EP3171996A1

EP3171996A1 - Cooling facility and method

Info

Publication number: EP3171996A1
Application number: EP15753101.3A
Authority: EP
Inventors: Vincent Duhoux; Bruno Magnin; Daniel BELLOT; José ROCHE; Pierre AUCOUTURIER
Original assignee: Constellium Neuf Brisach SAS
Current assignee: Constellium Neuf Brisach SAS
Priority date: 2014-07-23
Filing date: 2015-07-10
Publication date: 2017-05-31
Anticipated expiration: 2035-07-10
Also published as: EP3398696B1; KR20170039166A; MX2017000483A; JP2017521260A; US20180236514A1; KR102336948B1; DE15753101T1; CN106661648B; SA517380746B1; EP3171996B1; WO2016012691A1; BR112017000205B1; RU2017105464A3; TW201622843A; CA2954711C; CA2954711A1; US10130980B2; CN106661648A; EP3398696A1; FR3024058B1

Abstract

The invention relates to a method for cooling a sheet ingot made of an aluminium alloy, after the heat treatment for the metallurgical homogenisation of said ingot and before the hot-rolling thereof, characterised in that the cooling, representing a value of between 30 and 150°C, is carried out at a speed of between 150 and 500°C/h, with a homogeneity of less than 40°C over all of the treated part of the ingot. The invention also relates to the facility allowing the implementation of said method and to said implementation.

Description

Cooling method and equipment 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 invention also relates to the installation or equipment for implementing 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. 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).

". HTC · D

Bi =

AT

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.

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.

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

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 and controlled thermal field in the whole plateau Ensuring 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.

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 made with a zero heel, or continuous watering of the plate as in Figure 14, followed, without first phase of thermal uniformization, a second pass spraying with a heel of a pair of ramps as in 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 implementing the method as above, comprising a spraying cell provided with nozzle manifolds or nozzles for liquid spraying or mist cooling 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.

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. Preferably, the upper nozzle manifolds 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 upper nozzle ramps are oriented in opposition to one another.

- 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, spray cell and uniformization tunnel, is controlled by a thermal model coded on PLC, the thermal model determining the settings of the installation according to 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.

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 automaton, using the thermal model, of the settings of the spraying cell as a function of the target temperature of entry and the target temperature of exit, ie of the target cooling of the plate, including the determination of the number of activated ramps, the number of nozzles open on the banks, the speed of the tray in the spray cell, the start and stop of the spray booms, and the retention time in the tunnel. '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

- Hold the tray in the uniformization tunnel for a period determined by the PLC.

Description of figures

Figure 1 shows a block 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.

Figure 2 shows a block 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.

Figure 3 is a schematic plan of the sprinkler machine, seen in profile, the tray 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.

Figure 4 illustrates the impact of the upper liquid or mist jets, in top view of the plate. 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.

FIG. 5 represents the thermal kinetics of a 600 mm plate, calculated in the case of a mean cooling of 40 ° C., in one pass in the spraying machine, for an alloy of the AA3104 type according to the designations defined by "Aluminum Association" in the "Registration Record Series" that 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). FIG. 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 Series" that 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). FIGS. 7 to 9 illustrate three modes or strategies of watering in the direction of the spraying machine, with representation of the position of the nozzles on the spray bars, the spray machine being seen from the front in all cases :

Figure 7: Uniform thermal profile in the tray width

Figure 8: Thermal profile with cold banks, created by a surplus of watering on the banks of the plateau

Figure 9: Thermal profile with hot banks, created by a lack of irrigation on the banks of the plateau.

Figure 10 shows two modes or strategies of watering width of the same aluminum alloy plate 600 mm thick and 1700 mm wide, on the left a thermal profile in the transverse direction with cold edges with 11 nozzles in action, right a thermal profile with hot banks with 9 nozzles in action.

FIG. 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.

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. Figure 12 corresponds to a management of the thermal profile in the long direction with hot ends, Figure 13 with warm ends and Figure 14 with cold ends (with a run-off in 1).

Figure 15 illustrates the longitudinal thermal profiles (temperature in ° C as a function of the position in the length L of the plate in m) for the three thermal management strategies of the above-mentioned ends of the plate. 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.

FIGS. 16 to 18 illustrate the thermal field, in 3D visualization, of the same example, at the hot rolling input, for the three thermal management strategies of the aforementioned ends of the plate, FIG. 16 with hot ends, FIG. lukewarm and Figure 18 with cold extremities.

It can be seen that the irrigation initiation strategy clearly allows the longitudinal thermal profile of the plateau to be controlled.

Figure 19 illustrates the thermal field of a 600 mm thick AA6016 type alloy tray cooled by approximately 50 ° C in one pass in the set sprayer with a watering heel of only ramp at the ends of the plate, according to Figure 13. This setting 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 a plate or a rolling plate of aluminum alloy, from 30 to 150 ° C in a few minutes, that is to say at an average cooling rate of between 150 and 500 ° C / hour.

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 (ATmoy 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.

The homogeneity of cooling in the width of the plate is controlled by: a) The control of the width of irrigation in the cross direction of the plate, by the number of activated nozzles or the use of screens

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 in fact to match two ramps of nozzles, placed in opposition, as shown in particular in Figures 3 and 4.

The homogeneity of cooling in the length of the plate is controlled by: c) The control of the beginning and the end of the sprinkling by triggering of the spray bars at the desired position on the plateau 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.

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 typically greater than 80 ° C., it is possible to cycle the all the "spray" and "uniformization" phases several times, reducing each "spraying-uniformization" cycle. 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. The tray processing steps in this machine or installation are as follows:

1) Centering the plate at the entrance of the machine

2) Measurement of the upper surface temperature of the plateau

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) 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.

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 plate - 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 heart 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.

Figure 5 illustrates the cooling of 40 ° C of an AA3104 alloy plate according to the designations defined by "Aluminum Association" in the "Registration Record Series" 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.

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 time of calculation by the automat of the settings of the cooling machine (cell of spraying 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 l / (min.m ² ) on the two large faces of the tray. The watering heel is set at a ramp torque, as described in FIG. 12. At its exit from the spray 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 of 300 s, is 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.

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.

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

- 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 spraying is 800 l / (min.m ² ) on the two large faces of the plate. The watering heel is set to a ramp, as described in FIG. 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 standardization 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 l / (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.

- the lateral centering of the plateau

- the measurement of the upper surface temperature of the plateau

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 l / (min.m ² ) on the two large faces of the tray. The watering heel is zero, as described in Figure 14. The plate is thus watered completely identically, which generates a longitudinal thermal profile 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 l / (min.m ² ). The watering heel is of a pair of ramps, as described in FIG. 12. This adjustment tends to straighten the cold-end thermal profile, thus generating an almost flat longitudinal thermal profile at the outlet 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

claims

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 metallurgical homogenization heat treatment of said tray to 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 150 to 500 ° C / h, with a thermal difference of less than 40 ° C over the entire cooled plate from its homogenization temperature.

Process according to Claim 1, characterized in that the cooling is carried out in at least two phases:

Process according to Claim 2, characterized in that the spraying and thermal uniformization phases are repeated, in the case of very thick trays and for an average overall cooling of greater than 80 ° C.

Method according to one of claims 2 or 3, characterized in that the liquid, including in a fog, cooling is water, and preferably deionized water.

Method according to one of claims 1 to 4, characterized in that the head and the foot of the tray, typically 300 to 600 mm at the ends, are less cooled than the rest of the plate so as to maintain a head and a warm foot, favorable configuration for the engagement of the plate during a reversible hot rolling. 6. Method according to one of claims 2 to 5, characterized in that the cooling of the head and foot is modulated by the start or the extinction of the nozzle or spray nozzles ramps.

7. Method according to one of claims 2 to 5, characterized in that the cooling of the head and foot is modulated by the presence of screens.

8. Method according to one of claims 2 to 7, characterized in that the sprinkling phases, and no thermal uniformity, are repeated, and in that the head and the foot of the tray, is typically 300 to 600 mm at the ends, are cooled differently than the rest of the tray at least in one of the spraying cells.

9. A method according to claim 8, characterized in that the first spraying pass is carried out with a zero heel, or a continuous watering of the plate, followed, without first phase of thermal uniformization, a second spraying pass with a heel of a pair of ramps as in Figure 12, thereby significantly reducing the duration of the final phase of uniformization necessary for thermal balancing of the plate. 10. Method according to one of claims 2 to 9, characterized in that the longitudinal thermal uniformity of the plate is improved by a relative movement of the plate relative to the sprinkler system: parade or back and forth of the tray facing a stationary sprinkler system or vice versa. 11. The method of claim 10, characterized in that the tray scrolls horizontally in the spray cell and its running speed is greater than or equal to 20 mm / s, 1.2 m / min.

12. Method according to one of claims 2 to 11, characterized in that the transverse thermal uniformity of the plate is provided by modulating the spray in the width of the plate by ignition / extinguishing nozzles or nozzles, or screening said aspersion.

13. Installation for implementing the method according to one of claims 1 to 12, characterized in that it comprises:

A spraying cell provided with nozzle manifolds or nozzles for liquid spraying or cooling cooling mist arranged in the upper and lower parts of said cell, so as to spray the two large, upper and lower faces 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.

14. Installation according to claim 13, characterized in that:

The liquid nozzles or cooling mist of the spray cell generate solid cone jets whose angle is between 45 and 60 °

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

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 two paired nozzle ramps are oriented in opposition to one another.

- The jets have a normal border on the upper surface of the board

- The overlap of the jets of two paired ramps 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.

15. Installation according to one of claims 13 or 14, characterized in that the coolant is recovered after spraying, typically in a container located under the facility, recycled and thermally controlled. 16. Implementation of the installation according to one of claims 13 to 15, characterized in that the entire installation, spraying cell and uniformization tunnel, is controlled by a thermal model coded on 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 as a function of the target output temperature, in general the hot rolling start temperature.

17. Implementation of the installation according to claim 16, characterized in that it 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 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 ramps activated, the number of nozzles activated on the banks, the speed of travel of the plate in the spraying cell, the starting and stopping of the spray booms, and the holding time in the tunnel d 'standardization

- Transfer of the tray from the spray cell to the standardization tunnel