Selection and construction process of anti-corrosion coating for road spikes
- What are the common types of anti - corrosion coatings for spikes?
Hot - dip galvanizing coating is the most commonly used, with a zinc layer thickness of ≥85μm, which can form sacrificial anode protection, and the salt spray resistance is more than 1000 hours. It is widely used in ordinary railway spikes with moderate cost. The thickness of electroplating zinc coating is thin (10 - 20μm), with bright appearance and salt spray resistance of 300 - 500 and salt spray resistance of 300 - 500 hours. It is suitable for branch railways in dry areas, with cost 30% - 40% lower than hot - dip galvanizing. Dacromet coating (zinc - chromium coating) has a thickness of 5 - 10μm, salt spray resistance of 500 - 1000 hours, environmental protection and no hydrogen embrittlement risk. It is suitable for high - strength spikes (such as 10.9 grade screw spikes), especially excellent in coastal areas. Epoxy powder coating has a thickness of 50 - 100μm, good insulation, acid and alkali corrosion resistance, suitable for track circuit sections of electrified railways, salt spray resistance of 800 - 1200 hours, but high cost.
- How to select anti - corrosion coatings for spikes in different environments?
Coastal and saline - alkaline areas need coatings with salt spray resistance ≥1000 hours. Dacromet or hot - dip galvanizing (thickened to 100μm) can be used, which can resist chloride ion corrosion, and the service life of spikes can reach 8 - 10 years. In humid and rainy areas, hot - dip galvanizing or Dacromet coatings are preferred. The zinc layer can self - heal slight scratches, and the service life is 2 - 3 times longer than that of electroplating zinc. Ordinary railways in rainy provinces in the south often use this choice. In dry and rainless areas, electroplating zinc coatings can be used to reduce costs and meet basic anti - corrosion needs, applicable to branch railways in arid areas of northwest China, but the coating status must be checked every 2 - 3 years. Industrial areas (with acid - base pollution) need to use epoxy powder coatings, which have strong resistance to acid and alkali, and can work stably in the environment with pH value 3 - 11. Spikes in chemical industry park railways must use this coating.
- What are the key steps in the construction process of anti - corrosion coatings?
Pretreatment is key. Spikes must be degreased, pickled and phosphated to remove surface oil and rust. The phosphating film thickness is 5 - 10μm to enhance coating adhesion. The surface of treated spikes must be free of visible impurities. During hot - dip galvanizing, spikes must be immersed in zinc solution at 450 - 460℃ for 3 - 5 minutes to ensure uniform zinc layer. After taking out of the tank, cool to room temperature and remove excess zinc nodules. The zinc layer thickness is detected with a magnetic thickness gauge, and unqualified products must be reworked. Dacromet coating is applied by dipping or spraying, with coating thickness controlled at 5 - 10μm, baked and cured at 200 - 300℃ to form a zinc - chromium composite film. The baking time must be sufficient (≥30 minutes), otherwise the coating is easy to fall off. Epoxy powder coating must be electrostatically sprayed, with powder particle size 80 - 120μm, cured at 200 - 220℃ for 15 - 20 minutes to ensure no pinholes and bubbles in the coating, and adhesion ≥5N/cm (cross - cut test).
- How to detect the quality of spike anti - corrosion coatings?
Salt spray test is the core detection. Put the spike in a salt spray box with 5% NaCl solution. Hot - dip galvanized spikes must pass 1000 hours without red rust, Dacromet coating 500 hours without white rust, and epoxy coating 800 hours without damage. Coating thickness detection: use a magnetic thickness gauge to measure 3 points on different parts of the spike, take the average value. Hot - dip galvanizing ≥85μm, Dacromet 5 - 10μm, epoxy 50 - 100μm. Deviation exceeding ±10% is unqualified. Adhesion test: use a scribing knife to scribe 1mm×1mm grid on the coating surface, peel off after tape pasting. Coating peeling area ≤5% is qualified to ensure that the coating is not easy to peel off. Bending test: bend the spike 180°, the coating has no cracks and peeling, to verify the flexibility of the coating, especially for screw spikes, this test can detect the stability of the coating during installation bending.
- What are the repair measures after damage to anti - corrosion coatings?
Small area damage (≤5mm²) can be repaired with zinc paste or repair paint. First clean the damaged part, apply zinc paste to be flush with the surrounding coating. After curing, form protection, which can be used for ordinary railway spikes. When the damage area is large, local repainting is required. Sand the damaged area to expose the metal, spray the same type of coating after cleaning, with the same thickness as the original coating. High - speed railway spikes must strictly control the repair quality. For zinc layer damage of hot - dip galvanized spikes, cold - sprayed zinc can be used, with zinc content ≥95% and coating thickness 50 - 80μm, which has good compatibility with the original zinc layer. The salt spray resistance after repair can reach 80% of the original coating. Epoxy coating damage needs special epoxy repair agent, which has similar hardness and corrosion resistance to the original coating after curing. Adhesion test must be carried out after repair to ensure ≥3N/cm to prevent secondary peeling.