Wear mechanism and protective measures of fishplates
- What are the main types of fishplate wear?
Adhesive wear is the most common type. When the wheel drives the rail to slide, adhesion points will be generated on the contact surface between the fishplate and the rail. When separated, the material is torn off, forming wear. This kind of wear in the curve section is 2 - 3 times more serious than that in the straight section. Abrasive wear is caused by impurities (such as sand, iron filings) between the rail and the fishplate. After impurities are embedded in the surface, they scratch like abrasives, producing groove - like wear. Freight railways have more impurities due to goods falling, so abrasive wear is more obvious. Fatigue wear causes fatigue cracks on the surface due to alternating loads. After the cracks expand, the material peels off, forming pitting. Fishplates of heavy - haul railways are prone to such wear after 2 - 3 years of use, and the pitting depth can reach more than 0.5mm. Corrosive wear occurs in humid environments. After the surface rust layer is worn off, a new rust layer is formed, accelerating material loss. The corrosive wear rate of fishplates in coastal areas is twice that in inland areas.
- What factors affect the wear rate of fishplates?
Train speed and load are key factors. For every 10km/h increase in speed, the wear rate increases by 5% - 8%; for every 1t increase in axle load, the wear rate increases by 10% - 15%. The wear of fishplates of heavy - haul high - speed railways is much faster than that of ordinary railways. The material matching between rail and fishplate is very important. The hardness difference between them should be controlled at 50 - 100HV. Excessive difference (such as > 150HV) will cause hard materials to scratch soft materials and accelerate wear. Q345 steel fishplates have the best matching with U71Mn rails. Excessive installation clearance will cause relative sliding between the rail and the fishplate, increasing the wear rate by 20% - 30%. The clearance should be controlled within 0.1mm, and a feeler gauge should be used to check to ensure tight fit. Lubrication has a great impact. Regular coating of grease can reduce wear. The wear rate of unlubricated fishplates is 1.5 - 2 times that of lubricated ones. Curves need to be lubricated every quarter.
- How to detect the wear degree of fishplates?
Measuring thickness loss is a common method. Measure the thickness of the middle and edge of the fishplate with a caliper, compare with the new fishplate. If the wear loss exceeds 10% of the original thickness (such as 10mm thick worn to below 9mm), it needs to be replaced. Check the surface roughness, measure with a roughness tester. The Ra of new fishplates is ≤3.2μm. If Ra > 12.5μm after wear, it indicates that the surface is seriously worn, which will aggravate rail wear and needs to be repaired or replaced. Observe the wear form. If obvious grooves, pits or edge chamfers appear, with depth exceeding 0.5mm, it indicates serious wear, affecting connection strength and not suitable for continued use. Measure the wear of bolt holes. When the hole diameter is more than 0.5mm larger than the new hole, the 配合 between bolt and hole is loose, which will produce additional wear, and the fishplate needs to be replaced.
- What are the protective measures to extend the service life of fishplates?
Surface hardening treatment has a significant effect. Quenching + tempering the fishplate can increase the surface hardness from HB200 to HB300 - 350, and the wear resistance can be improved by 50% - 60%. The service life of Q345 steel fishplates after this treatment can be extended to 8 - 10 years. Coating wear - resistant coating (such as tungsten carbide coating) with thickness 0.1 - 0.3mm can form a hard protective layer, and the wear resistance is 2 - 3 times that of the original material, suitable for heavy - haul railways, but the cost increases by 20% - 30%. Optimize installation accuracy to ensure that the fishplate is closely attached to the rail, with a gap ≤0.1mm, reduce relative sliding. Tighten with a torque wrench according to the specified torque during installation to prevent loosening and additional wear. Clean impurities on the contact surface regularly, check once a month, blow off sand and iron filings with high - pressure air, and increase cleaning frequency in curve sections to reduce abrasive wear.
- What are the differences in fishplate replacement cycles of different railway types?
The fishplates of heavy - haul railways (annual traffic > 50 million tons) wear quickly, and the replacement cycle is 2 - 3 years. Coal transportation lines such as Daqin Railway even need to be replaced every 1.5 - 2 years to ensure connection strength. The replacement cycle of ordinary railways (annual traffic 10 - 50 million tons) is 4 - 6 years. For example, in some sections of Beijing - Guangzhou Railway, fishplate wear is relatively slow, and the service life can be extended through regular maintenance. High - speed railways have slow wear due to good train stability, and the replacement cycle is 6 - 8 years. The fishplates of Beijing - Shanghai High - speed Railway can have a service life of more than 7 years after surface hardening treatment. Urban rail transit (subways, light rails) has frequent start - stop, so the wear is faster than that of ordinary railways, and the replacement cycle is 3 - 5 years. Busy lines such as Metro Line 1 are usually replaced every 4 years.