thickness of the tin coating 2, which has been applied for example by a galvanic coating method, is typically 0.1 g / m 2 to 11 g / m 2 .
  • a radiation source 5 is provided, which emits an electromagnetic beam 6.
  • the beam 6 is expediently focused on the surface of the coating 2 by means of a deflecting and focusing device.
  • the deflection and focusing device comprises a deflecting mirror 7 and a focusing lens 8.
  • the focus of the beam 6 on the surface of the coating 2 is in FIG. 1 denoted by reference numeral 9.
  • the radiation source 5 may be, for example, a laser emitting a laser beam of high power density.
  • the laser beam 6 may be a pulsed laser beam.
  • the pulse duration corresponds to the desired irradiation time, which according to the invention is at most 10 .mu.s and is preferably below 100 ns.
  • the irradiation of a sufficient amount of heat is required, which heats the coating within the very short irradiation time of at most 10 ⁇ s to temperatures above the melting temperature of the coating material.
  • the melting point is 232 ° C.
  • the electromagnetic radiation emitted by the radiation source 5 expediently has power densities in the range from 1 ⁇ 10 6 to 2 ⁇ 10 8 W / cm 2 and which is radiated by the electromagnetic radiation within the irradiation time (t A ) to the surface of the Coating radiated energy density is in the range of 0.01 J / cm 2 to 5.0 J / cm 2 .
  • the radiation source 5 laser
  • the laser beam 6 is movable with respect to the steel sheet 1 provided with the coating 2.
  • the deflection and focusing consisting of the deflection mirror 7 and the focusing lens 8, in the transverse direction to the steel sheet 1 slidably.
  • the deflection and focusing device is moved stepwise in the transverse direction y to the steel sheet 1, so that the focus 9 travels over the surface of the coating 2.
  • the coating 2 heats up briefly within the prescribed irradiation time on its surface and - depending on the selected power of the laser beam 6 - over a part or its entire thickness to temperatures above the melting temperature. As a result, the coating 2 is partially or completely melted. The melting gives the surface of the coating 2 a shiny appearance and the structure of the coating 2 is compacted. In FIG. 1 If the area of the coating 2 which has been melted over the surface of the coating 2 when the focus 9 moves is denoted by the reference numeral 3.
  • a very thin alloy layer is formed at the boundary layer of the coating 2 to the steel sheet 1.
  • an iron-tin alloy layer is formed, which in FIG. 1 denoted by reference numeral 4.
  • the thickness of the iron-tin alloy layer is shown in FIG. 4 not drawn to scale.
  • the thickness of the resulting iron-tin alloy layer is usually very thin and typically corresponds to an alloy layer support having a basis weight of 0.05 to 0.3 g / m 2 .
  • an energy density between 0.01 J / cm 2 and 5.0 J / cm 2 is to be irradiated onto the surface of the coating 2.
  • Preferred ranges of the energy density to be irradiated are 0.03 J / cm 2 to 2.5 J / cm 2 .
  • a pulsed laser 5 it is also possible to use radiation sources emitting continuously electromagnetic radiation 6.
  • cw lasers can be used which emit laser radiation of sufficiently high power density.
  • the electromagnetic radiation 6 In order to be able to comply with the short irradiation time of a maximum of 10 ⁇ s, the electromagnetic radiation 6 must then be moved at high speed relative to the coated steel strip 1.
  • FIGS. 2 to 6 Corresponding embodiments in which the radiation source 5 and the emitted electromagnetic beam 6 are moved relative to a steel strip 2, is in the FIGS. 2 to 6 shown schematically.
  • a steel strip 1 shown, which moves at a tape speed v B in the longitudinal direction of the steel strip 1.
  • v B tape speed
  • belt speeds of a few hundred meters per minute up to 700 m / min are achieved. Typical belt speeds are 10 m / s.
  • a laser beam 6 of a cw laser 5 (which in FIG. 2 not shown) focused.
  • the focus can be formed either as a line focus 9, which extends in the transverse direction of the steel strip and has an extension x L in the tape longitudinal direction.
  • a plurality of radiation sources 5 laser
  • the line focus 9 or the irradiation belt 10 are fixedly arranged and the steel belt 1 moves relative to the line focus 9 or the irradiation belt 10 in the direction of belt travel with the belt speed v B.
  • the extension of the line focus 9 or of the radiation band 10 in the strip running direction x L then results, for example, at the predetermined maximum irradiation time of 10 ⁇ s and a strip running speed of 10 m / s to 0.1 mm.
  • FIG. 3 a further embodiment of an apparatus for carrying out the method according to the invention is shown.
  • a plurality of radiation sources 5 that is to say, for example, a plurality of cw lasers
  • the foci 9 are arranged in the form of a grid on the surface of the coating 2, as in FIG. 3 shown schematically.
  • the expansion of the individual foci 9 is adapted to the tape speed v B and the predetermined irradiation time t A of a maximum of 10 microseconds. Appropriately, this is formed from the foci 9 and in FIG.
  • the "radiation network" formed by the foci 9, in particular its lattice spacings and the tilting angle ⁇ , is arranged so that the entire surface of the coating 2 of the steel strip 1 moving at the belt running speed v B is irradiated with the electromagnetic radiation (laser radiation) ,
  • FIG. 4 a further embodiment of an arrangement for carrying out the method according to the invention is shown.
  • a laser beam 6 of a cw laser 5 is focused by means of a focusing on the surface of the coating, the focus 9 in the longitudinal direction of moving at the belt speed v B steel strip an extension y laser and in the transverse direction to an extent x laser has.
  • the focus 9 is moved transversely to the steel strip 1 over the entire width b B of the steel strip at a speed v x, laser .
  • Ü denotes the overlap of rays adjacent to the surface.
  • a beam is directed as a focus 9 onto the surface of a coated steel belt moving at a belt speed v B.
  • the focus 9 is guided via a scanner optics obliquely to the longitudinal direction of the steel strip at a speed of v x, laser . If the beam focus 9 has reached a band edge, it is again guided over the band to the opposite edge of the steel band, etc., while the band continues to move at the band travel speed v B. In this case, the successive beam bands that arise on the surface overlap to ensure that the entire surface is also detected by the radiation.
  • the focus 9 is moved biaxially relative to the steel strip, namely both in the longitudinal direction (x-direction) at a speed v x, laser and in the transverse direction (y-direction) at a speed v y, laser .
  • the velocity v y, laser in the transverse direction (y-direction) is suitably set so that over the entire width b B of the steel strip in the y-direction, a uniform overlap Ü is maintained.
  • FIG. 9 is the temperature profile T (x) resulting from the irradiation of the electromagnetic radiation during the heating of the coating by the thickness (x) of the coating and of the steel strip below for different irradiation times t.
  • T (x) results for very short irradiation times t in the ns and ⁇ s range.
  • a flat temperature profile is obtained, ie here the essential part of the radiated energy is dissipated into the steel strip.
  • the very short irradiation times of a maximum of 10 ⁇ s essentially only the coating, but not the underlying steel strip, is heated.
  • FIG. 7 the amount of heat applied per unit area in the coated steel strip is plotted as a function of the irradiation time for different surface temperatures. The calculation is lossless. For comparison, the "maximum energy density" (maximum energy) is entered in each case. The maximum energy required is the amount of energy needed to heat the entire cross section evenly.
  • the predetermined irradiation time which is a maximum of 10 ⁇ s according to the invention, determines which temperature profile is established across the thickness x of the coating and the steel strip ( FIG. 9 ).
  • a sufficiently low irradiation time t it can be achieved that the essential part of the radiated energy is limited to the area of the coating and the heat energy does not flow off into the steel strip below. In this way, can be dispensed with after quenching of the coating on a quenching in a water bath, because the heat in the coating by the (not heated) steel strip can be dissipated.
  • the coating Upon irradiation of a sufficiently high energy density - depending on the thickness of the metallic coating - the coating can be completely, ie over its entire thickness to the steel surface, melted.
  • a thin and very dense alloy layer which consists of atoms, forms in the area of the boundary layer to the steel surface (in comparison to the thickness of the coating) of the coating material and iron atoms.
  • the forming alloy layer is very thin and corresponds to an alloy layer of tinplate 0.05 to 0.3 g / m 2 .
  • the alloy layer forming in the treatment according to the invention has a fundamentally different microscopic appearance compared to the alloy layers which form in the known process procedure. This is from the in FIG. 8 shown microprobe recordings.
  • the FIGS. 8a and 8b show micro-probe images of alloy layers (after the detachment of the unalloyed tin), which have formed during the melting of a tin coating on a steel sheet in the boundary layer to the steel surface in carrying out the method according to the invention. In contrast, shows FIG.
  • Typical alloy layer coverings are in the range of 0.5 to 0.8 g / m 2 in the case of painted tinplate, and 0.8 to 1.2 g / m 2 in the case of unpainted tinplate with an increased requirement for corrosion resistance.
  • the method according to the invention it is possible to produce steel strips or sheets provided with a metallic coating, in which at the boundary layer of the steel for coating a thin and at the same time dense compared with the thickness of the coating Alloy layer of iron atoms and atoms of the coating material is formed.
  • the thickness of the alloy layer corresponds to an alloy film coating of less than 0.3 g / m 2.
  • tinned steel strips or sheets can be produced, which have a sufficiently good corrosion resistance despite a comparatively thin tin coating of less than 2.8 g / m 2 and in particular of less than 2.0 g / m 2 .

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  • Mechanical Engineering (AREA)
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Description

Die Erfindung betrifft ein Verfahren zum Veredeln einer metallischen Beschichtung auf einem Stahlband oder Stahlblech nach dem Oberbegriff des Anspruchs 1.The invention relates to a method for refining a metallic coating on a steel strip or steel sheet according to the preamble of claim 1.

Bei der Herstellung von galvanisch beschichteten Stahlbändern, beispielsweise bei der Herstellung von Weißblech, ist es bekannt, die Korrosionsbeständigkeit der Beschichtung durch ein Aufschmelzen der Beschichtung nach dem galvanischen Beschichtungsvorgang zu erhöhen. Hierzu wird die auf das Stahlband galvanisch abgeschiedene Beschichtung auf eine über dem Schmelzpunkt des Beschichtungsmaterials liegende Temperatur erhitzt und anschließend in einem Wasserbad abgeschreckt. Durch das Aufschmelzen der Beschichtung erhält die Oberfläche der Beschichtung ein glänzendes Aussehen und die Porösität der Beschichtung wird vermindert, wodurch sich deren Korrosionsbeständigkeit erhöht und ihre Durchlässigkeit für aggressive Stoffe, beispielsweise organische Säuren, vermindert.In the production of galvanically coated steel strips, for example in the production of tinplate, it is known to increase the corrosion resistance of the coating by melting the coating after the galvanic coating process. For this purpose, the galvanically deposited on the steel strip coating is heated to above the melting point of the coating material temperature and then quenched in a water bath. The melting of the coating gives the surface of the coating a shiny appearance and reduces the porosity of the coating, thereby increasing its corrosion resistance and reducing its permeability to corrosive substances such as organic acids.

Das Aufschmelzen der Beschichtung kann beispielsweise durch induktive Erhitzung des beschichteten Stahlbands oder durch elektrisches Widerstandsheizen erfolgen. Aus der DE 1 277 896 ist beispielsweise ein Verfahren zur Erhöhung des Korrosionsschutzes von metallisierten Eisenbändern oder -blechen bekannt, bei dem die metallische Beschichtung durch Erhöhung auf eine Temperatur oberhalb der Schmelztemperatur des Beschichtungsmaterials aufgeschmolzen und während des Kristallisationsvorgangs im Bereich zwischen Schmelztemperatur und Rekristallisationstemperatur Schwingungen höherer Frequenz ausgesetzt wird. Aus der DE 1 186 158-A ist eine Anordnung zum induktiven Erwärmen von metallischen Bändern für das Aufschmelzen von insbesondere elektrolytisch aufgebrachten Beschichtungen auf Stahlbändern bekannt.The melting of the coating can be done for example by inductive heating of the coated steel strip or by electrical resistance heating. From the DE 1 277 896 For example, a method for increasing the corrosion protection of metallized iron strips or sheets is known in which the metallic coating is melted by increasing to a temperature above the melting temperature of the coating material and exposed to higher frequency vibrations during the crystallization process in the range between melting temperature and recrystallization temperature. From the DE 1 186 158-A an arrangement for inductive heating of metallic strips for the melting of particular electrolytically applied coatings on steel strips is known.

Bei den bekannten Verfahren zum Aufschmelzen von metallischen Beschichtungen auf Stahlbändern oder -blechen wird in der Regel das gesamte Stahlband -bzw. Blech, einschließlich der aufgebrachten Beschichtung, auf Temperaturen oberhalb der Schmelztemperatur des Beschichtungsmaterials erwärmt und anschließend, beispielweise in einem Wasserbad, wieder auf Normaltemperatur abgekühlt. Hierfür ist ein erheblicher Energiebedarf notwendig.In the known method for melting metallic coatings on steel strips or sheets is generally the entire steel strip -bzw. Sheet metal, including the applied coating, heated to temperatures above the melting temperature of the coating material and then cooled again, for example in a water bath, back to normal temperature. This requires a considerable amount of energy.

Die DE 196 11 929 C1 und die DE 42 33 516 A1 offenbaren Verfahren, in denen metallische Beschichtungen von Schichtverbundwerkstoffen mittels hochenergetischer Strahlen, insbesondere Laserstrahlen, aufgeschmolzen werden. Die DE 199 49 972 C1 betrifft ein Verfahren zur Herstellung von Formkörpern oder zum Auftragen von Beschichtungen auf Werkstücken, wobei Schichten mittels Plasma-Auftragschweißen ausgebildet werden. Die WO 97/19816 -A beschreibt ein Verfahren zur Herstellung einer metallischen Druckform für den Tiefdruck, wobei auf die Oberfläche der Druckform eine Beschichtung aufgebracht und diese mittels eines fokussierten Strahls, insbesondere eines Laserstrahls, in gewünschten Bereichen der Oberfläche unmittelbar abgetragen wird und in den von der Beschichtung befreiten Bereichen der Oberfläche der Druckform durch Ätzen oder Elektrolyse ein Metallabtrag zur Erzeugung von Tiefdruck-Rasternäpfchen vorgenommen und die noch vorhandenen Teile der Beschichtung mittels eines Entfernungsprozesses von der Oberfläche der Druckform entfernt werden.The DE 196 11 929 C1 and the DE 42 33 516 A1 disclose methods in which metallic coatings of layered composites are melted by means of high-energy radiation, in particular laser beams. The DE 199 49 972 C1 relates to a method for the production of moldings or for applying coatings to workpieces, wherein layers are formed by means of plasma build-up welding. The WO 97/19816 -A describes a method for producing a metallic printing form for gravure printing, wherein a coating is applied to the surface of the printing form and this is removed directly by means of a focused beam, in particular a laser beam, in desired areas of the surface and in the areas freed from the coating the surface of the printing plate by etching or electrolysis made a metal removal for the production of gravure dot filter cups and the remaining parts of the coating are removed by means of a removal process from the surface of the printing plate.

Hiervon ausgehend liegt der Erfindung die Aufgabe zugrunde, ein Verfahren zum Veredeln einer metallischen Beschichtung auf einem Stahlband oder -blech aufzuzeigen, welches im Vergleich zu den bekannten Verfahren wesentlich energieeffizienter ist. Das Verfahren soll ferner eine hohe Korrosionsstabilität der verfahrensgemäß behandelten Beschichtung auch bei dünnen Beschichtungsauflagen erzielen.On this basis, the present invention seeks to provide a method for finishing a metallic coating on a steel strip or sheet, which is much more energy efficient compared to the known methods. The method should also achieve a high corrosion stability of the treated according to the method coating even with thin coating runs.

Gelöst werden diese Aufgaben mit einem Verfahren mit den Merkmalen des Anspruchs 1. Bevorzugte Ausführungsformen des erfindungsgemäßen Verfahrens sind in den Unteransprüchen angegeben.These objects are achieved by a method having the features of claim 1. Preferred embodiments of the method according to the invention are specified in the subclaims.

Bei dem erfindungsgemäßen Verfahren wird die metallische Beschichtung zumindest an ihrer Oberfläche und über einen Teilbereich ihrer Dicke durch Erhitzen auf eine Temperatur oberhalb der Schmelztemperatur des Beschichtungsmaterials aufgeschmolzen, wobei das Erhitzen durch eine Bestrahlung der Oberfläche der Beschichtung mit einer elektromagnetischen Strahlung hoher Leistungsdichte über eine begrenzte Bestrahlungszeit von höchstens 10 µs erfolgt. Der Energiebedarf ist unabhängig von der Blechdicke. Es hat sich in überraschender Weise gezeigt, dass gegenüber einer mittleren Standarddicke bei Weißblech von 0,2 mm bspw. bei einer beidseitigen Aufschmelzung innerhalb einer Bestrahlungszeit von höchstens 10 µs ca. 90 % weniger Wärmeenergie im Band benötigt wird. Für den Gesamtenergiebedarf ist der Absorptionsgrad - abhängig von Wellenlänge der Strahlung, Oberflächenbeschaffenheit der Beschichtung, usw. - sowie der Wirkungsgrad der Strahlungsquelle zu berücksichtigen.In the method according to the invention, the metallic coating is melted at least on its surface and over a portion of its thickness by heating to a temperature above the melting temperature of the coating material, wherein the heating by irradiation of the surface of the coating with a high power density electromagnetic radiation over a limited irradiation time of at most 10 μs. The energy requirement is independent of the sheet thickness. It has surprisingly been found that compared to a mean standard thickness of tinplate of 0.2 mm, for example, in a two-sided melting within an irradiation time of at most 10 microseconds about 90% less heat energy in the band is needed. For the total energy requirement, the degree of absorption - depending on the wavelength of the radiation, the surface quality of the coating, etc. - and the efficiency of the radiation source must be taken into account.

Die begrenzte Bestrahlungszeit kann dabei entweder durch Verwendung einer gepulsten Strahlungsquelle erreicht werden, welche die elektromagnetische Strahlung in kurzen Pulsen mit einer maximalen Pulsdauer von 10 µs emittiert. Die Bestrahlungszeit kann auch dadurch auf den Maximalwert von 10 µs begrenzt werden, dass eine kontinuierlich elektromagnetische Strahlung emittierende Strahlungsquelle verwendet wird, welche gegenüber dem beschichteten Stahlband mit hoher Geschwindigkeit bewegt wird. Diese Ausführungsform der Erfindung bietet sich insbesondere in Bandbeschichtungsanlagen an, in denen ein zu beschichtendes Stahlband eine Beschichtungsanlage in Bandlängsrichtung mit hoher Geschwindigkeit durchläuft. Bei der Herstellung von Weißblech in einer Bandverzinnungsanlage werden beispielsweise bei der elektrolytischen Verzinnung von Stahlband Bandgeschwindigkeiten von bis zu 700 m/min erreicht. Bei derart hohen Bandlaufgeschwindigkeiten können die erfindungsgemäß einzuhaltenden Bestrahlungszeiten von höchstens 10 µs durch Fokussierung der elektromagnetischen Strahlung auf die Oberfläche der Beschichtung eingehalten werden, ohne dass eine gepulste Einstrahlung der elektromagnetischen Strahlung notwendig wäre.The limited irradiation time can be achieved either by using a pulsed radiation source, which emits the electromagnetic radiation in short pulses with a maximum pulse duration of 10 microseconds. The irradiation time can also be limited to the maximum value of 10 μs by using a radiation source emitting continuous electromagnetic radiation, which is moved at high speed with respect to the coated steel strip. This embodiment of the invention is particularly suitable in strip coating systems in which a steel strip to be coated passes through a coating system in the strip longitudinal direction at high speed. In the manufacture of tinplate in a strip-tinning plant, for example, in the electrolytic tinning of Steel belt achieves belt speeds of up to 700 m / min. At such high belt speeds, the irradiation times of at most 10 μs to be observed according to the invention can be maintained by focusing the electromagnetic radiation on the surface of the coating, without pulsed irradiation of the electromagnetic radiation being necessary.

Zweckmäßig erfolgt die Bestrahlung der beschichteten Oberfläche des Stahlbands oder - blechs mittels eines Laserstrahls hoher Leistungsdichte. Aus dem Stand der Technik sind Kurzpuls-Laser bekannt, welche Laserstrahlen hoher Leistung mit Pulsdauern im Bereich von Nanosekunden (ns) emittieren. Mit solchen Kurzpuls-Lasern kann die Bestrahlungszeit bei dem erfindungsgemäßen Verfahren auch auf Werte von unter 100 ns reduziert werden. Denkbar ist das Erreichen dieser Bestrahlungszeiten auch mit einem cw-Laser.It is expedient to irradiate the coated surface of the steel strip or sheet by means of a laser beam of high power density. Short-pulse lasers which emit high-power laser beams with pulse durations in the nanosecond (ns) range are known in the prior art. With such short-pulse lasers, the irradiation time in the method according to the invention can also be reduced to values of less than 100 ns. It is also conceivable to reach these irradiation times with a cw laser.

Aufgrund der geringen Bestrahlungszeit erhitzt die auf die Oberfläche der Beschichtung eingestrahlte elektromagnetische Strahlung lediglich die Oberfläche und einen Teilbereich oder die gesamte Dicke der Beschichtung auf Temperaturen oberhalb der Schmelztemperatur des Beschichtungsmaterials. Das darunterliegende Stahlband oder -blech wird jedoch nur unwesentlich erwärmt. Ein nennenswerter Energieeintrag durch die Bestrahlung der beschichteten Oberfläche erfolgt bei dem erfindungsgemäßen Verfahren allenfalls in die obersten Lagen der Stahloberfläche. Dadurch kann nach dem kurzzeitigen Aufschmelzen der Beschichtung die in die Beschichtung eingetragene Wärme durch das noch kühle Stahlband bzw. -blech abgeführt werden. Der Temperaturausgleich nach dem Aufschmelzen der Beschichtung erfolgt damit bei dem erfindungsgemäßen Verfahren automatisch durch die Ableitung der Wärme in der Beschichtung durch das noch kühle Stahlband bzw. -blech. Eine anschließende Abschreckung in einem Wasserbad, wie bei den bekannten Verfahren, ist nicht mehr erforderlich. Dadurch kann erheblich Energie gespart werden, die bei den bekannten Verfahren durch die Aufheizung des gesamten Stahlbands bzw. -blechs auf Temperaturen oberhalb der Schmelztemperatur des Beschichtungsmaterials und die anschließende Abschreckung im Wasserbad eingesetzt werden muss.Due to the low irradiation time, the electromagnetic radiation radiated onto the surface of the coating merely heats the surface and a partial area or the entire thickness of the coating to temperatures above the melting temperature of the coating material. However, the underlying steel strip or sheet is heated only slightly. A significant energy input by the irradiation of the coated surface takes place in the inventive method at best in the uppermost layers of the steel surface. As a result, after the short-term melting of the coating, the heat introduced into the coating can be dissipated through the still cool steel strip or sheet. The temperature compensation after the melting of the coating is thus carried out automatically in the inventive method by the dissipation of heat in the coating by the still cool steel strip or sheet. A subsequent quenching in a water bath, as in the known methods, is no longer necessary. As a result, considerable energy can be saved, which must be used in the known method by heating the entire steel strip or sheet to temperatures above the melting temperature of the coating material and the subsequent quenching in a water bath.

In einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens wird eine Strahlungsquelle, welche eine elektromagnetische Strahlung emittiert, zur Erhitzung der Beschichtung in Querrichtung eines sich mit einer Bandgeschwindigkeit bewegenden Stahlbands bewegt. Zweckmäßig können für die Bestrahlung der Oberfläche der Beschichtung auch mehrere Strahlungsquellen verwendet werden, deren Strahlung so auf die Oberfläche der Beschichtung geführt wird, dass die gesamte Oberfläche der Beschichtung bestrahlt wird. Zweckmäßig werden die Strahlen der einzelnen Strahlungsquellen dabei nebeneinander liegend und sich in Teilbereichen überlappend auf die Oberfläche der Beschichtung geführt. Die verschiedenen Strahlungsquellen können dabei auch relativ zum beschichteten Stahlband bewegt werden, welches sich selbst mit einer vorgegebenen Bandlaufgeschwindigkeit in Bandlängsrichtung fort bewegt.In a preferred embodiment of the method according to the invention, a radiation source which emits electromagnetic radiation is moved in order to heat the coating in the transverse direction of a steel belt moving at a belt speed. Appropriately, for the irradiation of the surface of the Coating can also be used multiple radiation sources, the radiation is guided on the surface of the coating, that the entire surface of the coating is irradiated. The rays of the individual radiation sources are expediently placed next to one another and overlapping on the surface of the coating in subregions. The various radiation sources can also be moved relative to the coated steel strip, which moves itself away with a predetermined tape speed in the tape longitudinal direction.

Die von der Strahlungsquelle bzw. den Strahlungsquellen emittierte elektromagnetische Strahlung wird dabei mittels einer Umlenk- und Fokussiereinrichtung auf die Oberfläche der Beschichtung fokussiert. Zweckmäßig wird der Durchmesser bzw. die Ausdehnung des bzw. jedes Fokus so an die Geschwindigkeit des sich bewegenden Stahlbands (Bandgeschwindigkeit) angepasst, das ein vorgegebener Punkt auf der Oberfläche der Beschichtung die Ausdehnung des Fokus in Bandlaufrichtung innerhalb der vorgegebenen Bestrahlungszeit von maximal 10 µs durchläuft. Dadurch kann gewährleistet werden, dass jeder Punkt auf der Oberfläche der Beschichtung nicht länger als die maximale Bestrahlungszeit mit der elektromagnetischen Strahlung bestrahlt wird.The electromagnetic radiation emitted by the radiation source or radiation sources is thereby focused onto the surface of the coating by means of a deflecting and focusing device. The diameter or the extent of the or each focus is expediently adapted to the speed of the moving steel belt (belt speed) so that a predetermined point on the surface of the coating passes through the extent of the focus in the direction of belt travel within the predetermined irradiation time of a maximum of 10 μs , This can ensure that any point on the surface of the coating is not irradiated with the electromagnetic radiation for more than the maximum irradiation time.

Die Strahlungsquelle bzw. die Strahlungsquellen werden zweckmäßig so angeordnet, dass die gesamte Oberfläche der Beschichtung möglichst gleichmäßig und höchstens über eine Bestrahlungszeit, welche niedriger als die maximale Bestrahlungszeit von 10 µs ist, bestrahlt wird. Bevorzugt wird eine Fläche von mehr als 1m2 pro Sekunde durch Bestrahlung mit der Beschichtungsoberfläche mit der elektromagnetischen Strahlung behandelt.The radiation source or the radiation sources are expediently arranged so that the entire surface of the coating is irradiated as uniformly as possible and at most over an irradiation time which is lower than the maximum irradiation time of 10 μs. Preferably, an area of more than 1 m 2 per second is treated by irradiation with the coating surface with the electromagnetic radiation.

Bevorzugt wird die Energiedichte, welche durch die elektromagnetische Strahlung in die Beschichtung eingebracht wird, und die vorgegebene Bestrahlungszeit so ausgewählt und aufeinander abgestimmt, dass die Beschichtung vollständig über ihre gesamte Dicke bis zur Grenzschicht zum Stahlband aufschmilzt. Dadurch wird zwar ein Teil der eingetragenen Wärme auch in das Stahlband geleitet, wodurch Energie- bzw. Wärmeverluste entstehen. Allerdings bildet sich bei dieser bevorzugten Verfahrensführung überraschenderweise an der Grenzschicht zwischen der Beschichtung und dem Stahlband bzw. dem Stahlblech eine (verglichen mit der Dicke der Beschichtung) dünne Legierungsschicht aus, welche aus Eisenatomen und Atomen des Beschichtungsmaterials besteht. Die Energiedichte wird vorzugsweise so gewählt, dass nur ein Teil der Beschichtung mit den Stahlband bzw. dem Stahlblech legiert und daher noch unlegierte Beschichtung nach dem Aufschmelzen vorhanden ist. Bei verzinnten Stahlbändern bildet sich also beispielsweise an der Grenzschicht der Zinnbeschichtung zum Stahl eine sehr dünne Eisen-Zinn-Legierungsschicht aus. Die Dicke der Legierungsschicht entspricht dabei, je nach gewählten Prozessparametern, in etwa einem Flächengewicht von nur 0,05 bis 0,3 g/m2. Damit wird sicher gestellt das auch bei dünnen Gesamtzinnauflagen von z.B. 2.0 g/m2 eine sehr gute korrosionsbeständige Legierungssschicht bei optisch ansprechender Oberfläche erzielt wird. Diese sehr dünne Legierungsschicht führt zu einer erhöhten Korrosionsbeständigkeit des beschichteten Stahls und zu einer verbesserten Haftung der Beschichtung auf dem Stahlband bzw. -blech.Preferably, the energy density, which is introduced by the electromagnetic radiation in the coating, and the predetermined irradiation time is selected and matched so that the coating melts completely over its entire thickness to the boundary layer to the steel strip. As a result, although a part of the registered heat is also conducted into the steel strip, resulting in energy or heat losses. However, surprisingly, in this preferred process procedure, an alloy layer which is thin (compared to the thickness of the coating) and which consists of iron atoms and atoms of the coating material is formed at the boundary layer between the coating and the steel strip or steel sheet. The energy density is preferably chosen so that only a part of the coating with the steel strip or Steel sheet alloyed and therefore still unalloyed coating after melting is present. In tin-plated steel strips, for example, a very thin iron-tin alloy layer is formed at the boundary layer of the tin coating to the steel. Depending on the selected process parameters, the thickness of the alloy layer corresponds approximately to a basis weight of only 0.05 to 0.3 g / m 2 . This ensures that a very good corrosion-resistant alloy layer with a visually appealing surface is achieved even with thin total tin deposits of, for example, 2.0 g / m 2 . This very thin alloy layer leads to increased corrosion resistance of the coated steel and improved adhesion of the coating on the steel strip or sheet.

Nachfolgend wird die Erfindung anhand verschiedener Ausführungsbeispiele unter Bezugnahme auf die begleitenden Zeichnungen näher erläutert. Die Zeichnungen zeigen:

Fig. 1:
Schematische Darstellung einer ersten Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens, wobei ein mit einer metallischen Beschichtung versehenes Stahlblech im Querschnitt gezeigt ist;
Fig. 2:
Schematische Darstellung einer weiteren Anordnung zur Veredelung der metallischen Beschichtung auf einem sich bewegenden Stahlband in einer Draufsicht auf das beschichtete Stahlband;
Fig. 3:
Schematische Darstellung einer weiteren Anordnung zur Veredelung der metallischen Beschichtung auf einem sich bewegenden Stahlband in einer Draufsicht auf das beschichtete Stahlband;
Fig. 4:
Schematische Darstellung einer weiteren Anordnung zur Veredelung der metallischen Beschichtung auf einem sich bewegenden Stahlband in einer Draufsicht auf das beschichtete Stahlband;
Fig. 5:
Schematische Darstellung einer weiteren Anordnung zur Veredelung der metallischen Beschichtung auf einem sich bewegenden Stahlband in einer Draufsicht auf das beschichtete Stahlband;
Fig. 6:
Schematische Darstellung einer weiteren Anordnung zur Veredelung der metallischen Beschichtung auf einem sich bewegenden Stahlband in einer Draufsicht auf das beschichtete Stahlband;
Fig. 7:
Darstellung von aus Modellrechnungen entwickelten Diagrammen, welche die in das beschichtete Stahlband bzw. -blech durch Bestrahlung mit der elektromagnetischen Strahlung eingebrachte Wärmemenge pro Flächeneinheit in Abhängigkeit der Bestrahlungszeit für verschiedene Temperaturen an der Oberfläche der Beschichtung zeigt (Fig. 7a: 400°C Oberflächentemperatur; Fig. 7b: 700°C Oberflächentemperatur und Fig. 7c: 1000°C Oberflächentemperatur);
Fig. 8:
Mikrosonden-Aufnahmen der Legierungsschichten, die sich beim Aufschmelzen der Beschichtung im Bereich der Grenzschicht zur Stahloberfläche bei Durchführung des erfindungsgemäßen Verfahrens (Figuren 8a und 8b) und bei herkömmlicher Verfahrensführung gebildet hat;
Fig. 9:
Darstellung des sich bei Bestrahlung einer beschichteten Stahlbandoberfläche mit elektromagnetischer Strahlung ergebenden Temperaturprofils (T(x)) über die Banddicke (x) bzw. die Dicke der Beschichtung für verschiedene Bestrahlungszeiten t.
The invention will be explained in more detail with reference to various embodiments with reference to the accompanying drawings. The drawings show:
Fig. 1:
Schematic representation of a first embodiment of an apparatus for performing the method according to the invention, wherein a provided with a metallic coating steel sheet is shown in cross section;
Fig. 2:
Schematic representation of another arrangement for refining the metallic coating on a moving steel strip in a plan view of the coated steel strip;
3:
Schematic representation of another arrangement for refining the metallic coating on a moving steel strip in a plan view of the coated steel strip;
4:
Schematic representation of another arrangement for refining the metallic coating on a moving steel strip in a plan view of the coated steel strip;
Fig. 5:
Schematic representation of another arrangement for refining the metallic coating on a moving steel strip in a plan view of the coated steel strip;
Fig. 6:
Schematic representation of another arrangement for refining the metallic coating on a moving steel strip in a plan view of the coated steel strip;
Fig. 7:
Representation of diagrams developed from model calculations, which the amount of heat introduced into the coated steel strip or sheet by irradiation with the electromagnetic radiation per unit area in Dependence of irradiation time for different temperatures on the surface of the coating ( Fig. 7a : 400 ° C surface temperature; Fig. 7b : 700 ° C surface temperature and Fig. 7c : 1000 ° C surface temperature);
Fig. 8:
Microprobe exposures of the alloy layers, which occur during the melting of the coating in the region of the boundary layer to the steel surface when carrying out the method according to the invention ( FIGS. 8a and 8b ) and has formed in conventional process management;
Fig. 9:
Representation of the resulting upon irradiation of a coated steel strip surface with electromagnetic radiation temperature profile (T (x)) on the strip thickness (x) or the thickness of the coating for different irradiation times t.

Die Ausführungsbeispiele betreffen die Veredelung eines verzinnten Stahlblechs oder eines in einer Bandverzinnungsanlage durch galvanisches Abscheiden einer Zinnschicht beschichteten Stahlbands. Das erfindungsgemäße Verfahren kann jedoch nicht nur zur Veredelung von verzinnten Stahlbändern sondern ganz allgemein zur Veredelung von metallischen Beschichtungen auf Stahlbändern oder Stahlblechen eingesetzt werden. Bei den metallischen Beschichtungen kann es sich bspw. auch um Beschichtungen aus Zink oder Nickel handeln.The exemplary embodiments relate to the finishing of a tinned steel sheet or a steel strip coated in a strip tin plating plant by electrodeposition of a tin layer. However, the method according to the invention can be used not only for the finishing of tin-plated steel strips but in general for the finishing of metallic coatings on steel strips or steel sheets. The metallic coatings may, for example, also be coatings of zinc or nickel.

In Figur 1 ist schematisch eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens zum Veredeln einer metallischen Beschichtung auf einem Stahlblech gezeigt, wobei hier beispielhaft die Veredelung eines verzinnten Stahlblechs dargestellt ist. Das Stahlblech ist dabei mit Bezugsziffer 1 bezeichnet und die Zinn-Beschichtung ist mit Bezugsziffer 2 gekennzeichnet. Die Dicke der Zinnbeschichtung 2, welche beispielsweise in einem galvanischen Beschichtungsverfahren aufgebracht worden ist, beträgt typischerweise 0,1 g/m2 bis 11 g/m2. Zum Aufschmelzen der Beschichtung 2 ist eine Strahlungsquelle 5 vorgesehen, welche einen elektromagnetischen Strahl 6 emittiert. Der Strahl 6 wird zweckmäßig mittels einer Umlenk- und Fokussiereinrichtung auf die Oberfläche der Beschichtung 2 fokussiert. In dem hier gezeigten Ausführungsbeispiel umfasst die Umlenk- und Fokussiereinrichtung einen Umlenkspiegel 7 und eine Fokussierlinse 8. Der Fokus des Strahls 6 auf der Oberfläche der Beschichtung 2 ist in Figur 1 mit Bezugsziffer 9 gekennzeichnet.In FIG. 1 1 schematically shows a device for carrying out the method according to the invention for finishing a metallic coating on a steel sheet, the refinement of a tinned steel sheet being shown here by way of example. The steel sheet is designated by reference numeral 1 and the tin coating is indicated by reference numeral 2. The thickness of the tin coating 2, which has been applied for example by a galvanic coating method, is typically 0.1 g / m 2 to 11 g / m 2 . For melting the coating 2, a radiation source 5 is provided, which emits an electromagnetic beam 6. The beam 6 is expediently focused on the surface of the coating 2 by means of a deflecting and focusing device. In the exemplary embodiment shown here, the deflection and focusing device comprises a deflecting mirror 7 and a focusing lens 8. The focus of the beam 6 on the surface of the coating 2 is in FIG. 1 denoted by reference numeral 9.

Bei der Strahlungsquelle 5 kann es sich beispielsweise um einen Laser handeln, der einen Laserstrahl hoher Leistungsdichte emittiert. In einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens kann es sich bei dem Laserstrahl 6 um einen gepulsten Laserstrahl handeln. Die Pulsdauer entspricht dabei der gewünschten Bestrahlungszeit, welche erfindungsgemäß höchstens 10 µs beträgt und bevorzugt unter 100 ns liegt. Um die Beschichtung 2 zumindest an ihrer Oberfläche und über einen Teil ihrer Dicke aufzuschmelzen, ist die Einstrahlung einer ausreichenden Wärmemenge erforderlich, welche die Beschichtung innerhalb der erfindungsgemäß sehr kurzen Bestrahlungszeit von höchstens 10 µs auf Temperaturen oberhalb der Schmelztemperatur des Beschichtungsmaterials erhitzt. Bei der hier beispielhaft dargestellten Zinnbeschichtung 2 beträgt der Schmelzpunkt 232°C. Die von der Strahlungsquelle 5 (gepulster Laser) emittierte elektromagnetische Strahlung weist hierfür zweckmäßig Leistungsdichten im Bereich von 1•106 bis 2•108 W/cm2 auf und die durch die elektromagnetische Strahlung innerhalb der Bestrahlungszeit (tA) auf die Oberfläche der Beschichtung eingestrahlte Energiedichte liegt im Bereich von 0,01 J/cm2 bis 5,0 J/cm2.The radiation source 5 may be, for example, a laser emitting a laser beam of high power density. In one embodiment of the method according to the invention, the laser beam 6 may be a pulsed laser beam. The pulse duration corresponds to the desired irradiation time, which according to the invention is at most 10 .mu.s and is preferably below 100 ns. In order to melt the coating 2 at least on its surface and over part of its thickness, the irradiation of a sufficient amount of heat is required, which heats the coating within the very short irradiation time of at most 10 μs to temperatures above the melting temperature of the coating material. In the tin coating 2 exemplified here, the melting point is 232 ° C. For this purpose, the electromagnetic radiation emitted by the radiation source 5 (pulsed laser) expediently has power densities in the range from 1 × 10 6 to 2 × 10 8 W / cm 2 and which is radiated by the electromagnetic radiation within the irradiation time (t A ) to the surface of the Coating radiated energy density is in the range of 0.01 J / cm 2 to 5.0 J / cm 2 .

Um mit einem gepulsten Laserstrahl 6 die gesamte Oberfläche der Beschichtung 2 bestrahlen zu können, ist die Strahlungsquelle 5 (Laser) bzw. der Laserstrahl 6 in Bezug auf das mit der Beschichtung 2 versehene Stahlblech 1 beweglich. Hierfür ist bspw. bei dem in Figur 1 gezeigten Ausführungsbeispiel die Umlenk- und Fokussiereinrichtung, bestehend aus dem Umlenkspiegel 7 und der Fokussierlinse 8, in Querrichtung zum Stahlblech 1 verschiebbar. Zur vollflächigen Bestrahlung des beschichteten Stahlblechs wird die Umlenk- und Fokussiereinrichtung schrittweise in Querrichtung y zum Stahlblech 1 bewegt, so dass der Fokus 9 über die Oberfläche der Beschichtung 2 wandert.In order to be able to irradiate the entire surface of the coating 2 with a pulsed laser beam 6, the radiation source 5 (laser) or the laser beam 6 is movable with respect to the steel sheet 1 provided with the coating 2. This is, for example, in the in FIG. 1 Shown embodiment, the deflection and focusing, consisting of the deflection mirror 7 and the focusing lens 8, in the transverse direction to the steel sheet 1 slidably. For full-surface irradiation of the coated steel sheet, the deflection and focusing device is moved stepwise in the transverse direction y to the steel sheet 1, so that the focus 9 travels over the surface of the coating 2.

Durch die Einstrahlung der hochenergetischen Laserstrahlung 6 erhitzt sich die Beschichtung 2 kurzzeitig innerhalb der vorgegebenen Bestrahlungszeit an ihrer Oberfläche und - je nach gewählter Leistung des Laserstrahls 6 - über einen Teil oder ihre gesamte Dicke auf Temperaturen oberhalb der Schmelztemperatur. Dadurch wird die Beschichtung 2 teilweise oder vollständig aufgeschmolzen. Durch das Aufschmelzen erhält die Oberfläche der Beschichtung 2 ein glänzendes Aussehen und die Struktur der Beschichtung 2 wird verdichtet. In Figur 1 ist der bei Bewegung des Fokus 9 über die Oberfläche der Beschichtung 2 aufgeschmolzene Flächenbereich der Beschichtung 2 mit Bezugsziffer 3 gekennzeichnet.Due to the irradiation of the high-energy laser radiation 6, the coating 2 heats up briefly within the prescribed irradiation time on its surface and - depending on the selected power of the laser beam 6 - over a part or its entire thickness to temperatures above the melting temperature. As a result, the coating 2 is partially or completely melted. The melting gives the surface of the coating 2 a shiny appearance and the structure of the coating 2 is compacted. In FIG. 1 If the area of the coating 2 which has been melted over the surface of the coating 2 when the focus 9 moves is denoted by the reference numeral 3.

Wird innerhalb der kurzen Bestrahlungszeit eine so hohe Energiedichte in die Beschichtung 2 eingestrahlt, dass die Beschichtung 2 über ihre gesamte Dicke aufschmilzt, bildet sich an der Grenzschicht der Beschichtung 2 zum Stahlblech 1 eine sehr dünne Legierungsschicht aus. Bei einer Zinnbeschichtung 2 bildet sich beispielsweise eine Eisen-Zinn-Legierungsschicht aus, welche in Figur 1 mit Bezugsziffer 4 gekennzeichnet ist. Die Dicke der Eisen-Zinn-Legierungsschicht ist in der Darstellung der Figur 4 nicht maßstäblich gezeichnet. Die Dicke der sich bildenden Eisen-Zinn-Legierungsschicht ist in der Regel sehr dünn und entspricht typischerweise einer Legierungsschichtauflage mit einem Flächengewicht von 0,05 bis 0,3 g/m2.If such a high energy density is radiated into the coating 2 within the short irradiation time that the coating 2 melts over its entire thickness, a very thin alloy layer is formed at the boundary layer of the coating 2 to the steel sheet 1. In a tin coating 2, for example, an iron-tin alloy layer is formed, which in FIG. 1 denoted by reference numeral 4. The thickness of the iron-tin alloy layer is shown in FIG FIG. 4 not drawn to scale. The thickness of the resulting iron-tin alloy layer is usually very thin and typically corresponds to an alloy layer support having a basis weight of 0.05 to 0.3 g / m 2 .

Um die Beschichtung 2 innerhalb der kurzen Bestrahlungszeit von höchstens 10 µs zumindest an ihrer Oberfläche anschmelzen zu können, ist eine Energiedichte zwischen 0,01 J/cm2 bis 5,0 J/cm2 auf die Oberfläche der Beschichtung 2 einzustrahlen. Bevorzugte Bereiche der einzustrahlenden Energiedichte liegen bei 0,03 J/cm2 bis 2,5 J/cm2.In order to be able to melt the coating 2 at least on its surface within the short irradiation time of at most 10 μs, an energy density between 0.01 J / cm 2 and 5.0 J / cm 2 is to be irradiated onto the surface of the coating 2. Preferred ranges of the energy density to be irradiated are 0.03 J / cm 2 to 2.5 J / cm 2 .

Statt der Verwendung eines gepulsten Lasers 5 können auch kontinuierlich elektromagnetische Strahlung 6 emittierende Strahlungsquellen verwendet werden. So können beispielsweise cw-Laser verwendet werden, die eine Laserstrahlung ausreichend hoher Leistungsdichte emittieren. Um die kurze Bestrahlungszeit von maximal 10 µs einhalten zu können, muss die elektromagnetische Strahlung 6 dann gegenüber dem beschichteten Stahlband 1 mit hoher Geschwindigkeit bewegt werden.Instead of using a pulsed laser 5, it is also possible to use radiation sources emitting continuously electromagnetic radiation 6. For example, cw lasers can be used which emit laser radiation of sufficiently high power density. In order to be able to comply with the short irradiation time of a maximum of 10 μs, the electromagnetic radiation 6 must then be moved at high speed relative to the coated steel strip 1.

Entsprechende Ausführungsbeispiele, in denen die Strahlungsquelle 5 bzw. der emittierte elektromagnetische Strahl 6 gegenüber einem Stahlband 2 bewegt werden, ist in den Figuren 2 bis 6 schematisch dargestellt. In Figur 2 ist bspw. ein Stahlband 1 gezeigt, welches sich mit einer Bandlaufgeschwindigkeit vB in Längsrichtung des Stahlbands 1 bewegt. In Bandverzinnungsanlagen werden beispielsweise Bandgeschwindigkeiten von einigen Hundert Meter pro Minute bis zu 700 m/min erreicht. Typische Bandlaufgeschwindigkeiten liegen bei 10 m/s. Auf die Oberfläche des beschichteten Stahlbands 1 wird beim Ausführungsbeispiel der Figur 2 ein Laserstrahl 6 eines cw-Lasers 5 (der in Figur 2 nicht dargestellt ist) fokussiert. Der Fokus kann dabei entweder als Strichfokus 9 ausgebildet sein, der sich in Querrichtung des Stahlbands erstreckt und in Bandlängsrichtung eine Ausdehnung xL aufweist. Alternativ hierzu können auch mehrere Strahlungsquellen 5 (Laser) verwendet werden, deren Ausgangsstrahlung 6 als Punktfokus auf die Oberfläche des beschichteten Stahlbands 1 fokussiert wird, wobei die optische Anordnung zur Fokussierung der Strahlung 6 der verschiedenen Strahlungsquellen 5 so angeordnet wird, dass die einzelnen Punktfoki auf der Oberfläche der Beschichtung nebeneinander liegen und auf diese Art ein streifenförmiges Bestrahlungsband 10 auf der Oberfläche erzeugen. Der Strichfokus 9 bzw. das Bestrahlungsband 10 sind dabei fest angeordnet und das Stahlband 1 bewegt sich relativ zu dem Strichfokus 9 bzw. dem Bestrahlungsband 10 in Bandlaufrichtung mit der Bandgeschwindigkeit vB. Die Ausdehnung des Strichfokus 9 bzw. des Strahlungsbands 10 in Bandlaufrichtung xL ergibt sich dann beispielsweise bei der vorgegebenen maximalen Bestrahlungszeit von 10 µs und einer Bandlaufgeschwindigkeit von 10 m/s zu 0,1mm.Corresponding embodiments in which the radiation source 5 and the emitted electromagnetic beam 6 are moved relative to a steel strip 2, is in the FIGS. 2 to 6 shown schematically. In FIG. 2 is, for example, a steel strip 1 shown, which moves at a tape speed v B in the longitudinal direction of the steel strip 1. In strip-tinning systems, for example, belt speeds of a few hundred meters per minute up to 700 m / min are achieved. Typical belt speeds are 10 m / s. On the surface of the coated steel strip 1 is in the embodiment of the FIG. 2 a laser beam 6 of a cw laser 5 (which in FIG. 2 not shown) focused. The focus can be formed either as a line focus 9, which extends in the transverse direction of the steel strip and has an extension x L in the tape longitudinal direction. Alternatively, a plurality of radiation sources 5 (laser) can be used, whose Output radiation 6 is focused as a point focus on the surface of the coated steel strip 1, wherein the optical arrangement for focusing the radiation 6 of the different radiation sources 5 is arranged so that the individual Punktfoki lie on the surface of the coating next to each other and in this way a strip-shaped irradiation belt 10th on the surface. The line focus 9 or the irradiation belt 10 are fixedly arranged and the steel belt 1 moves relative to the line focus 9 or the irradiation belt 10 in the direction of belt travel with the belt speed v B. The extension of the line focus 9 or of the radiation band 10 in the strip running direction x L then results, for example, at the predetermined maximum irradiation time of 10 μs and a strip running speed of 10 m / s to 0.1 mm.

In Figur 3 ist eine weitere Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens gezeigt. Bei dieser Ausführungsform werden mehrere Strahlungsquellen 5 (also beispielsweise mehrere cw-Laser) verwendet, deren Strahlung 6 in Form von Punktfoki 9 auf die Oberfläche des beschichteten und sich mit einer Bandlaufgeschwindigkeit vB bewegenden Stahlbands 1 fokussiert werden. Die Foki 9 werden dabei in Form eines Gitternetzes auf der Oberfläche der Beschichtung 2 angeordnet, wie in Figur 3 schematisch gezeigt. Die Ausdehnung der einzelnen Foki 9 wird dabei an die Bandlaufgeschwindigkeit vB und die vorgegebene Bestrahlungszeit tA von maximal 10 µs angepasst. Zweckmäßig ist das aus den Foki 9 gebildete und in Figur 3 gezeigte "Bestrahlungsnetz" gegenüber der Längsrichtung des Stahlbands 1 um einen Winkel α gekippt, wie in Figur 3 gezeigt. Die zu wählende Ausdehnung xL der einzelnen Foki 9 auf der Oberfläche der Beschichtung ergibt sich bei einem beispielhaften Verkippungswinkel α von 15° zu 0,0966 mm.In FIG. 3 a further embodiment of an apparatus for carrying out the method according to the invention is shown. In this embodiment, a plurality of radiation sources 5 (that is to say, for example, a plurality of cw lasers) are used whose radiation 6 in the form of point foci 9 is focused on the surface of the coated steel belt 1 moving at a belt speed v B. The foci 9 are arranged in the form of a grid on the surface of the coating 2, as in FIG. 3 shown schematically. The expansion of the individual foci 9 is adapted to the tape speed v B and the predetermined irradiation time t A of a maximum of 10 microseconds. Appropriately, this is formed from the foci 9 and in FIG. 3 shown "irradiation network" with respect to the longitudinal direction of the steel strip 1 is tilted by an angle α, as in FIG. 3 shown. The extension x L of the individual foci 9 to be selected on the surface of the coating results at an exemplary tilt angle α of 15 ° to 0.0966 mm.

Das aus den Foki 9 gebildete "Bestrahlungsnetz", insb. dessen Gitterabstände und der Verkippungswinkel α, wird dabei so angeordnet, dass die gesamte Oberfläche der Beschichtung 2 des sich mit der Bandlaufgeschwindigkeit vB bewegenden Stahlbands 1 mit der elektromagnetischen Strahlung (Laserstrahlung) bestrahlt wird.The "radiation network" formed by the foci 9, in particular its lattice spacings and the tilting angle α, is arranged so that the entire surface of the coating 2 of the steel strip 1 moving at the belt running speed v B is irradiated with the electromagnetic radiation (laser radiation) ,

In Figur 4 ist eine weitere Ausführungsform einer Anordnung zur Durchführung des erfindungsgemäßen Verfahrens gezeigt. Bei dieser Ausführungsform wird ein Laserstrahl 6 eines cw-Lasers 5 mittels einer Fokussiereinrichtung auf die Oberfläche der Beschichtung fokussiert, wobei der Fokus 9 in Längsrichtung des sich mit der Bandlaufgeschwindigkeit vB bewegenden Stahlbands eine Ausdehnung yLaser und in Querrichtung dazu eine Ausdehnung xLaser aufweist. Der Fokus 9 wird in Querrichtung zum Stahlband 1 über die gesamte Breite bB des Stahlbands mit einer Geschwindigkeit vx,Laser bewegt. Die für die Einhaltung der maximalen Bestrahlungszeit von 10 µs auszuwählende Geschwindigkeit des Fokus 9 gegenüber dem Stahlband 1 (vx,Laser) ergibt sich dann bei einer beispielhaft vorgegebenen Ausdehnung des Fokus von xLaser = 5 mm zu 500 m/min. [ 24]In Figur 5 bezeichnet Ü die Überlappung von auf der Oberfläche benachbarten Strahlen.In FIG. 4 a further embodiment of an arrangement for carrying out the method according to the invention is shown. In this embodiment, a laser beam 6 of a cw laser 5 is focused by means of a focusing on the surface of the coating, the focus 9 in the longitudinal direction of moving at the belt speed v B steel strip an extension y laser and in the transverse direction to an extent x laser has. The focus 9 is moved transversely to the steel strip 1 over the entire width b B of the steel strip at a speed v x, laser . The speed of the focus 9 relative to the steel strip 1 ( v.sub.x, laser ) to be selected for maintaining the maximum irradiation time of 10 .mu.s is then given by an exemplary predetermined extent of the focus of x laser = 5 mm to 500 m / min. [24] In FIG. 5 Ü denotes the overlap of rays adjacent to the surface.

In den Figuren 5 und 6 sind weitere Ausführungsformen zur Durchführung des erfindungsgemäßen Verfahrens gezeigt, in denen ein Strahl als Fokus 9 auf die Oberfläche eines beschichteten und sich mit einer Bandlaufgeschwindigkeit vB bewegenden Stahlbands gerichtet wird. In dem Ausführungsbeispiel der Figur 5 wird der Fokus 9 dabei über eine Scanneroptik schräg zur Längsrichtung des Stahlbandes mit einer Geschwindigkeit von vx, Laser geführt. Hat der Strahlfokus 9 einen Bandrand erreicht, wird er wieder über das Band an den gegenüberliegenden Rand des Stahlbands geführt u.s.w., während sich das Band mit der Bandlaufgeschwindigkeit vB weiter bewegt. Dabei überlappen die aufeinanderfolgenden Strahlbänder, die sich auf der Oberfläche ergeben, um sicher zu stellen, dass auch die gesamte Oberfläche von der Strahlung erfasst wird.In the Figures 5 and 6 Further embodiments for carrying out the method according to the invention are shown, in which a beam is directed as a focus 9 onto the surface of a coated steel belt moving at a belt speed v B. In the embodiment of FIG. 5 the focus 9 is guided via a scanner optics obliquely to the longitudinal direction of the steel strip at a speed of v x, laser . If the beam focus 9 has reached a band edge, it is again guided over the band to the opposite edge of the steel band, etc., while the band continues to move at the band travel speed v B. In this case, the successive beam bands that arise on the surface overlap to ensure that the entire surface is also detected by the radiation.

In dem Ausführungsbeispiel der Figur 6 wird der Fokus 9 zweiachsig relativ zum Stahlband bewegt, nämlich sowohl in Längsrichtung (x-Richtung) mit einer Geschwindigkeit vx,Laser als auch in Querrichtung (y-Richtung) mit einer Geschwindigkeit vy,Laser. Die Geschwindigkeit vy,Laser in Querrichtung (y-Richtung) wird dabei zweckmäßig so eingestellt, dass über die gesamte Breite bB des Stahlbands in y-Richtung eine gleichmäßige Überlappung Ü eingehalten wird.In the embodiment of FIG. 6 the focus 9 is moved biaxially relative to the steel strip, namely both in the longitudinal direction (x-direction) at a speed v x, laser and in the transverse direction (y-direction) at a speed v y, laser . The velocity v y, laser in the transverse direction (y-direction) is suitably set so that over the entire width b B of the steel strip in the y-direction, a uniform overlap Ü is maintained.

In Figur 9 ist das sich beim Aufheizen der Beschichtung durch die Einstrahlung der elektromagnetischen Strahlung ergebende Temperaturprofil T(x) über die Dicke (x) der Beschichtung und des darunterliegenden Stahlbands für verschiedene Bestrahlungszeiten t dargestellt. Wie aus den Temperaturprofilen der Graphik von Figur 9 ersichtlich, ergibt sich ein steiles Temperaturprofil T(x) für sehr kurze Bestrahlungszeiten t im ns- und µs-Bereich. Bei Bestrahlungszeiten von mehr als 10 µs ergibt sich ein flaches Temperaturprofil, d.h. hier wird der wesentliche Teil der eingestrahlten Energie in das Stahlband abgeleitet. Bei den sehr kurzen Bestrahlungszeiten von maximal 10 µs wird dagegen im Wesentlichen nur die Beschichtung, nicht jedoch das darunterliegende Stahlband, aufgeheizt.In FIG. 9 is the temperature profile T (x) resulting from the irradiation of the electromagnetic radiation during the heating of the coating by the thickness (x) of the coating and of the steel strip below for different irradiation times t. As from the temperature profiles of the graphic of FIG. 9 As can be seen, a steep temperature profile T (x) results for very short irradiation times t in the ns and μs range. For irradiation times of more than 10 μs, a flat temperature profile is obtained, ie here the essential part of the radiated energy is dissipated into the steel strip. By contrast, with the very short irradiation times of a maximum of 10 μs, essentially only the coating, but not the underlying steel strip, is heated.

In Figur 7 ist die in das beschichtete Stahlband eingebrachte Wärmemenge pro Flächeneinheit in Abhängigkeit der Bestrahlungszeit für verschiedene Oberflächentemperaturen aufgetragen. Die Berechnung erfolgt verlustfrei. Zum Vergleich ist jeweils die "maximale Energiedichte" (Maximalenergie) eingetragen. Die maximal benötigte Energie ist die Energiemenge, die zur gleichmäßigen Erwärmung des kompletten Querschnitts benötigt wird.In FIG. 7 the amount of heat applied per unit area in the coated steel strip is plotted as a function of the irradiation time for different surface temperatures. The calculation is lossless. For comparison, the "maximum energy density" (maximum energy) is entered in each case. The maximum energy required is the amount of energy needed to heat the entire cross section evenly.

Wie sich aus den Diagrammen der Figur 7 entnehmen lässt, wird bei den erfindungsgemäßen Bestrahlungszeiten von höchstens 10 µs gegenüber der maximalen Energie (Maximalenergie) lediglich 12 % an Wärme in das beschichtete Stahlband eingetragen. Trotz dieses sehr geringen Wärmeintrags kann die Beschichtung vollständig bis zur Stahlband-Grenzschicht aufgeschmolzen werden. Entscheidend für das Aufschmelzen ist lediglich die (kurzzeitige) Erhitzung der Beschichtung auf Temperaturen oberhalb der Schmelztemperatur. Durch das erfindungsgemäße Verfahren kann also bei Einhalten der vorgegebenen Bestrahlungszeit von maximal 10 µs eine geringe Energiemenge von maximal 12 % der Maximalenergie in das beschichtete Stahlband eingebracht werden, um die Beschichtung vollständig aufzuschmelzen. Die vorgegebene Bestrahlungszeit, welche erfindungsgemäß maximal 10 µs beträgt, bestimmt dabei, welches Temperaturprofil sich über die Dicke x der Beschichtung und des Stahlbands einstellt (Figur 9). Je länger die gewählte Bestrahlungszeit für eine vorgegebene Oberflächentemperatur (welche oberhalb der Schmelztemperatur der Beschichtung liegen muss) ist, desto mehr Wärme fließt in die Tiefe des Stahlbands. Dies hat zur Folge, dass insgesamt mehr Wärme benötigt wird, um eine bestimmte Temperatur an der Oberfläche (die erfindungsgemäß oberhalb der Schmelztemperatur liegen muss) zu erreichen. Wird eine ausreichend geringe Bestrahlungszeit t gewählt, kann erreicht werden, dass der wesentliche Teil der eingestrahlten Energie auf den Bereich der Beschichtung beschränkt wird und die Wärmeenergie nicht in das darunterliegende Stahlband abfließt. Auf diese Weise kann nach der erfolgten Aufschmelzung der Beschichtung auf ein Abschrecken im Wasserbad verzichtet werden, weil die Wärme in der Beschichtung durch das (nicht aufgeheizte) Stahlband abgeführt werden kann.As can be seen from the diagrams of the FIG. 7 can be seen, is entered at the irradiation times of at most 10 microseconds compared to the maximum energy (maximum energy) according to the invention, only 12% of heat in the coated steel strip. Despite this very low heat input, the coating can be completely melted to the steel strip boundary layer. Crucial for the melting is only the (short-term) heating of the coating to temperatures above the melting temperature. By the method according to the invention, a minimum amount of energy of at most 12% of the maximum energy can thus be introduced into the coated steel strip while maintaining the predetermined irradiation time of a maximum of 10 μs in order to completely melt the coating. The predetermined irradiation time, which is a maximum of 10 μs according to the invention, determines which temperature profile is established across the thickness x of the coating and the steel strip ( FIG. 9 ). The longer the selected irradiation time for a given surface temperature (which must be above the melting temperature of the coating), the more heat flows into the depth of the steel strip. As a result, a total of more heat is required in order to achieve a certain temperature at the surface (which must be above the melting temperature according to the invention). If a sufficiently low irradiation time t is selected, it can be achieved that the essential part of the radiated energy is limited to the area of the coating and the heat energy does not flow off into the steel strip below. In this way, can be dispensed with after quenching of the coating on a quenching in a water bath, because the heat in the coating by the (not heated) steel strip can be dissipated.

Bei Einstrahlung einer ausreichend hohen Energiedichte kann - je nach Dicke der metallischen Beschichtung - die Beschichtung vollständig, d.h. über ihre gesamte Dicke bis zur Stahloberfläche, aufgeschmolzen werden. Bei vollständigem Aufschmelzen der Beschichtung bildet sich im Bereich der Grenzschicht zur Stahloberfläche eine (im Vergleich zur Dicke der Beschichtung) dünne und sehr dichte Legierungsschicht, welche aus Atomen des Beschichtungsmaterials und Eisenatomen besteht. Die sich ausbildende Legierungsschicht ist sehr dünn und entspricht bei Weißblech einer Legierungsschichtauflage von 0,05 bis 0,3 g/m2.Upon irradiation of a sufficiently high energy density - depending on the thickness of the metallic coating - the coating can be completely, ie over its entire thickness to the steel surface, melted. Upon complete melting of the coating, a thin and very dense alloy layer, which consists of atoms, forms in the area of the boundary layer to the steel surface (in comparison to the thickness of the coating) of the coating material and iron atoms. The forming alloy layer is very thin and corresponds to an alloy layer of tinplate 0.05 to 0.3 g / m 2 .

Beispielhaft kann für eine verzinnte Stahloberfläche durch Vergleichsversuche und Modellrechnungen gezeigt werden, dass die Bildung der Legierungsschicht wegen der kurzen Bestrahlungszeiten erst bei deutlich höheren Temperaturen als dem Schmelzpunkt des Beschichtungsmaterials einsetzt. Die sich bei der erfindungsgemäßen Behandlung bildende Legierungsschicht weist ein gegenüber den bei der bekannten Verfahrensführung sich bildenden Legierungsschichten ein grundsätzlich anderes mikroskopisches Aussehen auf. Dies ist aus den in Figur 8 gezeigten Mikrosonden-Aufnahmen ersichtlich. Die Figuren 8a und 8b zeigen Mikrosonden-Aufnahmen von Legierungsschichten (nach dem Ablösen des unlegierten Zinns), die sich beim Aufschmelzen einer Zinnbeschichtung auf einem Stahlblech im Bereich der Grenzschicht zur Stahloberfläche bei Durchführung des erfindungsgemäßen Verfahrens gebildet haben. Demgegenüber zeigt Figur 8c eine Mikrosonden-Aufnahme einer Eisen-Zinn-Legierungsschicht (nach dem Ablösen des unlegierten Zinns), die sich beim Aufschmelzen einer verzinnten Stahlblech-Oberfläche nach herkömmlichem Aufschmelzverfahren gebildet hat. Vergleichsversuche, in denen die Korrosionsbeständigkeit entsprechend behandelter Weißblech-Proben untersucht worden sind, haben gezeigt, dass die nach dem erfindungsgemäßen Behandlungsverfahren behandelten Proben eine wesentlich bessere Korrosionsbeständigkeit haben, verglichen mit den nach konventionellem Verfahren behandelten Proben. Die Korrosionsbeständigkeit von Weißblech, welche bspw. nach dem standardisierten Verfahren zur Ermittlung des sog. ATC-Werts (ASTN-Standard 1998 A623N-92, Kapitel A5 "method for alloy-tin couple test for electrolytic tin plate", veröffentlicht) gemessen werden kann, nimmt erfahrungsgemäß mit steigender Dicke der Legierungsschicht zu. Typische Legierungsschichtauflagen liegen bei lackiertem Weißblech im Bereich von 0,5 bis 0,8 g/m2, bei unlackiertem Weißblech mit erhöhtem Anspruch an die Korrosionsbeständigkeit bei 0,8 bis 1,2 g/m2. Für die gleiche Korrosionsbeständigkeit, d.h. für den gleichen ATC-Wert, wird nach konventionellem Verfahren mindestens eine doppelt so dicke Legierungsschicht benötigt wie bei dem erfindungsgemäßen Verfahren.By way of example, it can be shown for a tinned steel surface by comparison experiments and model calculations that the formation of the alloy layer only starts at temperatures significantly higher than the melting point of the coating material because of the short irradiation times. The alloy layer forming in the treatment according to the invention has a fundamentally different microscopic appearance compared to the alloy layers which form in the known process procedure. This is from the in FIG. 8 shown microprobe recordings. The FIGS. 8a and 8b show micro-probe images of alloy layers (after the detachment of the unalloyed tin), which have formed during the melting of a tin coating on a steel sheet in the boundary layer to the steel surface in carrying out the method according to the invention. In contrast, shows FIG. 8c a microprobe photograph of an iron-tin alloy layer (after the stripping of the unalloyed tin), which has formed during the melting of a tinned sheet steel surface by conventional reflow. Comparative tests in which the corrosion resistance of correspondingly treated tinplate samples has been investigated have shown that the samples treated by the treatment method according to the invention have a significantly better corrosion resistance compared to the samples treated by conventional methods. The corrosion resistance of tinplate, which can be measured, for example, according to the standardized method for determining the so-called ATC value (ASTN standard 1998 A623N-92, Chapter A5 "method for alloy-tin couple test for electrolytic tin plate", published) , Experience has shown that increases with increasing thickness of the alloy layer. Typical alloy layer coverings are in the range of 0.5 to 0.8 g / m 2 in the case of painted tinplate, and 0.8 to 1.2 g / m 2 in the case of unpainted tinplate with an increased requirement for corrosion resistance. For the same corrosion resistance, ie for the same ATC value, at least twice as thick an alloy layer is required by the conventional method as in the method according to the invention.

Mit dem erfindungegemäßen Verfahren lassen sich also mit einer metallischen Beschichtung versehene Stahlbänder oder -bleche herstellen, bei denen an der Grenzschicht des Stahls zur Beschichtung eine, verglichen mit der Dicke der Beschichtung, dünne und gleichzeitig dichte Legierungsschicht aus Eisenatomen und Atomen des Beschichtungsmaterials ausgebildet ist. Die Dicke der Legierungsschicht entspricht dabei einer Legierungsschichtauflage von weniger als 0,3 g/m2. So können bspw. verzinnte Stahlbänder oder -bleche hergestellt werden, welche trotz einer vergleichsweise dünnen Zinnauflage von weniger als 2,8 g/m2 und insbesondere von weniger als 2,0 g/m2 eine ausreichend gute Korrosionsbeständigkeit aufweisen. Vergleichsversuche haben bspw. ergeben, dass bei verzinnten Stahlblechen mit einer Zinnauflage von ca. 1,4 g/m2 durch die erfindungsgemäße Behandlung eine Eisen-Zinn-Legierungsschicht mit einer Legierungsschichtauflage von ca. 0,05 g/m2 gebildet hat und dass bei dem so behandelte verzinnten Stahlblech ATC-Werte von weniger als 0,15 µA/cm2 (nach ASTN-Standard) gemessen werden konnten.Thus, with the method according to the invention, it is possible to produce steel strips or sheets provided with a metallic coating, in which at the boundary layer of the steel for coating a thin and at the same time dense compared with the thickness of the coating Alloy layer of iron atoms and atoms of the coating material is formed. The thickness of the alloy layer corresponds to an alloy film coating of less than 0.3 g / m 2. Thus, for example, tinned steel strips or sheets can be produced, which have a sufficiently good corrosion resistance despite a comparatively thin tin coating of less than 2.8 g / m 2 and in particular of less than 2.0 g / m 2 . Comparative tests have shown, for example, that in tinned steel sheets with a tin coating of about 1.4 g / m 2 has formed by the treatment according to the invention, an iron-tin alloy layer having an alloy layer of about 0.05 g / m 2 and that ATC values of less than 0.15 μA / cm 2 (ASTN standard) could be measured on the tinned steel sheet thus treated.

Claims (15)

  1. Method for refining a metallic coating on a steel strip or steel plate, wherein the coating is melted on by heating to a temperature above the melting point of the material of the coating, characterised in that the heating is effected by irradiation of the surface of the coating with electromagnetic radiation of high power density over a limited irradiation time of no more than 10 µs, wherein the energy density introduced into the coating by the electromagnetic radiation and the preset irradiation time are selected so that the coating melts completely over its entire thickness as far as the boundary layer with the steel strip, as a result of which a thin alloy layer is formed at the boundary layer between the coating and the steel strip.
  2. Method according to claim 1, characterised in that the heating is effected by irradiation of the surface of the coating with electromagnetic radiation of high power density over a limited irradiation time of no more than 100 ns.
  3. Method according to claim 1 or 2, characterised in that the surface of the coating is irradiated with a laser beam of high power density.
  4. Method according to claim 3, characterised in that the laser beam is pulsed at a maximum pulse duration of 10 µs.
  5. Method according to one of the precedingclaims, characterised in that the steel strip coated with the metallic coating is moved relative to the radiation source of the electromagnetic radiation.
  6. Method according to claim 5, characterised in that the steel strip coated with the metallic coating is moved in the longitudinal direction of the steel strip at a strip velocity (vstrip).
  7. Method according to claim 6, characterised in that the radiation source of the electromagnetic radiation is moved in the transverse direction of the steel strip at a source velocity (vsource).
  8. Method according to one of the preceding claims, characterised in that for irradiation of the surface of the coating, a plurality of radiation sources is used which in each case emit electromagnetic radiation of high power density onto the surface.
  9. Method according to claim 8, characterised in that the electromagnetic radiation is focussed onto the surface of the coating, wherein the diameter of the focus is adapted to the strip velocity (vstrip) so that a preset point on the surface of the coating passes through the diameter of the focus within a preset irradiation time (tA) of no more than 10 µs.
  10. Method according to claim 1 or 8, characterised in that the emitted power density of the electromagnetic radiation emitted by a radiation source lies between 106 W/cm2 and 2·108 W/cm2.
  11. Method according to one of the precedingclaims, characterised in that an energy density of 0.01 J/cm2 to 5.0 J/cm2 is irradiated onto the surface of the coating by the electromagnetic radiation within the irradiation time (tA).
  12. Method according to one of the precedingclaims, characterised in that an energy density of 0.03 J/cm2 to 2.5 J/cm2 and preferably of 0.2 J/cm2 to 2.0 J/cm2 is irradiated into the coating by irradiation of the surface.
  13. Method according to one of the precedingclaims, characterised in that the metallic coating consists of tin with a tin overlay of less than 2.8 g/m2 and in that the thickness of the alloy layer corresponds to an alloy layer overlay with a weight per unit area of 0.05 to 0.3 g/m2.
  14. Method according to one of the preceding claims, characterised in that the energy density introduced into the coating by the electromagnetic radiation and the preset irradiation time are selected so that the coating melts completely over its entire thickness as far as the boundary layer with the steel strip, but an unalloyed coating region is still present on the surface.
  15. Method according to one of the precedingclaims, characterised in that a surface area of more than 1 m2 per second and preferably of more than 5 m2 per second is treated.
EP12700622.9A 2011-03-01 2012-01-02 Method for refining a metallic coating on a steel strip Not-in-force EP2681348B1 (en)

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DE102011000984A DE102011000984A1 (en) 2011-03-01 2011-03-01 Process for refining a metallic coating on a steel strip
PCT/EP2012/050012 WO2012116847A1 (en) 2011-03-01 2012-01-02 Method for enhancing a metallic coating on a steel strip

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WO2012116847A1 (en) 2012-09-07
CN103476967A (en) 2013-12-25
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BR112013022008A2 (en) 2016-11-29
RU2560468C2 (en) 2015-08-20
EP2681348A1 (en) 2014-01-08
RU2013141507A (en) 2015-04-10
DE102011000984A1 (en) 2012-09-06
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US9115428B2 (en) 2015-08-25
CA2827617A1 (en) 2012-09-07

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