Anti-wear protection innovation for submersible pumps

Our country began to apply epoxy resin and its compound to submersible pumps for anti-wear protection in the 1960s and 1970s. In the 1980s, non-metallic coatings such as composite dragon coating, polyurethane coating imitation ceramic coating and rubber coating were successively developed. In addition, there are some non-metallic coatings formed using fast titanium glue, rubber, enamel, ceramics, glass and other materials, which are less used due to complex processing techniques. In the 1990s, high-molecular polymer materials such as American DEVCON repair agent, ARC composite coating, and artificial rubber coating were also introduced in the industrial field. These non-metallic coating materials are often difficult to achieve the expected anti-cavitation and anti-abrasion effects due to the poor bonding ability of the coating and the metal substrate and the insufficient hardness of the material itself in the harsh environment of the pumping station.

1. Research on metal coating

      Metal surface protective layers are also widely used in the anti-abrasion surface protection technology of submersible pumps. The most used are welding rod surfacing and wire spraying. The surfacing method using stainless steel electrode can ensure that the welding layer and the substrate have a high bonding strength, but the surfacing method has a large dilution rate, uneven thickness of the welding layer and large machining allowance, which requires high weldability of the working substrate material . The surface of the submersible pump blade treated by the surfacing method, generally before cavitation damage occurs at the surfacing welding place, new cavitation damage occurs rapidly around the surfacing welding point, until the bottom of the surfacing layer. The stainless steel mist particle coating formed by wire spraying is mainly mechanically combined, which is not suitable for the impact load and anti-cavitation repair of submersible pumps. For some large-scale submersible pump workpieces, such as the impeller chamber of the axial flow pump with a large diameter (above 3 meters in diameter), a layer of stainless steel plate can be embedded on the surface to increase the abrasion resistance. However, this method requires the workpiece to be sent to a large submersible pump factory for special processing, turning, inlaying, and welding, which is expensive and has a long cycle time, which is not implemented by ordinary submersible pumping stations. Alloy powder spraying is developed on the basis of wire spraying. Compared with the surfacing method, the forming is beautiful and smooth, the thickness is easy to control, the dilution rate is small, the method is simple, the heat source is easy to obtain, and the processing is not restricted by the climate and site. However, because the sprayed layer is formed by regularly superimposing the semi-molten alloy powder particles on the surface of the substrate at high speed, it is a layered structure, and its physical properties are directional, and during the spraying process, every The powder particles all appear condensation, shrinkage, deformation and other phenomena, which develop an internal stress in the coating. Therefore, alloy powder spraying is generally only used for surface protection of small and medium-sized submersible pumps with less severe cavitation and abrasion.

2. Requirements for surface protection materials and processes

      (1) The technical requirements for surface protection materials. The anti-abrasion coating must have: ① Very high strength and hardness to resist cavitation and abrasion damage; ② Have a toughness to absorb impact energy; ③ Have high adhesion Strength, to ensure that the coating will not peel off under the impact of the high-speed water flow of 30-35 meters per second in the pump; ④The coating material must be moderately priced to ensure that it can be used in large and medium-sized submersible pumping stations and large-scale rural small and medium-sized diving Promote the use in pumping stations; ⑤The coating material should be non-toxic, non-flammable and explosive, convenient for storage and transportation, and not pollute the surrounding environment.

      (2) Processing technology requirements In order to ensure the promotion and application of surface protection technology, the processing technology must be as follows: ①The technology is simple and can be mastered by operators of different levels; ②The tools (appliances) used in the processing should be in the market Easy to buy or necessary for general pump station maintenance work, and the price is moderate, without special and expensive equipment; ③The process should not be affected by the season and the surrounding environment to ensure that the pump station can be carried out during the winter and spring maintenance period ④The coating does not require special insulation and maintenance, and can be quickly cured or put into use after coating to shorten the maintenance period.

3. Progress in alloy powder spray welding technology

    Spray welding protection technology is a metal surface protection technology developed on the basis of spraying and surfacing welding with the successful development of low melting point powder materials. Because the spray layer undergoes a remelting process, the coating is dense and non-porous, and the surface is smooth and flat. It has the advantages of material saving, good quality and high efficiency. The surface hardness of the spray solder layer can be as high as HRC60-70, which can be extended several times or even ten times. The service life of submersible and water pump flow parts.

4. Optimization of spray welding alloy powder materials

    Optimization points In order to ensure the quality of the spray welding layer and prevent the deformation of the workpiece and the generation of coating cracks, the technical route of coating material research and optimization is: (1) Through the optimization of the proportion, the particle size, quantity and crystal grain of the hardened phase are changed In order to obtain a reasonable organizational structure and distribution status. (2) According to the characteristics of cavitation and abrasion of the submersible pump, the performance index of the material is adjusted in a targeted manner, which not only ensures the excellent anti-abrasion resistance of the material, but also minimizes or reduces the generation of cracks and improves the weldability. (3) Determine reasonable technical parameters and process parameters to improve the restraint state of the coating under the conditions of use.