1 Corrosion Resistant Coating
According to the design life, environmental media, construction conditions, economy and other factors, the corrosion resistant coatings were analyzed comprehensively, and the types, thickness and surface treatment grade of coatings were determined. Aluminum (zinc) spraying is a long-term corrosion resistance technology. Aluminum (zinc) is sprayed on the surface of steel to form electrochemical corrosion coatings, which can significantly improve the anti-corrosion effect. Because of its good adhesion and above-mentioned characteristics sheet pile manufacturers, aluminum (zinc) spraying has been widely used in steel structure surface in wet environment or in areas with harsh conditions, such as ebb and flow areas (between rivers and oceans) and other high environmental chloride ion content.
Surface treatment should be carried out before painting, and the quality of surface treatment has a great influence on the quality of painting. Different coatings meet different quality requirements for steel rust removal. Generally speaking, conventional oily coatings with better wettability and permeability require slightly lower rust removal quality, while high-performance coatings such as zinc-rich coatings require high-quality rust removal.
Coatings should be carried out under the conditions of relative humidity less than 85% and temperature more than 5 C. Open-air construction is not allowed in rainy, snowy and foggy days, otherwise it will have adverse effects on the adhesion of coatings. The temperature and relative humidity of steel plate must be measured before painting. Only when the surface temperature of steel plate is above 3 C higher than dew point can construction be carried out.
The coating method should be selected according to the physical properties of the coating, the construction conditions, the requirements of the coating and the conditions of the structure to be coated. Coating methods include brushing, roll coating and high-pressure airless spraying. Coating can also be carried out according to manufacturer's instructions. Metal spraying can be divided into crucible spraying, powder spraying, wire spraying and plasma spraying, depending on the type of spraying gun used. Because of inconvenience in use, crucible spraying has been eliminated, because the paint should be melted in the crucible, and then sprayed with compressed air. For powder spraying, metal powder is fed into powder spraying gun by powder feeder, fueled by fuel gas, and then injected by compressed air. Because it is difficult to obtain metal powder, this method is seldom used at present. As a substitute for metal powder spraying, wire spraying is a common method in the case of arc melting and fuel gas melting. However, this method is only applicable to metals with low melting point and can be transformed into wires. High temperature plasma flame can be produced by plasma spraying of refractory metals and their oxides, carbides, silicides and borides.
Inspection criteria for coatings:
(1) Anti-corrosion of coatings
(1) Appearance standard of coatings: uniform appearance and smooth gloss of coatings; no defects such as lifting, cracking and pinhole peeling are allowed. Allow slight local sagging, brush marks, wrinkles and a small amount of particulate dust, which has no effect on performance.
(2) Coating thickness standard: Coating thickness measured by coating thickness gauge must conform to the design standard. Acceptability criteria: Coatings with a total average thickness of 90% of the nominal thickness are considered qualified; when calculating the average thickness, the thickness of the measuring point is 20% larger than the nominal thickness, and the nominal thickness is 120%.
(2) Anti-corrosion of sprayed metal coatings
(1) Appearance standard of coating: uniform appearance of coating, no peeling, expansion, cracking and fragmentation.
(2) Coating thickness standard: Coating thickness must conform to the design standard; the arithmetic average value of measuring point thickness measured by magnetic thickness tester is used as the coating thickness of the research position; the testing position and quantity and acceptability standard are determined according to the design requirements.
(3) Testing criteria for coating adhesion: the parallel scribed grid on the coating, with a spacing of 3-5 mm, is bonded tightly with tape, then pulled up vertically; the coating that does not fall off and shows the base is regarded as qualified. 5-10 points should be sampled randomly and uniformly.