Process principle and technical characteristics of flame wire spray gun

       Steel wire flame coating takes oxyacetylene flame as heat source and steel wire as coating material for thermal coating. This was the earliest thermal spray method and is still widely used today.



1. The principle of spray

The spray material is introduced into acetylene, oxygen and compressed air respectively through the siphon nozzle, heated and atomized by a flame spray gun, and then mixed with oxygen to generate a flame at the nozzle outlet. The wire feed roll drives the wire continuously from the center of the nozzle into the flame and melts in the flame. The compressed air passes through the air cap to form a conical high-speed airflow, which atomizes the molten wire into tiny particles. Propelled by a flame and high-velocity airflow, the molten particles are sprayed onto the pretreated substrate surface to form a coating.

The output per unit time of smelting wire depends on the flame power. By changing the flow ratio of oxygen and acetylene, an oxidizing flame or a neutral flame can be obtained, which will enhance the combustion of carbon in the wire and increase the oxides in the coating. Neutralizing the flame can reduce the degree of oxidation of the sprayed material to a certain extent.

The working principle of the compressor is to separate and atomize the molten metal. Generally, the compressed air consumption is between 0.8~1.2m3/min, and the pressure is between 0.40~0.60MPa.

The wire feeding depends on the gas turbine or motor in the gun, and the wire feeding speed is controlled by adjusting the rotational speed. Gas turbine spray gun, compact structure, light weight, suitable for manual operation. However, the wire feeding speed is difficult to fine-tune, easily affected by compressed air, and difficult to keep constant. With motor-driven spray guns, the wire feed speed is easy to adjust and can be kept constant, so this form of spray gun is increasingly used.

The diameter of the spinneret is generally Φ1.6mm-Φ4.8mm, and the spray gun is equipped with different types of nozzles and air hoods to meet the spraying requirements of different diameters and materials.

2. Equipment composition

The typical composition of the flame spray line device, including the oxyacetylene feeding system, the compressed air feeding system, the spray line machine gun, etc.

1. Acetylene oxygen supply system. It consists of gas source, pressure and flow regulating device, anti-backfire device and gas delivery pipeline. The air source is mainly bottled oxygen and acetylene. The oxygen pressure reducing valve and acetylene pressure reducing valve used for pressure regulation should be purchased from regular manufacturers, checked regularly, and can be used only after they are qualified. Float flowmeter is used to control the flow. The needle valve should be sensitive and accurate, and the use value should be between 40-70% of the full scale. An anti-backlash valve must be installed between the nozzle and the flowmeter to ensure safety during the injection process.

2. Compressed air supply system. In order to ensure the coating quality, the compressed air of the feeder and spray gun must be clean and dry, that is, oil-free and water-free. Therefore, the compressed air supply system should include an air compressor and an air purifier.

3. Spray gun. There are two main types of spray guns currently used in my country: one is domestically produced, typically the SQX-1 pneumatic spray gun, and the other is imported, mainly the 12E and 14E flame wire spray guns produced by Metco in the United States. , This spray gun adopts pneumatic turbine wire feeding, and its pneumatic part has high processing precision, stable wire feeding speed, wide speed regulation range, and high and low melting point materials can be sprayed.



3. Characteristics of coating and process technology

1) The structure and properties of the coating. The coating structure of the flame sprayed line is obviously delaminated, and there are a lot of pores and oxide slag in the coating. Different spraying processes and spraying materials have different coating properties.

2) Process characteristics. Oxy-acetylene wire flame spraying equipment is simple, easy to operate, low cost of use, and has a wide range of uses. Its main features are:

The equipment is simple, the operation is convenient, the cost is low, and it can be repaired on site.

There are many spraying materials, almost all metal materials that can be brushed can be sprayed, and composite wire can also be sprayed.

In the spraying process, the heat transfer to the substrate is small, the workpiece is not easily deformed by heat, and a thick layer can be sprayed.