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　　1、 Project overview

　　The reconstruction of yunzaobinxi sluice is the first gate of Shanghai water environment construction project, which belongs to Baoshan area. The reconstruction design is undertaken by Shanghai Water Conservancy Survey and Design Institute, and the fabrication of steel structure is undertaken by Liuli branch of Shanghai Shipyard, in which the steel structure coating area of gate is 300m2

　　。 According to the requirements of the owner and the design unit, the gate adopts a novel coating matching system, which uses zinc plus (commonly known as cold galvanizing system) instead of hot spraying zinc as the primer, and re coating heavy anti-corrosion coatings such as epoxy micaceous iron intermediate coat and chlorinated rubber finishing coat, so that the steel gate has a service life of more than 15 years.

　　2、 Painting matching

　　According to the requirements of the owner and the above design principles, it is determined that the coating matching of the gate is listed in Table 1.

　　3、 Coating process

　　The fabrication and painting of gate steel structure are undertaken by Liuli branch of Shanghai shipyard. According to the specific situation of Liuli branch, master the following key points in the coating process.

　　1. Process flow

　　Steel - steel cutting, welding and assembly - sand blasting and derusting - pre zinc coating on weld joint - zinc coating - epoxy micaceous iron intermediate coat spraying the first finishing coat - General Assembly, welding site - grinding and cleaning of weld joint and damaged and rusted parts - zinc coating - spraying the last finishing coat - Inspection of coating quality - Repair - Acceptance

　　2. Surface treatment of steel structure sluice gate

　　The quality of steel surface treatment is the key to coating quality.

　　According to the requirements of the owner for the corrosion protection life of the gate steel structure, the type and thickness of the steel plate and the zinc addition for the surface treatment, Liuli branch has undergone sand blasting during the coating construction, and the cleanliness of the steel surface treatment has reached siso55900 Sa2.5 (equivalent to SSPC in the United States SP10 is close to the white level standard), and its text definition is "after sand blasting, the steel surface is free of oil, rust, oxide skin and other dirt, or only slight traces, 95% of the steel surface is impacted by the steel shot, exposing the metal color". After sandblasting, the surface roughness of steel plate is about 70UM. In the process interval, the local secondary rust spots or electric welds, cutting and other parts shall be polished and cleaned by hand; the cleanliness shall reach SIS ST3 level.

　　3. Grasp of painting environment conditions

　　(1) Keep the working site of the gate clean and dry, and remove the pollution on the surface of the steel to be coated and the surface of the paint film;

　　(2) The coating period is in the winter in Shanghai. During the coating construction of epoxy micaceous iron intermediate coat and chlorinated rubber top coat, Liuli branch, in order to prevent the steel surface from condensation, will facilitate the solidification when the relative humidity is less than 85% and the steel surface temperature is higher than the dew point by 5 ℃;

　　(3) According to the technical specification of zinc addition, there is no requirement for steel surface temperature, air temperature and relative humidity when coating zinc, and even coating can be done on the wet steel surface. However, Liuli branch is specially equipped with a mixer when coating zinc addition, so as to mix and spray at the same time.

　　4. Airless spraying technical conditions

　　Except for pre coating, airless spraying method is adopted for gate coating, in which qpt3256c zinc rich coating spraying machine of Chongqing Changjiang Machinery Works is adopted for "zinc addition"; qpt6528 spraying machine is adopted for epoxy micaceous iron, and see Table 2 for specific technical conditions

　　5. Other painting technical conditions

　　For the mixing ratio, special diluent, dilution ratio, service life after mixing and other technical conditions, Liuli branch operates according to zinc addition and corresponding paint instructions during coating construction.

　　The drying time and coating interval of Liuli branch shall be as shown in Table 3.

　　4、 Coating quality

　　1. Surface quality of paint film

　　The surface is bright and clean, without any defects such as sagging, leakage, pinhole, whitening, blistering, shrinkage and so on.

　　2. Film thickness mass

　　The film thickness quality includes two aspects: first, each matching coating should meet the specified film thickness requirements. In particular, the zinc addition must reach 60um to ensure the corrosion resistance of the steel gate; the second is the total film thickness of the coating. According to the inspection of coating process quality inspector in Liuli branch, the dry film thickness of zinc addition can reach two 85% requirements, that is, 85% of measuring points can reach or exceed the specified film thickness; the dry film thickness of other testing points shall not be less than 85% of the specified film thickness.

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