Track Bolt Torque Attenuation and Long-Term Loosening Control
Why are track bolts so prone to loosening?
High-frequency train vibration; wheel-rail impact; longitudinal forces generated by temperature expansion and contraction; repeated tension and compression during braking and starting; slippage of contact surfaces, gasket compression, and coating deformation.
What is torque decay?
After bolts are tightened, the preload gradually decreases over time, under load, and with vibration, and may even be completely lost. When decay reaches a certain level, joint failure, fastener failure, gauge widening, and track creep occur.
Several technical approaches to preventing loosening:
Friction locking: spring washers, double nuts, nylon lock nuts; Mechanical locking: cotter pins, anti-lock washers, locking plates; Thread locking: thread locking adhesive, special-shaped threads; Structural locking: conical surface fitting, self-locking structure, preload retention design.
Why must installation be strictly based on torque?
Insufficient torque → rapid loosening; excessive torque → bolt yielding, elongation, fatigue fracture; different lubrication conditions result in different torques; different strength grades of bolts require different torques.
Key points for on-site control:
Use torque wrenches, and never use adjustable wrenches by feel; tighten new lines 3-6 months after laying; strengthen inspections during the rainy season and freeze-thaw period; upgrade anti-loosening structures in frequently loosened sections.