Magnetic Particle Testing for Electric Scooters

Magnetic Particle Testing for Electric Scooters

1. Principle of Magnetic Particle Testing

1.1 Mechanism of Magnetic Field and Magnetic Particles
Magnetic particle testing is a non-destructive testing method based on the interaction between magnetic field and magnetic particles, and is widely used in defect detection of electric scooter parts. The principle is that after the ferromagnetic material is magnetized under the action of a magnetic field, defects on the surface or near the surface will interfere with the magnetic field distribution, thereby generating a leakage magnetic field at the defect, attracting magnetic particles to gather, and forming visible magnetic particle traces, so as to judge the existence and location of defects.
When a magnetic field is applied to the ferromagnetic parts of an electric scooter, the parts are magnetized. If there are defects such as cracks, pores, and inclusions on the surface or near the surface of the parts, these defects will interfere with the uniform distribution of the magnetic field, causing the magnetic field to be distorted at the defect, generating a leakage magnetic field. The strength of the leakage magnetic field is related to factors such as the size, shape, depth of the defect, and the strength of the magnetization field. Under the action of the leakage magnetic field, the magnetic particles are attracted to the defect and accumulate at the defect, forming clearly visible magnetic particle traces. By observing the shape, size, and position of the magnetic particle traces, the inspector can judge the nature and severity of the defect.
For example, when the frame of an electric scooter is subjected to magnetic particle testing, if there are cracks on the surface of the frame, the magnetic particles will gather at the cracks, forming a trace similar to the shape of the cracks. The inspector can judge the size and location of the cracks based on the length, width and distribution of the magnetic particle traces, thereby evaluating the safety and reliability of the frame.

2. Inspection parts of electric scooters

2.1 Inspection of key parts of the frame
The frame is the core component of the electric scooter, which bears the structural support and load transfer functions of the entire vehicle. Its quality is directly related to the safety and stability of the electric scooter. In practical applications, the key parts of the frame mainly include the connection points of the frame, the bending stress concentration area, and the welding parts.
Connection point detection: The connection points of the frame are the parts where the various components are connected to each other and are subject to complex stresses. For example, the connection points between the frame and the handlebars, wheels and other components are prone to cracks and other defects due to frequent vibration and impact during driving. Through magnetic particle testing, tiny cracks at the connection points can be found. According to statistics, in actual testing, about 15% of the frame connection points have potential cracks. If these cracks are not discovered and handled in time, they may cause the frame to break, which in turn causes safety accidents.
Detection of bending stress concentration areas: During the use of the frame, bending stress will be generated due to the weight of the rider and various forces during driving. In some parts of the frame, such as the middle part of the frame and the wheel installation part, the bending stress is large and fatigue cracks are prone to occur. Magnetic particle testing can effectively detect cracks in these areas. Studies have found that after a certain period of use, the crack incidence rate in the bending stress concentration area of ​​the frame is about 10%. Magnetic particle testing can detect these cracks in time to prevent them from further expansion.
Welding part detection: The welding part of the frame is an area prone to defects in the manufacturing process. Defects such as pores, slag inclusions, and incomplete penetration may occur during welding, which will reduce the strength and reliability of the frame. Magnetic particle testing can detect these defects in the welding part. When testing a batch of electric scooter frames, it was found that the defect rate of welding parts was about 8%. Magnetic particle testing can accurately locate these defects and ensure the quality of the frame.
2.2 Testing of connecting parts such as shafts
The shaft is an important part of the electric scooter. It is used to connect the wheel and the frame and bear the rotational force of the wheel and the load of the vehicle. The quality of the shaft directly affects the operation of the wheel and the stability of the vehicle. In addition to the shaft itself, other connecting parts of the electric scooter, such as the connection between the handlebar and the frame, and the connection between the pedal and the frame, also need to be tested.
Shaft detection: The shaft will be subjected to frequent rotation and impact during use, and it is prone to defects such as wear and cracks. Magnetic particle testing can detect these defects on the surface and near the surface of the shaft. When testing the shaft of the electric scooter, it was found that about 12% of the shafts had surface cracks, which may cause the shaft to break and affect the normal operation of the wheel. Through magnetic particle testing, these cracks can be found in time, and defective shafts can be replaced to ensure the safe operation of the vehicle.
Detection of the connection between the handlebar and the frame: The connection between the handlebar and the frame is the key part for the rider to control the vehicle, and the firmness of the connection is directly related to the safety of riding. In this part, due to the operating force of the rider and the vibration during the vehicle's driving, defects such as looseness and cracks are prone to occur. Magnetic particle testing can detect defects such as cracks in the connection. In actual testing, about 5% of the handlebars and frames have cracks. Through magnetic particle testing, these defects can be discovered in time to prevent the handlebars from loosening or falling off, and ensure the safety of the rider.
Detection of the connection between the pedal and the frame: The connection between the pedal and the frame bears the weight of the rider and the operating force of the foot, and is prone to wear, looseness and other defects. Magnetic particle testing can detect defects in the connection. When testing the connection between the pedal and the frame of the electric scooter, it was found that about 7% of the connection parts had cracks caused by wear. Through magnetic particle testing, these cracks can be discovered in time to prevent the pedal from loosening or falling off, and ensure the normal use of the vehicle.

3. Preparation before testing

3.1 Calibration of testing equipment
The accuracy of the testing equipment is a key factor in the reliability of the magnetic particle testing results. Before conducting magnetic particle testing of electric scooter parts, the testing equipment must be strictly calibrated.
Magnetic field strength calibration: Magnetic field strength is one of the core parameters of magnetic particle testing. According to the standard requirements, the magnetic field strength of the testing equipment needs to be within the specified range to ensure that the leakage magnetic field can be effectively generated and the magnetic particles can be attracted. Usually, the calibration of the magnetic field strength requires testing with a standard test block to ensure that the equipment can achieve the required magnetic field strength under different working conditions. For example, for the inspection of the frame of an electric scooter, the magnetic field strength should reach 100-150 A/m to ensure that tiny cracks and defects can be detected.
Magnetic particle quality inspection: The quality of the magnetic powder directly affects the accuracy of the test results. The particle size, magnetism, color and other characteristics of the magnetic powder need to meet the standard requirements. Before testing, the magnetic powder should be sampled and tested to ensure that its particle size is uniform, the magnetism is good, and the color contrast is high, so that a clear and visible trace can be formed at the defect. According to relevant standards, the particle size of magnetic powder should be controlled between 50-100 mesh, the magnetic strength should reach more than 80%, and the color contrast should reach more than 90%.
Equipment stability test: The performance of the detection equipment may fluctuate during long-term use, so a stability test is required before the test. Through multiple consecutive tests, ensure that the detection results of the equipment at different time points are consistent and repeatable. For example, when the same standard test block is tested multiple times, the position and shape of the magnetic powder traces should remain consistent, and the fluctuation range of the magnetic field strength should be controlled within ±5%.
3.2 Cleaning of the tested part
The cleanliness of the tested part directly affects the effect of magnetic powder testing. Any impurities such as dirt, oil, rust, etc. may interfere with the adsorption and distribution of magnetic powder, resulting in inaccurate test results.
Surface cleaning: Before magnetic particle testing, the surface of the electric scooter parts needs to be thoroughly cleaned. Use special cleaning agents and tools to remove impurities such as oil, dust, rust, etc. on the surface. For example, for the surface of the frame, you can use anhydrous ethanol and a soft brush to clean it to ensure that the surface is clean, smooth, and free of any residue. Studies have shown that the detection sensitivity can be increased by more than 30% after the surface is cleaned.
Removing the coating: If there is a coating (such as paint, anti-rust paint, etc.) on the detected part, it needs to be removed. The presence of the coating will hinder the penetration of the magnetic field and the adsorption of magnetic particles, affecting the detection results. The coating can be removed by chemical paint strippers or mechanical polishing, but be careful not to damage the surface of the parts. For example, when removing the anti-rust paint on the surface of the shaft, soak it in a chemical paint stripper for 10-15 minutes, then wipe it clean with a soft cloth to ensure that there is no residual coating on the surface.
Drying: The cleaned parts need to be dried to prevent moisture from affecting the adsorption and distribution of magnetic particles. You can use hot air drying equipment or natural drying methods to ensure that the surface of the parts is dry. For example, after cleaning the frame and shaft parts, use hot air drying equipment to dry them at a temperature of 50-60℃ for 10-15 minutes to ensure that there is no residual moisture on the surface.

4. Implementation steps of magnetic particle testing

4.1 Magnetic field application method
The application of magnetic field is a key link in magnetic particle testing, and the choice of its method directly affects the detection effect and efficiency.
Direct power-on method: For shaft and tube parts such as the frame and shaft of electric scooters, the direct power-on method is a commonly used magnetic field application method. By connecting the parts to the power supply, they become magnetization sources and generate circumferential magnetic fields. The advantages of this method are simple operation, uniform magnetic field intensity, and can effectively detect circumferential defects on the surface and near the surface of parts. For example, when testing the shaft of an electric scooter, the direct power-on method can detect cracks on the surface of the shaft with a detection sensitivity of more than 95%.
Coil method: For some parts with complex shapes or large sizes, such as the frame of an electric scooter, the coil method is an effective magnetic field application method. The parts are placed in a powered coil, and the magnetic field generated by the coil is used to magnetize the parts to generate a longitudinal magnetic field. The advantage of this method is that the entire part can be uniformly magnetized, which is suitable for detecting longitudinal defects. In practical applications, the coil method can detect longitudinal cracks in the frame with a sensitivity of more than 90%.
Magnetic yoke method: The magnetic yoke method is suitable for local detection, such as the connection points, welding parts and other local areas of the electric scooter frame. By placing the two magnetic poles of the magnetic yoke on both sides of the detected part, a local magnetic field is formed. The advantage of this method is that it is flexible in operation, and the position and spacing of the magnetic poles can be adjusted as needed, and the detection effect of local defects is better. When testing the connection points of the frame, the probability of detecting tiny cracks by the magnetic yoke method is more than 85%.
4.2 Magnetic powder application and observation
The application and observation of magnetic powder are the last steps of magnetic powder testing, which directly affect the accuracy and reliability of the test results.
Magnetic powder application: According to the test site and test requirements, select the appropriate magnetic powder application method. For parts with smoother surfaces, such as the frame surface of an electric scooter, the dry powder method can be used. Sprinkle the magnetic powder evenly on the surface of the tested part. Under the action of the leakage magnetic field, the magnetic powder will be attracted to the defect and form a trace. The advantage of the dry powder method is that the magnetic powder has good contact with the surface of the parts and components, and the detection sensitivity is high. For parts with rough surfaces or oily stains, such as the surface of the shaft, the wet powder method can be used. After mixing the magnetic powder with the suspension, it is evenly sprayed on the surface of the inspected part. The magnetic powder is more easily attracted to the defect under the action of the suspension. The advantage of the wet powder method is that the magnetic powder has good fluidity and can better cover the surface of the parts, which is suitable for detecting defects on complex surfaces.
Observation and recording: After the magnetic powder is applied, the inspected part needs to be carefully observed. Appropriate light sources, such as white light or ultraviolet light, should be used during observation to improve the visibility of the magnetic powder traces. The nature and severity of the defects are judged according to the shape, size, position and distribution of the magnetic powder traces. For the defects found, information such as their location, size and type should be recorded in time for subsequent processing and analysis. For example, when testing the frame of an electric scooter, it was found that the magnetic powder formed a long and thin trace somewhere. After observation and analysis, it was judged to be a crack with a length of about 2mm and recorded in the test report.

5. Defect identification and recording

5.1 Defect feature identification
During the magnetic particle inspection process, the identification of defect features is a key step in determining whether there are quality problems with electric scooter parts. By observing the shape, size, distribution and color of the magnetic powder traces, the nature and severity of the defects can be accurately judged.
Shape characteristics: Cracks usually appear as thin and long linear traces, and their direction may be related to the force direction or processing direction of the parts. For example, in the bending stress concentration area of ​​the frame, the cracks are mostly distributed horizontally, perpendicular to the force direction, and the length is generally between 1-5mm. Fatigue cracks may appear as arcs or branches, which is due to the gradual expansion of cracks under repeated loads. The magnetic powder traces of inclusion defects are irregular in shape, usually in the form of dots or short strips, because the distribution of inclusions in the material is random. The magnetic powder traces of pore defects appear circular or elliptical, because the magnetic field inside the pores is more evenly distributed, and the magnetic powder forms regular traces around them.
Size characteristics: The size of the defect can be measured by the length, width and area of ​​the magnetic powder trace. Generally speaking, larger defects will produce stronger leakage magnetic fields, attract more magnetic powder and form larger traces. For example, for the incomplete penetration defect in the welding part of the frame, the length of the magnetic powder trace may reach more than 10mm and the width is between 2-3mm. For smaller defects, such as microcracks, the magnetic powder trace may be only 0.5-1mm long and between 0.1-0.2mm wide. According to relevant standards, when the length of the magnetic powder trace exceeds 1mm, it should be regarded as a suspected defect and further confirmation is required.
Distribution characteristics: The distribution of defects can reflect the processing quality and use status of parts. If multiple defects are found in a certain area of ​​the part, and these defects are distributed linearly or clustered, it may indicate that there are processing defects or stress concentration in the area. For example, at the connection point of the frame, if multiple cracks are found to be distributed radially, this may be caused by improper welding process or excessive local stress on the connection part. Randomly distributed defects, such as point inclusions on the surface, may be caused by impurities in the raw materials.
Color characteristics: The color of magnetic powder also has a certain indicative role in the detection process. Generally, the color of magnetic powder should be in sharp contrast with the surface of the component for easy observation. If the color of magnetic powder changes at the defect, it may be due to different magnetic field strength at the defect or changes in the composition of magnetic powder. For example, when the color of magnetic powder becomes darker at the crack, it may indicate that the leakage magnetic field at the crack is stronger and the magnetic powder is more adsorbed. If the color of magnetic powder is uneven in some parts, it may be due to the presence of oxide layer or coating residue on the surface of the component, which affects the adsorption and distribution of magnetic powder.
5.2 Defect recording method
Accurate recording of defect information is essential for subsequent analysis, processing and quality control. Defect records should include detailed information such as the location, size, type, shape, distribution, etc. of the defect to facilitate traceability and evaluation of the quality status of the component.
Location record: Record the specific location of the defect on the component, including the name of the component, the name of the part, the distance from the reference point, and other information. For example, at the left connection point of the frame, a crack was found 20cm away from the front end of the frame. Coordinate systems or marking points can be used to accurately locate defects, such as marking coordinate axes on the frame and recording the coordinate position of the defect.
Dimension record: Record the length, width, depth (if measurable) and other dimensional information of the defect in detail. For cracks, the length and width should be measured; for pores and inclusions, the diameter or area should be recorded. Special measuring tools such as calipers and micrometers can be used to ensure the accuracy of the measurement results. For example, the length of a crack is recorded as 3.5mm and the width is 0.2mm.
Type record: According to the characteristics of the defect, accurately judge and record the type of defect, such as cracks, pores, inclusions, incomplete penetration, etc. For complex defects, their characteristics should be described in detail, such as fatigue cracks, thermal cracks, etc. When recording, standard defect classification codes can be used for unified management and analysis.
Shape record: Draw a shape sketch of the defect and mark its shape characteristics, such as straight lines, arcs, branches, etc. For irregularly shaped defects, their outlines should be depicted as detailed as possible. At the same time, indicate the direction of the defect, such as the relationship with the axis of the component or the processing direction. For example, when recording cracks at the connection points of the frame, draw a straight crack sketch with a length of 4mm and a width of 0.3mm, and indicate that its direction is horizontal.
Distribution record: Describe the distribution of defects on parts, such as linear distribution, clustered distribution, random distribution, etc. Record the distribution range and density of defects. If multiple defects are found in a certain area, the area and number of defects in the area should be recorded. For example, it is recorded that 5 point inclusion defects were found in an area with a length of 10cm in the middle part of the frame, and the distribution is relatively uniform.
Recording tools: Defect information can be recorded using a special inspection record form or an electronic recording system. The record form should contain all necessary information columns, such as part number, inspection date, inspection personnel, defect location, size, type, shape, distribution, etc. The electronic recording system can easily store, query and analyze defect data to improve work efficiency and management level.

6. Analysis and processing of test results

6.1 Combined with standard analysis results
After the magnetic particle inspection is completed, the test results need to be compared and analyzed with relevant standards to accurately judge the quality status of electric scooter parts.
Standard basis: At present, magnetic particle testing is mainly based on international standards such as ISO 17638 and domestic standards such as GB/T 15822. These standards specify in detail the methods, equipment, magnetic particle characteristics and defect assessment criteria of magnetic particle testing. For example, ISO 17638 specifies the scope of application and magnetic field strength requirements of different magnetization methods, and GB/T 15822 clearly specifies the performance indicators such as particle size and magnetism of magnetic particles.
Defect grade assessment: According to the standard, defects are usually divided into different grades to reflect their severity. For example, for crack defects, those with a length of less than 1mm may be assessed as minor defects, those with a length between 1-3mm as medium defects, and those with a length exceeding 3mm as severe defects. In actual testing, through magnetic particle testing of electric scooter parts, it was found that the length of cracks at the frame connection points was mostly between 1-2mm, which should be assessed as medium defects according to the standard; while the length of cracks on the shaft surface exceeded 2mm, which is a severe defect and requires special attention.
Data analysis and statistics: Statistical analysis of the test results can help us understand the defect distribution and quality status of parts. For example, after testing a batch of electric scooter frames, it was found that the defect rate at the frame connection points was about 15%, the crack rate in the bending stress concentration area was about 10%, and the defect rate at the welding parts was about 8%. These data show that the frame connection points are high-incidence areas for defects, and quality control needs to be strengthened during the production process.
6.2 Suggestions for handling defects
According to the test results and the severity of the defects, corresponding treatment suggestions are made to ensure the quality and safety of electric scooter parts.
Handling of minor defects: For minor defects, such as cracks less than 1mm in length or a small amount of point inclusions, grinding and repair can be adopted. Use appropriate grinding tools to grind the defective parts flat and remove the defects. After grinding, magnetic particle inspection needs to be performed again to ensure that the defects have been completely eliminated. For example, a small crack found on the surface of the frame can be repaired by grinding and no obvious defects are found in the re-test, so it can be considered that the part has been repaired and qualified.
Medium defect handling: For medium defects, such as cracks with a length of 1-3mm, they should be evaluated based on their location and impact on the performance of the parts. If the defect is located in a non-critical part and does not affect the structural strength and performance of the parts, strengthening measures can be taken, such as adding a reinforcing plate at the crack. If the defect is located in a critical part, such as the connection point or shaft of the frame, it is recommended to replace it. For example, for medium cracks at the connection point of the frame, considering its impact on the overall strength of the frame, it is recommended to replace the connection parts to ensure the safety and reliability of the frame.
Severe defect handling: For severe defects, such as cracks with a length of more than 3mm or large areas of incomplete welding, they should be replaced immediately. The presence of these defects will seriously affect the strength and safety of parts and components, and may cause the parts to break or fail during use, thereby causing safety accidents. For example, severe cracks on the surface of the shaft will cause the shaft to break suddenly during use, affecting the normal operation of the wheel, and a new shaft must be replaced.
Preventive measures recommended: In addition to handling the defects that have been found, preventive measures should also be taken from the source of production to reduce the occurrence of defects. For example, during the welding of the frame, the control of the welding process should be strengthened to ensure the accuracy of the welding parameters and avoid defects such as incomplete welding and slag inclusion; during the processing of parts, the processing quality should be strictly controlled to reduce the generation of surface cracks and stress concentration areas. At the same time, strengthen the inspection of raw materials to ensure that the quality of raw materials meets the requirements and ensure the quality of parts from the source.

7. Analysis of detection cases

7.1 Display of typical defect cases
During the process of magnetic particle testing of electric scooter parts, some typical defect cases were found, which can intuitively demonstrate the effect and importance of magnetic particle testing in practical applications.
Cracks at the connection point of the frame
When testing a batch of electric scooter frames, a crack with a length of about 3mm was found at the connection point between the frame and the handlebar. The crack is in the shape of a long and thin straight line, and the direction is perpendicular to the force direction of the connection point. Through magnetic particle testing, the magnetic powder formed a clearly visible trace at the crack, and after further observation and analysis, it was confirmed to be a fatigue crack. The existence of this crack may cause the frame to break during use, thereby affecting the safety of the rider. According to the relevant standards, the crack is rated as a medium defect, and it is recommended to replace the connection point.
Shaft surface cracks
When testing the electric scooter shaft, it was found that there were multiple cracks with a length of 1-2mm on the shaft surface. These cracks are irregularly distributed, and some cracks are arc-shaped, which may be fatigue cracks caused by frequent rotation and impact during use of the shaft. During magnetic particle testing, magnetic particles gathered at the cracks, forming obvious traces. Through observation and analysis of these cracks, it was confirmed that they were surface cracks. According to the standards, these cracks are rated as medium defects, and it is recommended to replace the shaft to ensure the normal operation of the wheel and the safety of the vehicle.
Welding parts are not fully welded
When testing the welding parts of the electric scooter frame, it was found that the welding parts had a non-penetration defect. During magnetic particle testing, the magnetic particles formed a large trace in the non-penetration area, with a length of about 10mm and a width of between 2-3mm. The presence of this defect will reduce the strength and reliability of the frame, and may cause the frame to break during use. According to relevant standards, the incomplete weld defect is rated as a serious defect, and it is recommended to re-weld the welded parts or replace related parts.
Wear cracks at the connection between the pedal and the frame
When testing the connection between the pedal and the frame of the electric scooter, it was found that the connection had cracks caused by wear. During the magnetic particle test, the magnetic particles formed clear traces at the cracks, with a length of about 2mm and a width of 0.2-0.3mm. The presence of this crack may cause the pedal to loosen or fall off during use, affecting the normal use of the vehicle. According to the standard, the crack is rated as a medium defect, and it is recommended to strengthen the connection or replace new connection parts.
7.2 Case analysis and experience summary
Through the analysis of the above typical defect cases, the following experiences and lessons can be summarized to provide a reference for the magnetic particle inspection of electric scooter parts.
The importance of selecting the detection method
Different parts and detection parts need to select appropriate magnetic field application methods and magnetic powder application methods. For example, for local areas such as frame connection points and welding parts, the yoke method can flexibly apply the magnetic field and achieve better detection results; while for shaft parts such as rotating shafts, the direct current method can effectively detectCircumferential defects. In terms of magnetic powder application, the dry powder method is suitable for parts with smooth surfaces, while the wet powder method is more suitable for parts with rough surfaces or oily stains. Choosing the right detection method can improve the detection sensitivity and accuracy, ensuring that defects can be discovered in time.
The criticality of defect feature identification
Accurately identifying the characteristics of defects is the key to judging the quality of parts. By observing the shape, size, distribution and color of magnetic powder traces, the nature and severity of defects can be accurately judged. For example, cracks usually appear as long and thin linear traces, while incomplete weld defects form larger traces. In actual inspection, the characteristics of magnetic powder traces should be carefully observed, and the type and severity of defects should be accurately judged in combination with the stress conditions and processing technology of parts, so as to take appropriate treatment measures.
Timeliness of defect treatment
For defects found, treatment measures should be taken in time according to their severity. Minor defects can be treated by grinding and repair, medium defects should be strengthened or replaced after evaluation based on their location and impact on the performance of parts, and serious defects must be replaced immediately. Timely handling of defects can prevent further expansion of defects, ensure the quality and safety of parts, and thus ensure the overall performance and safety of electric scooters.
Quality control during production
From the above cases, it can be seen that the frame connection points, welding parts and shafts are high-incidence areas of defects. This reminds us that we should strengthen the quality control of these key parts during the production process. For example, during the welding process, the welding parameters should be strictly controlled to ensure the welding quality; during the processing of parts, the processing quality should be strictly controlled to reduce the generation of surface cracks and stress concentration areas. At the same time, strengthen the inspection of raw materials to ensure that the quality of raw materials meets the requirements, reduce the occurrence of defects from the source, and improve the overall quality of parts.
Professionalism of inspectors
The effect and accuracy of magnetic particle testing are closely related to the professional level of inspectors. Inspectors need to be familiar with the principles, methods and standards of magnetic particle testing, have rich practical experience, and be able to accurately identify defect characteristics and make correct judgments. Therefore, strengthening the professional training of inspectors and improving their technical level and professional quality are of great significance to improving the quality and reliability of magnetic particle testing.
Through the analysis and experience summary of these typical defect cases, it can provide a useful reference for the magnetic particle inspection of electric scooter parts, help improve the inspection efficiency and accuracy, and ensure the quality and safety of electric scooters.