The problem of excessive wear of pantograph strips frequently occurs on China’s Z City Metro Line 1. After on-site investigation and analysis by the metro operating company, it was speculated that the problem was related to abnormal track irregularities. Therefore, taking Z City Metro Line 1 as the main research object, the measured track irregularity of the whole line was analyzed and compared with other typical track spectra, and a track-vehicle-pantograph-catenary coupling dynamics model was established to analyze the relationship between the pantograph-catenary dynamic characteristics and the track irregularity. The two frequency ranges of the track irregularity that have a significant impact on the pantograph-catenary contact were found. Finally, after numerical calculation and analysis, it is recommended to focus on the irregularities with the two wavelength ranges of 9~16m and 3~4m in the maintenance.
Recently, derailments have been occurring frequently at the guardrail position of double-slip turnouts. In order to provide a theoretical basis for effectively avoiding derailment at the guardrail position of turnouts, this study presented a derailment mechanism, discussed the rationality of the current guardrail interval limit and its calculation method, and proposed a method for calculating the guardrail interval limit based on the vehicle running attitude and wheelset angle of attack. Based on the established calculation model, this paper calculated the guardrail interval limit for the main types of single turnouts and double-slip turnouts in China, and studied the main factors influencing the interval limit and corresponding patterns. The following conclusions were drawn. (1) In actual maintenance, it suggested to set the guardrail interval limit at 1365 mm, which can meet the requirements of the most turnouts and avoid wear incurred by vehicle–track interactions at the opening section of guardrails and derailment. (2) For single turnouts, the required guardrail interval limit becomes smaller with the decrease of the frog number, radius of the lead curve, and the increase in gage width. Further, the interval limit decreases when the endpoints of the lead curve and gage widening become closer to the buffer segment at the toe end of the guardrail. Adopting straight-track design at the restoring segment of gage widening is more likely to cause a larger twisting angle of the bogie than a curved-track design, and larger twisting angle means requiring a smaller guardrail interval limit. (3) For double-slip turnouts, the required guardrail interval limit is reduced with the decrease in the frog number and increase in gage width. The broken rail comprising the switch rail and stock rail in front of the guardrail can also enable the bogie to approach or reach the inscribing state, resulting in a negative impact not smaller than that produced by a curved rail. The larger the attack angle at the tip of the switch rail and the closer the tip of the switch rail and the end of gage widening to the buffer segment of the guardrail, the smaller the guardrail interval limit.
Based on the research and development demand of the 400 km/h high-speed turnout, a new type of elastic iron tie plate based on stiffness optimization is proposed. The new elastic iron tie plate is expected to reduce the stiffness unevenness and effectively solve the problems in the use of existing elastic iron tie plates. However, the new plate uses rubber bosses instead of rubber washers. There are certain differences in the force transmission mechanism from the original tie plate because of the change in structure of the new tie plate. In this paper, a series of experiments are designed to quantitatively compare and analyze the overall stiffness characteristics of different tie-plate structures and the differences in bolt force transmission and distribution laws. The main conclusions are as follows. The laws of vertical load transfer and distribution in the new tie plate are remarkably different from those for the original tie plate because of the differences in their structures. Under the rated bolt torque, the force transferred to the upper surface of the tie plate through the rubber boss in the new tie plate is less than that in the original tie-plate structure by 5.18 kN in the assembled state. Further, the new structure also has lower tie plate precompression; hence, the influence on the stiffness characteristics of the tie plate is less than that in the original structure. However, the steel sleeve deflection in the new tie plate is greater than that in the original tie plate; that is, a larger proportion of the bolt preload force is borne by the steel sleeve, thus making the vulcanized rubber under the steel sleeve more vulnerable to shear damage. If put into actual use, the tie plate bolt torque will be somewhat different from the rated torque; because of the difference in the torques coupled with the different vertical load transfer mechanisms between the new and the original tie-plate structures, the precompression and the proportion of the bolt preload force borne by the steel sleeves of the two tie plates will also show different degrees of deviation corresponding to different deviations of the tie plate bolt torque. Therefore, the new tie plate structure needs to be further optimized to make the transfer mechanism of preload force of bolt as consistent with the original tie plate as possible. In addition, the vibration and deformation characteristics and long-term service performance of the new type of plate under the condition of vehicle passing will be studied through a small-scale field trial and systematic dynamic tests.
In this paper, to address the shortcomings of the crossing structure design based on the elastic bending center method and the lack of related research, an optimization method for high-speed turnout crossing structures was proposed based on the actual elastic deformations of point and splice rails. Based on the finite element theory, the actual loading characteristics and spatial variable section characteristics of point and splice rails were fully considered, and a refined simulation analysis model of the switching system of point and splice rails in crossing areas was established. Moreover, the elastic deformation lines of point and splice rails in the nonworking state were obtained for the first time, which were consistent with actual situations. On this basis, system optimization was performed for the connecting parts of the crossing with a movable point in a high-speed turnout. In the crossing structure simulation model, the length adjustment values of the first–sixth spacer blocks between the branch line–wing and point rails and between the mail line–wing splice rails were ≤1 mm. Moreover, the lengths of the seventh–ninth spacer blocks decreased by gradually increasing amounts, and the length of the ninth spacer block decreased the most (∼6 mm). The length of the second spacer block between the point and splice rails slightly increased, but the length of the third spacer block significantly decreased by 6 mm. The length adjustment value of the distance block between the point and splice rails was smallest (0.7 mm). The calculated optimal lengths of the connecting parts of the crossing were found to be close to the empirical values used in actual manufacturing processes, and the dimension optimization patterns were completely consistent with actual situation, which validates the proposed optimization method. Thus, the proposed method can effectively improve the coordination between rails and connecting parts in crossing areas, substantially reduce internal stresses in crossing systems, and improve their assembly performance and service life. Moreover, the proposed optimization parameters can provide valuable references for the research on next-generation high-speed turnouts (400 km/h) and for improving the designs of existing high-speed turnouts.
PurposeIt is quite universal for high-speed turnouts to be exposed to the wear of the stock rail of the switch rail during the service process. The wear will cause the change of railhead profile and the relative positions of the switch rail and the stock rail, which will directly affect the wheel–rail contact state and wheel load transition when a train passes the turnout and will further impose serious impacts on the safety and stability of train operation. The purpose of this paper is to provide suggestions for wear management of high-speed turnout.Design/methodology/approachThe actual wear characteristics of switch rails of high-speed turnouts in different guiding directions were studied based on the monitoring results on site; the authorized wear limits for the switch rails of high-speed turnout were studied through derailment risk analysis and switch rail strength analysis.FindingsThe results show that: the major factor for the service life of a curved switch rail is the lateral wear. The wear characteristics of the curved switch rail of a facing turnout are significantly different from those of a trailing turnout. To be specific, the lateral wear of the curved switch rail mainly occurs in the narrower section at its front end for a trailing turnout, but in the wider section at its rear end when for a facing turnout. The maximum lateral wear of a dismounted switch rail from a trailing turnout is found on the 15-mm wide section and is 3.9 mm, which does not reach the specified limit of 6 mm. For comparison, the lateral wear of a dismounted switch rail from a facing turnout is found from the 35-mm wide section to the full-width section and is greater than 7.5 mm, which exceeds the specified limit. Based on this, in addition to meeting the requirements of maintenance rules, the allowed wear of switch rails of high-speed turnout shall be so that the dangerous area with a tangent angle of wheel profile smaller than 43.6° will not contact the switch rail when the wheel is lifted by 2 mm. Accordingly, the lateral wear limit at the 5-mm wide section of the curved switch rail shall be reduced from 6 mm (as specified) to 3.5 mm.Originality/valueThe work in this paper is of reference significance to the research on the development law of rail wear in high-speed turnout area and the formulation of relevant standards.
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