Pretreatment of spraying line All kinds of oil stains (such as lubricating oil, emulsion, grease, sweat, etc.) and dust on the surface of the coated object make the cleaning process of the coated surface clean, which is an essential process for the pretreatment process of painting; What kind of chemical treatment (or conversion film treatment) or mechanical processing (such as shot blasting treatment) shall be carried out on the clean coated surface (whether or not) according to the substrate and surface state of the coated object and the coating process requirements.
It mainly includes: treatment method, treatment time, process flow, etc.
1 Treatment method Workpiece treatment method refers to the way in which the workpiece contacts with the tank liquid to achieve the purpose of chemical pretreatment, including full immersion type, full spray type, spray immersion combination type, brush coating type, etc. It mainly depends on the geometric size and shape of the workpiece, site area, investment scale, production capacity and other factors. For example, workpieces with complex geometric dimensions are not suitable for spraying; Oil tank, oil barrel and other workpieces are not easy to sink into the liquid, so they are not suitable for immersion.
1.1 The full immersion method is a common treatment method to completely immerse the workpiece in the bath solution, take it out after a period of treatment, and complete the goal of degreasing, rust removal and phosphating. The geometric shapes of the workpiece are complex and simple. As long as the liquid can reach the place, the treatment goal can be achieved. This is the unique advantage of the immersion method, which is unmatched by spraying and brushing. The disadvantage is that there is no auxiliary use of mechanical scouring, so the processing speed is relatively slow and the processing time is long, especially when the workpiece is continuously suspended and transported, in addition to the running time of the workpiece in the trough, there is also the time for the workpiece to go up and down the slope, which increases the equipment, the site area and investment. As far as phosphating is concerned, foreign countries tend to adopt full immersion phosphating. It is said that full immersion phosphating is easy to form granular crystalline phosphating film with high iron content, which has good compatibility with cathodic electrophoresis.
1.2 In the full spray mode, the liquid is pressurized by a pump, and the liquid is atomized at a pressure of 0.1~0.2Mpa, which is sprayed on the workpiece to achieve the treatment effect. Due to mechanical flushing and liquid renewal during spraying, the treatment speed is accelerated and the time is shortened. The length of the production line is shortened, and the corresponding section includes the site and equipment. The disadvantage is that for workpieces with complex geometric shapes, such as cavities, corners and other liquids are not easy to reach, and the treatment effect is not good, so it is only suitable for processing workpieces with simple geometric shapes. The spraying method is also not suitable for pickling, which will bring a series of problems such as equipment corrosion, rust between processes, etc., so you must be very careful when selecting spraying pickling. It is reported that full spray phosphating is easy to form a phosphating film with coarse crystal dendrites and low iron content, which is not recommended as the pretreatment of cathodic electrophoretic paint primer abroad. The full spray mode is mainly used for powder coating, electrostatic coating, anode electrophoresis, etc. of household appliances and parts.