Automobile parts include frame, chassis, engine and wheels, etc. There is no requirement for their decoration, but mainly for protective and special protective functions.
The frame is made of 4~6mm thick hot-rolled steel plate, which is stamped, riveted or welded. It is at the bottom of the car and often meets muddy water at an angle, requiring the coating to have better anti-corrosion performance.
Since the frame material is a hot-rolled steel plate, it should be pickled separately to remove the scale before going online, and the frame sent to the painting workshop should be free of scale and rust. The early frames were dip-coated with solvent-based asphalt paint, but now they are dip-coated with solvent-based acrylic or acrylic water-based paint, and some are painted with anodic electrophoresis. The coating process is safe and low pollution. After zinc salt phosphating treatment, the salt spray resistance of the coating can reach 400h.
Due to the complex structure of the frame and other auto parts, there are often thick oil stains. It is better to use hot water high-pressure pre-spray washing before degreasing, and high-pressure spray washing with alkaline cleaning agent for degreasing. The assembly process is shown in Table 76.
The material of the wheel varies according to the type of car. The wheels of the heavy-duty car are generally welded by 4~6mm hot-rolled steel plates; the wheels of cars and light vehicles are welded by cold-rolled steel plates, and some are made of aluminum alloy materials. made. The wheels are often eroded by the intense erosion of muddy water, so the requirements for the protection performance of the wheels are relatively high. Because the wheels are exposed on the west side of the car, for high-end cars such as cars, the appearance of the wheel coating has higher requirements, and the protection requirements are higher. Therefore, thick film cathodic electrophoretic coating is mostly used for car wheels, and some are powder sprayed; heavy-duty vehicles generally use a cathodic electrophoretic primer or spray primer and top coat; aluminum alloy wheels need to be chemically oxidized and then sprayed with metallic flash paint.
Iron wheels can be phosphated with iron, zinc or zinc-calcium before painting. The shape of the wheels is relatively simple, and the pre-treatment process of full spraying can be adopted. The lubricating oil remaining on the steel ring after forming is difficult to wash off due to high temperature aging during welding. If cathodic electrophoretic coating is used, the degreasing process should be strengthened. Now take the one-time cathodic electrophoretic primer coating process as an example to illustrate the coating process of automobile wheels.
①The upper part is derusted by sand blasting.
② Degreasing 45~55℃, alkalinity 10~15 points, 150~200kPa.
③Wash tap water, 150~200kPa, the alkalinity of the water should be less than 2 points, otherwise it should be drained and replaced with new water.
④Wash tap water, 150~200kPa, the alkalinity of the water should be less than 1.5 points, otherwise it should be drained and replaced with new water.
⑤Phosphating TA23~27 point, FA1.2~1.5 point, 45~55℃, 150~200kPa.
⑥ The electrical conductivity of the cyclic de-higher water washing should be less than 50µs/cm.
⑦ The conductivity of freshly degreasing water should be less than 20µs/cm.
⑧Chodic electrophoresis conductivity should be less than 1000µs/cm, pH value greater than 4, working voltage 180~230v, 30~35μm
⑨Washing cycle: ultrafiltration washing, fresh ultrafiltration washing, cycle degaozi washing, fresh degaozi washing.
⑩Dry at 180℃ for 15~20min.
⑪Cooling Forced cooling.
⑫The dry film thickness of spraying acrylic silver powder paint is 20μm
Alternatively, a water-based primer or a solvent-based primer can be dip-coated.
An example of the coating process for axles and drive shafts is as follows.
Upper piece—hot alkali degreasing (50~60°C, 1~1.5min)—hot water washing (50~60°C, 0.5min)—hot water washing (50~60°C, 0.5min)—hot air drying (100~110°C Blow dry and cool)-spray chlorinated rubber thick film chassis paint [viscosity 18~20s (apply with a 4-cup viscometer, 25℃), dry film thickness not less than 35µm]-dry (80~100℃, 10~15min ) Off-line inspection (the coating film should be complete, no bottoming phenomenon, the surface of the coating film should be non-sticky, allow further drying during the assembly process).
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