The difference between oxy-acetylene flame powder spraying and spray melting

       Oxy-acetylene flame powder spraying and spray melting have many differences from the process method to the scope of application. The main differences between the two are as follows:



    1) Different process methods

    Although spraying and spray melting both use a spray gun to spray alloy powder on the surface of the workpiece, the specific process methods are different, from the pretreatment, preheating, powder spraying, cooling to the processing after spraying of the workpiece. There are different process requirements. The main difference is that the spray melting process includes a process of remelting the powder layer sprayed on the surface of the workpiece with a flame, that is, remelting. The spray coating process does not have a remelting process.

    2) The properties of the spray coating and the spray melting layer are different

    The properties of the spray coating and the spray melting layer are different, especially the mechanical properties are very different. The combination of the melt spray layer and the workpiece matrix is welded together, which is called metallurgical bonding. The normal tensile bonding strength is about 400MPa (about 40 kgf/mm2), which is similar to the welding strength and has good impact resistance. The combination of the spray coating and the workpiece matrix is mainly based on the mechanical combination of mutual anchoring, and the normal tensile bonding strength is 30MPa~50MPa. At present, some spraying processes can reach up to 150MPa, which is far lower than that of the spray melt layer. The bonding strength, the texture is relatively loose, and the impact resistance is also poor. The corrosion resistance of the two is also different. The corrosion resistance of the spray melt layer is strong, which can effectively protect the workpiece from corrosion. The spray coating is loose and porous. Although the coating itself has a certain anti-corrosion ability, the corrosive gas or liquid will reach the workpiece substrate through the pores and corrode the workpiece. Therefore, the spray coating cannot be used in a corrosive environment without sealing.

    3) Different effects on the substrate

    Melting has a greater impact on the substrate. The remelting process brings the local temperature of the substrate to 900°C or higher. On the one hand, it will cause changes in the metallographic structure, and on the other hand, thermal deformation will occur due to uneven heating of various parts of the workpiece. While spraying has no remelting process, the temperature of the substrate does not exceed 250 ℃ at most, which is far lower than the phase transition temperature of the iron alloy, the metallographic structure will not change, and the thermal deformation is very small.

    4) The tools and materials used are different

    Different guns should be used for spraying and spraying. The power of the spray gun is large, and the flame is large and dispersed, which is conducive to heating the powder in flight; the power of the spray gun is slightly smaller, but the flame is more concentrated, which is conducive to remelting.

    Spray powder and spray melt powder are generally not universal. Melting mainly uses self-fluxing alloy powder. The self-fluxing alloy powder can self-deoxidize and form slag during remelting to form a solid and dense spray-melt layer. For sprayed powder, it is not required to generate slag by itself, but it is required to have high bonding strength between the sprayed layer and the substrate. Therefore, spraying emphasizes the use of coated powders with self-heating properties. Due to different requirements for powder, the alloy composition and composition ratio of spray powder and spray powder are different.