Thermal sprayed ceramic powders mainly refer to oxide, carbide, nitride, boride and silicide powders, and commonly used thermal sprayed ceramic powders mainly include Al2O3, ZrO2, TiO2, WC and Cr2O3. Ceramic coating has outstanding advantages such as high hardness, good wear resistance and heat resistance. Plasma spraying can solve the problem of high melting point of materials. Almost all ceramic materials can be sprayed, and some ceramic coatings can be obtained by flame spraying.
2, thermal spraying plastic
Spraying plastic on metal and nonmetal surfaces has the characteristics of beauty and corrosion resistance. If the hard phase is added to the plastic powder, the coating can also have certain wear resistance. The polyethylene coating can resist the temperature of 250℃, the corrosion of dilute sulfuric acid and dilute hydrochloric acid at room temperature, the corrosion of concentrated hydrochloric acid, hydrofluoric acid and phosphoric acid, and has insulation and self-lubricating properties. Commonly used thermal spraying plastics include nylon and epoxy resin.
Thermal spraying technology is a new technology to strengthen and protect the surface of materials, which plays an important role in surface modification technology. This technology started in China in the 1950s and took shape in the late 1970s. At present, it has developed rapidly in equipment, materials, technology and scientific research, and has become an important part of surface technology. Its development trend is: the equipment (spray gun) develops to high energy, high enthalpy and high speed; Materials are developing in the direction of serialization, standardization and commercialization to ensure the demand of multifunctional and high-quality coatings; The process is developing towards mechanization and automation, such as computer control and manipulator operation. Nowadays, thermal spraying technology has been widely used in various fields of national economy, and its popularization and application prospects are broad.
First, the new development of thermal spraying equipment
Recently, China has accelerated the pace of equipment development and production, and has now formed a complete scientific research and production system. More than 20 units have been engaged in the development and production of thermal spraying equipment, which can produce various types of oxyacetylene flame spraying equipment and spray melting equipment. New arc spraying equipment: complete plasma spraying equipment and spray welding equipment; All kinds of special machine tools; Thermal spraying air purification equipment, pretreatment and post-treatment equipment. The variety of single machine has reached more than 100. The development and production of these products ensure the development of thermal spraying technology, among which the following are prominent:
1, high-speed flame spraying device At present, high-speed flame spraying devices (HVOF) and (HVAF) and supersonic plasma spraying equipment imported from abroad are characterized by high particle flying speed, high bonding strength between coating and substrate and low porosity. These equipments have played an important role in aerospace, aviation, metallurgy, chemical industry and power industry. However, imported equipment is expensive, and fuels (propane and propylene) are not easy to popularize. In view of the above situation, combined with China's national conditions, Sichuan Great Wall Spraying Technology Research Institute has successfully developed a high-speed spray gun with oxyacetylene flame as the heat source. Due to the limitation of acetylene pressure, although the flying speed of particles is not supersonic at present, it is 4 ~ 5 times higher than that of conventional oxyacetylene flame powder spraying and 1 ~ 2 times higher than that of atmospheric plasma spraying. Sprayable metal and alloy powder materials include al2o 3-TiO 2-Co-WC and thermoplastic powder materials such as polyethylene and nylon. In addition, Xi Jiaotong University and other units have successfully developed a high-speed flame (HVOF) spraying device and started to apply it.
2. High-speed arc spraying equipment Because arc spraying has the advantages of high bonding strength, low energy consumption and low cost, this kind of equipment has been paid more and more attention in China in recent years and has been actively adopted, especially in large-scale long-term protection projects of steel structures and thermal corrosion of boiler tubes in power stations. On the basis of ordinary arc spraying, the Armored Forces Engineering College of Industry-University-Research Equipment Engineering Center and the Second Artillery Engineering College of Xi 'an recently developed a high-speed arc spraying gun. The air velocity is over 600m/s, and its coating bonding strength, porosity and other indicators are better than ordinary arc spraying, which is being further promoted and applied.
3. Oxygen-acetylene flame metal powder spraying device Oxygen-acetylene flame metal powder spraying technology is widely used in China at present, and almost all large enterprises regard it as a means to repair the old and make use of the waste. Shanghai, Jiangsu, Wuhan, Sichuan and other places have developed and produced various types of spraying and spray welding guns, which have been widely used in spraying units. Shanghai Welding, Cutting and Spraying Machinery Factory recently improved the original QHT-7/h flame spray gun, using two sets of nozzles and two heat sources: oxygen? Acetylene flame and oxygen? Liquefied petroleum gas (domestic bottled). Using bottled liquefied petroleum gas as combustible gas can greatly reduce the cost and bring greater convenience to spraying operation.
4. Aerospace Company 62 1 Research Institute began to develop gas explosion spraying device in 1960s, and now it has installed a complete gas explosion spraying device, spraying many high-density and high-quality coatings for aerospace, aviation and other military departments. The equipment has reached or approached the level of similar products abroad. In recent years, Beijing Great Wall Titanium Industry Co., Ltd. cooperated with Ukraine to establish a Sino-foreign joint venture Beijing Titanium New Materials Co., Ltd., and introduced the manufacturing technology of explosive spraying equipment from Ukraine. At present, it has been able to produce explosive spraying equipment with computer-controlled three-dimensional walking mechanism, and has been sold to the United States and Taiwan Province Province.
5. Oxygen-acetylene flame plastic powder spraying device In recent years, a flat and smooth plastic coating can be obtained by using oxygen-acetylene flame and boiling powder feeding method to spray plastic powder with a special spray gun. This provides a new method for plastic coating of large workpieces, various storage tanks and pipelines. For this reason, Shenyang Thermal Spraying Factory, Wuhan Institute of Material Protection and Academy of Armored Forces Engineering have successively developed different types of flame plastic powder spraying devices, and carried out large-scale construction, and achieved good results. Among them, FSP-ⅱ plastic powder flame spray gun developed by Wuhan Institute of Material Protection has reached the level of I-SPRAY-JET spray gun of UTP Company.
6. New plasma spray gun Tsinghua University and other units have successfully developed QZNI high-energy inner hole plasma spray gun. The power of the gun can reach 75kW, and the thermal efficiency, average enthalpy of plasma jet, jet temperature, spray gun power and powder deposition rate all reach the level of Metco large bore spray gun. Recently, Beijing Entropy Cole Institute of Applied Technology has successfully developed BT-G 1, BT-G2, BT-G3 new plasma spray guns and BT-NI large-caliber spray guns. At the same time, BT-F 1 double-barrel superfine powder feeder and physical cooling system were successfully developed, which raised the level of domestic plasma spraying equipment to a new level and shortened the gap with foreign equipment.
7. New sandblasting equipment appeared in Beijing, Shanghai and other places. Recently, small recyclable sandblasting equipment and large environmentally friendly sandblasting equipment were successfully developed, which greatly improved working conditions and reduced environmental pollution, and played a positive role in promoting the development of thermal spraying technology in China.
Second, the new development of thermal spraying materials
People refer to thermal spraying materials as thermal spraying "particles". The performance, quality and variety of spraying materials are one of the important standards to measure the quality of coatings, and also the key factors affecting economic benefits. Although China's thermal spraying materials started late, they have developed quite rapidly since the 1970s. At present, more than 40 manufacturers have produced nearly 100 varieties, which can basically meet the domestic demand. The thermal spraying materials developed and produced by these scientific research and production units can be roughly divided into (recent new varieties):
1. Powder materials The yttria partially stabilized zirconia thermal gap coating material and the Ni-Cr-Al-Co yttria primer material with high temperature oxidation resistance developed by Beijing Research Institute of Mining and Metallurgy have been widely used in aero-engines. The thermal barrier coating of air sprayed zirconia developed by Chongqing Institute of Instrument Materials also meets the requirements. Nickel-chromium-chromium carbide composite powder material successfully developed by Beijing Institute of Mining and Metallurgy has been used as a high-temperature corrosion-resistant and wear-resistant coating on water wall tubes of many power plants, and the application effect is good. Alumina and alumina-titanium oxide powder successfully developed by Shenyang Grinding Wheel Factory have been widely used in textile machinery and metallurgical equipment, and the application of CrB2 powder successfully developed by Shenyang Grinding Wheel Factory in roller and bottom roller of continuous caster has achieved initial results. XTiC+yCr3C2+zNi composite ceramic material developed by Beijing Iron and Steel Research Institute by self-propagating method is suitable for plasma spraying. The hardness of the coating can reach 54HRC and can withstand the high temperature of 800℃. Co-WC alloy powder produced by Zigong cemented carbide factory has been widely used. The molybdenum-based alloy powder successfully developed in Sichuan and other places has been successfully applied to the spraying of automobile synchronous rings.
2. Wire Rod Beijing University of Technology has successfully developed and mass-produced wear-resistant and corrosion-resistant thermal spraying metal core wires containing rare earth elements. Typical welding wires are 7Cr 13, 3Cr 13 and low carbon martensite, which are suitable for arc and flame spraying. The average bonding strength of the coating is 50MPa, the porosity is less than 7%, and the average hardness of the coating is 40 ~ 50 HRC. Recently, Beijing Nonferrous Metals Research Institute has successfully developed Ni-Al alloy wire for arc spraying primer and Ni-Cr alloy wire for arc spraying, which are used for high temperature corrosion and abrasive wear resistance (equivalent to 45 CT). American TAFA Company). Academy of Armored Forces Engineering developed SL30 Ni-Cr alloy wire coating+organic metal composite coating, which successfully replaced the president of 45CT TAFA Company. Shenyang University of Technology has successfully developed iron-based alloy arc spraying back wire to replace aluminum bronze wire. Shanghai, Beijing, Zhejiang, Sichuan and other places have developed and produced Fe-Cr-Al wire, Al-Mg alloy wire, Zn-Al alloy wire and Babbitt alloy wire.
3. Plastic Powder On the basis of developing polyethylene, polypropylene, nylon and other powders for oxyacetylene flame spraying, the relevant units have recently successfully developed chlorinated polyether and modified fluoroplastic powder, which has broadened the application scope of plastic coatings and has been applied in anti-corrosion projects.
4. Spraying materials for ceramic rods imported from the United States have been successfully applied to textile machinery, and domestic trial-produced ceramic rods and flexible ceramic wires have come out and will be put on the market soon. The above materials are all new varieties in China recently. The development and production of these materials have created favorable conditions for the development of thermal spraying technology in China.
Third, the new development of thermal spraying technology
Thermal spraying technology has been widely used in China at present, and its development trends and characteristics in recent years are as follows:
(1) Large-area long-term protection technology has been widely used. For steel structures exposed to outdoor atmosphere for a long time, spraying aluminum, zinc and their alloys instead of traditional painting methods and implementing cathodic protection for long-term atmospheric corrosion protection have developed rapidly in recent years. Such as TV towers, bridges, highway facilities, sluices, microwave towers, high-voltage transmission towers, underground cable supports, buoy drums, shafts and other large-scale projects, all adopt the method of spraying aluminum, zinc and their alloys for anticorrosion. At present, there are dozens of professional spraying factories engaged in this work in China, with an annual spraying area of more than several million square meters. This technology has been widely used not only in China, but also in foreign aid projects.
(2) Using thermal spraying technology to repair and strengthen the localization of large-scale key equipment and imported parts. In recent years, there have been many successful application examples in this field, such as: one meter seven rolling mill, high-speed fan rotor, large extruder plunger, large gear, electrode extrusion nozzle, high-power automobile crankshaft and so on. To carry out these tasks, first, to solve the urgent needs of production; The second is to save a lot of foreign exchange.
(3) Application of Supersonic Flame Spraying Technology With the development and perfection of thermal spraying technology in China, the requirements for the quality of sprayed coatings are getting higher and higher. In recent years, the high-velocity gas (HVOF) method developed by the United States and other countries is a new process for preparing high-quality coatings. Due to the advantages of supersonic flame spraying, nearly a dozen equipments have been imported from abroad, which play an important role in various industrial sectors.
(4) The gas deflagration spraying technology has been further applied. Because the flying speed of particles can reach more than 800m/s, the bonding strength between coating and substrate can reach more than 100MPa, and the porosity is less than 1%, this spraying technology is superior to other spraying methods in some fields. At present, more than 10 sets have been installed in China.
(5) As mentioned above, oxyacetylene flame plastic powder spraying technology has developed rapidly. In recent years, a batch of spraying equipment for producing oxyacetylene flame plastic powder has appeared in China. After adopting this technology, it has been well applied in chemical storage tanks, pipelines, mud filter frames in ceramic industry, cloth guide rollers in printing and dyeing industry, cast iron idlers in belt conveyors in coal industry, polymer injection equipment in petroleum industry, surface decoration and so on, which makes up for the shortcomings of electric spraying. It opens up a new way for the application of plastic coatings.
(6) The application of thermal spraying technology in chemical anti-corrosion engineering is one of the main reasons for the failure of mechanical parts under the chemical or electrochemical action of surrounding media. It not only makes a lot of metal materials suffer losses, but also makes the loss of production stoppage more difficult to estimate, so people pay special attention to chemical corrosion protection. The application of thermal spraying coating in corrosive medium, especially in strong medium corrosion, has not been broken before, mainly because the hole sealing agent has not been solved. As we all know, the spray coating is porous. If the pores are not closed, various acids, alkalis and organic media will penetrate into the pores, which will make the coating fall off and affect the anticorrosion effect. According to the requirements of anti-corrosion engineering, China has recently successfully developed dozens of types of hole sealing agents such as polyester, organic polymer, resin, plastic and adhesive, which are suitable for corrosive environments such as acid, alkali, salt and organic matter, and the service temperature is 80 ~ 350℃. Using ceramic coating, oxide coating or metal or alloy coating, and selecting appropriate hole sealing agent according to different media, has been applied in a variety of chemical corrosive media, and the effect is good. This series of sealants has been patented and won the national invention award. The successful development of these sealing agents has made new progress for the application of thermal spraying technology in chemical anticorrosion engineering.
(7) Application of laser remelting technology In recent years, high-frequency induction remelting and vacuum induction remelting have only been applied in a certain range. Laser remelting technology has been tested in a small scale several years ago, but it has not been widely used. Recently, Tsinghua University applied laser remelting technology to valve production, and Shanghai No.2 Textile Machinery Factory applied laser remelting technology to textile machinery.
(8) Thermal spraying technology is also applied to architectural decoration and medical care. In recent years, Sichuan, Shanghai, Shenyang, Yunnan and other places have used thermal spraying technology to spray various statues, decorations and large walls, and achieved good results. For example, the triumphant mural in Shenyang International Mall uses thermal spraying technology. With the development and perfection of thermal spraying technology, this technology has penetrated into other fields, such as the manufacture of artificial bone by thermal spraying in the biological field. At present, there are more than 200 clinical cases in China, and the effect is very good. In addition, the artificial teeth made by thermal spraying method have also been preliminarily applied.
Fourthly, it is of great significance to further popularize and apply thermal spraying technology.
Wear and corrosion are the main reasons for the failure of materials and parts. According to relevant reports, the loss caused by wear and corrosion in developed countries accounts for about 3% ~ 5% of the total national economic output value, and the loss caused by corrosion in China 1993 reached more than1000 billion yuan, with an average of 300 million yuan per day. From 65438 to 0994, China's national economic output value was 4.38 trillion yuan. If the loss was calculated by 4%, it exceeded170 billion yuan, and the direct economic benefit of popularizing and applying thermal spraying technology during the Eighth Five-Year Plan period was about 3.5 billion yuan. With the further improvement of people's requirements for material properties, more in-depth research and exploration will be carried out on thermal spraying equipment, technology and materials. The data show that thermal spraying technology, as an excellent surface modification technology, has broad development prospects, and it is of great significance to further popularize and apply this technology.
Brief introduction of plastics
[1] Plastic is a synthetic polymer, which can also be called polymer or macromolecule, also known as plastic or resin, and its shape can be changed freely. It is a substance polymerized by monomer raw materials through synthesis or condensation reaction. It consists of synthetic resin, filler, plasticizer, stabilizer, lubricant, pigment and other additives. Its main component is synthetic resin. The word resin was originally named after the lipids secreted by animals and plants, such as rosin and shellac. At present, resin refers to polymers without various additives. Resin accounts for about 40% ~ 100% of the total weight of plastics. The basic properties of plastics mainly depend on the properties of resin, but additives also play an important role. Some plastics are basically composed of synthetic resin with little or no additives, such as plexiglass and polystyrene. The so-called plastic is actually a synthetic resin, which is similar in shape to turpentine in natural resin, but it is called plastic because it is synthesized by chemical force.
According to the definition of American Society for Testing Materials, plastic is a material with high molecular weight organic matter as its main component. It takes on a solid shape when it is processed, and can be modeled by flow during manufacturing and processing.
Therefore, from this explanation, we can get the following understanding:
It is a polymer organic compound.
It can exist in many forms, such as liquid solid colloidal solution.
It can be molded.
There are many kinds of plastics because of different monomer components.
● The products are various and diversified.
Have different properties.
● Different treatment methods can be used.
The terms plastic and resin are often used interchangeably. Figure 1. 1 shows the process of plastic production.
Figure 1. 1 Plastic Production Process
Plastics can be divided into thermosetting and thermoplastic, the former can not be used in plastic, and the latter can be produced repeatedly. There are basically two kinds of plastic polymer structures: the first is linear structure, and the polymer compound with this structure is called linear polymer compound; The second is the bulk structure, and the polymer compound with this structure is called bulk polymer compound. Some polymers have branched chains, which are called branched polymers and belong to linear structure. Although some polymers are cross-linked between molecules, the degree of cross-linking is low, which is called network structure and belongs to bulk structure.
Molecular structure classification of polymers;
Linear structure
(b) Linear structure (with branches)
(c) network structure (small amount of cross-linking between molecular chains)
(d) Body structure (a lot of cross-linking between molecular chains)
Two different structures show two opposite properties. Linear polymers (including branched chains) have the characteristics of elasticity and plasticity because of the existence of independent molecules, which can be dissolved in solvents and melted by heating, with less hardness and brittleness. Because there are no independent macromolecules, the polymer with block structure has no elasticity and plasticity, can not be dissolved and melted, but can only swell, with high hardness and brittleness. There are two kinds of polymers in plastics, one is thermoplastic made of linear polymer, and the other is thermosetting plastic made of bulk polymer.
Compared with other materials, plastics have the following characteristics:
Chemical corrosion resistance
< 2 > shiny, partially transparent or translucent.
< 3 > most of them are good insulators.
< 4 > light and strong
(5) Easy processing, mass production and low price.
↓6↓ It has a wide range of uses, diverse functions, easy coloring and local high temperature resistance.
Plastics are divided into general-purpose plastics and engineering plastics, which are mainly defined by the universality of use. For example, PE and PP are cheap and can be produced on many different types of machines. Engineering plastics are more expensive, but the stability and physical properties of raw materials are much better. Generally speaking, they have both rigidity and toughness. Table 1. 1 is the comparison table of plastic raw materials, items 1 to 8 are general plastics, and items 9 and 10 are in between. Generally speaking, PP, HDPE, LDPE, PVC and PS are the five general plastics.
Table 1. 1 comparison table of common plastic raw materials
scientific name
English abbreviation
gingkgo
Be popularly named/addressed.
polypropylene
Parcel Post
polypropylene
High density polyethylene
High density polyethylene (same as high-densitypolyethylene)
High density polyethylene
Hard and soft rubber
LDPE
Low density polyethylene (short for low-density polyethylene)
Low density polyethylene (short for low-density polyethylene)
Linear low density polyethylene
LLDPE
Linear low density polyethylene
polyvinyl chloride
polyvinyl chloride
polyvinyl chloride
general purpose polystyrene
GPPS
Ordinary grade polystyrene
hard rubber
Expandable polystyrene
EPS
foamed polystyrene
polyfoam
Impact polystyrene
buttock
Impact polystyrene
Impact resistant hard rubber
Styrene-acrylonitrile copolymer
As, three
Styrene-acrylonitrile copolymer
Transparent strong adhesive
Acrylonitrile butadiene styrene
Anti-lock braking device
Acrylonitrile-butadiene-styrene polymer
Super unbreakable glue
Polymethyl methacrylate
Polymethyl methacrylate
polymethacrylate
acryl
Ethylene-vinyl acetate copolymer
extravehicular activity
* * * Polymer of ethylene and vinyl acetate
Rubber glue
polyethylene glycol terephthalate
Positron emission computed tomography (positron emission computed tomography)
polyethylene glycol terephthalate
polyester
Poly (butylene terephthalate)
Polybutylene terephthalate (short for polybutylene terephtalate)
Polybutyl terephthalate
Polyamide (nylon 6.66)
Panama
Polyamide nylon
polycarbonate
personal computer
Polycarbonate resin
Bulletproof glue
Polyacetal resin
Bang!
Polyacetal resin
Compete and seize steel
polyphenylene oxide
Polyphenylene Oxide (short for polyphenylene oxide)
Xylene oxide
Defoyl group
polyphenylene sulfide
Postscript
polyphenylene sulfide
polyurethane
polyurethane
Polyurethane carbamate
[Edit this paragraph] Characteristics of plastics
Plastics mainly have the following characteristics:
① Most plastics are light, chemically stable and will not rust; ② Good impact resistance; ③ Good transparency and wear resistance; ④ Good insulation and low thermal conductivity; ⑤ Good overall formability and coloring, and low processing cost; ⑥ Most plastics have poor heat resistance, high thermal expansion rate and are easy to burn; ⑦ Poor dimensional stability and easy deformation; 8 Most plastics have poor low temperature resistance and become brittle at low temperature; Pet-name ruby easy to aging; Attending some plastics are soluble in solvents.
Plastics can be divided into thermosetting and thermoplastic, the former can not be used in plastic, and the latter can be produced repeatedly.
There are basically two kinds of plastic polymer structures: the first is linear structure, and the polymer compound with this structure is called linear polymer compound; The second is the bulk structure, and the polymer compound with this structure is called bulk polymer compound. Some polymers have branched chains, which are called branched polymers and belong to linear structure. Although some polymers are cross-linked between molecules, the degree of cross-linking is low, which is called network structure and belongs to bulk structure.
Two different structures show two opposite properties. Linear polymers (including branched chains) have the characteristics of elasticity and plasticity because of the existence of independent molecules, which can be dissolved in solvents and melted by heating, with less hardness and brittleness. Because there are no independent macromolecules, the polymer with block structure has no elasticity and plasticity, can not be dissolved and melted, but can only swell, with high hardness and brittleness. There are two kinds of polymers in plastics, one is thermoplastic made of linear polymer, and the other is thermosetting plastic made of bulk polymer.