EP0979879B1 - Method for the galvanization of metallic strip - Google Patents

Method for the galvanization of metallic strip Download PDF

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Publication number
EP0979879B1
EP0979879B1 EP99401700A EP99401700A EP0979879B1 EP 0979879 B1 EP0979879 B1 EP 0979879B1 EP 99401700 A EP99401700 A EP 99401700A EP 99401700 A EP99401700 A EP 99401700A EP 0979879 B1 EP0979879 B1 EP 0979879B1
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EP
European Patent Office
Prior art keywords
injected
hydrogen
inert gas
flow rate
annealing furnace
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EP99401700A
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German (de)
French (fr)
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EP0979879A1 (en
Inventor
Serban Cantacuzene
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide SA
LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude
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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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
    • 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
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • 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
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C23C2/004—Snouts
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments

Definitions

  • the invention relates to a method of galvanizing a part metallic (strip, sheet ...) in a continuous galvanizing line, the galvanizing line comprising, arranged in series and connected to each other others by conduits to form a circulation duct of a reducing atmosphere most often essentially composed of a gas inert such as nitrogen or argon, and hydrogen, a preheating oven, an oven annealing, a cooling station and a quenching station for said part metallic in a bath of liquid zinc or a zinc alloy, in which, before immersing the metal part in the liquid bath, it is exposed to this reducing atmosphere to remove oxides from the surface of the metal part.
  • a gas inert such as nitrogen or argon
  • a continuous galvanizing line includes at least four metal strip processing areas to galvanize: a preheating zone, an annealing zone, a cooling and a quenching zone comprising a zinc bath in which is dipped the metal strip to be galvanized.
  • the area preheating includes an oven with open flame burners serving on the one hand to rapidly reheat the metal strip to be treated at a temperature typically between 400 ° C and 700 ° C, and on the other hand subject the laminating oils present on the surface to pyrolysis the band.
  • the burners are operated in the absence of air to ensure an atmosphere non-oxidizing towards iron.
  • the different processing areas of the line galvanization are connected to each other by conduits to form a duct for circulating the reducing atmosphere.
  • the mixture of nitrogen and hydrogen is injected into a pipe also called a horn or bell one end of which is immersed in the zinc bath and the other end of which is connected to the outlet end of the cooling station, so that the reducing atmosphere circulates in the opposite direction to the direction of travel of the metal strip to be treated.
  • the flow rate of the nitrogen and hydrogen mixture and the hydrogen content of this mixture are maintained at the same level, regardless of characteristics and running speed of the metal strips at treat.
  • the flow rate of the nitrogen and hydrogen mixture and the hydrogen content of this mixture are set at a high level so as to allow treatment even the most unfavorable cases, i.e. the metal strips of large surface dimensions and / or treated at high speeds. But as we can see, this excess of quality represented by a mixture rich in hydrogen injected at a high rate entails a significant cost for this reducing atmosphere.
  • the invention aims to propose a method for optimizing the use of the reducing atmosphere in order to reduce the cost generated by this in the operation of the galvanizing line as well as better maintain the level of quality of products coming out of the line.
  • the invention relates to a galvanizing process of a metal strip in a continuous galvanizing line, the line of galvanizing comprising, arranged in series and connected to each other by conduits to form a continuous circulation sheath of a reducing atmosphere comprising an inert gas and hydrogen, a preheating, an annealing furnace, a cooling station and a soaking said metal strip in a bath of liquid zinc or a liquid zinc alloy, in which, before plunging the metal strip in the bath, it is exposed to this reducing atmosphere to eliminate oxides present on its surface, characterized in that to renew the reducing atmosphere in said sheath, the inert gas is injected therein and hydrogen by adjusting the flow of hydrogen according to the amount of metal strip surface to be treated per unit of time.
  • a reducing atmosphere comprising, arranged in series and connected to each other by conduits to form a continuous circulation sheath of a reducing atmosphere comprising an inert gas and hydrogen, a preheating, an annealing furnace, a
  • Figure 1 is shown schematically a line 1 for galvanizing a metal strip 3, for example steel.
  • the galvanizing line 1 comprises, arranged in series, an oven 5 preheating, an annealing oven 7, a cooling station 9 and a quenching station 11 comprising a bath 13 of liquid zinc or of alloy liquid.
  • the preheating oven 5 is for example equipped with burners 15 with an open flame used on the one hand to quickly heat the metal strip 3 to be treated, at a temperature typically between 400 ° C. and 700 ° C., and on the other hand to subject to a pyrolysis the rolling oils present on the surface of the strip.
  • the annealing furnace 7 is for example equipped with resistors electric or radiant tubes diagrammed in 8.
  • the cooling station 9 is used to cool the metal strip 3 at the outlet of the annealing oven 7, at a value for example close to 470 ° C.
  • the preheating oven 5, the annealing oven 7, the station 9 cooling and the station 11 quenching which each have a form of tunnel, are connected to each other by conduits 17, 19 and 21 for forming with them a continuous sheath 23 of circulation of an atmosphere reducing essentially composed of nitrogen and hydrogen.
  • conduit 21 connecting the outlet end of the station 9 of cooling at quenching station 11 is tilted down and plunges with its end 25 in the liquid bath 13.
  • This conduit 21 is often called horn or bell.
  • the galvanizing line 1 comprises according to the invention, on the one hand, an injector 30 of an inert gas, for example nitrogen, arranged in the wall of the tube 21 at a first location 30A located at near the end 25 of the tube immersed in the liquid bath 13, at above it, and on the other hand, a hydrogen injector 31 (or a mixture of hydrogen and an inert gas) arranged in the wall of the proboscis 21 at a second location 31A located near the end 33 thereof which is connected to the cooling station 9.
  • an injector 30 of an inert gas for example nitrogen
  • a hydrogen injector 31 or a mixture of hydrogen and an inert gas
  • the injector 30 is connected to a supply conduit 32 in which is arranged a member 34 regulating flow and the injector 31 is connected to a supply conduit 36 in which is arranged a flow regulating member 38.
  • line 1 includes means 40 for determining and for adjusting the running speed of the metal strip 3.
  • a gas sample point 42 inside the oven annealing used to return atmospheric samples for analysis, for example as shown in the figure to an analyzer 47 of the hydrogen content of the sample, and to an analyzer 46 of the water vapor content of the sample.
  • the means 40 as well as the analyzers 46 and 47, are connected to a data processing unit 50 (for example an automaton programmable), unit in turn able to control the operation of two flow regulators 34 and 38.
  • a data processing unit 50 for example an automaton programmable
  • the metal strip 3 guided by rollers 27 pass successively into the preheating oven 5 to be brought to a temperature here between 400 ° C and 700 ° C, then in the oven 7 annealing to ensure its metallurgical characteristics, in station 9 cooling to be brought to a temperature close to 470 ° C and finally in the quenching station 11 so as to be covered with zinc.
  • the unit 50 falls as described above, the running speed of the metal strip 3, the dew point and the hydrogen content of the atmosphere in at least one point (42) of the furnace 7 of annealing and controlling the flow rates via regulators 34 and 38 nitrogen and / or hydrogen injected into the tube 21, in accordance with one of the embodiments of the invention described above in the present description.
  • Unit 50 regulates these nitrogen and hydrogen flow rates as a function of the amount of surface of the metal strip to be treated per unit of time.
  • the speed is taken into account of running of the strip in the line supplied by the means 40, and the strip width 3.
  • the assembly making it possible to keep the hydrogen flow rate constant at S / t constant, at a value close to 0.009 m 3 of hydrogen per m 2 of strip.
  • Figure 2 therefore illustrates an example of abacuses that it is possible to carry out on a given line, for one or more steels treated, in adopting a medium gas setting, and sweeping a typical range of variation of the surface treated per unit of time (which takes into account the range of line speed usually practiced, and the range of widths of products treated on the line considered), reading these charts for determining changes in settings gas supply which it is advantageous to adopt in each case.
  • one realizes hydrogen zoning of the cooling zone by injecting, in addition nitrogen in the sheath 23 at the first location 30A at a substantially constant flow, and the hydrogen at location 31A, nitrogen in the annealing oven 7, preferably in the last portion of exit from it. And in this case, we can adjust the nitrogen flow injected into the annealing furnace 7 as a function of a set point value dew at this oven.
  • This provision allows on the one hand to locally raise the hydrogen concentration at cooling station 9, thus protecting the surface of the strip against oxidation before being immersed in the zinc bath 13, and on the other hand to contribute to the belt cooling 3.
  • the process of the invention not only reduces consumption of hydrogen and thus the operating cost to regenerate the atmosphere reductive but on the other hand to get more surely and under conditions that are not the simple implementation of an excess of quality consistency of the characteristics of the products released by the galvanizing line.

Description

L'invention est relative à un procédé de galvanisation d'une pièce métallique (bande, tôle...) dans une ligne de galvanisation en continu, la ligne de galvanisation comprenant, disposés en série et reliés les uns aux autres par des conduits pour former une gaine de circulation d'une atmosphère réductrice le plus souvent essentiellement composée d'un gaz inerte tel l'azote ou l'argon, et d'hydrogène, un four de préchauffage, un four de recuit, un poste de refroidissement et un poste de trempe de ladite pièce métallique dans un bain de zinc liquide ou d'un alliage de zinc, dans lequel, avant de plonger la pièce métallique dans le bain liquide, on l'expose à cette atmosphère réductrice pour éliminer des oxydes présents sur la surface de la pièce métallique.The invention relates to a method of galvanizing a part metallic (strip, sheet ...) in a continuous galvanizing line, the galvanizing line comprising, arranged in series and connected to each other others by conduits to form a circulation duct of a reducing atmosphere most often essentially composed of a gas inert such as nitrogen or argon, and hydrogen, a preheating oven, an oven annealing, a cooling station and a quenching station for said part metallic in a bath of liquid zinc or a zinc alloy, in which, before immersing the metal part in the liquid bath, it is exposed to this reducing atmosphere to remove oxides from the surface of the metal part.

On parlera dans la description qui suit de « bande » métallique pour fixer les esprits, ainsi que indifféremment de bain de zinc liquide ou d'un alliage de zinc liquide, sans que l'appellation choisie puisse être considérée comme restrictive. On sait en effet que l'industrie utilise des alliages extrêmement variés, notamment dans leur teneur en zinc et/ou en aluminium.We will speak in the following description of metallic "strip" to fix the spirits, as well as indifferently of bath of liquid zinc or a liquid zinc alloy, without the chosen designation being considered as restrictive. We know that the industry uses alloys extremely varied, especially in their zinc and / or aluminum content.

Généralement donc, une ligne de galvanisation en continu comprend au moins quatre zones de traitement de la bande métallique à galvaniser : une zone de préchauffage, une zone de recuit, une zone de refroidissement et une zone de trempe comprenant un bain de zinc dans lequel est plongée la bande métallique à galvaniser.Generally therefore, a continuous galvanizing line includes at least four metal strip processing areas to galvanize: a preheating zone, an annealing zone, a cooling and a quenching zone comprising a zinc bath in which is dipped the metal strip to be galvanized.

On connaít des lignes de galvanisation dans lesquelles la zone de préchauffage comprend un four équipé de brûleurs à flamme nue servant d'une part à réchauffer rapidement la bande métallique à traiter à une température typiquement comprise entre 400° C et 700° C, et d'autre part à soumettre à une pyrolyse les huiles de laminage présentes sur la surface de la bande.We know galvanizing lines in which the area preheating includes an oven with open flame burners serving on the one hand to rapidly reheat the metal strip to be treated at a temperature typically between 400 ° C and 700 ° C, and on the other hand subject the laminating oils present on the surface to pyrolysis the band.

Pour prévenir une oxydation de la bande métallique ainsi traitée, on fait fonctionner les brûleurs en défaut d'air pour assurer une atmosphère non oxydante vis-à-vis du fer. To prevent oxidation of the metal strip thus treated, the burners are operated in the absence of air to ensure an atmosphere non-oxidizing towards iron.

Pour pouvoir assurer une bonne galvanisation c'est à dire notamment une bonne adhérence entre couche et bande métallique, il est indispensable d'éliminer toute couche d'oxyde en surface avant de plonger la bande métallique dans le bain de zinc. Ceci est réalisé en exposant la bande métallique dans le four de recuit à une atmosphère réductrice constituée le plus souvent d'un mélange d'azote et d'hydrogène, la teneur en hydrogène étant en général comprise entre 15% et 40%.To be able to ensure good galvanization, that is to say in particular good adhesion between layer and metal strip, it is essential to remove any oxide layer on the surface before immersing the metal strip in the zinc bath. This is achieved by exposing the tape metal in the annealing furnace to a reducing atmosphere constituted the more often a mixture of nitrogen and hydrogen, the hydrogen content being generally between 15% and 40%.

A cet effet, les différentes zones de traitement de la ligne de galvanisation sont reliées les unes aux autres par des conduits pour former une gaine de circulation de l'atmosphère réductrice.For this purpose, the different processing areas of the line galvanization are connected to each other by conduits to form a duct for circulating the reducing atmosphere.

Pour régénérer constamment cette atmosphère réductrice dans cette gaine et conserver ainsi son caractère réducteur, le mélange d'azote et d'hydrogène est injecté dans un conduit également appelé trompe ou cloche dont une extrémité plonge dans le bain de zinc et dont l'autre extrémité est raccordée à l'extrémité de sortie du poste de refroidissement, de sorte que l'atmosphère réductrice circule en sens opposé au sens de défilement de la bande métallique à traiter.To constantly regenerate this reducing atmosphere in this sheath and thus retain its reducing nature, the mixture of nitrogen and hydrogen is injected into a pipe also called a horn or bell one end of which is immersed in the zinc bath and the other end of which is connected to the outlet end of the cooling station, so that the reducing atmosphere circulates in the opposite direction to the direction of travel of the metal strip to be treated.

A l'heure actuelle, pour une ligne de galvanisation donnée, le débit du mélange d'azote et d'hydrogène et la teneur en hydrogène de ce mélange sont maintenus à un même niveau, indépendamment des caractéristiques et de la vitesse de défilement des bandes métalliques à traiter.At present, for a given galvanizing line, the flow rate of the nitrogen and hydrogen mixture and the hydrogen content of this mixture are maintained at the same level, regardless of characteristics and running speed of the metal strips at treat.

En pratique, pour permettre aussi bien le traitement de bandes métalliques de grande largeur que celles présentant une petite largeur, pour accommoder tant les faibles vitesses de défilement que les vitesses élevées, le débit du mélange d'azote et d'hydrogène et la teneur en hydrogène de ce mélange sont fixés à un niveau élevé de façon à permettre le traitement même des cas les plus défavorables, c'est-à-dire les bandes métalliques de grandes dimensions surfaciques et/ou traitées à des vitesses élevées. Mais on le conçoit, cet excès de qualité que représente un mélange riche en hydrogène injecté à un débit élevé entraíne un coût non négligeable pour cette atmosphère réductrice. D'autre part les conditions d'injection d'atmosphère étant fixées, alors que la surface a traiter par unité de temps peut varier, la production de vapeur d'eau dans l'enceinte du fait de la réduction des oxydes va bel et bien faire varier le caractère réducteur de l'atmosphère et donc entraíner des variations de qualité du produit final.In practice, to allow both processing of tapes of larger width than those with a small width, for accommodate both low and high frame speeds, the flow rate of the nitrogen and hydrogen mixture and the hydrogen content of this mixture are set at a high level so as to allow treatment even the most unfavorable cases, i.e. the metal strips of large surface dimensions and / or treated at high speeds. But as we can see, this excess of quality represented by a mixture rich in hydrogen injected at a high rate entails a significant cost for this reducing atmosphere. On the other hand, the injection conditions of atmosphere being fixed, while the surface to be treated per unit of time may vary, the production of water vapor in the enclosure due to the reduction of oxides will indeed vary the reducing nature of the atmosphere and therefore lead to variations in the quality of the final product.

L'invention vise à proposer un procédé permettant d'optimiser l'utilisation de l'atmosphère réductrice en vue de réduire le coût engendré par celle-ci dans l'exploitation de la ligne de galvanisation ainsi que mieux maintenir le niveau de qualité des produits qui sortent de la ligne.The invention aims to propose a method for optimizing the use of the reducing atmosphere in order to reduce the cost generated by this in the operation of the galvanizing line as well as better maintain the level of quality of products coming out of the line.

A cet effet, l'invention a pour objet un procédé de galvanisation d'une bande métallique dans une ligne de galvanisation en continu, la ligne de galvanisation comprenant, disposés en série et reliés les uns aux autres par des conduits pour former une gaine continue de circulation d'une atmosphère réductrice comportant un gaz inerte et de l'hydrogène, un four de préchauffage, un four de recuit, un poste de refroidissement et un poste de trempe de ladite bande métallique dans un bain de zinc liquide ou d'un alliage de zinc liquide, dans lequel, avant de plonger la bande métallique dans le bain, on l'expose à cette atmosphère réductrice pour éliminer des oxydes présents sur sa surface, caractérisé en ce que pour renouveler l'atmosphère réductrice dans ladite gaine, on y injecte le gaz inerte et l'hydrogène en réglant le débit d'hydrogène en fonction de la quantité de surface de bande métallique à traiter par unité de temps.To this end, the invention relates to a galvanizing process of a metal strip in a continuous galvanizing line, the line of galvanizing comprising, arranged in series and connected to each other by conduits to form a continuous circulation sheath of a reducing atmosphere comprising an inert gas and hydrogen, a preheating, an annealing furnace, a cooling station and a soaking said metal strip in a bath of liquid zinc or a liquid zinc alloy, in which, before plunging the metal strip in the bath, it is exposed to this reducing atmosphere to eliminate oxides present on its surface, characterized in that to renew the reducing atmosphere in said sheath, the inert gas is injected therein and hydrogen by adjusting the flow of hydrogen according to the amount of metal strip surface to be treated per unit of time.

Le procédé selon l'invention peut de plus comporter une ou plusieurs des caractéristiques suivantes :

  • on détermine la quantité de surface de bande métallique à traiter par unité de temps à partir de la largeur de la bande métallique à traiter et à partir de la vitesse de défilement de celle-ci dans la ligne de galvanisation ;
  • on maintient, en au moins un point de ladite gaine, le rapport entre la concentration d'hydrogène et la concentration en vapeur d'eau de l'atmosphère , sensiblement à un niveau prédéfini ;
  • on maintient ledit rapport à un niveau prédéfini en au moins un point du four de recuit ;
  • on injecte le gaz inerte au niveau d'un premier emplacement dans ladite gaine, et de l'hydrogène ou bien un mélange gaz inerte/hydrogène au niveau d'un second emplacement distant du premier emplacement et plus éloigné du bain liquide dudit poste de trempe ;
  • on injecte le gaz inerte, et l'hydrogène ou le mélange gaz inerte/hydrogène, dans le conduit de raccordement dudit poste de refroidissement audit poste de trempe ;
  • on fixe le débit de gaz inerte injecté dans la gaine au niveau du premier emplacement, et on règle le débit d'hydrogène ou de mélange gaz inerte/hydrogène injecté au niveau du second emplacement, en fonction d'une valeur de consigne de teneur en vapeur d'eau au niveau d'un point du four de recuit ;
  • on fixe le débit de gaz inerte injecté dans la gaine au niveau du premier emplacement, et on règle le débit d'hydrogène ou de mélange gaz inerte/hydrogène injecté au niveau du second emplacement, de façon à effectuer ledit maintient en au moins un point du four de recuit dudit rapport entre la concentration d'hydrogène et la concentration en vapeur d'eau de l'atmosphère sensiblement audit niveau prédéfini ;
  • on règle le débit de gaz inerte injecté dans la gaine au niveau du premier emplacement, en fonction d'une valeur de consigne de teneur en vapeur d'eau au niveau d'un point du four de recuit ;
  • on règle le débit de gaz inerte injecté dans la gaine au niveau du premier emplacement, de façon à effectuer ledit maintient en au moins un point du four de recuit dudit rapport entre la concentration d'hydrogène et la concentration en vapeur d'eau de l'atmosphère sensiblement audit niveau prédéfini ;
  • on injecte le gaz inerte dans la gaine au niveau du premier emplacement à débit sensiblement constant, et on injecte en outre du gaz inerte dans le four de recuit, le débit de gaz inerte injecté dans le four de recuit étant réglé en fonction d'une valeur de consigne de teneur en vapeur d'eau au niveau d'un point du four de recuit ;
  • on injecte le gaz inerte dans la gaine au niveau du premier emplacement à débit sensiblement constant, et on injecte en outre du gaz inerte dans le four de recuit, le débit de gaz inerte injecté dans le four de recuit étant réglé de façon à effectuer ledit maintient en au moins un point du four de recuit, dudit rapport entre la concentration d'hydrogène et la concentration en vapeur d'eau de l'atmosphère sensiblement audit niveau prédéfini.
The method according to the invention can also include one or more of the following characteristics:
  • the quantity of metal strip surface to be treated per unit of time is determined from the width of the metal strip to be treated and from the running speed of the latter in the galvanizing line;
  • maintaining, at at least one point of said sheath, the ratio between the concentration of hydrogen and the concentration of water vapor in the atmosphere, substantially at a predefined level;
  • said ratio is maintained at a predefined level at at least one point in the annealing furnace;
  • the inert gas is injected at a first location in said sheath, and hydrogen or else an inert gas / hydrogen mixture at a second location distant from the first location and further from the liquid bath of said quenching station ;
  • the inert gas, and the hydrogen or the inert gas / hydrogen mixture, are injected into the conduit connecting said cooling station to said quenching station;
  • the flow rate of inert gas injected into the sheath is fixed at the first location, and the flow rate of hydrogen or of inert gas / hydrogen mixture injected at the second location is adjusted, as a function of a setpoint value of steam at a point in the annealing furnace;
  • the flow rate of inert gas injected into the sheath is fixed at the first location, and the flow rate of hydrogen or of inert gas / hydrogen mixture injected is adjusted at the second location, so as to carry out said maintenance at at least one point the annealing furnace of said ratio between the hydrogen concentration and the water vapor concentration of the atmosphere substantially at said predefined level;
  • the flow rate of inert gas injected into the sheath is adjusted at the first location, as a function of a set point of water vapor content at a point in the annealing furnace;
  • the flow rate of inert gas injected into the sheath is adjusted at the first location, so as to effect said maintenance at at least one point in the annealing furnace of said ratio between the concentration of hydrogen and the concentration of water vapor of l 'atmosphere substantially at said predefined level;
  • the inert gas is injected into the sheath at the first location at a substantially constant flow rate, and the inert gas is further injected into the annealing furnace, the flow rate of inert gas injected into the annealing furnace being adjusted according to a setpoint for water vapor content at a point in the annealing furnace;
  • the inert gas is injected into the sheath at the first location at a substantially constant flow rate, and the inert gas is further injected into the annealing furnace, the flow rate of inert gas injected into the annealing furnace being adjusted so as to effect the said maintains at least one point in the annealing furnace, said ratio between the concentration of hydrogen and the concentration of water vapor in the atmosphere substantially at said predefined level.

D'autres caractéristiques et avantages de l'invention ressortiront de la description suivante, donnée à titre d'exemple, sans caractère limitatif, en regard des dessins annexés sur lesquels :

  • la figure 1 est une représentation schématique d'une ligne de galvanisation en continu fonctionnant selon un procédé conforme à l'invention ;
  • la figure 2 montre une courbe représentant l'évolution du logarithme du rapport de la teneur en vapeur d'eau sur la teneur en hydrogène de l'atmosphère en un point du four de recuit, en fonction de la surface de bande métallique traitée, ceci pour un réglage d'atmosphère donné.
Other characteristics and advantages of the invention will emerge from the following description, given by way of example, without limitation, with reference to the appended drawings in which:
  • Figure 1 is a schematic representation of a continuous galvanizing line operating according to a method according to the invention;
  • FIG. 2 shows a curve representing the evolution of the logarithm of the ratio of the water vapor content to the hydrogen content of the atmosphere at a point in the annealing furnace, as a function of the surface of the metal strip treated, this for a given atmosphere setting.

Sur la figure 1 est représentée de façon schématique une ligne 1 de galvanisation d'une bande métallique 3, par exemple en acier.In Figure 1 is shown schematically a line 1 for galvanizing a metal strip 3, for example steel.

La ligne de galvanisation 1 comprend, disposés en série, un four 5 de préchauffage, un four 7 de recuit, un poste 9 de refroidissement et un poste 11 de trempe comprenant un bain 13 de zinc liquide ou d'alliage liquide.The galvanizing line 1 comprises, arranged in series, an oven 5 preheating, an annealing oven 7, a cooling station 9 and a quenching station 11 comprising a bath 13 of liquid zinc or of alloy liquid.

Le four 5 de préchauffage est par exemple équipé de brûleurs 15 à flamme nue servant d'une part à réchauffer rapidement la bande métallique 3 à traiter, à une température typiquement comprise entre 400° C et 700° C, et d'autre part à soumettre à une pyrolyse les huiles de laminage présentes sur la surface de la bande.The preheating oven 5 is for example equipped with burners 15 with an open flame used on the one hand to quickly heat the metal strip 3 to be treated, at a temperature typically between 400 ° C. and 700 ° C., and on the other hand to subject to a pyrolysis the rolling oils present on the surface of the strip.

Le four 7 de recuit est par exemple équipé de résistances électriques ou de tubes radiants schématisés en 8.The annealing furnace 7 is for example equipped with resistors electric or radiant tubes diagrammed in 8.

Le poste 9 de refroidissement sert à refroidir la bande métallique 3 en sortie du four 7 de recuit, à une valeur par exemple proche de 470°C.The cooling station 9 is used to cool the metal strip 3 at the outlet of the annealing oven 7, at a value for example close to 470 ° C.

Par ailleurs, le four 5 de préchauffage, le four 7 de recuit, le poste 9 de refroidissement et le poste 11 de trempe, qui ont chacun une forme de tunnel, sont reliés les uns aux autres par des conduits 17, 19 et 21 pour former avec ceux-ci une gaine continue 23 de circulation d'une atmosphère réductrice essentiellement composée d'azote et d'hydrogène.Furthermore, the preheating oven 5, the annealing oven 7, the station 9 cooling and the station 11 quenching, which each have a form of tunnel, are connected to each other by conduits 17, 19 and 21 for forming with them a continuous sheath 23 of circulation of an atmosphere reducing essentially composed of nitrogen and hydrogen.

De plus, le conduit 21 reliant l'extrémité de sortie du poste 9 de refroidissement au poste 11 de trempe est incliné vers le bas et plonge avec son extrémité 25 dans le bain liquide 13. Ce conduit 21 est souvent appelé trompe ou cloche.In addition, the conduit 21 connecting the outlet end of the station 9 of cooling at quenching station 11 is tilted down and plunges with its end 25 in the liquid bath 13. This conduit 21 is often called horn or bell.

En outre, la ligne de galvanisation 1 comprend selon l'invention, d'une part, un injecteur 30 d'un gaz inerte, par exemple d'azote, disposé dans la paroi de la trompe 21 au niveau d'un premier emplacement 30A situé au voisinage de l'extrémité 25 de la trompe plongée dans le bain liquide 13, au dessus de celui-ci, et d'autre part, un injecteur d'hydrogène 31 (ou d'un mélange d'hydrogène et d'un gaz inerte) disposé dans la paroi de la trompe 21 au niveau d'un second emplacement 31A situé au voisinage de l'extrémité 33 de celle-ci qui est raccordée au poste 9 de refroidissement.In addition, the galvanizing line 1 comprises according to the invention, on the one hand, an injector 30 of an inert gas, for example nitrogen, arranged in the wall of the tube 21 at a first location 30A located at near the end 25 of the tube immersed in the liquid bath 13, at above it, and on the other hand, a hydrogen injector 31 (or a mixture of hydrogen and an inert gas) arranged in the wall of the proboscis 21 at a second location 31A located near the end 33 thereof which is connected to the cooling station 9.

Cette disposition avantageuse où l'azote est injecté au niveau du premier emplacement 30A qui se trouve à proximité de l'extrémité 25 de la trompe 21 plongée dans le bain de liquide 13, permet dans la partie inférieure de la trompe 21 de former un tampon qui empêche l'hydrogène injecté à distance au niveau de l'emplacement 31A de se dissoudre dans le bain de zinc liquide 13.This advantageous arrangement where nitrogen is injected at the level of the first location 30A which is near the end 25 of the horn 21 immersed in the liquid bath 13, allows in the lower part of the tube 21 to form a buffer which prevents the hydrogen injected into distance from location 31A to dissolve in the bath liquid zinc 13.

Comme on peut le constater à la lecture de la figure, l'injecteur 30 est relié à un conduit d'alimentation 32 dans lequel est disposé un organe 34 de régulation de débit et l'injecteur 31 est relié à un conduit d'alimentation 36 dans lequel est disposé un organe 38 de régulation de débit.As can be seen from the figure, the injector 30 is connected to a supply conduit 32 in which is arranged a member 34 regulating flow and the injector 31 is connected to a supply conduit 36 in which is arranged a flow regulating member 38.

En outre, la ligne 1 comprend des moyens 40 de détermination et de réglage de la vitesse de défilement de la bande métallique 3.In addition, line 1 includes means 40 for determining and for adjusting the running speed of the metal strip 3.

Par ailleurs, une prise d'échantillon de gaz 42 à l'intérieur du four de recuit, par exemple en milieu de four ou encore dans le dernier 1/3 du four, permet de renvoyer des prélèvements d'atmosphère à des fins d'analyse, par exemple comme représenté sur la figure vers un analyseur 47 de la teneur en hydrogène du prélèvement, et vers un analyseur 46 de la teneur en vapeur d'eau du prélèvement.Furthermore, a gas sample point 42 inside the oven annealing, for example in the middle of the oven or in the last 1/3 of the oven, used to return atmospheric samples for analysis, for example as shown in the figure to an analyzer 47 of the hydrogen content of the sample, and to an analyzer 46 of the water vapor content of the sample.

Bien entendu, en lieu et place de cette analyse ex-situ, on pourrait également sans sortir du cadre de la présente invention, utiliser une sonde à oxygène dans le four, sonde qui délivre un potentiel corrélé au rapport H2/H2O.Of course, instead of this ex-situ analysis, it could also without departing from the scope of the present invention, use an oxygen probe in the oven, probe which delivers a potential correlated to the H 2 / H 2 O ratio.

Les moyens 40, ainsi que les analyseurs 46 et 47, sont reliés à une unité 50 de traitement de données (par exemple un automate programmable), unité apte à son tour à commander le fonctionnement des deux régulateurs de débit 34 et 38.The means 40, as well as the analyzers 46 and 47, are connected to a data processing unit 50 (for example an automaton programmable), unit in turn able to control the operation of two flow regulators 34 and 38.

Lors de son traitement, la bande métallique 3 guidée par des rouleaux 27 passe successivement dans le four 5 de préchauffage pour être amenée à une température située ici entre 400°C et 700°C, puis dans le four 7 de recuit pour assurer ses caractéristiques métallurgiques, dans le poste 9 de refroidissement pour être amenée à une température proche de 470°C et enfin dans le poste 11 de trempe afin d'être recouverte de zinc. During its treatment, the metal strip 3 guided by rollers 27 pass successively into the preheating oven 5 to be brought to a temperature here between 400 ° C and 700 ° C, then in the oven 7 annealing to ensure its metallurgical characteristics, in station 9 cooling to be brought to a temperature close to 470 ° C and finally in the quenching station 11 so as to be covered with zinc.

En même temps, l'unité 50 relève comme décrit précédemment, la vitesse de défilement de la bande métallique 3, le point de rosée ainsi que la teneur en hydrogène de l'atmosphère en au moins un point (42) du four 7 de recuit, et commande par l'intermédiaire des régulateurs 34 et 38 les débits d'azote et/ou d'hydrogène injectés dans la trompe 21, en conformité avec l'un des modes de mise en oeuvre de l'invention décrits plus haut dans la présente description.At the same time, the unit 50 falls as described above, the running speed of the metal strip 3, the dew point and the hydrogen content of the atmosphere in at least one point (42) of the furnace 7 of annealing and controlling the flow rates via regulators 34 and 38 nitrogen and / or hydrogen injected into the tube 21, in accordance with one of the embodiments of the invention described above in the present description.

L'unité 50 règle ces débits d'azote et d'hydrogène en fonction de la quantité de surface de la bande métallique à traiter par unité de temps.Unit 50 regulates these nitrogen and hydrogen flow rates as a function of the amount of surface of the metal strip to be treated per unit of time.

Avantageusement, pour déterminer la quantité de surface de la bande métallique à traiter par unité de temps, on prend en compte la vitesse de défilement de la bande dans la ligne fournie par les moyens 40, et la largeur de la bande 3.Advantageously, to determine the amount of surface of the metal strip to be treated per unit of time, the speed is taken into account of running of the strip in the line supplied by the means 40, and the strip width 3.

Afin d'illustrer plus clairement cette notion de réglage des débits en fonction de la quantité de surface de la bande métallique à traiter par unité de temps (facteur que l'on évalue en ne considérant qu'une face de la bande), considérons la courbe présentée figure 2, qui a été obtenue pour un acier donné ayant une application dans l'industrie du bâtiment, dans les conditions suivantes

  • injection en 30A: de l'azote d'origine cryogénique, à un débit de 50 Nm3/h; injection en 31A: de l'ammoniac craqué, à un débit de 70 Nm3/h (de telles conditions donnent donc globalement un débit de mélange de 120 Nm3/h, un débit d'hydrogène de 52,5 Nm3/h, et une concentration d'hydrogène dans le mélange de 43,8%) ;
  • le point de prélèvement d'atmosphère (42) était situé à environ 1m de la fin du four de recuit (en considérant le sens de déplacement de la bande) ;
  • la vitesse de la ligne était comprise entre 25 et 80 m/min, pour une largeur de bande toujours comprise dans l'intervalle allant de 1m à 1,20m.
In order to illustrate more clearly this notion of adjusting the flow rates as a function of the quantity of surface of the metal strip to be treated per unit of time (factor which is evaluated by considering only one face of the strip), let us consider the curve shown in Figure 2, which was obtained for a given steel having an application in the building industry, under the following conditions
  • injection in 30A: nitrogen of cryogenic origin, at a flow rate of 50 Nm 3 / h; injection in 31A: cracked ammonia, at a flow rate of 70 Nm 3 / h (such conditions therefore generally give a mixing flow of 120 Nm 3 / h, a hydrogen flow of 52.5 Nm 3 / h , and a hydrogen concentration in the mixture of 43.8%);
  • the atmospheric sampling point (42) was located approximately 1m from the end of the annealing furnace (considering the direction of movement of the strip);
  • the line speed was between 25 and 80 m / min, for a bandwidth always in the range from 1m to 1.20m.

On voit bien alors sur cette figure l'augmentation du rapport H2O/H2 dans le four de recuit lorsque la surface traitée par unité de temps (S/t) croit, signe d'une production croissante de vapeur d'eau. On constate donc qu'il est possible sur cette courbe de définir pour cette ligne de galvanisation et ce réglage moyen de gaz qui a été mis en oeuvre, deux grands domaines de surface traitée par unité de temps : un domaine où S/t est inférieur à environ 50m2/min, et un domaine où S/t est compris entre environ 50m2/min et 90m2/min.We can therefore clearly see in this figure the increase in the H 2 O / H 2 ratio in the annealing furnace when the surface treated per unit of time (S / t) increases, a sign of an increasing production of water vapor. We therefore see that it is possible on this curve to define for this galvanizing line and this average gas adjustment which has been implemented, two large areas of surface treated per unit of time: a field where S / t is less at around 50m 2 / min, and an area where S / t is between around 50m 2 / min and 90m 2 / min.

Il apparaít alors avantageux pour des conditions de production correspondant au premier domaine, de diminuer le débit d'hydrogène injecté en 31 et/ou la teneur en hydrogène du mélange, en se permettant ainsi de dégrader légèrement le rapport H2O/H2 en ramenant le point de rosée de l'atmosphère autour de -15°C, alors que pour des conditions de production correspondant au second domaine, il serait avantageux d'améliorer le point de rosée de l'atmosphère (diminution du rapport H2O/H2) en augmentant le débit d'hydrogène injecté en 31 etlou la teneur en hydrogène du mélange, et permettre ainsi au point de rosée de l'atmosphère de descendre au voisinage de -15 à -20°C, compte tenu de l'acier traité sur cette ligne.It then appears advantageous for production conditions corresponding to the first field, to reduce the flow of hydrogen injected at 31 and / or the hydrogen content of the mixture, thereby allowing to slightly degrade the H 2 O / H 2 ratio. bringing the dew point of the atmosphere around -15 ° C, while for production conditions corresponding to the second domain, it would be advantageous to improve the dew point of the atmosphere (decrease in the H 2 O / H 2 ) by increasing the flow rate of hydrogen injected at 31 and / or the hydrogen content of the mixture, and thus allow the dew point of the atmosphere to descend in the vicinity of -15 to -20 ° C, taking into account the steel treated on this line.

On peut alors proposer pour chacun des domaines les conditions suivantes :

  • pour le domaine où S/t est inférieur à environ 50m2/min : un débit de mélange N2/H2 de 130 Nm3/h, pour un débit d'hydrogène de 27 Nm3/h, et une concentration d'hydrogène dans le mélange de 20,7% ;
  • pour le domaine où S/t est compris entre environ 50m2/min et 90m2/min : un débit de mélange N2/H2 de 150 Nm3/h, pour un débit d'hydrogène de 48,5 Nm3/h, et une concentration d'hydrogène dans le mélange de 32,3%
The following conditions can then be proposed for each of the fields:
  • for the area where S / t is less than about 50m 2 / min: a N2 / H2 mixture flow rate of 130 Nm 3 / h, for a hydrogen flow rate of 27 Nm 3 / h, and a hydrogen concentration in the mixture of 20.7%;
  • for the area where S / t is between approximately 50m 2 / min and 90m 2 / min: an N2 / H2 mixture flow rate of 150 Nm 3 / h, for a hydrogen flow rate of 48.5 Nm 3 / h, and a hydrogen concentration in the mixture of 32.3%

L'ensemble permettant de maintenir constant le débit d'hydrogène rapporté à S/t, à une valeur voisine de 0,009 m3 d'hydrogène par m2 de bande. The assembly making it possible to keep the hydrogen flow rate constant at S / t constant, at a value close to 0.009 m 3 of hydrogen per m 2 of strip.

La figure 2 illustre donc un exemple d'abaques qu'il est possible de réaliser sur une ligne donnée, pour un ou plusieurs aciers traité(s), en adoptant un réglage de gaz moyen, et en balayant une gamme typique de variation de la surface traitée par unité de temps (qui tient compte de la gamme de vitesse de ligne habituellement pratiquée, et de la gamme de largeurs de produits traités sur la ligne considérée), la lecture de ces abaques permettant de déterminer les modifications des réglages d'alimentation en gaz qu'il est avantageux d'adopter dans chaque cas.Figure 2 therefore illustrates an example of abacuses that it is possible to carry out on a given line, for one or more steels treated, in adopting a medium gas setting, and sweeping a typical range of variation of the surface treated per unit of time (which takes into account the range of line speed usually practiced, and the range of widths of products treated on the line considered), reading these charts for determining changes in settings gas supply which it is advantageous to adopt in each case.

On a décrit dans ce qui précède un mode de réalisation où le débit d'azote injecté par l'intermédiaire de l'injecteur 30 est maintenu constant lors du fonctionnement de la ligne de galvanisation et seul le débit d'hydrogène en 31 est réglé et modifié en fonction de la quantité de surface de bande métallique à traiter.We have described in the above an embodiment where the flow rate of nitrogen injected via injector 30 is kept constant during operation of the galvanizing line and only the flow of hydrogen at 31 is adjusted and modified according to the amount of surface of metal strip to be treated.

Mais on conçoit que selon le cas considéré (amélioration ou dégradation du point de rosée de l'atmosphère), l'on puisse également ou en remplacement agir sur l'injection de gaz inerte au point 30A.But we can see that depending on the case considered (improvement or degradation of the dew point of the atmosphere), we can also or by replacement act on the injection of inert gas at point 30A.

Selon une autre variante du procédé selon l'invention, on réalise un zonage en hydrogène de la zone de refroidissement, en injectant, outre de l'azote dans la gaine 23 au niveau du premier emplacement 30A à un débit sensiblement constant, et l'hydrogène au niveau de l'emplacement 31A, de l'azote dans le four 7 de recuit, de préférence dans la dernière portion de sortie de celui-ci. Et dans ce cas de figure, on peut régler le débit d'azote injecté dans le four 7 de recuit en fonction d'une valeur de consigne du point de rosée au niveau de ce four.According to another variant of the method according to the invention, one realizes hydrogen zoning of the cooling zone, by injecting, in addition nitrogen in the sheath 23 at the first location 30A at a substantially constant flow, and the hydrogen at location 31A, nitrogen in the annealing oven 7, preferably in the last portion of exit from it. And in this case, we can adjust the nitrogen flow injected into the annealing furnace 7 as a function of a set point value dew at this oven.

Cette disposition permet d'une part d'élever localement la concentration d'hydrogène au niveau du poste 9 de refroidissement, protégeant ainsi la surface de la bande contre une oxydation avant d'être plongée dans le bain de zinc 13, et d'autre part de contribuer au refroidissement de la bande 3. This provision allows on the one hand to locally raise the hydrogen concentration at cooling station 9, thus protecting the surface of the strip against oxidation before being immersed in the zinc bath 13, and on the other hand to contribute to the belt cooling 3.

On voit donc que selon ses multiples mode de mise en oeuvre, le procédé de l'invention permet non seulement de réduire la consommation d'hydrogène et ainsi le coût d'exploitation pour régénérer l'atmosphère réductrice, mais d'autre part d'obtenir plus sûrement et dans des conditions économiques qui ne soient pas la simple mise en place d'un excès de qualité d'atmosphère, une constance des caractéristiques des produits que sort la ligne de galvanisation.We therefore see that according to its multiple modes of implementation, the process of the invention not only reduces consumption of hydrogen and thus the operating cost to regenerate the atmosphere reductive but on the other hand to get more surely and under conditions that are not the simple implementation of an excess of quality consistency of the characteristics of the products released by the galvanizing line.

Claims (13)

  1. Process for galvanizing a metal strip (3) in a continuous galvanizing line (1), the galvanizing line (1) comprising, placed in series and connected to each other by ducts (17, 19, 21) in order to form continuous ducting (23) for circulating a reducing atmosphere which comprises an inert gas and hydrogen, a preheat furnace (5), an annealing furnace (7), a cooling station (9) and a station (11) for dipping the said metal strip into a bath (13) of liquid zinc or of a liquid zinc alloy, in which process, before the metal strip (3) is dipped into the bath (13), it is exposed to this reducing atmosphere in order to remove oxides present on its surface, characterized in that, in order to replenish the reducing atmosphere in the said ducting (23), the inert gas and the hydrogen are injected into it by using means (34, 38) allowing the hydrogen flow rate to be adjusted depending on the area of the metal strip to be treated per unit time, in order thus to optimize the use of the reducing atmosphere during changes of strip width and/or of strip run speed during the galvanizing process.
  2. Process according to Claim 1, characterized in that the area of metal strip to be treated per unit time is determined from the width of the metal strip (3) to be treated and from the speed at which the latter runs through the galvanizing line (1).
  3. Process according to Claim 1 or 2, characterized in that the ratio of the hydrogen concentration to the water vapour concentration of the atmosphere is maintained, at least at one point in the said ducting (23), substantially at a predefined level.
  4. Process according to Claim 3, characterized in that the said ratio is maintained at a predefined level at least at one point in the annealing furnace.
  5. Process according to one of the preceding claims, characterized in that the inert gas is injected at a first location (30A) into the said ducting (23) and hydrogen, or an inert-gas/hydrogen mixture, is injected at a second location (31A) a certain distance from the first location (30A) and further away from the liquid bath (13) of the said dipping station (11).
  6. Process according to Claim 5, characterized in that the inert gas and the hydrogen, or the hydrogen inert-gas mixture, are/is injected into the duct (21) which connects the said cooling station (9) to the said dipping station (11).
  7. Process according to Claim 5 or 6, characterized in that the flow rate of inert gas injected into the ducting (23) at the first location (30A) is fixed and in that the flow rate of hydrogen or of mixture injected at the second location (31A) is adjusted depending on a set-point value of the water vapour content at a point in the annealing furnace (7).
  8. Process according to Claim 5 or 6 in its dependence on Claim 4, characterized in that the flow rate of inert gas injected into the ducting (23) at the first location (30A) is fixed and in that the flow rate of hydrogen or of mixture injected at the second location (31A) is adjusted so as to carry out the said operation of maintaining, at least at one point in the annealing furnace, the said ratio of the hydrogen concentration to the water vapour concentration of the atmosphere substantially at the said predefined level.
  9. Process according to Claim 5 or 6, characterized in that the flow rate of inert gas injected into the ducting (23) at the first location (30A) is adjusted depending on a set-point value of the water vapour content at a point in the annealing furnace (7).
  10. Process according to Claim 5 or 6, in its dependence on Claim 4, characterized in that the flow rate of inert gas injected into the ducting (23) at the first location (30A) is adjusted so as to carry out the said operation of maintaining, at least at one point in the annealing furnace, the said ratio of the hydrogen concentration to the water vapour concentration of the atmosphere substantially at the said predefined level.
  11. Process according to Claim 6, characterized in that the inert gas is injected into the ducting (23) at the first location (30A) at a substantially constant flow rate and in that inert gas is also injected into the annealing furnace (7), the flow rate of inert gas injected into the annealing furnace (7) being adjusted depending on a set-point value of the water vapour content at a point in the annealing furnace (7).
  12. Process according to Claim 6, in its dependence on Claim 4, characterized in that the inert gas is injected into the ducting (23) at the first location (30A) at a substantially constant flow rate and in that inert gas is also injected into the annealing furnace (7), the flow rate of inert gas injected into the annealing furnace (7) being adjusted so as to carry out the said operation of maintaining, at least at one point in the annealing furnace, the said ratio of the hydrogen concentration to the water vapour concentration of the atmosphere substantially at the said predefined level.
  13. Process according to one of the preceding claims, characterized in that the said inert gas is nitrogen.
EP99401700A 1998-08-13 1999-07-07 Method for the galvanization of metallic strip Expired - Lifetime EP0979879B1 (en)

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FR9810392 1998-08-13
FR9810392A FR2782326B1 (en) 1998-08-13 1998-08-13 METHOD FOR GALVANIZING A METAL STRIP

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FR2782326A1 (en) 2000-02-18
DE69912698T2 (en) 2004-09-23
EP0979879A1 (en) 2000-02-16
DE69912698D1 (en) 2003-12-18
FR2782326B1 (en) 2000-09-15
AR020168A1 (en) 2002-04-10
US6224692B1 (en) 2001-05-01
JP2000064006A (en) 2000-02-29
CA2280405A1 (en) 2000-02-13
ATE254190T1 (en) 2003-11-15
ES2211006T3 (en) 2004-07-01

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