ISO 8251-2011 pdf free.Anodizing of aluminium and its alloys – Measurement of abrasion resistance of anodic oxidation coatings.
4 Characteristics of abrasion tests
There are three kinds of abrasion tests: abrasive-wheel-wear test, abrasive jet test and falling sand abrasion test.
4.1 Abrasive-wheel-wear test
Determination of the resistance to abrasion by movement of a test specimen relative to an abrasive paper under a specified pressure. The wear resistance or the wear index of the layers of oxide near the surface, or of the whole oxidation coating thickness, or of any selected intermediate zone may be determined by the method described. For most purposes the wear index (see 5.4.3) or the mass wear index (see 5.4.4) will be the most appropriate characteristic to determine.
The method is applicable to all anodic oxidation coatings of thickness more than 5 pm on flat aluminium or its alloy specimens.
This method is not applicable to concave or convex specimens: these may be examined using the abrasive jet test method which will give an average value for the abrasive resistance of the coating (see 4.2 and Clause 6).
NOTE Minimum test specimen dimensions of 50 mm x 50 mm are normally required.
4.2 Abrasive jet test
Determination of the resistance to abrasion by the impact of abrasive particles projected onto a test specimen. The mean specific abrasion resistance of anodic oxidation coatings may be determined.
NOTE 1 Different batches of the same abrasive are liable to give different results and for this reason the test is a comparative one.
NOTE 2 With a suitably designed abrasive jet and film-thickness-measuring devices with a small probe, it is possible to conduct a depth survey which indicates how abrasion resistance varies through the coating thickness (see Annex B). However, this property is preferably measured using the abrasive-wheel-wear test.
The method described is applicable to all anodic oxidation coatings of thickness more than 5 pm on aluminium or its alloys. It is primarily intended for surfaces which are not flat. If suitable flat test surfaces are available, the abrasive-wheel-wear test is the preferred method. Production components may be tested without cutting if the apparatus chamber can accommodate these.
NOTE 3 This method is particularly suitable for small test specimens because the individual test area required is only about 2 mm in diameter.
4.3 Falling sand abrasion test
Determination of the resistance to abrasion by the impact of freely falling abrasive particles onto anodic oxidation coatings.
The method described is applicable to the thin anodic oxidation coatings.
5 Abrasive-wheel-wear test
5.1 Principle
The anodic oxidation coatings on a test specimen are abraded, under defined conditions, by reciprocal motion against a strip of silicon carbide paper attached to the outer circumference of a wheel. After each double stroke, the wheel turns through a small angle to bring an unused portion of the abrasive strip into contact with the test area. The decrease in coating thickness or mass obtained is used to calculate the wear resistance or wear index. This result is compared with that obtained using a standard specimen (see Annex A) or reference specimen (see 3.3).
The method normally requires an eddy-current meter with a probe of less than 12 mm diameter. If this is not available, the method of loss in mass should be used.
NOTE A complete presentation of the wear characteristics of the anodic oxidation coatings can be obtained by progressively abrading the test area, until the substrate metal is revealed, and then constructing a graph to show the relation between the coating thickness removed and the number of double strokes used. This is referred to as a depth survey of the anodic oxidation coatings (see Annex B).
The testing environment should be at room temperature and the relative humidity should be under 65 %.
5.2 Apparatus
5.2.1 AbrasIve-wheel-wear test apparatus
The apparatus consists of a clamping device or pressure plate for holding the test specimen (see 5.3.2) level and rigid, and a 50 mm diameter wheel to the outer circumference of which is attached a 12 mm wide strip of silicon carbide paper (see 5.2.2). The force between the wheel and the test surface shall be capable of being varied from zero to at least 4,9 N with an accuracy of ±0.05 N. The abrasive action is produced either by the fixed wheel sliding to and fro in a horizontal plane in parallel contact with the test surface over a 30 mm length or, alternatively, by the test specimen sliding in a similar way over the stationary wheel. Typical apparatus is illustrated in Figure Cl.
After each double stroke, the wheel is advanced through a small angle to bring a fresh area of the silicon carbide paper into contact with the surface before making the next double stroke. The angle of rotation is such that, after 400 ds, the wheel will have made one complete revolution. At this stage, the strip of silicon carbide paper shall be renewed. The relative speed of movement shall be (40 ± 2) ds per minute. The number of double strokes can be registered by means of a counter, and provision is normally made for the apparatus to switch off automatically after a preset number of double strokes has been reached (400 ds maximum). The test surface shall be kept free from loose powder or abrasion detritus during the test.ISO 8251 pdf download.