Anodizing defects: stripes from matrix marks, welds and sink marks
This type of defect – Type 1-B – species “banding”, but because of contaminated metal from the surface layer of the ingot, as in Type 1-A, or strips with a large grain, “rough” structure, as in Type 1-B. Defects of this type arise due to damage to the girdle matrix, as well as violations of profiles extrusion technology for anodizing, for example, too short press residue.
See. Defects aluminum anodizing – classification
Matrix traces (risks)
English term
Die lines.
defect Source
Pressing
The manifestation of the defect
Pressing - Anodizing.
Details of the defect
This type of anodizing defect is usually separate marks on the surface of the extruded aluminum profile (Figure 1.7), which result from damage or girdle matrix gripping them contaminants, included, steel particles (for example, particles of the nitrided layer or friction products of the container wall). Depending on their depth, some traces of matrices may only manifest after etching, others will be visible even after the mechanical polishing or machining profile and abrasive brushes.
Figure 1.7
Preventing defect
Avoid traces of matrices is possible only with full confidence, what:
- on the workpiece and the tool prior to compression and in the course of it completely lacks any contamination,
- girdle in the matrix no damage.
Not too deep traces of the matrix are removed or masked after alkali etching E6.
Transverse welds
English term
Тransverse welds
defect Source
Pressing.
The manifestation of the defect
Travlenye - Anodyrovanye.
Details of the defect
This defect occurs at the front end of each workpiece (except for the first) when pressing solid aluminum profiles on a matrix with a welding chamber and for all hollow profiles. This defect arises due to the inevitable oxide layer, appearing at the junction between the cut surface in the aluminum matrix ports and the front end face of the next workpiece.
The defect is in the form V-shaped edge strip with V, directed toward the front end of the pressed aluminum profile. This defect is shown in Figure 1.8.
For aluminum profiles, to anodization, it is often (but not always) necessary to cut these areas and send them to scrap. Many Extruders are looking to reduce the amount of internal scrap, and therefore increase the risk of manufacturing profiles, comprising transverse seams.
Figure 1.8
Preventing defect
- Avoid the use of ingots from a variety of sources, various heat treatments or different mold structure for manufacturing a batch of profiles.
- One way to reduce the length of the transverse seal is to decrease the volume of metal in the matrix ports. This makes the stitch shorter, but more prominent, that makes sense, if it will later be removed.
- Net of the discard cut surface makes it possible to "mask" the transverse seams, including, by a minimum of grease on the blade of the knife compartment of the discard mechanism.
Utyazhina
English term
Back-end-Defect (also coring and piping)
defect Source
Pressing.
The manifestation of the defect
Travlenye - Anodyrovanye
Details of the defect
dark streaks, usually, inclined at an angle to the pressing direction. They usually are not visible on the profiles of the pressed state or after mechanical processing. Shown after etching and anodizing of aluminum profiles. This type of "banded" material contains defects "segregate" and oxides from the peripheral zone of the ingot. This material must not enter the profile, but it can reach the last stage of compression of the end of the blank.
In the book T. Sheppard "Extrusion of Aluminium Alloys" this defect appears as shown in Figure 1.9.1. The figure 1.9.2 from book P. K. Saha “Aluminium Extrusion Technology” shows a model of the formation of this defect. Often this defect has a tubular shape, and it is also called «piping -« sink mark ".
Figure 1.9.1
Figure 1.9.2
Preventing defect
Increasing the thickness of the discard.
Source: Barry R. Ellard, Aluminum Extrusion Technology, 2000
