Corrosion Protection Technology and Environmental Adaptation of Fishplates
What are the core steps of the hot-dip galvanizing anti-corrosion process for fishplates?
The core steps of the hot-dip galvanizing anti-corrosion process for fishplates include three stages: pre-treatment, hot-dip galvanizing and post-treatment. Pre-treatment is a key link. First, the fishplate needs to be degreased to remove oil stains and impurities on the surface, and then pickling is used to remove surface oxide scale and rust to ensure that the zinc layer can adhere tightly. After pickling, water washing and drying are required to avoid residual acid corrosion of the substrate. In the hot-dip galvanizing stage, the dried fishplate is immersed in molten zinc solution at about 450℃ for 1-2 minutes, so that a uniform zinc-iron alloy layer and pure zinc layer are formed on the surface of the fishplate. Post-treatment includes cooling, passivation and inspection. Passivation treatment can form a protective film on the surface of the zinc layer to improve the corrosion resistance of the zinc layer. Finally, the anti-corrosion effect is ensured to meet the standard through appearance and thickness detection.
What are the advantages of the sherardizing process compared with hot-dip galvanizing?
The first advantage of the sherardizing process compared with hot-dip galvanizing is that the sherardized layer is more firmly combined with the substrate. During the sherardizing process, zinc atoms will diffuse into the steel to form a zinc-iron alloy layer, with a bonding strength of more than 200MPa, and the zinc layer is not easy to fall off. The second advantage is that the uniformity of the sherardized layer is better. For complex parts such as threaded holes and corners of fishplates, the sherardizing process can achieve full coverage, while hot-dip galvanizing is prone to insufficient zinc layer thickness in these parts. The third advantage is that the sherardized layer has stronger corrosion resistance. Under the same thickness, the salt spray corrosion resistance time of the sherardized layer is 1.5-2 times that of the hot-dip galvanized layer. In addition, the temperature of the sherardizing process is lower, which has less impact on the mechanical properties of the fishplate and is suitable for the anti-corrosion treatment of high-strength fishplates.
Which anti-corrosion process should be selected for fishplates in coastal areas?
Coastal areas have high air humidity and contain a lot of salt, which belong to a highly corrosive environment. Fishplates should preferentially use the sherardizing + closed coating composite anti-corrosion process. The sherardized layer can provide long-term cathodic protection to resist salt erosion, and the closed coating can isolate air and moisture to further improve the anti-corrosion effect. Compared with the single hot-dip galvanizing process, the salt spray corrosion resistance time of the composite anti-corrosion process can be extended to more than 2000 hours, which can meet the anti-corrosion needs of coastal areas for more than 15 years. If the fishplate is used in heavy-haul lines, a cathodic protection device can be added on the basis of composite anti-corrosion to form a multi-layer anti-corrosion barrier. Selecting a suitable anti-corrosion process can greatly reduce the replacement frequency of fishplates in coastal areas and reduce maintenance costs.
What are the performance requirements for the anti-corrosion coating of fishplates?
First of all, the anti-corrosion coating of fishplates must have excellent adhesion. The adhesion grade between the coating and the substrate must reach level 1 to ensure that it will not fall off under the action of train vibration load. The second is the corrosion resistance requirement. The coating must pass a salt spray test of more than 1000 hours. After the test, the coating shall not have blistering, rusting and cracking phenomena. The third is the wear resistance requirement. The pencil hardness of the coating must reach above 2H to resist friction damage during installation and use. In addition, the coating must have good weather resistance, and will not chalk or discolor under ultraviolet radiation and temperature changes. For different environments, the coating must also have corresponding special properties, such as high temperature resistance in high-temperature areas and chemical corrosion resistance in acid-base areas.
How to test the anti-corrosion treatment effect of fishplates?
The first step to test the anti-corrosion treatment effect of fishplates is appearance inspection, observing whether the anti-corrosion layer on the surface of the fishplate is uniform and smooth, and whether there are defects such as missing plating, peeling and bubbles. The second step is thickness detection. A magnetic thickness gauge is used to measure multiple points on different parts of the fishplate. The thickness of the hot-dip galvanized layer should be ≥85μm, and the thickness of the sherardized layer should be ≥60μm to ensure that the thickness meets the standard requirements. The third step is adhesion detection. The cross-cut test is used for testing. After scribing the coating surface, it is pasted and torn with tape, and the peeling of the coating is observed to judge the adhesion grade. The fourth step is corrosion resistance detection. The corrosion environment is simulated through a salt spray test, and the rusting of the fishplate after a certain period of time is observed to evaluate the protective effect of the anti-corrosion layer. Only through comprehensive multiple test results can it be comprehensively determined whether the anti-corrosion treatment of the fishplate meets the standard.