Rail Pad Thickness Selection and Track Adjustment
- What are the common thicknesses of under-rail pads? What are the applicable scenarios for different thicknesses?
Common thicknesses of under-rail pads are 6mm, 8mm, 10mm, 12mm, and 15mm. Pads with thicknesses of 6mm and 8mm are suitable for newly built tracks, where track settlement is small and no excessive adjustment is needed, ensuring accurate initial elevation of the rail. Pads with thicknesses of 10mm and 12mm are often used in the maintenance of existing lines, which can cope with slight track settlement and adjust the track height by replacing pads of different thicknesses. Pads with a thickness of 15mm are suitable for lines with obvious settlement, such as railways in soft soil areas, which can provide a larger adjustment margin and maintain track smoothness.
- What is the relationship between the thickness of under-rail pads and rail type?
Different types of rails have different requirements for the thickness of under-rail pads. The thickness of pads supporting 50kg/m rails is mostly 8-10mm. Because of their moderate height, this thickness can balance the buffering effect and track stability. 60kg/m rails are heavier and have stronger impact force, so pads with a thickness of 10-12mm need to be selected to enhance the buffering performance and reduce the impact on sleepers. Foreign standard UIC60 rails are usually matched with 12mm thick pads, which match their solid section design to ensure uniform load transmission.
- How to select the thickness of under-rail pads according to track settlement?
When the track settlement is within 5mm, pads 5mm thicker than the original can be used for replacement. For example, the original 6mm pad can be replaced with an 11mm pad (12mm is commonly used in practice). When the settlement is 5-10mm, 15mm thick pads must be selected, and adjusted together with sleeper heightening fasteners. If the settlement exceeds 10mm, in addition to replacing with 15mm thick pads, the ballast bed must be cleaned or replaced, and then fine-tuned through pads. Newly built lines should reserve a settlement adjustment thickness of 5-8mm and select slightly thicker pads.
- What impact does the thickness deviation of under-rail pads have on track smoothness?
When the thickness deviation exceeds 1mm, it will cause excessive local height deviation of the track, resulting in bumps when the train passes, affecting driving comfort. The accumulation of thickness deviations of multiple consecutive pads will cause obvious slope changes of the track, exceeding the allowable value (no more than 1‰ for main lines), which may cause abnormal contact between train wheels and rails and aggravate wear. Pads that are too thin are easily crushed under load, losing their buffering effect, causing increased stress on rails and sleepers, and shortening their service life.
- What is the specific method for adjusting the thickness of under-rail pads?
When the track elevation is low, remove the original pad and replace it with a thicker one. The thickness increase of a single pad should not exceed 5mm. If a larger adjustment is needed, the method of overlapping pads can be adopted, but the number of overlapping layers should not exceed 2, and the total thickness should not exceed 20mm. When the track elevation is high, replace it with a thinner pad, or grind the original pad (only for rubber materials). The thickness after grinding must not be less than 70% of the original thickness. After adjustment, a track gauge should be used to measure the gauge and level to ensure they meet the line standards, and the height deviation of each 25-meter track should not exceed 4mm.