Hollow cathode central axial powder-feeding plasma spraying gun

Abstract

The present invention is one plasma spray gun with hollow cathode and powder feeding in central axle direction. The hollow cathode is made of concentric inner tube and outer tungsten tube, and the anode has nozzle cavity with trapezoidal cross section. The plasma spray gun in such a structure can control effectively the flying locus of powder inside the plasma jet and feed powder to the center of the plasma jet to heat and accelerate sprayed particles effectively, and has stable arc burning, less adhesion of powder and long service life of the electrodes.

Description

1. Technical field [0001] The invention relates to a structure of a plasma spraying gun mainly used in the field of machinery and electric appliance manufacturing, in particular to a plasma spraying gun with hollow cathode central axial feeding powder. 2. Background technology [0002] Plasma spraying uses the non-transferred plasma arc generated by the plasma spray gun as the heat source. When the working gas passes through the nozzle hole, it is heated to a very high temperature by the arc, and it expands violently and sprays out rapidly, forming a high-temperature and high-speed plasma jet. The sprayed material is in the form of powder The form is sent to the plasma jet, where it is heated and accelerated to form a molten particle flow, which hits the surface of the substrate at high speed to form a coating. [0003] The traditional plasma coating guns adopt the powder feeding method outside the gun (referred to as the powder feeding method) or the powder feeding method i...

AI Technical Summary

Problems solved by technology

[0003] The traditional plasma coating guns adopt the powder feeding method outside the gun (referred to as the powder feeding method) or the powder feeding method inside the gun through the anode nozzle (referred to as the powder feeding method). Due to the joint influence of powder gas flow rate, powder particle size distribution and powder material density, as well as the temperature gradient and velocity gradient of the plasma jet, the trajectory of the particles diverges and it is difficult to fully enter the high temperature region of the plasma jet, and the dispersion of the particle trajectory makes the particles flow in different directions The state of the collision with the matrix increases the inhomogeneity of the coating structure and performance, especially when the spraying material is two or more mixed powders with different densities, the problem of particle state parameter dispersion is more serious, which will lead to the coating performance Serious non-uniformity occurs, and it is difficult for traditional plasma spray guns to effectively solve this problem

[0004] The more common method is to make up for the uneven heating and acceleration of particles by increasing the arc power, but the increase in plasma arc power also brings other problems, such as the reduction in the heating efficiency of the arc (the heat used to heat the powder only accounts for the arc 3% to 5% of the heat), when spraying smaller parts, the larger diameter of the plasma jet deposition beam spot leads to lower powder deposition efficiency, etc.

[0005] In order to improve the heating efficiency of the powder and improve the uniformity of the coating performance, a high-power plasma spray gun with axial powder feeding mode appeared in the 1990s, and its structure mostly adopts a multi-electrode structure, such as a three-cathode structure spray gun and a multi-pair electrode structure spray gun. , under this structure, the powder can be fed from the axis of the spray gun, as a result, the uniformity of heating acceleration of the particles and the efficiency of powder deposition are improved, but the structure of the spray gun is complicated and the equipment cost is high

However, the method of processing the powder feeding channel at the center of the solid cathode has the following problems: first, the cathode is always in a high temperature state during the spraying process, and the powder is easy to melt near the end of the cathode to block the powder feeding channel, especially for metals with a low melting point Therefore, continuous spraying cannot be achieved. Secondly, the powder feeding airflow in the center hole directly enters the arc, causing disturbance to the arc, resulting in fluctuations in arc voltage and poor stability, making it difficult to meet the requirements of spraying.

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