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　　The steel structure coating of the main terminal building of Guangzhou New Baiyun International Airport is carried out in two stages, the first stage is in the factory (workshop); outdoor steel structure - sand blasting and rust removal - arc spraying aluminum - epoxy micaceous iron primer - spraying the first coat of acrylic polyurethane finish - delivered to the site

　　For indoor steel structure, after sand blasting and derusting, inorganic zinc rich primer will be sprayed without arc spraying aluminum, and the rest is the same as outdoor. No matter outdoor or indoor, in order to ensure the welding quality and coating quality of steel structure, after sandblasting, 5-10cm shall be reserved at both ends of steel for welding without aluminum spraying and painting. The second stage of coating is to weld the steel structure which has been pre coated in the workshop on site for general assembly, but before spraying the second coat of acrylic polyurethane finish on site, it is necessary to focus on the treatment of the spot weld. If the treatment of the electric weld is improper, the part is easy to rust after painting. The main reasons are as follows:

　　One is that when the steel structure of the terminal is painted in the first stage, the sand blasting of the reserved parts of the electric welding is not thorough, which may leave oxide skin and other impurities, and various rust spots will be produced in the process interval; the other is that the impurities such as "spatter" and "welding slag" formed during the welding are attached to the steel surface;

　　After the general assembly of electric welding for the indoor structure of the terminal building, polish to st 3, and then apply inorganic zinc rich coating. After the outdoor steel structure is assembled at high altitude, it is impossible to spray aluminum on the electric welding seam, and "zinc addition" is the best material for repairing the Korean seam.

　　1、 Reasons for choosing zinc addition

　　1. Excellent corrosion resistance

　　The content of zinc in the dry film was over 96%, and the purity of zinc particles was 99.995%. It has the same excellent cathodic protection function as aluminum spray coating.

　　2. Zinc addition has low requirements for surface treatment

　　According to the national standard, the cleanliness of the surface treatment of arc spraying aluminum steel must reach level 3 of GB 8923 SA. For new steel, the requirement of zinc coating on the cleanliness is level 2.5 of GB 8923 SA. For the surface of the electric welding seam treated by sandblasting, it is only necessary to manually grind it to level 2-st 3 of GB 8923 St.

　　3. Zinc addition is easy to use

　　Zinc addition is a single component coating, which can be applied not only by air spraying and airless spraying, but also by brush (roll) coating and dip coating.

　　4, others

　　In addition to alkyd coating, zinc coating has good matching performance with epoxy, polyurethane, chlorinated rubber, acrylic acid and other heavy-duty anticorrosive coatings.

　　2、 Technical and quality requirements of zinc coating on weld

　　According to the environmental conditions in Guangzhou area and the requirements of the owner of Baiyun Airport for the anti-corrosion life of steel structure to reach 30a, and the corrosion of the electric weld is particularly serious, we design the specified film thickness of zinc plus coating to reach 60um.

　　During the construction, the film thickness shall be measured at any time by the film thickness gauge. According to the statistics and summary, the film thickness detection value must meet two 90% requirements, i.e. 90% of the film thickness detection value exceeds the specified film thickness of 60um, and the film thickness at the measurement point that fails to meet the specified film thickness must reach 90% of the specified film thickness (i.e. 54um).

　　3、 Zinc coating process of Guangzhou New Baiyun International Airport Terminal

　　Zinc addition is only used for repair of outdoor steel structure electric weld and repair of small area coating.

　　1. Process flow

　　Field assembly and welding of outdoor steel structure of terminal - grinding treatment of weld joint - zinc coating plus - epoxy micaceous iron primer - first coat of acrylic polyurethane finish paint - second coat of acrylic polyurethane finish paint for all steel structures - quality inspection - Completion

　　2. Zinc addition construction conditions

　　(1) Before zinc addition, it must be fully stirred, and stirred again every 15-20min during construction;

　　(2) Professional diluent zingasolv must be used, with dilution ratio less than 3%;

　　(3) Brush coating method shall be adopted for zinc plus coating to ensure uniformity without omission.

　　3. Recoat interval

　　According to the drying mechanism and drying rate of zinc addition, the interval of zinc addition self recoating is 1H, and the interval of zinc addition coating recoating other coatings is 2H.

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