A strip steel oxidation color difference control method

Abstract

The application discloses a strip steel oxidation color difference control method, relates to the technical field of strip steel oxidation color difference control, and comprises the following operation steps: S1, instrument installation; S2, preset oxygen content limit value; S3, limit fan speed power; S4, image assistance; S5, fan power adjustment; S6, wind fan oxygen absorption setting and S7, limited warning. The strip steel oxidation color difference control method solves the problem of oxidation color defects caused by the most common slow cooling fan and fast cooling fan leakage, can not only solve the traditional oxidation color defect problem, but also solve the problem of oxidation color difference defects in the strip steel width direction caused by fan micro-leakage, realizes automatic control of the oxidation color difference defects, greatly improves the automation level of the unit, can timely lock the problem fan, alarms the abnormality, reminds the operator to timely dispose the unit abnormality, shortens the leakage point checking time, and effectively reduces the occurrence amount of the oxidation color difference defects.

Description

Technical Field

[0001] This invention relates to the field of strip steel oxidation color difference control technology, specifically a method for controlling strip steel oxidation color difference. Background Technology

[0002] During continuous strip annealing, if the furnace atmosphere is not properly controlled, the strip is prone to oxidation defects. This is especially true for continuous strip annealing units producing ultra-high strength steel. Because ultra-high strength steel substrates contain a large amount of reinforcing alloying elements such as Si and Mn, these alloying elements diffuse and accumulate to the surface of the strip during annealing and oxidize. This makes ultra-high strength steel more prone to surface oxidation than ordinary strength carbon steel, especially ultra-low carbon steel. After surface oxidation, the strip surface will turn yellow or even blue, which is unacceptable to many users. Therefore, it is necessary to control the surface oxidation defects of strip during continuous strip annealing.

[0003] Application number CN201611013306.6 discloses a method for eliminating oxide color in strip steel. In the production process, the heating temperature is controlled at 770-800℃, the slow cooling temperature at 630-680℃, the rapid cooling temperature at 250-310℃, and the over-aging temperature at 240-300℃; the furnace speed of the strip steel is controlled to be less than 200m / min with a fluctuation of ±10m / min; and the furnace leakage point temperature is controlled to be -55℃ to -45℃.

[0004] The aforementioned method for eliminating oxide discoloration in steel strip currently has the following drawbacks:

[0005] The application of this method has obvious limitations. Different steel grades have different characteristics, and the required strip heating temperature range is also different. There are strict process regulations in the production process, and it is not possible to limit it to a certain range. Therefore, it is not convenient to use it widely.

[0006] Therefore, in view of this, we studied and improved the existing structure and its shortcomings, and proposed a method for controlling the color difference of strip oxidation. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for controlling the color difference of strip oxidation, thus solving the problems mentioned in the background section.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for controlling the oxidation color difference of strip steel, the method comprising the following operational steps:

[0009] S1. Instrument Installation:

[0010] A set of ppm-level oxygen content measuring instruments is installed in the furnace and air duct of the slow cooling section and the furnace and air duct of the fast cooling section, respectively, for fixed-point real-time online cyclic detection of oxygen content in each air duct of the slow cooling section furnace and the slow cooling section fan, and in each air duct of the fast cooling section furnace and the fast cooling section fan.

[0011] S2, Preset oxygen content limit:

[0012] The slow-cooling fan control PLC and the fast-cooling fan control PLC are respectively preset with the oxygen content limit value of the air duct. The speed and power limit values ​​of the slow-cooling section furnace and the fast-cooling section furnace corresponding to the slow-cooling fan control PLC and the fast-cooling fan control PLC are determined according to the fan leakage test results.

[0013] S3, Limit fan speed and power:

[0014] Based on the actual measured oxygen content of the air ducts in the slow cooling section and the fast cooling section, and compared with their preset air duct oxygen content limits, the fan speed and power of the slow cooling section and the fast cooling section are limited to avoid the fan speed being too fast and causing oxygen absorption and oxidation of the strip steel.

[0015] S4, Image Assistance:

[0016] An oxidation color difference detector is installed at the outlet of the annealing furnace. The detector has multiple high-speed cameras on the upper and lower surfaces of the strip along the width of the strip. The degree of oxidation color difference is characterized by the difference in grayscale on the strip surface along the width of the strip by taking pictures.

[0017] S5, Fan power adjustment:

[0018] The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan with the smallest difference based on the average gray value Y of the upper and lower surfaces of the strip detected by the online oxidation colorimeter and the difference between the measured oxygen content of each fan and the preset limit value of oxygen content in each air duct. The PLC then performs fixed-point detection on the fan and limits the power of the fan in that area. If the difference between the measured oxygen content of that air duct and the preset limit value of oxygen content in that air duct is not the smallest, the PLC automatically switches to the fan with the smallest difference for fixed-point detection and limits the power of the fan in that area until the average gray value Y of the oxidation color meets the release standard.

[0019] Similarly, the slow-cooling fan control PLC and the fast-cooling fan control PLC are also preset with grayscale difference ΔY limit values ​​at different positions along the width of the strip. This grayscale difference ΔY is related to the oxygen content of the fan. The difference between the measured oxygen content in the air duct and the limit value of the oxygen content in the air duct is used to determine which fan is related to the grayscale difference ΔY exceeding the limit value. The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan with the air duct oxygen content closest to the limit value of the air duct oxygen content, lock the oxygen content detection in that area, and perform feedback control on the fan speed and power. When the difference between the measured oxygen content in that air duct and the preset limit value of the oxygen content in that air duct is not the minimum, the fan with the smallest difference is automatically switched to perform fixed-point oxygen content detection and the fan power in that area is limited and feedback controlled until the grayscale difference ΔY value of the oxidation color meets the release standard.

[0020] S6, Oxygen intake setting for windproof fan:

[0021] During production, glow discharge heaters are used to consume residual oxygen in the furnace, and the shafts of SCS and RCS fans are sealed with high-pressure nitrogen gas with a pressure of 3 kg or more in addition to carbon seals to reduce the risk of oxygen intake by the fans.

[0022] S7, Restricted Warning:

[0023] When the fan speed and power of the slow cooling section and the fast cooling section are limited, a visual and audio alarm will be triggered. In addition, when the oxygen content in the furnace of the slow cooling section and the furnace of the fast cooling section exceeds the oxygen content limit of the air duct, a visual and audio alarm will also be triggered.

[0024] Furthermore, in step S2, the oxygen content limit value is determined based on the actual oxygen content value corresponding to the strip oxidation limit sample.

[0025] Furthermore, in step S2, the specific method for the wind turbine leakage test is as follows:

[0026] Plot the curves of speed and power versus oxygen content for different fans. Determine the corresponding fan speed and power value based on the oxygen content limit value on the curve. Use this fan speed and power value as the initial limit value for fan speed and power.

[0027] Furthermore, both the slow-cooling fan control PLC and the fast-cooling fan control PLC are equipped with curve characteristic parameters corresponding to different fan speeds and power and oxygen content, which can be dynamically maintained and modified according to the real-time status of the unit to adjust the fan speed and power corresponding to the oxygen content.

[0028] Furthermore, in step S3, the measured oxygen content in the slow cooling section and the fast cooling section air ducts is obtained by a ppm-level oxygen content measuring instrument.

[0029] Furthermore, in step S4, the average gray level is represented by Y, which is obtained by taking pictures to characterize the degree of oxidation color difference on the strip surface along the width direction. The gray level difference at different positions along the width direction of the strip is represented by ΔY. That is, not only can the average gray level Y be used to characterize the traditional oxidation color defect (with oxidation color, the gray level Y is low), but also the oxidation color difference defect along the width direction of the strip can be measured. The larger the gray level difference ΔY, the more serious the color difference along the width direction of the same plate. The slow cooling fan control PLC and the fast cooling fan control PLC limit and control the fan speed and power of the slow cooling section and the fast cooling section according to the difference between the measured oxygen content and the limited oxygen content of their respective sections and the gray level difference ΔY.

[0030] Furthermore, in step S6, the glow discharge heater is disposed in both the SCS and RCS segments.

[0031] Furthermore, in step S6, the furnace dew point of both the SCS and RCS sections is controlled below -40°C to reduce the risk of strip oxidation.

[0032] Furthermore, the conical guide port after the heat exchanger of all fans adopts a double-layer sealing structure and is sealed with high-pressure nitrogen gas with a pressure of 3 kg or more to reduce the risk of leakage.

[0033] Furthermore, a method for controlling the oxidation color difference of strip steel is provided, which is applied to the field of continuous annealing technology for strip steel.

[0034] This invention provides a method for controlling the color difference of steel strip oxidation, which has the following beneficial effects:

[0035] This strip steel oxidation color difference control method is used to solve the most common oxidation color defects caused by leaks in slow-cooling and fast-cooling fans. Moreover, this method can not only solve traditional oxidation color defects, but also solve the oxidation color difference defects along the width of the strip steel caused by micro-leakage of the fans. It achieves automatic control of oxidation color difference defects, which greatly improves the automation level of the unit. It can also promptly locate the problematic fans and alarm the operators to remind them to deal with the abnormalities of the unit in a timely manner. This can shorten the time for leak point investigation and effectively reduce the occurrence of oxidation color difference defects. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a continuous strip annealing unit, which is an embodiment of a method for controlling the oxidation color difference of strip steel according to the present invention.

[0037] Figure 2 This is a schematic diagram of the RCS rapid cooling section equipment layout of a continuous annealing unit for strip steel, as an embodiment of the present invention for controlling the oxidation color difference of strip steel.

[0038] Figure 3This is a schematic diagram of the control system of the strip steel RCS fast cooling fan, which is an embodiment of the method for controlling the oxidation color difference of strip steel according to the present invention.

[0039] Figure 4 This is a schematic diagram of the overall process of a method for controlling the color difference of strip oxidation according to the present invention. Detailed Implementation

[0040] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0041] like Figures 1-4 As shown, the present invention provides a technical solution: a method for controlling the oxidation color difference of strip steel, the method comprising the following steps:

[0042] S1. Instrument Installation:

[0043] A set of ppm-level oxygen content measuring instruments is installed in the furnace and air duct of the slow cooling section and the furnace and air duct of the fast cooling section, respectively, for fixed-point real-time online cyclic detection of oxygen content in each air duct of the slow cooling section furnace and the slow cooling section fan, and in each air duct of the fast cooling section furnace and the fast cooling section fan.

[0044] S2, Preset oxygen content limit:

[0045] The slow-cooling fan control PLC and the fast-cooling fan control PLC are respectively preset with the oxygen content limit value of the air duct. The speed and power limit values ​​of the slow-cooling section furnace and the fast-cooling section furnace corresponding to the slow-cooling fan control PLC and the fast-cooling fan control PLC are determined according to the fan leakage test results.

[0046] The oxygen content limit value is determined based on the actual oxygen content value corresponding to the strip oxidation limit sample. The specific method for the fan leakage test is as follows:

[0047] Plot the curves of speed and power versus oxygen content for different fans. Determine the corresponding fan speed and power value based on the oxygen content limit value on the curve. Use this fan speed and power value as the initial limit value for fan speed and power.

[0048] Furthermore, the slow-cooling fan control PLC and the fast-cooling fan control PLC are equipped with curve characteristic parameters corresponding to different fan speeds and power and oxygen content, and can be dynamically maintained. The fan speed and power corresponding to oxygen content can be modified according to the real-time status of the unit.

[0049] S3, Limit fan speed and power:

[0050] Based on the actual measured oxygen content of the air ducts in the slow cooling section and the fast cooling section, and compared with their preset air duct oxygen content limits, the fan speed and power of the slow cooling section and the fast cooling section are limited to avoid the fan speed being too fast and causing oxygen absorption and oxidation of the strip steel.

[0051] Among them, the measured oxygen content in the air ducts of the slow cooling section and the fast cooling section was obtained by a ppm-level oxygen content measuring instrument;

[0052] S4, Image Assistance:

[0053] An oxidation color difference detector is installed at the outlet of the annealing furnace. The detector has multiple high-speed cameras on the upper and lower surfaces of the strip along the width of the strip. The degree of oxidation color difference is characterized by the difference in grayscale on the strip surface along the width of the strip by taking pictures.

[0054] In this method, the degree of oxidation color difference is characterized by the gray difference on the strip surface along the width direction obtained by taking pictures. The average gray value is represented by Y, and the gray difference at different positions along the width direction of the strip is represented by ΔY. That is, not only can the average gray value Y be used to characterize the traditional oxidation color defect (with oxidation color, the gray value Y is low), but also the oxidation color difference defect along the width direction of the strip can be measured. The larger the gray value difference ΔY, the more serious the color difference along the width direction of the same plate. The slow cooling fan control PLC and the fast cooling fan control PLC limit and control the fan speed and power of the slow cooling section and the fast cooling section according to the difference between the measured oxygen content and the limited oxygen content and the gray value difference ΔY of their respective sections.

[0055] S5, Fan power adjustment:

[0056] The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan with the smallest difference based on the average gray value Y of the upper and lower surfaces of the strip detected by the online oxidation colorimeter and the difference between the measured oxygen content of each fan and the preset limit value of oxygen content in each air duct. The PLC then performs fixed-point detection on the fan and limits the power of the fan in that area. If the difference between the measured oxygen content of that air duct and the preset limit value of oxygen content in that air duct is not the smallest, the PLC automatically switches to the fan with the smallest difference for fixed-point detection and limits the power of the fan in that area until the average gray value Y of the oxidation color meets the release standard.

[0057] Similarly, the slow-cooling fan control PLC and the fast-cooling fan control PLC are also preset with grayscale difference ΔY limit values ​​at different positions along the width of the strip. This grayscale difference ΔY is related to the oxygen content of the fan. The difference between the measured oxygen content in the air duct and the limit value of the oxygen content in the air duct is used to determine which fan is related to the grayscale difference ΔY exceeding the limit value. The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan with the air duct oxygen content closest to the limit value of the air duct oxygen content, lock the oxygen content detection in that area, and perform feedback control on the fan speed and power. When the difference between the measured oxygen content in that air duct and the preset limit value of the oxygen content in that air duct is not the minimum, the fan with the smallest difference is automatically switched to perform fixed-point oxygen content detection and the fan power in that area is limited and feedback controlled until the grayscale difference ΔY value of the oxidation color meets the release standard.

[0058] S6, Oxygen intake setting for windproof fan:

[0059] During production, glow discharge heaters are used to consume residual oxygen in the furnace, and the shafts of SCS and RCS fans are sealed with high-pressure nitrogen gas with a pressure of 3 kg or more in addition to carbon seals to reduce the risk of oxygen intake by the fans.

[0060] Among them, the glow discharge heaters are set in the SCS section and the RCS section. The furnace dew point in both the SCS and RCS sections is controlled below -40℃ to reduce the risk of strip oxidation.

[0061] S7, Restricted Warning:

[0062] When the fan speed and power of the slow cooling section and the fast cooling section are limited, a visual and text alarm and an audio alarm will be triggered. Also, when the oxygen content in the furnace of the slow cooling section and the furnace of the fast cooling section exceeds the oxygen content limit of the air duct, a visual and text alarm and an audio alarm will be triggered.

[0063] All fan heat exchangers have a conical guide port with a double-layer sealing structure and are sealed with high-pressure nitrogen gas with a pressure of 3 kg or more to reduce the risk of leakage.

[0064] A method for controlling the oxidation color difference of strip steel, wherein the method is applied in the field of continuous annealing technology for strip steel.

[0065] like Figures 1-4 As shown, the embodiment is as follows: Figure 1 As shown, a continuous annealing unit includes a preheating section 12, a radiant tube heating section 13, a radiant tube soaking section 14, an SCS slow cooling section 15, an RCS rapid cooling section 16, a reheating section 17, an over-aging section 18, a final jet cooling section 19, a WQ water cooling section 20, and a hot air drying section 21. The strip steel thickness range is 0.35~1.6mm, and the width range is 800~1550mm. The strip steel 11 enters the annealing furnace for annealing treatment, and after being dried by hot air, it continues to run. In this embodiment, an online oxidation color difference detector 22 is set in the hot air drying section 21 to quantitatively measure the oxidation color on the surface of the strip steel after hot air drying.

[0066] The online oxidation color difference detector 22 has four high-speed cameras installed on each of the upper and lower surfaces of the strip along the width direction of the strip to take pictures of the strip. Then, the gray values ​​are extracted to characterize the degree of oxidation color on the surface of the strip. Each high-speed camera can measure a strip with a width of 400mm. The four cameras can cover the entire strip with a maximum width of 1550mm. Moreover, the online oxidation color difference detector 22 has an automatic edge finding system that can automatically find the edge of the strip and automatically discard the strip without strip at the edge, and process the data of the effective width range of the strip.

[0067] The grayscale values ​​obtained from the camera on the upper surface strip are taken as the overall average value, which is used as the average grayscale value Y of the upper surface. The grayscale values ​​obtained from the camera on the lower surface strip are taken as the overall average value, which is used as the average grayscale value Y of the lower surface. The allowable average thickness values ​​are different for different steel grades, and the grayscale values ​​required by different users may also be different.

[0068] For example, User A requires that the grayscale value of a certain high-strength steel strip be above 35, but User J requires that the grayscale value of the high-strength steel strip be above 40. In order to avoid the influence of ambient brightness on the grayscale detection results of the strip surface, the online oxidation color difference detector 22 in this embodiment is equipped with a special stable strong light illumination system to ensure that the grayscale values ​​measured during the day and at night have reliable stability. In addition, in order to characterize the color difference of the strip oxidation along the width direction, the online oxidation color difference detector 22 also performs partitioning processing on the images taken by each camera. In this embodiment, each photo is divided into 8 regions along the width direction, that is, each region is 50mm wide. The thickness value of each region is averaged, and then the maximum grayscale value Ymax and the minimum grayscale value Ymin of the strip surface in each region of the upper and lower surfaces of the strip are taken. Ymax is subtracted to obtain the grayscale difference ΔY between the upper and lower surfaces. In this embodiment, the grayscale difference ΔY limit value is set to 2, that is, if the grayscale difference ΔY>2, the oxidation color difference is considered to be excessive.

[0069] The layout of the RCS rapid cooling section equipment of the strip continuous annealing unit in this embodiment is as follows: Figure 2 As shown, the RCS rapid cooling section 16 is equipped with 4 rapid cooling fans, namely rapid cooling section fan 1 31, rapid cooling section fan 32, rapid cooling section fan 33 and rapid cooling section fan 4 34. Among them, rapid cooling section fan 1 31 and rapid cooling section fan 2 32 blow against each other to maintain pressure balance, and rapid cooling section fan 33 and rapid cooling section fan 4 34 blow against each other to maintain pressure balance.

[0070] The unit is equipped with a ppm-level RCS section air duct dedicated oxygen content detector 51. The sampling ports are set on the blowing pipe 42 of the No.1 fan in the fast cooling section, the blowing pipe 44 of the No.2 fan in the fast cooling section, the blowing pipe 46 of the No.3 fan in the fast cooling section, and the blowing pipe 48 of the No.4 fan in the fast cooling section. The oxygen content in each fan pipe is detected in real time in a cyclical manner, with a cycle of 200 seconds.

[0071] The RCS rapid cooling fan control system for this strip steel is as follows: Figure 3 As shown, the system is equipped with an RCS fan control PLC61, which limits and controls the fan speed and power of the fast cooling section No. 1 fan 31, fast cooling section No. 2 fan 32, fast cooling section No. 3 fan 33 and fast cooling section No. 4 fan 34 based on the real-time detection of the average thickness Y upper surface value, Y lower surface value, gray scale difference ΔY upper surface, ΔY lower surface, and oxygen content ppm value of different air ducts by the online oxidation color difference detector 22.

[0072] For example, Table 1 shows the duct oxygen content limits for different RCS fans during a certain period, and the graph showing the relationship between fan speed and duct oxygen content obtained from the leakage test of fan No. 1 in the fast cooling section is shown below. Figure 4 As shown, input the corresponding relationship into the RCS fan control PLC61. The RCS fan control PLC61 can calculate the fan speed and power limit values ​​using the interpolation method.

[0073] When the oxygen content limit in the duct of the No. 1 fan in the rapid cooling section is 28ppm, the maximum speed and power of the No. 1 fan in the rapid cooling section can be limited to 80%. If the oxygen content limit in the duct changes, the corresponding limit value in the real-time maintenance system can be used to achieve real-time and accurate limitation of the fan speed and power.

[0074] Fast cooling section No. 1 fan Fast cooling section No. 2 fan Fast cooling section No. 3 fan Fast cooling section No. 4 fan 28 30 36 38

[0075] The table above shows the oxygen content limits (ppm) for different RCS fans in the duct. If, under these limits, high-strength steel is produced for user J, and the average grayscale value (Y) of the upper surface is 38 (meaning the upper surface oxidation color exceeds the standard), and the average grayscale value (Y) of the lower surface is 41 (meaning the lower surface oxidation color is still within the acceptable range), then the RCS fan control PLC61 will issue both visual and audible alarms. Simultaneously, it will compare the actual oxygen content in the ducts corresponding to the fast-cooling section's No. 1 fan 31 and No. 3 fan 33 on the upper surface of the strip with the duct oxygen content limits. For example, if the oxygen content in the blowing duct 42 of the fast-cooling section's No. 1 fan is 26 ppm, and the oxygen content in the blowing duct 46 of the fast-cooling section's No. 3 fan is 30 ppm, although the absolute value of the oxygen content in the blowing duct 46 of the fast-cooling section's No. 3 fan is higher, it still exceeds the duct limit. The oxygen content difference is 6 ppm, while the oxygen content in the blowing duct 42 of the No. 1 fan in the rapid cooling section is only 2 ppm different from the oxygen content limit in its duct. Therefore, the RCS fan control PLC61 locks the blowing duct 42 of the No. 1 fan in the rapid cooling section to measure its oxygen content, and controls the No. 1 fan 31 and the No. 2 fan 32 in the rapid cooling section to reduce their fan speed and power values ​​simultaneously until the average gray scale Y upper surface value reaches 40 or above. If the speed of the No. 1 fan 31 in the rapid cooling section drops to the minimum speed or the difference between its oxygen content and the limit value is greater than 6 ppm, and the average gray scale Y upper surface value still exceeds the standard, then the RCS fan control PLC61 locks the blowing duct 46 of the No. 3 fan in the rapid cooling section to measure its oxygen content, and controls the No. 3 fan 33 and the No. 4 fan 34 in the rapid cooling section to reduce their fan speed and power values ​​simultaneously, and so on.

[0076] In actual production, when operators discover an alarm, they will promptly go to the site to locate the leak. If the leak is in the expansion joint, it will be sealed with high-temperature silicone. If the leak is in the fan shaft seal, the nitrogen pressure of the fan shaft seal will be increased. If the nitrogen pressure of the shaft seal is at its maximum and the normal fan power cannot be restored, it will be dealt with during the next scheduled shutdown maintenance. The principle of limiting and controlling the grayscale difference ΔY upper and lower surfaces is the same, and will not be elaborated here.

[0077] The method for detecting and judging the oxygen content in the air duct of the slow-cooling fan is the same as that of the fast-cooling fan, and will not be elaborated here. When both the fast-cooling fan and the slow-cooling fan are equipped with this patented technology, if the strip steel shows an excessive gray scale due to oxidation color difference, it is necessary to take an additional step to determine whether to lock the RCS fan or the SCS fan. The principle is the same, and the determination is made by using the minimum difference between the measured oxygen content and the limit oxygen content on the upper and lower surfaces. This will not be elaborated here.

[0078] As can be seen, in this embodiment, the oxygen content detection does not cyclically detect the RCS rapid cooling furnace. This is because conventional RCS rapid cooling furnaces are equipped with oxygen content and dew point cyclic detection devices; their detection results can be directly obtained and applied. Of course, it is also possible to set an additional cyclic detection point in this embodiment, which can be understood and flexibly applied by those skilled in the art.

[0079] To better control oxidation color difference defects, this embodiment also includes glow discharge heaters in the SCS and RCS sections. During production, these heaters consume residual oxygen in the furnace. In addition to carbon seals, the shafts of the SCS and RCS fans are also sealed with high-pressure nitrogen gas at a pressure greater than or equal to 3 kg to reduce the risk of oxygen intake from the fans. The conical guide port after the fan heat exchanger uses a double-layer sealing structure and is sealed with high-pressure nitrogen gas at a pressure greater than or equal to 3 kg to reduce the risk of leakage. Furthermore, the furnace dew point in both the SCS and RCS sections is controlled below -40°C to reduce the risk of strip oxidation. Moreover, dew points are controlled separately for different steel grades to further mitigate oxidation color difference defects.

[0080] It should also be noted that, as is well known to those skilled in the art, a ppm-level oxygen content detector needs to be configured and used in conjunction with a percentage-level oxygen content detector. The ppm-level oxygen content detector should only be activated when the measured result of the percentage-level oxygen content detector drops below 1%.

[0081] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for controlling the color difference of steel strip oxidation, characterized in that: The method for controlling the color difference of strip oxidation includes the following steps: S1. Instrument Installation: A set of ppm-level oxygen content measuring instruments is installed in the furnace and air duct of the slow cooling section and the furnace and air duct of the fast cooling section, respectively, for fixed-point real-time online cyclic detection of oxygen content in each air duct of the slow cooling section furnace and the slow cooling section fan, and in each air duct of the fast cooling section furnace and the fast cooling section fan. S2, Preset oxygen content limit: The slow-cooling fan control PLC and the fast-cooling fan control PLC are respectively preset with the oxygen content limit value of the air duct. The speed and power limit values ​​of the slow-cooling section furnace and the fast-cooling section furnace corresponding to the slow-cooling fan control PLC and the fast-cooling fan control PLC are determined according to the fan leakage test results. S3, Limit fan speed and power: Based on the actual measured oxygen content of the air ducts in the slow cooling section and the fast cooling section, and compared with their preset air duct oxygen content limits, the fan speed and power of the slow cooling section and the fast cooling section are limited to avoid the fan speed being too fast and causing oxygen absorption and oxidation of the strip steel. S4, Image Assistance: An oxidation color difference detector is installed at the outlet of the annealing furnace. The detector has multiple high-speed cameras on the upper and lower surfaces of the strip along the width of the strip. The degree of oxidation color difference is characterized by the difference in grayscale on the strip surface along the width of the strip by taking pictures. S5, Fan power adjustment: The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan with the smallest difference based on the average gray value Y of the upper and lower surfaces of the strip detected by the online oxidation colorimeter and the difference between the measured oxygen content of each fan and the preset limit value of oxygen content in each air duct. The PLC performs fixed-point detection on the air duct where the fan with the smallest difference is located and performs feedback control to limit the fan power in the area where the fan with the smallest difference is located. When the difference between the measured oxygen content of the air duct and the preset limit value of oxygen content in the air duct is not the smallest, the PLC automatically switches to a new fan with the smallest difference. The PLC performs fixed-point detection on the air duct where the new fan with the smallest difference is located and performs feedback control to limit the fan power in the area where the new fan with the smallest difference is located until the average gray value Y of the oxidation color meets the release standard. Similarly, the slow-cooling fan control PLC and the fast-cooling fan control PLC are also preset with grayscale difference ΔY limit values ​​at different positions along the strip width direction. This grayscale difference ΔY is related to the oxygen content of the fan. The difference between the measured oxygen content in the air duct and the limit value of the air duct oxygen content is used to determine which fan is related to the grayscale difference ΔY exceeding the limit value. The slow-cooling fan control PLC and the fast-cooling fan control PLC select the fan whose air duct oxygen content is closest to the limit value of the air duct oxygen content, lock the oxygen content detection in the area where the fan closest to the limit value of the air duct oxygen content is located, and perform feedback control on the fan speed and power. When the difference between the measured oxygen content in the air duct and the preset limit value of the air duct oxygen content is not the minimum, it automatically switches to the new fan with the smallest difference. The air duct where the new fan with the smallest difference is located is subjected to fixed-point oxygen content detection, and the fan power in the area where the new fan with the smallest difference is located is subject to limit feedback control until the grayscale difference ΔY value of the oxidation color meets the release standard. S6, Oxygen intake setting for windproof fan: During production, glow discharge heaters are used to consume residual oxygen in the furnace, and the shafts of the fans in the slow cooling section and the fast cooling section are sealed with high-pressure nitrogen gas with a pressure of 3 kg or more in addition to carbon seals to reduce the risk of oxygen intake by the fans. S7, Restricted Warning: When the fan speed and power of the slow cooling section and the fast cooling section are limited, a visual and audio alarm will be triggered. In addition, when the oxygen content in the furnace of the slow cooling section and the furnace of the fast cooling section exceeds the oxygen content limit of the air duct, a visual and audio alarm will also be triggered.

2. The method for controlling the color difference of strip oxidation according to claim 1, characterized in that: In step S2, the oxygen content limit value is determined based on the actual oxygen content value corresponding to the strip oxidation limit sample.

3. The method for controlling the color difference of strip oxidation according to claim 1, characterized in that: In step S2, the specific method for the wind turbine leakage test is as follows: Plot the curves of speed and power versus oxygen content for different fans. Determine the corresponding fan speed and power value based on the oxygen content limit value on the curve. Use this fan speed and power value as the initial limit value for fan speed and power. Furthermore, both the slow-cooling fan control PLC and the fast-cooling fan control PLC are equipped with curve characteristic parameters corresponding to different fan speeds and power and oxygen content, which can be dynamically maintained and modified according to the real-time status of the unit to adjust the fan speed and power corresponding to the oxygen content.

4. The method for controlling the color difference of strip oxidation according to claim 1, characterized in that: In step S3, the measured oxygen content in the slow cooling section and the fast cooling section air ducts is obtained by a ppm-level oxygen content measuring instrument.

5. The method for controlling the color difference of strip oxidation according to claim 1, characterized in that: In step S4, the degree of oxidation color difference is characterized by the gray difference on the strip surface along the width direction obtained by taking pictures. The average gray value is represented by Y, and the gray value difference at different positions along the width direction of the strip is represented by ΔY. That is, not only can the average gray value Y be used to characterize the traditional oxidation color defect, but also the oxidation color difference defect along the width direction of the strip can be measured. The larger the gray value difference ΔY, the more serious the color difference along the width direction of the same plate. The slow cooling fan control PLC and the fast cooling fan control PLC limit and control the fan speed and power of the slow cooling section and the fast cooling section according to the difference between the measured oxygen content and the limited oxygen content of their respective sections and the gray value difference ΔY.

6. The method for controlling the color difference of strip oxidation according to claim 1, characterized in that: In step S6, the furnace dew point in both the slow cooling section and the fast cooling section is controlled below -40°C to reduce the risk of strip oxidation.

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