Requirements for salt spray corrosion resistance of fastening systems
- What is the salt spray resistance standard for railway fastening systems in coastal areas?
Fastening system components must pass a 500-hour salt spray test, with surface rust area ≤5%, no obvious coating peeling and matrix corrosion. The galvanized layer thickness of steel components such as elastic clips and bolts should be ≥8μm, among which the coating thickness of bolt thread parts should be ≥6μm to ensure good corrosion resistance. After the salt spray test, the clamping force attenuation rate of the elastic clip should be ≤10%, and the preload loss of the bolt should be ≤8%.
- What are the differences in salt spray resistance treatment methods for different fastening system components?
The elastic clip is treated with hot-dip galvanizing and passivation, and the passivation film thickness is ≥0.5μm, forming a double-layer protection, and the salt spray resistance is 50% higher than that of ordinary galvanizing. Bolts adopt dacromet coating with thickness 8-12μm, and their salt spray resistance is 3-5 times that of galvanizing, especially suitable for corrosion protection of thread parts. Pressing plates and fishplates are treated with galvanizing + painting composite treatment, first galvanizing 8μm, then applying epoxy paint 30-40μm to enhance salt spray resistance.
- What are the effects of salt spray corrosion on the mechanical properties of fastening systems?
It will reduce the elastic modulus of the elastic clip by 5%-10%, and the clamping force will gradually decay over time. After 500 hours of salt spray test, the clamping force may decrease by 15%-20%. The thread of the bolt will be corroded, resulting in preload loss, and in severe cases, it cannot be disassembled. Local corrosion will occur in the coating peeling area, forming stress concentration points, which will shorten the fatigue life of the component by 30%-40%.
- How to test the salt spray corrosion resistance of fastening systems?
Put the components into a salt spray test chamber, spray continuously with 5% sodium chloride solution, and keep the temperature at 35℃±2℃. Take it out every 100 hours to observe and record the rust area and coating condition. After the test, test the clamping force of the elastic clip, the preload and tensile strength of the bolt, compare with those before the test, and calculate the performance attenuation rate. For key components, bending test is also required to check whether cracks are generated due to corrosion.
- What is the difference in maintenance cycle of fastening systems between coastal areas and inland areas?
The maintenance cycle of fastening systems in coastal areas is 30%-40% shorter than that in inland areas. Ordinary railways are shortened from 3 years to 2 years, and high-speed railways from 2 years to 1.5 years. Each maintenance must focus on checking the coating condition, and replace components with rust area exceeding 10%. Regularly clean the salt frost on the surface of components, apply anti-rust grease every 6 months, and supplement the anti-corrosion layer to prolong the service life.