BS EN ISO 3613-2021 pdf free download – Metallic and other inorganic coatings — Chromate conversion coatings on zinc, cadmium, aluminium-zinc alloys and zinc- aluminium alloys — Test methods.
For comparison purposes, test an untreated surface similarly.Untreated zinc and cadmium surfaces, orthe surfaces that have been treated for the chromate conversion coating but do not have a continuouscoating,will react with the lead acetate solution to form a black stain on the untreated or bare zinc andcadmium surfaces almost immediately, within 2 s to 5 s, after the application of the test solution.
No significance is to be placed upon any differences in the reaction time to black-spot formation between1 min and 3 min on a zinc substrate, or between 5 s and 60 s on a cadmium substrate, with a colourlesschromate conversion treatment. Factors such as substrate surface texture (roughness), chromate filmthickness variations (due to processing conditions), variations in the ambient temperature of the testand precise pHl control of the lead acetate solution have an influence on the reaction time, and thereforepreclude any rating based upon times beyond those already stated. Similarly, the test cannot be usedto compare the corrosion protection of chromate conversion coatings made from various types ofchromate treatment solutions.
Because of the sensitivity of the method, the test is considered to be a quality control tool for theprocess. Items with damaged chromate layers should not be tested by this method.
Chromate conversion coatings exposed to temperatures above 60 C will have considerably reducedresistance to corrosion in the accelerated test method (see 6.10). They will show a black stain in lessthan 60 s on zinc and less than 5 s on cadmium.
6.4Test for the presence of a colourless chromate coating on zinc-aluminium (massfraction of aluminium: 5 %) alloys
Expose the test specimen for 24 h to an accelerated damp heat test in accordance with IEC 60068-2-30.The formation of a dark grey to black stain over the main part of the area shall be deemed to indicatethe absence of a chromate conversion coating.
NOTE This test does not have any significant effect on the surface appearance if a chromate conversioncoating is present.
6.5Test for the presence of hexavalent chromium in both colourless and colouredchromate coatings
6.5.1 General
Carry out the following test methods for the presence of hexavalent chromium.
6.5.2 Test method employing test solution C 1
Place one to five drops of test solution C 1(4.3.1) on the surface to be tested.lf hexavalent chromium ispresent, a red to violet colour will appear within a few minutes. Ignore any colour that appears muchlater, e.g.on drying.For comparison purposes, test an untreated surface similarly.
NOTE The treatment will not have any significant effect on the surface appearance.
6.5.3 Test method employing alternative test solution C 2 (destructive)
ln this test method, the Cr(Vl) content of a coated part is extracted by boiling in water.The extractedsolution is examined according to the colour reaction with 1,5-diphenylcarbazide. Cr(Vl) oxidizes 1,5-diphenylcarbazide to 1,5-diphenylcarbazone, which forms a red-violet coloured complex with thedeveloped Cr(1m).
The sample to be tested should have a surface area of (50 ± 5) cm2.For fasteners or samples with asmaller surface area, use a suitable number of samples to obtain the total required surface area. Incases where obtaining a total surface area of (50± 5)cm2 is not possible, a reduced total sample surfacearea may be used by reducing the water extraction volume, while maintaining the same surface areato extraction volume ratio (1cm2:1 ml).A minimum surface area of 25 cm2 is recommended.Similarly,a higher sample surface area can be used by keeping the same ratio. The type of adjustment shall berecorded in the final report. Remove any sealing,such as paint or wax, etc., by scraping the surface.Theresulting abrasion shali also be analysed.
Fill 50 ml of distilled water or water of equivalent purity with anti-bumping granules into a beaker withvolume graduation, cover it with a watch glass and bring it to boiling temperature. Let the water boilfor at least 10 min to deoxygenate it. Then totally immerse the sample into the boiling water and coverthe beaker again with a watch glass.Extract the sample for (10 ± 0,5) min once boiling is resumed. lfnecessary, add water to ensure that the sample is totally submerged during the extraction. Remove thesample and allow the beaker content to cool to ambient temperature.The solution should be colourlessand free of precipitate.Adjust the volume to 50 ml. lf necessary, filter the solution through a 0,45 ummembrane filter into a dry beaker.Make up the solution to the mark with water (see Clause 4) or reduceit to the mark by boiling.Add 1 ml of orthophosphoric acid (4.3.2) per 50 ml volume and mix well. Pour25 ml of the solution using a graduated cylinder into another dry beaker.Add 1 ml of diphenylcarbazidesolution (4.3.2) and mix well. Allow the solution to stand for 10 min for the colour reaction to becompleted.The remaining portion of the extract will serve as the blank.BS EN ISO 3613 pdf download.