Before spraying the workpiece, remove all kinds of stains and impurities (such as lubricating oil, emulsion, grease, rust, scale, welding slag, salt-alkali spots, dust, etc.) on the surface of the workpiece to make it clean and stain-free, so as to meet the requirements of powder spraying or painting. This is an essential basic process in the coating production line, which is usually called coating pretreatment. According to the material, size, dimensions, weight and other factors of the workpiece, the choice of chemical treatment (or conversion film treatment) or mechanical processing treatment (such as shot blasting, etc.) is what customers and engineers need to clarify. Different workpieces have different pretreatment methods. However, most of the current pretreatments include degreasing (degreasing), rust removal (for metal workpieces), water washing, coating, (pure) water washing, drying and other basic steps. Engineers need to design various non-standard pretreatment steps and parameters according to customer needs and the characteristics of the workpiece.
Degreasing:
Degreasing is a basic process before coating. The oil, rust, scale, etc. remaining on the surface of the workpiece will seriously hinder the growth of the film, and will also affect the adhesion, drying performance, decorative performance and corrosion resistance of the coating. Only after these foreign matters are completely removed can a high-quality film be formed on the surface of the workpiece to achieve an ideal spraying effect. Degreasing can usually be divided into pre-degreasing and main degreasing steps.
Washing:
After degreasing, certain non-ionic surfactants and degreasing agents are easily attached to the surface of the workpiece. These residual substances need to be washed with water. Water washing can be divided into ordinary water washing and pure water washing. Pure water washing is suitable for workpieces with higher surface cleanliness.
Pretreatment Silane Technology:
Traditional phosphating has been widely used in the pre-treatment process of coating. However, harmful heavy metals such as nickel, zinc, and manganese will be produced in the phosphating process, which is difficult to meet environmental protection requirements, will cause serious pollution to the environment, and will endanger people's health. Therefore, silanization technology has gradually replaced phosphating technology. Silane treatment does not produce harmful substances such as nickel, zinc, and manganese, does not contain phosphorus, does not require heating, has fewer treatment steps, can save the surface adjustment and passivation process, and is simple to maintain. It has become a coating technology that is generally recognized and adopted in the pre-treatment process.
Drying of the film:
After the workpiece is coated, it will enter the drying tunnel to dry the film, which can play two roles. On the one hand, it is to prepare for the next painting process to remove moisture from the surface of the film. On the other hand, it is to further improve the corrosion resistance of the film after painting.
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