Introduction of surface protection technology :
Study on the non metallic coating in China in twentieth Century 60, 70s began to epoxy resin composite was applied to pump for anti abrasion protection. In 1980s, the composite dragon coating, polyurethane coating and rubber coating were developed. In addition, there are a number of non metal coating materials such as titanium rubber, rubber, enamel, ceramic, glass and other materials, because of the complexity of the processing technology and other reasons. 1990s, in the industrial field also introduced the United States DEVCON repair agent, ARC composite coating, synthetic rubber coating and other polymer materials. These non metal coating materials used in the pump under harsh, often because of the coating and metal substrate is poor and the hardness of the material itself is not enough, it is difficult to achieve the anti cavitation, abrasion resistance of the desired effect.
Research progress in the research of anti cavitation wear protection technology of water pump :
In the pump abrasion resistant surface protection technology is also widely used in metal surface protective layer. Use the most is the welding rod and wire coating. Using the welding method of stainless steel welding rod can ensure the welding layer and the substrate has a high bonding strength, but the dilution rate of welding process is large, and the thickness of the welding layer is not uniform and the machining allowance is large. The surface of the water pump blade treated by surfacing welding method, the welding point of the welding spot is rapidly destroyed, and the new cavitation damage occurs in the welding spot, until the bottom of the surfacing layer. The stainless steel spray coating formed by wire spraying is mainly based on mechanical combination, which is not suitable for the shock loading and anti cavitation of water pump. For some large water pump parts, such as large diameter (diameter 3 meters) axial flow pump impeller chamber, can be embedded in the surface layer of stainless steel to increase abrasion resistance. But this method needs to be sent to the large water pump factory specialized processing, turning, mosaic, welding, expensive, long cycle, the general pump station can be implemented. Alloy powder coating is developed on the basis of on-line material spraying. Compared with the welding process, the formation of beautiful appearance, easy to control the thickness, the dilution rate is small, the method is simple, the heat source is easy to get, processing is not affected by climate, site restrictions. But because the spraying layer is composed of high speed jet to semi molten alloy powder particles on the surface of the substrate layer is formed by stacking rules, which belongs to the layered structure, with the direction of their physical characteristics, and in the spraying process, each powder particles are condensation occurs, shrinkage and deformation phenomena and development a kind of internal stress in the coatings, the alloy powder coating generally used in small and medium-sized water pump cavitation and abrasion of the surface protection is not too serious.
Surface protection materials and process requirements :
The material surface protection technology must have anti abrasion coating:
1. High strength and hardness, resistance to cavitation abrasion;
2. Has a toughness, in order to absorb the impact energy;
3. Has a high bond strength, to ensure that the coating in the pump 30-35 meters per second under the impact of high speed flow will not peel off;
4. Coating materials must be moderately priced, to ensure that the large and medium-sized pumping stations and large areas of large and small pumping stations in rural areas to promote the use of;
5. Coating material should be non-toxic, non flammable, explosive materials, easy to keep transport, not pollute the surrounding environment.
Processing technology requirements in order to ensure the promotion and application of surface protection technology, processing technology must be done:
1. The process is simple and can be mastered by operators of different degrees;
2. Tools used in the process (appliances) should be in the market is easy to purchase or general pumping station maintenance work is necessary, and the price is moderate, no special and expensive equipment;
3. Process should not be affected by the seasons and the surrounding environment, to ensure that the pump station in winter and spring maintenance period can be carried out;
4.The coating does not require special heat preservation, and can be quickly solidified or put into use after coating, so as to shorten the maintenance period.
Development of alloy powder spray welding technology:
Spray welding technology is a kind of metal surface protection technology developed on the basis of spraying and surfacing with the development of the low melting point powder material. The spray layer through the remelting process, coating density without holes, smooth surface, has the advantages of material saving, good quality and high efficiency, the surface hardness of spray welding layer can be as high as HRC60-70, can flow part several times or even ten times prolong the service life of the pump.
Optimization of spray welding alloy powder materials:
In order to ensure the quality of the spray welding layer and prevent the deformation of the workpiece and the crack of coating, the technical route for the research of coating material is:
1.By optimizing the ratio, the size and quantity of the hardening phase and the size of the crystalline grain size were changed to obtain the reasonable structure and distribution.
2. According to the characteristics of pump cavitation, abrasion, the performance index to adjust the material, can ensure material with excellent abrasion resistance, and can minimize or reduce the cracks, improve the weldability.
3. To determine the reasonable technical parameters and process parameters, to improve the condition of the use of the coating.