Pretreatment before powder coating/painting

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When we make design, we try to choose surface treatment processes and methods that are highly targeted, have good treatment effects and are relatively cheap as much as possible according to the coating method, the material of the workpiece and its surface state. 

The surface treatment of the workpiece before powder coating/painting is one of the important parts. It mainly includes degreasing, rust removal, surface adjustment, phosphating, passivation and other processes.

The quality of pretreatment will not only affect the appearance of the film, reduce the anti-corrosion performance, but also destroy the stability of the paint/powder solution. 

Therefore, for the surface of the workpiece before powder coating/painting, it is required to be free of grease, rust, pre-treatment chemicals and phosphating sediments, etc., and the phosphating film crystallization is dense and uniform.

There are some points need to be noted when we try to choose surface treatment processes:

1) If the grease and rust removal is not be cleaned, it will not only hinder the formation of phosphating film, but also affect the bonding force, decorative performance and corrosion resistance of the coating.

2) Phosphating: The purpose is to improve the adhesion and anti-corrosion ability of the powder and electrophoretic film. Its role is as follows:

• A. Due to physical and chemical effects, the adhesion of the organic coating film to the substrate is enhanced.
• B. The phosphating film changes the metal surface from a good conductor to a poor conductor, thereby inhibiting the formation of micro-batteries on the metal surface, effectively hindering the corrosion of the coating, and multiplying the corrosion resistance and water resistance of the coating.

In addition, only on the basis of thorough degreasing can a satisfactory phosphating film be formed on a clean, uniform, and grease-free surface. From this aspect, the phosphating film itself is the most intuitive and reliable self-test for the effect of the pre-treatment process.

3) Passivation: Refers to the protective film formed by the pigments in the paint on the metal surface, such as chromate antirust pigments.

4) Washing: The quality of washing at each stage of pretreatment will have a great impact on the entire pretreatment and the quality of the powder/paint film. The last deionized water cleaning before painting should ensure that the drip conductivity of the coated object is not greater than 30μs/cm.

If you’re planning to set up a powder coating line/painting plant, welcome to contact us, we will provide the most suitable solution according to your situation.

Claire Shi

Phone/Whatsapp/Wechat: +86 15131185156

Email: sales02@coating-equipment.com

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