Etching of aluminum (products made of this metal) is carried out in order to clean its surface from the top, unnecessary layer or from rust. There is also such a variety of it - artistic etching, when it is necessary to engrave a pattern on the surface of a metal part.
Types of pickling
Etching of metals in general and aluminum in particular can be of two main types: chemical and galvanic. The last method is just artistic.
In case of chemical: the product is placed in a container into which a solution of hydrochloric or sulfuric acid is first poured. In the same way, an aluminum billet is etched with alkali, such as caustic soda.
And galvanic (otherwise - electrolytic or electrochemical) is due to the electric battery. The process itself is carried out in a special bath, where there is an anode and a cathode.
Next, each of the aluminum etching methods will be discussed in more detail. We also find out whichthe safest method at home.
Aluminum etching with acid
Due to the fact that very strong acids are used in this process, it is first of all necessary to observe increased precautions when working with them. The operator must wear gloves, mask, apron. It is important that the room where the process takes place is well ventilated. It is not recommended to work with acids without certain skills and without certain protective equipment.
As noted above, an aluminum product is placed in a container with acid. Most often, the following reagents are used in the chemical etching of aluminum with acid: hydrochloric or sulfuric acid. When they interact with metal, hydrogen is released. Outwardly, it looks like this: the surface of the product is covered with small bubbles. But, in principle, this can be prevented by adding a special ingredient to the container in advance. Thus, the metal will be protected from bubbles by the thinnest film.
A very important point: all operations for etching an aluminum product with acid must be performed intensively so that the metal surface itself remains intact.
The described method is recommended to be carried out in containers made of wood or concrete. At the same time, its inner surface must be lined with acid-resistant tiles so that the walls of the container do not corrode.
This method is not used very often in practice.
Etching aluminum with alkali
Most often this method uses an aqueous solution of caustic soda(available with or without additives).
And it is used to clean the surface of an aluminum product from oxide or unnecessary grease and get a smoother (matte or glossy) surface.
Why do you need to clean so thoroughly? To ensure that the finished product (for example, decorative architectural elements, plaques) has an ideal surface. And also this method is used for deep engraving.
The method of etching aluminum with alkali, on the one hand, is quite inexpensive, but it is very laborious.
Features of this method
The solutions used contain four to ten percent sodium. The temperature for alkali pickling is approximately 40-90 degrees Celsius.
If necessary, apply a moisturizer or special additive to achieve a light foamy finish on the workpiece.
The average temperature at the height of the process is sixty degrees. It is with such thermal performance that high-quality surface cleaning occurs.
Optimal aluminum purity is 99.5%, and the concentration of caustic soda solution is 10, 15, or 20%.
Thus, during the reaction, aluminum dissolves in caustic soda, and hydrogen is released. As a result, a composite aluminate is formed, and it exists only in an alkali solution.
Further processes occurring during alkali etching
During this processgradually the amount of caustic soda becomes less. And thus the speed of the process itself decreases, but the viscosity increases.
Provided that no sodium hydroxide was added to the container at all, the reaction can be very slow. But in the end, a brownish or clear aluminum pickling solution turns white.
And from now on, the speed of the process increases.
As a result of the reaction, alumina hydrate precipitates, which looks like a suspension. And also caustic soda is released, which is also necessary for the etching process to continue.
Results with the considered method
It was experimentally recorded that a solution of caustic soda with its intensive use in the etching process begins to "absorb" aluminum. And this happens until the amount of caustic soda decreases to one fourth of the original volume. And after that, the process will continue with free caustic soda, fluctuating in its quantity. And this, in turn, depends on temperature, frequency of use and intensity of stops (pauses).
In this case, the hydrate will slowly settle or form crystals at the bottom and/or sides of the container. The resulting hydrate will be quite dense, and it will not be easy to remove it. Sometimes it tries to settle right on the surface of the heating coils.
There is another important point regarding the aluminum content. During the pickling of products from this metal in caustic soda, it is necessary to strictly observealuminum to sodium ratio. Because the more aluminum there is, the slower the process will be. From a practical point of view, it becomes clear that it is necessary to constantly increase the amount of caustic soda as the amount of aluminum in the container increases.
Thus, the process of etching aluminum with alkali can be continued continuously. And the loss of caustic soda will occur only due to its entrainment with steam.
This method is really applicable in terms of practice. But there are several nuances that should not be forgotten: from time to time remove the hardened hydrate sediment; clean the filter; remember that the capacity in which the process is carried out, with constant use, can last no more than two years.
And otherwise, no complications regarding the use of this method have been identified.
Total, after chemical etching of an aluminum billet, its surface must be thoroughly washed, neutralized and clarified with a 15-20% nitric acid solution. This process is called decapitation.
Galvanic method
The second etching method is galvanic. It is simpler and much faster in time. And the result is a very high-quality surface of the product, clear contours of the pattern (with an artistic method, as a variety of galvanic).
The peculiarity of this method is that it uses a source of electrical energy (4-5 V).
You will also need a tub large enough to fit the aluminum piece. material, fromwhich the bath is made must be a dielectric. The composition of the aluminum pickling bath is a solution of copper sulphate and common s alt.
Before starting the process, the workpiece must be cleaned and degreased. Next, solder a copper wire to the product with tin and lower it into a solution of caustic soda, and then into a solution of sulfuric acid. After 2 minutes, remove and rinse under a stream of hot water. It is forbidden to touch the product at this moment.
If some parts of the workpiece do not need to be etched, mastic is applied to them. After that, you can start the process itself.
This method uses two so-called supports, which must be connected to the anode (positive charge) and cathode (negative) of the power source. It is important that these supports are located across the tub. An aluminum billet is attached to the support with an anode, and a billet of another metal is attached to the second one.
All this is lowered into the bath and aged for a certain amount of time. After that, it is washed with turpentine and finished by grinding and polishing.
Artistic etching
This kind of galvanic method is quite popular at present. With it, you can make author's drawings, engraving, artistic prints, ornaments on any metal blank.
And the result is a very clear, beautiful drawing. So to speak, the author's work, which you can keep or give.
The original image itself can be drawn by yourself or printed(using a laser printer) on paper. Next, stick adhesive tape on the surface and wash off the paper with hot water. As a result, the image should remain on the adhesive tape. Leave to dry. In the meantime, it is necessary to prepare the surface of the metal on which the drawing will be applied - degrease it with alcohol.
Then stick adhesive tape with a pattern on the surface of the workpiece, while releasing air bubbles from under it. The excess glue and everything unnecessary is removed with a hot awl, except for the image itself.
Etching is carried out in the same way that has already been described above - galvanic.
Attention: this process is likely to release harmful gases, so it is better for people to leave the room.
Thus, aluminum etching at home is quite feasible. Just be sure to follow all the most important precautions!
