Why should the workpiece be preheated before spraying?

       The purpose of preheating the workpiece before spraying is to:



1) Reduce the temperature difference between the coating and the substrate. During the spraying process, when the sprayed particles solidify on the surface of the substrate, different types of stress will be generated, and these stresses will affect the self-strength and bonding strength of the coating. The main cause of this stress is the temperature difference between the coating and the substrate. No matter what material is sprayed, reasonable preheating on the surface of the substrate is beneficial to improve the bonding strength of the coating and make the coating less prone to cracks.

2) Remove moisture and activate the surface, which is beneficial to the combination of the coating and the substrate, and to control the thermal expansion of the substrate relative to the coating.

3) Reduce the stress. For some thin-walled parts, it can reduce the stress caused by the inconsistency of the shrinkage of the parts and the coating during cooling after spraying, which is beneficial to the combination of the coating and the substrate.

4) Control the temperature of the substrate. For iron-based powder, control the temperature of the substrate before spraying, and preheat it to about 150 °C, which can fully analyze the carbide phase in the coating and improve the wear resistance of the coating.

5) Improve the fatigue resistance, preheating before spraying can also reduce the drop in the fatigue resistance of the coating after the parts are sprayed, and improve the service life of the coating. The optimal preheating temperature can increase the working life of the coating by 2 to 5 times.