Cold-roll steel sheet surface color difference defect control method

Abstract

The invention discloses a cold-roll steel sheet surface color difference defect control method, and relates to the related field of cold-roll steel sheet machining. According to the cold-roll steel sheet surface color difference control method, online spectrum color difference detection and annealing furnace emission smell characteristic monitoring are combined, two-dimensional judgment of the atmosphere state and surface oxide film change in the annealing process is achieved, and compared with a traditional mode that postmortem adjustment is carried out only depending on a color difference result, the real-time performance and predictability are better, and the method is suitable for large-scale popularization and application. The system can recognize the atmosphere abnormal trend in advance through the smell characteristic change before the color difference has obvious deviation, and automatically executes the compensation adjustment of the hydrogen proportion, the dew point and the furnace temperature, so that the color difference defect is effectively prevented; and when the synchronization of the color difference and smell signals is abnormal, the system can quickly respond and recover to a stable interval, the color difference control precision is greatly improved, and the method can remarkably improve the consistency of the surface brightness and color of the steel plate, improve the color difference qualification rate and reduce the product waste caused by abnormal annealing.

Description

Technical Field

[0001] This invention relates to the field of cold-rolled steel sheet processing, and in particular to a method for controlling color difference defects on the surface of cold-rolled steel sheets. Background Technology

[0002] Chinese Patent Publication No.: CN113522971B A method for controlling surface color difference of steel for engineering machinery. The method specifically includes the following steps: (I) Adjusting the temperature of the heating section and the soaking section of the steel for engineering machinery according to the thickness of the steel plate. The heating section is controlled at about 1230-1240℃, and the heating time is controlled at 198-330min. If the heating time of the billet in the furnace exceeds the control node of 230min, the temperature should be reduced by 5℃ for every 10 minutes of extension. The heating time should not exceed the upper limit of 330min. The minimum temperature of the heating section should not be lower than 1230℃, and the soaking section is controlled at 1210-1230℃; (II) Pressing according to the thickness of the steel plate for engineering machinery. This invention can effectively control the surface color difference of the steel plate, solve the surface defects such as regular strip red rust after the steel plate is taken off the production line and the "water ripple" similar pitted surface at the red rust after shot blasting, and improve the surface aesthetics of the steel for engineering machinery.

[0003] Compared to hot-rolled steel sheets, which control color difference through temperature, cold-rolled steel sheets are prone to color difference defects during continuous annealing. These defects manifest as uneven brightness, color banding, and localized dark or bright areas. These defects not only affect the appearance quality and customer acceptance but can also lead to instability in subsequent coating, hot-dip galvanizing, or cold working performance. Currently, defects are primarily detected through online color difference detection or manual visual inspection during production. After a problem is identified, process parameters such as annealing furnace temperature, atmosphere composition, or belt speed are adjusted. However, existing methods suffer from significant delays: color difference defects are often only discovered after they have formed on the steel sheet surface, making it difficult to completely eliminate them, resulting in high scrap rates and increased production costs. Furthermore, current annealing furnace atmosphere control relies mainly on macroscopic control of oxygen content, temperature, and humidity parameters, lacking real-time monitoring of changes in volatile substances during the furnace's chemical reactions. This makes it difficult to accurately assess the oxide film formation state and the potential risks of color difference defects. Summary of the Invention

[0004] Therefore, in order to overcome the above-mentioned shortcomings, the present invention provides a method for controlling color difference defects on the surface of cold-rolled steel sheets.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for controlling color difference defects on the surface of cold-rolled steel sheets, the specific steps of which are as follows:

[0006] S1 reference acquisition: After cleaning, degreasing and drying, the cold-rolled steel sheet is used to acquire the initial brightness value and reference color coordinates of the steel sheet surface through an online spectral brightness detection device;

[0007] S2 Annealing Atmosphere Control: The steel plate is fed into a continuous annealing furnace, and the ratio of hydrogen to nitrogen, furnace temperature curve and dew point parameters in the annealing atmosphere are controlled to ensure the stable formation of oxide film on the surface of the steel plate. The furnace atmosphere parameters are collected in real time.

[0008] S3 Surface Color Difference Detection: After annealing, the brightness, color difference deviation value and local color spots of the steel plate are measured by an online color difference detection system. When any indicator exceeds the preset threshold, an abnormal alarm is triggered.

[0009] S4 Odor Monitoring Data Fusion Judgment: The odor characteristics of the gas emitted from the annealing furnace are collected in real time by the odor monitoring device, and an atmosphere deviation judgment signal is formed by matching and analyzing with the standard odor model;

[0010] S5 process automatic control: The color difference detection signal and the odor judgment signal are input into the process control system. When either signal reaches the judgment condition, the hydrogen ratio, dew point and furnace temperature compensation parameters are automatically adjusted to keep the color difference on the steel plate surface within the allowable range.

[0011] Preferably, the color difference detection system is an online spectral color difference detection system that covers the entire width of the steel plate and supports surface partition data output.

[0012] Preferably, the odor monitoring device is used to continuously sample the gas emitted from the annealing furnace, and to predict abnormal atmospheric trends in advance by observing changes in odor characteristics. The odor monitoring device includes:

[0013] The gas acquisition module is used for online acquisition of gas samples from the exhaust port of the continuous annealing furnace;

[0014] An odor sensing module, including at least one electronic nose array sensor, for identifying changes in the composition of hydrocarbon-containing, sulfur-containing, or nitrogen-containing volatile gases;

[0015] The odor feature analysis module is used to extract odor fingerprints and compare them with standard odor models in the database;

[0016] The anomaly detection module determines the oxide film formation offset trend based on a preset threshold and outputs an anomaly signal.

[0017] The feedback control module is used to feed back abnormal signals to the process control system to perform annealing atmosphere adjustment operations.

[0018] 4. Preferably, the process control system includes:

[0019] The data acquisition module is used to receive the brightness data, color difference offset and surface defect location signal output by the online color difference detection system, and simultaneously receive the odor characteristic parameters and atmosphere offset judgment signal output by the odor monitoring device.

[0020] The data fusion and analysis module is used to perform time series fusion, trend matching analysis, and anomaly type identification on color difference detection data and odor monitoring data, and generate corresponding process adjustment instruction parameters based on the deviation level;

[0021] The process parameter calculation module is used to automatically calculate the hydrogen ratio adjustment amount, dew point adjustment compensation value, furnace temperature fine-tuning range, and protective gas flow rate adjustment amount based on the fusion analysis results.

[0022] The execution control module is used to send the adjustment commands generated by the process parameter calculation module to the atmosphere control system, dew point adjustment device and temperature control system of the continuous annealing furnace, thereby performing hydrogen / nitrogen ratio adjustment, furnace temperature compensation and furnace area pressure fine adjustment operations.

[0023] The feedback monitoring module is used to continuously monitor the color difference recovery trend, oxide film formation stability and furnace atmosphere changes after process adjustment, and to perform secondary compensation or maintain steady-state control of the adjustment parameters based on the feedback results.

[0024] The beneficial effects of this invention are:

[0025] The proposed method for controlling surface color difference in cold-rolled steel sheets combines online spectral color difference detection with monitoring of odor characteristics emitted from the annealing furnace. This enables a two-dimensional assessment of the atmosphere state and surface oxide film changes during the annealing process. Compared to traditional methods that rely solely on color difference results for post-processing adjustments, this method offers greater real-time capability and predictability. The system can identify abnormal atmosphere trends in advance through changes in odor characteristics before a significant color difference shift occurs, and automatically adjusts the hydrogen ratio, dew point, and furnace temperature to effectively prevent color difference defects. When color difference and odor signals are simultaneously abnormal, the system can also respond quickly and recover to a stable range, significantly improving the accuracy of color difference control. This method can significantly improve the consistency of steel sheet surface brightness and color, increase the color difference pass rate, and reduce product waste caused by annealing anomalies. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process of this invention. Detailed Implementation

[0027] To further explain the technical solution of the present invention, a detailed description is provided below through specific embodiments.

[0028] This invention provides a method for controlling color difference defects on the surface of cold-rolled steel sheets, the steps of which are as follows:

[0029] Before the steel plate enters the continuous annealing process, its surface is first cleaned, degreased and dried to ensure that the subsequent optical detection signal is not affected by oil, water film and residual particles on the surface. The treated steel plate passes through the online spectral brightness detection equipment arranged in the entrance section. The equipment adopts multi-band spectral acquisition technology to detect the brightness value and chromaticity coordinates of the current surface of the steel plate in real time. The collected data is used as the initial reference value of the steel coil and is used for subsequent color difference offset judgment and comparative analysis with the detection results after annealing.

[0030] After the steel plate enters the continuous annealing furnace at a set speed, the process system precisely configures the ratio of hydrogen to nitrogen in the protective gas according to the preset process requirements of different furnace sections, and sets the furnace temperature curves for different temperature zones according to the oxide film formation mechanism. At the same time, the system continuously monitors the fluctuation of dew point, oxygen content and hydrogen concentration in the furnace through a dew point meter and atmosphere analyzer. The system adjusts the atmosphere composition according to real-time data to ensure that the high-temperature oxide film on the surface of the steel plate forms stably and uniformly in the heating zone, soaking zone and cooling zone.

[0031] After the steel plate is annealed and exits the furnace, an online color difference detection system is set up at the exit section to scan the entire width of the steel plate in the transverse direction. The system uses a multi-point array sensor to acquire the brightness value, color shift, and possible local color spots at each position of the steel plate in real time. The system compares the detection results with the reference threshold. When the brightness of any area decreases or the color difference increases beyond the set range, the system immediately issues an abnormal alarm and transmits the deviation data to the downstream process control system to trigger automatic adjustment.

[0032] An odor monitoring device is installed at the exhaust system pipeline of the annealing furnace. By continuously sampling the exhaust gas in the furnace, changes in hydrocarbons, sulfides and nitrogen-containing volatile components are detected. The monitoring system matches and analyzes the collected odor characteristic signals with the established standard odor fingerprint model. When a deviation in the characteristic odor profile is detected, it is determined that the annealing atmosphere has changed or the oxide film formation mechanism is abnormal, and an atmosphere deviation judgment signal is generated as an auxiliary judgment basis.

[0033] When the color difference detection system or odor monitoring system outputs any abnormal signal, the process control system automatically calculates the process adjustment amount to be executed based on the deviation type, affected area and offset trend. The system can directly adjust the proportion of protective gas hydrogen, adjust the output parameters of the dew point control device, or make fine adjustments to the furnace temperature setpoint. Through continuous adjustment, the color difference on the steel plate surface is gradually restored to the allowable range, realizing closed-loop automatic control of the annealing process.

[0034] In this embodiment, the online spectral color difference detection system adopts a wide-width line scan structure. By arranging multiple photoelectric array modules, it achieves full-width scanning coverage of the steel plate. The data output by the system not only includes the overall average color difference value, but can also be divided into multiple horizontal partitions according to the width of the steel strip. The color difference changes in each region can be analyzed independently. This partition detection function can be used to determine the formation location of problems such as local color spots and local oxide film abnormalities, providing a more accurate control basis for subsequent process adjustments.

[0035] The odor monitoring device has a continuous sampling port on the exhaust pipe of the annealing furnace. It continuously samples through a gas pump with a set flow rate. The monitoring system observes the fluctuation of the odor characteristic signal in real time. By identifying the characteristic peak, characteristic ratio and signal change trend, it can identify possible deviations in the annealing atmosphere in advance. Compared with the traditional monitoring method that relies solely on atmosphere sensors, this odor monitoring method can detect the trend of atmosphere imbalance, abnormal oxygen content or increased impurity gas in the furnace earlier, thereby improving the lead time for color difference control.

[0036] The odor monitoring device includes the following modules: Gas acquisition module: Located at the exhaust end of the annealing furnace, it continuously collects exhaust gas samples through a high-temperature resistant extraction pipeline and a flow stabilization unit, ensuring the stability of the odor analysis input; Odor sensing module: This module uses an electronic nose array sensor, which responds to volatile components such as hydrocarbons, sulfides, and amines through various sensitive materials, outputting multidimensional electrical signals representing different gas characteristics; Odor feature analysis module: It extracts features from the response matrix output by the electronic nose, including principal component analysis and feature vector construction, and compares the extracted odor fingerprint with a standard odor model database to identify whether the current atmosphere has deviated; Anomaly judgment module: Based on a set judgment threshold, when the odor feature change reaches a critical value, it judges that the oxide film formation trend is abnormal and generates an anomaly signal output; Feedback control module: It submits the anomaly judgment signal to the process control system, which then performs atmosphere adjustment operations, such as increasing the hydrogen ratio and adjusting the dew point control unit, to restore the normal atmosphere environment inside the furnace.

[0037] In this embodiment, when the odor monitoring device detects that the fluctuation of the odor characteristic exceeds a preset proportional threshold, such as the characteristic peak change exceeding 10% or the characteristic vector offset exceeding a set distance, the process system automatically starts a compensation mechanism. The compensation operation may include: temporarily increasing the hydrogen concentration in the protective gas to suppress oxidation, performing furnace depressurization to eliminate the accumulation of impurities, or slightly increasing or decreasing the temperature of some furnace areas to bring the oxide film formation kinetics back to a stable range.

[0038] The process control system consists of multiple functional modules that work together to automatically adjust the annealing color difference: Data acquisition module: simultaneously receives data from the color difference detection system and odor monitoring device, including brightness, color difference amount, defect location, odor characteristic values, and atmosphere offset signals, and performs time synchronization processing on the data; Data fusion and analysis module: fuses optical and odor data in the time and trend dimensions, determines the deviation type through trend analysis algorithms, and outputs the type and level of the required adjustment command; Process parameter calculation module: automatically calculates the hydrogen / nitrogen ratio adjustment range, dew point compensation value, and temperature fine-tuning amount based on the deviation level, ensuring that the adjustment parameters are quantified and accurate; Execution control module: sends the calculated process adjustment commands to the relevant execution units of the annealing furnace through the control interface, including the atmosphere control valve group, dew point adjustment equipment, and temperature control system; Feedback monitoring module: continues to monitor color difference and atmosphere changes after adjustment, further optimizing the adjustment range through closed-loop control algorithms to maintain the stability of the furnace atmosphere and the steel plate surface state.

[0039] Example 1

[0040] This embodiment involves annealing a batch of cold-rolled steel sheet coils with a specification of 0.35mm×1250mm to verify the effectiveness of the dual-signal fusion control method of the present invention.

[0041] Baseline acquisition:

[0042] Before entering the annealing furnace, the roll material is cleaned with alkaline solution, rinsed with hot water and dried with an air knife, and then tested by a spectral brightness detector at the entrance section.

[0043] The test results show that the initial brightness L0 = 82.5 and the initial chromaticity coordinates (a0, b0) = (0.5, -1.8). These results are used as the evaluation benchmark for color difference of the steel coil after annealing.

[0044] Annealing atmosphere settings:

[0045] According to the annealing process requirements of this specification of steel plate, the protective gas settings of the annealing furnace are as follows: hydrogen gas integral: 6%, nitrogen gas integral: 94%, dew point setting: -25℃, furnace temperature setting curve: heating zone 780℃, soaking zone 820℃, rapid cooling zone 450℃. The hydrogen concentration, oxygen content and dew point in the furnace are continuously recorded by the atmosphere monitoring instrument.

[0046] Color difference detection results and alarm triggering:

[0047] After the coil material exits the furnace, an online color difference system scan detects that the brightness L value in the central area of ​​the steel plate has dropped to 78.2, which deviates from the reference value by more than 3 points; at the same time, the b value in a local area shows a shift trend of +1.2. The system triggers a color difference abnormality alarm, and the deviation is judged to be: the oxide film is too thick, resulting in a decrease in brightness.

[0048] Odor monitoring results:

[0049] The odor monitoring system detected that the peak value of hydrocarbon odor characteristics increased by about 14% compared with the standard model during the same time period, which was determined to be a trend of "insufficient reducing power in the furnace", and output an atmosphere deviation judgment signal.

[0050] Control system regulation and execution:

[0051] After integrating the two signals, the process control system automatically performs the following adjustments: increasing the hydrogen ratio from 6% to 8%, adjusting the dew point from -25℃ to -30℃, and increasing the furnace temperature in the rapid cooling zone by +8℃ as brightness compensation. After 10 minutes of adjustment, the system is tested again: the brightness has recovered to 81.4, the color difference has recovered to the allowable range, and the odor characteristic model has returned to the normal range.

[0052] Example 2

[0053] In this embodiment, high-strength steel with a specification of 0.28mm×980mm is continuously annealed, and process compensation is performed in advance based on the trend judgment of odor monitoring.

[0054] Baseline acquisition:

[0055] After cleaning and drying, the steel plate was tested by a spectrometer: initial brightness L0 = 79.8, initial chromaticity coordinates (a0, b0) = (–0.2, –2.3), which were recorded as the reference for subsequent comparison.

[0056] Annealing atmosphere and furnace temperature settings:

[0057] The protective gas is set as follows: hydrogen gas integral: 5%, nitrogen gas integral: 95%, dew point: -20℃, furnace temperature setting curve: heating zone 760℃, soaking zone 800℃, slow cooling zone 520℃.

[0058] The color difference detection system initially showed no abnormalities.

[0059] Fifteen minutes before the roll material was removed from the oven, the color difference detection system did not detect any deviation, and the brightness remained within the range of 79–80.

[0060] Odor monitoring trend judgment triggers advance compensation operation:

[0061] Before the color difference shifted, the odor monitoring device detected that the peak value of hydrocarbon characteristics increased by 9% compared with the standard model, and the response of sulfide characteristics shifted by 11%. Although the color difference warning standard was not reached, the trend analysis module judged that the atmosphere would shift, which may lead to the subsequent thinning of the oxide film or local yellowing. The system generated an atmosphere shift prediction signal in advance.

[0062] Process control system advance compensation execution:

[0063] The control system automatically adjusts the following parameters based on the odor trend: the hydrogen ratio increases from 5% to 6.2%, the dew point is lowered to -24°C, and the furnace temperature in the soaking zone is lowered by -6°C to suppress excessive reduction. This advance operation avoids the occurrence of an excessively thin oxide film.

[0064] Color difference test results after baking:

[0065] After the steel plate came out of the furnace, the following measurements were taken: the brightness was 80.1 and the color difference (ΔE) was 0.7, both of which were within the excellent range, and no color difference defects were found.

[0066] The results of the two sets of embodiments demonstrate that the control method of "color difference detection + odor monitoring" dual-signal fusion in this invention can significantly improve the real-time control capability of color difference on the steel plate surface during the annealing process. In Embodiment 1, when both color difference and odor signals are abnormal, the system automatically increases the hydrogen ratio, adjusts the dew point, and fine-tunes the furnace temperature, so that the brightness and color difference can be restored to the reference range in a short time. In Embodiment 2, even if the color difference has not yet deviated, the odor monitoring has identified the abnormal trend of the furnace atmosphere in advance. The process system effectively avoids color difference deviation caused by subsequent oxide film abnormalities through advance compensation. Combining the results of the two sets, this invention achieves a leap from "correction after anomaly" to "control before trend," which significantly enhances the stability of steel plate color difference, improves the color difference qualification rate, and speeds up the process response.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling surface color difference defects of a cold-rolled steel sheet, characterized by: The specific steps are as follows: S1 reference collection: after the cold-rolled steel plate is cleaned, degreased and dried, the initial brightness value and the reference color coordinates of the steel plate surface are collected by an online spectral brightness detection device; S2 annealing atmosphere control: the steel plate is sent into a continuous annealing furnace, the hydrogen / nitrogen ratio in the annealing atmosphere, the furnace temperature curve and the dew point parameters are controlled, the oxide film on the surface of the steel plate is stably formed, and the atmosphere parameters in the furnace are collected in real time; S3 surface color difference detection: after annealing, the brightness, color difference deviation value and local color spot of the full-width area of the steel plate are measured by using an online color difference detection system, and an abnormal alarm is triggered when any index exceeds the preset threshold value; S4 odor monitoring data fusion judgment: the odor characteristics of the exhaust gas of the annealing furnace are collected in real time by an odor monitoring device, and the atmosphere deviation judgment signal is formed by matching analysis with the standard odor model; S5 process automatic control: the color difference detection signal and the odor judgment signal are input into the process control system, and when any signal reaches the judgment condition, the hydrogen ratio, the dew point and the furnace temperature compensation parameters are automatically adjusted to maintain the surface color difference of the steel plate within the allowable range.

2. A method of controlling surface color difference defects of a cold-rolled steel sheet according to claim 1, characterized by: The color difference detection system is an online spectral color difference detection system, which detects the full-width area of the steel plate and supports surface partition data output.

3. The method for controlling color difference defects on the surface of a cold-rolled steel sheet according to claim 1, characterized by: The odor monitoring device is used for continuous sampling of the exhaust gas of the annealing furnace, and the abnormal trend of the atmosphere is predicted in advance through the change of the odor characteristics. The odor monitoring device comprises: A gas collection module for online collection of gas samples from the exhaust port of the continuous annealing furnace; An odor sensing module comprising at least one electronic nose array sensor for identifying changes in volatile gas components containing hydrocarbons, sulfur or nitrogen; An odor characteristic analysis module for extracting odor fingerprints and comparing with database standard odor models; An abnormality judgment module for judging the oxidation film formation deviation trend according to the preset threshold value and outputting an abnormal signal; A feedback control module for feeding back the abnormal signal to the process control system to perform annealing atmosphere adjustment operation.

4. The method for controlling color difference defects on the surface of a cold-rolled steel sheet according to claim 1, characterized by: The process control system comprises: A data collection module for receiving the brightness data, color difference deviation and surface defect position signal output by the online color difference detection system, and synchronously receiving the odor characteristic parameters and atmosphere deviation judgment signal output by the odor monitoring device; A data fusion analysis module for time series fusion, trend matching analysis and abnormal type identification of the color difference detection data and odor monitoring data, and generating corresponding process adjustment instruction parameters according to the deviation level; A process parameter calculation module for automatically calculating the hydrogen ratio adjustment amount, the dew point adjustment compensation value, the furnace temperature fine tuning amplitude and the protective gas flow adjustment amount according to the fusion analysis result; An execution control module for issuing the adjustment instruction generated by the process parameter calculation module to the atmosphere control system, the dew point adjustment device and the temperature control system of the continuous annealing furnace, so as to perform hydrogen / nitrogen ratio adjustment, furnace temperature compensation and furnace zone pressure fine tuning operation; A feedback monitoring module for continuously monitoring the color difference recovery trend, the oxidation film formation stability and the furnace atmosphere change after process adjustment, and making secondary compensation or maintaining steady state control on the adjustment parameters according to the feedback result.

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