flame spray

       flame spray

Flame spraying includes wire flame spraying and powder flame spraying.

Wire flame spraying method: It is the first spraying method invented. It is to send the metal wire into the spray gun at a certain speed, so that the end is melted in the high temperature flame, and then atomized and blown away with compressed air, and deposited on the surface of the pretreated workpiece.

The spray source is a nozzle, the wire passes through the center of the nozzle, and the tip of the wire is continuously heated to its melting point through an annular flame formed around the nozzle and the hood. Then, it is atomized into spray particles by the compressed air passing through the air hood, which is accelerated and sprayed onto the substrate by the air flow, so that the molten particles are cooled to a plastic or semi-molten state, and a certain degree of oxidation also occurs. Particles that collide with the substrate flatten and bond to the surface of the substrate, and subsequent particles that impinge with the substrate also flatten and bond to particles previously bonded to the substrate, thereby building up a coating.

The wire is conveyed by the rotation of the air turbine or electric motor in the spray gun, the speed of which can be adjusted to control the wire feeding speed. Using the air turbine spray gun, it is difficult to fine-tune the wire feeding speed, and its speed is difficult to be constant due to the influence of compressed air, but the spray gun is light in weight and suitable for manual operation; The speed is easy to adjust and can be kept constant, and the spraying automation is high, but the spray gun is cumbersome and only suitable for mechanical spraying. In the wire flame spray gun, the gas flame is mainly used for the melting of the wire, and the diameter of the wire suitable for spraying is generally 1.8 to 4.8 mm. However, sometimes larger diameter bars and even some strips can be sprayed, but at this time, a specific spray gun must be used.

Powder flame spraying method: It is different from wire flame spraying in that the spraying material is not wire but powder.

A combination of acetylene and oxygen is usually used to provide heat in flame spraying, but methylacetylene, propadiene (MPS), propane, hydrogen or natural gas can also be used. Flame spraying can spray metals, ceramics, plastics and other materials, the application is very flexible, the spraying equipment is light and simple, movable, the price is lower than other spraying equipment, the economy is good, and it is a widely used method in spraying technology. However, flame spraying also has obvious shortcomings. For example, the speed of the sprayed particles is small, the flame temperature is low, the bonding strength of the coating and the comprehensive strength of the coating itself are relatively low, and the porosity obtained by other methods is lower. In addition, the center of the flame is an oxidizing atmosphere, so attention should be paid to the use of high melting point materials and easily oxidized materials. In order to improve the deficiencies of flame spraying and improve the bonding strength and coating density, compressed air or airflow acceleration devices can be used to increase the particle velocity; the compressed air flow can also be changed from air to inert gas to reduce the degree of oxidation, but this It also increases costs.