EP3171996B1 - Cooling facility and method - Google Patents

Description

Field of the invention

The invention relates to the field of rolling plates or trays made of aluminum alloys.

More specifically, the invention relates to a particularly rapid, homogeneous and reproducible cooling process of the plate between the homogenization and hot rolling operations. The document DE 198 23790 A1 discloses a method according to the preamble of claim 1. The invention also relates to the installation or equipment for carrying out said method.

State of the art

The transformation of the aluminum alloy rolling trays resulting from the casting requires, before hot rolling, a metallurgical homogenization heat treatment. This heat treatment is operated at a temperature close to the solvus of the alloy, higher than the hot rolling temperature. The difference between the homogenization temperature and the hot rolling temperature is between 30 and 150 ° C, depending on the alloys. The plate must therefore be cooled between its exit from the homogenization furnace and its hot rolling. For reasons of productivity or of metallurgical structure, in particular to avoid certain surface defects on the finished sheet, it is very desirable to be able to carry out the cooling of the plate between its exit from the homogenization furnace and the hot rolling mill in a fast manner. .

This desired plate cooling rate is between 150 and 500 ° C / h.

Given the large thickness of the aluminum alloy rolling platens, between 250 and 800 mm, the air cooling is particularly slow: the air cooling rate of a 600 mm plate of air thickness is included between 40 ° C / h in calm air or under natural convection, and 100 ° C / h in ventilated air or forced convection.

Air cooling therefore does not achieve the desired cooling rates.

The cooling by means of a liquid or a mist (mixture of air and liquid) is much faster because the value of the exchange coefficient, known to those skilled in the art as the HTC (Heat Transfer Coefficient), between a liquid or a mist and the hot surface of the metal plate is well above the value of the same coefficient between the air and the plate.

The liquid chosen alone or in the mist is for example water and, in this case, ideally deionized water. Thus, the coefficient HTC is between 2000 and 20000 W / (m ² .K) between water and the hot plate while it is between 10 and 30 W / (m ² .K) between air and the hot tray.

• Le nombre adimensionnel de Biot illustre l'homogénéité thermique du refroidissement. Il correspond au rapport de la résistance thermique interne d'un corps (transfert de chaleur interne par conduction) à sa résistance thermique de surface (transfert de chaleur par convection et rayonnement). $$\mathit{Bi}=\frac{\mathit{HTC}•D}{\lambda }$$
  
  • HTC étant le coefficient d'échange entre le fluide et le plateau,
  • D, la dimension caractéristique du système, ici la demi-épaisseur du plateau,
  • λ, la conductivité thermique du métal, par exemple, pour un alliage d'aluminium, 160 W/(m².K).

On the other hand, the cooling by means of a liquid or fog usually generates in a natural way strong thermal gradients in the plateau:

• The dimensionless number of Biot illustrates the thermal homogeneity of the cooling. It corresponds to the ratio of the internal thermal resistance of a body (internal heat transfer by conduction) to its surface thermal resistance (heat transfer by convection and radiation). $$\mathit{Bi}=\frac{\mathit{HTC}•D}{\lambda }$$
  
  • HTC being the exchange coefficient between the fluid and the plate,
  • D, the characteristic dimension of the system, here the half-thickness of the plate,
  • λ, the thermal conductivity of the metal, for example, for an aluminum alloy, 160 W / (m ² .K).

If Bi << 1, the system is practically isothermal, the cooling is uniform. If Bi >> 1, the system is thermally very heterogeneous and the plateau is the seat of strong thermal gradients.

• Entre 0.02 et 0.06 pour un refroidissement à l'air calme ou ventilé. Le nombre de Biot est faible devant 1, le plateau est refroidi de manière isotherme.
• Entre 4 et 40 pour un refroidissement à l'eau. Le nombre de Biot est fort devant 1, le plateau est refroidi de manière très hétérogène dans son épaisseur.

For a 600 mm thick plate, the number of Biot is:

• Between 0.02 and 0.06 for cooling in calm or ventilated air. The number of Biot is small in front of 1, the plate is cooled isothermally.
• Between 4 and 40 for cooling with water. The number of Biot is strong before 1, the plate is cooled very heterogeneously in its thickness.

This heterogeneity is also reflected in the width of the plate, because of the effects of edges and edges, naturally cooler than the large faces of the plate.

It is also reflected in the length of the plate, by wedge effect, naturally cooled according to the three faces constituting it.

Thermal heterogeneity is a major handicap for cooling with a liquid or mist. It poses a problem not only for the following process, ie hot rolling, but it is also potentially harmful for the final quality of the product, namely the aluminum alloy sold in the form of coils or sheets at high temperatures. mechanical characteristics.

The devices known from the prior art do not seek to limit this heterogeneity of cooling.

Cooling processes using a cooling liquid known in the prior art, especially for heavy plates, operate either by immersion in a tank, or by passage in a spray box but without special attention to control of the thermal equilibrium of the product.

• Ni d'obtenir un champ thermique uniforme dans le plateau refroidi
• Ni de garantir la reproductibilité du refroidissement d'un plateau à l'autre.

Thus, these methods do not allow:

• Neither to obtain a uniform thermal field in the cooled tray
• Nor to guarantee the reproducibility of cooling from one tray to another.

Problem

• Un refroidissement rapide, à une vitesse d'au moins 150°C/h, et conséquent, soit de 30 à 150°C de refroidissement à partir d'une température de l'ordre de 450 à 600°C
• Un champ thermique homogène et maitrisé dans l'ensemble du plateau
• L'assurance d'une parfaite reproductibilité d'un plateau épais à l'autre.

The purpose of the invention is to correct all of the major defects related to thick plate cooling processes of the prior art and to ensure:

• Rapid cooling, at a speed of at least 150 ° C / h, and therefore, from 30 to 150 ° C of cooling from a temperature of the order of 450 to 600 ° C
• A homogeneous thermal field and mastered throughout the plateau
• The assurance of perfect reproducibility from one thick plate to another.

Object of the invention

The subject of the invention is a method of cooling an aluminum alloy rolling plate of typical dimensions of 250 to 800 mm in thickness, 1000 to 2000 mm in width and 2000 to 8000 mm in length, after the heat treatment. metallurgical homogenization of said platen at a temperature typically between 450 to 600 ° C depending on the alloys and before its hot rolling, characterized in that the cooling, a value of 30 to 150 ° C, is carried out at a speed of from 150 to 500 ° C / h, with a thermal difference of less than 40 ° C over the entire cooled plate from its homogenization temperature.

By thermal difference is meant the maximum difference between temperatures recorded over the entire volume of the tray, or DTmax.

• Une première phase d'aspersion au cours de laquelle le plateau est refroidi dans une enceinte comportant des rampes de buses ou tuyères d'aspersion de liquide ou brouillard de refroidissement sous pression, réparties en parties haute et basse de ladite cellule, de façon à asperger les deux grandes faces, supérieure et inférieure dudit plateau,
• Une phase complémentaire d'uniformisation thermique à l'air calme, dans un tunnel aux parois intérieures réflectives, d'une durée de 2 à 30 minutes selon le format du plateau et la valeur du refroidissement.

Advantageously, the cooling is carried out in at least two phases:

• A first spraying phase during which the plate is cooled in an enclosure comprising nozzle or nozzle nozzles for liquid spraying or cooling cooling mist, distributed in the upper and lower parts of said cell, so as to spray the two large faces, upper and lower of said plateau,
• A complementary phase of thermal uniformization in calm air, in a tunnel with reflective interior walls, lasting from 2 to 30 minutes according to the format of the plate and the value of the cooling.

Typically, this time is about 30 minutes for a total cooling of the order of 150 ° C from substantially 500 ° C, and a few minutes for a cooling of the order of 30 ° C.

According to a variant of the invention, the phases of spraying and thermal uniformization are repeated, in the case of very thick trays and for overall average cooling greater than 80 ° C.

Most commonly, the coolant, including in a mist, is water, and preferably deionized water.

According to a particular embodiment, the head and foot of the tray, typically 300 to 600 mm at the ends, are less cooled than the rest of the tray, so as to maintain a head and a warm foot, a configuration favorable to the plate engagement during reversible hot rolling.

To this end, the cooling of the head and the foot can be modulated either by starting or extinguishing the nozzle or spray nozzles or by the presence of screens preventing or reducing the spray by said nozzles or nozzles. Moreover, the sprinkling phases, and not thermal uniformization, can be repeated, and the head and the foot of the tray, is typically 300 to 600 mm at the ends, cooled differently than the rest of the tray at least in a spraying cells.

According to a version according to the latter option, the first spraying pass is performed with a zero heel, or a continuous watering of the tray as in figure 14 followed, without first thermal uniformization phase, with a second spraying pass with a bead of a pair of ramps as figure 12 , thereby significantly reducing the duration of the final phase of uniformization necessary for the thermal balancing of the plate.

According to a preferred variant of the invention, the longitudinal thermal uniformity of the plate is improved by a relative movement of the plate with respect to the spraying system: deflected or back and forth from the plate facing a fixed spraying system or vice versa, displacement of the nozzles or nozzles relative to the plate.

Typically, the tray scrolls horizontally in the spray cell and its running speed is greater than or equal to 20 mm / s, ie 1.2 m / min.

Also preferably, the transverse thermal uniformity of the plate is ensured by modulation of the spray in the width of the plate by ignition / extinction of nozzles or nozzles, or screening of said spray.

The invention also relates to an installation for carrying out the method as above, comprising a spraying cell provided with nozzle manifolds or nozzles for liquid spraying or cooling mist under pressure arranged in the upper parts and base of said cell, so as to sprinkle the two large faces, upper and lower of said plate,

A uniform air tunnel at the exit of the spray cell, in a tunnel with interior walls and roof in an internally reflective material, allowing a thermal uniformization of the plate by diffusion of heat in said plate, the heart by warming the surfaces.

• Les buses de liquide ou brouillard de refroidissement génèrent des sprays ou jets à cône plein dont l'angle est compris entre 45 et 60°

According to a preferred embodiment:

• Liquid nozzles or cooling mist generate sprays or jets with a solid cone whose angle is between 45 and 60 °

The axes of the lower nozzles are oriented normally to the lower surface

• Les jets des deux rampes de buses supérieures appariées soient orientés en opposition l'un de l'autre.
• Les jets présentent une bordure normale à la surface supérieure du plateau
• Le recouvrement des deux jets soit compris entre le 1/3 et les 2/3 de la largeur de chaque jet, et préférentiellement sensiblement de la moitié
• L'enveloppe des deux jets ainsi formée constitue un profil en M.

Preferably, the upper nozzle ramps are matched in the direction of travel of the tray. In the same pair, the upper ramps are inclined so that:

• The jets of the two paired top nozzle ramps are oriented in opposition to each other.
• The jets have a normal border on the upper surface of the board
• The overlap of the two jets is between 1/3 and 2/3 of the width of each jet, and preferably substantially half
• The envelope of the two jets thus formed constitutes a profile in M.

The pairs of upper and lower nozzle ramps are placed substantially facing each other, so that the upper and lower spray lengths are substantially equal and in facing relation.

Due to the pairing of the upper nozzles in opposition and the M profile of the jets, the spray length is controlled so as to promote the lateral evacuation of the liquid or mist sprayed on the upper face, by guiding it towards the banks of the plateau where it evacuated in the form of a cascade without touching the small faces of the plate thus allowing a very homogeneous cooling temperature in the longitudinal and transverse directions of the plate.

As for the liquid alone or contained in the cooling mist, it can be recovered, typically in a container located under the facility, recycled and thermally controlled.

According to an improved mode of implementation, the entire installation, spraying cell and uniformization tunnel, is controlled by a thermal model coded on a PLC, the thermal model determining the settings of the installation as a function of the temperature estimated by thermal measurement at the beginning of the spray cell and in depending on the target output temperature, usually the hot rolling start temperature.

• Centrage du plateau, à l'entrée de l'installation
• Mesure de la température de surface supérieure du plateau
• Calcul par l'automate, à l'aide du modèle thermique, des réglages de la cellule d'aspersion en fonction de la température cible d'entrée et de la température cible de sortie, c'est dire du refroidissement cible du plateau, incluant la détermination du nombre de rampes activées, du nombre de buses ouvertes en rives, de la vitesse de défilement du plateau dans la cellule d'aspersion, des démarrages et arrêts des rampes d'aspersion, et du temps de maintien dans le tunnel d'uniformisation
• Défilement du plateau dans la cellule d'aspersion, arrosage supérieur et inférieur suivant les calculs de l'automate
• Transfert du plateau de la cellule d'aspersion vers le tunnel d'uniformisation
• Maintien du plateau dans le tunnel d'uniformisation pendant une durée déterminée par l'automate.

According to an advantageous embodiment, the implementation of the installation comprises the following steps:

• Centering the tray at the entrance of the installation
• Measurement of the upper surface temperature of the plateau
• Calculation by the controller, using the thermal model, of the settings of the spray cell according to the target inlet temperature and the target output temperature, ie the target cooling of the plateau, including determination of the number of activated ramps, the number of nozzles open on the banks, the speed of travel of the plate in the spray cell, start and stop of the spray bars, and the holding time in the tunnel of standardization
• Scroll of the tray in the spray cell, upper and lower watering according to the calculations of the automaton
• Transfer of the tray from the spray cell to the standardization tunnel
• Maintenance of the tray in the uniformization tunnel for a period determined by the automaton.

Description of figures

• The figure 1 represents a schematic diagram of the method according to the invention in one pass. The plate is removed from the homogenization furnace 1 at its homogenization temperature. It is transferred to the cooling machine, laterally centered and its surface temperature is measured (2) by surface thermocouple, by contact or with an infrared pyrometer but which will be less precise. The thermal model determines the setting of the spraying cell 3 (number of activated ramp pairs and plateau speed). Then the tray is treated in the spray cell. At its exit, it is dry and transferred (4) to a uniformization tunnel 5 for a duration determined by thermal model or according to the amplitude of the cooling undergone. At the end, it is transferred to the hot rolling mill 6.
• The figure 2 represents a schematic diagram of the method according to the invention in two or more passes. When the target cooling amplitude is greater than 100 ° C, a single passage in the cooling machine may be insufficient. In this case, the plate is cooled a first time in the first spraying cell 3. Then, with or without passage in the intermediate uniformization tunnel 5, the plate is transferred into the second cooling machine composed of the elements 6, 7 and 8, where it undergoes a complete cycle: spraying cell then obligatorily tunnel of uniformization 8. The duration of the last phase of uniformization depends on the thermal diffusivity of the material, therefore of the alloy, of the amplitude cooling target, and the severity of target thermal uniformity before hot rolling 9.
  The multi-pass cooling can also be achieved with a single machine, by successive passages.
• The figure 3 is a schematic plan of the sprinkling machine, seen in profile, the plateau scrolling from left to right. It illustrates the disposition of the jets of liquid or mist sprayed on the plate, seen in profile, in the upper face and in the lower face. The upper and lower irrigation booms are paired and in pairs, to ensure a good uniformity of cooling in the thickness of the tray. The paired upper ramps are oriented in opposition, which ensures an evacuation of liquid or mist sprayed transversely to the plate. The axes of the lower nozzles are oriented normally to the lower surface of the tray, the liquid flows by gravity. Ramps of compressed air (1 to 4) surround the ends of the spray cell to prevent residual runoff of liquid on the tray outside said cell.
• The figure 4 illustrates the impact of higher liquid jets or fog, in top view of the plateau. We note the concentration of the surface flow of liquid or fog at the intersection of the jets in opposition. This watering scheme is favorable to the evacuation of the liquid along this transverse line with a high surface flow rate.
• The figure 5 represents the thermal kinetics of a 600 mm plate, calculated in the case of an average cooling of 40 ° C, in one pass in the spray machine, for an AA3104 alloy according to the designations defined by " Aluminum Association "in the" Registration Record Sériés "it publishes regularly. There are the evolutions of the minimum temperatures Tmin, maximum Tmax and average Tmoy in the plateau, as well as the maximum temperature difference in the whole volume of the plateau, over time (DTmax).
• The figure 6 represents the thermal kinetics of a 600 mm plate, calculated in the case of an average cooling of 130 ° C, in two passes in the spray machine, for an alloy of the AA6016 type according to the designations defined by " Aluminum Association "in the" Registration Record Sériés "it publishes regularly. There are the same evolutions of the minimum temperatures Tmin, maximum Tmax and average Tmoy in the plateau, as well as the maximum temperature difference in the whole volume of the plateau, over time (DTmax).
• The Figures 7 to 9 illustrate three modes or strategies of sprinkling in the direction of the sprinkling machine, with representation of the position of the nozzles on the spray booms, the sprinkler being seen from the front in all cases:
  • Figure 7 : Uniform thermal profile in the tray width
  • Figure 8 : Thermal profile with cold edges, created by a surplus of watering on the banks of the plateau
  • Figure 9 : Thermal profile with hot banks, created by a lack of watering on the banks of the plateau.
• The figure 10 presents two modes or strategies of width of irrigation of the same plate of alloy of aluminum of 600 mm of thickness and 1700 mm of width, on the left a thermal profile in the direction transverse with cold edges with 11 nozzles in action on the right, a thermal profile with hot banks with 9 nozzles in action.
• The figure 11 is the consequence on the thermal profile (temperature in ° C as a function of the position in the cross direction, from the axis of the plate, in m) of these two modes of spraying.
• The Figures 12 to 14 illustrate three examples of modes or strategies for triggering watering.

Indeed, the thermal profile in the long direction of the plateau is controlled by: The absence or very low runoff in the long direction of the plateau, thanks to the mounting of the upper ramps in opposition,

The triggering and stopping of the watering of each pair of ramps at a precise position of the plateau: this is the notion of watering heel.

The figure 12 corresponds to a management of the thermal profile in the long direction with hot ends, the figure 13 with warm ends and the figure 14 at cold ends (with a runoff in 1).

The Figure 15 illustrates the longitudinal thermal profiles (temperature in ° C as a function of the position in the length L of the plateau in m) for the three thermal management strategies of the above-mentioned ends of the plateau. In this example, the plate is alloy type AA6016, thickness 600 mm, its average cooling is 100 ° C in two passes, and the thermal uniformization box time is 10 min.

The Figures 16 to 18 illustrate the thermal field, in 3D visualization, of the same example, at the hot rolling inlet, for the three thermal management strategies of the above-mentioned ends of the plateau, the figure 16 with hot ends, the figure 17 with warm ends and the figure 18 with cold ends.

It can be seen that the sprinkler initiation strategy clearly makes it possible to control the longitudinal thermal profile of the plateau.

The Figure 19 illustrates the thermal field of an alloy plate of type AA6016, 600 mm thick, cooled by approximately 50 ° C in a pass in the spray machine set with a single boom irrigation nozzle ends of the tray in accordance with figure 13 . This adjustment leads to a very uniform thermal field with slightly warmer ends, which is favorable to rolling.

Description of the invention

The invention essentially consists in a method of cooling with a cooling liquid or mist of an aluminum alloy rolling plate or plate, from 30 to 150 ° C. in a few minutes, that is, at an average cooling rate of between 150 and 500 ° C / hour.

• Une première phase d'aspersion du plateau à l'aide d'un liquide ou brouillard de refroidissement, typiquement au défilé
• Une deuxième phase d'uniformisation thermique du plateau.

It consists mainly of two phases:

• A first phase of sprinkling the plate with a liquid or cooling mist, typically at the parade
• A second phase of thermal uniformization of the plateau.

During the first spraying phase, the plate is cooled in an enclosure comprising nozzles or spray nozzles for liquid or mist cooling under pressure, typically water and preferably deionized.

The nozzles or nozzles are distributed in the upper and lower parts of said cell, so as to spray the two large faces, upper and lower, of the tray. The option of a parade method limits the risk of hot spots related to the contacts between the plate and its support, usually consisting of cylindrical or conical rollers.

The average cooling of the plateau (ΔTmoy plateau) is controlled by the duration of spray seen by each section of the plateau.

During this phase, the plateau is thermally very heterogeneous in its thickness, due to a high value of the Biot number.

1. a) Le contrôle de la largeur d'arrosage dans le sens travers du plateau, par le nombre de buses activées ou l'utilisation d'écrans
2. b) Une méthode d'aspersion favorisant l'évacuation latérale de l'eau aspergée en face supérieure. En effet, le liquide de refroidissement est guidé vers les rives du plateau et s'évacue sous forme d'une cascade sans toucher les petites faces dudit plateau. Le refroidissement du plateau est de ce fait très homogène. Cette méthode consiste en fait à apparier deux rampes de buses, placées en opposition, comme le montrent notamment les figures 3 et 4.

The homogeneity of cooling in the width of the plate is mastered by:

1. a) The control of the watering width in the cross direction of the plate, by the number of nozzles activated or the use of screens
2. b) A method of spraying favoring the lateral evacuation of the water sprayed on the upper face. Indeed, the coolant is guided towards the banks of the plate and evacuated in the form of a cascade without touching the small faces of said plate. The cooling of the plate is therefore very homogeneous. This method consists of matching two nozzle ramps, placed in opposition, as shown in particular by Figures 3 and 4 .

• c) Le contrôle du début et de la fin de l'aspersion par déclenchement des rampes d'aspersion à la position souhaitée sur le plateau ou, à nouveau, par l'utilisation d'écrans. Ainsi la tête et le pied du plateau peuvent ne pas être aspergés. On obtient alors un plateau avec une tête et un pied chaud, ce qui est favorable à son engagement lors du laminage réversible à chaud
• d) La forte réduction du ruissellement dans le sens long du plateau. Ce très faible ruissellement est obtenu grâce à la caractéristique b) ci-dessus de l'invention, favorisant l'évacuation latérale du liquide de refroidissement aspergé en face supérieure du plateau.

The homogeneity of cooling in the length of the plate is mastered by:

• c) The control of the start and end of sprinkling by triggering the spray bars at the desired position on the plate or, again, by the use of screens. Thus the head and the foot of the tray may not be sprayed. We then obtain a plate with a head and a hot foot, which is favorable to its engagement during hot reversing rolling.
• d) The strong reduction of runoff in the long direction of the plateau. This very low runoff is obtained by virtue of the characteristic b) above of the invention, favoring the lateral evacuation of the cooling liquid sprayed on the upper face of the plate.

The spraying phase is therefore designed to limit thermal heterogeneities in the three directions of the plateau. The invention makes it particularly possible to control the thermal profiles in the cross direction and in the long direction of the plate, which is very significant since any thermal gradients along these two large dimensions would be difficult to absorb in a short time.

• Après aspersion, le plateau est maintenu quelques minutes dans une configuration de faible échange de chaleur avec son environnement. Ces conditions thermiques permettent l'uniformisation thermique du plateau, en quelques minutes pour les refroidissements de moins de 30°C et en environ 30 minutes maximum pour des refroidissements de 150°C. Cette phase est essentielle à l'atteinte des spécifications d'uniformité thermique demandées. Elle permet d'atteindre un écart thermique DTmax de moins de 40°C sur un plateau de grandes dimensions.

Follows the phase of thermal uniformization of the plateau:

• After spraying, the tray is held for a few minutes in a configuration of low heat exchange with its environment. These thermal conditions allow the thermal uniformization of the plate, in a few minutes for cooling of less than 30 ° C and in about 30 minutes maximum for cooling of 150 ° C. This phase is essential to achieving the required thermal uniformity specifications. It makes it possible to reach a thermal difference DTmax of less than 40 ° C on a large plate.

The invention can also be adapted to absolute values of high cooling. Thus, when the average cooling of the desired plateau is greater than typically 80 ° C, it is possible to cycle several times all the phases "spraying" and "uniformization", reducing each cycle "spraying-standardization" the average temperature of a very thick plate.

The method thus described ensures rapid and controlled cooling of a thick plate, in particular a rolling plate, made of aluminum alloy. It is also robust and avoids the known risks of local overcooling.

The machine, or cooling system, itself consists of at least one spraying cell, typically horizontal to the parade, on the one hand and, on the other hand, at least one thermal uniformization tunnel.

The spraying cell allows the implementation of phase 1 of the method described above.

1. 1) Centrage du plateau, à l'entrée de la machine
2. 2) Mesure de la température de surface supérieure du plateau
3. 3) Calcul par l'automate, à l'aide du modèle thermique, des réglages de la cellule d'aspersion en fonction de la température d'entrée et de la température cible de sortie, c'est à dire du refroidissement cible du plateau, incluant la détermination du nombre de rampes de buses activées, du nombre de buses ouvertes en rives, de la vitesse de défilement du plateau dans la cellule d'aspersion, des démarrages et arrêts des rampes d'aspersion, du temps de maintien dans le tunnel d'uniformisation
4. 4) Défilement du plateau dans la cellule d'aspersion, arrosage supérieur et inférieur suivant les calculs de l'automate.

The tray processing steps in this machine or installation are as follows:

1. 1) Centering the plate at the entrance of the machine
2. 2) Measurement of the upper surface temperature of the plateau
3. 3) Calculation by the automaton, using the thermal model, of the settings of the spraying cell as a function of the inlet temperature and the target output temperature, ie the target cooling of the plateau , including the determination of the number of activated nozzle ramps, the number of nozzles open on the banks, the speed of travel of the plate in the spray cell, the start and stop of the spray bars, the holding time in the standardization tunnel
4. 4) Scroll of the tray in the spray cell, upper and lower watering according to the calculations of the automaton.

The spraying cell consists of ramps provided with nozzles or nozzles for dispensing under pressure the liquid or cooling mist.

In the case where the latter is water, it is ideally deionized or at least very clean and not very mineralized, to avoid clogging of the nozzles and to ensure the stability of the heat transfer between the water and the plateau. The spraying machine can advantageously, for reasons of economy in particular, operate in a closed cycle, with for example a recovery tank placed under the spray machine.

• Les jets des deux rampes soient orientés en opposition l'un de l'autre
• Les jets présentent une bordure normale à la surface supérieure du plateau
• Le recouvrement des deux jets soit compris entre le 1/3 et les 2/3 de la largeur du jet, et préférentiellement sensiblement de la moitié
• L'enveloppe des deux jets ainsi formée constitue donc un profil en M
• Les paires de rampes de buses supérieures et inférieures sont placées sensiblement en vis-à-vis, de façon à ce que les longueurs d'aspersion supérieures et inférieures soient sensiblement égales et en vis-à-vis.

The selected coolant or coolant nozzles generate full cone sprays or jets with an angle between 45 and 60 ° (in the example: LECHLER brand 60 ° angled solid cone nozzles) . The axes of the nozzles of the lower ramps are oriented normally to the lower surface. The upper ramps are paired. In the same pair of upper ramps, the ramps are inclined so that:

• The jets of the two ramps are oriented in opposition to each other
• The jets have a normal border on the upper surface of the board
• The overlap of the two jets is between 1/3 and 2/3 of the width of the jet, and preferably substantially half
• The envelope of the two jets thus formed thus constitutes a profile in M
• The pairs of upper and lower nozzle ramps are placed substantially facing each other, so that the upper and lower spray lengths are substantially equal and in facing relation.

In the case of a parade treatment, the speed of travel of the tray is greater than or equal to 20 mm / s, ie 1.2 m / min.

On leaving the spraying cell, the plate is transferred, for example by means of automatic trolleys, into one or more tunnel (s) of uniformity. The aim of the tunnel is to minimize the heat transfer between the plateau and the air, which is favorable to a better thermal uniformity of the plateau. This thermal uniformization takes place by diffusion of heat in the tray, the core warming the surfaces of the tray.

The uniformization tunnel consists of vertical walls and a roof in an ideally reflective material on the inside of the tunnel.

It avoids drafts around the tray, ensuring the absence of heat transfer by forced convection. In addition, it reduces natural convection heat transfer and limits radiative transfer if the walls are reflective.

Finally, the machine or cooling system composed of the spraying cell and the uniformization tunnel is controlled by a thermal model coded on the automaton of the machine. The thermal model determines the settings of the machine according to the temperature at the start of the spray cell, or inlet temperature, and depending on the target output temperature, usually the rolling temperature.

Examples Example 1: Uniform cooling of 40 ° C of an alloy plate AA3104 type.

The figure 5 illustrates the 40 ° C cooling of an alloy plate type AA3104 according to the designations defined by the "Aluminum Association" in the "Registration Record Sériés" it publishes regularly. The thickness of the board is 600 mm, its width 1850 mm and its length 4100 mm. The tray leaves the homogenizing oven at 600 ° C.

The plate cooling process is the one-pass process described in figure 1 .

• le déplacement du plateau entre la sortie du four et l'entrée de la machine de refroidissement
• le centrage latéral du plateau
• la mesure de la température de surface supérieure du plateau
• le temps de calcul par l'automate des réglages de la machine de refroidissement (cellule d'aspersion et tunnel).

The tray is transferred to the cooling machine in 180 s. This transfer time includes:

• the displacement of the plate between the exit of the oven and the entrance of the cooling machine
• the lateral centering of the plateau
• the measurement of the upper surface temperature of the plateau
• the calculation time by the controller of the settings of the cooling machine (spray cell and tunnel).

Then the tray scrolls in the spray cell, each point of the plate off ends (head and foot) is watered for 46 seconds. The surface flow rate of spray is 500 1 / (min.m ² ) on the two large faces of the plate. The watering heel is set to a ramp torque, as described in figure 12 . At its exit from the spraying cell, the plate is dry and transferred in 30 s to a uniformization tunnel for a duration determined by the thermal model coded in the automaton, here 300 s, or 5 minutes. At the end, the tray is transferred to the hot rolling mill, with thermal uniformity better than 40 ° C on the complete tray.

The plateau surface temperature drops to about 320 ° C, while the core of the plateau remains almost isothermal during the spraying phase. Then, by diffusion of heat between the heart and the surface, the heart gives up heat to the surface, the plate becomes thermally uniform.

The thermal gap in the plateau (DTmax) is maximum at the end of the spraying phase, its value is 280 ° C for this configuration. It reduces rapidly when the sprinkling stops: in 6 minutes of waiting (transfer and then uniformization in the tunnel), the thermal deviation DTmax is reduced to less than 40 ° C.

Example 2: 135 ° C uniform cooling of an alloy plate AA6016 type.

The figure 6 illustrates the 135 ° C cooling of an alloy plate of the AA6016 type. The thickness of the plate is 600 mm, its width 1850 mm and its length 4100 mm. The tray leaves the homogenization oven at 530 ° C.

The plate cooling process is the two-pass process described in figure 2 .

• le déplacement du plateau entre la sortie du four et l'entrée de la machine de refroidissement
• le centrage latéral du plateau
• la mesure de la température de surface supérieure du plateau
• le temps de calcul par l'automate des réglages des machines de refroidissement.

The tray is transferred to the cooling machine in 100 s. This transfer time includes:

• the displacement of the plate between the exit of the oven and the entrance of the cooling machine
• the lateral centering of the plateau
• the measurement of the upper surface temperature of the plateau
• the calculation time by the controller of the settings of the cooling machines.

Then the tray scrolls in the spraying cell, each point of the plate off ends (head and foot) is watered for 51 seconds. The surface flow rate of spray is 800 1 / (min.m ² ) on the two large faces of the plate. The watering heel is set to a ramp, as described in figure 13 . At its exit from the spraying cell, the plate is transferred in 60 s to the second spraying cell without passing, in this example, through the optional intermediate uniformization tunnel. The plateau then undergoes a second watering, identical to the first one: each point of the plateau out ends undergoes a watering of 51 seconds, at the surface flow rate of 800 1 / (min.m ² ). On leaving the second spraying cell, the plate is transferred to the uniformization tunnel in 30 seconds. The board waits several minutes in the standardization tunnel. At the end, the tray is transferred to the hot rolling mill, with thermal uniformity better than 40 ° C on the complete tray.

The surface temperature of the tray drops to about 60 ° C. The core of the plate remains almost isothermal during the first phase of spraying and then cools during the second phase of spraying. Then, by diffusion of heat between the heart and the surface, the heart gives up heat to the surface, the plate becomes thermally uniform.

The thermal gap in the plateau (DTmax) is maximum at the end of each of the sprinkling phases, its value is 470 ° C for this configuration. It is reduced rapidly when the sprinkling of the plateau ceases: the temperature difference DTmax plateau is 55 ° C after 13 minutes waiting in the tunnel and becomes less than 40 ° C after 23 minutes spent in the tunnel.

Example 3: Uniform cooling of 125 ° C of an alloy plate of the AA6016 type.

The thickness of the plate is 600 mm, its width 1850 mm and its length 4100 mm. The tray leaves the homogenization oven at 530 ° C.

The plate cooling process is the two-pass process described in figure 2 .

• le déplacement du plateau entre la sortie du four et l'entrée de la machine de refroidissement
• le centrage latéral du plateau
• la mesure de la température de surface supérieure du plateau
• le temps de calcul par l'automate des réglages des machines de refroidissement.

The tray is transferred to the cooling machine in 100 s. This transfer time includes:

• the displacement of the plate between the exit of the oven and the entrance of the cooling machine
• the lateral centering of the plateau
• the measurement of the upper surface temperature of the plateau
• the calculation time by the controller of the settings of the cooling machines.

Then the tray scrolls in the spray cell, each point of the tray is watered for 51 seconds. The surface flow rate of spray is 500 1 / (min.m ² ) on the two large faces of the plate. The watering heel is zero, as described in figure 14 . The plate is thus completely completely watered, which generates a longitudinal thermal profile with cold ends. At its exit from the spraying cell, the plate is transferred in 60 s to the second spraying cell without passing, in this example, through the optional intermediate uniformization tunnel. The plateau then undergoes a second watering, different from the first. The plateau, but this time out of the ends, undergoes a second watering of 51 seconds, at the surface flow rate of 500 1 / (min.m ² ). The watering heel is a couple of ramps, as described figure 12 . This adjustment tends to straighten the cold-end thermal profile, thus generating a nearly flat longitudinal thermal profile at the exit of the second spray cell. At its exit from the second spraying cell, the plate is transferred to the standardization tunnel in 30 seconds. The plateau is waiting only 10 minutes in the tunnel of standardization. At the end, the tray is transferred to the hot rolling mill, with thermal uniformity better than 40 ° C on the complete tray.

Example 3 shows that the judicious choice of watering heels makes it possible to significantly reduce the uniformization time after spraying. For a multi-pass cooling process, the choice of heels may be different from one pass to another. For a cooling process in 2 passes, the heel chosen in the first pass wins to be opposite to the heel chosen in the second pass. In an optimized way and for a 2-pass cooling, a first pass with a zero heel (continuous watering of the plate) followed by a second pass with a heel of a pair of ramps can significantly reduce the uniformization time required for the thermal balancing of the plate.

Claims (17)

1. Method for cooling an aluminium alloy rolling ingot of typical dimensions, 250 to 800mm thick, 1000 to 2000mm wide and 2000 to 8000mm long, after metallurgic homogenising heat treatment of said ingot at a temperature typically between 450 to 600°C according to the alloys and before it is hot rolled, the cooling being of a value of 30 to 150°C, characterised in that the cooling is carried out at a speed of 150 to 500°C/h, with a thermal differential of less than 40°C over the entire ingot cooled from the homogenisation temperature thereof.
2. Method according to claim 1, characterised in that the cooling is carried out in at least two phases:

   A first spraying phase during which the ingot is cooled in a chamber comprising ramps of nozzles or tuyeres for spraying pressurised cooling liquid or mist, distributed into high and low parts of said chamber, so as to spray the two large, upper and lower faces of said ingot.

   An additional, still air thermal equalisation phase, in a tunnel with reflective inner walls, for a duration of 2 to 30 minutes according to the format of the ingot and the cooling value.
3. Method according to claim 2, characterised in that the spraying and thermal equalisation phase are repeated, in the case of very thick ingots and for an average overall cooling of more than 80°C.
4. Method according to one of claims 2 or 3, characterised in that the cooling liquid, including in a mist, is water, and preferably deionised water.
5. Method according to one of claims 1 to 4, characterised in that the head and the foot of the ingot, that is typically 300 to 600mm at ends thereof, are less cooled than the rest of the ingot, so as to maintain a hot head and the foot, a configuration that is favourable for inserting the ingot during reversible hot rolling.
6. Method according to one of claims 2 to 5, characterised in that the cooling of the head and the foot is modulated by the starting up or turning off of ramps of nozzles or tuyeres.
7. Method according to one of claims 2 to 5, characterised in that the cooling of the head and the foot is modulated by the presence of screens.
8. Method according to one of claims 2 to 7, characterised in that the spraying and not thermal equalisation step phases are repeated, and in that the head and the foot of the ingot, that is typically 300 to 600mm at ends thereof, are cooled differently to the rest of the ingot at least in one of the spraying chambers.
9. Method according to claim 8, characterised in that the first spray pass is carried out with a zero heel, that is a continuous spraying of the ingot, followed, without a first thermal equalisation phase, by a second spray pass with a heel of a pair od ramps such as in figure 12, thus enabling to particularly reduce the duration of the final equalisation phase needed to thermally balance the ingot.
10. Method according to one of claims 2 to 9, characterised in that the longitudinal thermal equalisation of the ingot is improved by a relative movement of the ingot in relation to the spraying system: scrolled or moving back and forth from the ingot opposite a stationary spraying system or vice versa.
11. Method according to claim 10, characterised in that the ingot scrolls horizontally in the spraying chamber and the scrolling speed thereof is higher than or equal to 20mm/s, that is 1.2m/min.
12. Method according to one of claims 2 to 11, characterised in that the transversal thermal equalisation of the ingot is ensured by modulating the spraying in the width of the ingot by switching nozzles or tuyeres on or off, or screening said spraying.
13. Facility for implementation of the method according to one of claims 1 to 12, characterised in that it comprises:

    A spraying chamber (3) equipped with ramps of nozzles or tuyeres for spraying pressurised cooling liquid or mist arranged in the top and bottom parts of said chamber, so as to spray the two large, upper and lower faces of said ingot,

    A still air equalisation tunnel (5) at the end of the spraying chamber (3), in a tunnel with lower walls and a roof made of a reflective material inside, enabling a thermal equalisation of the ingot by distributing heat in said ingot, in the mid thickness of the ingot the core warming the surfaces.
14. Facility according to claim 13, characterised in that:

    The cooling liquid or mist nozzles of the spraying chamber generate full cone jets with an angle of between 45 and 60°,

    The axes of the lower nozzles are oriented normally to the lower surface,

    The upper nozzle ramps are paired in the scrolling direction of the ingot. In one same pair, the upper nozzles are tilted such that:

    - The jets of the two paired nozzle ramps are oriented opposite each other,

    - The jets have a normal edge to the upper surface of the ingot,

    - The jet coverage of the two paired ramps are between 1/3 and 2/3 of the width of each jet, and preferably substantially half,

    - The envelope of the two jets thus formed constitutes an M-shape.

    The pairs of upper and lower nozzle ramps are placed substantially opposite each other, such that the upper and lower spraying lengths are substantially equal and opposite each other.
15. Facility according to one of claims 13 or 14, characterised in that the cooling liquid is collected after spraying, typically in a container located under the facility, recycled and thermally controlled.
16. Implementation of the facility according to one of claims 13 to 15, characterised in that the whole of the facility, spraying chamber (3) and equalisation tunnel (5), is controlled by an automaton-coded heat model, the heat model determining the settings of the facility according to the temperature estimated by measuring the heat at the start of the spraying chamber and according to the target temperature at the outlet, in general, the temperature at the start of hot rolling.
17. Implementation of the facility according to claim 16, characterised in that it comprises the following steps:

    - Centring the ingot, at the entrance of the facility,

    - Measuring the upper surface temperature of the ingot,

    - Calculating by the automaton, using the heat model, the settings of the spraying chamber (3) according to the inlet temperature and the target temperature at the outlet, in other words, the target cooling of the ingot, including determining the number of ramps activated, the number of nozzles activated at the edges, the scrolling speed of the ingot in the spraying chamber (3), the start-ups and stoppings of the spraying ramps, and the holding time in the equalisation tunnel (5),

    - Scrolling of the ingot in the spraying chamber (3) , upper and lower spraying according to the automaton's calculations,

    - Transfer of the ingot from the spraying chamber to the equalisation tunnel (5),

    - Holding the ingot in the equalisation tunnel (5) for a duration determined by the automaton.

Images