How to choose thermal spraying method and thermal spraying process

       In order to obtain a coating that meets the requirements for the use of the parts, the appropriate spraying materials should be determined in combination with the working conditions of the parts and the composition, performance, process characteristics, coating performance and applicable use environment of various spraying materials. Thermal spray process.



There are many thermal spraying process methods, but each method has its own advantages and limitations. Different results will be obtained when the thermal spraying process is selected from different angles. Taking high-speed flame spraying (HVOF for short) as an example, when the HVOF process is used to spray metals, alloys and cermet materials, high bonding strength (> 70MPa), high density (porosity <1%), and low oxide content can be obtained. However, this process also has disadvantages such as high operating cost, large heat input to the substrate, and inability to spray oxide ceramics.



Therefore, when choosing a thermal spraying process, specific analysis should be carried out according to specific needs.



1. Selection principle based on coating performance



1) The performance requirements of the coating are not high, the use environment has no special requirements, and the melting point of the spraying material is lower than 2500 ° C, the oxygen-acetylene flame spraying process with simple equipment and low cost can be selected. Such as general workpiece size repair and conventional surface protection.



2) For precious or key parts with high coating performance requirements and harsh working conditions, plasma spraying can be used. Compared with oxy-acetylene flame spraying, plasma spraying has high flame temperature, sufficient melting, non-oxidizing properties, high coating bonding strength and low porosity.



3) When the coating requires high bonding strength and extremely low porosity, high-speed flame (HVOF) spraying can be used for metal or cermet coatings; high-speed plasma spraying (such as Plaz) can be used for oxide ceramic coatings. Jet plasma spray). If spraying easily oxidized metal or cermet, controlled atmosphere or low pressure plasma spraying process must be used, such as Ti, B4C and other coatings.



2. Selection principle based on the type of spray material



1) For spraying metal or alloy materials, the arc spraying process can be preferred.



2) When spraying ceramic materials, especially oxide ceramic materials or carbide and nitride ceramic materials with a melting point exceeding 3000 ° C, the plasma spraying process should be selected.



3) Spray carbide coating, especially WC-Co, Cr3C2-NiCr carbide coating, high-speed flame spraying process can be used, and the coating can obtain good comprehensive performance.



4) When spraying the biological coating, the controlled atmosphere or low pressure plasma spraying process should be used.



3. Selection principle based on coating economy



Under the condition that the cost of spraying raw materials is not much different, among all thermal spraying processes, arc spraying has the lowest relative process cost, and this process has the characteristics of high spraying efficiency, high bonding strength between coating and substrate, and suitable for on-site construction. Use the arc spraying process as much as possible.



4. Selection principle based on on-site construction as the starting point



When making process selection with on-site construction as the starting point, arc spraying should be the first choice, followed by flame spraying. Portable HVOF and low-power plasma spraying equipment can also be sprayed on site. At present, some people install the plasma spraying equipment on the mobile motor vehicle to form a mobile spraying workshop, so as to complete the long-distance on-site spraying operation.