EP1134298B1 - Improvements in preheating metal strips, especially in galvanising or annealing lines - Google Patents

Improvements in preheating metal strips, especially in galvanising or annealing lines Download PDF

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Publication number
EP1134298B1
EP1134298B1 EP01400142A EP01400142A EP1134298B1 EP 1134298 B1 EP1134298 B1 EP 1134298B1 EP 01400142 A EP01400142 A EP 01400142A EP 01400142 A EP01400142 A EP 01400142A EP 1134298 B1 EP1134298 B1 EP 1134298B1
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European Patent Office
Prior art keywords
zone
preheating
burners
length
temperature
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EP01400142A
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German (de)
French (fr)
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EP1134298A1 (en
Inventor
Didier Delaunay
Alain Morel
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Fives Stein SA
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Stein Heurtey 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
    • C23C2/02—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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/52—Methods of heating with flames
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • 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
    • C23C2/34—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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments

Definitions

  • the present invention relates to improvements made to the preheating of metal strips, especially steel strips, in direct fire preheating sections, installed in particular at the inlet of the dip galvanizing lines or in annealing lines.
  • the preheating is carried out according to several zones whose temperature regulation is independent, generally according to four zones for the lines of high capacity and following two zones for the lines of weak capacity, each of these zones being provided, for example, with four to six burners on each side of the furnace.
  • the galvanized or annealed strips in the continuous lines have varying shades, widths or thicknesses and they also scroll to variable speeds, which conditions the heat demand of the zones of the oven which can vary in important proportions.
  • variable speeds which conditions the heat demand of the zones of the oven which can vary in important proportions.
  • only a small number of these preheating zones are generally used, stopping the first zones in the direction of advancement of the zone. band, or keeping them at a minimum thermal regime, equivalent to about 15 to 20% of their rated power.
  • FIG. 1 of the accompanying drawings schematically shows, in side elevation, an exemplary embodiment of a preheating installation comprising two zones of preheating.
  • FIG. 1A associates FIG. 1A, which represents the heating power used in the two preheating zones and the variation curve of the temperature of the strip in said zones.
  • the preheating installation of the strip 1 comprises two preheating zones 2 and 3. Each of these zones is equipped with burners 4 supplied with combustion air by a manifold 5 and with fuel by a manifold 7
  • the power injected into each zone is controlled by combustion and fuel flow control valves 6 and 8, respectively.
  • the heating power represented by the shaded area of the graph of FIG. 1A corresponds to 60% of the nominal power of the second zone 3, the first zone 1 operates at least its power, for example 15%.
  • Curve 9 shows the temperature rise of the strip in the preheating zones. Under these conditions, the gas and wall temperature of the second preheating zone 3 stabilizes at low levels, of the order of 1150 ° C or lower.
  • the oxidation formed on the surface of the strip under these conditions must be eliminated, which requires the establishment, downstream of the zone of the preheat, of a holding zone, under an atmosphere containing hydrogen, long enough to suppress the oxides formed by reduction.
  • This reduction must be carried out at high temperature, which generally requires reheating of the strip to levels which are often only achieved with the aim of obtaining this reduction, whereas they are not necessary for the metallurgical treatment of the mixture. steel grade of the band.
  • the object of the present invention is to solve the above-mentioned technical problem by providing a novel process and an improved furnace for heating webs in direct fire preheat sections with limited oxidation for all production configurations (line speed, processing characteristics, product characteristics including shade and format).
  • this invention in addition to improving the quality of the finished product that it provides, solves the problem of congestion of the installations, encountered in the prior state of the art mentioned above, since its implementation This work makes it possible to limit the dimensions and consequently the costs of the annealing or galvanizing lines to which it is applied.
  • this invention relates first of all to a method for reheating metal strips, in particular steel in direct fire preheating sections, in order to limit the oxidation of the heated metal strips, irrespective of the production configurations, which consists in implementing a preheating zone that can be divided, according to its length, into a plurality of unit length zones corresponding to a burner, each of said burners being individually controllable at a fixed speed in order to adjust accurately the air / gas regulation and thus the resulting atmosphere in the furnace, characterized in that a number of burners are ignited from the downstream of the preheating zone, the length of the zone of the furnace concerned by the ignition of said burners and the length of the recovery zone, that is to say of the zone in which the burners are extinguished being ariables in according to the heat demand and in that each burner operates at full power and with a constant air / gas adjustment.
  • the originality of the method that is the subject of the present invention resides in the simultaneous implementation of a certain number of characteristics (burner control in all or nothing or proportional mode, preheating zone with variable lengths, feed ratio adapted air / gas burners) in a configuration such that the fineness of operation of the line thus produced makes it possible to improve the quality of the finished product in very large production ranges.
  • the ambient and wall temperature of the preheating zone is between 1250 and 1300 ° C.
  • the outlet temperature of the preheating zone is adapted to this treatment, which makes it possible to limit or even eliminate the length of the cooling zones installed in downstream of the preheating zone.
  • the minimum outlet temperature of the preheating zone is adapted to this treatment in order to limit or even eliminate, if necessary, the length of the heating zones provided downstream of the preheating zone.
  • An oven for carrying out the process as specified above comprises a preheating zone divided into a plurality of unit length zones each corresponding to a burner, each of said burners being controlled individually at a fixed speed, characterized in that each burner is controlled individually by means of valves on the oxidizer feed and valves on the fuel supply so as to ignite a number of burners, starting from the downstream of the preheating zone, which corresponds to the heat demand and in that said burners operate at full power and with a constant air / gas adjustment.
  • FIGS. 3 and 3A of the appended drawings respectively represent an installation according to the invention and the curve showing the evolution of the temperature of the strip. for an exit temperature of the preheater identical to that of Figure 1A.
  • FIG. 3 shows that according to the invention the cutting of the preheating zone is replaced by conventional control zones comprising several burners of the prior art by cutting this preheating zone into a plurality of zones. of unit length corresponding to a burner.
  • the burners are controlled by a separate control system that can be conventional proportional type or all-or-nothing type.
  • the preheating zone is divided into two preheating zones fed with oxidant and fuel by collectors 5 and 7, each of the burners 4 of the two preheating zones can be controlled individually by means of valves 10 on the circuit. oxidant and valves 11 on the fuel system. These valves can be controlled in proportional mode in order to obtain an adjustment of the power injected by the variation of the flow rates of oxidizer or fuel, or in all or nothing mode, the adjustment of the power injected into the zone then being adjusted by the ratio between the operating time of the burner and its downtime or even adjusted by the choice of the number of burners operating at full power.
  • the present invention to operate a number of burners corresponding to the heat demand of the oven at full speed so that the area in which these burners are located is raised to the required temperature level, for example 1300 ° C.
  • This heat demand is measured and controlled by an oven control system controlling the ignition of the corresponding number of burners, these burners operating at full speed.
  • the four burners implanted at the outlet of the preheating zone operate permanently at 100% of their nominal capacity, the fifth burner of this zone adjusting the amount of power injected, or in proportional mode control of its flow, either by adjusting its operating time.
  • the variations in the heat demand of the furnace related to changes in the speed or the format of the product to be treated result in an increase or a reduction in the number of ignited burners, therefore by a variation of the length of the zone in which the temperature conditions are combined to maintain the band in a temperature zone where its oxidation is reduced.
  • the zone in which the burners are stopped then behaves as a recovery zone extending that existing upstream of the preheating.
  • FIG. 3A the curve of the evolution of the temperature of the strip is plotted for a preheating outlet temperature identical to that of FIG. 1A.
  • the final temperature range of the strip for which the oxidation is reduced is used to optimize the length of the oven.
  • a strip outlet temperature of the preheating zone of 500 ° C., which is sufficient for its treatment, will be chosen, replacing the temperature of 650 ° C. traditionally imposed by the preheating means. according to the prior art. It is obvious, the band being less hot, that the cooling equipment located at the end of line will be reduced by decreasing the size of the equipment and therefore its cost.
  • the limitation of the oxidation obtained by the implementation of the method which is the subject of the invention makes it possible to limit the residence time of the strip under a reducing atmosphere, so again, to reduce the length of the line or decrease the hydrogen content of this zone where the reduction of the oxides takes place.
  • the reduction of the oxidation of the band provided by the implementation of the method which is the subject of the invention makes it possible to improve the quality of the finished product, its surface state and the quality of the coating produced, for example on the galvanizing lines.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)

Abstract

A method for the preheating of metal strip uses a preheating zone that can be divided into a plurality of zones of unitary length each corresponding with a burner. Each burner can be controlled individually with a fixed regime in order to precisely adjust the air/gas regulation and thus the resultant atmosphere in the furnace. A certain number of burners in the downstream part of the preheating zone are lit, the length of the zone of the furnace affected by the lit burners and the length of the recuperation zone are varied as a function of the calorific demand and each burner functions at full power and with a constant air/gas regulation. An Independent claim is included for a furnace using this method for preheating metal strip.

Description

La présente invention concerne des perfectionnements apportés au préchauffage de bandes métalliques, notamment de bandes d'acier, dans des sections de préchauffage à feu direct, installées en particulier en entrée des lignes de galvanisation au trempé ou dans des lignes de recuit.The present invention relates to improvements made to the preheating of metal strips, especially steel strips, in direct fire preheating sections, installed in particular at the inlet of the dip galvanizing lines or in annealing lines.

On sait que la préchauffe à feu direct avant galvanisation ou recuit, telle que réalisée à l'heure actuelle remplit trois fonctions :

  • chauffage de la bande;
  • élimination des résidus d'huiles de laminage ou de protection, présents lorsque la ligne n'est pas équipée d'une section préalable de dégraissage, et
  • limitation ou élimination de l'oxydation de la bande d'acier, inhérente au chauffage par brûleurs.
It is known that preheating with direct fire before galvanizing or annealing, as currently performed, fulfills three functions:
  • heating the band;
  • elimination of residues of rolling or protective oils present when the line is not equipped with a preliminary degreasing section, and
  • limiting or eliminating the oxidation of the steel strip inherent in burner heating.

Dans les lignes continues réalisées selon l'état actuel de la technique, la préchauffe est réalisée suivant plusieurs zones dont la régulation de température est indépendante, généralement suivant quatre zones pour les lignes de forte capacité et suivant deux zones pour les lignes de faible capacité, chacune de ces zones étant munie, par exemple, de quatre à six brûleurs de chaque côté du four.In the continuous lines produced according to the current state of the art, the preheating is carried out according to several zones whose temperature regulation is independent, generally according to four zones for the lines of high capacity and following two zones for the lines of weak capacity, each of these zones being provided, for example, with four to six burners on each side of the furnace.

Les bandes galvanisées ou recuites dans les lignes continues ont des nuances, des largeurs ou épaisseurs variables et elles défilent également à des vitesses variables, ce qui conditionne la demande calorifique des zones du four qui peut varier dans des proportions importantes. Pour faire face à cette demande calorifique variable, par exemple lorsque les formats ou la vitesse de bande sont faibles, on n'utilise généralement qu'un nombre réduit de ces zones de préchauffage en arrêtant les premières zones dans le sens d'avancement de la bande, ou en les maintenant à un régime thermique minimum, équivalent à environ 15 à 20% de leur puissance nominale.The galvanized or annealed strips in the continuous lines have varying shades, widths or thicknesses and they also scroll to variable speeds, which conditions the heat demand of the zones of the oven which can vary in important proportions. In order to cope with this variable heat demand, for example when the formats or the band speed are low, only a small number of these preheating zones are generally used, stopping the first zones in the direction of advancement of the zone. band, or keeping them at a minimum thermal regime, equivalent to about 15 to 20% of their rated power.

Une pratique pareille est adoptée dans FR-A-2 406 667 .Such practice is adopted in FR-A-2 406 667 .

Dans ce dernier cas, en particulier pour le préchauffage des produits les plus minces, on utilise peu de puissance.In the latter case, especially for preheating the thinnest products, little power is used.

Le contrôle "en cascade" de la température d'ambiance d'un four est divulgué dans JP-A-56 072 134 .The "cascade" control of the ambient temperature of an oven is disclosed in JP-A-56 072 134 .

Afin de bien faire comprendre le problème technique résolu par la présente invention on se réfère à la figure 1 des dessins annexés sur laquelle on a représenté de façon schématique, en élévation latérale, un exemple de réalisation d'une installation de préchauffage comportant deux zones de préchauffage. A cette figure 1 on a associé la figure 1A qui représente la puissance calorifique mise en oeuvre dans les deux zones de préchauffage et la courbe de variation de la température de la bande dans lesdites zones.In order to clearly understand the technical problem solved by the present invention, reference is made to FIG. 1 of the accompanying drawings, which schematically shows, in side elevation, an exemplary embodiment of a preheating installation comprising two zones of preheating. FIG. 1A associates FIG. 1A, which represents the heating power used in the two preheating zones and the variation curve of the temperature of the strip in said zones.

Sur cette figure 1 on voit que l'installation de préchauffage de la bande 1 comporte deux zones de préchauffage 2 et 3. Chacune de ces zones est équipée de brûleurs 4 alimentés en air de combustion par un collecteur 5 et en combustible par un collecteur 7. La puissance injectée dans chaque zone est contrôlée par des vannes de réglage de débit de comburant et de carburant, respectivement 6 et 8. Dans cet exemple, la puissance calorifique représentée par la zone hachurée du graphe de la figure 1A correspond à 60% de la puissance nominale de la deuxième zone 3, la première zone 1 fonctionne au minimum de sa puissance, par exemple 15%. La courbe 9 présente l'élévation de température de la bande dans les zones de préchauffage. Dans ces conditions, la température de gaz et de parois de la deuxième zone de préchauffage 3 se stabilise à des niveaux faibles, de l'ordre de 1150°C ou inférieurs.In this Figure 1 it can be seen that the preheating installation of the strip 1 comprises two preheating zones 2 and 3. Each of these zones is equipped with burners 4 supplied with combustion air by a manifold 5 and with fuel by a manifold 7 The power injected into each zone is controlled by combustion and fuel flow control valves 6 and 8, respectively. In this example, the heating power represented by the shaded area of the graph of FIG. 1A corresponds to 60% of the nominal power of the second zone 3, the first zone 1 operates at least its power, for example 15%. Curve 9 shows the temperature rise of the strip in the preheating zones. Under these conditions, the gas and wall temperature of the second preheating zone 3 stabilizes at low levels, of the order of 1150 ° C or lower.

Il est connu que l'oxydation de la bande est d'autant plus faible que la température d'ambiance ou de parois de la zone du four de préchauffe à feu direct est importante. A cet égard, on peut se reporter en particulier à l'article «Direct-fired heating in continuous hot-dip galvanizing lines » publié dans le n° 4/1991 de « MPT-Metallurgical Plant and Technology International », dont la figure 2 est reprise dans les dessins annexés. Cette figure présente en ordonnée l'épaisseur de la couche d'oxyde formée à la surface de la bande, exprimée en Angstrôms, en fonction de la température des gaz ou des parois de la zone du four, présentée en abscisse, pour une température de sortie de la bande de la zone de préchauffe de 650°C. On voit sur cette figure que la formation des oxydes est maximale pour des températures de gaz ou de parois de 1150°C et qu'elle est beaucoup plus faible pour des températures de gaz ou de parois supérieures à 1250°C.It is known that the oxidation of the strip is even lower than the ambient or wall temperature of the zone of the kiln preheated direct fire is important. In this regard, reference can be made in particular to the article "Direct-fired heating in continuous hot-dip galvanizing lines" published in No. 4/1991 of "MPT-Metallurgical Plant and Technology International", of which FIG. is shown in the accompanying drawings. This figure shows on the ordinate the thickness of the oxide layer formed on the surface of the strip, expressed in Angstroms, as a function of the temperature of the gases or the walls of the zone of the furnace, presented on the abscissa, for a temperature of strip outlet of the preheating zone of 650 ° C. It can be seen in this figure that oxide formation is maximum for gas or wall temperatures of 1150 ° C and much lower for gas or wall temperatures above 1250 ° C.

On voit également que le fonctionnement du four pour des cas de marche tels qu'évoqués ci-dessus place la bande dans des conditions où son oxydation est maximale.We also see that the operation of the oven for walking cases as mentioned above places the band in conditions where its oxidation is maximum.

L'oxydation formée à la surface de la bande dans ces conditions doit être éliminée, ce qui impose la mise en place, en aval de la zone de la préchauffe, d'une zone de maintien, sous une atmosphère contenant de l'hydrogène, assez longue pour supprimer par réduction les oxydes formés. Cette réduction doit être réalisée à haute température ce qui impose généralement le réchauffage de la bande à des niveaux qui ne sont souvent atteints qu'uniquement dans le but d'obtenir cette réduction alors qu'ils ne sont pas nécessaires pour le traitement métallurgique de la nuance d'acier de la bande.The oxidation formed on the surface of the strip under these conditions must be eliminated, which requires the establishment, downstream of the zone of the preheat, of a holding zone, under an atmosphere containing hydrogen, long enough to suppress the oxides formed by reduction. This reduction must be carried out at high temperature, which generally requires reheating of the strip to levels which are often only achieved with the aim of obtaining this reduction, whereas they are not necessary for the metallurgical treatment of the mixture. steel grade of the band.

Cette absence de souplesse dans le contrôle de l'apport calorifique dans la préchauffe selon l'état actuel de la technique ainsi que l'impossibilité de placer la bande dans des conditions où son oxydation peut être limitée débouchent généralement sur des températures de bande qui sont la conséquence de l'inadaptation de la ligne au cas de marche considéré. La conception des fours découle également de ces imperfections et elle conduit à la réalisation de lignes de grande longueur et dont les équipements de refroidissement sont importants. Il est évident que cette longueur supplémentaire de four augmente le prix de l'installation, son encombrement ainsi que les coûts de maintenance et d'exploitation.This lack of flexibility in the control of heat input in preheating according to the state of the art as well as the impossibility of placing the band in conditions where its oxidation can be limited generally result in band temperatures which are the consequence of the unsuitability of the line to the market case considered. The Furnace design also stems from these imperfections and leads to the production of long lines with important cooling equipment. It is obvious that this additional length of oven increases the price of the installation, its size and the maintenance and operating costs.

La présente invention s'est fixée pour objectif de résoudre le problème technique mentionné ci-dessus en apportant un nouveau procédé et un four perfectionné permettant le chauffage de bandes dans des sections de préchauffe à feu direct, avec une oxydation limitée, ceci pour toutes les configurations de production (vitesse de la ligne, caractéristiques de traitement, caractéristiques des produits notamment nuance et format).The object of the present invention is to solve the above-mentioned technical problem by providing a novel process and an improved furnace for heating webs in direct fire preheat sections with limited oxidation for all production configurations (line speed, processing characteristics, product characteristics including shade and format).

Par ailleurs, cette invention, outre l'amélioration de la qualité du produit fini qu'elle apporte résoud le problème de l'encombrement des installations, rencontré dans l'état antérieur de la technique mentionné ci-dessus, étant donné que sa mise en oeuvre permet de limiter les dimensions et par conséquent les coûts des lignes de recuit ou de galvanisation sur lesquelles elle est appliquée.Moreover, this invention, in addition to improving the quality of the finished product that it provides, solves the problem of congestion of the installations, encountered in the prior state of the art mentioned above, since its implementation This work makes it possible to limit the dimensions and consequently the costs of the annealing or galvanizing lines to which it is applied.

En conséquence, cette invention selon la revendication 1, concerne en premier lieu un procédé de réchauffage de bandes métalliques, notamment d'acier dans des sections de préchauffage à feu direct en vue de limiter l'oxydation des bandes métalliques chauffées, quelles que soient les configurations de production, qui consiste à mettre en oeuvre une zone de préchauffage pouvant être fractionnée, selon sa longueur, en une pluralité de zones de longueur unitaire correspondant à un brûleur, chacun desdits brûleurs pouvant être commandé individuellement à un régime fixe afin d'en ajuster avec précision le réglage air/gaz donc l'atmosphère résultante dans le four, caractérisé en ce qu'on allume un certain nombre de brûleurs en partant de l'aval de la zone de préchauffage, la longueur de la zone du four concernée par l'allumage desdits brûleurs et la longueur de la zone de récupération, c'est-à-dire de la zone dans laquelle les brûleurs sont éteints étant variables en fonction de la demande calorifique et en ce que chaque brûleur fonctionne à pleine puissance et avec un réglage air/gaz constant.Accordingly, this invention according to claim 1, relates first of all to a method for reheating metal strips, in particular steel in direct fire preheating sections, in order to limit the oxidation of the heated metal strips, irrespective of the production configurations, which consists in implementing a preheating zone that can be divided, according to its length, into a plurality of unit length zones corresponding to a burner, each of said burners being individually controllable at a fixed speed in order to adjust accurately the air / gas regulation and thus the resulting atmosphere in the furnace, characterized in that a number of burners are ignited from the downstream of the preheating zone, the length of the zone of the furnace concerned by the ignition of said burners and the length of the recovery zone, that is to say of the zone in which the burners are extinguished being ariables in according to the heat demand and in that each burner operates at full power and with a constant air / gas adjustment.

La mise en oeuvre du procédé objet de l'invention tel que spécifié ci-dessus apporte, notamment les résultats ci-après qui sont impossibles à obtenir avec les équipements selon l'état actuel de la technique, pour toutes les vitesses de lignes :

  • la bande est chauffée dans une zone de préchauffage dont la longueur est variable mais les conditions de température et d'atmosphère sont optimales en regard de l'oxydation, ceci à tous les régimes de fonctionnement de la ligne, pour toutes les caractéristiques de bandes ou de cycles de traitement, la longueur de la zone de préchauffage ainsi définie est adaptée au tonnage produit par la ligne de traitement (notamment ligne de recuit ou de galvanisation), quels que soient les formats des produits traités ou la vitesse de ladite ligne;
  • les brûleurs fonctionnent tous à un régime et à un réglage tels qu'ils offrent une géométrie et des caractéristiques de flamme optimales en regard du traitement chimique devant être opéré sur la surface de la bande.
The implementation of the method according to the invention as specified above brings, in particular the following results which are impossible to obtain with the equipment according to the current state of the art, for all the line speeds:
  • the strip is heated in a preheating zone whose length is variable but the temperature and atmosphere conditions are optimal with respect to the oxidation, this at all operating conditions of the line, for all the characteristics of bands or of treatment cycles, the length of the preheating zone thus defined is adapted to the tonnage produced by the treatment line (in particular annealing or galvanizing line), regardless of the formats of the products treated or the speed of said line;
  • the burners all operate at a speed and a setting such that they offer optimum geometry and flame characteristics compared to the chemical treatment to be operated on the surface of the strip.

On comprend que l'originalité du procédé objet de la présente invention réside dans la mise en oeuvre simultanée d'un certain nombre de caractéristiques (commande des brûleurs en mode tout ou rien ou proportionnel, zone de préchauffage à longueurs variables, rapport d'alimentation des brûleurs air/gaz adapté) dans une configuration telle que la finesse de fonctionnement de la ligne ainsi réalisée permet d'améliorer la qualité du produit fini dans de très larges gammes de production.It is understood that the originality of the method that is the subject of the present invention resides in the simultaneous implementation of a certain number of characteristics (burner control in all or nothing or proportional mode, preheating zone with variable lengths, feed ratio adapted air / gas burners) in a configuration such that the fineness of operation of the line thus produced makes it possible to improve the quality of the finished product in very large production ranges.

Selon la présente invention, la température d'ambiance et de parois de la zone de préchauffage est comprise entre 1250 et 1300°C.According to the present invention, the ambient and wall temperature of the preheating zone is between 1250 and 1300 ° C.

Selon un mode de mise en oeuvre de la présente invention appliqué au traitement thermique de bandes, la température de sortie de la zone de préchauffage est adaptée à ce traitement, ce qui permet de limiter, voire de supprimer la longueur des zones de refroidissement installées en aval de la zone de préchauffage.According to an embodiment of the present invention applied to the heat treatment of strips, the outlet temperature of the preheating zone is adapted to this treatment, which makes it possible to limit or even eliminate the length of the cooling zones installed in downstream of the preheating zone.

Selon un autre mode de mise en oeuvre de la présente invention appliqué au traitement thermique de bandes d'acier, la température minimale de sortie de la zone de préchauffe est adaptée à ce traitement afin de limiter ou même de supprimer, le cas échéant, la longueur des zones de chauffage prévues en aval de la zone de préchauffage.According to another embodiment of the present invention applied to the heat treatment of steel strips, the minimum outlet temperature of the preheating zone is adapted to this treatment in order to limit or even eliminate, if necessary, the length of the heating zones provided downstream of the preheating zone.

Un four pour la mise en oeuvre du procédé tel que spécifié ci-dessus comporte une zone de préchauffage fractionnée en une pluralité de zones de longueur unitaire correspondant chacune à un brûleur, chacun desdits brûleurs étant commandé individuellement à un régime fixe, caractérisé en ce que chaque brûleur est contrôlé individuellement à l'aide de vannes sur l'alimentation en comburant et de vannes sur l'alimentation en carburant de façon à allumer un nombre de brûleurs, en partant de l'aval de la zone de préchauffage, qui correspond à la demande calorifique et en ce que lesdits brûleurs fonctionnent à pleine puissance et avec un réglage air/gaz constant.An oven for carrying out the process as specified above comprises a preheating zone divided into a plurality of unit length zones each corresponding to a burner, each of said burners being controlled individually at a fixed speed, characterized in that each burner is controlled individually by means of valves on the oxidizer feed and valves on the fuel supply so as to ignite a number of burners, starting from the downstream of the preheating zone, which corresponds to the heat demand and in that said burners operate at full power and with a constant air / gas adjustment.

D'autres caractéristiques et avantages de la présente invention ressortiront de la description faite ci-après en référence aux figures 3 et 3A des dessins annexés qui représentent respectivement une installation selon l'invention et la courbe montrant l'évolution de la température de la bande pour une température de sortie de la préchauffe identique à celle de la figure 1A.Other features and advantages of the present invention will emerge from the description given hereinafter with reference to FIGS. 3 and 3A of the appended drawings, which respectively represent an installation according to the invention and the curve showing the evolution of the temperature of the strip. for an exit temperature of the preheater identical to that of Figure 1A.

Sur la figure 3 on a désigné par les mêmes références les éléments similaires à ceux décrits ci-dessus en référence à la figure 1.In FIG. 3 the same references denote elements similar to those described above with reference to FIG. 1.

Sur cette figure 3 on voit que selon l'invention on remplace le découpage de la zone de préchauffage en zones de régulation classiques regroupant plusieurs brûleurs de l'état antérieur de la technique, par un découpage de cette zone de préchauffage en une pluralité de zones de longueur unitaire correspondant à un brûleur. Les brûleurs sont commandés par un système de régulation séparé pouvant être du type proportionnel classique ou du type tout ou rien.FIG. 3 shows that according to the invention the cutting of the preheating zone is replaced by conventional control zones comprising several burners of the prior art by cutting this preheating zone into a plurality of zones. of unit length corresponding to a burner. The burners are controlled by a separate control system that can be conventional proportional type or all-or-nothing type.

Dans cet exemple de réalisation, la zone de préchauffage est découpée en deux zones de préchauffage alimentées en comburant et carburant par des collecteurs 5 et 7, chacun des brûleurs 4 des deux zones de préchauffage pouvant être commandé individuellement au moyen de vannes 10 sur le circuit comburant et de vannes 11 sur le circuit carburant. Ces vannes peuvent être commandées en mode proportionnel afin d'obtenir un réglage de la puissance injectée par la variation des débits de comburant ou de carburant, ou en mode tout ou rien, le réglage de la puissance injectée dans la zone étant alors ajusté par le rapport entre le temps de fonctionnement du brûleur et son temps d'arrêt ou bien encore ajusté par le choix du nombre de brûleurs en service à pleine puissance.In this embodiment, the preheating zone is divided into two preheating zones fed with oxidant and fuel by collectors 5 and 7, each of the burners 4 of the two preheating zones can be controlled individually by means of valves 10 on the circuit. oxidant and valves 11 on the fuel system. These valves can be controlled in proportional mode in order to obtain an adjustment of the power injected by the variation of the flow rates of oxidizer or fuel, or in all or nothing mode, the adjustment of the power injected into the zone then being adjusted by the ratio between the operating time of the burner and its downtime or even adjusted by the choice of the number of burners operating at full power.

Il est ainsi possible, selon la présente invention de faire fonctionner un nombre de brûleurs correspondant à la demande calorifique du four à plein régime pour que la zone dans laquelle sont implantés ces brûleurs soit portée au niveau de température requis, par exemple 1300°C. Cette demande calorifique est mesurée et contrôlée par un système de régulation du four commandant l'allumage du nombre de brûleurs correspondant, ces brûleurs fonctionnant à plein régime. Dans l'exemple considéré, les quatre brûleurs implantés à la sortie de la zone de préchauffage fonctionnent en permanence à 100% de leur capacité nominale, le cinquième brûleur de cette zone ajustant la quantité de puissance injectée, soit selon une régulation en mode proportionnel de son débit, soit en ajustant son temps de fonctionnement.It is thus possible, according to the present invention to operate a number of burners corresponding to the heat demand of the oven at full speed so that the area in which these burners are located is raised to the required temperature level, for example 1300 ° C. This heat demand is measured and controlled by an oven control system controlling the ignition of the corresponding number of burners, these burners operating at full speed. In the example considered, the four burners implanted at the outlet of the preheating zone operate permanently at 100% of their nominal capacity, the fifth burner of this zone adjusting the amount of power injected, or in proportional mode control of its flow, either by adjusting its operating time.

Les variations de la demande calorifique du four liées aux modifications de vitesse ou de format du produit à traiter se traduisent par une augmentation ou une réduction du nombre de brûleurs allumés, donc par une variation de la longueur de la zone dans laquelle les conditions de température sont réunies pour maintenir la bande dans une zone de température où son oxydation est réduite. La zone dans laquelle les brûleurs sont arrêtés se comporte alors comme une zone de récupération prolongeant celle qui existe en amont de la préchauffe.The variations in the heat demand of the furnace related to changes in the speed or the format of the product to be treated result in an increase or a reduction in the number of ignited burners, therefore by a variation of the length of the zone in which the temperature conditions are combined to maintain the band in a temperature zone where its oxidation is reduced. The zone in which the burners are stopped then behaves as a recovery zone extending that existing upstream of the preheating.

Sur la figure 3A on a tracé la courbe de l'évolution de la température de la bande pour une température de sortie de la préchauffe identique à celle de la figure 1A.In FIG. 3A, the curve of the evolution of the temperature of the strip is plotted for a preheating outlet temperature identical to that of FIG. 1A.

La plage de température finale de la bande pour laquelle l'oxydation est réduite est mise à profit pour optimiser la longueur du four. Par exemple, pour des aciers laminés à chaud, on choisira une température de sortie de bande de la zone de préchauffage de 500°C qui est suffisante pour son traitement, en remplacement de la température de 650°C traditionnellement imposée par les moyens de préchauffage suivant l'état antérieur de la technique. Il est évident, la bande étant moins chaude, que les équipements de refroidissement situés en sortie de ligne seront réduits en diminuant d'autant l'encombrement de l'équipement et donc son coût.The final temperature range of the strip for which the oxidation is reduced is used to optimize the length of the oven. For example, for hot-rolled steels, a strip outlet temperature of the preheating zone of 500 ° C., which is sufficient for its treatment, will be chosen, replacing the temperature of 650 ° C. traditionally imposed by the preheating means. according to the prior art. It is obvious, the band being less hot, that the cooling equipment located at the end of line will be reduced by decreasing the size of the equipment and therefore its cost.

Il est également possible, grâce au procédé objet de l'invention, de chauffer une bande en acier doux, par exemple de qualité commerciale, à des températures de l'ordre de 730°C au moins, sans augmenter son oxydation, ce qui permet de réduire d'autant, voire de supprimer la longueur de la zone de chauffage complémentaire sous atmosphère réductrice que l'on utilise traditionnellement en aval des zones de préchauffage des lignes de traitement selon l'état actuel de la technique. Cette réduction de la longueur de la zone de chauffage complémentaire sous atmosphère aura également une incidence directe sur l'encombrement et sur le prix de l'équipement.It is also possible, thanks to the method of the invention, to heat a mild steel strip, for example of commercial quality, at temperatures of the order of at least 730 ° C, without increasing its oxidation, which allows to reduce by the same or even eliminate the length of the additional heating zone under a reducing atmosphere that is traditionally used downstream of the preheating zones of the treatment lines according to the current state of the art. This reduction in the length of the additional heating zone under atmosphere will also have a direct impact on the size and on the price of the equipment.

Pour tous les types de produits à traiter, la limitation de l'oxydation obtenue par la mise en oeuvre du procédé objet de l'invention permet de limiter le temps de séjour de la bande sous atmosphère réductrice, donc là encore, de réduire la longueur de la ligne ou de diminuer le taux d'hydrogène de cette zone où s'effectue la réduction des oxydes.For all the types of products to be treated, the limitation of the oxidation obtained by the implementation of the method which is the subject of the invention makes it possible to limit the residence time of the strip under a reducing atmosphere, so again, to reduce the length of the line or decrease the hydrogen content of this zone where the reduction of the oxides takes place.

Dans tous les cas, la réduction de l'oxydation de la bande apportée par la mise en oeuvre du procédé objet de l'invention permet d'améliorer la qualité du produit fini, son état de surface et la qualité du revêtement réalisé, par exemple sur les lignes de galvanisation.In all cases, the reduction of the oxidation of the band provided by the implementation of the method which is the subject of the invention makes it possible to improve the quality of the finished product, its surface state and the quality of the coating produced, for example on the galvanizing lines.

Le procédé objet de l'invention permet de réaliser des cycles de traitement à basse température grâce à la possibilité de limiter l'oxydation de la bande dans la préchauffe :

  • il n'est plus nécessaire de surchauffer la bande pour réduire les oxydes formés, ce qui offre la possibilité de réaliser des cycles à basse température, avantage se traduisant par une diminution de la consommation d'énergie et des fours plus courts;
  • lorsque le cycle de traitement s'effectue à basse température, il est possible de réduire, voire de supprimer les équipements de refroidissement de bandes en sortie de lignes et
  • l'oxydation étant limitée, le temps de réduction des oxydes est plus court donc le four en aval est plus court. De même lorsque l'oxydation dans la préchauffe est réduite il est possible de chauffer à température plus élevée dans cette zone, donc de réduire la longueur de la zone de chauffage sous atmosphère.
The method which is the subject of the invention makes it possible to carry out low temperature treatment cycles thanks to the possibility of limiting the oxidation of the strip in the preheating:
  • it is no longer necessary to overheat the strip in order to reduce the oxides formed, which offers the possibility of making cycles at low temperature, an advantage resulting in a reduction in energy consumption and shorter furnaces;
  • when the treatment cycle is carried out at low temperature, it is possible to reduce or even eliminate the band cooling equipment at the output of lines and
  • the oxidation being limited, the reduction time of the oxides is shorter so the downstream furnace is shorter. Similarly, when the oxidation in the preheat is reduced, it is possible to heat at a higher temperature in this zone, thus to reduce the length of the heating zone under atmosphere.

La lecture de la description qui précède fait ressortir que la présente invention permet de réaliser des installations de traitement thermique plus polyvalentes, plus performantes et moins chères que les installations selon l'état actuel de la technique.From reading the foregoing description, it is clear that the present invention makes it possible to provide heat treatment installations more versatile, more efficient and less expensive than the installations according to the current state of the art.

Claims (3)

  1. Method of treating steel strips in direct-fired preheating sections with a view to limiting the oxidation of the metal strips, whatever the production configurations, which consists of using a preheating zone that can be divided, along its length, into a plurality of zones of unit length corresponding to a burner, each of the said burners being able to be controlled individually at a fixed operating level in order to adjust with precision its air/gas setting and therefore the resulting atmosphere in this furnace, characterised in that a certain number of burners are ignited starting from the downstream end of the preheating zone, the length of the zone of the furnace affected by the ignition of the said burners and the length of the recovery zone, that is to say the zone in which the burners are switched off, being variable according to the heat demand, and in that each burner functions at full power with a constant air/gas setting, so that the ambient and wall temperature of the preheating zone is between 1250° and 1300°C.
  2. Treatment method according to claim 1, characterised in that the temperature of the strip at the exit from the preheating section is 500°C.
  3. Treatment method according to claim 1 or 2, characterised in that it is applied to low-temperature heat treatments.
EP01400142A 2000-03-08 2001-01-18 Improvements in preheating metal strips, especially in galvanising or annealing lines Expired - Lifetime EP1134298B1 (en)

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FR0002990 2000-03-08
FR0002990A FR2806097B1 (en) 2000-03-08 2000-03-08 IMPROVEMENTS RELATING TO THE PREHEATING OF METAL STRIPS, PARTICULARLY IN GALVANIZING OR ANNEALING LINES

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FR2852330B1 (en) * 2003-03-12 2007-05-11 Stein Heurtey METHOD OF CONTROLLED OXIDATION OF STRIPS BEFORE CONTINUOUS GALVANIZATION AND LINE OF GALVANIZATION
DE102006005063A1 (en) * 2006-02-03 2007-08-09 Linde Ag Process for the heat treatment of steel strip
JP4718381B2 (en) * 2006-06-21 2011-07-06 株式会社神戸製鋼所 Hot dip galvanizing equipment
FR2917817B1 (en) * 2007-06-21 2016-05-27 Stein Heurtey DEVICE FOR LIMITING THE EXHAUST OF COMBUSTION FUME AT THE ENTRANCE OF A STEEL HEATING FURNACE
DE102008006248A1 (en) * 2008-01-25 2009-07-30 Schwartz, Eva Apparatus and method for heating workpieces
DE102009014223A1 (en) * 2009-03-25 2010-09-30 Hitachi Power Europe Gmbh Firing system of a designed for the oxyfuel operation steam generator
CN103225016B (en) * 2013-04-27 2014-12-24 宝山钢铁股份有限公司 Strip steel surface flame cleaning method and apparatus thereof
AT517848B1 (en) * 2016-04-15 2017-05-15 Andritz Tech And Asset Man Gmbh METHOD AND OVEN SYSTEM FOR HEAT-TREATING METAL TAPES

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US6761779B2 (en) 2004-07-13
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JP2001294941A (en) 2001-10-26
DE60130823D1 (en) 2007-11-22
US20020162612A1 (en) 2002-11-07
DE60130823T2 (en) 2008-07-17
KR100785255B1 (en) 2007-12-13
PT1134298E (en) 2007-10-24
FR2806097B1 (en) 2002-05-10
ATE375408T1 (en) 2007-10-15
CN1315584A (en) 2001-10-03
ES2161660T3 (en) 2008-03-01
KR20010088418A (en) 2001-09-26
DE1134298T1 (en) 2002-04-18
ES2161660T1 (en) 2001-12-16
CN1179056C (en) 2004-12-08

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