Publish Time: 2023-07-07 Origin: Site
Electrophoresis is a relatively common process for aluminum alloy surface treatment. It can form a dense resin film on the aluminum alloy surface to protect the aluminum alloy.
1. This treatment method uses water as the dispersion medium, and there are less co-solvents in it. Can reduce air and water pollution, reduce the occurrence of fire;
2. The coating of electrophoretic coating has good permeability, and the coating can cover the edges and gaps of the profile, forming a dense and uniform oxide film, and improving the overall anti-corrosion and anti-oxidation ability;
3. Due to the small amount of solvent in it, there will be no solvent cooling and condensation on the surface of the profile. The aluminum profile treated with electrophoretic coating has good appearance quality and no sag phenomenon;
4. Electrophoretic coating generally adopts RO circulation system, and the recovery rate of coating is 98% and above. The discharge of waste water is less, reducing environmental pollution and saving costs.
At present, aluminum alloy electrophoresis treatment is mainly divided into anodic electrophoresis treatment and cathodic electrophoresis treatment. Aluminum alloy electrophoretic coatings can be divided into anodic electrophoretic coatings and cathodic electrophoretic coatings according to the polarity of charged particles generated after dissociation in water. Correspondingly, electrophoretic coating methods can be divided into anodic electrophoretic coating and cathodic electrophoretic coating. When the charged particles are cationic, the electrophoretic coating is called cathodic electrophoretic coating. At this time, the aluminum alloy profile is connected to the cathode of the electrophoretic power supply, and the coating method is called cathodic electrophoretic coating; when the charged particles are anionic, the electrophoretic coating is called anodic electrophoretic coating. At this time, the aluminum profile is connected to the anode of the electrophoretic power supply, and the coating method is called anodic electrophoretic coating.
Cathodic electrophoretic paint mainly uses cationic resin as the film-forming polymer, and the neutralizer is formic acid, acetic acid, lactic acid and other organic acids, which can be dissociated into cationic polymers in water. The most commonly used resins are epoxy resin and Polyurethane etc.
Cathodic electrophoretic paint film-formers are generally polymer compounds with amine groups, which are soluble in water after being neutralized by carboxylic acid to form a salt, and ionized into positively charged polymer film-former ions and loaded carboxylic acid during electrophoresis. Ions, the polymer film-formers deposited on the metal surface have amine groups, and the deposits do not contain metal soaps.
The cathodic electrophoretic paint is a new product born after the anodic electrophoretic paint. Compared with the anodic electrophoretic paint, it has more advantages:
1. The throwing power of cathodic electrophoretic paint is 1.3-1.5 times higher than that of anodic electrophoretic paint. Therefore, even when complex workpieces are processed by cathodic electrophoresis, the inner cavity can be well coated, which can effectively omit the auxiliary electrode and simplify the process. Electrophoretic coating process and material consumption reduce costs.
2. The corrosion resistance of cathodic electrophoretic paint is good, and its corrosion resistance time on degreased steel plate exceeds that of anodic electrophoretic paint after phosphating treatment; the electrophoresis of the same bare steel plate is generally 3-4 times that of anodic electrophoretic paint. On the zinc salt phosphating steel plate, its corrosion resistance is 2-3 times that of anodic electrophoretic paint, and in some cases it can even be as much as 10 times, and its corrosion resistance can be said to be quite remarkable.
3. According to relevant experimental data, the alkali resistance of cathodic electrophoretic paint is higher than that of anodic electrophoretic paint, and the alkali resistance (5% NaOH solution) of the cathodic electrophoretic processed film can usually be compared with that of anodic electrophoretic paint. The film is 20-40 times taller. Moreover, the cathodic electrophoretic paint liquid is relatively stable and easy to control, unlike the anodic electrophoretic paint, which is not easily affected by impurity ions and microorganisms and deteriorates.
Causes of adverse phenomena and corrective methods
| Unpleasant sight | Cause | Approach |
| Rough surface | The voltage is too high, the solution temperature is too high, the solid content is too high, the pole distance is too close, baking and heating are too fast, and the PH value is too high | Reduce the voltage, reduce the temperature, dilute the solution, increase the polar distance, blow dry with compressed air, and then bake with organic acid to adjust |
| Pinholes or pitting | The solid content is too low, the pH value is too low, the cleaning water is not clean, the conductivity of the solution is too high, the film thickness is too thin, and the pinholes on the plating surface are baked too quickly. | Adjust to the process range, reduce the acidity of the solution, replace the cleaning water with ultrafiltration, remove impurity ions, increase the electrophoresis voltage or time, prevent pinhole parts from entering the tank, blow dry with compressed air, and then bake |
| Crater or oil point | There are oil stains on the workpiece. There are oil stains on the liquid surface of the tank. The pollution voltage is high and the film layer is thick. | Strengthen the degreasing process to prevent the bath from being polluted by oil, strengthen circulation filtration and ultrafiltration, and reduce electrophoresis voltage and time |
| Iridescent | film is too thin | Increase electrophoresis voltage |
| Color mismatch | When the film layer is too thick or too thin to prepare the paint, the color ratio is wrong Too many solvents, poor penetration ability, uneven film thickness | Select the appropriate working voltage and time, prepare the electrophoretic paint strictly according to the process formula, and adjust the solvent content to make it meet the process specifications |
| Irregular shape | Incomplete pretreatment | Strengthen the pre-treatment process |
| Hard enough | Short baking time or low temperature | Strictly follow the process specification |
| Spot or flake color difference on painted surface | There are pinholes or trachoma in the parts. The emulsification and stirring of the pigment are uneven. There are water droplets on the surface. Baking before electrophoresis. | Put an end to unqualified workpieces in the lower tank, strengthen electrophoretic paint stirring, use compressed air to dry, use compressed air to dry, strengthen the cleaning of parts before entering the tank |
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