Abstract: The early failure of NJ3226 Passenger railroad car bearing with a very small proportion is analyzed, and it is considered that the early failure of the bearing is caused by the coupling of the processing quality of bearing rollers and inner raceway plain lines, the deflection deformation of Passenger railroad car axle, the discreteness of the processing dimensions of bearing parts, and the quality defects of bearing materials, heat treatment and grinding burns, and the improvement measures in the process of bearing production and assembly are given.
Key words: Passenger railroad car bearing; Cylindrical roller bearings; failure analysis
The bearing of Passenger railroad car is the key component to ensure the normal operation of Passenger railroad car. It is most likely to fail during the operation of Passenger railroad car. Early failure accidents often occur, and bring huge economic losses and even safety accidents. In order to improve its reliability and reduce its early failure accident rate, it has always been an important subject for the research of Passenger railroad car bearings. This paper analyzes the early failure of NJ3226 bearing used in Passenger railroad car in order to find improvement methods.
1. Early Failure Mode Statistics
A set of NJ3226 and NJP3226 bearings (Figure 1) is installed at each end of the axle of the Passenger railroad car. In addition to bearing all the weight of the vehicle body, the bearing also bears the axial and radial impact loads generated during the operation of the passenger train.
1-wheel；2-NJ3226X1；3-NJP3226X1; 4-axle
Figure 1 Assembly Drawing of Passenger railroad car Bearings on Axles
A total of 40 early failure accidents occurred between November 2005 and August 2009 for NJ3226 and NJP3226 bearings, all of which were caused by early fatigue peeling of the raceway. The actual installation and operation time of these bearings is less than 2 years, and the proportion of early fatigue peeling is about 0.2%. The main bearing that experienced early failure was NJ3226, accounting for 96% of the total number of failed bearings. The proportion of fatigue spalling on the inner raceway was 87%, and fatigue spalling mainly occurred at the raceway about 8 mm away from the retaining edge, as shown in Figure 2. The early peeling of the outer raceway and rollers mainly occurs in the raceway corresponding to the inner ring. The classification and statistics of early failure NJ3226 and NJP3226 bearings by failure mode are shown in Table 1.
Figure 2 Early fatigue peeling photos of NJ3226 inner race raceway
Table 1 Classification Statistics of Early Failure of Passenger railroad car Bearings
Bearing model | Fatigue type | number |
NJ3226 | inner raceway peeling; Outer raceway, roller surface peeling; outer raceway peeling, hot axis; Outer raceway peeling; Peeling and cracking of the inner raceway, and burrs in the oil groove; | 22 1 2 2 3 |
NJ( P) 3226 | inner raceway peeling; Multiple peeling of rollers and inner rings; peeling of inner and outer raceways; | 2 1
6 |
NJP3226 | inner raceway peeling | 1 |
1. Failure analysis
Early fatigue spalling mainly occurs at a distance of about 8 mm from the inner raceway of NJ3226 bearing to the retaining edge, which is very regular. This indicates that the premature failure of the bearing is influenced by systemic factors. The early fatigue peeling caused by grinding burns and material defects should be randomly distributed on the raceway. Multiple failed parts of NJ3226 and NJP3226 were inspected and analyzed, and no grinding burns or material defects were found. Therefore, the early failure was not caused by grinding burns or material defects.
An analysis was conducted on the heat treatment quality of the inner and outer rings of early failed bearings and normal bearings, and it was found that the heat treatment quality of early failed bearings was good, with no significant difference from that of normal bearings. This indicates that the early failure of bearings is not caused by the quality of heat treatment.
A comprehensive inspection was conducted on the geometric dimensions of more than 20 sets of normal bearings, including inner rings, outer rings, and rollers. It was found that the two ends of the plain line of the NJ3226 inner ring raceway were inclined downwards by about 1-2 degrees μ M (designed as a straight line), with the transition zone located exactly 8-10 mm from the inner ring edge of the raceway (Figure 3); There is a problem with the correction of the roller centerline, which has a slope of approximately 8 mm at both ends (Figure 4). The designed roller centerline is shown in Figure 5. After correcting the shape of the roller plain line, the problem has not been solved, but it can be confirmed that the processing quality of the plain line of the NJ3226 bearing roller and inner raceway is one of the systematic factors causing its premature failure. As the premature Failure rate efficiency of bearing is very low, it can be seen from the above analysis that the premature failure of NJ3226 bearing is the result of complex multi factor coupling.
Figure 3 NJ3226 Inner Race Raceway Plain Line
Figure 4 NJ3226 Roller Plain Line
Figure 5 External dimensions of roller design
3 Force analysis
The force state of the axle movement is shown in Figure 6. F1 and F4 in the figure are the radial impact loads on the axle; F2, F5 are the pressure of Passenger railroad car mass on the axle; F3 and F6 are the supporting force of Passenger railroad car wheels on axles; F7 is the axial impact load. F2 and F5 are in equilibrium with F3 and F6, respectively; M1 and M2 are the additional moments generated by F2 and F3, as well as F5 and F6 due to different points of action, causing a certain amount of bending deformation of the axle, as shown in Figure 7. Axial and radial impact loads are variable loads, and their values are influenced by road conditions, passenger vehicle load capacity, and operating speed. F1, F2, F4, F5 are balanced by installing them on F3 and F6; M1 and M2 are the additional moments generated by F2 and F3, as well as F5 and F6 due to different points of action, causing a certain amount of bending deformation of the axle, as shown in Figure 7. Axial and radial impact loads are variable loads, and their values are influenced by road conditions, passenger vehicle load capacity, and operating speed. F1, F2, F4, F5 are transmitted to the axle through NJ3226 and NJP3226 bearings installed at the end of the axle.
Figure 6 Force state of axle movement
Figure 7 Flexural deformation of the axle
Without considering the deflection and deformation of the Passenger railroad car axle, the stress distribution of F1, F2, F4 and F5 generated inside the bearings NJ3226 and NJP3226 is shown in Figure 8 (only the stress distribution of the inner ring is analyzed here, and the stress distribution of the outer ring and roller is symmetrical with this).
Figure 8 Stress distribution status of inner ring
Due to the logarithmic curve of the roller element line, there is a slope of approximately 8 mm at both ends during machining due to overcorrection; At the same time, the inner raceway plain line has a length range of 1.5-2.0 within a distance of 8 mm from the curb μ The sinking of m (a total of 20 inner rings were detected, all of which have the same shape as the plain lines), resulting in lower stress at the end of the inner raceway than in the middle. However, due to the deflection and deformation of the Passenger railroad car axle, F1, F2, F4 and F5 are unevenly distributed on the NJ3226 and NJP3226 bearings, which makes the NJ3226 bear more load than the NJP3226, and makes the contact stress distribution inside the two bearings change significantly, resulting in stress concentration. The maximum stress is located at the raceway 8 mm away from the inner ring edge of the NJ3226, as shown in Figure 9. F'9 in Figure 9 is the additional load caused by the axial impact load F7.
F7 is mainly borne by the inner ring edge of NJ3226 and transmitted to the roller, generating force F'7 on the roller, as shown in Figure 10. Force F'7 pushes the roller to interact with the outer ring edge, generating force F8 on the corresponding roller. Due to the different action points of F'7 and F8, an additional torque M3 is generated on the roller, causing the roller to deflect. When the roller deflects, it acts on the inner ring, generating force F9, which acts on the outer ring, generating force F10. The reaction force F'9 of F9 acts on the inner raceway, further increasing the force on the inner raceway. Additionally, the two ends of the plain lines of the NJ3226 inner raceway tilt downwards and the roller plain lines are overcorrected, The point of application of force is located on the raceway 8 mm away from the inner ring edge of NJ3226, further increasing the stress in this area. At the same time, the reaction force F'10 of F10 acts on the outer ring raceway, further increasing the force on the outer ring raceway. However, the point of application of this force is far away from the outer ring raceway corresponding to the inner raceway with a distance of 8 mm from the NJ3226 inner ring edge. Therefore, the maximum stress on the outer ring raceway will not increase, resulting in a higher stress on the inner raceway with a distance of 8 mm from the NJ3226 inner ring edge. Based on the above analysis, the inner raceway with a distance of 8 mm from the inner ring edge of NJ3226 has the highest contact stress in the entire bearing and is most prone to contact fatigue peeling. It can be seen that the deflection deformation of Passenger railroad car axle is one of the factors leading to the premature failure of NJ3226 bearing.
Figure 9 Internal stress concentration of bearings caused by axle deflection deformation
Figure 10 Force state of rollers
In addition, most users generally choose the inner race diameter of NJ3226 to be 0.005 mm larger than that of NJP3226 during installation, in order to increase the force on the NJ3226 inner race and reduce the deflection deformation of the journal. Any increase in contact stress may lead to a sharp decrease in bearing fatigue life. Therefore, this measure is also one of the factors that cause the early fatigue peeling of Passenger railroad car bearing, which mainly occurs on NJ3226 bearing.
4 Results and Analysis
The proportion of early fatigue peeling of Passenger railroad car bearings is about 0.2%, which indicates that although there are system factors that lead to the premature failure of NJ3226 bearings under normal operating conditions, these system factors are not enough to cause early fatigue peeling of bearings, but their superposition with one or several other accidental factors leads to a small proportion of early fatigue failure of Passenger railroad car bearings. These accidental factors are divided into the following two types. (1) The discreteness of the machining dimensions of each bearing component. For example, the radial clearance of NJP3226 and NJ3226 bearings is 0.12-0.17 mm. If a pair of NJP3226 and NJ3226 bearings are used together, the radial clearance of NJP3226 bearings is relatively large, while the radial clearance of NJ3226 bearings is relatively small, which inevitably leads to an increase in the load borne by NJ3226 bearings and a decrease in the load borne by NJP3226 bearings. (2) Quality defects such as material, heat treatment, grinding burns, etc. of bearings. For example, small inclusions inside the material, slight network and banded carbides, locally mild decarburization, and locally mild burns. These quality defects can lead to a decrease in the fatigue strength of the NJ3226 inner race raceway.
5 Improvement Measures and Effects
(1) Strictly control the radial clearance of NJ3226 and NJP3226 bearings to prevent the load borne by NJ3226 from further increasing due to radial clearance deviation of paired bearings, and improve the uniformity of load distribution between NJ3226 and NJP3226 bearings.
(2) When assembling and installing bearings, the inner race diameter of NJ3226 bearing should not be 0.005 mm larger than that of NJP3226 bearing.
(3) Strictly control the inclination of the NJ3226 inner race raceway within the tolerance, and the inclination should be from low to high from the retaining edge to the small end face.
(4) Prevent both ends of the plain line of the NJ3226 bearing inner race from tilting downwards.
(5) Strictly follow the drawing to process the shape of the roller centerline and prevent excessive correction of the roller centerline.
(6) Reduce the discreteness of dimensional and geometric tolerances of bearing inner rings, outer rings, and rollers. Through strict control of bearing production and installation, the early failure accident rate of NJ3226 and NJP3226 bearings has been reduced by 60%.
6 Conclusion
Through the analysis of the early failure case of NJ3226 Passenger railroad car bearing, it is considered that the very small proportion of the early failure of the bearing is caused by the superposition and coupling of the system factors, such as the machining quality of bearing rollers and inner raceway plain lines, and the deflection and deformation of Passenger railroad car axle, with the discrete processing dimensions of bearing parts and the quality defects of bearing materials, heat treatment, grinding burns and other accidental factors. Through the strict control of bearing production and installation, the reliability of Passenger railroad car bearings can be effectively improved.
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2023-06-20