Aluminum anodizing (anodic oxidation, anodic oxidation) is a unique electrolytic process, which is used to protect the surface of extruded aluminum corrosion, as well as giving it an attractive appearance.
Under “aluminum anodizing” always mean “anodizing aluminum sulfate”. Feature anodizing is, that during the chemical preparation of the surface prior to anodizing aluminum profiles and of the anodizing process can be detected hidden surface defects or profiles unfavorable for anodizing metallurgical microstructure.
Anodizing of aluminum profiles
Final quality estimates anodized aluminum profiles manufacturer anodizing, anodirovschik, before sending them to the customer, and it is responsible for the end result. meanwhile, the cause of the defects may be located in a completely different place: at the bar manufacturer, caster, or manufacturer of extruded profiles, pressman. Often there are differences between the three manufacturers in the, Who is to blame in the event of a specific defect in the final product anodized.
The problem is solved easily, if all three artists are included in the same company. If they belong to different companies, then there may be a serious debate about the responsibility for the occurrence of defects.
However, in terms of ensuring the ultimate high quality of anodized aluminum profiles, the responsibility of these three manufacturers is quite clear:
- The caster is responsible for the homogeneity of the chemical composition of the A-pillars ingots, the right technology of casting and homogenization.
- Press operator is responsible for the quality of compaction, and heat treatment of aluminum profiles displacement intrashop, and correct their packaging, storage and transport for delivery to anodirovschiku.
- Finally, anodirovschik responsible for quality before storage anodized aluminum profiles, preparation of the surface, anodizing, staining and sealing anodic coating of aluminum profiles, and correct their packaging, storage and transportation to the customer.
Anodizing defects: basic types
Detailed classification of defects colorless anodizing aluminum profiles presented Barry R. Ellard of Alcan company in its capital article in the materials of the international seminar Aluminum Extrusion Technology 2000 of the year. It has about a 30 types of defects, which are grouped into four main types, categorized by their causes.
A type 1 - Strips: pressing and ingot quality
These defects in anodized profiles are associated with the transverse or longitudinal inhomogeneity of the material properties (microstructure, chemical composition, degree of deformation). This inhomogeneity manifests itself in the form of longitudinal or transverse bands in aluminum profiles with the inhomogeneity of color or reflectivity of an anodized surface.
Anodizing defects: stripes from microstructure
Anodizing defects: stripes from structure, geometry and welds
Anodizing defects: stripes from matrix marks, welds and sink marks
A type 2 – Stripes: mechanical surface preparation
These defects arise during the mechanical preparation of the aluminum surface before the anodization, for example, when polishing (drawing 1) or grinding (picture 2).
Figure 1 – Defects mechanical polishing
Figure 2 – grinding defects
A type 3 - Corrosion Defects
Defects of anodizing aluminum profiles from the effects of various types of corrosion: friction, overall, alkaline, acid, galvanic, chloride.
A type 4 – Do not strip, and corrosion
Defects inhomogeneity appearance, different from the "banding" and "corrosion defects". Usually, this is – spots, "Divorce", "Sparkles" and like "nonbanded" defects. The reasons arise at various stages of the technology: from uneven cooling by the section of the profile at the exit from the press to violations of the anodizing technology.
Sources anodization defects
Each defect has one or two 'originators' - caster, Extruders or anodirovschika. For each defect it is important to know:
- at some stages of the production defect arises and
- at what stage of the manufacturing defect is clearly seen.
Founding and pressing
For defects of aluminum profiles pressing origin, even if their "primary source" is in the ingot-column, responsible pressman. he has, in turn, can make a complaint to the caster, change it and / or tighten the input control bars. for instance, defects such as "banding" may have its own reasons as in foundry, for example, due to too thick segregation (or inverse) surface layer of the ingot and insufficient homogenization, and at Extruders – due to too uneven flow of metal through the die, mixing in a matrix of various alloys or excessively thin press residue.
Defects such as "banding" and can bring anodirovschik, for example, at excessive machining surface before anodizing.
Manufacturer anode coating must monitor the conditions of delivery of aluminum profiles, them inside- and mezhdutsehovyh movements, as well as their storage before and after anodization. Defects can occur in the process of anodizing, if it is broken technology, for example, poorly controlled by the composition of working and rinsing baths.
cooperation caster, Extruders and anodirovschika
In most cases, anodizing the defect can not be detected until the aluminum profile is out of the line of anodizing, and the process will be fully completed. At this point, for the manufacture of defective Profile irretrievably spent material, energy and human resources, and correct defects, usually, longer possible. It is therefore important to understand, that to ensure high quality, close cooperation of anodized profile manufacturers is necessary at all stages of its production: at the foundry, from Extruders and anodirovschika.
Source: Barry R. Ellard, Aluminum Extrusion Technology, 2000