The railway passenger car bearing is a key component to ensure the normal operation of the railway passenger car. It is most likely to fail during the operation of the railway passenger car. Early failure accidents frequently 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 of railway passenger car bearing research. The early failure of cylindrical roller bearing NJ3226 bearings used in railway passenger cars is analyzed in order to find improvement methods.
1 Statistics of early failure modes
A set of NJ3226 and NJP3226 bearings are installed at each end of the railway passenger car axle (Fig. 1). The bearings not only bear the full weight of the car body, but also bear the axial and radial impact loads generated during the operation of the passenger car.
A total of 40 early failure accidents occurred in NJ3226 and NJP3226 bearings from November 2005 to August 2009, and all the failure modes were early fatigue spalling of the raceway. The actual running time of these bearings is less than 2 years, and the proportion of early fatigue spalling is about 0. 2% . Bearings with early failure are mainly NJ3226, accounting for 96% of the total number of failed bearings, and the proportion of inner raceway fatigue spalling is 87%. Fatigue spalling mainly occurs at the raceway about 8 mm away from the rib, as shown in Figure 2. The early spalling of the outer raceway and rollers also mainly occurs in the raceway portion corresponding to the inner ring. Classification statistics of early failure NJ3226 and NJP3226 bearings by failure mode
2 Failure analysis
The early fatigue spalling mainly occurs in the NJ3226 bearing where the inner raceway is about 8 mm away from the rib, which is very regular, which indicates that the premature failure of the bearing has the effect of systematic factors. Whereas, early fatigue spalling caused by grinding burns and material defects should be randomly distributed on the raceway. A number of NJ3226 and NJP3226 failed parts were inspected and analyzed, and no grinding burns and material defects were found, so the early failure was not caused by grinding burns and material defects.
The heat treatment quality of the inner and outer rings of the early failure bearing and the normal bearing was tested and analyzed, and it was found that the heat treatment quality of the early failure bearing was good, and there was no significant difference with the heat treatment quality of the normal bearing, indicating that the early failure of the bearing was not caused by the heat treatment quality.
The geometric dimensions of the inner ring, outer ring and rollers of more than 20 sets of normal bearings were comprehensively inspected, and it was found that both ends of the element line of the inner ring raceway of NJ3226 were inclined downward by about 1 ~ 2 μm (designed to be straight lines) , the transition area is located at the raceway 8 to 10 mm away from the inner ring rib; the roller element line has been corrected, and its two ends have a slope of about 8 mm, the designed roller element line. After correcting the shape of the plain line of the roller, the problem has not been solved, but it is certain that the machining quality of the plain line of the NJ3226 bearing roller and inner raceway is one of the systematic factors that cause its premature failure. Since the premature failure rate of the bearing is very low, it can be seen from the above analysis that the premature failure of the NJ3226 bearing is the result of complex multi-factor coupling.
3 Force analysis
The motion force state of the axle is shown in Figure 6. In the figure, F1, F4 are the radial impact loads on the axle; F2, F5 are the pressure of the railway passenger car mass on the axle; F3, F6 are the supporting force of the railway passenger car wheel on the axle; F7 is the axial impact load. F2 and F5 are in balance with F3 and F6 respectively; M1 and M2 are the additional moments generated by F2 and F3 and F5 and F6 due to different points of action, which cause the axle to produce a certain deflection deformation, as shown in Figure 7. Axial and radial shock loads are variable loads whose values are affected by road conditions, passenger onboard mass, and operating speed. F1, F2, F4, F5 are transmitted to the axle through NJ3226 and NJP3226 bearings installed at the axle end.
When the flexural deformation of the railway passenger car axle is not considered, the stress distribution generated by F1, F2, F4, F5 inside the bearings NJ3226 and NJP3226 is shown in Figure 8 (here only the stress distribution of the inner ring is analyzed, the outer ring and the roller The stress distribution is symmetrical with this).
Since the rolling element line is a logarithmic curve, there is a slope of about 8 mm at both ends due to over-correction during processing; at the same time, the inner raceway element line has a length of 1.8 mm from the rib. 5 to 2. 0 μm subsidence (a total of 20 pieces of inner circle are detected, all the shapes of the prime lines are the same), so that
The stress at the end of the inner raceway is lower than that in the middle. However, due to the flexural deformation of the railway passenger car axle, F1, F2, F4, and F5 are unevenly distributed on the NJ3226 and NJP3226 bearings, so that the NJ3226 bears a larger load than the NJP3226, and the contact stress distribution inside the two bearings changes significantly. Stress concentration occurs, the maximum stress is located at the raceway part 8 mm away from the inner ring rib of NJ3226, 9 is the additional load caused by the axial impact load F7. F7 is mainly borne by the NJ3226 inner ring rib, and transmitted to the roller, which generates a force F’7 on the roller to push the roller to interact with the outer ring rib, and generates a force F8 on the corresponding roller. Because the action points of F’7 and F8 are different, an additional moment M3 is generated on the rollers, which makes the rollers deflect, and the rollers act on the inner ring under the deflection to generate force F9, which acts with the outer ring and generates forces F10 and F9. The reaction force F’9 acts on the inner raceway, which further increases the force on the inner raceway, and the two ends of the prime line of the NJ3226 inner ring raceway are inclined downward and the roller prime line is overcorrected, so that the acting point of the force is located at a distance from the inner race. NJ3226 The raceway part of the inner ring rib of 8 mm further increases the stress of this part. At the same time, the reaction force F’10 of F10 acts on
The outer ring raceway further increases the force on the outer ring raceway. However, the action point of the force is far from the outer ring raceway part corresponding to the inner raceway part that is 8 mm away from the NJ3226 inner ring rib. Therefore, the outer ring rolling The maximum stress in the raceway will not increase, resulting in a higher stress on the inner raceway portion 8 mm from the NJ3226 inner race rib than on the corresponding outer raceway portion. Based on the above analysis, the inner raceway with a distance of 8 mm from the NJ3226 inner ring rib has the largest contact stress in the entire set of bearings, and is most prone to contact fatigue spalling. It can be seen that the flexural deformation of the railway passenger car axle is one of the factors leading to the premature failure of the NJ3226 bearing.
In addition, most users generally choose the inner ring raceway diameter of NJ3226 to be 0.005 mm larger than that of NJP3226 during installation, so as to increase the force of the NJ3226 inner ring and reduce the deflection 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 spalling of railway passenger car bearings to mainly occur on NJ3226 bearings.
4 Results and Analysis
The proportion of early fatigue spalling of railway passenger car bearings is about 0. 2%, which means that, although there are system factors that lead to premature failure of NJ3226 bearing under normal operating conditions, these system factors are not enough to cause early fatigue spalling of the bearing, but it is related to one or more other factors. The superposition of accidental factors results in a very small percentage of early fatigue failures of railway passenger car bearings. These contingency factors are divided into the following two types. (1) The discreteness of the machining dimensions of each part of the bearing. For example, NJP3226, NJ3226 bearing radial clearance is 0. 12 to 0. 17 mm, if a pair of NJP3226 and NJ3226 bearings are used in a pair, the radial clearance of the NJP3226 bearing is larger, while the radial clearance of the NJ3226 bearing is smaller, which will inevitably lead to an increase in the load on the NJ3226 bearing and a decrease in the load on the NJP3226 bearing. Small. (2) Quality defects such as bearing materials, heat treatment, grinding burns, etc. For example, small inclusions inside the material, slight network and ribbon carbides, local slight depletion of carbon and
Local minor burns, etc. These quality defects will cause the fatigue strength of the inner ring raceway of NJ3226 to decrease.
5 Improvement measures and effects
(1) Strictly control the radial clearance of NJ3226 and NJP3226 bearings to prevent the load on NJ3226 from further increasing due to the deviation of radial clearance of matched bearings, and improve the uniformity of load distribution among NJ3226 and NJP3226 bearings.
(2) When assembling and installing bearings, the inner ring raceway diameter of NJ3226 bearing should not be larger than that of NJP3226 bearing inner ring raceway by 0.0. 005 mm.
(3) Strictly control the inclination of the NJ3226 inner ring raceway within the tolerance, the inclination should be from low to high from the rib to the small end face.
(4) Prevent the downward slope of both ends of the inner ring raceway line of the NJ3226 bearing.
(5) Strictly process the shape of the roller element line according to the drawing to prevent the over-correction of the roller element line.
(6) Reduce the dispersion of dimensional tolerances and geometric tolerances of parts such as the inner ring, outer ring and rollers of the bearing. Through strict control of bearing production and installation, the early failure accident rate of NJ3226 and NJP3226 bearings has been reduced by 60%.
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Through the analysis of the early failure cases of NJ3226 railway passenger car bearings, it is considered that the very small proportion of early failure of the bearing is due to the processing quality of the bearing rollers and the inner raceway element line and the deflection and deformation of the railway passenger car axle. These system factors are related to the processing of various parts of the bearing The discreteness of size and the quality defects of bearing material, heat treatment, grinding burn and other accidental factors are superimposed and coupled. Through strict control of bearing production and installation, the reliability of railway passenger car bearings can be effectively improved.