EP1339891A1 - Method and installation for hot process and continuous dip coating of a metal strip - Google Patents

Method and installation for hot process and continuous dip coating of a metal strip

Info

Publication number
EP1339891A1
EP1339891A1 EP01993387A EP01993387A EP1339891A1 EP 1339891 A1 EP1339891 A1 EP 1339891A1 EP 01993387 A EP01993387 A EP 01993387A EP 01993387 A EP01993387 A EP 01993387A EP 1339891 A1 EP1339891 A1 EP 1339891A1
Authority
EP
European Patent Office
Prior art keywords
metal
liquid
bath
liquid metal
installation according
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.)
Granted
Application number
EP01993387A
Other languages
German (de)
French (fr)
Other versions
EP1339891B1 (en
Inventor
Didier Dauchelle
Hugues Baudin
Patrice Lucas
Laurent Gacher
Yves Prigent
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ArcelorMittal France SA
Original Assignee
Sollac SA
Lorraine de Laminage Continu SA SOLLAC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sollac SA, Lorraine de Laminage Continu SA SOLLAC filed Critical Sollac SA
Publication of EP1339891A1 publication Critical patent/EP1339891A1/en
Application granted granted Critical
Publication of EP1339891B1 publication Critical patent/EP1339891B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0034—Details related to elements immersed in bath
    • C23C2/00342—Moving elements, e.g. pumps or mixers
    • C23C2/00344—Means for moving substrates, e.g. immersed rollers or immersed bearings
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—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
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/50—Controlling or regulating the coating processes
    • C23C2/52—Controlling or regulating the coating processes with means for measuring or sensing
    • C23C2/523—Bath level or amount

Definitions

  • the present invention relates to a method and an installation for hot-dip and continuous coating of a metal strip, in particular a steel strip.
  • steel sheets are used coated with a protective layer, for example against corrosion, and most often coated with a layer of zinc.
  • This type of sheet is used in various industries to produce all kinds of parts and in particular appearance parts.
  • continuous dip coating installations are used in which a steel strip is immersed in a bath of molten metal, for example zinc, which may contain other chemical elements such as l aluminum, iron, and possible additives such as lead, antimony, etc.
  • molten metal for example zinc
  • the temperature of the bath depends on the nature of the metal and in the case of zinc the temperature of the bath is l 'around 460 ° C.
  • this steel strip Before the steel strip passes through the molten metal bath, this steel strip first circulates in an annealing furnace under a reducing atmosphere in order to recrystallize it after the significant work hardening associated with the operation. cold rolling, and to prepare its surface chemical state in order to favor the chemical reactions necessary for the actual quenching operation.
  • the steel strip is brought to around 650 to 900JC depending on the grade for the time necessary for recrystallization and surface preparation. It is then cooled to a temperature close to that of the molten metal bath using exchangers.
  • the steel strip After passing through the annealing furnace, the steel strip passes through a sheath also called "bell descent" or "horn” under a protective atmosphere with respect to steel and is immersed in the bath of molten metal.
  • the lower part of the sheath is immersed in the metal bath to determine, with the surface of said bath and inside this sheath, a liquid seal which is crossed by the steel strip during its scrolling in said sheath.
  • the steel strip is deflected by a roller immersed in the metal bath and it emerges from this metal bath, then passes through wringing means serving to regulate the thickness of the coating of liquid metal on this steel strip .
  • the surface of the liquid seal inside the sheath is generally covered with zinc oxide, resulting from the reaction between the atmosphere inside this sheath and the zinc of the liquid seal and solid mattes from the dissolution reaction of the steel strip.
  • These mattes or other particles in supersaturation in the zinc bath, have a density lower than that of liquid zinc and rise to the surface of the bath and in particular to the surface of the liquid seal.
  • the movement of the steel strip through the surface of the liquid seal causes entrainment of the stagnant particles.
  • These particles entrained by the movement of the liquid seal linked to the speed of the steel strip are not discharged into the volume of the bath and emerge in the zone of extraction of the strip, creating appearance defects.
  • the coated steel strip has appearance defects which are amplified, or even revealed during the zinc wringing operation.
  • the intruded particles are retained by the pneumatic wringing jets before being ejected or disintegrated, thus creating streaks in under thickness in the liquid zinc with a length of a few millimeters - very few centimeters.
  • a first solution to avoid these drawbacks is to clean the surface of the liquid seal by pumping zinc oxides and mattes from the bath.
  • a second solution consists in reducing the surface of the liquid seal at the point of passage of the steel strip by placing a sheet or ceramic plate at the level of this liquid seal to keep part of the particles away from the strip. on the surface and obtain a self-cleaning of the liquid seal by this strip.
  • This arrangement does not make it possible to remove all the particles present on the surface of the liquid seal and self-cleaning is all the more important as the surface of the liquid seal is reduced, which is incompatible with the conditions industrial operating.
  • Another solution is to add a frame to the surface of the liquid seal in the sheath and surrounding the steel strip.
  • This arrangement does not make it possible to completely eliminate the defects linked to the entrainment of zinc oxides and mattes by the running of the steel strip.
  • a solution is also known which aims to obtain cleanliness of the liquid seal by renewing the bath of liquid metal.
  • the renewal is carried out by introducing liquid zinc pumped into the bath in the vicinity of the immersion zone of the steel strip.
  • the piping ensuring the renewal of the liquid zinc can cause scratches on the steel strip before its immersion and it is itself a source of defects by accumulation of condensed zinc vapors above the liquid joint.
  • a process is also known which is based on the renewal of zinc at the level of the liquid seal and in which this renewal is carried out using a stainless steel box surrounding the steel strip and opening onto the surface of the liquid seal.
  • a pump sucks the particles entrained by the spillage thus created and discharges them into the volume of the bath.
  • This process also requires a very high pumping rate to maintain a permanent spill effect insofar as the box surrounding the strip in the volume of the bath above the bottom roller cannot be hermetically sealed.
  • the object of the invention is to propose a method and an installation for continuous galvanizing of a metal strip which makes it possible to avoid the abovementioned drawbacks and to achieve the very low density of the defects satisfying the requirements of customers desiring surfaces without appearance defects.
  • the subject of the invention is therefore a process for the continuous dipping of a metal strip in a tank containing a bath of liquid metal, a process in which the metal strip is continuously scrolled, in a protective atmosphere whose lower part is immersed in the liquid metal bath to determine with the surface of said bath and inside this sheath, a liquid seal, the metal strip is deflected on a deflector roller placed in the bath of metal and the coated metal strip is wrung out at the outlet from the metal bath, characterized in that a natural flow of the liquid metal is produced from the surface of the liquid seal in two discharge compartments formed in said sheath and each comprising a wall internal extending the sheath at its lower part and at least opposite each side of the strip, the upper edge of each compartment being
  • the subject of the invention is a continuous hot dip coating installation of a metal strip, of the type comprising:
  • each compartment has a lower part flared towards the bottom of the tank and an upper part parallel to the metal strip
  • the means for maintaining the level of liquid metal in the compartments are formed by a pump connected on the suction side to each of said compartments by a connection conduit and provided on the discharge side with an evacuation conduit in the volume of the metal bath liquid collected,
  • the installation comprises means for displaying the level of liquid metal in each compartment, the means for displaying are formed by a reservoir disposed outside the sheath and connected to the base of each compartment by a connecting pipe,
  • the sheath is extended, at its lower part and facing each lateral edge of the metal strip, by an internal wall directed towards the surface of the liquid seal, the upper edge of which is positioned below said surface and forming a compartment liquid metal spill.
  • FIG. 1 is a schematic elevation view of a continuous tempering coating installation, in accordance with the invention
  • Fig. 2 is a sectional view of the sheath along line 2-2 of FIG. 1
  • FIG. 3 is a schematic elevation view of a first embodiment of the upper edge of the discharge compartments of the installation according to the invention
  • FIG. 4 is a schematic elevation view of a second embodiment of the upper edge of the discharge compartments of the installation according to the invention.
  • FIG. 5 is a schematic view in cross section of a variant of the sheath of the installation according to the invention.
  • the description will be made for a continuous galvanizing installation of a metal strip.
  • the invention applies to any continuous soaking process in which surface pollution appears and for which a clean liquid seal must be kept.
  • the steel strip 1 passes through an annealing furnace, not shown, under a reducing atmosphere with a view to recrystallizing it after the significant work hardening associated with cold rolling, and to prepare its surface chemical state in order to favor the chemical reactions necessary for the galvanizing operation.
  • the steel strip is brought to a temperature of, for example, between 650 and 900 ° C.
  • the steel strip 1 passes through a galvanizing installation shown in FIG. 1 and designated by the general reference 10.
  • This installation 10 comprises a tank 11 containing a bath 12 of liquid zinc which contains chemical elements such as aluminum, iron and possible addition elements such as lead, antimony, in particular.
  • the temperature of this liquid zinc bath is of the order of 460 ° C.
  • the steel strip 1 On leaving the annealing furnace, the steel strip 1 is cooled to a temperature close to that of the bath of liquid zinc using exchangers and is then immersed in the bath 12 of liquid zinc. During this immersion, an Fe-Zn-AI intermetallic alloy is formed on the surface of the steel strip 1, making it possible to bond between the steel strip and the zinc remaining after spinning.
  • the galvanizing installation 10 comprises a sheath 13 inside which the steel strip 1 runs under a protective atmosphere with respect to the steel.
  • This sheath 13 also called “bell descent” or “horn” has, in the embodiment shown in the figures, a rectangular cross section.
  • the lower part 13a of the sheath 13 is immersed in the zinc bath 12 so as to determine with the surface of said bath 1 and inside this sheath 13, a liquid seal 14.
  • the steel strip 1 is deflected by a roller 15 commonly called a bottom roller and placed in the zinc bath 12.
  • a roller 15 commonly called a bottom roller and placed in the zinc bath 12.
  • the coated steel strip 1 passes through wringing means 16 which are for example constituted by nozzles 16a for air projection and which are directed towards each face of the steel strip 1 to regulate the thickness of the coating of liquid zinc.
  • the lower part 13a of the sheath 13 is extended, on the opposite side of the face of the strip 1 situated on the side of the deflecting roller 15, by an internal wall 20 directed towards the surface of the liquid seal 14 and which cleaning with said lower part 13a of the sheath 13, a first compartment 25 for pouring the liquid zinc.
  • the upper edge 21 of the internal wall 20 is positioned below the surface of the liquid seal 14 to produce a natural flow of liquid zinc from this surface of said seal 14 to this compartment 25.
  • the lower part 13a of the sheath 13 located opposite the face of the strip 1 placed opposite the deflector roller 15, is extended by. an internal wall 26 directed towards the surface of the liquid seal 14 and mena- giant with said lower part 13a a second compartment 29 for pouring liquid zinc.
  • the upper edge 27 of the internal wall 26 is positioned below the surface of the liquid seal 14 and the compartment 29 is provided with means for maintaining the level of liquid zinc in said compartment at a level below the surface of the liquid seal 14 to produce a natural flow of liquid zinc from this surface of said liquid seal 14 to this compartment 29.
  • the height of fall of the liquid metal in the compartments 25 and 29 is determined to prevent the rise of the particles of metal oxide and of intermetallic compounds against the flow of the flow of the liquid metal and this height is greater than 50 mm and preferably 100mm.
  • the internal walls 20 and 26 have a lower part flared towards the bottom of the tank 11.
  • the internal walls 20 and 26 of the compartments 25 and 29 are made of stainless steel and have a thickness of between 10 and 20 mm.
  • the upper edges 21 and 27 of the internal walls 20 and 26 are rectilinear and preferably tapered.
  • the upper edges 21 and 27 of the internal walls 20 and 26 comprise, in the longitudinal direction, a succession of recesses 22 and projections 23.
  • the recesses 22 and the projections 23 have the shape of arcs of a circle and the amplitude "a" between said recesses and said projections is preferably between 5 and 10 mm.
  • the distance "d" between the recesses 22 and the projections 23 is for example of the order of 150mm.
  • the upper edges 21 and 27 of the internal walls 20 and 26 are preferably tapered. According to another embodiment, one of the upper edges
  • compartments 25 or 29 may be rectilinear and the other may comprise a succession of hollows and projections.
  • the means for maintaining the level of liquid zinc in the discharge compartments 25 and 29 are formed by a pump 30 connected on the suction side to said compartment 25 and 29 by a connecting duct, respectively 31 and 33.
  • the pump 30 is provided on the side of the discharge of an evacuation conduit 32 in the volume of the bath 12 of the zinc withdrawn.
  • the installation includes means for viewing the level of liquid zinc in the discharge compartments 25 and 29 or any other means making it possible to view the level of liquid zinc.
  • these display means are formed by a reservoir 35 arranged outside the sheath 13 and connected to the base of each of the compartments 25 and 29 by a connecting pipe, respectively 36 and 37.
  • connection point of the pump 30 on the discharge compartments 25 and 29 is situated above the connection point of the reservoir 35 on said compartments 25 and 29.
  • the external reservoir 35 makes it possible to transfer the level of the discharge compartments 25 and 29 outside the lower part 13a of the sheath 13 in a suitable environment so as to easily detect this level.
  • the reservoir 35 can be equipped with a liquid zinc level detector, such as for example a contactor supplying an indicator, a radar or a laser beam.
  • the sheath 13 is extended to the lower part and facing each lateral edge of the steel strip 1, by an internal wall 49 directed towards the surface of the liquid seal 14 and the upper edge 41 of which is positioned above below said surface of the liquid seal 14.
  • Each internal wall 41 provides with the lower part of the sheath 13 a pouring compartment 42 for the liquid zinc.
  • the steel strip 1 enters the zinc bath 12 via the sheath 13 and the liquid seal 14 and this strip entrains zinc oxides and mattes from the bath, thereby creating appearance defects in the coating.
  • the surface of the liquid seal 14 is reduced thanks to the internal walls 20 and 26 and the surface of the liquid seal 14 insulated between said walls 20 and 26 flows into the discharge compartments 25 and 29 passing over it. upper edges 21 and 27 of the internal walls 20 and 26 of said compartments 25 and 29. '
  • the oxide particles and the mattes or other particles which float on the surface of the liquid seal 14 and which are the cause of the appearance defects, are entrained in the discharge compartments 25 and 29 and the liquid zinc contained in these compartments 25 and 29 are pumped in order to maintain a sufficient level below to allow the natural flow of zinc from the surface of the liquid seal to these compartments 25 and 29.
  • the steel strip 1 at immersion scrolls through the surface of the liquid seal 14 continuously cleaned and leaves the zinc bath 12 with a minimum of defects.
  • the external reservoir 35 makes it possible to detect the level of liquid zinc in the discharge compartments 25 and 29 and to adjust this level so as to keep it below the bath 12 by acting for example on the introduction of zinc ingots into the tank 11.
  • the installation comprises, in addition to the discharge compartments 25 and 29, two lateral discharge compartments 42, the efficiency of the installation is significantly increased.
  • the density of defects on the surfaces coated with the steel strip is considerably reduced and the quality of appearance thus obtained from this coating meets the criteria demanded by customers wishing parts. whose surfaces have no appearance defects.
  • the invention applies to any metallic coating by dipping.

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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)
  • Coating Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Abstract

The invention concerns a method for continuous dip coating of a metal strip (1) in a tank (11) containing a liquid metal bath (12), method which consists in: continuously unwinding the metal strip (1) in a sheath (13) whereof the lower part (13a) is immersed in the liquid metal bath (12) to constitute with the surface of said liquid metal a liquid pressure seal (14); producing a natural flow of the liquid metal from the surface of the liquid pressure seal (14) into two overflow compartments (25, 29) arranged in said sheath (13) and comprising each an inner wall extending the sheath (13) at its lower part and maintaining the level of the metal liquid in said compartments at a level below the surface of the liquid seal (14). The invention also concerns an installation for implementing the method.

Description

Procédé et installation de revêtement au trempé à chaud et en continu d'une bande métallique. Process and installation of continuous hot dip coating of a metal strip.
La présente invention concerne un procédé et une installation de revêtement au trempé à chaud et en continu d'une bande métallique, notamment d'une bande d'acier.The present invention relates to a method and an installation for hot-dip and continuous coating of a metal strip, in particular a steel strip.
Dans de nombreuses applications industrielles, on utilise des tôles d'acier revêtues d'une couche de protection par exemple contre la corrosion et le plus souvent revêtue d'une couche de zinc.In many industrial applications, steel sheets are used coated with a protective layer, for example against corrosion, and most often coated with a layer of zinc.
Ce typé de tôles est utilisé dans diverses industries pour réaliser toute sorte de pièces et en particulier des pièces d'aspect.This type of sheet is used in various industries to produce all kinds of parts and in particular appearance parts.
Pour obtenir ce genre de tôles, on utilise des installations de re- vêtement au trempé en continu dans lesquelles une bande d'acier est immergée dans un bain de métal fondu par exemple en zinc, qui peut contenir d'autres éléments chimiques tels que l'aluminium, le fer, et d'éventuels éléments d'addition comme par exemple le plomb, l'antimoine, etc.. La température du bain dépend de la nature du métal et dans le cas du zinc la température du bain est de l'ordre de 460°C.To obtain this type of sheet, continuous dip coating installations are used in which a steel strip is immersed in a bath of molten metal, for example zinc, which may contain other chemical elements such as l aluminum, iron, and possible additives such as lead, antimony, etc. The temperature of the bath depends on the nature of the metal and in the case of zinc the temperature of the bath is l 'around 460 ° C.
Dans le cas particulier de la galvanisation à chaud, lors du défilement de la bande d'acier dans le bain de zinc fondu, il se forme à la surface de ladite bande un alliage Intermétallique Fe-Zn-AI d'une épaisseur de quelques dizaine de nanomètres. La résistance à la corrosion des pièces ainsi revêtues est assurée par le zinc donc l'épaisseur est réalisée le plus souvent par essorage pneumatique. L'adhérence du zinc sur la bande d'acier est assurée par la couche d'alliage intermétallique mentionné précédemment.In the particular case of hot-dip galvanizing, during the running of the steel strip in the bath of molten zinc, an Fe-Zn-AI intermetallic alloy with a thickness of a few tens is formed on the surface of said strip. of nanometers. The corrosion resistance of the parts thus coated is ensured by zinc, therefore the thickness is most often produced by pneumatic spinning. The adhesion of zinc to the steel strip is ensured by the layer of intermetallic alloy mentioned above.
Avant le passage de la bande d'acier dans le bain de métal fon- du, cette bande d'acier circule d'abord dans un four de recuit sous atmosphère réductrice en vue de la recristalliser après l'écrouissage important lié à l'opération de laminage à froid, et de préparer son état chimique de surface afin de favoriser les réactions chimiques nécessaires à l'opération de trempé proprement dite. La bande d'acier est portée aux environs de 650 à 900JC selon la nuance pendant le temps nécessaire à la recristallisation et à la préparation de surface. Elle est ensuite refroidie à une température voisine de celle du bain de métal fondu à l'aide d'échangeurs. Après son passage dans le four de recuit, la bande d'acier défile dans une gaine appelée aussi "descente de cloche" ou "trompe" sous atmosphère protectrice vis à vis de l'acier et est immergée dans le bain de métal fondu.Before the steel strip passes through the molten metal bath, this steel strip first circulates in an annealing furnace under a reducing atmosphere in order to recrystallize it after the significant work hardening associated with the operation. cold rolling, and to prepare its surface chemical state in order to favor the chemical reactions necessary for the actual quenching operation. The steel strip is brought to around 650 to 900JC depending on the grade for the time necessary for recrystallization and surface preparation. It is then cooled to a temperature close to that of the molten metal bath using exchangers. After passing through the annealing furnace, the steel strip passes through a sheath also called "bell descent" or "horn" under a protective atmosphere with respect to steel and is immersed in the bath of molten metal.
La partie inférieure de la gaine est immergée dans le bain de mé- tal pour déterminer, avec la surface dudit bain et à l'intérieur de cette gaine, un joint d'étanchéité liquide qui est traversé par la bande d'acier lors de son défilement dans ladite gaine.The lower part of the sheath is immersed in the metal bath to determine, with the surface of said bath and inside this sheath, a liquid seal which is crossed by the steel strip during its scrolling in said sheath.
La bande d'acier est défléchie par un rouleau immergé dans le bain de métal et elle ressort de ce bain métal, puis traverse des moyens d'esso- rage servant à réguler l'épaisseur du revêtement de métal liquide sur cette bande d'acier.The steel strip is deflected by a roller immersed in the metal bath and it emerges from this metal bath, then passes through wringing means serving to regulate the thickness of the coating of liquid metal on this steel strip .
Dans le cas particulier de la galvanisation à chaud, la surface du joint liquide à l'intérieur de la gaine est généralement recouverte d'oxyde de zinc, provenant de la réaction entre l'atmosphère à l'intérieur de cette gaine et le zinc du joint liquide et de mattes solides provenant de la réaction de dissolution de la bande d'acier.In the particular case of hot-dip galvanizing, the surface of the liquid seal inside the sheath is generally covered with zinc oxide, resulting from the reaction between the atmosphere inside this sheath and the zinc of the liquid seal and solid mattes from the dissolution reaction of the steel strip.
Ces mattes ou autres particules, en sursaturation dans le bain de zinc ont une masse volumique inférieure à celle du zinc liquide et remontent à la surface du bain et notamment à la surface du joint liquide. Le défilement de la bande d'acier à travers la surface du joint liquide provoque l'entraînement des particules stagnantes. Ces particules entraînées par le mouvement du joint liquide lié à la vitesse de la bande d'acier ne sont pas évacuées dans le volume du bain et ressortent dans la zone d'extraction de la bande en créant des défauts d'aspect. De ce fait, la bande d'acier revêtue présente des défauts d'aspect qui sont amplifiés, voire révélés lors de l'opération d'essorage du zinc.These mattes or other particles, in supersaturation in the zinc bath, have a density lower than that of liquid zinc and rise to the surface of the bath and in particular to the surface of the liquid seal. The movement of the steel strip through the surface of the liquid seal causes entrainment of the stagnant particles. These particles entrained by the movement of the liquid seal linked to the speed of the steel strip are not discharged into the volume of the bath and emerge in the zone of extraction of the strip, creating appearance defects. As a result, the coated steel strip has appearance defects which are amplified, or even revealed during the zinc wringing operation.
En effet, les particules intruses sont retenues par les jets d'essorage pneumatique avant d'être éjectées ou désagrégées, créant ainsi des traînées en sous épaisseur dans le zinc liquide d'une longueur de quelques millimè- très à quelques centimètres.In fact, the intruded particles are retained by the pneumatic wringing jets before being ejected or disintegrated, thus creating streaks in under thickness in the liquid zinc with a length of a few millimeters - very few centimeters.
Pour tenter d'éliminer les particules de zinc et les mattes à la surface du joint liquide, différentes solutions ont été proposées. - Une première solution pour éviter ces inconvénients consiste à nettoyer la surface du joint liquide par pompage des oxydes de zinc et des mattes en provenance du bain.In an attempt to remove zinc particles and mattes from the surface of the liquid seal, various solutions have been proposed. - A first solution to avoid these drawbacks is to clean the surface of the liquid seal by pumping zinc oxides and mattes from the bath.
Ces opérations de pompage permettent de nettoyer la surface du joint liquide que de manière très locale au point de pompage et ont une efficacité et un rayon d'action très faibles ce qui ne garantit pas un nettoyage complet du joint liquide traversé par la bande d'acier.These pumping operations make it possible to clean the surface of the liquid seal only very locally at the pumping point and have a very low efficiency and radius of action which does not guarantee complete cleaning of the liquid seal traversed by the strip of steel.
Une deuxième solution consiste à réduire la surface du joint liquide au point de passage de la bande d 'acier en disposant une plaque de tôle ou de céramique au niveau de ce joint liquide pour maintenir à l'écart de la bande une partie des particules présente à la surface et obtenir un auto-nettoyage du joint liquide par cette bande.A second solution consists in reducing the surface of the liquid seal at the point of passage of the steel strip by placing a sheet or ceramic plate at the level of this liquid seal to keep part of the particles away from the strip. on the surface and obtain a self-cleaning of the liquid seal by this strip.
Cette disposition ne permet pas d'écarter la totalité des- particules présentes à la surface du joint liquide et l'auto-nettoyage est d'autant plus impor- tant que la surface du joint liquide est réduite, ce qui est incompatible avec les conditions industrielles d'exploitation.This arrangement does not make it possible to remove all the particles present on the surface of the liquid seal and self-cleaning is all the more important as the surface of the liquid seal is reduced, which is incompatible with the conditions industrial operating.
De plus, au bout d'un temps de fonctionnement donné, le stockage des particules à l'extérieur de la plaque croît de plus en plus et des amas de particules finissent par se détacher et revenir sur la bande d'acier. L'ajout d'une plaque débouchant à la surface du joint liquide forme également un lieu privilégié pour piéger les poussières de zinc.In addition, after a given operating time, the storage of particles outside the plate increases more and more and clusters of particles eventually detach and return to the steel strip. The addition of a plate opening to the surface of the liquid seal also forms a privileged place to trap zinc dust.
Une autre solution consiste à ajouter un cadre à la surface du joint liquide dans la gaine et entourant la bande d'acier.Another solution is to add a frame to the surface of the liquid seal in the sheath and surrounding the steel strip.
Cette disposition ne permet pas d'éliminer en totalité les défauts liés à l'entraînement des oxydes de zinc et des mattes par le défilement de la bande d'acier.This arrangement does not make it possible to completely eliminate the defects linked to the entrainment of zinc oxides and mattes by the running of the steel strip.
En effet, les vapeurs de zinc au niveau du joint liquide vont se condenser sur les parois du cadre et au moindre remous occasionné par les vibrations ou les plis thermiques de la bande à l'immersion, les parois du cadre vont s'encrasser et ainsi devenir des zones de stockage de corps étrangers. Cette solution ne peut donc fonctionner que quelques heures, voire quelques jour avant de devenir elle-même une source supplémentaire de défauts.In fact, the zinc vapors at the level of the liquid seal will condense on the walls of the frame and at the slightest swirl caused by vibrations or thermal folds of the strip upon immersion, the walls of the frame will become dirty and thus become storage areas for foreign bodies. This solution can therefore only work for a few hours or even a few days before becoming itself an additional source of faults.
Ainsi, cette solution ne traite que partiellement le joint liquide et ne permet pas d'atteindre une densité très" faible de défauts satisfaisant les exigences des clients désirant des surfaces sans défauts d'aspect.Thus, this solution only partially treats the liquid seal and does not make it possible to achieve a very " low density of defects satisfying the requirements of customers desiring surfaces without appearance defects.
On connaît également une solution qui vise à l'obtention de la propreté du joint liquide par renouvellement du bain de métal liquide.A solution is also known which aims to obtain cleanliness of the liquid seal by renewing the bath of liquid metal.
Le renouvellement est réalisé par introduction de zinc liquide pompé dans le bain au voisinage de la zone d'immersion de la bande d'acier.The renewal is carried out by introducing liquid zinc pumped into the bath in the vicinity of the immersion zone of the steel strip.
Cette solution présente de grosses difficultés de mise en œuvre.This solution presents major implementation difficulties.
En effet, elle nécessite un énorme débit de pompage pour assurer un effet de déversement et le zinc pompé et injecté au niveau du int liquide contient les mattes générées dans le bain de zinc. Par ailleurs, la tuyauterie assurant le renouvellement du zinc liquide peut provoquer des rayures sur la bande d'acier avant son immersion et elle est elle-même source de défauts par accumulation de vapeurs de zinc condensées au-dessus du joint liquide.Indeed, it requires a huge pumping rate to ensure a spill effect and the zinc pumped and injected at the level of the liquid int contains the mattes generated in the zinc bath. In addition, the piping ensuring the renewal of the liquid zinc can cause scratches on the steel strip before its immersion and it is itself a source of defects by accumulation of condensed zinc vapors above the liquid joint.
On connaît également un procédé qui est basé sur le renouvel- lement du zinc au niveau du joint liquide et dans lequel ce renouvellement est effectué à l'aide d'une boîte en acier inoxydable entourant la bande d'acier et débouchant à la surface du joint liquide. Une pompe aspire les particules entraînées par le déversement ainsi créé et les refoule dans le volume du bain.A process is also known which is based on the renewal of zinc at the level of the liquid seal and in which this renewal is carried out using a stainless steel box surrounding the steel strip and opening onto the surface of the liquid seal. A pump sucks the particles entrained by the spillage thus created and discharges them into the volume of the bath.
Ce procédé nécessite aussi un débit de pompage très important pour maintenir un effet de déversement permanent dans la mesure où la boîte entourant la bande dans le volume du bain au-dessus du rouleau de fond ne peut être hermétiquement étanche.This process also requires a very high pumping rate to maintain a permanent spill effect insofar as the box surrounding the strip in the volume of the bath above the bottom roller cannot be hermetically sealed.
L'invention a pour but de proposer un procédé et une installation de galvanisation en continu d'une bande métallique qui permettant d'éviter les inconvénients précédemment mentionnés et d'atteindre la densité très faible des défauts satisfaisant aux exigences des clients désirant des surfaces sans défauts d'aspect. L'invention a donc, pour objet un procédé de revêtement au trempé en continu d'une bande métallique dans une cuve contenant un bain de métal liquide, procédé dans lequel on fait défiler en continu, sous atmosphère protectrice, la bande métallique dans une gaine dont la partie inférieure est im- mergée dans le bain de métal liquide pour déterminer avec la surface dudit bain et à l'intérieur de cette gaine, un joint d'étanchéité liquide, on dévie la bande métallique sur un rouleau déflecteur disposé dans le bain de métal et on essore la bande métallique revêtue à la sortie du bain de métal, caractérisé en ce que on réalise un écoulement naturel du métal liquide, de la surface du joint liquide dans deux compartiments de déversement ménagés dans ladite gaine et comportant chacun une paroi interne prolongeant la gaine à sa partie inférieure et au moins en regard de chaque face de la bande, l'arête supérieure de chaque compartiment étant positionnée au-dessous de ladite surface et la hauteur de chute du métal liquide dans les compartiments étant déterminée pour empêcher la remon- tée des particules d'oxyde de métal et de composés intermétallique à contre- courant de l'écoulement du métal liquide et on maintient le niveau de métal liquide dans lesdits compartiments à un niveau au-dessous de la surface du joint liquide.The object of the invention is to propose a method and an installation for continuous galvanizing of a metal strip which makes it possible to avoid the abovementioned drawbacks and to achieve the very low density of the defects satisfying the requirements of customers desiring surfaces without appearance defects. The subject of the invention is therefore a process for the continuous dipping of a metal strip in a tank containing a bath of liquid metal, a process in which the metal strip is continuously scrolled, in a protective atmosphere whose lower part is immersed in the liquid metal bath to determine with the surface of said bath and inside this sheath, a liquid seal, the metal strip is deflected on a deflector roller placed in the bath of metal and the coated metal strip is wrung out at the outlet from the metal bath, characterized in that a natural flow of the liquid metal is produced from the surface of the liquid seal in two discharge compartments formed in said sheath and each comprising a wall internal extending the sheath at its lower part and at least opposite each side of the strip, the upper edge of each compartment being positioned below said surface and the height of fall of the liquid metal in the compartments being determined to prevent the rise of the particles of metal oxide and of intermetallic compounds against the flow of the flow of the liquid metal and the the level of liquid metal in said compartments at a level below the surface of the liquid seal.
L'invention a pour objet une installation de revêtement au trempé à chaud et en continu d'une bande métallique, du type comprenant :The subject of the invention is a continuous hot dip coating installation of a metal strip, of the type comprising:
- une cuve contenant un bain de métal liquide,- a tank containing a bath of liquid metal,
- une gaine de défilement de la bande métallique sous atmosphère protectrice et dont la partie inférieure est immergée dans, le bain de métal liquide pour déterminer avec la surface dudit bain et à l'intérieur de cette gaine, un joint d'étanchéité liquide,a sheath for passing the metal strip under a protective atmosphere and the lower part of which is immersed in the liquid metal bath to determine with the surface of said bath and inside this sheath a liquid seal,
- un rouleau déflecteur de la bande métallique disposé dans le bain de métal, et- a deflector roll of the metal strip placed in the metal bath, and
- des moyens d'essorage de la bande métallique revêtue à la sortie du bain de métal, caractérisée en ce que la gaine est prolongée, à sa partie inférieure et en regard de chaque face de la bande, par une paroi interne dirigée vers la surface du joint liquide et dont l'arête supérieure est positionnée au-dessous de ladite surface, lesdites parois formant deux compartiments de déversement du métal liquide munis de moyens de maintien du niveau de métal liquide dans lesdits compartiments à un niveau au-dessous de la surface du joint liquide pour réaliser un écoulement naturel du métal liquide de cette surface vers ces compartiments, la hauteur de chute du métal liquide dans lesdits compartiments étant supérieure à 50mm pour empêcher la remontée des particules d'oxyde de métal et de composés intermétalliques à contre-courant de l'écoulement du métal liquide. Selon d'autres caractéristiques de l'invention :- means for wringing out the coated metal strip at the outlet from the metal bath, characterized in that the sheath is extended, at its lower part and facing each face of the strip, by an internal wall directed towards the surface of the liquid seal and the upper edge of which is positioned below said surface, said walls forming two liquid metal discharge compartments provided with means for maintaining the level of liquid metal in said compartments at a level below the surface of the liquid seal to produce a natural flow of liquid metal from this surface to these compartments, the height of fall of the liquid metal in said compartments being greater than 50 mm to prevent the rise of particles of metal oxide and of intermetallic compounds against the flow of the flow of liquid metal. According to other characteristics of the invention:
- la paroi interne de chaque compartiment présente une partie inférieure évasée vers le fond de la cuve et une partie supérieure parallèle à la bande métallique,the internal wall of each compartment has a lower part flared towards the bottom of the tank and an upper part parallel to the metal strip,
- la hauteur de chute du métal liquide dans chaque compartiment est supérieure à 100mm,- the drop height of the liquid metal in each compartment is more than 100mm,
- les moyens de maintien du niveau de métal liquide dans les compartiments sont formés par une pompe raccordée du côté aspiration à chacun desdits compartiments par un conduit de liaison et munie du côté refoulement d'un conduit d'évacuation dans le volume du bain du métal liquide prélevé,- The means for maintaining the level of liquid metal in the compartments are formed by a pump connected on the suction side to each of said compartments by a connection conduit and provided on the discharge side with an evacuation conduit in the volume of the metal bath liquid collected,
- l'installation comporte des moyens de visualisation du niveau de métal liquide dans chaque compartiment, - les moyens de visualisation sont formés par un réservoir disposé à l'extérieur de la gaine et relié à la base de chaque compartiment par une tuyauterie de raccordement,the installation comprises means for displaying the level of liquid metal in each compartment, the means for displaying are formed by a reservoir disposed outside the sheath and connected to the base of each compartment by a connecting pipe,
- la gaine est prolongée, à sa partie inférieure et en regard de chaque bord latéral de la bande métallique, par une paroi interne dirigée vers la surface du joint liquide dont l'arête supérieure est positionnée au-dessous de ladite surface et formant un compartiment de déversement du métal liquide.the sheath is extended, at its lower part and facing each lateral edge of the metal strip, by an internal wall directed towards the surface of the liquid seal, the upper edge of which is positioned below said surface and forming a compartment liquid metal spill.
D'autres caractéristiques et avantages de l'invention apparaîtront au cours de la description qui va suivre, donnée à titre d'exemple, et faite en référence aux dessins annexés, sur lesquels : - la Fig. 1 est une vue schématique en élévation d'une installation de revêtement au trempé en continu, conforme à l'invention, la Fig. 2 est une vue en coupe de la gaine selon la ligne 2-2 de la Fig. 1 ,Other characteristics and advantages of the invention will appear during the description which follows, given by way of example, and made with reference to the accompanying drawings, in which: - FIG. 1 is a schematic elevation view of a continuous tempering coating installation, in accordance with the invention, Fig. 2 is a sectional view of the sheath along line 2-2 of FIG. 1,
- la Fig. 3 est une vue schématique en élévation d'un premier mode de réalisation de l'arête supérieure des compartiments de déversement de l'installation conforme à l'invention,- Fig. 3 is a schematic elevation view of a first embodiment of the upper edge of the discharge compartments of the installation according to the invention,
- la Fig. 4 est une vue schématique en élévation d'un second mode de réalisation de l'arête supérieure des compartiments de déversement de l'installation conforme à l'invention,- Fig. 4 is a schematic elevation view of a second embodiment of the upper edge of the discharge compartments of the installation according to the invention,
- la Fig. 5 est une vue schématique en coupe transversale d'une variante de la gaine de l'installation conforme à l'invention.- Fig. 5 is a schematic view in cross section of a variant of the sheath of the installation according to the invention.
Dans ce qui suit, la description sera faite pour une installation de galvanisation en continu d'une bande métallique. Mais l'invention s'applique à tout procédé de trempage en continu dans lequel apparaît une pollution de surface et pour lequel il faut garder un joint liquide propre. Tout d'abord, à la sortie du train de laminage à froid, la bande d'acier 1 passe dans un four de recuit, non représenté, sous atmosphère réductrice en vue de la recristalliser après l'écrouissage important lié au laminage à froid, et de préparer son état chimique de surface afin de favoriser les réactions chimiques nécessaires à l'opération de galvanisation. Dans ce four, la bande d'acier est portée à une température comprise par exemple entre 650 et 900°C.In the following, the description will be made for a continuous galvanizing installation of a metal strip. However, the invention applies to any continuous soaking process in which surface pollution appears and for which a clean liquid seal must be kept. First of all, at the outlet of the cold rolling train, the steel strip 1 passes through an annealing furnace, not shown, under a reducing atmosphere with a view to recrystallizing it after the significant work hardening associated with cold rolling, and to prepare its surface chemical state in order to favor the chemical reactions necessary for the galvanizing operation. In this furnace, the steel strip is brought to a temperature of, for example, between 650 and 900 ° C.
A la sortie du four de recuit, la bande d'acier 1 passe dans une installation de galvanisation représentée à la Fig. 1 et désignée par la référence générale 10. Cette installation 10 comporte une cuve 11 contenant un bain 12 de zinc liquide qui contient des éléments chimiques tels que l'aluminium, le fer et d'éventuels éléments d'addition comme le plomb, l'antimoine, notamment.At the outlet of the annealing furnace, the steel strip 1 passes through a galvanizing installation shown in FIG. 1 and designated by the general reference 10. This installation 10 comprises a tank 11 containing a bath 12 of liquid zinc which contains chemical elements such as aluminum, iron and possible addition elements such as lead, antimony, in particular.
La température de ce bain de zinc liquide est de l'ordre de 460°C. A la sortie du four de recuit, la bande d'acier 1 est refroidie à une température voisine de celle du bain de zinc liquide à l'aide d'échangeurs et est ensuite immergée dans le bain 12 de zinc liquide. Lors de cette immersion, il se forme à la surface de la bande d'acier 1 un alliage intermétallique Fe-Zn-AI permettant d'assurer la liaison entre la bande d'acier et le zinc restant après l'essorage.The temperature of this liquid zinc bath is of the order of 460 ° C. On leaving the annealing furnace, the steel strip 1 is cooled to a temperature close to that of the bath of liquid zinc using exchangers and is then immersed in the bath 12 of liquid zinc. During this immersion, an Fe-Zn-AI intermetallic alloy is formed on the surface of the steel strip 1, making it possible to bond between the steel strip and the zinc remaining after spinning.
Ainsi que représenté à la Fig. 1 , l'installation de galvanisation 10 comporte une gaine 13 à l'intérieur de laquelle défile la bande d'acier 1 sous atmosphère protectrice vis à vis de l'acier.As shown in FIG. 1, the galvanizing installation 10 comprises a sheath 13 inside which the steel strip 1 runs under a protective atmosphere with respect to the steel.
Cette gaine 13 aussi appelée "descente de cloche" ou "trompe" présente, dans l'exemple de réalisation représenté sur les figures, une section transversale rectangulaire. La partie inférieure 13a de la gaine 13 est immergée dans le bain de zinc 12 de façon à déterminer avec la surface dudit bain 1 et à l'intérieur de cette gaine 13, un joint d'étanchéité liquide 14.This sheath 13 also called "bell descent" or "horn" has, in the embodiment shown in the figures, a rectangular cross section. The lower part 13a of the sheath 13 is immersed in the zinc bath 12 so as to determine with the surface of said bath 1 and inside this sheath 13, a liquid seal 14.
Ainsi, la bande d'acier 1 à l'immersion dans le bain de zinc 12 liquide, traverse la surface du joint liquide 14 dans la partie inférieure 13a de la gaine 13.Thus, the steel strip 1 when immersed in the bath of liquid zinc 12 crosses the surface of the liquid seal 14 in the lower part 13a of the sheath 13.
La bande d'acier 1 est défléchie par un rouleau 15 couramment appelé rouleau de fond et disposé dans le bain de zinc 12. A la sortie de ce bain de zinc 12, la bande d'acier 1 revêtue passe dans des moyens d'essorage 16 qui sont par exemple constitués par des buses 16a de projection d'air et qui sont di- rigées vers chaque face de la bande d'acier 1 pour réguler l'épaisseur du revêtement de zinc liquide.The steel strip 1 is deflected by a roller 15 commonly called a bottom roller and placed in the zinc bath 12. At the exit of this zinc bath 12, the coated steel strip 1 passes through wringing means 16 which are for example constituted by nozzles 16a for air projection and which are directed towards each face of the steel strip 1 to regulate the thickness of the coating of liquid zinc.
Ainsi que représenté sur les Figs. 1 et 2, la partie inférieure 13a de la gaine 13 est prolongée, sur le côté en regard de la face de la bande 1 située du côté du rouleau déflecteur 15, par une paroi interne 20 dirigée vers la surface du joint liquide 14 et qui ménage avec ladite partie inférieure 13a de la gaine 13, un premier compartiment 25 de déversement du zinc liquide.As shown in Figs. 1 and 2, the lower part 13a of the sheath 13 is extended, on the opposite side of the face of the strip 1 situated on the side of the deflecting roller 15, by an internal wall 20 directed towards the surface of the liquid seal 14 and which cleaning with said lower part 13a of the sheath 13, a first compartment 25 for pouring the liquid zinc.
L'arête supérieure 21 de la paroi interne 20 est positionnée au- dessous de la surface du joint liquide 14 pour réaliser un écoulement naturel de zinc liquide de cette surface dudit joint 14 vers ce compartiment 25. De même, la partie inférieure 13a de la gaine 13 située en regard de la face de la bande 1 placée à l'opposé du rouleau déflecteur 15, est prolongée par. une paroi interne 26 dirigée vers la surface du joint liquide 14 et mena- géant avec ladite partie inférieure 13a un second compartiment 29 de déversement du zinc liquide.The upper edge 21 of the internal wall 20 is positioned below the surface of the liquid seal 14 to produce a natural flow of liquid zinc from this surface of said seal 14 to this compartment 25. Similarly, the lower part 13a of the sheath 13 located opposite the face of the strip 1 placed opposite the deflector roller 15, is extended by. an internal wall 26 directed towards the surface of the liquid seal 14 and mena- giant with said lower part 13a a second compartment 29 for pouring liquid zinc.
L'arête supérieure 27 de la paroi interne 26 est positionnée au- dessous de la surface du joint liquide 14 et le compartiment 29 est muni de moyens de maintien du niveau de zinc liquide dans ledit compartiment à un niveau au-dessous de la surface du joint liquide 14 pour réaliser un écoulement naturel de zinc liquide de cette surface dudit joint liquide 14 vers ce compartiment 29.The upper edge 27 of the internal wall 26 is positioned below the surface of the liquid seal 14 and the compartment 29 is provided with means for maintaining the level of liquid zinc in said compartment at a level below the surface of the liquid seal 14 to produce a natural flow of liquid zinc from this surface of said liquid seal 14 to this compartment 29.
La hauteur de chute du métal liquide dans les compartiments 25 et 29 est déterminée pour empêcher la remontée des particules d'oxyde de métal et de composés intermétalliques à contre-courant de l'écoulement du métal liquide et cette hauteur est supérieure à 50mm et de préférence à 100mm.The height of fall of the liquid metal in the compartments 25 and 29 is determined to prevent the rise of the particles of metal oxide and of intermetallic compounds against the flow of the flow of the liquid metal and this height is greater than 50 mm and preferably 100mm.
De préférence, les parois internes 20 et 26 présentent une partie inférieure évasée vers le fond de la cuve 11. Les parois internes 20 et 26 des compartiments 25 et 29 sont en acier inoxydable et ont une épaisseur comprise entre 10 et 20mm.Preferably, the internal walls 20 and 26 have a lower part flared towards the bottom of the tank 11. The internal walls 20 and 26 of the compartments 25 and 29 are made of stainless steel and have a thickness of between 10 and 20 mm.
Selon un premier mode de réalisation représenté à la Fig. 3, les arêtes supérieures 21 et 27 des parois internes 20 et 26 sont rectilignes et de préférence effilées. Selon un second mode de réalisation représenté à la Fig. 4, les arêtes supérieures 21 et 27 des parois internes 20 et 26 comportent, dans le sens longitudinal, une succession de creux 22 et de saillies 23.According to a first embodiment shown in FIG. 3, the upper edges 21 and 27 of the internal walls 20 and 26 are rectilinear and preferably tapered. According to a second embodiment shown in FIG. 4, the upper edges 21 and 27 of the internal walls 20 and 26 comprise, in the longitudinal direction, a succession of recesses 22 and projections 23.
Les creux 22 et les saillies 23 ont la forme d'arcs de cercle et l'amplitude "a" entre lesdits creux et lesdites saillies est comprise de préférence entre 5 et 10mm.The recesses 22 and the projections 23 have the shape of arcs of a circle and the amplitude "a" between said recesses and said projections is preferably between 5 and 10 mm.
De plus, la distance "d" entre les creux 22 et les saillies 23 est par exemple de l'ordre de 150mm.In addition, the distance "d" between the recesses 22 and the projections 23 is for example of the order of 150mm.
Dans ce mode de réalisation également, les arêtes supérieures 21 et 27 des parois internes 20 et 26 sont de préférence effilées. Selon un autre mode de réalisation, l'une des arêtes supérieuresIn this embodiment also, the upper edges 21 and 27 of the internal walls 20 and 26 are preferably tapered. According to another embodiment, one of the upper edges
21 ou 27 des compartiments 25 ou 29 peut être rectiligne et l'autre comporter une succession de creux et de saillies. Les moyens de maintien du niveau de zinc liquide dans les compartiments de déversement 25 et 29 sont formés par une pompe 30 raccordée du côté aspiration audit compartiment 25 et 29 par un conduit de liaison, respectivement 31 et 33. La pompe 30 est munie du côté du refoulement d'un conduit d'évacuation 32 dans le volume du bain 12 du zinc prélevé.21 or 27 of compartments 25 or 29 may be rectilinear and the other may comprise a succession of hollows and projections. The means for maintaining the level of liquid zinc in the discharge compartments 25 and 29 are formed by a pump 30 connected on the suction side to said compartment 25 and 29 by a connecting duct, respectively 31 and 33. The pump 30 is provided on the side of the discharge of an evacuation conduit 32 in the volume of the bath 12 of the zinc withdrawn.
Par ailleurs, l'installation comporte des moyens de visualisation du niveau de zinc liquide dans les compartiments de déversement 25 et 29 ou tout autre moyen permettant de visualiser le niveau de zinc liquide. Dans ce mode de réalisation préférentiel, ces moyens de visualisation sont formés par un réservoir 35 disposé à l'extérieur de la gaine 13 et relié à la base de chacun des compartiments 25 et 29 par une tuyauterie de raccordement, respectivement 36 et 37.Furthermore, the installation includes means for viewing the level of liquid zinc in the discharge compartments 25 and 29 or any other means making it possible to view the level of liquid zinc. In this preferred embodiment, these display means are formed by a reservoir 35 arranged outside the sheath 13 and connected to the base of each of the compartments 25 and 29 by a connecting pipe, respectively 36 and 37.
Comme représenté à la Fig. 1 , le point de raccordement de la pompe 30 sur les compartiments de déversement 25 et 29 est situé au-dessus du point de raccordement du réservoir 35 sur lesdits compartiments 25 et 29.As shown in Fig. 1, the connection point of the pump 30 on the discharge compartments 25 and 29 is situated above the connection point of the reservoir 35 on said compartments 25 and 29.
L'ajout du réservoir externe 35 permet de reporter le niveau des compartiments de déversement 25 et 29 à l'extérieur de la partie inférieure 13a de la gaine 13 dans un environnement propice de façon à détecter facilement ce niveau. A cet effet, le réservoir 35 peut être équipé d'un détecteur de niveau de zinc liquide, comme par exemple un contacteur alimentant un voyant, un radar ou un faisceau laser.The addition of the external reservoir 35 makes it possible to transfer the level of the discharge compartments 25 and 29 outside the lower part 13a of the sheath 13 in a suitable environment so as to easily detect this level. To this end, the reservoir 35 can be equipped with a liquid zinc level detector, such as for example a contactor supplying an indicator, a radar or a laser beam.
Selon une variante représentée à la Fig. 5, la gaine 13 est prolongée à se partie inférieure et en regard de chaque bord latéral de la bande d'acier 1 , par une paroi interne 49 dirigée vers la surface du joint liquide 14 et dont l'arête supérieure 41 est positionnée au-dessous de ladite surface du joint liquide 14.According to a variant shown in FIG. 5, the sheath 13 is extended to the lower part and facing each lateral edge of the steel strip 1, by an internal wall 49 directed towards the surface of the liquid seal 14 and the upper edge 41 of which is positioned above below said surface of the liquid seal 14.
Chaque paroi interne 41 ménage avec la partie inférieure de la gaine 13 un compartiment de déversement 42 du zinc liquide. D'une manière générale, la bande d'acier 1 pénètre dans le bain de zinc 12 par l'intermédiaire de la gaine 13 et du joint liquide 14 et cette bande entraîne des oxydes de zinc et les mattes en provenance du bain en créant ainsi des défauts d'aspect dans le revêtement.Each internal wall 41 provides with the lower part of the sheath 13 a pouring compartment 42 for the liquid zinc. In general, the steel strip 1 enters the zinc bath 12 via the sheath 13 and the liquid seal 14 and this strip entrains zinc oxides and mattes from the bath, thereby creating appearance defects in the coating.
Pour éviter cet inconvénient, la surface du joint liquide 14 est réduite grâce aux parois internes 20 et 26 et la surface du joint liquide 14 isolée entre lesdites parois 20 et 26 s'écoule dans les compartiments de déversement 25 et 29 en passant au-dessus des arêtes supérieures 21 et 27 des parois internes 20 et 26 desdits compartiments 25 et 29. ' To avoid this drawback, the surface of the liquid seal 14 is reduced thanks to the internal walls 20 and 26 and the surface of the liquid seal 14 insulated between said walls 20 and 26 flows into the discharge compartments 25 and 29 passing over it. upper edges 21 and 27 of the internal walls 20 and 26 of said compartments 25 and 29. '
Les particules d'oxyde et les mattes ou autres particules qui surnagent à la surface du joint liquide 14 et qui sont à l'origine des défauts d'aspect, sont entraînées dans les compartiments de déversement 25 et 29 et le zinc liquide contenu dans ces compartiments 25 et 29 est pompé afin de maintenir un niveau suffisant en contre-bas pour permettre l'écoulement naturel du zinc de la surface du joint liquide vers ces compartiments 25 et 29.The oxide particles and the mattes or other particles which float on the surface of the liquid seal 14 and which are the cause of the appearance defects, are entrained in the discharge compartments 25 and 29 and the liquid zinc contained in these compartments 25 and 29 are pumped in order to maintain a sufficient level below to allow the natural flow of zinc from the surface of the liquid seal to these compartments 25 and 29.
De cette manière, la surface libre du joint liquide 14 isolée entre les parois 20 et 26 est renouvelée en permanence et le zinc liquide aspiré par la pompe 30 dans ces compartiments 25 et 29 est injecté dans le bain de zinc 12 par le conduit d'évacuation 32.In this way, the free surface of the isolated liquid seal 14 between the walls 20 and 26 is constantly renewed and the liquid zinc drawn up by the pump 30 in these compartments 25 and 29 is injected into the zinc bath 12 through the conduit. evacuation 32.
Par l'effet ainsi créé, la bande d'acier 1 à l'immersion défile à travers la surface du joint liquide 14 nettoyée en permanence et ressort du bain de zinc 12 avec un minimum de défauts.By the effect thus created, the steel strip 1 at immersion scrolls through the surface of the liquid seal 14 continuously cleaned and leaves the zinc bath 12 with a minimum of defects.
Le réservoir externe 35 permet de détecter le niveau de zinc liquide dans les compartiments de déversement 25 et 29 et d'ajuster ce niveau de manière à le maintenir au-dessous du bain 12 en agissant par exemple sur l'introduction de lingots de zinc dans la cuve 11. Dans le cas où l'installation comporte en plus des compartiments de déversement 25 et 29, deux compartiments de déversement latéraux 42, l'efficacité de l'installation est sensiblement augmentée.The external reservoir 35 makes it possible to detect the level of liquid zinc in the discharge compartments 25 and 29 and to adjust this level so as to keep it below the bath 12 by acting for example on the introduction of zinc ingots into the tank 11. In the case where the installation comprises, in addition to the discharge compartments 25 and 29, two lateral discharge compartments 42, the efficiency of the installation is significantly increased.
Grâce à l'installation selon l'invention, la densité de défauts sur les surfaces revêtues de la bande d'acier est considérablement réduite et la qua- lité d'aspect ainsi obtenue de ce revêtement convient aux critères exigés par des clients désirant des pièces dont les surfaces sont sans défauts d'aspect.Thanks to the installation according to the invention, the density of defects on the surfaces coated with the steel strip is considerably reduced and the quality of appearance thus obtained from this coating meets the criteria demanded by customers wishing parts. whose surfaces have no appearance defects.
L'invention s'applique à tout revêtement métallique par trempé. The invention applies to any metallic coating by dipping.

Claims

REVENDICATIONS
1. Procédé de revêtement au trempé en continu d'une bande métallique (1 ) dans une cuve (11 ) contenant un bain de métal (12) liquide, procédé dans lequel on fait défiler en continu, sous atmosphère protectrice, la bande mé- tallique (1 ) dans une gaine (13) dont la partie inférieure (13a) est immergée dans le bain de métal (12) liquide pour déterminer avec la surface dudit bain et à l'intérieur de cette gaine (13), un joint d'étanchéité (14) liquide, on dévie la bande métallique (1 ) sur un rouleau (15) déflecteur disposé dans le bain de métal (12), et on essore la bande métallique (1) revêtue à la sortie du bain de métal (12), carac- térisé en ce que on réalise un écoulement naturel du métal liquide de la surface du joint liquide (14) dans deux compartiments de déversement (25 ; 29) ménagés dans ladite gaine (13) et comportant chacun une paroi interne (20 ; 26) prolongeant la gaine (13) à sa partie inférieure et en regard de chaque face de la bande (1), l'arête supérieure (21 ; 27) de chaque compartiment (25 ; 29) étant position- née au-dessous de ladite surface et la hauteur de chute du métal liquide dans les compartiments (25 ; 29) étant déterminée pour empêcher la remontée des particules d'oxyde de métal et de composés intermétalliques à contre-courant de l'écoulement du métal liquide et on maintient le niveau de métal liquide dans lesdits compartiments (25; 29) à un niveau au-dessous de la surface du joint liquide (14).1. A method of continuously dipping a metallic strip (1) in a tank (11) containing a bath of liquid metal (12), a process in which the metallic strip is continuously scrolled under a protective atmosphere metal (1) in a sheath (13) the lower part (13a) of which is immersed in the bath of liquid metal (12) to determine with the surface of said bath and inside this sheath (13), a joint d liquid tightness (14), the metal strip (1) is deflected on a deflector roller (15) disposed in the metal bath (12), and the coated metal strip (1) is wrung out at the outlet of the metal bath ( 12), characterized in that natural liquid metal flows from the surface of the liquid seal (14) into two discharge compartments (25; 29) formed in said sheath (13) and each having an internal wall ( 20; 26) extending the sheath (13) at its lower part and facing each side of the ba nde (1), the upper edge (21; 27) of each compartment (25; 29) being positioned below said surface and the height of fall of the liquid metal in the compartments (25; 29) being determined to prevent the rise of particles of metal oxide and intermetallic compounds against the current of liquid metal flow and the level of liquid metal in said compartments (25; 29) is maintained at a level below the surface of the liquid seal (14).
2. Installation de revêtement au trempé à chaud et en continu d'une bande métallique (1 ), du type comprenant :2. Installation of continuous hot-dip coating of a metal strip (1), of the type comprising:
- une cuve (11 ) contenant un bain de métal liquide (12),- a tank (11) containing a bath of liquid metal (12),
- une gaine (13) de défilement de la bande métallique (1 ) sous atmosphère protectrice et dont la partie inférieure (13a) est -immergée dans le bain de métal liquide (12) pour déterminer avec la surface dudit bain (12) et à l'intérieur de cette gaine (13), un joint d'étanchéité liquide (14),. - a sheath (13) for passing the metal strip (1) under a protective atmosphere and the lower part (13a) of which is immersed in the bath of liquid metal (12) to determine with the surface of said bath (12) and to inside this sheath (13), a liquid seal (14) ,.
- un rouleau (15) déflecteur de la bande métallique (1) disposé dans le bain de métal (12) et, - des moyens (16) d 'essorage de la bande métallique (1 ) revêtue à la sortie du bain de zinc (12), caractérisée en ce que la gaine (13) est prolongée, à sa partie inférieure (13a) et en regard de chaque face de la bande (1 ), par une paroi interne (20 ; 26) dirigée vers la surface du joint liquide (14) et dont l'arête supérieure (21 ; 27) est positionnée au-dessous de ladite surface, lesdites parois (20 ; 26) formant deux com- partiments de déversement (25 ; 29) du métal liquide, munis de moyens (30) de maintien du niveau de métal liquide dans lesdits compartiments (25 ; 29) à un niveau au-dessous de la surface du joint liquide (14) pour réaliser un écoulement naturel du métal liquide de cette surface vers ces compartiments (25 ; 29), la hauteur de chute du métal liquide dans lesdits compartiments étant supérieure à 50mm pour empêcher la remontée des particules d'oxyde de métal et de composés intermétalliques à contre-courant de l'écoulement du métal liquide.- a roller (15) deflector of the metal strip (1) disposed in the metal bath (12) and, - means (16) for wiping the metal strip (1) coated at the outlet of the zinc bath ( 12) characterized in that the sheath (13) is extended, at its lower part (13a) and facing each face of the strip (1), by an internal wall (20; 26) directed towards the surface of the liquid seal (14 ) and the upper edge (21; 27) of which is positioned below said surface, said walls (20; 26) forming two compartments for pouring (25; 29) of the liquid metal, provided with means (30) maintaining the level of liquid metal in said compartments (25; 29) at a level below the surface of the liquid seal (14) in order to produce a natural flow of liquid metal from this surface to these compartments (25; 29), the height of fall of the liquid metal in said compartments being greater than 50 mm to prevent the rise of particles of metal oxide and of intermetallic compounds against the flow of the flow of liquid metal.
3. Installation selon la revendication 2, caractérisée en ce que la hauteur de chute du métal liquide dans chaque compartiment (25, 29) est supérieure à 100mm. 3. Installation according to claim 2, characterized in that the height of fall of the liquid metal in each compartment (25, 29) is greater than 100mm.
4. Installation selon la revendication 2, caractérisée en ce que la paroi interne (20 ; 26) de chaque compartiment (25 ; 29) présente une partie inférieure évasée vers le fond de la cuve (11) et une partie supérieure parallèle à la bande métallique (1).4. Installation according to claim 2, characterized in that the internal wall (20; 26) of each compartment (25; 29) has a lower part flared towards the bottom of the tank (11) and an upper part parallel to the strip metallic (1).
5. Installation selon la revendication 2 ou 3, caractérisée en ce que l'arête supérieure (21 ; 27) de la paroi interne (20 ; 26) de chaque compartiment (25 ; 29) est rectiligne.5. Installation according to claim 2 or 3, characterized in that the upper edge (21; 27) of the internal wall (20; 26) of each compartment (25; 29) is rectilinear.
6. Installation selon la revendication 2 ou 3, caractérisée en ce que l'arête supérieure (21 ; 27) de la paroi interne (20 ; 26) de chaque compartiment (25. ; 29) comporte, dans le sens longitudinal, une succession de creux (22) - et de saillies (23).6. Installation according to claim 2 or 3, characterized in that the upper edge (21; 27) of the internal wall (20; 26) of each compartment (25.; 29) comprises, in the longitudinal direction, a succession hollows (22) - and projections (23).
7. Installation selon la revendication 6, caractérisée en ce que les creux (22) et les saillies (23) ont la forme d'arcs de cercle.7. Installation according to claim 6, characterized in that the recesses (22) and the projections (23) have the form of arcs of a circle.
8. Installation selon la revendication 6 ou 7, caractérisée en ce que l'amplitude entre les creux (22) et les saillies (23) est comprise entre 5 et 10mm.8. Installation according to claim 6 or 7, characterized in that the amplitude between the recesses (22) and the projections (23) is between 5 and 10mm.
9. Installation selon la revendication 6 ou 7, caractérisée en ce que la distance entre les creux (22) et les saillies (23) est de l'ordre de 150mm. 9. Installation according to claim 6 or 7, characterized in that the distance between the recesses (22) and the projections (23) is of the order of 150mm.
10. Installation selon l'une quelconque des revendications précédentes, caractérisée en ce que l'arête supérieure (21 ; 27) des parois internes (20; 26) de chaque compartiment (25 ; 29) est effilée.10. Installation according to any one of the preceding claims, characterized in that the upper edge (21; 27) of the internal walls (20; 26) of each compartment (25; 29) is tapered.
11. Installation selon l'une quelconque des revendications précé- dentés, caractérisée en ce que la paroi interne (20 ; 26) de chaque compartiment11. Installation according to any one of the preceding claims, characterized in that the internal wall (20; 26) of each compartment
(25 ;29) est en acier inoxydable et à une épaisseur comprise par exemple entre 20 et 10mm.(25; 29) is made of stainless steel and has a thickness of, for example, between 20 and 10 mm.
12. Installation selon la revendication 2, caractérisée en ce que les moyens de maintien du niveau de métal liquide dans les compartiments (25 ; 29) sont formés par une pompe (30) raccordée du côté aspiration à chacun desdits compartiments par un conduit de liaison (31 ; 33) et munie du côté refoulement d'un conduit d'évacuation (32) dans le volume du bain (12) du métal liquide prélevé.12. Installation according to claim 2, characterized in that the means for maintaining the level of liquid metal in the compartments (25; 29) are formed by a pump (30) connected on the suction side to each of said compartments by a connecting duct. (31; 33) and provided on the discharge side with a discharge conduit (32) in the volume of the bath (12) of the liquid metal withdrawn.
13. Installation selon l'une quelconque des revendications précé- dentés, caractérisée en ce qu'elle comporte des moyens (35) de visualisation du niveau de métal liquide dans chaque compartiment (25 ; 29).13. Installation according to any one of the preceding claims, characterized in that it comprises means (35) for viewing the level of liquid metal in each compartment (25; 29).
14. Installation selon la revendication 13, caractérisée en ce que les moyens de visualisation sont formés par un réservoir (35) disposé à l'extérieur de la gaine (13) et relié à la base de chaque compartiment (25 ; 29) par une tuyauterie de raccordement (36 ; 37).14. Installation according to claim 13, characterized in that the display means are formed by a reservoir (35) disposed outside the sheath (13) and connected to the base of each compartment (25; 29) by a connection piping (36; 37).
15. Installation selon les revendications 12 et 14, caractérisée en ce que le point de raccordement de la pompe (30) sur chaque compartiment (25 ; 29) est situé au-dessus du point de raccordement du réservoir (35) dans chaque compartiment (25 ; 29). 15. Installation according to claims 12 and 14, characterized in that the connection point of the pump (30) on each compartment (25; 29) is located above the connection point of the reservoir (35) in each compartment ( 25; 29).
16. Installation selon la revendication 14, caractérisée en ce que le réservoir (35) forme une capacité tampon de métal liquide pour chaque compartiment (25 ; 29).16. Installation according to claim 14, characterized in that the reservoir (35) forms a liquid metal buffer capacity for each compartment (25; 29).
17. Installation selon la revendication 14, caractérisée en ce que le réservoir (35) est équipé d'un détecteur de niveau de métal liquide. 17. Installation according to claim 14, characterized in that the reservoir (35) is equipped with a liquid metal level detector.
18. Installation selon l'une quelconque des revendications précédentes, caractérisée en ce que la gaine (13) est prolongée, à sa partie inférieure (13a) et en regard de chaque bord latéral de la bande métallique (1), par une pa- roi interne (40) dirigée vers la surface du joint de liquide (14) dont l'arête supérieure (41 ) est positionnée au-dessous de ladite surface et formant un compartiment de déversement (42) du métal liquide. 18. Installation according to any one of the preceding claims, characterized in that the sheath (13) is extended, at its lower part (13a) and opposite each lateral edge of the metal strip (1), by a pa- internal king (40) directed towards the surface of the liquid seal (14) whose upper edge (41) is positioned below said surface and forming a pouring compartment (42) of the liquid metal.
EP01993387A 2000-11-10 2001-11-07 Method and installation for hot process and continuous dip coating of a metal strip Expired - Lifetime EP1339891B1 (en)

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FR0014481 2000-11-10
FR0014481A FR2816640B1 (en) 2000-11-10 2000-11-10 HOT AND CONTINUOUS TEMPERATURE COATING INSTALLATION OF A METAL STRIP
PCT/FR2001/003456 WO2002038825A1 (en) 2000-11-10 2001-11-07 Method and installation for hot process and continuous dip coating of a metal strip

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