Due to the many technological means of thermal spraying technology, the choice of spraying materials is very wide. From plastics, low melting point metals, to refractory metals, ceramics and their mixtures. Any material that has a stable liquid state can be sprayed by at least one of these methods. At the same time, the properties of thermal spray coating materials vary.
Thermal spray coating has the functions of friction resistance and lubrication, thermal protection, oxidation resistance, corrosion resistance, electrical conductivity and electrical insulation, biomedicine, chemical catalysis, composite material preparation and component repair.
Wear-resistant coating
Wear resistance is the most widely used field of thermal spraying technology, and usually has the advantages of high hardness, low porosity, toughness, and strong bonding with the substrate. The use of suitable components can also reduce friction. The main spraying materials are nickel-based alloys and cobalt-based alloys, carbides, borides, oxides, etc. Tungsten carbide, aluminum oxide, and diatomite coatings are sprayed by plasma to improve wear resistance and sealing performance; boiler combustion chambers or valves with high temperature or combustion are protected by heat-resistant coatings. Valves in the chemical fiber industry with alumina-titanium oxide coating can improve the wear resistance of parts and eliminate static electricity. Valves and components in the petrochemical industry are coated with chromium oxide, aluminum oxide, and titanium oxide coatings to solve the problems of leaking, leaking, leaking, and dripping. The working conditions that may cause wear of the valve include fretting, sliding, impact, abrasion, erosion, etc. By thermal spraying the valve, the surface hardness can be enhanced, the service life can be improved, and the maintenance cost can be reduced. Various valve sealing surfaces adopt oxyacetylene flame spraying and plasma spray welding technology to greatly improve the service life. At present, it has been promoted and used in more than 150 valve factories, and the economic benefits are considerable.
2. Thermal insulation coating
Thermal barrier coating, also known as thermal barrier coating, mainly consists of alumina and CaO, MgO, YO, CeO 2 and stabilized zirconia. These coatings with high melting point and low thermal conductivity contain numerous pores with a volumetric porosity between 5% and 30%. The existence of pores further reduces the thermal conductivity of the coating and improves the thermal insulation effect of the coating. In order to improve the bonding force between the oxide thermal insulation coating and the substrate, various metal coatings such as NiCr, NiA1, and NiAICrY are usually used as bonding coatings. Heat-resistant coatings can be used for high-temperature thermal protection in the chemical industry and metallurgical industry. In order to reduce the thermal stress between the coating and the base metal and improve the thermal shock capability of the coating, a metal-ceramic gradient coating has been successfully developed in recent years. The thermal spraying market for automotive engines has great potential and is expected to develop greatly in the next ten years. American automakers have active research and development plans for thermal spray coatings. They plan to use thermal barrier coatings on the cylinder lining and exhaust parts of automobiles, and use wear-resistant coatings on piston rings, valves, cams, crankshafts and other parts. Coatings will improve component life and thermal efficiency. Generally used in valves and flame stabilizers of diesel engines.
After thermal spraying treatment, it can resist high temperature and high pressure in the working environment, and reduce the working temperature of the substrate to 10-65°C.
Some valves are used on pipelines with gas erosion and corrosion. The cavity of the valve receives the erosion and corrosion of air flow, and it is also prone to problems such as wall thickness reduction. By spraying a cavitation-resistant coating, the service life of the valve can be improved.
For ceramic valves, if the valve is partially damaged and cannot be used, the ceramic coating is sprayed with oxyacetylene flame, and then sealed, it can be repaired as new, and the repair and benefits are considerable.
3.Anti-oxidation and anti-corrosion coating
The anti-oxidation and anti-corrosion coatings are mainly metal and oxide coatings. The former is the alloy of NiCr, NiA1, NiA1CrY, W CoCr, Zn, A1 and znAl, and the latter is mainly ZrSiO, M gO —ZrO, A 1: 0, coating. MgO—ZrO: The coating has excellent anti-melting and corrosion resistance, which can prevent the contamination of the graphite crucible during the melting process. After the alumina coating is impregnated with organic resin, it can be used to resist acid and alkali corrosion of pipeline valves and other devices in the chemical industry. N iCrBSi and WC coatings have good anti-cavitation ability and can be used for anti-cavitation of valves. Flame-sprayed zn, Al and zn-A1 alloy coatings are very effective for long-term anti-corrosion, and can be used for large-scale outdoor engineering valves. In recent years, a sealing agent has been added to the surface of the arc sprayed aluminum alloy coating, and a very satisfactory effect has been achieved on the anticorrosion of ship valves.
4. Spray molding
The coating is formed by the accumulation of melted particles, and the coating has a certain strength. Special-shaped and complex-shaped parts can be prepared by thermal spraying technology, which is more economical and convenient than conventional methods. Tungsten and molybdenum crucibles and tubes with excellent performance have been prepared by vacuum plasma spraying and graphite as a model. High-power plasma spraying equipment (above 100kW) is used to spray alumina and zirconia materials, and successfully prepares large-scale products with a thickness of 15mm. Its economy and practicability are better than traditional ceramic products. In addition, composite materials reinforced by particles, whiskers and fibers can also be prepared by plasma spraying technology. Thermal spraying is a cost-effective method of restoring dimensions.
Whether it is due to work wear or machining tolerances, the size of the workpiece does not meet the requirements, and thermal spraying can provide a new surface. This method has neither welding deformation nor is it as expensive as a special electroplating process. At the same time, the new surface consists of a wear-resistant or corrosion-resistant material, or is made of the same material as the workpiece. For example, for many large valves or imported valve stems, if the size is insufficient due to wear, and the remanufacturing cost is high or the manufacturing is difficult, the size can be restored by thermal spraying.
5. Material substitution
If some valves are all made of precious metal materials, the cost is very high. From the perspective of use, the contact point between the valve and the medium is mainly the surface. If there are only precious metals on the surface, the manufacturing cost can be greatly reduced. For example, a valve made of ordinary steel is sprayed with 1 Crl8N i9Ti or 0Cr, 00Cr and other stainless steel materials on its surface, and then sealed, instead of making stainless steel as a whole. There have been many application examples in other products. In valve products It is also worthy of popularization and application in the design and manufacture of .