What is Surface Pre-treatment for Plasma Spraying?

Surface pre-treatment for thermal spraying is divided into three stages: surface pre-machining, surface cleaning, and surface roughening.

1. Surface Pre-machining

This stage aims to prepare the workpiece surface for coating deposition, increasing the bonding area and helping to overcome the coating's shrinkage stress. Specific areas of the workpiece may undergo pre-machining to disperse local stresses in the coating and improve its shear resistance. Common methods include rounding corners and prefabricating coating grooves. Rough turning threads are also a frequently used method for the surfaces of large workpieces.

2. Surface Cleaning

Methods such as solvent cleaning, alkaline cleaning, and heated degreasing are commonly employed to remove surface contaminants and maintain cleanliness. Common cleaning solvents include gasoline, acetone, carbon tetrachloride, and trichloroethylene. Alkaline cleaning is often used for large repair workpieces, typically using sodium hydroxide or sodium carbonate, as this is a more economical approach.

3. Sandblasting Roughening Treatment

Sandblasting is an essential pre-treatment method for thermal spraying. It creates a uniform, rough surface on the cleaned surface, facilitating mechanical bonding of the coating. Clean compressed air drives clean sand particles to impact the workpiece surface, generating compressive stresses, removing surface oxide films, and causing some surface metal to undergo lattice distortion, which enhances the physical bond of the coating. The metal substrate achieves a clean, rough, and highly active surface after sandblasting.

This overview of surface pre-treatment related to supersonic spraying technology is intended to be helpful.