Gap control between fishplate and rail and its impact on performance
- What are the types of gaps between fishplates and rails, and what are the standard requirements?
Longitudinal gaps (along the length of the rail) are the main type, with a standard requirement of ≤0.3mm. Excessively large gaps (>0.5mm) will cause impact when the train passes, increasing the vibration acceleration by 20% - 30%. Ordinary railways allow slightly larger gaps (≤0.5mm), and high - speed railways strictly control them to ≤0.2mm. Lateral gaps (perpendicular to the length of the rail) must be ≤0.2mm. Exceeding 0.3mm will make the fishplate stress uneven, with a bolt preload deviation of 15% - 20%. Lateral gaps in curve sections are controlled more strictly (≤0.1mm) to resist lateral forces. Vertical gaps (between the rail head and the top of the fishplate) should be ≤0.3mm. Excessively large gaps (>0.5mm) will cause the rail to jump up and down under load, accelerating fishplate wear. Heavy - haul railways need to control them to ≤0.2mm to ensure stable load transmission. The standard for bolt hole gaps (between bolts and holes) is 0.2 - 0.4mm. Too small gaps (<0.1mm) make installation difficult, and too large gaps (>0.5mm) will make bolts bear additional bending moments, reducing service life. The gap must be precisely controlled to match the bolt diameter.
- What impact do excessively large gaps have on the performance of fishplates and rails?
Excessively large longitudinal gaps create steps at rail joints, increasing the impact force when wheels pass by 30% - 50%. The fatigue life of fishplates and rails is shortened by 40% - 60%. This problem is more serious in heavy - haul railways and may lead to rail fracture at joints. Excessively large lateral gaps will deform fishplates under lateral forces, increasing the bolt loosening rate by 2 - 3 times, with gauge deviation exceeding ±1mm, requiring frequent adjustment and increasing maintenance costs. Excessively large vertical gaps will reduce the contact area between rails and fishplates by 10% - 15%, increase local pressure, and cause plastic deformation on the rail bottom and fishplate surface, with dents (depth >0.5mm), affecting connection strength. Uneven gaps (with differences >0.3mm in various parts) will unbalance the stress on fishplates, with a stress concentration factor of 1.5 - 2.0, prone to cracks. Grinding is needed to ensure uniform gaps with a deviation ≤0.2mm.
- How to measure the gap between fishplates and rails?
Feeler gauge measurement is a common method. Use feeler gauges of 0.02 - 1mm to measure different parts (longitudinal, lateral, vertical) between fishplates and rails, measure 3 points at each part, and take the maximum value. Ordinary railways can sample (5 points per kilometer), high - speed railways need 100% detection. Dial indicator measurement has higher accuracy. Fix the gauge base on the rail, touch the feeler gauge to the fishplate, and read the gap value with an accuracy of ±0.01mm, suitable for key parts such as turnout areas to ensure the gap ≤0.1mm. Laser gap meters are used for batch detection, measuring gaps through laser scanning, with data transmitted to the terminal in real time, which can quickly judge whether the gap is qualified. The detection efficiency is 5 - 10 times that of feeler gauges, suitable for large - scale laying. After installation, indirectly judge through train vibration tests. If the vibration acceleration at the joint is 20% higher than that at other parts, it may be that the gap is too large, and targeted measurement and adjustment are needed.
- What are the specific measures to control the gap between fishplates and rails?
Precisely grind the contact surfaces of rails and fishplates to make the surface roughness Ra ≤3.2μm and flatness deviation ≤0.1mm/m. After grinding, the gap can be reduced by 30% - 40%. High - speed railway joints must adopt this method to ensure that the gap meets the standard. Select high - precision fishplates (hole position deviation ≤0.3mm), with a fitting gap 20% - 30% smaller than that of ordinary fishplates. Although the cost increases by 10% - 15%, it can maintain small gaps for a long time, and heavy - haul railways prefer this method. Tighten bolts in a symmetrical order during installation: first pre - tighten diagonal bolts (50% torque), then tighten other bolts to the specified torque in turn to make the gap evenly distributed with a deviation ≤0.2mm, avoiding excessive unilateral gaps. Fill the gap with sealing materials (such as high - temperature resistant silica gel) with a thickness of 0.2 - 0.3mm. After curing, it can eliminate 50% - 60% of small gaps, and prevent rainwater and debris from entering. Coastal areas must adopt this measure to reduce gap corrosion.
- What are the differences in gap control and maintenance measures among different railway types?
High - speed railways have the strictest gap requirements (longitudinal ≤0.2mm, lateral ≤0.1mm), using high - precision fishplates and numerical control grinding, detecting gaps every six months, and dealing with exceeding gaps immediately to ensure stable train operation (vibration acceleration ≤30m/s²). Heavy - haul railways focus on controlling longitudinal and vertical gaps (both ≤0.2mm), using thickened fishplates (2mm thicker than ordinary ones) to enhance deformation resistance, replacing sealing materials every 2 years to prevent gap corrosion from expanding. Ordinary railways allow slightly larger gaps (longitudinal ≤0.5mm), adopt economical maintenance, detect once a year, grind and adjust when gaps exceed the standard, without frequent component replacement, balancing cost and performance. Due to frequent start - stop of urban rail transit, gaps change quickly, with inspections once a year, focusing on joint gaps within 200m at both ends of the station, and timely handling of exceeding parts to avoid excessive vibration affecting passenger comfort.