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powder flame spraying

00862799362022-01-24
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Powder flame spraying is a thermal spraying method that uses an oxygen-acetylene flame as a heat source and the spraying material is powder.

It is a spraying method after flame wire spraying. Due to the simple equipment and many kinds of spraying materials, it is the most commonly used thermal spraying process in China.
1. The principle of spraying
Powder flame spraying is carried out with the aid of a powder flame spray gun. Oxygen and acetylene are respectively introduced into the spray gun through the siphon nozzle, and the two are mixed to generate a combustion flame at the nozzle outlet. The spray gun is equipped with a powder hopper or a powder inlet. The negative pressure generated by the air flow is used to suck the powder in the powder hopper, so that the powder is ejected from the center of the nozzle into the flame with the air flow, heated or softened, and the flame flow pushes the molten particles at a certain speed. Spray onto the workpiece surface to form a coating. In order to increase the flying speed of the particles, some spray guns are equipped with compressed air nozzles, which give additional thrust to the particles with the help of compressed air.
In the process of being heated, the powder melts from the surface layer to the core, and the molten surface layer tends to be spherical under the action of surface tension, and there is no atomization process in which the powder particles are broken again. Therefore, the size of the powder particles determines the size and surface roughness of the deformed particles in the coating to a certain extent. In the process of being heated and accelerated by the flame, the powder is heated to different degrees due to the different positions of the powder in the flame. Some are melted or semi-melted, and some are only softened or semi-softened. This is quite different from the melting-atomization process of wire flame spraying, so that the bonding strength and compactness of powder flame spraying coatings are generally not as good as wire flame spraying.

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