Do you hold on to the significant increase in anti-corrosion performance of thermal spraying?

With the implementation of the West to East Gas Pipeline and South to North Water Diversion Project, the use of hydraulic steel structures has rapidly increased. Developing a new type of anti-corrosion technology for hydraulic steel structures is crucial for reducing project costs and extending project life. Therefore, metal thermal spraying metal step coatings with complementary advantages of various metal coatings are gradually being applied to hydraulic steel structures, becoming a new technology for metal anti-corrosion.

Metal thermal spraying is a process of overlaying and spraying on the same workpiece substrate, using a zinc coating as the bottom layer and then a stainless steel coating as the surface layer, ultimately forming a stepped coating. It is applied to hydraulic steel structures through extensive research and experimentation?? Obtained both economical and satisfactory anti-corrosion effects. The principle is to use a certain form of heat source to heat the metal spraying material, forming particles in a molten state. These particles are impacted and deposited on the surface of the substrate at a certain speed under the action of power, forming a metal coating with certain characteristics. The surface of substrate materials such as hydraulic steel structural components is treated with thermal spraying technology to obtain a metal protective coating that is corrosion-resistant and wear-resistant, thereby enhancing the corrosion resistance and wear resistance of hydraulic steel structural components. There are many materials that can be used for metal spraying, such as zinc, stainless steel, etc. The stainless steel coating has the characteristics of wear resistance and long protection period; Zinc coating not only has coverage and corrosion resistance, but more importantly, it has cathodic protection function (primary battery principle). They are important materials for anti-corrosion spraying of hydraulic steel structures, and therefore have been widely used.

The process flow of thermal spraying metal step coating is divided into four stages. One is surface treatment of steel structures, the second is thermal spraying of zinc, the third is spraying of stainless steel, and the fourth is coating of epoxy cloud iron. According to the China Epoxy Resin Industry Association (www.epoxy e.cn), the coating of epoxy mica iron adopts a manual brushing combined with air spraying method, which requires no brush marks, no bubbles, no sagging, and no missed spraying. The silver gray appearance is neat and uniform. In 2002, Jiangsu Sanhe Sluice Steel Structure Anti corrosion Company applied this technology earlier in the anti-corrosion of hydraulic steel structures in the national engineering project of the Huaihe River estuary coastal hub overpass. The bottom layer of the stepped coating achieves fine zinc particles, small pores, uniform coating, and good compactness, and the thickness of the zinc layer meets the design requirements. Due to the thickness of the zinc layer being only half of the original, the adhesion becomes strong. The stainless steel coating covers it in a gray black color with coarse particles and larger pores, but it is hard and wear-resistant. Due to the overlapping spraying thickness being only half of the original, the adhesion is also good, providing good protection for the zinc layer. After construction, epoxy cloud iron coating is used for sealing, and chlorinated rubber aluminum powder paint is used as the topcoat, which has good waterproof and anti-seepage performance. Through separate inspections of each process by the Shanghai Survey and Design Institute of the Ministry of Water Resources and the Jiangsu Provincial Quality Inspection, it was found that the quality of the thermal sprayed metal step coating is excellent and meets the design requirements.

Compared with commonly used spraying techniques, this technology has significant comprehensive advantages. From a quality perspective, the surface hardness of zinc spray is poor, the wear resistance is insufficient, and the resistance to damage is weak. The anti-corrosion effect of stainless steel spray is poor, prone to rust, rough surface, strong water permeability, poor coverage density, and easy peeling. The thermal spray metal step coating cannot meet the underwater anti-corrosion needs of hydraulic steel structures. From the perspective of economic benefits, choosing the spray stainless steel process for corrosion prevention alone has a higher initial investment cost compared to using zinc spray. Although the stainless steel coating is hard, wear-resistant, and has a protection period of up to 45 years, it is not suitable for corrosion prevention in underwater engineering of hydraulic steel structures; Choosing the zinc spraying process alone for corrosion prevention may result in lower initial investment compared to using stainless steel and thermal spraying metal step coating for corrosion prevention. However, the wear resistance of the zinc layer is poor (with a protection period of only 15 years), especially in areas near the gate waterline that are often subjected to friction and erosion, which increases the cost of the project's lifespan; The thermal spraying metal ladder coating anti-corrosion technology has the advantages of wear-resistant coating, clean appearance, uniform and dense coverage, long protection period, good anti-corrosion performance, strong resistance to damage, no need for secondary construction, significantly reducing the cost of engineering life cycle. It is a anti-corrosion technology for hydraulic steel structures.

In China, there are many Rivers and Lakes, long coastline, and many water conservancy projects. At the same time, many hydraulic structures will be built for projects such as the South to North Water Diversion Project. There are a large number of anti-corrosion working faces for hydraulic steel structures. During the operation of various parts of the hydraulic steel gate, the degree of corrosion and damage on the water surface, underwater, and water line varies, and the degree of wear and tear varies. For example, the embedded parts such as the gate rollers and tracks are prone to damage due to friction from the rollers. This complex corrosion situation poses high requirements for corrosion prevention. The thermal spraying metal step coating anti-corrosion technology is economical, practical, and can achieve the expected results, so it should be vigorously promoted and used.