Plasma spraying will become a new support for the development of thermal spraying industry in the future

       With the continuous development of science and technology, there are more and more types of surface modification technologies, such as surface coating method, ion implantation method and ion extraction method. These methods have significant effects in improving the surface hardness, fracture toughness, and bending strength of ceramic materials, reducing friction coefficient, improving wear resistance, chemical properties, high temperature oxidation resistance and mechanical properties. Plasma spraying is a new type of plasma spraying method developed for the shortcomings of conventional atmospheric plasma spraying. The principle is: the main gas and the secondary gas are input from the gun body after the spray gun. The main gas flow between the tungsten electrode and the primary nozzle is small, and the large flow of secondary gas passes through the secondary nozzle through the gas swirl ring. Squirting. The coating processed by plasma spraying has the following characteristics: the coating of the high melting point material is uniform, the coating is dense and hard, the porosity is small, and the ceramic coating of the high melting point material has high bonding strength.



   Plasma spraying processing is a new type of multi-purpose precision spraying method vigorously developed after flame spraying. It has: ① Ultra-high temperature characteristics, which is convenient for spraying high melting point materials. ②The speed of spraying particles is high, the coating is dense, and the bonding strength is high. ③Because the inert gas is used as the working gas, the spraying material is not easy to oxidize.



   Plasma spray processing is carried out by plasma arc. Ion arc is a compressed arc. Compared with free arc, its arc column is thin, current density is large, gas ionization degree is high, so it has the characteristics of high temperature, concentrated energy and good arc stability. .

According to different power connection methods, there are three forms of plasma arc:



   ① Non-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, and an arc is generated between the cathode and the inner wall of the nozzle. 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. Plasma flame (or plasma jet).



Plasma spray processing uses this type of plasma arc.



   ②Transfer arc: the arc is transferred from the spray gun to the plasma arc on the processed part. In this case, the nozzle is not connected to the power source, 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 sent in around the arc and then ejected from the nozzle.



   Plasma cutting, plasma arc welding, and plasma arc smelting use this type of plasma arc.



   ③Combined 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.