Causes and countermeasures of coating defects of aluminum profiles by electrophoresis
Electrophoretic painting is under the action of applied electric field, the suspended in electrophoresis liquid pigment and resin in the directional movement and deposition in the electrode coating method, is popular for plating lacquer, it can make the aluminum to obtain uniform flat surface, it is a very complex chemical reaction process, in the process of electrophoretic coating also can appear a lot of defects, today in a table in the form of a summary of the causes of these defects and how to solve these problems.
Defect name | A detailed description | Cause the reason | The solution |
| 1, foaming | Bubbles form on the surface of the film | When the aluminum profile is immersed in the tank liquid, there are bubbles on the surface of the tank liquid or bubbles involved in the air;Air entrapment in the circulation system, or the anode shielding is not in place, resulting in bubbles in the paint;Air bubbles resulting from poor thermal fluidity of paint. | When dipping the aluminum profile into the electrophoresis tank, pay attention to the direction and keep the tilt slightly.Check circulation system for air involvement, check anode shielding is in place;Maintain good thermal fluidity of the paint and prevent the formation of air bubbles. |
| 2. No paint film | No paint film is formed on the surface | Failure of the conductive system;The anodic oxide film is completely sealed. | First check whether the power is switched on;Then check whether the whole conductive system is smooth;See whether the washing time and temperature after anodic oxidation and hot water washing are within the range. |
| 3. Abnormal electrolysis | There is gas residue inside the paint film, the surface of the film is rough | Poor electrification, unreasonable liquid composition, concentrated or abnormal current, forming bubbles and rough surfaces. | Maintain a smooth flow of electricity and regulate the composition of liquids, especially nitrites. |
| 4. The paint film turns yellow | The surface of the film is yellow | The paint film is too thick;Caused by long baking time or high temperature;The soaking time in the water bath after oxidation is too long;Impurity ions, especially sulfate ions, are too high. | Paint film should not be too thick, control baking time and temperature, control the content of impurities, do not soak in the bath for too long. |
| 5, stalemate | The glue of the paint is attached to the surface of the film | Acid was mixed in the bath after the electrophoresis.Resin condenses in the paint onto the surface of the aluminum profile. | Check whether the filter system is qualified or not, change the filter element if unqualified, analyze the reason of resin condensation in the paint and remove it |
| 6. Rough surface | The surface of the film is uneven | The concentration of amine in the bath was too high;Low solid content;Tank fluid is contaminated;Coating aging;Dust may stick during electrophoresis or baking. | The concentration of amine is reduced by ion exchange.Control the solids within the range;Replace tank fluid and paint, check the source of dust and control. |
| 7, acid | There are traces of gelatinized flow on the surface of the film | There is residual acid on the fixture during the oxidation process, and it is not washed clean. | Improve fixture construction and wash thoroughly. |
| 8, pinhole | There are pinholes in the film | Air bubbles in the paint;Paint is contaminated;The binding Angle of the workpiece is not enough;Bubble retention due to insufficient flow of the tank;Poor cathode cover | Check the backflow drop of the notch, circulation pump and its pipeline for suction;Stop circulating filtration and remove the bubbles after they float to the liquid level.Adjust the binding Angle or hoisting Angle of aluminum profiles above 5°;Increase the flow of circulating pump. |