Analysis and control method of black spot defects on hot galvanized strip surface

Abstract

The embodiment of the application provides a hot galvanizing strip surface black spot defect analysis and control method, relates to the hot galvanizing strip production technical field, and the method comprises the following steps: performing energy spectrum analysis, roughness analysis and morphology analysis on the black spot defect position and normal position of the strip surface, and confirming the generation reason of the black spot defect; based on the generation reason of the black spot defect, the rolling process of the strip is adjusted. The technical scheme of the application can quickly and accurately determine the reason for the generation of the black spot defect on the surface of the strip through energy spectrum analysis and three-dimensional morphology analysis of the strip; and then based on the reason for the generation of the black spot defect, the rolling process parameters of the strip are optimized, the problem of the black spot defect on the surface of the strip is effectively solved, and the product quality is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot-dip galvanized strip production, in particular to a method for analyzing and controlling black spot defects on the surface of hot-dip galvanized strip. BACKGROUND

[0002] Hot-dip galvanized strip has excellent processability, corrosion resistance and aesthetic appearance, and is widely used in the fields of national life such as automobiles, household appliances and buildings.

[0003] Due to the extremely strict requirements of downstream customers on the surface quality of hot-dip galvanized strip, any surface quality defect that affects use and appearance is not allowed. The product structure of a certain high-strength hot-dip galvanizing production line is mainly high-strength hot-dip galvanized cold forming strip, and also includes a part of ordinary hot-dip galvanized strip. During the finishing rolling process from high-strength steel to ordinary strip, dense black spot defects appear on the surface of the ordinary strip, covering the upper and lower surfaces of the strip, which seriously affects the quality of the product and customer delivery.

[0004] The production line can only meet the surface quality requirements of the product by frequent roll replacement, resulting in a decrease in the production capacity of the unit and an increase in the cost of roll consumption. Therefore, there is an urgent need for a method for analyzing and controlling black spot defects on the surface of hot-dip galvanized strip to meet the production needs of customers in batches. SUMMARY

[0005] The embodiments of the present application provide a method for analyzing and controlling black spot defects on the surface of hot-dip galvanized strip. The causes of the black spot defects on the surface of hot-dip galvanized strip are determined through energy spectrum analysis and three-dimensional morphology analysis, and the black spots on the surface of hot-dip galvanized strip are avoided by optimizing the rolling process parameters, thereby improving the product quality.

[0006] Other characteristics and advantages of the present application will become apparent from the following detailed description, or will be learned by practice of the present application.

[0007] According to a first aspect of the embodiments of the present application, a method for analyzing and controlling black spot defects on the surface of hot-dip galvanized strip is provided, comprising:

[0008] Performing energy spectrum analysis, roughness analysis and morphology analysis on the positions of black spot defects and normal positions on the surface of the strip to confirm the causes of the black spot defects;

[0009] Based on the causes of the black spot defects, adjusting the rolling process of the strip, comprising:

[0010] Optimizing the roughening process of the finishing mill roll;

[0011] Adjusting the rolling force of the finishing mill;

[0012] Adjusting the conductivity of the finishing liquid and the drying temperature at the post-pulling straightening machine of the finishing mill;

[0013] Adjust the elongation of the bending unit of the tension leveller unit and the elongation of the straightening unit of the tension leveller unit.

[0014] Optimize the passivation process parameters to improve the thickness of the passivation film on the surface of the strip.

[0015] In some embodiments of the present application, based on the foregoing scheme, energy spectrum analysis is performed on the black spot defect position and the normal position on the surface of the strip, including:

[0016] Detecting the element information of the black spot defect position and the element information of the normal position;

[0017] Comparing the element information between the two positions to confirm the element difference between the two positions.

[0018] In some embodiments of the present application, based on the foregoing scheme, topography analysis is performed on the black spot defect position and the normal position on the surface of the strip, including:

[0019] Using a three-dimensional topography instrument to detect the peak height and peak density of the black spot defect position and the normal position;

[0020] Comparing the peak height and peak density between the two positions to confirm the difference between the peak height and peak density of the black spot defect position and the peak height and peak density of the normal position.

[0021] In some embodiments of the present application, based on the foregoing scheme, the optimization of the roughening process of the skin pass mill roll includes:

[0022] Reducing the roughness of the work roll of the skin pass mill;

[0023] Reducing the roughening current of the work roll while extending the current time;

[0024] After the roughening of the roll, using a super-fine grinding process to eliminate local peak points on the surface of the roll.

[0025] In some embodiments of the present application, based on the foregoing scheme, the adjustment of the rolling force of the skin pass mill includes:

[0026] Controlling the skin pass rolling force to be 2500-4500 kn.

[0027] In some embodiments of the present application, based on the foregoing scheme, the adjustment of the conductivity of the skin pass liquid and the drying temperature at the rear of the skin pass mill includes:

[0028] Controlling the conductivity of the skin pass liquid to be 350-450 us / cm;

[0029] Controlling the drying temperature at the rear of the skin pass mill to be 60-70°C.

[0030] In some embodiments of the present application, based on the foregoing scheme, adjusting the elongation of the bending unit of the tension leveller set comprises:

[0031] setting the elongation of the bending unit of the tension leveller set to 0.

[0032] In some embodiments of the present application, based on the foregoing scheme, adjusting the elongation of the straightening unit of the tension leveller set comprises:

[0033] setting the elongation of the straightening unit of the tension leveller set to 0.05-0.1%.

[0034] In some embodiments of the present application, based on the foregoing scheme, the optimization of the passivation process parameters comprises:

[0035] controlling the speed of the coating roller at 80-150 m / min;

[0036] controlling the inter-roller pressure at 2.5-4 KN;

[0037] controlling the speed ratio of the coating roller and the strip steel at 100-110%;

[0038] controlling the speed ratio of the pickup roller and the strip steel at 70-80%;

[0039] controlling the strip steel drying temperature at 120-150℃;

[0040] controlling the chromic acid point at 60-70.

[0041] In some embodiments of the present application, based on the foregoing scheme, the strip steel grade is DX51D, DX52D or DX53D.

[0042] The technical scheme of the present application can quickly and accurately determine the cause of the black spot defects on the surface of the strip steel through energy spectrum analysis and three-dimensional topography analysis; and then based on the cause of the black spot defects, the rolling process parameters of the strip steel are optimized, effectively solving the problem of black spot defects on the surface of the strip steel and improving the product quality.

[0043] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0044] The drawings herein are incorporated into the specification and form part of the specification, showing embodiments consistent with the present application, and together with the specification, serve to explain the principles of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings from these drawings without creative labor. In the drawings:

[0045] Figure 1 Fig. 1 shows a flowchart of a method for analyzing and controlling black spot defects on a hot-dip galvanized steel strip according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] Example implementations are now described with reference to the drawings; however, these implementations are merely examples for illustrating aspects of the present application, and should not be construed as being limiting in any way. Although example implementations can be described in sufficient detail to enable those having ordinary skill in the art to practice the implementations, other implementations can be employed, as can be readily appreciated by one of ordinary skill in the art, as such variations are deemed to be within the scope of the present application. Thus, the present application should not be construed as being limited to the examples described in the following detailed description.

[0047] Furthermore, described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the application. One skilled in the relevant art will recognize, however, that the

[0048] The flowcharts shown in the drawings are merely illustrative, and do not necessarily include all contents and operations / steps, nor are they necessarily executed in the order described. For example, some operations / steps can be further broken down, and some operations / steps can be combined or partially combined, so the actual execution order can be changed according to actual conditions.

[0049] In order to make the objects, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by one of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0050] Some embodiments of the present application will be described in detail below with reference to the drawings. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0051] Referring to Figure 1 Fig. 1 shows a flowchart of a method for analyzing and controlling black spot defects on a hot-dip galvanized steel strip according to an embodiment of the present application.

[0052] As Figure 1As shown, a hot galvanized steel surface black spot defect analysis and control method is shown, first, through the defect position and normal position energy spectrum analysis and three-dimensional morphology analysis, determine the cause of the hot galvanized steel surface black spot defect; again through the improvement of the light straightening machine after the drying temperature, adjust the roughness of the light straightening machine work roll, optimize the roughening process parameters, increase the thickness of the passivation film on the surface of the strip and the passivation process, reduce the severity and intensity of the hot galvanized steel surface black spot defect, improve the product quality; specifically, the method comprises steps S100 to S200.

[0053] Step S100, the black spot defect position and normal position of the strip surface are analyzed by energy spectrum analysis, roughness analysis and morphology analysis, and the cause of the black spot defect is confirmed.

[0054] It can be understood that the energy spectrum analysis can determine the element information of the black spot defect position and the normal position, based on the element information, whether some normal elements are missing in the black spot defect position compared with the normal position can be determined, and then the cause of the defect is found out; roughness analysis can determine the roughness of the black spot defect position and the normal position; morphology analysis can determine the peak height and density of the black spot defect position and the normal position, and the cause of the black spot defect is further confirmed according to the difference of the morphology.

[0055] In some possible embodiments, the black spot defect position and normal position of the strip surface are analyzed by energy spectrum analysis, specifically including:

[0056] The element information of the black spot defect position and the element information of the normal position are detected;

[0057] The element information between the two positions is compared, and the element difference between the two positions is confirmed.

[0058] Exemplarily, the black spot defect position and the normal position are analyzed by energy spectrum analysis, and it is detected that the normal position exists phosphorus and chromium elements, while the black spot defect position does not detect phosphorus and chromium elements. Since phosphorus and chromium elements are typical elements of passivation liquid, it is judged that the defect position does not exist passivation film, which leads to oxidation phenomenon at the defect position and causes surface black spot problem. In addition, chlorine element is detected at the defect position, since chlorine element mainly comes from the desalination water of the finishing liquid, the existence of water on the surface of the strip without drying further aggravates the oxidation of the defect position.

[0059] In some possible embodiments, the black spot defect position and normal position of the strip surface are analyzed by roughness analysis through a roughness meter. The analysis result shows that the roughness of the black spot defect position is higher than that of the normal position.

[0060] In some possible embodiments, the black spot defect position and normal position of the strip surface are analyzed by morphology analysis, including:

[0061] Detecting the peak height and the peak density of the black spot defect position and the normal position by using the three-dimensional profiler;

[0062] Comparing the peak height and the peak density between the two positions, confirming the difference between the peak height and the peak density of the black spot defect position and the peak height and the peak density of the normal position.

[0063] For example, by analyzing the black spot defect position and the normal position by using the three-dimensional profiler, the peak height of the black spot defect position is higher than the peak height of the normal position; therefore, it is determined that the excessive peak height and the low peak density of the surface of the strip steel cause the damage of the passivation film (the thickness is generally about 1 um) at the local position, thereby causing the oxidation black spot problem on the surface of the strip steel.

[0064] According to the energy spectrum analysis, the roughness analysis and the topography analysis of the black spot defect position and the normal position, it is confirmed that the reason for the black spot defect of the strip steel is that there is no passivation film or the passivation film is damaged at the black spot defect position, thereby causing the oxidation of the strip steel.

[0065] With reference to Figure 1 , at step S200, based on the cause of the black spot defect, the rolling process of the strip steel is adjusted, including: optimizing the roughening process of the finishing mill roll; adjusting the rolling force of the finishing mill; adjusting the conductivity of the finishing liquid and the drying temperature at the post-finishing mill stretch-straightening mill; adjusting the elongation of the bending unit of the stretch-straightening mill unit and the elongation of the straightening unit of the stretch-straightening mill unit; optimizing the passivation process parameters to improve the thickness of the passivation film on the surface of the strip steel.

[0066] It can be understood that, after knowing that the cause of the black spot defect is that there is no passivation film or the passivation film is damaged at the black spot defect position, some parameters of the strip steel in the rolling process are adjusted to ensure the integrity of the passivation film on the surface of the strip steel.

[0067] In some possible embodiments, the roughening process of the finishing mill roll is optimized, including:

[0068] reducing the roughness of the work roll of the finishing mill;

[0069] reducing the roughening current of the work roll while prolonging the current time;

[0070] adopting the super-fine grinding process after the roughening of the roll to eliminate the local peak high points on the surface of the roll.

[0071] For example, the roughness of the work roll of the finishing mill is reduced from 6.0 um to 4.5 um, the mode of “small current + long current time” is adopted to improve the uniformity of the roughness of the surface of the roll, and the super-fine grinding process is adopted after the roughening of the roll to eliminate the local peak high points on the surface of the roll. The roughening process parameters of the work roll of the finishing mill are specifically shown in Table 1.

[0072] Table 1 finishing mill work roll roughening process parameters

[0073] Texturing process Target roughness / um Texturing current / A On-time / us Superfinishing pressure / Mpa Old pattern 4.5 3.2-3.4 8.0-9.6 --- New pattern 4.5 2.6-2.8 14.8-16.0 0.6-0.8

[0074] In some possible embodiments, the strip steel grade is DX51D, DX52D, DX53D, etc., the thickness is 0.7-1.0mm, the width is 1200-1450mm, the finishing elongation is 0.9-1.1%, and the coating thickness is 80-160g / m 2 .

[0075] In some possible embodiments, the adjusting the rolling force of the finishing mill comprises:

[0076] controlling the finishing rolling force at 2500-4500kn.

[0077] It can be understood that controlling the finishing rolling force at 2500-4500kn can ensure that the strip steel surface roughness is 0.8-1.1um, and is as small as possible compared to the passivation film thickness of the strip steel surface, so as to meet the roughness standard of 0.8-1.5um of the hot galvanized finished strip steel.

[0078] In some possible embodiments, the adjusting the conductivity of the finishing liquid and the drying temperature at the post-finishing mill stretcher leveler comprises:

[0079] controlling the conductivity of the finishing liquid at 350-450us / cm;

[0080] controlling the drying temperature at the post-finishing mill stretcher leveler at 60-70℃.

[0081] It can be understood that controlling the conductivity of the finishing liquid at 350-450us / cm and the drying temperature at the post-finishing mill stretcher leveler at 60-70℃ can avoid the oxidation phenomenon of the strip steel surface due to water.

[0082] In some possible embodiments, the adjusting the elongation of the bending unit of the stretcher leveler unit and the elongation of the straightening unit of the stretcher leveler unit comprises:

[0083] setting the elongation of the bending unit of the stretcher leveler unit to 0;

[0084] setting the elongation of the straightening unit of the stretcher leveler unit to 0.05-0.1%.

[0085] It can be understood that setting the elongation of the bending unit of the stretcher leveler unit to 0 can reduce the black spot defects caused by the relative sliding friction between the work roll of the bending unit and the strip steel, and setting the elongation of the straightening unit to 0.05-0.1% can ensure that the strip steel does not have warping problems or poor passivation at the edge.

[0086] In some possible embodiments, the optimizing the passivation process parameters comprises:

[0087] The coating roller speed is controlled at 80-150 m / min;

[0088] The inter-roller pressure is controlled at 2.5-4 KN;

[0089] The speed ratio of the coating roller and the strip steel is controlled at 100-110%;

[0090] The speed ratio of the pickup roller and the strip steel is controlled at 70-80%;

[0091] The strip steel drying temperature is controlled at 120-150℃;

[0092] The chromic acid point is controlled at 60-70.

[0093] It can be understood that the main purpose of optimizing the passivation process parameters is to increase the thickness of the passivation film on the surface of the strip steel, and to prevent the local zinc layer peak on the surface of the strip steel before passivation from damaging the passivation film. The thickness of the passivation film should be controlled at 1.3-1.5 um. The passivation process parameters are shown in Table 2.

[0094] Table 2: Passivation process parameters

[0095]

[0096] The method provided by the embodiments of the present application can quickly and accurately determine the causes of the black spot defects on the surface of the strip steel, and adjust the rolling parameters based on the causes, thereby effectively reducing the severity and density of the black spot defects and improving the product quality.

[0097] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. The specification and examples given herein are not intended to be exhaustive or limiting, and other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. The present application as claimed is intended to cover any and all variations of the present application which are encompassed by the language of the claims and are within the scope of the present application. It is submitted that the present application not be limited to the precise construction and the arrangements of the parts and instrumentalities shown in the drawings and described above, and that various modifications and changes can be made without departing from the scope of the present application. The scope of the present application is limited only by the claims appended hereto.

Claims

1. A method for analyzing and controlling surface black spot defects of hot-dip galvanized steel strips, characterized by, The application relates to a method for eliminating black point defects on a strip steel surface. The method comprises the following steps: carrying out energy spectrum analysis, roughness analysis and morphology analysis on the position of the black point defects and the normal position of the strip steel surface to confirm the causes of the black point defects; adjusting the rolling process of the strip steel based on the causes of the black point defects, including: optimizing the roughing mill roll roughening process; adjusting the rolling force of the roughing mill; adjusting the conductivity of the roughing liquid and the drying temperature of the roughing mill rear tension and straightening mill; adjusting the elongation of the bending unit of the tension and straightening mill unit and the elongation of the straightening unit of the tension and straightening mill unit; optimizing the passivation process parameters and improving the passivation film thickness of the strip steel surface; the adjusting of the conductivity of the roughing liquid and the drying temperature of the roughing mill rear tension and straightening mill comprises: controlling the conductivity of the roughing liquid to be 350-450 us / cm; 2. The method of claim 1, wherein, controlling the drying temperature of the roughing mill rear tension and straightening mill to be 60-70 DEG C. The energy spectrum analysis on the position of the black point defects and the normal position of the strip steel surface comprises: detecting the element information of the position of the black point defects and the element information of the normal position; 3. The method of claim 2, wherein, comparing the element information between the two positions to confirm the element difference between the two positions. The morphology analysis on the position of the black point defects and the normal position of the strip steel surface comprises: detecting the peak height and the peak density of the position of the black point defects and the normal position by using a three-dimensional morphology instrument; 4. The method of claim 1, wherein, comparing the peak height and the peak density between the two positions to confirm the difference between the peak height and the peak density of the position of the black point defects and the peak height and the peak density of the normal position. The optimization of the roughing mill roll roughening process comprises: reducing the roughness of the working roll of the roughing mill; reducing the roughening current of the working roll while prolonging the current time; 5. The method of claim 1, wherein, adopting the super-abrasive process to eliminate the local peak high points on the surface of the roll after the roll roughening. The adjustment of the rolling force of the roughing mill comprises:

6. The method of claim 1, wherein, controlling the rolling force of the roughing mill to be 2500-4500 kn. The adjustment of the elongation of the bending unit of the tension and straightening mill unit comprises:

7. The method of claim 6, wherein, setting the elongation of the bending unit of the tension and straightening mill unit to be 0. The adjustment of the elongation of the straightening unit of the tension and straightening mill unit comprises:

8. The method of claim 1, wherein, setting the elongation of the straightening unit of the tension and straightening mill unit to be 0.05-0.1%. The optimization of the passivation process parameters comprises: controlling the coating roll speed to be 80-150 m / min; controlling the roll pressure to be 2.5-4 KN; controlling the speed ratio of the coating roll and the strip steel to be 100-110%; controlling the speed ratio of the material pickup roll and the strip steel to be 70-80%; controlling the strip steel drying temperature to be 120-150 DEG C; 9. The method of claim 1, wherein, controlling the chromic acid point to be 60-70. The strip steel grade is DX51D, DX52D or DX53D.

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