EP2100673A1 - Method and device for blowing a gas onto a moving strip - Google Patents

Abstract

The process comprises projecting gas jets or water/gas mixture jets on each side of the strip, and distributing the impacts of gas or water/gas mixture jets on each surface of the strip in nodes of a two-dimensional network. The jet impacts on one side (A) of the strip, and does not impact on the other side (B) of the strip. The gas or water/gas jets are obtained from tubular nozzles (23, 33) fed by a distribution box (21). The tubular nozzles extend away from the distribution box so as to leave a free space for gas or water/gas circulation. The process comprises projecting gas jets or water/gas mixture jets on each side of the strip, and distributing the impacts of gas or water/gas mixture jets on each surface of the strip in nodes of a two-dimensional network. The jet impacts on one side (A) of the strip, and does not impact on the other side (B) of the strip. The gas or water/gas jets are obtained from tubular nozzles (23, 33) fed by a distribution box (21). The tubular nozzles extend away from the distribution box so as to leave a free space for gas or water/gas circulation that is parallel or perpendicular to the longitudinal direction of the strip. The axis of gas or water/gas mixture jet forms a perpendicular angle with the strip surface. The two-dimensional networks for distribution of jet impacting on each side of the strip are hexagonal, periodical, same type and same pace. The impacts of jets on the same face of the strip distributed in nodes of two-dimensional network form a polygonal mesh complex having 3-20 sides and periodicity of 1 pace across the strip and 3-20 paces in the longitudinal direction of the strip. The network corresponding to one side and another side are spaced apart from each other with a gap of of pace and 3/4 of pace. An independent claim is included for a device for blowing a cool or hot gas or a water/gas mixture on a rolling strip to act on its temperature for cooling or heating.

Description

The present invention relates to the blowing of gas or a water / gas mixture on a moving strip in order to act on its temperature to cool or to heat it.

At the outlet of some scrolling metal strip processing plants, the cooling chambers are arranged in which the strips run vertically between two gas blowing modules intended to cool the strip, the gas being either air or a gas neutral, a mixture of neutral gas.

The blowing modules generally consist of distribution boxes fed with pressurized gas, each having a face provided with openings constituting nozzles, arranged opposite one another on either side of a blowing zone traversed by the moving strip.

The openings may be either slots extending the full width of the strip, or point openings arranged in a two-dimensional array for distributing gas streams over a surface extending across the width and over a certain length of the scrolling the tape. In order to balance the effects of the jets generated by each of the blowing modules arranged opposite one another, the modules are adapted so that the jets of one module are facing the jets of the other module.

It can be seen that the gas blowing generates vibrations of the moving strip resulting in torsional deformations and lateral displacements of the strip from one blowing module to the other blowing module facing it. The torsional deformations are made by twisting the band about an axis generally parallel to the running direction of the band. The lateral displacements are made by displacement of the strip in a direction perpendicular to the median plane of the strip running zone, generally parallel to the surface of the strip. These vibrations are all the more important as the blowing intensity is high. It follows that the intensity of the blowing, so the cooling, must be limited to avoid excessive vibrations that can lead to deterioration of the bands.

In order to overcome this drawback, it has been proposed to shorten the blow boxes so as to have a plurality of boxes separated by band holding means such as rollers or aeraulic stabilizing means. But these devices have the disadvantage of either imposing a contact of the strip with stabilizing rollers, which is unsuited to certain applications such as hot-dip galvanizing output, or to impose particular cooling in areas of Aeraulic stabilization that is poorly controlled.

It has also been proposed to stabilize the band by acting on the traction of the band, and in particular by increasing it. But, this technique has the disadvantage of generating significant stresses in the band that can have an adverse effect on its properties.

Attempts have also been made to reduce the vibration of the web by acting on the blowing rates or the distances between the nozzle heads and the blast band or flow rate. But, all these means lead to a reduction in the cooling efficiency and thus the performance of the installation.

Devices have finally been proposed in which a plurality of nozzles are fed by distribution boxes, the nozzles being tubes extending in the direction of the surface of the strip to be cooled, the tubes being inclined perpendicular to the surface of the strip. the band, the inclination of the tubes being all the more important that they are distant from the median line of the passage zone of a band. In this device, the nozzles are arranged in two-dimensional arrays so that the points of impact of the gas jets on each side of the strip are facing each other. This device has the particular disadvantage of generating vibrations of the band which force to limit the blowing pressure, therefore, the cooling efficiency.

The object of the present invention is to remedy these drawbacks by proposing a means of acting on the temperature of a strip in the course of blowing a gas which, when passing through the cooling or reheating zone, generates band vibrations in the passage of the cooling or heating zone limited, even for large blowing pressures.

For this purpose, the invention relates to a method of action on the temperature of a gas-blowing strip according to which a plurality of gas jets extending towards the surface is projected on each side of the strip. of the band, and arranged so that the impacts of the gas jets on each side of the band are distributed at the nodes of a two-dimensional network. The impacts of the jets on one side are not compared to the impacts of the jets on the other side, and the gas jets are derived from tubular nozzles fed by at least one distribution box and extending away from the distribution box so as to leave free a gas circulation space back parallel to the longitudinal direction of the strip and perpendicular to the longitudinal direction of the strip.

The gas jets may be perpendicular to the surface of the strip.

The axis of at least one jet of gas may form an angle with the perpendicular to the surface of the strip.

Preferably, the two-dimensional networks for distributing jet impacts on each of the faces of the strip are periodic, of the same type and the same pitch.

The networks are for example of the hexagonal type.

More preferably, the impacts of the jets on the same face of the strip are distributed at the nodes of the two-dimensional network to form a complex polygonal mesh whose number of sides is between 3 and 20, of periodicity equal to 1 step in the transverse direction of the band and between 3 and 10 steps in the longitudinal direction of the strip, so that the traces of the impacts of adjacent blowing jets are contiguous on a face of the strip in the cross direction of said strip. It should be noted that the joined nature of the traces of adjacent blast impacts means that the traces may also overlap.

Preferably, the network corresponding to one face and the network corresponding to the other face are offset relative to each other and the offset is between ¼ steps and ¾ steps.

The gas may be a cooling gas, a gas / water mixture, or a hot gas, in particular a combustion gas of a burner.

The invention also relates to a device comprising at least two blowing modules arranged facing one another on either side of a strip running zone, each blowing module being constituted by a plurality of tubular nozzles extending from at least one distribution box, in the direction of the running zone of a strip, the nozzles being arranged in such a way that the impacts of the jets on each face of a strip are distributed at the nodes of a two-dimensional network, and the blowing modules are adapted so that the impacts of jets on one side are not compared to the impacts of jets on the other side.

Preferably, two-dimensional networks, according to which jet impacts are distributed, are periodic networks of the same type and not even.

The networks can be of hexagonal type.

More preferably, the impacts of the jets on the same face of the strip are distributed at the nodes of the two-dimensional network to form a complex polygonal mesh whose number of sides is between 3 and 20, of periodicity equal to 1 step in the transverse direction of the band and between 3 and 10 steps in the longitudinal direction of the strip, so that the traces of the impacts of adjacent blowing jets are contiguous on a face of the strip in the cross direction of said strip.

Preferably, the blowing modules are adapted so that the network corresponding to one face and the network corresponding to the other face are offset relative to each other, the offset being between ¼ steps and ¾ steps. .

The nozzle blowing axes may be perpendicular to the running plane of a strip.

The blowing axis of at least one nozzle may form an angle with the perpendicular to the running plane of a strip.

The nozzle discharge ports may have a round, polygonal, oblong or slot-shaped section.

The blowing modules are of the type with gas recovery or without gas recovery.

Preferably, each blowing module consists of a distribution box on which the blowing nozzles are implanted.

The invention is particularly applicable to continuous processing facilities for thin metal strips such as steel or aluminum strips. These treatments are for example continuous annealing, dip coating treatments such as galvanizing or tinning. It allows to obtain heat exchange intensities with high band without generating unacceptable vibrations of the band.

• la figure 1 est une vue schématique en perspective d'une bande en défilement dans un module de refroidissement par soufflage d'un gaz ;
• la figure 2 est une vue de la répartition des impacts de jets de gaz sur les zones de soufflage d'une première face et de la deuxième face d'une bande ;
• la figure 3 montre la superposition des répartitions des impacts de jets de refroidissement sur les deux faces d'une même bande ;
• la figure 4 est une représentation schématique de la mesure du déplacement latéral d'une bande dans un dispositif de refroidissement ;
• la figure 5 représente l'évolution du déplacement latéral de la bande dans un dispositif de refroidissement par soufflage d'une part dans le cas où les jets de soufflage d'une face et d'une autre face sont décalés l'un par rapport à l'autre, et d'autre part dans le cas où les jets des deux faces sont en regard l'un de l'autre ;
• la figure 6 est une représentation de la torsion moyenne d'une bande en défilement dans un dispositif de refroidissement par soufflage en fonction de la pression de soufflage, d'une part dans le cas où les jets de soufflage des deux faces sont décalés les uns par rapport aux autres, et d'autre part dans le cas où les jets de soufflage des deux faces sont en regard les uns des autres ;
• la figure 7 représente l'évolution du déplacement latéral de la bande dans un dispositif de refroidissement par soufflage d'une part dans le cas où la bande est refroidie par un dispositif de soufflage conforme à l'invention, et d'autre part dans le cas où la bande est refroidie par un dispositif de soufflage au travers de fentes conforme à l'art antérieur ;
• la figure 8 est la représentation schématique de la sortie d'une installation de revêtement au trempé comportant un dispositif de refroidissement.
• la figure 9 représente l'évolution du déplacement latéral de la bande refroidie dans un dispositif de refroidissement par soufflage dans l'installation de revêtement au trempé de la figure 8, mesurée au niveau du module d'essorage, d'une part dans le cas où les jets de soufflage d'une face et d'une autre face sont décalés l'un par rapport à l'autre, et d'autre part dans le cas où les jets de soufflage des deux faces sont en regard l'un de l'autre ;
• la figure 10 représente l'évolution du déplacement latéral de la bande refroidie dans un dispositif de refroidissement par soufflage dans l'installation de revêtement au trempé de la figure 8, mesuré au niveau du module de refroidissement, d'une part dans le cas où les jets de soufflage d'une face et d'une autre face sont décalés l'un par rapport à l'autre, et d'autre part dans le cas où les jets de soufflage des deux faces sont en regard l'un de l'autre ;
• la figure 11 présente l'évolution dans du coefficient d'échange thermique en fonction de la puissance de soufflage des modules de soufflage, dans un dispositif de refroidissement par soufflage de la figure 8, d'une part selon l'invention où les jets de soufflage d'une face et d'une autre face sont décalés l'un par rapport à l'autre, et d'autre part dans un dispositif de refroidissement conforme à l'art antérieur où les jets de soufflage des deux faces sont en regard l'un de l'autre ;
• la figure 12 représente une répartition des impacts des jets de gaz sur une face d'une bande en défilement assurant un soufflage uniforme sur la surface de la bande.

The invention will now be described in a more precise but nonlimiting manner with reference to the appended figures in which:

• the figure 1 is a schematic perspective view of a strip moving in a cooling module by blowing a gas;
• the figure 2 is a view of the distribution of the impacts of gas jets on the blowing zones of a first face and the second face of a strip;
• the figure 3 shows the superimposition of the distribution of the impacts of cooling jets on both sides of the same band;
• the figure 4 is a schematic representation of the measurement of the lateral displacement of a band in a cooling device;
• the figure 5 represents the evolution of the lateral displacement of the strip in a blow-cooling device on the one hand in the case where the blowing jets of one face and another face are offset with respect to each other and on the other hand, in the case where the jets of the two faces are opposite one another;
• the figure 6 is a representation of the average torsion of a moving strip in a blast chiller as a function of the blowing pressure, on the one hand in the case where the blast jets of the two faces are offset relative to each other. others, and secondly in the case where the blowing jets of the two faces are facing each other;
• the figure 7 represents the evolution of the lateral displacement of the strip in a blast chiller on the one hand in the case where the strip is cooled by a blowing device according to the invention, and secondly in the case where the band is cooled by a blowing device through slots according to the prior art;
• the figure 8 is the diagrammatic representation of the output of a dip coating installation with a cooling device.
• the figure 9 represents the evolution of the lateral displacement of the cooled strip in a blow-cooling device in the dip coating installation of the figure 8 , measured at the level of the dewatering module, on the one hand in the case where the blowing jets of one face and another face are offset with respect to each other, and secondly in the case where the blowing jets of the two faces are facing each other;
• the figure 10 represents the evolution of the lateral displacement of the cooled strip in a blow-cooling device in the dip coating installation of the figure 8 , measured at the level of the cooling module, on the one hand in the case where the blowing jets of one face and another face are offset relative to each other, and secondly in the case where the jets of blowing of the two faces are opposite one of the other;
• the figure 11 presents the evolution in the heat exchange coefficient as a function of the blowing power of the blowing modules, in a blow-cooling device of the figure 8 , on the one hand according to the invention where the blowing jets of one face and another face are offset relative to each other, and secondly in a cooling device according to the prior art where the blowing jets of the two faces are facing each other;
• the figure 12 represents a distribution of the impacts of the gas jets on a face of a moving strip ensuring uniform blowing on the surface of the strip.

The installation for cooling by blowing a gas generally identified by 1 to the figure 1 consists of two blowing modules 2 and 3 arranged on either side of a moving strip 4. Each blowing module consists of a distribution box 21 on the one hand and 31 on the other hand, all both fed with pressurized gas.

Each of the distribution boxes is of generally parallelepipedal shape with one face 22 for one and 32 for the other, of generally rectangular shape, arranged facing one another and on which are implanted a plurality of nozzle nozzles. cylindrical blowing 23 on the one hand and 33 on the other. These cylindrical nozzles are tubes of a length of the order of 100 mm and which can be between 20 mm and 200 mm, preferably between 50 and 150 mm, and having an internal diameter of for example 9.5 mm but can be between 4 mm and 60 mm. These tubes are distributed on the faces 22 and 32 of the distribution boxes so that the impacts of the blowing jets on one face of the strip are distributed according to a two-dimensional network which, preferably, is a periodic network whose mesh may to be square or rhombus so as to constitute a distribution of the hexagonal type. The distance between two adjacent tubes is for example 50 mm, and may be between 40 mm and 100 mm. The number of nozzles per side of a distribution box of a cooling module, can reach a few hundred. The distance between the nozzle head and the band can be between 50 and 250 mm. In order to obtain such a distribution of the impacts of the jets on the strip, when the nozzles generate jets parallel to each other, the distribution of the nozzles on each box is made according to a two-dimensional network identical to the two-dimensional network of distribution of jet impacts on the bandaged. But when the jets are not all parallel to each other, the distribution of the nozzles on a box is different from the distribution of the impacts of the jets on the surface of the strip.

In the embodiment, shown in figure 2 the tubes are distributed so that the impacts 24 of the jets emitted by the blowing module 2 on the side A of the strip are distributed at the nodes of a two-dimensional network which, in the example represented, is a periodic network of the hexagonal type whose step p is indicated. The blowing nozzles of the second blowing module 3 are distributed over the distribution box 31 so that the impacts 34 of the gas jets on the side B of the strip are equally distributed at the nodes of a periodic two-dimensional network of type also hexagonal, and mesh also equal to p . The two two-dimensional networks corresponding on the one hand to the face A and the other to the face B are offset relative to each other so that the impacts 34 of the gas jets of the face B are not not facing the impacts 24 gas jets on the side A, so that these impacts are staggered.

The offset is adapted so that the impacts of the jets on one side are opposite spaces left free between the impacts of the jets on the other side.

As a result, as shown in figure 3 , in which the impacts of the jets on the face A and the jets on the face B are represented in a superimposed manner, one obtains a dense distribution of all the points of impact of the jets of blowing on both sides.

Such a distribution of the impact points of the blowing jets on each of the faces of the strip has the advantage of better distributing the contacts of the blowing jets with the surfaces of the strip, and thus of ensuring a more favorable cooling. homogeneous only when the jets are facing each other. As a result, the heat exchange coefficient between the strip and the gas is improved. This distribution of the jets also has the advantage of reducing the stresses exerted on the surface of the strip. In addition, this distribution of the jets substantially reduces the vibrations of the band and consequently the lateral deflection and the torsion of the band.

The inventors have found that in order to obtain a significant reduction of the vibrations of the strip, the distribution of the points of impact on the surface of the strip does not necessarily have to be in a two-dimensional hexagonal network, nor that the offset between the two networks is equal to half a step.

Indeed, the essential is on the one hand that the back gas, that is to say the gas that has been blown against the band and must be released, can escape by circulating between the nozzles as well perpendicularly than parallel to the direction of travel of the strip, and secondly that the points of impact are not opposite each other, the offset between the two networks can be understood, for example, between a quarter of a step and three quarters of a step. This offset can be done either in the direction of travel of the band, or in the direction perpendicular to the scrolling of the band.

The inventors have also found that the gas blowing nozzles may have sections of various shapes. This may be for example blowholes of circular section or polygonal section, for example such as squares or triangles, or oblong shapes, or even in the form of slits of short length.

On the other hand, it is important that the blowing is done by means of tubular type nozzles which extend at a sufficiently large distance from the lateral faces of the distribution boxes so as to allow the return gas to be evacuated by circulation at both parallel to the direction of travel of the strip and perpendicular to the running direction of the strip. Indeed, it is the combination of the good distribution of the evacuation of the gas and the distribution of the points of impact of the gas jets on the surface of the strip which makes it possible to obtain a good stability of the strip.

By way of example, the vibratory behavior of a strip running between two rectangular-shaped blowing modules of a length has been compared. 2200 mm, equipped with cylindrical tubes with a length of 100 mm and a diameter of 9.5 mm arranged in a hexagonal pattern with a pitch of 50 mm, the two blowing modules being arranged opposite one another. the other so that the distance between the head of the nozzles and the band is 67 mm. Between these two blowing modules, a steel strip 950 mm wide, 0.25 mm thick, was placed under constant tension. The supply pressure of the distribution boxes was varied between 0 and 10 kPa above atmospheric pressure, and the lateral displacement of the strip was measured using three lasers arranged in the width direction. of the band as shown in the figure 4 with a laser 40A disposed in the axis of the strip which measures the distance d _a , a laser 40G disposed on the left side of the strip which measures the distance dg at a distance D of approximately 50 mm from the edge of the strip, and on the other hand a third laser 40D disposed on the right side of the strip at a distance D of about 50 mm from the edge of the strip, and which measures the distance d _d .

The distances d _a , d _g , d _d are the distances to a line parallel to the median plane of the band scroll zone.

Using these measurements, we can determine the average displacement of the band equal to 1/3 (dg + d _a + d _d ), and the torsion which is equal | d _g - d _d | (absolute value of the difference between the lateral displacements).

To measure these two quantities, recordings are made during blowing. For lateral displacement, the mean distance from peak to peak of the lateral displacements is determined. For torsion, the average amplitude of the torsion is determined.

On the Figures 5 and 6 , on the one hand, the lateral displacements, and on the other hand the mean torsions, are represented for the cooling modules according to the invention, the gas jets of which are offset with respect to each other (the gas jets of one face are offset with respect to the gas jets of the other face), and secondly for blowing cooling modules identical to the preceding modules, but for which the blowing jets of one face are facing the jets blowing the opposite side.

As can be seen from the figure 5 , the curve 50 which relates to blowing modules according to the invention, shows a slow evolution of the peak to peak displacement amplitudes of the band which goes from approximately 15 mm to a blast overpressure of 1 kPa, at about 30 mm for a blast overpressure of 10 kPa. In this figure also, the curve 51 which represents the evolution of the peak-to-peak displacement amplitude for blowing modules whose blowing jets of one face are in front of the blowing jets on the other side, shows that the amplitude of displacement of the band for a blow-molding overpressure of the order of 1 kPa is still 15 mm but that this amplitude increases more significantly than in the previous case, and reaches about 55 mm for a blow pressure of 9 kPa and then exceeds 100 mm for a blowing pressure of 10 kPa.

These curves show that with the device according to the invention, it is possible to pass the strip between the two blowing modules spaced apart by a distance such that the distance between the nozzle head and the strip is 67 mm, with blowing pressures of up to 10 kPa, while with blowing modules in which the blowing jets on one side are facing the blowing jets on the other side, it is possible to use these devices that for blast overpressures substantially lower than 9 kPa.

In the same way, the curve 52 of the figure 6 , which represents the evolution of twisting or twisting as a function of the blowing pressure shows that with the devices according to the invention, the twisting remains less than 4 mm even for blast overpressures of up to 10 kPa. On the other hand, with casings whose jets are not offset relative to the others, the twisting can reach 24 mm for overpressures of blowing of 9 kPa.

In order to compare the behavior of the strip when it is cooled using the blowing modules according to the invention and blowing modules according to the prior art in which the distribution boxes blow air through laterally extending slits, the displacement amplitude of the strip was measured as a function of the blast overpressure, for distances between the heads of the blast nozzles and the surface of the strip of 67 mm, 85 mm and 100 mm. mm, on the one hand with the blowing modules according to the invention, on the other hand with blowing modules according to the prior art.

These results are represented in figure 7 in which the curves 54, 55, 56 relating to the strip cooled by a blowing device according to the invention for distances of respectively 67 mm, 85 mm and 100 mm, are almost superimposed and show that for blast pressures of up to 10 kPa, the displacement amplitudes remain less than 30 mm.

The curves 57, 58, 59 relating to the strip cooled with the devices according to the prior art which blow the gas through slots extending over the width of the strip, correspond to distances between the nozzles of blowing and the strip respectively of 67 mm, 85 mm and 100 mm. These curves show that for blowing pressures up to 4 kPa, the displacement of the strip exceeds 100 mm and can reach 150 mm.

The vibratory behavior of a moving strip in the industrial coating plant has also been characterized by dipping in a bath of liquid metal generally identified by 200 at figure 8 , comprising at the outlet of the bath 201 a wiper module 202, and downstream of the wiper module a cooling module generally identified by 203. This cooling module comprises four blowing modules 203A, 203B, 203C and 203D, rectangular shape with a length of about 6500 mm and a width of 1600 mm. Each blowing module is equipped with cylindrical nozzles with a length of 100 mm and a diameter of 9.5 mm arranged in a hexagonal type grating, with a pitch of 60 mm. The four blowing modules are arranged so as to form two blocks 204 and 205 of two modules 203A, 203B and 203C, 203D respectively, arranged facing each other on either side of a scrolling zone. of a strip 206. The distance between the nozzle head and the strip is 100 mm. In addition, in order to carry out the tests described below, on the one hand a first means for measuring the lateral displacements of the strip 207 between the two blocks 205 and 205 of blowing modules, at about 13 meters downstream of the wiper module, and secondly disposed a second means for measuring the lateral displacements of the strip 208 at the outlet of the wiper module 202. The two measuring means are of the type of the one shown in FIG. figure 4 . However, while the first measuring means 207 disposed at the level of the blowing modules comprises lasers, the second measuring means 208 disposed at the output of the spin module comprises inductive sensors.

To carry out the tests, a 0.27 mm thick strip of steel was passed through, which, at the outlet of the bath, had a high temperature, of the order of 400 ° C., which had to have a temperature less than 250 ° C at the exit of cooling module. The belt was scrolled at constant speed and the blowing pressure was varied. In addition, tests were carried out on the one hand with blow boxes in accordance with the invention, that is to say the nozzles are arranged in such a way that the impacts of the jets on one side of the strip are not facing the impacts of the jets on the other side of the strip, on the other hand with boxes according to the prior art, that is to say such that the impacts of the jets on one side are opposite the jets impact on the other side.

A first series of measurements of the displacement of the strip was carried out using the first measuring means 207 placed between the two blocks of blowing modules. For this purpose, the supply pressure of the blowing modules was varied and the displacement of the strip was measured using three lasers arranged in the direction of the width of the moving strip.

A second series of measurements of the displacement of the strip was also performed upstream of the cooling module in the running direction of the strip and downstream of the spin module, at a distance of a few centimeters from the latter. This second series of measurements was carried out using the second measurement means 208.

To obtain these two series of measurements, recordings are made during blowing, under identical production conditions for the tests relating to the prior art and to the invention. To measure the lateral displacement of the band, the average peak-to-peak amplitude of the lateral displacements of the band was determined.

On the figure 9 the results of the first series of measurements are shown, ie the lateral displacements of the strip (peak-to-peak distance) as a function of the blowing power effected at the level of the blowing module.

The curve 91 which relates to a cooling module 203 according to the invention, shows a quasi-constant amplitude of peak to peak displacement of the band. The displacement amplitudes oscillate around 2 to 3 mm for a blast overpressure varying from 0.7 kPa to 4 kPa.

Curve 92 represents the evolution of peak-to-peak displacement amplitudes for a cooling module according to the prior art. This curve 92 shows that the amplitudes of displacement of the band for an overpressure of blowing ranging from 1.5 kPa to 2.7 kPa increase exponentially. These deformations limit the cooling capacity of the device and consequently the productivity of the manufacturing process. Indeed, it was found that the deformations caused a degradation of the quality of the product when they are too important, which leads to limit the blowing pressures to at most 2.5 kPa.

When the deformations of the band at the blowing modules are too large, there is also a deterioration of the product at the level of the spin module, upstream of the cooling module. Indeed vibrations propagate along the band from the blowing modules to the spin module, and can cause defects in the quality of the product. The second series of measurements carried out at the level of the dewatering module, makes it possible to evaluate the repercussion at the level of the dewatering module of the band vibrations generated at the level of the blow modules.

On the figure 10 the results of the second series of measurements are shown. The curve 102 represents the peak-to-peak displacement amplitudes in the case of the device according to the prior art. For a blowing pressure ranging from 1.2 to 3.0 kPa, the displacement amplitudes at the wiper module increase exponentially from about 2.5 mm to about 9 mm, up to the deterioration of the product. This effect of high blowing pressures on the amplitude of the deformations of the strip, requires limiting the blowing power substantially below 2.8 kPa.

In this same figure, the curve 101, relative to the cooling device according to the invention, remains substantially horizontal, below 1.8 mm, for a blowing pressure ranging from 0.5 kPa to 3.5 kPa.

These results show that with blowing modules according to the invention, the amplitudes of the lateral displacements of the strip are considerably reduced, this reduction being able to go as far as to divide them by a factor which can exceed 5.

In addition, the inventors have noticed the disappearance of the torsional setting of the band in the case of the device according to the invention, both at the level of the cooling module and at the level of the dewatering module, and what it whatever the power of the cooling jets.

Moreover, it has been shown on the figure 11 the evolution of the heat exchange coefficient as a function of the blowing pressure of the blowing modules, in order to compare the cooling performance of the cooling devices according to the invention with those of the cooling devices according to the prior art . In this figure, the curve 111 corresponds to the invention and the curve 112 to the prior art. The two curves are increasing and show that the cooling power increases as the blowing pressure increases. However, the curve relating to the prior art stops for a blowing pressure of 2.0 kPa because, beyond, the vibrations cause a deterioration of the product. Thus, the maximum cooling power is 160 W / m ² . ° C. On the other hand, the curve relating to the invention is extended for blowing pressures of up to 3.5 kPa, which makes it possible to reach a cooling power of 200 W / m ² . ° C. The invention therefore makes it possible to increase the extraction power of the heat of the moving strip very substantially.

These results show that by using a device according to the invention, it is possible to cool the strip with relatively large blowing pressures while having very limited band vibrations.

The reader will understand that the numerical values given above for the areas of use of the cooling module correspond to the particular test conditions and in particular to the thickness, the width and the running speed of the strip.

In the example just described, the blowing jets are directed perpendicular to the surface of the strip, but it may be advantageous to incline all or part of the blowing jets with respect to the perpendicular to the strip. In particular, it may be advantageous to orient the gas jets located on the edges of the strip towards the outside of the strip. It may also be advantageous to orient all or part of the jets in the direction of travel of the strip or, conversely, opposite to the direction of travel of the strip, so as to force the evacuation of the blown gas or gas / water mixture after impact on the band and thus promote heat exchange.

It will also be noted that the blowing gas, which is a pure gas or a mixture of gases, may be air or a mixture consisting of nitrogen and hydrogen or any other gas mixture. This gas may be at a temperature below the temperature of the strip. The blowing is then used to cool the strip. This is the case, for example, at the hot-dip galvanizing outlet or at the outlet of a annealing treatment of a strip.

But, the blown gas may be a hot gas, and in particular may be a burner combustion gas, and may be intended to preheat a strip before it enters a heat treatment plant.

The nozzles may all be arranged on a single distribution box, generally of flat shape, or be distributed over a plurality of distribution boxes, these distribution boxes may be for example tubes extending over the width of the bandaged.

When the distribution boxes are tubes, they can also be oriented parallel to the direction of travel of the strip.

It is therefore possible with the invention to very substantially reduce the band vibrations generated at the distribution boxes, to very substantially reduce the band vibrations at the wiper module, to substantially increase the cooling powers of the boxes. distribution, to ensure a very good product quality, and consequently to significantly increase the productivity of the manufacturing process.

In a preferred embodiment of the invention, the blowing nozzles are arranged on the distribution boxes, so that the impacts of the blowing jets overlap on one side of the strip in the cross direction of said strip.

This arrangement in which the impacts of blowing jets on one face of the strip are not opposite jet impacts on the other side of the strip, but in which the impacts of the jets on each of the faces of the strip overlap has the advantage of avoiding the formation of defects on the strip, called lines of jets, in the direction of travel of the strip and parallel to each other in the cross-machine direction of the strip.

Indeed, when the impacts of the gas jets are arranged so that they form lines of jets, these jet lines are manifested by oxidation streaks in the case of reheating of a strip by blowing a hot gas, like for example hot air. In the case of cooling a coated strip not hot dipped in a bath of liquid metal, they are manifested on the strip by a succession of coating lines of different surface appearance. For example, in the case of the galvanization of a strip, it has after cooling in a cooling device not including overlapping impact jets on the same side of the strip, by a succession lines of shiny surface appearance and matte surface appearance lines.

To avoid the formation of these jet lines, the nozzles can be arranged in such a way that the impacts of the jets on one face of the strip are distributed along several lines each extending over the width of the strip, each line comprising a plurality of impacts of diameter d determined and distributed regularly in a pitch p, the impacts of two successive lines or of two groups of successive lines being offset laterally such that the lines of jets resulting from the different lines lead to lines of jets which cover the entire width of the band.

To the figure 12 an example of distribution of the impacts is shown which ensures a good uniformity of the actions of the jets on the whole surface of the band.

This figure shows a part of the network formed by the impacts of the jets on a face of a band 300. This network is formed by a pattern consisting of four lines of impacts that can be divided into two groups: one first group consisting of two impact lines 301 A and 301 B, and a second group of two impact lines 304A and 304B. Each line 301A, 301B, 304A and 304B consists of impacts 302A, 302B, 305A and 305B, respectively, distributed regularly with a pitch p. In each of the groups, the second line 301 B or 304B is deduced from the first line 301 A or 301 B, respectively, firstly by a lateral translation of a half step or p / 2, and secondly by a longitudinal translation of a length I. In addition, the second group of lines, consisting of the lines 305A and 305B, is deduced from the first group of lines 301A and 301B by a lateral translation of a distance d equal to diameter d of an impact. With this arrangement, the traces left by the impacts on the strip 303A, 303B for the impacts 302A and 302B, and 306A, 306B for the impacts 305A and 305B, form strips that are contiguous when the diameter an impact is at least equal to a quarter of the pitch p separating two adjacent impacts on the same line. When it is desired to increase the number of impacts, the network can be extended by reproducing the distribution of impacts that has just been described by translation of a length equal to four times the distance I separating two successive lines. We thus obtain a periodic network whose mesh is a complex polygon.

In the example just described, four lines of impact are used to ensure good coverage of the band by the traces of the impacts. But, those skilled in the art will understand that other arrangements are possible. And, in particular the good coverage of the surface of the strip can be obtained by a distribution of the impacts of the jets of the blowing nozzles on the same face of the band at the nodes of a two-dimensional network by forming a complex polygonal mesh whose number of sides is between 3 and 20, of periodicity equal to 1 step in the direction of the width of the strip and between 3 and 20 steps in the longitudinal direction of the strip. This distribution must be adapted taking into account in particular the width of an impact of a jet of a blowing nozzle. The skilled person knows how to make such an adaptation.

With such impact distributions, the inventors have noted the disappearance of the defect of jet lines in the case of cooling modules according to the invention.

Claims (19)

A method of action on the temperature of a strip (4) in the course of blowing gas or a water / gas mixture, in which a plurality of gas jets or a mixture is sprayed on each side of the strip water / gas extending towards the surface of the strip and arranged in such a way that the impacts (24, 34) of the gas jets or the water / gas mixture on each surface of the strip are distributed at the nodes of a two-dimensional network, characterized in that the impacts (24) of the jets on one face (A) of the strip are not opposite the impacts (34) of the jets on the other side (B) of the strip, and in that that the jets of gas or water / gas mixture are from tubular nozzles (23, 33) supplied by at least one distribution box (21, 31) and extending away from the distribution box so as to leave a free circulation space for the gas or the water / gas mixture back parallel to the longitudinal direction of the strip and perpendicular to the longitudinal direction dinal of the band. Process according to Claim 1, characterized in that the jets of gas or of the water / gas mixture are perpendicular to the surface of the strip. Process according to Claim 1, characterized in that the axis of at least one jet of gas or of the water / gas mixture forms an angle with the perpendicular to the surface of the strip. Process according to any one of Claims 1 to 3, characterized in that the two-dimensional networks for distributing jet impacts on each of the faces of the strip are periodic, of the same type and at the same pitch. Method according to Claim 4, characterized in that the networks are of the hexagonal type. Method according to one of claims 1 to 3, characterized in that the impacts of the jets on the same face of the strip are distributed at the nodes of the two-dimensional network to form a complex polygonal mesh whose number of sides varies from 3 to 20, of periodicity equal to 1 step in the transverse direction of the strip and between 3 and 20 steps in the longitudinal direction of the strip, so that two adjacent traces of blowing jets on one side of the strip are joined in the cross direction of said strip. Method according to one of Claims 4 to 6, characterized in that the network corresponding to one face and the network corresponding to the other face are offset relative to each other, and in that the offset is between ¼ steps and ¾ steps. Process according to one of Claims 1 to 7, characterized in that the gas is a cooling gas. Process according to any one of claims 1 to 7, characterized in that the gas is a hot gas. Device for implementing the method according to any one of claims 1 to 9, of the type comprising at least two blowing modules (2, 3) arranged facing each other on both sides of a running zone of a strip (4), each blowing module (2, 3) consisting of a plurality of tubular nozzles (23, 33) extending from at least one distribution box (21, 31) ) towards the running zone of a strip, the nozzles being arranged such that the impacts (24, 34) of the jets on each face (A, B) of the strip are distributed at the nodes of a two-dimensional network , characterized in that the blowing modules (2, 3) are adapted so that the impacts (24) of jets on one side (A) are not opposite the impacts (34) of jets on the other side (B). ). Devices according to claim 10, characterized in that the two-dimensional networks, according to which the jet impacts are distributed, are periodic networks of the same type and the same pitch. Device according to Claim 11, characterized in that the networks are of the hexagonal type. Device according to Claim 10, characterized in that the impacts of the jets on the same face of the strip are distributed at the nodes of the two-dimensional network to form a complex polygonal mesh whose number of sides varies from 3 to 20, with a periodicity equal to 1 not in the cross-machine direction and between 3 and 20 steps in the longitudinal direction of the strip, so that the traces of the impacts of the adjacent blast jets are contiguous on one side of the strip in the cross direction of said strip bandaged. Device according to one of Claims 11 to 13, characterized in that the blow modules (2, 3) are adapted so that the network corresponding to one face (A) and the network corresponding to the other face (B) are offset with respect to each other, the offset being between ¼ steps and ¾ steps. Device according to any one of claims 10 to 14, characterized in that the blowing axes of the nozzles are perpendicular to the plane of travel of said strip (4). Device according to any one of claims 10 to 14, characterized in that the blowing axis of at least one nozzle forms an angle with the perpendicular to the plane of travel of said strip (4). Device according to any one of claims 10 to 16, characterized in that the nozzle blowing holes have a round, polygonal, oblong or slot-shaped section. Device according to any one of claims 10 to 17, characterized in that the blowing modules are of the type with gas recovery or without gas recovery. Device according to any one of claims 10 to 18, characterized in that each blowing module (23) consists of a distribution box (21, 31) on which the blowing nozzles (23, 33) are located.

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