BS EN 4195-2011 pdf download.Aerospace series Paints and varnishes Test method for determination of chromate leaching.
EN 2090, Aerospace senes – Aluminium alloy AL-P2024-T3 – Clad sheet and strip 0,3 mm <a <6 mm
EN 2334, Aerospace series — Chromic-sulphuric acid pickle of aluminium and aluminium alloys
EN ISO 3696, Water for analytical laboratory use — Specification and test methods (ISO 3696)
3 PrInciple
The test involves placing a dry film of chromate primer in distilled water in accordance with EN ISO 3696 for a period of time at a controlled temperature to allow soluble chromate to leach from the film into solution in the water. The water is collected for the measurement of dissolved hexavalent chromate by a suitable means.
Because the rate of leaching can vary considerably over a period of time the collection time is divided into a number of periods of different duration appropriate to the rate of leaching over the collection period.
Some of the water collected in the collection periods is not used for measurement because normally sufficient data is gained from other collections.
Values of chromate leaching can be numerically expressed or for convenience plotted on a graph.
4 Specimens and test apparatus
The apparatus shall consist of a stoppered test tube to hold the water and the painted test specimens. The test tube shall be maintained at a constant temperature, as specified, in a suitably controlled chamber.
Test specimens shall be of aluminium alloy EN 2090.
Test specimens shall be prepared by chrome sulphuric acid pickling in accordance with EN 2334 or other non chromate leaching pretreatment as may be specified in the relevant material specification. They shall then be sprayed with primer within four hours to give the paint thickness prescribed in the relevant material specification.
When dried and preconditioned as prescribed in the relevant material specification an area of 40 cm2 shall be cut from the panel for leaching test immersion. All edges shall be uncoated. Using a test tube for the Immersion, it is convenient to cut two panels of dimensions (10 x 2) cm. This assumes that the panels are coated on one side only arid are then placed back to back in the test tube.
5 Test procedure
A test specimen, prepared as above, shall be totally immersed in a stoppered tube containing 50 ml of distilled water maintained at a temperature of (40±2) °C.
The distilled water shall be renewed after 1, 2, 3. 4, 7, 10, 14. 18, 23, 29 and 36 days. The samples collected at the end of 2, 10 and 36 days only shall be analysed for chromate content as normally this is sufficient to determine the leach rate characteristics of the paint sample under test. However samples from other collection periods can also be measured if additional data is required.
At the end of the appropriate immersion time, the water in wtich the painted specimens have been immersed shall be poured into a 100 ml volumetric flask.
The specimen and the test container shall be rinsed with a volume of distilled water not exceeding 25 ml and this shall be added to the volumetric flask containing the first solution. Another 50 ml of distilled water shall be added to the original container to proceed with the test for the next immersion period.
A suitable method of analysis for chromate determination has been outlined in Annex A. Whether this or another method is employed for chromate concentration determination, the final volume of chromate containing solution, tube washings and reagents shall be 100 ml.
The concentration of hexavalent chromium in the solution shall be measured and calculated as milligrams of chromate leached per square decimetre of paint film.
6 Analysis of hexavalent chromium
A sample shall be taken from the 100 ml container and analysed for hexavalent chromium content.
The result shall be determined as mg Cr per I and expressed as mg Cr042- per dm2 of paint film tested.
NOTE For a 40 om2 exposed primer area this involves multiplying the quantity of hexavalent chromium in mgil by a factor of 0,557 7. Details of the calculation of the factor fo this case are given in Annex B.
The quantity of Cr042 per dm2 shall be converted into Cr042- per dm2 per day leaching rate. This means that the value calculated for the test sample needs to be divided by the number of days over which the paint sample had been in contact with that sample of water since it had been previously renewed.
Sample at 2 days duration 1 d to 2 d divide by 1
Sample at 10 days duration 7 d to 10 d divide by 3
Sample at 36 days duration 29 d to 36 d divide by 7
The results can be numerically expressed or for convenience can be plotted on a semi-logarithmic graph.
7 Test report
The test report shall contain at least the following information:BS EN 4195-2011 pdf download.