Torque Attenuation Mechanism and Long-Term Anti-Loosening Technology of Rail Bolts
Q1: What is the core mechanism of track bolt torque attenuation?
A1: Train vibration causes micro-slip on the bolt contact surface, and repeated slip will reduce the friction between threads, resulting in torque attenuation; at the same time, the longitudinal force generated by rail expansion and contraction and temperature change will make the bolts bear tensile and compressive alternating stress, accelerating the loss of preload and aggravating torque attenuation.
Q2: What is the difference in anti-loosening principle between spring washers and nylon locking nuts?
A2: Spring washers generate friction through elastic deformation and prevent bolt loosening by frictional resistance, suitable for conventional lines; nylon locking nuts provide locking force through the extrusion deformation of nylon rings and screws, with a more durable anti-loosening effect, suitable for curve and turnout sections with severe vibration.
Q3: How does the bolt lubrication status affect torque attenuation?
A3: The thread friction coefficient of bolts is high in dry state, the torque is easy to be falsely high, and the actual preload is insufficient; after applying special thread grease, the friction coefficient is stable, the corresponding relationship between torque and preload is more accurate, which can effectively delay torque attenuation and improve fastening stability.
Q4: Why is a composite anti-loosening scheme required for bolt anti-loosening in heavy-haul lines?
A4: The wheel-rail impact and longitudinal force are large in heavy-haul lines, and a single anti-loosening structure is easy to fail; the composite anti-loosening scheme combines mechanical anti-loosening and thread anti-loosening, such as self-locking nut + locking adhesive + anti-loosening washer, which can form multiple constraints, completely inhibit bolt loosening and ensure joint fastening performance.
Q5: How to monitor and restore bolt torque in operation and maintenance?
A5: Regularly use torque wrenches to spot-check bolt torque, and retighten newly laid lines at 1 month, 3 months and 6 months respectively; for bolts with excessive torque attenuation, clean the threads first and then retighten to the standard torque, and replace severely loosened or corroded bolts directly to avoid fastening failure.