Ⅰ Electrophoretic Treatment Of Aluminum
Color electrophoretic coating of aluminum is a novel surface treatment process. It uses electrochemical methods to deposit colloidal particles of organic resin on the parts to form transparent or organic coating layers of various colors.
According to the different charged condition of resin particles in electrophoretic paint after ionization, it can be divided into anodic electrophoresis (resin particles ionize into negative ions) and cathodic electrophoresis (resin particles ionize into positive ions).
Electrophoretic coating layer has excellent corrosion resistance (can pass neutral salt spray test for more than 400 hours), strong resistance to discoloration; Good bonding force with the base metal, and can be subjected to a variety of mechanical processing; The coating layer is brightly colored, and according to the user's requirements can be formulated into a variety of colors, commonly gold, coffee, gunmetal, black, etc.; Compared with paint, the construction performance is good, and the pollution and harm to the environment is small. Therefore, it is used in automobile shell and various accessories, bicycle handlebar and accessories, various daily-use small hardware accessories, furniture, handicrafts and so on.
Ⅱ Since cathodic electrophoresis is more advanced, we take cathodic electrophoresis is more advanced, we take cathodic electrophoresis as the main subject of our introduction below.
Cathodic electrophoresis is a complex electrochemical and colloid chemical process. The electrophoretic paint itself is a multicomponent system of colloid and suspensions, with two components the diffuse phase (resin, pigment particles) and the continuous phase (water).
Ⅲ Four processes of cathodic electrophoresis:
1.Electrophoresis positively charged water-soluble resin particles and their absorbed pigments move toward the cathode.
2.Electrodeposition positively charged resin particles arrive at the surface of the part (cathode) and discharge, forming a water -insoluble deposition layer, which is backed to form a paint flim.
3.Electro-osmotic moisture precipitates out of the sedimentary layer and can be baked when the moisture content drops to 5-15%.
4.Electrolyzed water is electrolyzed by direct current, releasing H2 and oxygen. Due to electrolysis, the penetration is reduced, which affects the appearance of the paint film, reduces the adhesion of the paint film, and increases the power consumption, so it is necessary to attenuate the electrolysis of water.
Ⅳ Process flow of electrophoresis:
Degreasing→De-oxidizing→Chromating→Electrophoresis→Drying→Packaging
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Appearance |
Causes |
Methods of correction |
|
Orange peel or rough surface |
Too high voltage, too high solution temperature, too high solids, too close poles, too fast baking temperature, too high PH value |
Reduce voltage, reduce temperature, dilute solution, increase pole distance, compress air, blow dry and then bake, adjust with organic acid |
|
Pinholes or pockmarks |
Solid fraction is too low, PH value is too low, cleaning water is not clean, solution conductivity is too high, film thickness is too thin, pinholes on plating surface, baking temperature is too fast |
Adjust to the process range, reduce the acidity of the solution, change the cleaning water, ultrafiltration to remove impurity ions, increase the electrophoresis voltage or time, eliminate the pinhole parts into the tank, compressed air blowing and then drying |
|
Crater or oil spot |
Oil stains on workpiece, oil stains on tank surface, particle contamination, high voltage, thick film layer |
Strengthen the oil removal process to prevent the tank liquid from being contaminated oil, strengthen the circulation filtration and ultrafiltration to reduce the electrophoresis voltage and time |
|
Rainbow |
Film layer too thin |
Increase electrophoresis voltage |
|
The colors do not match |
The film layer is too thick or too thin, when mixing paint, the color ratio is wrong, too much solvent, poor penetration ability, uneven thickness of the film layer |
Choose the appropriate working voltage and time, formulate the electrophoretic paint strictly according to the process formula, and adjust the solvent content to make it conform to the process specification |
|
Irregular shapes |
Incomplete pre-treatment |
Enhanced pre-treatment process |
|
Not hard enough |
Short baking time or low temperature |
Strictly according to process specifications |
|
Differences in color or painted surfaces in dots or flakes |
Parts with pinholes or sand holes, color emulsification, uneven mixing, water droplets on the surface not yet dry, i.e., not thoroughly washed before baking electrophoresis |
Eliminate unqualified workpieces from the tank, strengthen the electrophoretic paint mixing, blow dry with compressed air, strengthen the cleaning of parts before entering the tank |
Ⅴ Quality Standards
1.No color difference, orange peel, pinholes, rainbow, bumps, scratches and other abnormalities in appearance.
2.Film thickness of 40-60um, salt spray test more than 400 hours, more than CNS standard grade 9.
3.The film can pass the 60-degree bending test without peeling.
4.Hundred grams test and ball drop test can meet the national standard.
