Insufficient preload on joint bolts negatively impacts track smoothness
Q1: Why does insufficient bolt preload cause frequent opening and closing of rail gaps?
A1: Insufficient preload fails to provide enough friction to restrain rail expansion and contraction, leading to repeated joint opening and closing during train passage. Rail gap jumping forms steps, enhances wheel impact and rapidly develops vertical irregularity. Long-term opening and closing also causes bolt fatigue and fishplate wear, continuously worsening joint conditions.
Q2: How does low preload affect track vertical smoothness?
A2: Reduced joint stiffness increases rail settlement and forms joint collapse. Severe impact occurs when wheels pass, aggravating pad crushing and clip fatigue. Vertical deviation gradually expands, line wavy irregularity becomes obvious, driving turbulence intensifies and comfort decreases significantly.
Q3: Why does uneven bolt preload lead to gauge deviation?
A3: Loosening of some bolts causes uneven joint lateral stiffness, rail deflection under lateral force, and gauge widening or narrowing. Unilateral loosening also results in fishplate eccentric wear and joint step, disordering track geometry and threatening driving safety in severe cases.
Q4: Why is the harm of insufficient preload more prominent on heavy-haul lines?
A4: Heavy-haul lines have large axle loads and strong impacts, with joint stress much higher than ordinary lines. Insufficient preload leads to seriously inadequate joint stiffness, further amplified dynamic loads, and rapid fatigue damage to bolts and fishplates. Joint collapse, step and other defects develop faster and are more difficult to rectify.
Q5: How to ensure sustained and stable joint bolt preload?
A5: Construct with calibrated torque wrenches and fasten strictly according to design values. Adopt lock washers and lock nuts to reduce loosening. Intensify retightening in the initial stage of new lines or overhauls to offset early torque attenuation. Regularly sample and inspect torque, and supplement retightening in a timely manner to ensure joints are always in a rigid state.