Electrostatic powder spraying is an efficient and environmentally friendly coating technology that is widely used in various industrial fields. However, to ensure the spraying effect and coating quality, the workpiece must be strictly pretreated before spraying. The purpose of pretreatment is to remove oil, rust and oxides on the surface of the workpiece and enhance the adhesion and durability of the coating. This article will introduce in detail the steps and functions of workpiece pretreatment before electrostatic powder spraying.

1. Necessity of pretreatment

In the process of electrostatic powder spraying, pretreatment is an indispensable link, and its main purpose is to:
• Remove surface pollutants: including oil, dust, oxides, etc., which will affect the adhesion of powder coating.
• Improve coating adhesion: Through surface treatment, the surface of the workpiece is formed with a certain degree of roughness to enhance the mechanical adhesion of the coating.
• Prevent coating defects: Effective pretreatment can avoid defects such as peeling, pinholes, bubbles, etc. in the coating.
• Extend coating life: Pretreatment enables the coating to better protect the workpiece and extend its service life.

2. Pretreatment steps and functions

2.1 Degreasing
Steps: Immerse the workpiece in a degreasing tank or use a spray device to degrease the workpiece, usually using an alkaline solvent or emulsifier.
Function: The main function of degreasing is to remove oil and other organic pollutants on the surface of the workpiece. This step is very important because oil will affect the adhesion of the coating, causing the coating to fall off or bubbles to appear.

2.2 Water washing
Steps: The degreased workpiece needs to be washed with water several times to ensure that the degreaser and residue on the surface of the workpiece are completely removed.
Function: The purpose of water washing is to remove the chemicals and solvents remaining on the surface of the workpiece during the degreasing process, so as not to affect the subsequent processing steps and coating quality.

2.3 Rust removal

Steps: According to the degree of rust and material properties of the workpiece, choose mechanical rust removal (such as sandblasting) or chemical rust removal (such as pickling) methods.

Function: Rust removal is to remove rust and scale on the surface of the workpiece, ensure that the surface of the workpiece is clean and provide a good basis for coating adhesion.

2.4 Phosphating

Steps: Immerse the workpiece in the phosphating solution, and after a certain period of reaction, wash it with water.

Function: Phosphating can form a tiny, porous phosphate film on the surface of the workpiece. This film can effectively improve the adhesion of the coating, and has a certain anti-corrosion effect, protecting the workpiece from environmental influences.

2.5 Neutralization

Steps: After phosphating, the workpiece will be neutralized, usually using a weak acid or weak base solution.

Function: The purpose of neutralization is to adjust the pH value of the workpiece surface to prevent the residual chemicals in the phosphating process from having an adverse effect on the subsequent coating.

2.6 Passivation

Steps: Apply or soak the passivation solution on the phosphated workpiece, and then dry it.

Function: Passivation can improve the corrosion resistance of the workpiece surface and further enhance the adhesion and durability of the coating.

2.7 Drying

Steps: After the pretreatment is completed, the workpiece is sent to the drying furnace or air drying equipment for drying.

Function: The purpose of drying is to completely remove moisture from the surface of the workpiece to avoid bubbles or pinholes caused by evaporation of moisture during spraying.

Conclusion

Pretreatment is an indispensable step in the electrostatic powder spraying process, which directly affects the quality of spraying and the service life of the workpiece. Through systematic degreasing, rust removal, phosphating and passivation treatment, the workpiece surface can achieve an ideal state, ensuring good adhesion and durability between the coating and the workpiece.

Reasonable pretreatment process can not only improve the coating quality, but also bring higher production efficiency and economic benefits to the enterprise.