Electrophoretic coating process and other process comparison

First, electrophoresis classification

The electrophoresis process is divided into anode electrophoresis and cathodic electrophoresis.

If the paint particles are negatively charged and the workpiece is an anode, the deposition of the coating particles on the workpiece under the action of the electric field force is called anodic electrophoresis; conversely, if the paint particles are positively charged, the workpiece is the cathode, and the coating particles are deposited on the workpiece. Cathodic electrophoresis.

Second, the process characteristics

● Characteristics of anodic electrophoresis:

1. The raw material price is cheap (generally 50% cheaper than cathodic electrophoresis);

2. The equipment is simpler and has less investment (generally 30% cheaper than cathodic electrophoresis);

3. The technical requirements are lower; the corrosion resistance of the coating is worse than that of cathodic electrophoresis (about 1/4 of the life of cathodic electrophoresis).

●Causes of high corrosion resistance of cathodic electrophoretic coatings:

1. The workpiece is a cathode, the anode is not dissolved, and the surface of the workpiece and the phosphate film are not destroyed;

2. Electrophoretic coatings (generally nitrogen-containing resins) have a protective effect on metals, and the paints used are of high quality and high quality.

Third, the process

The general process flow of electrophoresis is as follows:

Pre-treatment of workpiece (de-oiling → hot water washing → descaling → cold water washing → phosphating → hot water washing → passivation) → electrophoresis → water washing → drying

Degreasing

The solution is generally a hot alkaline chemical degreasing liquid, the temperature is 60 ° C (steam heating), and the time is about 20 min.

2. Hot water wash

Temperature 60 ° C (steam heating), time 2 min.

3. Rust removal

Use H2SO4 or HCl, for example with hydrochloric acid to remove rust, HCl total acidity ≥ 43 points; free acidity > 41 points; add cleaning agent 1.5%; wash at room temperature for 10 ~ 20min.

4. Cold water wash

Wash in cold water for 1 min.

5. Phosphating

Phosphate with medium temperature (phosphating for 10 min at 60 ° C).

Passivation

Use a drug that is compatible with the phosphating solution, and it can be used for 1 to 2 minutes at room temperature.

7. Anode electrophoresis

Electrolyte composition: solid fraction by mass of 9% to 12%, and distilled water mass fraction of 88% to 91%.

Voltage: (70 ± 10) V; time: 2 ~ 2.5min;

Paint liquid temperature: 15 ~ 35 ° C;

Paint liquid PH value: 8 ~ 8.5.

During the electrophoresis process, the current will gradually decrease with the thickening of the paint film, and the workpiece should be disconnected from the tank.

8. Washing with water

Wash in flowing cold water.

9. Drying

It can be baked in an oven at a temperature of (165 ± 5) °C for 40 to 60 minutes.

Fourth, the process comparison

Comparison of electrophoresis and electroplating :

1. The electrophoretic paint layer has high and low potential and uniform thickness; generally, the plating thickness is large at high and low potentials.

2. The electrophoretic paint layer can completely cover the concealed area; generally, the electroplating cannot be deep into the concealed place.

3. Electrophoresis, commonly known as lacquering, is the deposition of polymer resins; electroplating is the process of metal ion deposition.

Comparison of electrophoresis and spray:

1. The paint spray adhesion is not strong, easy to fall off; the electrophoretic coating has strong adhesion and it is difficult to fall off.

2. Paint spray has low corrosion resistance; electrophoretic coating has strong corrosion resistance.

3. The surface of the paint spray is rough and the smoothness is low; the electrophoretic coating is flat and smooth, and the decoration is high.

4. Paint spraying is seriously polluted and environmentally friendly; electrophoretic coating meets environmental protection requirements.