Cavitation, abrasion and the joint damage of the pump have always been an important issue in the operation, maintenance and management of the pump. The traditional surface protection materials and processes are far from meeting the requirements of the pump for cavitation and erosion resistance. In order to enhance the ability of anti-cavitation and abrasion on the surface of pump overcurrent parts, besides constant use of stainless steel or other cemented carbide to manufacture blades and impellers, the surface protection technology is continuously tested. This article describes its progress as follows:
Research Status of Surface Protection Technology

Surface Protection Technology Introduction

Non-metallic coating research China in the 20th century, 60, 70 began to epoxy resin and its compounds used in water pump anti-erosion protection. In the 1980s have also developed a composite dragon coating, polyurethane coating imitation ceramic coating and rubber coating and other non-metallic coatings. In addition, there are some non-metallic coatings formed using materials such as quick-acting titanium rubber, rubber, enamel, ceramic, glass and the like, which are less used due to complicated processing techniques and the like. In the 90s of the 20th century, the United States also introduced the United States DEVCON DEV agent, ARC composite coatings, synthetic rubber and other polymer materials. These non-metallic coating materials in pumping station harsh environment, often due to the coating and the metal matrix bonding ability and the material itself is not enough hardness, it is difficult to achieve the desired anti-cavitation, anti-erosion effect.

Research on metal coatings

In the pump anti-erosion surface protection technology is also widely used metal surface protective layer. The most widely used is electrode surfacing and wire coating. The use of stainless steel electrode surfacing method to ensure that the welding layer and the substrate with a high bonding strength, but the surfacing fade rate, the welding thick and uneven processing margin, the solderability of the work of the substrate material demanding . The surface of the pump blade treated by the surfacing welding method is generally subjected to new cavitation destruction immediately around the surfacing spot until no cavitation damage occurs at the surfacing zone until the bottom of the surfacing layer. The stainless steel spray particle coating formed by wire spraying is mechanically combined, which is not suitable for the pump impact load and anti-cavitation repair. For some large-scale pump workpieces, such as large diameter (more than 3 meters in diameter) axial-flow pump impeller chamber, a stainless steel plate can be inlaid on the surface to increase the anti-abrasion ability. However, this method needs to be sent to large-scale pump plant specialized processing, turning, inlay, welding, expensive, long cycle, non-ordinary pumping station can be implemented. Alloy powder coating is developed on the basis of wire spraying. Compared with the surfacing method, the molding is smooth, the thickness is easy to control, the fading rate is small, the method is simple, the heat source is easily obtained, and the processing is not limited by the climate and the site. However, since the sprayed layer is formed by regularly stacking alloy powder particles in a semi-molten state sprayed onto the surface of a substrate at a high speed and in a layered structure, the physical properties of the sprayed layer are directional and, in each spraying process, Powder particles are condensation, shrinkage, deformation and other phenomena in the coating to develop an internal stress, so the alloy powder coating is generally only used for cavitation and abrasion less serious surface protection of small and medium-sized pumps.

Surface protection materials and process requirements

Technical Requirements for Surface Protection Materials Anti-wear coatings must have

(1) high strength and hardness to resist cavitation, abrasion damage; (2) has a toughness to absorb the impact energy; (3) has a high bond strength to ensure that the coating in the pump 30 -35 meters per second high-speed flow will not peel off under the impact; (4) coating materials must be affordable, in order to ensure that large and medium-sized pump stations and large-scale rural small and medium-sized pump station promotion; (5) Layer material should be non-toxic, non-flammable, explosive materials, easy to store and transport, do not pollute the surrounding environment.

Processing requirements In order to ensure the promotion and application of surface protection technology, processing technology must be:

(1) The process is simple and can be mastered by operators of different degrees; (2) The tools (tools) used in the process should be easy to get in the market or necessary for general pumping station maintenance, and the price is moderate , Without special and expensive equipment; (3) the process should not be affected by the seasons and the surrounding environment to ensure that pumping stations can be carried out during the winter and spring maintenance; (4) the coating does not require special thermal maintenance, after coating Can be quickly cured or put into use to shorten the same period of maintenance.

Progress of Alloy Powder Spray Welding Technology

Spray-welding protection technology is a metal surface protection technology developed on the basis of spraying and surfacing with the successful development of low melting point powder materials. As the spray layer undergoes remelting process, the coating is dense and non-porous, the surface is smooth and flat, with the advantages of material saving, good quality and high efficiency. The surface hardness of the spray coating layer can be up to HRC60-70 and can be extended several times or even ten times Pump over-current components of the service life.

Spray welding alloy powder material optimization

Optimization Tips In order to ensure the quality of spray coating, to prevent the deformation of the workpiece and the generation of coating cracks, coating material research and optimization of the technical route: (1) through the ratio optimization, change the hardened phase particle size, the number of crystal grains Degree of size, in order to obtain a reasonable organizational structure and distribution status. (2) According to the cavitation and erosion characteristics of the pump, the performance indexes of the materials are adjusted in a targeted manner, which not only ensures the excellent abrasion resistance of the material, but also can suppress or reduce the crack generation to the maximum extent and improve the solderability. (3) Determine reasonable technical parameters and process parameters to improve the binding conditions under the conditions of use of the coating.

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