Process principle and equipment composition of AC-HVAF spraying

       

This article talks about the process principle and equipment composition of AC-HVAF spraying. After HVOF, the United States and Japan have developed a high-speed flame spraying system with gas and air mixed combustion, called HVAF for short, in order to further reduce the oxidation of powder materials and the consumption of oxygen in the spraying process. However, the HVAF system at that time did not receive the expected effect because of the low powder deposition rate and the potential safety hazard. In 2001, based on the scientific research achievements of the former Soviet Union, the United States TSR (uniquecoat) company successfully developed AC-HVAF high-speed flame spraying system, which makes HVAF spraying technology take on a new look and show its unique coating and process characteristics. Wococarbide provides HVOF and HVAF spraying powder.

1. Principle of AC-HVAF spraying process

The process is similar to HVOF spraying principle, which uses the energy of supersonic airflow formed by combustion of gaseous fuel and air to accelerate and heat the sprayed material. Compared with the traditional HVOF, AC-HVAF process has higher flame velocity but lower temperature. The velocity of sprayed particles is 700-800m / s, and the particle temperature is generally below its melting point. When the hot softened particles impact on the surface of the substrate, they undergo sufficient plastic deformation to form a dense coating. Generally, propane is used as fuel gas. When spraying high melting point materials, propylene can replace propane to increase flame temperature. The spray gun is cooled by compressed air.

2. Equipment composition

The AC-HVAF spraying system consists of spray gun, console, vaporizer, powder feeder and auxiliary device.

(1) There are two types of spray guns, hand-held and Machine-mounted. The Machine-mounted spray gun is equipped with a nozzle assembly specially used for spraying self fluxing alloy. Axial powder feeding, internal spark plug ignition and air cooling spray gun are adopted. The secondary nozzle is designed with different length, so that the system can spray a variety of materials.

(2) The console touch screen type automatic control, the operation is simple and reliable.

(3) The vaporizer gasifies liquid propane and propylene through an electric heater under preset pressure and temperature.

(4) The powder feeder is a spray gun for continuous conveying of powder. The powder feeding rate is up to 40 kg / h and the working pressure is up to 1.2 MPa.

3. Coating and process characteristics

(1) Coating characteristics.

1) The coating has high density and the porosity can be less than 0.5%.

2) The oxide content is low, close to the level of vacuum spraying.

3) The bonding strength with carbon steel is more than 75 MPa.

4) The coating has smooth appearance and can reach the optical mirror after grinding.

(2) Process characteristics.

1) Simple equipment configuration, no oxygen, no water cooling heat exchange system, low production cost.

2) The production efficiency can reach 30kg / h.

3) The coating has low oxygen content and can be sprayed with copper, silver, titanium and other metal coatings; Good combination with active metals

4) In the working process, the process parameters should be strictly controlled, especially the powder size.

 

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