Electrical steel coating adhesiveness rating method

Abstract

The invention discloses an electrical steel coating adhesiveness rating method. The method comprises the following steps: manufacturing an electrical steel sample coated with an insulating coating; performing a bending test on the sample; collecting a coating adhesiveness image; processing the coating adhesiveness image to obtain white pixel points representing a coating falling area and black pixel points representing a coating non-falling area; calculating a coating falling ratio, and rating the coating adhesiveness of the electrical steel sample. The method has the advantages that visualization and visual analysis technologies are introduced, quantitative data of the adhesiveness of the coating are obtained, the adhesiveness of the coating is graded according to the data, the grading method is objective, the result accuracy is high, and errors and deviations caused by manual visual evaluation are reduced.

Description

Technical Field

[0001] The invention relates to the field of detection technology, and in particular to a method for rating the adhesion of an electrical steel coating. Background Art

[0002] Electrical steel, also known as silicon steel sheet, is an important soft magnetic alloy indispensable to the power, electronics and military industries. It is also the metal functional material with the largest output. It is mainly used as the iron core of various motors, generators and transformers. In the manufacture of electrical steel sheet products, the formation of insulating coating is a process belonging to the final manufacturing process. Usually, electrical steel is coated with an insulating coating on its surface. The adhesion of electrical steel coating reflects the bonding strength between the electrical steel coating and the steel substrate. It is an important indicator of coating performance and is directly related to the insulation performance and life of electrical steel products.

[0003] At present, the national standard (GB / T2522-2017) is usually used to grade the adhesion of electrical steel coatings. The main process of this test method is: use a shearing machine and a punching machine to process the coated electrical steel sample to the specified size, then bend it tightly around the brass cylinder 180°, then straighten the bent sample, visually determine the shedding of the coating on the sample, and give A, B, C, D, E, F grades. The main problems of this test method are: 1. The manual operation is not standard. The sample is bent 180° around the brass cylinder. On the one hand, the sample may not be close to the cylinder, and on the other hand, it may not reach 180° when bent, which affects the test results; 2. The severity and level of coating shedding are defined in language, and there is no quantitative evaluation method: in actual operation, due to the different skill levels and understanding abilities of each operator, inconsistent and unstable judgments may occur, and the reliability of the test results is insufficient; 3. The coating shedding level is divided into levels according to the range, and detailed values ​​cannot be given. The adhesion of the same level of coating cannot be further subdivided, which increases the difficulty of finding the best process parameters on site. In summary, the current mainstream method uses manual bending of the specimen and then qualitative evaluation by naked eye, which results in large fluctuations in measurement results and cannot be accurately evaluated or calculated. Summary of the invention

[0004] The purpose of the present invention is to provide a highly accurate and objective method for evaluating the adhesion of electrical steel coatings in view of the shortcomings of the prior art.

[0005] The technical solution adopted by the present invention is: a method for rating the adhesion of electrical steel coatings, the method comprising:

[0006] S1. Prepare electrical steel samples coated with insulating coatings;

[0007] S2. Perform bending test on electrical steel samples;

[0008] S3, collecting the coating image after the bending test to obtain the original coating adhesion image;

[0009] S4. Rotate, grayscale, crop, and binarize the coating adhesion image to obtain the number of white pixels representing the coating peeling area and the number of black pixels representing the coating non-peeling area:

[0010] S5. Calculate the coating shedding ratio respectively, coating shedding ratio=number of white pixels / (number of black pixels+number of white pixels);

[0011] S6. Rating the coating adhesion of the electrical steel samples based on the coating shedding ratio.

[0012] According to the above scheme, the electrical steel sample is a oriented electrical steel sample or a non-oriented electrical steel sample.

[0013] According to the above scheme, in S2, when the sample is an oriented electrical steel sample, the method for performing the bending test is: placing the oriented electrical steel sample horizontally and pressing both ends; pressing three brass cylinders with diameters of 10 mm, 20 mm, and 30 mm, respectively, side by side and synchronously downward to the surface of the oriented electrical steel sample, so that the oriented electrical steel sample completes a 180° bend in the corresponding three areas where the cylinders are pressed downward; and then pulling the bent 180° oriented electrical steel sample into a horizontal state.

[0014] According to the above scheme, in S2, when the sample is a non-oriented electrical steel sample, the method for performing the bending test is as follows: the non-oriented electrical steel sample is placed horizontally and the two ends are tightened and transported to the top of the tape; then a brass cylinder with a diameter of 10 mm under the tape is pressed from bottom to top to the tape and the surface of the non-oriented electrical steel sample in sequence, so that the tape is tightly attached to the lower surface of the non-oriented electrical steel sample, and the non-oriented electrical steel sample is bent 180° in the top pressing area of ​​the cylinder and maintained for at least 5 seconds; after removing the brass cylinder, the tape tightly attached to the lower surface of the non-oriented electrical steel sample is pulled into a straight state, and the tape falls off from the surface of the non-oriented electrical steel sample under the tension, and the tape image is collected after the non-oriented electrical steel sample is removed.

[0015] According to the above scheme, when the sample is a oriented electrical steel sample, the surface morphology of the oriented electrical steel sample after being bent and then stretched into a straight state is collected as the coating adhesion image.

[0016] According to the above scheme, when the sample is a non-oriented electrical steel sample, the surface morphology of the tape that is released after the non-oriented electrical steel sample is compacted by the tape is collected as the coating adhesion image.

[0017] According to the above scheme, for the oriented electrical steel sample, the coating adhesion image is rotated, grayed, and cropped, and the X, Y, and Z regions corresponding to the brass cylinders with diameters of 10 mm, 20 mm, and 30 mm in the framed image are respectively obtained; the coating shedding ratios in the three regions are calculated, and the coating shedding ratio in the X region is α1 , the coating shedding ratio in the Y graph area is α 2 , the coating shedding ratio in the Z region is α 3 ; The three image areas are rated separately, and the rating levels are divided into six grades: A, B, C, D, E, and F, among which grade A is the best and grade F is the worst; the grading of each image area can include all the above grades, or only include a few of them (for example, the X image area is only divided into grades A, B, C, and D); finally, the coating adhesion rating of the entire electrical steel sample is obtained according to the rating of each image area, and the rating method is:

[0018] In the X region: when α 1 <5.0%, the grade of the X-chart area is A; when 5.0%≤α 1 When <30.0%, the grade of the X-graph area is B; when 30.0%≤α 1 <50.0%, the grade of the X-graph area is C; when α 1 When ≥50.0%, the grade of the X-graph area is D;

[0019] In the Y graph area: when α 2 <1.0%, the grade of the Y graph area is A; when 1.0%≤α 2 When α is less than 20.0%, the grade of the Y graph area is C; 2 When ≥20.0%, the grade of the Y graph area is D;

[0020] In the Z region, when α 3 <1.0%, the grade of the Y graph area is A; when 1.0%≤α 2 When α is less than 10.0%, the grade of the Y graph area is E; 3 When ≥10.0%, the grade of the Y graph area is F;

[0021] When the ratings of the three graphic areas are all A, the coating adhesion rating of the oriented electrical steel sample is A; when the ratings of the three graphic areas are inconsistent, the rating of the lowest-grade graphic area is used as the coating adhesion rating of the oriented electrical steel sample.

[0022] According to the above scheme, for non-oriented electrical steel samples, α is the coating shedding ratio of the non-oriented electrical steel samples, and the rating grades are divided into four grades: A, B, C and D. The specific rating method is:

[0023] When α < 5.0%, the coating adhesion rating of the non-oriented electrical steel sample is A;

[0024] When 5.0%≤α<30.0%, the coating adhesion rating of the non-oriented electrical steel sample is B;

[0025] When 30.0%≤α<50.0%, the coating adhesion rating of the non-oriented electrical steel sample is C;

[0026] When α≥50.0%, the coating adhesion rating of the non-oriented electrical steel sample is D.

[0027] According to the above scheme, in S2, the method of image binarization is: converting the image into pixel values, calculating the dynamic threshold to distinguish the image, setting the pixels above the dynamic threshold as the maximum value, the pixel of the maximum value is white, representing the area where the coating has fallen off; setting the pixels below the dynamic threshold as the minimum value, the pixel of the minimum value is black, representing the area where the coating has not fallen off.

[0028] According to the above scheme, the method for obtaining the dynamic threshold is as follows:

[0029] 1) Calculate the grayscale histogram of the image, and the grayscale value of each pixel is counted into the histogram;

[0030] 2) Calculate the grayscale value and probability of each type of pixel. For each possible threshold T, divide the image into two categories: pixels with grayscale values ​​less than T and pixels with grayscale values ​​greater than or equal to T. Calculate the average grayscale value of the two types of pixels respectively.

[0031] 3) Calculate the inter-class variance, which is the square of the difference between the average grayscale values ​​of the two classes of pixels multiplied by the sum of the probabilities of the two classes of pixels;

[0032] 4) Find the optimal threshold, traverse all possible thresholds and calculate their corresponding inter-class variances. The threshold with the largest inter-class variance is the optimal global threshold, which is also the dynamic threshold required.

[0033] The beneficial effects of the present invention are as follows: the present invention introduces visualization and visual analysis technology, collects coating adhesion images through industrial cameras, binarizes the images, calculates and obtains quantitative data of coating adhesion, and rates the coating adhesion based on the data. This rating method is objective, greatly reduces the errors and deviations caused by manual visual evaluation, and the rating results are highly accurate, which can provide a reference for improving the quality of coating adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an image of a oriented electrical steel sample after bending.

[0035] Figure 2 The images of coating adhesion of oriented electrical steel samples were collected.

[0036] Figure 3 Schematic diagram of image cropping and framing.

[0037] Figure 4 This is a schematic diagram of the image after binarization processing.

[0038] Figure 5 Schematic diagram for determining the dynamic threshold of an image. DETAILED DESCRIPTION

[0039] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0040] like Figure 1 The electrical steel coating adhesion rating method shown is specifically a quantitative rating method for electrical steel coating adhesion, which is:

[0041] S1. Prepare electrical steel samples coated with insulating coatings;

[0042] S2. Perform a bending test on the sample;

[0043] S3, collecting the coating image after the bending test to obtain the original coating adhesion image;

[0044] S4, rotating, graying, clipping, and binarizing the coating adhesion image to obtain the number of white pixels representing the coating peeling area and the number of black pixels representing the coating non-peeling area;

[0045] The binarization method refers to: converting the image into pixel values, calculating the dynamic threshold to distinguish the image, setting the pixels above the dynamic threshold to the maximum value, the pixel with the maximum value is white, representing the coating shedding area; setting the pixels below the dynamic threshold to the minimum value, the pixel with the minimum value is black, representing the coating not shedding area;

[0046] S5. Calculate the coating shedding ratio respectively, coating shedding ratio=number of white pixels / (number of black pixels+number of white pixels);

[0047] S6. Rating the coating adhesion of the electrical steel samples based on the coating shedding ratio.

[0048] The present invention can quantitatively grade the coating adhesion performance by taking oriented electrical steel and non-oriented electrical steel as samples respectively.

[0049] In S1, the oriented electrical steel samples used are 0.10-0.35 mm thick and 7.65 g / cm 3 The w(Si+Al) content of the electrical steel sheet is generally below 6.5%, and the sample size is 320×30mm (length×width). The non-oriented electrical steel sample used has a thickness of 0.10-0.65mm and an agreed density of 7.60-7.85g / cm 3 The electrical steel sheet has a w (Si + Al) content of generally less than 4.5% and a size of 320mm × 30mm (length × width).

[0050] In S2, the bending test of the oriented electrical steel samples is different from that of the non-oriented electrical steel samples.

[0051] When the sample is an oriented electrical steel sample, the first bending device is used to perform a bending test on the oriented electrical steel sample, and the bending method is as follows: the oriented electrical steel sample is placed horizontally and both ends are pressed tightly; three brass cylinders with diameters of 10 mm, 20 mm, and 30 mm are pressed down to the surface of the oriented electrical steel sample side by side and synchronously, so that the oriented electrical steel sample completes a 180° bend in the corresponding three areas where the cylinders are pressed down; and then the bent 180° oriented electrical steel sample is pulled into a horizontal state.

[0052] The first bending device includes a bending mechanism, a pneumatic clamping mechanism, a servo control mechanism and a sample clamping and stretching mechanism. When working, the oriented electrical steel sample is moved to the bending area of ​​the bending mechanism, the pneumatic clamping mechanism clamps the two ends of the horizontal oriented electrical steel sample, and the servo control mechanism synchronously controls three brass cylinders with diameters of 10mm, 20mm and 30mm to press down on the surface of the oriented electrical steel sample to complete the 180° bending; the servo control mechanism controls the three brass cylinders to move upward, and the sample clamping and stretching mechanism pulls the oriented electrical steel sample into a straight state. In this method, the diameter error of the brass cylinder fluctuates within -0.5mm to 0.1mm.

[0053] When the sample is a non-oriented electrical steel sample, a second bending device is used to perform a bending test on the non-oriented electrical steel sample. The specific bending method is: the non-oriented electrical steel sample is placed horizontally and the two ends are tightened and transported to the top of the tape; then a brass cylinder with a diameter of 10 mm under the tape is pressed from bottom to top to the tape and the surface of the non-oriented electrical steel sample in sequence, so that the tape is tightly attached to the lower surface of the non-oriented electrical steel sample, and the non-oriented electrical steel sample is bent 180° in the top pressing area of ​​the cylinder and maintained for at least 5 seconds; after removing the brass cylinder, the tape tightly attached to the lower surface of the non-oriented electrical steel sample is pulled into a straight state, and the tape falls off from the surface of the non-oriented electrical steel sample under the tension, and the tape image is collected after the non-oriented electrical steel sample is removed.

[0054] In S2, the second bending device includes a bending mechanism, a pneumatic clamping mechanism, a servo control mechanism, a tape pulling mechanism and a sample clamping and stretching mechanism; the sample clamping and stretching mechanism pulls the bent non-oriented electrical steel sample into a straight state and moves it to the bending area of ​​the bending mechanism, and the servo control mechanism controls the bending mechanism (a brass cylinder with a diameter of 10 mm) to press upward to the tape and the surface of the non-oriented electrical steel sample in turn to complete the 180° bending, which is maintained for at least 5 seconds; after the servo control mechanism controls the brass cylinder to move downward, the tape pulling mechanism pulls the tape that is closely attached to the lower surface of the non-oriented electrical steel sample into a straight state and detaches from the non-oriented electrical steel sample, and the sample clamping and stretching mechanism removes the non-oriented electrical steel sample and collects the tape image. In this method, the diameter error of the brass cylinder should fluctuate within -0.5mm to 0.1mm.

[0055] In the present invention, the various mechanisms in the first bending device and the second bending device, such as the bending mechanism, the pneumatic clamping mechanism, the servo control mechanism, the tape pressing mechanism and the sample clamping and stretching mechanism, are all conventional mechanisms existing in the industry; the structure and function of the bending device are all existing and are not the invention point of this application, and will not be repeated here.

[0056] In S3, an industrial camera system is used to collect coating images to obtain the original coating adhesion image. When the sample is an oriented electrical steel sample, the surface morphology of the sample after being bent and then pulled into a straight state is collected as the original coating adhesion image, such as Figure 1 As shown; when the sample is a non-oriented electrical steel sample, the surface morphology of the tape that was pressed on the surface by the tape for 5 seconds and then removed was collected as the original coating adhesion image.

[0057] In S3, the industrial camera system includes a camera, a lens and a light source. The camera is a color camera with a resolution of not less than 4024×3036, a maximum frame rate of not less than 29.2fps, an exposure time of not less than 20μs, and a single pixel accuracy of not less than 0.08mm. The focal length of the lens should not exceed 16mm, the image plane diameter should be at least 17.6mm, the working distance should not be less than 400mm, and the field of view should not be less than 350×258mm. The light source is an LED ring light source with an operating voltage of 24V, a working distance of not less than 120mm, and a spacing of not less than 200mm; the light source is positioned on both sides of the sample to avoid direct reflection and ensure uniform lighting, which can effectively highlight the texture and details of the sample. In the present invention, the industrial camera systems are all existing and will not be repeated here.

[0058] In S4, the collected coating adhesion image is rotated, grayed, cropped, and binarized in sequence to obtain the number of white pixels representing the coating peeling area and the number of black pixels representing the coating non-peeling area.

[0059] When the sample is an oriented electrical steel sample, the collected coating adhesion image is rotated, grayed, and cropped in turn, and three pressing areas corresponding to the brass cylinders with diameters of 10 mm, 20 mm, and 30 mm are framed: X area, Y area, and Z area, and then the images of the three areas are binarized. When the sample is a non-oriented electrical steel sample, the collected coating adhesion image is directly rotated, grayed, cropped, and binarized without marking the pressing area.

[0060] The image binarization processing method is as follows: convert the image into pixel values, distinguish the image based on the dynamic threshold, set the pixel values ​​above the dynamic threshold to the maximum value, and the pixel points of the maximum value are white; set the pixel values ​​below the dynamic threshold to the minimum value, and the pixel points of the minimum value are black.

[0061] In the present invention, an image recognition system is used for image processing. The image recognition system is an image processing and visual recognition system developed based on OpenCV, including image rotation, grayscale, cropping, and binarization processing.

[0062] The specific method of image rotation processing is: using the image rotation function, adjust the function's parameter angle so that the image position is displayed correctly. The specific method of image grayscale processing is: using the grayscale algorithm to convert the color image into a grayscale image, that is, converting the RGB value into a brightness value. The specific method of image cropping is: using Canny edge detection (an algorithm used for image edge detection) to obtain the top, bottom, left and right boundary coordinates of the image area, using the image array slicing function to crop the coordinate edge area, and based on the actual physical size, according to the ratio of the actual distance to the image pixel; for oriented electrical steel samples, use the OpenCV function drawing library on the image to frame the downward pressure areas corresponding to the brass cylinders with diameters of 10mm, 20mm, and 30mm respectively (that is, the areas corresponding to the bending diameters of 10mm, 20mm, and 30mm), such as the X area, Y area, and Z area in the figure. Figure 2 As shown, the three regions are half of the circumference of the brass cylinder cross section.

[0063] The image binarization processing method is as follows: use the OpenCV image processing library cv2.threshold() function to convert the grayscale images of the three areas into simplified pixel values, and the pixel values ​​fluctuate between 0 and 255; distinguish the pixel values ​​based on the dynamic threshold, and assign the maximum pixel value of 255 to the pixel points whose pixel values ​​are greater than the dynamic threshold, and the corresponding pixel points are white; the pixel points whose pixel values ​​are less than the dynamic threshold are assigned the minimum pixel value of 0, and the corresponding pixel points are black.

[0064] In the present invention, the dynamic threshold is obtained by Ostu algorithm, and the specific acquisition method is as follows:

[0065] 1) Calculate the grayscale histogram of the image. The sample size of the histogram is usually equal to the total number of pixels in the image. The grayscale value of each pixel (usually an integer between 0 and 255) is counted into the histogram;

[0066] 2) Calculate the grayscale value and probability of each type of pixel. For each possible threshold T, divide the image into two categories: pixels with grayscale values ​​less than T and pixels with grayscale values ​​greater than or equal to T. Calculate the average grayscale value of the two types of pixels respectively.

[0067] 3) Calculate the inter-class variance, which is the square of the difference between the average grayscale values ​​of the two classes of pixels multiplied by the sum of the probabilities of the two classes of pixels;

[0068] 4) Find the optimal threshold, traverse all possible thresholds and calculate their corresponding inter-class variance. The threshold with the largest inter-class variance is the optimal global threshold, which is also the dynamic threshold required. The dynamic threshold is usually between 120 and 180.

[0069] In S5, the coating shedding ratio is calculated, where coating shedding ratio=the number of white pixels / (the number of black pixels+the number of white pixels).

[0070] For oriented electrical steel samples, the coating shedding ratios in the three regions were calculated respectively.

[0071] The quantitative calculation method of the detached area is as follows: the number of pixels with a pixel value of 255 and a pixel value of 0 in the statistical area is counted. The white pixel with a pixel value of 255 represents the coating detached area, and the black pixel with a pixel value of 0 represents the coating non-detached area. The detached area = the number of white pixels / (the number of black pixels + the number of white pixels).

[0072] S6. Determine the level of coating adhesion of the electrical steel sample based on the coating shedding ratio.

[0073] In the present invention, for oriented electrical steel samples, three brass cylinders with diameters of 10 mm, 20 mm and 30 mm are used to perform bending tests on the samples. The coating adhesion image is rotated, grayed and cropped, and the X, Y and Z regions corresponding to the brass cylinders with diameters of 10 mm, 20 mm and 30 mm in the framed image are respectively obtained; the coating shedding ratios in the three regions are calculated, and the coating shedding ratio in the X region is α 1 , the coating shedding ratio in the Y graph area is α 2 , the coating shedding ratio in the Z region is α 3; The three areas are rated respectively, and the rating levels are divided into six grades, namely A, B, C, D, E, and F, according to the coating adhesion performance, among which grade A is the best and grade F is the worst; the grading of each area can include all the above grades, or only include a few of them (for example, the X area is only divided into grades A, B, C and D); finally, the coating adhesion rating of the entire electrical steel sample is obtained according to the rating of each area, and the rating method is:

[0074] In the X region: when α 1 <5.0%, the grade of the X-chart area is A; when 5.0%≤α 1 When <30.0%, the grade of the X-graph area is B; when 30.0%≤α 1 <50.0%, the grade of the X-graph area is C; when α 1 When ≥50.0%, the grade of the X-graph area is D;

[0075] In the Y graph area: when α 2 <1.0%, the grade of the Y graph area is A; when 1.0%≤α 2 When α is less than 20.0%, the grade of the Y graph area is C; 2 When ≥20.0%, the grade of the Y graph area is D;

[0076] In the Z region, when α 3 <1.0%, the grade of the Y graph area is A; when 1.0%≤α 2 When α is less than 10.0%, the grade of the Y graph area is E; 3 When ≥10.0%, the grade of the Y graph area is F;

[0077] When the ratings of the three image areas are all Grade A, the coating adhesion rating of the oriented electrical steel sample is Grade A; when the ratings of the three image areas are inconsistent, the grade of the lowest image area is used as the coating adhesion rating of the oriented electrical steel. For example, when the X image area is Grade A, the Y image area is Grade D, and the Z image area is Grade E, the coating adhesion rating of the oriented electrical steel sample is Grade E.

[0078] For non-oriented electrical steel samples, α is the coating shedding ratio of the non-oriented electrical steel samples. According to the coating adhesion performance, the rating levels are divided into four levels: A, B, C and D, among which A is the best and D is the worst. The specific rating method is:

[0079] When α < 5.0%, the coating adhesion rating of the non-oriented electrical steel sample is A;

[0080] When 5.0%≤α<30.0%, the coating adhesion rating of the non-oriented electrical steel sample is B;

[0081] When 30.0%≤α<50.0%, the coating adhesion rating of the non-oriented electrical steel sample is C;

[0082] When α≥50.0%, the coating adhesion rating of the non-oriented electrical steel sample is D.

[0083] In the present invention, due to the differences in the characteristics of different electrical steel coatings themselves, the thresholds of different levels in a certain area can be appropriately adjusted.

[0084] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0085] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein with equivalents. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rating the adhesion of electrical steel coatings, characterized in that: The method is: S1. Prepare electrical steel samples coated with insulating coatings; S2. Perform bending test on electrical steel samples; S3, collecting the coating image after the bending test to obtain the original coating adhesion image; S4. Rotate, grayscale, crop, and binarize the coating adhesion image to obtain the number of white pixels representing the coating peeling area and the number of black pixels representing the coating non-peeling area: S5. Calculate the coating shedding ratio respectively, coating shedding ratio=number of white pixels / (number of black pixels+number of white pixels); S6. Rating the coating adhesion of the electrical steel samples based on the coating shedding ratio.

2. The method for evaluating the adhesion of electrical steel coatings according to claim 1, characterized in that: The electrical steel sample is a oriented electrical steel sample or a non-oriented electrical steel sample.

3. The method for evaluating the adhesion of electrical steel coatings according to claim 2, characterized in that: In S2, when the sample is an oriented electrical steel sample, the method for performing the bending test is: placing the oriented electrical steel sample horizontally and pressing both ends; pressing three brass cylinders with diameters of 10 mm, 20 mm, and 30 mm, respectively, side by side and synchronously downward to the surface of the oriented electrical steel sample, so that the oriented electrical steel sample completes a 180° bend in the corresponding three areas where the cylinders are pressed downward; and then pulling the bent 180° oriented electrical steel sample into a horizontal state.

4. The method for evaluating the adhesion of electrical steel coatings according to claim 2, wherein: In S2, when the sample is a non-oriented electrical steel sample, the method for performing the bending test is as follows: the non-oriented electrical steel sample is placed horizontally and the two ends are tightened and transported to the top of the tape; then a brass cylinder with a diameter of 10 mm under the tape is pressed from bottom to top to the tape and the surface of the non-oriented electrical steel sample in sequence, so that the tape is tightly attached to the lower surface of the non-oriented electrical steel sample, and the non-oriented electrical steel sample is bent 180° in the top pressure area of ​​the cylinder and maintained for at least 5 seconds; after removing the brass cylinder, the tape tightly attached to the lower surface of the non-oriented electrical steel sample is pulled into a straight state, and the tape falls off from the surface of the non-oriented electrical steel sample under the tension, and the tape image is collected after the non-oriented electrical steel sample is removed.

5. The method for evaluating the adhesion of electrical steel coatings according to claim 2, characterized in that: When the sample is a oriented electrical steel sample, the surface morphology of the oriented electrical steel sample after being bent and then pulled into a straight state is collected as the coating adhesion image.

6. The method for evaluating the adhesion of electrical steel coatings according to claim 2, wherein: When the sample is a non-oriented electrical steel sample, the surface morphology of the tape after the non-oriented electrical steel sample is compacted by the tape and then released is collected as the coating adhesion image.

7. The method for evaluating the adhesion of electrical steel coatings according to claim 2, wherein: For the oriented electrical steel sample, the coating adhesion image is rotated, grayed, and cropped, and the brass cylinders with diameters of 10 mm, 20 mm, and 30 mm in the framed image correspond to the X-area, Y-area, and Z-area respectively; the coating shedding ratios in the three areas are calculated, and the coating shedding ratio in the X-area is α1, the coating shedding ratio in the Y-area is α2, and the coating shedding ratio in the Z-area is α3; the three areas are rated respectively, and the rating levels are divided into six levels: A, B, C, D, E, and F, among which A is the best and F is the worst; the coating adhesion rating of the entire electrical steel sample is obtained according to the rating of each area, and the rating method is: In the X-chart area: when α1<5.0%, the grade of the X-chart area is A; when 5.0%≤α1<30.0%, the grade of the X-chart area is B; when 30.0%≤α1<50.0%, the grade of the X-chart area is C; when α1≥50.0%, the grade of the X-chart area is D; In the Y-graph area: when α2<1.0%, the grade of the Y-graph area is A; when 1.0%≤α2<20.0%, the grade of the Y-graph area is C; when α2≥20.0%, the grade of the Y-graph area is D; In the Z area, when α3 < 1.0%, the grade of the Y area is A; when 1.0% ≤ α2 < 10.0%, the grade of the Y area is E; when α3 ≥ 10.0%, the grade of the Y area is F; When the ratings of the three graphic areas are all A, the coating adhesion rating of the oriented electrical steel sample is A; when the ratings of the three graphic areas are inconsistent, the rating of the lowest-grade graphic area is used as the coating adhesion rating of the oriented electrical steel sample.

8. The method for evaluating the adhesion of electrical steel coatings according to claim 2, wherein: For non-oriented electrical steel samples, α is the coating shedding ratio of the non-oriented electrical steel samples. The rating levels are divided into four levels: A, B, C and D. The specific rating method is as follows: When α < 5.0%, the coating adhesion rating of the non-oriented electrical steel sample is A; When 5.0%≤α<30.0%, the coating adhesion rating of the non-oriented electrical steel sample is B; When 30.0%≤α<50.0%, the coating adhesion rating of the non-oriented electrical steel sample is C; When α≥50.0%, the coating adhesion rating of the non-oriented electrical steel sample is D.

9. The method for evaluating the adhesion of electrical steel coatings according to any one of claims 1 to 8, characterized in that: In S2, the method of image binarization is as follows: converting the image into pixel values, calculating the dynamic threshold to distinguish the image, setting the pixel points above the dynamic threshold as the maximum value, and the pixel point with the maximum value is white, representing the coating peeling area; The pixels below the dynamic threshold are set to the minimum value, and the pixels with the minimum value are black, representing the area where the coating has not fallen off.

10. The method for evaluating the adhesion of electrical steel coatings according to claim 9, characterized in that: The method for obtaining the dynamic threshold is as follows: 1) Calculate the grayscale histogram of the image, and the grayscale value of each pixel is counted into the histogram; 2) Calculate the grayscale value and probability of each type of pixel. For each possible threshold T, divide the image into two categories: pixels with grayscale values ​​less than T and pixels with grayscale values ​​greater than or equal to T. Calculate the average grayscale value of the two types of pixels respectively. 3) Calculate the inter-class variance, which is the square of the difference between the average grayscale values ​​of the two types of pixels multiplied by the sum of the probabilities of the two types of pixels; 4) Find the optimal threshold, traverse all possible thresholds and calculate their corresponding inter-class variances. The threshold with the largest inter-class variance is the optimal global threshold, which is also the dynamic threshold required.

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