Supersonic spraying

The core of high-speed flame spraying (HVOF) equipment is the spray gun, which consists of three parts: the combustion chamber (which can fully heat and accelerate the spraying material particles), the Laval nozzle (which can accelerate the flame flow to supersonic speed), and the equal cross-sectional length nozzle (which can fully heat and accelerate the spraying material particles).

Supersonic spraying has the characteristics of high hardness, low porosity, low surface roughness, good wear resistance and corrosion resistance, and has a wide range of application prospects in industry, especially in anti-corrosion and wear-resistant materials. The supersonic arc spraying operation is flexible and can obtain high-performance coatings over a wide range of skill spraying. After being developed, the device has been widely used.

This supersonic spraying process has high requirements for operators and is usually completed by experienced technicians to ensure the spraying effect. During supersonic spraying construction, the following process flow should be followed:

1. Surface cleaning: mainly using mechanical means such as steel balls, supplemented by alkaline cleaning solution, to remove rust and oil stains on the surface of pipelines and other loose layers, with a cleanliness level of Sa3, to ensure a firm bonding foundation for supersonic spraying.

2. Surface roughening: Common methods include sandblasting and electrical treatment, which increase the mechanical bonding between the coating and the substrate. The standard roughness is 6.5~25.

3. Bottom layer spraying: The expansion coefficient of the bottom layer is very close to that of the substrate, mainly to enhance the bonding strength and thermal shock resistance of the working layer.

4. Spray working layer: The working layer is on the outer layer and comes into direct contact with the smoke. The spray layer formed by supersonic spraying equipment has high resistance to temperature corrosion and wear.

5. Sealing treatment: After the coating is formed, there is a certain porosity, especially the permeability porosity. The use of high-temperature wear-resistant and anti-corrosion sealing coating to seal the gap between the spray holes of the working layer can improve the performance of supersonic spray coating.

According to the principle of supersonic spraying, the performance of the coating is determined by the state of the particles before deposition, including particle velocity, temperature, and melting state. The particle velocity plays an important role in the performance of the coating.

When particles impact the surface of an individual, high speed can create a significant impact, and the particles have strong deformation ability, which is beneficial for improving the adhesion and density of the coating. The surface characteristics of supersonic spraying are due to its high particle velocity, which has been widely applied in the industry.