Anti-loosening design and service stability of rail bolts
What are the applicable scenarios of conventional anti-loosening schemes for national standard track bolts?
The spring washer anti-loosening scheme is suitable for ordinary sections of conventional speed railways. It generates preload through the elastic deformation of the washer to prevent bolts from loosening due to slight vibration. This scheme is low-cost and easy to install, adapting to low-load working conditions. The double nut anti-loosening scheme is mostly used in key sections of heavy-haul railways. It forms double constraints by the locking force of two nuts, which can effectively resist the loosening risk caused by large loads and ensure connection reliability. The split pin anti-loosening scheme is suitable for bolt connections of special equipment such as turnouts. It limits nut rotation through mechanical blocking, with stable anti-loosening effect and easy maintenance, suitable for areas with extremely high safety requirements. For bolts in electrified sections, insulating anti-loosening washers will be used to ensure electrical insulation while preventing loosening and avoid stray current leakage. In addition, in inland lines with less wind and sand, the glue coating anti-loosening scheme can also be adopted, which fills the thread gap with anaerobic glue to achieve long-term anti-loosening.
What are the core advantages of the anti-loosening coating technology of foreign standard track bolts?
The anti-loosening coatings of foreign standard track bolts are mostly nylon or microcapsule anaerobic adhesive coatings. This coating can form stable bonding force on the thread engagement surface, and the anti-loosening effect is not affected by vibration frequency, adapting to the high-frequency vibration conditions of high-speed lines. The anti-loosening coating can automatically fill the thread gap during bolt installation, form uniform stress distribution, reduce thread stress concentration, and extend the fatigue life of the bolt. Its anti-loosening validity period can reach more than 15 years, far exceeding the 3-5 years of traditional spring washers, which greatly reduces the frequency of later maintenance. The coating also has certain anti-corrosion performance, which can isolate air and water vapor, prevent disassembly difficulties caused by thread rust, and take into account both anti-loosening and anti-corrosion functions. In addition, the anti-loosening coating bolts do not require additional accessories during installation, simplifying the construction process and improving installation efficiency.
What is the anti-loosening principle and applicable working conditions of self-locking thread bolts?
The thread profile of self-locking thread bolts is a special wedge-shaped structure. When engaged, a large normal pressure and friction force will be generated on the thread surface, thereby forming a self-locking effect and preventing the bolt from reversing due to vibration. Its anti-loosening principle is to use the mechanical locking of wedge-shaped teeth instead of traditional friction anti-loosening, with higher anti-loosening reliability and not easily affected by load fluctuations. This bolt is suitable for ballastless track sections of high-speed railways. The high-frequency vibration of high-speed trains is likely to cause loosening of ordinary bolts, and self-locking threads can ensure long-term tightness. At the same time, it is also suitable for underground lines of urban rail transit. The underground environment is humid and the maintenance space is limited, and long-term anti-loosening can reduce maintenance workload. In addition, self-locking thread bolts are often selected for long and steep slope sections of heavy-haul railways. The large axle load and slope longitudinal force are likely to cause bolt loosening, and its self-locking structure can effectively cope with it.
What key points should be noted in the anti-loosening design of track bolts in alpine regions?
The anti-loosening components of track bolts in alpine regions should be made of low-temperature resistant materials. For example, spring washers should be made of 60Si2MnA cold-resistant spring steel to avoid anti-loosening failure caused by low-temperature brittle fracture. The anti-loosening coating should have low-temperature resistance, and can still maintain bonding force at -40℃ without coating peeling or embrittlement. The thread accuracy of the bolt should be improved, and high-precision 6g grade threads should be adopted to reduce the gap change caused by low-temperature shrinkage and ensure the stability of the anti-loosening structure. During installation, the low-temperature compensation of preload should be controlled. The steel will shrink in low-temperature environments, and the preload should be increased by 5%-10% compared with normal temperature conditions to prevent insufficient preload after temperature rises. In addition, it is necessary to regularly conduct flaw detection on anti-loosening components in low-temperature environments, and replace aging or failed components in a timely manner to ensure the operation safety of winter lines.
How to conduct on-site detection of the anti-loosening performance of track bolts?
When conducting on-site detection of the anti-loosening performance of track bolts, first, a torque wrench will be used to retest the preload, and compare it with the initial torque value during installation. If the attenuation range exceeds 10%, the anti-loosening is judged to be invalid. For bolts with anti-loosening coatings, the integrity of the coating will be checked through appearance inspection, and if the coating is peeled or cracked, it needs to be replaced. The percussion detection method will also be adopted: tap the bolt head with a small hammer, and judge whether the bolt is loose by the sound. A loose bolt will emit a turbid abnormal sound, while a tight bolt will emit a crisp sound. For self-locking thread bolts, a special tool will be used to detect the self-locking torque of the thread. If the torque is lower than 80% of the design value, it needs to be re-tightened or replaced. In addition, the vibration data of bolts will be collected regularly, and the attenuation trend of anti-loosening performance will be predicted through data analysis to carry out preventive maintenance in advance.