In the 1960s and 1970s, China started applying epoxy resins and their derivatives for anti-abrasion protection in submersible pumps. By the 1980s, various non-metallic coatings were developed, including composite dragon coatings, polyurethane coatings, ceramic-like coatings, and rubber coatings. Additionally, some non-metallic materials such as quick-setting titanium rubber, enamel, ceramics, and glass were also used, although they saw limited application due to complex processing techniques.
In the 1990s, the United States introduced materials like DEVCON DEV agent, ARC composite coatings, and synthetic rubbers. Despite these advancements, many of these non-metallic coatings struggled in harsh pumping station environments because of weak adhesion to metal substrates and insufficient hardness, which limited their effectiveness against cavitation and erosion.
Metal coating research became a key area, with electrode surfacing and wire coating being widely adopted for surface protection. While electrode surfacing offers strong bonding, it often results in uneven thickness, high fading rates, and strict requirements on the base material. The surface treated with this method is prone to cavitation damage near the welding spots, and the coating may eventually fail entirely.
Wire-sprayed stainless steel coatings, though easier to apply, are not ideal for submersible pumps subjected to impact loads or cavitation. For large components, such as axial pump impellers with diameters over three meters, stainless steel plates can be embedded to enhance erosion resistance. However, this approach requires specialized factory processing, leading to high costs and long lead times.
Alloy powder coating was developed as an improvement over wire spraying. It offers smoother application, better thickness control, and lower fading rates. The process is simple, cost-effective, and not restricted by environmental conditions. However, due to the layered structure formed by semi-molten particles, internal stresses and defects like cracking or deformation can occur, limiting its use to less severe wear scenarios.
Surface protection materials must meet specific technical requirements: high strength and hardness to resist cavitation and abrasion, good toughness to absorb impact, strong adhesion to prevent spalling at high flow speeds (30–35 m/s), affordability for widespread use in both large and small pumping stations, and safety in terms of being non-toxic and non-flammable.
Processing technology should also be user-friendly, requiring minimal specialized equipment and being adaptable to different seasons and environments. Coatings should cure quickly without needing special thermal treatment, allowing for faster maintenance cycles.
Recent progress in alloy powder spray welding has shown promising results. This technique combines spraying and welding, using low-melting-point powders to create dense, smooth coatings with high hardness (up to HRC 60–70). It significantly extends the service life of pump components and improves efficiency.
Material optimization for spray-welding involves adjusting the composition and particle size to achieve a balanced microstructure. Targeted performance adjustments ensure excellent wear resistance while minimizing cracks and improving weldability. Proper process parameters are essential to enhance adhesion and durability under real operating conditions.
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