Anti-loosening structure design of railway spikes and their adaptation to the dynamic runout of switch rails in turnout areas
Why do the anti-loosening requirements for spikes on switch point rails in turnout areas far exceed those for spikes on ordinary lines?
Rail displacement on ordinary lines is mainly longitudinal creep and minor lateral displacement, with relatively stable dynamic loads. In turnout areas, switch point rails perform reciprocating "closing-separating" movements driven by point machines; meanwhile, when a train passes, the point rails generate vertical dynamic bouncing with an amplitude of up to 3-5mm, synchronized with the impact frequency of train wheels. This reciprocating bouncing subjects the spikes to combined alternating tension, compression, and shear loads, making ordinary anti-loosening structures prone to failure. Spike loosening reduces the tight contact between point rails and stock rails, causing train derailment-thus, the anti-loosening requirements are more stringent.
What are the classic mechanical locking anti-loosening structure designs for spikes that adapt to the dynamic bouncing of switch point rails?
Classic mechanical locking designs adapted to point rails include two types: 1) Double-ear lock washers-the two ears of the washer are respectively buckled on the spike nut and the protrusion of the sleeper, forming mechanical locking to prevent nut rotation, and the elasticity of the washer can adapt to the minor bouncing of point rails; 2) Wedge-locking nuts-the nut has internal wedge threads that lock tighter under vibration after tightening, effectively resisting alternating loads from point rail bouncing. Both designs feature "zero-clearance locking," avoiding loosening gaps in the anti-loosening structure caused by bouncing.
What are the limitations of "thread adhesive-coated" anti-loosening spikes in the application of switch point rails in turnout areas?
Thread adhesive-coated spikes form bonding locking through anaerobic adhesive applied to the threads, which cures and hardens. Their limitations are mainly reflected in three points: 1) Insufficient temperature resistance-frictional heat generated by switch point rails can raise the temperature to over 60℃, softening the anaerobic adhesive and reducing anti-loosening performance; 2) Non-reusability-spikes need to be removed during point rail maintenance, damaging the adhesive layer; reapplication of adhesive is required for reinstallation, reducing construction efficiency; 3) Weak shear resistance-shear force from point rail bouncing easily fails the bonding layer, causing spike loosening. Therefore, adhesive-coated anti-loosening is only suitable for non-moving components in turnouts and is strictly prohibited for point rail fixation.
For the composite movement of "lateral oscillation + vertical bouncing" of point rails, how do the anti-loosening structures of spikes achieve "bidirectional restraint"?
The core of bidirectional restraint is a composite design of "friction enhancement + mechanical locking." A serrated anti-loosening washer is installed between the spike and the sleeper; the serrations of the washer bite into the sleeper surface, enhancing lateral frictional resistance and constraining the lateral oscillation of the point rail. A spring lock washer is installed under the spike nut; the continuous elastic pressure of the spring washer offsets the gap caused by the vertical bouncing of the point rail, maintaining the spike preload, and cooperates with the wedge-locking nut to form mechanical locking. This composite structure resists both lateral shear and adapts to vertical bouncing, perfectly matching the composite movement state of point rails.
How to reversely judge the failure of spike anti-loosening structures through switch point rail tight contact inspection data during on-site maintenance?
A switch point rail tight contact tester is used to measure the gap between the point rail and the stock rail, focusing on the "free movement distance" between traction points. If the free movement distance exceeds 0.5mm and increases significantly after a train passes, it indicates that the spikes fixing the point rail have loosened and the anti-loosening structure has failed. Additionally, observing the rotation angle of the spike nut-if the relative position between the nut and the spike changes (e.g., misalignment of marking lines), or if the ears of the lock washer are broken or detached, these are direct evidence of anti-loosening structure failure. Upon discovery, spikes with effective anti-loosening structures must be replaced immediately, and the point rail tight contact must be readjusted.