1 Introduction
In recent years, the catenary system that provides power for the operation of locomotives has suffered from the continuous occurrence of bow-net accidents on several passenger-dedicated lines, which brings hidden dangers to the safety of railway operations. According to the analysis of the accidents organized by the power supply department of the Ministry of Railways, the agreement is concluded that the nut loosening system leads to The important reason for the bow network accident is that the anti-loose study of the contact thread fasteners is necessary for the safety of railway operations.
2 Analysis of the causes of looseness of threaded fasteners
Threaded fasteners are widely used in the connection of contact net parts. Due to the easy assembly and disassembly and reusable characteristics of threaded fasteners, looseness may occur under working conditions, especially in vibration, shock and variable load. And when the temperature difference is too large, it is more likely to cause looseness and even the nut will fall off.
It is analyzed that under dynamic load, under the action of vibration and impact, the threaded fastener produces microscopic slip on the thread and the bearing surface. This relative microscopic motion changes the friction coefficient from a relatively high static value. For very low dynamic values, the threaded connection is in a free friction state in all directions. At this time, the axial force acting on the thread forms an inner release torque in the circumferential direction which causes the nut to loosen, so that the nut starts to loosen. This loosening is called self-loose of the threaded connection. Tens of thousands of vibration cycles deplete the anti-loose frictional resistance of the threaded connection, allowing it to be slightly loosened until it is completely loose.
How is the microscopic slip of the threaded part on the threaded surface and the bearing surface? For the threaded member subjected to the axial dynamic load, the axial external force causes the nut to radially expand elastically near the bearing surface, causing microscopic slippage on the thread surface and the bearing surface; for the threaded member subjected to the lateral dynamic load, the lateral external force The bolt is rocked inside the nut to cause microscopic slippage, or the nut swings on the bolt to cause microscopic slippage. Tests have shown that lateral external forces can cause greater microscopic slip than axial external forces. Therefore, the lateral external force is a more dangerous factor, and the pure lateral external force perpendicular to the thread axis is the most severe condition for the looseness of the threaded connection compared to the lateral external force at various angles to the thread axis. The actual experience also shows that lateral impact and vibration are more likely to cause loosening of the threaded connection.
3 Overview of contact vibrations on different parts of the network
(1) Since the distance between the contact network facility and the center of the line is generally within 5 meters, the vibration generated by the locomotive passes over the contact net wrist arm base, the support device, the positioning device, the lower anchor device and the terminal anchor clamp, the center Threaded fasteners such as anchoring, integral hanging strings and hanging string clamps, soft spans, and electrical connecting clips have a large influence.
(2) Environmental impact. The contact net is in the external environment and is affected by various meteorological conditions, such as vibration of the contact net parts caused by wind loads.
4 Analysis of the anti-loose condition of the contact thread fastener
The anti-loose principle of the general threaded fastener connection can be divided into the following three types: friction anti-loose, mechanical anti-loose, permanent anti-loose.
4.1 friction and anti-loose generally use double nut, spring washer, self-locking nut, etc.;
4.2 Mechanical anti-loose mainly uses stop washers, slotted nuts and split pins;
4.3 Permanent anti-loose measures such as anchoring glue.
The above-mentioned ten kinds of anti-loose measures are also used in the thread fasteners of railway equipment and facilities.
Use of flat washers and spring washers
It has been used for the part structure not applicable to the stopper washer, such as the joint of the wrist arm insulator and the wrist arm tube, the wind-proof cable positioning hook, the wire fixing hook, the sleeve single ear and the like.
Use of double nuts
It has been used for the connection of the wrist arm base and the pillar, the connection of the wrist arm insulator and the wrist arm tube, and the like.
Use of nylon insert nuts
It has been used to position the support, the bushing seat, and the 70-type bushing single ear.
In recent years, some new anti-loose measures have been applied to the maintenance and repair of subway contact networks. According to relevant feedback opinions, compared with the traditional anti-loose measures, the new anti-loose measures have obvious anti-loose effect.
Double stack locking anti-loose gasket
The double stack locking lock washer includes a pair of washers, one side of which is a flange surface having a flange angle "α" greater than the thread angle "β". In addition, the other side of the gasket has radial serrations, and the pre-assembled gaskets are flanged surfaces that are mounted in pairs on the flange surface. Its advantages are: (1) to prevent loosening caused by vibration or dynamic load; (2) easy to assemble and disassemble; (3) the locking function is not affected by lubrication; (4) controllable pre-stressing; Loose washers must not be used with other unlocked washers. The hardness of the clamped parts should be lower than the hardness of the washers.
The double-stack locking anti-loose gasket vibration test conforms to the DIN65151 standard. In the vibration test, the bolt is forced to move laterally, and the clamping force is continuously measured by the load sensor. The test results are as follows:
According to the test results, the performance of ordinary fasteners during vibration testing is very limited. The double-stack locking anti-loose gasket showed good results in the test. The vibration test report No. 879-130-19 released by TUV of Germany confirmed that after two million cycles of vibration, the clamping force remained unchanged. The experiment showed that the double-stack locking anti-loose gasket can be used safely.
5 Contact net fasteners anti-loose advice
There are many reasons for the looseness of the fasteners of the contact net equipment, and the solution is also diversified. This paper mainly analyzes the loosening principle and solution of contact net fasteners from the perspective of vibration. The following recommendations are made for the maintenance and looseness prevention of fasteners in existing contact network facilities.
5.1 Focus on repairing contacts on the network with large amplitude vibration, frequent vibration and uneven load parts
Through the analysis of the overall structure and force of the contact net: the positioner and the limit positioning support, the bearing cable base, the contact line, the anchor cable center anchor line clamp, the contact line, the load cable suspension string clamp, Threaded fasteners such as anchor support locating clips and elastic sling clips are more likely to loosen. In response to this situation, it is important to overhaul the fasteners in the above parts of the contact net.
5.2 Double-stack locking anti-loose gasket is indeed a better anti-loose device. The import price is quite expensive. It is recommended that the local bearing force in the positioning support, the bearing cable base, the anchor cable center anchor clamp and so on is relatively large. The vibration is used frequently on the threaded connection.
6 Conclusion
The contact net fasteners are important for the safe operation of electrified railways. The traditional thread fastener anti-loose method is widely used on the contact network. The actual use also proves that many traditional anti-loose methods are simple and applicable, and the effect is better, such as double nut anti-loose and nylon insert nut anti-loose; Development, some new threaded fastener anti-loose parts are constantly used in all corners of the machinery industry, and also in the railway, subway applications, such as double-stack locking lock washers. The anti-loose method is constantly updated, but the anti-loose principle has hardly changed much. How to fundamentally solve the anti-loose problem of the contact net fasteners, perhaps it is necessary to make a deeper exploration from the structural innovation of the catenary system. And research.
references
[1] Qiu Xuanhuai. Mechanical Design [M]. Higher Education Press, 1996 (4).
[2] Yang Guangxue. Research on the anti-loose mechanism of a new type of nut based on finite element[M]. Beijing Jiaotong University Railway Vehicle Structural Reliability and Application Testing Technology Engineering Research Center of the Ministry of Education.
[3] Fan Houjun. Fastener Manual [M]. China Mechanical Engineering Society.
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