Thermal spraying technology can be used in the maintenance of equipment to repair the old and make end-of-life parts "back from the dead"; can also be strengthened in the manufacture of new products and pre-protection, so that it "life extension". Can save energy, save materials, improve efficiency, reduce costs, especially suitable for China's national conditions, in line with China's current economic policy. It is an important practical technology of energy saving and emission reduction, low energy consumption and high efficiency advocated by our country.
1.History of Thermal Spraying
Thermal spraying technology has a history of more than one hundred years since the original molten metal spraying device was completed in 1910 by Dr M.U. Schoop of Switzerland.
Initially, thermal spraying was mainly used for spraying decorative coatings, with oxygen-acetylene flame or arc spraying aluminium and zinc wires. In the last century, 30 ~ 40 years, with the flame and arc wire spraying equipment and flame powder spray gun, thermal spraying technology from the initial spraying decorative coatings for the development of steel wire repair of mechanical parts, spraying aluminium or zinc as a corrosion-resistant coatings for steel structures.
Explosive spraying technology in the 1950s and then the successful development of plasma spraying technology, thermal spraying technology in aerospace and other fields have been widely used. During the same period of time developed a successful self-melting alloy powder, so that through the coating remelting process to eliminate pores in the coating, and the substrate to achieve metallurgical bonding has become possible, expanding the application of thermal spraying technology.
In the early 80's, the development of successful supersonic flame spraying technology, in the early 90's has been widely used, so that the application of WC-Co cemented carbide coating from the aerospace field to a variety of industrial fields. Power up to 200kW high-energy plasma spraying technology, supersonic plasma spraying technology, and axial powder feeding plasma spraying technology, especially the emergence of high-efficiency supersonic plasma spraying technology, for the further and effective use of thermal spraying technology in various industrial fields to provide a powerful means.
China's thermal spraying technology began in the 1950s, when Wu Jianchun and others in Shanghai set up the first domestic specialised spraying plant, the development of oxyacetylene flame wire spraying and electrospray device, and foreign metal spraying business.
In the 1960s, a few military units began to study plasma spraying technology (such as the Beijing Institute of Aeronautical Technology, Aerospace Corporation Rocket Technology Research Institute 703, aviation sector 410, 420, 430 plants and other units), began to be applied in China's military sector.
To the mid to late 70s appeared many varieties of oxyacetylene flame metal powder spraying (fusion) equipment and a variety of nickel, iron, cobalt-based self-melting alloy powder and composite powder coating materials, to the rapid forward development of thermal spraying technology has laid a solid foundation. Thermal spraying materials are thermal spraying technology, "cooking food", the increase in the variety of materials and performance improvement will directly improve the quality of the coating.
It is worth mentioning that Beijing General Research Institute of Mining and Metallurgy (BGRIMM) and other units have developed exothermic spraying materials such as nickel-coated aluminum and a variety of composite powder materials at this stage, which broadened the scope of application of coatings and brought vitality to China's thermal spraying technology, and this stage can be said to be the primary stage of development of China's thermal spraying technology, although there has been a certain degree of progress at this stage, but the progress has been slow in general, and it is only in the mid-to-late 1970s It was only in the mid-late 70's and early 80's that it gained faster development. Especially after the former State Economic Commission took the thermal spraying technology as the national key promotion project, the development speed was faster and achieved remarkable economic benefits.
From 21 to 27 October 1981 by the State Economic Commission, the State Science and Technology Commission hosted the first National Thermal Spraying Conference in Beijing, where it was announced that the National Thermal Spraying Collaborative Group was set up under the leadership of the State Economic Commission and attached to the General Research Institute of Mining and Metallurgy in Beijing. The group contacted the State Economic and Trade Commission, and contacted the Science and Technology Department of the Economic Commission of each province, city and autonomous region, and the Science and Technology Bureau of each department, as well as large and medium-sized enterprises, colleges and universities, scientific research institutions, etc., which formed a network system for promoting and applying thermal spraying technology across regions, industries and departments.
In 1991, the Wuhan Institute of Materials Protection of the Ministry of Mechanical and Electrical Engineering applied to the Ministry of Civil Affairs for the establishment of the China Surface Engineering Association Thermal Spraying Professional Committee, which is now attached to the China Agricultural and Mechanical Institute. The successive establishment of these two spraying industry organizations has greatly promoted the development of China's thermal spraying technology, practitioners from dozens of units in the early 1980s to the present has developed to nearly 2,000 professional spraying manufacturers, it can be said that this stage of China's thermal spraying technology development to a prosperous stage, the scope of application is gradually expanding.
In machinery, metallurgy, petrochemical, electric power, railway, paper, textile, medical and health, military and national defence and many other sectors of the national economy has been widely used. In the 1990s to a new stage of development, the development of this stage is characterized by: equipment to high-energy, high enthalpy, high-speed direction; materials to the series, standardization, commercialization direction to ensure that multi-functional high-quality coating needs; process technology to the direction of mechanization, automation, such as computer control, mechanical operation, and so on;
The promotion and application focuses on:
(1) To grasp the main problems in the promotion and application. Various industries and regions to grasp a large number of typical pieces of widespread application, such as: metallurgical industry, blast furnace wind mouth, continuous casting machine rolls, furnace rolls, power industry, the boiler four tubes, the coal industry, scraper machine in the middle of the slot, the hydraulic strut, the machinery industry valves, the paper industry, the drying cylinder, the textile industry, roller, over the silk wheel, the petroleum industry, the drilling rod, the plunger, the bottom of the sugar industry, the face of the comb, and so on.
(2) Grasp the maintenance and strengthening of large-scale key equipment, such as: metallurgical industry, 10,000 tonnes of oil press plunger, ironworks, blast furnace big material bell, high-temperature furnace rolls of Baosteel, Dushanzi refinery's gas turbine blades as well as the carbon dioxide compressor cylinders of the Weifang Soda Ash Plant, the value of these equipments are in the millions of dollars or more, or even every day to create a value of one million dollars or more, the restoration of the significance of the significant.
(3) Grasp the maintenance and strengthening of imported parts and components. In recent years, many departments have imported more equipment, the use of thermal spray technology to repair and strengthen both the production of urgent needs and can save a lot of foreign exchange.
4) Carry out socialist collaboration, the major equipment to take expert consultation, collaborative research. Such as Baosteel introduction of German 6500m3 induced draft fan shaft, Beijing Dongfanghong Oil Refinery introduced Japan's key equipment, Wuhan Iron and Steel 1.7m mill, Southwest Aluminium Processing Plant, known as the "national treasure" 10,000 tonnes of oil press plunger, Guizhou Aluminium Plant, carbon electrode extrusion forming mouth and other large-scale imports of key equipment have been organised to expert consultation, collaborative efforts to address the problem, and successful Repair, not only solved the enterprise production difficulties, but also for the country to save a lot of foreign exchange, its economic and social benefits.
Since entering the 21st century, China's thermal spraying technology has developed rapidly, equipment and materials after decades of independent development and the introduction of advanced technology from abroad, at present, China has been able to develop and produce vacuum plasma, atmospheric plasma (high-energy plasma), explosion spraying, plasma cladding, arc spraying, and flame powder spraying and flame wire spraying equipment, production of metal powder (Ni, Co, Fe-based), a variety of composite powders, ceramics, metal ceramic powder, various alloy wire and powder core wire, etc., basically can meet the needs of the domestic thermal spraying market. Fe-based), a variety of composite powders, ceramics, metal ceramic powder, various alloy wires and powder core wires, etc., basically to meet the needs of the domestic thermal spray market. Some varieties have reached the international advanced level.
The emergence of a variety of new coating materials, further expanding the scope of flame spraying technology. New flame spraying gun can spray a variety of metals, ceramics, metal and ceramic composite materials and a variety of plastic powder material coating. Although plasma and HVOF/HVAF supersonic and explosive spraying coatings are superior to conventional flame spraying and arc spraying, but due to the large investment, complex operation and control system, bulky equipment, cannot be on-site construction and other shortcomings, the scope of application is greatly restricted in the anticorrosion and maintenance market is difficult to promote popularity.
New flame spraying equipment and technology and supersonic arc spraying equipment and technology in the industrial anti-corrosion and parts repair market will always be the main technical force. It is particularly worth pointing out that arc spraying is both an ancient spraying technology and a brand new spraying technology. The technology arose in the early 20th century, at that time, due to the limitations of the performance of the spraying equipment, can only spray some low melting point of the metal material to prevent the surface corrosion of steel. With the development and improvement of thermal spraying technology, arc spraying technology is also progressing. By the middle of the 20th century, arc spraying technology has occupied an important position. Later, due to the emergence of plasma, explosion and other spraying technologies, which can meet the needs of aviation, spaceflight, rockets and other cutting-edge technologies, the development of arc spraying technology has been limited to some extent.
Into the 90's, due to the Beijing Institute of Technology successfully developed powder core wire material, to the arc spraying technology has brought life. Powder core wire material not only to overcome the difficulties of high alloy composition is difficult to pull the wire, but also to make some non-conductive particles of material (ceramics and carbide) filled with powder core wire material, in the arc spraying on the application, such as Al2O3, TiO2, TiB2 and Cr3C2, etc.. Due to the powder core wire material composition is easy to adjust, short production cycle, convenient material selection, lower cost and other advantages, thus promoting the development of arc spraying technology.
In recent years the emergence of high alloy, zinc-aluminum alloy (85/15) of the wire material, so that the arc spraying technology to develop faster. With the arc spraying material varieties continue to increase, performance continues to improve, arc spraying equipment and to precision, automation direction. Such as supersonic arc spraying, high-speed pulse arc spraying, composite arc spraying, protective gas arc spraying and vacuum arc spraying, etc., the emergence of these new arc spraying process technology, greatly improving the spraying efficiency, improve the quality of the coating, and broaden the application of arc spraying technology. Currently this technology is very popular, in many sectors of the national economy plays an important role, so that the ancient arc spraying technology has been rejuvenated.
Thermal spraying equipment and materials After decades of independent development and the introduction and reference to foreign advanced technology, at present, China has been able to develop and produce vacuum plasma, atmospheric plasma, explosion spraying, plasma cladding, arc spraying, flame powder spraying, flame wire spraying equipment, production of metal powders (Ni, Co, Fe-based, totaling about 300t/year), ceramics, metal ceramic powder (Al2O3 , Al2O3+TiO2, Cr2O3, WC-Co, etc., totaling about 200t/year), wire (Al, Zn, Cu, stainless steel, etc., totaling about 1000t/year).
Although the overall equipment has not yet reached the world's advanced level, and there are still many improvements in materials, China has become one of the few countries in the world that can be self-sufficient in thermal spraying equipment and materials, which basically meets the needs of the thermal spraying industry. At the same time, about 10 per cent of the equipment and materials still need to be imported.
2.Application status of thermal spraying technology
Thermal spraying technology as a technology involving a wide range of processing technology is relatively simple and flexible, a wide range of applications, economic benefits of the new modern processing technology, which can make the surface with wear-resistant, corrosion-resistant, adiabatic, heat-resistant, electrically conductive, insulating, anti-erosion, oxidation-resistant, friction-reducing, lubrication, radiation protection and other functions. Not only can be used for mechanical parts of the repair and surface strengthening, but also can be used for manufacturing.
Due to the wide range of choice of spraying materials, not subject to the overall material alloying restrictions, can be more convenient to obtain super-hard alloys, a variety of ceramic or metal-ceramic coatings as well as a variety of functional coatings, and coatings relative to the overall high-level material for the amount of material is less than the overall improvement of the material is undoubtedly much more economical, and therefore can be boldly used in the use of valuable materials, its cost will not increase a lot, while the surface performance of the material can be obtained The cost will not increase much, but the surface performance of the material can be greatly improved, the service life of the parts repaired by thermal spraying can generally reach or even several times more than the new product.
3.Thermal spraying technology future development trend and outlook
From the future development trend, the research of thermal spraying system engineering will receive more and more attention. At present, many countries have strengthened the research on thermal spray system engineering, that is, starting from the failure analysis, through the surface pretreatment, spraying equipment, spraying materials and spraying process optimisation, to develop a thermal spraying implementation process plan. In the process of development, thermal spray technology and other disciplines cross-pollinate to form a new surface treatment process. Future thermal spraying technology may be developed in the following aspects:
(1) in the choice of coating materials: flame spraying technology, plasma spraying technology and supersonic flame spraying technology used in the powder-type coating materials will also be the mainstream of market demand, arc spraying technology and cold spraying technology spraying material selection, although there are certain limitations, but the future with the progress of the process and updating, but also will be further expanded.
(2) in the combination strength of the coating and the substrate: cold spraying, supersonic flame spraying, supersonic plasma spraying and LPPS-TF coating and other relatively high strength of the combination with the substrate, will play a greater role.
(3) In the research of basic theory: thermal spraying technology is a marginal discipline involving multiple disciplines and strong intersectionality. It is affected by high temperature, high speed and mechanical non-uniformity and other parametric factors, thermal spray technology basic theory research faces great difficulties, the basic theory of the research is particularly important.
(4) In the research and development of new spraying materials: the general development trend of thermal spraying materials is: the composite and low impurity coating composition, the structure of the ultra-micro and nano, and nano-structured composite, multi-alloys and other new materials for the development of research hot spots.
(5) in the spraying process and equipment research and development: to improve the coating quality and expand the key to the sprayed material is to improve the energy and speed of the sprayed particles, therefore, the improvement and development of thermal spraying process and equipment should be developed in the direction of high-energy and high-speed development.
(6) in the expansion of new applications: thermal spray technology and other disciplines with each other penetration, interlinked characteristics, the use of this feature of the continuous development of new thermal spray technology, and the development of new applications of thermal spray technology. The combination of thermal spray technology and other related technologies is an effective way to explore and develop new applications of thermal spray technology.