The process is applicable to the phosphating, oxidation, electrophoretic coating and other pretreatments of aluminum and its alloys. The treated film and various coating layers (paint, plastic powder, electrophoretic paint, etc.) have strong adhesion. The film formed by the work piece after the process has strong anti-corrosion performance and can significantly improve the overall anti-corrosion performance of the work piece when combined with the coating layer.
2 Process Introduction
Aluminum coating has excellent corrosion resistance and weather resistance, strong and durable, good appearance decoration, production process is simpler than anodizing, environmental protection and safety, and is widely used in decoration, transportation and other industries. The aluminum must be chemically cleaned and etched prior to painting to remove contaminants such as grease, natural oxide film, and dust that adhere to the surface, leaving the aluminum alloy matrix exposed and forming a uniform activated surface. This ensures conversion. The key to film quality and spray quality. The acid-removal process researched by Youju Metal Surface Technology Co., Ltd. of Taiyuan City combines the three processes of degreasing, alkali etching, and decontamination and light extraction of traditional processes into one process, which reduces costs and saves energy. The surface of the treated aluminum alloy is smooth and clean. To maintain the original luster of aluminum alloys, aluminum dissolution loss and sedimentation of the bath liquid, and a variety of conversion processing supporting performance, especially for aluminum surface treatment before coating.
3 process characteristics
1). The acid stripping process completes the processes of degreasing, alkali etching, and decontamination and light extraction at one time. Compared with the separation process, the process is simplified, the area and equipment investment are reduced, and chemical raw materials and cleaning water are saved.
2). When used at room temperature, the bath requires no heating, saves energy, has no evaporation of the acid mist, does not pollute the working environment, can inhibit the erosion of the acidic materials on the equipment and the plant, and prolongs the service life of the equipment and the plant.
3). Strong oil removal ability, quick removal of oxide film, high corrosion inhibition efficiency, no corrosion of workpieces for a long period of time (such as one day), little loss of aluminum dissolution, no over-corrosion and black ashing. After processing, the workpiece is silver white, bright and shiny, and the surface quality is good.
4). The solution has stable performance, convenient management and maintenance, and the bath can be continuously recycled for a long period of time. Each tank can be used for more than 2 years.
5). The domestic aluminum alloy pickling process, most of them use a period of time will have a precipitate, and the process after a long period of heavy use of a small amount of sediment.
4. Process flow
Workpiece loading→Aluminum removal→Washing→Washing→Phosphating→Washing→Pure washing→Draining→Drying→Spraying→curing
5. The main equipment
Equipment name Quantity Lining requirements Heating facility Air-drawing facility remarks Acid removal tank 1 PVC 0°C or so need not need Water tank 2-3 No need No Phosphate tank 1 PVC Not required 6. Process conditions6.1 Aluminum removal
Yj-1360 Acid Remover 20～50g/L Temperature Normal Time 5～20min
6.2 Phosphating
Yj-6104 Phosphating agent 20～50g/L
Oxidants 5 to 15 points
Temperature 5 ~ 40 °C time 5-20min
Note: The preparation method of bath is very simple, first add about half the volume of water in the tank, then add Yj-136050Kg or Yj-610450Kg, (concentration can be lower according to actual use conditions) and then add enough water.
7 Process Operation Instructions
7.1 Pre-inspection: There shall be no defects such as glue, paint, aluminum scrap, sand, burr, etc. on the surface of the parts. 7.2 Acid stripping: The workpiece is immersed in the acid deliquoring, and the workpiece can be shaken in order to speed up the degreasing.
Inspection standard: visual inspection, the surface of the aluminum alloy exposed after the acid liquid treatment shows the true color of the metal, smooth, bright, oil and natural oxide film in addition to the net, after washing, the water film is continuous, complete, the surface is completely wet, do not hang water, No black ash and excessive corrosion.
7.3 Washing: Clean the workpiece in water. 7.4 Phosphating: The workpiece is immersed in a phosphating solution for phosphating, and the workpiece may be moved up and down in order to evenly phosphating the film. 7.5 Washing: Wash the phosphatized parts with running water. There must be no unwashed phosphating solution in the parts.
8 Precautions 8.1 Heat treatment and welding parts: After the workpiece is heat-treated or welded, oil-sintered char is formed on the surface, and the degreasing time can be prolonged or the concentration of the degreasing liquid can be completely removed. 8.2 Bundling of parts: 8.2.1 The materials used for lashing should be aluminum wire. Copper wires and galvanized wires are prohibited. The wire that is stripped of zinc can be used. 8.2.2 Slightly larger single pieces should be tied together as much as possible in the hole closest to the edge of the part to reduce the influence on the surface of the workpiece. 8.2.3 Different kinds of workpieces should not be tied together in a string, because the time for phosphating the aluminum of different compositions (brands) is different. 8.2.4 Pay attention to the direction in which the bundled workpieces are to be suspended, and avoid the concave surface facing downwards and make gas. 8.3 Temperature:
The removal rate of oil-removing oxide film increases with increasing temperature. The increase in temperature can reduce the viscosity and interfacial tension of oil stains, improve the etching ability of acid deliquoring on aluminum materials, and enhance the emulsification of acid deliquoring and oil contamination. When the temperature is lower than 5°C, the speed of deoiling the oxide film is slowed down, which affects the progress of production. When the temperature is higher than 40°C, the acid deliquoring components tend to volatilize, resulting in acid mist, increased acid loss, and energy consumption. Increased, aluminum is prone to over-corrosion and black ash. Therefore, the use temperature of the acid deliquoring should be controlled within the range of 5°C-40°C.
8.4 hours:
If the treatment time is too short, the oil stain and natural oxide film on the surface of the workpiece will not be completely removed, which will hinder the normal progress of the transformation filming reaction. If the treatment time is too long, the loss of aluminum will increase, the surface roughness of the workpiece will be reduced, and the gloss will decrease. Reduced efficiency. The treatment time is closely related to the composition of aluminum, the amount of oil on the surface, the thickness of the natural oxide film, the processing temperature and the method, etc. Generally, it takes 5 minutes to 20 minutes to determine the acid stripping time based on the principle that the oil stain and the natural oxide film are completely removed.
9 bath management
9.1 Acid de-slotting: As the aluminum alloy processing volume increases continuously, the acid de-draining solution is continuously consumed and brought out during use, the acidity and degreasing effect are reduced, and various effective components are gradually decreased. Therefore, regular analysis of the bathing fluid should be performed at regular intervals. Yj-1360 shall be added in time to keep the process parameters of the bath within the specified range. The oil on the surface of the workpiece is displaced, dispersed, and agglutinated and then suspended on the acid deliquored surface. The oil on the surface must be frequently spilled to prevent the workpiece from being contaminated with oil for the second time. After long-term use, when the accumulation of aluminum ions in the bath solution is too high, the bath solution should be partially or completely replaced.
9.2 Phosphate bath: As the concentration of the active ingredient in the solution is gradually reduced as production proceeds, Yj-6104 should be added. After long-term use, when the aluminum ion accumulation in the bath is too high, the bath should be partially or completely replaced.
10 Phosphating solution analysis
Accurately weigh 10ml of working solution in a 250ml Erlenmeyer flask and add distilled water 50ml. Add 10 ml of a 1:1 mixture of sulfuric acid and phosphoric acid, and 2.3 g of potassium iodide. Shake well and add 1 ml of starch indicator. With 0.05mol/L sodium thiosulfate standard drop to colorless, the number of milliliters consumed is the number of solution points.