Dimensional Tolerances of External Standard Rails and Track Laying Accuracy
- What are the characteristics of the dimensional tolerance standards for common foreign - standard rails?
The European EN standard has strict control over the rail height tolerance, generally ±0.5mm, to ensure the consistency of the rail surface height and reduce the impact between the wheel and the rail; the American AREA standard focuses on the tolerance of the rail head width, which is controlled within ±0.3mm to ensure good wheel - rail contact; the Japanese JIS standard requires the tolerance of the rail base width to be ±0.8mm to meet the stability requirements of the track structure. These standards also have detailed regulations on the dimensional tolerances of rail length, camber, etc., and the tolerance range is adjusted according to the rail type and application scenario.
- How does dimensional tolerance affect track laying accuracy?
When the rail height tolerance exceeds the limit, the rail surface will be uneven, causing vertical vibration when the train passes, accelerating the wear of the wheels and rails, and seriously affecting driving safety. If the tolerance of the rail head width does not meet the requirements, the wheel - rail contact area will be reduced or uneven, increasing the wheel - rail force and triggering derailment risks. If the tolerance of the rail base width is too large, it will affect the connection stability between the rail and the sleeper, resulting in lateral displacement of the track and destroying the integrity of the track structure.
- How to detect the dimensional tolerances of foreign - standard rails?
Use high - precision measuring tools, such as calipers to measure the width of the rail head and the width of the rail base with an accuracy of up to ±0.05mm; use a micrometer to measure the rail height with an accuracy of ±0.01mm. For the rail length, a laser rangefinder is used for measurement with an error controlled within ±1mm. The camber of the rail is measured by a chord and a straightedge. Under a specified chord length (such as a 10m chord), the maximum sagitta of the rail and the chord is measured and compared with the standard allowable value, with a deviation not exceeding ±1mm.
- How to control the dimensional tolerances of foreign - standard rails during the track laying process?
When the rails enter the site, sample and detect the dimensional tolerances by batch, and the sampling ratio is not less than 10%. Unqualified products are strictly prohibited from being used. Before laying, pre - straighten the rails using a press or a stretcher to adjust the camber of the rails within the standard range. During the laying process, use a track measuring instrument to monitor parameters such as rail surface height and gauge in real - time. If dimensional deviations are found, adjust them in time. Adjust the tightness of the fasteners, add shim pads, etc. to ensure that the track laying accuracy meets the requirements.
- What are the treatment measures when dimensional tolerances of foreign - standard rails deviate?
For slight dimensional deviations (such as a height deviation within ±0.8mm, a rail head width deviation within ±0.5mm, and a rail base width deviation within ±1.0mm), the rail surface can be polished for correction, but the amount of polishing must be strictly controlled to avoid affecting the rail strength. For large dimensional deviations, such as exceeding the above range, the rails should be replaced in time to ensure the track laying quality. At the same time, analyze the causes of the deviations. If it is a problem of the manufacturer, feedback in time and request rectification; if it is due to improper transportation or storage, optimize the corresponding links.