Normal defects of aluminum profile anodizing process and their solutions

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In the aluminum extrusion production process, fine extrusion mill finished (Substrate) aluminum profiles surface provide a basic role for anodizing surface treatment. Anodizing process plays an important role of getting a superior surface of aluminum profile. Here are some defects of aluminum profile in the anodizing process:

1. Not ideal electrical conductivity of oxidation films

Reason: The time of anodizing is so long that the oxidation films are too thick.

According to operation of aluminum anodizing process in 30 to 60 seconds, oxidation film presents iridescence color and good conduction effect without any resistance. But if the time of anodizing is too long, the thickness of oxidation films may increase, which not only affects conduction, but khaki color on the films also looks obsolete.

Solution: Strict control the anodizing operation time.

2. Poor adhesive force of oxidation film

Reasons:

1) Over thickness of oxidation films;

2) Excessive concentration of oxidation liquor;

3) Over heat of oxidation liquor;

4) lack of ageing treatment on films

Solutions: Adjustment to four above points can improve the adhesive force of oxidation films.

3. Difficulty of forming oxidation films in and around aluminum profile’s eyelets.

Reasons:

1) Washing and cleaning is not complete enough to aluminum profile after alkali washing. If the alkali liquor which enters into the aluminum profile’s eyelets is not clear out, it will be flow out after oxidation disposal and cause of corrosion on films around eyelets.

2) There are butter around of the aluminum profile’s eyelets. When making screw hole on aluminum profile, the operator uses the butter to lubricate the because of dry, but it is difficult to eliminate them without emulgator.

Solutions:

(1) Before alkali washing, aluminum profile should be cleaned by gasoline and emulgator should be added into the alkali liquor.

(2) Completely wash the aluminum profile after alkali washing.

4. Difficulty on partial surfaces of aluminum profile to form oxidation films

This phenomenon always happens to flat workpieces.

Reasons:

1) The densification burnt stuffs are common on surfaces of rolled aluminum plate, which can not be eliminated easily when alkali washing.

2) Work piece does not get complete rinse in nitric acid after alkali washing.

Parts of surfaces of aluminum profile are alkaline so that it is easy to form a thin autoxidation films under the reaction in the air. Due to conductive oxide solution is faint acid, the autoxidation films can not be gotten rid of, not even to form conductive oxidation films. Therefore, workpieces after alkali washed must be rinsed thoroughly in nitric acid in case of autoxidation.

3) Excessive accumulation of aluminium iron in lye

It is difficult to elute lye from surfaces of workpiece because of the viscosity of solution, which obstructs the appetence between aluminium profile surface and oxidation liquor, resulting in yellow and white striations (the yellow part is because barriers items are eluted and get oxidation films; the white part doesn’t get oxidation film because of aluminium hydroxide of barriers existing.

Solutions:

(1) Before alkali washing, we can use fine sands to eliminate burnt stuffs on aluminium profile surface by blasting.

(2) Workpiece should get complete rinse in nitric solution and after alkali washing.

(3) Change the lye.

5. Dark yellow spots on and around blind holes of oxidic workpiece

Reasons: Workpiece is not clear enough when washing in the water, leaving vestigital liquor flowing out from blind holes in drying process.

Solutions: After oxidation, workpiece must get rid of liquor, and medical syringes are needed if necessary.

6. Deep and shallow spots appear on the surface of aluminium profile

Reasons: When one of layer of cladding aluminum are cut apart, we can see that aluminium outside is superior material while inside is inferior materail. Owing to such a disparity, spots like Vitiligo appear after oxidation.

Solutions: Manufacturor has to explain the whole story to customers in case of any misunderstanding.

7. Appearance of contact shadow printing on oxidation films of large workpieces

Reasons: The area of workpieces is so large that we have to adopt subsection of oxidation.

Solutions: Bulk treatment. First, pave a piece of plastic cloth on the floor. Then, put pieces of wood or brick around to build a pool about 100 millimeters high. Flat workpiece can be directly operated in the pool while three dimensional ones have to be operated on faces in turns. Doing this can be obtained the same effect in the large oxidation tank.

8. Non-uniform colors on surfaces of oxidation film

Reasons: Contact, update and exchange between edge and centre of aluminium profiles and liquor are much different because aluminum profile area is large area and the range of swing is large in the oxidation tank, which leads to non-uniform colors of oxidation film.

Solutions: Range of swing when oxidation workpiece should be minimized. However, when the temperature of liquor is abnormal, map-like spots may appear; which make products look unnatural.

9. Grey shadow printing in colligation of oxidic workpiece

Reasons: Use galvanized iron wire to colligate workpiece.

Solutions: Zinc layer should be eliminated before using iron wire.
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