Oil removal and polishing for Aluminum alloy surface Treatment
In order to make the surface of aluminum products bright and smooth. after the formation of aluminum products are generally after mechanical polishing.However, mechanical polishing after oxidation, only to get a smooth oxide film, gloss is often not enough. For products requiring high gloss decorative oxide film, chemical or electrolytic polishing is required after mechanical polishing. After chemical polishing or electrolytic polishing, pure aluminum or high-purity aluminum-magnesium alloy can obtain high reflection coefficient gloss surface, especially electrolytic polishing, can obtain very satisfactory results. Unfortunately, the triacid chemical polishing solution contains nitric acid (HNO3) , heating operation, decomposition of nitrogen dioxide gas and "Huanglong" pollution. The high quality and stable electrolytic polishing solution contains chromic anhydride, which results in chromium-containing wastewater, environmental pollution and three waste treatment problems. It is natural that people want to try chemical polishing without "Huanglong" and electrolytic polishing without chromium.
MECHANICAL POLISHING OF ALUMINIUM SURFACES:
1. Mechanical Polishing Process: Rough Grinding, fine grinding, polishing, sandblasting, brushing or rolling, according to the surface of the appropriate to take a different process.
The process of chemical deoiling removes oil from the surface of the workpiece through chemical reactions and physical chemistry. The chemical deoiling is carried out in a weak alkaline solution.
Chemical deoiling fluid formulation and process conditions:
1. Formula: Sodium Hydroxide 30-50G / L, industrial detergent 0.5-1ML / L, water 70-125G.
2. Technological Conditions: Temperature: 50-60 °C time: 1-2 Min
3. Wash with clean water after removing oil.
4. Chemical Deoxidization Film: Acid pickling is carried out to neutralize the lye remaining on the surface of the parts and to remove the natural oxidation film so as to expose the aluminum and aluminum alloy matrix of the parts. For the production of aluminum alloys containing silicon, acid pickling must be carried out in a mixed solution To remove the dark silica float ash from its surface.
FORMULA FOR PICKLING SOLUTION:
Concentrated Saltpeter 200ー270 ML / L
Temperature: Room temperature time: 1-3 Min
ACID cleaning solution for removing oxide film and floating ash on the surface of silicon-containing Aluminum Alloy Parts
Concentrated Nitric Acid 3 volume; concentrated hydrofluoric Acid 1 volume.
Temperature: Room temperature time: 5-15 Min
Aluminum and aluminum alloy parts after chemical pickling must be immediately cleaned with warm and cold running water to remove residual acid, and then immersed in water for chemical polishing.
5. Chemical Polishing:
Chemical polishing is a chemical process in which aluminum and aluminum alloys are selectively autolyzed in an acidic or alkaline electrolyte solution to smooth and Polish the surface to reduce the Surface roughness and Ph. This polishing method has the advantages of simple equipment, no power supply, no restriction on the external dimension of parts, high polishing speed and low processing cost.
The purity of aluminum and aluminum alloy has a great influence on the quality of chemical polishing. The higher the purity of aluminum and aluminum alloy, the better the polishing quality, and vice versa.
Chemical Polishing is carried out by means of a brief theory of viscous liquid film.
FORMULA AND PROCESS CONDITIONS FOR POLISHING SOLUTION:
Recipe 1: (by weight)
Concentrated phosphoric acid 75% ; concentrated sulfuric acid 8.8% ; concentrated nitric acid 8.8% ; urea 3.1% ; amine sulfate 4.4% ; copper sulfate 0.02% .
Temperature: 100-200 °C time: 2-3 Min
Recipe 2: (by weight)
Phosphoric acid 85% ; nitric acid 5% ; glacial acetic acid 10% .
Temperature: 90-105 °C Time: 2-5 Min
PREPARATION OF POLISHING SOLUTION:
First, the phosphoric acid, sulfuric acid and nitric acid according to a certain (%) weight, gradually pour into the polishing trough, carefully block uniform.
2, according to the composition of the formula, respectively with water to dissolve a certain weight (%) of glacial acetic acid, urea, ammonium sulfate, copper sulfate into the tank to mix well.
3, then, in the state of agitation, gradually adjust the above-mentioned polishing liquid to the required temperature range of each formula, chemical polishing can be carried out.
3. EFFECTS OF CHEMICAL POLISHING PROCESS CONDITIONS:
1. Temperature effect: The temperature should be controlled between 90-115 °C, the best temperature is 105 °C.
2. INFLUENCE OF POLISHING TIME: Polishing time is inversely proportional to polishing temperature, low temperature prolongs polishing time, high temperature reduces polishing time.
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