What are the advantages and development prospects of plasma spraying?

Advantages and development prospects of plasma spraying:

1. Easy to operate, low equipment maintenance cost, and good adjustment performance.

2. The working gas is an inert gas, which protects the substrate and powder from oxidation and reduces impurities in the coating.

3. The substrate is not charged during the spraying process. Not melting, the substrate and spray gun move quickly, keeping the substrate structure unchanged. The shape and properties of the matrix will not change.

4. The flying speed of sprayed particles can reach 200~500m/s, resulting in a smooth coating. High density, high powder deposition rate.

5. Compared with oxyacetylene flame spraying, plasma jet has a higher temperature, concentrated energy beam, and can melt all high hardness materials. High melting point powders can be used as a wide range of spraying materials and can be used to prepare various coatings.

On the basis of plasma spraying, several new plasma spraying technologies have been developed, such as:

1. Gas stable plasma spraying

The principle of gas stable plasma spraying is that the plasma spray gun (plasma arc) generates a plasma jet (arc flame). The electrode (bright pole) and nozzle (anode) of the spray gun are respectively connected to the positive and negative poles of the rectifier power supply, providing working gas (Ar, n2, etc.) to the spray gun and igniting the arc through high-frequency sparks. ）The arc heats the gas to a high temperature, causing ionization of the gas. Under the effects of thermal contraction, self magnetic contraction, and mechanical effects, the arc is compressed into a plasma arc. After spraying high-temperature plasma gas from the nozzle, the volume rapidly expands, forming a high-temperature and high-speed plasma jet. After the powder is pushed into the plasma jet by the powder feeding airflow, it is quickly heated to a melted or semi melted state, accelerating the plasma jet and forming a spray ion beam of flying substrate, which impacts the surface of the pre treated substrate and forms a coating. Argon, hydrogen, and hydrogen are used as plasma for atmospheric plasma spraying.

2. Water stable plasma spraying

The working medium of the plasma spraying mentioned above is gas, and the working medium of this method is water instead of gas. It is a high-power or high-speed plasma spraying method, and its working principle is as follows:

The spray gun enters high-pressure water flow, forming a vortex on the inner wall of the gun barrel. At this point, a direct current arc is generated between the cathode at the rear of the gun body and the rotating anode at the front of the gun body, evaporating, decomposing, and generating plasma, resulting in a continuous plasma arc. Due to the focusing effect of rotating vortex water, the energy density is increased, combustion is stable, and high melting point materials, especially oxide ceramics, can be sprayed with high spraying efficiency.

3. Vacuum plasma spraying (also known as low-pressure plasma spraying)

Vacuum plasma spraying is a technique of spraying in a sealed chamber with controllable atmosphere and a pressure range of 4~40kPa.

Because the working gas is ionized and sprayed out while expanding its volume in a low-pressure atmosphere, the jet velocity is supersonic and very suitable for materials that are highly sensitive to oxidation.