Corrosion Protection Technology and Application of Rail Fasteners
What are the common anti-corrosion technologies for rail fasteners.and what are the core advantages and applicable environments of eachtechnology?
Common anti-corrosion technologies include hot-dip galvanizing,Dacromet treatment, powder coating and zinc-aluminum coating. Hotdip galvanizing has a zinc layer thickness of ≥85um and strongadhesion, which is suitable for humid areas with heavy rain, but it isprone to white rust in coastal high-salt spray environments; Dacromettreatment contains more than 90% zinc-aluminum flakes, with salt sprayresistance of more than 1000 hours, suitable for coastal and chemical-polluted areas; powder coating has a smooth appearance, optionalcolors and good weather resistance, mostly used in urban rail transit;zinc-aluminum coating combines the cathodic protection of zinc and thebarrier effect of aluminum, and its corrosion resistance is 3-5 times thatof hot-dip galvanizing, suitable for alpine and high-corrosion areas.
In the hot-dip galvanizing process, how to control the thickness anduniformity of the zinc layer? What are the common zinc layer defects?
Controlling the quality of the zinc layer requires efforts from bothpretreatment and galvanizing parameters: the pretreatment adopts athree-step method of "degreasing-pickling-fluxing" to ensure no oilstains and oxide scales on the fastener surface, during galvanizing, thezinc liquid temperature is controlled at 440-460'c, the zinc dipping timeis adjusted to 30-60 seconds according to the fastener thickness, andthe excess zinc liquid is removed by centrifugal zinc throwing. Commondefects include sagging caused by excessive zinc layer, missing platingcaused by too low zinc liquid temperature, bubbles caused by residuaflux, and zinc layer cracking caused by too fast cooling speed.
What is the construction process of Dacromet coating? Comparedwith traditional galvanizing, where are its environmental advantagesreflected?
The construction process of Dacromet coating is: workpiecedegreasing-shot blasting derusting - Dacromet liquid coating 一120'c pre-baking -300'℃ curing - cooling finished product. Comparedwith traditional galvanizing, its environmental advantages aresignificant: no high-temperature zinc liquid is needed, and energyconsumption is reduced by 60%; no pickling waste liquid is dischargedduring the production process, only a small amount of volatile organiccompounds are generated, which can be treated by activated carbonadsorption; the coating does not contain heavy metals such aschromium, which complies with the EU RoHs directive, and the wastecan be harmlessly treated to reduce environmental pollution.
What special challenges does fastener anti-corrosion face in alpineregions, and how to improve anti-corrosion effects through technicaloptimization?
Challenges in alpine regions include coating peeling caused byfreeze-thaw cycles, accelerated corrosion caused by deicing agenterosion, and increased coating brittleness due to low temperature.Technical optimization schemes: select a composite coating system ofelastic polyurethane primer + fluorocarbon topcoat, the primer elasticitycan absorb the stress generated by freeze-thaw; add graphene modifierto the coating to improve coating compactness and prevent deicingagent penetration; adopt low-temperature curing process to ensure thatthe coating can still adhere well in -10'c environment, and at the sametime, use cathodic electrophoresis as the base to enhance the bondingforce between the coating and the substrate.
How to evaluate the performance of fastener anti-corrosioncoatings? What anti-corrosion related indicators should be focused onduring daily maintenance?
Coating performance evaluation is carried out through four coretests: salt spray test (to judge corrosion resistance), cross-cut test (totest adhesion), impact test (to detect impact resistance), and bendingtest (to verify flexibility). Daily maintenance should focus on checking:whether the coating appearance has peeling, bulging, scratches; use acoating thickness gauge to detect the thickness of the zinc layer orcoating to ensure it is not lower than the design value; in electrifiedrailways, it is also necessary to detect the insulation performance of thecoating to avoid insulation failure caused by corrosion damage.