The painting quality of the axle car body is the highest, and it is the representative of automobile painting. The modern painting process generally adopts a three-coat (primer layer + intermediate layer + topcoat layer) coating system, including the pre-painting process. process.
① After passing the inspection of the body-in-white (smooth surface and no rust), it is hung on the transport chain.
②Pre-cleaning: Washing to remove the dirt that is not easy to wash off the body by alkali washing, usually by manual operation. Scrub with petroleum solvent oil.
③ Degreasing: Rinse with hot lye at 60°C for 1 to 2 minutes, then use hot lye at 50°C to 70°C to remove oil by soaking and spraying, rinse with warm water at 40°C for half a minute, and then combine with diffuse spray at room temperature Way to wash. In order to refine the crystallization of the hair film, a surface regulator is added to the water.
④Phosphating: use zinc salt pounding liquid, use the combined method of immersion and spraying to convert at 50℃~60℃ for 1~2 minutes, rinse with water at room temperature for half a minute, then rinse with water immersion and spraying at room temperature for half a minute, and finally Rinse with deionized water for 0.1 minute, dry with hot air or dry for 5-10 minutes and then cool. (Related instrument: oven)
Cathodic electrophoretic primers are usually used, which can be divided into thick film (25 microns ~ 35 microns) and thin film (15 microns ~ 20 microns). (Related Instruments: Thickness Gauge)
①The body is electrophoresis fine painted, the time is 2~3 minutes, and the voltage is 200~350V.
② After electrophoresis, wash in water several times, wash with ultrafiltrate for 3 times, then wash with water and rinse with deionized water.
③ Bake at 170℃~l80℃ for 20 minutes.
④ cooling, inspection, repair defects.
⑤ Spray the underbody paint on the bottom of the car body, and apply sealant on the welding bell inside the car body.
①Wipe the painted surface.
② Spraying: (electrostatic spraying or robotic automatic spraying) the middle layer (sometimes two consecutive sprays, wet on wet).
③ Bake at 130℃~140℃ for 25~30 minutes.
④ After cooling, perform wet grinding and wipe clean.
⑤ Rinse with deionized water.
⑥Dry the water, bake at l20℃~l40℃ for S~10 minutes.
There are two types of topcoats: natural color coatings and metallic flash coatings. The natural color coating is generally applied in two coats, and there are different processes of two coats and two bakes, wet to wet and bake → sanding and bake, that is, re-leveling. Metallic flash coating has different processes of wet-on-wet varnish, and one-time drying of base paint and varnish.
Natural color coatings usually use amino paints and thermosetting acrylic paints.
①Wipe the surface to be painted.
②Automatic spraying and manual electrostatic spraying topcoat. When using the wet-on-wet process, spray the first coat and let it dry for 5-10 minutes, then spray the second coat of topcoat, let it dry for 5-10 minutes, and then dry it together. The re-leveling process is suitable for acrylic paint. After spraying a coat of paint, bake it at a lower temperature of 60°C~80°C for about 15.~30 minutes to make the surface semi-hardened. After cooling it, use 500~60o Lightly wet sand with No. 2 fine sandpaper to eliminate the defects of the paint film, clean it, and then send it to the baking tunnel for baking, so that it can be "re-leveled" by heat and completely cured. (Related instrument: drying time Tester)
Metallic glitter coatings are usually done using thermosetting acrylic paints or non-water dispersible acrylic paints. Generally, two coats of color paint and one coat of varnish are applied, with a film thickness of about 50 microns to 60 microns. Usually, after spraying the first coat of paint, let it sit flat for a few minutes, then spray the second coat of the same color paint, let it dry for a few minutes, and then spray again. The varnish 1 is aired for a few minutes, then baked at 140°C for about 30 minutes, and the three paint films are dried at one time. There is also a process of spraying two coats of varnish and drying it once after drying it with one coat of color paint.
After the topcoat is applied, after cooling, the final inspection is carried out: the surface of the paint film is free of defects and meets the requirements; the thickness and hardness of the paint film meet the technical requirements. Qualified car bodies are sent to the assembly workshop. Unqualified sound products need to be repaired and sprayed.
The total thickness of the car body coating is about 80 microns to 110 microns.