EP1339891B1 - 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 Download PDF

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Publication number
EP1339891B1
EP1339891B1 EP01993387A EP01993387A EP1339891B1 EP 1339891 B1 EP1339891 B1 EP 1339891B1 EP 01993387 A EP01993387 A EP 01993387A EP 01993387 A EP01993387 A EP 01993387A EP 1339891 B1 EP1339891 B1 EP 1339891B1
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EP
European Patent Office
Prior art keywords
metal
liquid
compartment
liquid metal
bath
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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.)
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EP01993387A
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German (de)
French (fr)
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EP1339891A1 (en
Inventor
Didier Dauchelle
Hugues Baudin
Patrice Lucas
Laurent Gacher
Yves Prigent
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ArcelorMittal France SA
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ArcelorMittal France SA
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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
    • C23C2/34—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 coating and continuous coating of a metal strip, in particular a steel strip.
  • steel sheets coated with a protective layer for example against corrosion and usually coated with a zinc layer are used.
  • This type of sheet is used in various industries to make all kinds of parts and in particular appearance parts.
  • an Fe-Zn-Al intermetallic alloy is formed on the surface of said strip with a thickness of some ten nanometers.
  • the corrosion resistance of the parts thus coated is ensured by the zinc, so the thickness is most often achieved by pneumatic spinning.
  • the adhesion of zinc to the steel strip is provided by the intermetallic alloy layer mentioned above.
  • this steel strip Before the passage of the steel strip in the bath of molten metal, this steel strip first circulates in a annealing furnace under a reducing atmosphere in order to recrystallize it after the important work hardening related to the rolling operation. cold, and prepare its chemical surface state to promote the chemical reactions necessary for the soaking operation itself.
  • the steel strip is brought to about 650 to 900 ° C depending on the grade for the time required 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 drop” or “horn” under a protective atmosphere with respect to the steel and is immersed in the bath of molten metal.
  • a sheath also called "bell drop” or “horn” under a protective atmosphere with respect to the 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 traversed by the steel strip when it is moved through said sheath.
  • the steel strip is deflected by a roll immersed in the metal bath and it emerges from the metal bath, then passes through the wiper means for regulating the thickness of the liquid metal coating on the 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, supersaturation in the zinc bath have a lower density than liquid zinc and go back to the surface of the bath and in particular to the surface of the liquid seal.
  • 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 sub-thick streaks in the liquid zinc of a length of a few millimeters to a few centimeters.
  • a first solution to avoid these disadvantages consists in cleaning the surface of the liquid seal by pumping zinc oxides and mattes from the bath.
  • a second solution is to reduce the surface of the liquid seal at the point of passage of the steel strip by placing a plate of sheet metal or ceramic at this liquid seal to keep away from the band a portion of the particles present on the surface and get a self-cleaning of the liquid seal by this tape.
  • This arrangement does not allow to remove all the particles present on the surface of the liquid seal and the self-cleaning is all the more important that the surface of the liquid seal is reduced, which is incompatible with the industrial conditions of exploitation.
  • 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 completely eliminate the defects related to the entrainment of zinc oxides and mattes by the scrolling of the steel strip.
  • This solution can only work a few hours or even a day before becoming an additional source of defects.
  • this solution only partially processes the liquid seal and does not achieve a very low density of defects satisfying the requirements of customers wanting surfaces without appearance defects.
  • Renewal is achieved 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 liquid zinc can cause scratches on the steel strip before immersion and is itself a source of defects by accumulation of condensed zinc vapor above the liquid seal.
  • a process is also known which is based on the renewal of zinc at the liquid seal and wherein this renewal is carried out using a stainless steel box surrounding the steel strip and opening on the surface of the liquid seal .
  • a pump sucks the particles entrained by the spill thus created and pushes them back into the volume of the bath.
  • This method also requires a very high pumping rate to maintain a permanent spill effect in that the box surrounding the strip in the bath volume above the bottom roller can not be hermetically sealed.
  • JP-A-04120258 discloses a coating installation by dipping a metal strip having a sheath, immersed in the bath of liquid metal and having two liquid metal spill compartments.
  • the object of the invention is to provide a method and an installation for continuously galvanizing a metal strip which makes it possible to avoid the above-mentioned drawbacks and to achieve the very low density of defects satisfying the requirements of customers desiring surfaces without appearance defects.
  • the subject of the invention is therefore a process for the continuous coating of a metal strip in a tank containing a bath of liquid metal, a process in which the metal strip is continuously deflected under a protective atmosphere in a sheath of which the lower part is immersed in the bath of liquid metal to determine with the surface of said bath and inside this sheath, a liquid seal, the metal strip is deflected on a baffle roll disposed in the metal bath and the coated metal strip is dewatered at the outlet of the metal bath, characterized in that a natural flow of the liquid metal, of the surface of the liquid seal, is carried out in two discharge compartments formed in said sheath and each having an internal wall extending the sheath at its lower part and at least opposite each face of the strip, the upper edge of each compartment being positioned at below said surface, the level of liquid metal in said compartments is detected and the level of liquid metal in said compartments is maintained at a level below the surface of the liquid seal so that the drop height of the liquid metal in compartments st greater
  • the steel strip 1 passes into an annealing furnace, not shown, under a reducing atmosphere in order to recrystallize it after the cold-rolling-forming process, and prepare its chemical surface state to promote the chemical reactions necessary for the galvanizing operation.
  • the steel strip is brought to a temperature for example between 650 and 900 ° C.
  • the steel strip 1 passes into a galvanizing installation shown in FIG. 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 additives such as lead, antimony, in particular.
  • the temperature of this liquid zinc bath is of the order of 460 ° C.
  • the steel strip 1 is cooled to a temperature close to that of the liquid zinc bath using exchangers and is then immersed in the bath 12 of liquid zinc.
  • an Fe-Zn-Al intermetallic alloy is formed on the surface of the steel strip 1 to ensure the connection between the steel strip and the zinc remaining after the spinning.
  • the galvanizing installation 10 comprises a sheath 13 inside which the steel strip 1 passes under a protective atmosphere with respect to the steel.
  • This sheath 13 also known as "bell drop” 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 12 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. At the outlet of this zinc bath 12, the coated steel strip 1 passes into spinning means 16 which are for example constituted by air jet nozzles 16a and which are directed towards each side of the steel strip 1 to regulate the thickness of the liquid zinc coating.
  • the lower part 13a of the sheath 13 is extended, on the opposite side of the face of the strip 1 located on the side of the baffle roller 15, by an inner wall 20 directed towards the surface of the liquid seal 14 and which is in keeping with said lower part 13a of the sheath 13, a first compartment 25 for pouring liquid zinc.
  • the upper edge 21 of the inner 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 portion 13a of the sheath 13 facing the face of the strip 1 placed opposite the deflector roll 15, is extended by an inner wall 26 facing the surface of the liquid seal 14 and gentle with said lower portion 13a a second compartment 29 for pouring liquid zinc.
  • the upper edge 27 of the inner 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 for producing a natural flow of liquid zinc from this surface of said liquid seal 14 to this compartment 29.
  • the height of drop of the liquid metal in the compartments 25 and 29 is determined to prevent the rise of the particles of metal oxide and intermetallic compounds against the current of the liquid metal flow and this height is greater than 50 mm and of preferably 100mm.
  • the inner walls 20 and 26 have a lower portion flared towards the bottom of the tank 11.
  • the inner 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 inner walls 20 and 26 are rectilinear and preferably tapered.
  • the upper edges 21 and 27 of the inner 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 circular arcs 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 inner walls 20 and 26 are preferably tapered.
  • one of the upper edges 21 or 27 of the compartments 25 or 29 may be rectilinear and the other comprise a succession of recesses and projections.
  • the means for maintaining the level of liquid zinc in the pouring compartments 25 and 29 are formed by a pump 30 connected on the suction side to said compartment 25 and 29 by a connection duct, respectively 31 and 33.
  • the pump 30 is provided on the discharge side of a discharge pipe 32 in the volume of the bath 12 of the zinc removed.
  • the installation comprises means for displaying the level of liquid zinc in the pouring compartments 25 and 29 or any other means for visualizing the level of liquid zinc.
  • these display means are formed by a reservoir 35 disposed 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.
  • the point of connection of the pump 30 to the overflow compartments 25 and 29 is located above the point of connection of the reservoir 35 to said compartments 25 and 29.
  • the external reservoir 35 makes it possible to postpone the level of the dumping compartments 25 and 29 to the outside of the lower part 13a of the sheath 13 in a favorable environment so as to easily detect this level.
  • the reservoir 35 may be equipped with a liquid zinc level detector, such as for example a contactor supplying a light, a radar or a laser beam.
  • the sheath 13 is extended to be lower and facing each side edge of the steel strip 1, by an inner wall 49 facing the surface of the liquid seal 14 and whose upper edge 41 is positioned below of said surface of the liquid seal 14.
  • Each inner wall 41 with the lower part of the sheath 13 houses a spill compartment 42 of the liquid zinc.
  • the steel strip 1 enters the zinc bath 12 via the sheath 13 and the liquid seal 14 and this strip causes zinc oxides and matts from the bath thereby creating appearance defects in the coating.
  • the surface of the liquid seal 14 is reduced by the internal walls 20 and 26 and the surface of the liquid seal 14 between said walls 20 and 26 flows into the overflow compartments 25 and 29 passing over upper edges 21 and 27 of the inner 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 at the origin of the defects of appearance, are entrained in the dumping compartments 25 and 29 and the liquid zinc contained in these Compartments 25 and 29 are pumped 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 to the immersion scrolls through the surface of the permanently cleaned liquid gasket 14 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 pouring 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 in the tank 11.
  • the installation further comprises spill compartments 25 and 29, two lateral spill compartments 42, the efficiency of the installation is substantially increased.
  • the density of defects on the coated surfaces of the steel strip is considerably reduced and the resulting appearance quality of this coating is suitable for the criteria required by customers wishing pieces whose surfaces are free of defects in appearance.
  • the invention applies to any metal coating by dipping.

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  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
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Description

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 coating 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 coated with a protective layer for example against corrosion and usually coated with a zinc layer are used.

Ce type 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 make all kinds of parts and in particular appearance parts.

Pour obtenir ce genre de tôles, on utilise des installations de revêtement 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 dipping 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 aluminum. , iron, and possible elements of addition 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 of order of 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-Al d'une épaisseur de quelques dizaine de nanomètres.In the particular case of hot-dip galvanizing, during the running of the steel strip in the molten zinc bath, an Fe-Zn-Al intermetallic alloy is formed on the surface of said strip with a thickness of some ten nanometers.

La résistance à la corrosion des pièces ainsi revêtues est assurée par le zinc donc l'épaisseur est réalisée le plus souvent par essorage pneu-matique. L'adhérence du zinc sur la bande d'acier est assurée par la couche d'alliage intermétallique mentionné précédemment.The corrosion resistance of the parts thus coated is ensured by the zinc, so the thickness is most often achieved by pneumatic spinning. The adhesion of zinc to the steel strip is provided by the intermetallic alloy layer mentioned above.

Avant le passage de la bande d'acier dans le bain de métal fondu, 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 900°C 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.Before the passage of the steel strip in the bath of molten metal, this steel strip first circulates in a annealing furnace under a reducing atmosphere in order to recrystallize it after the important work hardening related to the rolling operation. cold, and prepare its chemical surface state to promote the chemical reactions necessary for the soaking operation itself. The steel strip is brought to about 650 to 900 ° C depending on the grade for the time required for recrystallization and surface preparation. It is then cooled to a temperature close to that of the molten metal bath using exchangers.

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.After passing through the annealing furnace, the steel strip passes through a sheath also called "bell drop" or "horn" under a protective atmosphere with respect to the steel and is immersed in the bath of molten metal.

La partie inférieure de la gaine est immergée dans le bain de métal 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 traversed by the steel strip when it is moved through 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'essorage servant à réguler l'épaisseur du revêtement de métal liquide sur cette bande d'acier.The steel strip is deflected by a roll immersed in the metal bath and it emerges from the metal bath, then passes through the wiper means for regulating the thickness of the liquid metal coating on the 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, on 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.These mattes or other particles, supersaturation in the zinc bath have a lower density than liquid zinc and go back to the surface of the bath and in particular to the surface of the liquid seal.

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.The movement of the steel strip through the surface of the liquid seal causes the entrainment of the stagnant particles. These particles caused 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 extraction zone of the band by creating appearance defects.

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.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 millimètres à quelques centimètres.In fact, the intruded particles are retained by the pneumatic wringing jets before being ejected or disintegrated, thus creating sub-thick streaks in the liquid zinc of a length of a few millimeters to a few centimeters.

Pour tenter d'éliminer les particules de zinc et les mattes à la surface du joint liquide, différentes solutions ont été proposées.In an attempt to eliminate the zinc particles and the matts on the surface of the liquid seal, various solutions have been proposed.

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.A first solution to avoid these disadvantages consists in cleaning 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 a very small radius of action, which does not guarantee a complete cleaning of the liquid seal traversed by the sealing strip. 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 is to reduce the surface of the liquid seal at the point of passage of the steel strip by placing a plate of sheet metal or ceramic at this liquid seal to keep away from the band a portion of the particles present on the surface and get a self-cleaning of the liquid seal by this tape.

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 important que la surface du joint liquide est réduite, ce qui est incompatible avec les conditions industrielles d'exploitation.This arrangement does not allow to remove all the particles present on the surface of the liquid seal and the self-cleaning is all the more important that the surface of the liquid seal is reduced, which is incompatible with the industrial conditions of exploitation.

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.In addition, after a given operating time, the storage of the particles outside the plate grows more and more and clusters of particles eventually detach and return to the steel strip.

L'ajout d'une plaque débouchant à la surface du joint liquide forme également un lieu privilégié pour piéger les poussières de zinc.The addition of a plate opening on the surface of the liquid seal also forms a privileged place for trapping 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 completely eliminate the defects related to the entrainment of zinc oxides and mattes by the scrolling 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.Indeed, the zinc vapors at the liquid seal will condense on the walls of the frame and the slightest swirl caused by the vibrations or thermal folds of the strip to immersion, the walls of the frame will become dirty and so become foreign body storage areas.

Cette solution ne peut donc fonctionner que quelques heures, voire quelques jour avant de devenir elle-même une source supplémentaire de défauts.This solution can only work a few hours or even a day before becoming an additional source of defects.

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 processes the liquid seal and does not achieve a very low density of defects satisfying the requirements of customers wanting 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.There is also known a solution that aims to obtain cleanliness of the liquid seal by renewal of the liquid metal bath.

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.Renewal is achieved 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 oeuvre.This solution presents great difficulties of implementation.

En effet, elle nécessite un énorme débit de pompage pour assurer un effet de déversement et le zinc pompé et injecté au niveau du joint liquide contient les mattes générées dans le bain de zinc.Indeed, it requires a huge pumping rate to ensure a spill effect and the zinc pumped and injected at the liquid seal contains matts generated in the zinc bath.

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.Furthermore, the piping ensuring the renewal of liquid zinc can cause scratches on the steel strip before immersion and is itself a source of defects by accumulation of condensed zinc vapor above the liquid seal.

On connaît également un procédé qui est basé sur le renouvellement 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 liquid seal and wherein this renewal is carried out using a stainless steel box surrounding the steel strip and opening on the surface of the liquid seal . A pump sucks the particles entrained by the spill thus created and pushes them back 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 method also requires a very high pumping rate to maintain a permanent spill effect in that the box surrounding the strip in the bath volume above the bottom roller can not be hermetically sealed.

JP-A-04120258 décrit une installation de revêtement au trempé d'une bande métallique comportant une gaine, immergée dans le bain de métal liquide et comportant deux compartiments de déversement de métal liquide. JP-A-04120258 discloses a coating installation by dipping a metal strip having a sheath, immersed in the bath of liquid metal and having two liquid metal spill compartments.

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.The object of the invention is to provide a method and an installation for continuously galvanizing a metal strip which makes it possible to avoid the above-mentioned drawbacks and to achieve the very low density of defects satisfying the requirements of customers desiring surfaces without appearance defects.

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 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, 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, on détecte le niveau de metal liquide dans lesdits compartiments et on maintient le niveau de métal liquide dans lesdits compartiments à un niveau au-dessous de la surface du joint liquide de telle sorte que la hauteur de chute du métal liquide dans les compartiments st supérieur à 50 mm pour empêcher la remontée des particules d'oxyde de métal et de composés intermétallique à contre-courant de l'écoulement du métal liquide.The subject of the invention is therefore a process for the continuous coating of a metal strip in a tank containing a bath of liquid metal, a process in which the metal strip is continuously deflected under a protective atmosphere in a sheath of which the lower part is immersed in the bath of liquid metal to determine with the surface of said bath and inside this sheath, a liquid seal, the metal strip is deflected on a baffle roll disposed in the metal bath and the coated metal strip is dewatered at the outlet of the metal bath, characterized in that a natural flow of the liquid metal, of the surface of the liquid seal, is carried out in two discharge compartments formed in said sheath and each having an internal wall extending the sheath at its lower part and at least opposite each face of the strip, the upper edge of each compartment being positioned at below said surface, the level of liquid metal in said compartments is detected and the level of liquid metal in said compartments is maintained at a level below the surface of the liquid seal so that the drop height of the liquid metal in compartments st greater than 50 mm to prevent the rise of metal oxide particles and intermetallic compounds against the flow of the liquid metal.

L'invention a pour objet une installation de revêtement au trempé à chaud et en continu d'une bande métallique, du type comprenant :

  • une cuve contenant un bain de métal liquide,
  • 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,
  • un rouleau déflecteur de la bande métallique disposé dans le bain de métal, et
  • 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 et l'installation comporte des moyens de visualisation du niveau de métal liquide dans chaque compartiment.The subject of the invention is a system for hot dip coating and continuous coating of a metal strip, of the type comprising:
  • a tank containing a bath of liquid metal,
  • a sheath for scrolling the metal strip under a protective atmosphere and 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,
  • a deflector roll of the metal strip disposed in the metal bath, and
  • means for dewatering the coated metal strip at the outlet of the metal bath,
characterized in that the sheath is extended, at its lower part and opposite each face of the strip, by an inner wall directed towards the surface of the liquid seal and whose upper edge is positioned below said surface, said walls forming two liquid metal spill 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 achieve a natural flow of the liquid metal from that surface to these compartments, the drop height of the liquid metal in said compartments being greater than 50 mm to prevent the rise of the particles of metal oxide and of intermetallic compounds against the flow of the liquid metal and the installation comprises means for visualizing the level of liquid metal in each compartment.

Selon d'autres caractéristiques de l'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,
  • la hauteur de chute du métal liquide dans chaque compartiment est supérieure à 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,
  • 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,
  • 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.
According to other features of the invention:
  • the inner wall of each compartment has a lower part flared towards the bottom of the tank and an upper part parallel to the metal band,
  • the drop height of the liquid metal in each compartment is greater than 100mm,
  • 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 connecting pipe and provided on the discharge side of a discharge pipe in the liquid metal bath volume taken,
  • the display means 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 inner wall directed towards the surface of the liquid seal whose upper edge is positioned below said surface and forming a compartment of 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,
  • 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,
  • 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,
  • la Fig. 5 est une vue schématique en coupe transversale d'une variante de la gaine de l'installation conforme à l'invention.
Other features and advantages of the invention will become apparent from the following description given by way of example and with reference to the accompanying drawings, in which:
  • the Fig. 1 is a diagrammatic elevational view of a continuous dipping coating plant according to the invention,
  • the Fig. 2 is a sectional view of the sheath along the line 2-2 of the Fig. 1 ,
  • the Fig. 3 is a schematic view in elevation of a first embodiment of the upper edge of the discharge compartments of the installation according to the invention,
  • the Fig. 4 is a schematic view in elevation of a second embodiment of the upper edge of the discharge compartments of the installation according to the invention,
  • the Fig. 5 is a schematic cross-sectional view 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.In what follows, the description will be made for a continuous galvanizing installation of a metal strip. But the invention applies to any continuous dipping process in which there appears a surface pollution and for which it is necessary to keep a clean liquid seal.

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.First of all, at the outlet of the cold rolling mill, the steel strip 1 passes into an annealing furnace, not shown, under a reducing atmosphere in order to recrystallize it after the cold-rolling-forming process, and prepare its chemical surface state to promote the chemical reactions necessary for the galvanizing operation.

Dans ce four, la bande d'acier est portée à une température comprise par exemple entre 650 et 900°C.In this furnace, the steel strip is brought to a temperature 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.At the outlet of the annealing furnace, the steel strip 1 passes into a galvanizing installation shown in FIG. Fig. 1 and designated by the general reference 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.This installation 10 comprises a tank 11 containing a bath 12 of liquid zinc which contains chemical elements such as aluminum, iron and possible additives such as lead, antimony, in particular.

La température de ce bain de zinc liquide est de l'ordre de 460°C.The temperature of this liquid zinc bath is of the order of 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.At the outlet of the annealing furnace, the steel strip 1 is cooled to a temperature close to that of the liquid zinc bath using exchangers and is then immersed in the bath 12 of liquid zinc.

Lors de cette immersion, il se forme à la surface de la bande d'acier 1 un alliage intermétallique Fe-Zn-Al permettant d'assurer la liaison entre la bande d'acier et le zinc restant après l'essorage.During this immersion, an Fe-Zn-Al intermetallic alloy is formed on the surface of the steel strip 1 to ensure the connection between the steel strip and the zinc remaining after the 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 represented in Fig. 1 the galvanizing installation 10 comprises a sheath 13 inside which the steel strip 1 passes 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.This sheath 13 also known as "bell drop" or "horn" has, in the embodiment shown in the figures, a rectangular cross section.

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 12 et à l'intérieur de cette gaine 13, un joint d'étanchéité liquide 14.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 12 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 to immersion in the liquid zinc bath 12, passes through 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 dirigées 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 outlet of this zinc bath 12, the coated steel strip 1 passes into spinning means 16 which are for example constituted by air jet nozzles 16a and which are directed towards each side of the steel strip 1 to regulate the thickness of the liquid zinc coating.

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 on the 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 located on the side of the baffle roller 15, by an inner wall 20 directed towards the surface of the liquid seal 14 and which is in keeping with said lower part 13a of the sheath 13, a first compartment 25 for pouring 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.The upper edge 21 of the inner 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.

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 ménageant avec ladite partie inférieure 13a un second compartiment 29 de déversement du zinc liquide.Similarly, the lower portion 13a of the sheath 13 facing the face of the strip 1 placed opposite the deflector roll 15, is extended by an inner wall 26 facing the surface of the liquid seal 14 and gentle with said lower portion 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 inner 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 for producing 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 drop of the liquid metal in the compartments 25 and 29 is determined to prevent the rise of the particles of metal oxide and intermetallic compounds against the current of the liquid metal flow and this height is greater than 50 mm and of 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 est ont une épaisseur comprise entre 10 et 20mm.Preferably, the inner walls 20 and 26 have a lower portion flared towards the bottom of the tank 11. The inner 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.According to a first embodiment shown in Fig. 3 the upper edges 21 and 27 of the inner walls 20 and 26 are rectilinear and preferably tapered.

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 second embodiment represented at Fig. 4 , the upper edges 21 and 27 of the inner 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 circular arcs 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.In this embodiment also, the upper edges 21 and 27 of the inner walls 20 and 26 are preferably tapered.

Selon un autre mode de réalisation, l'une des arêtes supérieures 21 ou 27 des compartiments 25 ou 29 peut être rectiligne et l'autre comporter une succession de creux et de saillies.According to another embodiment, one of the upper edges 21 or 27 of the compartments 25 or 29 may be rectilinear and the other comprise a succession of recesses and projections.

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.The means for maintaining the level of liquid zinc in the pouring compartments 25 and 29 are formed by a pump 30 connected on the suction side to said compartment 25 and 29 by a connection duct, respectively 31 and 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.The pump 30 is provided on the discharge side of a discharge pipe 32 in the volume of the bath 12 of the zinc removed.

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.Furthermore, the installation comprises means for displaying the level of liquid zinc in the pouring compartments 25 and 29 or any other means for visualizing the level of liquid zinc.

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.In this preferred embodiment, these display means are formed by a reservoir 35 disposed 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 represented in Fig. 1 the point of connection of the pump 30 to the overflow compartments 25 and 29 is located above the point of connection of the reservoir 35 to 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 postpone the level of the dumping compartments 25 and 29 to the outside of the lower part 13a of the sheath 13 in a favorable environment so as to easily detect this level. For this purpose, the reservoir 35 may be equipped with a liquid zinc level detector, such as for example a contactor supplying a light, 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 represented in Fig. 5 , the sheath 13 is extended to be lower and facing each side edge of the steel strip 1, by an inner wall 49 facing the surface of the liquid seal 14 and whose upper edge 41 is positioned below of 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.Each inner wall 41 with the lower part of the sheath 13 houses a spill compartment 42 of the liquid zinc.

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.In general, the steel strip 1 enters the zinc bath 12 via the sheath 13 and the liquid seal 14 and this strip causes zinc oxides and matts 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, the surface of the liquid seal 14 is reduced by the internal walls 20 and 26 and the surface of the liquid seal 14 between said walls 20 and 26 flows into the overflow compartments 25 and 29 passing over upper edges 21 and 27 of the inner 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 at the origin of the defects of appearance, are entrained in the dumping compartments 25 and 29 and the liquid zinc contained in these Compartments 25 and 29 are pumped 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 liquid gasket 14 isolated between the walls 20 and 26 is constantly renewed and the liquid zinc sucked by the pump 30 into these compartments 25 and 29 is injected into the zinc bath 12 through the duct. 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 to the immersion scrolls through the surface of the permanently cleaned liquid gasket 14 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.The external reservoir 35 makes it possible to detect the level of liquid zinc in the pouring 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 in the tank 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.In the case where the installation further comprises spill compartments 25 and 29, two lateral spill compartments 42, the efficiency of the installation is substantially 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 qualité 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 coated surfaces of the steel strip is considerably reduced and the resulting appearance quality of this coating is suitable for the criteria required by customers wishing pieces whose surfaces are free of defects in appearance.

L'invention s'applique à tout revêtement métallique par trempé.The invention applies to any metal coating by dipping.

Claims (17)

  1. Process for the continuous dip-coating of a metal strip (1) in a tank (11) containing a liquid metal bath (12), in which process the metal strip (1) is made to run continuously, in a protected atmosphere, through a sheath (13), the lower part (13a) of which is immersed in the liquid metal bath (12) in order to define, with the surface of said bath and inside this sheath (13), a liquid seal (14), the metal strip (1) is deflected around a deflector roll (15) placed in the metal bath (12), and the coated metal strip (1) is dried on leaving the metal bath (12), characterized in that a natural flow of liquid metal from the surface of the liquid seal (14) is produced in two overflow compartments (25; 29) provided in said sheath (13), each compartment having an internal wall (20; 26) extending the sheath (13) in its lower part and facing each side of the strip (1), the top edge (21; 27) of each compartment (25; 29) being positioned below said surface, the level of liquid metal in said compartments is detected and the level of liquid metal in said compartments (25; 29) is maintained at a level below the surface of the liquid seal (14) in such a way that the drop height of the liquid metal in the compartments (25; 29) is greater than 50 mm so as to prevent the metal oxide particles and particles of intermetallic compounds from rising countercurrently to the flow of the liquid metal.
  2. Installation for the continuous hot-dip coating of a metal strip (1), of the type comprising:
    - a tank (11) containing a liquid metal bath (12),
    - a sheath (13) through which the metal strip (1) runs in a protected atmosphere, the lower part (13a) of said sheath being immersed in the liquid metal bath (12) in order to define, with the surface of said bath (12) and inside this sheath (13), a liquid seal (14);
    - a deflector roll (15) for deflecting the metal strip (1), placed in the metal bath (12); and
    - means (16) for drying the coated metal strip (1) on leaving the zinc bath (12),
    characterized in that the sheath (13) is extended, in its lower part (13a) and facing each side of the strip (1), by an internal wall (20; 26) directed towards the surface of the liquid seal (14), the top edge (21; 27) of said wall being positioned below said surface, said walls (20; 26) forming two liquid-metal overflow compartments (25; 29), which are provided with means (30) for 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 the liquid metal from this surface towards these compartments (25; 29), the drop height of the liquid metal in said compartments being greater than 50 mm in order to prevent metal oxide particles and particles of intermetallic compounds from rising countercurrently to the flow of the liquid metal and in that it includes means (35) for displaying the level of liquid metal in each compartment (25; 29).
  3. Installation according to Claim 2, characterized in that the drop height of liquid metal in each compartment (25, 29) is greater than 100 mm.
  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 metal strip (1).
  5. Installation according to Claim 2 or 3, characterized in that the top edge (21; 27) of the internal wall (20; 26) of each compartment (25; 29) is straight.
  6. Installation according to Claim 2 or 3, characterized in that the top edge (21; 27) of the internal wall (20; 26) of each compartment (25; 29) comprises, in the longitudinal direction, a succession of hollows (22) and projections (23).
  7. Installation according to Claim 6, characterized in that the hollows (22) and the projections (23) are in the form of circular arcs.
  8. Installation according to Claim 6 or 7, characterized in that the amplitude of the hollows (22) and the projections (23) is between 5 and 10 mm.
  9. Installation according to Claim 6 or 7, characterized in that the distance between the hollows (22) and the projections (23) is around 150 mm.
  10. Installation according to any one of the preceding claims, characterized in that the top edge (21; 27) of the internal walls (20; 26) of each compartment (25; 29) is tapered.
  11. Installation according to any one of the preceding claims, characterized in that the internal wall (20; 26) of each compartment (25; 29) is made of stainless steel and has a thickness of, for example, between 20 and 10 mm.
  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 via connecting ducts (31; 33) and provided on the discharge side with a discharge duct (32) in the volume of the liquid metal bath (12) removed.
  13. Installation according to any one of Claims 2 to 12, characterized in that the display means are formed by a reservoir (35) placed outside the sheath (13) and connected to the base of each compartment (25; 29) by a connection pipe (36; 37).
  14. Installation according to Claims 12 and 13, characterized in that the point of connection of the pump (30) to each compartment (25; 29) is located above the point of connection of the reservoir (35) in each compartment (25; 29).
  15. Installation according to Claim 13, characterized in that the reservoir (35) forms a buffer tank of liquid metal for each compartment (25; 29).
  16. Installation according to Claim 13, characterized in that the reservoir (35) is equipped with a liquid metal level detector.
  17. Installation according to any one of Claims 2 to 16, characterized in that the sheath (13) is extended, in its lower part (13a) and facing each lateral edge of the metal strip (1), by an internal wall (40) directed towards the surface of the liquid seal (14), the top edge (41) of which is positioned above said surface and forming a liquid metal overflow compartment (42).
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)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR0014481A FR2816640B1 (en) 2000-11-10 2000-11-10 HOT AND CONTINUOUS TEMPERATURE COATING INSTALLATION OF A METAL STRIP
FR0014481 2000-11-10
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

Publications (2)

Publication Number Publication Date
EP1339891A1 EP1339891A1 (en) 2003-09-03
EP1339891B1 true EP1339891B1 (en) 2009-12-23

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EP01993387A Expired - Lifetime EP1339891B1 (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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US (1) US6939586B2 (en)
EP (1) EP1339891B1 (en)
JP (2) JP3753693B2 (en)
KR (1) KR100725558B1 (en)
CN (1) CN1279205C (en)
AR (1) AR034181A1 (en)
AT (1) ATE452998T1 (en)
AU (2) AU2377802A (en)
BG (1) BG65788B1 (en)
BR (1) BR0100009B1 (en)
CA (1) CA2428488C (en)
CZ (1) CZ299077B6 (en)
DE (1) DE60140896D1 (en)
DK (1) DK1339891T3 (en)
EA (1) EA004449B1 (en)
EC (1) ECSP034593A (en)
EE (1) EE04820B1 (en)
ES (1) ES2336306T3 (en)
FR (1) FR2816640B1 (en)
HR (1) HRP20030363B1 (en)
HU (1) HUP0303834A2 (en)
MA (1) MA25855A1 (en)
ME (1) ME00841B (en)
MX (1) MXPA03004132A (en)
NO (1) NO20032092L (en)
PL (1) PL201518B1 (en)
PT (1) PT1339891E (en)
RS (1) RS49958B (en)
SK (1) SK287885B6 (en)
TW (1) TW554071B (en)
UA (1) UA74223C2 (en)
WO (1) WO2002038825A1 (en)
ZA (1) ZA200303502B (en)

Cited By (2)

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DE102013104267B3 (en) * 2013-04-26 2014-02-27 Thyssenkrupp Steel Europe Ag Device, useful for continuous hot dip coating of metal strip i.e. steel strip (claimed) for industrial applications, has molten bath vessel including opening with trunk part for introducing metal strip into molten metal bath
US11850634B2 (en) 2019-05-08 2023-12-26 Sms Group Gmbh Method and device for rinsing an overflow chamber at the bath-side end of a snout of a hot-dip coating device

Families Citing this family (11)

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Publication number Priority date Publication date Assignee Title
EP1538233A1 (en) * 2002-09-13 2005-06-08 JFE Steel Corporation Method and apparatus for producing hot-dip coated metal belt
PL2098607T3 (en) 2008-02-25 2011-10-31 Arcelormittal France Method of coating a metal strip and installation for implementing the method
DE102013101131A1 (en) * 2013-02-05 2014-08-07 Thyssenkrupp Steel Europe Ag Apparatus for hot dip coating of metal strip
WO2017187226A1 (en) * 2016-04-26 2017-11-02 Arcelormittal Apparatus for the continuous hot dip coating of a metal strip and associated method
WO2017187225A1 (en) * 2016-04-26 2017-11-02 Arcelormittal Apparatus for the continuous hot dip coating of a metal strip and associated method
WO2019175623A1 (en) 2018-03-12 2019-09-19 Arcelormittal Method for dip-coating a metal strip
FR3105796B1 (en) * 2019-12-26 2022-06-10 Fives Stein DEVICE FOR THE EVACUATION OF MATTE FROM THE SURFACE OF A LIQUID METAL BATH INSIDE A CHAMBER DROP OF A CONTINUOUS COATING LINE WITH A METALLIC STRIP
CN212404238U (en) * 2020-04-30 2021-01-26 武汉钢铁有限公司 Furnace nose annular overflow device of hot coating production line
CN112695265A (en) * 2020-12-11 2021-04-23 华菱安赛乐米塔尔汽车板有限公司 Method for controlling liquid level of zinc pot
EP4215637A1 (en) 2022-01-25 2023-07-26 John Cockerill S.A. Device for cleaning a snout in a hot-dip galvanization installation
WO2024110603A1 (en) * 2022-11-24 2024-05-30 Tata Steel Ijmuiden B.V. A hot dip coating device and a method of operating thereof

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US4759807A (en) * 1986-12-29 1988-07-26 Rasmet Ky Method for producing non-aging hot-dip galvanized steel strip
JPH02305948A (en) * 1989-05-19 1990-12-19 Kawasaki Steel Corp Dross removing device for inside of snout for continuous hot dip metal coating
JPH03150338A (en) * 1989-11-07 1991-06-26 Nippon Steel Corp Production of continuous alloying hot dip galvanized steel sheet
JP2501654B2 (en) * 1990-06-28 1996-05-29 川崎製鉄株式会社 Continuous hot dip galvanizing equipment
JPH04120258A (en) * 1990-09-12 1992-04-21 Kawasaki Steel Corp Method and device for continuous hot dip galvanizing
JPH05279827A (en) * 1992-03-31 1993-10-26 Kawasaki Steel Corp Device for removing dross in snout in hot-dip metal coating
JP2001335906A (en) * 2000-05-26 2001-12-07 Nippon Steel Hardfacing Co Ltd Device for removing foreign matter in snout

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102013104267B3 (en) * 2013-04-26 2014-02-27 Thyssenkrupp Steel Europe Ag Device, useful for continuous hot dip coating of metal strip i.e. steel strip (claimed) for industrial applications, has molten bath vessel including opening with trunk part for introducing metal strip into molten metal bath
WO2014173663A1 (en) 2013-04-26 2014-10-30 Thyssenkrupp Steel Europe Ag Device for the continuous hot-dip galvanizing of metal strip
US9745653B2 (en) 2013-04-26 2017-08-29 Thyssenkrupp Steel Europe Ag Apparatus for the continuous hot-dip coating of metal strip
US11850634B2 (en) 2019-05-08 2023-12-26 Sms Group Gmbh Method and device for rinsing an overflow chamber at the bath-side end of a snout of a hot-dip coating device

Also Published As

Publication number Publication date
CZ20031293A3 (en) 2004-01-14
ZA200303502B (en) 2004-07-19
JP2004513239A (en) 2004-04-30
EE04820B1 (en) 2007-04-16
ATE452998T1 (en) 2010-01-15
EP1339891A1 (en) 2003-09-03
ES2336306T3 (en) 2010-04-12
JP4823634B2 (en) 2011-11-24
US6939586B2 (en) 2005-09-06
FR2816640B1 (en) 2003-10-31
NO20032092L (en) 2003-07-08
PT1339891E (en) 2010-02-11
EE200300208A (en) 2003-08-15
BR0100009A (en) 2002-07-09
MA25855A1 (en) 2003-07-01
YU36503A (en) 2005-11-28
CA2428488A1 (en) 2002-05-16
HRP20030363B1 (en) 2011-05-31
UA74223C2 (en) 2005-11-15
MXPA03004132A (en) 2003-08-19
PL201518B1 (en) 2009-04-30
KR100725558B1 (en) 2007-06-08
JP2006063453A (en) 2006-03-09
FR2816640A1 (en) 2002-05-17
DK1339891T3 (en) 2010-04-26
PL362649A1 (en) 2004-11-02
WO2002038825A1 (en) 2002-05-16
HRP20030363A2 (en) 2003-06-30
CZ299077B6 (en) 2008-04-16
CA2428488C (en) 2010-10-19
AU2377802A (en) 2002-05-21
CN1479798A (en) 2004-03-03
BR0100009B1 (en) 2012-02-07
BG107785A (en) 2003-12-31
BG65788B1 (en) 2009-11-30
DE60140896D1 (en) 2010-02-04
TW554071B (en) 2003-09-21
KR20030048136A (en) 2003-06-18
CN1279205C (en) 2006-10-11
AR034181A1 (en) 2004-02-04
EA200300554A1 (en) 2003-10-30
EA004449B1 (en) 2004-04-29
US20040052959A1 (en) 2004-03-18
HUP0303834A2 (en) 2004-03-01
ME00841B (en) 2008-09-29
NO20032092D0 (en) 2003-05-09
AU2002223778B2 (en) 2006-04-27
SK5582003A3 (en) 2004-01-08
ECSP034593A (en) 2003-09-24
JP3753693B2 (en) 2006-03-08
RS49958B (en) 2008-09-29
SK287885B6 (en) 2012-02-03

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