BS EN ISO 8251:2018 pdf download – Anodizing of aluminium and its alloys – Measurement of abrasion resistance of anodic oxidation coatings (ISO 8251:2018)
6.3.3 Calibration of apparatus Select and mark the areas of the standard specimen to be abraded. Accurately measure the anodic oxidation coating thickness (d) in each test area by means of an eddy-current meter. Fix the standard specimen in position in the test apparatus with the selected test area beneath the jet orifice and at the correct angle to the jet axis. Fill the hopper with sufficient silicon carbide for the test. If the abrasion resistance is being determined in terms of the mass of abrading medium used, weigh the hopper and abrading medium to the nearest 1 g using the balance. Set the air or gas pressure, to the specified (or selected) value, which shall be accurately maintained throughout each test and any series of tests. The air or gas pressure should be adjusted to give a rate of abrasion that is convenient for both the standard specimen being tested and for the test specimen. The preferred pressure, is normally indicated by the instrument manufacturer but it may be varied this for very soft, hard or thin coatings. Start the flow of abrading medium and simultaneously start a timer. Throughout the test, ensure that the abrading medium flows freely. Keep the standard specimen under observation; when a small black spot appears in the centre of the abraded area and rapidly enlarges to approximately 2 mm in diameter terminate the test by stopping the abrading medium flow and the timer simultaneously. It is recommended that the end point be determined by using a circuit tester to measure the electrical resistance at the abraded area on the standard specimen. Record the time, in seconds, taken for the test. If required, weigh the hopper and residual abrading medium, calculate the mass in grams. The results give the abrasion of the standard specimen (S s ) in either seconds or grams. Carry out at least two further tests on other parts of the standard specimen. Follow the procedure specified in to
6.3.4 Calibration of jet nozzle General Since individual jets can vary with use and one with another, it is necessary to correct each set of measurements by means of calibration determinations using a standard specimen as in 6.3.3. This enables the abrasive jet factor for the set of measurements to be calculated. Change of jet nozzle or abrasive characteristics with time For any series of test measurements, repeat the procedure specified in 6.3.3 once or twice daily in order to allow a correction to be made for changes of jet nozzle or abrasive characteristics with time. Jet nozzle replacement After jet nozzle replacement, repeat the procedure specified in 6.3.3 to allow correction for changes in jet nozzle characteristics.
6.3.5 Determination
Carry out the procedure specified in 6.3.3 using the test specimen instead of the standard specimen.
6.3.6 Use of a reference specimen
Under some circumstances, for example for control purposes, it is common practice to use a reference specimen for comparison and, if this is required, the procedure specified in 6.3.3 shall be followed using the reference specimen in place of the standard specimen.
6.4 Expression of results
6.4.1 General
The expression of results should be chosen from 6.4.2 to 6.4.4.BS EN ISO 8251 pdf download.