Views: 50017 Author: Site Editor Publish Time: 2021-05-12 Origin: Site
Aluminum and its alloys are placed in the corresponding electrolyte (e.g. sulfuric acid, chromic acid, oxalic acid, etc.) as the anode and electrolyzed under specific conditions as well as by the action of the applied current. The anode of aluminum or its alloy undergoes oxidation reaction and a thin layer of aluminum oxide is formed on the surface, the thickness of which is 5 - 20 microns, and the hard anodic oxide film is up to 60 - 200 microns. The anodized aluminum or its alloy improves its hardness and wear resistance up to 250--500 kg/mm2, and also enhances its good heat resistance, with the melting point of hard anodized film up to 2320K; excellent insulation, with breakdown voltage resistance up to 2000V; enhanced corrosion resistance, in ω = 0.03 NaCl salt spray after several thousand hours without corrosion. Because the thin layer of oxide film has a large number of microporous, can adsorb various lubricants, so it is suitable for manufacturing engine cylinders or other wear-resistant parts, and the film microporous adsorption capacity, so it can also be colored into a variety of beautiful and bright colors. Non-ferrous metals or their alloys (such as aluminum, magnesium and its alloys, etc.) can be anodized, and this method is widely used for mechanical parts, aircraft and automobile parts, precision instruments and radio equipment, daily necessities and architectural decoration.
The process of physical or chemical treatment of the oxide film after anodizing aluminum alloy, reduce the porosity and adsorption capacity of the oxide film in order to seal the dye in the micropores and at the same time improve the corrosion resistance, wear resistance and other properties of the film. The sealing of oxide film basically uses three processes, such as heat sealing, cold sealing and medium temperature sealing, but currently there is a trend of expanding medium temperature sealing.
1. Heat sealing hole
a. Boiling water sealing: In pure water close to boiling point (temperature above 95 degrees, deionized water), the amorphous alumina is transformed into hydrated alumina through the hydration reaction of alumina, as the hydrated alumina is 30% larger than the original volume, the volume expansion makes the microporous filling of the oxide film closed.
b. High temperature steam sealing, the principle is the same as boiling water sealing, advantages: fast, less dependence on water quality, less white ash, less risk of discoloration. The equipment needs to be sealed to ensure the temperature and humidity, generally the temperature is 115 - 120 degrees, the pressure is better at 0.7 - 1 atm, relatively speaking, the cost will be higher.
Since heat sealing has better sealing effect, people have developed high temperature sealer based on heat sealing, which can reduce the temperature of the system and still have better sealing efficiency.
2. cold sealing
Cold sealing is the most commonly used and basic sealing technology in China, the operation temperature is room temperature, so it is also called room temperature sealing, the time is half shorter than that of hot sealing, it relies on the deposition of filler in the microporous to seal the hole, the most mature process is the cold sealing process with nickel fluoride as the main component. In recent years, more experience has been put into the development of nickel-free sealers because of the difficulty of handling nickel salts in water bodies and the greatly increased cost of wastewater treatment.
3. Medium temperature sealing
Medium-temperature sealing refers to a sealing technology where the sealing temperature is between high-temperature sealing and cold sealing, due to this feature, medium-temperature sealing has many advantages that the former two do not have. The medium temperature sealing temperature is not high, the energy consumption is low, the sealing speed is 1-1.3μm/min, the efficiency is relatively high, and the sealing effect is excellent. Moreover, the main sealer is inorganic salt, which is stable and easy to control and meets the national environmental requirements.