Development and application of thermal spraying te

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Development and application of thermal spraying technology abroad

thermal spraying technology has been developed for more than 50 years. Because of its important role in industry, many large and small companies have emerged. However, due to the development of global economy in recent years, the relationship between companies has gradually shifted from competition to alliance. Today, the major thermal spraying technology companies in the world are:? Sulzermetco. The company was formed by the merger of the former Swiss Pt company and the American Metco company. Headquartered in Switzerland, the company now has assets of US $4 ~ 5billion. Its business covers more than 140 countries and regions around the world. It is the largest thermal spraying technology company in the world.? Praxair Surface Technology Engineering Co., Ltd. The company used to belong to union carbide company, headquartered in the United States, mainly producing various powders. Now it has purchased Miller thermal spraying company, and formed a thermal spraying technology company with relatively perfect varieties in which I have also participated in this competition.? Eutectic. It is a subsidiary of eutecticcastolin, headquartered in the United States, and has now merged with TAFA, which previously belonged to the metallurgical technology company (MTI) in Hobart, Texas

2 main thermal spraying technologies and development trends

at present, thermal spraying technology mainly includes plasma spraying, arc spraying and flame spraying

2.1 plasma spraying

plasma spraying has been widely used because it can spray almost all kinds of materials, has a simple process, and has a good combination between the coating and the substrate. However, the control of a large number of parameters related to the spraying process is more complex, which has become the main obstacle for plasma spraying to obtain high-quality coatings. One of the main aspects of the past research is to improve the performance of the spray gun, including the research on electrode ablation and plasma jet instability caused by hydrodynamic performance and arc performance. Now, after analyzing the model of turbulent plasma jet, it is considered that the jet is a two fluid system composed of two parts of cold and hot fluids that interact with each other to improve the economic efficiency. It is difficult to compare the experimental data and theoretical analysis of the distribution of temperature field and velocity field in the plasma jet because the plasma jet observed in the experiment has a wave phenomenon.? At present, another research direction is to study the formation process of coatings, including the bonding between coatings, the bonding between coatings and matrix, the control of porosity and unmelted particles. The ultimate goal of these studies is to lay a foundation for the whole process control and automation of plasma spraying

2.2 arc spraying

arc spraying is an economical and reliable thermal spraying process. The spraying materials are generally limited to metals and alloys, and can be sprayed on a variety of substrates. The scope of application includes wear-resistant coating, structural anti-corrosion coating and repair of worn parts. It may also be used in the sealing field in the future. At present, the main aspect of arc spraying research is the research and development of tubular metal powder cored wire. The current research work mainly focuses on how to realize the automatic control of spraying process

2.3 flame spraying

traditional flame spraying uses the combustion flame of combustible gas as the heat source to heat the spraying material until it melts and spray it onto the substrate surface to form a coating. Now, new flame spraying methods are continuously developed for the development of flame spraying process and equipment.? High speed oxygen fuel spraying (HVOF) is a main technical field of flame spraying. This process was developed by Union Carbide in the early stage, and the D-gun system using oxyacetylene fuel was invented in 1953. The following jetkote, topgun and CDs, which used oxypropane, oxypropylene and oxyhydrogen as fuel, have continuously improved the technical level of this process.? At present, Praxair company has launched Jetstar high-speed air fuel spraying technology and high-speed combustion wire spray gun. It uses liquid fuels such as kerosene and diesel oil; The combustion supporting material is industrial compressed air, which is used to cool the spray gun, avoiding the additional cooling requirements of many HVOF spray guns and reducing the operating costs. The jettstar system uses 19l/h liquid fuel and 4m? The operating cost of 3/min compressed air is only $7 per hour, while that of oxykerosene is $29 per hour, oxyacetylene is $38 per hour, and oxyhydrogen is $85 per hour.? Another new process developed by Praxair company is flamestar III high-speed combustion wire spraying (hvcw) process using silk instead of powder. At present, the company is exploring the best uniform wire feeding speed matching the high spraying quality.? Eutectic has recently entered the ranks of HVOF with its first high-speed impact melting (hvif plastic becomes the core material of power cable electronics and other products) process system. The company's new terojet system utilizes the high pressure of oxygen at the inlet (about 2MP) to obtain full combustion of gas and high particle velocity. According to eutectic, when the slowly heated particles reach a high speed of 610m/s, a coating with good bonding and dense structure will be produced. The system is light, compact and easy to operate. It only needs to input three parameters, such as oxygen pressure, air pressure and powder feeding wheel speed. The process uses kerosene as fuel and the spray gun adopts water-cooling mode. The operating cost of terojet system is $20 less per hour than that of equipment using hydrogen or acetylene as fuel. It is reported that its spraying speed and deposition efficiency are equivalent to that of HVOF.? The bonding strength of the coating produced by Praxair's ultra-polar D-gun process can reach 210mpa. The test results show that the wear resistance, corrosion resistance and micro vibration wear resistance of the coating are much higher than those of explosive spraying

3 application field of thermal spraying

because thermal spraying can provide coatings with various properties, this process has received extensive attention in the industry. At present, the automobile industry and mold industry have the most research on the application field of thermal spraying

3.1 automobile industry

synchronizing ring. There are many synchronous rings in the automobile gearbox. After a layer of molybdenum is sprayed, the gear can have a self-locking function when working, so as to ensure the safety and stability of driving. At present, China has built a large production base for spraying synchronous rings.? Piston ring. The outer surface of the aluminum piston ring is provided with a groove, which is in contact with the inner surface of the piston cylinder hole during operation. After spraying a layer of molybdenum powder containing NiCrBSi by plasma spraying, the wear resistance of the whole component can be improved.? Exhaust gas sensor. The sensor is made of alumina based electrolyte, which is shaped like a test tube and attached with a platinum electrode. In order to prevent the erosion of platinum electrode by high temperature gas, spinel coating should be sprayed on the electrode. When the sensor is put into the automobile exhaust stream, the coating can not only protect the electrode, but also make the hot gas reach the electrode.? Cylinder bore. Spraying molybdenum alloy on cylinder bore may be the largest application of plasma spraying in automobile industry. At present, sulzermetco has developed a complete set of systems from cleaning, sand blowing to spraying for engine cylinders, with excellent coating quality. This system can spray 200 cylinder liners of ten cylinder engines every day.? Roof connection. There will be a depression at the weld between the roof and the front panel of the car. The previous method to make up for this defect was to polish off the excess solder, thus reducing the strength of the weld. At present, several automobile companies have adopted the method of arc spraying silicon bronze to supplement this joint area, which not only beautifies the appearance of the car body, but also enhances the weld strength.? Thermal barrier coating. The thermal barrier coatings originally applied to aircraft engines have been applied to automotive engines (mainly diesel engines) and exhaust systems

3.2 mold

at present, the rapid prototyping and die making technology is more studied in the application of thermal spraying. This is a technology that uses thermal spraying metal materials or welding metals to produce the whole part. The spraying process used is mainly arc spraying. This process can obtain parts of any shape. Therefore, some people even think that rapid prototyping will lead to the next material revolution. Sulzermetco has done a lot of research on this technology and has been applied in actual production. In the past three years, they have used this technology to make more than 100 horizontal turbine buckets for customers.? Nottingham, UK, has improved the accuracy of experimental results for the development of spray forming. Ltd. has obtained a patent for rapid tooling processing, which is used to manufacture steel models and production tools. This method is by spraying molten metal onto an aluminum refractory sample with low cost and accurate size. In the past two years, the tooling made by this method has been extensively tested by several large companies, and the plastic mold and metal forming process have shown good performance. The first batch of production tooling was manufactured in Britain in september1996. These tooling are expected to produce more than 1million parts. At a recent demonstration meeting of this process, the whole process of using three spray guns installed on an industrial robot to spray 19mm thick steel coating, then installing aluminum pipes, and then continuing to spray metal coating on them until the required thickness, and finally melting and flowing out the lead to form a smooth water-cooling channel was demonstrated

3.3 other application fields

the application field of thermal spraying covers almost all industrial production departments. In addition to the previously introduced applications in the automobile and mold industry and the well-known applications in aviation, navigation, textile, machinery, etc., it has also rapidly expanded to other fields. For example, spray aluminum on the outside of the oil pipeline welds, and spray wear-resistant coatings on the oil equipment valves, overflow blockers and drilling pin tools; The artificial joint was sprayed with carbonylapatite to enhance the biocompatibility between titanium matrix and organism; Ceramic coating is sprayed on the printing roller, and then laser engraving lines are used to send the ink from the ink pool to the printing room. Steel is sprayed on the aluminum valve lifting rod cap of the air conditioning compressor to achieve the purpose of weight reduction and wear resistance, etc. It can be predicted that with the continuous research on thermal spraying technology and the continuous improvement of people's requirements for material properties, thermal spraying technology will be further developed

4 conclusion

with the continuous progress of science and technology, other coating manufacturing technologies, such as magnetron sputtering, chemical vapor deposition, physical vapor deposition and laser spraying, have also made great progress. The coatings produced by these technologies have exceeded the thermal spraying coatings in some properties. Therefore, in order to maintain the vitality of thermal spraying technology, it is necessary to strengthen the basic research of thermal spraying technology and develop new spraying methods and application fields. At present, great progress has been made in this field abroad, while little progress has been made in the development work in China. The thermal spraying technology basically stays at the original level, which also limits the expansion of the application field of coatings. Therefore, strengthening basic research and developing new application fields are our main work in the future, and also the life of thermal spraying technology

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