Coating pretreatment includes oil removal, rust removal, film (phosphating, phosphorus-free transformation) three parts.
Film (phosphating, no phosphorus transformation) is an important link, oil removal
And rust removal is preparation process before skin membrane (phosphating, no phosphorus transformation),therefore, in the practice of the electrophoretic coating production line , take the film (phosphating ,no phosphating ) as the key and make sure the oil removal and cleaning work from requirement of quality, pay special attention to the interaction between them.
High quality film (phosphating, no phosphorus transformation) only forms on surface of the workpiece which oil, rust, oxide things are completely removed. Because the residual oil ,rust, oxide on the surface could seriously hinder the formation of film. In addition, it will also affect the adhesion of the coating, drying performance, decorative performance and corrosion resistance, the complete removal of these foreign matter is the necessary condition of the film.
Degreasing and derusting is two basic processing for film before (phosphating, no phosphorus transformation), oil is more harmful than rust, and working pieces with oil could directly affect the derusting speed. So derusting is based on degreasing,
But for the workpiece with less oil and more rust, we can merge the 2 basic processing, finishing degreasing and derusting in one tank, it can shorten E-coating production line, lower the investment cost of the plant and equipment . It can be used on occasions with low requirements, because separating the 2 basic processing has better excellent performance.
After using this process, acid reagent and rust remover should also be selected. Derusting still uses hydrochloric acid, hydrochloric acid derusting speed is high, derusting clean thoroughly, also has a good removal function for oxide skin, and is used at room temperature, the drawback is hydrochloric acid derusting acid fog is larger, harmful to health, serious environmental pollution.
With the development of industry, environmental protection and the improvement of working conditions have become the common concern of people. Therefore, the need of environmental protection should be taken into account when selecting agents. Therefore, the choice of oil removal agent requires simple preparation, detergency ability is strong, does not contain sodium hydroxide, silicate, OP emulsifier and other components that are difficult to clean at room temperature, easy to wash at room temperature, does not contain toxic substances, do not produce harmful gases; When selecting rust remover, it is required to contain promoter, corrosion inhibitor and inhibitor, which can improve the speed of rust removal, prevent the workpiece from over-corrosion and hydrogen embrittlement, and inhibit acid fog better.
Acid mist inhibiting is worthy of paying attention to ,The acid mist occurring in the process of pickling , not only corrode equipment and plant ,pollute the environment, and can also cause tooth decay, dental conjunctival redness, tears, pain, dry throat, cough and other symptoms, so effectively inhibit acid mist, is not only the need of environmental protection, but also plant itself requirements.