Method for digitally controlling surface parameters of floating-coating-free cold-rolled automobile steel plate

Abstract

The invention relates to the technical field of cold-rolled strip steel surfaces, in particular to a method for digitally controlling surface parameters of a floating-coating-free cold-rolled automobile steel plate, which comprises the steps of hot-rolled steel plate surface control, cold rolling process surface control and annealing leveling process surface control. The method has the beneficial effects that the technological parameters such as the surface parameters of a cold rolling roller, a chilled plate and a finishing roller are finely designed in a full-flow mode based on the surface appearance of the strip steel, and the surface parameters of the cold rolling roller, the chilled plate and the finishing roller are effectively controlled; effective control over surface parameters can be completed without other auxiliary equipment and large-scale transformation, comprehensive control over the surface parameters Ra, RPc and Wa of the hot-rolled strip steel is achieved, the higher strip steel surface parameter requirement is met, the method can be directly applied to an industrial production line, the production process is simplified, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of cold-rolled strip steel surfaces, and particularly to a method for digitally controlling the surface parameters of cold-rolled automotive steel sheets for use without intermediate coating. Background Art

[0002] The traditional painting system process in the automotive industry is called the three-coat two-bake (3C2B) system. After several years of evolution and development, the painting system process uses direct spraying of metallic basecoat and clearcoat, and the intermediate coat drying process is cancelled, so it is called the 3CIB process; the current latest process is the two-coat painting process of 2C1B (i.e., the technology without intermediate coating). 2C refers to the process of spraying the basecoat and the process of spraying the clearcoat, and 1B refers to the process of drying the basecoat and the clearcoat together. By cancelling the intermediate coat, the mechanical properties, weather resistance and surface decoration properties of the primer and the topcoat can be improved, achieving the functions of the three-coat painting process. Compared with the previous painting processes, the current process significantly reduces equipment investment, enhances energy conservation and emission reduction, reduces the process usage area and production operation costs, representing the most advanced technical development direction of automotive painting in the world today. At present, it has been widely adopted by major vehicle manufacturers. However, with the improvement of the new generation of automotive painting requirements, higher requirements are put forward for the control of the surface parameters of automotive steel sheets for use without intermediate coating, that is, while ensuring a relatively small change in Ra on the strip steel surface, improving RPc and reducing related parameters such as Wa to improve the painting quality.

[0003] At present, the requirements of downstream users of cold-rolled automotive steel sheets for surface parameters in the procurement technical agreement are mainly reflected in Ra. At the same time, the control of the surface parameters of rolls and strip steel during the production of cold-rolled automotive steel sheets by large domestic tandem cold rolling and pickling units also focuses on Ra, and less research has been done on the control of RPc and Wa. It is relatively difficult to achieve full-process surface parameter control in the cold rolling and annealing processes, and multi-faceted control and refined design are required for the surface parameters of cold rolling rolls, the cold rolling transfer process, the surface parameters of cold rolled sheets, the surface parameters of skin pass rolls and the skin pass transfer process. Therefore, designing a method for digitally controlling the surface parameters of cold-rolled automotive steel sheets for use without intermediate coating is of great significance for the automotive steel products to adapt to the technological upgrading of downstream users.

[0004] Patent Publication No. CN116694884A, "A Method for Controlling the Surface Quality of Thin-Specification Heat-Treated Steel Plates", discloses controlling the conveying speed of the steel plate and the shot peening parameters of the shot peening machine according to the measured thickness; after the steel plate is shot peened, the steel plate is controlled to continuously enter the quenching section and the tempering section in sequence to obtain the steel plate with surface quality controlled; this invention realizes the full-process automatic control of producing thin-specification heat-treated steel plates with high surface quality and realizes the regulation of the oxide layer depth of the steel plate surface quality. However, it does not involve the control of the surface roughness and surface waviness of the steel plate, and cannot meet the surface quality requirements of downstream products. The control of the steel plate surface quality relies on the shot peening machine equipment for on-line continuous production. For other production lines, shot peening transformation is required, which has little significance for improving the strip surface quality of the actual production line. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a method for digitally controlling the surface parameters of cold-rolled automotive steel plates for primerless painting. By finely controlling the surface topography of the hot-rolled steel plate throughout the process and digitally controlling the surface parameters in the cold rolling process and the annealing and skin pass processes, the effective control of the surface parameters of the hot-rolled strip is completed, thereby realizing the comprehensive control of the surface parameters Ra, RPc, and Wa of the hot-rolled strip to meet higher requirements for strip surface parameters.

[0006] To achieve the above object, the present invention is realized by adopting the following technical solutions:

[0007] A method for digitally controlling the surface parameters of cold-rolled automotive steel plates for primerless painting, including the surface control of the hot-rolled steel plate, the surface control of the cold rolling process, and the surface control of the annealing and skin pass processes. This method completes the effective control of the surface parameters of the hot-rolled strip through the full-process fine control of the surface topography of the hot-rolled steel plate and the digital control of the surface parameters in the cold rolling process and the annealing and skin pass processes. The method for digitally controlling the surface parameters of cold-rolled automotive steel plates for primerless painting specifically includes the following steps:

[0008] S1. Surface control of the hot-rolled steel plate:

[0009] Fine control the camber and flatness of the hot-rolled steel plate;

[0010] S2. Surface control of the cold rolling process:

[0011] Automatically adjust the rolling tension between each stand according to the reduction rate of each stand and the target roughness, including the following steps:

[0012] 1) Set the target surface roughness Ra t , that is, initialize the tension parameters of the cold rolling process;

[0013] 2) By measuring the surface roughness Ra s5 at the outlet of the five stands, calculate the target roughness Ra t and the actual roughness Ras5 The error e;

[0014] 3) According to the PID control algorithm, calculate the adjustment amount ΔT of the tension; as shown in the calculation formula of the PID control algorithm:

[0015]

[0016] Where K p , K i , K d are the proportional, integral and differential coefficients respectively, and t is the time factor;

[0017] 4) According to the calculated tension adjustment amount ΔT, first verify the ratio of the adjusted tension T i to the strip steel specification, that is, whether the unit tension is ≥5 MN / m. If the unit tension meets the requirements, transmit ΔT to the primary control system to automatically adjust the tension parameters during the cold rolling process. If the unit tension does not meet the requirements, calculate the value of ΔT with the unit tension = 5 MN / m and transmit it to the primary control system;

[0018] 5) Repeat steps 2) to 4) until e ≤ 0.1 or the unit tension remains unchanged at 5 MN / m;

[0019] S3. Surface control in the annealing and skin pass process:

[0020] The Ra of the skin pass work roll is 1.7 ± 0.2 μm, RPc ≥ 100, Wa ≤ 0.5 μm; the wet skin pass and constant elongation control mode are adopted during the skin pass process, and the elongation is controlled at 0.5% and above.

[0021] Furthermore, the refined control of the surface convexity of the hot-rolled steel plate in step S1 is as follows: when the thickness of the hot-rolled steel plate ≤ 3 mm, the convexity is less than 0.045 for a width ≤ 1000 mm; the convexity is less than 0.040 for a width of 1000 - 1200 mm; the convexity is less than 0.035 for a width > 1200 mm; when the thickness of the hot-rolled steel plate is 3.0 - 4.0 mm, the convexity is less than 0.040 for a width ≤ 1000 mm; the convexity is less than 0.035 for a width of 1000 - 1200; the convexity is less than 0.030 for a width > 1200 mm; when the thickness of the hot-rolled steel plate is 4.0 - 6.0 mm, the convexity is less than 0.040 for a width ≤ 1000 mm; the convexity is less than 0.030 for a width of 1000 - 1200 mm; the convexity is less than 0.030 for a width > 1200 mm.

[0022] Furthermore, the refined control of the surface flatness of the hot-rolled steel plate in step S1 is that the flatness of the hot-rolled steel plate with a width <

[0023] 1000 mm is 3; the flatness of the hot-rolled steel plate with a width ≥ 1000 mm is 5.

[0024] Furthermore, in the hot-rolled steel sheet in step S1, at least two sets of descaling water are turned on at the rough rolling and finishing rolling inlets, and the descaling water pressure ≥ 18 MPa.

[0025] Furthermore, after cold rolling in step S2, the finished strip steel has Ra of 0.6 - 1.0 μm, RPc ≥ 40, and Wa ≤ 0.45 μm.

[0026] Furthermore, in step S2, cold rolling is carried out by method C, 5 stands adopt constant rolling force control, and the unit rolling force is controlled above 5 MN / m; the shape adjustment of the cold hard plate is controlled in the direction of micro-edge waves, and the average shape value ≤ 5I; to ensure the surface lubrication and transfer state of the strip steel during the rolling process, the surface parameter requirements of the cold rolling work rolls are as follows: the Ra of the 1#, 2#, and 3# work rolls is 0.6 - 0.8 μm, the Ra of the 4# work roll is 0.4 - 0.6 μm; the 5# work roll is treated by EDT texturing plus SF superfinishing, with Ra of 3.75 - 4.25 μm, RPc ≥ 60, and Wa ≤ 0.5 μm.

[0027] Furthermore, after annealing and skin pass in step S3, the finished cold-rolled strip steel has Ra of 0.8 - 1.2 μm, RPc ≥ 70, and Wa ≤ 0.4 μm.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The surface parameter control scheme described in the present invention is different from the previous preparation methods of high-surface-grade steel sheets. Through the mechanism analysis of the cold rolling transfer process and the skin pass transfer process, based on the full-process refined design of the strip steel surface topography, process parameters such as the surface parameters of cold rolling rolls, cold hard plates, and skin pass rolls are designed, and the effective control of surface parameters can be completed without other auxiliary equipment and a large number of modifications, realizing the comprehensive control of the surface parameters Ra, RPc, and Wa of hot-rolled strip steel to meet higher strip steel surface parameter requirements.

[0030] (2) The automotive steel sheet for direct topcoat-free use obtained by the process described in the present invention meets the usage requirements of the downstream users' direct topcoat-free process. The proposed full-process surface topography refined design concept and specific process parameter requirements can be directly applied to industrial production lines, achieving the simplification of the production process and the reduction of production costs. Specific Embodiments

[0031] The following further describes the specific embodiments of the present invention:

[0032] A method for digitally controlling the surface parameters of cold-rolled automotive steel sheets for direct topcoat-free use specifically includes the following steps:

[0033] S1. Surface control of hot-rolled steel sheets:

[0034] During hot rolling, at least two sets of descaling water are turned on at the rough rolling and finish rolling inlets. When the descaling water pressure ≥ 18 MPa, there shall be no pitting, uneven surface, scratches, roll marks and other defects that affect the painting process on the surface of the hot-rolled plate, and there shall be no inclusions with peeling, scabs, folds and other defects that affect the stamping use of the automobile OEM; at the same time, to ensure the stability of cold rolling (the fluctuations of rolling parameters are not conducive to the control of plate shape and waviness) and the surface quality of the rolled product, the convexity and flatness of the hot-rolled steel plate are finely controlled;

[0035] The convexity requirements of hot-rolled strip are shown in Table 1.

[0036] Table 1 Convexity requirements of hot-rolled strip

[0037]

[0038] The flatness requirements of hot-rolled strip are shown in Table 2.

[0039] Table 2 Flatness requirements of hot-rolled strip

[0040] Width (mm) Flatness I ＜1000 3 ≥1000～＜1250 5 ≥1250～＜1600 5 ≥1600 5

[0041] S2. Surface control in cold rolling process:

[0042] The cold tandem rolling adopts C method for rolling, and the 5 stands adopt constant rolling force control, with the unit rolling force controlled above 5 MN / m; the shape adjustment of the cold hard plate is controlled in the direction of micro-edge wave, and the average shape value ≤ 5I; to ensure the surface lubrication and transfer state of the strip during the rolling process, the surface parameters requirements of the cold rolling work rolls are: the Ra of the 1#, 2#, and 3# work rolls is 0.6 - 0.8 μm, the Ra of the 4# work roll is 0.4 - 0.6 μm; the 5# work roll adopts EDT texturing plus SF superfinishing treatment, with Ra of 3.75 - 4.25 μm, RPc ≥ 60, and Wa ≤ 0.5 μm; according to the analysis of the transfer mechanism of the surface parameters in the cold rolling process, the surface topography of the strip after being rolled by the 1 - 4 stand work rolls is mainly transferred from the surface streaks of the ground rolls. The transfer rate of the 1st and 2nd work rolls to the strip surface is relatively large, and the transfer rate of the 3rd and 4th work rolls is continuously decreasing. Excessive surface roughness of the roll affects the rolling parameters and the strip surface by affecting the critical lubrication state of the rolling oil, while too low roll roughness affects the tension and strip slippage. Therefore, on the premise of ensuring the rolling stability, the Ra of the 1#, 2#, and 3# work rolls is designed to be 0.6 - 0.8 μm, and the Ra of the 4# work roll is designed to be 0.4 - 0.6 μm. The strip surface is rolled by the textured 5# work roll, and the transferred texture pit topography is the main factor determining the RPc and Wa of the strip surface after rolling. Therefore, the 5# work roll is designed to adopt EDT texturing plus SF superfinishing treatment, with Ra of 3.75 - 4.25 μm, RPc ≥ 60, and Wa ≤ 0.5 μm;

[0043] Automatically adjust the rolling tension of each rack component according to the reduction rate of each rack and the target roughness, including the following steps:

[0044] 1) Set the target surface roughness Ra t = 0.8μm, and initialize the tension parameters of the cold rolling process.

[0045] 2) By measuring the surface roughness Ra at the exit of the five-stand mill s5 , calculate the error e between the target roughness Ra t and the actual roughness Ra s5 .

[0046] 3) According to the PID control algorithm, calculate the tension adjustment amount ΔT; the calculation formula of the PID control algorithm is shown as follows:

[0047]

[0048] where K p , K i , K d are the proportional, integral, and differential coefficients respectively, and t is the time factor;

[0049] 4) According to the calculated tension adjustment amount ΔT, first verify the ratio of the adjusted tension T i to the strip specification, that is, whether the unit tension is ≥ 5 MN / m. If the unit tension meets the requirements, transmit ΔT to the first-level control system to automatically adjust the tension parameters during the cold rolling process. If the unit tension does not meet the requirements, calculate the value of ΔT with the unit tension = 5 MN / m and transmit it to the first-level control system;

[0050] 5) Repeat steps 2) to 4) until e ≤ 0.1 or the unit tension remains unchanged at 5 MN / m;

[0051] S3. Surface control in the annealing and skin pass process:

[0052] The Ra of the skin pass work roll is 1.7 ± 0.2 um, RPc ≥ 100, Wa ≤ 0.5μm; the skin pass process adopts wet skin pass and constant elongation control mode, and the elongation is controlled at 0.5% and above; the surface quality of the steel plate has a certain impact on the surface quality after electrophoresis. Due to the gravity or evaporation of the paint film, the microscopic unevenness of the substrate surface will be reflected on the paint film surface, that is, the Ra after electrophoresis will increase with the increase of the Ra of the steel plate. Therefore, designing a more strict Ra control standard for the steel plate will obtain automotive outer panels with better surface quality. In addition, compared with ordinary automotive outer panels, the RPc and Wa of the dedicated steel plate without intermediate coating are related to the short-wave (SW) value and distinctness of image (DOI) after automotive color clearcoat painting. Increasing the RPc of the steel plate and reducing the Wa of the steel plate can effectively reduce the short-wave value after painting, improve the distinctness of image (DOI) after painting, and can effectively control the generation of steel plate waves.

[0053] Furthermore, after cold rolling in step S2, the finished strip steel has Ra of 0.6 - 1.0 μm, RPc ≥ 40, and Wa ≤ 0.45 μm.

[0054] Furthermore, after annealing and skin - pass rolling in step S3, the finished cold - rolled strip steel has Ra of 0.8 - 1.2 μm, RPc ≥ 70, and Wa ≤ 0.4 μm.

[0055] The following are examples of the present invention. These examples only describe the best implementation mode of the present invention, but do not limit the scope of the present invention in any way.

[0056] The steel chemical compositions of Examples 1 - 8 are shown in Table 3:

[0057] Table 3 Chemical compositions of the steel plates in the examples:

[0058]

[0059] The surface conditions of the strip steel after hot - rolling in Examples 1 - 8 are shown in Table 4:

[0060] Table 4 Hot - rolling surface conditions of the steel plates in Examples 1 - 8:

[0061]

[0062] The parameters of the cold - rolling work rolls corresponding to the steel plates in Examples 1 - 8 are shown in Table 5.

[0063] Table 5 Parameters of the cold - rolling work rolls in Examples 1 - 8:

[0064]

[0065] The surface parameters after cold - rolling of the steel plates in Examples 1 - 8 are shown in Table 6.

[0066] Table 6 Surface parameters after cold - rolling of the steel plates in Examples 1 - 8:

[0067]

[0068]

[0069] The surface parameters of the skin - pass rolls and the finished products corresponding to the steel plates in Examples 1 - 8 are shown in Table 7.

[0070] Table 7 Surface parameters of the skin - pass rolls and the finished products in Examples 1 - 8:

[0071]

[0072] As can be seen from the above examples, by using the surface parameter control method of the present invention, the surface quality of the automotive steel plates for skip - primer is good, and the surface parameters meet the production requirements of downstream enterprises.

[0073] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and concept of the present invention, making equivalent replacements or changes should be covered within the protection scope of the present invention.

Claims

1. A method for controlling the surface parameters of cold-rolled automotive steel sheets without intermediate coating by digital control, including surface control of hot-rolled steel sheets, surface control in the cold-rolling process, and surface control in the annealing and tempering process, characterized in that, This method realizes the effective control of the surface parameters of hot-rolled strip steel through the whole-process refined control of the surface topography of hot-rolled steel sheets and the digital control of the surface parameters in the cold rolling process and the annealing and skin pass rolling process. The method for digitally controlling the surface parameters of cold-rolled automotive steel sheets without intermediate coating specifically includes the following steps: S1. Surface control of hot-rolled steel sheets: Refined control of the camber and flatness of hot-rolled steel sheets; S2. Surface control in the cold rolling process: Automatically adjust the rolling tension between each stand according to the reduction rate of each stand and the target roughness, including the following steps: 1) Set the target surface roughness Ra t , that is, initialize the tension parameters of the cold rolling process; 2) By measuring the surface roughness Ra at the outlet of the five-stand mill s5 , calculate the target roughness Ra t and the error e between the actual roughness Ra s5 ; 3) Calculate the adjustment amount ΔT of the tension according to the PID control algorithm; the calculation formula of the PID control algorithm is as follows: where K p , K i , K d are the proportional, integral and derivative coefficients respectively, and t is the time factor; 4) According to the calculated tension adjustment amount ΔT, first verify the adjusted tension T i and the ratio to the strip steel specification, that is, whether the unit tension is ≥ 5 MN / m. If the unit tension meets the requirements, transmit ΔT to the first-level control system to automatically adjust the tension parameters during the cold rolling process. If the unit tension does not meet the requirements, calculate the value of ΔT with the unit tension = 5 MN / m and transmit it to the first-level control system; 5) Repeat steps 2) to 4) until e ≤ 0.1 or the unit tension remains unchanged at 5 MN / m; S3. Surface control in the annealing and skin pass rolling process: The Ra of the skin pass work roll is 1.7 ± 0.2 μm, RPc ≥ 100, Wa ≤ 0.5 μm; the skin pass process adopts wet skin pass and constant elongation control mode, and the elongation is controlled at 0.5% and above.

2. A method for surface parameters of cold-rolled automotive steel sheets without intermediate coating using digital control according to claim 1, characterized in that, The refined control of the surface camber of the hot-rolled steel sheet in step S1 is that when the thickness of the hot-rolled steel sheet ≤ 3 mm, the camber is less than 0.045 for a width ≤ 1000 mm; the camber is less than 0.040 for a width of 1000 - 1200 mm; the camber is less than 0.035 for a width > 1200 mm; when the thickness of the hot-rolled steel sheet is 3.0 - 4.0 mm, the camber is less than 0.040 for a width ≤ 1000 mm; the camber is less than 0.035 for a width of 1000 - 1200; the camber is less than 0.030 for a width > 1200 mm; when the thickness of the hot-rolled steel sheet is 4.0 - 6.0 mm, the camber is less than 0.040 for a width ≤ 1000 mm; the camber is less than 0.030 for a width of 1000 - 1200 mm; the camber is less than 0.030 for a width > 1200 mm.

3. A method for the surface parameters of cold-rolled automotive steel sheets for digital control without intermediate coating according to claim 1, characterized in that, The refined control of the surface flatness of the hot-rolled steel sheet in step S1 is that the flatness of the hot-rolled steel sheet with a width < 1000 mm is 3; the flatness of the hot-rolled steel sheet with a width ≥ 1000 mm is 5.

4. A method for surface parameters of cold-rolled automotive steel plates for digital control without intermediate coating according to claim 1, characterized in that, In step S1, at least two sets of descaling water are turned on at the entrance of rough rolling and finish rolling of the hot-rolled steel sheet, and the descaling water pressure ≥ 18 MPa.

5. A method for the surface parameters of cold-rolled automotive steel sheets for digital control without intermediate coating according to claim 1, characterized in that, The Ra of the cold-rolled finished strip steel after step S2 is 0.6 - 1.0 μm, RPc ≥ 40, Wa ≤ 0.45 μm.

6. A method for the surface parameters of cold-rolled automotive steel sheets without intermediate coating using digital control according to claim 1, characterized in that, In step S2, cold rolling is carried out by the C method, and the 5 stands adopt constant rolling force control, and the unit rolling force is controlled above 5 MN / m; the shape adjustment of the cold hard plate is controlled in the direction of micro-edge wave, and the average shape value ≤ 5I; to ensure the surface lubrication and transfer state of the strip steel during the rolling process, the surface parameter requirements of the cold rolling work roll are as follows: the Ra of the 1#, 2#, and 3# work rolls is 0.6 - 0.8 μm, the Ra of the 4# work roll is 0.4 - 0.6 μm; the 5# work roll is treated with EDT texturing plus SF superfinishing, and the Ra is 3.75 - 4.25 μm, RPc ≥ 60, Wa ≤ 0.5 μm.

7. A method for surface parameters of cold-rolled automotive steel sheets without intermediate coating using digital control according to claim 1, characterized in that, The Ra of the cold-rolled strip steel finished product after step S3 of annealing and skin pass rolling is 0.8 - 1.2 μm, RPc ≥ 70, Wa ≤ 0.4 μm.

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