Method for preventing steel strip damage during continuous annealing furnace shutdown

Abstract

The application provides a method for preventing steel belt damage during shutdown of a continuous annealing furnace, and belongs to the technical field of cold-rolled continuous annealing, and comprises the following steps: S100, pulling the steel belt towards the center of the furnace zone so that the steel belt in the furnace zone is in a relaxed state; S200, when a predetermined shutdown time is reached, restoring the steel belt in the furnace zone to a tensioned state; S300, starting the conveyor at an initial speed of 5 m / min, and gradually increasing the conveying speed of the conveyor; S400, when the creased area of the steel belt enters the first section of the overaging furnace and the area of the creased area is not expanded, increasing the conveying speed of the conveyor and increasing the temperature of the furnace zone; S500, switching the tension control of the conveyor to an automatic mode; gradually increasing the temperature and the conveying speed until the temperature of the furnace zone and the conveying speed reach preset process values. The method for preventing steel belt damage during shutdown of a continuous annealing furnace aims to solve the problem that when a cold-rolled continuous annealing production line is forced to stop due to a fault, thin-gauge steel belts are prone to creasing, deviation and even breakage, thereby causing product rejection and production interruption.

Description

Technical Field

[0001] This invention belongs to the field of cold rolling continuous annealing technology, and more specifically, it relates to a method for preventing damage to steel strips when shutting down a continuous annealing furnace. Background Technology

[0002] The cold-rolled continuous annealing production line is a core piece of equipment for achieving efficient and stable production of cold-rolled thin sheets and ensuring the microstructure and surface quality of the strip. It is widely used in the continuous heat treatment of ultra-thin cold-rolled strips. With the continuous increase in demand for ultra-thin cold-rolled strips from high-end manufacturing, thin-gauge products (e.g., less than 0.21 mm thick) have become a regular product on the production line. The bending stiffness, torsional stiffness, and critical buckling tension of such thin strips decrease exponentially with thickness, making them extremely sensitive to disturbances in operating tension, furnace roll condition, and temperature environment.

[0003] In actual production, production lines are often forced to shut down due to equipment failures, process abnormalities, or defective incoming materials. At this time, the transmission and tension control system cannot maintain a stable constant tension output, and the strip steel experiences a sudden drop in tension, fluctuations, or even instantaneous loss of tension at the moment of shutdown. At the same time, the high-temperature section of the furnace area will significantly reduce the yield strength of the strip steel, further weakening its structural stability. Under the combined effects of insufficient stiffness, sudden tension changes, and high-temperature softening, thin strip steel is extremely prone to lateral instability, resulting in wrinkles and warping. Wrinkles and shape defects can quickly cause strip steel deviation and edge scraping, leading to stress concentration and edge crack propagation, ultimately resulting in strip steel breakage.

[0004] The aforementioned problems not only generate a large amount of scrap steel and prolong downtime, but may also damage key equipment such as furnace rollers and correction mechanisms, seriously affecting the operating efficiency, product qualification rate and operational safety of the continuous annealing production line. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preventing damage to steel strip during continuous annealing furnace shutdown. This method aims to solve the problem that when a cold rolling continuous annealing production line is forced to shut down due to a malfunction, thin-gauge steel strip is prone to wrinkling, deviation, or even breakage, which can lead to product scrap and production interruption.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preventing damage to steel strip during continuous annealing furnace shutdown is provided, comprising: S100. After shutdown, pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area to relax the strip steel in the furnace area, and then cool the furnace area. S200. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S300: Start the conveyor at an initial speed of 5 m / min and gradually increase the conveyor speed; monitor the wrinkling state of the strip in real time during operation. If the area of ​​the strip wrinkles increases, immediately reduce the conveyor speed. If the area of ​​the strip wrinkles does not increase, continue to increase the conveying speed; S400. When the folded area of ​​the strip enters the first stage of the aging furnace (OA1 stage) and the area of ​​the folded area does not expand, increase the conveyor speed and raise the temperature of the furnace area. S500: Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.6. The system will automatically adjust the actual tension according to the strip specifications. Gradually increase the temperature and conveying speed of the heating section, soaking section, aging furnace section 1, and aging furnace section 2 until the temperature and conveying speed of each section of the furnace area reach the preset process setting value.

[0007] In one possible implementation, S100 specifically includes: S110. Immediately after shutdown, activate the furnace zone central protection control to switch the heating section, soaking section, and over-aging furnace section 1 (OA1 section) to low-speed protection operation mode. S120. Pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area respectively, so that the strip steel in the furnace area is in a relaxed state. S130. Turn off the combustion aid device for burner heating, and introduce air into the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) to cool the radiant tubes.

[0008] In one possible implementation, S100 further includes a step following S130, specifically including: S140. Switch the tension control mode of the furnace area conveyor to manual mode and set the tension value to 180 DaN; S150, the furnace roller is rotated 180° by jogging to prevent deformation of the furnace roller due to uneven heating.

[0009] In one possible implementation, S200 specifically includes: S210. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S220, shut down the low-speed protection operation mode of the heating section, soaking section and over-aging furnace section 1 (OA1 section).

[0010] In one possible implementation, S300 specifically includes: S310. Start the conveyor at an initial speed of 5 m / min, and increase the speed of the conveyor to 20 m / min after 30 seconds. S320, real-time monitoring of the wrinkling state of strip steel in the heating section and soaking section of the furnace area; If the area of ​​the strip folds does not expand, gradually increase the conveying speed to 50 m / min so that the strip weld begins to enter the furnace zone of the annealing furnace. If the area of ​​the strip wrinkles expands, immediately reduce the conveyor speed to 5 m / min and repeat S310 until the area of ​​the strip wrinkles no longer expands.

[0011] In one possible implementation, S300 further includes: S330. When the weld of the strip steel enters the furnace area, stop the supply of cooling air to the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) and terminate the cooling purging.

[0012] In one possible implementation, S400 specifically includes: S410. When the folded area of ​​the strip enters the first stage of the aging furnace (OA1 stage) and the area of ​​the folded area does not expand, the conveyor speed is increased to 50 m / min. S420: Ignite the radiant tube that has passed the aging period and heat it up with the minimum output load.

[0013] In one possible implementation, S400 further includes the following following S420: S430. When the folded part of the strip enters the second stage of the aging furnace (OA2 stage), increase the conveyor speed to 100 m / min. S440. Hydrogen gas is introduced into the furnace area as a protective atmosphere. S450. Lift the water-quenched squeeze rolls to prevent the strip from breaking at the squeeze rolls. S460, Reheat the radiant tubes in the heating section with minimum output load, adjust the furnace zone tension to 150 DaN, and increase the conveying speed to 150 m / min.

[0014] In one possible implementation, S500 specifically includes: S510. Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.6. The system will automatically adjust the actual tension according to the strip specifications. The S520 controls the radiant tubes in the heating section to switch to high-fire combustion mode for heating, while gradually increasing the conveyor speed to 180 m / min, and then further increasing it to 200 m / min. S530: Simultaneously activate the electric heating device of the over-aging furnace section (OA section) to perform temperature compensation and stabilization control for OA1 and OA2 sections; S540, continue to gradually increase the conveyor speed to 230 m / min, and then to 260 m / min; during this speed increase, continuously monitor whether the newly generated wrinkles in the strip in the heating section have spread; if wrinkles spread, immediately stop the speed increase and return to the current stable speed, and continue to increase the speed after the wrinkles have stabilized.

[0015] In one possible implementation, the process before S520 includes: S511. When the folded position of the strip begins to exit the looper, close the lifting state of the water-quenched squeeze roller and reset the water-quenched squeeze roller to the working position.

[0016] The beneficial effects of the method for preventing strip damage during continuous annealing furnace shutdown provided by this invention are as follows: Compared with the prior art, the step-by-step operation of first relaxing the strip and then cooling it after shutdown, and then restoring it to a tensioned state after a predetermined time, avoids the initial damage to the strip caused by stress concentration and structural instability during the shutdown phase, effectively suppressing the formation and expansion of wrinkles and warping. During the restart phase, a refined control strategy of low-speed start-up, real-time monitoring of wrinkle status, and gradual acceleration and heating, especially through staged and regional tension and temperature coordinated control, precisely solves the problem of wrinkle diffusion, effectively suppressing the diffusion of wrinkles in the heating section during restart after a short shutdown, and avoiding the risk of strip deviation and breakage caused by wrinkles. Simultaneously, the process optimization of the first stage of the aging furnace provides favorable conditions for strip morphology correction.

[0017] Furthermore, switching the tension control to an automatic mode with a coefficient of 0.6, combined with adaptive tension adjustment based on strip specifications, ensures the stability of strip operation while avoiding the risk of edge cracking due to excessive tension. This invention not only significantly reduces the scrap rate after shutdown, shortens the time for troubleshooting and restart, and improves the operating efficiency and product qualification rate of the production line, but also reduces damage to key equipment such as furnace rolls and correction mechanisms caused by strip deviation and edge scraping, extending equipment lifespan, and lowering production and maintenance costs. It provides a reliable guarantee for the continuous and stable production of thin and even ultra-thin cold-rolled strip. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a method for preventing steel strip damage during continuous annealing furnace shutdown, as provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0021] In the claims, description, and accompanying drawings of this invention, unless otherwise expressly defined, the terms "first," "second," or "third," etc., are used to distinguish different objects and not to describe a specific order. Unless otherwise stated, other directional terms, such as "vertical," "clockwise," and "counterclockwise," indicate orientation or positional relationships based on the orientation and positional relationships shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, not to indicate or imply that the referred device or element must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention. In the claims, description, and accompanying drawings of this invention, unless otherwise expressly defined, the terms "fixed connection" or "fixed link" should be interpreted broadly, that is, any connection method in which there is no displacement relationship or relative rotation relationship between the two, that is, including non-removable fixed connections, detachable fixed connections, integral connections, and fixed connections through other devices or elements. In the claims, description, and accompanying drawings of this invention, the terms "comprising," "having," and their variations are intended to mean "including but not limited to."

[0022] It should be noted that "furnace area" refers to the area inside the annealing furnace.

[0023] Please see Figure 1 The present invention will now describe a method for preventing damage to steel strip during continuous annealing furnace shutdown. The method includes: S100. After shutdown, pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area to relax the strip steel in the furnace area, and then cool the furnace area. S200. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S300: Start the conveyor at an initial speed of 5 m / min, and gradually increase the conveyor speed; monitor the wrinkling state of the strip in real time during operation. If the area of ​​the strip wrinkles increases, immediately reduce the conveyor speed. If the area of ​​the strip wrinkles does not increase, continue to increase the conveying speed; S400. When the folded area of ​​the strip enters the first stage of the aging furnace (OA1 stage) and the area of ​​the folded area does not expand, increase the conveyor speed and raise the temperature of the furnace area. S500: Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.6. The system will automatically adjust the actual tension according to the strip specifications. Gradually increase the temperature and conveying speed of the heating section, soaking section, aging furnace section 1, and aging furnace section 2 until the temperature and conveying speed of each section of the furnace area reach the preset process setting value.

[0024] The method for preventing strip damage during continuous annealing furnace shutdown provided by this invention, compared with existing technologies, avoids initial damage to the strip caused by stress concentration and structural instability during the shutdown phase through a step-by-step operation of first relaxing the strip and then cooling it, followed by restoring it to a tensioned state after a predetermined time. This effectively suppresses the formation and expansion of wrinkles and warping. During the restart phase, a refined control strategy of low-speed start-up, real-time monitoring of wrinkle status, and gradual acceleration and heating, especially through staged and regional tension and temperature coordinated control, precisely solves the problem of wrinkle diffusion. This effectively suppresses the diffusion of wrinkles in the heating section during restart after a short shutdown, avoiding the risk of strip misalignment and breakage caused by wrinkles. Simultaneously, the process optimization of the first stage of the over-aging furnace provides favorable conditions for strip morphology correction.

[0025] Furthermore, switching the tension control to an automatic mode with a coefficient of 0.6, combined with adaptive tension adjustment based on strip specifications, ensures the stability of strip operation while avoiding the risk of edge cracking due to excessive tension. This invention not only significantly reduces the scrap rate after shutdown, shortens the time for troubleshooting and restart, and improves the operating efficiency and product qualification rate of the production line, but also reduces damage to key equipment such as furnace rolls and correction mechanisms caused by strip deviation and edge scraping, extending equipment lifespan, and lowering production and maintenance costs. It provides a reliable guarantee for the continuous and stable production of thin and even ultra-thin cold-rolled strip.

[0026] In some embodiments, S100 specifically includes: S110. Immediately after shutdown, activate the furnace zone central protection control to switch the heating section, soaking section, and over-aging furnace section 1 (OA1 section) to low-speed protection operation mode. S120. Pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area respectively, so that the strip steel in the furnace area is in a relaxed state. S130. Turn off the combustion aid device for burner heating, and introduce air into the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) to cool the radiant tubes.

[0027] Immediately after shutdown, the central protection control of the furnace area is activated, switching the heating section, soaking section, and OA1 section to low-speed protection operation mode. This avoids sudden changes in the operating conditions of critical sections of the furnace area during shutdown, providing a smooth transition environment for strip condition adjustment. By pulling the strip at the furnace area outlet and inlet towards the center of the furnace area, the strip in the furnace area is quickly brought to a relaxed state, eliminating the impact of sudden tension drop, fluctuation, or loss of tension on thin-gauge strip after shutdown. This avoids initial damage such as wrinkles and warping caused by tension imbalance and insufficient strip stiffness combined with high-temperature softening.

[0028] At the same time, shutting off the burner heating and combustion aid device and introducing air into the radiant tube for cooling not only achieves orderly control of the furnace temperature, avoiding the continuous effect of high temperature from aggravating the softening of the strip and structural instability, but also quickly cools the radiant tube, preventing local overheating damage to the strip due to high-temperature residual heat, and also protects the radiant tube itself from the impact of high temperature, extending the service life of the equipment.

[0029] Optionally, the duration of air being introduced into the radiant tube to cool it is determined based on the downtime. After restarting, the cooling and purging process is stopped once the folded area has stably passed through the heating section, soaking section, and over-aging furnace section 1 (OA1 section).

[0030] In some embodiments, S100 further includes a step following S130, specifically including: S140. Switch the tension control mode of the furnace area conveyor to manual mode and set the tension value to 180 DaN; S150, the furnace roller is rotated 180° by jogging to prevent deformation of the furnace roller due to uneven heating.

[0031] The S140 switches the conveyor tension control to manual mode and sets a fixed tension value of 180 DaN. This avoids disorderly tension fluctuations caused by automatic tension control failure and provides gentle support for the relaxed strip through precise tension setting, preventing the strip from stacking and wrinkling due to excessive relaxation. It also adapts to the stiffness characteristics of thin strip, avoiding initial stress damage caused by excessive tension. The S150 jogs the furnace rollers to rotate 180°, effectively eliminating thermal stress caused by uneven distribution of residual heat after shutdown. This prevents unevenness of the subsequent strip support surface due to furnace roller deformation, reducing the risk of strip deviation and scratches during operation from the source, while extending the service life and maintenance cycle of the furnace rollers.

[0032] In some embodiments, S200 specifically includes: S210. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S220, shut down the low-speed protection operation mode of the heating section, soaking section and over-aging furnace section 1 (OA1 section).

[0033] S210 restores the strip tension by pulling it outward from the furnace area, achieving a smooth transition from shutdown relaxation to restart tension. This lays a structurally stable foundation for subsequent low-speed startup and acceleration. S220 simultaneously shuts down the low-speed protection mode, allowing key sections of the furnace area (heating section, soaking section, OA1 section) to gradually return to normal production rhythm, ensuring process continuity during restart. The entire operation process, through the coordinated design of precise tension control, furnace roll calibration, and smooth tension restoration, significantly reduces the risk of strip damage during shutdown to restart, shortens the transition time between operating conditions, ensures the smoothness of subsequent production restarts and product quality stability, and further enhances the fault tolerance and operational reliability of the continuous annealing production line in the face of sudden shutdowns.

[0034] In some embodiments, S300 specifically includes: S310. Start the conveyor at an initial speed of 5 m / min, and increase the speed of the conveyor to 20 m / min after 30 seconds. S320, real-time monitoring of the wrinkling state of strip steel in the heating section and soaking section of the furnace area; If the area of ​​the strip folds does not expand, gradually increase the conveying speed to 50 m / min so that the strip weld begins to enter the furnace zone of the annealing furnace. If the area of ​​the strip wrinkles expands, immediately reduce the conveyor speed to 5 m / min and repeat S310 until the area of ​​the strip wrinkles no longer expands.

[0035] A stepped speed increase method, starting at a low speed of 5 m / min and then gradually increasing to 20 m / min after 30 seconds, avoids drastic tension fluctuations in the strip due to sudden speed changes during the initial restart, effectively reducing the risk of thin strip becoming unstable and wrinkling again. By monitoring the wrinkling status of the strip in the heating and soaking sections in real time and dynamically adjusting the conveyor speed according to changes in the wrinkled area, the speed is gradually increased to 50 m / min before the wrinkles expand, ensuring the safe entry of the strip weld into the furnace area and achieving an orderly resumption of the production process. Once the expansion of the wrinkled area is detected, the speed is immediately reduced to 5 m / min, and then gradually increased again, which can promptly curb the further spread of wrinkles and prevent accidents such as deviation, scraping, and strip breakage caused by wrinkle expansion from the source.

[0036] As a specific implementation of S320, if the area of ​​the strip wrinkled region expands in S320, the conveying speed of the conveyor is immediately reduced to 5 m / min, and the watermark material appearing in the water-quenched section is cut off and rewound.

[0037] During shutdown, cooling, and restart processes, the strip steel may experience defects such as watermarks, color differences, and cooling spots due to lingering in the water-quenching section, localized immersion in water, or uneven cooling. This portion of the strip steel is considered watermarked material. The shape and surface quality of this portion of the strip steel are already substandard and cannot be used as finished products. Therefore, while slowing down and stabilizing the strip, the watermarked defective section is cut off and separately coiled to prevent it from flowing into the next process or being shipped as a finished product.

[0038] "Water quenching section" refers to the water-cooled quenching area of ​​the strip steel after the continuous annealing furnace exit and the over-aging furnace section.

[0039] In some embodiments, S300 further includes: S330. When the weld of the strip steel enters the furnace area, stop the supply of cooling air to the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) and terminate the cooling purging.

[0040] When the strip weld enters the furnace area, promptly stop supplying cooling air to the heating section, soaking section, and OA1 section radiant tubes and terminate cooling purging. This allows for rapid restoration of the furnace area's thermal field conditions after the weld safely passes through the high-temperature zone, preventing excessive cooling that could lead to excessively low strip temperatures and difficulty in repairing the strip shape. It also shortens the furnace area's temperature recovery time, creating favorable conditions for subsequent speed increases and restoration of normal process temperatures, further ensuring the strip shape quality and production line restart efficiency.

[0041] In some embodiments, S400 specifically includes: S410. When the folded area of ​​the strip enters the first stage of the aging furnace (OA1 stage) and the area of ​​the folded area does not expand, the conveyor speed is increased to 50 m / min. S420: Ignite the radiant tube that has passed the aging period and heat it up with the minimum output load.

[0042] When the wrinkled area of ​​the strip enters the first stage of the over-aging furnace (OA1 stage) and does not expand further, the conveyor speed is increased to 50 m / min. This improves the restart efficiency of the production line while ensuring the stability of the strip shape, achieving a balance between safety and efficiency. Simultaneously, the radiant tubes in the over-aging section are ignited and heated with minimum output load. This avoids the impact of a sudden temperature rise on the strip's properties and shape, and gradually restores the furnace thermal field, providing a mild and stable heat treatment environment for the wrinkled area. This facilitates the smoothing and correction of residual wrinkles and prevents secondary instability caused by insufficient or fluctuating temperatures. This step achieves a coordinated match between speed and temperature, effectively suppressing wrinkle diffusion and laying a reliable foundation for the subsequent restoration of process parameters across the entire line, further improving the stability of the fault restart process and product quality.

[0043] In some embodiments, S400 further includes the following following S420: S430. When the folded part of the strip enters the second stage of the aging furnace (OA2 stage), increase the conveyor speed to 100 m / min. S440. Hydrogen gas is introduced into the furnace area as a protective atmosphere. S450. Lift the water-quenched squeeze rolls to prevent the strip from breaking at the squeeze rolls. S460, Reheat the radiant tubes in the heating section with minimum output load, adjust the furnace zone tension to 150 DaN, and increase the conveying speed to 150 m / min.

[0044] Once the wrinkled area enters section OA2, the speed is increased to 100 m / min to accelerate the strip's passage through the critical furnace section in its stable zone. Timely introduction of a hydrogen protective atmosphere effectively prevents high-temperature oxidation of the strip, ensuring stable surface quality and microstructure. The water-quenched squeeze rolls are lifted to prevent stress concentration and breakage at weak wrinkled areas, significantly reducing the risk of strip breakage. Subsequently, the radiant tubes in the heating section are reheated with minimal load, the furnace tension is adjusted to 150 DaN, and the speed is increased to 150 m / min. This precise matching of temperature, tension, and speed ensures the strip's operating state quickly stabilizes, providing a reliable guarantee for resuming normal production. This step forms a closed-loop protection system from multiple aspects, including wrinkle control, atmosphere protection, equipment protection, and parameter coordination. It not only inhibits wrinkle propagation but also improves restart safety and recovery efficiency, effectively guaranteeing the product quality of ultra-thin strip and the stability of the production line operation.

[0045] As a specific implementation of S460, if the transition material newly entering the heating section wrinkles before the heating section of S460 is reheated, the heating needs to be turned off again, and the heating can be restarted after the wrinkled transition material has passed through the heating section stably.

[0046] It can effectively prevent high temperatures from exacerbating the expansion of wrinkles in the transition material, prevent strip deviation, edge scraping and strip breakage, improve the safety and stability of the production line restart process, and allow the wrinkled transition material to pass through safely, at low speed and low temperature, and then be reheated to ensure absolute safety during the restart process.

[0047] "Transitional material" refers to strip steel whose shape and properties fluctuate due to unstable tension, temperature, and speed conditions before and after a production line is shut down, during shutdown cooling, and in the initial stage of restarting.

[0048] In some embodiments, S500 specifically includes: S510. Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.6. The system will automatically adjust the actual tension according to the strip specifications. The S520 controls the radiant tubes in the heating section to switch to high-fire combustion mode for heating, while gradually increasing the conveyor speed to 180 m / min, and then further increasing it to 200 m / min. S530: Simultaneously activate the electric heating device of the over-aging furnace section (OA section) to perform temperature compensation and stabilization control for OA1 and OA2 sections; S540, continue to gradually increase the conveyor speed to 230 m / min, and then to 260 m / min; during this speed increase, continuously monitor whether the newly generated wrinkles in the strip in the heating section have spread; if wrinkles spread, immediately stop the speed increase and return to the current stable speed, and continue to increase the speed after the wrinkles have stabilized.

[0049] Switching the tension control to automatic mode and setting the tension coefficient to 0.6 allows the system to adaptively adjust the tension according to the strip specifications, ensuring stable strip tension while avoiding excessive stress and improving the operational safety of thin-gauge strips. Switching the radiant heating tubes in the heating section to high-fire combustion mode for rapid heating, combined with a gradual increase in conveyor speed, enables rapid restoration of the furnace area's process temperature, shortening restart recovery time and improving production efficiency. Simultaneously activating the electric heating device in section OA1 and OA2 provides temperature compensation and stabilization control, ensuring uniform and stable temperature throughout the furnace area and preventing strip shape deterioration and uneven performance due to temperature deviations. During the gradual increase in speed to 230 m / min and 260 m / min, continuous monitoring is conducted to check for the spread of new folds in the heated strip. If spread occurs, the speed increase is immediately paused and the speed returned to a stable level. The speed increase is only resumed after the strip shape has stabilized, effectively preventing risks such as fold expansion, deviation, and strip breakage during high-speed recovery.

[0050] As a specific implementation of S540, after the conveyor speed is increased to 260 m / min, if new folds appear in the heating section but the area of ​​the newly appeared folded area does not spread, monitoring is maintained and the speed is increased again until it is restored to the process speed.

[0051] If new wrinkles appear in the heating section but the wrinkled areas do not spread after the conveyor speed is increased to 260 m / min, it indicates that the strip steel is still in a stable operating state. At this time, the control strategy of maintaining monitoring and continuing to increase speed can avoid the production line recovery time being prolonged due to excessive conservative speed reduction. It can also maximize the restart efficiency while ensuring that the strip steel does not become unstable, deviate, or break, thus achieving a balance between safe recovery and production efficiency. Finally, it can smoothly return to the normal process speed, ensuring that the ultra-thin strip steel continuous annealing production line returns to normal production status efficiently and stably.

[0052] In some embodiments, the process further includes the following steps prior to S520: S511. When the folded position of the strip begins to exit the looper, close the lifting state of the water-quenched squeeze roller and reset the water-quenched squeeze roller to the working position.

[0053] When the strip begins to exit the looper at the folded position, the water-quenched squeeze roll is promptly reset from the raised state to the working position. This effectively avoids stress concentration and strip breakage risk when passing through the weak folded section of the strip, and quickly restores the cooling and surface treatment functions after the strip shape stabilizes, ensuring the subsequent surface quality and shape control of the strip, and achieving precise matching between equipment operation and strip condition.

[0054] Example 1 This embodiment takes the production of T4 product with a specification of 0.198 mm × 920 mm as an example to provide a detailed description of the method for preventing steel strip damage by stopping the continuous annealing furnace as described in this invention.

[0055] 1. Shutdown Protection Phase At 16:20, the production line was forced to stop due to a runout at the inlet looper. At the time of shutdown, the strip weld was located at the inlet looper, in front of the furnace entrance, and the strip temperature in the furnace heating section was 660 ℃. The following operations were immediately performed after shutdown: 1) Activate the protection control in the middle of the furnace area and put the heating section, soaking section and over-aging furnace section 1 (OA1 section) into low-speed protection operation mode; 2) Pull the strip steel from the furnace outlet and furnace inlet toward the center of the furnace area respectively, so that the strip steel in the furnace is in a relaxed state and the tension is controlled at 120 DaN; 3) Turn off the burner heating and combustion aid device, and introduce air into the heating section, soaking section and OA1 section radiant tube for cooling; 4) Switch the tension control of the in-furnace conveyor to manual mode and set the tension value to 180 DaN; 5) Inching drive the furnace roller to rotate 180° to prevent thermal deformation caused by uneven heating.

[0056] 2. Restart and Recovery Phase The scheduled downtime was 10 minutes, during which a shutdown protection mechanism was implemented. The system restarted and resumed operations at 16:41. 1) Pull the strip steel outward from the furnace inlet and furnace outlet respectively to restore the strip steel in the furnace to a taut state; 2) Cancel the low-speed protection operation mode of the heating section, the heat soaking section, and the OA1 section; 3) Start the conveyor at an initial speed of 5 m / min, and after running for 30 seconds, increase the speed to 20 m / min. Monitor the folding status of the strip in the heating section and the soaking section in real time. No diffusion of the folded area was observed. 4) Continue to increase the speed to 50m / min, and the strip weld begins to enter the furnace area. Continuously monitor the strip folds and operating status. 5) Watermark defects appeared on the strip steel after it was output through the looper in the water-quenched section. The watermarked material was cut off and rewound. At the same time, the strip steel wrinkles in the heating section showed a tendency to spread. The conveyor speed was immediately reduced to 5m / min. After the strip steel wrinkles stabilized and stopped spreading, the subsequent steps were carried out. 6) At 16:52, stop supplying cooling air to the heating section, the heat spreader section, and the radiant tubes of section OA1, and terminate the cooling purging. 7) If the folded area of ​​the strip enters section OA1 without spreading, increase the conveyor speed to 50m / min; 8) Ignite the radiant tubes in the over-aged section and heat them up with 15% of the minimum output load; 9) When the folded part of the strip enters the second stage of the aging furnace (OA2 stage), increase the conveyor speed to 100m / min; because the newly entered transition material in the heating section has folds, turn off the heating again, and wait for the folds to pass through stably before reheating. 10) Introduce hydrogen gas into the furnace as a protective atmosphere; 11) Lift the water-quenched squeeze rolls to prevent the strip from breaking due to stress concentration at the squeeze roll position; 12) The radiant tubes in the heating section are reheated at 15% of the minimum output load, the furnace tension is adjusted to 150 DaN, and the conveyor speed is increased to 150 m / min; 13) Remove the looper from the pleated part of the strip and reset the water-quenched squeeze roll to the working position; 14) Switch the conveyor tension control to automatic mode, set the tension coefficient to 0.6, and let the system automatically adjust the actual tension according to the strip specifications; 15) The radiant tubes in the heating section are switched to high-fire combustion mode to raise the temperature, and the conveyor speed is gradually increased to 180m / min and 200m / min at the same time; 16) Turn on the electric heating device of section OA to perform temperature compensation and stabilization control for sections OA1 and OA2; 17) Continue to increase the conveyor speed to 230m / min. New folds appear in the heating section but do not spread. Continue to monitor and continue to increase the speed. 18) Increase the speed to 260m / min, gradually restore the process temperature and speed of each furnace section, and the production line resumes normal continuous production.

[0057] The results of this embodiment show that, by using the method described in this invention, strip wrinkles are effectively suppressed and controlled during the rapid restart of the production line after a short-term shutdown. No deviation, edge scraping, strip breakage, or batch quality defects occur. The production line can safely and smoothly return to normal operation within 60 minutes, significantly improving the operational stability and efficiency of the continuous annealing production line.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 preventing damage to steel strip during continuous annealing furnace shutdown, characterized in that, include: S100. After shutdown, pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area to relax the strip steel in the furnace area, and then cool the furnace area. S200. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S300: Start the conveyor at an initial speed of 5 m / min and gradually increase the conveyor speed; monitor the wrinkling state of the strip in real time during operation. If the area of ​​the strip wrinkles increases, immediately reduce the conveyor speed. If the area of ​​the strip wrinkles does not increase, continue to increase the conveying speed; S400. When the folded area of ​​the strip enters the first stage of the aging furnace and the area of ​​the folded area has not expanded, increase the conveyor speed and raise the temperature of the furnace area. S500: Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.

6. The system will automatically adjust the actual tension according to the strip specifications. Gradually increase the temperature and conveying speed of the heating section, soaking section, aging furnace section 1, and aging furnace section 2 until the temperature and conveying speed of each section of the furnace area reach the preset process setting value.

2. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 1, characterized in that, Specifically, S100 includes: S110. Immediately after shutdown, activate the furnace zone central protection control to switch the heating section, soaking section, and over-aging furnace section 1 to low-speed protection operation mode. S120. Pull the strip steel at the furnace exit and furnace entrance towards the center of the furnace area respectively, so that the strip steel in the furnace area is in a relaxed state. S130. Turn off the combustion aid device for burner heating, and introduce air into the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) to cool the radiant tubes.

3. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 2, characterized in that, S100 further includes a step following S130, specifically including: S140. Switch the tension control mode of the furnace area conveyor to manual mode and set the tension value to 180 DaN; S150, the furnace roller is rotated 180° by jogging to prevent deformation of the furnace roller due to uneven heating.

4. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 2, characterized in that, Specifically, S200 includes: S210. When the predetermined shutdown time is reached, the strip steel at the furnace inlet and furnace outlet is pulled outward from the furnace area to restore the strip steel in the furnace area to a taut state. S220, shut down the low-speed protection operation mode of the heating section, soaking section and over-aging furnace section 1.

5. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 1, characterized in that, Specifically, S300 includes: S310. Start the conveyor at an initial speed of 5 m / min, and increase the speed of the conveyor to 20 m / min after 30 seconds. S320, real-time monitoring of the wrinkling state of strip steel in the heating section and soaking section of the furnace area; If the area of ​​the strip folds does not expand, gradually increase the conveying speed to 50 m / min so that the strip weld begins to enter the furnace zone of the annealing furnace. If the area of ​​the strip wrinkles expands, immediately reduce the conveyor speed to 5 m / min and repeat S310 until the area of ​​the strip wrinkles no longer expands.

6. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 5, characterized in that, The S300 also includes: S330. When the weld of the strip steel enters the furnace area, stop the supply of cooling air to the radiant tubes of the heating section, soaking section and over-aging furnace section 1 (OA1 section) and terminate the cooling purging.

7. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 1, characterized in that, Specifically, S400 includes: S410. When the folded area of ​​the strip enters the first stage of the aging furnace and the area of ​​the folded area has not expanded, the conveying speed of the conveyor is increased to 50 m / min. S420: Ignite the radiant tube that has passed the aging period and heat it up with the minimum output load.

8. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 7, characterized in that, The S400 also includes the following after the S420: S430. When the folded part of the strip enters the second stage of the aging furnace, increase the conveyor speed to 100 m / min. S440. Hydrogen gas is introduced into the furnace area as a protective atmosphere. S450. Lift the water-quenched squeeze rolls to prevent the strip from breaking at the squeeze rolls. S460, Reheat the radiant tubes in the heating section with minimum output load, adjust the furnace zone tension to 150 DaN, and increase the conveying speed to 150 m / min.

9. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 1, characterized in that, The S500 specifically includes: S510. Switch the tension control of the conveyor to automatic mode and set the tension coefficient to 0.

6. The system will automatically adjust the actual tension according to the strip specifications. The S520 controls the radiant tubes in the heating section to switch to high-fire combustion mode for heating, while gradually increasing the conveyor speed to 180 m / min, and then further increasing it to 200 m / min. S530: Simultaneously activate the electric heating device of the over-aging furnace section to perform temperature compensation and stable control for sections OA1 and OA2; S540, continue to gradually increase the conveyor speed to 230 m / min, and then to 260 m / min; during this speed increase, continuously monitor whether the newly generated wrinkles in the strip in the heating section have spread; if wrinkles spread, immediately stop the speed increase and return to the current stable speed, and continue to increase the speed after the wrinkles have stabilized.

10. The method for preventing steel strip damage during continuous annealing furnace shutdown as described in claim 9, characterized in that, Prior to S520, the following also includes: S511. When the folded position of the strip begins to exit the looper, close the lifting state of the water-quenched squeeze roller and reset the water-quenched squeeze roller to the working position.

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