Corrosion Protection and Sealing Technology of Fishplates and Adaptation Solutions for Different Joint Types
What are the core anti-corrosion sealing technologies for fishplates of ordinary rail joints?
The core anti-corrosion sealing technology for fishplates of ordinary rail joints is to isolate moisture and oxygen. Firstly, the material used is weather-resistant steel Q355NH, which has a corrosion rate ≤0.04mm/year in outdoor environments, 60% lower than ordinary carbon steel. Surface treatment employs an arc-sprayed aluminum coating process, with a coating thickness ≥150μm. The aluminum coating forms a dense alumina protective film in the air, exhibiting excellent corrosion resistance, with a salt spray test corrosion resistance time ≥1500 hours. The sealing structure uses a double-seal design. The first layer is an elastic sealing gasket made of EPDM rubber, 5mm thick, installed on the contact surface between the fishplate and the rail, effectively preventing rainwater and moisture from entering. The second layer is a sealant, using polyurethane sealant, applied to the edges of the fishplate. The sealant has an elongation rate ≥300%, accommodating the thermal expansion and contraction of the rail. In addition, sealing gaskets made of nitrile rubber are installed at the bolt holes of the fishplate to prevent moisture from entering. After corrosion protection and sealing, the fishplate undergoes an immersion test, soaking in room temperature water for 30 days, with no rust or water seepage observed on the surface.
What are the special requirements for corrosion protection and sealing of insulated rail joint fishplates?
The corrosion protection and sealing of insulated rail joint fishplates must balance insulation and sealing performance. Firstly, glass fiber reinforced plastic (FRP) is selected as the material. This material not only has excellent corrosion resistance but also an insulation resistance ≥10¹⁰Ω, meeting the electrical insulation requirements of insulated joints. Surface treatment uses an epoxy resin coating process with a coating thickness ≥100μm. The epoxy resin coating has strong chemical corrosion resistance and can resist the erosion of acid and alkali media. The sealing structure uses insulating sealant made of silicone rubber with an insulation resistance ≥10⁹Ω. The sealant has a temperature resistance range of -50℃ to 150℃, adapting to temperature changes in different climate zones. Insulating gaskets are installed at the contact surfaces between the fishplate and the rail. These gaskets are made of PTFE (polytetrafluoroethylene) and are 3mm thick, serving both a sealing function and ensuring insulation performance. Furthermore, the bolts on the fishplate are insulated bolts, with insulating sleeves covering the bolt shanks to prevent current conduction through the bolts. The insulated joint after corrosion protection and sealing undergoes insulation performance testing; an insulation resistance ≥10⁸Ω is considered qualified. An immersion test is also performed, with an insulation resistance attenuation rate ≤10% after immersion.
What are the key design considerations for the dynamic sealing of the fishplate in a telescopic rail joint?
The dynamic seal of the fishplate in a telescopic rail joint must adapt to the expansion and contraction of the rail. Firstly, the sealing structure uses an elastic telescopic sealing strip made of neoprene rubber with an elongation rate ≥400%, accommodating rail expansion and contraction of ±10mm. The sealing strip is installed using a slot-type design, with stainless steel fasteners connecting the slot to the fishplate to prevent corrosion and maintain the sealing effect. The fishplate is made of high-strength alloy steel 42CrMo, with a tensile strength ≥1080MPa after tempering, meeting the stress requirements of the expansion joint. The surface treatment uses hot-dip galvanizing + sealant process, with a zinc layer thickness ≥120μm to enhance corrosion resistance. Furthermore, the contact area between the sealing strip and the fishplate is coated with lithium-based grease, with a temperature resistance range of -20℃ to 120℃, which reduces friction between the sealing strip and the fishplate, extending the service life of the sealing strip. After dynamic sealing, the expansion joint undergoes an expansion fatigue test. After 10⁵ expansion cycles, the sealing strip shows no damage or leakage.
What are the testing indicators and acceptance standards for the anti-corrosion sealing performance of the fishplate?
The testing indicators for the corrosion resistance and sealing performance of fishplates include corrosion resistance, sealing performance, and insulation performance (for insulated joints). Corrosion resistance is tested using a neutral salt spray test. The test time for fishplates with ordinary joints is ≥1500 hours, and for fishplates with insulated joints, it is ≥2000 hours. After the test, the surface should show no rust or bulging. Sealing performance is tested using a water immersion pressure test. The fishplate is installed on the rail joint, and a water pressure of 0.1 MPa is applied. No water leakage after immersion for 24 hours is considered qualified. Insulation performance is tested using an insulation resistance tester. The insulation resistance of the fishplate for insulated joints is ≥10⁸Ω to be considered qualified, and after immersion, the insulation resistance is ≥10⁷Ω to be considered qualified. Acceptance standards are categorized based on joint type. For ordinary joint fishplates, the salt spray test time must be ≥1500 hours, and no water leakage should be observed during the sealing test. For insulated joint fishplates, the salt spray test time must be ≥2000 hours, and the insulation resistance must be ≥10⁸Ω. For expansion joint fishplates, the expansion fatigue test must be ≥10⁵ cycles, and the sealing strip must remain undamaged. Ten fishplates are randomly selected from each batch for inspection; only batches meeting all standards are considered qualified. Batches failing the inspection require double the number of samples.
What are the maintenance strategies and lifespan extension measures for the fishplate anti-corrosion sealing system?
The maintenance strategy for the fishplate anti-corrosion sealing system needs to be tailored to the joint type. For ordinary joints, check the integrity of the sealant and gasket every six months. Repair any cracked sealant promptly, and replace aged gaskets immediately. For insulated joints, test the insulation resistance annually. Replace the insulating gasket and sealant when the insulation resistance is below 10⁷Ω. For expansion joints, check the wear of the sealing strip quarterly. Replace the sealing strip when the wear exceeds 1mm. Life extension measures include regularly cleaning dust and debris from the fishplate surface to prevent debris buildup and seal failure; regularly applying a fluorocarbon coating to the fishplate surface every two years to enhance corrosion resistance; and installing abrasion-resistant covers on fishplates for heavy-load lines to reduce wheel-rail impact damage to the sealing structure. In addition, a maintenance log should be established for the fishplates, recording the time and content of each inspection and maintenance. Based on the log, the failure cycle of the sealing system can be predicted, and a replacement plan can be developed in advance. Special tools must be used to remove the fishplate bolts during maintenance to avoid damaging the sealing components with force. Ensure that the tightening torque of the fishplate after maintenance meets design requirements: 400-450 N·m for ordinary joints and 500-550 N·m for heavy-load joints.