Principle of Plasma Spraying

       

Principle of Plasma Spraying

  The principle is to generate a plasma flame flow through a plasma spray gun (also called a plasma arc generator). The tungsten electrode (cathode) and nozzle (anode) of the spray gun are respectively connected to the negative and positive electrodes of the power supply (the workpiece is not charged), and the arc is ignited by a high-frequency spark, so that the working gas (Ar or N2) supplied to the spray gun is ionized under the action of the arc. plasma. Under the combined action of mechanical compression effect, self-magnetic compression effect and thermal compression effect, the arc is compressed to form a non-transferred plasma arc. The powder-feeding stream transports the powder spraying material into the plasma arc, and is quickly heated to a molten or semi-molten state, hits the surface of the pretreated substrate at high speed with the plasma stream, and forms a firm spray coating on the surface of the substrate. In this way, the sprayed surface of the parts can obtain various special physical and chemical properties such as different hardness, wear resistance, heat resistance, corrosion resistance, insulation, heat insulation, and lubrication to meet the requirements of different working conditions of the parts.

Plasma spraying process

  The plasma spraying process is a careful work, and there are many factors that can affect the quality of the large coating in this process. Then the main processes are: 1. Choose plasma gas. According to gas availability and economy, N2 is more appropriate. It is not only cheap, but its ion flame heat is relatively high, and the heat transfer is relatively fast. However, some materials that are prone to nitridation reaction are not available. In this case, a slightly more expensive Ar will be used. 2. The power of the arc. During the process, the power requirements for the arc are also very strict, neither too high nor too low. If the arc power is too high, the arc temperature will increase and the gas will be converted into plasma, and the plasma flame temperature will also increase, which may cause changes in the properties of the coating. If the arc power is too low, the plasma temperature will be too low and the properties of the coating will also be changed.






  The advantages of gas-stable plasma (GP) spraying: simpler mechanical structure, easier arc starting, long electrode life, stable combustion, independent air flow and pressure control efficiency is higher. Disadvantages: The carrier gas is expensive, the spraying rate of the two medium systems (arc stabilization and cooling) is small, and the quality of spraying materials is high.