Application areas
High-speed rail
High-speed railroad train is a railroad train that can run continuously at high speed, and the maximum driving speed should generally reach 200km/h and above. With the advantages of fast and comfortable, smooth and safe, energy-saving and environmental protection, it can meet the growing demand for travel and is popular among contemporary people.
The type of high-speed rail produced in China can be divided into the Harmony CRH series and the Fuxing CR400AF, etc. This type of vehicle can be largely considered by the vehicle body and vehicle bogie two parts.
The body includes roof, side walls, side beams, crossbeams and skeleton, etc., are made of large area aluminum alloy extrusion profiles after processing, plays a role in protecting the body strength, corrosion prevention and fire prevention.
The bogie is divided into moving car bogie and trailer bogie, and their main structures are basically the same, both adopt H-type frame, no rocker, hollow axle wheel pair, cast steel axle box, aluminum alloy front cover and cast aluminum overall gear box structure. The bogie supports the weight of the vehicle on the one hand, and connects the wheels and motor on the other, responsible for the traction and braking of the whole vehicle, and carries huge vibration and stress during the operation. At the same time, the bogie is composed of wheel pairs and bogie skeleton, once the parts of these key parts break in operation, it will immediately cause a large traffic accident, resulting in huge personal and property losses.
Therefore, in order to ensure that high-speed rail vehicles can run safely, the detection and early warning of defects in high-speed rail vehicles need to be carried out regularly. This is also the basis and necessary work of the high speed rail vehicle hidden danger rectification, and for the rail vehicle safety hidden danger rectification and prevent vehicle operation accident etc. have important guidance significance.
In China's high-speed rail manufacturing and maintenance process, non-destructive testing technology has made an important contribution to product quality and safety. With the development of China's railroad industry, the speed and load capacity of trains continue to improve, and accordingly the quality and reliability requirements for wagons are getting higher and higher, and the scope of nondestructive testing of key components of various models is gradually expanding. However, there are many existing NDT methods, and there is a lack of specific analysis and review of NDT methods corresponding to key parts of high-speed rail vehicles such as car bodies, bogies and wheel pairs. Therefore, this paper comprehensively compares and analyzes the application of different NDT methods in the field of defect detection of high-speed rail vehicles, and gives specific suggestions on NDT methods for defects in key parts of vehicles.
Introduction of common NDT methods
Nondestructive testing technology is to detect important machine parts on the basis of the structural and operational properties of the object under test without damaging them, using the characteristics of physical phenomena such as sound, light, electricity, heat, magnetism and rays interacting with the detected substances. The inspection includes surface defect detection and internal defect detection of parts, etc., and is used to determine the location, size, shape and type of defects and to evaluate material properties, thus ensuring the quality of parts and improving the performance of products. The scope of application of NDT is becoming more and more extensive with the development of science and production, involving almost all sectors of the national economy.
NDT is divided into six main categories: ultrasonic testing, radiographic testing, electromagnetic eddy current testing, magnetic particle testing, penetration testing and new techniques of nondestructive testing. In addition, the simplest visual inspection is also included.
Visual inspection
Visual inspection is the direct observation of the surface of the parts through the naked eye to determine whether the parts have defects. Although this inspection method is simple, fast and economical, there are obvious drawbacks, namely the need for good eyesight and the need to inspect only the surface of the part. Visual inspection is often used to inspect the welds of large parts, and is used more often in the rapid assessment of civil aviation.
Ultrasonic inspection
Ultrasonic inspection uses the principle of reflection or diffraction of ultrasonic waves encountering defects to determine the presence of defects. Its advantages are good directionality, strong penetration and harmless to the operator; disadvantage is that it is not suitable for large areas, complex shapes and rough surface parts. Ultrasonic inspection is also suitable for the application of defect detection on the surface of aluminum alloys.
X-ray inspection
Ray detection is the use of a variety of ray penetration properties of the material and different materials to the different degree of absorption and attenuation of rays, by the negative photoreceptor into different blackness of the image to detect. It is widely used in industry as a proven means of detecting internal defects in materials. Its advantages include wide applicability, no strict requirements for the shape of the part and its surface roughness, and can visually display the image of the defect, easy to locate the defect. Its disadvantages are radioactivity, high hazard, high cost, and low sensitivity to detection of flat defects, so radiation detection is more suitable for the detection of porosity, slag and other volumetric defects in the parts, which are mainly used in the detection of castings and weldments.
Electromagnetic eddy current inspection
Electromagnetic eddy current inspection is the use of electromagnetic induction principle, through the determination of the workpiece to be inspected by the changes in the induced eddy current to nondestructively determine the performance of conductive materials and their parts, or to find material defects in nondestructive testing methods. Its advantages include high sensitivity, wide range of applications, easier to achieve automation, especially for tubes, bars and other profiles have better detection efficiency. The disadvantage is that the efficiency of eddy current inspection is relatively low when detecting parts with more complex shapes. Therefore, electromagnetic eddy current inspection has a better application in the field of defect detection for conductive pipe and bar profiles and non-magnetic conductive materials.
Magnetic particle inspection
Magnetic particle inspection is a nondestructive testing method that uses the aggregation of magnetic powder to show the surface and near-surface defects of ferromagnetic materials and their workpieces. Its advantages are that it can visually show the shape, location and size of defects, high sensitivity, wide range of applications, fast detection and simple process. The disadvantage is that it is only suitable for the detection of defects on the surface and near surface of raw materials and semi-finished products such as plates, profiles, pipes, etc. It can also be used for periodic defect inspection of mechanical equipment and pressure vessels.
Penetration inspection
Penetrant inspection is a non-destructive testing method that uses capillary action to spray a colored penetrant solution on the surface of the material weld, allowing the penetrant solution to penetrate into the material, and after cleaning, applying a visualizer to show the color of the defect. It has the advantages of simple operation, intuitive display of defects, high sensitivity, and low cost of detection. However, it also has the disadvantage of not being suitable for the detection of defects in porous materials. Therefore the method is suitable for parts with delicate surface and delicate processing.
New Technologies
New technologies of NDT include magnetic memory detection technology, laser holography, microwave detection technology and infrared detection technology, etc. The effects of these new technologies in the field of defect detection of high-speed rail vehicles are subject to further analysis and research.
Non-destructive testing of defects in high-speed rail vehicles
01 Body defect detection
For the body of high-speed rail vehicles, the application of aluminum alloy steel plates is the most widespread. The body adopts the thin-walled cylindrical overall load-bearing lightweight structure, the main components such as roof, side walls, side beams, crossbeams and skeleton are made of large-area aluminum alloy extrusion profiles after processing, profiles and profiles between the corresponding mechanical structure formed by longitudinal welding seams.
It can be seen that there are a large number of welds in the manufacturing process of aluminum alloy steel body, and in the process of vehicle operation by its own tension and such as rain, hail, sand and dust and other external environment, it is very easy to produce damage to the body structure.
For the detection of body defects, the commonly used nondestructive testing methods are visual inspection and ultrasonic inspection method.
The visual inspection method means that the entire body is visually inspected by sight or with the help of a bright flashlight to observe defects such as weld porosity. Visual inspection is easy to operate, without the use of complex auxiliary equipment, suitable for more obvious, available for direct observation of the naked eye body welding defects.
However, the defects in the aluminum alloy weld joints of the car body are easily covered up after the primer, intermediate coating, putty, top coating and other processes, and most of the internal delamination defects are extremely difficult to find directly through visual inspection, which requires the use of ultrasonic detection method to detect internal delamination defects.
Ultrasonic inspection method requires the use of ultrasonic flaw detector, select the appropriate probe, and the body surface cleaning, but also need to pay attention to the body of aluminum alloy material grain is large, the instrument should not choose too high emission frequency. Ultrasonic inspection method is very suitable for the detection and diagnosis of delamination defects that appear inside the aluminum alloy plate, with high efficiency, fast speed and accurate detection.
02 Bogie defect detection
The vehicle bogie supports the weight of the vehicle body on the one hand, and connects the wheels and motor on the other hand, responsible for the traction and braking of the whole vehicle, and carries huge vibration and stress during the operation, once the ferromagnetic components of these key parts are broken in operation, it will immediately cause a large traffic accident, resulting in huge personal and property losses.
Ltd. produces the 250 km/h speed class rolling stock Harmony high-speed train CRH2A model CRH2A model, for example, the vehicle bogie including moving car bogie and trailer bogie, its main structure is basically the same, mainly by H-type frame, no rocker, hollow shaft wheel pair, cast steel axle box, aluminum alloy front cover and cast aluminum overall gear box structure, which frame as The main component of the bogie is the welded structure of steel plate, cast steel and seamless steel pipe, so there are ferromagnetic components in the bogie frame, such as steel plate and cast steel.
For the defect detection of vehicle bogie frame, ultrasonic detection method and magnetic particle detection method can be used, among which ultrasonic detection method is similar to vehicle body detection, while magnetic particle detection method is to use portable magnetic particle flaw detector to effectively locate and detect surface defects of bogie rigid structure. It is worth noting that if there is a paint layer on the surface of the bogie frame structure, the paint layer needs to be peeled off to avoid interference.
At the same time, the emerging magnetic memory detection technology can detect the early stress concentration of the bogie frame without damaging the components, thus playing the effect of defect positioning and early warning, which is also a good method.
03 Axle defect detection
The wheels of high-speed rail vehicles are composed of two parts: wheels and axles, of which the wheels, as an important part of the vehicle travel section, are prone to various types of defects, including wheel fractures, tread scrapes, chink injuries, rolling fatigue and stripping.
For relatively obvious wheel fractures and other defects, visual inspection can be performed directly. For other types of wheel defects, the magnetic particle detection method and ultrasonic detection method are mainly used, in which the magnetic particle detection method can effectively detect small defects on the wheel surface, while the ultrasonic detection method can detect defects inside the press-fit parts of the wheels and brake discs.
The axles of high-speed rail vehicles are generally sprayed with rust inhibitor, and although the magnetic particle inspection method can still be used, it is not convenient in practice, so the axles are usually visually inspected and ultrasonically inspected.
The visual inspection of axle needs to observe that there is no damage to the outer surface of the axle coating, such as spots, cuts, etc. If the damage is small and there is no exposed metal, ultrasonic inspection method can be used for internal defect detection. If there is a wider range of painted damage or obvious corrosion on the surface of the axle, the wheel pair must be replaced immediately and the necessary repair measures must be carried out.
04 Hook defect detection
The hook is a key component between the connecting locomotive and vehicle or vehicle and vehicle, and its main role is to transmit traction and impact force, and to keep a certain distance between vehicles. Magnetic particle testing, ultrasonic testing and radiographic testing are the common non-destructive testing methods used in hook maintenance.
Among them, magnetic particle inspection can diagnose the surface and near-surface defects of each part of the hook buffer, but cannot detect internal defects, which has certain limitations; ray inspection can visually display the shape of internal defects of the hook, and the sensitivity is higher, and the research shows that the minimum defect size detected by ray inspection is smaller than that of ultrasonic inspection, so ray inspection is suitable for the detection of smaller size defects; using ultrasonic Detection can get the depth of the defect information, it is suitable for the detection of hook material thicker location.
Source: Rail Technology Network
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