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　　In recent years, the construction of long-span bridges in China has developed rapidly, especially the Hangzhou Bay Bridge and Donghai Bridge, which are the longest sea crossing bridges in the world, have been invested and constructed successively, marking that the manufacturing technology of large-scale steel bridges in China has reached the advanced level in the world. Anticorrosive coating technology of steel structure is also an important part of it. For example, the painting system of pedestrian guardrail and lamp post of Caiyuanba bridge in Chongqing not only requires beautiful appearance, but also the maintenance free period of painting should be more than 20A.

　　In the coating specification of Caiyuanba bridge, the suggestions for the coating of pedestrian guardrail and lamp post are listed in Table 1.

　　Hot dip galvanizing process is not only a high energy consumption process, but also "three wastes" seriously pollute the environment, making the maintenance of zinc coating difficult. Therefore, it is recommended to the bridge headquarters and relevant steel structure plants that the cold galvanized material with excellent performance, strong zinc, be used as the supporting primer for the coating of pedestrian guardrail and lamp post.

　　1、 Painting matching

　　2、 Design principles

　　1. Strong zinc has double antiseptic effects of cathodic protection and barrier

　　2. Excellent matching performance of strong zinc and heavy anticorrosive coating

　　3. Fluorocarbon coating

　　4. Safety and environmental protection

　　5. Feasibility of coating process

　　3、 Painting process of pedestrian guardrail and lamp post

　　3.1 process flow

　　Steel pipe cutting - arranging into pieces - sand blasting and derusting - spraying with strong zinc - spraying with epoxy sealing paint - spraying with epoxy micaceous iron paint - spraying with the first fluorocarbon process - shipping to the bridge construction site - welding general assembly - weld grinding treatment - repainting with strong zinc or intermediate coating - spraying with the second fluorocarbon coating - checking the coating quality - repairing - Presentation

　　3.2 surface treatment before coating

　　Sand blasting. It is a high efficiency surface treatment method, which uses compressed air as power to spray sand (abrasive) on the surface of steel pipe to be treated at a certain speed, and remove oxide skin, rust and other dirt on the steel surface by the impact and grinding effect of abrasive on the steel surface.

　　matters needing attention:

　　(1) After the nozzle is used for a period of time, the nozzle is worn, the aperture becomes larger, the jet flow diffuses, and the cutting ability of sand particles is reduced, so it should be replaced in time;

　　(2) Ensure the effective pressure of compressed air;

　　(3) Compressed air must be treated by oil-water separator;

　　(4) operation. After spraying the single side of the arranged steel pipe, rotate the steel pipe 180 degrees, arrange the steel pipe in order again, spray the other side and pay attention to safety. Operators must have a high sense of responsibility. The whole surface to be cleaned shall be covered by manual sand blasting in sequence, and the angle of nozzle to surface shall be 70-80 degrees.

　　Surface quality requirements:

　　The cleanliness reaches Sa2.5 level of GB 8923 (or ISO 8501-1)

　　The design value of roughness is RZ = 40-60UM

　　This information is reproduced in "anticorrosive coating and coating" collected by Mr. Li Minfeng