Ferromagnetic object flaw detection device based on weak magnetic field measurement

Abstract

The invention relates to the crossing field of a nondestructive testing technology and a magnetic measurement technology, in particular to a ferromagnetic object flaw detection device based on weak magnetic field measurement. The device combines a weak magnetic field sensing technology, a ferromagnetic material uniform magnetization technology, an automatic control technology and a defect identification technology based on a magnetic flux leakage detection principle, and realizes non-contact and high-efficiency scanning type flaw detection of ferromagnetic workpiece defects by integrating a high-precision magnetic field sensor, a permanent magnet excitation structure and a step scanning mechanism; the defects that an ultrasonic flaw detector in the market is prone to loss and scattering in air, echo signals of coupling agent point-like slag inclusion are prone to generating false alarms, and a magnetic flaw detector in the market can only conduct segmented flaw detection on long workpieces and is low in efficiency can be effectively overcome. The device can be used for detecting ferromagnetic equipment in various scenes, such as flaw detection of gun barrels, gun barrels, tank reactive armors and aerospace metal parts after secondary recovery.

Description

Technical Field

[0001] This invention relates to the intersection of nondestructive testing (NDT) and magnetic measurement technologies, specifically to a flaw detection device for ferromagnetic objects based on weak magnetic field measurement. The device combines weak magnetic field sensing technology, ferromagnetic material magnetization technology, automated scanning control technology, and defect identification technology based on magnetic flux leakage detection principles. By integrating a high-precision magnetic field sensor, a permanent magnet excitation structure, and an automated scanning mechanism, it achieves non-contact, high-efficiency detection of surface and near-surface defects in ferromagnetic components. Ultimately, it can serve as a flaw detection device for inspecting ferromagnetic equipment and has significant application value. Background Technology

[0002] Non-destructive testing (NDT) technology plays a vital role in industrial production and equipment maintenance, serving as an essential means of inspecting industrial products. Currently, the mainstream NDT methods are ultrasonic testing and magnetic particle testing. However, commercially available ultrasonic flaw detectors suffer from limitations such as easy loss and scattering in air, the need for coupling agents to connect the object being tested, and the difficulty in distinguishing echo signals from point inclusions from point pores, leading to false alarms. Furthermore, commercially available magnetic particle flaw detectors, which rely on magnetic powder testing, have limitations such as only being able to perform segmented testing on long workpieces, failing to detect cracks from all directions in a single operation, and exhibiting relatively low testing efficiency.

[0003] Weak magnetic field measurement refers to the technology of detecting and quantifying weak magnetic fields using high-precision magnetic sensors and efficient signal processing. Currently available weak magnetic field measurement sensors can achieve measurement accuracy at the nanotesla (nT) or even picotesla (pT) level, sensitively capturing and analyzing the intensity, gradient, and distribution characteristics of subtle changes in magnetic fields. This rapid development has enabled weak magnetic field measurement to move from the laboratory to a wide range of applications, providing strong support for a series of engineering applications based on weak magnetic field measurement.

[0004] Flaw detection technology for ferromagnetic objects based on weak magnetic field measurement is a technique that directly detects flaws in ferromagnetic objects by measuring changes in weak magnetic fields. When a ferromagnetic material is free of defects, its internal magnetic field lines should be parallel or uniformly distributed after being uniformly magnetized. If defects exist, the magnetic field lines will be distorted due to the abrupt change in permeability at the defect location, and some magnetic field lines will overflow from the material surface, forming a leakage magnetic field. By capturing these leakage magnetic fields with a magnetic field sensor and combining them with the position parameters fed back by the stepper motor on the scanning guide, the location of the leakage magnetic field can be calculated, thus inferring the location of the damage to the ferromagnetic object. Summary of the Invention

[0005] The technical problem solved by this invention is as follows: Current non-destructive testing mainly uses ultrasonic testing and magnetic testing. However, the ultrasonic testing method used in commercially available ultrasonic flaw detectors has limitations such as easy loss and scattering in air, the need for coupling agents to connect the object being tested, difficulty in distinguishing echo signals from point inclusions from point pores due to their similarity, and a tendency to generate false alarms. To address these problems, this invention integrates an excitation device composed of an armature and neodymium magnet with a magnetic field sensor through a double-layer acrylic structure, forming a scanning device that directly measures changes in the leakage magnetic field for flaw detection. This eliminates the need for coupling agents and reduces the likelihood of false alarms caused by echo signals from point inclusions.

[0006] Secondly, commercially available magnetic particle flaw detectors have limitations, such as only being able to perform segmented flaw detection on long workpieces, not being able to detect all-around cracks at once, and having low flaw detection efficiency. To address this issue, the scanning device integrated in this invention, combined with a slide table and workpiece support, forms a flaw detection device for ferromagnetic objects. This device can stably perform scanning flaw detection on the entire workpiece with high flaw detection efficiency.

[0007] The technical solutions of this invention are as follows: 1. Direct measurement of leakage magnetic field changes for flaw detection. This invention uses an excitation device composed of an armature and neodymium magnets to uniformly magnetize ferromagnetic workpieces. A high-precision magnetic field sensor is then used to detect weak magnetic field changes for flaw detection. 2. Integrated device design. This invention integrates the excitation device composed of an armature and neodymium magnets with a magnetic field sensor through a double-layer acrylic structure, forming a scanning device that integrates uniform magnetization and magnetic field measurement. This device is then mounted on a scanning guide rail with an integrated stepper motor to achieve line scanning measurement of ferromagnetic workpieces. 3. Four-channel measurement improves accuracy. This invention uses a four-channel magnetic field sensor design. The independence of each magnetic field measurement device allows system errors to be partially offset during averaging. Simultaneously, the average value of the four magnetic field measurement devices is used as an unbiased estimate. The variance of the final measurement result is reduced by four times compared to a single magnetic field sensor measurement, significantly improving measurement accuracy.

[0008] The principle of this invention is: (1) To form a ring magnetic field for uniform magnetization An excitation device is constructed using a permanent magnet and an armature. The permanent magnet is mounted at both ends of the armature, creating a uniform ring-shaped magnetic field with the ferromagnetic workpiece to be tested. This uniformly magnetizes the workpiece, ensuring that the magnetic field lines passing through it are parallel or uniformly distributed. (See [link to relevant documentation]). Figure 3 .

[0009] (2) Magnetic flux is measured in real time by a sensor. A magnetic field sensor is placed in the part of the workpiece that forms a ring-shaped magnetic field. Specifically, the magnetic field sensor is installed between the armature and the workpiece, and between the two permanent magnets. The magnetic flux of the workpiece is measured in real time, and the data is transmitted back to the computer in real time. (See [link to relevant documentation]). Figure 4 .

[0010] (3) Detecting defects using the edge effect of magnetic fields The fringing effect refers to the phenomenon where, when a magnetic field passes through the edge of a magnetic material, the magnetic field lines change from their original parallel or uniform distribution to diffuse and bend outwards. The magnetic flux forms a fringing flux at the edge of the material, which is called a leakage magnetic field. This phenomenon is called the fringing effect.

[0011] Similarly, when ferromagnetic equipment has defects or air gaps, due to the edge effect of the magnetic field, the originally parallel or uniformly distributed magnetic flux lines will repel each other and bulge outwards. At the defect or air gap, they will diverge, bend, and extend beyond the edge of the air gap. See [link to relevant documentation]. Figure 5 At this point, the presence of defects in the workpiece can be determined based on the subtle changes in the magnetic field detected by the magnetic field sensor.

[0012] (4) Four-channel measurement improves accuracy According to random variable theory, each measurement of the magnetic field parameter X by each magnetic field measuring device is considered an independent observation. For a single-channel magnetic field measuring device, its measurement value may be affected by random errors. However, when using a four-channel magnetic field measuring device, the measurement value of each channel is considered a different observation of the random variable X. That is, by using multiple channels, multiple independent and identically distributed observations are obtained. Therefore, the average value of the four-channel magnetic field measuring device is taken as the unbiased estimate. The expected value is: Since the variances of the magnetic field measurement devices in each channel are similar, approximately Therefore, the variance of the four channels is approximately: The overall variance was reduced by a factor of 4 compared to the original variance, which means that four-channel measurement can effectively improve accuracy when measuring the magnetic field characteristics of an object.

[0013] Compared with existing solutions, the main advantages of this invention are: Both commercially available magnetic flaw detectors and the flaw detector designed by our team that measures weak magnetic field changes share a common limitation: they can only effectively detect flaws in magnetizable objects. This is unavoidable. However, the flaw detection device for ferromagnetic objects based on weak magnetic field measurement still has the following advantages compared to commercially available magnetic flaw detectors: (1) High degree of integration. Through a double-layer acrylic structure, the excitation device composed of armature and neodymium magnet is integrated with the magnetic field sensor to form a scanning device that integrates uniform magnetization and magnetic field measurement. Combined with the scanning guide rail, it can perform line scanning flaw detection on ferromagnetic workpieces, reducing the size and improving the deployment flexibility and operation convenience.

[0014] (2) High flaw detection efficiency. Compared with the magnetic flaw detectors on the market, the device realizes uniform linear scanning measurement, which can perform scanning flaw detection on the whole object. It is fast and highly sensitive, overcoming the limitations of magnetic flaw detectors, which can only perform segmented flaw detection on long workpieces, cannot detect all-round cracks at one time, and have low flaw detection efficiency.

[0015] (3) Results are visible in real time and can be saved for analysis. The magnetic field changes are visualized in real time, which makes it convenient to observe the changes in weak magnetic fields, determine the location of leakage magnetic fields, and then determine the location of damage. At the same time, the measured magnetic field data can be recorded and saved, which can be used for later analysis of magnetic field changes of different types of damage, so as to summarize the experience of directly determining the defect type through magnetic field changes.

[0016] (4) Improved measurement accuracy. The present invention uses a four-channel magnetic field sensor design. The independence of each magnetic field measurement device allows the system error to be partially offset during the averaging process. At the same time, the average value of the four magnetic field measurement devices is used as an unbiased estimate. The variance of the final measurement result is reduced by 4 times compared with the measurement by a single magnetic field sensor, and the measurement accuracy is significantly improved.

[0017] (5) Low false alarm rate. Compared with ultrasonic flaw detection, flaw detection is carried out by measuring weak changes, which can effectively overcome the limitation that the echo signal of point inclusions is similar to that of point pores, making it difficult to detect flaws accurately.

[0018] (6) It is easy to operate. Compared with the traditional magnetic powder method, there is no need to sprinkle and clean magnetic powder, which simplifies the steps and makes it easier to use in reality. It has a wide range of applications, is easy to operate, and is less affected by impurities and the surrounding environment. Attached Figure Description

[0019] Figure 1 A schematic diagram of a ferromagnetic flaw detection device based on weak magnetic field measurement; Figure 2 This is a schematic diagram of the four-channel distribution of the magnetic field sensor; Figure 3 Schematic diagram of the principle of uniform magnetization to form a ring magnetic field; Figure 4 Schematic diagram for real-time measurement of magnetic flux using sensors; Figure 5 Schematic diagram of the principle for detecting defects using the edge effect of a magnetic field; Figure 6This is a schematic diagram of the double-layer acrylic structure of the scanning device; Figure 7 This is a picture of the HWT3100-485 magnetic field sensor. Figure 8 The images show the actual slide table, drive motor, and control panel. Figure 9 This is a schematic diagram of the connection between the scanning device and the guide rail. Figure 10 This is a picture of the actual workpiece support. Detailed Implementation

[0020] (1) Design, introduction and installation process of the scanning device The scanning device consists of a fixing device, a magnetic field sensor, a powerful magnet, and an armature. The fixing device is made of acrylic sheet, which prevents the magnetic field generated by the device itself after magnetization from affecting the measurement. The entire device comprises an inner shell and an outer shell; see [link to documentation]. Figure 6 Based on the dimensions of the armature and magnetic field sensor, the basic dimensions of the mounting housing were determined as follows: inner housing height 8.4cm, width 8.4cm, length 25cm; outer housing height 10.6cm, width 10.6cm, length 20cm. During installation, a 1.1cm gap was left around the inner and outer housings on all four sides for placing the armature, and a 2.5cm gap was left at each end of the inner and outer housings for placing the magnets. Simultaneously, a custom-made acrylic plate had pre-drilled square holes with dimensions of 2mm in length and width. Self-locking nylon straps were passed through these holes to secure the magnetic field sensor and armature.

[0021] The magnetic field sensor selected is the HWT3100-485 magnetic field sensor. (See attached image.) Figure 7 It features high precision and fast response, and is used to measure weak magnetic fields. It can be directly connected to a computer terminal. The sensor is fixed to the inner shell of the mounting device by passing a self-locking nylon strap through a small hole.

[0022] The powerful magnet and armature are neodymium magnet and high-purity nickel block, respectively. They are used to create a uniform ring-shaped magnetic field to uniformly magnetize the ferromagnetic equipment under test. The armature is fixed between the inner and outer shells through small holes pre-drilled in the acrylic plate using self-locking nylon straps. The neodymium magnet is attracted to both ends of the high-purity nickel block and extends into the vicinity of the fixing device axis.

[0023] (2) Design, introduction and installation process of scanning guide rail The scanning guide consists of a 500mm travel 42mm feed slide, a drive motor, and a control panel. (See attached image) Figure 8 The 500mm stroke 42-position sliding table includes a slide rail and a sliding table for stable scanning; a drive motor and a control panel enable uniform linear movement of the sliding table. Small holes are pre-drilled on the sliding table for fixing the scanning device.

[0024] The scanning device is secured to the slide by passing a self-locking nylon strap through a pre-drilled hole in the device. See [link / reference]. Figure 9 This enables uniform linear scanning measurement.

[0025] (3) Design, introduction and installation process of workpiece support The workpiece support consists of an iron stand, a circular grooved arc-shaped bracket, and a laboratory cross clamp. The iron stand is used to stabilize the base, the circular grooved arc-shaped bracket is used to support the object being measured, and the laboratory cross clamp is used to fix the iron stand and stabilize the circular grooved arc-shaped bracket. See [link / reference needed]. Figure 10 .

[0026] The contents not described in detail in this invention are existing technologies known to those skilled in the art.

Claims

1. A flaw detection device for ferromagnetic objects based on weak magnetic field measurement, characterized in that: A novel flaw detection device for ferromagnetic objects is proposed. It integrates an excitation device consisting of an armature (1) and a neodymium magnet (2) with a magnetic field sensor (3) through a double-layer acrylic structure (4) to form a scanning device. The device is then installed on a scanning guide rail (6) and can perform scanning flaw detection on ferromagnetic workpieces located on an acrylic workpiece support (5). The device reduces the overall size of the device through the integrated design of the scanning device, realizing the miniaturization of the device. At the same time, by using acrylic material to build the structure, it effectively avoids the influence of the device being magnetized on the measurement.

2. The ferromagnetic object flaw detection device based on weak magnetic field measurement according to claim 1, characterized in that: A novel flaw detection method for ferromagnetic objects is proposed. Based on the edge effect of magnetic fields, a flaw detection device for ferromagnetic objects with a double-layer acrylic structure, an integrated excitation device and a magnetic field sensor is designed. The excitation device uniformly magnetizes the ferromagnetic object under test. When the ferromagnetic object under test is damaged, the magnetic field sensor can detect the weak magnetic field change at the damage site. Combined with the position parameters fed back by the stepper motor of the scanning guide, the location of the damage in the ferromagnetic object is calculated.

3. The ferromagnetic object flaw detection device based on weak magnetic field measurement according to claim 2, characterized in that: The method of uniformly magnetizing ferromagnetic objects using a ring magnetic field and the phenomenon of leakage magnetic field generated by the edge effect of the magnetic field are utilized. When the armature (1) and neodymium magnet (2) generate a uniform ring magnetic field that passes through the ferromagnetic object to be tested, the ferromagnetic object to be tested is uniformly magnetized, and the magnetic field lines inside are parallel or uniformly distributed. If the ferromagnetic object to be tested is damaged, the leakage magnetic field generated at the damaged location is captured by the magnetic field sensor (3). A peak or valley will appear in the time-magnetic field image fed back by the sensor. The peak and valley are related to the direction of the magnetic field. At this time, combined with the position parameters fed back by the stepper motor of the scanning guide rail (6), the location of the leakage magnetic field is calculated, and finally the location of the damage to the ferromagnetic object to be tested is obtained.

4. The ferromagnetic object flaw detection device based on weak magnetic field measurement according to claim 3, characterized in that: The magnetic field sensor has four channels (7)(8)(9)(10) distributed. For the workpiece to be measured (11), the measured value of each channel is a different observation value of the random variable X. That is, by using multiple channels, multiple independent and identically distributed observations are obtained. Therefore, when measuring the magnetic field characteristics of the object, the average value of the four channels of the magnetic field measuring device is used as an unbiased estimate. In the averaging process, the systematic error is partially offset. The variance of the measured result is reduced by 4 times compared with the measurement of a single magnetic field sensor, and the measurement accuracy is significantly improved.

Images