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Plasma spraying principle

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Author : Pei Ze Technology
Update time : 2021-12-13 11:43:00
  Plasma spraying is carried out by using plasma arc. Ion arc is a compression arc. Compared with free arc, its arc column is thin, the current density is large, and the gas ionization degree is high, so it has the characteristics of high temperature, concentrated energy and good arc stability.
  There are three forms of plasma arc according to different connection methods:
  ①Non-transferred arc: refers to the plasma arc generated between the cathode and the nozzle. In this case, the positive electrode is connected to the nozzle, the workpiece is not charged, an arc is generated between the cathode and the inner wall of the nozzle, and the working gas is heated by the arc between the cathode and the nozzle, causing full or partial ionization, and then ejected from the nozzle to form Plasma flame (or plasma jet).
  Plasma spraying uses this type of plasma arc.
  ②Transfer arc: The arc leaves the spray and transfers to the plasma arc on the processed part. In this case, the nozzle is not connected to the power supply, the workpiece is connected to the positive electrode, the arc flies between the cathode and the anode (workpiece) of the spray gun, and the working gas is fed into the arc around the arc, and then ejected from the nozzle.
  Plasma cutting, plasma arc welding, and plasma arc smelting use this type of plasma arc.
  ③ Combined arc: The non-transferred arc ignites the transfer arc and heats the metal powder, and the transfer arc heats the workpiece to generate a molten pool on the surface. In this case, the nozzle and the workpiece are connected to the positive electrode.
  Plasma spray welding uses this plasma arc. When plasma spraying is performed, a DC arc is first generated between the cathode and the anode (nozzle). The arc heats and ionizes the introduced working gas into high-temperature plasma, and sprays it from the nozzle to form a plasma flame. The temperature of the plasma flame is very high. High, its center temperature can reach 30,000°K, and the nozzle outlet temperature can reach 15,000-20,000°K. The flame velocity can reach 1000~2000m/s at the nozzle outlet, but it decays rapidly. The powder is sent into the flame by the powder feeding gas to be melted, and accelerated by the flame to obtain a speed higher than 150m/s, and sprayed onto the base material to form a film.
  Plasma spraying equipment: Plasma spraying equipment mainly includes:
 ①Spray: It is actually a non-transferred arc plasma generator, which is a key component, on which electricity, gas, powder, water, etc. of the entire system are concentrated.
  ②Power supply: used to supply direct current. Usually a full-wave silicon rectifier device.
 ③Powder feeder: a device used to store spray powder and deliver powder to spray according to process requirements.
  ④ Heat exchanger: It is mainly used to effectively cool the nozzle and prolong the life of the nozzle.
  ⑤Air supply system: including the supply system of working air and powder air.
  ⑥Control box: It is used to adjust and control water, electricity, gas and powder.

 
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