Anti-Corrosion Sealing for Ordinary Rail Joints
For ordinary joint fishplates, the core principle is to isolate moisture and oxygen from the steel. Weather-resistant steel with a low outdoor corrosion rate, roughly 60 percent lower than ordinary carbon steel, is a common base material. Surface treatment uses an arc-sprayed aluminum coating with a thickness of at least 150 micrometers; the aluminum forms a dense alumina film in air, giving excellent corrosion resistance and passing long salt spray tests. The sealing structure is a double-layer design: an elastic EPDM gasket about 5 mm thick between the fishplate and the rail prevents rainwater ingress, and a polyurethane sealant with high elongation is applied at the fishplate edges to accommodate rail thermal expansion. Sealing gaskets at the bolt holes stop moisture entering through the fastener path. Completed assemblies are verified by immersion testing in room-temperature water for 30 days with no rust or seepage.
Insulated Joint Fishplates
Insulated rail joint fishplates must balance insulation and sealing. Glass-fiber-reinforced plastic is a typical material, offering corrosion resistance and very high insulation resistance. The surface is coated with epoxy resin at least 100 micrometers thick for chemical resistance, and the sealing uses silicone insulating sealant with high insulation resistance and a temperature range from minus 50 to plus 150 degrees Celsius. Insulating PTFE gaskets 3 mm thick sit between the fishplate and the rail, and the bolts are insulated types with insulating sleeves on the shank to prevent current conduction. Acceptance requires an insulation resistance above the specified threshold, with an insulation resistance decay of no more than 10 percent after immersion.
Expansion Joint Dynamic Sealing
Telescopic rail joints must seal while the rail expands and contracts, typically by plus or minus 10 mm. The dynamic seal uses an elastic telescopic sealing strip made of neoprene rubber with elongation of at least 400 percent, installed in a slot-type design with stainless steel fasteners to prevent corrosion. The fishplate itself is high-strength alloy steel with a tensile strength above 1080 MPa after tempering, and the surface is protected by hot-dip galvanizing plus sealant with a zinc layer of at least 120 micrometers. Lithium-based grease between the strip and the fishplate reduces friction and extends the strip life. The finished joint must pass an expansion fatigue test of 100,000 cycles without damage or leakage.
Testing Indicators and Acceptance
Corrosion resistance is tested by neutral salt spray: at least 1500 hours for ordinary joints and 2000 hours for insulated joints, with no rust or blistering after the test. Sealing is verified by a water immersion pressure test: the fishplate installed on the joint withstands 0.1 MPa water pressure for 24 hours without leakage. Insulation is measured with an insulation resistance tester, with the pass values defined for dry and immersed conditions. Samples are taken from each batch, and batches that fail require double sampling. For expansion joints, the fatigue test is decisive.
Maintenance Strategy
Maintenance is tailored to the joint type. Ordinary joints need six-monthly checks of sealant and gasket integrity, with cracked sealant repaired and aged gaskets replaced immediately. Insulated joints require annual insulation testing, with gaskets and sealant replaced when resistance falls below the limit. Expansion joints need quarterly checks of sealing strip wear, with replacement when wear exceeds about 1 mm. Long-term measures include regular cleaning of the fishplate surface, periodic re-coating, protective covers on heavy-load lines, and a maintenance log that predicts failure cycles and drives replacement planning. Bolt torque after maintenance must meet the design values, which are higher for heavy-load joints.
Frequently Asked Questions
What is the basic anti-corrosion principle for fishplates? Isolate moisture and oxygen from the steel using corrosion-resistant material, protective coatings and sealing structures.
How are insulated joint fishplates sealed? With insulating silicone sealant, PTFE gaskets and insulated bolts, balancing sealing with electrical insulation.
How is expansion joint sealing tested? By an expansion fatigue test of 100,000 cycles with no damage or leakage of the sealing strip.
What salt spray time is required? t least 1500 hours for ordinary joints and 2000 hours for insulated joints, with no rust or blistering.
How often should insulated joints be tested? nnually, with gaskets and sealant replaced when insulation resistance falls below the specified limit.