EP2016202A2 - Improvement made to the rapid heating sections of continuous heat-treatment lines - Google Patents

Improvement made to the rapid heating sections of continuous heat-treatment lines

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Publication number
EP2016202A2
EP2016202A2 EP07731385A EP07731385A EP2016202A2 EP 2016202 A2 EP2016202 A2 EP 2016202A2 EP 07731385 A EP07731385 A EP 07731385A EP 07731385 A EP07731385 A EP 07731385A EP 2016202 A2 EP2016202 A2 EP 2016202A2
Authority
EP
European Patent Office
Prior art keywords
heating
heating means
strip
temperature
band
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07731385A
Other languages
German (de)
French (fr)
Inventor
Catherine Pasquinet
Frédéric MARMONIER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fives Stein SA
Original Assignee
Fives Stein SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fives Stein SA filed Critical Fives Stein SA
Publication of EP2016202A2 publication Critical patent/EP2016202A2/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • 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

Definitions

  • the present invention relates to improvements made to the heating sections of the continuous lines of heat treatment of metal strips. It is particularly intended to reduce the risk of thermal wrinkles forming on metal strips which are subjected to rapid heating in continuous heat treatment lines, in which said strips are passed through rapid heating zones provided with discontinuous heating means.
  • rapid heating is meant a heating which ensures a temperature rise of the band at a gradient of at least 100 ° C / second at the beginning of heating.
  • FIG. 1 of the accompanying drawings schematically shows an example of a heating section of a metal strip in a heat treatment line. .
  • the band 1 passes through the rapid heating section 2 by passing on an inlet roller 3 and an output roller 4.
  • the band 1 is exposed successively to four means 5, 5b, 5c, 5d, positioned on each side of the strip and distant in the direction of travel of the strip by a distance ⁇ , for example ⁇ ab between the heating means 5a and 5a, 5b, 5c, 5d. 5b.
  • the rapid heating causes a dilation of the material of the strip in directions parallel and perpendicular to the running direction of the strip. Expansion in the direction of travel of the web is compensated by the tape tensile control device which is provided with the heating section or the line in which this heating section is integrated.
  • FIG. 3 of the accompanying drawings shows the variation of these stresses during heating of the strip.
  • the curve T1 represents the temperature rise of the band, between Ta and Tb, during its passage in a heating means 5.
  • the curve C1 corresponds to the level of transverse stress in the band.
  • the horizontal line H passing through the point 0 of the stresses carried along the y-axis corresponds to a zero transverse stress.
  • a point of the curve C1 situated above the line H corresponds to a tensile stress, noted positive, while a point of the curve C1 situated below the line H corresponds to a compressive stress, denoted negative.
  • the first stress peak Ca corresponds to the point Ta of the curve T1 where the temperature increase begins. This is a tensile stress.
  • the second stress peak Cb corresponds to the point Tb of the curve T1 where the increase in temperature stops. This is a compression constraint.
  • the level of critical compressive stress beyond which a surface defect is generated is proportional to the mechanical strength of the web material. As the mechanical strength of the belt decreases as the temperature increases, and more and more rapidly as the temperature increases, the level of critical compressive stress is also reduced with temperature, thereby increasing the risk. as the temperature of the web increases.
  • the rapid heating sections of the continuous heat treatment lines of metal strips are dimensioned without taking into consideration the risk of fold formation. Therefore, for a given heating section, the operators in charge of the operation of the line must, in the absence of a known method, adapt by trial and error the setting of the oven until finding an operating point limiting these defaults. These settings lead to operation of the furnace not fully exploiting the available power which leads to a loss of production, for example when operators are led to reduce the speed of travel of the band.
  • the object of the invention is, above all, to provide a method which makes it possible to limit the formation of folds in the strip during rapid heating while keeping the nominal speed of the strip in passing through the rapid heating section, that is to say without loss of production.
  • the method of reducing the formation of folds on metal strips subjected to rapid heating in continuous heat treatment lines, wherein said strips are passed through heating sections comprising successive heating means and distinct is characterized in that the average slope of the temperature increase of the strip between the inlet and the outlet of a heating means decreases from one heating means to the next heating means.
  • the invention makes it possible to reduce the formation of folds on the strip in a strand placed between two drive rollers 3 and 4 according to FIGS. 1 and 2.
  • the folds that the invention makes it possible to reduce are generated by the thermal path of the tape, regardless of any contact of the tape with a baffle roll.
  • the ratio of the temperature difference of the strip, between the outlet and the inlet of a heating means, to the distance between the outlet and the inlet of this heating means decreases from a heating means to next heating means.
  • the instantaneous slope of the increase in temperature of the strip between the inlet and the outlet of a heating means, as a function of the distance traveled, is preferably greater at the inlet of the heating means than towards the outlet of this heating means.
  • the difference in heating intensity between two successive heating means can be progressively reduced to be low at high temperature so that the variation of the heating rate at all points of the strip is reduced as the temperature of the the band increases.
  • the intensity of heating between each heating means is gradually changed and the heating intensity between two successive heating means is reduced as the temperature of the band increases.
  • the band is injected with a larger heat flow when it is at low temperature, then gradually decreases the heat flow injected when the strip rises in temperature.
  • the heating may be provided to ensure a temperature rise of the strip in each heating means increasingly low from the first heating means where it is the most important.
  • the evolution of the flow exchanged between the strip and the heating means is progressive, that is to say that the variation of the heating slope is progressive.
  • the temperature rise gradient of the strip decreases by at least 15 ° C / second when passing from one heating section to the next.
  • Fig. 1 is a schematic vertical section of a rapid heating section of a heat treatment line of metal strips.
  • Fig. 2 is a diagram of FIG. 1 with, in correspondence, the heat flux injected by each heating means according to the state of the art.
  • Fig. 3 is a diagram illustrating the appearance of the stresses induced in a metal strip by a temperature variation.
  • Fig. 4 is a diagram illustrating several heating modes, including one according to the invention.
  • Fig. 5 is a diagram of FIG. 2 with, in correspondence, the heat flux injected by each heating means according to the invention.
  • Fig.6 is a diagram illustrating the stresses in a heated metal strip according to the method of the invention.
  • Fig.7 is a diagram illustrating the stresses in a heated metal strip according to a conventional method of the state of the art.
  • Fig.8 is a diagram illustrating the stresses in a heated metal strip according to the method of the invention.
  • Fig. 9 shows the diagram of FIG. 5, with the heat flux injected by each heating means according to the invention.
  • Fig. 10 shows, enlarged, the detail X of Fig.9.
  • Fig. 11 shows, enlarged, the detail Xl of Fig.9, and
  • Fig.12 is a diagram illustrating the stress variations and temperature variations in a heated metal strip according to the method of the invention.
  • FIG. 4 is a diagram on which is shown on the abscissa the length of the heating section equipped with four inductors traversed by a point of the metal strip, and the ordinate the temperature of the strip at this point. It can be seen that to achieve the same thermal objective corresponding to a temperature T at the end of the heating section, corresponding to the length L, it is possible to follow different thermal paths:
  • Path A corresponds to the same slope of temperature rise of the band in each heating means, .
  • the path B corresponds to a slope of temperature rise of the band in each degressive heating means from the first heating means where it is the most important,
  • the path C corresponds to a slope of temperature rise of the band in each heating means which increases progressively from the first heating means where it is the lowest.
  • Path D corresponds to a combination of paths B and C with a higher temperature rise slope of the band in the first and last heating means and lower for both central heating means.
  • the strip is heated in the heating section by following the thermal path B of temperature rise.
  • this thermal path is obtained by injecting a heat flow ⁇ a important to the band at the beginning of the heating, when this is at a lower temperature, then gradually limiting the injected flow ⁇ b, ⁇ c, ⁇ d as and as the temperature of the band increases.
  • the temperature rise gradient of the strip in the first heating section that is to say in the first heating means 5a, is greater than
  • the thermal path according to the invention makes it possible to limit the slope variation of the temperature curve at the outlet of each heating element as the strip rises in temperature. Compression stresses perpendicular to the axis of the strip, likely to generate folds, are thus increasingly weak at each successive output of the rapid heating zones: C2a>C2b>C2c> C2d.
  • the heating provided by the successive heating means 5a, 5b, 5c, 5d is such that the average curve representing the rise in temperature of the strip as a function of the length of the heating section has a concavity turned towards the axis of coordinates on which is the length.
  • mean curve is meant a curve passing through the midpoints of the horizontal straight segments of the actual temperature rise curve in Figure 6.
  • the average slope of the temperature increase of the strip between the inlet and the outlet of heating means decreases from one heating means to the next heating means.
  • the invention is also characterized by a method which consists in progressively modifying the intensity of the heating in each heating means 5 so that the evolution of the flow exchanged with the strip is progressive. that is, the change in the rate of change of the function (temperature / time) corresponding to a change in the heating slope is progressive.
  • FIG. 9 the flow variation between the strip and the heating means 5 is progressive according to the invention from the inlet to the outlet of each heating means while rapid heating according to the invention.
  • state of the art would lead to the flux curve P, shown in fine lines in Fig. 10 and 11, with abrupt changes in flux variation.
  • This gradual variation of the flow according to the invention is imaged in FIG. 9 by a rounded flow curve during changes in slope between rise in temperature, upper plateau, then descent and lower plateau, whereas these changes are at sharp angles on the curve P according to the state of the art.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Control Of Heat Treatment Processes (AREA)

Abstract

Method of reducing the formation of folds on metal strips (1) exposed to rapid heating in continuous heat-treatment lines, in which lines said strips are caused to pass through heating sections (2) comprising successive and separate heating means (5; 5a; 5b; 5c; 5d), wherein the average slope of the increase in temperature of the strip between the inlet and the outlet of a heating means decreases from one heating means to the following heating means.

Description

PERFECTIONNEMENT APPORTE AUX SECTIONS DE CHAUFFAGE RAPIDE DES LIGNES DE TRAITEMENT THERMIQUE EN CONTINU.IMPROVEMENT IN THE QUICK HEATING SECTIONS OF CONTINUOUS THERMAL TREATMENT LINES.
La présente invention concerne des perfectionnements apportés aux sections de chauffage des lignes continues de traitement thermique de bande métalliques. Elle se propose tout particulièrement de réduire le risque de plis d'origine thermique qui se forment sur des bandes métalliques soumises à un chauffage rapide dans des lignes continues de traitement thermique, dans lesquelles lesdites bandes sont amenées à traverser des zones de chauffage rapide munies de moyens de chauffage discontinus.The present invention relates to improvements made to the heating sections of the continuous lines of heat treatment of metal strips. It is particularly intended to reduce the risk of thermal wrinkles forming on metal strips which are subjected to rapid heating in continuous heat treatment lines, in which said strips are passed through rapid heating zones provided with discontinuous heating means.
Par chauffage rapide on désigne un chauffage qui assure une montée en température de la bande selon un gradient d'au moins 100°C/seconde en début de chauffage.By rapid heating is meant a heating which ensures a temperature rise of the band at a gradient of at least 100 ° C / second at the beginning of heating.
Afin de bien situer le domaine technique auquel s'applique la présente invention, on se réfère en premier lieu à la Figure 1 des dessins annexés qui représente de façon schématique un exemple de section de chauffage d'une bande métallique dans une ligne de traitement thermique.In order to properly locate the technical field to which the present invention applies, reference is first made to FIG. 1 of the accompanying drawings, which schematically shows an example of a heating section of a metal strip in a heat treatment line. .
Sur cette Figure 1 on voit que la bande 1 traverse la section de chauffage rapide 2 en passant sur un rouleau d'entrée 3 et un rouleau de sortie 4. Durant la traversée de la section 2, la bande 1 est exposée successivement à quatre moyens de chauffage 5 distincts, respectivement 5a, 5b, 5c, 5d, positionnés de part et d'autre de la bande et distants selon la direction de défilement de la bande d'une distance Δ, par exemple Δab entre les moyens de chauffage 5a et 5b.In this Figure 1 we see that the band 1 passes through the rapid heating section 2 by passing on an inlet roller 3 and an output roller 4. During the crossing of the section 2, the band 1 is exposed successively to four means 5, 5b, 5c, 5d, positioned on each side of the strip and distant in the direction of travel of the strip by a distance Δ, for example Δab between the heating means 5a and 5a, 5b, 5c, 5d. 5b.
Les moyens de chauffage 5 permettent une élévation rapide de la température de la bande, selon un gradient d'au moins 100°C/seconde , en l'exposant à un flux calorifique important. Le procédé mis en œuvre par ces moyens de chauffage rapide est par exemple le chauffage par induction à flux longitudinal ou à flux transversal. Le chauffage peut être réalisé à l'air ou sous une atmosphère non oxydante pour la bande. Comme représenté en Figure 2, entre deux moyens de chauffages 5 distincts, la bande n'est plus exposée à un flux d'apport calorifique. La bande est donc soumise à une discontinuité de la chauffe. Selon la qualité de l'isolation entre ces deux moyens de chauffage, au mieux la température de la bande atteinte à la sortie d'un moyen de chauffage est maintenue jusqu'à son entrée dans le moyen de chauffage suivant. La température de la bande peut également diminuer en raison de pertes calorifiques.The heating means 5 allow a rapid rise in the temperature of the strip, according to a gradient of at least 100 ° C / second, by exposing it to a large heat flow. The method implemented by these rapid heating means is for example the longitudinal flux or cross flow induction heating. The heating may be carried out in air or in a non-oxidizing atmosphere for the strip. As shown in FIG. 2, between two distinct heating means 5, the strip is no longer exposed to a heat input stream. The band is therefore subjected to a discontinuity of the heating. Depending on the quality of the insulation between these two heating means, at best the temperature of the band reached at the outlet of a heating means is maintained until it enters the next heating means. The temperature of the belt may also decrease due to heat loss.
Cette discontinuité de la chauffe induit des contraintes transversales de traction et des contraintes transversales de compression dans la bande, perpendiculaires à l'axe de la bande. Le phénomène à l'origine de ces contraintes est décrit ci-après.This discontinuity of heating induces transverse tensile stresses and transverse compression stresses in the strip, perpendicular to the axis of the strip. The phenomenon at the origin of these constraints is described below.
Le chauffage rapide provoque une dilatation du matériau de la bande suivant des directions parallèles et perpendiculaires à la direction de défilement de la bande. La dilatation suivant la direction de défilement de la bande est compensée par le dispositif de contrôle de traction de bande dont est munie la section de chauffage ou la ligne dans laquelle cette section de chauffage est intégrée.The rapid heating causes a dilation of the material of the strip in directions parallel and perpendicular to the running direction of the strip. Expansion in the direction of travel of the web is compensated by the tape tensile control device which is provided with the heating section or the line in which this heating section is integrated.
La dilatation s'effectuant selon la direction perpendiculaire au défilement de la bande génère des forces au sein du matériau. Ce sont des forces de traction lorsqu'elles sont dirigées de l'axe vers les rives de la bande et des forces de compression lorsqu'elles sont dirigées vers l'axe de la bande.The expansion taking place in the direction perpendicular to the running of the strip generates forces within the material. These are tensile forces when they are directed from the axis to the edges of the belt and compressive forces when directed towards the axis of the belt.
Sur toute la longueur du moyen de chauffage 5, si l'intensité du flux de chauffage de la bande est constante, il n'existe pas de différence importante entre les forces de compression existant dans une section de la bande et celle qui la précède dans la direction de défilement de cette bande.Over the entire length of the heating means 5, if the intensity of the heating flux of the strip is constant, there is no significant difference between the compression forces existing in one section of the strip and the one which precedes it in the scroll direction of this band.
Lorsque la bande entre dans le premier moyen de chauffage 5 ou les suivants, elle subit une variation positive très rapide de l'intensité du flux calorifique reçu correspondant à la reprise du chauffage. Ce changement de taux de variation de la fonction (dTempérature/dtemps) conduit à des forces de traction dans la bander De même, lorsque la bande quitte un moyen de chauffage 5, elle subit une variation négative très rapide de l'intensité du flux calorifique reçu correspondant à l'arrêt du chauffage. Ce nouveau changement du taux de variation de la fonction (dTempérature/dtemps), ou (dTempérature/dLongueur), conduit à des forces de compression dans la bande.When the band enters the first heating means 5 or the following, it undergoes a very rapid positive variation in the intensity of the heat flow received corresponding to the recovery of the heating. This change in the rate of change of the function (temperature / time) leads to tensile forces in the bander Likewise, when the strip leaves a heating means 5, it undergoes a very rapid negative variation in the intensity of the heat flow received corresponding to the stopping of the heating. This new change in the rate of change of the function (temperature / time), or (temperature / length), leads to compressive forces in the band.
La Figure 3 des dessins annexés représente la variation de ces contraintes lors du chauffage de la bande. La courbe T1 représente l'élévation de température de la bande, entre Ta et Tb, lors de son passage dans un moyen de chauffage 5. La courbe C1 correspond au niveau de contrainte transversale dans la bande. La ligne horizontale H passant par le point 0 des contraintes portées selon l'axe des ordonnées correspond à une contrainte transversale nulle. Un point de la courbe C1 situé au-dessus de la ligne H correspond à une contrainte de traction, notée positive, tandis qu'un point de la courbe C1 situé au-dessous de la ligne H correspond à une contrainte de compression, notée négativeFigure 3 of the accompanying drawings shows the variation of these stresses during heating of the strip. The curve T1 represents the temperature rise of the band, between Ta and Tb, during its passage in a heating means 5. The curve C1 corresponds to the level of transverse stress in the band. The horizontal line H passing through the point 0 of the stresses carried along the y-axis corresponds to a zero transverse stress. A point of the curve C1 situated above the line H corresponds to a tensile stress, noted positive, while a point of the curve C1 situated below the line H corresponds to a compressive stress, denoted negative.
On voit clairement que, à chaque changement du taux de variation de la fonction (dTempérature/dtemps), ou (dTempérature/dLongueur), correspondant à une modification de la pente de chauffage sur T1 , il apparaît un pic correspondant de la valeur absolue de contrainte sur la courbe C1. Le premier pic de contrainte Ca correspond au point Ta de la courbe T1 où débute l'accroissement de température. Il s'agit d'une contrainte de traction. Le second pic de contrainte Cb correspond au point Tb de la courbe T1 où s'arrête l'accroissement de température. Il s'agit d'une contrainte de compression.It is clearly seen that, with each change in the rate of change of the function (temperature / time), or (temperature / length), corresponding to a change in the heating slope on T1, a corresponding peak of the absolute value of constraint on the curve C1. The first stress peak Ca corresponds to the point Ta of the curve T1 where the temperature increase begins. This is a tensile stress. The second stress peak Cb corresponds to the point Tb of the curve T1 where the increase in temperature stops. This is a compression constraint.
L'importance de ces pics de contrainte dépend du format de la bande et de la variation de pente de la courbe de température en Ta et Tb, c'est-à-dire de la variation de la vitesse de chauffage au point de la courbe qui correspond au moment où la bande pénètre ou quitte la zone de chauffage correspondant à un moyen de chauffage 5.The importance of these stress peaks depends on the format of the band and the variation of slope of the temperature curve in Ta and Tb, that is to say of the variation of the heating rate at the point of the curve. which corresponds to the moment when the strip enters or leaves the heating zone corresponding to a heating means 5.
Les contraintes perpendiculaires à l'axe de la bande qui produisent des forces de compression peuvent générer, si elles atteignent un niveau trop important, des défauts de qualité de surface de la bande tels que des ondulations, des cloques, des plis ou des cassures. Ces défauts de surface peuvent prendre des formes variées, ils peuvent être continus sur la longueur de la bande ou discontinus, ils peuvent être parallèles à l'axe de la bande ou serpenter sur sa largeur. Ils peuvent être uniques ou se développer suivant la forme de plusieurs plis parallèles continus, discontinus, linéaires ou selon une courbe régulière ou non. Pour simplifier les explications, le terme de plis est utilisé par la suite pour désigner l'ensemble des défauts de la bande provoqués par des contraintes transversales de compression excessives.Stresses perpendicular to the axis of the strip which produce compressive forces may generate, if they reach a too high level, surface quality defects of the strip such as corrugations, blisters, folds or breaks. These surface defects can take various forms, they can be continuous along the length of the strip or discontinuous, they can be parallel to the axis of the strip or meander along its width. They can be unique or develop in the form of several continuous parallel folds, discontinuous, linear or in a regular curve or not. To simplify the explanations, the term folds is used later to designate all the defects of the band caused by excessive transverse compressive stresses.
Ces défauts apparaissent lorsque le niveau de contraintes transversales de compression dans la bande est supérieur à un seuil de contraintes qui constitue une limite appelée « contrainte critique » qui dépend principalement : . de la composition et des propriétés mécaniques de la bande, de son état métallurgique, . de la température de la bande,These defects appear when the level of transverse compressive stresses in the band is greater than a stress threshold which constitutes a limit called "critical stress" which mainly depends on: the composition and mechanical properties of the strip, its metallurgical state,. the temperature of the band,
. du format de la bande, sa largeur et son épaisseur.. the format of the tape, its width and thickness.
Le niveau de contrainte critique de compression au-delà duquel un défaut de surface est généré est proportionnel à la résistance mécanique du matériau de la bande. Comme la résistance mécanique de la bande décroît lorsque la température augmente, et ce de plus en plus rapidement au fur et à mesure que la température augmente, le niveau de contrainte critique de compression se réduit également avec la température, augmentant d'autant le risque de formation de plis au fur et à mesure que la température de la bande augmente.The level of critical compressive stress beyond which a surface defect is generated is proportional to the mechanical strength of the web material. As the mechanical strength of the belt decreases as the temperature increases, and more and more rapidly as the temperature increases, the level of critical compressive stress is also reduced with temperature, thereby increasing the risk. as the temperature of the web increases.
Selon l'état de la technique les sections de chauffage rapide des lignes continues de traitement thermique de bandes métalliques sont dimensionnées sans prendre en considération le risque de formation de plis. De ce fait, pour une section de chauffage donnée, les opérateurs en charge de l'exploitation de la ligne doivent, en l'absence de méthode connue, adapter par tâtonnements successifs le réglage du four jusqu'à trouver un point de fonctionnement limitant ces défauts. Ces réglages conduisent à un fonctionnement du four n'exploitant pas pleinement la puissance disponible ce qui conduit à une perte de production, par exemple lorsque les opérateurs sont amenés à diminuer la vitesse de défilement de la bande. L'invention a pour but, surtout, de fournir un procédé qui permet de limiter la formation des plis dans la bande en cours de chauffage rapide tout en conservant la vitesse nominale de la bande dans sa traversée de la section de chauffage rapide, c'est-à-dire sans perte de production.According to the state of the art the rapid heating sections of the continuous heat treatment lines of metal strips are dimensioned without taking into consideration the risk of fold formation. Therefore, for a given heating section, the operators in charge of the operation of the line must, in the absence of a known method, adapt by trial and error the setting of the oven until finding an operating point limiting these defaults. These settings lead to operation of the furnace not fully exploiting the available power which leads to a loss of production, for example when operators are led to reduce the speed of travel of the band. The object of the invention is, above all, to provide a method which makes it possible to limit the formation of folds in the strip during rapid heating while keeping the nominal speed of the strip in passing through the rapid heating section, that is to say without loss of production.
Selon l'invention, le procédé de réduction de la formation de plis sur des bandes métalliques soumises à un chauffage rapide dans des lignes continues de traitement thermique, dans lesquelles lesdites bandes sont amenées à traverser des sections de chauffage comportant des moyens de chauffage successifs et distincts, est caractérisé en ce que la pente moyenne de l'augmentation de température de la bande entre l'entrée et la sortie d'un moyen de chauffage diminue d'un moyen de chauffage au moyen de chauffage suivant.According to the invention, the method of reducing the formation of folds on metal strips subjected to rapid heating in continuous heat treatment lines, wherein said strips are passed through heating sections comprising successive heating means and distinct, is characterized in that the average slope of the temperature increase of the strip between the inlet and the outlet of a heating means decreases from one heating means to the next heating means.
L'invention permet de réduire la formation de plis sur la bande dans un brin placé entre deux rouleaux d'entraînement, 3 et 4 selon Fig.1 et 2. Les plis que l'invention permet de réduire sont générés par le chemin thermique de la bande, indépendamment de tout contact de la bande avec un rouleau déflecteur.The invention makes it possible to reduce the formation of folds on the strip in a strand placed between two drive rollers 3 and 4 according to FIGS. 1 and 2. The folds that the invention makes it possible to reduce are generated by the thermal path of the tape, regardless of any contact of the tape with a baffle roll.
Avantageusement, le rapport de la différence de température de la bande, entre la sortie et l'entrée d'un moyen de chauffage, à la distance entre la sortie et l'entrée de ce moyen de chauffage diminue d'un moyen de chauffage au moyen de chauffage suivant.Advantageously, the ratio of the temperature difference of the strip, between the outlet and the inlet of a heating means, to the distance between the outlet and the inlet of this heating means decreases from a heating means to next heating means.
La pente instantanée de l'augmentation de température de la bande entre l'entrée et la sortie d'un moyen de chauffage, en fonction de la distance parcourue, est de préférence plus forte à l'entrée du moyen de chauffage que vers la sortie de ce moyen de chauffage.The instantaneous slope of the increase in temperature of the strip between the inlet and the outlet of a heating means, as a function of the distance traveled, is preferably greater at the inlet of the heating means than towards the outlet of this heating means.
La différence d'intensité de chauffage entre deux moyens de chauffage successifs peut être réduite progressivement pour être faible à haute température de sorte que la variation de la vitesse de chauffage en tous points de la bande se réduise au fur et à mesure que la température de la bande augmente. L'intensité du chauffage entre chaque moyen de chauffage est progressivement modifiée et l'intensité de chauffage entre deux moyens de chauffage successifs est réduite au fur et à mesure que la température de la bande augmente.The difference in heating intensity between two successive heating means can be progressively reduced to be low at high temperature so that the variation of the heating rate at all points of the strip is reduced as the temperature of the the band increases. The intensity of heating between each heating means is gradually changed and the heating intensity between two successive heating means is reduced as the temperature of the band increases.
Avantageusement, on injecte à la bande un flux calorifique plus important lorsque celle-ci est à basse température, puis on diminue progressivement le flux calorifique injecté lorsque la bande monte en température.Advantageously, the band is injected with a larger heat flow when it is at low temperature, then gradually decreases the heat flow injected when the strip rises in temperature.
Le chauffage peut être prévu pour assurer une élévation de température de la bande dans chaque moyen de chauffage de plus en plus faible à partir du premier moyen de chauffage où elle est la plus importante.The heating may be provided to ensure a temperature rise of the strip in each heating means increasingly low from the first heating means where it is the most important.
De préférence, l'évolution du flux échangé entre la bande et les moyens de chauffage est progressive, c'est à dire que la variation de la pente de chauffage est progressive.Preferably, the evolution of the flow exchanged between the strip and the heating means is progressive, that is to say that the variation of the heating slope is progressive.
Le gradient d'élévation de température de la bande dans la première section de chauffage est avantageusement supérieur à 100°C/seconde.The temperature rise gradient of the web in the first heating section is preferably greater than 100 ° C / second.
L'importance de la diminution du gradient d'élévation de température lorsque l'on passe d'une section de chauffage à la suivante est déterminée en fonction du format de la bande et de la qualité de l'acier. Avantageusement, le gradient d'élévation de température de la bande diminue d'au moins 15°C/seconde lorsque l'on passe d'une section de chauffage à la suivante.The importance of decreasing the temperature rise gradient as one passes from one heating section to the next is determined depending on the strip format and the quality of the steel. Advantageously, the temperature rise gradient of the strip decreases by at least 15 ° C / second when passing from one heating section to the next.
Le procédé de l'invention permet de limiter le pic de contrainte correspondant dans le matériau et de réduire les forces de compression perpendiculaires à la direction de défilement de la bande, qui apparaissent en cet endroit entre deux sections consécutives de la bande en provoquant des plis dans cette dernière.The method of the invention makes it possible to limit the corresponding stress peak in the material and to reduce the compressive forces perpendicular to the running direction of the strip, which appear at this point between two consecutive sections of the strip causing folds. in the latter.
L'invention consiste, mises à part les dispositions exposées ci-dessus, en un certain nombre d'autres dispositions dont il sera plus explicitement question ci- après à propos d'exemples de réalisation décrits avec référence aux dessins annexés, mais qui ne sont nullement limitatifs. Sur ces dessins : Fig. 1 est une coupe schématique verticale d'une section de chauffage rapide d'une ligne de traitement thermique de bandes métalliques.The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed below with regard to embodiments described with reference to the accompanying drawings, but which are not in no way limiting. On these drawings: Fig. 1 is a schematic vertical section of a rapid heating section of a heat treatment line of metal strips.
Fig. 2 reprend le schéma de Fig. 1 avec, en correspondance, le flux thermique injecté par chaque moyen de chauffage selon l'état de la technique. Fig. 3 est un diagramme illustrant l'apparition des contraintes induites dans une bande métallique par une variation de température.Fig. 2 is a diagram of FIG. 1 with, in correspondence, the heat flux injected by each heating means according to the state of the art. Fig. 3 is a diagram illustrating the appearance of the stresses induced in a metal strip by a temperature variation.
Fig. 4 est un diagramme illustrant plusieurs modes de chauffage, dont un selon l'invention.Fig. 4 is a diagram illustrating several heating modes, including one according to the invention.
Fig. 5 reprend le schéma de Fig. 2 avec, en correspondance, le flux thermique injecté par chaque moyen de chauffage selon l'invention.Fig. 5 is a diagram of FIG. 2 with, in correspondence, the heat flux injected by each heating means according to the invention.
Fig.6 est un diagramme illustrant les contraintes dans une bande métallique chauffée selon le procédé de l'invention.Fig.6 is a diagram illustrating the stresses in a heated metal strip according to the method of the invention.
Fig.7 est un diagramme illustrant les contraintes dans une bande métallique chauffée selon un procédé classique de l'état de la technique. Fig.8 est un diagramme illustrant les contraintes dans une bande métallique chauffée selon le procédé de l'invention.Fig.7 is a diagram illustrating the stresses in a heated metal strip according to a conventional method of the state of the art. Fig.8 is a diagram illustrating the stresses in a heated metal strip according to the method of the invention.
Fig. 9 reprend le schéma de Fig. 5, avec le flux thermique injecté par chaque moyen de chauffage selon l'invention.Fig. 9 shows the diagram of FIG. 5, with the heat flux injected by each heating means according to the invention.
Fig. 10 montre, agrandi, le détail X de Fig.9. Fig. 11 montre, agrandi, le détail Xl de Fig.9, etFig. 10 shows, enlarged, the detail X of Fig.9. Fig. 11 shows, enlarged, the detail Xl of Fig.9, and
Fig.12 est un diagramme illustrant les variations de contraintes et les variations de température dans une bande métallique chauffée selon le procédé de l'invention.Fig.12 is a diagram illustrating the stress variations and temperature variations in a heated metal strip according to the method of the invention.
On se reporte à la Figure 4 qui est un diagramme sur lequel est porté en abscisse la longueur de la section de chauffage équipée de quatre inducteurs parcourue par un point de la bande métallique, et en ordonnée la température de la bande en ce point. On peut voir que pour atteindre un même objectif thermique correspondant à une température T en fin de section de chauffage, correspondant à la longueur L, il est possible de suivre différents chemins thermiques :Referring to Figure 4 which is a diagram on which is shown on the abscissa the length of the heating section equipped with four inductors traversed by a point of the metal strip, and the ordinate the temperature of the strip at this point. It can be seen that to achieve the same thermal objective corresponding to a temperature T at the end of the heating section, corresponding to the length L, it is possible to follow different thermal paths:
. Le chemin A correspond à une même pente d'élévation de température de la bande dans chaque moyen de chauffage, . Le chemin B correspond à une pente d'élévation de température de la bande dans chaque moyen de chauffage dégressive à partir du premier moyen de chauffage où elle est la plus importante,. Path A corresponds to the same slope of temperature rise of the band in each heating means, . The path B corresponds to a slope of temperature rise of the band in each degressive heating means from the first heating means where it is the most important,
. Le chemin C correspond à une pente d'élévation de température de la bande dans chaque moyen de chauffage qui augmente progressivement à partir du premier moyen de chauffage où elle est la plus faible.. The path C corresponds to a slope of temperature rise of the band in each heating means which increases progressively from the first heating means where it is the lowest.
. Le chemin D correspond à une combinaison des chemins B et C avec une pente d'élévation de température de la bande plus forte dans le premier et dernier moyen de chauffage et plus faible pour les deux moyens de chauffage centraux.. Path D corresponds to a combination of paths B and C with a higher temperature rise slope of the band in the first and last heating means and lower for both central heating means.
Ces quatre chemins thermiques sont donnés à titre d'exemple sachant qu'une multitude d'autres variantes sont possibles.These four thermal paths are given by way of example knowing that a multitude of other variants are possible.
Selon l'invention, la bande est chauffée dans la section de chauffage en suivant le chemin thermique B de montée en température. Comme représenté en Figure 5, ce chemin thermique est obtenu en injectant un flux calorifique Φa important à la bande au début du chauffage, lorsque celle-ci est à plus basse température, puis en limitant progressivement le flux injecté Φb, Φc, Φd au fur et à mesure que la température de la bande augmente.According to the invention, the strip is heated in the heating section by following the thermal path B of temperature rise. As represented in FIG. 5, this thermal path is obtained by injecting a heat flow Φa important to the band at the beginning of the heating, when this is at a lower temperature, then gradually limiting the injected flow Φb, Φc, Φd as and as the temperature of the band increases.
Les flux calorifiques sont avantageusement choisis de telle sorte que :The heat flows are advantageously chosen so that:
- le gradient d'élévation de température de la bande dans la première section de chauffage, c'est-à-dire dans le premier moyen de chauffage 5a, est supérieur àthe temperature rise gradient of the strip in the first heating section, that is to say in the first heating means 5a, is greater than
100°C/seconde.100 ° C / second.
- le gradient d'élévation de température de la bande diminue d'au moins 15°C/seconde lorsque l'on passe d'une section de chauffage à la suivante, c'est-à- dire d'un moyen de chauffage au suivant. Comme représenté en Figure 6, le chemin thermique selon l'invention permet de limiter la variation de pente de la courbe de température en sortie de chaque élément de chauffage au fur et à mesure que la bande monte en température. Les contraintes de compression perpendiculaires à l'axe de la bande, susceptibles de générer des plis, sont ainsi de plus en plus faibles à chaque sortie successive des zones de chauffage rapide : C2a>C2b>C2c>C2d.the gradient of temperature rise of the strip decreases by at least 15 ° C./seconds as one goes from one heating section to the next, that is to say from a heating means to the next. As shown in FIG. 6, the thermal path according to the invention makes it possible to limit the slope variation of the temperature curve at the outlet of each heating element as the strip rises in temperature. Compression stresses perpendicular to the axis of the strip, likely to generate folds, are thus increasingly weak at each successive output of the rapid heating zones: C2a>C2b>C2c> C2d.
Le chauffage assuré par les moyens de chauffage successifs 5a, 5b, 5c, 5d est tel que la courbe moyenne représentant l'élévation de température de la bande en fonction de la longueur de la section de chauffage présente une concavité tournée vers l'axe de coordonnées sur lequel est portée la longueur. Par courbe moyenne on désigne une courbe passant par les milieux des segments rectilignes horizontaux de la courbe réelle d'élévation de température sur la Figure 6. La pente moyenne de l'augmentation de température de la bande entre l'entrée et la sortie d'un moyen de chauffage diminue d'un moyen de chauffage au moyen de chauffage suivant.The heating provided by the successive heating means 5a, 5b, 5c, 5d is such that the average curve representing the rise in temperature of the strip as a function of the length of the heating section has a concavity turned towards the axis of coordinates on which is the length. By mean curve is meant a curve passing through the midpoints of the horizontal straight segments of the actual temperature rise curve in Figure 6. The average slope of the temperature increase of the strip between the inlet and the outlet of heating means decreases from one heating means to the next heating means.
Comme représenté en Figure 7, le niveau (en valeur absolue) de contrainte critique de formation de plis décroît lorsque la température augmente, selon une courbe K, la contrainte étant portée en ordonnée et la température en abscisse. Une section de chauffage réalisée selon l'état antérieur de la technique, c'est à dire sans appliquer le procédé de chauffage selon l'invention, conduirait par exemple à la courbe de contrainte C3, correspondant au chemin thermique A de la Figure 4. On peut constater sur cette courbe que les contraintes transversales de compression sont supérieures aux points C3b, C3c et C3d aux valeurs de seuils critiques. La bande sera donc recouverte de défauts de surface et non commercialisable.As represented in FIG. 7, the level (in absolute value) of critical stress of fold formation decreases when the temperature increases, according to a curve K, the stress being carried on the ordinate and the temperature on the abscissa. A heating section made according to the prior art, ie without applying the heating method according to the invention, would lead for example to the stress curve C3, corresponding to the thermal path A of Figure 4. It can be seen on this curve that the transverse compression stresses are greater than the points C3b, C3c and C3d at the critical threshold values. The strip will therefore be covered with surface defects and not marketable.
On comprend que les chemins thermiques type C et D ne sont pas adaptés car ils induisent des contraintes importantes supérieures à la contrainte critique dans les zones où la bande est la plus chaude.It is understood that the thermal paths type C and D are not suitable because they induce significant stresses greater than the critical stress in the areas where the band is the hottest.
Comme représenté précédemment en Figure 5, le procédé de chauffage selon l'invention consiste à injecter à la bande un flux calorifique plus important lorsque celle-ci est à basse température, puis à diminuer progressivement ce flux lorsque la bande monte en température. La Figure 8 correspond à la Figure 7, mais avec un chauffage effectué selon le procédé de l'invention. On peut constater sur la courbe de contrainte C2 de cette Figure 8 que les contraintes transversales de compression sont toujours inférieures (en valeur absolue) aux valeurs de seuils critiques suivant la courbe K. La bande sera exempte de plis et donc commercialisable.As previously shown in FIG. 5, the heating method according to the invention consists in injecting a larger heat flow into the strip when it is at a low temperature, and then progressively decreasing this flux as the strip rises in temperature. Figure 8 corresponds to Figure 7, but with heating performed according to the method of the invention. It can be seen on the stress curve C2 of this Figure 8 that the transverse compressive stresses are always lower (in absolute value) than the critical threshold values according to the curve K. The strip will be wrinkle-free and therefore marketable.
Pour limiter davantage le risque de formation de plis, l'invention est également caractérisée par un procédé qui consiste à modifier progressivement l'intensité du chauffage dans chaque moyen de chauffage 5 de sorte que le l'évolution du flux échangé avec la bande soit progressif, c'est à dire que l'évolution du taux de variation de la fonction (dTempérature/dtemps) correspondant à une modification de la pente de chauffage soit progressif.To further limit the risk of wrinkling, the invention is also characterized by a method which consists in progressively modifying the intensity of the heating in each heating means 5 so that the evolution of the flow exchanged with the strip is progressive. that is, the change in the rate of change of the function (temperature / time) corresponding to a change in the heating slope is progressive.
Ce procédé permet de limiter le pic de contrainte correspondant dans le matériau et de réduire ou de supprimer les forces de compression perpendiculaires à la direction de défilement de la bande, qui apparaissent en cet endroit entre deux sections consécutives de la bande en provoquant des plis dans cette dernière.This method makes it possible to limit the corresponding stress peak in the material and to reduce or eliminate the compression forces perpendicular to the running direction of the strip, which appear at this point between two consecutive sections of the strip causing folds in the strip. the latter.
Le procédé selon l'invention est illustré plus en détail sur Fig.9. Comme représenté sur cette Fig.9, la variation de flux entre la bande et les moyens de chauffage 5 est progressive selon l'invention depuis l'entrée jusqu'à la sortie de chaque moyen de chauffage alors qu'un chauffage rapide selon l'état de la technique conduirait à la courbe de flux P, représentée en trait fin sur Fig.1O et 11, avec des changements brutaux de la variation de flux. Cette variation progressive du flux selon l'invention est imagée sur la Figure 9 par une courbe de flux arrondie lors des changements de pente entre montée en température, plateau supérieur, puis descente et palier inférieur, alors que ces changements sont à angles vifs sur la courbe P selon l'état de la technique.The method according to the invention is illustrated in more detail in FIG. As represented in this FIG. 9, the flow variation between the strip and the heating means 5 is progressive according to the invention from the inlet to the outlet of each heating means while rapid heating according to the invention. state of the art would lead to the flux curve P, shown in fine lines in Fig. 10 and 11, with abrupt changes in flux variation. This gradual variation of the flow according to the invention is imaged in FIG. 9 by a rounded flow curve during changes in slope between rise in temperature, upper plateau, then descent and lower plateau, whereas these changes are at sharp angles on the curve P according to the state of the art.
Cette évolution progressive du flux conduit à une évolution progressive de la température de la bande pour chaque élément de chauffage, c'est à dire à une évolution progressive du taux de variation de la fonction (dTempérature/dTemps) par rapport à l'état de la technique, comme représenté en Figure 12. Ainsi les points de changement brusque de pente Ta1 et Tb1 de la courbe de température T1 selon l'état de la technique, correspondant à une chauffe avec une rapide évolution de l'intensité de chauffage, ont été supprimés sur la courbe T2 correspondant à une chauffe selon l'invention avec une évolution progressive de l'intensité de chauffage.This gradual evolution of the flow leads to a gradual evolution of the temperature of the strip for each heating element, that is to say to a progressive change in the rate of variation of the function (temperature / time) with respect to the state of the technique, as shown in Figure 12. Thus the points of abrupt change of slope Ta1 and Tb1 of the temperature curve T1 according to the state of the art, corresponding to a heating with a rapid change in the intensity of heating, were removed on the curve T2 corresponding to a heater according to the invention with a gradual change in the heating intensity.
On voit clairement sur cette Figure 12 que l'évolution de la température de bande représentée par la courbe T2 correspondant à une chauffe avec une évolution progressive du flux transmis à la bande conduit à une courbe de contrainte C2 dont l'importance des pics de contraintes de traction Ca2 et de compression Cb2 a été fortement réduite par rapport celle des pics correspondants Ca1, Cb1 de la courbe de contrainte C1 selon l'état de la technique : Ca2«Ca1 et Cb2«Cb1.It is clearly seen in this FIG. 12 that the evolution of the band temperature represented by the curve T2 corresponding to a heating with a progressive evolution of the flux transmitted to the strip leads to a stress curve C2 whose importance of the stress peaks Ca 2 tensile and Cb2 compression was significantly reduced compared to that of the corresponding peaks Ca1, Cb1 of the stress curve C1 according to the state of the art: Ca2 "Ca1 and Cb2" Cb1.
Le niveau réduit de contrainte transversale de compression Cb2 obtenu étant ainsi inférieur au seuil critique, la bande sera exempte de plis et donc commercialisable. The reduced level of transverse compressive stress Cb2 obtained thus being below the critical threshold, the band will be free of wrinkles and therefore marketable.

Claims

REVENDICATIONS
1 - Procédé de réduction de la formation de plis d'origine thermique sur des bandes métalliques (1) soumises à un chauffage rapide dans des lignes continues de traitement thermique dans lesquelles lesdites bandes sont amenées à traverser des sections de chauffage (2) comportant des moyens de chauffage (5 ;5a,5b,5c,5d) successifs et distincts, caractérisé en ce que la pente moyenne de l'augmentation de température de la bande entre l'entrée et la sortie d'un moyen de chauffage diminue d'un moyen de chauffage au moyen de chauffage suivant.A method for reducing heat-induced ply formation on metal strips (1) subject to rapid heating in continuous heat treatment lines in which said strips are passed through heating sections (2) having heating means (5; 5a, 5b, 5c, 5d) successive and distinct, characterized in that the average slope of the temperature increase of the strip between the inlet and the outlet of a heating means decreases heating means to the next heating means.
2. Procédé selon la revendication 1, caractérisé en ce que le rapport de la différence de température de la bande, entre la sortie et l'entrée d'un moyen de chauffage, à la distance entre la sortie et l'entrée de ce moyen de chauffage diminue d'un moyen de chauffage au moyen de chauffage suivant.2. Method according to claim 1, characterized in that the ratio of the temperature difference of the band, between the output and the input of a heating means, to the distance between the output and the input of this means of heating decreases from one heating means to the next heating means.
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que la pente instantanée de l'augmentation de température de la bande entre l'entrée et la sortie d'un moyen de chauffage, en fonction de la distance parcourue, est plus forte à l'entrée du moyen de chauffage que vers la sortie de ce moyen de chauffage.3. Method according to claim 1 or 2, characterized in that the instantaneous slope of the temperature increase of the strip between the inlet and the outlet of a heating means, as a function of the distance traveled, is stronger. at the inlet of the heating means to the outlet of this heating means.
4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que la différence d'intensité de chauffage entre deux moyens de chauffage successifs (5a,5b,5c,5d) est réduite progressivement pour être faible à haute température de sorte que la variation de la vitesse de chauffage en tous points de la bande se réduise au fur et à mesure que la température de la bande augmente.4. Method according to any one of claims 1 to 3, characterized in that the difference in heating intensity between two successive heating means (5a, 5b, 5c, 5d) is gradually reduced to be low at high temperature. so that the variation of the heating rate in all points of the band is reduced as the temperature of the band increases.
5 - Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que l'intensité du chauffage entre chaque moyen de chauffage est progressivement modifiée et en ce que l'intensité de chauffage entre deux moyens de chauffage successifs est réduite au fur et à mesure que la température de la bande augmente. 5 - Process according to any one of claims 1 to 3, characterized in that the intensity of heating between each heating means is gradually changed and in that the intensity of heating between two successive heating means is reduced as and as the temperature of the band increases.
6. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce qu' on injecte à la bande un flux calorifique (Φa) plus important lorsque celle-ci est à basse température, puis on diminue progressivement le flux calorifique injecté (Φb, Φc, Φd) lorsque la bande monte en température.6. Method according to any one of claims 1 to 3, characterized in that one injects to the band a heat flow (Φa) more important when it is at low temperature, then gradually decreases the heat flow injected ( Φb, Φc, Φd) when the strip rises in temperature.
7. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que le chauffage est prévu pour assurer une élévation de température de la bande dans chaque moyen de chauffage de plus en plus faible à partir du premier moyen de chauffage où elle est la plus importante.7. Method according to any one of claims 1 to 3, characterized in that the heating is provided to ensure a temperature rise of the band in each heating means increasingly low from the first heating means where it is the most important.
8 - Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que l'évolution du flux échangé entre la bande et les moyens de chauffage est progressive, c'est à dire que la variation de la pente de chauffage est progressive.8 - Process according to any one of claims 1 to 3, characterized in that the evolution of the flow exchanged between the strip and the heating means is progressive, that is to say that the variation of the heating slope is progressive .
9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le gradient d'élévation de température de la bande dans la première section de chauffage est supérieur à 100°C/seconde.9. Method according to any one of the preceding claims, characterized in that the temperature rise gradient of the strip in the first heating section is greater than 100 ° C / second.
10. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le gradient d'élévation de température de la bande diminue d'au moins 15°C/seconde lorsque l'on passe d'une section de chauffage à la suivante. Method according to one of the preceding claims, characterized in that the temperature rise gradient of the strip decreases by at least 15 ° C / second when switching from one heating section to the next .
EP07731385A 2006-05-02 2007-04-27 Improvement made to the rapid heating sections of continuous heat-treatment lines Withdrawn EP2016202A2 (en)

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