Metal surface conversion film general pretreatment 3 major purposes

Regardless of the surface treatment process, to achieve good results, cleaning the surface is the primary condition. Because the surface of the parts sent to the surface treatment plant usually has various defects such as wear marks, pits, burrs, scratches, etc., with lubricating oil traces or varying degrees of abrasive and some dirt. If the surface conversion film is not washed before treatment, it will be exposed after the conversion film treatment, affecting the performance of the film. Therefore, cleaning the surface is the primary process of the chemical conversion film treatment process.

Surface preparation includes mechanical treatment and chemical pretreatment. Mechanical treatment of grinding wheel grinding, mechanical polishing, sand blasting, and other polishing. Chemical pretreatment is divided into acid degreasing, alkaline degreasing, emulsion degreasing, solvent degreasing, electrolytic degreasing, ultrasonic degreasing, electrolytic polishing, chemical polishing and the like.

The following three purposes of metal surface conversion film pretreatment:

(1) Ensure that the coating film has good corrosion resistance and maintain good adhesion of the coating film to the surface of the substrate.

Oxide scale, rust, welding slag, oil stains, water, dust and old unstainable coatings on the metal surface affect the adhesion and corrosion resistance of the coating film to the surface of the substrate. The purpose of surface treatment is to thoroughly remove these contaminants to improve the adhesion and corrosion resistance of the film.

(2) Improve the appearance quality of the coating film.

The surface roughness of the substrate is different due to the nature of the material and the different processing methods. If the casting is molded by the common method, the surface is rough. The castings changed to resin sand have a smooth surface. Mechanical methods can be used to eliminate the machining defects of the substrate and to create the surface roughness required for the coating. Another example is that the large-scale welded parts are subjected to integral blasting treatment, and the flattening method is used to flatten the defects of the base sheet metal parts, and the castings are subjected to leveling pretreatment. With a flat substrate surface, the quality of the coating to be obtained depends on the properties of the selected coating and the correct method of construction.

(3) Improve the adhesion and corrosion resistance of the coating film.

For example, the steel parts are phosphatized before coating, and the aluminum parts are oxidized to improve the adhesion of the coating film to the workpiece base and enhance the corrosion resistance; before the coating of the plastic parts to be coated Special chemical treatment is carried out to improve the bonding between the coating film and the plastic surface.