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Conversion coating on the metal surface general pretreatment three purposes
no matter what kind of surface treatment technology, to obtain good effect, clean the surface is the primary condition. Because of the surface of the parts to the surface treatment workshop will usually exist all kinds of grinding crack, pits, burr, scratch defects, such as lubricating oil trace or covered with abrasive in different degrees, and some dirt. If not washed before conversion coating surface treatment, aluminum manufacturers will be exposed after conversion coating processing, affect the performance of the membrane. So clean surface is the first process of chemical conversion coating process. Surface pretreatment including mechanical processing and chemical pretreatment. Machinery processing grinding wheel grinding, polishing, sandblasting shot peening, other polishing. Chemical pretreatment acidic degreasing, basic degreasing, emulsion degreasing and solvent degreasing, electrolytic degreasing, ultrasonic degreasing, electrolytic polishing, chemical polishing, etc. To introduce the following conversion film on the metal surface pretreatment of three purposes: ( 1) Guarantee the coating has good corrosion resistance, and keep the coating has good adhesion with the substrate surface. Metal surface scale, rust, welding slag, oil, water, dust and the old is not solid coating, these are all affect the coating and the substrate surface adhesion and corrosion resistance. The purpose of surface treatment is to thoroughly remove these pollutants, in order to improve coating adhesion and corrosion resistance. （ 2) Improve the quality of the appearance of the coating. The surface roughness of the substrate, due to the nature of the material and surface condition caused by different processing methods of different aluminum manufacturers. If use common law modelling of casting, the surface rough. Instead of resin sand molding casting, the surface is flat and level. Can adopt the method of mechanical machining defects, to eliminate the matrix required to create the coating and surface roughness. And like a large weldments with the sandblasting processing, use the method of hammering flat substrate sheet metal pieces of the defect of uneven, to smooth the casting pretreatment, etc. A flat substrate surface, in order to get high quality coating, but also depends on the performance of the selected coating and the correct construction method. （ 3) To improve coating adhesion and corrosion resistance. As to phosphating of iron and steel parts before coating, oxidation on aluminum parts processing, aluminum manufacturers in order to improve the adhesion and artifacts substrate and enhance the corrosion resistance force; Plastic parts before coating of to be special chemical treatment, in order to improve the coating with the binding force of plastic material and so on.