Method for cleaning aluminum surface

The methods of aluminum surface cleaning are usually divided into physical cleaning and chemical cleaning.

(1) Physical cleaning method
Mainly use some organic solvents to dissolve oil, grease, paint and other substances, so as to remove dirt or other dirt on the surface of parts and get a cleaner surface. Physical cleaning usually uses organic solvents such as banana oil, turpentine, alcohol, gasoline and kerosene. In order not to affect the effect of chemical cleaning, parts must be dried or dried after organic solvent cleaning, so as not to mix these solvents into the next process (alkaline cleaning solution cleaning), which will affect the ability of alkali solution to remove oil stains.
Of all these solvents, the safest and cheapest is kerosene. The ignition point of kerosene is high, but because of its slow evaporation, it is easy to leave traces of oil on the surface of aluminum and its alloy parts. Therefore, kerosene is often used as a cleaning agent for dirty parts for the first time, and then cleaned with other solvents. Banana oil, turpentine and alcohol are irritating to people’s eyes and skin, and they are expensive. Especially, alcohol has a narrow use, and its ability to remove oil is not as good as that of banana oil, so it is not used much. Pay attention to safety when using gasoline to prevent fire.
As for chloride solvents, such as carbon tetrachloride, although it has strong decontamination ability, it is not suitable because of its high toxicity. For aluminum products with low requirements for mechanical properties and dimensional changes, the most simple burning method can be used to solve the grease and oil pollution on their surfaces. That is, put the parts in the muffle furnace and keep them at the temperature of 200-2500C for 1 hour, and the satisfactory degreasing effect can be achieved.

(2) Chemical cleaning method
Physical cleaning only plays a certain role in cleaning dirt, oil and other dirt, but it is not thorough enough, so chemical cleaning must also be used. After chemical reaction, a very clean surface can be obtained. It can be seen from practice that when the parts cleaned by chemical methods are taken out of water, the whole surface is wetted by water and a layer of water film is evenly hung, and there is no dirt on the surface. There are usually the following chemical cleaning methods.

1. Alkali cleaning
Alkali cleaning is the most important part in the cleaning of aluminum products. Alkaline cleaning agent has good wetting performance, strong emulsifying effect on oil and fat, and forms soluble soaps; At the same time, it also has an anti-coagulation effect on dirt particles, so that the dirt particles are dispersed in the solution in a colloidal form without being deposited on the surface of the parts, and the residual oil on the aluminum surface can be completely removed.
However, because aluminum is different from other metals, it is easy to be corroded in alkaline solution, so it is required that the alkalinity in alkaline cleaning agent should be limited to the lowest range, that is, the corrosion effect on aluminum should be controlled to the lowest limit. Generally, the PH value should be controlled between 9 and 11, and it should not be higher than this range, otherwise the erosion will be too fast and difficult to control, thus affecting the size of parts and even destroying parts. In order to ensure the stability and good cleaning performance of the alkaline cleaning agent, corrosion inhibitors, such as phosphate and silicate, should be added to the alkaline cleaning solution to form a protective film with the aluminum surface or surface oxide film.
With the increase of the use time of alkaline lotion, the solution is not only gradually depleted, but also the decontamination ability decreases. At this time, the cleaning time should be appropriately extended. After each use, the dirt floating on the surface of the solution or the garbage deposited on the bottom of the cleaning solution should be removed, and a new solution must be added or reconstituted after a certain period of time.
2. Acid cleaning
Pickling can further decontaminate. After chemical polishing and cleaning, the surface of aluminum products becomes dark, forming a gray film that can be erased. This film is composed of corrosion reaction products, which can be removed by washing with nitric acid solution to obtain a bright base metal surface.
After pickling, it needs to be washed with hot water and then washed with cold water. H+ is taken out due to the increase of water in the washing process, so the concentration of the corresponding acid decreases to a certain time after the pickling solution is used for a long time, and the corresponding acid should be added to supplement it.

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