A method for cooling treatment of aluminum-magnesium-manganese coil coating

Abstract

This invention relates to the field of metal surface treatment technology, specifically disclosing a method for cooling aluminum-magnesium-manganese coil coating. This method aims to solve the problems of decreased paint film adhesion, poor substrate shape, and appearance defects caused by traditional cooling methods. The steps include: after coating and baking, collecting initial data of the aluminum-magnesium-manganese alloy strip using a non-contact stress distribution detection device and an infrared thermometer array; dynamically adjusting the airflow distribution in the width direction of the first cooling zone based on a real-time stress distribution cloud map to achieve stress-relieving guided slow cooling; implementing gradient coordinated cooling with progressively decreasing supply air temperature in subsequent cooling zones, and performing zone-specific coordinated control based on stress information; and finally, performing homogenized final cooling. This invention achieves dynamic and precise control of the cooling process through stress feedback, effectively suppressing the generation of harmful thermal stress at the paint film-substrate interface, and simultaneously improving paint film performance and substrate shape quality.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for metal materials, and in particular to a method for cooling treatment of aluminum-magnesium-manganese coil coating. Background Technology

[0002] Aluminum-magnesium-manganese alloys are widely used in building roofs and exterior walls due to their lightweight, high strength, and excellent corrosion resistance. To enhance their durability and aesthetics, continuous roller coating is typically applied to their surface. The coated layer needs to be baked and cured, followed by cooling to stabilize its properties and facilitate winding. The quality of the cooling process directly affects the final product's paint film adhesion, hardness, gloss, weather resistance, as well as the substrate's smoothness and residual stress state.

[0003] Currently, the industry generally employs relatively crude methods for cooling coated aluminum-magnesium-manganese coils. Common cooling methods include natural air cooling, forced air cooling, and water mist cooling. Natural air cooling has a long cycle, low production efficiency, and its cooling uniformity is greatly affected by environmental factors, easily leading to transverse temperature differences in the coil and causing poor sheet shape. Although forced air cooling improves efficiency, if the air temperature, air speed, and air direction are not properly controlled, excessively rapid cooling can generate significant thermal stress inside the paint film and at its interface with the metal substrate. This thermal stress stems from the significant difference in the coefficients of thermal expansion between the paint film and the aluminum-magnesium-manganese alloy substrate. The aluminum-magnesium-manganese alloy substrate conducts heat quickly, and its cooling contraction rate is asynchronous with that of the paint film, resulting in shear stress at the interface, severely weakening the adhesion of the paint film, and potentially causing defects such as paint film cracking and peeling during subsequent processing or use. In addition, uneven cooling may also induce micro-stress concentration within the substrate, which, although not immediately manifested as macroscopic deformation, will reduce the material's fatigue life and forming stability. Water mist cooling carries even greater risks. If not properly controlled, localized overcooling can easily lead to surface defects such as "watermarks" and "orange peel" on the paint film. Furthermore, water vapor can penetrate into the incompletely cross-linked and cured paint film, affecting its corrosion resistance.

[0004] Current technologies lack sophisticated management methods for the coordinated control of temperature and stress field evolution during the cooling process of aluminum-magnesium-manganese coil coating. The cooling process is often viewed as a simple temperature reduction step rather than a critical process that determines the overall performance of the final product. Therefore, there is an urgent need to develop an innovative cooling method capable of dynamically and precisely controlling the cooling path to actively suppress harmful thermal stress at the paint-substrate interface while ensuring production efficiency and uniform cooling, thereby comprehensively improving the product quality and reliability of coated aluminum-magnesium-manganese coils. Summary of the Invention

[0005] Based on the above objectives, the present invention provides a method for cooling aluminum-magnesium-manganese coil coating. After the coating and baking process and before the winding process, the aluminum-magnesium-manganese alloy strip passes through a cooling section consisting of multiple independently temperature- and air-controlled cooling zones. Cooling devices are symmetrically arranged above and below the cooling section. The method includes the following steps: Step 1: Before the aluminum-magnesium-manganese alloy strip enters the cooling section, the initial temperature distribution data and initial stress distribution data of the aluminum-magnesium-manganese alloy strip are collected using a non-contact stress distribution detection device and an infrared thermometer array. Based on the specifications of the aluminum-magnesium-manganese alloy strip, the type of paint film, and the collected data, the initial air supply parameters of the first cooling zone of the cooling section are set. Step 2: Guide the aluminum-magnesium-manganese alloy strip into the first cooling zone. Based on the first real-time stress distribution cloud map obtained by the non-contact stress distribution detection device, dynamically adjust the airflow velocity distribution of each nozzle along the width direction of the first cooling zone to make the stress distribution of the aluminum-magnesium-manganese alloy strip in the width direction tend to be balanced and reduce the temperature of the aluminum-magnesium-manganese alloy strip to the first target temperature range. Step 3: When the aluminum-magnesium-manganese alloy strip enters at least two subsequent cooling zones, based on the real-time temperature and stress data of the aluminum-magnesium-manganese alloy strip, the supply air temperature is set to decrease step by step for each cooling zone, and the wind speed distribution is adjusted according to the second real-time stress distribution cloud map obtained in real time within each zone. At the same time, the stress information is transmitted to the next zone until the overall average temperature of the aluminum-magnesium-manganese alloy strip drops to the second target temperature. Step 4: Guide the aluminum-magnesium-manganese alloy strip into the last cooling zone, and use a supply air temperature close to the ambient temperature and a constant low wind speed for uniform blowing and cooling to ensure that the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction meets the preset requirements.

[0006] Preferably, the non-contact stress distribution detection device is a laser speckle interferometer. The measurement optical path of the laser speckle interferometer covers the entire width of the aluminum-magnesium-manganese alloy strip, and the measurement optical path forms a pre-set acute angle with the surface normal of the aluminum-magnesium-manganese alloy strip. In step 1, the specific process of collecting initial stress distribution data is as follows: During the stable travel section before the aluminum-magnesium-manganese alloy strip enters the cooling section, the laser speckle interferometer collects the laser speckle image sequence of the aluminum-magnesium-manganese alloy strip surface in a state without forced cooling at a first preset frequency. By processing the laser speckle image sequence, the residual stress distribution map accumulated on the surface of the aluminum-magnesium-manganese alloy strip due to baking and previous processes is calculated. This residual stress distribution map is the initial stress distribution data. The initial stress distribution data and the initial temperature distribution data collected by the infrared thermometer array are input into the cooling control system. The cooling control system, in conjunction with the grade, thickness, width and coating type of the aluminum-magnesium-manganese alloy strip, calculates the initial air supply temperature and initial reference wind speed of the first cooling zone by querying the process database. The initial air supply temperature is lower than the highest temperature value in the initial temperature distribution data, and the difference range is determined experimentally based on the thermal shock resistance temperature of the coating.

[0007] Preferably, the cooling device within the cooling zone includes multiple independent air nozzle units arranged along the width direction of the aluminum-magnesium-manganese alloy strip, each independent air nozzle unit having an independent air supply fan, electric heater, and air valve; In step 2, the specific process of dynamically adjusting the air velocity distribution of each nozzle along the width direction of the first cooling zone is as follows: the laser speckle interferometer scans the aluminum-magnesium-manganese alloy strip passing through the first cooling zone at a second preset frequency, generating a first real-time stress distribution cloud map that reflects the dynamic thermal stress field generated on the surface of the aluminum-magnesium-manganese alloy strip due to the cooling effect. The cooling control system performs image processing on the first real-time stress distribution cloud map, identifies areas with stress higher than the first stress threshold as high stress areas, identifies areas with stress lower than the second stress threshold as low stress areas, and the first stress threshold is greater than the second stress threshold. For the independent nozzle unit corresponding to the high stress area, the control system issues a command to reduce the opening of the air valve of the independent nozzle unit, so that the air velocity is reduced by a first adjustment amount. For the independent nozzle unit corresponding to the low stress area, the control system issues a command to increase the opening of the air valve of the independent nozzle unit, so that the air velocity is increased by a second adjustment amount. The specific values ​​of the first and second adjustment amounts are determined by using a pre-calibrated control relationship curve based on the stress difference between the high-stress and low-stress regions and the thickness of the aluminum-magnesium-manganese alloy strip.

[0008] Preferably, in step 2, the control logic for reducing the temperature of the aluminum-magnesium-manganese alloy strip to the first target temperature range includes a dual-loop synergy of a temperature control loop and a stress control loop. The temperature control loop uses the average surface temperature of the aluminum-magnesium-manganese alloy strip monitored in real time by the infrared thermometer array as feedback to adjust the overall air supply temperature of the first cooling zone, so that the rate of decrease of the average surface temperature of the aluminum-magnesium-manganese alloy strip is kept below the first safe cooling rate threshold. The stress control loop uses the overall stress non-uniformity index calculated from the first real-time stress distribution cloud map obtained by the laser speckle interferometer as feedback to adjust the overall airflow speed of the first cooling zone. The overall stress non-uniformity index is the standard deviation of the stress value at each point in the width direction of the aluminum-magnesium-manganese alloy strip. When the overall stress non-uniformity index increases, reduce the overall airflow velocity of the first cooling zone; When the overall stress non-uniformity index decreases, maintain or slightly increase the overall airflow velocity of the first cooling zone; The first target temperature range is the starting temperature range where the aluminum-magnesium-manganese alloy matrix material undergoes significant thermal stress relaxation. This temperature range is determined by testing the changes in the coefficient of thermal expansion and yield strength of the aluminum-magnesium-manganese alloy material to be treated with temperature. Within this temperature range, heat preservation or slow cooling helps to release existing stress.

[0009] Preferably, in step 3, when setting progressively decreasing supply air temperatures for each cooling zone, the process for determining the supply air temperature difference between two adjacent cooling zones is as follows: First, the glass transition temperature range of the coating film is determined based on the differential scanning calorimetry test results of the coating film formulation. Secondly, a critical temperature node is set, which is located above the upper limit of the glass transition temperature range of the coating film by a preset offset. Furthermore, when the overall average temperature of the aluminum-magnesium-manganese alloy strip is higher than the critical temperature node, the air supply temperature difference between adjacent cooling zones is set as the first temperature difference value. Finally, when the overall average temperature of the aluminum-magnesium-manganese alloy strip is within the glass transition temperature range of the coating film, the air supply temperature difference between adjacent cooling zones is set to a second temperature difference value that is less than the first temperature difference value, so as to reduce the cooling rate in this temperature range. The second temperature difference value is calculated based on the maximum allowable cooling rate of the coating film through the glass transition temperature range.

[0010] Preferably, in step 3, the specific process of adjusting the wind speed distribution in each cooling zone according to the second real-time stress distribution cloud map and transmitting the stress information to the next zone is as follows: Within the Nth cooling zone, the laser speckle interferometer acquires a second real-time stress distribution cloud map at a third preset frequency. The cooling control system analyzes the cloud map and generates an adjustment command for the wind speed distribution of the Nth cooling zone. Simultaneously, the control system extracts the stress values ​​at preset equally divided points along the width direction of the aluminum-magnesium-manganese alloy strip from the second real-time stress distribution cloud map, forming a set of stress distribution vectors. When the head of the aluminum-magnesium-manganese alloy strip is about to enter the N+1th cooling zone, the control system sends the stress distribution vector and the temperature distribution data of the aluminum-magnesium-manganese alloy strip at the outlet of the Nth cooling zone to the controller of the N+1th cooling zone. The controller of the N+1th cooling zone predicts the initial state of the aluminum-magnesium-manganese alloy strip when it enters based on the received stress distribution vector and temperature distribution data. Based on this, and combined with the set air supply temperature of the N+1th cooling zone, it calculates the initial wind speed distribution reference value of the N+1th cooling zone, thereby realizing the tracking and coordinated control of stress and temperature states between cooling zones.

[0011] Preferably, in step 4, the specific criterion for ensuring that the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction meets the preset requirements is as follows: At the outlet of the cooling section, the temperature of at least nine uniformly distributed points along the width direction of the aluminum-magnesium-manganese alloy strip is accurately measured using an array of infrared thermometers. Calculate the average temperature of these nine measurement points as the overall average temperature; Calculate the absolute difference between the temperature at each measurement point and the overall average temperature; The preset allowable deviation threshold is a positive temperature value set according to the final product's requirements for panel shape and paint film performance; When the absolute difference between the temperature of all nine measuring points and the overall average temperature is less than or equal to the allowable deviation threshold, the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction is deemed to meet the requirements. If the temperature deviation at any measurement point exceeds the allowable deviation threshold, the system will issue an alarm and record the cooling process data of the roll material for subsequent quality analysis and process optimization.

[0012] Preferably, after the method is completed, step 5 is further included: data recording and process closed-loop optimization; The specific process of step 5 is as follows: The cooling control system automatically records and stores the complete dataset of a single roll of aluminum-magnesium-manganese alloy strip throughout the entire cooling process. The complete dataset includes initial temperature distribution data, initial stress distribution data, air supply temperature, air supply speed and speed distribution adjustment records recorded minute by minute in each cooling zone, key feature values ​​of stress cloud map recorded by laser speckle interferometer in time series, and outlet temperature distribution data. The aluminum-magnesium-manganese alloy strip will be sampled for paint film performance testing during subsequent processing. The paint film performance testing includes at least the cross-cut adhesion test, the Erichsen cupping test, and the ultraviolet accelerated aging test. The results of the paint film performance test are correlated with the complete dataset recorded during the cooling process through big data analysis to analyze the correlation between specific parameters or combinations of parameters during the cooling process and specific paint film performance indicators. Based on the results of strong correlation analysis, the rules used for setting the initial parameters in step 1 in the process database are corrected in reverse, or the control logic parameters in steps 2 and 3 are optimized to guide the cooling process of subsequent products of the same grade, thickness, and type of paint film, so as to achieve continuous self-optimization of the process.

[0013] Preferably, the cooling section consists of four cooling zones arranged sequentially along the travel direction of the aluminum-magnesium-manganese alloy strip, namely the first cooling zone, the second cooling zone, the third cooling zone, and the fourth cooling zone. The first, second, and third cooling zones all employ the aforementioned cooling device with independent nozzle units and implement dynamic stress feedback and temperature gradient control. The fourth cooling zone, as the last cooling zone, uses a uniformly perforated air duct for its cooling device. It does not independently adjust the zone's air speed, but only controls the overall air supply temperature and total air supply volume. It is specifically used to perform the homogenization final cooling described in step 4. The length of the first cooling zone is designed to ensure that the aluminum-magnesium-manganese alloy strip has sufficient residence time within it to complete the cooling process from the initial temperature to the first target temperature range and the initial stress equalization process. This length is calculated and determined based on the maximum linear velocity of the aluminum-magnesium-manganese alloy strip, the first safe cooling rate threshold, and the required cooling range.

[0014] Preferably, the infrared thermometer array consists of three sets of infrared thermometers. The first set of infrared thermometers is installed at the inlet of the cooling section, close to the outlet of the baking oven, to collect initial temperature distribution data. The second set of infrared thermometers is installed between the third and fourth cooling zones to monitor the temperature of the aluminum-magnesium-manganese alloy strip before it enters the final uniform cooling stage. The third set of infrared thermometers is installed at the outlet of the cooling section to collect the final outlet temperature distribution data. The main unit and optical head of the laser speckle interferometer are mounted above the first cooling zone. The measurement area of ​​the laser speckle interferometer covers the entire area from the inlet to the outlet of the first cooling zone and extends partially to the inlet area of ​​the second cooling zone to ensure continuous monitoring of the stress state of the critical first cooling stage and transition area.

[0015] The beneficial effects of this invention are: 1. This invention breaks through the traditional view of cooling as a simple temperature reduction process. It introduces a laser speckle interferometer for non-contact, real-time stress distribution monitoring, using the monitoring data as the core feedback signal of a closed-loop control system. This method dynamically senses interfacial shear stress caused by uneven cooling and actively intervenes in the formation of the stress field by adjusting the wind speed distribution of independent nozzle units. This integrated "sensing-control" approach makes the thermal shrinkage between the paint film and the aluminum-magnesium-manganese alloy substrate more synergistic, effectively suppressing the accumulation of harmful interfacial stress. This effect is directly reflected in a significant improvement in paint film adhesion (reaching grade 0 in the cross-cut test), enhanced flexibility (increased cupping value), and improved long-term weather resistance (increased gloss retention), solving the risk of early paint film failure caused by traditional cooling methods. 2. This invention scientifically decomposes the cooling process by designing a multi-stage, zoned gradient cooling strategy and combining it with a dual-loop synergistic control logic of stress and temperature. In the first stage (stress release-oriented slow cooling), the focus is on equalizing the stress of the substrate at high temperatures; in the second stage (zoned gradient synergistic cooling), the cooling rate of the glass transition zone of the coating film is precisely controlled; and in the third stage (homogenization final cooling), microscopic temperature differences are eliminated. This structured cooling path avoids the severe thermal shock and stress concentration caused by single-stage strong cooling, while ensuring overall cooling efficiency through feedforward-feedback synergy between zones. As a result, while achieving excellent coating film performance, the flatness of the substrate is also greatly improved (the flatness I value is significantly reduced), resolving the contradiction between quality and efficiency, and between coating and substrate performance, which is difficult to balance in traditional processes. 3. The method of this invention is not merely a production process, but also constructs a complete data closed loop. The system automatically records stress, temperature, and wind speed parameters throughout the entire process from the initial state to the final outlet, and performs correlation analysis with subsequent laboratory performance test results (such as adhesion, cupping, and aging resistance data). Through big data analysis, the inherent laws between process parameters and product performance can be continuously revealed, thereby optimizing the setting rules and control logic parameters in the process database. This transforms the cooling process from a "static setting" relying on fixed experience into a "dynamic intelligent" system capable of adaptive adjustments based on material batches and environmental conditions, significantly improving the stability of the production line, product consistency, and the evolvability of process technology, providing a solid guarantee for the large-scale and stable manufacturing of high-quality products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0017] Figure 1This is a flowchart of the steps of the method of the present invention; Figure 2 The flowchart below shows the steps involved in determining the supply air temperature difference between two adjacent cooling zones in the method of this invention. Figure 3 This is a flowchart illustrating the specific process of step 5 in the method of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0019] Please see Figures 1-3 This invention provides a method for cooling aluminum-magnesium-manganese coil coating. The method uses a cooling section comprising multiple independent cooling zones, with cooling devices symmetrically arranged above and below the cooling section. The method first performs cooling pretreatment and initial parameter setting. Specifically, it uses a non-contact stress distribution detection device and an infrared thermometer array to collect initial data of the strip, and sets the initial air supply parameters of the first cooling zone based on the strip specifications. Then, in the first cooling stage, the air velocity of each air outlet unit along the width direction of the first cooling zone is dynamically adjusted based on the real-time stress distribution cloud map, promoting a balanced stress distribution and reducing the temperature to a first target temperature range.

[0020] The second cooling stage then begins, implementing gradient cooling with progressively decreasing supply air temperature in subsequent cooling zones. Within each zone, the airflow velocity is adjusted based on the stress cloud map, and stress information is transmitted to the next zone for coordinated control until the temperature reaches the second target temperature. Finally, the third cooling stage is performed, using a uniform low airflow velocity close to ambient temperature in the last zone for final cooling, ensuring the transverse temperature uniformity of the strip. This method achieves dynamic and precise control through stress feedback. Its beneficial effects include actively suppressing the generation of harmful thermal stress at the coating-substrate interface, and simultaneously improving coating quality such as coating adhesion and flexibility, as well as substrate shape.

[0021] In one possible implementation, the non-contact stress distribution detection device is specifically implemented as a laser speckle interferometer. The measurement optical path of the laser speckle interferometer covers the entire width of the aluminum-magnesium-manganese alloy strip. The axes of its laser emitter and imaging head are mounted at an acute angle of 30 degrees to the normal to the strip surface. This angle enhances the measurement sensitivity of the strain component in the width direction of the strip. When acquiring initial stress distribution data, in the stable phase before the strip enters the cooling section, the laser speckle interferometer continuously acquires five laser speckle images of the strip surface at a frequency of 10 Hz.

[0022] These images are fed into the processing system, where time-series subtraction and phase resolution algorithms are used to obtain a residual stress distribution map reflecting the residual stress accumulated in the strip due to baking and previous processes. This stress distribution map, along with temperature data from five points along the width direction collected by an infrared thermometer array, is input into the cooling control system. The system combines the input strip grade, thickness, width, and coating type parameters with its built-in process database. Based on the thermal shock resistance test data of the coating, the database outputs a guideline that the initial supply air temperature of the first cooling zone should be 50 to 70 degrees Celsius lower than the highest strip temperature, and recommends an initial reference wind speed based on thickness and linear velocity.

[0023] By using optical methods to obtain initial stress and temperature conditions non-contactly and across the entire field, a reliable initial data foundation is provided for subsequent personalized and precise cooling control, avoiding the blindness of setting parameters based on experience.

[0024] In one possible implementation, the cooling device within the cooling zone is specifically implemented as multiple independent nozzle units arranged along its width. Each independent nozzle unit includes a miniature centrifugal fan, a tubular electric heater, and an electrically proportional regulating damper, all three being linked and controlled in a coordinated manner. During the first cooling stage, when dynamically adjusting the airflow distribution, a laser speckle interferometer generates a stress contour map at a frequency of 50 Hz. The control system meshes the contour map and calculates the average stress value for each grid region. The system sets a first stress threshold of the overall average stress plus 0.5 times the standard deviation, and a second stress threshold of the overall average stress minus 0.5 times the standard deviation.

[0025] For the nozzle unit belonging to a grid with an average stress higher than the first threshold, the control system sends a command to reduce its valve opening according to the "stress difference - wind speed adjustment" relationship curve, thereby reducing the wind speed by the first adjustment amount, for example, 1.5 meters per second. For the grid with an average stress lower than the second threshold, the corresponding valve opening is increased, thereby increasing the wind speed by the second adjustment amount. The relationship curve was obtained through a calibration experiment in which a known temperature difference was applied to strips of different thicknesses and the stress response was measured.

[0026] By refining the macroscopic cooling zones into microscopic independent control units, precise "point-to-point" compensation cooling for local stress on the strip surface is achieved, which greatly improves the efficiency and effect of stress equalization and effectively prevents local overcooling or insufficient cooling.

[0027] In one possible implementation, the first cooling stage employs a dual-loop control logic involving both a temperature control loop and a stress control loop. The temperature control loop uses the average surface temperature of the strip as input from an infrared thermometer and adjusts the power of the electric heater in the main air duct of the first cooling zone using a PID algorithm to control the air supply temperature, thereby stabilizing the rate of temperature decrease of the strip's average temperature between 25 and 30 degrees Celsius per second. This first safe cooling rate threshold is determined through a rapid cooling cracking test of the paint film.

[0028] The stress control loop uses the overall stress non-uniformity index of the strip calculated by a laser speckle interferometer as input. This index is the standard deviation of the stress values ​​at each point along the width direction. When the index increases, the control system proportionally reduces the reference wind speed setpoint of all independent nozzle units, slowing down the overall cooling intensity. When the index decreases, the reference wind speed is maintained or slightly increased. The first target temperature range is set to 380°C to 350°C. This range is determined by testing the stress relaxation curve of the aluminum-magnesium-manganese alloy using a thermomechanical analyzer. Within this temperature range, the material creep effect is significantly beneficial for stress release.

[0029] By coupling the control loops of two key physical quantities, temperature and stress, dynamic decoupling and synergistic optimization of the cooling process and stress evolution process are achieved. While ensuring cooling efficiency, stress relaxation in the high-temperature stage is maximized, laying a good low-stress foundation for subsequent cooling.

[0030] In one possible implementation, when setting a progressively decreasing supply air temperature in the second cooling stage, the process for determining the temperature difference between adjacent zones is specifically implemented as follows: First, the glass transition temperature range of the coating film used is obtained by differential scanning calorimetry (DSC) as 110°C to 130°C. A critical temperature node is set as the upper limit of the glass transition range plus a 10°C offset, i.e., 140°C. When the average temperature of the strip is higher than this node, the supply air temperature difference between adjacent cooling zones adopts a first temperature difference value, for example, 70°C.

[0031] When the average temperature of the strip enters the glass transition range of 110 to 130 degrees Celsius, a second temperature difference value is adopted, which is calculated based on the maximum allowable cooling rate of the coating film. Specifically, through dynamic thermomechanical analysis experiments, it was determined that a cooling rate exceeding 15 degrees Celsius per second within this temperature range would lead to a decrease in coating film toughness. To ensure the strip safely passes through this 20-degree Celsius range within a 2-second residence time in the zone, the cooling rate needs to be controlled at 10 degrees Celsius per second. Therefore, within the transition range, the supply air temperature difference between adjacent zones, i.e., the second temperature difference value, is set at 40 degrees Celsius, supplemented by reducing the air velocity to further control the actual cooling rate.

[0032] Special slow cooling treatment is applied to the critical temperature stage of paint film curing, which significantly reduces the internal stress generated when the free volume inside the paint film freezes, directly improving the flexibility, impact resistance and long-term durability of the paint film.

[0033] In one possible implementation, the adjustment within the second cooling zone and the information transmission between zones are specifically implemented as follows: Within the second cooling zone, a laser speckle interferometer operates at a frequency of 30 Hz to generate a second real-time stress distribution cloud map, which the control system uses to adjust the wind speed distribution within that zone. Simultaneously, the system extracts the stress values ​​at five fixed lateral positions from the stress cloud map, forming a five-dimensional stress distribution vector. Just before the strip head enters the third cooling zone, the control system packages this stress distribution vector, along with five temperature data points measured by an infrared thermometer at the exit of the second zone, and sends them to the sub-controller of the third cooling zone. The third zone sub-controller uses this data as the predicted initial state for the strip's entry.

[0034] For example, if the stress vector shows that the predicted stress value on the right side of the strip is too high, the sub-controller will pre-set the wind speed setting value of the corresponding nozzle unit on the right side in the initial wind speed distribution setting of the third zone. This realizes the feedforward transmission and pre-compensation control of the cooling stress state on the process flow line, breaks down the control islands between cooling zones, forms a coherent and collaborative global cooling strategy, and improves the response speed and control accuracy of the entire system to dynamic changes.

[0035] In one possible implementation, the specific criteria for determining the temperature uniformity of the third cooling stage are as follows: At the cooling section outlet, an infrared thermometer array is used to measure the surface temperature at nine equally spaced points along the width of the strip. The arithmetic mean of the nine points is calculated as the overall average temperature. The absolute difference between the temperature at each measurement point and the overall average temperature is calculated. A preset allowable deviation threshold is set to ±3 degrees Celsius based on the stringent requirements for the shape of high-end building materials. The control system performs a logical judgment: the cooling temperature uniformity of the roll material is deemed to meet the requirements if and only if the absolute value of the temperature deviation at all nine points is less than or equal to 3 degrees Celsius.

[0036] If any deviation exceeds the threshold, the control system will not only issue an audible and visual alarm to indicate potential sheet shape risks, but will also automatically record the roll number and complete cooling process parameter curve, storing them in the abnormal process database for subsequent in-depth quality analysis.

[0037] Clear and quantifiable inspection standards were established for the ultimate quality objectives of the cooling process. Through automatic alarm and data archiving mechanisms, real-time monitoring and traceability management of production quality were achieved, ensuring product consistency and reliability.

[0038] In one possible implementation, the data recording and process closed-loop optimization steps are specifically implemented as follows: The cooling control system automatically stores over 100,000 data points throughout the entire cooling process of a single roll of strip, including initial data recorded per second, air temperature and velocity in each zone, stress cloud map characteristic values, outlet temperature, etc., forming a complete data package. After the roll of strip comes off the production line, a 1-meter sample is taken for cross-cut adhesion, cupping tests, and a 1000-hour UV aging test. The test results are associated with the corresponding data package through the product number and stored in the central process analysis database. The system periodically performs big data correlation analysis on data from similar products, for example, using multiple regression analysis to find the correlation between process parameters and cupping values.

[0039] When a strong positive correlation is found between the "stress non-uniformity index reduction rate in the first cooling stage" and the final cupping value, and the cupping value is generally better when the reduction rate is higher than 35%, the system automatically optimizes the process database in reverse: setting the target value of the reduction rate to greater than or equal to 35%, and fine-tuning the parameter weights of the dual-loop control algorithm in the first cooling stage to more actively achieve this new target. This transforms production experience into iterative digital knowledge, enabling the cooling process to continuously learn and optimize, thereby continuously improving the stability of product quality and the level of process technology.

[0040] In one possible implementation, the cooling section is specifically configured as a four-zone layout. The first, second, and third cooling zones employ forced convection cooling devices with independent nozzle units, performing dynamic control based on stress feedback. The fourth cooling zone uses a static pressure bellows-type uniform air supply device, controlling only the overall air temperature and airflow, dedicated to final uniform cooling. The length of the first cooling zone is designed to be 6 meters, determined through calculation: at the maximum production line speed of 2.5 meters per second, to cool the strip from a maximum of approximately 420 degrees Celsius to the lower limit of the first target temperature range at a rate not exceeding 30 degrees Celsius per second, at least approximately 4.7 seconds of cooling time is required, corresponding to a length of approximately 11.75 meters.

[0041] To allow for margin and promote stress equalization, the actual design is 6 meters, corresponding to a time of approximately 2.4 to 3 seconds. The actual cooling rate is controlled by adjusting the air supply intensity. Through reasonable functional zoning and length design, the process role and physical space of each zone are clearly defined, ensuring sufficient processing time and space for the critical first stage of stress release. At the same time, the entire system has a compact structure, clear functions, and is easy to implement and maintain.

[0042] In one possible implementation, the infrared thermometer array and the laser speckle interferometer are arranged as follows: The infrared thermometer array consists of three groups, each containing five temperature measuring heads. The first group is installed 1 meter after the oven outlet to capture the initial temperature distribution. The second group is installed above the transition roller between the third and fourth cooling zones to monitor the temperature state before entering final cooling. The third group is installed before the guide roller at the cooling section outlet to measure the final temperature distribution.

[0043] The optical head of the laser speckle interferometer is installed 2 meters above the entrance of the first cooling zone. Its laser beam irradiation range covers from the entrance to the exit of the first zone, and extends forward to 0.5 meters in front of the entrance to capture the initial stress, and extends backward to 0.5 meters inside the entrance of the second zone, ensuring seamless and continuous monitoring of the stress in the first cooling stage and the transition area to the second stage.

[0044] By optimizing the layout of sensors at key locations, blind-spot-free monitoring of temperature and stress status across the entire cooling process chain from inlet to critical process point to outlet is achieved. This provides a comprehensive and coherent real-time data stream for the closed-loop control system, which is the fundamental guarantee for the precise execution of the entire method.

[0045] Example This embodiment uses the production of fluorocarbon-coated aluminum-magnesium-manganese alloy coils for building roofs as an application scenario.

[0046] 1. Materials to be processed and initial conditions; Substrate: Aluminum-magnesium-manganese alloy of grade AA3004, with a thickness of 0.7mm and a width of 1250mm.

[0047] Coating: A two-coat system, with an epoxy primer and a PVDF fluorocarbon topcoat, with a total film thickness of approximately 25μm.

[0048] Post-baking condition: When the strip leaves the curing oven, the coating film has been completely cross-linked and cured. The initial temperature distribution on the strip surface is uneven. Due to the arrangement of the heating pipes inside the oven and the heat dissipation at the edges, the center temperature is high and the edge temperature is low. According to the measurement of the first set of infrared thermometer array, the initial temperature distribution data is as follows: center point temperature 405℃, quarter-width point temperatures 398℃ and 395℃ respectively, and edge point temperatures 388℃ and 385℃ respectively.

[0049] Production line speed: set to 2.0 m / s.

[0050] 2. Step S1: Cooling pretreatment and initial parameter setting; The system is activated just before the strip head enters the cooling section. First, a laser speckle interferometer located in the entry stabilization section acquires five laser speckle images of the strip under natural air cooling at a frequency of 10Hz (the first preset frequency). Through phase superposition and calculation, an initial stress distribution map is generated. This map shows that due to baking and the previous rolling process, there is slight residual compressive stress in the middle of the strip, while the edges are under tensile stress.

[0051] Simultaneously, the first array of infrared thermometers uploads the measured initial temperature distribution data (maximum value 405℃) to the control system. The control system then queries the process database based on the input parameters: grade AA3004, thickness 0.7mm, width 1250mm, and fluorocarbon topcoat.

[0052] Database rules indicate that, for this type of coating, to prevent thermal shock cracking, the initial air supply temperature of the cooling zone should be 50°C to 70°C lower than the maximum temperature of the strip. The control system takes the middle value and sets the initial air supply temperature of the first cooling zone to 360°C.

[0053] The database rules also indicate that, based on a thickness of 0.7 mm and a linear velocity of 2.0 m / s, the initial reference wind speed is recommended to be 8 m / s. This reference wind speed will be used as the initial wind speed setting for all nozzle units in the first cooling zone.

[0054] 3. Step S2: First cooling stage – stress relief-guided slow cooling; The strip enters the first cooling zone, which is designed to be 6 meters long to ensure that the strip has a 3-second residence time within it. The initial supply air temperature of the zone is 360℃, and the initial air velocity of all nozzle units is 8 m / s.

[0055] The laser speckle interferometer switches to a 50Hz frequency (the second preset frequency) and begins generating the first real-time stress distribution cloud map. The image processing module of the cooling control system processes each frame of the cloud map. First, it calculates the average and standard deviation of the stress values ​​of all pixels within the entire measurement area. The standard deviation is defined as the "overall stress non-uniformity index." Then, the cloud map is gridded, dividing it into control regions corresponding one-to-one with the independent air nozzle units below. The system identifies the average stress value of each control region.

[0056] Threshold settings: The first stress threshold is set to the overall average stress value plus 0.5 times the standard deviation. The second stress threshold is set to the overall average stress value minus 0.5 times the standard deviation. Areas above the first stress threshold are marked as "high stress areas," and areas below the second stress threshold are marked as "low stress areas."

[0057] Adjustment Calculation: The control system has a pre-stored "stress difference - wind speed adjustment" curve calibrated based on thickness and material elastic modulus. For example, for 0.7mm thick AA3004 material, if the stress value in a high-stress area exceeds the first stress threshold of 10MPa, referring to the curve shows that the wind speed of the corresponding nozzle unit should be reduced (first adjustment) by 1.5m / s. Similarly, for low-stress areas, the wind speed should be increased (second adjustment) by 1.5m / s. The control system issues commands in real time to adjust the proportional regulating damper opening of the corresponding nozzle unit.

[0058] Dual-ring synergy: Temperature control loop: Based on the average surface temperature of the strip as fed back by the infrared thermometer, the system controls the power of the electric heater in the main air supply duct of the first cooling zone, aiming to reduce the average temperature of the strip according to a preset "first safe cooling rate threshold". In this embodiment, the first safe cooling rate threshold is determined experimentally: identical painted samples are prepared, quenched at different cooling rates, and then the presence of microcracks in the paint film is detected. The experiment found that when the cooling rate exceeds 35℃ / s, the probability of microcracks in the paint film increases significantly. Therefore, the first safe cooling rate threshold is set at 30℃ / s, leaving a safety margin. The control system ensures that the actual cooling rate is stable between 25-30℃ / s by adjusting the air supply temperature.

[0059] Stress control loop: The system simultaneously monitors the "overall stress non-uniformity index." In the initial cooling phase, this index may rise due to initial temperature non-uniformity. At this time, the system will issue a command to slightly reduce the reference wind speed of all nozzle units in the first cooling zone (e.g., from 8 m / s to 7.5 m / s) to slow the overall cooling intensity and allow more time for stress redistribution. Once the index begins to decrease and stabilizes, the current reference wind speed is maintained.

[0060] The first target temperature range: AA3004 aluminum alloy undergoes creep at high temperatures, which facilitates stress relaxation. Stress relaxation curves of AA3004 samples were plotted at different temperatures using a thermomechanical analyzer. It was found that stress relaxation was very significant above 350℃, while the relaxation rate decreased sharply below 300℃. Therefore, the first target temperature range was set to 380℃ to 350℃. The goal of this stage is to smoothly cool the strip from an average temperature of approximately 405℃ to around 350℃ through the aforementioned dual-ring synergistic control, utilizing the material properties at high temperatures in conjunction with non-uniform air cooling to achieve a more balanced transverse stress distribution. After this stage of treatment, the overall stress non-uniformity index measured by laser speckle interferometer decreased by approximately 40%.

[0061] 4. Step S3: Second Cooling Stage – Partitioned Gradient Coordinated Intercooling; The strip sequentially enters the second and third cooling zones, each 4 meters long, providing a 2-second dwell time.

[0062] Determine the temperature difference between adjacent zones: First, the glass transition temperature range of the coating film was determined to be 120℃±10℃ (i.e., 110℃ to 130℃) by differential scanning calorimetry. The critical temperature node was set to 140℃ (i.e., the upper limit of the glass transition range of 130℃ plus a preset offset of 10℃).

[0063] When the strip leaves the first cooling zone, its average temperature is approximately 350°C, which is 140°C higher than the critical temperature node. Therefore, according to the rules, the supply air temperature difference between adjacent zones (i.e., between the first and second zones) is set as the first temperature difference value. This value is set based on the strip thickness and efficiency requirements. In this embodiment, the initial set supply air temperature of the second cooling zone is 280°C, and the first temperature difference value is 70°C.

[0064] When the average temperature of the strip enters the glass transition range of 110℃-130℃, the control system adopts a second temperature difference value. This second temperature difference value is calculated based on the maximum allowable cooling rate of the coating film. Experiments show that within this range, a cooling rate exceeding 15℃ / s will cause the free volume inside the coating film to freeze, generating excessive internal stress and affecting toughness. To ensure the strip passes through this 20℃ range within a 2-second dwell time in the zone, the cooling rate needs to be controlled at 10℃ / s. Therefore, within the transition range, the air supply temperature difference (second temperature difference value) between adjacent zones (between the second and third zones) should be small. In this embodiment, the air supply temperature of the third cooling zone is set to 80℃, and the second temperature difference value is 40℃ (the actual airflow speed will also be reduced within the transition range to control the rate).

[0065] Stress feedback within a zone and inter-zone coordination: Within the second cooling zone, a laser speckle interferometer operates at a frequency of 30Hz (a third preset frequency) to acquire a second real-time stress distribution cloud map. The control system analyzes this cloud map and generates an adjustment command for the wind speed distribution of the second cooling zone, following the same logic as step S2.

[0066] Simultaneously, the control system extracts the stress values ​​from five fixed points (corresponding to infrared thermometer locations) along the width of the strip in the cloud image, forming a five-dimensional "stress distribution vector". As the strip head is about to leave the second zone and enter the third zone, the control system packages this "stress distribution vector" and the temperature data measured by the infrared thermometer (second group) at the exit of the second zone and sends it to the controller of the third cooling zone.

[0067] After receiving this data, the controller of the third cooling zone uses it as the "predicted initial state" when the strip enters. For example, if the "stress distribution vector" shows that the stress on the right side is still too high, the controller of the third zone will pre-adjust the wind speed setpoint of the right-side nozzle based on its initial wind speed distribution reference, thereby achieving a kind of feedforward control and realizing stress and temperature state tracking and coordinated control between cooling zones.

[0068] At the end of this stage, the overall average temperature of the strip drops to about 90°C, which is below the glass transition temperature of the coating.

[0069] 5. Step S4: Third cooling stage – homogenization and final cooling; The strip enters the fourth cooling zone (3 meters long). The air supply temperature in this zone is set to the workshop ambient temperature of 32℃. A static pressure air box is used to blow air onto the upper and lower surfaces of the strip at a constant and uniform wind speed of 5 m / s. The purpose at this stage is no longer rapid cooling or stress control, but rather to eliminate any small lateral temperature differences that may have accumulated in the earlier stages, ensuring a highly uniform temperature field in the strip before winding. At the exit, a third array of infrared thermometers measures the temperature at nine points (0%, 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, and 100% of the width).

[0070] The allowable deviation threshold is set at ±3℃ based on the requirements for panel shape in high-end building materials. Measurements at nine points showed temperatures of 52℃, 53℃, 52℃, 54℃, 53℃, 53℃, 52℃, 53℃, and 52℃. The average temperature was approximately 52.8℃. The absolute difference between the temperature at all points and the average value was less than 1.5℃, meeting the requirement of ≤3℃, thus the uniformity was deemed acceptable.

[0071] 6. Step S5: Data recording and process closed-loop optimization; During the production of this roll material, the cooling control system records a data snapshot every second, including all temperature, stress, wind speed, and air temperature setpoints. A 1-meter sample of the finished roll material is taken for the following tests: Cross-cut adhesion test (ISO2409): Grade 0 (best).

[0072] Erichsen cupping test (ISO 1520): indentation depth is 7.8 mm.

[0073] Accelerated UV aging test (QUV-A, 1000 hours): gloss retention rate 95%.

[0074] These performance data are stored in association with the cooling process data package. By analyzing data from multiple rolls of similar products, the system found that when the "overall stress non-uniformity index reduction rate in the first cooling stage" is higher than 35%, the final cupping value is generally better than 7.5mm. Therefore, the system automatically optimized the process database: for the AA3004 / 0.7mm / fluorocarbon paint combination, the "target stress non-uniformity index reduction rate in the first cooling stage" was set to ≥35%, and the parameters of the control loop in step S2 were optimized in reverse to more actively achieve this goal, thereby realizing continuous self-optimization of the process.

[0075] To verify the effectiveness of the method of the present invention, AA3004 aluminum-magnesium-manganese coated coils of the same batch and specifications after baking were selected and treated with three different cooling processes, and the performance of the final products was compared and tested.

[0076] Comparative Example 1: Traditional forced-air cooling; Method Description: A 15-meter-long integrated cooling fan box with no zoned temperature control is used. The supply air temperature is ambient (approximately 30°C), and the fans are fully operational, generating a strong and uniform airflow of 15-20 m / s. The strip material is directly and rapidly cooled from approximately 400°C to below 50°C.

[0077] Key features: single-stage, high-speed, no stress feedback, and no temperature gradient control.

[0078] Comparative Example 2: Traditional water mist cooling; Method Description: After the strip exits the baking oven, it immediately passes through a set of spray beams, where a fine water mist at room temperature is sprayed onto the strip surface for quenching. The surface is then dried with cold air. The cooling intensity is controlled by adjusting the water pressure and flow rate.

[0079] Key features: It uses water as a medium, resulting in extremely high and uneven cooling intensity, which can easily cause localized overcooling.

[0080] Methods of this invention embodiment; Method Description: As detailed above, a four-zone gradient synergistic cooling method based on laser speckle interferometer stress feedback and infrared temperature measurement.

[0081] The products treated by the three methods were subjected to the same standard performance test, and the results are compared in the table below:

[0082] Conclusion: The above comparison shows that the aluminum-magnesium-manganese coil coating cooling treatment method provided by the present invention effectively solves the problems of decreased paint film adhesion, insufficient flexibility, appearance defects, and poor sheet shape caused by traditional cooling methods by introducing real-time stress feedback and multi-stage gradient collaborative control, and the overall performance is comprehensively improved.

[0083] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for cooling the coating of aluminum-magnesium-manganese coils, characterized in that, After the painting and baking process and before the winding process, the aluminum-magnesium-manganese alloy strip passes through a cooling section consisting of multiple independently temperature- and air-controlled cooling zones. Cooling devices are symmetrically arranged above and below the cooling section. The method includes the following steps: Step 1: Before the aluminum-magnesium-manganese alloy strip enters the cooling section, the initial temperature distribution data and initial stress distribution data of the aluminum-magnesium-manganese alloy strip are collected using a non-contact stress distribution detection device and an infrared thermometer array. Based on the specifications of the aluminum-magnesium-manganese alloy strip, the type of paint film, and the collected data, the initial air supply parameters of the first cooling zone of the cooling section are set. Step 2: Guide the aluminum-magnesium-manganese alloy strip into the first cooling zone. Based on the first real-time stress distribution cloud map obtained by the non-contact stress distribution detection device, dynamically adjust the airflow velocity distribution of each nozzle along the width direction of the first cooling zone to make the stress distribution of the aluminum-magnesium-manganese alloy strip in the width direction tend to be balanced and reduce the temperature of the aluminum-magnesium-manganese alloy strip to the first target temperature range. Step 3: When the aluminum-magnesium-manganese alloy strip enters at least two subsequent cooling zones, based on the real-time temperature and stress data of the aluminum-magnesium-manganese alloy strip, the supply air temperature is set to decrease step by step for each cooling zone, and the wind speed distribution is adjusted according to the second real-time stress distribution cloud map obtained in real time within each zone. At the same time, the stress information is transmitted to the next zone until the overall average temperature of the aluminum-magnesium-manganese alloy strip drops to the second target temperature. Step 4: Guide the aluminum-magnesium-manganese alloy strip into the last cooling zone, and use a supply air temperature close to the ambient temperature and a constant low wind speed for uniform blowing and cooling to ensure that the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction meets the preset requirements.

2. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 1, characterized in that, The non-contact stress distribution detection device is specifically a laser speckle interferometer. The measurement optical path of the laser speckle interferometer covers the entire width of the aluminum-magnesium-manganese alloy strip, and the measurement optical path forms a pre-set acute angle with the surface normal of the aluminum-magnesium-manganese alloy strip. In step 1, the specific process of collecting initial stress distribution data is as follows: During the stable travel section before the aluminum-magnesium-manganese alloy strip enters the cooling section, the laser speckle interferometer collects the laser speckle image sequence of the aluminum-magnesium-manganese alloy strip surface in a state without forced cooling at a first preset frequency. By processing the laser speckle image sequence, the residual stress distribution map accumulated on the surface of the aluminum-magnesium-manganese alloy strip due to baking and previous processes is calculated. This residual stress distribution map is the initial stress distribution data. The initial stress distribution data and the initial temperature distribution data collected by the infrared thermometer array are input into the cooling control system. The cooling control system, in conjunction with the grade, thickness, width and coating type of the aluminum-magnesium-manganese alloy strip, calculates the initial air supply temperature and initial reference wind speed of the first cooling zone by querying the process database. The initial air supply temperature is lower than the highest temperature value in the initial temperature distribution data, and the difference range is determined experimentally based on the thermal shock resistance temperature of the coating.

3. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 2, characterized in that, The cooling device within the cooling zone includes multiple independent air nozzle units arranged along the width direction of the aluminum-magnesium-manganese alloy strip. Each independent air nozzle unit has an independent air supply fan, electric heater, and air valve. In step 2, the specific process of dynamically adjusting the air velocity distribution of each nozzle along the width direction of the first cooling zone is as follows: the laser speckle interferometer scans the aluminum-magnesium-manganese alloy strip passing through the first cooling zone at a second preset frequency, generating a first real-time stress distribution cloud map that reflects the dynamic thermal stress field generated on the surface of the aluminum-magnesium-manganese alloy strip due to the cooling effect. The cooling control system performs image processing on the first real-time stress distribution cloud map, identifies areas with stress higher than the first stress threshold as high stress areas, identifies areas with stress lower than the second stress threshold as low stress areas, and the first stress threshold is greater than the second stress threshold. For the independent nozzle unit corresponding to the high stress area, the control system issues a command to reduce the opening of the air valve of the independent nozzle unit, so that the air velocity is reduced by a first adjustment amount. For the independent nozzle unit corresponding to the low stress area, the control system issues a command to increase the opening of the air valve of the independent nozzle unit, so that the air velocity is increased by a second adjustment amount. The specific values ​​of the first and second adjustment amounts are determined by using a pre-calibrated control relationship curve based on the stress difference between the high-stress and low-stress regions and the thickness of the aluminum-magnesium-manganese alloy strip.

4. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 3, characterized in that, In step 2, the control logic for reducing the temperature of the aluminum-magnesium-manganese alloy strip to the first target temperature range includes the dual-loop coordination of temperature control loop and stress control loop. The temperature control loop uses the average surface temperature of the aluminum-magnesium-manganese alloy strip monitored in real time by the infrared thermometer array as feedback to adjust the overall air supply temperature of the first cooling zone, so that the rate of decrease of the average surface temperature of the aluminum-magnesium-manganese alloy strip is kept below the first safe cooling rate threshold. The stress control loop uses the overall stress non-uniformity index calculated from the first real-time stress distribution cloud map obtained by the laser speckle interferometer as feedback to adjust the overall airflow speed of the first cooling zone. The overall stress non-uniformity index is the standard deviation of the stress value at each point in the width direction of the aluminum-magnesium-manganese alloy strip. When the overall stress non-uniformity index increases, reduce the overall airflow velocity of the first cooling zone; When the overall stress non-uniformity index decreases, maintain or slightly increase the overall airflow velocity of the first cooling zone; The first target temperature range is the starting temperature range where the aluminum-magnesium-manganese alloy matrix material undergoes significant thermal stress relaxation. This temperature range is determined by testing the changes in the coefficient of thermal expansion and yield strength of the aluminum-magnesium-manganese alloy material to be treated with temperature. Within this temperature range, heat preservation or slow cooling helps to release existing stress.

5. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 4, characterized in that, In step 3, when setting progressively decreasing supply air temperatures for each cooling zone, the process for determining the supply air temperature difference between two adjacent cooling zones is as follows: First, the glass transition temperature range of the coating film is determined based on the differential scanning calorimetry test results of the coating film formulation. Secondly, a critical temperature node is set, which is located above the upper limit of the glass transition temperature range of the coating film by a preset offset. Furthermore, when the overall average temperature of the aluminum-magnesium-manganese alloy strip is higher than the critical temperature node, the air supply temperature difference between adjacent cooling zones is set as the first temperature difference value. Finally, when the overall average temperature of the aluminum-magnesium-manganese alloy strip is within the glass transition temperature range of the coating film, the air supply temperature difference between adjacent cooling zones is set to a second temperature difference value that is less than the first temperature difference value, so as to reduce the cooling rate in this temperature range. The second temperature difference value is calculated based on the maximum allowable cooling rate of the coating film through the glass transition temperature range.

6. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 5, characterized in that, In step 3, the specific process of adjusting the wind speed distribution in each cooling zone based on the second real-time stress distribution cloud map and transmitting the stress information to the next zone is as follows: Within the Nth cooling zone, the laser speckle interferometer acquires a second real-time stress distribution cloud map at a third preset frequency. The cooling control system analyzes the cloud map and generates an adjustment command for the wind speed distribution of the Nth cooling zone. Simultaneously, the control system extracts the stress values ​​at preset equally divided points along the width direction of the aluminum-magnesium-manganese alloy strip from the second real-time stress distribution cloud map, forming a set of stress distribution vectors. When the head of the aluminum-magnesium-manganese alloy strip is about to enter the N+1th cooling zone, the control system sends the stress distribution vector and the temperature distribution data of the aluminum-magnesium-manganese alloy strip at the outlet of the Nth cooling zone to the controller of the N+1th cooling zone. The controller of the N+1th cooling zone predicts the initial state of the aluminum-magnesium-manganese alloy strip when it enters based on the received stress distribution vector and temperature distribution data. Based on this, and combined with the set air supply temperature of the N+1th cooling zone, it calculates the initial wind speed distribution reference value of the N+1th cooling zone, thereby realizing the tracking and coordinated control of stress and temperature states between cooling zones.

7. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 1, characterized in that, In step 4, the specific criteria for ensuring that the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction meets the preset requirements are as follows: At the outlet of the cooling section, the temperature of at least nine uniformly distributed points along the width direction of the aluminum-magnesium-manganese alloy strip is accurately measured using an array of infrared thermometers. Calculate the average temperature of these nine measurement points as the overall average temperature; Calculate the absolute difference between the temperature at each measurement point and the overall average temperature; The preset allowable deviation threshold is a positive temperature value set according to the final product's requirements for board shape and paint film performance; When the absolute difference between the temperature of all nine measuring points and the overall average temperature is less than or equal to the allowable deviation threshold, the temperature uniformity of the aluminum-magnesium-manganese alloy strip in the width direction is deemed to meet the requirements. If the temperature deviation at any measurement point exceeds the allowable deviation threshold, the system will issue an alarm and record the cooling process data of the roll material for subsequent quality analysis and process optimization.

8. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 1, characterized in that, After the method is completed, step 5 is also included: data recording and process closed-loop optimization; The specific process of step 5 is as follows: The cooling control system automatically records and stores the complete dataset of a single roll of aluminum-magnesium-manganese alloy strip throughout the entire cooling process. The complete dataset includes initial temperature distribution data, initial stress distribution data, air supply temperature, air supply speed and speed distribution adjustment records recorded minute by minute in each cooling zone, key feature values ​​of stress cloud map recorded by laser speckle interferometer in time series, and outlet temperature distribution data. The aluminum-magnesium-manganese alloy strip will be sampled for paint film performance testing during subsequent processing. The paint film performance testing includes at least the cross-cut adhesion test, the Erichsen cupping test, and the ultraviolet accelerated aging test. The results of the paint film performance test are correlated with the complete dataset recorded during the cooling process through big data analysis to analyze the correlation between specific parameters or combinations of parameters during the cooling process and specific paint film performance indicators. Based on the results of strong correlation analysis, the rules used for setting the initial parameters in step 1 in the process database are corrected in reverse, or the control logic parameters in steps 2 and 3 are optimized to guide the cooling process of subsequent products of the same grade, thickness, and type of paint film, so as to achieve continuous self-optimization of the process.

9. A method for cooling and coating aluminum-magnesium-manganese coils according to any one of claims 6, characterized in that, The cooling section consists of four cooling zones arranged sequentially along the travel direction of the aluminum-magnesium-manganese alloy strip, namely the first cooling zone, the second cooling zone, the third cooling zone, and the fourth cooling zone. The first, second, and third cooling zones all employ the aforementioned cooling device with independent nozzle units and implement dynamic stress feedback and temperature gradient control. The fourth cooling zone, as the last cooling zone, uses a uniformly perforated air duct for its cooling device. It does not independently adjust the zone's air speed, but only controls the overall air supply temperature and total air supply volume. It is specifically used to perform the homogenization final cooling described in step 4. The length of the first cooling zone is designed to ensure that the aluminum-magnesium-manganese alloy strip has sufficient residence time within it to complete the cooling process from the initial temperature to the first target temperature range and the initial stress equalization process. This length is calculated and determined based on the maximum linear velocity of the aluminum-magnesium-manganese alloy strip, the first safe cooling rate threshold, and the required cooling range.

10. The method for cooling and coating aluminum-magnesium-manganese coils according to claim 9, characterized in that, The infrared thermometer array consists of three sets of infrared thermometers. The first set of infrared thermometers is installed at the inlet of the cooling section, close to the outlet of the baking oven, to collect initial temperature distribution data. The second set of infrared thermometers is installed between the third and fourth cooling zones to monitor the temperature of the aluminum-magnesium-manganese alloy strip before it enters the final uniform cooling stage. The third set of infrared thermometers is installed at the outlet of the cooling section to collect the final outlet temperature distribution data. The main unit and optical head of the laser speckle interferometer are mounted above the first cooling zone. The measurement area of ​​the laser speckle interferometer covers the entire area from the inlet to the outlet of the first cooling zone and extends partially to the inlet area of ​​the second cooling zone to ensure continuous monitoring of the stress state of the critical first cooling stage and transition area.

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