EP2176438B1 - Combined annealing and galvanisation line and method for converting a continuous annealing line into such combined line - Google Patents

Abstract

The invention relates to a combined annealing and galvanisation line of a metal strip (1), that successively comprises an annealing station (2) with an annealing section (22), a quenching section (23), an over-ageing section (26) and a second slow-cooling section (25), and a galvanisation station (4) ending in a tempering bath. According to the invention, the galvanisation station (4) is integrated inside the annealing station (2) between the over-ageing section (26) and the second cooling section (25) and, at the output of the over-ageing section (26), the strip is directed by selective guiding means (80) either to the galvanisation station (4) and directly to the line output device (3), or directly to the second cooling section (25) and the line output device (3). The invention also relates to a particularly simple and economical method for converting an existing continuous annealing line into a combined annealing and/or galvanisation line.

Description

The invention relates to a combined annealing and galvanizing line of a metal strip and also covers a method of converting an existing annealing line into such a combined line.

The cold rolling of a steel strip causes hardening, by hardening, of the metal which causes a fragility making it more difficult and may even prohibit the subsequent use of the rolled strips.

In order to restore the ductility of a rolled strip, a so-called "recrystallization annealing" heat treatment is usually used. Such treatment can be performed statically in patch-annealing ovens on the coil-wound web. However, for some time, to prevent unwinding and winding of the coils and their transport from one facility to the next, it has been proposed to perform the treatment of these strips in continuous scrolling on specialized lines.

• Un dispositif d'entrée 1 comportant une ou deux dérouleuses de bande 11, une cisaille 12, par exemple à guillotine, une soudeuse de raboutage 13 permettant de raccorder la queue d'une bande issue d'une première dérouleuse à la tête de la bande suivante issue de la seconde dérouleuse afin d'assurer un fonctionnement continu de la ligne, et un accumulateur de bande 14 permettant, lorsque le déroulement est stoppé en amont, pour réaliser la soudure de raboutage, de délivrer à sa sortie, une certaine longueur de bande préalablement accumulée afin de poursuivre le défilement en continu de celle-ci dans les appareillages placés en aval.
• Une installation de recuit 2 comportant une section de préchauffage 21, une section 22 de chauffage et de maintien à la température de recuit pendant le temps nécessaire, une section de refroidissement rapide 23, une section de survieillissement 24 et une seconde section 25 de refroidissement lent.
• Un dispositif de sortie 3 comportant un accumulateur de bande 31, éventuellement un laminoir de skin-pass 32, une cisaille 33 et une ou deux enrouleuses 34 travaillant alternativement.

The figure 1 schematically shows, by way of example, the usual arrangement of such a continuous annealing line which comprises successively, in the running direction of the strip:

• An input device 1 comprising one or two belt unrollers 11, a shear 12, for example a guillotine, a splicing welder 13 for connecting the tail of a strip from a first unwinder to the head of the strip next from the second unwinder to ensure continuous operation of the line, and a strip accumulator 14 allowing, when the flow is stopped upstream, to perform the solder splicing, to deliver at its output, a certain length of previously accumulated tape in order to continue the continuous scrolling thereof in downstream equipment.
• An annealing plant 2 having a preheating section 21, a section 22 for heating and maintaining the annealing temperature for the necessary time, a section of rapid cooling 23, a supernatant section 24 and a second slow cooling section.
• An output device 3 comprising a tape accumulator 31, possibly a skin-pass rolling mill 32, a shear 33 and one or two winders 34 working alternately.

The entire annealing installation forms a furnace generally placed under a controlled atmosphere in a closed enclosure, and wherein the strip travels along a zig-zag path defined by a plurality of deflection rollers and which successively provides the heating of the band in section 21, its maintenance at the annealing temperature in section 22, a first cooling in section 23, fast enough to avoid oxidation, a complement of overaging treatment, in English "overaging" in the section 24, which usually comprises several successive units and a slow cooling in the section 25 which ends, usually, by quenching the strip in a final cooling liquid bath to room temperature.

• un dispositif d'entrée 1 du type décrit précédemment, comprenant une dérouleuse 11, une cisaille 12, une soudeuse de raboutage 13 et un accumulateur 14,
• une installation de recuit 2,
• une installation de galvanisation 4 comprenant un bain de métal liquide 41, un dispositif d'essorage 42, un circuit de sortie avec par exemple, un four d'alliation 43 et un équipement de refroidissement 44 et un bac de tempe 45,
• un dispositif 3 de sortie de la ligne comportant par exemple un laminoir skin-pass 32, une section de passivation 35, un accumulateur de sortie 31, une cisaille 33 et une ou deux enrouleuses 34 travaillant alternativement.

Furthermore, in order to improve the corrosion resistance of the metal sheets used in particular, in certain applications such as the building, the automobile or household appliances, it is common practice to deposit on the surface of these sheets a layer of cladding. zinc or a zinc-based alloy. For this, usually, the tape is passed over a roll immersed in a bath of liquid metal. It is therefore necessary that the band, before entering the bath, be brought to the desired temperature. Since, usually, the strip has undergone annealing treatment, it is possible to produce continuous annealing and galvanizing lines of the type shown schematically on the strip. figure 2 , comprising successively, in the direction of scrolling the product:

• an input device 1 of the type described above, comprising a unwinder 11, a shear 12, a splicing welder 13 and an accumulator 14,
• an annealing installation 2,
• a galvanizing installation 4 comprising a bath of liquid metal 41, a dewatering device 42, an output circuit with, for example, an alloying oven 43 and a cooling equipment 44 and a tundish 45,
• a device 3 for output of the line comprising for example a skin-pass 32, a passivation section 35, an output accumulator 31, a shear 33 and one or two winders 34 working alternately.

In such a continuous galvanizing line, the annealing installation 2 successively performs the metallurgical annealing and correct temperature-setting functions of the strip before it enters the metal bath 41. It therefore comprises a preheating section 21, a retention section 22 at the annealing temperature, a rapid cooling section 23 and a section 26 of galvanizing temperature in which can also be carried out an activation of the surface to be galvanized by surface chemical migrations.

In general, such lines of continuous processing constitute a heavy equipment with a very high cost and which requires, in order to be profitable, a large production. A modification of the adjustment parameters depending on the grade of the metal to be treated and the qualities to be obtained in fact leads to a stopping of the line with a loss of productivity and the production of waste.

Complete annealing lines of the type shown on the figure 1 are therefore normally provided for steel grades which justify a large tonnage and are equipped with all the equipment necessary to adapt to a new grade after modification of the adjustment parameters, in particular temperatures and the duration of the heat treatments.

However, market developments, especially for the automotive industry, are leading to a greater variety of steel grades and their metallurgy as well as a higher demand for galvanized strips.

In addition, the tonnages required in each grade are relatively small and require rapid changes in setting parameters, sometimes without stopping scrolling, the tail of a coil at the end of unwinding can be welded to the head of a next coil, of different quality and requiring other treatments.

As a result, a number of continuous line annealing facilities, planned for large tonnages, no longer become profitable due to market developments and decreasing tonnages demanded. On the other hand, the demand for galvanized sheet is increasing and it is therefore interesting to produce continuous lines that allow the demand to be met flexibly. It is therefore necessary to achieve new combined lines to continuously perform either an annealing treatment alone, or annealing followed by galvanization.

The document EP-A-0254633 for example, describes such a combined line comprising successively, between a reel and a winder, a horizontal annealing furnace, a temperature control section and a conventional type of galvanizing installation. There is also a coating coating installation. According to the invention, to allow a passage from one treatment to another, without increasing the complexity and the cost of such an installation, the treated metal flow must be at most 7 tons / hour, at a speed of passage at most equal to 12 meters per minute. The production capacity of such an installation, designed some twenty years ago, would have been very limited.

It was also proposed in the document WO-002/22894 placing a galvanizing plant downstream of an annealing plant between the controlled atmosphere cooling section and a final cooling tank to ambient temperature. The galvanizing installation is therefore added to the annealing installation and increases the bulk of the assembly.

The object of the invention is to solve such problems by means of a particular arrangement of the different equipment necessary, on the one hand for annealing and on the other hand for galvanization, making it possible to produce a combined line capable of performing either annealing alone, or an annealing followed by galvanization, without unduly increasing the congestion in length of the line.

In addition, this particular arrangement of the equipment makes it possible, according to the invention, to quite simply convert an existing continuous annealing installation to add galvanizing means without excessive modification of the existing installation and remaining in the floor area of the floor. it.

Thus, the invention makes it possible to continue a profitable exploitation of certain existing continuous annealing installations that are no longer adapted to the requirements of the market, by transforming them into a combined line capable of handling a very wide variety of products.

The invention therefore relates to a combined annealing and galvanizing line of a metal strip comprising means for controlling the movement of the strip in a continuous line, between an input device and an output device of the line, successively in a annealing apparatus and a galvanizing plant, the annealing apparatus having a section for heating and holding the band at an annealing temperature, a first annealing section after annealing, an overaging section and a second cooling section up to ambient temperature, and the galvanizing plant having an inlet section of the strip in a galvanizing metal bath, an outlet section of the metal bath of the strip covered on both sides with a layer coating, a cooling section of the coating and a final coolant bath.

According to the invention, the galvanizing plant is incorporated inside the annealing plant, between the overaging section and the second cooling section, and at the outlet of the overaging section, the band is directed by selective guiding means, either to the galvanizing plant and then, at the outlet of the final cooling bath, directly to the output device of the line, or directly to the second cooling section and then to the output device of the line.

In a preferred embodiment, the overfill section and the second cooling section of the annealing plant are each placed in a sealed enclosure filled with a protective gas and the inlet section in the galvanizing metal bath is placed in a sealed duct having an inlet connected to the outlet of the overflow section and two outlets, respectively a first outlet immersed in the metal bath and a second outlet on which is releasably connected a leaktight trough with the second section cooling and annealing installation, said second outlet being provided with removable sealing means.

According to another preferred feature, the combined line according to the invention comprises a plurality of deflection rollers defining two paths of the strip at the exit of the overaging section, respectively a first galvanization path comprising an inlet section in the metal bath. passing through the first outlet of the sealed conduit, an outlet section of the metal bath, a cooling section of the coating prior to entry into the final cooling bath, and an exit section of said cooling bath passing above or below the enclosure in which is placed the second cooling section, so as to connect directly to the output device of the line, and a second annealing path alone, passing through the removable connection channel between the second outlet of the sealed conduit and the enclosure of the second cooling section.

Particularly advantageously, the combined line comprises two liquid final cooling baths of the strip, respectively a first bath placed at the outlet of the galvanizing installation, and a second bath placed at the outlet of the second cooling section, the strip being directed towards the outlet device of the line after final cooling carried out, either in the first bath after galvanization, or in the second bath after an annealing treatment alone, without galvanizing.

Preferably, the first cooling bath is placed above the metal bath and offset to the inlet side thereof to reduce the bulk of the galvanizing plant.

To allow the incorporation of the galvanizing plant into the annealing installation without increasing the length of the line, the over-age section has a reduced length compared to the length usually required in a continuous annealing line. and the running speed of the web is adapted to this reduced length in order to obtain the necessary processing time.

The invention also covers a process for converting into a combined annealing and galvanizing line, an existing continuous annealing line of a metal strip comprising successively, in a running direction of the product, an input device in the line, a preheating section, an annealing section, a first rapid cooling section after annealing, a supercooling section, a slow cooling section under a protective atmosphere and a line output device.

According to the invention, part of the overaging section is removed leaving the other sections in place and a galvanizing installation is placed inside the annealing line, in the space thus released between the remaining part of the overfill section and the second slow cooling section, and connected to the scroll control means so as to achieve a combined annealing and galvanizing line without increasing the overall length of the annealing line.

According to another characteristic of the invention, the running speed of the web between the input device and the output device of the line is adapted either to the annealing process alone or to the galvanizing process.

According to another advantageous characteristic, the installation of The galvanization replaces only a part of the overaging section and the running speed of the band is adjusted, if necessary, so as to carry out a survival treatment in the remaining part of the corresponding section.

According to another preferred characteristic, the temperature in the annealing section is maintained at the desired level for annealing, taking into account the nature of the strip and the speed of travel and, between the exit of the overaging section and the inlet in the galvanizing bath, the installation comprises combined means of heating and cooling, for adjusting the temperature of the strip to a level suitable for the galvanizing process.

In a preferred embodiment, the galvanizing installation comprises means for controlling the running of the strip between a galvanizing metal bath and a quenching bath, along a continuous scrolling path passing over a plurality of deflection rollers. and having at least four portions, respectively a first connection portion between the quench section and the inlet to the metal bath, a second exit portion of the metal bath with coating thickness control, a third cooling portion coating before entering the quench bath and a fourth quenching bath outlet portion, connecting directly to the exit section of the annealing line, without passing through the slow cooling section.

Furthermore, to adapt the overall size of the galvanizing installation to the length of the space released in the annealing line, the quenching bath is placed above the metal bath and shifted towards the inlet side of the the line, so that in the third cooling part, the strip returns to the rear and, in the fourth quenching bath outlet portion, passes over the metal bath and then above or below the slow cooling section to connect directly to the output device of the line.

• La figure 1 montre schématiquement la disposition classique d'une ligne continue de recuit, suivie d'une section de finissage.
• La figure 2 montre schématiquement la disposition connue d'une ligne continue de galvanisation après recuit.
• La figure 3 est un diagramme représentant deux exemples de cycles thermiques de recuit continu.
• La figure 4 montre un cycle typique de recuit dans une ligne de galvanisation en continu.
• La figure 5 montre schématiquement la disposition, selon l'invention, d'une ligne combinée de recuit et de galvanisation.
• La figure 6 montre schématiquement, à échelle agrandie, la disposition selon l'invention d'une installation de galvanisation.
• La figure 7 et la figure 8 sont deux diagrammes indiquant, à titre d'exemple deux cycles complets de recuit dans une ligne combinée selon l'invention.
• La figure 9 montre schématiquement la disposition, selon l'invention, d'une installation de galvanisation à l'intérieur d'une ligne de recuit continu.
• La figure 10 montre de façon synthétique, les fonctions propres au recuit continu et à la galvanisation ainsi que celles communes aux deux traitements.

Other advantageous features of the invention will appear in the following description of certain particular embodiments, given by way of simple examples with reference to the accompanying drawings.

• The figure 1 schematically shows the conventional layout of a continuous annealing line, followed by a finishing section.
• The figure 2 shows schematically the known arrangement of a continuous line of galvanization after annealing.
• The figure 3 is a diagram showing two examples of continuous annealing thermal cycles.
• The figure 4 shows a typical annealing cycle in a continuous galvanizing line.
• The figure 5 shows schematically the arrangement according to the invention of a combined annealing and galvanizing line.
• The figure 6 schematically shows, on an enlarged scale, the arrangement according to the invention of a galvanizing installation.
• The figure 7 and the figure 8 are two diagrams indicating, by way of example, two complete cycles of annealing in a combined line according to the invention.
• The figure 9 schematically shows the arrangement, according to the invention, of a galvanizing installation inside a continuous annealing line.
• The figure 10 shows in a synthetic way, the functions of continuous annealing and galvanization as well as those common to both treatments.

As mentioned above, the figure 1 represents, schematically, the conventional arrangement of a continuous annealing line comprising, between an input device 1 and an output device 3, an oven 2 in which the strip travels along a zig-zag path, between two series baffle rollers, respectively upper and lower, and consisting of successive sections respectively heating the band M in section 21, maintaining it at the annealing temperature in section 22, rapid cooling in section 23, a complement of so-called over-aging or "over" treatment aging "in section 24 with several successive units and slow cooling to a moderate temperature, in section 25.

The figure 3 is a diagram showing two examples of continuous annealing cycles shown, respectively, by curve 5 for a direct flame furnace and by the 5 'curve for heating without direct flame, for example by reverberation.

The heating has no particular metallurgical impact up to 600 ° C and the rate of rise in temperature (51, 51 ') can be more or less rapid depending on the heating technology used. Beyond 600 ° C and up to the maximum temperature, heating is continued at a lower speed (52, 52 ') in order to improve the control of the temperature.

The annealing temperature (53, 53 ') depends on the metallurgical quality targeted. It is generally between 650 and 700 ° C for tinplate and 700 to 850 ° C for a thin strip for galvanizing. The holding time (53, 53 ') generally close to 15 to 30 seconds, makes it possible to stabilize the annealed structure.

This holding phase (53, 53 ') is followed by a controlled cooling (54, 54') at a slow speed, generally below 10 ° C./s up to a temperature of 600 to 700 ° C. to ensure the precipitation of Fe ₃ C carbides.

Then, in the section 23 of the furnace, a cooling is carried out to a temperature of about 350 to 450 ° C., which is rapidly conducted (55, 55 '), the cooling rate being greater than 100 ° C./s and up to 200 ° C / s to maintain carbon in solution.

The treatment then continues, in section 24, by maintaining the temperature for a period of one to several minutes (56, 56 '), in order to produce the precipitation of the interstitial carbon in a so-called overaging phase. .

The cycle ends with cooling (57, 57) to a moderate temperature, for example about 60.degree. possibly up to room temperature.

The figure 4 is a diagram showing a typical cycle of annealing in a galvanizing line of the type shown in FIG. figure 2 . The curve 5a which shows the evolution of the temperature as a function of time is analogous to the curves 5, 5 'described previously and therefore comprises the same portions (51a, 52a) of temperature rise, (53a) of maintenance at the temperature of annealing, (54a) controlled cooling at low speed, then (55a) rapid cooling.

As indicated above, the galvanizing line of the type shown on the figure 2 also comprises a thermal control section 26 for performing, first of all over-aging (56a) and then, by cooling (57a) or possibly heating, to bring the strip to the temperature (58a) desirable for the entering the galvanizing bath.

The thermal cycle 5a in the galvanizing line is therefore similar to the cycle 5 in an annealing line of the type shown in FIG. figure 1 , the differences coming essentially from the speed of movement imposed by the galvanizing process which must not exceed, normally, 200 m / min in order to be able to control the thickness of the coating deposited at the exit of the metal bath whereas the usual speeds of Continuous annealing lines for thin sheets are in the range of 300 to 500 m / min.

Such speeds are necessary to obtain the desired productivity in a conventional continuous annealing line which must be capable of treating steels of different types for which the heat treatment, in particular of over-aging, can be more or less complex and requires the use several successive processing units.

The invention is based on the idea that, even for conventional and relatively complex annealing treatments, it should be possible to reduce the length of the overaging section, as compared to the usual length, and that the removal of certain chambers of overaging would provide a space in which a galvanizing plant could be incorporated, without increasing the overall size of the annealing line, to achieve a combined line to perform either an annealing treatment alone or a treatment of galvanization preceded by annealing.

For example, if one-third of the passes in the overfill section of a continuous annealing furnace for thin sheets with equipment sizes are removed, for a given product format, to allow a speed of the order of 300 m / min, it is enough to reduce the running speed to 200 m / min to achieve the same treatment on a reduced section of a third, while maintaining the same temperature maintenance time. However, this speed of 200 m / min is close to the scroll speed usually imposed for the galvanizing process and is therefore suitable for a combined line.

This produces an installation of the type shown schematically on the figure 5 including, as in the case of figure 2 , an inlet device 1, an annealing furnace 2, a galvanizing plant 4 and an outlet device 3, but in which the galvanizing temperature setting section 26 corresponds to a part only 24 'of the over-aging 24 of the annealing furnace 2 shown in FIG. figure 1 . The galvanizing plant 4 'is therefore incorporated inside the annealing line since it is placed between the reduced overaging section 26 and the slow cooling section under a controlled atmosphere.

In addition, the output of the overaging section opens into a selective guiding device 80 for directing the band M, either directly to the slow cooling section 25, for an annealing treatment alone, or to the input T1 of the In this case, at the outlet of the final cooling bath 45, the strip is directed directly towards the outlet device 3 of the line, by short-circuiting the cooling section 25.

However, if one wishes not to increase the length In the overall annealing line, the space left by the removal of a portion of the overaging section must have a relatively small length, less than the normal footprint of a conventional galvanizing plant.

It is therefore interesting to realize a particularly compact galvanizing installation.

For this, one of the ideas of the invention consists in modifying the usual architecture of the continuous galvanizing lines by organizing in a new way the unwinding of the strip at the outlet of the zinc bath, as shown schematically on the figure 5 and more in detail on the figure 6 .

At the exit of the overaging section 26, the strip has been brought to the desired temperature for galvanizing, as shown in the diagram of FIG. figure 4 . The band leaving the section 26 passes over a deflector roll D1 which directs it to the galvanizing metal bath 41 formed in a tank and in which is immersed a deflection roll D2. The band M therefore follows a downward path T1 between the output roller D1 and the immersed roll D2 on which it bears by its upper face A.

The strip M then comes out of the bath 41 in an upward path T2 to an upper roll D3, passing in front of a wiper device 42 of known type for controlling the thickness of the coating.

All these provisions are classic and correspond to those shown schematically on the figure 2 .

In the invention, however, the band M bears on the upper roll D3 by the same side A passing on the immersed roll D2 and, therefore, instead of being directed towards the outside of the tank containing the metal bath 41, the band M returns back to the entrance side in the tray, that is to say the left side on the figures 5 and 6 .

In the case of figure 5 , the strip returns to an upper roll D'3 and descends, by a downward path T3, to a deflector roll D4 immersed in the quenching bath 45. The The strip then exits from this bath 45 along a rising path T4 to a pair of upper deflector rollers D5, 5 spaced apart from each other, so as to pass over the entire installation. galvanizing 41 and the slow cooling section 25, then descends, by a downward path T5, to a lower roller D6 to be directed to the accumulator 31 of the output device 3.

As a result of this arrangement of the path of the strip, the quenching bath 45 can be placed above the tank containing the galvanizing metal bath 41. Thus, the footprint of the galvanizing plant 4 is reduced by compared to the classic layout of the figure 2 since it covers substantially the same length as the galvanizing bath 41.

Admittedly, this arrangement requires the construction, above the metal bath 41, of a floor to support the quench tank 45 but this increase in height of the installation does not constitute a real disadvantage, particularly for the transformation of an existing installation. On the other hand, the return towards the rear of the strip from the upper roller D3 makes it possible to incorporate the entire galvanizing installation into the existing reduced space between the remaining part of the overaging section. and the slow cooling section 25.

In known manner, it is possible to perform a so-called alloy heat treatment which ensures the diffusion of iron from the band to the zinc coating to create a real iron / zinc alloy. For this purpose, it is possible to place an alloy oven 43 above the wiper device 42. This alloying oven can be followed by cooling cells 44a, 44b which can be placed not only on the upward path T2, upstream of the upper roller D3, but also on the descending path T3, before entering the quench bath 45.

To achieve sufficient cooling of the strip before quenching, without unduly increasing the height of the installation, it is also possible to make the arrangement schematically represented on the figure 6 in which, after passing over the upper roll D3, the strip descends to a lower roll D6, then back to an upper roller D'6 to descend into the quenching tank 45 by passing on the submerged roll D4 .

Such an arrangement is also particularly compact since, at each change of direction, the band passes on a single roll returning, as before, to the rear.

This arrangement also makes it possible to distribute cooling means 44, 44 'not only along the upward path T2 but also along the downward path T3 so as to provide sufficient cooling of the coating.

It should be noted that, thanks to this arrangement, the face A 'of the strip opposite the face A passing on the immersed roll D2, comes into contact with the lower roll D6 after the upward path T2 and the descending path T3 and, thus, not likely to be deteriorated before curing the coating. Such an arrangement is particularly advantageous in applications where an outer face of the sheet, called "exposed face" must have excellent surface quality, for example for the automobile body.

As shown in figure 6 , the cooling cells and, where appropriate, the alloying furnace 43, may advantageously be staggered on the ascending strand T2 and the descending arm T3 which, in the case of the figure 6 , are separated only by a single deflection roll D3, which further reduces the footprint of the assembly.

In addition, such an arrangement makes it possible to distribute the cooling cells 44a, 44b over a greater length of strip and thus to have a less violent blowing, which reduces the risks of vibration of the strip which may have an impact on the quality. coating, in particular the regulation of its thickness.

As mentioned above, even if its length is reduced compared to the usual arrangement of annealing furnaces shown on the figure 1 , the outlet section 26 of the oven 2 allows, by adjusting the speed of travel at a moderate level, for example 200 m / min, to perform a survival treatment adapted to the nature of the metal, then to ensure the implementation at the appropriate temperature of the strip before entering the zinc bath 41.

It should be noted, in particular, that the current evolution of the market leads to making steels for which the aging, after annealing, is carried out at a relatively low temperature.

The figure 7 , for example, shows a complete annealing cycle for a "TRIP" type steel which requires, after annealing, isothermal retention in the bainitic transformation zone, that is to say around 290 ° C. In this case, the outlet section 26 of the furnace must raise the temperature of the strip to a level compatible with the temperature of the zinc bath, for example 470 ° C.

The figure 8 on the other hand, corresponds to the case of a common steel requiring overaging, for example at 560 ° C. In this case, the temperature must be lowered to the temperature of the zinc bath.

The temperature control section 26 will therefore be equipped with heating means, preferably by induction and cooling, preferably by neutral gas jet.

It should be noted, on the other hand, that the galvanizing installation 4 placed, according to the invention, between the outlet section 26 of the oven 2 and the slow cooling section 25, is provided, at its output, with a quenching bath 45 at the output of which the strip is at a temperature close to ambient. Therefore, it is not necessary to pass the strip in the slow cooling section 25, the quenching bath 45 being connected directly to the output accumulator 31.

A combined line has thus been realized to ensure, as the case may be, the continuous annealing line functions in the oven 2 and the final cooling section 25 and galvanizing continuous line in the furnace 2 and the galvanizing plant 4 which ends with the quench bath 45.

The figure 9 schematically shows the layout of an installation to easily switch from one mode of operation to another.

The annealing to be carried out in a controlled atmosphere, the entire annealing furnace 2, with the overaging section 26, is placed in a closed enclosure 8 provided at its base with a conduit 80 which forms a branch with two outlets , respectively a first outlet 81 which plunges inside the metal bath 41 to ensure sealing, and a second outlet 82 which can be removably closed by a door 83.

On the other hand, the slow cooling section 25, also placed under a controlled atmosphere, is disposed in a sealed enclosure 8 'whose inlet 81' can be connected to the second outlet 82 of the duct 80 via a connecting chute 84 which can be moved, for example by pivoting, between the position shown on the figure 9 for which the chute 84 is tightly connected to the second outlet 82 of the duct 80 and a spaced apart position allowing the passage of the strip M along the path T2, at the outlet of the metal bath 41.

This mobile chute 84 thus forms a bypass tunnel allowing, when it is put in place and the door 83 open, to ensure the passage of the band M between the deflector roll D1 placed at the outlet of the oven and the section cooling 25, sealing between the two closed enclosures 8 and 8 'in which is formed a neutral atmosphere, for example a mixture of nitrogen and hydrogen.

The figure 10 is a schematic diagram of the operation of such a combined line.

To carry out a galvanization after annealing, the band M successively passes through the various sections of the annealing furnace 2 and, after being put into temperature in the outlet section 26, passes through the first outlet 81 of the duct 80 to open into the zinc bath 41. As shown in figure 9 at the outlet of the quenching bath 45, the strip M guided by the deflecting rollers D5, D5, D7, passes below or, optionally, above the slow cooling section 25 to be directed directly to the 3 output device of the line.

To perform annealing alone, the connecting trough 84 is put in place and the door 83 is opened. From the deflector roll D1, the band M passes into the connecting chute 84, then into the slow cooling section 25 which preferably terminates in a quenching tank 27 and is then directed by the drive rollers D8 to the output device 3 of the line.

The installation is equipped, on the other hand, with means not represented on the figure 9 , making it possible to cut the strip, either at a point 85, at the inlet into the connecting chute 84, or at a point 86, at the outlet of the cooling zone 25, upstream of the driving rollers D8.

At the end of a continuous annealing campaign, the strip is cut at these two points 85 and 86, the mobile tunnel 84 is raised vertically and held against the front wall of the enclosure 8 'containing the cooling section 25. A band portion remains engaged in the tunnel 84 and section 25. It will serve as a "pull tape" to put the line in annealing configuration in another campaign.

Similarly, at the end of a galvanizing campaign, the strip is cut at two points, respectively 87 at the exit of the zinc bath 41 and 88 after the exit of the quenching bath 45. The hanging strands of the strip are attached to the frame members carrying the galvanizing plant 4 '. A portion of band remains engaged in this area and will serve as a draw tape to put the line in galvanizing configuration, in another campaign.

To pass from one configuration to another, it suffices to weld or staple the relevant portion of "pulling strip" at the end of the new strip, at the level of the deflector roll D1, in the outlet duct 80 of the overaging zone 26, then to advance this pulling strip to the shear 33, at the exit of the line, to eliminate it.

The invention thus makes it possible to carry out either an annealing alone or a galvanization after annealing in a combined line of the type shown in FIG. figure 5 , the overall overall length of which is of the same order as that of a conventional continuous annealing line, insofar as the galvanizing installation, in particular if it is carried out in the particularly compact manner described above, can incorporated within the annealing line, between the overaging section and the slow cooling section.

Therefore, the invention will find a particularly interesting application for the transformation of existing continuous annealing lines whose profitability is no longer assured due to the variety of qualities of sheet required and the resulting tonnage decline.

Indeed, because the tonnages requested are lower, It will be possible to reduce the speed of scrolling and remove some units of the overaging section, the remaining portion of this section being sufficient to achieve the heat treatments necessary for most steel qualities currently required, the space thus cleared to accommodate a compact type galvanizing installation as described above.

It should be noted, moreover, that a number of the equipment used in the deleted part of the over-aging section, in particular the gas jet cooling cells and the auxiliary members may be used in the galvanizing plant.

The invention has further advantages and is not limited to the details of the embodiments which have been described as mere examples. For example, after sufficient cooling by the cells 44a, 44b placed in the path of the strip at the exit of the galvanizing bath 41, the band could pass over the cooling section 25 for descend directly into the quench bath 27 placed at the outlet thereof. However, the use, according to the preferred embodiment of the figure 9 , two separate quench tanks, respectively 45 at the exit of the galvanizing plant 4 and 27 at the outlet of the cooling zone 25, avoids the pollution by zinc dust cooling tank 27 in which pass the uncoated annealed strips, in case of annealing operation alone.

Claims (12)

1. Combined annealing and galvanisation line for a metal strip (1) having means to control the movement of the strip along a continuous line, between an input device (1) and an output device (3) of the line, successively in an annealing installation (2) and a galvanisation installation (4), the annealing installation (2) having a heating section (21), a section (22) for keeping the strip (M) at an annealing temperature, a first section (23) for rapid quenching following annealing, an over-ageing section (24) and a second slow quenching section (25), and the galvanisation installation (4) having a strip input section (T1) in a metal galvanisation bath (41), an output section (T2) from the metal bath of the strip covered, on both faces, with a coating, a section (T3) for quenching the coating and a final quenching liquid bath (45), characterised in that the galvanisation installation (4) is built inside the annealing installation, between the over-ageing section (24, 26), and the second quenching section (25) and that, at the output of the over-ageing section (24, 26), the strip is directed by selective guiding means (80), either towards the galvanisation installation (4) then, at the output of the final quenching bath (45), directly towards the line output device (3), or directly towards the second quenching section (25) and the line output device (3).
2. Combined line according to claim 1, characterised in that the over-ageing section (26) and the second quenching section (25) of the annealing installation (2) are each placed in a sealed enclosure (8, 8') filled with a protective gas and that the input section in the metal galvanisation bath (41) is placed in a sealed conduit (80) forming a junction with an input connected to the output of the enclosure (6) of the over-ageing section (26) and two outputs, respectively a first output (81) dropping into the metal bath (41) and a second output (82) to which is connected a detachable chute (84) making a sealed connection with the enclosure (81) of the second quenching section (25) of the annealing installation, said second output (82) being provided with detachable sealing means (83).
3. Combined line according to claim 2, characterised in that it has a plurality of deflector rolls defining two strip routes at the output of the over-ageing section (16), respectively a first galvanisation route having an input section (T1) in the metal bath passing via a first output (81) of the sealed conduit (80), an output section (T2) from the metal bath (41), a coating quenching section (T3) before input in the final quenching bath (45) and an output section (T4, T5) from said quenching bath (45), passing above or below the enclosure (8') in which is placed the second quenching section (25), such as to connect directly to the line output device (3), and a second annealing-only route, passing through a detachable linking chute (84) between the second output (82) of the sealed conduit (80) and the enclosure (81) of the second quenching section (25).
4. Combined line according to one of claims 1, 2, 3, characterised in that it has two final quenching liquid baths for the strip, respectively a first bath (45) placed at the output of the galvanisation installation (4), and a second bath (27) placed at the output of the second quenching section (25), the strip (M) being directed towards the line output device (3) once final quenching is complete, either in the first bath (45) after galvanisation, or in the second bath (27) after annealing-only treatment, without galvanisation.
5. Combined line according to one of the preceding claims, characterised in that the final quenching bath (45) of the galvanisation installation (4), is placed above the metal bath (41) and offset towards it in order to reduce the footprint of the galvanisation installation (4).
6. Combined line according to one of the preceding claims, characterised in that the length of the over-ageing section (26) is shorter than the length normally required in a continuous annealing line and that the strip movement speed is adjusted to this reduced length in order to achieve the required thermal treatment time.
7. Method for transforming a continuous annealing line for a metal strip in a combined annealing and galvanisation line, said annealing line (2) having means for controlling the continuous movement of the strip, successively, in an input device (1), a preheating section (21), an annealing section (22) with a temperature maintained at the level required depending on the type of strip, a first post-annealing quenching section (23), an over-ageing section (24), a second slow quenching section (25) in a protective atmosphere and an output device (3), characterised in that a part of the over-ageing section (24) is removed leaving the other sections in place and that a galvanisation installation (4) is placed inside the annealing line (2), in the space thus created between the remaining part (26) of the over-ageing section (24) and the second slow-quenching section (25), and connected to the movement control means such as to create a combined annealing and galvanisation line without increasing the overall length of the annealing line (2).
8. Method according to claim 7 for transforming an annealing line into a combined annealing and galvanisation line, characterised in that the strip movement speed between the input device (1) and the output device (3) of the strip is adapted to the galvanisation process.
9. Method according to claim 8, characterised in that the galvanisation installation (4) replaces just one part (26) of the over-ageing section (24) and that the movement speed of the strip (M) is adjusted, if necessary, such as to perform an over-ageing treatment in the remaining part (26) of the corresponding section (24).
10. Method according to claim 7, characterised in that the temperature in the annealing section is maintained at the level required for annealing, in consideration of the type of strip and the movement speed and that, between the output of the quick quenching section (21) and the input in the galvanisation bath (41), the remaining part (26) of the over-ageing section (24) has combined heating and quenching means for adjusting the temperature of the strip to the level required for the galvanisation process.
11. Method according to one of claims 7 to 10 for transforming a continuous annealing line (1, 2, 3) into a combined annealing and galvanisation line, characterised in that the galvanisation installation (4) has means to control the movement of the strip between a metal galvanisation bath (41) and a quench bath (45), along a continuous movement route defined by a plurality of deflector rolls (D1 ... D6) and comprising at least four parts, respectively a first part (T1) linking the quick quenching section (23) and the input in the metal bath (41), a second output part (T2) from the metal bath (41) with coating thickness check, a third part (T3) for quenching the coating before entry in the quench bath (45) and a fourth output part (T4, T5) from the quench bath (45), connected directly to the output section of the annealing line, without passing via the slow quenching section (25).
12. Method according to claim 11, characterised in that, to adapt the overall footprint of the galvanisation installation (4) to the length of the space created in the annealing line (2), the quench bath (45) is placed above the metal bath (41) and offset towards the line input side, such that, in the third quenching part (T3), the strip (M) turns backwards and, in the fourth output part (T4) from the quench bath (45), it passes above or below the metal bath (41) then the slow quenching section (25), in order to connect directly to the line output device (3).

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