A method for detecting defects on the surface and near-surface of a bar based on an ultrasonic inclined probe

Abstract

The application discloses a kind of based on ultrasonic oblique probe's bar surface and near surface defect detection method, including S1, using hand-held ultrasonic flaw detector and its oblique probe, oblique probe is equipped with with the concave arc surface of bar outer diameter curvature coincidence, then using standard test block calibration flaw detector's time base scanning line and sensitivity;S2: the surface of bar to be detected pre-coats a layer of ultrasonic coupling agent, and the concave arc surface of oblique probe is completely attached with bar circumference;S3: increase roller, along the circumferential direction of bar circumference is circumferentially scanned, and when scanning, probe sound beam axis is perpendicular to the suspected defect direction of bar, simultaneously, oblique probe is slowly moved along bar axis direction with certain pitch;S4: identify defect, calculate defect depth and circumferential position, carry out qualitative analysis and rough quantitative to defect;S5: record result, assess bar eligibility.The application has the advantages that the coupling effect of bar defect detection is good, the detection sensitivity is high, and the operation is simple and fast.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and particularly relates to a method for detecting surface and near-surface defects in bars based on an ultrasonic angle probe. Background Technology

[0002] During the production and processing of bar stock, due to the influence of processes such as billet preparation, rolling, and drawing, primary defects such as cracks, folds, laps, and scratches are easily generated on the surface and near the surface. These defects will be further expanded in subsequent forming processes such as cold extrusion, cold drawing, and forging, becoming sources of fatigue fracture during the service of parts, seriously affecting the fatigue strength and safety of subsequently processed parts.

[0003] Currently, the mainstream non-destructive testing methods for surface and near-surface defects in bars mainly include four categories: magnetic particle testing, penetrant testing, conventional ultrasonic straight probe testing, and conventional planar angle probe testing. However, each method has its own technical limitations. Magnetic particle testing: Magnetic particle testing is only applicable to ferromagnetic materials and can only detect open defects on the surface of the workpiece and very close to the surface. It has extremely low sensitivity for near-surface defects with a burial depth of more than 3mm and cannot detect non-ferromagnetic rods such as austenitic stainless steel and aluminum-magnesium alloys. At the same time, the workpiece surface needs to be thoroughly cleaned before testing to remove oxide scale, oil stains and other coverings. After testing, the workpiece needs to be demagnetized. The overall testing process is cumbersome, has a low degree of automation, cannot be adapted to high-speed production lines, and the testing efficiency is difficult to meet the needs of large-scale industrial production.

[0004] Penetrant testing: Although penetrant testing can be applied to most metal materials, it can only detect surface open defects and cannot detect internal near-surface defects. In addition, the testing process requires multiple steps such as penetrant, cleaning, drying and developing, which results in a long testing cycle. Some penetrant reagents contain flammable and toxic components, which can cause harm to the environment and the health of operators, thus its application has obvious limitations.

[0005] Conventional straight-probe ultrasonic testing: Straight probes rely on the perpendicular incidence of longitudinal waves to detect defects. Due to the existence of near-field blind zones in ultrasound, the sensitivity for detecting defects within 10mm of the surface of the bar is extremely low, resulting in a large-area detection blind zone that cannot meet the requirements for detecting surface and near-surface defects. At the same time, bars are mostly cylindrical curved surfaces, and conventional planar straight probes only have point or line contact with the bar surface, resulting in poor coupling stability and large sound energy scattering loss. This not only leads to a decrease in detection sensitivity but also causes large errors in the determination of defect location and size, making it difficult to achieve accurate qualitative and qualitative positioning of defects.

[0006] Conventional planar angle probe ultrasonic testing: Angle probes rely on transverse waves to detect defects, which are theoretically more suitable for identifying transverse cracks, circumferential folds, and other defects on the surface of bars. However, conventional angle probes have a planar contact surface, which also has the problem of small coupling contact area and poor coupling effect when used for testing the curved surface of cylindrical bars. The sound energy loss can reach more than 30%, which greatly reduces the detection sensitivity. More importantly, when the planar angle probe moves and scans on the curved surface, the incident point and refraction angle of the sound beam will continuously shift with the change of probe position, resulting in messy defect reflection waveforms, poor detection repeatability, large defect location error, insufficient reliability of detection results, and easy to miss or misjudge.

[0007] Furthermore, most mainstream ultrasonic testing of bars currently adopts a fixed bench operation mode, which requires manual rotation of the bars to complete the full surface scanning. This is not only labor-intensive and inefficient, but also prone to blind spots due to human error, further increasing the risk of missed detections. It can no longer meet the high precision and high efficiency requirements of modern industry for bar quality testing. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of poor coupling stability, low detection sensitivity, large near-surface blind zone, poor detection reliability, and low automation in existing defect detection methods. It provides a detection method for surface and near-surface defects of bars based on an ultrasonic angle probe, which can improve coupling stability and acoustic energy transmission efficiency, enhance detection sensitivity, locate the depth and circumferential position of defects relatively accurately, and improve detection efficiency and probe versatility.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for detecting surface and near-surface defects in bar stock based on an ultrasonic angle probe is disclosed. The method employs a handheld ultrasonic flaw detector and an angle probe. The angle probe has an arc surface that matches the curvature of the bar stock to be inspected. The process involves equipment preparation and calibration, surface arrangement and coupling, circumferential scanning and axial feeding, and defect identification and analysis to obtain the defect depth and circumferential location. The defects are then qualitatively analyzed and roughly quantified. Based on the recorded data, the passability of the bar stock is evaluated.

[0010] The above-mentioned detection methods specifically include: Step S1, Equipment Preparation and Calibration: S11 uses a pulse-reflection handheld ultrasonic flaw detector. Depending on the diameter and material of the bar to be inspected, one or more refraction angles are selected. The leading edge of the probe is a concave arc surface that matches the curvature of the outer diameter of the bar to ensure surface contact coupling. S12, use a standard test block to calibrate the time base scan line and sensitivity of the flaw detector.

[0011] Step S2: Detect surface arrangement and coupling: S21, a uniform layer of ultrasonic coupling agent is pre-coated on the surface of the bar to be inspected; S22, the arc-shaped angled probe is stably placed on the surface of the rod, so that the arc-shaped surface of the probe is completely in contact with the circumferential surface of the rod, forming a stable surface contact coupling.

[0012] Step S3: Circumferential scanning and axial feed: S31, a roller conveyor is added to the bench design to enable automatic turnover of round steel bars; S32. Place the probe along the circumference of the bar at a stable speed and pressure to perform a circumferential scan. During the scan, the probe's acoustic beam axis should be perpendicular to the direction of the suspected defect in the bar. S33, at the same time, the probe moves slowly along the axis of the bar with a certain pitch to achieve a spiral full-coverage scan of the entire surface of the bar.

[0013] Step S4: Defect Identification and Analysis S41. During the scanning process, observe the waveform on the flaw detector screen in real time. When a stable echo signal exceeding the preset alarm threshold is found, mark the location. S42, by analyzing the position of the echo on the time baseline, combined with the refraction angle of the probe and the known geometric relationship of the rod curvature, calculates the depth and circumferential position of the defect; S43 uses a micro-motion probe to observe changes in echo amplitude, enabling qualitative analysis and rough quantitative assessment of defects.

[0014] Step S5: Result Recording and Evaluation: S51, record the location, depth, amplitude, and indication length of all defects exceeding the standard; S52, assess the conformity of bar stock according to relevant product standards or technical agreements.

[0015] Furthermore, in step S11, the refraction angle is selected as 45°, 60°, or 70°.

[0016] Furthermore, in step S12, the time base scan line calibration includes sound path, level or depth calibration, and the sensitivity calibration includes creating a distance-amplitude curve, i.e., a DAC curve.

[0017] Furthermore, in step S33, the pitch is 1 / 2 to 2 / 3 of the probe width.

[0018] Furthermore, in step S41, the alarm threshold is set to -6dB or -12dB of the DAC curve.

[0019] Furthermore, in steps S42 and S43, the depth is the vertical distance from the surface, the qualitative analysis includes point defects or strip defects, and the rough quantitative analysis includes measuring the indicated length using the half-wave height method.

[0020] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: (1) More stable coupling performance: The arc-shaped angled probe structure can form a surface contact with the cylindrical surface to be tested, and the coupling state is stable, which greatly improves the sound energy transmission efficiency, effectively reduces the detection false alarm and missed alarm caused by coupling fluctuation, and improves the reliability of the detection results; (2) Higher sensitivity for detecting minute defects: By optimizing the sound beam incident method, the scattering effect of the cylindrical curved surface on the sound beam is reduced, making the sound energy more concentrated, and it has excellent detection capability for surface and near-surface minute defects, and can detect tiny defects that are difficult to identify by conventional probes. (3) Better defect location accuracy: With a standardized calibration process and a dedicated geometric calculation method, the depth and circumferential position of the defect can be accurately determined. The location accuracy is significantly better than the empirical estimation of conventional angle probes, providing a more accurate location basis for defect assessment. (4) More convenient and efficient on-site operation: It is compatible with handheld testing instruments and adopts a spiral scanning path. Only one person is needed to complete all testing operations. It has a fast testing speed and strong adaptability, and is especially suitable for on-site operations, in-service equipment testing and workpiece sampling inspection. (5) Wide range of applications and strong versatility: It can be equipped with arc-shaped angle probes with different curvature radii and different angles, and can adapt to the testing needs of bars with different diameter specifications. It can cover multiple specifications of workpieces without replacing the entire testing device, thus reducing the testing cost. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the arc-shaped surface of the ultrasonic angle probe of the present invention; Figure 2 This is a schematic diagram showing the interaction between the roller conveyor added to this invention and the round steel during scanning. Detailed Implementation Example 1

[0022] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] The standard test block used in this invention can be a CSK-IA test block, an IIW test block, or a special bar comparison test block.

[0024] In this embodiment, the detection of axial cracks on the surface of a 45# steel round bar with a diameter of Φ50mm is taken as an example, and the specific steps are as follows: Preparation: Select a digital ultrasonic flaw detector. The probe should be a 5MHz transverse wave angle probe (60° refraction angle, K value 2.0, arc curvature radius R = 25mm). Figure 1 The probe shown has an arc-shaped surface 1a. The probe chip is approximately 15 mm wide. The coupling agent is industrial paste.

[0025] Calibration: On the CSK-IA test block, set the instrument to "Shear Wave Depth Calibration" mode, find the highest echoes of the R50 and R100 arcs, and calibrate to the screen depth scale of 25mm and 50mm respectively. Then, use the Φ1mm transverse hole to create a DAC curve and set the evaluation line to DAC-10dB.

[0026] Scanning: Apply coupling agent to the surface of round steel 2. Place the shear wave angle probe 1 at one end of round steel 2, maintaining good coupling. Figure 2 As shown, the roller conveyor 3 rotates the round steel 2 and moves about 10mm along the axial direction to perform spiral forward scanning.

[0027] Defect discovered: At a distance of 300mm from the end, a stable echo with an amplitude of DAC-4dB appeared on the screen. Micro-scanning at the marked location revealed a sharp echo envelope; the echo rapidly increased and decreased when the probe was moved back and forth, consistent with the characteristics of point-like or short cracks.

[0028] Location assessment: The echo depth reading is 2.1 mm. Based on geometric calculations, the defect depth from the surface is approximately 2.0 mm. The circumferential indication length is approximately 3 mm. According to the standard, this is determined to be a single point-like defect exceeding the standard; therefore, it is recorded and marked. Example 2

[0029] In this embodiment, taking the inspection of finished 45# carbon structural steel round bars with a diameter of Φ80mm upon warehousing as an example, the specific steps are as follows: Preparation: Select a general-purpose pulse-echo handheld ultrasonic flaw detector. Based on the diameter and material parameters of the round bar, select a special arc-shaped angled probe with a refraction angle of 60°. The probe is machined into a concave arc-shaped leading edge that matches the curvature of the outer diameter of the Φ80mm round bar, ensuring that the probe and the outer circle of the workpiece can be completely fitted to form surface contact.

[0030] Calibration: The time base scan line of the flaw detector was calibrated using the CSK-IA standard test block to complete the calibration of depth and sound path parameters. Then, a DAC distance-amplitude curve was made using a comparison test block specifically for round bars of this specification. The rejection alarm threshold was set to DAC-6dB and the evaluation threshold was set to DAC-12dB.

[0031] Scanning: Apply machine oil evenly to the surface of the bar to be inspected as an ultrasonic coupling agent. Place the arc-shaped angled probe at the starting position on the end face of the bar, adjust the probe pressure to make the arc surface completely fit the outer circle of the workpiece, and confirm that the coupling state is stable.

[0032] The round bar to be inspected is placed on a testing stand with an automatic rotating roller conveyor. The roller conveyor is started to drive the round bar to rotate circumferentially at a uniform speed, realizing automatic circumferential scanning. At the same time, the operator holds the probe and feeds it slowly along the axial direction of the round bar with a pitch of 12mm. The arc-shaped angled probe used in this case has a width of 20mm, and the 12mm pitch is 3 / 5 of the probe width, ensuring 100% coverage of the scanning area without omission, and finally realizing a spiral full-coverage scanning of the entire round bar.

[0033] Results Assessment: During the inspection, the flaw detector triggered an alarm and detected a stable echo at a position 1.2m along the axial direction of the round bar. The echo amplitude exceeded the DAC-6dB rejection threshold. After marking this position, the defect depth was calculated to be 0.4~0.6mm based on the echo time base position, refraction angle, and geometric relationship of the round bar curvature. This defect was located in the near-surface region of the round bar. The axial indication length of the defect was measured to be 12mm using the half-wave height method. According to the national standard "Hot-rolled round and square bars of high-quality carbon structural steel", this defect is an excessive defect. Therefore, the round bar was deemed unqualified and scrapped.

[0034] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe, characterized in that: S1. Equipment preparation and calibration: Use a handheld ultrasonic flaw detector and its angle probe. Select one or more refraction angles according to the diameter and material of the bar to be inspected. The angle probe is equipped with a concave arc surface that matches the curvature of the outer diameter of the bar. Then use a standard test block to calibrate the time base scan line and sensitivity of the flaw detector. S2: Detection surface arrangement and coupling: A uniform ultrasonic coupling agent is pre-coated on the surface of the bar to be inspected, and the angled probe is stably placed on the surface of the bar so that its concave arc surface is completely in contact with the circumferential surface of the bar. S3: Circumferential scanning and axial feed: Add roller conveyor to the bench design, place the probe along the circumference of the bar at a stable speed and pressure for circumferential scanning, and during scanning, the probe beam axis is perpendicular to the suspected defect direction of the bar. At the same time, the angled probe moves slowly along the axial direction of the bar with a certain pitch. S4: Defect Identification and Analysis: Observe the waveform on the flaw detector screen in real time. When a stable echo signal exceeding the preset alarm threshold is found, mark the location. Analyze the position of the echo on the time baseline, combine the probe's refraction angle with the known geometric relationship of the bar's curvature, and calculate the depth and circumferential position of the defect. Then, observe the changes in echo amplitude by moving the probe back, forth, left, and right to perform qualitative analysis and rough quantitative analysis of the defect. S5: Results Recording and Evaluation: Record the location, depth, magnitude, and indicated length of all defects exceeding the standard, and evaluate the conformity of the bar stock according to the relevant product standards or technical agreements.

2. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1, characterized in that: In step S1, the refraction angle is selected as 45°, 60°, or 70°.

3. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1 or 2, characterized in that: In step S1, time base scan line calibration includes sound path, horizontal or depth calibration, and sensitivity calibration includes creating a distance-amplitude curve, i.e., a DAC curve.

4. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1 or 2, characterized in that: In step S3, the pitch is 1 / 2 to 2 / 3 of the probe width.

5. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1 or 2, characterized in that: In step S4, the alarm threshold is set to -6dB or -12dB of the DAC curve.

6. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1 or 2, characterized in that: In step S4, the qualitative analysis includes point defects or strip defects.

7. The method for detecting surface and near-surface defects in rods based on an ultrasonic angle probe according to claim 1 or 2, characterized in that: In step S4, the rough quantification includes measuring the indicated length using the half-wave height method.

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