What is surface pretreatment for thermal spraying

       The surface pretreatment of thermal spraying is generally divided into three steps: surface preprocessing, surface purification and surface roughening (or activation).

1 Surface preprocessing:

One is to make the surface of the workpiece suitable for coating deposition and increase the bonding area;

The second is to help overcome the shrinkage stress of the coating. Some parts of the workpiece are pre-processed to disperse the local stress of the coating and increase the shear resistance of the coating. Common methods are rounded corners and pre-coated grooves. Rough threading on the surface of the workpiece is also one of the commonly used methods, especially when spraying large workpieces, threading is often used to increase the bonding area.

2 Surface purification:

Solvent cleaning, lye cleaning and heating degreasing are often used to remove surface oil and maintain cleanliness. Commonly used cleaning solvents are: gasoline, acetone, carbon tetrachloride and trichlorohexene. Alkaline cleaning is often used for large repaired workpieces. The lye is generally prepared with sodium hydroxide or sodium carbonate, which is a relatively inexpensive method.

3. Sandblasting and roughening treatment: (This is an important pretreatment method for thermal spraying.)

Sandblasting can form a uniform and uneven rough surface on the cleaned surface to facilitate the mechanical bonding of the coating. Using clean compressed air to drive clean sand to spray on the surface of the workpiece can generate compressive stress on the surface of the substrate, remove the surface oxide film, and cause lattice distortion of part of the surface metal, which is conducive to the physical bonding of the coating. The substrate metal can be sandblasted to obtain a clean, rough and highly reactive surface.