Method for detecting black leather through eddy current

Abstract

The invention discloses a method for detecting a black leather material through eddy current, and relates to the technical field of nondestructive testing. Shot blasting current and revolution are controlled through shot blasting pretreatment, so that the surface roughness Ra of the black leather material is reduced to be less than or equal to 6.3 microns, a qualified detection surface is provided for eddy current flaw detection, and the detection precision is prevented from being influenced by the surface state; a special sample rod containing longitudinal and transverse artificial defects is prepared, the sensitivity of a flaw detection system to defects in different directions can be synchronously verified, the detection comprehensiveness is ensured, eddy current flaw detection parameters are optimized, defect signals and noise signals are effectively distinguished by adjusting a current gate, optimizing filtering setting and maintaining phase difference stability, and the signal recognition accuracy is improved; according to the multi-frequency eddy current detection, three excitation signals with different frequencies are applied, so that the coverage detection of the defects of different depths of the black skin material is realized, the defect detection rate is improved, eddy current flaw detection core parameters are dynamically adjusted, the influence of surface non-uniformity on an eddy current field is compensated, and the detection stability is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of non-destructive testing, in particular to a method for eddy current testing of black leather materials. Background Art

[0002] In the field of non-destructive testing of metal processing, it is difficult to detect internal and surface defects of black leather materials due to problems such as surface oxide scale and uneven roughness. Eddy current testing has become a common means of defect detection in black leather materials due to its advantages such as non-contact and high efficiency. However, during the production process of black leather materials, fluctuations in shot blasting quality lead to differences in surface conditions, traditional comparison samples cannot accurately simulate actual defects, and fixed eddy current testing parameters are difficult to adapt to complex working conditions. All of these bring challenges to the accurate detection of defects. There is an urgent need for a set of eddy current testing methods that can be dynamically adapted and accurately verified to ensure the accuracy of black leather material quality judgment.

[0003] In the existing technology, in order to meet the high requirements of eddy current testing on the surface condition of materials, it is usually necessary to peel the incoming materials to remove the oxide scale and burrs on the surface so that the material surface can reach the flatness and cleanliness required for eddy current testing. However, the peeling process not only increases production costs and reduces production efficiency, but also may cause certain damage to the material itself during the peeling process, affecting the final performance of the material. In addition, the peeling process will also generate a large amount of waste, causing certain pollution to the environment. Faced with the changes in the surface condition of black leather materials and the differences in defect types, real-time dynamic compensation cannot be made, and the detection sensitivity and accuracy are greatly reduced, making it difficult to meet the strict requirements of high-quality production for defect detection.

[0004] In summary, the existing eddy current flaw detection method for black leather material has poor detection effect on unpeeled black leather material. Therefore, developing a method that can directly perform eddy current flaw detection in the black leather state is of great significance for improving production efficiency and reducing costs. Summary of the Invention

[0005] The purpose of the present invention is to make up for the shortcomings of the existing technology and provide a method for eddy current detection of black leather materials. It can control the shot blasting current and rotation speed through shot blasting pretreatment, so that the surface roughness of the black leather material is reduced to Ra≤6.3μm, providing a qualified detection surface for eddy current flaw detection, avoiding the influence of surface state on detection accuracy, preparing special sample rods containing longitudinal and transverse artificial defects, and synchronously verifying the sensitivity of the flaw detection system to defects in different directions, ensuring comprehensive detection, optimizing eddy current flaw detection parameters, and effectively distinguishing defect signals from noise signals by adjusting the current gate, optimizing the filter settings and maintaining phase difference stability, thereby improving signal recognition accuracy. Multi-frequency eddy current detection achieves coverage detection of defects of different depths in black leather materials by applying three different frequency excitation signals, thereby improving defect detection rate, dynamically adjusting eddy current flaw detection core parameters, compensating for the influence of surface unevenness on eddy current field, ensuring detection stability, and a strict flaw detection result verification process. By calculating the missed alarm rate and false alarm rate, the reliability of the detection system is ensured, avoiding missed detection or misjudgment of defects.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for eddy current detection of black leather materials, the specific steps of the method are:

[0007] S100, shot blasting pretreatment: Shot blast the round steel black skin material, control the shot blasting current to 40±10A, shot blasting revolutions to 2000±1000 revolutions, to obtain the surface roughness that meets the requirements of eddy current testing;

[0008] S200, special sample rod preparation: prepare a special sample rod containing artificial defects of the same depth, wherein the artificial defects include longitudinal defects and transverse defects, for synchronously verifying the sensitivity of the flaw detection system to defects in different directions;

[0009] S300, Optimize Eddy Current Testing Parameters: When the signal-to-noise ratio of black leather material does not meet the testing conditions, adjust the current gate to amplify the lateral interference signal, optimize the filter settings to eliminate environmental electromagnetic interference, and maintain the eddy current detection phase difference at a stable 90° to distinguish defect signals from noise signals. The core parameters of eddy current testing are dynamically adjusted according to changes in the surface state of the black leather material.

[0010] S400, Multi-frequency Eddy Current Testing and Analysis: Black leather materials that have undergone shot blasting and parameter optimization are scanned and tested on the automatic flaw detection line A in the finishing plant using an array eddy current probe applying eddy current signals of three different frequencies, collecting test signals in real time.

[0011] S500, verification of flaw detection results: Before testing, use S200 special sample rods to verify the equipment's ability to detect longitudinal and transverse defects, and sample black leather materials after testing, verify the eddy current flaw detection results through ultrasonic testing, and calculate the missed alarm rate and false alarm rate.

[0012] Furthermore, the S100 uses a shot blasting machine to perform surface treatment on the round steel black skin material. When the shot blasting current is controlled to 50A during the treatment process, the surface of the black skin material can be effectively impacted and cleaned. At the same time, the speed of the shot blasting machine is adjusted to 3000 rpm, so that the shot blasting medium forms a uniform and dense impact trajectory on the surface of the black skin material, thereby achieving the purpose of removing surface oxide scale, burrs and uneven parts until the surface roughness is reduced to Ra≤6.3μm. After shot blasting, the surface of the round steel black skin material is cleaned to remove residual pellets and dust to meet the surface finish requirements of eddy current testing.

[0013] Furthermore, the S200 selects round steel of the same material and specification as the black leather material to be tested as the sample rod substrate, performs quenching and tempering heat treatment on the sample rod substrate, the quenching temperature is 840-860℃, the tempering temperature is 580-600℃, and the holding time is 2 hours. The longitudinal defects and transverse defects are processed on the surface of the sample rod substrate. The longitudinal defects extend along the axis of the sample rod, and the transverse defects are perpendicular to the axis of the sample rod. The spacing between adjacent defects is ≥20mm, wherein the size parameters of the longitudinal defects and transverse defects are:

[0014] Longitudinal defects: parallel to the axis of the sample rod, length 5mm-10mm, width 0.1mm-0.3mm, depth 0.5-0.55mm;

[0015] Transverse defects: perpendicular to the axis of the sample rod, length 3mm–8mm, width 0.1mm–0.3mm, depth 0.5-0.55mm.

[0016] Furthermore, the dynamic optimization of the S300 flaw detection parameters specifically includes:

[0017] The current gate amplification factor is set to 1.5–2.0 times to suppress the transverse interference signal with a frequency of 20kHz–50kHz;

[0018] Real-time monitoring of interference signal strength. When the strength exceeds the threshold of 100mV, the amplification factor is dynamically adjusted to the upper limit of 2.0 times.

[0019] Bandpass filter configuration: Optimize the filter settings, the passband frequency range is 10kHz–100kHz, the stopband attenuation is ≥40dB, and the filter center frequency is adaptively adjusted according to the diameter of the black leather material being tested:

[0020] When the diameter is ≤80mm, the center frequency is 80kHz±2kHz;

[0021] When the diameter is greater than 80mm, the center frequency is 30kHz±1kHz;

[0022] Input a standard sinusoidal signal with a frequency of 50kHz and an amplitude of 5V into the probe to stabilize the output phase difference at 90°±2°;

[0023] During the calibration period, the phase difference is sampled once per second, and an abnormal alarm is triggered when the offset is greater than ±5°.

[0024] Furthermore, based on the optimized flaw detection parameters, the S300 monitors the changes in the surface state of the black leather material in real time and dynamically adjusts the core parameters of eddy current flaw detection, including frequency, gain, and phase, to compensate for the impact of surface unevenness on the eddy current field. The adjustment process is as follows:

[0025] Measuring surface roughness, sampling interval mm, to obtain the surface micromorphology data of black leather in real time;

[0026] Based on the collected surface roughness data, the surface fluctuation coefficient CV value is calculated in real time, where CV = σ / μ × 100%, σ is the standard deviation of the surface roughness data, and μ is the average roughness;

[0027] Establish an association rule between surface fluctuation coefficient (CV) and eddy current testing parameters: when the CV value increases by 1%, the frequency is increased by 0.5kHz and the gain is decreased by 0.8dB to compensate for the influence of surface state changes on the testing signal.

[0028] Phase angle compensation follows the formula , the phase deviation caused by surface fluctuation is calculated by this formula, dynamic phase compensation is achieved, and the phase accuracy of the flaw detection signal is guaranteed;

[0029] After each parameter adjustment, 10 sets of eddy current flaw detection signals are collected and the signal-to-noise ratio improvement rate is calculated. When the signal-to-noise ratio improvement rate is ≥15%, it is confirmed that the dynamic compensation is effective, ensuring that the quality of the flaw detection signal after compensation meets the detection requirements.

[0030] Furthermore, the S400 uses a multi-channel eddy current detection system to simultaneously apply three sinusoidal wave excitation signals of different frequencies to detect defects of different depths in black leather materials:

[0031] Low-frequency channel 50-100kHz: for defect detection in the subsurface and near-core areas of black leather materials, with a depth of ≥2mm, the excitation signal amplitude is set to 5V, and the signal duty cycle is 50%;

[0032] Intermediate frequency channel 100-300kHz: covers defects in the middle layer of black leather, with a depth of 1-2mm, an excitation signal amplitude of 4V, and a duty cycle of 40%;

[0033] High-frequency channel 300-500kHz: Focus on the surface and near-surface defects of black leather, depth ≤ 1mm, excitation signal amplitude 3V, duty cycle 30%;

[0034] The continuous trigger period of each channel signal of the three frequency signals is 20ms, and the channel switching interval is ≤1ms.

[0035] Furthermore, the S400 performs energy entropy calculation on the response signals collected by the multi-frequency eddy current detection according to the nodes, and quantitatively extracts the defect features:

[0036] Signal preprocessing: low-pass filter the original signal of each channel to eliminate high-frequency noise interference, and map the signal amplitude to the 0-1 range through normalization processing to unify the feature calculation benchmark;

[0037] Energy entropy calculation: After preprocessing, the signal is divided into multiple subsequences by node, and the energy entropy of each node is calculated. , ,in For the The proportion of the energy of each subsequence to the total energy;

[0038] Effective defect judgment: Set the energy entropy threshold. When the node energy entropy , it is determined that there is a valid defect in the area corresponding to the node, and the defect location mark is triggered.

[0039] Furthermore, the S500 uses a dedicated sample rod to verify the device's ability to detect longitudinal and transverse defects. The specific steps include:

[0040] Sample bar test parameters: Use a special sample bar prepared by S200, pass through the test area at a constant speed of 1m / min to ensure the stability of the test process, and record the amplitude of the longitudinal defect signal and the amplitude of the transverse defect signal ;

[0041] Sensitivity ratio calculation and determination: Calculate sensitivity ratio ,in, is the peak amplitude of the longitudinal defect signal, reflecting the probe's ability to respond to defects along the material axis. It is the peak amplitude of the transverse defect signal, reflecting the detection sensitivity of the probe to defects perpendicular to the material axis. The detection requirements are: , ensuring that the probe has balanced detection capabilities for defects in different directions;

[0042] Repeatability test: perform three consecutive sample stick tests with an interval of ≤1 minute between each test and record the results of each test. and , calculate the signal amplitude fluctuation of three tests ,in, For the The signal amplitude of the test, , is the average amplitude of three tests, and Respectively The maximum and minimum values ​​of the signal amplitude of the test are as follows: , ensuring the stability and repeatability of the detection system.

[0043] Furthermore, in the calculation of the false alarm rate in S500, 5% of the black leather materials after testing are sampled and the ultrasonic flaw detection equipment is used to scan the sampled black leather materials. The proportion of defects identified by eddy current testing that are confirmed to be free of defects by ultrasonic re-inspection, among which: The number of false defects confirmed by ultrasonic re-inspection, that is, the number of defects determined by eddy current testing but not detected by ultrasonic testing, Total number of defects reported for eddy current testing, where the inspection requirements are: , ensuring that defects are not over-judged due to interference such as noise and surface texture.

[0044] Furthermore, for the calculation of the missed alarm rate in S500, a standard simulated defect is added to the area on the sample rod that is not identified by the eddy current detection. The simulated defect has a depth of 0.2 mm, a width of 0.4 mm, and a length of 5 mm. The missed alarm rate is defined as is the proportion of defects that have not been identified by eddy current testing after re-testing, is the number of simulated defects that were not identified by eddy current testing after retesting, The total number of simulated defects added is the detection requirement: , ensuring the system's ability to detect tiny and complex defects, and avoiding defective black leather materials from flowing into downstream processes due to missed detection.

[0045] Compared with the existing technology, this method of eddy current detection of black leather has the following beneficial effects:

[0046] 1. The present invention controls the shot blasting current and rotation speed through shot blasting pretreatment to reduce the surface roughness of black leather material to Ra≤6.3μm, providing a qualified detection surface for eddy current flaw detection, avoiding the impact of surface condition on detection accuracy, and preparing special sample rods containing longitudinal and transverse artificial defects. The sensitivity of the flaw detection system to defects in different directions can be simultaneously verified to ensure comprehensive detection, optimize eddy current flaw detection parameters, and effectively distinguish defect signals from noise signals by adjusting the current gate, optimizing the filter settings and maintaining phase difference stability, thereby improving signal recognition accuracy. Multi-frequency eddy current detection achieves coverage detection of defects of different depths in black leather material by applying three different frequency excitation signals, thereby improving defect detection rate. The core parameters of eddy current flaw detection are dynamically adjusted to compensate for the impact of surface unevenness on the eddy current field, ensuring detection stability. A strict flaw detection result verification process is implemented to ensure the reliability of the detection system by calculating the missed alarm rate and false alarm rate, avoiding missed detection or misjudgment of defects.

[0047] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0049] Figure 1 This is an operational flow chart of a method for eddy current probing of black leather;

[0050] Figure 2 A framework diagram of the steps of a method for eddy current probing of black leather. DETAILED DESCRIPTION

[0051] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0052] Example 1

[0053] This embodiment provides a method for eddy current detection of black leather material, such as Figure 2 As shown in the figure, through the steps of shot blasting pretreatment, special sample rod preparation, eddy current testing parameter optimization, multi-frequency eddy current detection and analysis, and flaw detection result verification, accurate detection of surface and internal defects of round steel black leather material can be achieved. This method can dynamically adapt to the changes in the surface state of black leather material, effectively distinguish defect signals from noise signals, improve the defect detection rate, ensure the reliability of the detection results, and provide strong support for the quality judgment of black leather material.

[0054] First of all, the working principle of this stage is to use the high-speed rotating impeller of the shot blasting machine to project the shot blasting medium onto the surface of the round steel black leather material, and remove the surface oxide scale, burrs and uneven parts through the impact force, so as to obtain the surface roughness that meets the requirements of eddy current flaw detection. The shot blasting machine is used for surface treatment of the round steel black leather material, and the shot blasting current is controlled at 50A. This is because under this current, the speed and projectile force of the impeller of the shot blasting machine can effectively impact and clean the surface of the black leather material. At the same time, the speed of the shot blasting machine is adjusted to 3000 rpm, so that the shot blasting medium forms a uniform and dense impact trajectory on the surface of the black leather material, and the shot blasting medium continuously hits the black leather material. The surface of the leather material is shot blasted to crack and fall off the oxide scale, and the burrs and uneven parts of the surface are polished. During the shot blasting process, the surface roughness is continuously monitored until it drops to Ra≤6.3μm. This roughness standard is to ensure that the probe can be well coupled with the surface during eddy current testing and reduce the signal interference caused by surface unevenness. After shot blasting, the surface of the round steel black leather material is cleaned by compressed air blowing or vacuum cleaning to remove residual pellets and dust to meet the surface finish requirements of eddy current testing. Residual pellets or dust will generate false signals in subsequent tests and affect the accuracy of the test results.

[0055] Then, enter the special sample rod preparation stage (S200), prepare a sample rod with the same material and specifications as the black leather material to be tested, and process artificial defects of known depth and size on it to verify the detection sensitivity of the flaw detection system to defects in different directions. Round steel with the same material and specifications as the black leather material to be tested is selected as the sample rod base material, and the sample rod base material is subjected to tempering heat treatment. The quenching temperature is controlled at 840-860℃, the tempering temperature is controlled at 580-600℃, and the holding time is 2 hours. The purpose of heat treatment is to make the organizational structure of the sample rod base material consistent with the black leather material to be tested, ensure that the physical properties of the sample rod are the same as those of the actual test material, thereby ensuring the reliability of the verification results. After heat treatment, the sample rod base material surface Surface processing longitudinal defects and transverse defects, longitudinal defects extend along the axis of the sample rod, transverse defects are perpendicular to the axis of the sample rod, and the spacing between adjacent defects is ≥20mm, among which the size parameters of the longitudinal defects are: parallel to the axis of the sample rod, length 5mm-10mm, width 0.1mm-0.3mm, depth 0.5-0.55mm; the size parameters of the transverse defects are: perpendicular to the axis of the sample rod, length 3mm-8mm, width 0.1mm-0.3mm, depth 0.5-0.55mm. The size and depth of the defects provided in this embodiment are determined according to the common defect types and sizes in actual production, which can effectively simulate actual defects and be used to verify the detection capability of the flaw detection system.

[0056] Next, the eddy current flaw detection parameter optimization stage (S300) is entered. In this stage, the defect signal and the noise signal are distinguished by adjusting the current gate, optimizing the filter setting and maintaining the phase difference stability. The parameters are dynamically adjusted according to the changes in the surface state of the black leather material to improve the accuracy and stability of the detection. Specifically, the current gate amplification factor is set to 1.5-2.0 times to suppress the lateral interference signal with a frequency of 20kHz-50kHz. During the eddy current flaw detection process, factors such as the unevenness of the black leather surface and the residual oxide scale will generate lateral interference signals. These signals will interfere with the identification of the defect signal. Such interference can be effectively suppressed by amplification. The interference signal strength is monitored in real time. When the strength exceeds the threshold of 100 mV, dynamically adjust the amplification factor to the upper limit of 2.0 times to enhance the ability to suppress strong interference signals; in terms of filtering settings, optimize the bandpass filter configuration, the passband frequency range is 10kHz-100kHz, the stopband attenuation is ≥40dB, and the center frequency of the filter is adaptively adjusted according to the diameter of the black leather material being measured: when the diameter is ≤80mm, the center frequency is 80kHz±2kHz; when the diameter is greater than 80mm, the center frequency is 30kHz±1kHz. The reason for this setting is that the electromagnetic characteristics of black leather materials of different diameters are different. Adaptive adjustment of the center frequency can better filter out environmental electromagnetic interference and retain effective defect signals. In addition, the input frequency of 50kHz and amplitude of 5V to the probe The standard sinusoidal signal is used to stabilize the output phase difference at 90°±2°. The phase difference is stable at 90° to accurately distinguish defect signals from noise signals. The phase characteristics of defect signals and noise signals are different. A stable phase difference can improve the accuracy of signal recognition. During the calibration period, the phase difference is sampled once per second. When the offset is greater than ±5°, an abnormal alarm is triggered to promptly detect and handle abnormal conditions of the probe or system to ensure the reliability of the detection. At the same time, based on the optimized flaw detection parameters, the surface state of the black leather material is monitored in real time, and the core parameters of eddy current flaw detection (frequency, gain and phase) are dynamically adjusted to compensate for the influence of surface unevenness on the eddy current field. The specific adjustment process is: measure the surface roughness, the sampling interval is ≤5 mm, in order to obtain the surface micromorphology data of black leather in real time. Based on the collected surface roughness data, the surface fluctuation coefficient CV value is calculated in real time, where CV=σ / μ×100%, σ is the standard deviation of the surface roughness data, μ is the average roughness, and the CV value reflects the degree of fluctuation of the surface roughness. The larger the CV value, the more uneven the surface. The association rule between the surface fluctuation coefficient CV and the eddy current testing parameters is established: when the CV value increases by 1%, the frequency is increased by 0.5kHz and the gain is decreased by 0.8dB. By increasing the frequency, the penetration depth of the eddy current is increased to adapt to the change of the surface state; the gain is decreased to reduce the amplification of the noise signal and improve the signal-to-noise ratio of the signal; the phase angle compensation follows the formula Δθ=arctan(0.15×CV). This formula is used to calculate the phase deviation caused by surface fluctuations, achieving dynamic phase compensation and ensuring the accuracy of the flaw detection signal phase. After each parameter adjustment, 10 sets of eddy current flaw detection signals are collected and the signal-to-noise ratio improvement rate is calculated. When the signal-to-noise ratio improvement rate is ≥15%, the dynamic compensation is confirmed to be effective, ensuring that the quality of the flaw detection signal after compensation meets the inspection requirements.

[0057] After that, the multi-frequency eddy current detection and analysis stage (S400) begins. Using a multi-channel eddy current detection system, three sinusoidal wave excitation signals of different frequencies are simultaneously applied. By taking advantage of the different penetration depths of eddy currents of different frequencies in the material, defects of different depths in black leather material can be detected. The defect characteristics are then quantitatively extracted through energy entropy calculation. Specifically, using a multi-channel eddy current detection system, three sinusoidal wave excitation signals of different frequencies are simultaneously applied:

[0058] Low-frequency channel (50-100kHz): For defect detection in the subsurface and near-core areas of black leather materials, with a depth of ≥2mm. The excitation signal amplitude is set to 5V, and the signal duty cycle is 50%. The penetration depth of low-frequency eddy current is large, and it can detect defects deeper inside the material.

[0059] Medium frequency channel (100-300kHz): covers defects in the middle layer of black leather, with a depth of 1-2mm, an excitation signal amplitude of 4V, a duty cycle of 40%, and a moderate penetration depth of the medium frequency eddy current, which is used to detect defects in the middle layer;

[0060] High-frequency channel (300-500kHz): Focuses on surface and near-surface defects of black leather materials, with a depth of ≤1mm, an excitation signal amplitude of 3V, and a duty cycle of 30%. The penetration depth of high-frequency eddy current is relatively small, and it is mainly used to detect surface and near-surface defects.

[0061] The continuous trigger period of each channel signal of the three frequency signals is 20ms, and the channel switching interval is ≤1ms to ensure the continuity and efficiency of the detection. The response signals collected by multi-frequency eddy current detection are calculated by node energy entropy. The original signals of each channel are low-pass filtered to eliminate high-frequency noise interference. The signal amplitude is mapped to the 0-1 interval through normalization processing to unify the feature calculation benchmark. The pre-processed signal is divided into multiple subsequences by node, and the energy entropy H of each node is calculated, where , pi is the ratio of the energy of the i-th subsequence to the total energy. The energy entropy can reflect the complexity and irregularity of the signal. Defective signals usually have higher energy entropy. The energy entropy threshold is set. When the node energy entropy H>2.5, it is determined that there is a valid defect in the corresponding area of ​​the node, triggering the defect location mark.

[0062] Finally, the flaw detection result verification stage (S500) is entered. In this stage, the equipment's detection capabilities for longitudinal and transverse defects are verified by using special sample rods. Ultrasonic testing is performed on samples of black leather after testing. The missed alarm rate and false alarm rate are calculated to ensure the reliability and accuracy of the detection system. Specifically, the special sample rod prepared in S200 is passed through the detection area at a constant speed of 1m / min to ensure the stability of the detection process. The amplitude of the longitudinal defect signal is recorded. and the amplitude of the transverse defect signal , calculate the sensitivity ratio ,in is the peak amplitude of the longitudinal defect signal, reflecting the probe's ability to respond to defects along the material axis. It is the peak amplitude of the transverse defect signal, reflecting the detection sensitivity of the probe to defects perpendicular to the material axis. The detection requirement is 0.9≤S≤1.1, ensuring that the probe has a balanced detection capability for defects in different directions. If the sensitivity ratio exceeds this range, it means that there is a deviation in the detection capability of the probe for defects in different directions, and the probe or detection parameters need to be adjusted. Repeatability test: perform three consecutive sample rod tests with an interval of ≤1 minute each time, and record the results of each test. and , calculate the signal amplitude fluctuation of three tests ,in is the signal amplitude of the i-th test, i=1, 2, 3, A is the average amplitude of the three tests, and the detection requirement is δ≤±2% to ensure the stability and repeatability of the detection system; for the calculation of the false alarm rate, the black leather material after the test is sampled at a ratio of 5%, and the ultrasonic flaw detection equipment is used to scan the sampled black leather material, and the definition is ,in The number of false defects confirmed by ultrasonic re-inspection, that is, the number of defects determined by eddy current testing but not detected by ultrasonic testing, The total number of defects reported by eddy current testing. The testing requirement is FAR ≤ 1.5% to ensure that defects are not over-judged due to interference such as noise and surface texture. If the false alarm rate is too high, it means that the eddy current testing system is not able to suppress noise and interference, and the testing parameters need to be further optimized. For the calculation of the missed detection rate, a standard simulated defect is added to the area on the sample rod that is not identified by the eddy current test. The simulated defect has a depth of 0.2mm, a width of 0.4mm, and a length of 5mm. Definition of missed detection rate ,in is the number of simulated defects that were not identified by eddy current testing after retesting; For the total number of simulated defects added, the detection requirement is MDR ≤ 0.5%, ensuring the system's ability to detect small and complex defects and avoiding defective black leather materials from flowing into downstream processes due to missed detection. If the missed detection rate is too high, it means that the eddy current detection system's detection capability for small defects is insufficient, and the detection parameters should be adjusted.

[0063] In summary, this embodiment reduces the surface roughness of round steel black leather material to Ra≤6.3μm through shot blasting pretreatment, providing a qualified testing surface for eddy current flaw detection and avoiding the influence of surface condition on detection accuracy. The preparation of special sample rods realizes the simultaneous verification of the defect detection sensitivity of the flaw detection system in different directions, ensuring the comprehensiveness of detection. The optimization of eddy current flaw detection parameters, including current gate, filter setting, phase difference control and dynamic adjustment based on surface condition, effectively distinguishes defect signals from noise signals and improves the accuracy of signal recognition. Multi-frequency eddy current detection achieves full coverage detection of defects of different depths in black leather material through the synergistic effect of three different frequency excitation signals, thereby improving the defect detection rate. The strict flaw detection result verification process ensures the reliability and accuracy of the detection system through sensitivity ratio calculation, repeatability testing, and calculation of false alarm rate and missed alarm rate. This method effectively solves the problem of poor eddy current flaw detection effect of black leather material in the existing technology, improves production efficiency, reduces production costs, and provides reliable technical support for the quality inspection of black leather material.

[0064] Example 2

[0065] This embodiment provides a method for eddy current flaw detection of black steel. The specific process of performing effective eddy current flaw detection on round steel black steel is as follows: Figure 1 As shown in the figure, the specific process is:

[0066] Shot blasting pretreatment:

[0067] Set the shot blasting machine current to 40±10A and the speed to 2000±1000 rpm;

[0068] Impact clean the surface of round steel black material to remove oxide scale and burrs;

[0069] Check the surface roughness and ensure it is reduced to Ra≤6.3μm;

[0070] Special sample stick preparation:

[0071] Use round steel with the same material and specifications as the black leather material to be tested as the base material;

[0072] Heat treatment of the substrate: quenching at 840-860℃ + tempering at 580-600℃, keeping warm for 2 hours;

[0073] Processing longitudinal defects (parallel to the axis, 5-10 mm long, 0.5-0.55 mm deep);

[0074] Processing transverse defects (vertical axis, length 3-8mm, depth 0.5-0.55mm), defect spacing ≥ 20mm;

[0075] Eddy current testing parameter optimization:

[0076] Adjust the current gate amplification factor to 1.5-2.0 times to suppress 20-50kHz lateral interference signals;

[0077] Configure bandpass filter: passband 10-100kHz, stopband attenuation ≥40dB, adaptive center frequency according to steel diameter;

[0078] Input a 50kHz standard sine signal and calibrate the phase difference to 90°±2°;

[0079] Real-time monitoring of surface roughness (sampling interval ≤ 5mm) and calculation of surface fluctuation coefficient;

[0080] Dynamically adjust parameters:

[0081] For every 1% increase in the surface fluctuation coefficient, the frequency is increased by 0.5kHz and the gain is decreased by 0.8dB to compensate for the phase angle deviation according to the surface fluctuation;

[0082] After each adjustment, verify that the signal-to-noise ratio improvement rate is ≥15%;

[0083] Multi-frequency eddy current testing:

[0084] Use an array probe to transmit three-frequency excitation signals simultaneously:

[0085] Low frequency 50-100kHz (amplitude 5V): detect defects with a depth of ≥2mm;

[0086] Medium frequency 100-300kHz (amplitude 4V): detects defects with a depth of 1-2mm;

[0087] High frequency 300-500kHz (amplitude 3V): detect defects with a depth of ≤1mm;

[0088] Each channel signal lasts 20ms, and the channel switching interval is ≤1ms;

[0089] Low-pass filtering and normalization of the response signal;

[0090] Split signal nodes and calculate energy entropy;

[0091] If the node energy entropy is greater than 2.5, it is marked as a defective area;

[0092] Verification of flaw detection results:

[0093] Sample bar verification: pass the probe at a speed of 1m / min and record the longitudinal / transverse defect signal amplitude;

[0094] Calculate the sensitivity ratio S = longitudinal amplitude / transverse amplitude, requiring 0.9≤S≤1.1;

[0095] Repeat the test 3 times, and the signal amplitude fluctuation is ≤±2%;

[0096] Sampling ultrasonic re-inspection: 5% of black leather materials are sampled, and the false alarm rate (the proportion of eddy current misjudgment of defects) is calculated to be ≤1.5%;

[0097] Missing rate test: Add simulated defects (0.2mm deep, 5mm long) to the undetected area of ​​the sample stick and calculate the missing rate (proportion of undetected defects) ≤ 0.5%;

[0098] If the output meets the flaw detection requirements, it will be judged as qualified. Otherwise, the parameters will be optimized and re-tested to complete the black leather material detection.

[0099] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form.

[0100] Although the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for eddy current detection of black leather material, characterized in that: The specific steps of this method are: S100, shot blasting pretreatment: Shot blast the round steel black skin material, control the shot blasting current to 40±10A, shot blasting revolutions to 2000±1000 revolutions, to obtain the surface roughness that meets the requirements of eddy current testing; S200, special sample rod preparation: prepare a special sample rod containing artificial defects of the same depth, wherein the artificial defects include longitudinal defects and transverse defects, for synchronously verifying the sensitivity of the flaw detection system to defects in different directions; S300, Optimize Eddy Current Testing Parameters: When the signal-to-noise ratio of black leather material does not meet the testing conditions, adjust the current gate to amplify the lateral interference signal, so that the eddy current detection phase difference is stable at 90°, which is used to distinguish defect signals from noise signals. The core parameters of eddy current testing are dynamically adjusted according to the changes in the surface state of the black leather material. S400, Multi-frequency Eddy Current Testing and Analysis: Black leather materials that have undergone shot blasting and parameter optimization are scanned and tested on the automatic flaw detection line A in the finishing plant using an array eddy current probe applying eddy current signals of three different frequencies, collecting test signals in real time. S500, verification of flaw detection results: Before testing, use S200 special sample rods to verify the equipment's ability to detect longitudinal and transverse defects, and sample black leather materials after testing, verify the eddy current flaw detection results through ultrasonic testing, and calculate the missed alarm rate and false alarm rate.

2. The method for eddy current probing of black leather according to claim 1, characterized in that: The S100 uses a shot blasting machine to perform surface treatment on round steel black leather material. During the treatment process, when the shot blasting current is controlled to 50A, the surface of the black leather material is effectively impacted and cleaned. At the same time, the speed of the shot blasting machine is adjusted to 3000 rpm so that the shot blasting medium forms a uniform and dense impact track on the surface of the black leather material, thereby removing surface oxide scale, burrs and uneven parts until the surface roughness is reduced to Ra≤6.3μm. After shot blasting, the surface of the round steel black leather material is cleaned to remove residual shot particles and dust.

3. The method for eddy current detection of black leather material according to claim 1, characterized in that: The S200 uses round steel of the same material and specification as the black leather material to be tested as the sample rod substrate, and performs tempering heat treatment on the sample rod substrate at a quenching temperature of 840-860°C, a tempering temperature of 580-600°C, and a holding time of 2 hours. Longitudinal defects and transverse defects are processed on the surface of the sample rod substrate. The longitudinal defects extend along the axis of the sample rod, and the transverse defects are perpendicular to the axis of the sample rod. The spacing between adjacent defects is ≥20mm. The dimensional parameters of the longitudinal defects and transverse defects are: Longitudinal defects: parallel to the axis of the sample rod, length 5mm-10mm, width 0.1mm-0.3mm, depth 0.5-0.55mm; Transverse defects: perpendicular to the axis of the sample rod, length 3mm–8mm, width 0.1mm–0.3mm, depth 0.5-0.55mm.

4. The method for eddy current detection of black leather material according to claim 1, characterized in that: The dynamic optimization of S300 flaw detection parameters specifically includes: The current gate amplification factor is set to 1.5–2.0 times to suppress the transverse interference signal with a frequency of 20kHz–50kHz; Real-time monitoring of interference signal strength. When the strength exceeds the threshold of 100mV, the amplification factor is dynamically adjusted to the upper limit of 2.0 times. Bandpass filter configuration: Optimize the filter settings, the passband frequency range is 10kHz–100kHz, the stopband attenuation is ≥40dB, and the filter center frequency is adaptively adjusted according to the diameter of the black leather material being tested: When the diameter is ≤80mm, the center frequency is 80kHz±2kHz; When the diameter is greater than 80mm, the center frequency is 30kHz±1kHz; Input a standard sinusoidal signal with a frequency of 50kHz and an amplitude of 5V into the probe to stabilize the output phase difference at 90°±2°; During the calibration period, the phase difference is sampled once per second, and an abnormal alarm is triggered when the offset is greater than ±5°.

5. The method for eddy current probing of black leather according to claim 1, characterized in that: Based on the optimized flaw detection parameters, the S300 monitors the changes in the surface state of the black leather material in real time and dynamically adjusts the core parameters of eddy current flaw detection, including frequency, gain, and phase, to compensate for the impact of surface unevenness on the eddy current field. The adjustment process is as follows: Measuring surface roughness, sampling interval mm, to obtain the surface micromorphology data of black leather in real time; Based on the collected surface roughness data, the surface fluctuation coefficient CV value is calculated in real time, where CV = σ / μ × 100%, σ is the standard deviation of the surface roughness data, and μ is the average roughness; Establish an association rule between surface fluctuation coefficient (CV) and eddy current testing parameters: when the CV value increases by 1%, the frequency is increased by 0.5kHz and the gain is decreased by 0.8dB to compensate for the influence of surface state changes on the testing signal. Phase angle compensation follows the formula , the phase deviation caused by surface fluctuation is calculated by this formula; After each parameter adjustment, 10 sets of eddy current flaw detection signals are collected and the signal-to-noise ratio improvement rate is calculated. When the signal-to-noise ratio improvement rate is ≥15%, it is confirmed that the dynamic compensation is effective.

6. The method for eddy current probing of black leather according to claim 1, characterized in that: The S400 uses a multi-channel eddy current testing system that simultaneously applies three sinusoidal excitation signals of different frequencies to detect defects of different depths in black leather materials: Low-frequency channel 50-100kHz: for defect detection in the subsurface and near-core areas of black leather materials, with a depth of ≥2mm, the excitation signal amplitude is set to 5V, and the signal duty cycle is 50%; Intermediate frequency channel 100-300kHz: covers defects in the middle layer of black leather, with a depth of 1-2mm, an excitation signal amplitude of 4V, and a duty cycle of 40%; High-frequency channel 300-500kHz: Focus on the surface and near-surface defects of black leather, depth ≤ 1mm, excitation signal amplitude 3V, duty cycle 30%; The continuous trigger period of each channel signal of the three frequency signals is 20ms, and the channel switching interval is ≤1ms.

7. The method for eddy current probing of black leather according to claim 6, characterized in that: The S400 calculates the energy entropy of the response signals collected by the multi-frequency eddy current detection according to the nodes, and quantitatively extracts the defect features: Signal preprocessing: low-pass filter the original signal of each channel to eliminate high-frequency noise interference, and map the signal amplitude to the 0-1 range through normalization. Unified feature calculation benchmark; Energy entropy calculation: After preprocessing, the signal is divided into multiple subsequences by node, and the energy entropy of each node is calculated. , ,in For the The proportion of the energy of each subsequence to the total energy; Effective defect judgment: Set the energy entropy threshold. When the node energy entropy , it is determined that there is a valid defect in the area corresponding to the node, and the defect location mark is triggered.

8. The method for eddy current probing of black leather according to claim 1, characterized in that: The S500 uses a dedicated sample bar to verify the equipment's ability to detect longitudinal and transverse defects. The specific steps include: Sample bar test parameters: Use the special sample bar prepared by S200, pass through the test area at a constant speed of 1m / min, and record the amplitude of the longitudinal defect signal and the amplitude of the transverse defect signal ; Sensitivity ratio calculation and determination: Calculate sensitivity ratio ,in, is the peak amplitude of the longitudinal defect signal, is the peak amplitude of the transverse defect signal, and the detection requirements are: ; Repeatability test: perform three consecutive sample stick tests with an interval of ≤1 minute between each test and record the results of each test. and , calculate the signal amplitude fluctuation of three tests ,in, For the The signal amplitude of the test, , is the average amplitude of three tests, and Respectively The maximum and minimum values ​​of the signal amplitude of the test are as follows: .

9. The method for eddy current probing of black leather according to claim 1, characterized in that: In the calculation of the false alarm rate in S500, 5% of the black leather materials after testing are sampled and the ultrasonic flaw detection equipment is used to scan the sampled black leather materials. The proportion of defects identified by eddy current testing that are confirmed to be free of defects by ultrasonic re-inspection, among which: The number of false defects confirmed by ultrasonic re-inspection, that is, the number of defects determined by eddy current testing but not detected by ultrasonic testing, Total number of defects reported for eddy current testing, where the inspection requirements are: .

10. The method for eddy current probing of black leather according to claim 1, characterized in that: In the S500, for the calculation of the missed alarm rate, a standard simulated defect is added to the area on the sample rod that is not identified by the eddy current detection. The simulated defect has a depth of 0.2 mm, a width of 0.4 mm, and a length of 5 mm. The missed alarm rate is defined as is the proportion of defects that have not been identified by eddy current testing after re-testing, is the number of simulated defects that were not identified by eddy current testing after retesting, The total number of simulated defects added is the detection requirement: .

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