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　　Label: Auckland Bay Bridge

　　In recent years, the quality of coating engineering in China has been improved. In order to develop the business channels of steel structure bridges abroad, Shanghai Zhenhua heavy industry group successfully completed the fabrication tasks of two steel structure bridges, Donghai Bridge and Sanchuan bridge in South Korea. In December 2008, Shanghai Zhenhua heavy industry group once again undertook the fabrication task of 45000 T steel structure of Auckland Bay Bridge in the United States. The bridge is a self anchored suspension bridge, the owner is the transportation department of the California government of the United States; Aksu Nobel (Suzhou) industrial coating company's supporting coating is designated to be used; after the steel structure is processed, the official coating engineering team of the coating workshop of Shanghai Zhenhua heavy industry group will contract all the coating industry services. In more than a year, the project team has grasped the key links of surface treatment and painting construction, and the painting quality has been praised by the American supervisor and the owner. In this paper, the coating process of Auckland bay bridge steel structure is summarized for reference.

　　1、 Matching coating and film thickness

　　1. Matching coating on external surface of steel box girder

　　See Table 1 for the supporting coating on the external surface of the steel box girder of the bridge.

　　2. Matching coating for inner surface of steel box girder

　　See Table 2 for the supporting coating on the inner surface of the steel box girder of the bridge.

　　3. Characteristic analysis of matching coating

　　The matching coating has three excellent characteristics:

　　First, excellent corrosion resistance. The dry film thickness of inorganic zinc rich primer is more than 90 μ m, in which zinc powder accounts for 80% of the dry film, and the cathodic protection effect of primer is obvious. The total film thickness is more than 240 μ m with high performance polysiloxane finish. According to the international standard ISO 12944-2008, under the atmospheric environment of C5, the service life of the matching coating is more than 15 years, reaching the highest level.

　　Second, excellent environmental protection and energy saving performance. Two kinds of products, interzine22 and interfine979, are used in the supporting coating of Auckland bay bridge steel structure. The lead content of interzine22 inorganic zinc rich primer meets the requirements of ASTM D 520typeii, which is a low lead product, while the interfine979 polysiloxane coating is a lead-free product. Some technical data of interzine22 and interfine979 are shown in Table 3.

　　These two products are heavy-duty anticorrosive coatings with high solid content and low VOC. The internal and external supporting coatings of the bridge steel structure only use these two kinds of coatings and spray three times, which is conducive to process conditions, paint consumption, film thickness control and other series of coating management work, and is an effective measure to reduce the coating cost and energy consumption.

　　Third, excellent construction performance. Excellent construction performance is an important mark of heavy-duty anticorrosive coating. The construction performance comparison between interzine22 and common inorganic zinc rich coating is shown in Table 4.

　　For interfine979 polysiloxane finish, not only the dry film thickness can reach 150 μ m at one time, but also it can be used as a sealing paint by mist spraying, and the epoxy micaceous iron intermediate paint can be omitted. The excellent construction performance can promote the film quality.

　　II. Coating process condition management

　　In heavy-duty anti-corrosion coating, coating process condition management includes process conditions, paint consumption, coating equipment, working hours quota and many other aspects. It runs through every process link of steel structure manufacturing. In order to ensure coating quality, it must be closely linked during construction. According to the actual situation of coating production line of Shanghai Zhenhua heavy industry group, aiming at the quality requirements of Auckland Bay Bridge for coating process, combined with the construction performance of coating products of Akzo Nobel (Suzhou) industrial coating Co., Ltd., the following aspects should be emphasized in coating process condition management:

　　First, design the correct painting process. The painting process of the outer steel box girder is designed as follows: surface inspection after pretreatment of steel structure → treatment of degreasing and steel structure defects → sandblasting → cleaning steel surface with clean compressed air → precoating primer → airless spraying primer → repairing primer → water washing primer → mist spraying sealer → precoating top coat → airless spraying top coat → coating quality inspection → repair → handover for inspection. Second, surface treatment. Third, painting process. (1) Preparation before painting. a. In order to ensure the quality of the coating, the supporting coating should be stored in the warehouse with a temperature of about 25 ℃, dry, sunshade, far away from the heat source and fire source. b. In order to ensure the welding quality and prevent the coating near the weld from being damaged, non dry adhesive tape shall be pasted within 5-10 cm from the weld. c. Check the model, batch number and color of various coatings, corresponding curing agents and diluents in detail, and make records. (2) Mix ratio. The mixing volume ratio of interzinc22 is 3.17:1, the zinc powder B is poured into the base material a and used while stirring, and the mixing period at 25 ℃ is 4 h; the mixing volume ratio of interfine 979 is 4:1, and the mixing period at 25 ℃ is 2 h. (3) Dilution. Interzinc22 and interfine979 shall be constructed under normal conditions without dilution as long as they are fully mixed. In case of low temperature in winter, pre coating by hand brush or reducing the film thickness, appropriate dilution can be carried out, and the proportion shall not be greater than 5%. (4) Environmental conditions for spraying construction. (5) Precoating is an essential process in spraying construction. The pre coated parts include all kinds of small holes (such as fan-shaped holes, flow holes, Manholes, etc.); the opposite side of stiffeners and profiles; nuts; back-to-back steel; manual welding seams and corner parts that are difficult to spray paint. For free edge, weld, cutting edge and other parts with thin film, complete precoating can be conducted before spraying the second coat of paint. Brush coating method must be used for precoating, but roller coating method cannot be used. (6) Airless painting technology. For Auckland bridge steel box girder project, Akzo Nobel coating company recommends that the two high-performance heavy-duty anticorrosive coatings must adopt airless painting method. Airless spray painting has the advantages of high coating efficiency, good coating quality and less environmental pollution.　

　　The above content is reproduced in "anticorrosive coating and coating" collected by Mr. Li Minfeng