With the continuous development and improvement of domestic production levels, people's requirements for product surfaces are getting higher and higher and different surface treatment processes have emerged as the times require. Casting electrophoresis, as a relatively common surface treatment method, can improve the surface quality and corrosion resistance of castings. The deposition of paint particles on the workpiece to form a film under the action of an electric field is called anodic electrophoresis. On the other hand, the paint is positively charged, the workpiece is the cathode, and the deposition of paint particles on the workpiece to form a film is called cathodic electrophoresis.
The characteristics of anodic electrophoresis: raw materials are cheap, the equipment is simple and the investment is low; also the technical requirements are low and the corrosion resistance of the coating is worse than that of cathodic electrophoresis.
The reasons for the high corrosion resistance of cathodic electrophoretic coatings are: the workpiece is a cathode, no anodic dissolution occurs, so the surface of the workpiece and the phosphating film are not damaged; the electrophoretic coating has a protective effect on the metal and the paint used is of high quality and price.
Personal protection of operating workers: the body should be protected according to the work requirements to ensure the life safety.
The general process flow of electrophoresis is: workpiece pre-treatment (Degreasing or oil removal) → hot water washing → rust removal → cold water washing → phosphating → hot water washing → passivation → anode electrophoresis → workpiece post-treatment (clean water washing → drying).
1. Degreasing: The solution is generally a hot alkaline chemical degreasing solution with a temperature of 60°C and a degreasing time of about 20 minutes.
2. Hot water washing: temperature 60℃, time 2 minutes.
3. Rust removal: Use H2SO4 or HCl, such as hydrochloric acid rust removal solution. The total acidity of HCl is ≥ 43 points; the free acidity is > 41 points; add 1.5% cleaning agent; wash at room temperature for 10 to 20 minutes.
4. Cold water washing: wash in running cold water for 1 minute.
5. Phosphating: Use medium temperature phosphating (phosphating for 10 minutes at 60°C). The phosphating solution can be commercially available finished products. The above process can also be replaced by sandblasting → water washing.
6. Passivation: Use chemicals matching the phosphating solution and leave it at room temperature for 1 to 2 minutes.
7. Anodic electrophoresis: Electrolyte composition: H08-1 black electrophoretic paint, solid content mass fraction 9%~12%, distilled water mass fraction 88%~91%. Voltage: (70±10)V, time: 2~2.5min, paint liquid temperature: 15~35℃, paint liquid PH value: 8~8.5. Note that the workpiece must be powered off when entering and exiting the slot. During the electrophoresis process, the current will gradually decrease as the paint film thickens.
8. Clean water: Wash in running cold water.
9. Drying: Dry in the oven at (165±5)℃ for 40~60 minutes. The coating can cure and form a thick film on the surface. Temperature, time and oven all need to be specified as they have a great impact on the quality of the coating. The higher the oven temperature, the thicker the coating will be and will result in a more durable coating.