Electrophoretic coating process flow and method of metal surface

(1) Electrophoretic coating of general metal surfaces, the process flow is: pre-cleaning → on-line → degreasing → washing → derusting → washing → neutralization → washing → phosphorization → washing → passivation → electrophoretic coating → on the tank Cleaning → ultrafiltration washing → drying → off the assembly line. (2) The substrate and pretreatment of the substrate to be coated have a great influence on the electrophoretic coating film. Castings are generally rusted by sandblasting or shot peening. The front cotton yarn removes dust from the workpiece surface, and 80#~120# sandpaper is used to remove debris such as steel pellets that remain on the surface. The surface of the steel is deoiled and rust-removed. Phosphating and passivating the surface are performed when the surface requirements are high. Before the anodic electrophoresis, the ferrous metal workpiece must be phosphatized, otherwise the corrosion resistance of the paint film is poor. Phosphate treatment, the general selection of zinc phosphate film, thickness of about 1 ~ 2um, requires a fine and uniform phosphating film crystal. (3) In the filtration system, one-stage filtration is generally adopted. The filter is a mesh bag structure with an aperture of 25 to 75 μm. The electrophoretic coating is filtered by a vertical pump to the filter. Considering the comprehensive replacement cycle and the quality of the paint film, the filter bag with an aperture of 50 μm is the best. It not only satisfies the quality requirements of the paint film, but also solves the plugging problem of the filter bag. (4) The size of the circulating system of electrophoretic coating directly affects the stability of the bath and the quality of the paint film. Increasing the amount of circulation will reduce the precipitation and air bubbles of the bath; however, the aging of the bath will increase, the energy consumption will increase, and the stability of the bath will deteriorate. It is ideal to control the circulation time of the bath to 6~8 times/h to ensure not only the quality of the paint film but also the stable operation of the bath. (5) As the production time increases, the impedance of the anode separator increases and the effective operating voltage drops. Therefore, in the production, the operating voltage of the power supply should be gradually increased to compensate for the voltage drop of the anode separator according to the loss of the voltage. (6) The ultrafiltration system controls the concentration of impurity ions in the workpiece and ensures the coating quality. In the operation of this system, it should be noted that the system should be continuously operated after running, and intermittent operation is strictly prohibited to prevent the ultrafiltration membrane from sticking. The resins and pigments after the dried citrus are attached to the ultrafiltration membrane and cannot be thoroughly cleaned , which will seriously affect the water permeability and the service life of the ultrafiltration membrane. The output rate of UF membranes is declining with the running time, and should be cleaned once for 30 to 40 days in order to ensure the ultrafiltration water required for ultrafiltration and washing. (7) The electrophoretic coating method is applicable to a large number of production lines. The electrophoresis bath should be refreshed within 3 months. Taking an electrophoresis production line with an annual output of 300,000 steel rings as an example, the scientific management of the bath fluid is extremely important. Various parameters of the bath fluid are periodically tested, and the bath fluid is adjusted and updated according to the test results. Generally, the parameters of the bath liquid are measured at the following frequencies: the electrophoretic liquid, the ultrafiltrate and the ultrafiltration cleaning solution, the yin (positive) polar solution, the circulating washing solution, the deionized cleaning solution, the pH value, the solid content, and the conductivity once per day;
The Yankee ratio, organic solvent content, laboratory tank test twice a week.
(8) For the management of paint film quality, the uniformity and film thickness of the paint film should be inspected frequently. The appearance should not be pinholes, sagging, orange peel, wrinkles, etc., and the adhesion and corrosion resistance of the paint film should be regularly checked. Physical and chemical indicators. Inspection cycle according to the manufacturer's inspection standards, generally every batch needs testing. Common paint film defects and prevention methods in electrophoresis construction Although electrophoretic coating is the dynamic balance of a large number of operating variables, the operator can monitor and adjust the control parameters of the electrophoretic coating process from time to time to obtain a good appearance, film thickness and physics characteristic. Therefore, when defects in the paint film are detected, a series of accurate and reliable analyses should be performed, and then solutions should be proposed in a timely manner.