Anti-corrosion processes and durability enhancement technologies for railway spikes
What are the core operational points of the hot-dip galvanizing anti-corrosion process for rail spikes?
The hot-dip galvanizing anti-corrosion of rail spikes requires thorough pre-treatment of the spikes first, including degreasing, pickling, water washing and drying, to ensure no oil, rust or oxide scale remains on the surface. The pre-treated rail spikes should be quickly immersed in molten zinc solution, and the temperature of the zinc solution must be strictly controlled between 440-460℃, which can ensure good metallurgical bonding between the zinc coating and the spike substrate. The immersion time of rail spikes in the zinc solution should be adjusted according to the spike thickness, generally controlled at 1-3 minutes; too short time will result in too thin zinc coating, while too long time will easily lead to zinc coating accumulation. After galvanizing, cooling and passivation treatment are required, and the passivation layer can further improve the corrosion resistance of the zinc layer and avoid white rust formation. The parameters of each link in the entire process must be strictly controlled to ensure that the anti-corrosion life of hot-dip galvanized rail spikes can reach more than 15 years.
What advantages does the sherardizing process have over hot-dip galvanizing in rail spike anti-corrosion?
The sherardizing process allows zinc atoms to penetrate into the surface layer of the rail spike substrate through high-temperature diffusion, forming a zinc-iron alloy layer, whose bonding force with the substrate is much higher than the physical adhesion layer of hot-dip galvanizing. The thickness uniformity of the sherardized layer is better; even for complex parts such as rail spike threads and corners, a continuous and complete protective layer can be formed, avoiding the "exposure" defect that is prone to occur in hot-dip galvanizing. The treatment temperature of the sherardizing process is lower than that of hot-dip galvanizing, which will not cause deformation of the rail spike substrate, and can better maintain the dimensional accuracy of the rail spike, especially suitable for high-precision threaded rail spikes. The sherardized layer has better wear resistance; during the installation and tightening of rail spikes, the coating is not easy to fall off, and the long-term anti-corrosion effect can be maintained. In addition, the sherardizing process has stronger environmental friendliness, produces fewer pollutants in the production process, and meets the requirements of modern green construction.
Why is the dacromet coating process preferred for rail spikes in coastal saline-alkali areas?
The air in coastal saline-alkali areas has high salt content, and chloride ions will accelerate the corrosion of the rail spike metal substrate. The ordinary hot-dip galvanized layer is prone to pitting corrosion in the chloride ion environment. The dacromet coating is an inorganic coating composed of zinc powder, aluminum powder and binder, which can form a dense protective film to effectively block the contact between chloride ions and the rail spike substrate. The dacromet coating has extremely strong salt spray corrosion resistance; tests show that its salt spray test resistance time can reach more than 1000 hours, far exceeding the 500-hour standard of hot-dip galvanizing. This coating has excellent weather resistance, can adapt to the strong sun, rain and temperature changes in coastal areas, and will not experience coating cracking or chalking. The dacromet coating also has good insulation performance, which can prevent the rail spike from becoming a path for stray current and protect the track signal system from interference. Therefore, in the coastal saline-alkali environment, the durability of dacromet-coated rail spikes is 2-3 times that of other processes.
What are the common methods for testing the thickness of rail spike anti-corrosion coatings?
The most commonly used method for testing the thickness of rail spike anti-corrosion coatings is the magnetic thickness gauge method. This method is easy to operate and non-destructive, suitable for rapid on-site testing. During testing, at least 5 measuring points should be selected on different parts of the rail spike, and the average value should be taken as the final thickness value. For the anti-corrosion coating of rail spikes with non-magnetic substrates, an eddy current thickness gauge can be used, which calculates the coating thickness by the change of eddy current induction intensity and is also suitable for on-site testing. For accurate laboratory testing, the metallographic microscope method can be adopted. After preparing the cross-section sample of the rail spike, the coating thickness is directly measured under the microscope, and this method can also observe the bonding state between the coating and the substrate. The micrometer measurement method is suitable for rail spikes with thick coatings. The coating thickness is calculated by measuring the dimensional difference of the rail spike before and after galvanizing, but the accuracy of this method is relatively low. Regardless of the method adopted, relevant standards must be followed to ensure accurate test data and judge whether the anti-corrosion coating meets the standard.
How to select the appropriate anti-corrosion process based on the application scenario of rail spikes?
For rail spikes of ordinary speed railways in ordinary inland areas, the hot-dip galvanizing process can meet the demand; this process has moderate cost, and the anti-corrosion effect can match the operating environment of the line. For rail spikes of heavy-haul railways, which bear greater impact force and friction, the sherardizing process is preferred; its high bonding force and wear resistance can avoid coating shedding during installation and use. Rail spikes in coastal saline-alkali areas and humid tunnels must use the dacromet coating process to resist the erosion of chloride ions and the influence of high-humidity environment. For rail spikes in alpine regions, it is recommended to use the composite process of hot-dip galvanizing plus sealing coating; the sealing coating can prevent water from infiltrating the zinc layer when ice and snow melt, avoiding cracking of the zinc layer at low temperatures. For rail spikes in track sections with insulation requirements, dacromet coating is the first choice; its insulation performance can ensure the normal operation of the track circuit without additional insulation components.