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Abstract: In order to meet the requirement of offshore wind turbine bearings with an anticorrosive life greater than 25 years, the anticorrosive spraying technology and performance of coating for the bearings are researched. The pretreatment process for the bearing steel before spraying is optimized, and the thickness of zinc sprayed coating and types of intermediate and finish paints are selected. The adhesion and corrosion resistance of different paint sprayed coating combinations are studied. The results show that; when the cleanliness level of substrate surface is 2. 5 ~ 3.5and the surface roughness Rz value is 80 125 um, the adhesion of anticorrosive coating meets the requirement of not less than 5 MPa: when the substrate adopts the anticorrosive coating combination of ” zinc spray + polyamide epoxy paint + two – component polyurethane paint” , the time for neutral salt spray resistance test and damp heat test is greater than 2 400 hours, meeting the durability design requirements of the bearings: the optimized processes are adopted for anticorrosive spraying treatment, all indicators meet the requirements of relevant standards
Anti-corrosion layer thickness testing methods include mechanical thickness measurement, optical thickness measurement, magnetic thickness measurement, ultrasonic thickness measurement, etc. This test adopts the magnetic thickness measurement method and uses a company’s 2812 magnetic film thickness tester to refer to GB/T 13452.2-2008 [13] for inter-process inspection and finished product film thickness inspection. The anti-corrosion layer must meet the requirements of GB/T 29717-2013. .
The main methods for testing the bonding strength of the anti-corrosion layer include the paint film circle test method, the paint film cross-hatch test method, the paint film pull-apart test method, etc. [14-15] This article uses multi-layer spray anti-corrosion film, and the bond strength test uses the paint film pull-apart test method. Test method, the instrument used is PosiTest AT-M adhesion tester. The test is carried out after the relevant film layer spraying process is completed. The test standard refers to GB/T 5210-2006[16] and the evaluation standard refers to GB/T 33423-2016[7]. The film adhesion is required to be not less than 5 MPa.
Based on the above tests, a spray anti-corrosion process that can meet the design life of offshore wind turbine bearings with a durability of not less than 25 years was obtained. Spray pre-treatment (cleanliness level 2.5~3.5) – electrothermal melt-blown zinc (thickness 150~200 um) leveling – intermediate paint ( The dry film thickness of polyamine epoxy shall not be less than 100 μm) and the topcoat (two-component polyurethane, dry film thickness shall not be less than 60 μm) shall be dried once it is dry.
Anti-corrosion layer and section
The finished test piece after spraying is shown in Figure 1. The surface is uniform, delicate and free of bubbles. The cross-sectional view of the spray coating is shown in Figure 2. It can be seen that the intermediate paint and the top paint are closely combined, the intermediate paint is fine and has no bubbles, and there are occasional bubbles inside the top paint. During the spraying process, the process should be strictly controlled to reduce the generation of bubbles in the paint film.
1) When the surface cleanliness level of the substrate is 2.5 ~ 3.5 and the surface roughness Rz is about 80 ~ 125, the binding force of the anti-corrosion layer is higher.
2) The bonding force between the substrate and the zinc spray layer is the key to the bonding force of the coating. The bonding force between the composite paint layer and the matrix is about 8.5 MPa, which can meet the requirements.
3) The comprehensive corrosion resistance of the polyamide epoxy intermediate paint-two-component polyurethane topcoat composite coating is better 4) The resulting spray anti-corrosion process can meet the requirements of the durability design life of offshore wind turbine bearings not less than 25 years