The technology of applying protective coatings
Thermal spray technologies for applying protective coatings.
Thermal spray coatings used during the repair of equipment and hardening of working surfaces of new details. The basic technological processes used in thermal spraying is high-speed spraying, plasma spraying in air using plasma gases such as argon, nitrogen, helium, air, a detonation and gas flame spraying and electric arc metallization and the cladding.
High-speed (HVOF, HVAF) spraying
Advantages of high speed (HVOF, HVAF) spraying
The advantages of plasma spraying
The advantages of flame spraying
The formation process of plating coating
The advantages of electric-arc metallization
Application of technology application of protective coatings by thermal spraying is one of the cardinal ways of solving this issue.
Using currently available equipment, materials and technologies of thermal spraying is made possible to significantly reduce or eliminate the influence on wear of components such factors as erosion, corrosion (including high temperature), cavitation etc. a Protective coating may also be designed, for example, to create a thermal barrier layer, ensuring electrical insulating properties, absorption of radiation from radioactive decay products, ensure certain optical properties, implementation of selective wetting, the creation of a bioactive surface properties for the various artificial organs and much more.
Thermal spray coatings used during the repair of equipment and hardening of working surfaces of new details. Depending on the purpose of the coating and its working conditions are changed accuracy requirements of compliance with the basic parameters of the coating – its composition, thickness, density and adhesion to the substrate.
Mastering the technique of thermal spraying solves environmental problems, displacing the electroplating of “dirty” technologies.
The basic technological processes used in thermal spraying is high-speed spraying, plasma spraying in air using a plasma of such gasesas argon, nitrogen, helium, air, a detonation and gas flame spraying and electric arc metallization and the cladding.
Benefits of thermal spraying:
– protective coating can be applied to objects of all sizes: bridges, ships, pipelines, building constructions, boilers, crank shafts, turbine blades,etc.
– the coating thickness may be from 0.01 to 10 mm;
coatings can have a given porosity (from 0 to 30 and more percent),
– protective coating can be made of any material having a melting point or softening interval,
– in substrate can be used as wood, glass, plastics, ceramics, composite materials, metals,
– application of protective coatings can be produced in a wide range of coating composition, temperature and pressure in a low vacuum in a special chamber with a controlled inert atmosphere, in air under normal conditions, under water,
– applying metallic and ceramic coatings does not cause significant heating of the surface, thereby maintaining the geometric dimensions of the parts.
High-speed (HVOF, HVAF) spraying:
Based on high-speed flame spraying lies in heating of the particles with their simultaneous acceleration and applied to the surface at supersonic speeds. As the deposited materials are used in different metal-ceramic and metal powders and wires. Since in this application the particles are not propellets, the method relates to the cold technology.
When high speed wire flame spraying the coating contains less oxides than in the high speed powder coating. It is particularly important to obtain a dense corrosion resistant coatings. However, the relatively low speed of the particles at high-speed flame spraying does not ensure the formation of dense coatings. The surface of the particles has time to oxidize.
Advantages of high speed (HVOF, HVAF) spraying:
– produced in the process of carbide coatings on all characteristics superior electroplate,
– produced reliable, durable coating with excellent performance properties,
– resistance to corrosion, abrasion, impact and other external influences
– increased lifespan of products for dozens of years,
– the cost of such protective coatings is much lower than electroplating.
When plasma spraying as a plasma-forming gas used argon, the secondary helium, hydrogen or nitrogen. When injected into the plasma arc, the powder material is melted and is transferred onto the surface. There it is crystallization. For this type of treatment uses ceramics and metal alloys.
At present, plasma torches of high power designed to feed powder into the plasma jet. This scheme does not affect the arc. Plasma torches have overstated the power to heat the plasma jet was enough to heat up the powder. The application is carried out by metallization.
The advantages of plasma spraying:
– protection of steel structures from corrosion in fresh and sea water,
– protection of steel structures against corrosion in highly aggressive environments
– reduced downtime for repair and maintenance,
– reducing the costs
– increasing the company’s profit.
Method is to spray the wire in the stream is burned in oxygen gas. For these purposes typically used propane or acetylene. In this case, the molten metal is transferred to the surface, where crystallization occurs and the formation of the protective layer. The coating can be used with any wire diameter from 3 to 3.17 mm. This method is a thermal spray coating refers to hot.
The advantages of flame spraying:
– restoration of the geometry of the parts,
– the ability to produce cervical shafts, covers protected motor, babbit bearings, seats,
– performing anti-corrosive treatment of steel structures.
Electric arc metallization:
Metallization arc spray (Twin wire arc spray), heat the wire to melting electric arc and subsequent contraction of the formed droplets towards the substrate. Usually performed in several passes. Most often used for the deposition of zinc, aluminum or Monel. Possible porosity of coatings is less than 2%.
The process of formation of plating coatings:
The advantages of electric arc metallization:
– the sea surface from the negative effects of aggressive environments and precipitation,
– increase of service life,
– ensuring high hardness and adhesion due to the protective properties,
– the application of such coatings can be carried out in the field.