Dusting compared with paint film, powder coating hasmore advantages, such as environmental pollution ofsmall, hard, tough film, strong adhesion to the substrate,the corrosion resistance of higher. However, higher requirements on the pretreatment
Compared with the paint film, powder coating has more advantages, such as low pollution to environment, the film hard, good toughness, strong adhesion to the substrate,the corrosion resistance of higher. However, higher requirements on the pretreatment, so the requirements of workpieces dusting mentioned pretreatment process anddusting system requirements, so as to give constraints onthe use of powder conditions.
In order to strengthen the metal surface into solid powderbinding force and improve the surface protectivetreatment before, whether steel or zinc, aluminum and its alloys are necessary.
Powder coating and blasted steel and no oil freegalvanized steel with pretreatment is quite good.However, when in the corrosive environment, the corrosive conditions even moderate, separation within a short period of time will cause the protective film and substrate. In addition, the binding force of plasticmembrane and effect of protective is also affected by theprocessing system and the powder itself quality.
Although most protective film is better than that of powderin the wet film, and specific humidity of the film more hard,more thick, but it is still a semi permeable membrane,oxygen, moisture, sulfur dioxide and other corrosive substances can still penetrate it, they were entered into the membrane, that is in contact with the base metal andcorrosion, the loss caused by the combination of forceorganic membrane and matrix, especially for the morezinc, aluminum this phenomenon seriously.
In order to enhance the binding force of the powder film and the substrate, increase the protection, can adoptdifferent treatments according to the type of metal.
Must pay attention to several powder film coating pretreatment important requirements:
1, in order to ensure the quality of the metal powder, the surface must be thoroughly remove oil, because oilpowder residue on the unbearable. To paint, thinners is the solvent, it usually can be a small amount of oil into thefilm, reduce the adverse effects of the adhesion, powderis not the performance, in the baking process is often leftholes or blisters burst open, or complete loss of binding capacity.
2, rust, oxide skin and ash is another important reason fordry film defects. When the workpiece surface is thepresence of dirt, combined with the powder film and theyare very reluctantly, by mechanical collision ordeformation, powder film will immediately run down, this kind of phenomenon is the most common. Various powderpretreatment left are also important reasons causing the binding force reduction.
3, the strong acid washing, especially for long time strongacid hot rolling steel wash, used as a powder coating is not suitable for. In strong acid pickling process, will be a lot of hydrogen permeation, whereas at high temperature(180-200 degrees Celsius) during the curing process of hydrogen is released, so that the formation of a large number of sand hole and film hole. Therefore it is necessary to use strong acid pickling, pickling andphosphating should be carried out after the addition of hydrogen.
4, in order to make the spraying aluminum pieces form abeautiful and attractive appearance, cleaning (oil) and corrosion (except for the natural oxide) is necessary to separate process. Cant believe the metal surface oilpollution oil pollution and the thickness is uniform, when the cleaning / corrosion in the process, in addition to the net before oil corrosion does not occur, but because ofpollution degree of each part of the metal surface of thedifferent parts of oil, oil light is in addition to the net andcorrosion, and corrosion will surface height pollution of the delay, resulting in uneven corrosion, resulting in metalsurface may generate visible damage shape, the final stage of the damaged surface shape of production,namely the use of powder coating can not cover up.
Principles for various pretreatment wet paint can be used for powder coating, which is different from the formerprocessing requirements are higher, more fineconversion film, film weight to below 3.0g/m2, and has good thermal stability.