Since the beginning of the new century, the sustained and rapid growth of China's national economy has placed high demands on the development of transportation infrastructure. Throughout the development of countries around the world, heavy-duty railways have very high efficiency and efficiency. Under the requirements of this situation, in order to rapidly improve the technical level of China's rolling stock equipment, China CRRC Datong Electric Locomotive Co., Ltd. specially developed and produced the highest test speed of 132km/h and the maximum operating speed of 120km/h for the heavy-duty transportation needs. HXD2 high-power AC drive freight electric locomotive with power of 10MW. With the introduction of HXD2 electric locomotive technology, the intensive development of digestion and absorption and innovation work, the development of parts and components is becoming more and more important. As a common connection form in mechanical connection and electrical connection, the locknut structure is subjected to complex dynamic loads during the running of the locomotive, so it must have sufficient strength and rigidity to ensure the safety, stability and service life of the locomotive. In addition, it is also necessary to effectively improve the electrical conductivity and avoid excessive tightening torque.
1 Development process of locknut for rolling stock
1.1 Trial production of locknuts
The first stage, analysis of NF E25 411 grooved full metal hexagonal self-locking nut, E-1-4 hexagonal self-locking nut (steel), E-1-5 hexagonal self-locking nut (stainless steel) and ISO 2320 effective torque steel Hexagon nuts - Mechanical and mechanical properties and Q/CR 343.1 - 2014 Locking nuts and washers for rolling stock Part 1 : Straight slot locknuts, preliminary trials, trials. The lock nut structure type [1] is shown in Figure 1 and Figure 2.
The trial installation of locknuts was carried out on the bogies of No. 90 and No. 116-124 locomotives produced by the company. The first batch of lock nuts were assembled on the bogies of nine locomotives on the 90th, 116th, 117th, 118th, 119th, 120th, 121th, 122nd, and 123th, and were found during the assembly process. A total of 165 axle box trolleys installed on the M20 nut buckled, the failure rate reached 14.3%. The second batch of locknuts were assembled on the No. 493, No. 494, and No. 495 bogies of No. 124 locomotive. During the assembly process, a total of 43 M20 nuts installed on the axle box rods were buckled. The pass rate reached 44.8%. The eight nuts installed on the 496 bogie assembly upper rod are the second batch of locknuts, and five of them have failed. Due to the assembly problems of the second batch of locknuts, the other 24 M20 nuts of the 496 bogie were assembled with the first batch of locknuts, and two of them were buckled.
1.2 Rectification and testing
1.2.1 Formulating corrective measures
1) The hardness of the first batch of nuts is low. During the assembly process, nut buckles and deformation phenomena are found. It is necessary to improve the heat treatment process of the nuts in the later stage of production and increase the frequency of sampling. The second batch of nuts has a high hardness value (although it meets the relevant standards), causing the bolts to buckle. In view of the wide range of hardness of bolts and nuts given by relevant standards, the grooved nut has no experience in the country, and the hardness matching of bolts and nuts is still in the process of exploration. Therefore, it should be summarized and improved during trial production and assembly, and bolts are given. , the hardness range of the lock nut.
2) Do not use lubricating oil or grease when installing the nut. Do not use more than 30r/min when using a torque wrench to avoid buckle. When tightening, ensure that the minimum is screwed into the three ends of the nut head end, and the maximum is screwed into the six ends of the nut head end.
3) In order to solve the problem of decarburization during the heat treatment of the thread, a method of first heat treatment and then processing the thread is adopted.
1.2.2 Sample test after rectification
1) According to the requirements, the rectified sample will be sent to the mechanical industry general parts and components product quality supervision and testing center within one month, and the screw-in and screw-out test, guaranteed load test, clamping force test and salt spray test will be carried out in order according to the standard requirements. Metallographic analysis test, hardness test, thread decarburization test, the latter three tests are done by the author's laboratory in accordance with the requirements of GB/T 3098.9 fastener mechanical performance effective torque steel lock nut [2].
2) The sample test did not find thread decarburization; the product was qualified for flaw detection.
3) The first screwing torque of all the locknuts is far below the standard value. The author believes that the reason is that the sample is made for the convenience of installation and the workload is reduced as much as possible. The clamping torque is taken as the standard given. The median of the range, not the maximum. The torque for the first tightening torque and clamping force to the standard specified value is in full compliance with the standard. The first screwing torque is based on the test data. One sample of each specification (2 samples) does not meet the standard. Taking into account the accuracy of the test instrument, the instrument dial display data has no decimal places, only one of the M20 (8) samples does not meet the standard. Re-create the sample, test again, the test results are qualified, meet the standard requirements.
4) Guaranteed load test, applying the standard specified load for 15 s, no thread tripping occurred in the specimen.
5) Add lateral vibration test items. The test is in accordance with the technical requirements of 5.1 in the TB/T3019-2001 variable-type locknuts. “Vibration 1000 times, no spring washers, tightening torque value according to Appendix B, the first test residual axial force shall not be tested. Less than 50%; after 10 times of tightness, the residual axial force of the test shall not be less than 45%". For the lateral vibration test, the ratio of the residual axial force of the three specimens to the initial axial force is greater than 86%, which is in full compliance with the standard. Can meet the requirements of use [3].
6) Metallographic analysis and hardness test. The sample is analyzed in the laboratory according to the standard requirements. The test results are as follows: the metallographic structure is tempered sorbite, the hardness is about 280 HV, and the hardness range is 250~ according to the standard. 353 HV, can meet the requirements of use.
1.3 Re-correction and loading verification for test problems
1) The tolerance class of the nut is in accordance with the standard 6H class specified in the standard NF E25 411 grooved all-metal hexagonal self-locking nut.
2) Continue to improve the performance of the locknut, especially the M20 specification, so that the screw-out test meets the standard requirements.
3) The single straight groove lock nut should be cut from the six aspects of the nut. The thickness of the remaining two parts after the groove is basically the same. The double straight slot locknuts are still made according to the original regulations.
4) After the agreement comes into effect, provide a qualified test report every year for three years before the supply. The batch of samples will be gradually reduced according to the situation. Each batch of products delivered should be accompanied by a flaw detection record or a flaw detection report.
5) It is recommended that the incoming inspection should be carried out according to the heat treatment batch. One sample per sample is tested for its Vickers hardness, metallographic structure and whether the thread is decarburized.
6) The quality management department of the company shall review the relevant qualifications of the heat treatment and coating outsourcers, and the plating thickness of the locknut shall be made at 8 μm.
7) In order to ensure the safety and reliability of the locknut during the loading operation, the performance quality of the locknut must be verified before mass purchase. The requirements, parameters, contents and execution standards of the loading verification are as follows: First, the verification is only in the company; second, the number of loading is 60 M16, 16 M20, 4 M24 per vehicle; the third is according to Q/DJ. J.51.002—2000 sampling inspection implementation plan for sampling inspection; Fourth, tightening torque according to Q/DJ.J.13.539—2009 fastener tightening torque tightening nut; fifth is the loading verification content: according to the fourth step Tighten the specified torque and observe whether the thread of the bolt or nut is damaged (so that the nut cannot be tightened normally); the sixth is the verification standard Q/DJ.J.51.002-2000 sampling inspection implementation plan; the seventh is the organization and confirmation form of the loading verification. Execute the first inspection management program of Q/DJ.G05.2813—2009.
2 Conclusion of the development of locknuts for rolling stock
First, the anti-loose nut sample meets GB/T 3098.9 fastener mechanical performance effective torque steel lock nut performance test; second, the guaranteed load test fully meets the standard requirements; third, the torque-clamping force test fully meets the standard The fourth is that the lateral vibration test fully meets the standard requirements; the fifth is that the hardness test fully meets the standard requirements; the sixth is that the thread decarburization test fully meets the standard requirements (no decarburization); the seventh is the metallographic examination result and the imported anti-loosening nut. Consistent; Eight is the chemical composition analysis results are basically consistent with the imported locknut; nine is the screw-in and screw-out test basically meets the standard requirements. In summary, according to the above test results, the performance of domestic locknuts can basically meet the performance requirements of locknuts, and can be loaded in batches.
3 anti-loose performance and basis
3.1 Theoretical analysis of anti-loose performance
Compared with ordinary locknuts, the temperature range is -50 ~ +300 °C, the anti-loose effect is good, and can be reused. According to the anti-loose nut technical specification E-1-4 hexagonal self-locking nut (steel), E-1-5 hexagonal self-locking nut (stainless steel), TGLS409869000 parts technical specifications and standard NF E25 411 slotted full metal self-locking hex nut, GB/T 3098.9 (idt ISO 2320) fastener mechanical properties effective torque steel lock nut provisions, the author to take two common specifications of the locknut for analysis, the data used in the analysis are based on the data in the original standard. Due to the universality of the above two types of locknuts, the analysis results can be pushed against such locknuts, as shown in Table 1. According to the above calculation results, it can be concluded that the anti-loosening performance of the locknut is reduced with the increase of the number of repeated uses, but the decrease value is small. Taking the M20 (Grade 8) nut as an example, the percentage reduction for each reuse is only 0.4%. At the same time, the reduction of the lock-proof property of the locknut does not mean that the bearing performance of the nut is lowered, that is, the nut is not loose. Therefore, in theory, there is no safety hazard in the repeated use of the locknut.
3.2 Comparison of anti-loose performance between old and new locknuts
Use the unused M20 (10 grade) locknuts and M20×120 (10.9 grade) bolts under the HXD2 two-year inspection and removal, and compare the screwing torque value with the screwing torque value. The test results are shown in Table 2.
3.3 Test conclusion
1) Since the clamping force is not considered, the torque wrench is adjustable, not with the indication value. There is no special test device to operate on the workpiece. Therefore, the value tested can only be used for comparison and cannot be used as a standard value.
2) The used bolt is combined with the locknut. Due to the long-term load, the screwing torque of the nut is reduced.
3) The ratio of the torque value of the locknut for the two-year inspection and disassembly of HXD2 to the torque value of the new locknut combination is as follows: minimum 310/410 = 75.6%, average 345/382 = 90.3%, most 360/330 = 109.1 %.
4) Use the removed bolts in combination with the locknuts to reuse the threads with severe thread damage.
4 Development results
1) Solved the problems occurred in the trial production, test and loading verification of locknuts, and realized the successful application of locknuts on locomotive bogies and electrical.
2) Compiled the enterprise standard of China Railway Corporation Q/CR343.1-2014 Locking nuts and washers for rolling stock Part 1: Straight slot locknuts.
references:
[1] China Railway Corporation Railway Construction Project Engineering Laboratory Q/CR 343.1-2014 Locking nuts and washers for rolling stock Part 1: Straight slot locknuts [S]. Beijing: China Railway Publishing House, 2014.
[2] General Administration of Quality Supervision, Inspection and Quarantine, National Standardization Administration Committee GB/T 3098.9-2010 Fastener Mechanical Properties Effective Torque Steel Lock Nut [S]. Beijing: China Standard Press, 2011.
[3] Ministry of National Railways. TB/T 3019-2001 variable tooth type locknut [S]. Beijing: China Railway Publishing House, 2001.
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