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Knowledge small classroom | degreasing process

Release time:

2022-07-18 15:16

degreasingAs the first process of chemical pretreatment of aluminum, the purpose is to remove the grease and dust and other pollutants on the aluminum surface, so that the subsequent alkali washing is more uniform, so as to improve the quality of the anodic oxide film. The quality of degreasing can be tested by the surface wettability effect. After degreasing and water washing, the surface of aluminum material shall be completely and evenly wetted, and the continuity of the wetting film shall be maintained for at least 30s. The degreasing of aluminum materials is roughly divided into three types: acid degreasing, alkaline degreasing and organic solvent degreasing.

1、acid degreasing

Acidic degreasing is mostly carried out at room temperature, production control is easy and low cost, usually acidic degreasing agent is sulfuric acid-based acidic liquid, oil hydrolysis reaction will occur, the generation of glycerol and the corresponding high fatty acids, in the solution to add a small amount of wetting agent and emulsifier, is conducive to oil softening, free, dissolved and emulsified, significantly improve the degreasing effect. When the sulfuric acid content in the acidic degreasing solution is insufficient, the waste sulfuric acid in the oxidation tank can be added.

2、alkaline degreasing

Alkaline degreasing is the traditional process of aluminum surface pretreatment, aluminum is an amphoteric metal, vulnerable to alkaline solution erosion, so the use of low alkaline solution for surface degreasing cleaning treatment. A degreasing solution that is too alkaline may cause uneven erosion of the aluminum surface because it tends to erode the clean surface of the aluminum faster and the surface with grease is slower, which may cause cleaning spots on the aluminum surface. The action principle of alkaline degreasing is the saponification reaction of alkali and grease to generate soluble soap. The saponification reaction is used to eliminate the combination of grease and aluminum surface, so as to achieve the purpose of degreasing. The reaction principle is as follows:

The biggest problem of alkaline degreasing is that the solution needs to be heated, which not only brings about an increase in production costs, but also brings certain difficulties to production control. The temperature of the alkaline degreasing solution is generally controlled to between 45 and 65 degrees Celsius, and the temperature often drops during the production process, and it has to be heated frequently.

3、organic solvent degreasing

Organic solvent degreasing is the use of oil soluble in organic solvent characteristics of degreasing; organic solvent can dissolve saponified oil, also can dissolve non-saponified oil, has a strong degreasing ability, and fast, non-corrosive to aluminum matrix, but the organic solvent is flammable and toxic, unless really needed, should be avoided as much as possible. Usually the main components of organic solvents are carbon tetrachloride, trichloroethylene, benzene, gasoline, kerosene, alcohol and acetone.