(1) washing
The purpose of water washing is to remove the floating paint that adheres to the surface of the coating film due to immersion during the electrophoretic coating process, so as to prevent the coating film from being stained, and at the same time prevent the adhered floating paint from re-dissolving the coating film.
Water washing includes ultrafiltration water washing and high sub-washing. Recently, the ultrafiltration washing process mainly adopts two-stage circulating ultrafiltration washing or one-stage ultrafiltration washing. The former is suitable for large-scale assembly line production, and the latter is usually used for small-batch intermittent production. The two-stage circulating ultrafiltration water washing system is shown in Figure 5-11.
Some nozzles are set above the overflow tank, and before the workpiece is opened to the electrophoresis tank, most of the floating paint is flushed back into the tank, which greatly reduces the burden of other washing processes.
Because the ultrafiltered water contains solvents, small molecule additives and inorganic salts, it is necessary to wash the ultrafiltered water on the surface of the coating with hypertronic water. Generally, one cycle is used for washing with decontamination water, and one process for washing with pure decontamination water. Adding 0.5%~3% surfactant in water is good for improving the appearance of the coating film, increasing the smoothness, and overcoming water marks.
(2) drying
160~180°C/30min. Infrared radiation plus convection is widely used in production. Since the electrophoretic coating uses water as a solvent, the evaporation of water is very high, the density is high, and the water vapor is not easy to get rid of. The coating film is easy to dissolve and lose light in the hot water vapor, so it is difficult to ensure the quality only by radiant heating. A certain proportion of hot air is discharged in time through convection to ensure the humidity of the hot air in the drying chamber, which is beneficial to ensure the quality of the coating.
(3) Inspection
In addition to inspecting the appearance of the coating film, such as whether it is flat, smooth, and dense, the thickness of the coating film (generally ~35µm), corrosion resistance, adhesion, and impact resistance are also inspected.
