In the 1960s and 1970s, China started using epoxy resin and its derivatives for anti-abrasion protection in submersible pumps. By the 1980s, various non-metallic coatings such as composite dragon coatings, polyurethane coatings, ceramic-like coatings, and rubber coatings were developed. Additionally, some non-metallic coatings were made from materials like quick-setting titanium rubber, enamel, ceramics, and glass, but they saw limited use due to complex manufacturing processes. In the 1990s, the U.S. introduced materials like DEVCON DEV agent, ARC composite coatings, and synthetic rubbers. However, these non-metallic coatings often failed to deliver effective anti-cavitation or anti-erosion performance in harsh pumping environments because of weak adhesion to metal substrates and insufficient hardness.
Metal coating techniques have also been widely used for surface protection in submersible pumps. Electrode surfacing and wire spraying are the most common methods. While electrode surfacing offers strong bonding between the coating and the base material, it has issues like uneven thickness, high dilution rates, and strict requirements on the substrate's weldability. The surface treated with this method often experiences cavitation damage near the welded area shortly after application. Wire-sprayed stainless steel coatings, formed by mechanical particle bonding, are not suitable for high-impact or cavitation-prone areas. For large components like axial pump impellers over 3 meters in diameter, stainless steel plates can be embedded on the surface to improve erosion resistance, but this method requires specialized facilities, leading to high costs and long lead times.
Alloy powder coating was developed based on wire spraying technology. Compared to traditional surfacing, it provides a smoother surface, better thickness control, lower dilution rates, and is easier to apply. It also doesn't require special equipment and is less affected by environmental conditions. However, since the coating is formed by high-speed sprayed particles that partially melt and stack, internal stresses can develop due to particle coagulation, shrinkage, and deformation, limiting its use to less severe wear areas.
For surface protection materials, key technical requirements include: (1) high strength and hardness to resist cavitation and abrasion; (2) good toughness to absorb impact energy; (3) strong bond strength to prevent spalling under high-speed flow (up to 30–35 m/s); (4) cost-effectiveness to support widespread use in both large and small pumping stations; and (5) safety, non-toxicity, and ease of transport and storage.
Processing techniques must also meet certain standards: (1) simple procedures that can be easily mastered by operators; (2) affordable and accessible tools without the need for expensive equipment; (3) adaptability to different seasons and environments to allow maintenance during winter and spring; and (4) fast curing times to minimize downtime.
Spray-welding alloy powder technology has advanced significantly, combining the benefits of spraying and welding. With low-melting-point powders, the resulting coating is dense, smooth, and highly efficient. Surface hardness can reach HRC 60–70, greatly extending the service life of pump components.
Material optimization for spray-welding involves adjusting the composition and microstructure to ensure good adhesion, crack resistance, and wear resistance. Proper process parameters are crucial to enhance coating performance under real-world operating conditions.
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