The coating pretreatment includes three parts of degreasing, descaling and phosphating. Phosphating is the central link. Degreasing and derusting are the preparation steps before phosphating. Therefore, in the practice of producing electrophoretic coating production line, it is necessary to focus on phosphating work and to proceed from the requirements of phosphating quality. Good degreasing and descaling work, pay special attention to the interaction between them.
Degreasing and derusting
A high-quality phosphating film is formed only on the surface of a workpiece that has been completely removed from foreign matter such as oil, rust, or scale. Because the oil, rust, scale, etc. remaining on the surface of the workpiece will seriously hinder the growth of the phosphating film. In addition, it also affects the adhesion of the coating, drying performance, decorative properties and corrosion resistance. Thorough removal of these foreign materials is a necessary condition for phosphating.
Degreasing and derusting are the two basic processes before phosphating. Relatively speaking, oil is more harmful than rust, and oily workpieces directly affect the descaling speed. Therefore, derusting should be carried out on the basis of degreasing. However, for the workpiece with less oil and less rust, the two basic processes of degreasing and derusting can be combined into one, and the degreasing and derusting process can be completed simultaneously in one tank, which can shorten the electrophoretic coating production line and reduce equipment and plant investment. The cost, but the processing quality is not as good as the slotting, and can be used for occasions where the requirements are not high. After using this process, the degreaser should also be selected with an acidic yao agent and a rust remover. Hydrochloric acid is still used for derusting. The descaling speed of hydrochloric acid is fast, the rust removal is thorough, the oxide scale is also well removed, and it is used at room temperature. The disadvantage is that the hydrochloric acid rust and acid mist is large, harmful to health and serious environmental pollution.
With the development of industry, environmental protection and improvement of working conditions have become a common concern. Therefore, the need for environmental protection should be considered when selecting a drug. Therefore, when degreaser is selected, it is required to be simple to prepare, strong in decontamination ability, and does not contain sodium hydroxide, silicate, OP emulsifier and the like which are difficult to clean at normal temperature. It is easy to be washed at normal temperature, contains no toxic substances, and does not generate harmful gases. Good working conditions; when selecting rust remover, it is required to contain accelerator, corrosion inhibitor and inhibitor, which can improve the descaling speed, prevent over-corrosion and hydrogen embrittlement of the workpiece, and can better suppress acid mist. Especially worthy of attention is acid mist suppression, acid mist generated during pickling and descaling, not only corrosive equipment and plant, pollute the environment, but also cause people’s teeth to corrode, reddened conjunctiva, tears, pain, dry throat, cough, etc. Symptoms, therefore, effectively suppress acid mist, not only the need for environmental protection, but also the needs of the unit itself.
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