Plasma spraying

In plasma spraying, an arc is ignited between an anode and a tungsten cathode using high frequency. During plasma spraying, the gas flowing through between the electrodes (argon, helium, hydrogen, nitrogen or mixtures) is ionized, resulting in a plasma jet several centimeters long. The process energy required for plasma spraying results from the dissociation or ionization of the gas or gas mixture flowing past the arc. Here, a highly heated (up to 20.000°C), electrically conductive gas (plasma jet) is generated from positive ions and electrons. Powder (usual particle size distribution: 5 – 120 μm, with certain devices a particle size of down to 100 nm is also possible) is injected into this generated plasma jet, which is melted by the high plasma temperature. During plasma spraying, the plasma stream entrains the powder particles and throws them onto the surface to be coated. Plasma coating during plasma spraying takes place both in a normal atmosphere and in an inert gas atmosphere (argon).

Furthermore, the plasma spraying is carried out in a vacuum or under water. The speed, temperature and composition of the plasma gas are important for the layer quality of a plasma-sprayed surface. The process of plasma spraying is extremely noisy and therefore only possible or sensible in a soundproof cabin and is normally only carried out automatically.