In railway, urban rail transit, and temporary line support for large-scale events, continuous welded rail is widely adopted due to the elimination of rail joints and reduction of vibration and noise. However, once the rail is locked, temperature variations can accumulate enormous internal stress, which may lead to track buckling or rail breakage if it exceeds the load-bearing limit. Mastering the basic methods for stress relief and adjustment of continuous welded rail is a core technical aspect of track maintenance and security systems.
1. What Are the Basic Methods for Stress Relief and Adjustment of Continuous Welded Rail?
Stress relief of continuous welded rail refers to releasing accumulated thermal stress to within the design locking rail temperature range by loosening fasteners, cutting, or stretching the rail. Stress adjustment, on the other hand, redistributes stress without changing the locking rail temperature, through localized loosening of fasteners, placing rollers, and tapping.
Both aim to achieve uniform and controllable longitudinal stress within the rail, avoiding localized stress concentration. A common question is "what is the difference between stress relief and adjustment"—relief focuses on "release," while adjustment focuses on "uniform distribution," and they are often used together on site.
2. How to Apply the Basic Methods for Stress Relief and Adjustment of Continuous Welded Rail?
In practice, there are mainly three methods:
1. Roller relief method: Place rollers at intervals under the rail, loosen fasteners, and use a rail impactor or tensioner to allow the rail to expand and contract freely. Lock the rail once the rail temperature reaches the design locking temperature. This is suitable for sections with concentrated stress in long rails.
2. Tension relief method: Apply tensile force to the rail using a hydraulic tensioner, combined with rollers to reduce friction, and adjust stress to the target value. This is often used in scenarios where natural relief is not possible during low or high temperature periods.
3. Local adjustment method: Loosen fasteners only in sections with abnormal stress, slightly lift the rail with a track jack, tap the rail web to release local stress, and then retighten the fasteners. This is suitable for short-distance, small-scale stress unevenness.
The operation process can be summarized as: measure rail temperature → determine relief amount → loosen fasteners → relief or tension → lock → re-measure. Each step requires recording rail temperature and displacement.
3. What to Pay Attention to in Stress Relief and Adjustment?
First, rail temperature is the core parameter. Relief must be performed within the design locking rail temperature range; otherwise, stress will still exceed limits after locking.
Second, the sequence of loosening and tightening fasteners should be symmetrical and segmented. Loosening all at once can cause rail instability; fasteners should be loosened at intervals, with each segment not exceeding 50 meters.
Third, in security scenarios for large-scale events, stress relief of temporary lines should avoid periods with heavy train or pedestrian traffic. Protective measures should be set at both ends of the work area to prevent sudden rail expansion or contraction from causing injuries.
Fourth, after relief, fasteners must be retightened and displacement observation markers installed, with intensified inspections within one week.
Fifth, operations are prohibited during thunderstorms, strong winds, or sudden changes in rail temperature to avoid abrupt changes in stress state.
4. Applicable Scenarios and Summary
The basic methods for stress relief and adjustment of continuous welded rail are applicable to: initial stress re-measurement after locking of new lines, preventive relief before high summer temperatures, repair after rail breakage in winter, and stress equalization after temporary track laying for large sports events or exhibitions.
For security technology, line stability is the underlying guarantee for event security. Daoxin Dechen continues to invest in track monitoring and stress early warning, using sensors and data analysis to assist maintenance personnel in determining relief timing, but specific operations still need to follow permanent way regulations.
In one sentence: measure rail temperature accurately, loosen fasteners symmetrically, relieve stress uniformly, lock promptly, and intensify re-measurement. By doing these five steps well, the stress risk of continuous welded rail can be controlled within an acceptable range.