Pretreatment before painting includes three parts: degreasing (degreasing), rust removing and phosphating. Phosphating is the central link. Oil removal and rust removal are the preparatory processes before phosphating. Therefore, in production practice, we should not only take phosphating work as the key point, but also proceed from the requirements of phosphating quality, do a good job of oil removal and rust removal, especially pay attention to their mutual influence. 1. The high-quality phosphating film for degreasing and rust removal can only be formed on the surface of the workpiece which completely removes foreign bodies such as oil, rust and oxide scale. Because oil residue, rust and oxide skin on the surface of the workpiece will seriously hamper the growth of phosphating film. In addition, the adhesion, drying performance, decorative performance and corrosion resistance of the coating will be affected, and the thorough removal of these foreign bodies is a necessary condition for phosphating. Oil removal and rust removal are two basic processes before phosphating. Relatively speaking, oil is more harmful than rust, and oil-bearing workpieces directly affect the speed of rust removal. Therefore, rust removal should be carried out on the basis of oil removal, but for workpieces with less oil and more rust, the two basic processes of oil removal and rust removal can also be combined into one slot. At the same time, it can shorten the production line and reduce the investment cost of equipment and plant, but the quality of treatment is not as good as that of grooving. It can be used in occasions of low requirements. After using this process, the degreasing agent should also be selected with acid and rust remover. Hydrochloric acid is still used for rust removal. Hydrochloric acid is fast, clean and thorough in rust removal. It also has a good removal function for oxide scale. It is also used at normal temperature. The disadvantages are that hydrochloric acid is 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, environmental protection needs should be considered when selecting pesticides. Therefore, the selection of degreaser requires simple preparation, strong decontamination ability, does not contain difficult to clean at room temperature sodium hydroxide, silicate, OP emulsifier and other components, easy to wash at room temperature, does not contain toxic substances, does not produce harmful gases, good working conditions; the selection of rust remover requires the inclusion of accelerators, corrosion inhibitors and inhibitors, can improve The rust removal speed can prevent the workpiece from corrosion and hydrogen embrittlement, and it can inhibit acid fog better. Especially it is worth paying attention to the inhibition of acid fog, acid fog produced in the process of acid cleaning and rust removal, not only corrosion equipment and factory buildings, pollution of the environment, but also can cause people's teeth corrosion, conjunctiva red, tears, pain, dry throat, cough and other symptoms, so, effectively suppressing acid fog, not only is the need of environmental protection, or this list Position itself needs.