Design of Anti-Loosening Structures for Rail Bolts and Stability Assurance Under Vibration Loads
Why do track bolts need special anti-loosening structure design?
Track bolts connect rails, fish plates and sleepers, and are core components of the track fastening system. The continuous vibration generated by train operation will gradually reduce the pre-tightening force of the bolts, eventually leading to bolt loosening. There are gaps in the threaded connection of ordinary bolts, which are prone to relative rotation under vibration. Without an anti-loosening structure, the bolts will fail quickly, causing serious problems such as rail displacement and gauge deviation. The working environment of track bolts is harsh, and they need to withstand wind, rain, temperature changes and load impacts. Ordinary anti-loosening methods are difficult to meet the long-term service needs. A special anti-loosening structure can effectively prevent the relative rotation between the bolt and the nut, lock the pre-tightening force, and ensure the stability of the connection even in a strong vibration environment. Therefore, the anti-loosening structure of track bolts is an important guarantee for the safe operation of the track.
What is the difference in the working principle between mechanical anti-loosening and friction anti-loosening structures?
The working principle of the mechanical anti-loosening structure is to directly limit the relative rotation of the bolt and the nut through mechanical constraints, which is a "locking" type anti-loosening. For example, split pin anti-loosening is to pass the split pin through the hole at the tail of the bolt and the nut to prevent the nut from rotating; the lock washer is to bend the fins of the washer to fit the surface of the nut and the connected part respectively to form a mechanical barrier. The working principle of the friction anti-loosening structure is to prevent the bolt from loosening by increasing the friction between the threaded contact surfaces, which is a "slip-proof" type anti-loosening. For example, double nut anti-loosening uses the opposite force after two nuts are tightened to generate continuous friction between the threads; the lock washer generates pre-tightening force through its elastic deformation, and the teeth on the washer surface can increase friction. Mechanical anti-loosening has higher reliability and is suitable for parts with severe loads; friction anti-loosening is easy to install and suitable for general working conditions.
Why do track bolts of high-speed railways prefer lock washers as the anti-loosening structure?
Track bolts of high-speed railways prefer lock washers mainly because the anti-loosening effect of lock washers is stable and they are suitable for the ballastless track structure of high-speed railways. The lock washer is composed of two washers with teeth. After installation, it can generate lasting elastic pre-tightening force, effectively offsetting the pre-tightening force loss caused by vibration, and its anti-loosening performance is better than that of double nuts. The installation accuracy of track components of high-speed railways is high. The lock washer is small in size and thin in thickness, which will not affect the fitting degree of track components. However, mechanical anti-loosening structures such as split pins and lock washers need additional drilling or bending, which will damage the component structure. In addition, the lock washer is easy to install and disassemble, convenient for later maintenance and replacement, and suitable for the large-scale laying needs of high-speed railways. The lock washer can also adapt to temperature changes and maintain good anti-loosening performance in high and low temperature environments.
What are the common anti-loosening structure combinations for track bolts of heavy-haul railways?
Track bolts of heavy-haul railways bear large loads and severe vibrations. A single anti-loosening structure is difficult to meet the requirements, so a combination of "friction anti-loosening + mechanical anti-loosening" is usually adopted. The most commonly used combination is "double nuts + split pins". The double nuts provide basic friction anti-loosening, and the split pins further lock the nuts, providing double protection against bolt loosening. Another combination is "lock washer + lock washer". The lock washer increases friction, and the lock washer prevents the nut from rotating through mechanical constraints, which is suitable for the connection of fish plate bolts. For special bolts in turnout areas, a combination of "thread locking adhesive + lock washer" is also used. The thread locking adhesive can fill the thread gaps, increase the bonding force, and cooperate with the lock washer to achieve a better anti-loosening effect. These combined anti-loosening structures can give full play to their respective advantages, adapt to the harsh working environment of heavy-haul railways, and ensure the long-term stability of bolts.
What are the key points of daily inspection of the anti-loosening structure of track bolts?
The key points of daily inspection of the anti-loosening structure of track bolts are to check whether the anti-loosening parts are intact and installed in place. For split pins, it is necessary to check whether they are broken, fallen off or bent. If the split pins are damaged, the nuts are prone to loosening and need to be replaced in a timely manner. For lock washers, it is necessary to check whether the fins are bent to fit the nut and the connected part. If the fins are warped, the washer needs to be re-bent or replaced. For lock washers, it is necessary to check whether there is deformation or damage. If the washer loses its elasticity, the anti-loosening effect will be greatly reduced. For double nuts, it is necessary to check whether the two nuts are tightened and whether there is a loose gap. During inspection, a torque wrench can be used to detect the bolt pre-tightening force. If the pre-tightening force is insufficient, even if the anti-loosening structure is intact, it needs to be re-tightened. In addition, it is necessary to clean the rust and debris on the surface of the anti-loosening structure to prevent corrosion from affecting the anti-loosening performance.