A method for controlling scratch defects in the pickling tank of hot-rolled pickling plate / coil in a continuous pickling process

Abstract

The invention relates to a method for controlling scratch defects in an acid tank of a hot-rolled pickling plate / coil in a continuous pickling process. The control method comprises the following steps: step 1: adjusting an operating mode of a straightening machine; step 2: optimizing a tension setting in a process section; step 3: optimizing an acceleration / deceleration rate in the process section; step 4: optimizing a tension adjustment rate; step 5: improving a structure of a stone support in the acid tank; step 6: periodically measuring and maintaining the elevation of a squeeze roller in the pickling section; and step 7: optimizing the adjustment of the acid solution circulation temperature according to actual pickling quality. Through the above, stable production of the process section of the unit is achieved. The scheme realizes stable production of continuous pickling products, reduces the occurrence of abnormal and major failures of production equipment, and simultaneously stabilizes the control of acid tank scratches, reduces the acid tank scratch degradation rate from 0.24% before the improvement to about 0.05%, and improves product efficiency.

Description

Technical Field

[0001] The invention relates to a control method, in particular to a method for controlling scratch defects in a pickling tank of a hot-rolled pickling plate / coil in a continuous pickling process, and belongs to the technical field of hot-rolled pickling plate (coil) production. Background Art

[0002] A continuous pickling line utilizes a three-stage shallow-tank turbulent pickling process. After years of continuous full-load operation, the line's expanded product specifications and the long-term use of the PPH pickling tanks in the process section have caused the tanks to expand and deform. This has led to frequent fine-line scratches on both sides of the strip's lower surface during normal production. These scratches are more frequent at the strip's head and tail, and the localized defects are noticeable, impacting the quality of the strip. Furthermore, to ensure stable production and prevent strip breakage, the weld seam over-tensioning leveler mostly uses an open roll gap. This results in poor strip shape at the strip's head and tail, making it more susceptible to damage to the tank's bottom support stones during passage through the pickling tanks, leading to scratches on the strip's lower surface. When these scratches occur, production operators are forced to increase the tension in the process section and reduce production speed to maintain production. Furthermore, the defective sections are removed by coiling at the line's exit, severely impacting the line's capacity and quality.

[0003] After searching Chinese patents and related papers, no literature directly related to the technology for controlling scratch defects in hot-rolled pickled plates (coils) was found. The following is an analysis of other patents that may be of some relevance:

[0004] A Chinese patent application, publication number CN215856353U, discloses a mechanism for extending the service life of pickling tank support stones. By adjusting the distribution of acid return ports or installing a diverter at the ports, this mechanism eliminates the vortex force generated by acid reflux on the strip and the wear on the support stones at the bottom of the tank, thereby extending the service life of the support stones. This patent does not specify the applicable specifications for pickling products, but primarily discusses improvements to reduce support stone consumption and indicates that the use of support stones does not cause scratches. The patent does not address techniques for controlling scratches in pickling tanks for hot-rolled pickled plate (coil) in a continuous pickling process.

[0005] The paper "Analysis and Improvement of Problems in Continuous Pickling Units Producing Thick Plates" (Metallurgical Equipment, Issue 3, June 2020) analyzes the causes of acid tank scratch defects from the perspective of strip sag in the acid tank, and discusses the improvement of scratches achieved by increasing the tension of the process section by increasing the transmission of the 4# tension roller at the exit of the rinsing section. However, it does not introduce the root causes of acid tank scratches in many aspects and systematic and comprehensive improvements. The detailed description of the optimization of the acid tank support stone structure is not as detailed as the description of the patented technology of this invention. Therefore, a new solution is urgently needed to solve the above technical problems. Summary of the Invention

[0006] The present invention is aimed at the problems existing in the prior art and provides a method for controlling acid tank scratch defects in hot-rolled pickling plates / coils in a continuous pickling process. This solution realizes the stable production of continuous pickling products and reduces the occurrence of abnormal and major failures of production equipment. At the same time, the acid tank scratch control is stable, and the acid tank scratch degradation rate is reduced from 0.24% before the improvement to about 0.05%, thereby improving product efficiency.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows: a method for controlling scratch defects in the pickling tank of hot-rolled pickling plate / coil in a continuous pickling process, the control method is as follows:

[0008] Step 1: Adjust the operation mode of the tension and straightening machine.

[0009] Step 2: Optimize the tension setting of the process section,

[0010] Step 3: Optimize the acceleration and deceleration rate of the process section,

[0011] Step 4: Optimize the tension adjustment rate,

[0012] Step 5: Improve the acid tank support stone structure,

[0013] Step 6: Periodic measurement and maintenance of the height of the squeeze roller in the pickling section.

[0014] Step 7: The acid solution circulation temperature is adjusted and optimized according to the actual pickling quality. Through the above steps, stable production of the unit process section is achieved.

[0015] Further, step 1: adjust the operation mode of the tension and leveling machine, as follows:

[0016] First, the high-power (12kW) laser welding weld over-tension straightening machine adopts "small pressure reduction" control to improve the quality of the strip head and tail plate shape. The laser welding weld over-tension straightening machine adopts "small pressure reduction" control technology. When the strip head and tail are about 15m through the straightening machine, the insertion amount of the bending unit and the straightening unit is automatically adjusted from the fully open state to 5mm (small pressure reduction state) through the L1 basic automation system, which improves the strip head and tail plate shape to a certain extent. Beyond about 15m of the strip head and tail, it is executed according to the value issued by the L2 process control system. In this solution, the L1 basic automation system refers to the electrical automation control system of the production unit, which is responsible for controlling the action of all single equipment of the unit and the production operation of the entire line. The L2 process control system refers to the process parameter control system of the main process equipment of the production unit, which is responsible for setting the process parameters of the main process equipment of the entire line of the unit, and then issuing them to the L1 basic automation system for execution.

[0017] Furthermore, in Step 2: Optimizing Process Section Tension Settings, the process control system model database for process section tension L2 was constructed, incorporating strip strength as an influencing factor. This optimized total tension value was determined by combining the strip strength range, strip cross-sectional area, and unit tension. This approach provides a more comprehensive approach than the previous method of determining total tension based solely on strip cross-sectional area and unit tension, and better meets actual on-site control needs. This model enables automated control of process section tension, avoiding issues caused by frequent switching between production specifications, untimely manual adjustments, or continuous operation at high tension.

[0018] Furthermore, in step 3: the acceleration and deceleration rates of the process section are optimized, the acceleration and deceleration rates of the process section are set to 15m / min / s, and the acceleration and deceleration points are adjusted. It has been verified on site that it does not affect the filling rhythm after the entrance welding. It is automatically controlled by the L1 basic automation system to reduce the fluctuation of the strip in the acid tank of each section of about 21.6m in length during the acceleration and deceleration of the process section, and to avoid the strip from rubbing against the bottom of the tank due to shaking during the acceleration and deceleration process.

[0019] Furthermore, in step 4, the tension adjustment rate is optimized, with the tension adjustment amplitude set to 5kN / s. When switching between production lines of different steel grades and specifications, the L1 basic automation system automatically adjusts the tension according to the values ​​issued by the L2 process control system at predetermined points. This reduces significant fluctuations in tension adjustment during process sections due to switching between production specifications, ensuring synchronized and stable tension adjustment across all process sections.

[0020] Furthermore, in step 5, the structure of the acid tank support stone was improved. The upper surface width of the support stone was set to 280mm, while the length and height remained unchanged at 985mm and 90mm. At the same time, the upper and lower bottom surfaces of the support stone were standardized to ensure that the support stone could be turned over for use, thereby improving the utilization rate and service life of the acid tank support stone. The improved support stone structure not only increases the support stone's deadweight and maintains its stability, but also prevents the support stone from shifting in position due to the turbulent acid flow in the acid tank. On the other hand, the contact mode between the strip and the support stone is adjusted from "point contact" and "line contact" to "surface contact", reducing the degree of "concentrated" wear on the support stone.

[0021] Furthermore, step 6: periodic measurement and maintenance of the pickling section squeeze roller elevation, according to the periodic detection results of the acid tank elevation, the pickling section squeeze roller elevation is adjusted synchronously by adding gaskets to compensate for the change in the plate passing line elevation after the acid tank is deformed, ensuring that the unit plate passing line height is constant.

[0022] Furthermore, in step 7, the acid solution large and small circulation temperatures are adjusted and optimized according to the actual pickling quality. When it is verified on site that there is no negative impact, the pickling large and small circulation temperature settings are optimized, and the large circulation temperature is adjusted to 70-75°C and the small circulation temperature is reduced to 40-45°C, thereby further reducing the degree of deformation of the PPH acid tank during long-term use, extending the service life of the tank body, and reducing the occurrence of acid tank scratch defects.

[0023] Compared with the existing technology, the present invention has the following advantages: 1) This technical solution realizes the stable production of continuous pickling products, reduces the occurrence of abnormal and major failures of production equipment, and at the same time, the acid tank scratch control is stable, and the acid tank scratch degradation rate is reduced from 0.24% before the improvement to about 0.05%, thereby improving product efficiency; 2) This technical solution realizes the domestic first launch and stable batch (≥800 tons / month) of pickling products with a tensile strength of less than 450MPa and ultra-thick specifications of 7.0-8.0mm in the continuous pickling process; 3) After the experiment of this technical solution, the service life of the acid tank and its support stone is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Production flow chart of the process section of the continuous pickling unit;

[0025] Figure 2 Flowchart for controlling scratch defects in the acid tank of hot-rolled pickled plates (coils) using continuous pickling process;

[0026] Figure 3 Diagram of optimized acid tank support stone structure. DETAILED DESCRIPTION

[0027] In order to deepen the understanding of the present invention, this embodiment is described in detail below with reference to the accompanying drawings.

[0028] Example 1: See Figure 1 A method for controlling scratch defects in a pickling tank of a hot-rolled pickled plate / coil in a continuous pickling process is provided, wherein the control method is as follows:

[0029] Step 1: Adjust the operation mode of the tension and straightening machine.

[0030] Step 2: Optimize the tension setting of the process section,

[0031] Step 3: Optimize the acceleration and deceleration rate of the process section,

[0032] Step 4: Optimize the tension adjustment rate,

[0033] Step 5: Improve the acid tank support stone structure,

[0034] Step 6: Periodic measurement and maintenance of the height of the squeeze roller in the pickling section.

[0035] Step 7: The acid solution circulation temperature is adjusted and optimized according to the actual pickling quality. Through the above steps, stable production of the unit process section is achieved.

[0036] Step 1: Adjust the operation mode of the tension and leveling machine as follows:

[0037] First, the high-power (12kW) laser welding weld over-tension straightening machine adopts "small pressure reduction" control to improve the quality of the strip head and tail plate shape. The laser welding weld over-tension straightening machine adopts "small pressure reduction" control technology. When the strip head and tail are about 15m through the straightening machine, the insertion amount of the bending unit and the straightening unit is automatically adjusted from the fully open state to 5mm (small pressure reduction state) through the L1 basic automation system, which improves the strip head and tail plate shape to a certain extent. Beyond about 15m of the strip head and tail, it is executed according to the value issued by the L2 process control system. In this solution, the L1 basic automation system refers to the electrical automation control system of the production unit, which is responsible for controlling the action of all single equipment of the unit and the production operation of the entire line. The L2 process control system refers to the process parameter control system of the main process equipment of the production unit, which is responsible for setting the process parameters of the main process equipment of the entire line of the unit, and then issuing them to the L1 basic automation system for execution.

[0038] Step 2: Optimize process section tension settings. This optimization involves constructing a model database for the process control system L2, incorporating strip strength as an influencing factor. This optimizes the overall tension by combining the strip strength range, cross-sectional area, and unit tension. This approach provides a more comprehensive approach than the previous method, which only determines overall tension based on cross-sectional area and unit tension. This approach better meets actual on-site control needs and enables automated model-based control of process section tension, avoiding issues caused by frequent switching between production specifications, untimely manual adjustments, or continuous operation at high tension.

[0039] Step 3: Optimize the acceleration and deceleration rate of the process section, set the process section acceleration and deceleration rate to 15m / min / s, and adjust the acceleration and deceleration points. It has been verified on site that it does not affect the filling rhythm after the entrance welding. It is automatically controlled by the L1 basic automation system to reduce the fluctuation of the strip in each section of the acid tank with a length of approximately 21.6m during the acceleration and deceleration of the process section, and avoid the strip from rubbing against the bottom of the tank due to shaking during the acceleration and deceleration process.

[0040] Step 4: Optimize the tension adjustment rate, setting the tension adjustment range to 5 kN / s. When switching between production lines for different steel grades and specifications, the L1 basic automation system automatically adjusts the tension according to the values ​​issued by the L2 process control system at the predetermined position. This reduces significant fluctuations in tension adjustment during process sections due to switching between production specifications, ensuring synchronized and stable tension adjustment across all process sections.

[0041] Step 5: Improve the structure of the acid tank support stone. Set the upper surface width of the support stone to 280mm, while maintaining the length at 985mm and the height at 90mm. At the same time, standardize the upper and lower surfaces of the support stone to ensure that the support stone can be flipped over for use, thereby increasing the utilization rate and service life of the acid tank support stone. Improving the support stone structure not only increases the support stone's deadweight and maintains its stability, preventing the support stone from shifting in position due to the turbulent acid flow in the acid tank, but also adjusts the contact mode between the strip and the support stone from "point contact" and "line contact" to "surface contact," reducing the degree of "concentrated" wear on the support stone.

[0042] Step 6: Periodically measure and maintain the height of the squeeze rollers in the pickling section. Based on the periodic test results of the acid tank elevation, adjust the elevation of the squeeze rollers in the pickling section by adding gaskets to compensate for the change in the elevation of the plate passing line after the acid tank is deformed, ensuring that the height of the plate passing line of the unit remains constant.

[0043] Step 7: The acid solution large and small circulation temperatures are adjusted and optimized according to the actual pickling quality. When it is verified on site that there is no negative impact, the pickling large and small circulation temperature settings are optimized, and the large circulation temperature is adjusted to 70-75°C and the small circulation temperature is reduced to 40-45°C. This will further reduce the deformation degree of the PPH acid tank during long-term use, extend the service life of the tank, and reduce the occurrence of acid tank scratch defects.

[0044] Specific embodiment: Figure 1 The process section equipment of the continuous pickling unit includes 2# tension roller 1, a straightening unit 2 of the straightening machine, a straightening unit 3 of the straightening machine, 3# tension roller 4, a measuring roller 5, an acid tank entrance roller 6, an acid tank entrance squeeze roller 7, a 1# acid tank body 8, an inter-tank squeeze roller 9, a 2# acid tank body 10, an inter-tank squeeze roller 11, a 3# acid tank body 12, an acid tank outlet squeeze roller 13, 1# to 5# rinsing sections 14, a dryer 15, a correction roller 16, and a 4# tension roller 17. The present invention starts with optimizing the operation mode of the straightening machine and makes systematic improvements to control the occurrence of acid tank scratches. The acid tank scratch defect control method of the present invention is further explained and illustrated in conjunction with specific examples below. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0045] like Figure 2 A method for controlling scratch defects in the acid tank of hot-rolled pickled plates (coils) in a continuous pickling process mainly includes adjusting the operating mode of the straightening machine, optimizing the tension setting of the process section, optimizing the acceleration and deceleration rate of the process section, optimizing the tension adjustment rate, improving the acid tank support stone structure, periodic measurement and maintenance of the height of the squeezing rollers in the pickling section, and adjusting and optimizing the acid solution circulation temperature according to the actual pickling quality. Through a series of improvements, stable production of the process section of the unit is achieved.

[0046] First, if Figure 3When the length of the laser welded strip about 15m before and after the head and tail passes through the tension leveler, the insertion amount of the bending unit and the straightening unit is automatically adjusted from the original system default value of -8.0mm (i.e. fully open state) to 5mm (small pressure reduction state) through the L1 basic automation system to improve the strip head and tail edge waves and other plate shape defects, and reduce the impact, wear and damage of the plate shape defects before and after the weld on the acid tank support stone; secondly, as shown in Table 1, the process section tension model data structure

[0047] Table 1: Process section tension model data structure

[0048]

[0049]

[0050]

[0051] When switching between steel grades and specifications, the L2 process control system determines the optimal total tension value based on the strip strength range, strip cross-sectional area, and unit tension, and sends it to the L1 basic automation control system for adjustment, so that the tension of the process section is automatically controlled by the L2 process control system model, avoiding the occurrence of abnormal operation of other production equipment due to continuous operation of artificial high tension; secondly, the speed increase and decrease rates of the process section are optimized in combination with the production rhythm of the unit, and the speed increase and decrease speed variation range of the process section is adjusted from 25m / min / s to 15m / min / s. After calculation, the speed of the process section is reduced from the maximum value of 160mpm to the minimum speed of 60mpm, and then increased to the maximum speed of 160mpm. The difference between the increase and decrease lengths of the two rates is only about 4.2m, and the speed increase and decrease points are adjusted accordingly. The speed adjustment is automatically controlled by the L1 basic automation system; thirdly, the tension adjustment change rate of the process section is optimized, and the tension adjustment range is reduced from 10kN / s to 5kN / s. When switching between different steel grades and different specifications of materials, the L1 basic automation system will adjust the speed according to the process section tension adjustment rate. The system automatically adjusts the value issued by the L2 process control system according to the predetermined position point, reducing the large fluctuations in the tension adjustment process of the process section due to switching production specifications; secondly, the structure of the acid tank support stone is optimized, and the upper surface width of the support stone is increased from 90mm to 280mm, while the length and height remain unchanged. At the same time, the upper and lower bottom surfaces of the support stone are standardized to ensure that the support stone can be turned over for use, thereby improving the utilization rate and service life of the acid tank support stone, and improving the actual application situation on site; thirdly, based on the periodic inspection results of the acid tank elevation, the elevation of the pickling section squeeze roller is synchronously adjusted by adding steel plates or gaskets of different thicknesses to the bearing seat to compensate for the change in the elevation of the plate passing line after the acid tank is deformed, ensuring the constant height of the plate passing line of the unit; finally, by optimizing the pickling large and small cycle temperature settings, after on-site verification that there is no negative impact, the large cycle temperature is reduced from the conventional 80℃ to 70-75℃, and the small cycle temperature is reduced from 50℃ to 40-45℃, further reducing the degree of deformation of the PPH acid tank during long-term use, extending the service life of the tank body, and reducing the occurrence of acid tank scratch defects.

[0052] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions fall within the scope of protection of the claims of the present invention.

Claims

1. A method for controlling scratch defects in the pickling tank of hot-rolled pickling plate / coil in a continuous pickling process, characterized in that: The control method is as follows: Step 1: Adjust the operation mode of the tension and straightening machine. Step 2: Optimize the tension setting of the process section, Step 3: Optimize the acceleration and deceleration rate of the process section, Step 4: Optimize the tension adjustment rate, Step 5: Improve the acid tank support stone structure, Step 6: Periodic measurement and maintenance of the height of the squeeze roller in the pickling section. Step 7: The acid solution circulation temperature is adjusted and optimized according to the actual pickling quality. Through the above steps, stable production of the unit process section is achieved; Among them, step 1: adjust the operation mode of the tension and leveling machine, as follows: First, a high-power 12kW laser welding weld straightening machine uses "small reduction" control to improve the flatness quality of the strip's head and tail. This technology applies to the laser welding weld straightening machine. When the strip's head and tail are approximately 15m long, the insertion amount of the bending and straightening units is automatically adjusted from a fully open state to 5mm through the L1 basic automation system. This improves the flatness quality of the strip's head and tail to a certain extent. Beyond approximately 15m, the values ​​issued by the L2 process control system are used. Step 2: Optimize the process section tension setting, optimize the construction of the process control system model database for the process section tension L2, and introduce the strip strength as the influencing factor of the process section tension; Step 3: Optimize the acceleration and deceleration rates of the process section. Set the process section acceleration and deceleration rate to 15m / min / s and adjust the acceleration and deceleration points. Field verification shows that this does not affect the filling rhythm after the entrance welding. Automatically controlled by the L1 basic automation system, this reduces the fluctuation of the strip steel in each section of the acid tank, which is approximately 21.6m long, during the acceleration and deceleration process of the process section. This prevents the strip steel from rubbing against the tank bottom due to vibration during the acceleration and deceleration process. Step 4: Optimize the tension adjustment rate and set the tension adjustment range to 5kN / s; Step 5: Improve the acid tank support stone structure by setting the upper surface width of the support stone to 280mm, while keeping the length 985mm and height 90mm unchanged. At the same time, make the upper and lower bottom surfaces of the support stone uniform. Step 6: Periodic measurement and maintenance of the pickling section squeeze roller elevation. Based on the periodic test results of the acid tank elevation, the pickling section squeeze roller elevation is adjusted by adding shims to compensate for the change in the plate feed line elevation after the acid tank deformation, ensuring that the plate feed line height of the unit remains constant. Step 7: The acid solution large and small circulation temperatures are adjusted and optimized according to the actual pickling quality. By optimizing the pickling large and small circulation temperature settings, the large circulation temperature is adjusted to 70~75℃ and the small circulation temperature is reduced to 40~45℃.

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