Application of supersonic spraying technology in remanufacturing (Tech Center of Shanghai HY Industry Co., Ltd)
By adopting advanced repair technology, strict product quality control and accurate cost accounting, the remanufacturing project can reuse the used products and achieve good technical and economic indexes. The remanufacturing project aims at high quality, high efficiency, energy saving, material saving and environmental protection, which is in line with the national sustainable development strategy. The remanufacturing project is based on advanced maintenance technology, among which, thermal spraying technology has wide application in remanufacturing due to its process flexibility, controllability of coating quality and cost advantage. From the principle of thermal spraying, it is known that the state of the particles before deposition determines the performance of the coating, including the velocity of the particles, the temperature of the particles and the melting state of the particles. The speed of the particles has an important role in the performance of the coating, when the particles hit the surface of the substrate, the high speed can form a large impulse, the strong deformation capacity of the particles, which is conducive to the improvement of the coating bonding force and density, supersonic spraying excellent coating performance thanks to the very high particle speed, the popular research in recent years, cold spraying technology, which relies entirely on the kinetic energy of high-speed particles to deposit the formation of coatings. According to aerodynamics and rocket engine principle, has successfully developed supersonic arc spraying technology (HVAS), multi-functional supersonic flame spraying technology (HVO / AF), can prepare high-performance metal, alloy, metal ceramics and oxide-free metal coatings, in the industry has been widely used.
1 Supersonic arc spraying technology
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Arc spraying has the advantages of high production efficiency, low production cost and small heat on the workpiece, which is widely used in long-lasting anti-corrosion and wear-resistant coatings and occupies an important position in thermal spraying, but, compared with plasma spraying and supersonic flame spraying, the coating quality of ordinary arc spraying is low, with a bonding strength of about 20 MPa and a porosity of 3%-10%, which limits the application of arc spraying. Supersonic arc spraying technology to improve the speed of the particles as a starting point, the use of Laval nozzle, improve the atomization effect of the gun, enhance the acceleration of the airflow on the particles, the speed of the particles was raised to supersonic speed, the preparation of the coating bond strength, low porosity, low surface roughness, compared with ordinary arc spraying, the quality of the coating has improved to a large extent, close to the level of plasma spraying, and improve the overall The quality of the arc spraying layer is improved.
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Principle of supersonic arc spraying is that the arc burning at the end of the wire melts the uniformly fed wire, and the supersonic airflow accelerated by the Laval nozzle atomizes the melted wire into particles with fine particle size and uniform distribution, which are sprayed to the workpiece to form the coating. Like ordinary arc spraying, supersonic arc spraying is a repeated melting-atomization-deposition process, but there is a difference between supersonic arc spraying and ordinary arc spraying in the atomization method, ordinary arc spraying adopts subsonic atomization, while supersonic arc spraying adopts supersonic atomization, the atomized particles are fine and uniform. The speed is high, which is conducive to obtaining high-quality coatings.
2 supersonic arc spraying in the application of remanufacturing
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Supersonic arc spraying layer bonding strength, low porosity, low surface roughness, good wear and corrosion resistance, there is a broad application prospect in industry, especially in the long-lasting anti-corrosion and wear-resistant coatings. Supersonic arc spraying process is flexible, in a considerable range of process parameters can get excellent performance of the coating, the equipment has been developed successfully and has been widely used.
2.1 long-lasting anti-corrosion coating
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Arc spraying aluminum, zinc coating corrosion resistance, good protection of the substrate. Because the self-corrosion potential of aluminum and zinc coatings are lower than the self-corrosion potential of carbon steel, therefore, aluminum and zinc coatings have a sacrificial anode cathodic protection, even if the coating has a local breakage, the substrate still has a good protective effect, in addition, arc spraying nickel-chromium and iron-chromium aluminum coatings can also effectively resist high-temperature corrosion. Supersonic arc spraying layer quality than ordinary arc spraying high, uniform and dense coating, low porosity, for the protection of corrosion provides a low cost, good effect of the way, especially bridges, steel towers, sluice gates, industrial boilers, etc. corrosion protection.
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Industrial boiler water-cooled tube wall corrosion is an important economic and technical problem, the replacement of the wall and the loss of production downtime is quite expensive. Boiler use process, high working temperature, high fuel sulfur content, boiler water-cooled tube wall corrosion caused by the reaction of Fe elements with high temperature air S elements to form FeS. In addition, the slag and soot on the tube wall has the effect of erosion, intensifying the corrosion of the tube wall. Supersonic arc spraying power plant water-cooled pipe wall, compared with ordinary arc spraying, the preparation of uniform and dense coating, low surface roughness, high bond strength, coating quality greatly improved, the expected anti-corrosion life of more than 5 years. With the development of the petrochemical industry, the trend of chemical storage tanks and pipelines causing accidents due to various corrosion reasons has increased significantly, which has not only caused a lot of economic losses and environmental pollution, but also caused many casualties. Therefore, the corrosion and maintenance of chemical equipment is one of the key problems in the development of the petrochemical industry. Supersonic arc spraying petrochemical plants of light dirt oil recovery tank, greatly improve the service life of the recovery tank, its service life from the original 3 years to 8 years.
2.2 Wear-resistant coating
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In surface of mechanical parts, the use of thermal spraying methods, the preparation of wear-resistant or wear-resistant corrosion-resistant coating, repair or strengthening of parts, is an important aspect of the application of thermal spraying technology. Supersonic arc spraying preparation of the coating bond strength, low porosity, easy to meet the accuracy and surface finish requirements after turning and grinding, at the same time, compared with other repair methods, its low cost, to create the conditions for its application in the field of repair, with good technical and economic benefits. The operating environment of construction machinery is becoming more and more severe, and the plunger of its hydraulic system often shows adhesive wear and abrasive wear due to overload and hydraulic oil pollution, resulting in the hydraulic system not working properly. The use of supersonic arc spraying wear-resistant anti-high-temperature alloy coating on the failure of the plunger repair, repair the plunger can not only resume use, and its service life is also the original average 15 ~ 20 days to an average of 45 days, the service life cycle increased by more than double, resulting in better economic benefits.
3 multi-functional supersonic flame spraying technology
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Principle of multi-functional supersonic flame spraying system is: the use of kerosene as fuel, oxygen and compressed air as an accelerant, the control system will kerosene and oxygen (compressed air, or a mixture of oxygen and compressed air) to a certain flow rate to the gun, by the high-performance atomization nozzle atomized and mixed into a combustible mixture and sprayed into the gun combustion chamber, the mixture is ignited by the spark plug combustion to form a high-temperature, high-pressure gas, through the Laval nozzle will be accelerated to supersonic speed. The powder feeding system sends the spraying powder from the low pressure area of the Laval nozzle into the supersonic jet, which is accelerated by the heating of the jet and then sprayed from the gun and deposited at high speed onto the surface of the workpiece to form the coating. The key to the spraying system is to regulate the speed and temperature of the flame stream by adjusting the ratio of the flow of kerosene and accelerant (a mixture of oxygen and compressed air) entering the gun, thus controlling the heating and acceleration of the sprayed powder to meet the requirements of the sprayed material to prepare high performance metal coatings, alloy coatings and oxide ceramic coatings.
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Figure 2 shows the flame flow diagram of the multifunctional supersonic flame spraying system. As can be seen from the diagram, the flame flow is concentrated, the jet diffusion angle is small, and the Mach cone, which is characteristic of supersonic flame flow, appears, indicating that the speed of the flame flow reaches supersonic speed. The bond strength of WC-12Co coating was tested, and the test results showed that the bond 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.
4 Multifunctional supersonic flame spraying technology application
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Multi-functional supersonic flame spraying with oxygen kerosene supersonic flame spraying (HVOF) and air kerosene supersonic flame spraying (HVAF) dual function, flame flow speed and temperature in a wide range of continuously adjustable, can meet the requirements of a variety of spraying materials, the preparation of the coating bond strength, low porosity, can be prepared wear-resistant, corrosion-resistant, thermal conductivity, insulation, electrical conductivity, sealing and other coatings, in machinery manufacturing, aerospace, water conservancy and electric power, mining and metallurgy, petrochemical, paper leather and other fields have broad application prospects.
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In metallurgical industry, there are many kinds of rolls and conveying rolls that need to be strengthened or repaired by wear resistance, among which, the cold rolled strip continuous annealing furnace bottom roll is an important one. Lumping of the roll surface is actually adhesive wear. In order to reduce the loss of steel strip production caused by nodules, thermal spraying method is widely used. Usually NiCr-Cr3C2 coating is sprayed on the roll surface, which has the characteristics of high temperature oxidation resistance, thermal shock resistance and wear resistance, and can make the furnace bottom roll work continuously for a long time under high temperature and withstand periodic thermal shock. When the furnace low roll working temperature exceeds 900℃, it is generally sprayed with Co-based alloy. Supersonic flame spraying has a unique advantage in spraying carbide ceramics, and the metallurgical industry has a great demand for carbide metal-ceramic coating, so it gets a lot of applications. Figure 3 shows the multifunctional supersonic flame spraying Co-based WC coating for surface strengthening of pickled galvanized rolls to improve their working life, and the equipment is used by Handan Iron and Steel Group.
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In the petroleum industry, there are a large number of mechanical equipment, such as: pumps, valves, drilling machinery, transmission equipment, lifting equipment, pipelines, etc. An important factor affecting their life is wear and corrosion. Multi-functional supersonic flame spraying has good application effect in strengthening and repairing the piston rod of pumping oil. After the piston rod is strengthened by spraying WC coating, the wear resistance is greatly improved and the service life is increased several times. In petroleum machinery, the valve seat and shaft parts are also more serious wear. Due to the multifunctional supersonic flame spraying preparation of Cobalt alloy-based WC coating, low residual stress, coating thickness up to 3mm, or even thicker, and good combination of coating and substrate, there are better applications in the size recovery of wear parts subjected to heavy loads.
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Pumps, cylinders and valves are the basic units of hydraulic and pneumatic systems, and wear and corrosion of media are the key factors that limit their service life. The use of multi-functional supersonic flame spraying technology can strengthen and repair the pump shaft, cylinder piston rod, valve spool, etc. These parts require high precision and surface finish, multi-functional supersonic flame spraying layer after grinding precision and surface finish are very high, can meet their use requirements.
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Hard seal ball valve has a wide range of applications in industry, it relies on the hard seal between the spool and the seat to control fluid flow through and through, because it does not require the use of non-metallic sealing materials, has a compact structure, reliable sealing, corrosion resistance, has a wide range of applications in the chemical industry. Prepare a certain thickness of wear and corrosion resistant metal ceramic coating on the spool of hard seal ball valve and grind it to the required precision and finish, which can greatly improve the sealing performance and service life. Wenzhou Chengda special valve factory use multi-functional supersonic flame spraying technology to strengthen the hard seal ball valve, greatly improving the valve performance and life, and can meet the needs of the petrochemical industry part of the special working conditions, by the user’s praise.
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In China, due to the constraints of the energy structure, for quite a long time, thermal power generation in the power occupies a considerable proportion. Wind turbines, impellers, boilers, turbine generator sets, etc. are important equipment in thermal power generation, due to different working environments and harsher working conditions, some equipment life is short, affecting the safety and economic efficiency of production. Due to the excellent performance of multifunctional supersonic flame spraying layer, there are very successful applications in power.
5 Conclusion
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To improve the speed of the particles as a starting point, the development of HVAA, HVO / AF supersonic spraying system, the test and application shows that the preparation of the coating performance is excellent, widely used in industry, and achieved very good application results, with further promotion and application, will create greater benefits and value.
