What is the application of supersonic spraying?

       The remanufacturing project adopts advanced maintenance technology, strict product quality control and accurate cost accounting, so the old products can be reused and achieve good technical and economic indicators. Remanufactured items are high quality, energy efficient and material saving. Environmental protection is the goal, in line with the national sustainable development strategy. Remanufacturing engineering is based on advanced maintenance techniques. Among them, thermal spraying technology has a wide range of applications in remanufacturing due to its process flexibility, controllability of coating quality and cost advantages. According to the principle of thermal spraying, the state of the particles before deposition determines the properties of the coating, including the speed of the particles, the temperature of the particles and the molten state of the particles. The velocity of the particles has a significant effect on the performance of the coating. When the particles hit the substrate surface, they form large pulses at high speed. The particles are highly deformable, which facilitates the improvement of coating adhesion and density. Supersonic spraying is excellent. The performance of the coating benefits from extremely high particle velocities. A popular research in recent years, cold spray technology completely relies on the kinetic energy of high-speed particles to form coatings. Based on the principles of aerodynamics and rocket engines, we have successfully developed hypersonic arc spraying technology (HVAS) and multifunctional hypersonic flame spraying technology (HVO/AF), which can prepare high-performance metals, alloys, cermets and non-oxidizing Metallic coatings have been widely used in industry.

 

1Supersonic spraying technology

 

      Arc spraying has the advantages of high production efficiency, low production cost and less heating of the workpiece. Widely used in long-term anti-corrosion and wear-resistant coatings. It plays an important role in thermal spraying. However, it is comparable to plasma spray and HVOF. Compared with ordinary arc spraying, the coating quality is lower, the bonding strength is about 20 MPa, and the porosity is 3%-10%, which limits the application of arc spraying. Supersonic arc spray technology is based on increasing the speed of particles. Laval nozzles are used to improve the atomization of the spray gun and enhance the particle addition effect of the airflow. The speed of particles is increased to supersonic speed, and a coating with high bonding strength, low porosity and low surface roughness is prepared, and the quality of the coating is greatly improved compared with ordinary arc spraying, which is close to the grade Plasma spraying improves the quality of the arc sprayed coating in an all-round way.

 

      The principle of supersonic arc spraying is that the arc burning at the end of the welding wire will melt the evenly fed welding wire, and the supersonic air flow accelerated by the Laval nozzle will atomize the atomized welding wire into a fine and uniform particle size distribution. The particles are sprayed onto the workpiece to form a coating. Like ordinary arc spraying, supersonic arc spraying is a continuous and repeated molten atomization deposition process, but in terms of the atomization method, supersonic arc spraying is different from ordinary arc spraying, which uses subsonic fog. Supersonic arc spraying adopts supersonic atomization, the atomized particles are fine and uniform, and the speed is fast, which is conducive to obtaining high-quality coatings.

2 The application of supersonic arc spraying in remanufacturing

 

      The supersonic arc spray coating has high bonding strength, low porosity, low surface roughness, good wear and corrosion resistance, and has broad application prospects in the industry, especially in long-term anti-corrosion and wear-resistant coatings. The supersonic arc spraying process is flexible and can obtain coatings with excellent performance within a considerable range of process parameters. After the successful development of the equipment, it has been widely used.

 

2.1 Long-lasting anti-corrosion coating

 

      Arc sprayed aluminum and zinc coatings have good corrosion resistance and good protection to the substrate. Since the self-corrosion potentials of aluminum and zinc coatings are lower than those of carbon steel, aluminum and zinc coatings have the cathodic protection effect of sacrificial anodes. Even if the coatings are partially damaged, they still have a good protective effect on the substrate. , In addition, arc sprayed nickel-chromium and iron-chromium-aluminum coatings can effectively resist high temperature corrosion. The quality of supersonic arc spraying is higher than that of ordinary arc spraying, the coating is uniform and dense, and the porosity is low, which provides a low-cost and effective way for corrosion protection, especially for bridges, steel towers, water gates, industrial boilers, etc. corrosion protection.

 

      Corrosion of the water-cooled tube walls of industrial boilers is an important economic and technical issue, and the cost of replacing the tube walls and shutting down production is quite expensive. During the use of the boiler, the working temperature is high, the sulfur content of the fuel is high, and the wall of the boiler water-cooled tube is corroded due to the reaction between Fe element and S element in the high temperature air to form FeS. In addition, slag and coal ash have an erosion effect on the pipe wall, aggravating the corrosion of the pipe wall. Compared with ordinary arc spraying, the supersonic arc spraying of the water-cooled pipe wall of the power plant produces a uniform and dense coating, with low surface roughness, high bonding strength, and greatly improved coating quality. The anticorrosion life is expected to be more than 5 years. With the development of the petrochemical industry, the trend of accidents in chemical storage tanks and pipelines due to various corrosion reasons has increased significantly, which not only caused a lot of economic losses and environmental pollution, but also caused many casualties. Therefore, anti-corrosion and maintenance of chemical equipment is one of the key problems to be solved in the development of petrochemical industry. The supersonic arc spraying of the light dirty oil recovery tank of the petrochemical plant has greatly improved the service life of the recovery tank, and its service life has been increased from the original 3 years to 8 years.

2.2 Wear-resistant coating

On the surface of mechanical parts, the use of thermal spraying method to prepare wear-resistant or wear-resistant and corrosion-resistant coatings to repair or strengthen parts is an important aspect of thermal spraying technology applications. The coating prepared by supersonic arc spraying has high bonding strength and low porosity, and is easy to meet the requirements of precision and surface finish after turning and grinding. The application creates conditions and has good technical and economic benefits. The working environment of construction machinery is getting worse and worse, and the plunger of its hydraulic system often suffers from adhesive wear and abrasive wear due to overload and hydraulic oil pollution, resulting in the failure of the hydraulic system to work normally. The failed plunger is repaired by supersonic arc spraying wear-resistant and high-temperature alloy coating. The repaired plunger can not only be restored to use, but also its service life has been extended from an average of 15 to 20 days to an average of 45 days. The cycle has more than doubled, resulting in better economic benefits.

 

3 Multifunctional supersonic flame spraying technology

 

      The principle of the multi-functional supersonic flame spraying system is: using kerosene as fuel, oxygen and compressed air as combustion accelerants, the control system delivers kerosene and oxygen (compressed air, or a mixture of oxygen and compressed air) to the spray gun at a certain flow rate It is atomized and mixed into a combustible mixture by a high-performance atomizing nozzle and then injected into the combustion chamber of the spray gun. The mixture is ignited and burned by a spark plug to form a high-temperature and high-pressure gas, which is accelerated to supersonic speed through a Laval nozzle. The powder feeding system sends the spray powder from the low pressure area of the Ladale nozzle into the supersonic jet. After the jet is heated and accelerated, it is sprayed from the spray gun, and is sprayed at a high speed to deposit on the surface of the workpiece to form a coating. The key of the spraying system is to adjust the speed and temperature of the flame by adjusting the flow ratio of kerosene and oxidant (mixed gas of oxygen and compressed air) entering the spray gun, so as to control the heating and acceleration of the spraying powder to meet the requirements of the spraying material , Preparation of high-performance metal coatings, alloy coatings and oxide ceramic coatings.

 

 This is the flame flow diagram of the multi-functional supersonic flame spraying system. It can be seen from the figure that the flame flow is concentrated, the jet diffusion angle is small, and the Mach cone unique to the supersonic flame flow appears, indicating that the flame flow speed reaches supersonic speed. The bonding strength of the WC-12Co coating was tested, and the test results showed that the bonding strength of the coating was greater than 70 MPa, and the fracture surface appeared in the adhesive layer during the test, indicating that the actual value was greater than the test value.