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Introduction to Thermal Spray Technology
Time:
2022-02-24 15:52
Overview Thermal spraying is a repair and pre-protection technology. With the development and improvement of modern technology, the performance requirements for industrial production equipment and mechanical parts are getting higher and higher. The overall casting or forging of relatively expensive metals, such as titanium, nickel, cobalt, tungsten, zirconium, etc., is very expensive and the casting, forging and welding methods are difficult, so on the working surface of ordinary materials, a special coating is sprayed. layer, so that it can achieve: anti-corrosion, wear-resistant, anti-wear, high temperature resistance, anti-oxidation, heat insulation, insulation, electrical conductivity, anti-microwave radiation and a series of functions, so that it can achieve the purpose of saving materials and saving energy.
Definition Thermal spraying refers to a spraying device that uses oxygen-acetylene flame, electric arc, plasma arc, explosion wave, etc. to provide different heat sources to generate high temperature and high pressure flame flow or supersonic flame flow, and the materials to be coated such as various metals, ceramics , Metal-ceramic composite materials, solid-state spraying materials of various plastic powders, instantaneously heated to a plastic state or molten state, and sprayed at high speed to the surface of pretreated (clean and rough) parts to form a surface processing method. We call the special working surface "coating" and the working method of making the coating "thermal spraying", which is a general term for spraying and spray welding using various heat sources.
History Thermal coating technology was first invented by Dr. Pu in 1910, named at that time: "metal spraying"
In 1943, the American METCO company published the "Metal Spraying" manual for the first time.
In 1959, the American METCO company published the manual "Flame Spray" for the seventh time.
On September 10-14, 1973, the 7th International Conference on Thermal Spraying was held in London, England, renamed "Metal Spraying"
From September 27 to October 1, 1979, the 8th International Thermal Spraying Conference was held in Miami, a well-known resort in Florida, USA, and the term "thermal spraying" was adopted. This is the origin of the term "thermal spraying".
my country's thermal spraying technology began in the 1950s. At that time, Wu Jianchun and Zhang Guanbao established the first domestic professional spraying factory in Shanghai to develop oxyacetylene flame spray and EFI devices, and to carry out metal spraying business. my country's thermal spraying technology started early, and wire arc spraying was developed in the 1950s; in the 1960s, some military departments began to study plasma spraying. High (40-80MPa) and porosity less than 5%, it is widely used in my country's military industry; in the 1970s, spraying equipment and materials with a complete range of varieties and models appeared, but overall progress was slow, only in recent years. obtained rapid development. Especially after the former State Economic Commission took thermal spraying as a national key promotion project, the development speed was faster and significant economic benefits were achieved. From October 21 to 27, 1981, the first National Thermal Spraying Conference was held in Beijing under the auspices of the State Economic Commission and the State Science and Technology Commission. At the meeting, it was announced that under the leadership of the State Economic Commission, the "National Thermal Spraying Collaboration Group" had been established, affiliated with the Beijing Mining and Metallurgical Research Director. The institute, the cooperation group contacted the State Economic and Trade Commission, and contacted the science and technology bureaus of the science and technology departments of various provinces, municipalities and autonomous regions, as well as large and medium-sized enterprises, colleges and universities, scientific research units, etc. to form cross-regional, cross-industry, cross-department promotion and application heat The spraying technology network system has more than 400 group members. In 1991, the Wuhan Institute of Materials Protection of the Ministry of Mechanical and Electrical Engineering applied to the Ministry of Civil Affairs to establish the "China Surface Engineering Association Thermal Spray Professional Committee", which is an industry organization voluntarily formed by enterprises and related units engaged in surface engineering across the country. It is now affiliated with Beijing Agricultural Machinery College. It has developed more than 400 group members and more than 150 overseas members.
Thermal spraying (welding) has the following advantages over electroplating hard chromium
(1) For the same production capacity, the capital cost and energy cost of hard chrome plating and hot dip plating are much higher.
(2) For the same production capacity, the site required for thermal spraying is only a fraction of that of hard chrome plating and hot dip plating.
(3) The price of chromium is more expensive than other materials, and the market supply is still very short. Thermal spraying uses a wide range of materials, and many materials are more wear-resistant than hard chromium.
(4) The waste liquid treatment cost of hard chrome plating is getting higher and higher, and thermal spraying has no pollution problem.
(5) Hard chrome plating can only be used for conductive materials and workpieces that can be placed in the plating tank, while thermal sprayed workpieces are not limited by material and geometry, and are almost suitable for surface spraying of any large metal and non-metallic structural parts. Partial spraying of various large workpieces can also be performed, both indoor processing and field spraying operations. It can spray various metals, ceramics, composite materials of metal and ceramics with different properties, and can also spray coatings of various plastic powder materials.
(6) The thermal spray coating can not only restore the size of all wear and out-of-tolerance mechanical parts, but also make the surface of any metal and non-metallic materials composite, surface modified, and surface strengthened to achieve: anti-corrosion, wear-resistant, wear-reducing, anti-corrosion A series of various functions such as high temperature, anti-oxidation, heat insulation, insulation, conduction, and microwave radiation resistance make it achieve the purpose of saving materials and energy. In this way, all kinds of mechanical equipment and vehicle parts can be "longevity and longevity", and the scrapped parts can be "revived". The bonding strength of the coating and the substrate is ≥6.5～10kg/mm2, the bonding strength of the spray welding layer and the substrate is ≥45kg/mm2, the hardness of the coating is from 15 to 69HRC, the roughness of the coating is Rz25～100um, and the thickness of the coating is 0.3～15mm. The roughness of the layer can be restored to Ra0.8~0.2um after machining, which can meet different technical requirements.
(7) Compared with electroplating or brush plating process, thermal spray coating has a high deposition rate, and the operating time is only a few percent of electroplating.
(8) Spray precious metals and functional materials on the surface of common material substrates, or choose high-quality materials to spray key parts of products. For example, chemical stainless steel reaction kettles can be made of carbon steel, and working surfaces are sprayed with stainless steel materials, which can greatly save your equipment cost and improve products. quality and extended service life.
(9) The parts and components of various large-scale key equipment and parts imported from abroad are not replaced with spare parts, or parts that are difficult to manufacture and expensive, using thermal spraying to repair is simple, reliable, fast, and can reduce the damage caused to the factory due to shutdowns. Economic losses.
(10) The technology has the characteristics of simple equipment, low investment, low cost, quick effect, high benefit and wide application.
In recent years, ceramic and plastic materials in thermal spraying materials have received attention and corresponding flame spraying devices have been developed; it should be particularly pointed out that the earliest flame spraying technology has not been eliminated in the rapidly developing thermal spraying technology. Instead, it continues to develop in spraying to adapt to various materials through continuous improvement. The emergence of various new spraying materials has further expanded the scope of application of flame spraying technology. The new flame spray gun can not only spray various metals, ceramics, composite materials of metal and ceramics, and various plastic powder materials. Although the coatings of plasma and HVOF/HVAF supersonic and explosive spraying are superior to conventional flame spraying, the application scope is greatly limited due to the large investment, complex operation control system, heavy equipment, and inability to perform on-site construction. It is difficult to popularize and popularize. New flame spraying equipment and technology and supersonic arc spraying equipment and technology will always be the main technical force in the industrial anti-corrosion and parts repair market.
The development status of thermal spraying in my country
The world's thermal spraying has a history of 100 years, and China's thermal spraying has a history of nearly 50 years. Especially in the past two decades, China's thermal spraying has made great progress and development. The following is a brief introduction to the overall level and status, equipment and materials, applications, scientific research and development.
1. Overall level and status According to incomplete statistics, during the "Eighth Five-Year Plan" period (1991-1995 including 1996), the total output value of China's thermal spraying industry was about 300 million yuan (including thermal spraying equipment, materials, construction and technology). services, auxiliary equipment materials, etc.). In 1996, the total output value of my country's national economy was about 7.5 trillion yuan (about 910 billion US dollars), and the output value of thermal spraying accounted for about 0.39/10000>.
According to the statistics of the association, there are about 3,000 thermal spraying practitioners in the country (excluding temporary workers in the construction team), and 300 to 350 units engaged in thermal spraying work, including thermal spraying equipment, materials, auxiliary machines, auxiliary materials production plants, thermal spraying Construction and technical service units, as well as scientific research, teaching, development units and trading companies engaged in thermal spraying.
Thermal spraying enterprises are still dominated by small units (<30 persons), accounting for more than 90% of the total. The per capita output value of the thermal spraying industry is about 100,000 yuan per person per year, which is a leader in the machinery industry (superior level).
According to relevant foreign materials, in recent years, the total output value of thermal spraying in the United States is about 2 billion US dollars, and Japan is 80 billion yen, accounting for 3.6/10000 and 2.3/10000 of its gross national economic output (GNP) respectively. The ratio of thermal spraying production value to GNP weight is an important symbol of whether the country's thermal spraying is developed or not. This ratio in China is only 11% of that of the United States and 17% of that of Japan. This shows that China's thermal spraying is still in the development stage, far from reaching the mature and saturated stage. Because of this, thermal spraying has a vast market in China, with many opportunities and promising development prospects.
2. After decades of independent development and introduction of thermal spraying equipment and materials, and drawing on foreign advanced technology, at present, China has been able to develop and produce vacuum plasma, atmospheric plasma, explosive spraying, plasma surfacing, arc spraying, flame powder spraying, Flame wire spraying equipment, producing metal powder (Ni, Co, Fe based, total about 300t/year), ceramic, cermet powder (Al2O3, Al2O3+TiO2, Cr2O3, WC-Co, etc., total about 200t/year), wire Materials (Al, Zn, Cu, stainless steel, etc., total about 1000t/year). Although the overall level of equipment is still not high, and there are still some quality problems in materials, China has become one of the few countries in the world that can be self-sufficient in thermal spray equipment and materials, basically meeting the needs of the thermal spray industry. . Meanwhile, about 10% of equipment and materials still need to be imported.
3. Application of thermal spraying technology At present, thermal spraying technology has been widely used in China, the main application fields are aviation, aerospace, steel, petrochemical, steel structure anticorrosion, machinery, light industry, textile, paper, energy, shipbuilding etc., the total output value is about 200 million yuan / year. my country's thermal spray application has the following characteristics:
(1) It has a wide range of applications and has a very high level in some fields, such as aero-engines (cooperation with Boeing), bottom rolls of annealing furnaces, galvanized guide rolls (steel industry), valves (petrochemical industry), wire drawing guide rolls, towers Wheels, wire drawing rings, etc. (textile industry), high-grade glass molds (light industry), valves (automotive industry), etc.
(2) A wide range of techniques and materials are used. Almost all thermal spraying techniques and materials currently used internationally are used in China, such as vacuum plasma spraying, atmospheric plasma spraying, explosive spraying, supersonic flame spraying, arc spraying, flame powder spraying, plasma spraying Surfacing, laser remelting, vacuum (protective atmosphere) remelting, etc.
⑶ The enterprises engaged in thermal spray application (Job Shop) are mainly small and medium-sized enterprises (<30 people), the number of people accounts for 2/3 of the total, and the output value accounts for more than 75% of the total output value. Joint-stock cooperative enterprises, private enterprises and collective enterprises account for a considerable proportion, and joint ventures and sole proprietorships have begun to appear.
⑷The use of thermal spraying as a maintenance method for equipment and components is relatively developed. For medium and small thermal spraying enterprises, more than half of the work is for repair.
⑸Relevant professional research offices, teaching and research offices of scientific research institutes, colleges and universities, such as welding (more than half), materials, surface processing and other majors, actively enter the domestic thermal spraying market. The main technical force of thermal spraying in my country is also in the above-mentioned units.
At present, the main problems in application are that the scale is small, the level is uneven, and there is a lack of unified management and standards, and it is impossible to form leading thermal spraying enterprises with influence at home and abroad (such as Tocal in Japan, Praxair in the United States, and Praxair in France). SNMI, etc.).