Thermal spraying process and its precautions

Thermal spraying process selection In order to meet the requirements of the parts used in the coating, should be combined with the working conditions of parts and conditions of various coating materials, performance, process characteristics, coating properties and applicable environment and other considerations to determine the appropriate spray Materials, careful selection of spraying process. There are many methods of thermal spraying, but each method has its own advantages and limitations. Different choices of thermal spraying process will result in different results. Take high-speed flame spraying as an example, when using the HVOF process to spray metal. When alloys and cermets are used, high quality coatings with high bonding strength, high void density (1% porosity), and low oxide content can be obtained. However, this process has high operating costs and heats up to several people. Large, can not spray oxide ceramics and other shortcomings.

When selecting the thermal spraying process, a specific analysis should be made according to the specific requirements. The following analysis shall be carried out from four aspects: coating performance, type of spray material, economic performance of spraying, and field construction adaptability.

1, spraying performance requirements are not high, the use of the environment without special requirements, and the melting point of the coating material is lower than 2500 °C, you can choose a simple, lower cost of oxygen - acetylene flame spray coating process. Such as the repair of the general workpiece size and conventional surface protection;

2, spray performance requirements higher. The plasma spraying process may be used for the precious or critical components with poor working conditions. Compared with oxyacetylene flame spraying, the plasma sprayed flame has high temperature, sufficient melting, non-oxidation, high bond strength, and low voidage.

3, the coating requires high bonding strength, very low porosity, the metal or cermet coating, high-speed flame spraying process can be used; for oxide ceramic coating, high-speed plasma spraying process can be used.

Industry experts believe that the thermal spray process needs to pay attention to the following points:

1, according to the workpiece materials, technical requirements and working conditions, such as the use of grass-roots and working layer materials. Refer to other relevant information when selecting materials. In general, fine powder is used for thin coating and coarse powder is used for thick coating.

2. The main purpose of parts spraying is to compensate for the wear size. In general, after the painting, it must be mechanically processed to meet the dimensional and geometric accuracy requirements. Therefore, the allowance should be considered when determining the coating thickness, and the difference in size between the hot and cold parts of the workpiece should be considered. The thickness of the compensation layer is preferably 0.4 to 1 mm, and the partial thickness should be 3 mm. The machining allowance is generally 0.40.8mm. For the small amount of wear of the workpiece, spray only the self-bonding composite material, and its thickness should be 0.3mm.

3, to determine the coating material properties, thickness and granularity of the spray parameters, including acetylene and oxygen pressure, spray distance, the relative velocity of the spray gun and the workpiece. In addition to referring to relevant data, these parameters should pay attention to the accumulation of empirical data.