The principle, composition and process characteristics of flame spraying for bars

       Using the flame of oxyacetylene combustion as a heat source, the bar is coated with a thermal coating material. Since metal materials are simply made of wires, metal oxides, that is, ceramic materials, cannot be processed into wires, and can only be made into rods of a certain length and thickness at most, so the flame coating of rods mainly refers to the flame coating of ceramic rods. This process first appeared in the 1960s. At that time, plasma spraying technology was not popular in China, and it has been successfully applied in military fields such as aviation and aerospace. In the middle and late 1970s, with the popularity of plasma spraying technology in China, flame sprayed ceramic rods gradually withdraw from the application field. However, in the early 1990s, China introduced the flame sprayed ceramic rod technology from Norton Corporation of the United States. Because the technology has its unique characteristics and has been successfully applied in some fields, the flame sprayed ceramic rod technology has once again attracted the attention of the industry.



1. The principle of spraying.

The spraying principle of metal wire flame spraying is exactly the same as that of metal wire flame spraying, and will not be repeated. The main feature of the coated ceramic rod is that the ceramic rod stays in the oxyacetylene flame for a long time, so that after the ceramic rod is fully melted in the flame, it is sprayed into particles to form a coating. This overcomes the shortcomings of high melting point of the ceramic powder, short residence time in the flame, insufficient melting and affecting the quality of the coating when the oxyacetylene flame powder is sprayed.

2. Equipment composition.

The structure of Norton's RokideCeramicSpraySystem in the United States includes an oxyacetylene supply system, a compressed air supply system, a bar conveying speed adjustment device and a spray gun. Except for certain differences in structure, the effects of other systems and wire flame spraying are basically the same.

The gun is compact, and the transport of the bars relies on a motor behind the gun. There is a control wire behind the motor that connects to the control box. The control box is equipped with a speed control knob, and the digital display is clear. The rod feeding speed is precisely controlled, and the motor has an automatic conversion function, which can adapt to different input voltages and frequencies around the world. For the convenience of operation, the spray gun is also equipped with a control button, which is used to control the feeding of the rod and the on-off of the gas.



3. Characteristics of coating and process technology.

1) The structure and properties of the coating. According to the characteristics of the ceramic rod spray gun, only after the end of the ceramic rod is fully heated and melted, can it be sprayed and atomized into droplets and sprayed from the nozzle. The spraying speed is about 150-250 m/s. The high kinetic energy and thermal energy keep the particles in a molten state when they reach the workpiece surface, thereby ensuring high bonding strength between the coating particles and high density of the coating.

(2) The following are the technical characteristics of the process.

The equipment is simple in structure and easy to operate. It can be operated in the thermal spraying workshop as well as on-site construction work.

2) There are many types of ceramic rods that can be sprayed, including 17 types of chromium oxide, aluminum oxide, zirconium oxide, titanium dioxide, etc., and the specifications are φ4.75mm, φ6.35mm, and φ7.94mm. At the same time, the powder core wire with a diameter of φ4.75mm is sprayed.



China currently has imitation similar equipment and ceramic rods, but there is still a gap between the level of equipment and materials. The development of high-performance ceramic bar coating mainly relies on imported equipment and bars.