The method of cleaning aluminum surface is usually divided into physical cleaning and chemical cleaning.
Physical cleaning
Mainly use some organic solvents to dissolve oils, lipids, paints and other substances to remove dirt or other dirt on the surface of the parts and get a relatively clean surface. Physical cleaning usually uses organic solvents such as banana water, turpentine, alcohol, gasoline and kerosene. In order not to affect the effect of chemical cleaning, after cleaning with organic solvents, the parts must be blown dry or wiped dry, so as not to mix these solvents into the next process (alkaline cleaning solution cleaning) and affect the ability of lye to remove oil stains.
Among all these solvents, the safest and cheapest is kerosene. The ignition point of kerosene is high, but because it evaporates slowly, it is easy to leave traces of oil stains on the surface of aluminum and its alloy parts. Therefore, kerosene is often used as a cleaning agent for dirty parts in the first pass, and then cleaned with other solvents. Banana water, turpentine oil, and alcohol have irritating effects on human eyes and skin, and are more expensive. Especially alcohol has a narrow purpose and its degreasing ability is not as good as banana water, so it is not used much. Pay attention to safety when using gasoline to prevent fire. As for chlorinated solvents, such as carbon tetrachloride, although it has strong decontamination ability, it is not suitable for use due to its high toxicity. For aluminum products that do not require high mechanical properties and dimensional changes, the grease and oil stains on the surface can be solved by the simplest burning method. That is, the parts are placed in a muffle furnace and kept at a temperature of 200-2500C for 1 hour to achieve a satisfactory degreasing effect.
Chemical cleaning
The physical cleaning method only plays a role in cleaning dirt, oil and other dirt, but it is not thorough enough, so chemical cleaning must be used to clean it. After a chemical reaction, a very clean surface can be obtained. It can be seen from practice that when the parts that have been chemically cleaned are taken out of the water, the entire surface is wetted with water and a water film is evenly hung on the surface without any dirt.There are usually the following chemical cleaning methods.
1.Alkaline cleaning
Alkaline cleaning is the most important part of the cleaning of aluminum products. Alkaline cleaning agent has good wetting performance, has a strong emulsification effect on grease, and forms soluble soaps; at the same time, it also has a reverse coagulation effect on dirt particles, so that the dirt particles are dispersed in the solution in a colloidal state. Deposited on the surface of the part, it can more thoroughly remove the residual oil stains on the aluminum surface.
However, because aluminum is different from other metals, it is easily corroded in alkaline solutions. Therefore, it is required that the alkalinity in the alkaline cleaning agent be limited to the minimum range, that is, the corrosion effect on aluminum should be controlled to the minimum. Generally, the PH value should be controlled between 9-11, not higher than this range, otherwise the erosion will be too fast and difficult to control, which will affect the size of the parts and even destroy the parts. In order to ensure that the alkaline cleaning agent has a certain stability and good cleaning performance, corrosion inhibitors such as phosphate and silicate should be added to the alkaline cleaning solution to form a layer of protection with the aluminum surface or surface oxide film membrane.
As the use time of the alkaline lotion increases, not only the solution is gradually lost, but also the decontamination ability also 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 must be removed. After a certain period of time, a new solution must be added or re-prepared.
2.Acid cleaning
Pickling has the effect of further decontamination. After the aluminum products are chemically polished and cleaned, the surface becomes dark, forming a gray film that can be wiped off. This layer of 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 rinsed with cold water. Due to the increase of water during the washing process, H+ is taken out, so the concentration of the corresponding acid is reduced to a certain time after the pickling solution is used for a long time, and the corresponding acid must be added to supplement it.
