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TECHNOLOGY ANODIZING ALUMINUM AND ITS ALLOYS
Parts and products of aluminum and its alloys are oxidized in air, resulting in the formation of gray spots on the surface, which spoil the appearance.
Duralumin (aluminum) will become more beautiful if it is subjected to anodizing, which results in the formation of a thinned passive layer on the surface, which prevents further oxidation.
Anodized surface owns flattering gray paint. In addition, later anodizing aluminum product can be easily painted in any color with conventional aniline dyes.
First, prepare separately a pair of saturated solution - drinking soda and salt also - in boiled water at room temperature. To obtain a saturated solution, the dissolution must be kept at least half an hour, stirring the solution periodically. After this, the solutions should be allowed to stand for 15 minutes, they should also be filtered.
Then prepare the electrolyte by mixing the nine volume elements of the solution of drinking soda plus one volume elements of the salt solution (9: 1).
The electrolyte is well mixed in a glass container.
Before anodizing, the part is thoroughly cleaned with fine emery paper, degreased (it is possible in a hot solution of laundry detergent) plus washed in running water, after which it should not be touched. Then the anodized part is immersed in an electrolyte solution, which is forced to be in an aluminum pan. An adjustable rectifier for 12 V can be used as a current source, as well as a current up to 2 A or a car battery.
The “plus” current source is attached to the part, the “minus” - to the aluminum electrolyte tank. The current density should be around 15 mA / cm2. To fulfill this condition, the required current density must be multiplied by the surface area of the part in square centimeters. The current value calculated in this way is maintained by adjusting the current source.
Anodizing lasts about 90 minutes - until the part is covered with a bluish-gray coating. The anodization process can be observed by the release of atmospheric bubbles as well as the appearance of a light gray deposit on the surface of the anodized part.
After the end of anodizing, the part is washed in running water and is also cleaned with a cotton swab moistened in a solution of potassium permanganate from the products of the electrochemical reaction. After that, the surface of the part is made smooth, with a light gray tint. The part is again washed in running water and also dried in air.
If desired, the detail later anodizing can be painted in a solution of aniline dye. The coloring solution contains 15 g of dye and also 1 ml of acetic acid per 1 l of water.
Coloring is carried out in a solution heated up to 60 ... 80 ° C. The duration of exposure to the solution depends on the required color saturation is also usually 10 ... 15 minutes to fix the color, the painted part is kept in boiling distilled water for 1 ... 1.5 minutes.
To protect the part from mechanical damage, it is useful to paint it with a colorless furniture lacquer (NC).