Aluminum is very unstable in the air, easy to generate oxide film tha is difficult to identify by t naked eye. Due to aluminum parts processing method of different, such as casting forming, forged,extruded, or CNC precision machining, or by different process forming then by heat treatment or welding,, artifacts surface will rendering different State, different degree of dirt real or traces, for in preprocessing choose the method according to artifacts surface. (1) problem need to be noted for CNC machined parts before anodizing:Though oxidation film exist on surface of CNC aluminum parts for not long time, more easy clear, but greasy heavy, especially eyelets within and around (for machine processing process in the lubrication need and added of), this class artifacts must first by organic solvent cleaning, if directly with alkali wash not only greasy heavy to except NET, and fine processing surface bear can't long time of alkali corrosion, results also will effect to artifacts surface of rough degree and tolerance of tie, eventually has may became waste. (2) before casting in dealing with problems in the process. Casting forming pieces is not all surface are after mechanical processing, without machine processing of surface left has casting process in the formed of had thick oxidation layer, some also clip has sand layer, at should first with machine processing or spray sand method first removed this a parts of original oxidation film, or by alkali wash Hou again processing, only such to both except NET not processing parts of original oxidation layer, and can avoid machine processing parts tolerance size of change. (3) after heat treatment or welding process of artifacts in pretrement process in the need note of problem: by process requirements, artifacts into heat treatment or welding process zhiqian needed by organic solvent cleaning, except net surface oil, but currently General do not to this is, so artifacts surface formed a layer oil sintering of coking real, this layer coking real in organic solvent in the is to except net of, if soaking in lye in the will caused local corrosion, produced Ma points or caused rugged, serious effect products quality. I soaked in concentrated nitric acid method for soft coking, coking materials soft slightly in alkaline solution after cleaning thoroughly cleanse. Some of the specific methods are as follows. ① organic solvent degreasing. Oil-less serious can be soaked in solvent in the short time; serious application of cotton dipped in solvent to wipe oil, or bristle brush to scrub. Operations to safety, residual solvent after use to keep well. ② to dry. Regardless of the organic solvent cleaning, drying process must not be omitted, otherwise it will lose meaning cleaning. ③ banding. Tie the material suitable for aluminium wire, disabling the copper wire and galvanized iron wire, available back layer of wire. Slightly larger single binding to consider tie position and tied to the holes closest to the part edge as much as possible, to reduce the impact on the surface of the workpiece. Different kinds of workpieces should not be tied to a string, because different components (grade) aluminum oxide processing time is different. Note the banding artifacts dangling in the direction, to avoid woqi concave part facing down. Washing up to the workpiece surface oil cleanse. ④ alkali cleaning. ⑤ water rinse. Washing after washing it is best to rinse with hot water, it is a good clean alkaline substances on the surface of the workpiece. A blind hole, slot to strengthen the position of the workpiece flush, and dumped a net residual solution of, and immediately turns nitrate to shine a light, so as not to suffer from oxidation. ⑥ nitric acid. If hybrid aluminum, cast aluminum or 50mL/L should be added based on this formula to hydrofluoric acid to speed up removing alkali adhesion on the surface of aluminum when insoluble substances. 2, the technical requirements of the oxide film forming process (1) oxidation. Solution composition and working conditions: Pre-treatment immediately after transferred to the oxidation process to prevent workpiece on hold for too long in the atmosphere and generate native oxide layer and affect the quality of the oxide layer. Soaked in water is superior to the exposed again in the atmosphere, but it also should not be soaked for too long, if soaked in a 3% soaked in a dilute nitric acid oxidation of L5~30min will continue to be, but if too long generates will have impact on the film, especially old nitric acid containing impurities such as copper. Oxidation temperature of the solution is a critical process in the solution temperature is too high, the film speed, prone to chalking the oxide film; the solution temperature is too low, slow film speed, the resulting film shades of light, poor adhesion. In the same type of aluminum to achieve consistent color on the surface, should be dealt with under the same temperature at the same time. In a certain range is inversely proportional to temperature and time, that is, higher temperature, the shorter the time required, whereas longer required. High purity aluminum oxide required longer processing time. Oxidation treatment of lack of time, the oxide film is too pale; aluminum purity and reduced oxide or oxide films of old, and even affect the conductivity of the film. To obtain an even film color, small pieces of rock in the oxidized in solution, large mixing solution can be adopted, or static (not mixing solution, don't shake the workpiece), in case the workpiece edge switches with the solution more than the center of the workpiece, uneven film colour. (2) wash cycle water. For a blind hole, slit the artifacts to enhance the parts of flushing, residual solution in the net and dumped to prevent oxidation solution flow out oxidation damage. (3) a self-test. After rinse cycle water, the workpiece should be from quality, if defects are found in alkaline solution of stripping, back after light oxidation. Drying after the removal, repair, stripping is harder, and more likely to damage the substrate. (4) dry. Dry is the key to maintaining quality, oxidation during drying before you shake free water on the surface of the workpiece, and then in the Sun. Can also be baked in a 45~50℃ under the condition of drying, the temperature is not too high so as not to scorch, aging, cracking, exterior color looks old. 3, a large area of chloride (1) unit. Based on the oxidation of the outer dimensions (appropriate to relax the allowances), made of wood or bricks to form a box, covered with plastic sheets in the box, forming a concave-shaped pool, the height if the plate, there are about 100MM operation only to be shaking under the artifacts on this pool, to make formation of oxide film on its surface. (2) parts. Implemented in parts that work in Groove (pool) has been a rapid change or turn in different sites were, finally makes the whole workpiece surface contact with the solution several times and gradually form a thicker oxide film method. The above two methods, can be prepared from making large bath, a large number of solutions, and reduce the waste caused by rare use for a long time, also from occupying workshop within production areas. 4, oxide film on three possible causes of uneven color (1) the area of the workpiece is too large, operation swing in the Groove is too large, the edges and the Center spot and the solution of contact, large updates, exchange differences, leading film color inconsistencies ... Preventive measures: oxidized workpiece swing a small, static can be, but when the temperature is too low, easy to map-like spots, appear unnatural. (2) aluminum processing part of the aluminium layer is destroyed, are cut off, aluminum outer Pack are the high quality aluminum, enclosed aluminum inner layer of hybrid, two aluminum difference, so the oxidation occurs after "good crazy wind" spot. Customers tend not to understand this phenomenon, manufacturers should do more to explain the work, explain why and how, so as not to cause misunderstanding. (3) operating aspects. ① parts alkaline etching process is not complete, original film, at the local dirt could not be removed; ② alkali corrosion not light immediately after treatment, the surface is alkaline; ③ workpiece contact with foreign bodies in the transfer process. These factors are important to make a high quality anodized aluminum machined parts,find the reason for uneven coating color to and take steps to solve them. 5, around the hole and the oxidation is more difficult to form an oxide film for two main reasons. (1) after washing rinse thoroughly of the workpiece. Washing the lye into the holes when fails to wash lye from the hole way out of oxidized, which corrode perforations around the film. (2) the butter around the workpiece hole. Aluminum tapping screw hole is very astringent, operators often use butter to grease, alkali lye when lack of emulsifier, butter is difficult to removed. Solution: (1) in alkali washing before use gasoline to wash again, washing liquid should be added emulsifier; (2) workpieces alkaline wash after wash. 6, should pay attention to four points in the post treatment procedures (1) hot water rinse. Hot water aimed at aging film. However, temperature and time must be strictly controlled, water temperature is too high film thickness reduction, Color Dodge. Takes too long to deal with similar problems can also occur, appropriate temperature and time are: Temperature 40～50℃ Time 0． 5~1MIN。 (2) dry. Dry to dry naturally for good, by hot water washing hanging from the shelf of artifacts, let free water in vertical downward flow of the working surface. Flow to the lower corners of drops with a towel, and dry coating colors according to this method are not affected, appears natural. (3) the aging process. Method can be decided according to the climatic conditions of aging, sunlight exposure in daylight in the summer, wet weather or winter is available oven bake process conditions are: Temperature 40~50℃ 10~15min. For more information about the anodizing problem,you can send a email to us for discussion.