[China Aluminum Industry Network] 1. Aluminum alloy electrochromic electrophoretic coating process principle Aluminum alloy extinction electrophoretic coating is performed on the surface of the anodized film. Similar to bright electrophoresis, the production process is as follows:
Degreasing → Washing → Alkali etching → Washing → Washing → Neutralization → Washing → Anodizing → Washing → Pure Washing → Electrolytic Coloring → Pure Washing → Hot Purge Washing → Pure Washing → Electrophoresis → RO1 Washing → RO2 Washing → Drying → Pre-treatment Dry→cured.
Extinction electrophoresis and transparent electrophoresis are basically the same, are based on aluminum as an anode, under the action of direct current, electrochemical reactions occur, charged coating particles by the role of electric field, move to the object to be coated, electrophoretic coating deposited precipitation in the profile On the surface, a layer of paint film is formed. The whole reaction includes four simultaneous processes of electrophoresis, electrolysis, electrodeposition and electroosmosis. The difference mainly includes the electrophoretic paint raw materials and production process parameters. The extinction electrophoretic paint has a much larger molecular weight than the bright electrophoresis paint and is generally between 70,000 and 80,000 g/mol. In addition, in the process control, the electrophoretic voltage and the trough Liquid temperature and electrophoresis time are different. Under normal circumstances, for the same color number material, extinction electrophoresis voltage, time and temperature should be higher than the transparent electrophoresis, in addition, compared with the bright electrophoresis more pre-drying process, reducing The traces of water that form when it dries on cold and wet weather are closely related to the properties of electrophoretic paint.
2. Vertical oxidation eletrodeposition electrophoretic coating quality influencing factors and control methods Ordinary electrophoretic coating can not cover the surface defects of the profile, and extinction electrophoresis can only cover up a small part of the substrate surface defects, and due to the oxidation process is long and running water Coherence of operations is strong, especially in the automatic production of oxidized standing cranes. Often there are many defects of the same type of products produced in one period of time. The defects produced in each process stage are basically exposed after the curing process. As a result, the yield of electrophoretic profiles is lower than that of ordinary oxidized profiles, and extinction electrophoresis is a high-end product, and the fine defects after surface treatment are more easily revealed. The causes of common defects in production and countermeasures are as follows:
(1) The water mark is more consistent with this type of defect is the non-uniformity of the water film on the surface of the profile before entering the electrophoresis tank. Especially in the cold days, there is a high probability of occurrence. We use reduced hot pure water washing to extend the drip time, or avoid concentrated production in cold and humid weather. For hot water production, a small amount of water marks are formed. Reenter the pure water tank before electrophoresis; then replace a certain amount of pure water in time to ensure that the pure water tank temperature is consistent with room temperature; thirdly, the profile is quickly transferred from the pure water tank to the electrophoresis tank, and the operator's motion coordination can avoid such defects. appeared. In addition, the stability of the electrophoresis bath is ensured.
(2) The dirt on the surface of the paint film causes different parts where the dirt collects. If the dirt on the upper part of the row of the material is obvious, it is generally caused by more foreign particles in the washing tank. This is because the oxide film has a positive charge and particles in the water have a negative charge, which is not easy to remove once adsorbed. If the dirt is on the outside of the hanging profile, it is usually the result of the electrophoretic profile being exposed to dirty air. When it is carried out to the drip dry stage after electrophoresis, because the paint film has a certain viscosity, when the dust in the air is more, it is easy to adhere to the paint film. Of course, when using an uncured curing oven, or if the screen of the curing oven is damaged, this type of defect can also occur. Therefore, the curing oven needs to be cleaned regularly. Spraying an appropriate solution into the furnace after cleaning can reduce the generation of dust.
(3) The cause of orange peel is uneven electrodeposition. Therefore, it is necessary to analyze the factors that accelerate the rate of electrodeposition, such as bath temperature, conductivity, painting voltage, and pH value. These factors accelerate the migration of charged particles. Once they fluctuate to critical values, they increase the probability of defects. In particular, when the bath temperature is greater than 25°C or the bath is contaminated with acid, the probability of such defects is higher. The parameters should be as stable as possible. In addition, the cleaning after oxidation is not clean, and the accumulation of acid in the film pores will cause orange peel phenomenon in the electrophoresis tank. Therefore, it is necessary to carefully maintain the electrophoretic bath and paint it in time to ensure the quality of the bath.
(4) Influence of electrically conductive beam on the quality of the paint film The anode conductive beam of the electrophoretic material must be cleaned (spray-rinsed) and wiped off before entering the electrophoresis process. Otherwise, the following problems will occur: 1 Water droplets containing acid and alkali The dripping on the good paint film leads to the partial paint filming; 2 the cleaning is not thorough, and the corroded surface of the conductive beam after contacting the chemical material is baked to produce powdery material falling down, which will result in particles contaminating the paint film. 3 acid droplets to the electrophoresis tank to produce "dead paint", "dead paint" attached to the surface of the profile will form a partial clot, often resulting in "dead paint" diffusion area within the rework or scrap. In addition, the profiles in the drop tank need to be salvaged in time, and the electrophoresis profiles cannot be cross-produced. Otherwise, the leaching of the lacquer film on the surface of the dropped material in the tank will also cause “dead lacquerâ€, and similar quality problems will occur in the cross-production drop drips. .
(5) During the process of lowering and scratching the varnish film of the lower frame and the packaging process, the varnish will be accumulated during the hanging process, causing the varnish film to rub against each other; or the tip ends will be uneven and each other will be scratched. Any irregularity in the process is detrimental to the decorative effect of the paint film. Therefore, in the process of racking and packaging, the operation should be standardized and placed neatly and orderly.
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