What are the characteristics of HOVF?
By centurytool
October 18th, 2023
351 views
Supersonic spraying is a widely used process in the field of cemented carbide production. The use of supersonic spraying technology can enhance the surface strengthening treatment of cemented carbide parts, making them more suitable for harsh working conditions in various industries such as machinery manufacturing, aerospace, transportation energy, and petrochemical industries. Today, the editor of Xidi will mainly introduce to you the characteristics of supersonic flame spraying.
The principle of the supersonic flame spraying method is to use a high-pressure water-cooled reaction chamber and a slender injection tube to send fuel and oxygen into the reaction chamber for combustion, thereby generating a high-pressure flame. The burning flame is then compressed and accelerated by the injection tube, and the thermal spray powder can be fed axially or from the side of the injection tube with high pressure.Another method is to inject fuel and oxygen through high-pressure and burn it outside the nozzle. The thermal spray powder is sprayed and the high-pressure gas is axially fed into the flame from the nozzle, and then the combustion flame is compressed by the compressed gas in the air cover outside the nozzle. Accelerate and spray the molten thermal spray powder towards the substrate.
The characteristics of supersonic flame spraying are: high jet velocity and lower flame temperature than explosive spraying, so it is suitable for carbide coatings. The coating obtained by supersonic flame spraying has a very high density, which can reach 99.9% of the theoretical density, and a strength of more than 70 MPa. The coating has few impurities and a small residual stress in the coating. In some cases, the designed residual stress can be obtained, so It can spray thicker coatings and has high spraying efficiency, but it also has the following disadvantages: high fuel consumption and relatively high cost.
Characteristics of thermal spraying process:
1. The operation is flexible and can spray objects of various specifications and shapes. It is especially suitable for large-area coating and can be used in the field.
2. The coating thickness range is wide, and coatings from tens of microns to several millimeters can be prepared, and are easy to control, with high spraying efficiency and low cost. The production efficiency during spraying ranges from several kilograms to dozens of kilograms per hour. However, as a surface treatment technology, it also has many shortcomings, mainly reflected in three aspects: low thermal efficiency, low material utilization, large waste and low strength of coating and substrate.
3. Coatings of various materials can be prepared on various substrates, including almost all solid materials such as metal, ceramics, cermets, engineering plastics, glass, wood, cloth, and paper.
4. The substrate temperature is low. The substrate temperature is generally between 30 and 200oC, the deformation is small, and the heat affected zone is shallow. In recent years, as people's requirements for coating performance have further improved, the majority of scientific workers have developed supersonic flame spraying and supersonic plasma spraying on the original basis through continuous innovation.
At the same time, they have also developed laser spraying and reaction heat spraying. Processes such as spraying and cold spraying.
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