The purpose of roughening before thermal spraying and the representation of roughening degree

       Correct mechanization is just as important as the cleaning process. During thermal spraying, heated particles in a molten or semi-molten state impinge on the surface of the substrate and deform to form flakes. When they cool or harden, they must adhere to the surface of the workpiece. The roughened surface facilitates the mechanical bonding of the coating.



1. Coarsening purpose



Coating-to-coating and coating-to-substrate bonding can be strengthened by roughening the surface of the part to be sprayed for the following reasons:



1) Put the surface in a state of compressive stress.



2) To form a stacked (or hierarchical) structure inlaid and interlocked between the deformed particles.



3) Increase the bonding area.



4) Decontaminate the surface.



2. Coarsening degree representation



In view of the different substrate materials and different coatings have different requirements on the roughness of the substrate surface before spraying, in order to obtain the ideal roughened surface required by the coating, it is necessary to carefully analyze the working conditions of the parts and carefully select the roughening materials and materials. Roughening method, and can measure the roughened surface in some way.



Generally, the surface roughness commonly used in mechanical design is used to represent the roughness of the surface of the part to be sprayed, and its unit is micrometer (um). Surface roughness mainly reflects the unevenness of the surface of the part.



In practical applications, the arithmetic mean deviation Ra of surface roughness is often used to represent the roughness of the surface of the part. It represents the degree of deviation between the uneven surface and the ideal neutral surface (the neutral surface represents an absolutely flat surface without unevenness, and the plane is used as the centerline of the upper and lower points of the measurement surface). The Ra value can be measured using a surface roughness meter, which uses a very fine pen tip to move over the entire work surface, measure the heights (hi) of multiple peaks and valleys to the centerline, and then take their average, i.e. Ra value can be obtained. 

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