EP1386016B1 - Method and device for dip coating a metal strip - Google Patents

Method and device for dip coating a metal strip Download PDF

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Publication number
EP1386016B1
EP1386016B1 EP02719575A EP02719575A EP1386016B1 EP 1386016 B1 EP1386016 B1 EP 1386016B1 EP 02719575 A EP02719575 A EP 02719575A EP 02719575 A EP02719575 A EP 02719575A EP 1386016 B1 EP1386016 B1 EP 1386016B1
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EP
European Patent Office
Prior art keywords
liquid metal
strip
narrow duct
duct
narrow
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EP02719575A
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German (de)
French (fr)
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EP1386016A1 (en
Inventor
Yves Hardy
Jean Crahay
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Centre de Recherches Metallurgiques CRM ASBL
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Centre de Recherches Metallurgiques CRM ASBL
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0035—Means for continuously moving substrate through, into or out of the bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/50—Controlling or regulating the coating processes
    • C23C2/52—Controlling or regulating the coating processes with means for measuring or sensing

Definitions

  • the present invention relates to a method for coating a metal strip by dipping, that is to say by continuous scrolling through a liquid metal.
  • the invention also relates to a device for implementing this method.
  • JP-A-2-8356 discloses a method and apparatus for coating a web of tempered steel by means of a liquid metal. We pass the band in a narrow channel traversed by the liquid metal on both sides of the band. The channel is fed by a separate reservoir comprising the liquid metal, coupled to a pump that creates a circulation movement in a closed circuit. The tank has a larger capacity than said channel. The liquid metal is filtered by a purification device before introducing it into said channel.
  • Galvanizing by dipping a steel strip generally comprises two main operations, namely annealing the strip and depositing the coating.
  • the corresponding installation therefore comprises two large parts, namely an oven annealing and a galvanizing tank.
  • annealing is to prepare the strip, in particular its surface, with a view to the following coating operation.
  • it ensures the recrystallization of hardened structure in the case of a cold rolled strip; it also operates, in all cases, cleaning and brightening the surface with an atmosphere suitable, generally reducing, comprising hydrogen and nitrogen.
  • conventional galvanizing involves passing a band of steel through a bath of molten zinc then, at the exit of this bath, to adjust the thickness the zinc layer by spinning with compressed air or nitrogen slats.
  • the strip is guided by several rollers, in particular a first roller, said bottom roller, entirely immersed in zinc, under which it passes before rising vertically towards the surface of the bath, and other rollers, called stabilizing, deflecting or guiding rollers, often partially or even totally immersed near the upper surface of the bath of liquid metal, intended to ensure the stabilization, possibly the flatness of the coated strip, before spinning.
  • rollers in particular a first roller, said bottom roller, entirely immersed in zinc, under which it passes before rising vertically towards the surface of the bath, and other rollers, called stabilizing, deflecting or guiding rollers, often partially or even totally immersed near the upper surface of the bath of liquid metal, intended to ensure the stabilization, possibly the flatness of the coated strip, before spinning.
  • rollers motorized or free, come into contact with the surface of the belt in movement and can thus cause surface defects. They must be frequently dismantled for inspection, repair or replacement as their condition significantly influences the quality of the zinc coating. As a result, frequent shutdown of the production line and significant loss of productivity.
  • the person skilled in the art is well aware of the difficulty of regulating and maintaining the composition of the coating metal. This is hardly ever a pure metal, but rather an alloy containing different elements in specific quantities but variables from one type to another, intended to improve the performance of coatings, as for example the additions of aluminum in galvanizing baths.
  • mattes that is to say aggregates of particles of compounds intermetallic compounds, formed inter alia by the dissolution of the extreme surface of steel strips by the liquid metal bath, also cause appearance defects well known, and should therefore be regularly eliminated. This results in losses of time and metal, which adversely affect the productivity and profitability of the processes conventional.
  • the object of the invention is to propose a method for coating a web tempered metal, which makes it possible to remedy the aforementioned drawbacks, in particular by removing all submerged rolls and ensuring a constant composition liquid metal in the coating zone.
  • it proposes a device for carrying out this method.
  • a method for coating a metal strip at quenched by means of a liquid metal in which said strip is passed through a volume of said liquid metal, is characterized in that said band is circulated in a thin channel, in that the liquid metal is introduced into said thin channel at less on both sides of the band, and in that a movement of circulating said liquid metal with respect to said band, inside said thin channel. It is found then that the coating is made by contact with the surface of the metal strip with a flow of liquid metal rather than a coating of said surface by immersion in a bath of liquid metal.
  • said thin liquid metal channel is fed from a source separate, constituted for example by a separate tank; such a separate tank is advantageously arranged higher than said thin channel, so as to ensure feeding at least partially by a gravimetric effect.
  • a source separate constituted for example by a separate tank; such a separate tank is advantageously arranged higher than said thin channel, so as to ensure feeding at least partially by a gravimetric effect.
  • the entire diet can also be provided by one or more pumps.
  • the liquid metal is subjected to at least one treatment before introducing it into said thin channel.
  • said treatment may include filtering the liquid metal before introducing it into the thin channel.
  • the chemical composition and / or the temperature of the liquid metal is measured at determined intervals, preferably continuously, the chemical composition and / or the temperature of the liquid metal and, if necessary, this chemical composition and / or this temperature is adjusted before introducing the liquid metal into said thin channel. It is thus possible to maintain less substantially constant these conditions governing the coating operation at dipped from the metal band.
  • the supply of said thin closed circuit channel avoids any contact of the liquid metal with the ambient air, and as a result any risk of alteration of the liquid metal, in particular by oxidation.
  • said thin channel is powered liquid metal under a pressure independently adjustable on each side of the band.
  • the feed pressure is regulated liquid metal, as the case may be, by varying the difference in level between the thin channel and the separate tank, or by changing the pressure provided by the pumps Power.
  • the speed of circulation of the liquid metal stream with respect to the band, inside said channel thin is between 0.1 m / s and 5 m / s.
  • a device for carrying out this method essentially comprises a thin channel, means for circulating the tape to be coated through said thin channel, as well as means for supplying said thin liquid metal channel and for create a circulation movement of the liquid metal with respect to the band, inside of the thin channel.
  • the section of the thin channel according to the invention is determined so as to allow the passage of the widest band to be covered, without the need for excessive liquid metal.
  • the width of the next thin channel the invention is generally between 1 m and 2 m. It goes without saying that this width could be increased or decreased depending on specific circumstances.
  • the height of the thin channel defines the thickness of the liquid metal layer in circulation, and therefore also influences the flow of liquid metal in the thin channel. This height is preferably less than 6 cm, and more preferably less than 3 cm, so as to be able to limit the flow of liquid metal in the thin channel.
  • the thin channel according to the invention may have a shape that is either flat or curved in particularly partially cylindrical. In the latter case, the curvature must be limited so as not to unnecessarily complicate the trajectory and guidance of the tape.
  • the tape to be coated flows through said channel under the action of the traction exerted by the drive systems of the coating line. Its trajectory is determined by guiding means, generally rollers, arranged outside the channel, upstream and downstream of it, so as not to damage the surface of the tape during the coating operation.
  • this distance is between 1 mm and 15 mm, depending on various parameters such as the speed and width of the band, the nature of the liquid metal, the length and / or shape of the path of the thin channel.
  • the thin channel according to the invention comprises, on the one hand, feed means liquid metal, and secondly means to create a circulation movement of the liquid metal with respect to the band, inside the thin channel.
  • Said supply means comprise at least one separate reservoir, a much larger capacity than the thin channel; this tank is connected to the thin channel by a supply circuit leading to means for introducing the metal liquid in the thin channel, on both sides of the band that circulates there.
  • These means of introduction can be constituted either by injectors arranged in at least one ends of the channel, or by injectors in the walls of the canal parallel to the plane of the band, either by a combination of these two types injectors.
  • the reservoir separated can be raised compared to the thin channel, or the supply circuit can have at least one pump.
  • the device also comprises means for control and adjustment of the temperature and / or composition of the liquid metal, means for adding fresh liquid metal as well as means for filtering the metal liquid before its introduction into the thin canal.
  • the channel is provided with sealing means, such as airlock at its ends, allowing passage of the band but preventing metal leakage liquid.
  • the channel can advantageously be integrated in a closed circuit, comprising also at least one feed tank, possibly raised, a circuit supply of the thin channel, an excess liquid metal recovery circuit, means for treating the liquid metal, and possibly at least one pump of circulation of the liquid metal.
  • the method and the device of the invention make it possible to coat a strip by immersion in a moving liquid metal stream of high velocities relative to the web. These speeds are higher than those resulting from the scrolling of the band in a bath of liquid metal at rest.
  • FIG. 1 represents a conventional device for galvanizing dipping a steel strip, integrated into a processing line.
  • a band coat 1 is treated in a continuous annealing furnace 2, from which it leaves by a trunk 3 to dive into a bath of molten zinc 4.
  • the strip 1 passes under a roll of bottom 5, completely immersed in the liquid zinc 4, then it is guided by 6 immersed stabilizing rollers near the upper surface of the bath of zinc 4, before leaving the zinc bath in a vertical path.
  • Excess zinc is dewatered by means of gas strips, generally air or nitrogen, under pressure 7.
  • the strip 1 then rises vertically up to an upper deflection roll 8, which is high enough for the zinc coating to solidify before reach it. Tape 1 then continues its way into the treatment line.
  • the strip to be coated 1 circulates through a zinc bath liquid at rest 4, and it is in direct contact with several submerged rollers 5, 6.
  • the strip to be coated 1 from a continuous annealing furnace (not shown), circulates through a thin channel 10 in which a stream of liquid metal 9 has been created.
  • the channel 10 is straight and slightly inclined upward, and the circulation of the metal liquid is provided by a pump 11.
  • the band 1 and the current of liquid metal 9 circulate in the ascending direction, indicated by arrows. of the sealing systems, not shown, are provided at the inlet and output of the band 1 in the channel 10.
  • FIG. 3 shows how it is possible to control, at least in part, the position of the band in a thin channel, according to the method of the invention.
  • a circulation movement of the liquid metal is created, for example molten zinc, in the channel 10, on either side of the strip 1.
  • This current flows preferably at high speed, and is inevitably accompanied by pressure gradients between the band 1 and the walls of the channel 10.
  • the paths hydraulic fluid that the liquid metal follows in channel 10 can be designed to create pressure differences between the faces of the band and thereby influence the position of the band in the channel. Indeed, even if they are of low amplitude, these pressure differences act on important surfaces, namely the surface both sides of the strip in the channel, and they can thus generate forces considerable.
  • FIG. 3a illustrates the simple case of a thin rectilinear channel 12, practically horizontal, in which the band 1 circulates equidistant from the two walls.
  • the 13 pressures on the underside of the strip are higher than those 14 on the upper side, to support the weight of tape 1 while now it in a centered position in the channel 12.
  • the channel 15 is in the form of a parabola, corresponding to the form called "chain” that takes naturally band 1 hanging freely between two upper rollers not shown.
  • Such a parabolic trajectory of the band 1 can be maintained by a control permanent speed of the band upstream and downstream of channel 15. It is also maintained by the pressures that the liquid metal exerts on the band; if the pressures 16 on the inner face are higher than those 17 on the face external, they are even able to compensate for traction in the band. In such a configuration of the channel, it is particularly easy to ensure the tightness of the channel, collecting the liquid metal overflowing at both ends of the channel for the reintroduce in the lower part, for example using pumps 18.
  • FIG. 3c shows a channel 15 of a shape close to that of the usual path of a strip 1 in a dip coating installation of the type illustrated in the In this configuration, the band 1, which undergoes the pull exerted by the line of treatment, is supported by the application of higher pressures 19 on the face internal than those exerted on the outer face.
  • band 1 can be guided in a controlled manner both at the inlet and the outlet of the canal, by means of pressure differentials 21, which advantageously replace, that is to say without contact, the guide rollers 6 of FIG.
  • the watertightness of the channel is assured with ease by collecting the metal excess liquid at both ends of the canal to reintroduce it into the lower, for example using a common pump 22.
  • the supply of the thin liquid metal channel is preferably provided by openings in the walls of the canal so as to distribute in a similar way as uniform as possible the pressures acting on the faces of the band.
  • Figure 4 shows various possible arrangements of these feed orifices in a portion of a channel wall 23.
  • the orifices can be either slits 24 parallel and / or perpendicular to the direction 25 of displacement of the strip (FIG 4a), or orifices, for example circular 26, arranged in lines parallel to the direction of movement of the the band (Fig. 4b), again orifices, for example circular holes 27, distributed regularly, for example in staggered rows, in the canal wall (Fig. 4c).
  • FIG. 5 illustrates various possible configurations of the liquid metal circuit, with a treatment unit, possibly combined with a raised outer tank.
  • a horizontal rectilinear channel 12 traversed by a band 1, is fed directly by means of a pump 28.
  • the liquid metal is recovered at the ends of the channel 12 and returned by the pump 28, first to a unit treatment 29 and then directly into the channel 12.
  • FIG. 5b also shows a horizontal rectilinear channel 12 traversed by a tape to be coated 1.
  • This channel 12 is fed by gravity from a raised tank 30 large capacity, while the excess liquid metal is recovered at ends of the channel 12 and returned, still by gravity, into a collection tank 32. From there, the liquid metal is then returned to the elevated tank 30 at by means of a pump 31.
  • a treatment unit 29 is placed between the reservoir 30 and the channel 12 and / or between the pump 31 and the reservoir 30.
  • Figure 5c The configuration of Figure 5c is similar to that of Figure 5a, with the difference that the channel 33 here marries the path of the band 1 in a coating line to conventional tempering.
  • the excess liquid metal is recovered at the ends elevated channel 33 and returned to the low point of this channel, through a pump 28 and a processing unit 29.
  • Figure 5d illustrates a layout, similar to that of Figure 5b, but where the channel 33 marries the path of the band 1 in a line of dipping coating conventional.
  • Channel 33 is fed directly at its low point by gravity, at from a raised tank 30 of large capacity; the excess liquid metal is recovered at the raised ends of the channel 33 and returned, also by gravity, in a collection tank 32. From this, the molten metal is returned to the raised tank 30 by means of a pump 31.
  • a treatment unit 29 is provided between the reservoir 30 and the channel 33, and / or between the pump 31 and the reservoir 30.
  • the present invention offers numerous advantages, both as regards the process itself and the quality of coated products.
  • the continuous circulation of the liquid metal between the coating channel and a Separate tank allows to process the liquid metal continuously.
  • mattes that is to say the particles of compounds intermetallic compounds that float in the liquid metal and may deposit on the bandaged. This elimination can be done by any appropriate method, such as filtering, decantation, centrifugation, etc., especially in the mentioned treatment unit upper.
  • the quality of the coating depends in particular on the reactivity between the metal of coating and the surface of the tape to be coated.
  • high-grade steels resistance to be galvanized for the automotive industry have a surface low reactivity to zinc; this results in a lack of wettability that can lead to serious coating defects.
  • the introduction of a significant relative speed, for example from 0.5 m / s to 1 m / s, between the strip and the liquid metal in the channel contributes to reducing the risk of sticking on the strip, particles suspended in the liquid metal. This effect is in addition to that of the matting removal operation mentioned above.
  • the method of the invention restores the symmetry between the two faces of the strip, because none of the two faces of the strip is now no longer in contact with rollers. The actual duration and the conditions of exposure of the two sides of the strip to the liquid metal are identical.
  • the device of the invention is much simpler than conventional devices dip galvanizing. It requires a smaller amount of liquid metal, it offers greater operational flexibility and allows you to obtain products coated with better quality. Finally, it can integrate, without significant difficulty, in an existing treatment line, as shown in Figure 3c.

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

Abstract

The invention concerns a method for dip coating a metal strip using a molten metal which consists in causing the metal strip to pass in a volume of said molten metal by causing said strip to circulate in a thin channel wherein the molten metal is introduced at least on either side of said strip and so as to generate a circulating movement of said molten liquid relative to the strip inside said thin channel. The pressure on the two surfaces of the strip inside said thin channel is adjusted independently of each other, and the circulating speed of the molten liquid current relative to the strip is adjusted at a value ranging between 0.5 m/s and 1 m/s.

Description

Domaine techniqueTechnical area

La présente invention porte sur un procédé pour le revêtement d'une bande métallique au trempé, c'est-à-dire par défilement continu à travers un métal liquide. L'invention concerne également un dispositif pour la mise en oeuvre de ce procédé.The present invention relates to a method for coating a metal strip by dipping, that is to say by continuous scrolling through a liquid metal. The invention also relates to a device for implementing this method.

Etat de la techniqueState of the art

L'invention sera décrite ici en faisant référence à la galvanisation au trempé d'une bande d'acier. Il faut cependant considérer que cette application n'est mentionnée qu'à titre d'exemple, et que l'invention peut aussi avantageusement être appliquée à d'autres types de substrats métalliques en forme de bande ou de fil, ainsi qu'avec d'autres métaux et alliages de revêtement.The invention will be described here with reference to dip galvanizing of a steel band. However, it must be considered that this application is only mentioned example, and that the invention can also be advantageously applied to other types of strip or wire-like metal substrates, as well as other metals and coating alloys.

JP-A-2-8356 décrit un procédé et un dispositif pour le revêtement d'une bande d'acier au trempé au moyen d'un métal liquide. On fait passer la bande dans un canal étroit parcouru par le métal liquide de part et d'autre de la bande. Le canal est alimenté par un réservoir séparé comprenant le métal liquide, couplé à une pompe qui crée un mouvement de circulation en circuit fermé. Le réservoir a une plus grande capacité que ledit canal. Le métal liquide est filtré par un dispositif de purification avant de l'introduire dans ledit canal.JP-A-2-8356 discloses a method and apparatus for coating a web of tempered steel by means of a liquid metal. We pass the band in a narrow channel traversed by the liquid metal on both sides of the band. The channel is fed by a separate reservoir comprising the liquid metal, coupled to a pump that creates a circulation movement in a closed circuit. The tank has a larger capacity than said channel. The liquid metal is filtered by a purification device before introducing it into said channel.

La galvanisation au trempé d'une bande d'acier comprend généralement deux opérations principales, à savoir un recuit de la bande et le dépôt du revêtement. L'installation correspondante comporte dès lors deux grandes parties, à savoir un four de recuit et une cuve de galvanisation.Galvanizing by dipping a steel strip generally comprises two main operations, namely annealing the strip and depositing the coating. The corresponding installation therefore comprises two large parts, namely an oven annealing and a galvanizing tank.

Le recuit a pour but de préparer la bande, en particulier sa surface, en vue de l'opération de revêtement qui suit. En particulier, il assure la recristallisation de la structure écrouie dans le cas d'une bande laminée à froid ; il opère également, dans tous les cas, un nettoyage et un avivage de la surface au moyen d'une atmosphère appropriée, généralement réductrice, comprenant de l'hydrogène et de l'azote.The purpose of annealing is to prepare the strip, in particular its surface, with a view to the following coating operation. In particular, it ensures the recrystallization of hardened structure in the case of a cold rolled strip; it also operates, in all cases, cleaning and brightening the surface with an atmosphere suitable, generally reducing, comprising hydrogen and nitrogen.

Schématiquement, la galvanisation conventionnelle consiste à faire passer une bande d'acier à travers un bain de zinc fondu puis, à la sortie de ce bain, à régler l'épaisseur de la couche de zinc par essorage au moyen de lames d'air ou d'azote sous pression.Schematically, conventional galvanizing involves passing a band of steel through a bath of molten zinc then, at the exit of this bath, to adjust the thickness the zinc layer by spinning with compressed air or nitrogen slats.

Au cours de son trajet dans le bain de zinc, la bande est guidée par plusieurs rouleaux, notamment un premier rouleau, dit rouleau de fond, entièrement immergé dans le zinc, sous lequel elle passe avant de remonter verticalement vers la surface du bain, et d'autres rouleaux, dits rouleaux de stabilisation, de déflexion ou de guidage, souvent partiellement ou même totalement immergés à proximité de la surface supérieure du bain de métal liquide, destinés à assurer la stabilisation, éventuellement la planéité de la bande revêtue, avant son essorage.During its journey in the zinc bath, the strip is guided by several rollers, in particular a first roller, said bottom roller, entirely immersed in zinc, under which it passes before rising vertically towards the surface of the bath, and other rollers, called stabilizing, deflecting or guiding rollers, often partially or even totally immersed near the upper surface of the bath of liquid metal, intended to ensure the stabilization, possibly the flatness of the coated strip, before spinning.

Ces rouleaux, motorisés ou libres, entrent en contact avec la surface de la bande en mouvement et peuvent ainsi engendrer des défauts de surface. Ils doivent donc être fréquemment démontés pour être inspectés, réparés voire remplacés, car leur état influence considérablement la qualité du revêtement de zinc. Il en résulte dès lors des arrêts fréquents de la ligne de production et une perte de productivité non négligeable. Par ailleurs, l'homme du métier connaít bien la difficulté de régler et de maintenir la composition du métal de revêtement. Celui-ci n'est pratiquement jamais un métal pur, mais plutôt un alliage contenant différents éléments en quantités déterminées mais variables d'un type à l'autre, destinés à améliorer les performances des revêtements, comme par exemple les additions d'aluminium dans les bains de galvanisation.These rollers, motorized or free, come into contact with the surface of the belt in movement and can thus cause surface defects. They must be frequently dismantled for inspection, repair or replacement as their condition significantly influences the quality of the zinc coating. As a result, frequent shutdown of the production line and significant loss of productivity. Moreover, the person skilled in the art is well aware of the difficulty of regulating and maintaining the composition of the coating metal. This is hardly ever a pure metal, but rather an alloy containing different elements in specific quantities but variables from one type to another, intended to improve the performance of coatings, as for example the additions of aluminum in galvanizing baths.

Enfin, les mattes, c'est-à-dire des agrégats de particules de composés intermétalliques, formés entre autres par la dissolution de l'extrême surface des bandes d'acier par le bain de métal liquide, entraínent également des défauts d'aspect bien connus, et doivent donc être régulièrement éliminées. Il en résulte des pertes de temps et de métal, qui nuisent à la productivité et à la rentabilité des procédés conventionnels.Finally, mattes, that is to say aggregates of particles of compounds intermetallic compounds, formed inter alia by the dissolution of the extreme surface of steel strips by the liquid metal bath, also cause appearance defects well known, and should therefore be regularly eliminated. This results in losses of time and metal, which adversely affect the productivity and profitability of the processes conventional.

Il a déjà été proposé de remplacer le rouleau de fond par un tube semi-circulaire fixe, également immergé dans le bain de métal liquide, et muni de fentes à travers lesquelles on injecte du métal liquide de revêtement. Il se forme ainsi une zone de métal sous pression qui maintient la bande à distance de la surface du tube immergé, sans toutefois que cette distance puisse être réglée et contrôlée de façon précise. Dans la pratique également, cette solution ne remédie pas aux problèmes de stabilité de la bande, ni aux défauts de surface causés par le contact avec les rouleaux de guidage, ni davantage à la difficulté de régler la composition du métal liquide, ni enfin aux problèmes liés aux mattes à éliminer.It has already been proposed to replace the bottom roller by a fixed semicircular tube, also immersed in the bath of liquid metal, and provided with slits through which is injected liquid coating metal. It thus forms a zone of pressurized metal that keeps the strip away from the submerged tube surface, however, this distance can not be adjusted and controlled accurately. In practice too, this solution does not solve the stability problems of the tape, or surface defects caused by contact with the rolls of guidance, no more to the difficulty of adjusting the composition of the liquid metal, nor finally Matter problems to be eliminated.

Présentation de l'inventionPresentation of the invention

L'invention a pour objet de proposer un procédé pour le revêtement d'une bande métallique au trempé, qui permet de remédier aux inconvénients précités, notamment en supprimant tous les rouleaux immergés et en assurant une composition constante du métal liquide dans la zone de revêtement. Dans un autre aspect, elle propose un dispositif pour la mise en oeuvre de ce procédé.The object of the invention is to propose a method for coating a web tempered metal, which makes it possible to remedy the aforementioned drawbacks, in particular by removing all submerged rolls and ensuring a constant composition liquid metal in the coating zone. In another aspect, it proposes a device for carrying out this method.

Conformément à l'invention, un procédé pour le revêtement d'une bande métallique au trempé au moyen d'un métal liquide, dans lequel on fait passer ladite bande dans un volume dudit métal liquide, est caractérisé en ce que l'on fait circuler ladite bande dans un mince canal, en ce que l'on introduit le métal liquide dans ledit mince canal au moins de part et d'autre de ladite bande, et en ce que l'on crée un mouvement de circulation dudit métal liquide par rapport à ladite bande, à l'intérieur dudit mince canal. On constate alors qu'on effectue donc le revêtement par contact de la surface de la bande métallique avec un flux de métal liquide plutôt que d'effectuer un revêtement de ladite surface par immersion dans un bain de métal liquide.According to the invention, a method for coating a metal strip at quenched by means of a liquid metal, in which said strip is passed through a volume of said liquid metal, is characterized in that said band is circulated in a thin channel, in that the liquid metal is introduced into said thin channel at less on both sides of the band, and in that a movement of circulating said liquid metal with respect to said band, inside said thin channel. It is found then that the coating is made by contact with the surface of the metal strip with a flow of liquid metal rather than a coating of said surface by immersion in a bath of liquid metal.

Selon l'invention, on alimente ledit mince canal en métal liquide à partir d'une source séparée, constituée par exemple par un réservoir séparé; un tel réservoir séparé est avantageusement disposé plus haut que ledit mince canal, de façon à assurer l'alimentation au moins partiellement par un effet gravimétrique. Une partie ou la totalité de l'alimentation peut cependant aussi être assurée par une ou plusieurs pompes.According to the invention, said thin liquid metal channel is fed from a source separate, constituted for example by a separate tank; such a separate tank is advantageously arranged higher than said thin channel, so as to ensure feeding at least partially by a gravimetric effect. Part or the However, the entire diet can also be provided by one or more pumps.

Selon une caractéristique intéressante, on soumet le métal liquide à au moins un traitement avant de l'introduire dans ledit mince canal. En particulier, ledit traitement peut consister à filtrer le métal liquide avant de l'introduire dans le mince canal. On réduit ainsi le risque de déposer des particules flottantes, telles que des composés intermétalliques, sur la surface de la bande.According to an interesting characteristic, the liquid metal is subjected to at least one treatment before introducing it into said thin channel. In particular, said treatment may include filtering the liquid metal before introducing it into the thin channel. We thus reduces the risk of depositing floating particles, such as compounds intermetallic, on the surface of the strip.

Suivant une autre caractéristique, on mesure à des intervalles déterminés, de préférence en continu, la composition chimique et/ou la température du métal liquide et, le cas échéant, on ajuste cette composition chimique et/ou cette température avant d'introduire le métal liquide dans ledit mince canal. Il est ainsi possible de maintenir au moins sensiblement constantes ces conditions régissant l'opération de revêtement au trempé de la bande métallique. According to another characteristic, it is measured at determined intervals, preferably continuously, the chemical composition and / or the temperature of the liquid metal and, if necessary, this chemical composition and / or this temperature is adjusted before introducing the liquid metal into said thin channel. It is thus possible to maintain less substantially constant these conditions governing the coating operation at dipped from the metal band.

Selon une autre caractéristique avantageuse, on réalise l'alimentation dudit mince canal en circuit fermé. On évite ainsi tout contact du métal liquide avec l'air ambiant, et de ce fait tout risque d'altération du métal liquide, en particulier par oxydation.According to another advantageous characteristic, the supply of said thin closed circuit channel. This avoids any contact of the liquid metal with the ambient air, and as a result any risk of alteration of the liquid metal, in particular by oxidation.

Selon une caractéristique particulièrement intéressante, on alimente ledit mince canal en métal liquide sous une pression réglable de façon indépendante sur chaque face de la bande. Suivant une méthode bien connue en soi, on règle la pression d'alimentation du métal liquide, selon le cas, en faisant varier la différence de niveau entre le mince canal et le réservoir séparé, ou en modifiant la pression fournie par les pompes d'alimentation.According to a particularly interesting characteristic, said thin channel is powered liquid metal under a pressure independently adjustable on each side of the band. According to a method that is well known per se, the feed pressure is regulated liquid metal, as the case may be, by varying the difference in level between the thin channel and the separate tank, or by changing the pressure provided by the pumps Power.

Suivant encore une autre caractéristique particulièrement avantageuse, la vitesse de circulation du courant de métal liquide par rapport à la bande, à l'intérieur dudit canal mince, est comprise entre 0,1 m/s et 5 m/s.According to yet another particularly advantageous characteristic, the speed of circulation of the liquid metal stream with respect to the band, inside said channel thin, is between 0.1 m / s and 5 m / s.

Il s'est avéré avantageux d'appliquer une pression identique de part et d'autre de la bande dans le mince canal. On peut cependant imaginer d'appliquer des pressions différentes de part et d'autre de la bande, notamment en vue d'influer sur la réactivité de surface de ladite bande métallique.It has proved advantageous to apply identical pressure on both sides of the band in the thin channel. However, we can imagine applying pressure on both sides of the band, in particular to influence responsiveness surface of said metal strip.

Un dispositif pour la mise en oeuvre de ce procédé comprend essentiellement un mince canal, des moyens pour faire circuler la bande à revêtir à travers ledit mince canal, ainsi que des moyens pour alimenter ledit mince canal en métal liquide et pour créer un mouvement de circulation du métal liquide par rapport à la bande, à l'intérieur du mince canal.A device for carrying out this method essentially comprises a thin channel, means for circulating the tape to be coated through said thin channel, as well as means for supplying said thin liquid metal channel and for create a circulation movement of the liquid metal with respect to the band, inside of the thin channel.

La section du mince canal suivant l'invention est déterminée de façon à permettre le passage de la bande la plus large qui doit y être revêtue, sans nécessiter de débit excessif de métal liquide.The section of the thin channel according to the invention is determined so as to allow the passage of the widest band to be covered, without the need for excessive liquid metal.

Compte tenu de la largeur des bandes actuelles, la largeur du mince canal suivant l'invention est généralement comprise entre 1 m et 2 m. Il va de soi que cette largeur pourrait être augmentée ou diminuée en fonction de circonstances particulières. Given the width of the current bands, the width of the next thin channel the invention is generally between 1 m and 2 m. It goes without saying that this width could be increased or decreased depending on specific circumstances.

La hauteur du mince canal définit l'épaisseur de la couche de métal liquide en circulation, et par conséquent influence aussi le débit de métal liquide dans le mince canal. Cette hauteur est de préférence inférieure à 6 cm, et de préférence encore inférieure à 3 cm, de façon à pouvoir limiter le débit de métal liquide dans le mince canal.The height of the thin channel defines the thickness of the liquid metal layer in circulation, and therefore also influences the flow of liquid metal in the thin channel. This height is preferably less than 6 cm, and more preferably less than 3 cm, so as to be able to limit the flow of liquid metal in the thin channel.

Le mince canal suivant l'invention peut présenter une forme soit plane, soit courbe, en particulier partiellement cylindrique. Dans ce dernier cas, la courbure doit être limitée afin de ne pas compliquer inutilement la trajectoire et le guidage de la bande.The thin channel according to the invention may have a shape that is either flat or curved in particularly partially cylindrical. In the latter case, the curvature must be limited so as not to unnecessarily complicate the trajectory and guidance of the tape.

La bande à revêtir circule à travers ledit canal sous l'action de la traction exercée par les systèmes d'entraínement de la ligne de revêtement. Sa trajectoire est déterminée par des moyens de guidage, généralement des rouleaux, disposés à l'extérieur du canal, en amont et en aval de celui-ci, de façon à ne pas endommager la surface de la bande pendant l'opération de revêtement.The tape to be coated flows through said channel under the action of the traction exerted by the drive systems of the coating line. Its trajectory is determined by guiding means, generally rollers, arranged outside the channel, upstream and downstream of it, so as not to damage the surface of the tape during the coating operation.

A l'intérieur du mince canal, la bande doit dès lors être maintenue à une distance minimale des parois du canal, afin d'éviter tout risque de contact avec celles-ci. En règle générale, cette distance est comprise entre 1 mm et 15 mm, en fonction de divers paramètres tels que la vitesse et la largeur de la bande, la nature du métal liquide, la longueur et/ou la forme de la trajectoire du mince canal.Inside the thin channel, the band must therefore be kept at a distance channel walls, to avoid any risk of contact with them. In In general, this distance is between 1 mm and 15 mm, depending on various parameters such as the speed and width of the band, the nature of the liquid metal, the length and / or shape of the path of the thin channel.

Le mince canal suivant l'invention comporte d'une part des moyens d'alimentation en métal liquide, et d'autre part des moyens pour créer un mouvement de circulation du métal liquide par rapport à la bande, à l'intérieur du mince canal.The thin channel according to the invention comprises, on the one hand, feed means liquid metal, and secondly means to create a circulation movement of the liquid metal with respect to the band, inside the thin channel.

Lesdits moyens d'alimentation comprennent au moins un réservoir séparé, d'une capacité nettement plus grande que le mince canal; ce réservoir est relié au mince canal par un circuit d'alimentation conduisant à des moyens d'introduction du métal liquide dans le mince canal, de part et d'autre de la bande qui y circule. Ces moyens d'introduction peuvent être constitués soit par des injecteurs disposés à au moins une des extrémités du canal, soit par des injecteurs ménagés dans les parois du canal parallèles au plan de la bande, soit encore par une combinaison de ces deux types d'injecteurs. Said supply means comprise at least one separate reservoir, a much larger capacity than the thin channel; this tank is connected to the thin channel by a supply circuit leading to means for introducing the metal liquid in the thin channel, on both sides of the band that circulates there. These means of introduction can be constituted either by injectors arranged in at least one ends of the channel, or by injectors in the walls of the canal parallel to the plane of the band, either by a combination of these two types injectors.

Pour assurer la circulation du métal liquide, y compris dans le mince canal, le réservoir séparé peut être surélevé par rapport au mince canal, ou le circuit d'alimentation peut comporter au moins une pompe.To ensure the circulation of the liquid metal, including in the thin channel, the reservoir separated can be raised compared to the thin channel, or the supply circuit can have at least one pump.

D'une façon également avantageuse, le dispositif comprend aussi des moyens de contrôle et de réglage de la température et/ou de la composition du métal liquide, des moyens pour ajouter du métal liquide frais ainsi que des moyens pour filtrer le métal liquide avant son introduction dans le mince canal.Also advantageously, the device also comprises means for control and adjustment of the temperature and / or composition of the liquid metal, means for adding fresh liquid metal as well as means for filtering the metal liquid before its introduction into the thin canal.

En outre, le canal est pourvu de moyens d'étanchéité, tels que des sas à ses extrémités, permettant le passage de la bande mais empêchant les fuites de métal liquide.In addition, the channel is provided with sealing means, such as airlock at its ends, allowing passage of the band but preventing metal leakage liquid.

Enfin, le canal peut avantageusement être intégré dans un circuit fermé, comprenant également au moins un réservoir d'alimentation, éventuellement surélevé, un circuit d'alimentation du mince canal, un circuit de récupération du métal liquide en excès, des moyens de traitement du métal liquide, et éventuellement au moins une pompe de circulation du métal liquide.Finally, the channel can advantageously be integrated in a closed circuit, comprising also at least one feed tank, possibly raised, a circuit supply of the thin channel, an excess liquid metal recovery circuit, means for treating the liquid metal, and possibly at least one pump of circulation of the liquid metal.

Le procédé et le dispositif de l'invention permettent de revêtir une bande par immersion dans un courant de métal liquide animé de vitesses élevées par rapport à la bande. Ces vitesses sont supérieures à celles qui résultent du défilement de la bande dans un bain de métal liquide au repos.The method and the device of the invention make it possible to coat a strip by immersion in a moving liquid metal stream of high velocities relative to the web. These speeds are higher than those resulting from the scrolling of the band in a bath of liquid metal at rest.

Par rapport à la technique antérieure, le procédé de l'invention offre de nombreux avantages, qui seront explicités plus loin, lors de la description des dessins annexés.Compared to the prior art, the method of the invention offers numerous advantages, which will be explained later, when describing the accompanying drawings.

Brève description des dessinsBrief description of the drawings

Des exemples de réalisation du dispositif de l'invention sont représentés de façon schématique dans les dessins annexés, dans lesquels la

Fig. 1
rappelle le principe d'une installation conventionnelle de revêtement au trempé de la technique antérieure; la
Fig. 2
montre le principe du procédé de la présente invention; la
Fig. 3
illustre un premier cas d'application du procédé de l'invention, avec un mince canal rectiligne pratiquement horizontal; la
Fig. 3b
illustre un deuxième cas d'application du procédé de l'invention, avec un mince canal courbe en forme de parabole; la
Fig. 3
illustre un troisième cas d'application du procédé de l'invention, avec un mince canal approchant la trajectoire habituelle de la bande dans un bain de métal liquide; la
Fig. 4
montre différentes dispositions des orifices d'alimentation en métal liquide, ménagés dans les parois du mince canal (Fig. 4a, b, c); et la
Fig. 5
illustre différentes configurations possibles du mince canal avec son circuit d'alimentation en métal liquide (Fig. 5a, b, c, d).
Embodiments of the device of the invention are schematically represented in the accompanying drawings, in which the
Fig. 1
recalls the principle of a conventional dip coating installation of the prior art; the
Fig. 2
shows the principle of the process of the present invention; the
Fig. 3
illustrates a first case of application of the method of the invention, with a thin substantially horizontal rectilinear channel; the
Fig. 3b
illustrates a second case of application of the method of the invention, with a thin curved channel in the form of a dish; the
Fig. 3
illustrates a third case of application of the method of the invention, with a thin channel approaching the usual trajectory of the strip in a bath of liquid metal; the
Fig. 4
shows different arrangements of the liquid metal feed orifices formed in the walls of the thin channel (Fig. 4a, b, c); and the
Fig. 5
illustrates different possible configurations of the thin channel with its liquid metal feed circuit (Fig. 5a, b, c, d).

Ces figures ne constituent que des représentations schématiques simplifiées, dans lesquelles on n'a reproduit que les éléments nécessaires à la compréhension de l'invention. Le sens de circulation du métal liquide est indiqué par des flèches. Des éléments identiques sont désignés par les mêmes repères numériques dans toutes les figures.These figures are only simplified schematic representations, in which only the elements necessary for the understanding of the invention. The flow direction of the liquid metal is indicated by arrows. of the identical elements are designated by the same numerical markers in all FIGS.

Modes de réalisation de l'inventionEmbodiments of the invention

La figure 1 représente un dispositif conventionnel de galvanisation au trempé d'une bande d'acier, intégré dans une ligne de traitement. Dans ce dispositif, une bande à revêtir 1 est traitée dans un four de recuit continu 2, dont elle sort par une trompe 3 pour plonger dans un bain de zinc en fusion 4. La bande 1 passe sous un rouleau de fond 5, complètement immergé dans le zinc liquide 4, puis elle est guidée par des rouleaux de stabilisation 6 immergés à proximité de la surface supérieure du bain de zinc 4, avant de quitter le bain de zinc suivant une trajectoire verticale. L'excès de zinc est essoré au moyen de lames de gaz, généralement d'air ou d'azote, sous pression 7. La bande 1 monte ensuite verticalement jusqu'à un rouleau de déviation supérieur 8, qui est situé suffisamment haut pour que le revêtement de zinc soit solidifié avant de l'atteindre. La bande 1 poursuit ensuite son chemin dans la ligne de traitement.FIG. 1 represents a conventional device for galvanizing dipping a steel strip, integrated into a processing line. In this device, a band coat 1 is treated in a continuous annealing furnace 2, from which it leaves by a trunk 3 to dive into a bath of molten zinc 4. The strip 1 passes under a roll of bottom 5, completely immersed in the liquid zinc 4, then it is guided by 6 immersed stabilizing rollers near the upper surface of the bath of zinc 4, before leaving the zinc bath in a vertical path. Excess zinc is dewatered by means of gas strips, generally air or nitrogen, under pressure 7. The strip 1 then rises vertically up to an upper deflection roll 8, which is high enough for the zinc coating to solidify before reach it. Tape 1 then continues its way into the treatment line.

Dans ce dispositif classique, la bande à revêtir 1 circule à travers un bain de zinc liquide au repos 4, et elle est en contact direct avec plusieurs rouleaux immergés 5, 6. In this conventional device, the strip to be coated 1 circulates through a zinc bath liquid at rest 4, and it is in direct contact with several submerged rollers 5, 6.

Le principe du procédé de l'invention est illustré dans la figure 2. Ici, la bande à revêtir 1, provenant d'un four de recuit continu non représenté, circule à travers un mince canal 10 dans lequel on a créé un courant de métal liquide 9. Dans cette figure, le canal 10 est rectiligne et légèrement incliné vers le haut, et la circulation du métal liquide est assurée par une pompe 11. Dans cette illustration, la bande 1 et le courant de métal liquide 9 circulent dans le sens ascendant, indiqué par des flèches. Des systèmes d'étanchéité, non représentés, sont prévus aux extrémités d'entrée et de sortie de la bande 1 dans le canal 10.The principle of the process of the invention is illustrated in FIG. 2. Here, the strip to be coated 1, from a continuous annealing furnace (not shown), circulates through a thin channel 10 in which a stream of liquid metal 9 has been created. In this figure, the channel 10 is straight and slightly inclined upward, and the circulation of the metal liquid is provided by a pump 11. In this illustration, the band 1 and the current of liquid metal 9 circulate in the ascending direction, indicated by arrows. of the sealing systems, not shown, are provided at the inlet and output of the band 1 in the channel 10.

D'autres configurations possibles sont illustrées et décrites dans la figure 3. Cette figure 3 montre comment il est possible de contrôler, au moins en partie, la position de la bande dans un mince canal, suivant le procédé de l'invention.Other possible configurations are illustrated and described in Figure 3. This Figure 3 shows how it is possible to control, at least in part, the position of the band in a thin channel, according to the method of the invention.

Comme on l'a indiqué plus haut, on crée un mouvement de circulation du métal liquide, par exemple du zinc en fusion, dans le canal 10, de part et d'autre de la bande 1. Ce courant circule de préférence à grande vitesse, et s'accompagne inévitablement de gradients de pression entre la bande 1 et les parois du canal 10. Les chemins hydrauliques que le métal liquide suit dans le canal 10 peuvent être conçus de façon à créer des différences de pression entre les faces de la bande et à influencer ainsi la position de la bande dans le canal. En effet, même si elles sont de faible amplitude, ces différences de pression agissent sur des surfaces importantes, à savoir la surface des deux faces de la bande dans le canal, et elles peuvent ainsi générer des forces considérables.As indicated above, a circulation movement of the liquid metal is created, for example molten zinc, in the channel 10, on either side of the strip 1. This current flows preferably at high speed, and is inevitably accompanied by pressure gradients between the band 1 and the walls of the channel 10. The paths hydraulic fluid that the liquid metal follows in channel 10 can be designed to create pressure differences between the faces of the band and thereby influence the position of the band in the channel. Indeed, even if they are of low amplitude, these pressure differences act on important surfaces, namely the surface both sides of the strip in the channel, and they can thus generate forces considerable.

A titre d'exemple, une différence de pression entre les deux faces de la bande peut être obtenue de plusieurs manières:

  • Figure 00080001
    en créant des débits de métal liquide différents sur les deux faces, tout en conservant des vitesses de circulation suffisantes;
  • en modifiant la distance entre la bande et la paroi du canal: à débit de métal égal, une diminution de cette distance entraíne une augmentation de la pression;
  • en différenciant l'injection de métal liquide entre les deux faces de la bande, en ce qui concerne aussi bien la pression d'injection que le nombre et/ou la disposition des injecteurs.
    • By way of example, a pressure difference between the two faces of the strip can be obtained in several ways:
  • Figure 00080001
    creating different liquid metal flow rates on both sides, while maintaining sufficient flow velocities;
  • by modifying the distance between the band and the wall of the channel: at equal metal flow rate, a decrease in this distance causes an increase in pressure;
  • by differentiating the injection of liquid metal between the two faces of the strip, as regards both the injection pressure as the number and / or the arrangement of the injectors.

    • La figure 3a illustre le cas simple d'un mince canal 12 rectiligne, pratiquement horizontal, dans lequel la bande 1 circule à égale distance des deux parois. Les pressions 13 exercées sur la face inférieure de la bande sont plus élevées que celles 14 appliquées sur la face supérieure, afin de supporter le poids de la bande 1 tout en maintenant celle-ci en position centrée dans le canal 12.FIG. 3a illustrates the simple case of a thin rectilinear channel 12, practically horizontal, in which the band 1 circulates equidistant from the two walls. The 13 pressures on the underside of the strip are higher than those 14 on the upper side, to support the weight of tape 1 while now it in a centered position in the channel 12.

    Dans la figure 3b, le canal 15 présente la forme d'une parabole, correspondant à la forme dite "en chaínette" que prend naturellement la bande 1 suspendue librement entre deux rouleaux supérieurs non représentés.In FIG. 3b, the channel 15 is in the form of a parabola, corresponding to the form called "chain" that takes naturally band 1 hanging freely between two upper rollers not shown.

    Une telle trajectoire parabolique de la bande 1 peut être maintenue par un contrôle permanent de la vitesse de la bande en amont et en aval du canal 15. Elle est aussi maintenue grâce aux pressions que le métal liquide exerce sur la bande; si les pressions 16 sur la face interne sont plus élevées que celles 17 exercées sur la face externe, elles sont même capables de compenser une traction dans la bande. Dans une telle configuration du canal, il est particulièrement aisé d'assurer l'étanchéité du canal, en recueillant le métal liquide débordant aux deux extrémités du canal pour le réintroduire dans la partie inférieure, par exemple à l'aide de pompes 18.Such a parabolic trajectory of the band 1 can be maintained by a control permanent speed of the band upstream and downstream of channel 15. It is also maintained by the pressures that the liquid metal exerts on the band; if the pressures 16 on the inner face are higher than those 17 on the face external, they are even able to compensate for traction in the band. In such a configuration of the channel, it is particularly easy to ensure the tightness of the channel, collecting the liquid metal overflowing at both ends of the channel for the reintroduce in the lower part, for example using pumps 18.

    Enfin, la figure 3c montre un canal 15 d'une forme proche de celle du trajet habituel d'une bande 1 dans une installation de revêtement au trempé du type illustré dans la figure 1. Dans cette configuration, la bande 1, qui subit la traction exercée par la ligne de traitement, est supportée par l'application de pressions 19 plus élevées sur la face interne que celles 20 exercées sur la face externe. En outre, la bande 1 peut être guidée de façon contrôlée tant à l'entrée qu'à la sortie du canal, par des pressions différentielles 21, qui remplacent avantageusement, c'est-à-dire sans contact, les rouleaux de guidage 6 de la figure 1.Finally, FIG. 3c shows a channel 15 of a shape close to that of the usual path of a strip 1 in a dip coating installation of the type illustrated in the In this configuration, the band 1, which undergoes the pull exerted by the line of treatment, is supported by the application of higher pressures 19 on the face internal than those exerted on the outer face. In addition, band 1 can be guided in a controlled manner both at the inlet and the outlet of the canal, by means of pressure differentials 21, which advantageously replace, that is to say without contact, the guide rollers 6 of FIG.

    Ici également, l'étanchéité du canal est assurée avec facilité en recueillant le métal liquide en excès aux deux extrémités du canal pour le réintroduire dans la partie inférieure, par exemple à l'aide d'une pompe commune 22. Here too, the watertightness of the channel is assured with ease by collecting the metal excess liquid at both ends of the canal to reintroduce it into the lower, for example using a common pump 22.

    L'alimentation du mince canal en métal liquide est de préférence assurée par des orifices ménagés dans les parois du canal, de façon à répartir d'une façon aussi uniforme que possible les pressions agissant sur les faces de la bande.The supply of the thin liquid metal channel is preferably provided by openings in the walls of the canal so as to distribute in a similar way as uniform as possible the pressures acting on the faces of the band.

    La figure 4 montre diverses dispositions possibles de ces orifices d'alimentation dans une portion d'une paroi de canal 23. Dans les exemples représentés, les orifices peuvent être soit des fentes 24 parallèles et/ou perpendiculaires à la direction 25 de déplacement de la bande (Fig. 4a), soit des orifices, par exemple circulaires 26, disposés suivant des lignes également parallèles à la direction 25 de déplacement de la bande (Fig. 4b), soit encore des orifices, par exemple circulaires 27, répartis régulièrement, par exemple en quinconce, dans la paroi du canal (Fig. 4c).Figure 4 shows various possible arrangements of these feed orifices in a portion of a channel wall 23. In the examples shown, the orifices can be either slits 24 parallel and / or perpendicular to the direction 25 of displacement of the strip (FIG 4a), or orifices, for example circular 26, arranged in lines parallel to the direction of movement of the the band (Fig. 4b), again orifices, for example circular holes 27, distributed regularly, for example in staggered rows, in the canal wall (Fig. 4c).

    Ces dispositions sont données à titre de simples exemples et n'excluent nullement toute autre disposition d'orifices permettant d'obtenir une répartition uniforme des pressions dans le canal.These provisions are given as simple examples and do not exclude any other arrangement of orifices which makes it possible to obtain an even distribution of pressures in the channel.

    On a déjà mentionné plus haut la possibilité, dans le procédé de l'invention, d'effectuer différentes opérations sur le métal liquide en circulation, en particulier de filtrer les particules de composés intermétalliques et de contrôler et/ou d'ajuster la température et/ou la composition chimique du métal liquide, avant de l'introduire dans le canal de revêtement.It has already been mentioned above the possibility, in the method of the invention, of carrying out different operations on the liquid metal in circulation, in particular to filter the particles of intermetallic compounds and to control and / or adjust the temperature and / or the chemical composition of the liquid metal, before introducing it into the coating.

    Par ailleurs, on a également souligné l'intérêt de prévoir un réservoir extérieur, c'est-à-dire distinct du mince canal proprement dit mais communiquant avec celui-ci, et de mettre le métal liquide en circulation entre le mince canal - de faible capacité - et le réservoir extérieur de plus grande capacité.Moreover, it was also emphasized the importance of providing an external reservoir, that is to say distinct from the actual channel but communicating with it, and circulate the liquid metal between the thin channel - of low capacity - and the outer tank of greater capacity.

    La figure 5 illustre différentes configurations possibles du circuit du métal liquide, avec une unité de traitement, éventuellement combinée à un réservoir extérieur surélevé.FIG. 5 illustrates various possible configurations of the liquid metal circuit, with a treatment unit, possibly combined with a raised outer tank.

    Dans la disposition de la figure 5a, un canal rectiligne horizontal 12, parcouru par une bande 1, est alimenté en direct au moyen d'une pompe 28. Le métal liquide est récupéré aux extrémités du canal 12 et renvoyé par la pompe 28, d'abord à une unité de traitement 29 et ensuite directement dans le canal 12. In the arrangement of FIG. 5a, a horizontal rectilinear channel 12, traversed by a band 1, is fed directly by means of a pump 28. The liquid metal is recovered at the ends of the channel 12 and returned by the pump 28, first to a unit treatment 29 and then directly into the channel 12.

    La figure 5b représente également un canal rectiligne horizontal 12 parcouru par une bande à revêtir 1. Ce canal 12 est alimenté par gravité à partir d'un réservoir surélevé 30 de grande capacité, tandis que le métal liquide en excès est récupéré aux extrémités du canal 12 et renvoyé, toujours par gravité, dans un réservoir de collecte 32. A partir de celui-ci, le métal liquide est alors renvoyé au réservoir surélevé 30 au moyen d'une pompe 31. Une unité de traitement 29 est placée entre le réservoir 30 et le canal 12 et/ou entre la pompe 31 et le réservoir 30.FIG. 5b also shows a horizontal rectilinear channel 12 traversed by a tape to be coated 1. This channel 12 is fed by gravity from a raised tank 30 large capacity, while the excess liquid metal is recovered at ends of the channel 12 and returned, still by gravity, into a collection tank 32. From there, the liquid metal is then returned to the elevated tank 30 at by means of a pump 31. A treatment unit 29 is placed between the reservoir 30 and the channel 12 and / or between the pump 31 and the reservoir 30.

    La configuration de la figure 5c est analogue à celle de la figure 5a, avec la différence que le canal 33 épouse ici le trajet de la bande 1 dans une ligne de revêtement au trempé conventionnelle. Le métal liquide en excès est récupéré aux extrémités surélevées du canal 33 et renvoyé au point bas de ce canal, à travers une pompe 28 et une unité de traitement 29.The configuration of Figure 5c is similar to that of Figure 5a, with the difference that the channel 33 here marries the path of the band 1 in a coating line to conventional tempering. The excess liquid metal is recovered at the ends elevated channel 33 and returned to the low point of this channel, through a pump 28 and a processing unit 29.

    Enfin, la figure 5d illustre une disposition, analogue à celle de la figure 5b, mais où le canal 33 épouse le trajet de la bande 1 dans une ligne de revêtement au trempé conventionnelle. Le canal 33 est alimenté directement en son point bas par gravité, à partir d'un réservoir surélevé 30 de grande capacité; le métal liquide en excès est récupéré aux extrémités surélevées du canal 33 et renvoyé, également par gravité, dans un réservoir de collecte 32. A partir de celui-ci, le métal liquide est renvoyé au réservoir surélevé 30 au moyen d'une pompe 31. Une unité de traitement 29 est prévue entre le réservoir 30 et le canal 33, et/ou entre la pompe 31 et le réservoir 30.Finally, Figure 5d illustrates a layout, similar to that of Figure 5b, but where the channel 33 marries the path of the band 1 in a line of dipping coating conventional. Channel 33 is fed directly at its low point by gravity, at from a raised tank 30 of large capacity; the excess liquid metal is recovered at the raised ends of the channel 33 and returned, also by gravity, in a collection tank 32. From this, the molten metal is returned to the raised tank 30 by means of a pump 31. A treatment unit 29 is provided between the reservoir 30 and the channel 33, and / or between the pump 31 and the reservoir 30.

    Par rapport à la technique antérieure d'immersion d'une bande en mouvement dans un bain de métal liquide, de grand volume, au repos, la présente invention offre de nombreux avantages, en ce qui concerne aussi bien le procédé proprement dit que la qualité des produits revêtus.Compared to the prior art of immersion of a moving band in a liquid metal bath, of large volume, at rest, the present invention offers numerous advantages, both as regards the process itself and the quality of coated products.

    En matière de procédé, un avantage important est la grande souplesse conférée à la ligne de traitement concernant la nature du métal déposé. Il suffit en effet de changer de réservoir d'alimentation pour passer d'un revêtement à un autre.In terms of process, an important advantage is the great flexibility conferred on the treatment line concerning the nature of the deposited metal. It is enough to change supply tank to switch from one liner to another.

    D'autre part, la circulation continue du métal liquide entre le canal de revêtement et un réservoir séparé permet de traiter le métal liquide en continu. On peut en effet contrôler, et au besoin ajuster, tant la température que la composition chimique du métal liquide.On the other hand, the continuous circulation of the liquid metal between the coating channel and a Separate tank allows to process the liquid metal continuously. We can indeed control, and if necessary adjust, both the temperature and the chemical composition of the liquid metal.

    Il est également possible d'éliminer les mattes, c'est-à-dire les particules de composés intermétalliques qui flottent dans le métal liquide et qui risquent de se déposer sur la bande. Cette élimination peut se faire par toute méthode appropriée, telle que filtrage, décantation, centrifugation, etc., en particulier dans l'unité de traitement mentionnée plus haut.It is also possible to remove the mattes, that is to say the particles of compounds intermetallic compounds that float in the liquid metal and may deposit on the bandaged. This elimination can be done by any appropriate method, such as filtering, decantation, centrifugation, etc., especially in the mentioned treatment unit upper.

    Enfin, il convient de souligner la facilité de maintenance du dispositif de l'invention. Les rouleaux immergés ayant disparu, la maintenance concerne essentiellement les pompes, qui peuvent d'ailleurs être doublées et dès lors entretenues en alternance sans que la ligne de revêtement doive être mise à l'arrêt.Finally, it should be emphasized the ease of maintenance of the device of the invention. The immersed rollers having disappeared, the main maintenance concerns pumps, which can be doubled and therefore maintained alternately without the coating line having to be shut down.

    La qualité du revêtement dépend notamment de la réactivité entre le métal de revêtement et la surface de la bande à revêtir. A titre d'exemple, les aciers à haute résistance destinés à être galvanisés pour l'industrie automobile, ont une surface faiblement réactive à l'égard du zinc; il en résulte un manque de mouillabilité qui peut conduire à de graves défauts de revêtement.The quality of the coating depends in particular on the reactivity between the metal of coating and the surface of the tape to be coated. For example, high-grade steels resistance to be galvanized for the automotive industry, have a surface low reactivity to zinc; this results in a lack of wettability that can lead to serious coating defects.

    A cet égard, on a constaté que la vitesse relative élevée entre la bande et le métal liquide dans le canal de revêtement provoquait une amélioration de la réactivité entre le métal liquide et la bande, et contribuait à supprimer les défauts de revêtement précités.In this respect, it has been found that the high relative velocity between the band and the metal liquid in the coating channel caused an improvement in the reactivity between the liquid metal and the tape, and helped to eliminate the coating defects supra.

    De même, l'instauration d'une vitesse relative significative, par exemple de 0,5 m/s à 1 m/s, entre la bande et le métal liquide dans le canal, contribue à réduire le risque de collage sur la bande, de particules en suspension dans le métal liquide. Cet effet s'ajoute à celui de l'opération d'élimination des mattes mentionnée plus haut.
    Enfin, le procédé de l'invention rétablit la symétrie entre les deux faces de la bande, du fait qu'aucune des deux faces de la bande n'est désormais plus en contact avec des rouleaux. La durée réelle et les conditions d'exposition des deux faces de la bande au métal liquide sont identiques.     Similarly, the introduction of a significant relative speed, for example from 0.5 m / s to 1 m / s, between the strip and the liquid metal in the channel, contributes to reducing the risk of sticking on the strip, particles suspended in the liquid metal. This effect is in addition to that of the matting removal operation mentioned above.
    Finally, the method of the invention restores the symmetry between the two faces of the strip, because none of the two faces of the strip is now no longer in contact with rollers. The actual duration and the conditions of exposure of the two sides of the strip to the liquid metal are identical.

    Le dispositif de l'invention est nettement plus simple que les dispositifs conventionnels de galvanisation au trempé. Il nécessite une moins grande quantité de métal liquide, il offre une plus grande souplesse de fonctionnement et il permet d'obtenir des produits revêtus de meilleure qualité. Enfin, il peut s'intégrer, sans difficulté importante, dans une ligne de traitement existante, comme le montre la figure 3c.The device of the invention is much simpler than conventional devices dip galvanizing. It requires a smaller amount of liquid metal, it offers greater operational flexibility and allows you to obtain products coated with better quality. Finally, it can integrate, without significant difficulty, in an existing treatment line, as shown in Figure 3c.

    Claims (22)

    1. Method for dip-coating a metal strip
      (1) in a liquid metal (4), in which:
      said strip is passed through a narrow duct (10,12,15,33) into which the liquid metal is injected at least on both sides of the strip;
      a circulatory movement of said liquid metal is created inside the narrow duct;
      characterised in that a difference is also created in the pressures (13,14; 16,17; 19,20) exerted on each of the two faces of the strip respectively, so as to control the position of the strip in the narrow duct;
    2. Method as in Claim 1, characterised in that said difference in the pressures exerted on each of the two faces of the strip is obtained by creating different flows of liquid metal over the two faces.
    3. Method as in Claim 1, characterised in that said difference in the pressures exerted on each of the two faces of the strip is obtained by modifying the distance between the strip and the wall of the narrow duct, a reduction of this distance leading to an increase in pressure for the same flow.
    4. Method as in Claim 1, characterised in that said difference in the pressures exerted on each of the two faces of the strip is obtained by differentiating the injection of liquid metal on the two faces of the strip.
    5. Method as in any one of the preceding claims, characterised in that the narrow duct (10,12,15,33) and hence the path of the strip have a curved shape, preferably a parabolic, catenary or partially cylindrical shape.
    6. Method as in any one of the preceding claims, characterised in that said narrow duct is supplied by gravity from a separate source (30) of liquid metal.
    7. Method as in any one of the preceding claims, characterised in that the liquid metal is filtered before it is introduced into the narrow duct.
    8. Method as in any one of the preceding claims, characterised in that the temperature of the liquid metal is measured and, if necessary, adjusted, preferably continuously, before it is introduced into the narrow duct.
    9. Method as in any one of the preceding claims, characterised in that the chemical composition of the liquid metal is measured and, if necessary, adjusted, preferably continuously, before it is introduced into the narrow duct.
    10. Method as in any one of Claims 6 to 9, characterised in that the narrow duct is supplied with a closed circuit.
    11. Method as in any one of the preceding claims, characterised in that the respective pressures on each of the two faces of the strip are regulated independently from one another inside the narrow duct.
    12. Method as in any one of Claims 1 to 11, characterised in that the circulation speed of the current of liquid metal relative to the strip inside the narrow duct is between 0.5 m/s and 1 m/s.
    13. Method as in any one of Claims 1 to 12, characterised in that the strip to be coated passes through the narrow duct under the effect of the traction exerted by drive systems operating the coating line, the path of the strip being determined by guiding means, preferably rollers, arranged outside the narrow duct, upstream and downstream from it.
    14. Method as in any one of Claims 1 to 13, characterised in that, inside the narrow duct, the strip is maintained at a minimum distance from the walls of the duct, between 1 and 15 mm, depending on parameters such as the speed and width of the strip, the nature of the liquid metal and the length and/or shape of the narrow duct.
    15. Device for dip-coating a metal strip according to the method of any one of Claims 1 to 14, characterised in that it comprises a narrow duct (10,12,15,33), means for passing the strip to be coated through the narrow duct as well as means, preferably comprising at least one pump (11,18,22,28,31), for supplying said narrow duct with liquid metal and for creating a circulatory movement of the liquid metal relative to the inside of the narrow duct.
    16. Device as in Claim 15, characterised in that said supplying means comprise at least one separate tank (30) with a larger capacity than the narrow duct and in that said separate tank is connected to the narrow duct by a supply circuit leading to means (24,26,27) for introducing the liquid metal into said narrow duct on both sides of the strip (1) passing through it.
    17. Device as in Claim 16, characterised in that said separate tank (30) is raised relative to the narrow duct so as to cause the circulation of the liquid metal by gravity on the one hand between the separate tank and the narrow duct and on the other hand inside the narrow duct.
    18. Device as in any one of Claims 15 to 17, characterised in that it comprises means (29) for filtering the liquid metal before it is introduced into said narrow duct.
    19. Device as in any one of Claims 15 to 18, characterised in that it comprises means (29) for measuring and, if necessary, adjusting the temperature of the liquid metal before it is introduced into said narrow duct.
    20. Device as in any one of Claims 15 to 19, characterised in that it comprises means (29) for measuring and, if necessary, adjusting the chemical composition of the liquid metal before it is introduced into said narrow duct.
    21. Device as in any one of Claims 15 to 20, characterised in that the narrow duct is incorporated into a closed circuit, also comprising at least one supply tank, possibly raised, a supply circuit for the narrow duct, a recovery circuit for the excess liquid metal, treatment means for the liquid metal and possibly at least one pump for the circulation of the liquid metal.
    22. Device as in any one of Claims 15 to 21, characterised in that the height of the narrow duct, defining the thickness of the layer of liquid metal in circulation, is less than 6 cm, and preferably less than 3 cm, so as to limit the flow of the liquid metal in the narrow duct.
    EP02719575A 2001-04-03 2002-03-28 Method and device for dip coating a metal strip Expired - Lifetime EP1386016B1 (en)

    Applications Claiming Priority (3)

    Application Number Priority Date Filing Date Title
    BE200100216 2001-04-03
    BE2001/0216A BE1014093A3 (en) 2001-04-03 2001-04-03 PROCESS AND DISPSOTIVE FOR COATING A METAL STRIP WITH HARDENING.
    PCT/BE2002/000047 WO2002083969A1 (en) 2001-04-03 2002-03-28 Method and device for dip coating a metal strip

    Publications (2)

    Publication Number Publication Date
    EP1386016A1 EP1386016A1 (en) 2004-02-04
    EP1386016B1 true EP1386016B1 (en) 2005-06-01

    Family

    ID=3896920

    Family Applications (1)

    Application Number Title Priority Date Filing Date
    EP02719575A Expired - Lifetime EP1386016B1 (en) 2001-04-03 2002-03-28 Method and device for dip coating a metal strip

    Country Status (6)

    Country Link
    EP (1) EP1386016B1 (en)
    AT (1) ATE296905T1 (en)
    BE (1) BE1014093A3 (en)
    DE (1) DE60204453T2 (en)
    ES (1) ES2242008T3 (en)
    WO (1) WO2002083969A1 (en)

    Family Cites Families (8)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    GB637537A (en) * 1941-01-29 1950-05-24 Gen Motors Corp Apparatus for coating or impregnating metal strip stock with metal
    DE1771662A1 (en) * 1968-06-24 1972-01-13 Jenoptik Jena Gmbh Device for tinning copper wires
    DE2105661A1 (en) * 1971-02-05 1972-08-10 Mandl J Hot dip metal coating - with melt flow along workpiece surface
    GB1532554A (en) * 1976-02-10 1978-11-15 Raymond A Metallic coating of metal tubes and similar work pieces
    JPS61199064A (en) * 1985-02-27 1986-09-03 Hitachi Cable Ltd Hot dip coating apparatus
    JPH028356A (en) * 1988-06-25 1990-01-11 Kawasaki Steel Corp Method and apparatus for metal hot dipping
    JPH02141564A (en) * 1988-11-21 1990-05-30 Furukawa Electric Co Ltd:The Production of hot dip sn coated wire
    JPH08337858A (en) * 1995-06-09 1996-12-24 Kawasaki Steel Corp Method for hot dip metal plating and equipment therefor

    Also Published As

    Publication number Publication date
    EP1386016A1 (en) 2004-02-04
    WO2002083969A1 (en) 2002-10-24
    ATE296905T1 (en) 2005-06-15
    BE1014093A3 (en) 2003-04-01
    DE60204453D1 (en) 2005-07-07
    ES2242008T3 (en) 2005-11-01
    DE60204453T2 (en) 2006-05-18

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